Do pesticide coatings on agricultural seeds pose a threat to earthworms and to the birds that eat them?

Science Center Objects

Earthworms are a vital part of a healthy, functioning soil ecosystem and are also an important protein-rich food source for wildlife, including many species of birds and mammals. In an agricultural setting, the presence of earthworms can increase crop yields by 25%, but can also expose earthworms to pesticides. Seed treatment is the principal application method for neonicotinoid insecticides, one of the most widely used classes of insecticides worldwide. However, few studies have examined the effects of commercially formulated coated seed on soil organisms, such as earthworms.

In collaboration with:

Michelle Hladik, USGS CA Water Sciences Center

Michael Gross, USGS CA Water Sciences Center

Carrie Givens, USGS Upper Midwest Water Science Center

Dana Kolpin, USGS Central Midwest Water Science Center

The Challenge: Pesticides are commonly present in the habitat of many organisms due to agricultural activity. Seeds coated with systemic insecticides such as neonicotinoids, pose potential risks for the health of soil organisms, as a high percentage of the insecticides leach into the soil and persist in the environment rather than being taken up by the plant. Earthworms are particularly likely to be exposed in agricultural settings and thereby can be affected acutely (direct mortality) or chronically, exhibiting sublethal physiological and behavioral effects that over time decrease survival. Because earthworms take up contaminants from the soil, they can also serve as a vector of pesticides to birds and other vertebrate consumers. The transfer of pesticides from coated seeds and resulting potential toxicity to earthworms has been poorly studied.

The Science: Using microcosms, we will simulate actual exposures of earthworms in agricultural fields through application of treated seeds that will be allowed to germinate and grow. We will be examining the movement of neonicotinoid pesticides from the coated seeds through the soil into earthworms and will examine pesticide and metabolite residues and biological effects, including potential differences in microbiota composition and metabolite profiles between pesticide-exposed and unexposed worms.

The Future: Studies examining the exposure to and potential effects of contaminants derived from food production and processing are important for clarifying actual hazard and risk, if any, to wildlife.