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Herbicide Harm to Biodiversity

Herbicides, a sub-category of pesticides, are considered pollutants.[1] Pollution is viewed as the 2nd or 3rd largest factor driving biodiversity loss in the U.S.[2] The two largest types of pollution impacting biodiversity are nutrient pollution followed by pesticide pollution.[3]

There is much uncertainty regarding the levels of impact on biodiversity; the heavy usage of herbicides and insecticides is a global experiment on a biodiverse planet.[4,5] High levels of complexity are due to varying impacts on individual species, interacting chemicals, the multitude of environmental stresses, and the fine-tuned balance of ecosystems.[6,7]

 

  1. Note: The 2 most common categories of pesticides are herbicides (targeting plants) and insecticides (targeting insects). Other pesticides include fungicides and rodenticides.
  2. See, Animal Ag Drivers of Biodiversity Loss Overview
  3. Kanter, D. et al., (2022) Science briefs on targets, goals and monitoring In support of the post-2020 global biodiversity framework negotiations. Secretariat of the Convention on Biological Diversity, p. 4. [“Pollutants of concern affecting biodiversity and nature’s contributions to people include nutrients, pesticides, plastics, industrial chemicals, heavy metals, light and noise. We provide background below on why nutrient (nitrogen and phosphorus) and pesticide pollution are of particular concern and are the focus of this brief.”]
  4. Battaglin, W. A., et al., (2014). Glyphosate and Its Degradation Product AMPA Occur Frequently and Widely in U.S. Soils, Surface Water, Groundwater, and Precipitation. Journal of the American Water Resources Association, 50(2), 275–290. p. 285. [“…the ecosystem effects of chronic low-level exposures to pesticide mixtures are uncertain.”]
  5. Mann, R. M., et al., (2009). Amphibians and agricultural chemicals: review of the risks in a complex environment. Environmental pollution, 157(11), 2903-2927, p. 2920. [“However, demonstrating a link between population declines and the toxic effects of agricultural chemicals is difficult.” “The uncertainties lie with the fact that the agricultural landscape is constantly in a state of flux.”]
  6. Wan, N.F., et al., (2025). Pesticides have negative effects on non-target organisms. Nature Communications, 16(1), 1360–16, p. 7. [“…pesticide use has the potential to result in wider perturbation of ecological communities and functions. While we identified responses for individual compounds, it is likely that these effects may be exacerbated through additive or potentially synergistic effects where compounds are applied in combination or to areas with existing residues present.”]
  7. Mann, R. M., et al., (2009), p. 2921. [“Clearly, the resource intensive nature of these kinds of studies and the countless combinations of chemicals and environmental factors that are likely to interact make it impossible to examine all possible scenarios.”]

Target plants – Herbicides are designed to kill a wide range of plants, especially those viewed as weeds – i.e., vigorously growing plants that are unwanted in a particular location. The loss of weeds affects the entire food chain since they provide “considerable benefits to the agroecosystem by supporting a range of organisms such as decomposers, predators, pollinators, and parasitoids.”[1]

Non-target plants – Herbicide drift and runoff into waterways eliminates many non-target plants and thereby impacts ecosystems that harbor a wide variety of species.[2,3]

Animals – The chemicals in herbicides directly and indirectly damage a wide range of animals.[4-7] Insect populations shrink due to loss of food supplies, along with insect-eating birds.[8]

Micro-organisms in soil – Herbicides build up in soil creating residues and high levels of toxicity, eventually altering soil ecosystems.[9]

 

