Volume index is strongly associated with cadmium and lead bioaccumulation in the freshwater mussel Anodontites trapesialis (Lamarck, 1819) from Barra Bonita reservoir, Brazil

Cadmium (Cd) and lead (Pb) are persistent potentially toxic metals in aquatic environments and can accumulate in filter-feeding organisms, making bivalves useful tools for environmental biomonitoring. This study aimed to evaluate Cd and Pb concentrations in Anodontites trapesialis collected from different sites in Barra Bonita Reservoir, São Paulo, Brazil, and to investigate the association between volume index and metal bioaccumulation. Thirty specimens were collected, three from each of ten sampling sites. Tissue Cd and Pb concentrations were determined by atomic absorption spectrophotometry. Differences among sites were evaluated using analysis of variance followed by Tukey’s test. Volume index, calculated as length × width × thickness, was included as a covariate in analysis of covariance (ANCOVA), and its relationship with metal concentrations was assessed using Pearson’s correlation and polynomial regression. Mean concentrations were 4.33 mg kg-1 dry weight for Cd and 115.42 mg kg-1 dry weight for Pb. Significant differences among sampling sites were observed for both metals; however, after adjustment for volume index, the site effect was no longer significant, whereas volume index remained significant. Volume index showed strong correlations with Pb (r = 0.930) and Cd (r = 0.910). These results indicate that A. trapesialis has potential for Cd and Pb biomonitoring, but volume index should be considered when interpreting metal bioaccumulation and comparing individuals or sampling sites.