天然有机质不同分子量组分对紫色土镉吸附-解吸的影响
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摘要
环境中广泛分布的天然有机质(NOM)对重金属土壤环境行为具有重要影响。为深化对NOM调控重金属土壤环境行为的认识,本文采用批量平衡试验方法,研究了NOM不同分子量组分(F0,未分级NOM;F1,<5000;F2,5000～10 000;F3,10 000～30 000;F4,>30 000)对紫色土Cd吸附-解吸的影响,分析了NOM效应与其组成和性质的关系。结果表明,添加NOM及其组分(0.1%、0.2%、0.5%C)均增加了土壤对Cd的吸附性能,与未添加NOM对照相比,土壤Cd吸附量增加6.25%～61.22%,而解吸率降低16.22%～56.52%;NOM组分添加量越高,对土壤Cd吸附能力的增加作用越显著;等添加量条件下(0.5%C),F1、F3、F4组分土壤Cd的吸附量明显高于F0,而F2的作用则相反,其中F1处理的土壤Cd吸附量较F0高约37.98%,解吸率降低了约38.63%,而F2则使土壤Cd吸附量降低了约6.68%,解吸率增加18.02%;随NOM组分分子量的增加,其C、H元素含量增加,而O含量减少,O/C、(N+O)/C元素比值降低,反映出高分子量组分氧化程度更低,极性更弱。研究表明,NOM组分对土壤Cd吸附的影响与其分子量大小的变化并不存在线性依存关系,低分子量组分F1可能主要通过影响土壤pH而改变对Cd的吸持能力,而高分子量组分则还受其结构复杂性的影响。
The widely distributed natural organic matter(NOM)in the environment has important influences on the environmental behavior of heavy metals in soils. In this study, bulk NOM was divided into four fractions according to their molecular weight(F0:bulk NOM as the control; F1:fraction with molecular weight <5000 Dalton; F2:5000～10 000 Dalton; F3:10 000～30 000 Dalton; and F4:>30 000 Dalton),and the effects of different NOM fractions on Cd adsorption and desorption in purple soil in relation to their structure and properties were studied using a batch experiment. The results showed that NOM and its fractions significantly enhanced the Cd adsorption ability of the soil. The Cd adsorption rates of the soil increased by 6.25% to 61.22%, while the desorption rates decreased by 16.22% to 56.52% with the addition of 0.1%, 0.2%, and 0.5% C of NOM or its fractions to the soil. The promoting effect increased with the increase in NOM addition.At the same addition amount(0.5% C)of NOM fractions, the amount of Cd adsorption for F1, F3, and F4 was significantly higher than that of the bulk NOM(F0), while F2 showedthe opposite effect; the amount of Cd adsorption with the addition of F1 was about 37.98% higher than that of F0, and the desorption rate was about 38.63% lower. F2 decreased the amount of Cd adsorption by 6.68% and increased the desorption rate by 18.02%. The contents of C and H increased in the NOM fractions with the increase in their molecular weight, while the O content decreased.Accordingly, the ratios of O/C and(N+O)/C in the NOM samples decreased, thereby showing a lower oxidation state and a weaker polarity for the fraction with higher molecular weight. However, no linear dependence existed between the molecular weight of the NOM fractions and their effects on soil Cd adsorption. F1, which was a low molecular weight fraction, promoted Cd adsorption by soil mainly by altering soil pH, while the effects of fractions with higher molecular weight were possibly also relevant to their structural complexity.
