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 (ku: 1.18–3.09
L g–1 d–1) and lower elimination
rate constants (ke: 0.008–0.017
d–1) than mussels (ku: 0.21–0.64 L g–1 d–1; ke: 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.