Department of Environment Science and Engineering, Southwest University, Chongqing, China; State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Department of Environmental Science, Chongqing University, China.
Department of Environment Science and Engineering, Southwest University, Chongqing, China.
Environ Pollut. 2020 Jun;261:114222. doi: 10.1016/j.envpol.2020.114222. Epub 2020 Feb 19.
Humic acid (HA) plays vital roles in regulating the environmental behaviors of metals and thus their toxicity to biota. However, the inner relation between metal bioavailability to soil organisms and the presence of HA with different molecular weight (Mw) is not well documented. In this study, we separated HAs into four fractions with Mw range of 5-30k Da, and discussed their ability to alleviating the toxicity of Cd and Pb to earthworm. The bioaccumulation capacities (C) increased in order of: UF1<UF2<UF3<UF4, which is in line with the variations of bioavailable concentrations of Cd and Pb in soil. Variations of Mw and binding capacities of HA determine the accumulation behavior in soil solution. The unsatisfactory of biotic ligand model fitting and the differences in fractions of the total biotic ligand sites (f) in earthworm bound by Cd and Pb suggested that only free species of Cd could be considered as biological available to earthworm, while the Pb-HAs complexes have potential ability to interact with earthworm membrane. Antioxidant enzymes are effective biomarkers, and HA with lower Mw play more important roles in restricting the toxicity of soil Cd and Pb to earthworm. These results reveal the different mechanism for HA controlling metal bioavailability between Cd and Pb in soil environment.
腐殖酸（HA）在调节金属的环境行为及其对生物群的毒性方面起着至关重要的作用。然而，金属对土壤生物的生物利用度与具有不同分子量（Mw）的 HA 的存在之间的内在关系尚未得到很好的记录。在这项研究中，我们将 HAs 分离成四个分子量范围为 5-30kDa 的分数，并讨论了它们减轻 Cd 和 Pb 对蚯蚓毒性的能力。生物积累能力（C）的顺序为：UF1<UF2<UF3<UF4，这与土壤中 Cd 和 Pb 的生物可利用浓度的变化一致。HA 的 Mw 和结合能力的变化决定了其在土壤溶液中的积累行为。生物配体模型拟合的不令人满意以及 Cd 和 Pb 结合的蚯蚓总生物配体位点（f）的分数差异表明，只有 Cd 的游离态才能被认为是对蚯蚓具有生物可利用性，而 Pb-HAs 配合物有可能与蚯蚓膜相互作用。抗氧化酶是有效的生物标志物，低分子量的 HA 在限制土壤 Cd 和 Pb 对蚯蚓的毒性方面发挥着更重要的作用。这些结果揭示了 HA 在土壤环境中控制金属生物利用度方面对 Cd 和 Pb 的不同作用机制。
