Relationships between metal bioaccumulation and metallothionein levels in larvae of Mytilus galloprovincialis exposed to contaminated estuarine sediment elutriate

The bioavailability of Cd, Cu and Zn from a metal-contaminated sediment was studied using Mytilus galloprovincialis embryos and larvae exposed to sediment elutriates, The elutriate concentrations tested were always lower than the threshold at which abnormal larval development appears. The Cd, Cu and Zn contents of the sediment, of the elutriate and of the larvae, as well as the larval growth, the condition index (CI), and the induction of metallothionein (NIT) in the larvae were measured. The Cl was only affected after 96 h of exposure, principally at the highest elutriate concentration (25%, corresponding to 0.1435 mug Cd l(-1) and 14 mug Zn l(-1)). Cd, Cu and Zn bioaccumulation was observed (48 and 96 h), in whole larvae as well as in the cytosolic fraction of their tissues, For the individual treatments (controls or different degrees of exposure), the lowest metal concentrations were observed in larvae after 96 h exposure, indicating biological dilution. Metallothionein induction in larvae was observed after 96 h exposure at the lowest elutriate concentrations tested, and was always strongly correlated with increasing metal contents in the cytosolic fraction, These relationships were significant for all 3 metals studied either individually or combined. The results indicate that these 3 metals are bioavailable to M galloprovincialis larvae and that NIT induction constitutes a more sensitive indicator of heavy metal pollution than embryotoxicity or larval growth experiments.