Rainwater harvesting in a Polish industrial park: Toxicity, treatment, and use

Rainwater quality is strongly influenced by industrial activity. Simultaneously, amid increasing water scarcity, it states a potential supplementary water resource. Therefore, monitoring its quality is essential. This is one of the first studies aiming to assess the quality of rainwater collected in an industrial area (in Lower Silesia, Poland), combined with an assessment of heavy metals (HMs) toxicity to evaluate its ecological risk. Rainwater samples were collected from five locations (drainage ditches and retention tanks). Selected physicochemical parameters (pH, electric conductivity, total suspended and dissolved solids, total phosphorus, BOD₅, and COD), ions (Ca, Cl⁻, SO₄²⁻, F⁻, Al, nitrogen compounds), and selected HMs (Cu, Ni, Cr, Cd) were analyzed in a certified laboratory. Ecological risk was assessed using the risk quotient (RQ) method by comparing maximum observed concentrations with literature-derived predicted no-effect concentrations (PNEC). Most parameters met World Health Organization guidelines, except for Ni (up to 0.098 mg/L), and Cl- (up to 302 mg/L), suggesting possible contamination from industrial emissions. Ca was the most abundant cation (108 mg/L). Rainwater pH was rather neutral. Cu was the most prevalent heavy metal (concentrations up to 0.1 mg/L), and RQ values up to 2000, indicating high ecological risk. Cr posed the lowest ecological risk. The elevated Ni, and Cl⁻ concentrations suggest that untreated rainwater is unsuitable for direct reuse. To mitigate risks, appropriate treatment, e.g., filtration, membrane processes, or disinfection (depending on the expected outcomes), is recommended. The findings highlight the need for effective rainwater management and the environmental impact of industrial activities.