Distribution, Sources And Ecological Risk Assessment Of Polychlorinated Biphenyls And Heavy Metals In The Dagu River Estuar

The estuary region is a transitional area between land and marine ecosystems.Wi th the rapid development of coastal urban economy,environmental pollution in the est uary region has become increasingly serious.Heavy metals and polychlorinated biphe nyls（PCBs）are common pollutants in the environment,and are widely concerned due to their characteristics of bioaccumulation and high toxicity.In this study,the soil and sediment in the Da Gu River estuary area were the main research objects.The concen trations of PCBs and heavy metals in different types of soil and sediment in the study area were determined.Principal component analysis and correlation analysis were use d to determine the sources of these two pollutants,and various pollution assessment m ethods were used to conduct ecological risk assessment.By analyzing and measuring t he concentration of PCBs in the soil and sediment from 0 to 30 cm,the vertical distrib ution and migration characteristics of PCBs in different types of soil were studied.Ind oor soil column leaching experiments were designed to study the influence of soil org anic matter content,p H,and salinity on the vertical migration of PCBs in soil sedimen t.The main conclusions are as follows:Σ₇PCBs were generally present in the Da Gu River estuary area,but the concentr ation level was low and much lower than that in industrialized estuaries.Pentachlorob iphenyl and hexachlorobiphenyl were the main components in sediment/soil.The con centration of PCBs in sediment/soil generally decreased with increasing depth.Princi pal component analysis indicated that most of the PCBs in the samples may come fro m transportation,aquaculture,and waste incineration.In addition,fishing and shippin g may also be important sources of PCBs.Ecological risk assessment results showed t hat the concentration of PCBs in all samples was below the ERL,and the total TEQ of all sampling points was below the TEC,indicating that the ecological risk of PCBs in the Da Gu River estuary was low and would not cause adverse effects on organisms.The content of Cr,Cu,Zn,As,Cd,and Pb in soil and sediment samples in the study area exceeded the background values of Shandong Province,and industrial activities had a significant impact on the distribution of heavy metals in the region.The results of geo-accumulation index evaluation and potential risk assessment showed that most sampling points were in a clean pollution level,and all heavy metal pollution levels were low-risk.Principal component analysis showed that the main sources of Cr,Zn,and As were traffic and natural sources,the main sources of Cd and Pb were agricultural sources,while Cu pollution may be caused by composite pollution from transportation,industrial,and agricultural activities.Laboratory soil column simulation experiments showed that the migration of PC Bs in soil sediment with different organic matter mainly occurred in the 0～6cm layer.The downward migration trend of PCBs was more obvious in low organic matter soil.Changes in soil organic matter content could affect the migration behavior of differen t PCB congeners,with higher chlorinated congeners being more prone to downward migration.In addition,p H and salinity also had an impact on PCB migration,with alk aline conditions favoring PCB migration in soil,while acidic conditions inhibited mig ration.Under appropriate salinity,the migration depth of PCBs increased.