CT Pesticide Reform News Release: Widely Used Insecticides Found in Connecticut Waters Pose a Deadly Threat to Aquatic Ecosystems and A Risk to Human Health

“It’s these high harm, low benefit uses … that we need to take out of circulation in Connecticut right away.”

January 27, 2025—A University of Connecticut study combining two decades of data with recent tests reveals widespread contamination of the state’s surface and groundwater by an insecticide linked to falling populations of bees and birds.

The study, by UConn’s Center for Environmental Sciences and Engineering, adds to the growing body of research and evidence that neonicotinoid insecticides are finding their way into streams and rivers from turf grass including lawns and golf courses as well as from agricultural uses. In addition to the connection to pollinator and bird declines, neonics also pose a health risk to humans.

The study recommends that Connecticut enact stronger regulations to further restrict the use of neonics in the state.

Titled “Neonicotinoids in Connecticut Waters,” it presents a comprehensive analysis of data collected by the U.S. Geological Survey starting in 2001 and data from last year by the Clean Rivers Project. 

 Neonicotinoids in Connecticut Waters. Read the UConn report here.

It was commissioned by Connecticut Pesticide Reform, a grassroots coalition of individuals and conservation organizations in Connecticut united to advocate for a massive reduction in dangerous pesticides. Connecticut Audubon is part of the Coalition’s leadership. (A list of members appears below.)

Coalition Chair Louise Washer, a Norwalk resident, said: “Neonics are devastating insect populations, killing birds, hollowing out our river ecosystems, and they’re threatening human health, especially children’ s health. To make it worse, many of the applications are not even benefitting users economically.  

“It’s these high harm, low benefit uses—the low-hanging fruit—that we need to take out of circulation in Connecticut right away.”

Three UConn researchers conducted the study: Steven J. Presley, Ph.D., Postdoctoral Associate, Center for Environmental Sciences & Engineering, Institute of the Environment, and Department of Ecology & Evolutionary Biology; Christopher R. Perkins, M.S. Director of Environmental Laboratories, Center for Environmental Sciences & Engineering and Institute of the Environment; and Michael R. Willig, Ph.D., Board of Trustees Distinguished Professor Emeritus, Department of Ecology & Evolutionary Biology, Center for Environmental Sciences & Engineering, and Institute of the Environment, University of Connecticut.

The study found that neonicotinoid levels often exceed the EPA’s benchmark for aquatic life for chronic exposure by as much as five times, indicating potential harm to the insects and other invertebrates in the state’s streams and rivers. Those creatures are an important food source for birds and fish.

In a case study of the Norwalk River, which the USGS has tested regularly for 24 years, neonics levels are highest in summer, coinciding with typical application times for agriculture and turf management. Yet levels remain consistently above the chronic benchmark year-round, posing a constant threat to aquatic insects.

The report urges policymakers and stakeholders to:

• Strengthen regulations to limit the use of neonicotinoids on turfgrass.
• Implement a ban on the use of neonicotinoid-treated seeds used for corn and soybeans.
• Promote the adoption of alternative pest control methods, such as biological control and natural products.
• Expand monitoring efforts to include a wider range of neonicotinoids and focus on understudied areas, particularly groundwater sources.

Key findings include:

• Increasing Prevalence: Neonicotinoids, specifically imidacloprid, which we have the most data on, have become increasingly prevalent in Connecticut’s surface waters over the past 12 years. While detection rates were initially low, they have since surged, with imidacloprid now detected in nearly half of all surface water samples.
• Concentrations Exceed Safe Levels: A significant portion of the samples tested positive for imidacloprid at concentrations above the EPA’s chronic benchmark for aquatic life, indicating potential long-term harm to insects such as mayflies, which are essential components of the food web and are key to river ecosystem health.
• Groundwater Contamination: Imidacloprid is also present in Connecticut’s groundwater, raising concerns about potential contamination of drinking water sources, particularly for residents relying on private wells. Widespread, consistent testing is needed to fully understand the extent of groundwater contamination.
• Coastal Concern: The study revealed a trend of increasing imidacloprid concentration toward the coast, suggesting potential accumulation and transport of the insecticide through the state’s river systems.

The study highlighted mayflies as a crucial indicator for assessing the health of freshwater because of their high sensitivity to neonicotinoids. Dozens if not scores of species of mayflies live in Connecticut’s rivers.

The study showed that between 1989 and 2020, the total population of mayflies in the Norwalk River and its tributaries fell by 75 percent and the number of different taxa of mayflies — genus or species — fell by 66 percent. 

Exposure to imidacloprid can make mayflies less healthy in general, more susceptible to harms arising from low levels of oxygen in the water, and increase the risk of predation.

The report suggests that increasing imidacloprid concentrations may be contributing to the mayfly declines in the Norwalk River.

The report emphasizes the need for further research to establish a clearer link between imidacloprid exposure and mayfly population declines, and recommends studies designed to examine the effects of pesticide concentrations on aquatic invertebrate communities.

Connecticut Pesticide Reform organizational members
Pollinator Pathway
Norwalk River Watershed Association
CT Audubon Society
Audubon Connecticut
Rivers Alliance
Save the Sound
Friends of the Earth
Sierra Club CT
American Bird Conservancy
Surfrider
Inter-Religious Eco-Justice Network
East Norwalk Blue
Clean Water Action
CT League of Conservation Voters
Aspetuck Land Trust
Natural Resource Defense Council
Xerces Society
Protect Our Pollinators, Newtown
Pollinator Pathway, Stamford
Sustainable Fairfield County
CT Butterfly Association
Conservation Law Foundation
Greenwich Pollinator Pathway
Greenwich Sustainability Committee
Beyond Pesticides
Huneebee Project
Sierra Club CT
Farmington Valley Trout Unlimited
The Bee Conservancy
Hartford Audubon
CT Ornithological Association