An assessment of neonicotinoid exposure risks through drinking water in Iowa

Neonicotinoids are a relatively new class of insecticides that have found widespread use. They are highly water-soluble and have been shown to persist in soil and water. In Iowa, neonicotinoid contamination has been documented in waterways, but little is known regarding possible groundwater contamination. Groundwater is an important source of drinking water for 42 million Americans and over 2 million Iowans. Previous studies have documented other pesticide contamination, such as herbicides in the state’s groundwater. To my knowledge, the findings of this dissertation presents the first documentation of the occurrence of neonicotinoids in Iowa’s groundwater.

Groundwater samples were analyzed for six neonicotinoid compounds. Neonicotinoids were found to be prevalent in the groundwater. Neonicotinoids were most frequently detected in shallow wells from vulnerable aquifers. Tests of samples from different seasons and before and after treatment also suggest that neonicotinoid contamination is present year-round and may be a source of chronic and acute exposure. Although estimates of daily intake indicate that, this exposure is less than 1% of the current World Health Organization’s acceptable daily intake (ADI).

Even though these exposure estimates are low, human exposure to neonicotinoids likely occurs through different routes, including ingestion (e.g., water, food), inhalation (e.g., dust), and dermal exposure. It is currently unknown, which route serves as the primary pathway of exposure for humans. In addition, no epidemiologic studies have been performed that have the ability to determine if there are potential adverse human health risks from chronic neonicotinoid exposure. Future studies are required to evaluate the magnitude of human exposure to neonicotinoids and to understand the long-term health consequence of chronic exposure.