砷的水地球化学及其环境效应

砷在水环境中的迁移和富集可以产生严重的砷污染，砷在自然水系中主要以无机砷酸盐（AsO4^3-）和亚砷酸盐（AsO3^3-）两种形式存在，而砷的有机化合物的含量一般都很低，砷酸盐在富氧化性的水体中占优势，而亚砷酸盐则富集于还原性水体中，水体中As3 和As5 的相对含量主要受氧化还原条件和一些吸附一解吸平衡过程控制，As3 类比As5 类的毒性强得多，而无机砷化合物比有机砷化合物的毒性大，在pH值为5－6时，As^5 不易被还原成气态AsH3，而s^3 却能定量地被还原出来，根据这一性质，可完成水体中As3 和As5 的测定，砷在饮用水中的安全阀值仅为10ug/L，水体中高砷的危害可以通过水质净化予在消除或降低，铁的化学沉淀和吸附法，石灰软化法，活性氧化铝净化法和逆流渗透法等都可以有效地去除或降低饮用水中砷的含量。

HYDROGEOCHEMISTRY OF ARSENIC AND ITS ENVIRONMENTAL EFFECTS

Arsenic is one of typical toxic elements and its migration and enrichment in the aquatic environment can cause serious arsenic contamination.The inorganic arsenates(AsO43-) and the arsenites (AsO33-) are the main species of arsenic in natural water,while the concentrations of organic arsenic compounds are generally low.Under well-oxygenated conditions,arsenates predominate whereas under mildly reducing conditions,arsenites are most common.The concentrations of arsenic species are mainly controlled by the oxidizing-reducing condition and the adsorption-desorption processes.The trivalent As-species is more toxic than the pentavalent As-species,and inorganic arsenic compounds are higher in toxicity than the organic compounds.Determination of the valency states of As is made based on the fact that As5+is not reduced to arsine at a pH of 5－6 whereas As3+is quantitatively reduced.The safe limit for arsenic in drinking water is only 10 μg/L.While the potential risk of high arsenic in drinking water can be eliminated or alleviated by removing the arsenic from the water.Such methods as the chemical precipitation and adsorption of iron,the lime softening,the activated alumina,and reverse-osmosis can effectively remove the arsenic in the drinking water.