Acute Toxicity of Organochiorine Pesticides to Fishes and Shellfishes of a Tropical Estuary

3種の有機塩素系殺虫剤(DDT、リンデン、エンドサルファン)が熱帯河口域の魚貝類5種(二枚貝3種、魚類2種)におよぼす急性毒性を連続フローシステムの実験系を期いて明らかにした。まず各殺虫剤ごとに半数致死濃度LC50の24、48、72、96、120時間値を測定し、これらの値から初期半数致死濃度ILC50(Incipient Median Lethal Concentration)を推定した。毒性試験の結果、供試殺虫剤の中ではDDTの毒性が最も強かった。5種の試験生物の中で、殺虫剤に対する感受性は魚類のM.cephalusで最も高く、一方抵抗性は二枚貝で高かった。試験生物にとって無害な各殺虫剤の濃度(Safe Concentration)を求め、またこれらの殺虫剤が試験生物の行動におよぼす影響を詳述した。

In the present study, acute toxicity data were obtained for different organochlorine pesticides (DDT, lindane and endosulfan) to estuarine fishes and shellfishes under continuous flow through system. Median lethal concentration (LC50) was obtained for different time intervals (24, 48, 72, 96 and 120 hr.) and the toxicity curves were drawn using these values to determine the incipient lethal concentration (ILC50) values. Increase in the exposure time decreased the LC50 values of the pesticides to the organisms. DDT was found to be highly toxic to the organisms tested followed by lindane and endosulfan. Of the organisms studied, Mugil cephalus was found to be most sensitive to the pesticides. Bivalves were highly resistant to the pesticides tested than fishes. Behavioral responses of the test organisms to the toxicant was also described in detail. Safe concentrations and the relative resistance of these organochlorine pesticides to the organisms were discussed.