Making Acute Tests More Ecologically Relevant: Cadmium Bioaccumulation and Toxicity in an Estuarine Clam under Various Salinities Modeled in a Toxicokinetic–Toxicodynamic Framework

Salinity
has considerable effects on the toxicity of metals in estuarine waters.
The effects of salinity are manifold, making it difficult to summarize
for risk assessments. In this study, we separated and quantified the
multiple effects of salinity on cadmium (Cd) in a toxicokinetic–toxicodynamic
framework. The estuarine clam, Potamocorbula laevis, was used as a model organism. Cd bioaccumulation was measured using
a stable-isotope-tracer technique; in parallel, toxicity tests were
conducted. With the increase of salinity from 5 to 30, Cd uptake decreased
monotonically. In contrast, the intrinsic sensitivity of organisms,
measured by the toxicodynamic parameters, reached its minimum at intermediate
salinities (i.e., 10 to 20). The overall salinity effects were dominated
by the effects on Cd bioaccumulation; therefore, Cd toxicity decreased
monotonically with the increases of salinity. The model developed
in this study could provide predictions of no-effect concentration
(1.7 to 34.9 μg L–1, end point mortality)
and the median lethal concentration (LC50) of Cd at different
salinities. In conclusion, we developed a framework for quantifying
the multiple effects of salinity and a method for estimating no-effect
concentration from acute toxicity tests, which can be used for better
assessments of metal risks in estuarine waters.