Beyond atmospheric deposition: tracing lateral remobilization's influence on the sediment record of PCBs in the Xizang Plateau

Lake sediment cores from remote alpine regions are crucial for investigating historical emissions of persistent organic pollutants (POPs), predominantly transported via long-range atmospheric transport (LRAT), with negligible local contributions. This study emphasized the overlooked aspect of lateral remobilization's impact on POPs deposition history on the Xizang Plateau, distinguishing it from direct atmospheric deposition. Through analyzing vertical profiles and compositional variations of polychlorinated biphenyls (PCBs) in a dated sediment core from the Tibetan lake of Yamzho Yumco, the emission history of PCBs in Asia could be reconstructed, with notably emission peaks in the 1970 s. Importantly, fluctuations in total PCB fluxes during flood events indicated significant lateral remobilization of older PCBs from surrounding soils into the lake, marked by an increased presence of hexa- and hepta-CBs relative to atmospheric deposits. A strong correlation between the ratio of (tri- + tetra- + penta-CBs) to (hexa- + hepta-CBs) and total PCB flux highlighted the critical influence of remobilization on the sediment's PCB profile. Our findings reveal that temporal and compositional PCB variations would align with the both direct contribution of atmospheric deposition and secondary source of lateral remobilization, enhancing the understanding of POPs dynamics in sediment cores.