| Polychlorinated biphenyls?PCBs?are difficult to degrade,which has bioenriched,long-range transport and biotoxic characteristics.They can exist in nature and accumulate in animals and plants for a long time,and pose a threat to the ecological environment and human health.PCBs has been listed as one of the first controlled persistent organic pollutants under the Stockholm Convention.The atmosphere is an important medium for the existence and propagation of PCBs.PCBs in the atmosphere diffuses globally through"grasshopper hopping transport",and migrates to other environmental media by dry and wet deposition.PCBs pollution in urban atmosphere has become a problem that can not be ignored.Gas phase and particle phase(PM2.5,PM10,TSP)samples were collected in 21 sites in Beijing,to study the pollution characteristics,spatial distribution,homologue composition and gas particle distribution of PCBs systematically.The total concentrations of 28 PCBs in the atmosphere of Beijing were 44.0-403pg/m3 and the average concentration was 88.5pg/m3.The PCBs concentration in gas phase were 34.4pg/m3-331pg/m3 and the average concentration was 71.3pg/m3,while the PCBs concentrations in total particle phase was 8.40-72.0pg/m3 and the average was 17.3pg/m3.The level of PCBs pollution in Beijing was lower than that at home and abroad.The homologues were mainly composed of trichlorodiphenyl to hexachlorobiphenyl,which accounted for 83.22%of the total PCBs.The concentration of low chlorinated PCBs monomer such as CB-18?CB-28?CB-44 was generally higher.In several areas,low chlorinated PCBs monomer was the main source of atmospheric PCBs pollution.The study on the spatial distribution of PCBs in the atmosphere of Beijing showed that the regions with higher concentration were Research Center for Eco-environmental Sciences Chinese Academy of Sciences,Yizhuang Development Zone and Zhongguancun area,which were scientific research unit,chemical enterprises and electronic products accumulation areas.The atmospheric PCBs concentrations in other regions were below 100pg/m3.There was no significant difference in PCBs content among urban,suburban and rural areas.The concentrations of PCBs in different size particles were analyzed.The PCBs concentrations in atmospheric PM2.5 in Beijing were 54.6-429 ng/g,the average value was 188ng/g,while the concentrations in PM10 were 31.1-313 ng/g with the average of 136ng/g,and the concentrations in TSP were 28.0-193 ng/g,with the average of100ng/g.The concentration levels of PCBs in different particulate matter were PM2.5>PM10>TSP.The distributions of PCBs in the PM2.5?PM100 and TSP were similar,there was no obvious regional characteristic.The proportion of PCBs in the atmosphere in Beijing is mostly 15-25%.The higher the total concentration of PCBs in the atmosphere,the lower the PCBs ratio of the carrier phase in the particulate phase.The distribution of PCBs in gas/particle phase has difference because of the number of chlorides.The high chlorine PCBs tend to distribute in particle phase,and the low chlorine PCBs tend to distribute in gas phase.This is because that high chlorinated PCBs has low vapor pressure and is more easily attached to the particle phase,while low chlorinated PCBs has high vapor pressure and is more easily diffused into the gas phase.Use regression analysis of lgKp-lgPL0 and lgKp-lgKOAA to analyse the distribution of PCBs in gas/particle phase,both of the slope deviate from the theoretical value of equilibrium state,indicating that the distribution of PCBs gas particles is not balanced.The Junge-Pankow model and Harner-Bidleman model are used to compare the predicted and measured values of the percentage of PCBs particle states,respectively.The two models have better predictability for the PCBs of the intermediate chlorine algebra,while for low chlorinated or high chlorinated biphenyls are overestimate or underestimiate.The toxic equivalent range of 12 kinds of DL-PCBs in the atmosphere of Beijing is 97-1337 fg/m3,the range of Beijing residents daily respiratory exposure of PCBs is 16.3-224.6 fg WHO-TEQ kg-11 BW·d-1,which is 1.63%-22.4%of WHO minimum daily allowable intake.Beijing residents have lower PCBs exposure risk.CB126 has the greatest contribution to residents PCBs daily exposure,which is more than 90%in various regions.The CR and HQ of PCBs in Beijing are?5.04-43.3?×10-9??0.13-1.08?×10-3,both of them are far below the reference value,the carcinogenic risk and non carcinogenic risk of PCBs in the atmosphere of Beijing are at a low level. |
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