College of Resources and Environment, Department of Environment Science and Engineering, Southwest University, Chongqing 400715, China; Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400715, China; China Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing 400715, China.
College of Resources and Environment, Department of Environment Science and Engineering, Southwest University, Chongqing 400715, China; Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400715, China; China Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing 400715, China.
J Environ Sci (China). 2018 Aug;70:154-165. doi: 10.1016/j.jes.2017.11.028. Epub 2017 Dec 10.
Molecular weight (Mw) is a fundamental property of humic acids (HAs), which considerably affect the mobility and speciation of heavy metals in the environment. In this study, soil humic acid (HA) extracted from Jinyun Mountain, Chongqing was ultra-filtered into four fractions according to the molecular weight, and their properties were characterized. Complexation of cadmium was investigated by titration experiments. For the first time, Langmuir and non-ideal competitive adsorption-Donna (NICA-Donnan) models combined with fluorescence excitation-emission matrix (EEM) quenching were employed to elucidate the binding characteristics of individual Mw fractions of HA. The results showed that the concentration of acidic functional groups decreased with increasing Mw, especially the phenolic groups. The humification degree and aliphaticity increased with increasing Mw as indicated by elemental composition analysis and FT-IR spectra. The binding capacity of Cd to Mw fractions of HA followed the order UF1 (<5kDa)>UF2 (5-10kDa)>UF4 (>30kDa)>UF3 (10-30kDa). Moreover, the distribution of cadmium speciation indicated that the phenolic groups were responsible for the variations in binding of Cd among different Mw fractions. The results of fluorescence quenching illustrated that the binding capacity of Cd to Mw fractions was controlled by the content of functional groups, while the binding affinity was largely influenced by structural factors. The results provide a better understanding of the roles that different HA Mw fractions play in heavy metal binding, which has important implications in the control of heavy metal migration and bio-toxicity.
分子量（Mw）是腐殖酸（HA）的基本性质，它会极大地影响重金属在环境中的迁移和形态。本研究中，从重庆缙云山土壤中提取的腐殖酸（HA），通过超滤按分子量分成四个部分，并对其性质进行了表征。通过滴定实验研究了镉的络合作用。首次采用Langmuir 和非理想竞争吸附-Donna（NICA-Donnan）模型结合荧光激发-发射矩阵（EEM）猝灭法，阐明了 HA 各分子量分数的结合特性。结果表明，随着分子量的增加，酸性官能团的浓度降低，特别是酚类基团。元素组成分析和傅里叶变换红外光谱（FT-IR）表明，腐殖化程度和脂肪族增加。HA 各分子量分数对 Cd 的结合能力顺序为 UF1（<5kDa）>UF2（5-10kDa）>UF4（>30kDa）>UF3（10-30kDa）。此外，镉形态分布表明，酚类基团是不同分子量分数间 Cd 结合变化的原因。荧光猝灭的结果表明，Cd 与分子量分数的结合能力受官能团含量控制，而结合亲和力则主要受结构因素影响。该研究结果为深入了解不同 HA 分子量分数在重金属结合中的作用提供了依据，这对于控制重金属的迁移和生物毒性具有重要意义。
