Trends and patterns of polycyclic aromatic hydrocarbons (PAHs) in forest fire-affected soils and water mediums with implications on human health risk assessment

Abstract

Forest fires are extreme natural/artificial events releasing polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic. Most of the released PAHs are trapped in burnt ash, a part of which is transported and settle on different mediums like soil and water. After strong rainfall events, PAHs enter into surface water bodies through surface runoff, thereby deteriorating water quality. Changes in PAHs levels during the post-fire duration and human health risks due to PAHs released from forest fires need attention. This study aim to explain the trends and patterns of PAHs and health risks due to exposure to soil and water contaminated with PAHs. Forest fires release a higher percentage of low molecular weight PAHs (LMW PAHs) than high molecular weight PAHs (HMW PAHs). Ash and burnt soils contain a higher percentage of LMW PAHs since biomass burning releases huge amounts of LMW PAHs. Whereas, sediments contain a higher percentage of HMW PAHs since most of the LMW PAHs are already degraded. HMW PAHs were causing higher risk to humans (both cancer and non-cancer) due to their higher oxidation potential. Exposure to water contaminated by PAHs resulted in higher health risks for both BaP equivalent and a mixture of PAHs. Exposure to sediment produced the highest health risk due to a higher percentage of HMW PAHs, followed by surface water, burnt soil, ash, and unburnt soil. Cancer and non-cancer risk due to dermal exposure was more elevated than oral exposure. The mixture of PAHs in sediment produced a higher average dermal risk for children (2.21E+00 for cancer and 7.69E+03 for non-cancer risk) and oral cancer risk for adults (7.11E-03). However, exposure to BaP equivalent in sediment produced higher oral non-cancer risk (7.01E+02) for children. Thus, effective PAHs monitoring is required in both soil and surface water mediums for ensuring proper treatment in water supply systems.