Air-water exchange: Toxicities, risks and PAHs compounds in the three gorges reservoir of China

Air-water exchange is inevitably accompanied by the transportation of contaminants between atmosphere and water, which significantly leads to the alterations of toxicity and risks. However, the resulting changes of toxicity and risk in water and air due to the cross-interfacial transport of pollutants are still unclear. In this study, the water and atmospheric samples at the Pengxi River located in the Three Gorges Reservoir (TGR), China, were collected in winter and summer seasons respectively. The contaminated water exhibited higher toxicity effects than air in multiple toxicity endpoint tests. Besides, waters collected during winter exhibited greater toxicity effects than in summer. The concentrations of ΣPAHs were 48.0-445 ng L^-1 in the water and 9.44-82.3 ng/m³ in the air, with ΣPAHs significantly higher in winter than in summer for water samples. Notably, the 2-3 ring PAHs showed a tendency to volatilize from water to air and may increase atmospheric toxicity, whereas the 4-6 ring PAHs tend to be deposited from air to water and may heighten toxicity in the water. Correlation analysis indicated that PAHs were important toxicants in the air, posing higher incremental carcinogenic risk, particularly during winter. Thus, the changes in toxicity and risk caused by the water-air exchange of pollutants cannot be ignored. This research contributes to a deeper understanding of the changes in toxicity effects and health risks caused by the air-water exchange of pollutants. The importance of considering the toxic effects and health concerns of micropollutants in the air as important as in water is emphasized.