Pollution Level And Ecological Risk Assessment Of Phthalate Esters In Chaohu Lake Basin

Phthalate esters(PAEs)are one of the most commonly detected environmental hormone-based contaminants in all types of environmental media.PAEs in the natural environment are chemically stable and do not degrade easily.Moreover,they can affect the normal physiological activities of animals and humans even at very low environmental concentrations.Therefore,the pollution status of PAEs and their ecological risks attract more and more attentions.In this paper,five representative PAEs(dimethyl phthalate(DMP),diethyl phthalate(DEP),dibutyl phthalate(DBP),diisobutyl phthalate(Di BP),di(2-ethylhexyl)phthalate(DEHP))were selected as the study objects and five typical wastewater treatment plants,the pollution levels of PAEs in the water bodies and sediments of Chaohu Lake,and the current ecological risk status of PAEs in the Chaohu Lake basin were evaluated.Since PAEs in the water environment are closely related to the residual PAEs in the effluent of wastewater plants.Therefore,the pollution level of PAEs in wastewater treatment plants and its removal law are the focus of this paper,and the research contents and conclusions are as follows:(1)The total PAEs concentration in the influent water of the Chaohu basin wastewater plant ranged from 10.142 μg/L to 33.928 μg/L,which was in the middle level at home and abroad as a whole.The total concentration of PAEs in the effluent was 6.047μg/L～12.852 μg/L.Among them,DEHP,DBP and DEP all meet the relevant standards in the Discharge Standards for Pollutants from Urban Wastewater Treatment Plants(GB18918-2002)and Environmental Quality Standards for Surface Water(GB3838-2002).However,for Di BP and DMP,there are no clear discharge standards at home and abroad,and further research is needed.The concentrations of total PAEs in the residual sludge ranged from 22.093 μg/L to 61.153 μg/L.DEHP was the highest PAEs with concentrations of 5.891 μg/L to 44.157 μg/L.(2)The total removal rate of PAEs by wastewater plants ranged from 32.72%to 76.56%,which was in the middle level in China.The removal rate of total PAEs in summer(65.13%)is higher than that in winter(50.34%),and the removal effect of PAEs was DMP > DEP > DBP > Di BP > DEHP.the biological reaction tank of biochemical treatment section was the most core structure for removing PAEs in each treatment process.The combination of A2O+MBR process to enhance biological treatment can effectively improve the removal effect and stability of PAEs in the treatment process.In the pretreatment and deep treatment sections of wastewater plants,only the Fenton fluidized bed reaction system can remove PAEs from wastewater more effectively.(3)The concentration levels of PAEs in water samples(mean concentration of 3.338 μg/L)were higher than those in sediment samples(mean concentration of2.476 μg/L)at the 14 monitoring sites in Chaohu Lake selected for this paper.The average concentrations of the five PAEs in the water samples were Di BP > DBP > DEHP >DEP > DMP.In the sediment samples,Di BP > DEHP > DBP > DEP > DMP.Di BP had higher concentrations in both water and sediment samples at each sampling location,and its pollution in Chaohu Lake may be all-round.In addition,the concentrations of total PAEs in water and sediment at the sampling sites in the inlet area of Chaohu Lake were significantly higher than those at other sites.The river input was closely related to the pollution of PAEs in the waters of Chaohu Lake.(4)The concentration levels of the five PAEs in the effluent of sewage plants were significantly higher compared to the water bodies and sediments of Chaohu Lake.The residual PAEs in the effluent of the sewage plants in the Chaohu basin were a major source of PAEs pollution in the water environment of Chaohu Lake with the exogenous input from the rivers entering the lake.(5)The ecological risk assessment results showed that Di BP and DEHP in the effluent of the wastewater plant and the water body of Chaohu Lake both had high ecological risk to sensitive aquatic organisms in the aquatic environment,DBP had medium risk,and DMP and DEP had low current ecological risk.In the sediment,the exceedance rate of Di BP was as high as 92.9%,and the exceedance rates of DEHP and DBP were 35.7% and 28.6%,respectively,all of which may pose risks to the ecological environment of the study area.The current environmental risk situation of PAEs-like chemicals in the Chaohu Lake basin is not optimistic,which urgently requires the implementation of measures for the elimination,restriction and substitution of PAEs-like chemicals.