Neonicotinoid contaminants in Wisconsin groundwater: relationships to landscape cropping systems

Neonicotinoids are a popular and widely-used class of insecticides whose water-soluble nature and 20-year usage history has led to questions about their potential to accumulate in the environment and harm local ecosystems. Over 6.7 million pounds of neonicotinoid insecticides are now applied annually on 140 different crops in the United States, with the three most popular compounds, imidacloprid (IMD), clothianidin (CLO), and thiamethoxam (TMX), making up over 90% of agricultural usage nationally and generating over $4.6 billion in market activity in 2013. Neonicotinoid usage in the United States remained below 500,000 pounds per year until 2003, when the expansion of crop registrations and the introduction of additional active ingredients led to a rapid increase in total usage. Virtually all corn and soybean seeds planted in the United States are now treated with either IMD or TMX seed treatments intended to protect the developing seedlings from early-season pests. This heavy usage, combined with the water-soluble nature of neonicotinoids and their potential to harm beneficial wildlife, has brought their environmental fate (e.g., the life cycle of a chemical) into sharp focus. Contamination of surface and groundwater specifically, may occur from major agricultural sources such as spray drift during application, deposition of contaminated dusts released during drilling of treated seeds, surface runoff and leaching, greenhouse runoff, as well as human error or irresponsibility, sewer and storm water drainage, and residential usage. High water solubility and long environmental persistence times contribute to the potential for these compounds to migrate through the soil column and contaminate groundwater-fed streams, the consequences of which for aquatic invertebrates remain unknown.

Objectives: Objective 1: Utilize a calibrated groundwater flow model developed for the Central Sands Region to delineate groundwater-contributing areas to streams and relate local landscape compositions and associated detections of neonicotinoid insecticides. Objective 2: Refine our understanding of the spatial and temporal variations in groundwater and base flow along discrete sections of Fourteen Mile Creek relating groundwater flow to surface water insecticide detection frequency and concentrations.