The Wood Wide Web: Underground Fungi-Plant Communication Network
By Annie Chen, Environmental Science and Management ’19
Author’s note: When people think of ecosystems, trees and animals usually come to mind. However, most often we neglect an important part of the ecosystem — Fungi. Without us noticing, the fungi stealthily connects the organisms underground, creating a communication network that helps organisms interact with one another.
Picture yourself walking your dog in a quiet, peaceful natural forest, where you imagine the two of you as the only organisms capable of interacting with one another here. However, you are not alone; the plants can communicate and those trees and grasses are always speaking to each other without you taking notice. The conversation between vascular plants in this forest started before any of us are old enough to remember, and will likely continue if this forest is untouched. These conversations between seemingly disconnected organisms have helped this forest survive and thrive to become what you see today. You might wonder, what do these plants talk about, and most importantly, how do the plants communicate if they cannot move freely and have no vocal cords? The secret lies underground in an extensive network.
The underground network connects different immobile creatures to one another. Much like the above-ground biological interactions, the underground ecosystem is diverse, and not only houses many animals, but also consists of roots of different plants, bacteria, and fungal mycelium. The plant roots interact with their immediate neighbors, but in order for plants to communicate with plants further away from them, they rely on the underground fungal network, or according to Dr. Suzanne Simard who popularized the idea, the “Wood Wide Web” (WWW).
What is the underground “Wood Wide Web”, and how is it built?
This communication network is not made up of invisible radio waves like our Wifi, but rather relies on a minuscule and dense fungi network to deliver various signals and information [6]. These fungi, using their branching and arm-like membranes, build a communication network called the mycelium that connects between individual plants, and even the whole ecosystem. The mycelium deliver nutrients, sugar, and water, and in a more complex dynamic with the plants, deliver chemical signals. The fungi’s ability to expand their mycelium through reproduction and growth of fungi individually helps build these connections within the network. To expand their mycelium and link the network together with different individual plants, it must be evolutionarily advantageous for the fungi species to create such an extensive system. That is where the plant roots and their cooperative interactions come into play.
This communication network builds upon the foundation of mutualistic relationships between plants and fungi called mycorrhizae. Mutualism is the relationship that allows plants to provide sugars for the fungi in exchange for limiting nutrients such as phosphorus, nitrogen, and sometimes water (figure 1). According to an article published by Fleming, around 80-90% of the earth’s vascular plants have this mutualistic relationship, which allows plants and fungi to connect with one another through the plant roots. Without the mutually beneficial relationship, the fungi are not obligated to expand their network to connect to the plant roots and “help” these plants deliver chemical signals.
Not only is there nutrient and informational exchange, but the plants benefit from fungi priming, where the initial fungi infection that creates the exchange interface between plant roots and fungi cells force the plant immune systems to increase immunity. The increased immunity in the infected plant indirectly increases the chances of the plants in resisting major changes such as a disease in the ecosystem [6]. This continuous plant-fungi network through nutrient exchange and strengthening each species’ survival connects the whole ecosystem together.
Figure 1: A simplified visual of species interactions within the fungal network.
(Source: BBC)
That being said, the plant and fungal species that make up the WWW can vary by the participants who built the ecosystems. The interaction also means that the plants can selectively provide carbon or release defense chemicals to decide which fungus remains and has a mutualistic relationship with them [1]. When introducing a non-native species, it can alter the new ecosystem by encouraging different types of mycorrhiza. One such example was the introduction of European cheatgrass in Utah, U.S.A. The mycorrhizal makeup in Utah initially does not have significant changes prior to the introduction. However, upon European cheatgrass introduction to the Utahn site, despite the cheatgrass that does not contain European fungi, the site showed a shifted fungi genetic makeup [8]. Each plant individual, or species, using their preferences and abilities to “choose” their mutualistic partners, can diversify the fungal network to become more extensive and powerful, both to benefit and to harm other species of the ecosystem. The interspecies perspective is important in understanding the WWW.
Plants talk and interact through the “Wood Wide Web”
The communication extends to others in the ecosystem — the plants can “speak” to each other interspecifically, too. The individuals in an ecosystem are closely linked to one another, and so are relationships between plant individuals, whether it is directly with each other, indirectly through the fungal network, or both. The indirect communication relies on the fungal network, where various chemical signals pass through. For instance, the increased phosphorus level in the soil signals other plants that there is a plant-fungal interaction, and they may respond to this signal in different ways to ensure the situation is to their advantage — they could try to have their share of nutrients by producing sugars to attract these types of fungi, or they could make their plant competitors less healthy by excreting chemicals to weaken the fungus’ abilities to provide nutrients [13]. The WWW provides an internet that allows the plants to select a variety of methods to interact with one another, near or far.
The plants can choose to actively help each other through this fungal network, and allow both individuals, or species, to thrive in the ecosystem. Evolutionarily speaking, a plant individual could benefit from their own kind to thrive for the benefit of their survival. When an individual plant is thriving and producing excess carbon, they can help other plants by transferring excess nutrients through the fungal network [6]. An older, dying tree can also choose to transfer its resources to the younger neighbors through the fungal network, or donate its stored nutrients to the entire ecosystem through the decaying process that is aided by the extensive fungal network from fungal hyphae growth over the material [5]. Furthermore, through the WWW, the plants are able to communicate with one another about the possible threats including herbivores and parasitic fungi. In the research of Song et al, tomato plants infected with pathogens are able to send various defensive chemical signals, such as enzymes, into the existing fungal network for healthy neighbors in the network, warning them of the dangers nearby before they are infected themselves; using this mechanism, the plants can concentrate defensive chemicals with neighbors to minimize the spreading of this parasitic fungus in the area.
Not only can plants benefit one another, they can also use this network to put others at a disadvantage, such as to wipe out another competing or predating species that threaten their own survival. Allelopathy, or the exuding of chemicals to ward off enemies, usually gives off the impression that the plants use this method to discourage herbivores from consuming them, such as the milky sap that causes skin rashes and inflammation when a cucumber vine is cut, but the allelopathy is also active underground through the WWW. Barto et al, through their research on allelopathy, shows that even within a disturbed habitat, when there is competition between plant species, one species may utilize the regional network of fungi attached to them to deliver allelochemicals from one plant species to its neighboring species, preserving the fitness of their own kind.
Passive Animals, Active Plant and Fungi
We always think of herbivores as active players impacting the ecosystem. In the WWW, they are the last to respond to changes. Plants and fungi signal each other when an herbivore is present in the network, well before it has established its presence in the neighboring plants. Fungi are an important and active part of this ecosystem because they can also choose to exclude herbivores through chemical allelopathy. While it is possible that the fungi can choose to colonize a separate species that provides more benefits for them, they can concentrate their energy on defending its current host. Before the herbivore can expand its population, the plants have already communicated with one another through excretion of allelopathic chemicals, not only to ward off the herbivores that are causing potential damage, but also to warn other plants of the herbivore presence [1]. The fungi colonization of two nightshade species, Solanum ptycanthum and Solanum dulcamara, showed an increase of defense protein levels against the feeding caterpillars. This is just one example of herbivory defense mechanisms that results in decreased predator fitness, specifically in reduced growth rate and feeding rates [11]. When caterpillars feed on the Solanum spp., the active players in this relationship, the fungi and their plant hosts use chemical defense mechanisms indirectly induced by the fungi to discourage herbivores from feeding, and through evolution, eventually they drive out predators who are disadvantageous to the fungi-plant fitness.
Alone without the Wood Wide Web: Human Impacts
The network is built on a web of hyphae connections that is barely visible to the human eye, and even more vulnerable to changes. Older ecosystems not only have a higher percentage of larger trees with broader root systems, but are also denser in number, which both lead to a more extensive mycorrhizal fungal network. The species diversity, on top of age and density, contributes to a complex and healthy WWW that supports all plants in the ecosystem [3]. However, a disturbed ecosystem severs the connections in this network, making the previously extensive system difficult to repair.
Human activities that disturb the soil can affect this fragile yet powerful connection: seasonal tilling in agriculture, intensive logging, and change of soil chemistry and structure by laying concrete inhibits the soil from building an extensive web. Physically turning and chemically altering the soil is a direct human impact that cuts off hyphae connections between plant individuals in the system. According to Dr. Simard’s statement in a Biohabitat interview, the urban plants are less healthy because they lack the WWW to help them thrive through nutrient, water, and chemical signal exchange; they must do all those things or rely on humans to provide these needs. Indirectly, the larger-scale deaths and removal of plant individuals from logging also no longer foster a healthy mutualistic relationship between plants and fungi. If an individual plant is prevented from connecting with its mutualistic partners, whether that is through disturbance in the soil or the death of these partners, prevent the extensiveness of the WWW, and the isolation makes the urban tree population vulnerable to diseases if the humans do not diligently maintain them.
It is true that the smaller versions of the WWW still develop between periods of disturbance, proven indirectly by the fungal colonization ability in off-site lab experiments such as those included in the studies of Barto et al and Hawkes et al. However, important interspecies collaborations and perhaps lack thereof that is missing compared to a minimally disturbed habitat functions much better in resisting climate change and increased foreign and invasive species that threaten the health of the ecosystem.
Fortunately, despite the growing demand of land produced by economic growth and population, there is an increased awareness of the importance of plants and the health of the ecosystem. Over the last two decades, the addition of policies and practices indicated that major western conservation agencies have started to take on an interspecies perspective. One notable example is the inclusion of ecosystem management in the Clean Water Act, which adapts to the notion that endangered flora or fauna species is dependent on the health of an ecosystem [14]. The increased understanding of how interconnected the flora species are, in addition to conservation methods that have existed before the western colonization, have changed how governments aim to preserve nature.
Regardless of the level of human impacts, the WWW holds important communication between plants, fungi, and herbivores through chemical signals and nutrient exchange to sustain or to outcompete each other. The connectivity to relay information within this network is key to the healthy plant community, and further the health of the ecosystem. Next time when you walk your dog in the woods, remember that the plants around you are capable of communicating thanks to this underground network. In order to keep this forest healthy for generations on, it is up to us to rethink development strategies to preserve this network that helps them thrive to continue the species’ communication in the WWW in this forest.
References
- Biere, Arjen, Hamida B. Marak, and Jos MM van Damme. “Plant chemical defense against herbivores and pathogens: generalized defense or trade-offs?.” Oecologia 140.3 (2004): 430-441.
