Transport of phthalates from Nepal to the southern Himalayas: Distribution, source analysis and environmental risk

The Tibetan Plateau (TP) represents an important region for studying long-range atmospheric transport behavior of pollutants, owing to its roles in high-altitude condensation and global distillation. Situated downwind in South Asia and connected to the TP through Gyirong and Zhangmu valleys, Nepal constitutes a vital area for monitoring such transport. Focusing on this specialized geo-atmospheric corridor along the southern Himalayan slope, this study investigates the dominant sources and transport mechanisms of phthalates (PAEs). A total of 57 surface soil samples were collected and analyzed to characterize distribution and transport behaviors of PAEs. PAE concentrations ranged from 37.7 to 1337 ng/g dw, dominated by bis(2-ethylhexyl) phthalate (DEHP). Mean levels were highest in agricultural soils (375 ng/g dry weight), followed by forest (292 ng/g dry weight) and meadow soils (262 ng/g dry weight), a pattern mainly linked to the use of plastic mulch films, fertilizers, and irrigation. PAE concentrations decline at higher altitudes. While low-K_OA congeners are prone to deposition, high-K_OA congeners show enhanced long-range transport potential to the TP. Spatial analysis points to Kathmandu as a significant PAE source in Nepal, with PAEs displaying a distinct regional dispersion pattern. Ongoing plastic product usage poses potential ecological risks from PAEs and other plasticizers to the TP. This study provides the first comprehensive evidence of PAE contamination in Nepal and underscores the combined influence of localized anthropogenic activities and regional atmospheric processes on pollution patterns.