Tan Q.G., Lu S.H., Chen R. and Peng J.H.. 2019. Environmental Science & Technology, 53(5) :2873-2880.

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.

Figure 1. Survivorship of the clam P. laevis during the exposure to a high concentration of Cd (nominal: 550 μg L⁻¹) at different salinities. The points are observed values (mean ± standard deviation, n = 3); the curves are model fits.

Figure 2. Survivorship of the clam P. laevis after 88 h of exposure to 550 μg L⁻¹ of Cd (panel A), the internal threshold concentration (C_IT, panel B) and the killing rate (k_k, panel C) of Cd at different salinities. Linear decrease of C_IT and linear increase of k_k was assumed when salinity deviated from the “optimal” values.