Cattani I, Zhang H, Beone G M, Del Re A A M, Boccelli R, Trevisan M
Inst. of Agricultural and Enviromental Chemistry, Università Cattolica del Sacro Cuore, Via Emilia Parmense 29100, Piacenza- Italy.
J Environ Qual. 2009 Feb 6;38(2):493-501. doi: 10.2134/jeq2008.0175. Print 2009 Mar-Apr.
Contamination of soils with mercury can be a serious problem. It can be mobilized or stabilized by humic substances (HS) containing binding sites with reduced sulfur that can have different binding capacities for CH(3)Hg(+) and for Hg(2+). In this work we investigated the influence of different humic acids (HAs, extracted from lignite, compost, and forest soil) on mercury mobility and availability, both in a model solution and in soil samples from a mercury-polluted region. The technique of diffusive gradients in thin-films (DGT), which is capable of measuring: (i) free metal in solution; (ii) dissociated metal complexes previously mobilized by HA; (iii) mobilized metal-HA complexes that liberate metals by dissociation or by exchange reaction between the metal-HA complexes and the chelating groups on the resin-gel, was used in solutions and soils. The DGT measurements in solution, together with ultrafiltration, allowed estimation of the lability of Hg-HA complexes. Ultrafiltration results were also compared with predictions made by the windermere humic-aqueous model (WHAM). According to both these different approaches, Hg(2+) resulted nearly 100% complexed by HAs, whereas results from ultrafiltration showed that 32 to 72% of the CH(3)Hg(+) was bound to the HAs, with higher values for compost and lower values for forest and Aldrich HA. The DGT-measured mercury in soils was below 0.20 microg L(-1), irrespective of the extent of the contamination. Addition of HA increased the concentration of DGT-measured mercury in soil solution up to 100-fold in the contaminated soil and up to 30-fold in the control soil. The level of the increase also depended on the HA. The smallest increase (about 10 times) was found for lignite HA in both control and contaminated soils. The addition of forest HA gave the largest increases in DGT-measured mercury, in particular for the contaminated soil. Overall, the results demonstrated that DGT can be used for estimating the lability of mercury complexes in solution and for verifying enhanced mercury mobility when HA is added to contaminated soils.
土壤汞污染可能是一个严重问题。汞可通过含有还原态硫结合位点的腐殖质（HS）被活化或固定，这些结合位点对甲基汞离子（CH(3)Hg(+)）和汞离子（Hg(2+)）具有不同的结合能力。在本研究中，我们研究了不同腐殖酸（从褐煤、堆肥和森林土壤中提取的HA）对汞迁移性和有效性的影响，研究在模型溶液和汞污染地区的土壤样品中进行。薄膜扩散梯度技术（DGT）能够测量：（i）溶液中的游离金属；（ii）先前被HA活化的解离金属络合物；（iii）通过解离或金属 - HA络合物与树脂 - 凝胶上螯合基团之间的交换反应释放金属的活化金属 - HA络合物，该技术用于溶液和土壤。溶液中的DGT测量与超滤相结合，可估算Hg - HA络合物的活性。超滤结果还与温德米尔腐殖质 - 水模型（WHAM）的预测结果进行了比较。根据这两种不同方法，Hg(2+)几乎100%被HA络合，而超滤结果表明，32%至72%的CH(3)Hg(+)与HA结合，堆肥中的值较高，森林和Aldrich HA中的值较低。无论污染程度如何，DGT测量的土壤汞含量均低于0.20μg L(-1)。添加HA使污染土壤中DGT测量的土壤溶液汞浓度增加高达100倍，对照土壤中增加高达30倍。增加水平也取决于HA。在对照土壤和污染土壤中，褐煤HA的增加最小（约10倍）。添加森林HA使DGT测量的汞增加最大，特别是对于污染土壤。总体而言，结果表明DGT可用于估算溶液中汞络合物的活性，并用于验证向污染土壤中添加HA时汞迁移性的增强。
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