岩溶地下河中砷迁移过程及其影响因素分析——以广西南丹县里湖地下河为例

Transport process of arsenic in karst subterranean stream and analysis on the influence factors:A case in Lihu subterranean stream of Nandan county,Guangxi

以广西南丹县里湖地下河作为研究区,对砷在地下河中的存在形态,迁移过程及其影响因素进行了分析。结果发现,里湖地下河中砷浓度较高且与人类活动密切相关;由于地下河中相对较低的氧化还原环境,使毒性更强的As(III)含量超过As(V),占总无机砷的53%,增加了该地区发生砷中毒的风险;总As、As(III)和As(V)在地下河中衰减了51%、36%、59%。相关性分析结果表明,沉积物中的Fe、Ca、Mn、有机质及水体中的Ca2+与沉积物中的砷呈现显著正相关关系,有助于水体中砷的吸收;而水体中的Cl-、SO2-4、HCO-3与沉积物中的砷呈现负相关关系,不利于砷的吸附,其中HCO-3的抑制作用最为明显。与非岩溶区水体相比,Ca和HCO-3成为影响砷迁移转化的主要因素,因此在岩溶地下河砷污染治理中应考虑岩溶区的水文地质特点,提高砷的污染治理效率。

The arsenic pollutants generated by the arsenic industries and mining enterprises in karst area flow into subterranean streams and contaminate groundwater easily because of the unique hydrogeological charac-teristics of karst area,which is a serious threat to the water ecologic security and local residents’health.In order to elucidate the geochemistry reaction mechanisms of arsenic in karst subterranean streams,the Lihu subterranean stream in Nandan county,Guangxi Province,Southwest China,is selected for the study.The main outcropped lithology in the Lihu subterranean stream catchment is Carboniferous-Triassic limestone and the karstification rate is 31.67 %.Arsenic species,sediment physical-chemical properties and hydro-chemical characteristics of the water are analyzed by inductively coupled plasma mass spectrometer （ICP-MS）,X-ray fluorescence spectrometer （XRF）and plasma spectrometer （ICP）respectively.The results show that arsenic concentration in the Lihu subterranean stream is high and it is closely related to human activities.The con-tent of As （III）,higher than As （V）,occupies 53 % of the total inorganic arsenic in the Lihu subterranean stream due to the low redox environment,which increase the arsenic ecological risk in this region.The con-tents of total arsenic and As （III）as well as As （V）are attenuated by 5 1 %,36 %,59 % respectively in the underground river.Correlation coefficient analysis calculated with SPSS indicates that sediment Fe,sediment Ca,sediment organic matter,sediment Mn and water Ca2 ＋ are the positive factors that promoting the deposi-tion of arsenic from water.While water Cl- ,SO 2 -4 and HCO -3 ,negatively correlated with arsenic in the wa-ter,do not facilitate to absorb arsenic.Compared with other water bodies,such as Quaternary groundwater, surface rivers and lakes waters,Ca and HCO -3 turn out to be the important factors for mobilization and transformation of arsenic due to the high calcium and bicarbonate content in karst water.Therefore,karst hydrogeological characteristics should be considered during arsenic contamination treatment in karst ground-water.