There have been limited studies on the effects of toxicity-modifying factors, such as dissolved organic matter (DOM), on the toxicity of metal mixtures to aquatic biota. The present study investigated the effects of DOM concentration (low, 2.8 ± 0.1 mg C/L; high, 11 ± 1.0 mg C/L) and DOM source (predominantly terrestrial or microbial) on the chronic toxicity of copper (Cu) and nickel (Ni) binary mixtures to the green freshwater microalga Chlorella sp. This was assessed by using a full factorial design of 72-h growth inhibition bioassays. Measured algal growth rate was compared with growth predicted by the concentration addition and independent action reference models. Model predictions were based on concentrations of dissolved metals, labile metals (measured by diffusive gradients in thin films [DGT]), and calculated free metal ions (determined by the Windermere Humic Aqueous Model). Copper/Ni mixture toxicity was synergistic to Chlorella sp. in the absence of added DOM, with evidence of metal concentration-dependent toxicity at low effect concentrations. As DOM concentration increased, the mixture interaction changed from synergism to noninteraction or antagonism depending on the metal speciation method used. The DOM source had no significant effect on mixture interaction when based on dissolved and free metal ion concentrations but was significantly different when based on DGT-labile metal concentrations. Ratio-dependent mixture interaction was observed in all treatments, with increased deviation from the reference model predictions as the mixture changed from Ni- to Cu-dominated. The present study demonstrated that both DOM concentration and source can significantly change metal mixture toxicity interactions and that these interactions can be interpreted differently depending on the metal speciation method used. Environ Toxicol Chem 2021;40:1908–1918. © 2021 SETAC

中文翻译：

---

溶解有机物浓度和来源对铜和镍混合物对小球藻慢性毒性的影响。

关于溶解有机物 (DOM) 等毒性调节因素对金属混合物对水生生物群的毒性影响的研究有限。本研究调查了 DOM 浓度（低，2.8 ± 0.1 mg C/L；高，11 ± 1.0 mg C/L）和 DOM 来源（主要是陆地或微生物）对铜 (Cu) 和镍的慢性毒性的影响(Ni) 二元混合物对绿色淡水微藻小球藻sp。这是通过使用 72 小时生长抑制生物测定的全因子设计来评估的。将测量的藻类生长速率与浓度添加和独立作用参考模型预测的生长进行比较。模型预测基于溶解金属、不稳定金属的浓度（通过薄膜中的扩散梯度 [DGT] 测量）和计算的游离金属离子（由温德米尔腐殖水模型确定）。铜/镍混合物毒性对小球藻有协同作用sp。在没有添加 DOM 的情况下，有证据表明在低效应浓度下存在金属浓度依赖性毒性。随着 DOM 浓度的增加，混合物相互作用从协同作用变为非相互作用或拮抗作用，具体取决于所使用的金属形态分析方法。当基于溶解和游离金属离子浓度时，DOM 源对混合物相互作用没有显着影响，但当基于 DGT 不稳定金属浓度时，则显着不同。在所有处理中都观察到了与比例相关的混合物相互作用，随着混合物从 Ni 为主变为 Cu 为主，与参考模型预测的偏差增加。环境毒物化学2021；40:1908–1918。© 2021 SETAC