Searching for neonicotinoid depositional patterns in riparian and aquatic systems

Neonicotinoids are a heavily used class of agricultural chemicals worldwide. These compounds are ideal for seed coatings because of high water solubility and relatively small molecule size. Neonicotinoid seed treatments (NSTs) are used in most major field crop systems (e.g. cotton, corn, soybean and small grains). They are applied to nearly 100% of the approximately ninety-million acres of corn planted annually across the United States. NSTs are intended to provide crops with protection against soil-dwelling pests for the first several weeks of seedling establishment. Although they are effective at reducing insect damage in high pest pressure scenarios, concerns that their ecotoxicological effects may be outweighing their protection benefits put their current use patterns under scientific scrutiny. Studies have demonstrated most of the active ingredient is not translocated to the plant. Additionally, the physiochemical characteristics that make neonicotinoids systemic also give them a propensity to leach out of agricultural fields through surface and/or subsurface flow pathways. Their ubiquitous use and low uptake efficiency make exposure scenarios for stream-residing arthropods a serious concern. Surface-water detection frequencies have exceeded 90% in several studies. We conducted an observational study on neonicotinoid depositional patterns by measuring insecticide concentrations in riparian and within-stream biological compartments along two stream reaches within and above an agricultural stream catchment. Our research provides data to help characterize risks posed by these compounds to aquatic macroinvertebrate communities.