- Barto, E. Kathryn, et al. “The fungal fast lane: common mycorrhizal networks extend bioactive zones of allelochemicals in soils.” PLoS One 6.11 (2011): e27195.
- Beiler, Kevin J., et al. “Architecture of the wood‐wide web: Rhizopogon spp. genes link multiple Douglas‐fir cohorts.” New Phytologist 185.2 (2010): 543-553.
- Belnap, Jayne, and Susan L. Phillips. “Soil biota in an ungrazed grassland: response to annual grass (Bromus tectorum) invasion.” Ecological applications 11.5 (2001): 1261-1275.
- Biohabitats. “Expert Q&A: Suzanne Simard.” Biohabitats Newsletter 14.4 (2016).
- Fleming, Nic. “Plants talk to each other through a network of fungus.” BBC Earth. (2014).
- Gehring, Catherine, and Alison Bennett. “Mycorrhizal fungal–plant–insect interactions: the importance of a community approach.” Environmental entomology 38.1 (2009): 93-102.
- Hawkes, Christine V., et al. “Arbuscular mycorrhizal assemblages in native plant roots change in the presence of invasive exotic grasses.” Plant and Soil 281.1-2 (2006): 369-380.
- Hawkes, Christine V., et al. “Plant invasion alters nitrogen cycling by modifying the soil nitrifying community.” Ecology letters 8.9 (2005): 976-985.
- Macfarlane, Robert. “The Secrets of the Wood Wide Web.” The New York Times. (2016).
- Minton, Michelle M., Nicholas A. Barber, and Lindsey L. Gordon. “Effects of arbuscular mycorrhizal fungi on herbivory defense in two Solanum (Solanaceae) species.” Plant Ecology and Evolution 149.2 (2016): 157-164.
- Song, Yuan Yuan, et al. “Interplant communication of tomato plants through underground common mycorrhizal networks.” PloS one 5.10 (2010): e13324.
- Van der Putten, Wim H. “Impacts of soil microbial communities on exotic plant invasions.” Trends in Ecology & Evolution 25.9 (2010): 512-519.
- Doremus, H., Tarlock, A. Dan. “Can the Clean Water Act Succeed as an Ecosystem Protection Law?” George Washington Journal of Energy and Environmental Law 4 (2013): 49.
Not All Heroes Wear Capes: How Algae Could Help Us Fight Climate Change
By Robert Polon, Biological Sciences Major, ’21
Author’s Note: In my UWP 102B class, we were assigned the task of constructing a literary review on any biology-related topic of our choice. A year ago, in my EVE 101 class, my professor briefly mentioned the idea that algae could be used to sequester atmospheric carbon dioxide in an attempt to slow the rate of climate change. I found this theory very interesting, and it resonated with me longer than most of the other subject matter in that class. I really enjoyed doing the research for this paper, and I hope it gives people some hope for the future. I’d like to thank my UWP professor, Kathie Gossett, for pointing me in the right direction throughout the process of writing this paper.
Abstract
With climate change growing ever more relevant in our daily lives, scientists are working hard to find solutions to slow and reverse the damage that humans are doing to the planet. Algae-based carbon sequestration methods are a viable solution to this problem. Photosynthesis allows algae to remove carbon dioxide from the atmosphere and turn it into biomass and oxygen. It has even been proposed that raw algal biomass can be harvested and used as a biofuel, which can provide a greener alternative to fossil fuel usage. Though technology is not yet developed enough to make this change in our primary fuel source, incremental progress can be taken to slowly integrate algal biofuel into daily life. Further research and innovation on the subject could allow full-scale replacement of fossil fuels with algal biofuel to be a feasible option. Methods of algal cultivation include open-ocean algal blooms, photo bioreactors, algal turf scrubbing, and BICCAPS (bicarbonate-based integrated carbon capture and algae production system). There are many pros and cons to each method, but open-ocean algal blooms tend to be the most popular because they are the most economical and produce the most algae, even though they are the most harmful to the environment.
Keywords
Algae | Biofuel | Climate Change | Carbon Sequestration
Introduction
As we get further into the 21st century, climate change becomes less of a theory and more of a reality. Astronomically high post-Industrial Revolution rates of greenhouse gas emissions have started to catch up with humans, as the initial consequences of these actions are now coming to light with fear that worse is on the way. Many solutions have been proposed to decrease greenhouse gas emissions, but very few involve fixing the damage that has already been done. It has been proposed that growing algae in large quantities could help solve this climate crisis.
According to the Environmental Protection Agency, 76% of greenhouse gas emissions come in the form of carbon dioxide. As algae grows, it removes carbon dioxide from the atmosphere by converting it to biomass and oxygen via photosynthesis. Algae convert carbon dioxide to biomass at relatively fast rates. On average, one kilogram of algae utilizes 1.87 kilograms of CO2 daily, which means that one acre of algae utilizes approximately 2.7 tons of CO2 per day [1]. For comparison, one acre of a 25-year-old maple beech-birch forest only utilizes 2.18 kilograms of CO2 per day [2]. This amount of carbon dioxide sequestration can be done by only 1.17 kilograms of algae. After its photosynthetic purpose has come to an end, the raw algal biomass can be harvested and used as an environmentally-friendly biofuel. This literary review will serve as a comprehensive overview of the literature on this proposal to use algae as a primary combatant against global warming.
Carbon Dioxide
For centuries, heavy usage of fossil fuels has tarnished Earth’s atmosphere with the addition of greenhouse gases [3]. These gases trap heat by absorbing infrared radiation that would otherwise leave Earth’s atmosphere. This increases the overall temperature of the earth, which leads to the melting of polar ice caps, rising sea levels, and strengthening of tropical storm systems, among many other devastating environmental effects [4]. The most commonly emitted greenhouse gas, carbon dioxide, tends to be the primary focus of global warming treatments.
These algal treatment methods are no different. Any algal treatment option is dependent upon the fact that algae sequester atmospheric carbon dioxide through photosynthesis. It converts carbon dioxide into biomass and releases oxygen into the atmosphere as a product of the photosynthetic process [5].
Algal Cultivation
There are four proposed methods of algal cultivation: open-ocean algal blooms, photobioreactors, algal turf scrubbing, and BICCAPS. These techniques all differ greatly, with various benefits and drawbacks to each.
Open-Ocean Algal Blooms
Algae is most abundant on the surface of the open ocean. With the addition of its limiting nutrient, iron, in the form of iron(ii) sulfate (FeSO4), massive algal blooms can be easily sparked anywhere in the ocean [3]. This seems to be the way that most scientists envision sequestration because, of all proposed cultivation techniques, this one produces the most algae in the least amount of time. Intuitively, this method removes the most carbon dioxide from the atmosphere, as the amount of CO2 removed is directly proportional to the quantity of algae undergoing photosynthesis.
There are many benefits to open-ocean algal blooms. There is no shortage of space on the surface of the ocean, so, hypothetically, there is a seemingly infinite amount of algal mass that can be cultivated this way. This technique is also very cost-efficient, as all you need to employ it is some iron(ii) sulfate and nature will do the rest [3].
Once the algal bloom has grown to its maximum size, there is an overabundance of algal biomass on the surface of the ocean. Some researchers have proposed that this mass be collected and used as a biofuel [5,6,7]. Others have proposed that we let nature play its course and allow the dead algae to sink to the bottom of the ocean. This ensures that the carbon dioxide it has taken out of the atmosphere is stored safely at the bottom of the ocean [8]. Here, the algal biomass is easily accessible for consumption by shellfish, who store the carbon in their calcium carbonate shells [3].
This solution is not an easy one to deploy, however, because algal blooms bring many problems to the local ecosystems. Often referred to as harmful algal blooms (HABs), these rapidly growing algae clusters are devastating to the oceanic communities they touch. They increase acidity, lower temperature, and severely deplete oxygen levels in waters they grow in [9]. Most lifeforms aren’t prepared to handle environmental changes that push them out of their niches, so it’s easy to see why HABs kill significant portions of marine life.
HABs can affect humans as well. Many species of alga are toxic to us, and ingestion of contaminated fish or water from areas affected by these blooms can lead to extreme sickness and even death. Some examples of these diseases are ciguatera fish poisoning, paralytic shellfish poisoning, neurotoxic shellfish poisoning, amnesic shellfish poisoning, and diarrheic shellfish poisoning [10]. The effects of harmful algal blooms have only been studied in the short-term, but from what we have seen, they are definitely a barrier in using this form of algae cultivation [11].
Photobioreactors
Photobioreactors are another frequently-proposed tool for cultivating algae. These artificial growth chambers have controlled temperature, pH, and nutrient levels that make for optimal growth rates of algae [12]. They can also run off of wastewater that is not suitable for human consumption. Photobioreactors minimize evaporation and, with the addition of iron, magnesium, and vitamins, increase rates of carbon dioxide capture are increased [1]. Due to the high concentration of algae in a relatively small space, photobioreactors have the highest rates of photosynthesis (and subsequently carbon dioxide intake) out of all of the cultivation methods mentioned in this paper.
This innovative technology was driven primarily by the need to come up with an alternative to triggering open-ocean algal blooms. Photobioreactors eliminate pollution and water contamination risks that are prevalent in harmful algal blooms. Furthermore, they make raw algal biomass easily accessible for collection and use as a biofuel, which open-ocean algal blooms do not [12].
The main drawback to this method is that the cost of building and maintaining photobioreactors is simply too high to be economically feasible right now [12]. Technological developments need to be made to lower the short-term cost of operation and allow for mass production if we want to use them as a primary source of carbon sequestration. Their long-term economic feasibility still remains unknown, as most of the cost is endured during the production of the photobioreactors. Money is made back through the algae cultivated, but the technology hasn’t been around long enough to show concrete long-term cost-benefit analyses without speculation [14].
Algal Turf Scrubbing (ATS)
Proposed in 2018 by botanist Walter Adey, algal turf scrubbing (ATS) is a new technique created to efficiently cultivate algae for use in the agriculture and biofuel industries. The process involves using miniature wave generators to slightly disturb the flat surface of a floway and stimulate the growth of numerous algal species in the water. Biodiversity in these floways increases over time, and a typical ATS floway will eventually have over 100 different algae species [11].
