Evaluation of acute toxicity of cadmium and lead to amphibian tadpoles (Toad: Bufo maculatus and frog: Ptychadena bibroni)

Abstract

Reported declines in amphibian faunal diversity in Nigeria Niger Delta due to chemical contamination and habitat alteration provided the impetus for this study. The potential for anthropogenic metal contamination to affect amphibian survival was examined by evaluation of acute toxicity of heavy metals cadmium (Cd) and lead (Pb) to early larval stages of B. maculatus and P.bibroni at varying post-hatch maturation stages (3 days, 1, 2, 3 and 4 weeks) under laboratory conditions. The larval stages were exposed to nominal Cd and Pb concentrations of 0.10, 0.15, 0.20, 0.25 and 0.50 μg /l. Derived 96-hour LC₅₀ values decreased with increase in maturation stages in both B. maculatus and P. bibroni. Mortality also increased with concentrations and exposure time for both species. Differential acute toxicity of Cd and Pb was observed in both species (P < 0.001), with Cd showing much higher toxicity than Pb. Tadpoles of B. maculatus and P.bibroni showed species specific sensitivity to Pb and Cd respectively. The conclusion from the present study suggests that amphibian larval stages are very sensitive to anthropogenic stressors containing heavy metals. Thus, environmental caution should be exercised when discharging metal containing effluents into the aquatic ecosystem during amphibians breeding period usually in the wet season.

Key words: Acute, Toxicity, Cadmium, Lead, Tadpoles.

Journal of Aquatic Sciences Vol.20(1) 2005: 33-38