Temporal dynamics and seasonal variation of organochlorine pesticides in harvested rainwater: Implications for urban water quality management in Lagos, Nigeria

This study investigates the temporal dynamics and seasonal variation of 18 organochlorine pesticides (OCPs) in harvested rainwater across Lagos, Nigeria, from April to August 2024, to assess their sources, environmental drivers and associated human health risks. Monthly samples were collected from five representative rooftop catchments during the peak rainy season, and OCPs were extracted through liquid-liquid extraction and quantified using gas chromatography with electron capture detection. Statistical techniques including ANOVA, correlation analysis, diagnostic ratio evaluation and human health risk assessment were applied. Significant temporal fluctuations were observed, with peak concentrations for several OCPs including endosulfan I, dieldrin, heptachlor epoxide and BHC isomers occurring in April and May. Strong correlations between α-BHC, β-BHC, heptachlor and electrical conductivity indicated notable anthropogenic inputs. Human health risk assessment revealed hazard quotient values above 1 for dieldrin and heptachlor epoxide, signalling potential non-cancer risks, while cancer risk values for these compounds fell within ranges of concern. These findings underscore the influence of seasonal rainfall patterns and urbanization on OCP mobilization and highlight serious public health implications for populations reliant on untreated harvested rainwater, emphasizing the urgent need for regulatory enforcement, public awareness and improved water treatment strategies in Lagos and similar megacities.