Heavy metals and other toxic pollutants occasionally make their way into the floways; however, they are promptly removed, to ensure that the product is as nontoxic as possible. The algal biomass is harvested bi-weekly and has a variety of uses. Less toxic harvests can be used as fertilizers in the agricultural industry, which research claims is the most economically efficient use for the harvest. It can also go towards biofuel use, although the creators of the ATS system believe the majority of their product will go towards agricultural use because they will not be able to produce enough algae to keep up with the demand (if our society moves towards using it as a biofuel) [11].
The problems with ATS are not technological, but sociopolitical, as the research team behind it fears that they will not get the funding and resources needed to perform their cultivation at an effective level [11].
BICCAPS
The bicarbonate-based integrated carbon capture and algae production system (BICCAPS) was proposed to reduce the high costs of commercial algal biomass production by recycling bicarbonate that is created when algae capture carbon dioxide from the atmosphere and using it to culture alkalihalophilic microalgae (algae that thrive in a very basic pH above 8.5). Through this ability to culture more algae, the system should, in theory, cut costs of carbon capture and microalgal culture. It is also very sustainable, as it recycles nutrients and minimizes water usage. The algae cultivated can also be turned into biofuel to lower fossil fuel usage [13].
The main drawback to this closed-loop system is that it does not cultivate as much algae as the other systems, though work is currently being done to improve this. It has been proven that the efficiency of BICCAPS significantly improves with the addition of sodium to the water, which stimulates the growth of alkalihalophilic microalgae [13]. This means that, with a little bit of improvement to the efficiency of the system, BICCAPS could become a primary algal biomass production strategy because of its low cost and sustainability.
Use of Algae as a Biofuel
While algae may not have the energetic efficiency of fossil fuels, it is not far behind. It can be burned as a biofuel to power transportation, which would allow us to lower our use of fossil fuels and, subsequently, our greenhouse gas emissions. When dry algal biomass is burned, it releases more oxygen and less carbon dioxide than our current fuel sources. The increase in oxygen released into the atmosphere not only helps to lower CO2 emissions but increases the overall atmospheric ratio of oxygen to carbon dioxide. More research still has to be done to find the best possible blend of algal species for fuel consumption [12]. Solely using algae as a biofuel would not meet the world’s energy demand, but the technology for photobioreactors continues to improve, giving hope to one day use algae more than fossil fuels [6].
A common counterargument to proposals for algal biofuel usage is that burning dry algae only provides half the caloric value of a similarly-sized piece of coal. While this is true, it should be taken into consideration that that coal has an extraordinarily high caloric value and that the caloric value of algae is still considered high relative to alternative options [3].
It is often suggested that bioethanol, which essentially uses crops as fuel, should be used over algal biofuel. The main problem with this proposal is that farmers would spend more time cultivating inedible crops because they make for better fuel. This would lead to food shortages on top of the current hunger problem in our world. Farming crops also take up land, while growing algae does not [7].
Drawbacks
The main problems associated with using algae as a biofuel are technological and economical. We simply do not have the technology in place right now to produce enough algae to completely replace fossil fuels with it. In order to do this, we would have to establish full-scale production plants, which is not as economically viable as simply continuing to use the fossil fuels that degrade our planet [12]. Receiving funding for the commercialization of algae is the biggest obstacle this plan faces. It’s difficult to get money allocated to environmental conservation efforts because, unfortunately, it doesn’t rank very highly in our government’s priorities. Algal carbon sequestration has also never been observed at a commercial scale, so there is hesitation to fully commit resources to something that seems like a gamble.
Alternative Uses
It has also been proposed that algal biomass grown to sequester carbon dioxide should be used in the agricultural industry. As previously mentioned, the creators of ATS have suggested using it as a fertilizer [11]. Others say that it can be used to feed livestock or humans, as some cultures actually consume algae already [12]. The seemingly infinite supply of microbes can also be harvested and used heavily in the medical industry in the form of antimicrobial, antiviral, anti-inflammatory, anti-cancer, and antioxidant treatments [7].
Conclusion
Algae can be used to fight climate change because it removes carbon dioxide from our atmosphere, stores it as biomass, and replaces it with oxygen. Arguments have been made in many directions over the best method of algal cultivation. Triggering open-ocean algal blooms is certainly the most cost-efficient of these methods, and it produces the most algal biomass. The problem with using this technique is that these algal blooms have devastating ecological effects on the biological communities they come in contact with. Photobioreactors are another popular method among those who favor this strategy because of their ability to efficiently produce large quantities of algae; however, the main inhibition to their usage is the extremely high cost of construction and operation. With more focus on developing lower cost photobioreactors, they can potentially become the primary source of algal growth. Algal turf scrubbing is another strategy of algae cultivation that struggles with the problem of acquiring adequate funding for the operation. BICCAPS is a relatively inexpensive and eco-friendly way to grow algae in a closed system, but it yields low quantities of algal biomass compared to the other systems.
The raw algal biomass from these growth methods can potentially be used as a biofuel. Dry alga has a high caloric value, which makes it great for burning to power equipment. It does not burn as well as fossil fuels, but it does release more oxygen and less carbon dioxide than fossil fuels when burned. Of course, funding will be needed for increased algae production to make this a possibility, but with more research and advances in the field, algal growth would be a great way to remove large amounts of carbon dioxide that is stuck in Earth’s atmosphere and become our primary fuel source down the line.
References
- Anguselvi V, Masto R, Mukherjee A, Singh P. CO2 Capture for Industries by Algae. IntechOpen. 2019 May 29.
- Toochi EC. Carbon sequestration: how much can forestry sequester CO2? MedCrave. 2018;2(3):148–150.
- Haoyang C. Algae-Based Carbon Sequestration. IOP Conf. Series: Earth and Environmental Science. 2018 Nov 1. doi:10.1088/1755-1315/120/1/012011
- Climate Science Special Report.
- Nath A, Tiwari P, Rai A, Sundaram S. Evaluation of carbon capture in competent microalgal consortium for enhanced biomass, lipid, and carbohydrate production. 3 Biotech. 2019 Oct 3.
- Ghosh A, Kiran B. Carbon Concentration in Algae: Reducing CO2 From Exhaust Gas. Trends in Biotechnology. 2017 May 3:806–808.
- Kumar A, Kaushal S, Saraf S, Singh J. Microbial bio-fuels: a solution to carbon emissions and energy crisis. Frontiers in Bioscience. 2018 Jun 1:1789–1802.
- Moreira D, Pires JCM. Atmospheric CO2 capture by algae: Negative carbon dioxide emission path. Bioresource Technology. 2016 Oct 10:371–379.
- Wells ML, Trainer VL, Smayda TJ, Karlson BSO, Trick CG. Harmful algal blooms and climate change: Learning from the past and present to forecast the future. Harmful Algae. 2015;49:68–93.
- Grattan L, Holobaugh S, Morris J. Harmful algal blooms and public health. Harmful Algae. 2016;57:2–8.
- Calahan D, Osenbaugh E, Adey W. Expanded algal cultivation can reverse key planetary boundary transgressions. Heliyon. 2018;4(2).
- Adeniyi O, Azimov U, Burluka A. Algae biofuel: Current status and future applications. Renewable and Sustainable Energy Reviews. 2018;90:316–335.
- Zhu C, Zhang R, Chen L, Chi Z. A recycling culture of Neochloris oleoabundans in a bicarbonate-based integrated carbon capture and algae production system with harvesting by auto-flocculation. Biotechnology for Biofuels. 2018 Jul 24.
- Richardson JW, Johnson MD, Zhang X, Zemke P, Chen W, Hu Q. A financial assessment of two alternative cultivation systems and their contributions to algae biofuel economic viability. Algal Research. 2014;4:96–104.
Where the Bison Roam and the Dung Beetles Roll: How American Bison, Dung Beetles, and Prescribed Fires are Bringing Grasslands Back
By John Liu, Wildlife, Fish, and Conservation Biology ‘21
Author’s Note: In this article, I will explore the overwhelming impact that the teeny tiny dung beetles have on American grasslands. Dung beetles, along with reintroduced bison and prescribed fires, are stomping, rolling, and burning through the landscape; all in efforts to revive destroyed grassland habitats. Barber et. al. looks at how the beetles are reacting to the bison herds and prescribed fires. Seemingly unrelated factors interact with each other closely, producing results that bring hope to one of the most threatened habitats.
Watching grass grow: its lit
Grasslands are quiet from afar, often characterized by windblown tallgrasses and peaking prairie dogs. But in fact, they are dynamic. Historically, grasslands were constantly changing: fires ripping through the landscape, bison stampedes kicking up dust, and grasses changing colors by the season [2]. However, climate change, increasing human populations, and agricultural conversions all contribute to an increasing loss of critical habitats; grasslands being amongst the most affected [7]. A loss of grasslands not only results in the extermination of previously residing fauna, but also a reduction of ecosystem services that they once provided. Thus, it is of increasing concern to restore grassland habitats. With the help of bison, dung beetles, and prescribed fires, recovery of grasslands is promising and likely swift.
Eat, poop, burn, repeat
As previously mentioned, grasslands thrive when continuously disturbed. The constant disturbance keeps woody vegetation from encroaching, nonnative plants from invading, and biodiversity from declining as a result of competitive exclusion between species [12]. To accomplish this, grasslands rely on large herbivore grazers such as American bison (Bison bison) to rip through the vegetation and fires to clear large areas of dry debris [9].
American bison are herbivore grazers- animals that feed on plant matter near the ground. The presence of these grazers alter available plant biomass, vegetation community structures, and soil conditions. This is the result of constant trampling, consuming, and digesting of the plant matter [9, 11]. Due to their valuable impact on the landscape, bison are considered keystone species- species that have an overwhelming, essential role in the success of an ecosystem [8]. Grasslands would look vastly different without bison walking, eating, and defecating on them [9].
But bison do not aimlessly roam the grasslands, eating anything they come across. They specifically target areas that have been recently burned. These scorched areas present themselves with new growth, higher in nutritional content [3, 5]. Historically, lightning strikes or intense summer heats caused these fires, driving the movement of grazers, but human intervention inhibits these natural occurrences. Instead, prescribed fires- planned, controlled burnings performed by humans- now mitigate the loss of natural fires, encouraging the bison’s selective foraging behaviors [4, 12]. Inciting bison to follow burned patches benefits the grasslands in more ways than one. First, this prevents overgrazing of any one particular area. By moving throughout the landscape, particular areas will reestablish while others are cleared by the bison. Second, the simple act of traversing large distances physically changes the landscape. Bison are large animals that travel in herds. When moving about the grasslands, they trample vegetation and compact the soil beneath their hoofs. Finally, grazing bison interrupt the process of competitive exclusion- limiting success as a result of competition for resources- amongst native plants. They indiscriminately consume vegetation in these areas, leaving little room for any one species of plant to out compete another [9].
