Toxicokinetics and Mussel Watch: Addressing Interspecies Differences for Coastal Cadmium Contamination Assessment

Bivalves are often employed for biomonitoring contaminants in marine environments; however, in these large-scale programs, unavoidably, using multiple species presents a significant challenge. Interspecies differences in contaminant bioaccumulation can complicate data interpretation, and direct comparisons among species may result in misleading conclusions. Here, we propose a robust framework based on toxicokinetic measurements that accounts for interspecies differences in bioaccumulation. Specifically, via a recently developed double stable isotope tracer technique, we determined the toxicokinetics of cadmium (Cd)─a metal known for its high concentrations in bivalves and significant interspecies bioaccumulation variability─in six widespread bivalve species including mussels (Perna viridis, Mytilus unguiculatus, Mytilus galloprovincialis) and oysters (Magallana gigas, Magallana hongkongensis, Magallana angulata). Results show that oysters generally have higher Cd uptake rate constants (k_u: 1.18-3.09 L g^-1 d^-1) and lower elimination rate constants (k_e: 0.008-0.017 d^-1) than mussels (k_u: 0.21-0.64 L g^-1 d^-1; k_e: 0.018-0.037 d^-1). The interspecies differences in tissue Cd concentrations are predominantly due to Cd uptake rather than elimination. Utilizing toxicokinetic parameters to back-calculate Cd concentrations in seawater, we found that the ranking of Cd contamination levels at the six sites markedly differs from those based on tissue Cd concentrations. We propose that this approach will be useful for interpreting data from past and future biomonitoring programs.