Temporal changes in river water toxicity revealed by shrimp-test in a river system flowing through a rural district composed mainly of paddy fields (1)

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Changes with time in river water toxicity were monitored by 14-d shrimp test from April to October 1995. Tests were conducted 3 times a week during spring and summer. Water samples were collected from 3 sampling sites on the Koise River system, which flows through a rural district composed mainly of paddy fields. Shrimp mortalities and the concentrations of several pesticides changed in parallel between the middle and lower stations, 8 km apart. This strongly suggests that the shrimp mortality is due mainly to overall pesticide effects in the river water. The mean 14-d shrimp mortalities were 67% and 48% at the 2 stations during the summer. Several organophosphorus insecticides might have caused the shrimp mortality at the middle station in August. However, the cause of mortality from May to July was not clear, even thoughfenobucarb, a carbamate insecticide, was detected continuously from spring to early summer with a peak concentration of 1.6 μg/L. Other possible causes are discussed, Concurrently, macrobenthic fauna at the upper and middle sites was investigated; this is reported in the following paper.
日本環境毒性学会の論文