The world is your toilet…. with dung beetles!
What goes in must come out, and bison are no exception to that rule. After digestion of the grasses they eat, bison leave behind a trail of dung and urine. The nitrogen rich waste feeds back into the ecosystem, offering valuable nutrients to the plants and soil-dwelling organisms alike [1]. But a recent study by Barber et. al. highlights a small, but critical component that ensures nutrient distribution is maximized in grasslands: the dung beetles (Scarabaeidae: Scarabaeinae and Aphodiinae, and Geotrupidae).
Dung beetles rely on the solid waste from their mammalian partners. The beetles eat, distribute, and even bury the dung; which helps with carbon sequestration [10]. They are found around the world- from the rainforests of Borneo to the grasslands of North America- and interact with each environment differently. In Borneo, dung beetles distribute seeds found in the waste of fruit loving Howler monkeys (Alouatta spps) [6]. While in North America, they spread nutrients found in the waste of grazing bison. They provide unique ecosystem functions- shattering of nutrient rich dung throughout vast landscapes. These attributes led to their increasing popularity in science research as a study taxon in recent years.
Figure 1: Grassland health is largely dependent on the interplay of multiple living and non-living elements. In 1.1, the area is dominated by woody vegetation and few grasses due to a lack of disturbance. In 1.2, the introduction of prescribed fires clears some woody vegetation, allowing grasses to compete. In 1.3, bison introduce nutrients into the landscape, increasing productivity. However, the distribution of dung is limited. In 1.4, the addition of dung beetles lead to better distribution of nutrients thus more productivity and species diversity.
Barber et. al. took a closer look to see how exactly dung beetles were reacting to bison grazing and prescribed fires blazing through their grassy fields. They found significant contributions from each; both noticeably directing the movement and influencing the abundance of these beetles. As the bison followed the flames, so did the beetles. The beetles’ dependence on the bison’s dung showed when researchers looked at beetle abundance in two key areas: those with bison and those without. There were significantly more beetles in areas with bison, likely feeding on their dung, scattering it, and burying it; all while simultaneously feeding the landscape. Prescribed fires also lead to increases in beetle abundance. Whether it be 1.5 years post-restoration or 30 years post-restoration, researchers consistently saw increases in beetle abundance when prescribed fires were performed. This further amplifies the importance of disturbances in grassland habitats, for ecosystem health but also for species richness.
And the grass keeps growing
The reintroduction of bison in the grasslands of America proved successful in rebuilding a lost habitat, with the help of dung beetles and prescribed fires. However, bison and dung beetles are just one of many examples of unlikely pairings rebuilding lost habitats. Although the large-scale ecological processes have been widely studied, species-to-species interactions are often overlooked. Continued surveys of the grasslands will reveal more about the interactions of contributing factors and their effects on each other and the habitat around them.
Citations
- Barber, Nicholas A., et al. “Initial Responses of Dung Beetle Communities to Bison Reintroduction in Restored and Remnant Tallgrass Prairie.” Natural Areas Journal, vol. 39, no. 4, 2019, p. 420., doi:10.3375/043.039.0405.
- Collins, Scott L., and Linda L. Wallace. Fire in North American Tallgrass Prairies. University of Oklahoma Press, 1990.
- Coppedge, B.R., and J.H. Shaw. 1998. Bison grazing patterns on seasonally burned tallgrass prairie. Journal of Range Management 51:258-264.
- Fuhlendorf, S.D., and D.M. Engle. 2004. Application of the fire–grazing interaction to restore a shifting mosaic on tallgrass prairie. Journal of Applied Ecology 41:604-614.
- Fuhlendorf, S.D., D.M. Engle, J.A.Y. Kerby, and R. Hamilton. 2009. Pyric herbivory: Rewilding landscapes through the recoupling of fire and grazing. Conservation Biology 23:588-598.
- Genes, L. , Fernandez, F. A., Vaz‐de‐Mello, F. Z., da Rosa, P. , Fernandez, E. and Pires, A. S. (2018), Effects of howler monkey reintroduction on ecological interactions and processes. Conservation Biology. . doi:10.1111/cobi.13188
- Gibson, D.J. 2009. Grasses and Grassland Ecology. Oxford University Press, Oxford, UK.
- Khanina, Larisa. “Determining Keystone Species.” Ecology and Society, The Resilience Alliance, 15 Dec. 1998, www.ecologyandsociety.org/vol2/iss2/resp2/.
- Knapp, Alan K., et al. “The Keystone Role of Bison in North American Tallgrass Prairie: Bison Increase Habitat Heterogeneity and Alter a Broad Array of Plant, Community, and Ecosystem Processes.” BioScience, vol. 49, no. 1, 1999,
- Menendez, R., P. Webb, and K.H. Orwin. 2016. Complementarity of ´ dung beetle species with different functional behaviours influence dung–soil carbon cycling. Soil Biology and Biochemistry 92:142-148
- Mcmillan, Brock R., et al. “Vegetation Responses to an Animal-Generated Disturbance (Bison Wallows) in Tallgrass Prairie.” The American Midland Naturalist, vol. 165, no. 1, 2011, pp. 60–73., doi:10.1674/0003-0031-165.1.60.
- Packard, S., and C.F. Mutel. 2005. The Tallgrass Restoration Handbook: For Prairies, Savannas, and Woodlands. Island Press, Washington, DC.
- Raine, Elizabeth H., and Eleanor M. Slade. “Dung Beetle–Mammal Associations: Methods, Research Trends and Future Directions.” Proceedings of the Royal Society B: Biological Sciences, vol. 286, no. 1897, 2019, p. 20182002., doi:10.1098/rspb.2018.2002.
Gene editing invasive species out of New Zealand
By Jessie Lau, Biochemistry and Molecular Biology ‘20
Authors Note: Since the advent of Clustered Regularly Interspaced Short Palindromic Repeats-CRISPR Associated Protein 9 (CRISPR/Cas9) discovery and biotechnological breakthroughs thereafter, this revolutionary application has been primarily focused on human health, particularly fostering solutions to numerous debilitating ailments. However, the general public has offered little attention towards the use of this engineering feat in a broader ecological system. Upon watching the new Netflix original Unnatural Selection, discussion of considering the use of CRISPR/Cas9 in New Zealand’s effort to completely eradicate invasive species piqued my interest. The following article is an exploration of CRISPR/Cas9 prospect into New Zealand’s bold environmental pursuit and its potential ecological impact.
Abstract
Since it has become feasible to cross oceans to reach unforeseeable land masses, invasive alien species (IAS) are an increasing threat to international biodiversity. Moreover, no other region faces as great of a peril as New Zealand (NZ), which holds the record as the nation with the highest survival rate of threatened avifauna (birds of a particular region) species [5]. In 2012, New Zealand physicist Sir Paul Callaghan introduced a large-scale eradication program to permanently remove eight invasive mammalian predators (rodents: Rattus rattus, Rattus norvegicus, Rattus exulans, Mus musculus; mustelids: Mustela furo, Mustela erminea, Mustela nivalis; and the common brushtail possum: Trichosurus vulpecula) [5]. Four years after this grand proposal, the NZ government committed to a national challenge titled “Predator Free 2050” (PF 2050) to pursue this audacious goal.
Introduction
Approximately 85 million years ago, NZ was one of the first landmasses to split from the supercontinent Gondwana and as it shifted away, it did not carry mammals until bats flew and aquatic species swam to this island. [7]. With the introduction of rodent species initially through Polynesian settlement some 750 years ago and thereafter European seafaring ventures, the endemic species of NZ have been left vulnerable to novel predators. Consequently, at least 51 native bird species that have evolved adaptive skills of remaining close to the ground have been unsuccessful at surviving alongside these rodent predator species [4]. These invasive omnivorous rodents prey on birds, eggs, seeds, snails, lizards, and fruits. As a result, their varied diets prompt competition with the native fauna, further placing pressure on their vulnerable survival [7]. Despite CRISPR/Cas9 modifications offering the greatest potential in gene drive to eliminate these unwanted predators, several techniques implemented to control these invasive populations, such as pesticides, trapping innovations, and biological factors have given favorable results.
Past Successes and Future Endeavors
For decades, the NZ government has pursued eradication initiatives to permanently eliminate foreign invasive species on small local islands. Through concerted efforts, several of these projects have proven successful in the restoration of the natural biodiversity this island nation boasts.
In June of 2009, the NZ Department of Conservation (DOC) undertook a multi-action plan to simultaneously eradicate rodent, rabbit, stout, hedgehog, and cat species in Rangitoto and Motutapu islands. After three years of aerial dispersion of anticoagulant Pestoff 20RTM combined with trapping and indicator dogs, the island witnessed total elimination of the islands’ stoats and four rodent species; declination of rabbit and hedgehog population by 96%; and over 50% reduction in cats [7].
Despite these successful feats, the invasive species fecundity and ability to adapt to these challenges still present an overwhelming challenge to reach the goal of complete eradication. Recently, more direct approaches delving into novel genetic inheritance techniques have been explored to serve as a potential permanent solution. Termed the“Trojan Female Technique” (TFT), the method makes use of the correlation of sperm fitness dependence on the abundance of mitochondrial DNA (mtDNA) [2]. Healthy sperm is dependent on sufficient mitochondrial level for energy production to manage motility and fertilization. For example, experiments conducted on Drosophila melanogaster supports the causation of reduced spermatogenesis and sperm maturation due to induced mutations in cytochrome mitochondrial gene [9]. Contrasting female eggs, the asymmetric greater dependence of sperm on mtDNA for normal functionality results in only male populations to be the sole source of target. Induction of mitochondrial mutations in females to compromise total sperm viability in future male progenies will serve as an effective control to population growth.
Although seemingly promising, TFT is not guaranteed to completely eradicate propagation for several reasons. For starters, males with impaired fertility can still provide sufficient sperm count to fertilize eggs on a population-based scale. Furthermore, in circumstances where females do receive nonviable sperm count, they can still seek adequate functioning sperm through matings with other males. On a larger scale, should the mutation pervade, selection pressures could still inadvertently choose for nuclear modifications to make up for the mitochondrial defects [2]. These flaws raise the need for more pervasive and permanent resolutions.
