New Fact Sheet Highlights Risks to California’s Surface Water from Insecticides

Neonicotinoids, a widely used class of systemic insecticides, have received lots of attention in recent years with research demonstrating a variety of lethal and sub-lethal impacts on bees and on other beneficial insects. There is also evidence of the effects of neonicotinoids on aquatic systems, with a growing number of studies showing impacts in prairie pothole wetlands of the northern Great Plains. With this as background, Xerces Society scientists began analyzing information about how neonicotinoids harm aquatic invertebrates and found a valuable resource in the detailed water quality sampling and pesticide-use records available from the California Department of Pesticide Regulation (DPR). This analysis found evidence of neonicotinoids in surface water at levels that will harm or even kill invertebrates. The findings are summarized in a new fact sheet, based on the results from our report, Neonicotinoids in California’s Surface Waters, which identifies the threats associated with contamination of California’s rivers and streams from the use of neonicotinoids, including the impacts such contamination may have on aquatic invertebrates and their habitat.

Because neonicotinoids are water-soluble, they can move easily from where they are applied into surface water. In comparing levels of neonicotinoids found in California’s surface waters with those known from studies to be harmful to aquatic invertebrates, our analysis shows that levels of imidacloprid (the oldest and most commonly used neonicotinoid) are frequently found in California’s surface water at levels that can harm and even kill sensitive aquatic invertebrates such as mayflies and other species critical to maintaining healthy freshwater ecosystems. Our findings also signal potential risks from other neonicotinoids, whose use is on the rise in California.

A map showing California’s surface water monitoring data for imidicloprid, the oldest and most widely used neonicotinoid. Across the U.S., neonicotinoids are now routinely found in waterways.

Neonicotinoid contamination has also been identified in other regions of the country, including a recent USGS study that found complex mixtures of pesticides in streams throughout the Midwest. Imidacloprid was a major contributor to toxicity in the samples analyzed, both from agricultural and urban settings. Research has also found that imidacloprid is not removed in many water treatment plants.

Despite many studies showing that neonicotinoids commonly occur in surface water at levels which may cause harm, the U.S. EPA has still not proposed any federal action to protect aquatic systems, and has set comparatively high water-quality reference values for imidacloprid. These values determine the level at which the concentration of the insecticide in a body of water is high enough to trigger action. In comparison, the European Union and Canada have established vastly lower levels at which contamination from imidacloprid would prompt a regulatory response.

Neonicotinoids have been found in California’s rivers and streams at levels know to harm or outright kill aquatic invertebrates such as the mayfly shown here. Loss of these species will have cascading effects throughout the ecosystem, harming fish and other wildlife that depend upon them. Photo by Judy Gallagher /

California DPR has been involved in assessing the risks of neonicotinoids along with U.S. EPA, and has expressed concerns about aquatic contamination. DPR has the knowledge and authority to act in addressing the risks associated with neonicotinoid contamination of the state’s rivers and streams.  In the face of abundant science and research into the risks associated with neonicotinoid contamination of our rivers and streams, Xerces urges DPR to take a greater role to protect California’s fragile aquatic ecosystems.

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