平原河湖系统中典型全氟化合物的胶体吸附特征及生态风险评估

Adsorption characteristics of perfluorinated compounds from colloids in the river-lake system of the plain and their ecological risk

胶体作为水环境中广泛存在的一类纳米颗粒物,因其粒径小、比表面积大、吸附位点多等特点,能够吸附有机污染物,并改变和控制其环境行为.全氟化合物(PFCs)疏水疏油、环境持久性强,在水环境中势必与胶体介质结合,形成复合污染效应.本文以不同受纳河湖系统作为研究区域,选取4种典型的PFCs为目标物,主要包括:全氟辛酸(PFOA)、全氟壬酸(PFNA)、全氟辛烷磺酸(PFOS)、全氟正癸酸(PFDA),研究其在传统溶解相中的空间分布特征及胶体吸附潜能,并评估其生态风险水平,主要结果如下:(1)4种PFCs在研究区域传统溶解相和胶体相中均被检出,检出率为78.8%~100%,总浓度范围分别在12.5~92.1和5.4~49.9 ng/L之间.在传统溶解相和胶体相中,PFOA均为最主要的PFCs,贡献率在65%以上,其次是PFOS、PFNA和PFDA.(2)从介质分布来看,胶体是PFCs的重要吸附载体,平均吸附贡献率在42.6%~66.1%之间,其中胶体对PFDA的吸附潜能最大,平均吸附贡献率为66.1%,其次是PFNA(53.5%)、PFOA(47.0%)和PFOS(42.6%),胶体对PFCs的吸附贡献率与其正辛醇水分配系数(lgK_(OW))呈显著正相关.(3)从空间分布来看,PFCs在居民聚集区污染水平最高,平均浓度为71.2 ng/L,其次是溱湖湿地公园,平均浓度为43.3 ng/L.工业区、农业区及城市区,PFCs污染水平相当,平均浓度在30~40 ng/L之间,水产养殖区污染水平最低.(4)通过风险熵值法(RQ)和水环境质量基准对检出PFCs进行风险评价,发现58%水域中的水生生物处于PFOS引起的低风险状态,主要集中于工业区以及居民聚集区.且所有采样点中PFOS的污染水平均高于欧盟委员会设定的PFOS在淡水环境中的年均环境质量标准(0.65 ng/L),低于最大允许浓度36μg/L.PFOS在水环境长期赋存引起的慢性毒理风险不容忽视.

In the aquatic environment,colloids are ubiquitous and have small particle size,large specific surface areas and multiple adsorption sites.Colloids can adsorb the organic contaminants,and change and control their environmental behavior.Perfluorinated compounds(PFCs)may be associated with the colloids in surface water to form effects of combined pollution due to non-hydrophilic and non-lipophilic properties and persistence of PFCs.In this paper,river-lake system of a national ecological demonstration area was selected as the study area,spatial distribution characteristics and colloidal adsorption potential for 4 typical PFCs including pentadecafluorooctanoic acid(PFOA),perfluorononanoic acid(PFNA),perfluorooctane sulfonate(PFOS),perfluorooctanoic acid(PFDA)were investigated in the traditionally dissolved phase to assess their ecological risk level.The main results were as follows:(1)All four PFCs were detected in the traditionally dissolved phase and colloidal phase,with the detection rate of 78.8%-100%and the total concentrations of 12.5-92.1 ng/L and 5.4-49.9 ng/L,respectively.In the traditional dissolved phase and colloidal phase,PFOA are the main PFCs.The contribution rates of PFOA to PFCs were more than 65%,followed by PFOS,PFNA,PFDA.(2)From the medium distribution,colloids are an important"sink"of PFCs,average adsorption contribution rates of colloids to PFCs are between 42.6%and 66.1%.PFDA showed the greatest adsorption potential,with an average absorption contribution rate of 66.1%,followed by PFNA(53.5%),PFOA(47.0%)and PFOS(42.6%).The adsorption contribution rate of colloids to PFCs was significantly positive correlation with the lgK_(OW) of PFCs.(3)In terms of spatial distribution,residential areas have the highest pollution levels,with an average concentration of 71.2 ng/L,followed by Qinhu Wetland Park(43.3 ng/L).In industrial,agricultural and urban areas,PFCs have comparable pollution levels,with average concentrations between 30 ng/L and 40 ng/L.Aquaculture area showed the lowest pollution levels.(4)Using risk quotient(RQ)and water quality benchmark to assess the water environment risk,we found that the aquatic organisms in 58%of sampling sites were in low-risk state caused by PFOS,mainly located in industrial areas and residential areas.And PFOS pollution levels in all the sampling sites were higher than the annual average environmental quality standard(0.65 ng/L)setting by the European Commission for PFOS in freshwater environments,which is lower than the maximum acceptable concentration environmental quality standard of 36μg/L.Chronic ecological risks caused by long-term occurrence of PFOS in aquatic environment should not be ignored.