Compilation of a decade of scientific research confirms that pesticides are harming the health of crucial Bay ecological systems
May 27, 2025 | Annapolis, Maryland – A new report summarizes more than a decade of research findings about how pesticides are putting water quality at risk in the Chesapeake Bay, and may be affecting drinking water and harming the regional watershed.
The report, “Communicating Recent Pesticide Research Findings to Inform Stakeholders, 2010-2021,” was released by the Maryland Pesticide Education Network’s program, the Pesticides and the Chesapeake Bay Watershed Project. The report summarizes the findings of over 30 research papers on the effects and interactions of dozens of pesticides in Bay watershed water quality and the drinking water for nearly 13 million people, as well as aquatic life and wildlife in the watershed.
The Chesapeake Bay and its watershed are integral to the health and wellbeing of more than 18 million people. Scientists from a broad range of institutions, including EPA’s Chesapeake Bay Program, U.S. Geological Survey, NOAA, numerous academic labs and organizations have analyzed and published the effects of numerous pesticides on Chesapeake Bay ecosystems. This report is the first to compile and summarize this scientific literature and is intended to inform policy and decision makers, environmental advocates, conservationists and others concerned about the health of the Chesapeake Bay watershed.
“This important report provides a critical summary of the latest research into the broad presence of pesticides in the Chesapeake Bay watershed,” said Dr. Greg Allen, co-lead of the Working Group and retired EPA Chesapeake Bay Program scientist. “These summary findings should generate additional questions for policymakers for needed responses that will help mitigate the risk caused by pesticides.”
The report found that there is an interesting trend in new pesticides that are fluorinated agrochemicals and PFAS (per- and polyfluoroalkyl substances) pesticides—some 66 pesticides where PFAS is the active ingredient. These active ingredients are extremely persistent, highly mobile in the environment, and bioaccumulate in crops, fish, wildlife, and ultimately, in humans. PFAS were detected in every smallmouth bass blood sample from four varying land use locations, with agriculture land use having some of the highest prevalence, raising the question of the synergistic and detrimental effects of pesticides when combined with PFAS.
Report findings include:
- Studies in the Shenandoah River and Chesapeake Bay found 17 detections of seven PFAS chemicals illustrating the need for more analysis and probable data gaps.
- Pesticides have sublethal effects on the Chesapeake Bay. While these effects are not severe enough to cause death, they can negatively impact health, development, behavior or reproduction in various species. Sublethal effects may also cause significant loss of key helpful microbe species and advance unhealthy pathogenic bacteria in species such as oysters and frogs.
- Complex mixtures of pesticides, including widely used neonicotinoids and atrazine, may be contributing to endocrine disruption, physiological impairment, immunodeficiency, and intersex characteristics in fish.
- Many pesticides are seen to co-occur within the Chesapeake Bay and the report finds atrazine and metolachlor are some of the most prevalent herbicides in this trend.
- Neurotoxic organophosphates and endocrine-disrupting synthetic pyrethroid insecticides have been detected in fish tissue and shown to be immunotoxic from chronic exposure.
- Health risks associated with pesticides in soil contribute to large non-target population losses, as well as impacts on children causing loss of coordination and memory, reduced speed of response to stimuli, reduced visual ability and altered mood.
- The report also documented positive trends. For one, despite a scarcity of papers on the effects of pesticides on wildlife, it was found that osprey populations are rebounding. Research has found a decrease in the parent compound of a DDT degradant in egg production, indicating the positive effect of federal and state bans of certain pesticides.
Six key Best Management Practices are identified to help further reduce pesticide impacts or increase available data needed to address pesticide issues. These include cost-saving collaborations to increase pesticide contaminant monitoring in Bay waterways and better implementation of pesticide use reporting laws.
“Communicating Recent Pesticide Research Findings to Inform Stakeholders” is a project of the Research and Data Gaps (RDG) Working Group of the Pesticides and the Chesapeake Bay Watershed Project, established in 2007 – a collaborative effort of more than 100 stakeholders and technical experts that has grown today to over 300 participants with a shared mission: to reduce risk of adverse effects to living resources from pesticides in the Chesapeake Bay and its tributaries. The Since May of 2007, the working groups meet several times annually and its stakeholder community of hundreds have come together for eighteen annual conferences.
The Project’s RDG Working Group includes scientists from federal agencies with regulatory responsibilities, as well as representatives from state agencies, local government agency representatives, and scientists from research institutions. Technical experts contributing to this report included scientists from federal agencies and research institutions including the U.S. Geological Survey and the Environmental Protection Agency’s Chesapeake Bay Program. Recommendations included in this paper were developed by the working group members and inclusion does not indicate full endorsement by individual working group members.
Maryland Pesticide Education Network (MPEN) is dedicated to protecting the public and the environment from toxic pesticides and promoting healthy alternatives. The Pesticides and the Chesapeake Bay Watershed Project is one of MPEN’s primary programs since 2007.
Download: “Communicating Recent Pesticide Research Findings to Inform Stakeholders, 2010-2021″.
Photos courtesy of Steve McDaniel, www.mcdanielphotography.com
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