Seasonal dynamics and source apportionment of toxic metals in harvested rainwater: A geochemical and statistical approach

Abstract

This study investigates the seasonal dynamics, source apportionment, and human health risks of toxic metals in harvested rainwater (HRW) using a geochemical and statistical approach. Monthly samples were collected from April to August to capture wet-season variations. Results show significantly elevated metal concentrations at the onset of the rainy season, particularly for Cd (3.30 mg/L), Pb (3.02 mg/L), and As (0.30 mg/L), reflecting the “first-flush” effect. Concentrations declined over time, indicating wash-off of accumulated atmospheric and rooftop contaminants. Geoaccumulation index (Igeo) and enrichment factor (EF) analyses reveal Cd and Se as the most critical pollutants, with Igeo > 3 and EF > 5000, pointing to strong anthropogenic sources. Health risk assessment indicates severe non-carcinogenic risks, especially for children, with hazard quotients (HQ) exceeding safe limits (HQ > 1) for Cd (HQ = 21.83) and Pb (HQ = 32.53). Arsenic and Se also contribute significantly to health risks. Binary elemental ratios (e.g., Ca/Mg, Na/K) support source differentiation between natural and anthropogenic inputs. The findings highlight that HRW, despite its utility, poses serious health risks without treatment. Mitigation strategies such as first-flush diversion, improved roofing materials, and regular maintenance are essential for safe utilization. This work supports SDG 6 by promoting safe water practices in vulnerable communities.