  1. Schütte, G. et al., (2017). Herbicide resistance and biodiversity: agronomic and environmental aspects of genetically modified herbicide-resistant plants. Environmental Sciences Europe, 29(1), 5, p. 8. [“(Weeds) fulfil certain functions within the agroecosystem which becomes obvious when they are missing…”]
  2. Sánchez-Bayo, F. & Wyckhuys, K. A. G. (2019). Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation, 232, 8–27, p. 20.. [“Herbicides, however, reduce the biodiversity of vegetation within the crops and in surrounding areas through drift and runoff, thus impacting indirectly on the arthropod species that depend upon wild plants, which either disappear completely or decline significantly in numbers.“]
  3. Schütte, G. et al., (2017), p. 8. [“Herbicide drift to field margins is a concern to nature conservation and biodiversity of agricultural landscapes, as field margins and hedgerows often harbour rare plant species,”]
  4. Farruggia, F. T., et al., (2016). Refined ecological risk assessment for atrazine. US Environmental Protection Agency, Office of Pesticide Programs: Washington, DC, USA, Abstract. [For atrazine, “EPA levels of concern for chronic risk are exceeded by as much as 22, 198, and 62 times for birds, mammals, and fish, respectively.”]
  5. U.S. EPA (2021) Final National Level Listed Species Biological Evaluation for Glyphosate, Chapter 4: Appendix 4-1, Species Effects Determinations, Summary Tables. [The EPA has determined that glyphosate is “likely to adversely affect” almost 90% of the nation’s listed endangered animal species. (736 / 847 = ~87%.]
  6. Mikaela Conley (May 4, 2024) Atrazine, an endocrine-disrupting herbicide banned in Europe, is widely used in the U.S. U.S. Right to Know. https://usrtk.org/pesticides/atrazine/ [A recap of many reports that explore atrazine’s impacts on human and animal health.]
  7. International Agency for Research on Cancer. (2015). IARC Monographs Volume 112: evaluation of five organophosphate insecticides and herbicides. World Health Organization, Lyon. p. 1. [“The herbicide glyphosate and the insecticides malathion and diazinon were classified as probably carcinogenic to humans.”]
  8. Sánchez-Bayo, F. (2011). Impacts of agricultural pesticides on terrestrial ecosystems. Ecological impacts of toxic chemicals, 2011, 63-87. [“The routine application of herbicides has produced a net loss of plant biomass and biodiversity in many landscapes, which indirectly reduces the associated arthropod communities and leads to population declines in many species of birds, and possibly amphibians too, due to lack of food.”]
  9. van Bruggen, A. H. C., et al., (2018). Environmental and health effects of the herbicide glyphosate. The Science of the Total Environment, 616–617, 255–268, p. 14. [“Thus, the presence of glyphosate in soil could change the community compositions of bacteria and fungi, in turn altering soil ecosystem functions and plant and animal health.”]

 Glyphosate – By far, the most common herbicide is glyphosate. About 280 million pounds were applied in 2018, which was about 44% of the total volume of herbicides in that year.[1,2]

Atrazine – The 2nd most common herbicide is atrazine. About 72 million pounds were applied in 2018, approximately 11% of the total.[3,4]

 

  1. U.S. EPA (April 18, 2019) Memorandum: Glyphosate: Response to Comments, Usage, and Benefits (PC Codes: 103601 103604, 103605, 103607, 103608, 103613, 417300), p. 2. [“About 280 million pounds of glyphosate are applied to an average of 298 million acres of crop land annually.” 280/632.6 = 44%. FAOSTAT for total herbicide usage for 2018 = 632.6 million lbs. Federal agencies do not track total usage on a regular basis.]
  2. USGS, Pesticide National Synthesis Project (2021) Estimated Annual Agricultural Pesticide Use, Glyphosate 2018. https://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2019&map=GLYPHOSATE&hilo=L [Chart estimates glyphosate at about 275 – 280 million pounds for 2018]
  3. USGS,  Pesticide National Synthesis Project (2021) Estimated Annual Agricultural Pesticide Use, Atrazine 2018. [Chart estimates atrazine usage at approximately 72 million pounds for 2018. 72/632.6 = 11%.]
  4.  Beaulieu, M., et al., (2020). Predicting atrazine concentrations in waterbodies across the contiguous United States: The importance of land use, hydrology, and water physicochemistry. Limnology and Oceanography, 65(12), 2966-2983. p. 2966. [“Atrazine, an herbicide, is the second most used pesticide in the United States…”]

Herbicides are ubiquitous in the nation’s waterways, especially glyphosate and atrazine, the two most common herbicides.

 Glyphosate – In 2 separate studies, USGS scientists detected glyphosate (or its degradation product AMPA) in more than half of tested rivers and streams.[1,2]

 Atrazine – USGS scientists found atrazine “exceeded benchmarks” at 45% of tested river sites.[3] The EPA detected atrazine at low levels in more than 40% of lakes throughout the country.[4]

Herbicides are present in soil, sediment, and even precipitation, thereby affecting biodiversity throughout entire ecosystems. Most Americans have detectable levels of glyphosate in their urine.[5]

 

