Polychlorinated naphthalenes (PCNs) in surface soils, indoor and outdoor dusts in Lahore, Pakistan

Polychlorinated naphthalenes (PCNs) are thermally stable and inert chemicals that have been widely used as Halowax mixtures and are also unintentionally produced during combustion processes. Lahore, Pakistan, was recently ranked by the World Health Organization as one of the cities with the worst air quality in the world, highlighting the importance of investigating combustion-related pollutants such as PCNs for effective air quality management and improvement. This study investigated the levels, composition, sources and health risks of PCNs in soil and dust in Lahore, Pakistan. Soil, indoor and outdoor dust samples were collected from residential, commercial, industrial areas, and vehicle cabins, and analyzed for 32 congeners using triple quadrupole gas chromatography/mass spectrometry. The median concentrations of Ʃ₃₂PCNs in indoor dust, outdoor dust and soil were 7.9, 7.1 and 0.30 ng/g, respectively, and higher levels (12 ng/g) were found in house and industrial dusts. Mono- to tetra-CNs dominated all sample types. Compositional similarity to Halowax mixtures, combustion indicators, and spatial patterns suggest legacy sources of PCNs, while their ongoing and widespread presence likely results from continuous emissions related to combustion processes. Health risk assessment indicated that PCN exposure posed negligible cancer and non-cancer risks in most areas except for few sites reflecting high cancer risks for toddlers. Nevertheless, considering the short half-lives and international production regulations of PCNs, the present findings suggest ongoing emissions and potential human exposure. To our knowledge, this is the first study to examine PCNs in vehicle cabin dust, providing a solid reference for future studies and national management policies for PCNs.