Lead elimination and size effects on accumulation by two freshwater gastropods

Freshwater gastropods,Physa integra andCampeloma decisum, inhabiting a small reservoir with elevated levels of lead displayed widely differing soft tissue lead concentrations. Analysis of environmental factors did not fully explain these differences. Several physiological characteristics of the two gastropods were examined. The influence of snail size on concentrations of naturally-accrued lead was examined as was the rate of lead elimination from the two species. Lead concentrations inP. integra were independent of animal size, while those ofC. decisum were described by the curvilinear model:μg Pb/g dry wt=2.29(g dry wt)^?0.25. Naturally-accrued lead inP. integra was eliminated rapidly during the first four days of clearance but slowly thereafter; a portion of the lead is apparently bound strongly. In contrast, no significant change in lead concentration of gravid or nongravidC. decisum occurred during a three to four week period in which the animals were maintained in a lead-free environment.