新疆奎屯河流域地下水砷超标原因分析

新疆奎屯河流域是我国大陆第一个地方性砷中毒的区域,然而在人类活动与自然条件下,对该区地下水砷超标的原因未得到清楚的解释。通过2017年在研究区采集地表水、地下水样品51组,分析了主、微量元素组分;2019年在典型的高砷区钻井2个孔,采集沉积物样品44组,分析了粒径、化学成分。结果表明,研究区地下水砷浓度范围为10~887 μg/L,平均为55.8μg/L,沉积物中砷最高为28.41 mg/kg,砷超标(As≥10 μg/L)较为严重。周边山区分布的菱铁矿、砷酸钙、砷酸锰等矿物,为该区地下水砷含量超标提供了物质来源;强烈的蒸发浓缩作用与岩石风化作用使得地下水中的砷浓度进一步升高;高pH值、低Eh的地下水化学环境,造成砷酸盐从矿物表面解吸附聚集在地下水中;沉积物中Fe、Mn氧化物矿物和黏土矿物的还原过程使与之共存的砷被释放,也是该区地下水中砷超标的原因。

Causes of Excessive Arsenic in Groundwater of Kuitun River Basin in Xinjiang

Kuitun River Basin in Xinjiang is the first endemic arsenic poisoned area in mainland China. The causes of excessive arsenic in the groundwater in Kuitun River Basin have not been clarified due to human activities and natural conditions. In the present research, we analyzed the main and trace element components in 51 groups of surface water and groundwater samples collected in 2017, as well as the particle size and chemical composition of 44 groups of sediment samples from two boreholes in typical high arsenic content area in 2019. Results unveiled that the concentration of arsenic in groundwater of Kuitun River Basin ranged from 10-887 μg/L, averaging 55.8 μg/L, and in sediment reaching 28.41 mg/kg to the maximum, which exceeded the standard (10 μg/L) largely. Siderite, calcium arsenate, manganese arsenate and other minerals distributed in the surrounding mountainous areas provided material sources for the excessive arsenic concentration in groundwater; strong evaporation and rock weathering further aggravated the arsenic concentration in groundwater; high pH and low Eh values of groundwater caused arsenate to desorb from the mineral surface and accumulate in groundwater. The reduction process of Fe/Mn oxide minerals in sediments and clay minerals released the coexisting arsenic, which is also the reason why arsenic in groundwater exceeded standard.