The widely distributed natural organic matter(NOM)in the environment has important influences on the environmental behavior of heavy metals in soils. In this study, bulk NOM was divided into four fractions according to their molecular weight(F0:bulk NOM as the control; F1:fraction with molecular weight <5000 Dalton; F2:5000～10 000 Dalton; F3:10 000～30 000 Dalton; and F4:>30 000 Dalton),and the effects of different NOM fractions on Cd adsorption and desorption in purple soil in relation to their structure and properties were studied using a batch experiment. The results showed that NOM and its fractions significantly enhanced the Cd adsorption ability of the soil. The Cd adsorption rates of the soil increased by 6.25% to 61.22%, while the desorption rates decreased by 16.22% to 56.52% with the addition of 0.1%, 0.2%, and 0.5% C of NOM or its fractions to the soil. The promoting effect increased with the increase in NOM addition.At the same addition amount(0.5% C)of NOM fractions, the amount of Cd adsorption for F1, F3, and F4 was significantly higher than that of the bulk NOM(F0), while F2 showedthe opposite effect; the amount of Cd adsorption with the addition of F1 was about 37.98% higher than that of F0, and the desorption rate was about 38.63% lower. F2 decreased the amount of Cd adsorption by 6.68% and increased the desorption rate by 18.02%. The contents of C and H increased in the NOM fractions with the increase in their molecular weight, while the O content decreased.Accordingly, the ratios of O/C and(N+O)/C in the NOM samples decreased, thereby showing a lower oxidation state and a weaker polarity for the fraction with higher molecular weight. However, no linear dependence existed between the molecular weight of the NOM fractions and their effects on soil Cd adsorption. F1, which was a low molecular weight fraction, promoted Cd adsorption by soil mainly by altering soil pH, while the effects of fractions with higher molecular weight were possibly also relevant to their structural complexity.
引文
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[2]环境保护部，国土资源部.全国污染土壤状况调查公报[J].中国环保产业, 2014(5):10-11.Ministry of Environmental Protection, Ministry of Land and Resources.The report on the national general survey of soil contamination[J]. China Environmental Protection Industry, 2014(5):10-11.
[3]杨冰雪,方晨,王宏,等.临安市底泥重金属污染特征及潜在生态危害评价[J].安徽农业科学, 2017, 45(29):45-49.YANG Bing-xue, FANG Chen, WANG Hong, et al. Investigation of heavy metal pollution characteristics and potential ecological risk assessment in Lin′an City[J]. Journal of Anhui Agricultural Sciences,2017, 45(29):45-49.
[4] Wang L, Cui X F, Cheng H G, et al. A review of soil cadmium contamination in China including a health risk assessment[J]. Environmental Science and Pollution Research, 2015, 22(21):16441-16452.
[5] Chen C H, Teng Y G, Lu S J, et al. Contamination features and health risk of soil heavy metal in China[J]. Science of the Total Environment,2015, 512/513:143-153.
[6]李裕,王刚.有机农业与可持续发展[J].应用生态学报, 2004,15(12):2377-2382.LI Yu, WANG Gang. Organic agriculture and sustainable development[J]. Chinese Journal of Applied Ecology, 2004, 15(12):2377-2382.
[7]宋玉婷,雷泞菲.我国土壤镉污染的现状及修复措施[J].西昌学院学报（自然科学版）, 2018, 32(3):79-83.SONG Yu-ting, LEI Ning-fei. China′s cadmium pollution land status and restoration measures[J]. Journal of Xichang University(Natural Science Edition), 2018, 32(3):79-83.
[8] Xiong J, Koopal L K, Weng L, et al. Effect of soil fulvic and humic acid on binding of Pb to goethite-water interface:Linear additivity and volume fractions of HS in the stern layer[J]. Journal of Colloid and Interface Science, 2015, 457(1):121-130.
[9] Xu J, Tan W, Xiong J, et al. Copper binding to soil fulvic and humic acids:NICA-Donnan modeling and conditional affinity spectra[J]. Journal of Colloid and Interface Science, 2016, 473(1):141-151.
[10] Xu J, Koopal L, Fang L, et al. Proton and copper binding to humic acids analyzed by XAFS spectroscopy and isothermal titration calorimetry[J]. Environmental Science&Technology, 2018, 52(7):4099-4107.
[11]王青清.腐植酸活性组分含量和比例对紫色潮土中铅的形态转化及生物有效性的影响[D].重庆：西南大学, 2017.WANG Qing-qing. Effects of the content and proportion of humic acid active components on the speciation and bioavailability of Pb in purple alluvial soil[D]. Chongqing:Southwest University, 2017.
