Bioconcentration of cadmium and toxic effects on life-history traits of pond snails (Lymnaea palustris and Lymnaea stagnalis) in laboratory bioassays.

We studied the bioconcentration and the individual effects of Cd on life-history traits of Lymnaea stagnalis and Lymnaea palustris exposed to increasing Cd concentrations for 4 weeks in controlled conditions. Internal Cd concentrations were linearly correlated to Cd concentrations of exposure in both foot and viscera of L. stagnalis and in the foot of L. palustris, and they were linked by a logistic relationship with environmental contamination in the viscera of L. palustris. If LC50S were higher than the highest Cd concentrations of exposure (L. stagnalis: 160 microg L(-1); L. palustris: 320 microg L(-1)), other dose-dependent responses affecting life-history traits were noted in both species. In L. stagnalis, EC50 for growth was evaluated at 142 microg L(-1) and growth inhibition was correlated with internal Cd concentrations by a linear relationship. L. palustris was more sensitive to Cd than L. stagnalis because its EC50-growth was three times lower (58 microg L(-1) after 28 days). Dose-dependent responses were obtained for several parameters of fecundity of L. palustris. EC50 for the mean number of egg masses or mean number of eggs per individual were close to 60 microg L(-1), whereas for the mean number of eggs per egg mass, the EC50 was higher, with a value of 124 microg L(-1). The percentage of hatching versus the total number of eggs was 60% in controls, and no embryos were able to hatch at the lowest tested Cd concentration, 40 microg L(-1). The high sensitivity of fertility was due to Cd blocking embryo development, particularly for the latest embryonic stages just before hatching. The present results constitute useful data to develop laboratory tests using pond snails for freshwater risk assessment.