The vital function of humic acid with different molecular weight in controlling Cd and Pb bioavailability and toxicity to earthworm (Eisenia fetida) in soil. (June 2020)

• Record Type: Journal Article
• Authors: Bai, Hongcheng; Luo, Mei; Wei, Shiqiang; Jiang, Zhenmao; He, Mingjing
• Is Part Of: Environmental pollution. Volume 261(2020)
• Publication Date: 2020-06
• Subjects: Humic acid -- Molecular weight -- Earthworm -- Toxicity -- Bioavailability; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2020.114222
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: 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 max ) 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. Graphical abstract: Image 1 Highlights: Mw and binding capacities of HA determine the metal accumulation behavior. Biotic ligand model could evaluate the effect of Mw fractions on metal toxicity. Complexes between HAs and Pb may act biological available to earthworm. HA with lower Mw play more important roles in ameliorating oxidative stress.