Source patterns, storage-associated changes, and public health implications of metals in harvested rainwater from an oil-impacted environment, Niger Delta

Rainwater harvesting is widely practiced in sub-Saharan African communities as an alternative water supply; however, atmospheric deposition, roofing materials, and storage conditions may influence its chemical quality and potential health implications. This study investigated seasonal variation, storage effects, and health risks of metals in rooftop-harvested rainwater from Chokocho and Diobu, Rivers State, Nigeria. Rainwater was collected from five catchment surfaces (asbestos sheet roof, aluminium roof, zinc roof, stone-coated roof, and ambient collection), during early, mid, and late rainfall periods. Fresh samples were analyzed after collection, while a second portion was stored under mesophilic conditions for six months prior to re-analysis to depict the condition of usage by the locals. Metal concentrations were determined and chemometric techniques were applied for source identification. Non-carcinogenic risks via ingestion and dermal exposure were assessed. Results revealed strong first-flush effects in Chokocho with early rain samples showing elevated Na (5.64 mg L⁻¹) and Zn (1.10 mg L⁻¹), but declined to < 0.2 mg L⁻¹ during mid- and late-rain periods. Stored samples of Chokocho showed lower concentrations of Fe, K, Na, Zn, and Cu, than their corresponding fresh samples, especially during early and mid-rain periods. Fresh and stored pH ranged from 5.1 to 7.9 (Chokocho) and 6.0 -7.8 (Diobu). PCA explained 86.1% of the variance, while PMF identified three sources: atmospheric deposition/first-flush wash-off, crustal dust, and roofing material weathering. Hazard index values for ingestion and dermal exposure were all < 1. Overall, harvested rainwater posed low non-carcinogenic risk, though first-flush diversion and proper storage are recommended to improve water quality.