重工业区高脆弱岩溶含水层中多环芳烃污染的初步研究

以西南岩溶地区某市重工业区为研究对象，采集水文地质单元内地下水和土壤样品，利用气相色谱-质谱法（GC-MS)测试美国环保署16 种多环芳烃（PAHs）优控物。初步研究表明，研究区地下水16种PAHs均被检出，浓度为1 135.79～1 361.26 ng/L，以菲、蒽、萘、屈、芘为主；地下水处于中等污染程度，其中苯并a]蒽、屈、苯并b]荧蒽、苯并k]荧蒽4种浓度超过美国EPA2009《国家推荐的优先有毒污染物水质标准》标准；PAHs特征比值显示含水层中的PAHs来源于燃煤和炼焦污染源，与钢铁厂和化肥厂排放的特征有机污染物一致。研究区污染源下游大面积区域地下水已经受到PAHs污染，且出现排泄区PAHs浓度高于径流区的现象，岩溶含水层PAHs的污染主要受两方面影响:一是洼地、裂隙发育,断层破碎带和强风化白云岩等为PAHs在含水层中的运移提供了有利条件，同时污染源区内地下水大量开采加速了污染物向地下水的入渗；二是水电站建坝蓄水发电，江水水位抬高，河岸地下水排泄速度减慢，可能致使岩溶含水层中PAHs的自净能力减弱。生态风险评价显示地下水中菲、蒽、芘、苯并a]蒽、苯并b]荧蒽处于重污染风险，应采取措施降低污染风险。 

Preliminary study on contaminant of polycyclic aromatic hydrocarbons in vulnerable karst aquifer in a heavy industry district

One heavy industry district (steel and fertilizer plants) in the karst area of southwestern China was selected as the study area. The groundwater and soil samples in the hydrogeological units were collected, from which 16 polycyclic aromatic hydrocarbons (PAHs) prioritised by USEPA were analysed using GC/MS method. The results show that total concentration of the PAHs in groundwater ranges from 1135.79 to 1361.26 ng/L, with dominant species as phenanthrene, anthracene, naphthalene, chrysene and pyrene. Compared with other regions, groundwater pollution due to the PAHs in the study area is of a middle level. According to National Recommended Water Quality Standards of priority toxic pollutants (2009 USEPA)，it is found that benzoa]anthracene, chrysene, benzob]fluoranthene, and benzok]fluoranthene exceed the standard. The figures of PAHs characteristic ratio suggest that the PAHs sources in the karst aquifer were derived from incompletely burning and coking of coal, which are similar to contaminant sources discharged by steel and fertilizer plants. The karstic groundwater in the downstream areas have been highly polluted; and it appears that the PAHs concentration in the discharge area is a higher than that of runoff area. Impact of the PHAs on the karst aquifers is sever, which can be attributed to the following two aspects. On the one hand, common presence of karstic depressions, dense fissures developed in the karst, weathered dolomite and fault fracture zones provides a favorable condition for PAHs migration in the karst aquifers which are high vulnerable to the contaminant. Meanwhile, large quantity of groundwater in source areas has been extracted for industrial use, which speeds up the infiltration of pollutants into the karst aquifers. On the other hand, the surface water level in the study area has been raised owing to the construction of the Honghua hydropower station dam which stores huge amount of water in the reservoir; this in turn elevates the groundwater level and slows down its discharge to the stream system. As a result, the self-purification ability of PAHs in the karst aquifer decreases. The location of pollution sources in the groundwater system is also one of the factors that impact of the PAHs migration in karst aquifer. Risk assessment of groundwater suggests that the content of phenanthrene, anthracene, pyrene, benzoa]anthracene and benzob]fluoranthene in the karst groundwater is at a very high risk grade. Thus, it is suggested that local government should take immediate intervention to reduce this pollution risk.