Year-round presence of neonicotinoid insecticides in tributaries to the Great Lakes, USA
To provide data on neonicotinoid loading in the Great Lakes, researchers took monthly samples from 10 riverine sites for a full year. Sites represented a range of land use from urban to agricultural as well as forested. Researchers looked for six neonicotinoids: acetamiprid (ACE), clothianidin (CLO), dinotefuran (DIN), imidacloprid (IMD), thiacloprid, and thiamethoxam (TMX). Five of the six neonicotinoids were found at the following frequencies: IMD, 53%; CLO 44%; TMX 22%; ACE 2%; and DIN 1%. The frequency of detection reflects use patterns. The researchers found at least one neonicotinoid in 74% of the samples, at least 2 neonicotinoids in 38% of the samples and 3 neonicotinoids in 10% of the samples. No neonicotinoids were found in the only tributary that was dominated by forest. The researchers also did a more intensive “nested” study in a highly agricultural area during the spring and summer.
IMD detections increased as the percent of urban land cover increased while CLO and TMX concentrations increased as the percent of croplands increased. In the agriculturally dominated basins, detection concentrations increased in the spring and summer. The spring increase could be due to the planting of neonicotinoid-treated seed. The summer increase could possibly be due to broadcast applications or runoff from previous applications.
Researchers acknowledge that their sampling methods could miss peak concentrations. Previous research has linked neonicotinoid water contaminations with rain events and the samples for this study were not timed to coincide with rain events. In fact the summer sampling event was 11 days after a rain event.
Acute aquatic life benchmarks, designed to help assess risk, were not exceeded in this study. However, the chronic aquatic life benchmark for imidacloprid (which was recently revised) was exceeded. Aquatic life benchmarks for the other neonicotinoids have not yet been updated. The study provides evidence of potential harm to aquatic invertebrates with possible effects on ecosystem function. Researchers also suggest that more study is needed into the effects on aquatic invertebrates from year-round exposure to neonicotinoids.
