Spatiotemporal Variation and Health Risk Assessment of Selected Polycyclic Aromatic Hydrocarbons and Pesticides in Ogun River, Lagos, Nigeria

Abstract

Studying the spatiotemporal distribution and health risks associated with polycyclic aromatic hydrocarbons and pesticides in a river is crucial for understanding the impacts of these contaminants on human health. Hence, the objective of this paper was to investigate the spatiotemporal variation and health risk assessment of selected polycyclic aromatic hydrocarbons and pesticides in Ogun River, Lagos, Nigeria. The water samples were analyzed using gas chromatography coupled with MSD model 5977A. The results show a diverse distribution of PAHs across the sites, with Naphthalene and Acenaphthylene being the most frequently detected, having significantly higher concentrations in the dry season than in the rainy season. There was a significant difference in the mean amounts of pesticides at site 1 compared to other sites.  While some pesticides recorded higher mean values in the rainy season, others had higher mean values in the dry season. Similar to PAHs, most pesticides had higher mean values in year 1 than in year 2. Most of the pesticides and PAHs posed significant non-cancer risks (HQ > 1) through oral exposure, except Glyphosate and Imidacloprid at all the sites; and Acenaphthene and Anthracene at site 4. There was also a significant health risk through dermal exposure to Heptachlor and Dichlorvos at S4 and Aldrin at S1. The cancer risk through oral exposure to all the detected carcinogenic pollutants is significant (CR >1×10^-4), except Lindane at S4, which was within the acceptable range. Benzo[a]anthracene and Benzo[a]pyrene posed significant cancer risk through dermal exposure at S3 and heptachlor at S1. The study indicated that the observed spatial and temporal variations are different for specific pollutants. There is a high probability of adverse carcinogenic and non-carcinogenic risks for people who rely on the river for various purposes.