Heavy metals in the clam Tivela mactroides Born, 1778 (Bivalvia: Veneridae) from coastal localities with different degrees of contamination in Venezuela

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We compared heavy metal levels (manganese, iron, zinc, cadmium, copper, chromium, and lead) in tissues and shells of juveniles (13±2.2 mm), medium-size organisms with mature gonads (25±4.1mm), and adults (35±1.2 mm) of the clam Tivela mactroides from three different locations along the Venezuelan coast: Playa Güiria, on the northeastern coast, was not affected by environmental pollution, but Río Chico and Boca de Paparo, influenced by the Tuy River on the central coast, were. Heavy metal concentrations were related to shell size, with significant differences among populations and shell sizes. Specimens from Boca de Paparo and Río Chico had the highest heavy metal concentrations in tissues and shells, in contrast with the levels found in specimens from Playa Güiria, in which chromium and lead were absent. The high heavy metal concentrations found in tissues from specimens collected at Boca de Paparo and Río Chico were possibly of anthropogenic origin and generated by the Tuy River. The environmental conditions at Boca de Paparo may have favored the bioaccumulation of most heavy metals in specimen tissues. At Playa Güiria, however, the heavy metal concentrations were found to be within a natural range. Our results show that T. mactroides is a good biological indicator of the presence of heavy metals in the littoral waters they inhabit.