Daisy Chain CRISPR Gene Drive
The recent biochemical breakthrough underpinning the ability to effectively and precisely modify genes with CRISPR/Cas9 has allowed for potential biotechnology to boom in the realm of ecology. The simple generation of a short RNA sequence into a virus or bacterium to serve as a vector, guides the cutting mechanism of Cas9 to specific regions in the genome to be excised, prompting for these double stranded breaks to be fixed through DNA repair mechanisms. While these fixtures can potentially repair the gene, it can also raise the possibility for the gene to be disabled, introduce a new function, or create an unforeseen mutation. Given the right specific targeting in the germ line, this approach houses the innovation for exterminating entire species through gene drive [6].
The mechanism behind gene drive overthrows the traditional Mendelian sexual reproduction concept of proportional contribution from both the male and female parent. The power comes from the ability of one genetically modified (GM) contributor encoding for the ‘gene drive’ to cut the other set of chromosomes lacking these genes and replace this excision with a self-replicating copy. In effect, this divisive modification would push for an otherwise heterozygous offspring from a wild-type mating with a GM partner to become homozygous for certain genes to be carried on and propagated by future generations. Given that these genetic alterations do not affect the fitness of the organism, dissemination of 1% of the population with CRISPR modified genes can lead to 99% of the local population carrying the genetic indicator in as little as nine generations (The use of gene editing to create gene drives for pest control in New Zealand).
Such a unilateral approach poses political and ethical challenges amongst neighboring nations with diverging ecological approaches to confront pest control. Should this pervasive gene drive program reach beyond its intended border, great difficulty would arise in maintaining this ecological enclosure. For example, possum is on the list of invasive species in NZ while just 2,500 miles west, its neighbor Australia keeps this species of marsupials under protection. As such, scientists have devised a simple model to localize gene alterations, coined The Daisy Chain.
Unlike the original gene drive method in which all components necessary for transformation (CRISPR, edited DNA, and guide RNAs) are provided on the same chromosome, Daisy Chain provides a self-exhaustive means of guaranteeing genetic edits. This tool is designed so that each component required for genetic alteration is dependent on the presence of a different element upstream on the gene found on the same locus to be activated [8]. The most downstream portion of this chain contains the “load” of engineered dominant lethal genes preventing reproduction, which will be promoted to higher frequency in the population within several generations. For instance, should an engineered allele contain three elements A, B, and C, element C would render element B to drive, which will in turn cause element A carrying the final load to drive. The initial element (C in this case) does not actually drive, thus is restricted by the number of altered individuals released into the wild and will be lost via natural selection over time. During initial implementation, the presence of C will increase B in abundance, but B will eventually decline and finally disappear as C is lost in the population. The rapid rise in abundance of B will also cause A to increase in frequency within the local population; however, with the decrease of B, A would not be driven and will ultimately vanish as well [1]. Using MIT Professor Esvelt’s analogy, “… the elements of a daisy drive system are similar to booster stages of a genetic rocket: those at the bottom of the base of the daisy-chain help life the payload until they run out of fuel and are successively lost.”
Challenges with Daisy Chain CRISPR Gene Drive
CRISPR/Cas9 technology’s ability to potentially alter these invasive species’ fecundity provides an avenue of pursuing NZ’s goal of PF 2050. Despite the developed understanding of how to carry out this plan, scientists in NZ are still working to piece together the genomes of stoats and possums in order to understand where to properly facilitate the engineered RNA sequence. Other barriers that must be acknowledged are the unprecedented approach to genetically modify marsupials and the difficulty of implanting hundreds to thousands of oocytes to be dispersed amongst their population.
Beyond these known difficulties, scientists still tread in unknown terrains pertaining to whether these mutations can have pernicious effects in the survival, health, and reproductive success in propagating these mutations within their populations. Further exploration into the development of these modifications, and the potential impacts they can have on these animals, must be investigated on model organisms prior to widespread use.
Of the eight listed mammalian species vied to be permanently eradicated from NZ, Mus musculus holds the most promise, given the extensive knowledge of the Mus musculus genome. With the help of scientists outside of New Zealand, joining in on the efforts to identify which germline gene to focus on, this project has received international attention.
Although the daisy drive provides promising potential, research collaborators at MIT and Harvard have identified a possible risk of, “… DNA encoding a drive component from one element to another, thereby creating a ‘daisy necklace’ capable of a global drive” [1]. Due to this rare recombinatory event arising from the similarity of DNA sequences, these investigators have looked into circumventing the problem by creating numerous alternatives to CRISPR components and selecting the model with the greatest diversity.
Conclusion
From their renowned aviary to reptilian species, New Zealand’s islandic geographical region houses some of the most biodiverse fauna known to man. The arrival of human settlement has introduced predatory species, causing endemic species to experience extinction at concerning rates [4]. With the purpose of preserving their unique remaining diversity, New Zealand has committed to concerted efforts of varying methods to eradicate these invasive vertebrate pests. Investigation into genetic modifications can provide for more expansive and thorough techniques to eliminate these human introduced pests and allow for these endangered species to thrive once again. By further exploring daisy chain CRISPR/Cas9, this effort can be genetically inherited by offspring, allowing for nature to carry out this effort. As opposed to continued efforts of targeting each individual one by one, conservation ecologists can borrow from molecular biologist’s toolkit to revolutionize the means of pursuing pest control and perhaps even pave the road for future endeavors with similar pursuits.
References
- Esvelt, Kevin M. “Daisy Drives.” Sculpting Evolution, www.sculptingevolution.org/daisydrives.
- Gemmell, Neil J., et al. “The Trojan Female Technique: a Novel, Effective and Humane Approach for Pest Population Control.” Proceedings of the Royal Society B: Biological Sciences, vol. 280, no. 1773, 2013, pp. 1–6., doi:10.1098/rspb.2013.2549.
- Griffiths, Richard, et al. “Successful Eradication of Invasive Vertebrates on Rangitoto and Motutapu Islands, New Zealand.” Biological Invasions, vol. 17, no. 5, 2014, pp. 1355–1369., doi:10.1007/s10530-014-0798-7.
- Owens, Brian. “The Big Cull: Can New Zealand Pull off an Audacious Plan to Get Rid of Invasive Predators by 2050?” Nature, vol. 541, 12 Jan. 2017, pp. 148–150.
- Russell, James C., John G. Innes, Philip H. Brown, and Andrea E. Byrom. “Predator-Free New Zealand: Conservation Country.” BioScience 65, no. 5 (October 2015): 520–25. https://doi.org/10.1093/biosci/biv012.
- Saey, Tina Hesman. “Explainer: How CRISPR Works.” Science News for Students, 4 Dec. 2017, www.sciencenewsforstudents.org/article/explainer-how-crispr-works.
- “Why Predator Free 2050?” Department of Conservation. Accessed November 18, 2019. http://www.doc.govt.nz/nature/pests-and-threats/predator-free-2050/why-predator-free-2050/.
- Dearden, Peter K., et al. “The Potential for the Use of Gene Drives for Pest Control in New Zealand: a Perspective.” Journal of the Royal Society of New Zealand, vol. 48, no. 4, 2017, pp. 225–244., doi:10.1080/03036758.2017.1385030.
- Wolff, Jonci N., et al. “Mitonuclear Interactions, MtDNA-Mediated Thermal Plasticity and Implications for the Trojan Female Technique for Pest Control.” Scientific Reports, vol. 6, no. 1, 2016, doi:10.1038/srep30016.
- Min, John, Jason Olejarz, Joanna Buchthal, Alejandro Chavez, Andrea L. Smidler, Erika A. DeBenedictis, George M. Church, Martin A. Nowak, Kevin M. Esvelt, and Charleston Noble. “Daisy-Chain Gene Drives for the Alteration of Local Populations.” PNAS. National Academy of Sciences, April 23, 2019. https://www.pnas.org/content/116/17/8275.
Genetically Engineered Crops: A Food Security Solution?
By Roxanna Pignolet, Biochemistry and Molecular Biology 20’
Author’s Note: Since I started working on plant metabolites as an undergraduate researcher in the Shih Lab, I’ve developed a great appreciation for the power of plant genetic engineering to address a wide variety of problems. A uniquely global and increasingly relevant concern is how to continue to feed the world’s growing population in the face of climate change. I decided to write this paper to provide a snapshot of the current research being done to innovate crop species that will survive in the face of climate change. As part of this review. I also wanted to address ongoing concerns about the safety and impact of GMOs on consumers and the environment, and whether these genetic engineering strategies have the potential to make a positive impact on food security.
Introduction
As the world population continues to rise, climate change is also having an increasingly large impact on agriculture in the form of rising temperatures and intensified weather variations. Population growth is challenging researchers and farmers to find new ways to increase crop yields without access to more land or freshwater. Population is expected to increase from the current 7.7 billion to 9 billion by 2050 (1,2). However, it was found in 2000 that about 70% of the available freshwater was already in use. Meanwhile, climate change is introducing new challenges to crop productivity and stability. By 2050, the global crop demand may increase as much as 110%, which emphasizes the need for new, powerful strategies for crop improvement.
Genetically engineered crops have been used in agriculture since the mid-1990s, and have been instrumental in overcoming serious agricultural challenges such as disease outbreaks and overuse of toxic insecticides (3). In contrast to traditional breeding, genetic engineering allows for a direct transfer of one or more genes of interest from either closely or distantly related organisms. In some cases, a plant is modified solely by turning on or off one of its own genes (4). These methods allow for fast and precise changes that target a specific trait. Since their introduction, numerous studies have measured their potential for health and environmental risks, as well as their benefits. This review will discuss the impacts of genetically engineered crops from an environmental and health perspective. Additionally, I will look at how genetically engineered crops are currently being applied to address food security concerns in the face of climate change.
What is the Impact of Genetically Engineered Crops?