  1. Battaglin, W. A., et al., (2014). Glyphosate and Its Degradation Product AMPA Occur Frequently and Widely in U.S. Soils, Surface Water, Groundwater, and Precipitation. Journal of the American Water Resources Association, 50(2), 275–290, p. 279. [In 38 states, glyphosate was detected in more than 50% of large rivers and streams.]
  2. Medalie, L., et al., (2020). Influence of land use and region on glyphosate and aminomethylphosphonic acid in streams in the USA. Science of the Total Environment, 707, 136008. [“Glyphosate and AMPA were found in 74% and 90%, respectively, of 70 streams and rivers sampled throughout the US from 2015 to 17…”]
  3. Stackpoole, S. M., et al., (2021). Pesticides in US rivers: regional differences in use, occurrence, and environmental toxicity, 2013 to 2017. Science of the Total Environment, 787, 147147, p. 7. [33 of 74 sites exceeded benchmarks.]
  4. U.S. EPA (2024) National Lakes Assessment: The fourth collaborative survey of lakes in the United States. EPA 841-R-24-006. [“Detections of atrazine increased by 11 percentage points, to 41%.”]
  5. CDC (2022) National Health and Nutrition Examination Survey: 2013-2014 Data Documentation, Codebook, and Frequencies for Glyphosate (GLYP) and Urine (SSGLYP_H). [NHANES testing showed 1885 of 2310 subjects had glyphosate “at or above the detection limit.”]

Broadly estimated, about half of all herbicides used in the U.S. is applied to corn and soybean crops, and ~30% of total use is applied to that portion of corn and soybean crops going specifically to animal feed. In addition, millions of pounds of herbicides are applied to other crops used for animal feed, such as sorghum and alfalfa/hay which is steadily moving to GE production with growing glyphosate usage.[1]

 

  1. See, Herbicide Use on Feed Crops

Broadly estimated, ~60-70% of all U.S. glyphosate volume was applied to corn and soybeans in 2018.[1] And most of those crops are used for animal feed.[2]

 

  1. See, Herbicide Use on Feed Crops
  2. See, Total Feed Crops Share [question: “What share of all crops harvested in the U.S. are used for animal feed?”]

It is generally accepted that glyphosate has wide-ranging negative effects on non-target plants, micro-organisms, and animals.[1]

The EPA has determined that glyphosate is “likely to adversely affect” 93% of the nation’s endangered species (1,676 species) and 96% of critical habitats.[2] Many scientific journals have documented the negative effects of glyphosate and its formulations on animals.[3,4]

Glyphosate has been found to distort microbial communities in soil, plants, and animals, which increases risk of disease.[5] Reports have documented the damage of glyphosate to amphibians;[6] honeybees;[7] and earthworms.[8]

The species that may have seen the steepest decline in the U.S. are monarch butterflies, which have declined by 85% or more due to widespread and increased use of glyphosate and the adoption of herbicide resistant crops that have decimated milkweed – the host plants for egg-laying female monarchs.[9]

Adding to, and in many cases exceeding, the toxicity of glyphosate as an active ingredient, are the chemicals added to glyphosate formulations. These additives have been found to make glyphosate formulations more toxic than the active ingredient by itself, particularly for aquatic animals.[10,11]

 

  1. Klátyik, S., et al., (2023). Terrestrial ecotoxicity of glyphosate, its formulations, and co-formulants: evidence from 2010–2023. Environmental Sciences Europe, 35(1), 51–29. [“Both GLY (glyphosate) alone and GBHs (glyphosate-based herbicides) have unintended side-effects on many terrestrial organisms, including non-target plants, microorganisms, insects, spiders, or earthworms, as well as vertebrates such as amphibians, reptiles, or mammals.”]
  2. U.S. EPA (2021) Final National Level Listed Species Biological Evaluation for Glyphosate, Chapter 4: Appendix 4-1, Species Effects Determinations, Summary Tables.
  3. Evalen, P. S., et al., (2024). Toxicity of glyphosate to animals: A meta-analytical approach. Environmental Pollution, 347, 123669, p. 5. [“Nonetheless, we conservatively demonstrate that GLY/GBH can be sub-lethally toxic for animals, particularly for animals in aquatic or marine habitats.”]
  4. van Bruggen, A. H. C., et al., (2018). Environmental and health effects of the herbicide glyphosate. The Science of the Total Environment, 616–617, 255–268, p. 14. [“Chronic low dose effects on animals and humans have been documented recently.”]
  5. van Bruggen, A. H. C., et al., (2018), p. 14. [“Thus, the presence of glyphosate in soil could change the community compositions of bacteria and fungi, in turn altering soil ecosystem functions and plant and animal health.”]
  6. Mann, R. M., et al., (2009). Amphibians and agricultural chemicals: Review of the risks in a complex environment. Environmental Pollution (1987), 157(11), 2903–2927.
  7. Balbuena, M.S., et al., (2015) Effects of sublethal doses of glyphosate on honeybee navigation. The Journal of Experimental Biology, 218, 2799.
  8. Gaupp-Berghausen, M., et al., (2015). Glyphosate-based herbicides reduce the activity and reproduction of earthworms and lead to increased soil nutrient concentrations. Scientific Reports, 5(1), 12886-.
  9. Wepprich, T., et al., (2019). Butterfly abundance declines over 20 years of systematic monitoring in Ohio, USA. PloS One, 14(7), e0216270, p. 2.
  10. Klátyik, S., et al., (2023), p. 2. [“Recently, numerous studies have confirmed the high individual toxicity of co-formulants…”]
  11. van Bruggen, A. H. C., et al., (2018), p. 260. [“ Glyphosate formulations with POEA are generally more toxic than those without this surfactant. Aquatic animals seem to be more sensitive to POEA than terrestrial animals.”]

