Concentrations, sources and health risk of nitrated- and oxygenated-polycyclic aromatic hydrocarbon in urban indoor air and dust from four cities of Nepal

Although the fate and behavior of parent polycyclic aromatic hydrocarbon (PAHs) have been documented worldwide, the information about PAH-derivatives (NPAHs and OPAHs) is limited, especially in developing countries, including Nepal. Moreover, the greater parts of the investigations concentrating on NPAHs/OPAHs are on the air (borne) particulate phase only; and are primarily based on a limited number of compounds analyzed. Little is known about the environmental concentration, fate, and behavior of NPAHs and OPAHs in air gas phase and dust. In this study, the concentration, fate, spatial distributions of 26 NPAHs and 3 OPAHs in the air ( n  = 34) and dust ( n  = 24) were investigated in suspected source area/more densely populated areas of Nepal. Four critical source areas in Nepal were considered as it was conjectured that the urban areas are more prone to NPAH/OPAH contamination due to the high density of automobiles and industrial activities. Overall, the measured ∑ 19 NPAHs in air and dust were 5 and 2 times lower than their parent-PAHs, respectively. Highest levels of NPAHs/OPAHs were measured in Birgunj, followed by Kathmandu, Biratnagar, and Pokhara, respectively, while Biratnagar showed the highest level of ∑OPAHs. 3-Nitrodibenzofuran (3-NDBF) was the most abundant NPAHs measured both in air and dust, whereas 9-Fluorenone (9-FLUONE) prevailing OPAHs. The molecular diagnostic ratio (MDR) of 2-Nitrofluoranthene/1-Nitropyrene indicated the contribution from secondary emission via photochemical reaction as the primary source of NPAHs, while solid fuel combustion and crop residue burning were identified as the essential sources of OPAHs. The human exposure to NPAH/OPAH through the different route of intake suggested dermal contact via dust as the primary pathway of NPAH/OPAH exposure for both adult and children. However, other routes of exposure, for instance, dietary intake or dermal absorption via soil may still be prominent in case of Nepal.