焦化厂土壤和地下水中PAHs分布特征及其污染过程

以煤炭为原料的焦化厂是环境中PAHs的主要人为污染源. 针对US EPA(美国国家环境保护局)优先控制的16种PAHs,对苏南某生产历史长达16 a、面积为44.58×104 m2的焦化厂土壤样品中的w(PAHs)以及地下水样品中的ρ(PAHs)进行了分析,并采用统计学方法对PAHs的分布规律进行了研究. 结果表明:表层土壤中除二苯并[a,h]蒽外,其他15种PAHs均被检出；w(2~3环PAHs)平均值占w(∑PAHs)平均值的92.6%,明显高于w(4~6环PAHs). 地下水中只检出强亲水性的萘、二氢苊、苊、芴、菲、蒽等6种低环PAHs,但未迁移至厂外. 厂区内土壤和地下水中PAHs污染均具有典型的区域分布特征,并且均为化厂车间最严重. 土壤防污性能的差异使PAHs在3.0 m黏土层〔K_y(垂向渗透系数)=1.28×10-8 cm/s〕中富集. 高环PAHs主要与有机质结合以固相迁移,因w(TOC)随深度增加而下降,部分高w(高环PAHs)点位土壤有机质吸附过饱和,未被吸附的高环PAHs向深层迁移至5.0 m含水层顶板,但因强疏水性未进入7.0 m含水层. 强亲水性低环PAHs以溶解态迁移进入含水层,但因地下水流动缓慢(流速为3.71×10-6 cm/s),PAHs污染区仅集中在化厂车间及其附近区域. 

Distribution Characteristics and Polluting Process of PAHs in Soil and Groundwater at a Coking Plant Site

Soil and groundwater were sampled at a 44.58×104 m2 coking plant with 16 years production history located in the southern part of Jiangsu Province. Distribution characteristics of 16 USEPA priority PAHs were assessed with statistical methods, and the polluting process was preliminarily discussed, providing data to support pollution control at the site. In the surface soil, 15 PAHs were found besides DBA, and the average of w(2-3rings PAHs), which accounted for 92.6% of w(∑PAHs), was more than that of w(4-6rings PAHs). On the other hand, high hydrophily naphthalene, acenaphthylene, acenaphthene, fluorene two hydrogen, phenanthrene and anthracene were found in groundwater under the plant, but did not migrate outside. PAHs pollution in both the soil and groundwater had typical regional distribution characteristics, and were the most serious at the chemical factory workshop. PAHs were enriched in the clay layer with antifouling property (K_y =1.28×10-8cm/s) at 3.0 m. Combined with the organic matter, refractory high ring PAHs migrated in solid form. As the total organic carbon (TOC) decreased with depth, in some high-concentration sampling points, high ring PAHs which could not be absorbed by the organic matter migrated to the aquifer roof (at 5.0 m) not the aquifer (at 7.0 m) as the strong hydrophobicity. Meanwhile, low ring PAHs migrated into the aquifer in dissolved form. Groundwater PAHs pollution was only investigated around the factory workshop due to the low flowing velocity (3.71×10-6cm/s).