In 2018, more than 80% of all atrazine usage was for corn.[1] About 64% of corn is used for animal feed.[2] Atrazine is the 2nd most common herbicide.[3]

 

  1. See, Herbicide Use on Feed Crops
  2. See, Total Feed Crops Share [question: “What share of all crops harvested in the U.S. are used for animal feed?”]
  3. Beaulieu, M., et al., (2020). Predicting atrazine concentrations in waterbodies across the contiguous United States: The importance of land use, hydrology, and water physicochemistry. Limnology and Oceanography, 65(12), 2966-2983. [“Atrazine, an herbicide, is the second most used pesticide in the United States…”]

The EPA has determined that atrazine is likely to adversely affect 56% of endangered or threatened species and 41% of critical habitats.[1] The abstract of a 500-page EPA analysis of the many confirmed damages to species makes for head-scratching reading, given the continued use and agency approval.[2]

Scientific studies have shown that atrazine causes testicular disfunction in certain fish, amphibians, and reptiles resulting in partial or complete feminization of males.[3,4] These findings have not been consistent across many studies. However, a meta-analysis of these reports found that “seven of the 10 studies including results on males and females reported strong trends or statistically significant alterations (6 studies) in at least one aspect of general gonadal morphology associated with atrazine exposure.”[5] A more recent review concludes generally that “atrazine is known to be an endocrine-disrupting chemical.”[6]  

Atrazine was banned by the EU in 2004 and is currently banned in more than 30 other countries.[7-9]

 

  1. U.S. EPA (2021) Final National Level Listed Species Biological Evaluation for Atrazine, Chapter 4: Appendix 4-1, Species Effects Determinations, Summary Tables, Table 4-1, 4-2. 
  2. Farruggia, F. T., et al., (2016). Refined ecological risk assessment for atrazine. US Environmental Protection Agency, Office of Pesticide Programs: Washington, DC, USA, Abstract. [“Based on the results from hundreds of toxicity studies on the effects of atrazine on plants and animals, over 20 years of surface water monitoring data, and higher tier aquatic exposure models, this risk assessment concludes that aquatic plant communities are impacted in many areas where atrazine use is heaviest, and there is potential chronic risk to fish, amphibians, and aquatic invertebrates in these same locations.” “EPA levels of concern for chronic risk are exceeded by as much as 22, 198, and 62 times for birds, mammals, and fish, respectively.”]
  3. Hayes, T. B., et al., (2011). Demasculinization and feminization of male gonads by atrazine: consistent effects across vertebrate classes. The Journal of steroid biochemistry and molecular biology, 127(1-2), 64-73.2.
  4. Hayes, T. B., et al., (2002). Hermaphroditic, Demasculinized Frogs after Exposure to the Herbicide Atrazine at Low Ecologically Relevant Doses. PPNAS, 99(8), 5476–5480.
  5. Rohr, J. R. & McCoy, K. A. (2010). A Qualitative Meta-Analysis Reveals Consistent Effects of Atrazine on Freshwater Fish and Amphibians. Environmental Health Perspectives, 118(1), 20–32, p. 26. 
  6. Stradtman, S. C. & Freeman, J. L. (2021). Mechanisms of Neurotoxicity Associated with Exposure to the Herbicide Atrazine. Toxics (Basel), 9(9), 207, p. 5. See also, Mikaela Conley (May 4, 2024) Atrazine, an endocrine-disrupting herbicide banned in Europe, is widely used in the U.S., U.S. Right to Know. https://usrtk.org/pesticides/atrazine/ [Listing studies of health impacts on both humans and animals]
  7. Legislation.gov.uk (2004) Commission Decision concerning the non-inclusion of atrazine, 2004/248/EC. [“Measures should be taken to ensure that existing authorisations for plant protection products containing atrazine are withdrawn within a prescribed period and are not renewed and that no new authorisations for such products are granted.”]
  8. Bethsass, J., & Colangelo, A. (2006). European Union bans atrazine, while the United States negotiates continued use. International journal of occupational and environmental health, 12(3), 260-267.
  9. Pesticide Action Network International (2022) PAN International Consolidated List of Banned Pesticides (spreadsheet download) https://pan-international.org/pan-international-consolidated-list-of-banned-pesticides/  

