Guizhou Academy of Testing and Analysis, Guiyang, Guizhou, China.
Department of Environmental Science and Engineering, School of Environmental and Geographical Sciences, Shanghai Normal University, Shanghai 200234, China.
Sci Total Environ. 2019 Jun 1;667:435-443. doi: 10.1016/j.scitotenv.2019.02.418. Epub 2019 Feb 27.
Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are two types of perfluorinated compounds (PFCs) frequently studied in recent years due to their potential for bioaccumulation and toxicity to humans. Usually, PFCs can co-exist in various environment. Therefore, over- or under-estimated risk assessments would result if antagonism or synergism occurred in mixture toxicity. In the present study, the acute and chronic toxicities of single and mixtures of PFOA and PFOS to Daphnia magna were investigated. PFOS was more toxic than PFOA, both in 48-h acute toxicity and 21-d chronic toxicity. In acute toxicity tests, mixture toxicities showed strong synergistic effects on mortality. The experimental EC of the mixture is 4.44 × 10 mol/L, whereas the predicted EC is 8.19 × 10 mol/L by Concentration Addition Model and 9.73 × 10 mol/L by Independent Action Model. In chronic toxicity tests, synergistic effects were also found in the aspects of offspring. The offspring rate is reduced significantly to 39.8% at the 9.61 × 10 mol/L of mixture, while, PFOS and PFOA do not have effects when they are tested individually at corresponding concentrations. To explore the potential mechanism of the synergistic effect, the interactions between PFCs and proteins, including acetylcholinesterase, superoxide dismutase, catalase, ecdysone receptor and glutathione-S-transferase, were investigated by the Molecular Docking. The docking results revealed that the driving forces for the binding of PFCs with proteins were predominantly hydrophobic and hydrogen-bonding interactions. Based on the binding models, we deduced that the potential mechanism of synergism is that PFOS and PFOA have similar binding modes with catalase and have different binding modes with superoxide dismutase. Overall, these data provide experimental evidence that there is strong synergism in acute and chronic toxicity of mixtures to D. magna and demonstrate that molecular structure of some components of the antioxidant defence system contributes to the synergistic interaction.
全氟辛烷磺酸（PFOS）和全氟辛酸（PFOA）是近年来研究较多的两种全氟化合物（PFCs），因为它们具有生物蓄积性和对人类的毒性。通常，PFCs 可以在各种环境中共存。因此，如果混合物毒性中存在拮抗或协同作用，那么风险评估就会过高或过低。本研究中，研究了 PFOA 和 PFOS 单一物质及其混合物对大型溞的急性和慢性毒性。在 48 小时急性毒性和 21 天慢性毒性试验中，PFOS 的毒性均大于 PFOA。在急性毒性试验中，混合物的毒性对死亡率表现出强烈的协同作用。混合物的实验 EC 值为 4.44×10−mol/L，而浓度加和模型预测的 EC 值为 8.19×10−mol/L，独立作用模型预测的 EC 值为 9.73×10−mol/L。在慢性毒性试验中，在后代方面也发现了协同作用。混合物在 9.61×10−mol/L 时，后代率显著降低至 39.8%，而当它们在相应浓度下单独测试时，PFOS 和 PFOA 没有影响。为了探索协同作用的潜在机制，通过分子对接研究了 PFCs 与包括乙酰胆碱酯酶、超氧化物歧化酶、过氧化氢酶、蜕皮激素受体和谷胱甘肽 S-转移酶在内的蛋白质之间的相互作用。对接结果表明，PFCs 与蛋白质结合的驱动力主要是疏水相互作用和氢键相互作用。基于结合模型，我们推断协同作用的潜在机制是 PFOS 和 PFOA 与过氧化氢酶具有相似的结合模式，而与超氧化物歧化酶具有不同的结合模式。总的来说，这些数据为混合物对大型溞的急性和慢性毒性存在强烈协同作用提供了实验证据，并表明抗氧化防御系统的一些成分的分子结构有助于协同相互作用。
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