Environmental Behavior Of Polychlorinated Biphenyls And Polybrominated Biphenyls In The Southeast Tibetan Plateau

Polychlorinated biphenyls（PCBs）and polybrominated biphenyls（PBBs）are two typical persistent organic pollutants（POPs）,which have characteristics such as persistence,high toxicity,bioaccumulation and long-range atmospheric transport.Although the production and use of these substances have been banned in most countries,PCBs and PBBs are still widely detected in the environment.The study of their occurrence and environmental behavior is of great significance for understanding the environmental fate of POPs.The Tibetan Plateau,known as the"third pole"of the Earth,has a unique geographical location and climate,which provides an ideal site for environmental behavior studies of POPs.Extensive researches on the environmental behavior of POPs in the Tibetan Plateau were conducted in the past,such as pollutant concentration,composition variation,distribution characteristics,interface exchange flux,and environmental model evaluation,which provided an important foundation for understanding the sources and fate of POPs in high mountain environments.In recent years,compound-specific isotope analysis（CSIA）has shown promising application prospects in tracing organic pollutant.In this study,we conducted a comparative study of PCBs and PBBs in the atmosphere and soil of the Shergyla Mountain in the southeastern Tibetan Plateau based on high-resolution gas chromatography/high-resolution magnetic mass spectrometry（HRGC/HRMS）,which clarified their distribution characteristics and typical environmental behaviors,and meanwhile revealed the soil-air exchange pattern and altitude-dependence.In addition,we revealed the potential sources of POPs by the compound-specific isotope analysis of chlorine（CSIA-Cl）.This paper mainly includes the following contents:（1）The distribution characteristics of PCBs and PBBs in atmospheric samples（including active and passive atmospheric samples）were studied from the Shergyla Mountain in the southeastern Tibetan Plateau.The results showed that the concentration ranges ofΣ₁₈PCBs andΣ₁₈PBBs in passive air samples were 0.26～1.05 pg/m³ and n.d.～0.15 pg/m³,respectively,while the concentration ranges ofΣ₁₈PCBs andΣ₁₈PBBs in active air samples were 1.41～5.82pg/m³ and 0.04～2.70 pg/m³,respectively.Whether in passive or active atmospheric samples,the concentration levels of PBBs were relatively lower overall than PCBs.Moreover,we found the PCBs concentration in active atmospheric samples were relevant to the altitude,and the PCBs concentrations were significantly higher at the low-altitude sampling sites than that at the high-altitude sampling sites.We further studied the gas-particle partitioning,which showed that the gas-particle distribution of PCBs in the Shergyla atmosphere had not reached equilibrium,and it was dominated by absorption mechanism.J-P adsorption model,H-B absorption model,D-E model and steady state model（L-M-Y model）were used to predict gas-particle distribution in the atmosphere.The predicted the particulate phase fractionφand gas-particle distribution coefficient K_P by the four models were mostly lower than the measured values.In this study,the root mean square error（RMSE）was used for evaluation predictive accuracy of different models at different altitude sampling points.The results showed that the steady-state L-M-Y model had a better predictive accuracy at low-altitude sites,while the D-E model at high-altitude sites.（2）The distribution characteristics of PCBs and PBBs in soil samples were studied from the Shergyla Mountain in the southeastern Tibetan Plateau.The results showed that the total concentration range ofΣ₁₈PCBs in soil samples was 12.9～106.3 pg/g dw,and the concentration range ofΣ₁₈PBBs was n.d.～2.92 pg/g dw.Indicator PCBs were the dominant type of PCBs,while the monomer distribution of PBBs in soil was mainly dominated by low-brominated monomers.On the eastern slope of the Shergyla Mountain,the concentration of several PCBs corrected for total organic carbon（TOC）showed a significant positive correlation with the altitude,indicating an alpine cold condensation effect of POPs.Furthermore,the soil-air exchange of PCBs in the Shergyla Mountain were studied,which showed that equilibrium between air and soil has not been reached and it is mainly dominated by atmospheric deposition.（3）CSIA-Cl analysis was performed on the indicator PCBs in active atmospheric samples from the Shergyla Mountain in the southeastern Tibetan Plateau.The calculated results showed that the average value ofδ³⁷Cl in atmospheric samples ranged from-33.93‰to 8.91‰,which did not show a significant decreasing trend with the increasing level of the chlorine substitution.This result was obviously different from the previous analysis results of the group about the Antarctic samples,indicating that the atmospheric PCBs in the Southeast Tibetan region were influenced by the emission from the surrounding sources.Related studies still need to be further developed.