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The sedimentary core in remote alpine lakes has been recognized as an ideal proxy to reconstruct the emission and air deposition histories of persistent organic pollutants (POPs). Nevertheless, POPs formerly stored in a catchment might also contribute to the variation in the lake sediment by lateral remobilization. In this study, to reveal the relative importance of lateral remobilization, we measured the vertical profiles and isomeric ratios of dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs) and endosulfan in a dated sedimentary core collected from Lake Yamzho Yumco in the southern Tibetan Plateau. In addition to the flux peaks in the 1970s corresponding to the heavy atmospheric deposition of DDTs and HCHs, these pollutants' fluxes displayed rebounds in the flood periods, with characteristic low ratios of DDT/DDE (α-/β-HCH). This might indicate a massive remobilization of "weathered" pesticides from catchment soil to the lake because of strong hydro-dynamics. Moreover, the relative contribution of lateral remobilization to the lake sediment in the past decades was recognized through the correlation between DDT/DDE (α-/β-HCH) ratios and ∑DDT (∑HCH) fluxes. The results showed that the lateral remobilization contributed to 20-42% of the total fluxes. This study discriminated the air deposition from the contribution of lateral remobilization, which improves current understanding of the vertical POPs profiles in the sedimentary core., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Glacier alluvial deposits record persistent organic pollutants (POPs) not only derived from the atmospheric deposition but also from the release of glacial melting. The evidence for melting glacier in the Tibetan Plateau (TP) as a secondary source of pollutants is introduced through investigating the concentration of organochlorine pesticides (OCPs) in four deposited profiles collected at the edge of the Changwengluozha glacier. Two concentration peaks were observed for dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) in the past century. The first peak was observed in the 1970s, corresponding with the heavy usage of HCHs and DDTs in the surrounding countries and regions. The second one was in 2000 when the production and usage of DDTs and HCHs were strictly limited, which possibly indicated a significant release from melting glacier. This result was further supported by the enantiomeric fraction values for α-HCH and o,p'-DDT. On the other hand, the dramatic increase of polycyclic aromatic hydrocarbons (PAHs) from atmospheric deposition, which was associated with the socioeconomic development in Tibet, shaded the release of PAHs from melting glacier. This study reveals not only the air deposition history of legacy POPs but also a substantial release of OCPs from glacier to the adjacent environment. Our research supports the hypothesis that the melting glacier in the TP represents a secondary source of OCPs, which is consistent with the findings in the Alps glaciers., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Enantiomeric fraction (EF) of organochlorine pesticides (OCPs) has been used as a signature for tracing the source and following pathways. The chiral analysis was performed for α-HCH and o,p'-DDT in paired soil and grass samples from the Central Tibetan Plateau (CTP), a unique background region. In the case of α-HCH, excess of (-) α-HCH was predominant in 83.3% of soil samples, and 80% of grass samples showed excess of (+) enantiomer. For o,p'-DDT, 90.9% of grass samples showed excess of (-) o,p'-DDT while 50% of soil samples showed excess of the (-) enantiomer. A correlation between EFs of soil and grass was not observed for either compound. The EFs of both compounds were correlated with soil concentration and with change of sampling altitude, within EFs being lower than racemic. However, these trends were not found in grass. Our study provides a database of EFs and signatures for OCPs in the CTP, one background region of the world., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Forty-four soil samples were collected across the Central Tibetan Plateau (CTP) at elevations of between 3711 and 5352 m. The scatter diagram shows that the soil concentrations of organochlorine pesticides (OCPs) were associated with the altitude of sampling site, soil clay minerals, soil organic carbon (SOC) and the fine particle fractions of soil. Pearson correction analysis and principle component analysis were used to deduce the relationship between the OCP concentrations and these factors logically. It was determined that the altitude and clays functioned as the primary factors influencing OCP accumulation, and SOC was weakly related to OCPs. The fitting equation closely matches the observations in the field while only taking the altitude and clay minerals into account. Our study found that clay minerals dominated the sorption of OCPs in soil, whereas the altitude contributed to temperature-driven condensation for the accumulation of OCPs at high altitudinal CTP.