Human exposure to size-segregated particulate polycyclic aromatic hydrocarbons during residential cooking in northeastern India

More than 50% of the population in the Indian subcontinent still depends on solid fuel for cooking purposes, and around 0.5 million yearly deaths are attributed to household air pollution. Despite the poor indoor air quality, especially in the rural spheres of the country, there is a lack of comprehensive field-based understanding of exposure to toxic chemical components such as polycyclic aromatic hydrocarbons (PAHs) associated with particulate matter (PM). This study attempts to quantify and assess the exposure to and inhalation health risk from 16 US EPA priority PAHs in size-segregated PM collected from relatively unexplored rural kitchens of northeastern India. A total of 44 sets of samples (5 from kitchens using liquefied petroleum gas (LPG), 18 using firewood (FW), 18 using a mixture of biomass (MB), and 3 non-cooking blanks) were collected and characterized from 6 locations. The sum of PM₁₀-associated 16 priority PAHs (∑₁₆ PAHs) was observed to be 258, 745, and 2554 ng m^-3 for LPG, MB, and FW using kitchens, respectively. Size fraction-wise, the highest concentration of ∑₁₆ PAHs was observed in PM_0.25 and the least in PM_1-10 across kitchen categories, with PM₁ associated ∑₁₆ PAHs comprising 80-92% of the total. ∑₁₆ PAHs in kitchen settings were enriched by factors of 1.7-16.5 in comparison to the non-cooking background. Fuel-wise, stark differences were observed between kitchen categories. Within biomass using kitchens, the type of biomass and combustion (flaming vs smoldering) influenced the PAHs concentration and composition, e.g., ∑₁₆ PAHs were enriched by factors of 3.4 for smoldering combustion of FW compared to flaming combustion of MB. Composition-wise, 2-3 ring PAHs dominated the total PAHs concentration in LPG kitchens (82%), while it constituted 43 and 25% in MB and FW using kitchens, respectively. In contrast, 5-6 ring PAHs showed dominance in FW using kitchens (52%), followed by MB (40%). This suggested a greater release of high molecular weight PAHs during biomass combustion with an increased contribution during the smoldering phase. Estimation of the total BaP equivalent concentration (BaP_eq) revealed a similar profile as ∑₁₆ PAHs with the lowest values in LPG using kitchens (29 ng m^-3) followed by MB (235 ng m^-3), and the highest in FW (856 ng m^-3). Incremental lifetime cancer risk (ILCR) estimation via the inhalation pathway showed values above the acceptable risk for LPG (3.2×10^-5), and much above tolerance levels for biomass using kitchens (MB: 2.6×10^-4; FW: 9.4×10^-4). Overall, these findings warrant immediate intervention into the cooking practices prevalent in northeastern India, with an emphasis on biomass-dependent households, in order to alleviate health risks.