Changes of concentrations, shipment amounts and ecological risk of pesticides in river water flowing into Lake Biwa.

A survey of various pesticide contaminations was performed for water in Yanamune River flowing into Lake Biwa from 1988 to 2009. Ten pesticides (diazinon and fenitrothion as insecticides, iprobenfos and isoprothiolane as fungicides and chlornitrofen, thiobencarb, molinate, bromobutide, simetryne and pretilachlor as herbicides) were selected and concentration changes of the pesticides were evaluated based on their shipment amounts. Yearly maximum concentrations of eight of the pesticides in Yanamune River water were compared with their no observed effect concentration and their predicted no effect concentration values and initial ecological risk assessment was conducted for five pesticides (diazinon, fenitrothion, iprobenfos, isoprothiolane and thiobencarb) by their predicted no effect concentration values. All of the diazinon (0.01-0.28 μg/L) and fenitrothion (0.005-0.31 μg/L) concentrations from 1988 to 2007, the iprobenfos (2.7 and 2.4 μg/L) concentrations in 1988 and 1990 and the thiobencarb (0.24-2.7 μg/L) concentrations in 1988, 1992, 1993 and 1995 exceeded their predicted no effect concentration (PNEC) (0.00026, 0.00021, 1.0 and 0.17 μg/L) values.