Hazardous substances, such as microcystin-LR (MC-LR) and phenanthrene (Phe) are ubiquitous co-contaminants in eutrophic freshwaters, which cause harms to aquatic organisms. However, the risks associated with the co-exposure of aquatic biota to these two chemicals in the environment have received little attention. In this study, the single and mixture toxic effects of MC-LR and Phe mixtures were investigated in Daphnia magna after acute and chronic exposure. Acute tests showed that the median effective concentrations (48 h) for MC-LR, Phe and their mixtures were 13.46, 0.57 and 8.84 mg/L, respectively. Mixture toxicity prediction results indicated that the independent action model was more applicable than the concentration addition model. Moreover, combination index method suggested that the mixture toxicity was concentration dependent. Synergism was elicited at low concentrations of MC-LR and Phe exposure (≤4.04 + 0.17 mg/L), whereas antagonistic or additive effects were induced at higher concentrations. The involved mechanism of antagonism was presumably attributable to the protective effects of detoxification genes activated by high concentrations of MC-LR in mixtures. Additionally, chronic results also showed that exposure to a MC-LR and Phe mixture at low concentrations (≤50 +2 μg/L) resulted in greater toxic effects on D. magna life history than either chemical acting alone. The significant inhibition on detoxification genes and increased accumulation of MC-LR could be accounted for their synergistic toxic effects on D. magna. Our findings revealed the exacerbated ecological hazard of MC-LR and Phe at environmental concentrations (≤50 +2 μg/L), and provided new insights to the potential toxic mechanisms of MC-LR and Phe in aquatic animals.

微囊藻毒素-LR（MC-LR）和菲（Phe）等有害物质是富营养化淡水中普遍存在的共污染物，对水生生物造成危害。然而，与水生生物群共同暴露于环境中这两种化学物质的相关风险很少受到关注。在本研究中，研究了 MC-LR 和 Phe 混合物在大溞中的单一和混合毒性作用急性和慢性接触后。急性试验表明，MC-LR、Phe 及其混合物的中位有效浓度（48 小时）分别为 13.46、0.57 和 8.84 mg/L。混合物毒性预测结果表明，独立作用模型比浓度加法模型更适用。此外，组合指数法表明混合物的毒性是浓度依赖性的。在低浓度的 MC-LR 和 Phe 暴露（≤4.04 + 0.17 mg/L）下会引起协同作用，而在较高浓度下会引起拮抗或累加效应。所涉及的拮抗机制可能归因于混合物中高浓度 MC-LR 激活的解毒基因的保护作用。此外，D. magna生活史比任何一种化学都单独作用。对解毒基因的显着抑制和 MC-LR 积累的增加可以解释它们对D. magna的协同毒性作用。我们的研究结果揭示了 MC-LR 和 Phe 在环境浓度 (≤50 +2 μg/L) 下的生态危害加剧，并为水生动物中 MC-LR 和 Phe 的潜在毒性机制提供了新的见解。