Residual pesticides and their toxicity to freshwater shrimp in the littoral and pelagic zones of Lake Kasumigaura, Japan.

Pesticide residues in water and their toxicity to the freshwater shrimp (Paratya compressa improvisa) were studied in a river mouth in Takahamairi Bay, Lake Kasumigaura, from April to July in 1987. Concentrations of fenthion, diazinon and fenobucarb in water of the littoral zone were lower than that in the pelagic zone. The maximum concentration of fenthion, diazinon, iprobenfos and simetryn in water were 1.9, 0.8, 6.5, and 1.1 micrograms 1(-1), respectively. The 4-day mortality of the freshwater shrimp increased in lake water at Takahamairi Bay, reaching 50% at maximum in May. The mortality was probably due to residual insectside fenthion.