Predicting Risks of Cadmium Toxicity in Salinity-Fluctuating Estuarine Waters Using the Toxicokinetic–Toxicodynamic Model

In
estuaries, salinity fluctuates rapidly and continuously, greatly
affecting the bioavailability and thus toxicity of contaminants, especially
metals, causing difficulties in deriving site-specific water quality
criteria. We developed a method for predicting the toxicity of the
metal cadmium (Cd) in estuarine waters of any salinity fluctuation
scenario. Cd bioaccumulation and toxicity were measured in an estuarine
clam Potamocorbula laevis under stable salinities
(salinity = 5, 15, 25) and fluctuating salinities (5–25), using
the toxicokinetic–toxicodynamic (TK–TD) framework. Cd
bioaccumulation decreases with increasing salinity; whereas intrinsic
Cd sensitivity of organisms reaches the minimum at an intermediate
salinity around 20. At each specific Cd level, interpolating TK–TD
parameters measured at the stable salinities well predicts the Cd
bioaccumulation and toxicity under fluctuating salinities. To extend
the model for various Cd levels, the biotic ligand model (BLM) was
integrated into the TK–TD framework. The BLM-based TK–TD
model was successfully applied to scenarios of simulated and monitored
salinity fluctuations in estuarine waters, for which the median lethal
concentrations and no-effect concentrations (2.0–3.1 μg
L–1) of Cd were derived. Overall, we integrated
the BLM and TK–TD models and provided a useful tool for predicting
metal risks and deriving criteria values for salinity-fluctuating
estuarine waters.