南宁市朝阳溪岸边地下水持久性有机污染物的污染特征

为了查清南宁市污染内河对岸边地下水持久性有机污染物的污染规律,选择典型污染河道朝阳溪为研究对象,采取野外水文地质调查与钻探工程手段,采集降雨前、后地下水以及地表水、土壤和沉积物样品测试,分析了污染河道岸边地下水持久性有机物多环芳烃荧蒽、芘和六六六(HCHs)的降雨前、后的污染特征。结果表明,降雨前、后地下水荧蒽和芘多环芳烃的平均浓度分别为24.11、7.98ng/L;HCHs的平均浓度分别为19.75、13.24ng/L;朝阳溪地下水有机污染物荧蒽、芘、有机氯农药的检出率和浓度降雨前高于降雨后。有机污染物荧蒽和芘浓度分布随远离朝阳溪的距离增大逐渐升高,而HCHs浓度分布则相反;推测由于物理化学性质的差异,疏水性较强的荧蒽和芘被含水层中悬浮物和河底沉积物强烈吸附,显示近岸未被检出;然而,疏水性较弱的HCHs则有较高浓度,并形成污染源,导致HCHs历史残留源在含水层的"二次释放"。总体上,降雨对地下水中有机污染物有稀释作用,但局部HCHs有扰动释放作用;相关性分析显示地下水中悬浮物浓度与多环芳烃的荧蒽、芘呈中等程度负相关,而与HCHs则呈极强程度正相关,因此含水层中悬浮物对荧蒽、芘的"过滤效应"比HCHs要高。朝阳溪岸边地下水中持久性有机污染物的运移影响因素与地下水包气带、含水层结构以及地下水系统补、径、排条件和污染源所处位置密切相关。

Contamination of Persistent Organic Pollutants in the Offshore Groundwater of Chaoyangxi River in Nanning City, China

In order to understand contamination of persistent organic pollutants(POPs) in the offshore groundwater in Nanning City, China caused by polluted rivers, Chaoyangxi River was selected to study as a typical polluted river. Methods of field survey and drilling engineering were taken to study hydrogeology in this area, and then groundwater, surface water, soils and sediment samples were collected and tested. The characteristics of hexachlorocyclohexane(HCHs), and fluoranthene and pyrene in the offshore groundwater before and after rainfall were also discussed. Results show that average concentrations of fluoranthene and pyrene in groundwater before and after the rainfall are 24.11 ng/L and 7.98 ng/L, respectively. The average concentrations of HCHs are 19.75 ng/L and 13.24 ng/L, respectively. The detection rates and concentrations of fluoranthene, pyrene and HCHs after rainfall are higher than those before. Concentrations of fluoranthene and pyrene gradually increase with increasing distance away from Chaoyangxi River, but those of HCHs are the opposite. This study speculates that hydrophobic stronger fluoranthene and pyrene are strongly adsorbed by suspended solids in the aquifer and the bottom sediment of river because of the difference of physical and chemical properties, so that they are not detected in groundwater near the offshore. However, hydrophobic weaker HCHs have higher concentrations due to residual, form pollution source, and result in a "secondary release" of HCHs in aquifer. Overall, rainfall has dilution effect on organic pollutants in groundwater, but HCHs at some local area are disturbed by rainfall to release. Relationship between the concentrations of fluoranthene and pyrene and the suspended material in the groundwater shows a negative moderate correlation, while that of HCHs concentrations and the suspended solids shows a very strong correlation, so the "filtering effect" of fluoranthene and pyrene of the suspended solids in the aquifer is higher than HCHs. Thus, this study suggests that the impact factors of POPs migration in the offshore groundwater are closely related with the structures of vadose zone and aquifer, hydrogeological conditions, and locations of pollution sources