13
Jun
Report Stresses Findings of Pesticide Contamination of Largest U.S. Estuary Shared by Six States—Chesapeake Bay
(Beyond Pesticides, June 13, 2025) A report highlights the ongoing stress to the Chesapeake Bay Watershed from pollutants, particularly pesticides. The Chesapeake Bay is the largest estuary in the contiguous United States, with tributaries shared among six states and the District of Columbia. It receives runoff from nine major river systems traversing a wide mix of land uses, with significant agricultural and urban areas nearest the Bay and forest along the western boundary. Nearly 13 million people get their drinking water from the watershed.
The watershed report by the Maryland Pesticide Education Network focuses primarily on the herbicide atrazine, the neonicotinoid insecticide thiamethoxam, and per- and polyfluorinated compounds (PFAS).
Atrazine needs little introduction, being notorious for disrupting hormones, particularly estrogen, as demonstrated by the pioneering work of Tyrone Hayes and more recent research analyzed by Beyond Pesticides here, here and here. In male fish, it can trigger production of egg proteins, especially vitellogenin, and development of eggs in their testicles. These are manifestations of intersex, in which an organism shows forms of sexual differentiation of both sexes.
The Chesapeake watershed report notes that atrazine and metolachlor (also an estrogen/androgen disruptor and suspected human carcinogen) occur together frequently in the Chesapeake Bay. While many estrogen-related compounds in waterways are thought to come from wastewater treatment plants, agricultural runoff containing these pesticides can also trigger endocrine reactions.
Among their possible victims are the world-famous Chesapeake Bay oysters, which are an important part of the Bay’s food web. Oysters filter millions of gallons of water a day. The report cites research showing that oysters lose their beneficial microbes when exposed to low concentrations of atrazine. This leads to opportunistic colonization by pathogenic microbes, posing a risk to the long-term survival of oysters and to the health of the bay generally.
The neonicotinoids are also implicated. The watershed report cites research showing that thiamethoxam, a known bee-killer banned for outdoor use in the European Union, correlates with intersex in fish. In Beyond Pesticides’ 2017 Pesticides and You report, its presence in the Chesapeake watershed was noted. Under chronic exposures, neonicotinoids are known to bind to estrogen and androgen receptors, affecting vitellogenin production.
But perhaps the most unnerving threat to the health of Chesapeake Bay is from PFAS. In addition to the atrazine, metolachlor, thiamethoxam, glyphosate, and legacy organochlorine pesticides found in the watershed, the report notes, “Within the Chesapeake Bay watershed, PFAS were detected in every smallmouth bass plasma sample amongst four varying land use locations (agriculture versus developed land).” This raises the question, the authors write, “whether pesticides of concern described within this report may have synergistic and detrimental effects when combined with per-and polyfluoroalkyl substances.”
Concern has been building about these “forever chemicals” because they do not break down in the environment and are so ubiquitous that they are “present from the far Arctic reaches of the planet to urban rainwater,” as a 2024 Science magazine article put it. A growing body of research is identifying their deleterious effects on ecosystems and individual species, including humans, as detailed in Beyond Pesticides’ news brief here. The EPA itself found that reducing PFAS exposure would induce “kidney cancers, heart attacks, strokes, and developmental effects, as well as a general reduction in harms to the immune, developmental, cardiovascular, hepatic, endocrine, metabolic, reproductive, and musculoskeletal systems,” according to a 2024 review in Environmental Health Perspectives.
Several years ago, Beyond Pesticides and other concerned citizen groups raised alarms about the leaching of PFAS from pesticide containers into the products themselves. In 2022 EPA admitted as much. In July 2024, EPA granted a petition from a group of citizen organizations to address the problem in pesticide containers. In fact, the leaching of PFAS into high-density polyethylene (HDPE) containers goes far beyond pesticides, as food is often stored in them as well. See our analysis here.
But it is not just containers. It is the pesticides themselves. Despite the evidence and EPA’s own admission of PFAS’s toxicities, the number of products containing PFAS is burgeoning out of control to replace banned organochlorines such as DDT and methoxychlor. In 2020, fluorinated agrochemicals comprised about nine percent of the pesticide market, and have now reached almost 70 percent of newly-approved pesticides, according to a 2025 review in the Journal of Agricultural and Food Chemistry.
In fact, the pesticide industry is charging full steam ahead on PFAS, apparently ignoring the harms acknowledged by EPA. A 2022 review by Portuguese researchers noted that “Fluorine-based agrochemicals have been benchmarked as the golden standard in pesticide development.” A Chinese-Swedish review that year stated, “We believe the fluorine introduction methods described here can provide ideas for the development of new and economical pesticide synthetic routes, and stimulate researchers to develop new fluorine incorporation methods and create new pesticides…The dramatic effect of fluorine on the biological activity of agrochemicals such as fungicides, insecticides, herbicides, acaricides, and nematicides has earned fluorine a unique place in the toolbox of the agrochemical chemists.”
Syngenta has even put out a call for ideas to “enable the fluorine-efficient design of new agro-chemical products,” to counteract “emerging regulatory trends [that] have led to increased scrutiny of all fluorinated compounds, regardless of their demonstrated properties.”
The chemical industry’s appalling lack of attention to—or even awareness of—the downstream unintended ecological and health consequences of pesticide chemistry is nowhere better illustrated than in this line of research. There is clearly no industry intention to reduce the development and marketing of PFAS pesticides. The firewall between industrial chemistry and public health must be dismantled, not reinforced, for there to be any lasting improvement in planetary and human health.
