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.

在河口（estuaries）环境中，盐度（salinity）呈现快速且持续的波动，这极大地影响了污染物（contaminants，尤其是重金属）的生物可利用性（bioavailability），进而改变其毒性，为制定特定场地水质标准（site-specific water quality criteria）带来了挑战。本研究开发了一种可预测任意盐度波动情景下河口水体中金属镉（cadmium, Cd）毒性的方法。本研究以河口生物光滑河蓝蛤（Potamocorbula laevis）为实验对象，通过毒代动力学-毒效动力学（toxicokinetic–toxicodynamic, TK–TD）框架，测定了其在稳定盐度（盐度分别为5、15、25）与波动盐度（5–25）条件下的镉生物富集与毒性效应。研究结果显示，镉的生物富集量随盐度升高而降低；而生物体对镉的本征敏感性在约20的中等盐度条件下达到最低值。在特定镉浓度水平下，基于稳定盐度条件下测定的TK–TD参数进行插值运算，即可准确预测波动盐度条件下的镉生物富集与毒性效应。为将该模型拓展应用至不同镉浓度场景，本研究将生物配体模型（biotic ligand model, BLM）整合至TK–TD框架中。基于生物配体模型的TK–TD模型已成功应用于河口水体的模拟盐度波动与实测盐度波动情景，并据此推导得到镉的半数致死浓度与无效应浓度（2.0–3.1 μg·L⁻¹）。综上，本研究整合了生物配体模型与TK–TD模型，为盐度波动的河口水体的金属生态风险预测与水质标准制定提供了实用工具。