2022 Volume 45 Issue 6 Pages 257-270
The first basin-scale survey of concentration levels and regional distributions of major systemic insecticides and their metabolites were conducted in the Lake Hachiro Basin in Akita Prefecture in June and August 2020. Dinotefuran, imidacloprid, thiacloprid, thiamethoxam, clothianidin, ethiprole, fipronil, and thiacloprid amide were detected in the tested samples. The highest detection frequencies of dinotefuran and thiacloprid amide were respectively observed in August (100%) and June (80%) . Such trends seem to be affected by the rice production and productivity in the basin. The highest concentration among the parent pesticides was dinotefuran at 2,200 ng L-1 detected from Lake Hachiro in August and those in metabolites were thiacroprid amide at 60 ng L-1 detected from tributaries in June. Dinotefuran was widely detected from the Lake Hachiro Basin, and its concentration was 1–3 orders of magnitude higher than those of other pesticides. The ecotoxicological risk assessment value (maximum measured environmental concentration/ predicted no effect concentration, MECmax/PNEC) , which was calculated using the PNEC value estimated as the acute toxicity test value of a highly sensitive species (Chironomus yoshimatsui) to dinotefuran was greater than 1. However, the environmental behavior and fate of target pesticides during all seasons were unknown in this study. Further detailed studies are required in the Lake Hachiro Basin.
