Chronic toxicity of lead to three freshwater invertebrates— Brachionus calyciflorus, Chironomus tentans , and Lymnaea stagnalis

Chronic lead (Pb) toxicity tests with Brachionus calyciflorus, Chironomus tentans , and Lymnaea stagnalis were performed in artificial freshwaters. The no‐observable‐effect concentration (NOEC), lowest‐observable‐effect concentration (LOEC), and calculated 20% effect concentration (EC20) for the rotifer B. calyciflorus were 194, 284, and 125 μg dissolved Pb/L, respectively. The midge C. tentans was less sensitive, with NOEC and LOEC of 109 and 497 μg dissolved Pb/L, respectively, and the snail L. stagnalis exhibited extreme sensitivity, evident by NOEC, LOEC, and EC20 of 12, 16, and <4 μg dissolved Pb/L, respectively. Our findings are presented in the context of other reports on chronic Pb toxicity in freshwater organisms. The L. stagnalis results are in agreement with a previous report on pulmonate snails and should be viewed in the context of current U.S. Environmental Protection Agency (U.S. EPA) hardness adjusted water quality criteria of 8 μg Pb/L. The present findings and earlier reports indicate that freshwater pulmonate snails may not be protected by current regulatory standards. Measurements of whole‐snail Na + and Ca 2+ concentrations following chronic Pb exposure revealed that Na + homeostasis is disturbed by Pb exposure in juvenile snails in a complicated pattern, suggesting two physiological modes of action depending on the Pb exposure concentration. Substantially reduced growth in the snails that exhibit very high Ca 2+ requirements may be related to reduced Ca 2+ uptake and thereby reduced shell formation.