Effects of season and sediment-water exchange processes on the partitioning of pesticides in the catchment environment: implications for pesticides monitoring.

Current and historic pesticide use has potential to compromise e.g. drinking water sources due to both primary and secondary emission sources. Understanding the spatial and temporal dynamics of emissions might help inform management decisions. To explore this potential; water, sediment and soil samples were concurrently collected from the River Ugie, Scotland over four seasons. Occurrence and fate of nine pesticides including four historic-use pesticides (HUPs): simazine, atrazine, isoproturon and permethrin, and five current-use pesticides (CUPs): metaldehyde, chlorpyrifos, chlortoluron, epoxiconazole and cypermethrin were analysed. Concentrations of target pesticides in water, sediments and soils were 4.5–45.6 ng·L−1, 0.9–4.6 ng·g−1 dw (dry weight) and 1.7–8.0 ng·g−1 dw, respectively. Concentrations of pesticides in water were found to significantly differ between seasons (p [less than] 0.05). Significant differences in pesticide concentrations also occurred spatially within sediments (p[less than]0.01), indicating spatial and temporal associations with pesticide use. Sediment-water exchange showed that the sediment acts as an important secondary emission source particularly for the HUPs, while current local application and sediment emission are both major driving forces for CUPs in the riverine environment. These findings were supported by concentration ratios between different media, which showed potential as a preliminary assessment tool for identifying the source of pollutants in aquatic environments