珠江三角洲典型区水土中砷的分布

Distribution of Arsenic in Water and Soil in the Representative Area of the Pearl River Delta

为了解研究区水土中砷的来源及分布，采集地表水样5组、土壤样32组、地下水样14组进行分析。结果表明研究区地表水已受到砷污染。表层土壤（0—10cm）中砷全量为19．8～27．4mg／kg，平均全量为23．7mg／kg，土壤中砷的形态分布以极难迁移的残渣态为主，各形态平均含量的顺序依次为残渣态〉弱有机结合态〉氧化物结合态〉碳酸盐态〉强有机结合态〉水溶态〉离子交换态。底层土壤（30～40cm）中砷全量为11．5。28．1mg／kg，平均全量为21．2mg／kg，土壤中砷的形态也以残渣态为主，土壤中砷的各种形态的平均含量顺序依次为残渣态〉弱有机结合态〉氧化物结合态〉碳酸盐态〉强有机结合态〉离子交换态〉水溶态，底层土壤中砷的各种形态的均量均低于表层土壤。包气带砷全量随深度增加先降低后升高，水溶态、离子交换态以及碳酸盐态的含量均随深度的增加而逐渐降低；而弱有机结合态、氧化物结合态、强有机结合态以及残渣态的含量随深度增加均呈无规律变化。地下水砷含量在0．0028～0．021mg／L之间，均值为0．0114mg／L，超标率达42．9％。地表污水灌溉下渗以及含水介质中原生砷的释放是研究区地下水砷的主要来源。

Five surface water samples, 32 soil samples and 14 groundwater samples have been taken from the representative area of the Pearl River Delta, in order to understand arsenic origin and distribution in water and soil of this area. The results show that surface water in this area has suffered arsenic pollution. Total arsenic content of topsoil （0 - 10cm） is from 19. 8 to 27.4 mg/kg, with an average value of 23.7 mg/kg. The most of arsenic content in topsoil is residual fraction. The sequence of arsenic average content of seven forms in topsoil is residual fraction 〉 weak organic fraction 〉 oxide fraction 〉 carbonate fraction 〉 strong organic fraction 〉 water soluble fraction 〉 ion exchange fraction. Total arsenic content of subsoil （30 -40cm） is from 11.5mg/kg to 28. 1 mg/kg, with an average value of 21.2 mg/kg. The most of arsenic content in subsoil also is residual fraction. The sequence of arsenic average contents of seven forms in subsoil is residual fraction 〉 weak organic fraction 〉 oxide fraction 〉 carbonate fraction 〉 strong organic fraction 〉 ion exchange fraction 〉 water soluble fraction. Average contents of all arsenic forms are higher in topsoil than in subsoil. In unsaturated zone, total arsenic content decreaseds firstly and then increases with the depth. The contents of water soluble fraction, ion exchange fraction and carbonate fraction decrease gradually with the depth. The contents of weak organic fraction, oxide fraction, strong organic fraction and residual fraction do not show regular variation with the depth. The arsenic content of groundwater is from 0. 0028 to 0. 021mg/L, with an average value of 0. 0114mg/L. The arsenic content exceeds 42.9% compared with the Chinese drinking water quality standards （0. 01mg/L）. Industrial wastewater infiltration and original arsenic released from aquifer medium are the main origin of arsenic in groundwater.