Environment
As genetically engineered crops have now been used in the field for many years, the environmental impacts can be assessed. The most abundant type of genetically engineered crops are insect resistant crops, specifically Bacillus thuringiensis (Bt) resistant corn and cotton. Bt is a soil bacterium which produces proteins that are toxic to certain insects (5). Bt crops have been modified to produce Bt genes as protection against specific pests (3). These crops have been grown commercially since 1996 (2), which has allowed long term environmental studies to be conducted. In a two-year field trial on the impact of transgenic maize on soil fauna, Fan et al. found that there was no impact on biodiversity, abundance or composition of the soil fauna. They compared samples taken in varying conditions from either transgenic maize or non-transgenic maize controls. The researchers found that the insecticide transgene did not affect the soil ecosystem, while factors such as time of year, pH, sampling time, and root-biomass all had significant effects (6). In a 2003 review on Bt crops, Mendelsohn et al. also found that there were no negative impacts observed on species of endangered insects, earthworms, or non-target insects. However, one negative that applies to all insecticides is that pests will eventually gain resistance. Engineering crop varieties to have several different resistance genes has been shown to slow this process (2).
Another class of genetically modified crops that are currently in use are herbicide-tolerant crops. Herbicide-tolerant crops are designed to be tolerant to broad-spectrum herbicides that can be used to control surrounding weeds. Use of herbicide-tolerant corn and soybeans has been shown to decrease the use of highly toxic herbicide sprays in favor of an amino-acid derived, non-toxic alternative (Roundup), and has also encouraged low-till farming practices which have been correlated to significant reductions in greenhouse gasses (2). Weed resistance is a concern with herbicide-resistant crops, especially when a single herbicide gene is overused. In some cases, high selection pressures caused by overuse of a single broad-spectrum herbicide have led to resistant weeds. If unchecked, these resistant weeds can spread across farms and negatively impact crop growth (7). New varieties of crops resistant to multiple types of herbicides should help mitigate this problem by allowing farmers to rotate several types of herbicides. A widespread adaptation of these new varieties and consistent practice of sustainable herbicide application will be important to avoiding negative outcomes of herbicide-tolerant crop use.
Implementing these genetically engineered crops has contributed to overall decreases in the amount of toxic insecticide and herbicide sprayed. Just as with chemical pesticide and herbicide sprays, proper steps must be taken with insect-resistant or herbicide-resistant crops to delay resistance in the affected insect or weed. These steps include rotating planting of herbicide-resistant crops and using weed control tactics with different modes of action to avoid putting high selection pressure on one type of resistance.
Health
The consensus from long term studies carried out to address biosafety concerns of genetically modified crops, is that they are just as safe as their natural counterparts. Genetically engineered crops are subjected to a variety of tests on a case by case basis before they are implemented, and now long term data shows that there have been no side effects from possible unintended chemical compositions of crops, making them just as safe as those derived from traditional breeding. There are, however, concerns about next generation genetic engineering, which targets regulator genes instead of a single functional gene. Targeting regulator genes could allow scientists to target plant stress response pathways, and engineer plants to have multiple desirable traits (8). Additional research must be conducted to assess the plant-wide changes caused by affecting a player in a signaling cascade.
New Approaches to Crop Improvement
While the current genetically engineered crops have been found to have a positive effect on crop yields, the increases are not enough to keep up with projected population growth. Additionally, climate change is predicted to cause stressors to crops such as drought, rising temperatures, and weather variations among other things (2). Therefore, scientists are looking for new and creative genetic engineering techniques to create robust and high-yielding crops for our future.
One of the main targets for genetically engineered crops is adaptions to grow and produce quality yields under higher temperatures. In a study investigating the genes responsible for creating lower quality, chalky rice grains under high temperature conditions, Nakata et al. looked at the role of a starch metabolizing enzyme, known as amylase, in the packing of starch into rice grains. Their team used transgenic rice modified with a reporter gene attached to each isotype of the amylase gene. By comparing the activity of plants overexpressing each variety, they were able to identify specific amylase genes as targets for genetic modification. Rice variants with these modifications would remain higher quality, with tightly packed starch, even if grown under non-optimal higher temperatures (9). Another study tested the responses of a previously created transgenic rice line called HOSUT under high amounts of carbon dioxide (CO2), a heat wave, and nitrogen enriched conditions. They found that the transgenic line, which has enhanced sucrose transport, has a superior yield than the control line (Certo), and that increased CO2 conditions resulted in higher yields in Certo with only minimal increases for HOSUT. They concluded that the minimal response of HOSUT to the increased CO2 was indicative of HOSUT already being saturated due to its optimized transport capabilities. The HOSUT line is already optimized for translocation of carbon, which they were able to show by increases in starch in the grains in HOSUT only. HOSUT also produced more yield in response to increased nitrogen, making it a good option for producing high rice yields under variable climate change conditions (10) The HOSUT line is a great example of how genetic engineering can be used to fortify and optimize crops to both survive under atypical conditions and produce enough yield to keep up with demand.
Another problem that researchers are addressing through genetic engineering, is drought. Selvaraj et al., developed and field tested two drought tolerant rice lines, created by introducing an Arabidopsis stress response gene (galactinol synthase) with a maize promoter. Galactinol synthase produces galactinol, a sugar that functions as an osmoprotectant, keeping water from leaving the cells. These galactinol synthase genes were introduced into two commercially available rice lines and tested in the field under drought and well-watered conditions. Under drought conditions, the collection of galactinol resulted in higher grain yields, while under well-watered conditions no significant yield increase was observed. Galactinol is a sugar that functions as an osmoprotectant, keeping water from leaving the cells. The results of these field trials show that these rice lines are ready to be integrated into ongoing breeding programs (11). Wang et al. also tackled the problem of drought stress caused by global warming on fruit such as apple trees. They transgenically expressed an aquaporin gene found in Fuji apples that has increased expression during fruit growth in tomato. The transgenic plants did have an increased drought tolerance, observed as an increased sensitivity of their stomata to water loss, and a larger fruit size when compared to wild type. This research will be continued in apples next with the goal of producing plants with larger fruits when well-watered, which will also be more tolerant to drought due to increased water transport efficiency (12).
A third target for genetic engineering solutions is circadian rhythms. Understanding and controlling circadian rhythms in crop plants has the potential to adapt plants to radically different environments. One group at the Guru Jambheshwar University of Science and Technology is tackling this challenge in rice. This group expressed an Arabidopsis transcription factor known as Circadian Clock Associated1 (CCA1) under the Timing Of Cab Expression 1 (TOC1) promoter, which are both part of the circadian clock machinery in Arabidopsis. They found that overexpression of the CCA1 in rice had negative results, while repressing it caused positive changes to plant morphology. The researchers used RNAi, which is a biological process where small fragments of RNA are used by the cell to target complementary mRNA for destruction, thus silencing expression of the encoded protein. By comparing RNAi constructs based off of three different parts of the CCA1 gene for silencing the gene expression, they found that the RNAi derived from the 3’-terminal end of the CCA1 gene had the best impact on plant morphology (13). This study is an important first step towards unlocking the power of using circadian clock genes to breed plants better adapted to a changing environment.
One new strategy being considered is a CRISPR/Cas9 genome editing method that could be used to quickly develop improved crop varieties without transgenes. CRISPR/Cas9 can introduce specific changes into a plant genome without being limited by existing variation. Applying this method, scientists will be able to stack multiple edits into a plant within a single generation, resulting in transgene-free progeny. One benefit of this method is that it may allow for more complex changes to polygenetic traits or signaling pathways. For example, this could be helpful for targeting complex plant stress response pathways. This technology is currently limited by the availability of annotated reference genome sequences for plants other than Arabidopsis. Scheben et al. suggest that taking a genomics-based approach would allow for a comparison of species-wide genome diversity, making differences in copy-number visible and thus available for editing. While the authors suggest that this method creates plants that are indistinguishable from those created through natural breeding and random mutations, bans against genetically modified crops may target methodologies rather than the final result (14).
Conclusion
Currently implemented genetically engineered crops, have been shown, through years of testing and trials to be at least as safe, both towards the environment and in terms of human health, as naturally bred varieties. While new transgenic lines must be screened and tested on a case-by-case basis, the overall benefits of this technology make it an important tool that may be necessary to confront upcoming challenges to agriculture. Climate change and population growth are putting steep demands on crops to survive in more hostile environments while also producing higher yields. Current efforts are focusing on vital crops, such as rice, corn, wheat, and fruits, to create drought-tolerant, heat-tolerant, and yield-optimized plants.
References
- “World Population Clock: 7.7 Billion People (2019) – Worldometers.” n.d. Accessed November 18, 2019. https://www.worldometers.info/world-population/.
- Ronald, Pamela. 2011. “Plant Genetics, Sustainable Agriculture and Global Food Security.” Genetics; Bethesda 188 (1): 11–20.
- Mendelsohn, Mike, John Kough, Zigfridais Vaituzis, and Keith Matthews. 2003. “Are Bt Crops Safe?” Nature Biotechnology 21 (9): 1003–9. https://doi.org/10.1038/nbt0903-1003.
- “Genetic Engineering and GM Crops | ISAAA.Org.” n.d. Accessed November 18, 2019. https://www.isaaa.org/resources/publications/pocketk/17/default.asp.
- “Bacillus Thuringiensis (Bt).” n.d. Accessed November 18, 2019. http://npic.orst.edu/ingred/bt.html.
- Fan, Chunmiao, Fengci Wu, Jinye Dong, Baifeng Wang, Junqi Yin, and Xinyuan Song. 2019. “No Impact of Transgenic Cry1Ie Maize on the Diversity, Abundance and Composition of Soil Fauna in a 2-Year Field Trial.” Scientific Reports 9 (1): 1–9. https://doi.org/10.1038/s41598-019-46851-z.
- Resources, University of California, Division of Agriculture and Natural. n.d. “Herbicide Tolerance.” Accessed November 18, 2019. http://sbc.ucdavis.edu/Biotech_for_Sustain_pages/Herbicide_Tolerance.
- Ortiz, R., Andy Jarvis, P. Fox, Pramod K. Aggarwal, and Bruce M. Campbell. 2014. “Plant Genetic Engineering, Climate Change and Food Security.” Working Paper. CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS). https://cgspace.cgiar.org/handle/10568/41934.
- Nakata, Masaru, Yosuke Fukamatsu, Tomomi Miyashita, Makoto Hakata, Rieko Kimura, Yuriko Nakata, Masaharu Kuroda, Takeshi Yamaguchi, and Hiromoto Yamakawa. 2017. “High Temperature-Induced Expression of Rice α-Amylases in Developing Endosperm Produces Chalky Grains.” Frontiers in Plant Science 8. https://doi.org/10.3389/fpls.2017.02089.