Further, regulatory momentum is likely to slow considerably. EPA has demonstrated some confusion since the November 2024 presidential election. That month, the agency issued a document stating, “PFAS …are an urgent threat to public health and the environment…The science is clear: exposure to certain PFAS poses significant risks to human health, including cancer, even at very low levels.” The document is a “strategic roadmap” for restricting and remediating PFAS in the environment and investing in more research.
But most recently, on May 14, the Trump administration delayed implementation of the National Primary Drinking Water Regulation PFAS standards and declined to reduce the maximum levels of PFOA and PFOS in drinking water. Even during the last year of the Biden administration, Trump-appointed EPA officials prevented EPA staffers from warning the Senate Environment and Public Works Committee about a loophole that would allow companies to avoid reporting releases of PFAS in the Toxics Release Inventory and avert a designation of PFAS as “chemicals of special concern.”
Thus, for the Chesapeake Bay Watershed and the thousands of other ecosystems around the world, there is still a strong headwind obstructing real progress. The report does highlight one bright ray of light: Since organochlorine pesticides have been banned, “[T]here is no longer a discernible relation between halogenated contaminants in osprey eggs and their reproductive success in Chesapeake Bay. Osprey populations are thriving in much of the Chesapeake, with productivity rates exceeding those required to sustain a stable population. These results highlight the positive effect of federal or state banning of pesticides.” The report cites an estimate that the total population of ospreys has increased from 1,450 pairs in the 1970s to nearly 10,000 pairs today.
The report also stresses a set of best management practices that can have real benefits by preventing the flow of agricultural runoff, wastewater plant effluent, and other terrestrial contaminant sources into the Chesapeake basin. These include filtration systems, stormwater systems, permeable pavement, and riparian buffer zones. According to the report, riparian buffer zones alone can reduce pesticide presence by 70-94 percent. In urban settings, best management practices can cut pesticide pollution by 25 percent.
Beyond Pesticides has been supporting concrete approaches to these practices for decades, such as organic land and lawn care on state and local public lands, residential properties, schools, golf courses, and in agriculture; and the transition to regenerative agriculture. The return of the osprey to Chesapeake Bay shows that change can happen, and the citizen energy that saved the birds can continue to fuel the transition to a truly healthy world.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources:
Pesticides and the Chesapeake Bay Watershed: Communicating Recent Pesticide Research
Findings to Inform Stakeholders | 2010-2021
Pesticides & the Chesapeake Bay Watershed Project Research & Data Gaps Working Group, MPEN
May 27, 2025
https://y6bcan6ab.cc.rs6.net/tn.jsp?f=001gtW_lwTJX1A97NSFqkBSBljtkcihyCOCk7n6mufEXAJRUez0wdz1GB2Ovj6INMOSjBwiJH396_TGZAiSCmr_M4kfVmEvQs8TJrV4oWSm-o0oNy-XWqr1UNPOdO2Sd9yDZyQ0RyZDgV9BWl9g6rq29BcYsuXXFoCrNGVjKYQ6MK8eO0RaIEqyJA2nKG2HhrXRK9JrsN2wXPrhoMWkDhj6pQUPJMMHUTi2ZtYIH1Lq-iHHM66-oPCNCOgmg8BUtuDRO9hyuImsM6M=&c=VQ3A1HRLB_Q-JQv7WLqiObLkH_2RgLWh5iT2NA7xgsYBHRF4nfaweg==&ch=CcRoX4OaF-gHvTjzcNYqo_hOQ_NFUpietAQUOft5V9Yx0XQ4nHs25g==
Forever Pesticides: A Growing Source of PFAS Contamination in the Environment
Donley et al.
Environmental Health Perspectives July 2024
https://ehp.niehs.nih.gov/doi/epdf/10.1289/EHP13954
EPA Confirms PFAS “Forever Chemicals” Leach into Pesticides from Storage Containers
Beyond Pesticides, September 14, 2022
https://beyondpesticides.org/dailynewsblog/2022/09/epa-confirms-pfas-forever-chemicals-leach-into-pesticides-from-storage-containers/
Science on “Forever Chemicals” (PFAS) as Pesticide Ingredients and Contaminants Documented
Beyond Pesticides, July 31, 2024
https://beyondpesticides.org/dailynewsblog/2024/07/science-on-forever-chemicals-pfas-as-pesticide-ingredients-and-contaminants-supports-need-for-immediate-action-to-end-their-use/
The Rise and Risks of Fluorinated Pesticides: A Call for Comprehensive Research to Address Environmental and Health Concerns
Ravikumar Jagani, Hiraj Patel, Jasmin Chovatiya, and Syam S. Andra
Journal of Agricultural and Food Chemistry 2025 73 (4), 2217-2220
DOI: 10.1021/acs.jafc.4c12827
https://pubs.acs.org/doi/epdf/10.1021/acs.jafc.4c12827?ref=article_openPDF
New Study Finds Alarming Rise in Persistent ‘Forever Chemicals’ in Pesticides—
PFAS From Pesticide Products Detected in Rivers, Streams Throughout United States
Center for Biological Diversity, July 2024
https://biologicaldiversity.org/w/news/press-releases/new-study-finds-alarming-rise-in-persistent-forever-chemicals-in-pesticides-2024-07-24/
Per- and polyfluoroalkyl substances in the environment
Evich et al.
Science February 2022
https://pmc.ncbi.nlm.nih.gov/articles/pmid/35113710/
