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

Abstract

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 were collected in the littoral zone of Lake St. Louis and Lake St. Pierre, two shallow fluvial lakes of the St. Lawrence River, at sampling stations chosen to represent a metal concentration gradient in sediments. The soft body tissues of snails were analyzed for Cd, Cu, Ni, Pb, and Zn. Metal concentrations in snail tissues were related to those in macrophytes, on which the snails were collected, and in nearby sediments, where the metal ion concentrations at the water-sediment interface were estimated. There was a significant effect of age on the essential metals Cu and Zn, adults of B. tentaculata 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 the water-sediment interface). Some other relationships were also obtained with Ni, Pb, and Cu in P. gyrina. Bithynia tentaculata appears to be a promising biomonitor species, particularly for Cd and Zn.