- Weichert, Heiko, Petra Högy, Isabel Mora-Ramirez, Jörg Fuchs, Kai Eggert, Peter Koehler, Winfriede Weschke, Andreas Fangmeier, and Hans Weber. 2017. “Grain Yield and Quality Responses of Wheat Expressing a Barley Sucrose Transporter to Combined Climate Change Factors.” Journal of Experimental Botany 68 (20): 5511–25. https://doi.org/10.1093/jxb/erx366.
- Selvaraj, Michael Gomez, et al. “Overexpression of an Arabidopsis Thaliana Galactinol Synthase Gene Improves Drought Tolerance in Transgenic Rice and Increased Grain Yield in the Field.” Plant Biotechnology Journal, vol. 15, no. 11, Nov. 2017, pp. 1465–77. PubMed, doi:10.1111/pbi.12731.
- Wang, Lin, Qing-Tian Li, Qiong Lei, Chao Feng, Xiaodong Zheng, Fangfang Zhou, Lingzi Li, Xuan Liu, Zhi Wang, and Jin Kong. “Ectopically Expressing MdPIP1;3, an Aquaporin Gene, Increased Fruit Size and Enhanced Drought Tolerance of Transgenic Tomatoes.” BMC Plant Biology 17, no. 1 (December 19, 2017): 246. https://doi.org/10.1186/s12870-017-1212-2.
- Chaudhury, Ashok, Anita Devi Dalal, and Nayan Tara Sheoran. 2019. “Isolation, Cloning and Expression of CCA1 Gene in Transgenic Progeny Plants of Japonica Rice Exhibiting Altered Morphological Traits.” PLOS ONE 14 (8): e0220140. https://doi.org/10.1371/journal.pone.0220140.
- Scheben, Armin, Felix Wolter, Jacqueline Batley, Holger Puchta, and David Edwards. 2017. “Towards CRISPR/Cas Crops – Bringing Together Genomics and Genome Editing.” New Phytologist 216 (3): 682–98. https://doi.org/10.1111/nph.14702.
A Chemical Report on Heptachlor (Heptachlor Epoxide)
By Kaiming Tan
Author’s Note: This report analyzes and explains the biological, chemical, and environmental importance of heptachlor. More and more in today’s society, we are utilizing synthetic compounds as agricultural insecticides, which makes understanding what these chemicals do to our bodies and the environment of utmost importance. Farming strategies may seem far-removed from our daily lives, but these chemicals do not stay on the farm. They travel to our cities, to our grocery stores and markets, then make their way onto our dinner plates and into our children’s stomachs. I am constantly amazed at the power of scientific research to transform and demystify the detrimental nature of environmental and biological toxicants; this, combined with my passion in toxicology, has inspired me to research this topic and write this manuscript.
Keywords
Heptachlor, heptachlor epoxide, insecticide, environmental toxicology, biological toxin
Introduction
Heptachlor was introduced into the United States in the 1940s and 1950s, among the other chlorinated hydrocarbon insecticides, such as DDT (4). In 1971, 500,000 kilograms of heptachlor were applied to agricultural fields in soils and seeds to prevent termite infection in woods (4). However, after it became evident that heptachlor’s toxicity was a serious health concern, the Environmental Protection Agency (EPA) banned all registered use of heptachlor because of its carcinogenic properties and bioaccumulation in food and water. With the exception of treatment of fire ants in underground power transformers, there is no use of heptachlor in the United States now (2). In contrast, heptachlor is still used as an insecticide in some areas in Asia, Africa, and Eastern Europe (5). The form of greater toxicological concern is heptachlor epoxide, which is a metabolite of heptachlor in soil and the human body. Heptachlor epoxide is more toxic because it degrades slower than heptachlor, thus, is more persistent in the environment. Both heptachlor and heptachlor epoxide can be found in freshwater, estuarine, and marine systems (6). This review will cover the current literature on heptachlor toxicity and investigate the impact of heptachlor on biological systems.
Biological Fate (Absorption, Distribution, Metabolism, Elimination)
Humans and animals can be exposed to heptachlor and heptachlor epoxide through soil, air and water; however, the main route of exposure is oral, through consuming contaminated food or drinking contaminated water. Children and infants are especially vulnerable to heptachlor exposure if they consume large amounts of breast milk from their mother. For instance, if the mother’s breast milk is contaminated by heptachlor, heptachlor can be easily consumed by the infant through breast milk feeding. In human breast milk, heptachlor epoxide was detected ranging from 0.13 to 128 ppb (parts per billion) (8). Another route of exposure is through inhalation. When heptachlor is deposited into the soil, it becomes heptachlor epoxide, which then spreads into the air. As a result, workers who use heptachlor to kill termites are potentially susceptible to inhaling heptachlor epoxide from the air (2). In addition, touching contaminated soils causes exposure to heptachlor dermally (1).
Heptachlor persists in the environment after agricultural application. Even though there was no information on the background levels of heptachlor and heptachlor epoxide in the air or soil, there are 20 to 800 ppt (parts per trillion) heptachlor in drinking water and groundwater in the United States (2). Contaminated fish and shellfish were detected with levels of 2 to 750 ppb of heptachlor and 0.1 to 480 ppb of heptachlor epoxide. To date, there is no available data regarding the biological fate of heptachlor on humans. However, in rats, at least 50% of the orally-administered dose of heptachlor is absorbed in the gastrointestinal tract.The absorption is indicated by the presence of heptachlor and/or heptachlor epoxide in the rats’ liver (9). When heptachlor epoxide enters the bloodstream after absorption, it becomes the predominant metabolite in the body of laboratory female rats. Heptachlor epoxide in the bloodstream is positively correlated to the heptachlor dose administered (10). In other words, the higher heptachlor dose one consumed, the more heptachlor epoxide would appear in the bloodstream.
Because of heptachlor epoxide’s high lipophilicity (likelihood in dissolving fats), its residue is found highest in adipose tissue in human infants (0.32±0.10ppm), while undetectable in the brain. These data also suggest that heptachlor epoxide can be transferred between pregnant women and their babies through the placenta (11). Furthermore, heptachlor and heptachlor epoxide can be stored in human breast milk. Jonsson et al.’s study in 1977 sampled the breast milk of 51 women who had no previously known exposure to heptachlor and detected an average concentration of heptachlor epoxide between 0.0027ppm and 0.019ppm (12). To the researchers, the results proved worrisome as the women’s breast milk contained high levels of heptachlor, which could damage the infant. The results were even more of a concern because there was no known interaction between the women studied and heptachlor.
After heptachlor is absorbed in the body, the primary metabolite of heptachlor in humans and rats is heptachlor epoxide. Heptachlor and heptachlor epoxide are usually metabolized by Cytochrome P450 (CYP450) enzymes. CYP450 enzymes are the body’s major class of enzymes responsible for detoxification. Moreover, heptachlor alters liver function by increasing gluconeogenic enzymes’ activities, which upregulates glucose synthesis from glycogen. Since most of heptachlor is metabolized in the liver, humans with liver diseases may have increased bioaccumulation of heptachlor epoxide because of decreased CYP450 enzyme activity (13). Despite the metabolism of heptachlor in the liver, most heptachlor epoxide can be stored in the adipose tissue because of its high lipophilicity and long half-life (1).
In terms of excretion, orally-administered heptachlor in rats was excreted in the form of heptachlor epoxide and also as heptachlor. Radiolabeled heptachlor epoxide is excreted ten times more in the feces compared to urine after ten days of oral administration in rats, due to the high lipophilicity of heptachlor metabolites (8).
Mechanism of Action
The primary organ and organ systems that heptachlor targets are the liver, central nervous system and reproductive system, while secondary target organs include kidneys and lungs. Heptachlor is primarily metabolized in the liver into heptachlor epoxide, which has the same toxic potential. The reproductive system is a sensitive target for heptachlor toxicity because this system lacks a comprehensive detoxification system like the CYP450 enzymes in liver. CYP450 enzymes facilitate chemical reactions that chemically convert the toxicant into a more hydrophilic metabolite, thereby enhancing toxicant elimination by urine. Oral exposure of 1.8 mg/kg/day to female rats over 14 days caused decreased fertility due to decreased estradiol and progesterone levels. Estradiol and progesterone are important hormones produced by the ovaries, placenta, and adrenal glands; decreased levels may result in endocrine disruption and delayed sexual development. Oral exposure of 0.65 mg/kg/day over 70 days caused decreased sperm count in male rats. The mechanism of heptachlor’s reproductive toxicity remains unknown (1-2).
GABA, the molecule that normally binds the GABA receptor, is an amino acid which can also serve as an inhibitory neurotransmitter in the mammalian brain. Heptachlor primarily acts as a noncompetitive antagonist of the chloride channels of the GABAA receptors in mammals. In other words, heptachlor blocks the Chlorine channel in the cells thus preventing GABAA activation (1-2, 14). By inhibiting the inhibitory neuron, heptachlor causes hyperexcitability of the cells. Although the heptachlor toxicity mechanism in liver is unknown, it is observed that in rats that presence of heptachlor elevates intracellular calcium levels and induces protein kinase C (PKC), which in turn activates the activator protein-1 DNA binding thereby causing tumorigenesis (2, 14).
When animals are exposed to heptachlor above the toxic threshold, symptoms occur including tremors, convulsions, ataxia, and changes in EEG patterns (1). Also, rats who were orally exposed to >320 ppm of heptachlor had consistently lower body weight than rats that were unexposed (15). In humans, clinical symptoms of heptachlor toxicity include seizure, vomiting, and convulsions (2).
Although heptachlor epoxide is theoretically an effective mutagen because of its high reactivity as an electrophile, research studies on heptachlor mutagenicity yielded mostly negative results. For example, heptachlor was not mutagenic in the auxotrophic strains of E. coli by reversion bioassays (14,15). In addition, heptachlor is proven to increase liver tumor incidence as an epigenetic promoter in previously initiated B6C3F1 mice. Heptachlor is a carcinogen in mice by inhibiting intercellular communications to promote tumor growth (14,16). On the other hand, research studies that investigate heptachlor’s teratogenicity, or tendency to disturb embryonic development, yielded mostly negative results. For instance, although feeding rats with diets containing heptachlor produces pups with higher mortality, no congenital malformation was found (2, 14, 17).
In male rats, oral LD50 (lethal dose for 50% of the study population) of heptachlor is 40 to 100 mg/kg body weight based on data from two studies. In contrast, the oral LD50 of heptachlor in male chickens is 62 mg/kg body weight (1, 17). Symptoms displayed by heptachlor acute toxicity in animal subjects include hyperexcitability, tremors, convulsions and paralysis (18).
