西溪湿地底泥质量现状与生态风险初步评价

为了解西溪湿地底泥质量现状,2012年9月采集保护区内不同干扰类型的底泥样本,测试了底泥中重金属和POPs中PCBs、OCPs和PAHs的含量,并对湿地底泥污染进行了生态风险初步评价。结果表明,底泥中未检出PCBs和OCPs,但检测出14种EPA优控PAHs,总PAHs的浓度范围为115.9～217.8 ng·g^-1,低于潜在生态风险的效应区间低值ERL,其中列入中国＂水中优先控制污染黑名单＂的7种PAHs均有检出并且其总量占∑PAHs 1/2左右（平均为50.08%）;底泥中8种重金属含量平均值低于《土壤环境质量标准》（GB 15618—1995）的二级标准,但Hg、Zn、Pb、Ni含量在多个位点已超过一级标准;分别采用土壤背景值和国家一级标准为参比值对湿地底泥中重金属进行单因子污染风险指数评价,发现分别有7种和4种元素的污染指数大于1;综合分析不同干扰类型的底泥质量,发现底泥疏浚能有效降低有机质含量、全氮和PAHs含量,但对全磷、重金属含量则无明显效果,封闭水体的干塘措施能显著减少污泥量和有机物含量。研究结果表明,西溪湿地底泥中高环PAHs和重金属污染水平可能对西溪湿地生物具有潜在的生物毒性作用及不利的生态影响效应,其疏浚底泥农用则无生态风险。

The Quality Status and Preliminary Ecological Risk Assessment of Sediments of Xixi Wetland,China

To understand the quality status of Xixi wetland sediments,sediment samples of different interference type were collected in protection zones in September 2012,the contents of heavy metals,PCBs,PAHs and OCPs in sediment were tested,and the ecological risk of wetland′s sediments was preliminarily assessed. The results showed that PCBs and OCPs were not detected in sediments,but 14 priority PAHs from USEPA were detected. Total PAHs concentration was in the range of 115.9 ～ 217.8 ng·g^-1,which was under the effects range low（ERL） of potential ecological risk. Among them,total concentration of 7 PAHs blacklisted priority pollutants in China ′s water was half of the total amount for 14 PAHs（average 50.08%）. Although the average content of 8 heavy metals in sediments was lower than the secondary standard of Soil Environment Quality Standard（GB 15618—1995）,the Hg,Zn,Pb,and Ni contents had been exceeded first standard in more than one sampling site. Using soil background values and national first standards as reference values,ecological risk of heavy metals in wetland sediments was preliminarily assessed by single factor pollution index method. It was found that pollution index of seven and four heavy metals were greater than 1,respectively. By comprehensive analysis to qualities of various interference type sediments,it had been showed that sediment dredging could effectively reduce the contents of organic matter,total nitrogen and PAHs,but the contents of total phosphorus and heavy metals had no obvious effect. The dry pond measures of the closed aquifer could significantly reduce the amount of sludge and contents of organic compound in sediments. The results also showed that the pollution levels of high ring PAHs and heavy metals in the Xixi wetland′s sediments might have potential biological toxicity and adverse ecological effect to wetland′s living things,but there was no ecological risk by using the dredged sediment as farming.