Temporal and spatial variations in airborne PCDD/F and dl-PCB concentrations in Hanoi, Vietnam, during and after the COVID-19 pandemic.

The airborne polychlorodibenzo-p-dioxins and polychlorodibenzofurans (PCDD/Fs), and dioxin-like polychlorobiphenyls (dl-PCBs) were monitored by using passive air samplers during and after the COVID-19 pandemic (2021-2024) in Hanoi, Vietnam. The acceleration of production activities in Quang Minh Industrial (QMI) area increased PCDD/Fs and dl-PCBs in ambient air. The total toxic equivalents (∑TEQs) of PCDD/Fs and dl-PCBs in QMI area were highest (445-11328 fg TEQ/PUF day, average: 2486 fg TEQ/PUF day). The temporal, seasonal, and spatial variations in their concentrations depended on distance from the QMI area and wind direction. ∑TEQs in the Nghia Do urban area (289-615 fg TEQ/PUF day, average: 438 fg TEQ/PUF day) and the Dong Da urban core area (282-572 fg TEQ/PUF day, average: 412 fg TEQ/PUF day) were 6 times lower than those in the QMI area, while ∑TEQs in the Ba Vi rural area (71-332 fg TEQ/PUF day, average: 193 fg TEQ/PUF day) were 13 times lower. The annual average ∑TEQs varied widely at the QMI area (555-5941 fg TEQ/PUF day); in contrast, in the Nghia Do urban area (393-465 fg TEQ/PUF day), the Dong Da urban core area (354-495 fg TEQ/PUF day), and the Ba Vi rural area (150-226 fg TEQ/PUF day) showed no significant differences. Average daily doses through inhalation in the QMI area (36.3-3666 fg TEQ/kg BW/day) exceeded 10% of the WHO-estimated tolerable daily intake and were greater than in the former hotspot in Da Nang airport.