Long-term exposure to heptachlor can cause liver damage in animals. In rats, prolonged exposure of sub-lethal doses of heptachlor is associated with increased CYP450 enzyme induction and other hepatic microsomal enzymes, in addition to liver hypertrophy (18). In humans, chronic exposure to heptachlor results in storage in adipose tissue and breast milk, because heptachlor is very lipophilic. Infants are at risk of being exposed to large doses of heptachlor if they consume contaminated breast milk (17). Despite the lack of human studies on long-term exposure, a multi-generation study conducted on rats concluded that oral exposure of 6 mg/kg/day of heptachlor is associated with decreased litter size, increased mortality and lens cataract (2). Because of its high lipophilicity, heptachlor residues can remain in the body over time. Heptachlor’s long-term toxicity damages the body gradually, further underlying the need for strict regulations of heptachlor use worldwide.
Overview of Latest Research
Recent research on heptachlor focuses on its toxicity, specifically on the oxidative stress caused by heptachlor and its metabolism in aquatic animals. For example, Vineela et al.’s study investigates the impact of sub-lethal concentrations of heptachlor on carp fish Catla catla by measuring enzymatic activities of mostly Phase II enzymes (19). Phase II enzymes, a part of the CYP450 enzyme class, primarily perform conjugation reactions to convert the chemical into more water-soluble form to enhance urine elimination. Oral exposure of heptachlor at 1.46mg/L (20% of LC50 concentration) for 45 days causes a significant increase in lipid peroxidation, superoxide dismutase, glutathione-S-transferase and catalase activity in Catla catla. The results suggest that carp fish have a sensitive biological defense system against heptachlor, because low concentration activates the detoxification by increased biomarkers of primarily Phase II activity to prevent heptachlor toxicity and organ damage (19).
In addition to heptachlor toxicity, current research also focuses on how to remove existing heptachlor from the environment via microbial degradation, as this method is more environmentally mindful and cost-effective than current physicochemical methods. Qiu et al.’s study discovered a novel strain of bacteria, named strain H, that can metabolize heptachlor efficiently. Strain H is a Gram-negative, short rod-shaped, single-cell bacterial strain that can degrade heptachlor at a rate of 88.2% degradation in 130 hours when exposed to 300 μg/L of heptachlor at 30oC. The main metabolites of heptachlor by strain H include heptachlor epoxide, chlordane epoxide, and 1-hydroxychorodene. This innovation allows possible bioremediation by microorganisms like strain H in heptachlor-contaminated soil and water to reduce heptachlor toxicity and threat to the environment and animals (20).
Recent studies on heptachlor took a creative approach in gaining a deeper understanding in reducing heptachlor toxicity by enzymatic activity in aquatic model organisms and inventing novel microorganisms to metabolize heptachlor into less toxic metabolites. These new techniques will benefit public health by developing cost-effective ways for toxicant removal and controlling the environmental/biological fate of toxicants without causing additional harm.
Conclusions
When initially used as an insecticide, heptachlor’s toxicity became a threatening health concern. The ban of commercial heptachlor use in the United States was a step in the right direction, as misuse of heptachlor can cause severe environmental consequences such as prolonged residue in soil and water habitats along with toxicities in humans and animals. Based on this research, other countries should pursue a substitute pesticide that has less potential for environmental and biological damage than heptachlor.
Most studies conducted regarding heptachlor toxicity were conducted between the 1950s and the late 1980s. Future research can focus on the dose-response relationship of heptachlor exposure within large populations and whether genetic polymorphism contributes to the metabolism of heptachlor. Environmental toxicologists can also study the synergistic toxicity of heptachlor on environmental damage with other pesticides, since common pesticides often contain more than one chemical (1,2).
Acknowledgment
The author would like to thank Dr. Matthew Wood and Mr. Thomas Sears for providing feedback on early versions of this manuscript.
Works Cited (in order of appearance)
- Reed, N.R., & Koshlukova, S. (2014). Heptachlor. In Encyclopedia of Toxicology (pp. 840-844).
- United States. Agency for Toxic Substances Disease Registry, & Syracuse Research Corporation. (2007). Toxicological Profile for Heptachlor and Heptachlor Epoxide.
- Ivie, G., Knox, W., Khalifa, J., Yamamoto, R., & Casida, S. (1972). Novel photoproducts of heptachlor epoxide, Trans -chlordane, and Trans -nonachlor. Bulletin of Environmental Contamination and Toxicology, 7(6), 376-382.
- Hodgson, E. (2004). A textbook of modern toxicology (3rd ed.). Hoboken, N.J.: Wiley-Interscience.
- United States. Environmental Protection Agency. Office of Research Development. (2002). The Foundation for Global Action on Persistent Organic Pollutants a United States Perspective.
- Schimmel, S., Patrick, J., & Forester, J. (1976). Heptachlor: Toxicity to and uptake by several estuarine organisms. Journal of Toxicology and Environmental Health, 1(6), 955-965.
- Mnif, W., Hassine, A. I. H., Bouaziz, A., Bartegi, A., Thomas, O., & Roig, B. (2011). Effect of Endocrine Disruptor Pesticides: A Review. International Journal of Environmental Research and Public Health, 8(6), 2265–2303. http://doi.org/10.3390/ijerph8062265
- Savage, E., Keefe, T., Tessari, J., Wheeler, H., Applehans, F., Goes, E., & Ford, S. (1981). National study of chlorinated hydrocarbon insecticide residues in human milk, USA. I. Geographic distribution of dieldrin, heptachlor, heptachlor epoxide, chlordane, oxychlordane, and mirex. American Journal of Epidemiology, 113(4), 413-22.
- Tashiro, S., & Matsumura, F. (1978). Metabolism of trans -nonachlor and related chlordane components in rat and man. Archives of Environmental Contamination and Toxicology, 7(1), 113-127.
- Radomski, J., & Davidow, B. (1953). The metabolite of heptachlor, its estimation storage, and toxicity. The Journal of Pharmacology and Experimental Therapeutics, 107(3), 266-72.
- Curley, A., Copeland, M., & Kimbrough, R. (1969). Chlorinated Hydrocarbon Insecticides in Organs of Stillborn and Blood of Newborn Babies. Archives of Environmental Health: An International Journal, 19(5), 628-632.
- Adeshina, F., & Todd, E. (1990). Organochlorine compounds in human adipose tissue from north Texas. Journal of Toxicology and Environmental Health, 29(2), 147-156.
- Komori, Nishio, Kitada, Shiramatsu, Muroya, Soma, . . . Kamataki. (1990). Fetus-specific expression of a form of cytochrome P-450 in human livers. Biochemistry, 29(18), 4430-3.
- Whitacre, David M. (2008). Reviews of Environmental Contamination and Toxicology(Vol. 234). New York, NY: Springer New York.
- Moriya, Ohta, Watanabe, Miyazawa, Kato, & Shirasu. (1983). Further mutagenicity studies on pesticides in bacterial reversion assay systems. Mutation Research, 116(3-4), 185-216.
- Williams, G., & Numoto, S. (1984). Promotion of mouse liver neoplasms by the organochlorine pesticides chlordane and heptachlor in comparison to dichlorodiphenyltrichloroethane. Carcinogenesis, 5(12), 1689-96.
- United Nations Environment Programme, World Health Organization, International Labour Organisation, & Commission of the European Communities. (1976). Environmental health criteria. Geneva: World Health Organization.
- World Health Organization, & International Program on Chemical Safety. (1988). Heptachlor health and safety guide. Geneva : Albany, NY: World Health Organization ; WHO Publications Center USA [distributor].
- Vineela, D., Janardana Reddy, S., & Kiran Kumar, B. (2017). Impact of Heptachlor on Antioxidant Enzyme Markers of Fish Catla Catla. World Journal of Pharmaceutical Research, 6(12), 759-771. doi:10.20959/wjpr201712-9679
- Qiu, Liping, Wang, Hu, & Wang, Xuntao. (2018). Conversion mechanism of heptachlor by a novel bacterial strain. RSC Advances, 8(11), 5828-5839.
Davis Downfall According to Sierra Club
By Mari Hoffman
Authors note: UC Davis does an immense amount of waste reduction and energy conservation practices, but after writing this essay in my Water Quality at Risk class I wondered if it is enough. In 2018, UC Davis did not make it on the “Cool Schools” list by Sierra Club Magazine. The previous year we were ranked as number 32. I was assigned this essay to compare some of the practices that UC Davis does with other schools to get an understanding on what we are excelling at and where we can improve. I chose to focus on how we can improve in regards to water waste with an implementation of porous concrete.
Cultured Meat: Teaching an Old Cell New Tricks
By Tannavee Kumar, Genetics and Genomics ‘20
Author’s Note
Cultured meat has been a topic of great discussion as we try to understand the extent to which animal agriculture contributes to greenhouse gas emissions and other environmental issues. While plant-based imitation meats have been on the market for decades, I was particularly interested in this lab-grown alternative when I heard that stem cells were being used to produce actual meat without having to raise animals themselves. This could potentially reduce the environmental footprint of the agricultural industry while providing a viable solution for consumers. While it is critical to understand how consumption levels of animal-based products have had an effect on health, and particularly how the change in consumption of these products have changed average human health, my research focused more on how traditional meat impacts environmental health and how cultured meat can help mitigate some of these problems.
RoboBees: The Future of Food and Society?
By Tannavee Kumar, Genetics & Genomics, ’20
Author’s Note
Going into my research on fully automated and autonomous bee swarms, I was aware that there was much controversy on how we as a society should address and work to solve the problem of the drastically declining honeybee population. Upon coming across the large initiative that a team at Harvard University is spearheading, I was interested whether robotic bees are the future of agriculture and moreover part of the tidal wave of automation.
The Relationship Between Genetic Diversity and Disturbance in the Eelgrass Species Zostera marina
By Ryan Green
Author’s note:
This piece was written for my upper division university writing class, Writing in the Sciences. We were required to write a review article on a topic of our choice, and I chose the relationship between genetic diversity and disturbance of Zostera marina. I decided to pursue this topic because I was concurrently working in a molecular ecology eelgrass lab on campus, and I believed to get the most out of this lab experience I should have a good grasp of the current research that is already published and what still needs to be published within the subject. I hope this review gives readers a better understanding of where we now stand in eelgrass molecular ecology research, just as it did for myself.