[12]王俊.腐植酸对砷在土壤中形态转化和生物有效性的影响研究[D].重庆：西南大学, 2017.WANG Jun. Effects of humic acid on the speciation and bioavailability of arsenic in soils[D]. Chongqing:Southwest University, 2017.
[13]李光林,魏世强,青长乐,等.镉在腐植酸上的吸附与解吸特征研究[J].农业环境科学学报, 2003, 22(1):34-37.LI Guang-lin, WEI Shi-qiang, QING Chang-le, et al. Characteristics of adsorption and desorption of cadmium on humic acids[J]. Journal of Agro-Environment Science, 2003, 22(1):34-37.
[14] Yang K, Miao G F, Wu W H, et al. Sorption of Cu2+on humic acids sequentially extracted from a sediment[J]. Chemosphere, 2015, 138:657-663.
[15] Lee H H, Weng Y, Li K. Electro-ultrafiltration study on Aldrich humic substances with different molecular weights[J]. Separation and Purification Technology, 2008, 63(1):23-29.
[16] Marsac R, Banik N L, Lützenkirchen J, et al. Modeling metal ionhumic substances complexation in highly saline conditions[J]. Applied Geochemisty, 2017, 79:52-64.
[17] Wu J, Zhang H, He P, et al. Insight into the heavy metal binding potential of dissolved organic matter in MSW leachate using EEM quenching combined with PARAFAC analysis[J]. Water Research,2011, 45(4):1711-1719.
[18] He E, LüC, He J, et al. Binding characteristics of Cu2+to natural humic acid fractions sequentially extracted from the lake sediments[J].Environment Science and Pollution Research, 2016, 23(22):22667-22677.
[19] Jiang T, Wei S, Flanagan D C, et al. Effect of abiotic factors on the mercury reduction process by humic acids in aqueous systems[J]. Pedosphere, 2014, 24(1):125-136.
[20]杨剑虹,王成林,代亨林.土壤农化分析与环境监测[M].北京：中国大地出版社, 2008:257-279.YANG Jian-hong, WANG Cheng-lin, DAI Heng-lin. Soil agrochemical analysis and environmental monitoring[M]. Beijing:China Land Press, 2008:257-279.
[21]邬洪源,黄海涛,赵烨萍.腐植酸中官能团的测定方法的研究[J].高师理科学刊, 2000, 20(1):31-33.WU Hong-yuan, HUANG Hai-tao, ZHAO Ye-ping. Study on the determination of the functional group in humic acid[J]. Journal of Science of Teachers′College and University, 2000, 20(1):31-33.
[22] Rice J A, Maccarthy P. Statisitical evaluation of the elemental composition of humic substances[J]. Organic Geochemistry, 1991, 17(5):634-638.
[23] Hargital L. Biochemical of elemental characteristics of humic substances during humification related to their environmental functions[J]. Environmental International, 1994(20):43-48.
[24] Kin J I, Buckau G, Li G H. Characterization of humic and fulvic acids from Gorleben groundwater[J]. Fresenius Journal of Analytical Chemistry, 1990, 338(3):245-252.
[25]赵楠,吴贻忠.不同施肥处理对潮土胡敏酸结构特性的影响[J].光谱学与光谱分析, 2012, 32(7):1856-1859.ZHAO Nan, WU Yi-zhong. Effects of different fertilization treatments on soil humic acid structure characteristics[J]. Spectroscopy and Spectral Analysis, 2012, 32(7):1856-1859.
[26] Gonzalez-Vila F J, Martin F, Del Rio J C, et al. Structure characteristics and geochemical significance of humic acids isolated from three Spanish lignite deposits[J]. Science of the Total Environment, 1992,117/118(17):335-343.
[27] Chen S Y, Huang S W, Chiang P N, et al. Influence of chemical compositions and molecular weights of humic acids on Cr（Ⅵ）photo-reduction[J]. Journal of Hazardous Materials, 2011, 197(15):337-344.
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