ASSESSMENT OF RESIDUAL FENTHION IN SEDIMENT BASED ON GROWTH-INHIBITION AND MORTALITY OF A FRESH-WATER SHRIMP, PARATYA-COMPRESSA-IMPROVISA

The subacute toxicity of fenthion (an organophosphorous insecticide)-c ontaminated sediment to a freshwater shrimp was assessed. Lake Kasumig aura sediments were contaminated with 0.1, 0.2, 0.4, 0.8 or 1.6 mg/l f enthion for 3 days and the shrimps were reared in now-through aquaria holding these sediments. No observable adverse effect was recognized i n shrimps released into aquaria holding sediments contaminated with 80 ng/g fenthion (wet wt.). Growth impairment was observed at the levels around 300 ng/g. A probit equation at 48-h between mortality and fent hion concentrations (C) of the sediment contaminated with 1.6 mg/l-fen thion is: P = 4.68 log(C) - 9.23. The LC(50) of the dietary fenthion w as calculated to be ca. 1110 ng/g (wet wt.), whereas its value was ca. 440 ng/g in sediment contaminated with 0.8 mg/l. The reason for this discrepancy is discussed. It is considered, therefore, that dietary fe nthion is much less toxic than waterborne fenthion in the realistic aq uatic environments. Because, the fenthion concentration of the sedimen t at these concentrations (400-1100 ng/g) was not realistic when the s ediment was exposed to 1 mu g / 1 fenthion, which is the waterborne 48 -h LC(50) value of fenthion to the shrimp.