Surface runoff and subsurface tile drain losses of neonicotinoids and companion herbicides at edge-of-field

This experiment was designed to quantify loss of thiamethoxam and clothianidin as well as herbicides during storm events through surface and subsurface tile drain flows from a corn-soy rotation field in Quebec with no irrigation. Both thiamethoxam and clothianidin were detected in almost all of the samples (thiamethoxam in 100% and clothianidin in 92%), even though the only neonicotinoid application was the planting of thiamethoxam-coated corn seeds in the first year (fungicide-coated soy was planted in the second year). Thiamethoxam and clothianidin were detected up to 527 days after seeding. In the first year of sampling, thiamethoxam concentrations had a median of 0.46 µg/L (maximum 2.20 µg/L) in surface runoff and 0.16 µg/L (maximum 0.44 µg/L) in tile drains. Both flows transported a similar amount of the measured mass lost (53% for surface and 47% for tile drains). An important finding was that thiamethoxam and clothianidin were both identified during the second growing season (when no coated seed was planted), demonstrating that neonicotinoids remain on the landscape. Most of the pesticide export occurred during the first storm events after planting.