Integrative Monitoring of Neonicotinoid Insecticides in Baseflow-Dominated Streams on the Wisconsin Central Sand Plain

Neonicotinoid insecticides are used widely across the Wisconsin Central Sand Plain (WCSP) to control various pests that inflict damage to crops such as potatoes, corn and soybeans. They are often used as seed coatings, but also sprayed upon foliage, or applied as granules in furrows. Neonicotinoids are systemic insecticides that are considered very water soluble and mobile in groundwater. Coarse sandy soils on the WCSP, a shallow water table, and irrigation increase the propensity for leaching of water-soluble pesticides and nutrients from soil to groundwater. The WCSP has many natural streams that are often connected by drainage ditches to lower the water table for agricultural purposes. These streams and ditches are primarily fed by groundwater discharge and supply a cold-water habitat for aquatic life. The US Environmental Protection Agency (EPA) has adopted acute and chronic aquatic life benchmarks (ALB) for neonicotinoids to aquatic invertebrates, plants, and fish. Of the neonicotinoids targeted, imidacloprid has the most stringent EPA ALB for invertebrates. Acute exposure criteria for aquatic invertebrates often relate to a 48-hour exposure period while chronic assessment criteria are often set at 7-40 days, depending upon species. As a result, traditional grab sampling may not provide an accurate representation of water quality over an extended period which is necessary to address chronic criteria. An evaluation of a passive sampling device to assess chronic toxicity criteria is included in this study.