Heavy Metal Contamination in Roof-Harvested Rainwater from Different Roofing Materials in Calabar Metropolis, Nigeria

 Rainwater harvesting, heavy metals, roofing materials, cadmium, lead, arsenic, water quality.

*Corresponding Author: emmanuelakwa24@gmail.com
DOI:https://doi.org/10.61594/tnpr.v7i4.2026.181

Page No: 348-354
Volume: 7, Issue 4, 2026
Trends in Natural Products Research
Copy Right: NAPREG

Abstract

The increasing reliance on roof-harvested rainwater as an alternative water source in many developing regions raises concerns regarding its safety, particularly due to contamination from roofing materials and environmental deposition. This study assessed the concentrations of selected heavy metals (cadmium, lead, arsenic, nickel, and copper) in rainwater collected from different roofing materials (Nigerian zinc, Cameroon zinc, long-span aluminium, and corrugated roofing sheets) of varying ages (0–5, 6–10, 11–15, 16 –20, and ≥20 years) within Calabar Metropolis, Nigeria. Rainwater samples were collected during rainfall events and analyzed using standard analytical techniques, including hydride generation spectrophotometry, electrothermal atomic absorption spectrometry, and dithizone extraction methods. Data were statistically analyzed using one-way ANOVA. Results revealed a significant increase in cadmium, lead, arsenic, and copper concentrations with increasing roofing age (P < 0.001) across most roofing types. Cadmium levels in Nigerian zinc roofs increased from 0.10 ± 0.01 mg/L to 1.30 ± 0.61 mg/L, while lead concentrations in corrugated roofs increased from 0.22 ± 0.01 mg/L to 0.60 ± 0.01 mg/L. Arsenic exhibited a marked increase across all roofing types, with Cameroon zinc roofs recording the highest values (up to 22.80 ± 0.01 mg/L). Copper concentrations also increased significantly with roof age, reaching 2.10 ± 0.01 mg/L in Nigerian zinc roofs. Nickel was not detected in any roofing samples, indicating minimal contribution from roofing materials. Control and bottled water samples generally showed negligible or stable metal concentrations. The findings demonstrate that roofing material type and age significantly influence heavy metal contamination in harvested rainwater, with progressive leaching observed in older roofing systems. This poses potential public health risks when such water is consumed without treatment. Regular monitoring of roof-harvested rainwater, replacement of aged roofing materials, and appropriate treatment interventions are therefore recommended to safeguard water quality.