Acute toxicity of dieldrin and carbofuran in single and mixed solutions to common silver barb, Puntius gonionotus (Bleeker)

Abstract

The acute toxicity of dieldrin and carbofuran to common silver barb, Puntius gonionotus (Bleeker) was studied by using 96-h static bioassays method in water of moderate hardness (110-120 mg/l) as CaCO(,3)and temperature 25 -28 degree C. Five experiments were conducted: two for single toxicant (dieldrin and carbofuran) and three for mixtures of dieldrin and carbofuran at the toxicity ratios of 1:1, 2:1 and 1:2. Concentrations of mixtures were expressed in "toxic unit" by taking them as proportion of 96-h LC(,50) values. The results showed that the incipient lethal levels (96-h LC(,50) and the 95% confidence limits were 0.0113 (0.0106-0.0119) mg/l for dieldrin and 1.275 (1.201-1.343) mg/l for carbofuran. The incipient lethal levels (96-h LC(,50)) and the 95% confidence limits of dieldrin to carbofuran at the toxicity ratios of 1:1 and 1:2 were 1.04 (0.98-1.10) and 1.09 (1.02-1.15) toxic units, respectively, which indicated additive joint action. The toxicity ratio of dieldrin to carbofuran at 2:1, the incipient lethal level (96-h LC(,50)) and the 95% confidence limits were 1.44 (1.38-1.50) which exhibited less than additive joint action. Dieldrin was significantly (P < 0.05) 112.389 folds more active than carbofuran, with 95% confidence limits ranging between 102.172 and 123.628. For dieldrin-carbofuran mixtures at 1:1 and 1:2, the relative potency did not differ significantly from dieldrin. For dieldrin-carbofuran mixtures at 2:1, the results showed that dieldrin was significantly 1.44 folds more toxic than dieldrin-carbofuran mixtures (2:1), with 95% confidence limits ranging between 1.309 and 1.584. There were no difference among 96-h LC(,50) values and relative potency values calculated by the methods of Finney (1971) and Litchfield and Wilcoxon (1949).