Highly Volatile POPs in Urban Air across Asia and Africa: Dominance of Volatile Methylsiloxanes

Highly volatile persistent organic pollutants (HV-POPs) are characterized by high volatility, environmental persistence, bioaccumulative potential, toxicity, and ability for long-range transport, posing environmental and health concerns. However, research on HV-POPs remains limited, particularly in rapidly urbanizing regions, constraining understanding of their sources, environmental fate, and risks. This study investigated 52 HV-POPs, including Stockholm Convention-listed POPs like hexachlorobutadiene (HCBD) and hexa-/pentachlorobenzene (HCB/PeCB), and nonlisted HV-POPs such as volatile methylsiloxanes (VMS) and chlorinated nitrobenzenes (CNBs), using active air samplers in six major cities across Asia and Africa. The median total concentrations of HV-POPs were highest in Guangzhou (351 ng/m³), followed by Kuala Lumpur (167 ng/m³), Accra (82.4 ng/m³), Dhaka (73.3 ng/m³), Nairobi (44.9 ng/m³), and Islamabad (33.5 ng/m³). VMS dominated at all sites, accounting for 84 ± 18% of total HV-POPs, up to 2-5 orders of magnitude higher than other compounds. Source analysis showed VMS emissions in Guangzhou were mainly from industrial activities, while in the other cities, they were from usage of personal care products. Inhalation risk assessments indicated negligible noncarcinogenic and carcinogenic risks at all sites. This study provides the first multiregional HV-POPs data set in urban air, supporting chemical risk assessment efforts and broader international regulatory initiatives.