Stauder S, Raue B, Sacher F
DVGW-Technologiezentrum Wasser, Karlsruher Strasse 84, 76139 Karlsruhe, Germany.
Environ Sci Technol. 2005 Aug 15;39(16):5933-9. doi: 10.1021/es048034k.
It has long been recognized that the formation of soluble arsenic sulfur complexes plays a key role for the mobility and toxicity of arsenic in sulfate-reducing environments. Knowledge of the exact arsenic species is essential to understand the behavior of arsenic in sulfidic aquifers and to develop remediation strategies. In the past, monomeric and trimeric thioarsenites were assumed to be the existing species in sulfidic systems. In this study, thioarsenates were identified by IC-ICP/MS in arsenite- and sulfide-containing solutions as well as in a reduced groundwater from a contaminated site. The unexpected finding of an oxidation of As(lll) to As(V) in thioarsenates in strongly reducing systems can be explained by the high affinity between As(Ill) and sulfur. In sulfide-containing solutions without oxidant, As(lll) therefore undergoes disproportionation to thioarsenates (As(V)) and elemental arsenic. It has previously been supposed that mobility as well as toxicity of arsenic increases if the redox state decreases. For sulfidic waters, the opposite is probably the case. Thus, the formation of thioarsenates could be used in connection with remediation strategies. Thioarsenates are highly sensitive to oxygen and pH. This is important for analytical procedures. A loss of soluble arsenic as well as a conversion to arsenite and arsenate may occur if water samples containing thioarsenates are analyzed with conventional methods.
长期以来，人们一直认识到可溶性砷硫络合物的形成对砷在硫酸盐还原环境中的迁移性和毒性起着关键作用。了解确切的砷物种对于理解砷在硫化含水层中的行为以及制定修复策略至关重要。过去，单体和三聚硫代亚砷酸盐被认为是硫化系统中的现有物种。在本研究中，通过IC-ICP/MS在含亚砷酸盐和硫化物的溶液以及受污染场地的还原地下水中鉴定出了硫代砷酸盐。在强还原系统中硫代砷酸盐中As(III)氧化为As(V)这一意外发现，可以用As(III)与硫之间的高亲和力来解释。因此，在没有氧化剂的含硫化物溶液中，As(III)会歧化为硫代砷酸盐（As(V)）和元素砷。以前人们认为，如果氧化还原状态降低，砷的迁移性和毒性会增加。对于含硫的水，情况可能相反。因此，硫代砷酸盐的形成可与修复策略结合使用。硫代砷酸盐对氧气和pH值高度敏感。这对分析程序很重要。如果用传统方法分析含有硫代砷酸盐的水样，可能会出现可溶性砷的损失以及向亚砷酸盐和砷酸盐的转化。
