Plants mediate precipitation-driven transport of a neonicotinoid pesticide

Neonicotinoid insecticides provide crop protection via water solubility and systemicity, yet these chemical characteristics, combined with high toxicity to non-target invertebrates (e.g., honeybees), elicit concern of environmental transport. Neonicotinoids have been detected in soil and surface water throughout North America; however, no investigation has defined a direct connection to planted seed dressings. We quantified the physical transport of thiamethoxam (TMX), a neonicotinoid, under field conditions. We planted TMX-coated corn seeds and maintained plots with and without viable crops (n = 3 plots per treatment) to determine plant influence on pesticide transport. TMX concentrations were measured in soil and drainage throughout the growing season. Storm-generated runoff was the dominant transport mechanism (maximum TMX concentration 1.72 ± 0.605 μg L^-1; no viable plants), followed by shallow (<72 cm) lateral drainage (0.570 ± 0.170 μg L^-1; no viable plants), and deep (110 cm) drainage (0.170 ± 0.265 μg L^-1; viable plants). Soil samples confirmed vertical and lateral movement within 23 and 36 days of planting, respectively. Plants facilitated downward migration of TMX in soil but restricted TMX drainage. Altogether, these study results revealed that neonicotinoids can be transported from seed coatings both above and through the soil profile, which may enable migration into surrounding ecosystems.