大沽排污河污灌区土壤重金属富集特征和来源分析

测定了天津大沽排污河污灌区耕作层(0～25cm)和底层(25～50cm)土壤中重金属、As、Fe及TN、TP和有机质等的含量,采用污染指数、相对富集系数和聚类分析等方法研究了重金属的富集特征和可能来源.结果表明, Hg、Cd、Pb和zn达到土壤环境质量二级标准, As、Ni和Cr达到一级标准.耕作层Hg的含量为0.323mg/kg,污染指数(CF)和相对富集系数(REF)分别为10.8和7.2,属于严重污染和重度富集, Cd的含量为0.341mg/kg, CF和REF分别为3.8和4.5,属于重度污染和中度富集, Pb、Zn和As的含量分别为44.7,108.29和11.2mg/kg, CF和REF均小于3,呈现中度污染和低度富集, Ni和Cr的含量分别为29.86和66.6mg/kg,基本没有富集. Hg、Pb和Zn在耕作层土壤中富集较严重, As在底层土壤富集较严重, Cd、Ni和Cr在两层的含量接近.与1985年的调查结果相比, Cd和As的含量有所增加, Hg、Pb和Zn的含量有所下降, Cr和Ni的含量略低于土壤环境背景值.通过聚类分析并结合大沽排污河污染源调查,表明Hg除受污水灌溉的影响外,燃煤释放的Hg可能是重要来源之一,也是As含量增加的主要原因, Cd、Pb和Zn可能来自污水灌溉和大气沉降,以污水灌溉的贡献为主, Ni和Cr以自然来源为主.

Source and Enrichment of Heavy Metals in Sewage-irrigated Area Soil of Dagu Sewage Discharge Channel

Concentrations of metals, total nitrogen, total phosphorus and organic matter were determined in topsoil (0-25 cm) and subsoil (25-50 cm) samples collected from 16 selected blocks in the sewage-irrigated area of Dagu Sewage Discharge Channel in Tianjin, China. Contamination factors (CF), relative enrichment factors (REF) and cluster analysis (CA) were taken to analyze the source and enrichment of heavy metals. The results show that the concentrations of Hg, Cd, Pb and Zn are above the 1st limit value of Environmental Quality Standard for Soils (China), while those of As, Ni and Cr are below the 1st limit value of the standard. The concentrations of Hg, Cd, Pb, Zn, As, Ni and Cr in topsoil are 0.323, 0.341, 44.7, 108.29, 11.2, 29.86 and 66.6 mg/kg, respectively. CF and REF of Hg in topsoil are 10.8 and 7.2, respectively, which indicates very high contamination and moderately severe enrichment. Both factors of Cd are 3.8 and 4.5, and indicate considerable contamination and moderate enrichment. Those of Pb, Zn and As are all less than three, which indicates moderate contamination and minor enrichment. As for Ni and Cr, their contamination is low and no enrichment occurs. REF for Hg, Pb and Zn in topsoil is relatively higher than that in subsoil while As in subsoil is higher. When compared with data measured in 1985, the concentrations of Cd and As increase while those of Hg, Pb and Zn decrease. Furthermore, measures, including CA and in situ investigation, are taken to identify the main sources of heavy metal contamination, and it shows that Hg and As contamination result from anthropogenic effect as well as deposition of coal combustion. Cd, Zn and Pb contamination are mainly from sewage irrigation, and atmosphere deposition also makes certain contribution. Ni and Cr contamination are attributed to natural sources.