MONITORING OF THE OVERALL PESTICIDE TOXICITY OF RIVER WATER TO AQUATIC ORGANISMS USING A FRESH-WATER SHRIMP, PARATYA-COMPRESSA IMPROVISA

River water samples were bioassayed from July 1988 to March 1989 using the freshwater shrimp, Paratya compressa improvisa, to establish the variation in the overall toxicity of the rivers to aquatic organisms. Water was collected from four sampling stations in the three small rivers surrounded by paddy fields. The 4-day mortality of the shrimp increased to 100% for several days after aerial spraying of insecticides and fungicides, which was conducted between late July and early August. However mortality gradually decreased to a few or zero percent by the end of August and showed similar low values until the end of the survey in March 1989. The cause of the high mortality of the shrimp is attributed largely to the pesticides, such as fenitrothion, fenthion, and/or BPMC (organophosphorus insecticide), although the contribution of herbicides and fungicides is unclear at the present time. While, high mortality of the shrimp suggested an existence of another toxic pesticides, which were over-looked in routine analysis.