The state of Wisconsin estimates that approximately 43 percent of private wells contain detectable levels of pesticides. This alarming statistic comes from a recent statewide survey of 380 private wells, conducted by the Department of Agriculture, Trade and Consumer Protection (DATCP). The survey, carried out every five to ten years, assesses the presence of pesticides and nitrates in groundwater. Results from the most recent survey indicate an increase in pesticide contamination compared to 2016, when 41.7 percent of wells were found to be affected.
The survey detected 29 pesticide compounds out of the 107 tested. Among these were neonicotinoids, a class of insecticides known for their harmful effects on bees and birds. However, of the pesticides detected, more than half remain unregulated in terms of groundwater standards at both the state and federal levels.
Health Concerns and Lack of Regulation
Despite the widespread presence of pesticides in groundwater, only one of the wells tested exceeded health advisory levels set by the Wisconsin Department of Health Services (DHS). Nevertheless, Carla Romano, a groundwater specialist at DATCP, warns that for some of the pesticides found in the wells, there is insufficient research to establish health benchmarks.
“DHS has conducted reviews of studies available for some of these pesticides,” Romano stated, “and unfortunately cannot assess a threshold or a health benchmark because of the lack of studies on some of these chemicals.”
The most commonly detected pesticides in the wells included breakdown products of herbicides such as metolachlor, alachlor, and atrazine, which are frequently used in corn and soybean farming. Although none of these exceeded established groundwater limits, concerns persist due to the lack of regulation for many other detected pesticides. Of the 29 pesticides identified, only 13 have official groundwater standards, while nine lack any regulation. Seven pesticides have only health advisory levels, which are less stringent than formal standards.
Calls for Stronger Groundwater Standards
Environmental groups and public health officials have been advocating for action to address the backlog of pesticides that lack groundwater standards. Sara Walling, water and agriculture program director at Clean Wisconsin, emphasized the urgency of setting limits on pesticide contamination.
“Without groundwater standards for these chemicals, there’s nothing we can do as a state to protect ourselves and our citizens and our communities against the impacts of these contaminants in our drinking water systems,” Walling said.
Despite these concerns, efforts by Wisconsin’s Department of Natural Resources (DNR) to establish groundwater standards for pesticides have not been successful. The agency has indicated plans to revisit pesticide recommendations once they receive updated health information on PFAS, another class of concerning contaminants.
Economic Importance of Pesticides in Wisconsin
Agriculture is a major driver of Wisconsin’s economy, contributing an estimated $104.8 billion annually. With such high stakes, farmers rely heavily on pesticides to protect their crops from pests and ensure high yields. Growers in the state use millions of pounds of pesticides each year, particularly on corn, soybeans, and potatoes, crops which cover millions of acres across Wisconsin.
In 2022, Wisconsin farmers planted 4 million acres of corn and 2.1 million acres of soybeans, with insecticides used on a significant portion of these fields. For potatoes, which are grown on 66,000 acres, thiamethoxam, a neonicotinoid, was applied to over half of the crop.
Russ Groves, chair of the Department of Entomology at the University of Wisconsin-Madison, explained that the reliance on pesticides is a logical outcome of intensive farming practices.
“Those are the tools that we have relied upon so that we don’t have real significant economic losses for a producer or an industry,” Groves said. However, he also advocates for exploring alternatives to reduce the frequency of pesticide detections in groundwater.
Increasing Detection of Neonicotinoid Insecticides
The recent survey found that neonicotinoids—imidacloprid, clothianidin, and thiamethoxam—were detected in roughly 5 percent of private wells. While this is a small percentage, it represents a concerning trend, as these insecticides are widely used in Wisconsin agriculture, homes, and gardens.
The detection rates for these chemicals may have increased due to advancements in testing technology, which allow for lower detection levels. However, the presence of neonicotinoids in groundwater is particularly troubling due to their impact on pollinators, including bees. These insecticides are designed to target the nicotine receptors in insects, which leads to their death. Although initially believed to be safer for humans and wildlife, research has since shown that neonicotinoids can have widespread environmental consequences.
Environmental Impact and Threat to Pollinators
Neonicotinoids have been linked to the decline of bee populations, as well as other insects that play a crucial role in ecosystems. James Crall, an assistant professor of entomology at UW-Madison, explained that these insecticides disrupt various aspects of bee colony health over time, even at low concentrations.
“Lots of parts of the bee life cycle and the things that bees have to do to fuel long-term growth are being disrupted even at these levels that are well below acute toxicity,” Crall said.
The issue extends beyond bees. A recent report by DATCP found that levels of neonicotinoids like imidacloprid and clothianidin exceeded health benchmarks for aquatic organisms in some surface waters. These findings raise concerns about the broader ecological impacts of pesticide use on freshwater ecosystems.
Steve Corsi, a research hydrologist with the U.S. Geological Survey, has co-authored studies that show neonicotinoids are among the most frequently detected insecticides in Great Lakes tributaries. Corsi pointed out that it’s not just neonicotinoids but a combination of multiple pesticides found in both urban and agricultural areas that pose risks to aquatic organisms.
“We recognize that in order to have successful agricultural producers in our state, many of them need to use pesticides,” Corsi noted. “It’s a balancing act—what can we do to minimize the impact of these pesticides while still having successful agricultural producers?”
Limited Research on Human Health Effects
While much research has focused on the environmental impact of neonicotinoids, less is known about their effects on human health. Some studies have suggested links between these pesticides and developmental or neurological issues, such as autism spectrum disorder and memory loss. The Environmental Protection Agency (EPA) is currently reviewing the safety of neonicotinoids and expects to release interim findings in 2025.
At least 11 states have already restricted the residential use of neonicotinoids, with New York taking the bold step of banning seeds treated with the chemicals last year. In Wisconsin, a similar legislative effort aimed at protecting pollinators failed to advance. Democratic lawmakers had introduced a package of bills that would have, among other things, banned the DNR from using neonicotinoids on state-managed lands.
The contamination of Wisconsin’s groundwater with pesticides, particularly neonicotinoids, represents a significant environmental and public health concern. Although many of these pesticides are essential to modern agriculture, the risks to pollinators, aquatic ecosystems, and potentially human health cannot be ignored. With more than half of the detected pesticides lacking regulatory standards, there is an urgent need for Wisconsin to take action to safeguard its groundwater and drinking water systems.
Let us leave you with this one question; do you think your state is that much different?
Solutions and Water Treatment Options
Given the scale of the issue, state officials are encouraging private well owners to stay informed about the presence of pesticides in their water and consider treatment options. The state provides resources on detected pesticides and their potential health effects.
One effective solution for well owners is the use of reverse osmosis filtration systems, which can remove a wide range of contaminants, including pesticides. Reverse osmosis systems use a semi-permeable membrane to filter out molecules and ions, making them particularly effective for small, unregulated pesticide compounds. For homeowners looking for broader water treatment, whole-home water conditioners can also offer protection against various contaminants, including nitrates and other chemicals frequently found in groundwater.
Source: Wisconsin Public Radio