Acute and chronic toxicity of lead in water and diet to the amphipod Hyalella azteca

We evaluated the influence of waterborne and dietary lead (Pb) exposure on the acute and chronic toxicity of Pb to the amiphipod Hyidella azteca. Test solutions were generated by a modified diluter with an extended (24-h) equilibration period. Acute (96-h) toxicity of Pb varied with water hardness in the range of 71 to 275 mg/L as CaCO3, despite similar dissolved Pb concentrations. Acute toxicity was greatest in soft test water, with less than 50% survival at the lowest dissolved Pb concentration (151 mu g/L). Survival also was significantly reduced in medium-hardness water but not in hard test water. In chronic (42-d) studies, amphipods were exposed to waterborne Ph and fed either a control diet or a diet equilibrated with waterborne Ph levels. For animals fed the control diet. the median lethal concentration (LC50) for Ph was 24 mu g/L (as dissolved Pb), and significant reductions in Survival occurred at 16 mu g/L. Exposure to Pb-treated diets significantly increased toxicity across a wide range of dissolved Ph concentrations, with a LC50 of 16 mu g/L and significant reductions in growth and reproduction at 3.5 mu g/L. Significant effects oil growth and reproduction Occurred at dissolved Pb concentrations close to the current U.S. chronic water-quality criterion. Our results Suggest that both aqueous- and dietary-exposure pathways contribute significantly to chronic Ph exposure and toxic effects in aquatic biota.