河道疏浚底泥还田利用潜在污染和生态风险评价

Potential pollution and ecological risk assessment of dredged sewageriver sediment utilization on agriculture

为探索上海市奉贤区主要河道疏浚底泥还田利用的可行性,通过分析底泥还田后的土壤养分及属性、重金属和有毒有害物质含量,并采用耕地生产性能综合指数、单项污染指数、综合污染指数和潜在生态危害指数对其土壤环境质量、污染程度及生态风险进行评价。结果表明:河道疏浚底泥还田后的耕地地力等级较高,处于一级地和二级地(即高产田)的面积占97.02%,不存在等级最差的五级地。对土壤养分和属性元素进行等级评价时发现,除容重(CY)的平均含量处于5级(低)水平外,其余土壤养分元素和属性指标[有机质(SOM)、全氮(TN)、有效磷(AP)、速效钾(AK)、pH、耕层厚度(Apl)、水溶性盐总量(TDS)和阳离子交换量(CEC)]均处于1级(高)—3级(中)水平。底泥还田土壤中的Hg、As、Cd、Cr、Pb、Cu、Zn和Ni的均值分别为0.20 mg∕kg、8.43 mg∕kg、0.114 mg∕kg、53.00 mg∕kg、22.87 mg∕kg、26.93 mg∕kg、87.73 mg∕kg和25.42 mg∕kg,未超过《土壤环境质量农用地土壤污染风险管控标准(试行)》农用地土壤污染风险筛选值,且有毒有害物质六六六(BHC)、滴滴涕(DDT)和苯并[a]芘(BaP)未检出,土壤环境质量较好,可作为耕地使用。重金属的污染指数和生态风险评价总体结果为安全,但Hg对潜在生态风险指数的贡献率最大,危害级别达到强,是重金属中最主要的潜在生态风险来源。其他重金属元素都属于轻微级别。因此,奉贤区河道疏浚底泥农用是安全的,但需要进行跟踪监测和评价。

For explore the availability of dredged sewage river sediment utilization on agriculture in Fengxian District,the contents of soil nutrients,properties,heavy metals,toxic and harmful substances were analyzed.It evaluated the soil environment quality,pollution levels and ecological risks by analyzing cultivated land productivity grade system,single pollution index,composite pollution index and potential ecological risk index.The result showed that the dredged sewage river sediment utilization on agriculture had a higher soil fertility grade,with the fertility grade of 1^(st) and 2^(nd)(high yield fields)accounted for 97.02%of the total.The worst fertility grade of 5^(th) was non-existent.Although the grading standard of CY content was in 5^(th)(low),the others were at 1^(st)(high)to 3^(rd)(medium).The average contents of Hg,As,Cd,Cr,Pb,Cu,Zn and Ni were 0.20 mg∕kg,8.43 mg∕kg,0.114 mg∕kg,53.00 mg∕kg,22.87 mg∕kg,26.93 mg∕kg,87.73 mg∕kg and 25.42 mg∕kg,which were lower than the risk screening value of“Environmental quality standards for soils”,and the toxic and harmful substances of BHC,DDT and BaP were not detected.It explained that the soil environmental quality was better in farmland. The evaluation results of single pollution index,composite pollutionindex and potential ecological risk index of eight heavy metal elements showed the soil was relatively safe andnon-pollution. However,Hg had the largest contribution ratio and its potential ecological risk level was severe,which was the main potential ecological risk source of heavy metal. The level of other heavy metal elements weremild. Therefore,the dredged sewage river sediment could be ecologically safe as agriculture land uses,but followupmonitoring and evaluation were needed.