Metal concentrations in two freshwater gastropods (Mollusca) in the St. Lawrence River and relationships with environmental contamination

This study assesses the potential use of two dominant freshwater gastropod species of the St. Lawrence River, Bithynia tentaculata (Prosobranchia) and Physa gyrina (Pulmonata), as biomonitors of metal pollution. Gastropods we re collected in the Littoral zone of Lake St. Louis and Lake St. Pierre, tw o shallow fluvial lakes of the SI. Lawrence River, at sampling stations cho sen to represent a metal concentration gradient in sediments. The soft body tissues of snails were analyzed for Cd, Cu, Ni, Pb, and Zn. Metal concentr ations in snail tissues were related to those in macrophytes, on which the snails were collected, and in nearby sediments, where the metal ion concent rations at the water-sediment interface were estimated. There was a signifi cant effect of age on the essential metals Cu and Zn, adults of B. tentacul ata showing higher concentrations than juveniles. Significant relationships were obtained between Cd and Zn concentrations in snail tissues and those in the environment (macrophytes or the estimated free metal ion levels at t he water-sediment interface). Some other relationships were also obtained w ith Ni, Pb, and Cu in P. gyrina. Bithynia tentaculata appears to be a promi sing biomonitor species, particularly for Cd and Zn.137.