Polychlorinated biphenyls and polybrominated diphenyl ethers in a forest-grassland ecotone of Inner Mongolia, China: Distribution, sources and health risks

The forest–grassland ecotone (FGE) in northern China is likely to become a significant sink of persistent organic pollutants (POPs) because of its high altitude, dense vegetation, and low temperatures. However, data on POPs contamination and risks in this region are limited. In this study, soil, air, and birch leaf from an FGE in Inner Mongolia, China, were collected and analyzed to investigate the distribution, possible sources, soil air exchange and health risks of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). The results revealed that the PCB concentrations in the soil, air and birch leaf samples ranged from 12.4 to 30.4 ng g −1 dry weight (dw), 1.8–5.5 pg m −3 , and 10–19 ng g −1 dw, respectively, whereas the PBDE concentrations ranged from 44.2 to 154.9 pg g −1 dw, 5.4–16.8 pg m −3 , and 26.3–116.3 pg g −1 dw, respectively. Notably, pollutants distribution varied across land-use types and were dominated by low-halogen congeners. Backward trajectory air mass analysis revealed two main presumed pollution pathways: cross-border long-range atmospheric transport of pollutants from northern Eurasia and contributions from surrounding industrial areas. PCBs mainly stemmed from transformer oil leaks, capacitors, and vehicle exhaust, while PBDEs were linked to building materials and textile flame retardants. Fugacity modeling revealed net soil-to-air volatilization, identifying soils as a secondary emission source. Although overall health risks of the two pollutants were low, adults faced a higher potential carcinogenic risk than children. These findings offer valuable insight into POP dynamics and risks in rural ecotones. • PCBs and PBDEs were detected and dominated by lower-halogenated congeners in the FGE. • Pollutants in the FGE were mainly from neighboring countries or regions through LRAT. • Net volatilization of pollutants from soil to air was identified in the FGE. • PCBs and PBDEs had higher carcinogenic risk to adults than children in the FGE.