pH值、腐植酸类型以及铝对亚砷酸盐和砷酸盐与溶解腐植酸络合的影响

Arsenite and Arsenate Binding to Dissolved Humic Acids: Influence of pH, Type of Humic Acid, and Aluminum

溶解的天然有机质(DOM)会影响水环境中砷(As)的存在形式。在环境相关的砷/溶解有机质(DOC)比率和p H条件下,使用平衡透析法研究了As(Ⅲ)和As(Ⅴ)络合到两种商业腐植酸的条件分布系数(Dom)。在所有p H值范围内,As(Ⅴ)比As(Ⅲ)能更好地络合到腐植酸上,p H值为7左右时腐植酸的络合能力最强,因为在低p H值时,H+会与As竞争络合位点;而在高p H值时,OH-会与腐植酸竞争As。对于这两种氧化态,Dom的值会随着As/DOC比率减少而增加。对As(Ⅲ)和As(Ⅴ)来说,Dom值可以和As/DOC比值拟合为一个函数。在相同的条件下,陆生的腐植酸与As的络合能力比水生的腐植酸高1.5~3倍。在As/DOC比值较低时,Al3+也可以与As竞争络合位点。在正常环境条件下,约10%的As(Ⅴ)可以与天然有机质络合,而只有在As/DOC比值较低时,才会有】10%的As(Ⅲ)被络合到腐植酸上。在将As络合到自然有机物上时,应考虑到自然环境。

The fate of arsenic in the aquatic environment is influenced by dissolved natural organic matter(DOM). Using an equilibrium dialysis method, conditional distribution coefficients(Dom) for As(Ⅲ) and As(Ⅴ) binding onto two commercial humic acids were determined at environmentally relevant As/dissolved organic carbon(DOC) ratios and as a function of p H. At all p H values, As(Ⅴ) was more strongly bound than As(Ⅲ). Maximum binding was observed around pH 7, which is consistent with H+ competition for binding sites at low p H values and OH- competition for the arsenic center at high p H. For both oxidation states, Dom values increased with decreasing As/DOC ratios. Dom values were fitted as a function of the As/DOC ratio for As(Ⅲ) and As(Ⅴ). Compared to the aquatic humic acid, the terrestrial humic acid had a higher affinity for arsenic binding with 1.5-3 times higher Dom values under the same conditions. Al3+in excess to arsenic successfully competed for strong binding sites at low As/DOC ratios. Under environmentally relevant conditions, about 10% of total As(Ⅴ) may be bound to DOM, whereas >10% of As(Ⅲ) is bound to DOM at very low As/DOC ratios only. Binding of arsenic to DOM should be considered in natural systems.