Toxicity of lead to clarias lazera, oreochromis niloticus, chironomus tentans and benacus sp.

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The 48 and 96-hr LC50 values of Pb (Pb(NO3)2) with O. niloticus were 3.34 and 2.15 mg L−1, respectively, compared to 1.91 and 1.72 mg L−1, respectively, for C. lazera. C. tentans larvae and Benacus sp. demonstrated 48-hr LC 50 of 2.68 and 1.89 mg l−1 respectively. The 96-hr LC50 value was 1.77 mg L−1 for Chironomus and 1.36 mg L−1 for Benacus. Clarias appeared to be the most susceptible of the four to Pb poisoning; Chironomus being the least susceptible. Uptake pattern of Pb by fingerlings of O. niloticus and C. lazera exposed to 0.33 and 0.27 mg L−1 Pb, respectively, and the clearance of accumulated Pb were curvilinear. There was an initial ‘fast’ phase of accumulation occurring during the first 96 hr, followed by a slower phase over the remaining 240 hr. Mean Pb concentrations in gills, intestine, liver, muscle, bone, skin and whole body of O. niloticus were 33.30, 22.2, 5.3, 2.8, 1.8 and 14.9 μg g−1, respectively, compared to 28.7, 6.5, 11.5, 2.5, 5.6, 5.9 and 6.8 µg g−1 respectively in C. lazera. The half life of Pb in Oreochromis was 20 hr compared to 43 hr in C. lazera. Bioconcentration factors in Oreochromis and Clarias were 78.3 and 33.8, respectively. The data suggest that O. niloticus accumulates and eliminates Pb faster than C. lazera.