Very little, given the scientific evidence. There are many legislative and political barriers to the agency’s ability to protect biodiversity.[1,2]

When the EPA evaluates risks to the environment prior to registering a pesticide for use, the agency relies on the pesticide manufacturer’s data in its evaluation.[3] This clearly presents a conflict of interest which may have played a role in the initial registration of atrazine.[4]

 The agency is required by law to go through complex evaluation processes that require balancing the environmental damages against the benefits to farmers. In 2022, the EPA acknowledged that it has not been able to keep pace with its ESA (Endangered Species Act) workload, “resulting not only in inadequate protections for listed species but also successful litigation against the Agency that has increased in frequency in recent years.”[5]

Lobbyists can exert power both in Congress and within the EPA to discourage assessments of chemicals.[6]

Agricultural interests play a role in the EPA’s approvals of herbicides. There exists a legislative and regulatory deference to farmers and farm states and an unwillingness to create “uncertainty” for producers and pesticide manufacturers.[7]

Funding, staffing, and leadership are influenced by the administration in power.[8]

 

  1. U.S. EPA (2022) Balancing Wildlife Protection and Responsible Pesticide Use, [See, Executive Summary on p. 4 for a surprisingly candid view of the barriers to effective monitoring and regulation of pesticides. “The reasons for this failure are multifold…”]
  2. Lisa Held (August 2023) The EPA Ignored the Endangered Species Act for 50 Years. That’s Changing, But Is Time Running Out? Civil Eats.  https://civileats.com/2023/08/22/the-epa-has-ignored-the-endangered-species-act-for-50-years-its-changing-but-time-is-running-out/ [This article offers a good overview of the many issues facing the EPA.]
  3. U.S. EPA (2023) Data Requirements for Pesticide Registration. https://www.epa.gov/pesticide-registration/data-requirements-pesticide-registration
  4. Rohr, J. R. (2021). The Atrazine Saga and its Importance to the Future of Toxicology, Science, and Environmental and Human Health. Environmental Toxicology and Chemistry, 40(6), 1544–1558, p. 1551. [“USEPA’s conclusion that atrazine does not adversely affect amphibians was based on a single published study funded by Syngenta (shaping science), claiming that this was the only reliable study (attacking science).”]
  5. U.S. EPA (July 2023) Draft Herbicide Strategy Framework to Reduce Exposure of Federally Listed Endangered and Threatened Species and Designated Critical Habitats from the Use of Conventional Agricultural Herbicides, Executive Summary, p. 4. https://www.regulations.gov/document/EPA-HQ-OPP-2023-0365-0009
  6. Sharon Lerner (June 30, 2021) The Department of Yes: How Pesticide Companies Corrupted the EPA and Poisoned America, The Intercept. https://theintercept.com/2021/06/30/epa-pesticides-exposure-opp/ [Reports on a reassessment of pelargonic acid that was thought by the EPA’s Cancer Assessment Review Committee to be warranted but  was shut down by the pesticide office when it was learned that the chemical was a co-formulant in Roundup.]
  7. U.S. EPA (2022) Balancing Wildlife Protection and Responsible Pesticide Use, p. 4. [“This situation creates significant uncertainty for farmers, other pesticide users, and pesticide registrants. For example, if a court vacates a pesticide action, users may lose access to the pesticide for the several years likely needed for EPA to meet its ESA obligations for that action. Without certain pesticide products, farmers could have trouble growing crops that feed Americans and public health agencies could lack the tools needed to combat insect-borne diseases.”]
  8. Steve Cohen (June 5, 2023) President Biden’s Environmental Record, Columbia Climate School, State of the Planet, https://news.climate.columbia.edu/2023/06/05/president-bidens-environmental-record/
    [“At its peak in Fiscal 1999, the EPA had 18,110 staff (thank you, Bill Clinton). Under President Obama (yes, Obama), it shrunk from about 17,000 to 15,000, and under Trump, it bottomed out at 14,172. And during Trump’s term, many of the agency’s top scientists fled due to political interference in their work.”]

Drivers of Biodiversity Loss