The Impact Of Suspended Particulate Matter On The Environmental Behaviors Of Phthalate Esters In Turbulent Waters:the Multiple Mechanism Investigation

Phthalate esters（PAEs）are organic compounds that are widely used in industry.Because of their unique physical and chemical properties,they have been distributed widely in air,water,soil,sediment,and organisms.Meanwhile,researches have shown that as a typical environmental hormone,PAEs have the potential of reproductive toxicity,immunotoxicity,and carcinogenicity.In this study,the occurrence of PAEs in the Yulin River,a tributary of the Three Gorges Reservoir Area,was determined in December 2019.The potential sources and the parameters that influenced the occurrence of PAEs were evaluated.Then,Di-n-butyl phthalate（DBP）,a typical type of PAEs that is widely identified in aquatic environments,was employed to discuss the adsorptive capacity by the suspended particulate matter（SPM）with different particle sizes.Finally,the potential process that would influence the transformation of DBP in turbulent waters was identified.The main conclusions are as follows:（1）The results of in situ investigations of 6 kinds of PAEs（DEP,DMP,DBP,BBP,DEHP and Dn OP,according to US EPA）in five sites of the Yulin River revealed that the total concentration of PAEs was 0.381～0.867μg/L.The average total concentrations of PAEs in the five sites were:Hekou（0.771μg/L）>Paihua（0.638μg/L）>Meixi（0.613μg/L）>Donghe（0.566μg/L）>Shujia（0.421μg/L）with DMP,DBP,and DEHP being the main monomers.The main PAEs pollutants in the five sites near the mainstream of the Yangtze River,such as Hekou and Paihua,were as follows:DBP>DEHP>DMP,and in the location that far from the mainstream of Yangtze River（Shujia,Meixi,and Donghe）,the profile was DBP>DMP>DEHP.Based on the correlation analysis and principal component analysis,it was found that there was a significant positive correlation between DBP and DEHP,which may be related to industrial and agricultural production activities.（2）The partition was the main mechanism for the removal of DBP by SPM,and the adsorption capacity of different grain-sized SPM for DBP was followed by:clay-fine sand（<8μm）>fine sand（8～20μm）>medium sand（20～32μm）>coarse sand（32～63μm）>sand（>63μm）.Total organic carbon was the main factor that affected the partition of DBP by different grain-sized SPM.Meanwhile,the difference in organic matter composition in clay-very fine silt SPM might be the reason for its high adsorption capacity for DBP.The specific surface area,pore-volume,and humification degree of organic matter affected its adsorption of DBP by silt-sand SPM.（3）DBP in aqueous phase can be degraded by the joint efforts of adsorption/partition,biodegradation and photolysis in the turbulent experimental system that contained water and SPM.The·OH induced by Chromophoric dissolved organic matter（CDOM）can dealkylate DBP into phthalic acid（DBP-P4）and other photodegradation products to achieve initial photolysis of DBP.The adsorption-biodegradation was the main approach that contributed to the reduction of both DBP and DOC in the aqueous phase.With the continuous increase of polysaccharides and other organic matters in SPM and its attached biofilm,DBP in more aqueous phase can be adsorbed onto the surface of SPM through surface adsorption/partition.Next,the DBP-P4 was subjected to decarboxylation and turned to DBP-P5 due to the bacteria and enzyme.Subsequently,DBP-P5 was converted to DBP-P6 and CH₃CHO due to the cleavage of the benzene ring,which was finally decomposed to CO₂ and H₂O,thus realizing the effective removal of DBP and its degradation products in the turbulent experimental system.