Water quality index assessment of toxicity in direct and roofs runoff rainwater in industrial and remote areas of Eastern Nigeria

Our plain-English summary of Water quality index assessment of toxicity in direct and roofs runoff rainwater in industrial and remote areas of Eastern Nigeria, by E.S. Nicholas, C.C. Okudo, P.O. Ukoha (Scientific Reports, 2025).

The study

• Authors: E.S. Nicholas, C.C. Okudo, P.O. Ukoha
• Journal: Scientific Reports
• Published: 2025;15(1):36068
• Read it: PubMed · Publisher · Free full text

Abstract

Rainwater may be contaminated by leaching from roofing materials and industrial activities, rendering it unsuitable for potable use. In this study, the physico-chemical, microbiological and heavy metals parameters were investigated in harvested rainwater quality from various roof types in the urban and rural areas of Enugu State, Nigeria, between April-July, 2018. Metal compositions of asbestos, corrugated iron, Cameroun zinc, Stone-coated tiles and long span aluminium were also assessed. Thirty-six (36) harvested rainwater samples were forwarded to the laboratory after determination of pH, temperature, TDS and electrical conductivity at the point of collection. Titration, Electrometric and spectrophotometric methods of analysis were used. Results were compared with the WHO, USEPA and NSDWQ water quality standards. The weighted arithmetic method was obtained for the assessment of the water quality index. Results for heavy metals (mg/L) gave values which ranged from 0.00 to 0.20, metal concentrations (mg/kg) of digested roofs gave 0.00-63.78, and other parameters gave 6.50-7.60 for pH and Escherichia coli (no detection). The obtained results met the national and global standards except for a few samples. The WQI gave values which ranged from 3.00 to 78.46 and were rated excellent to very poor water quality. It was concluded that harvested rainwater should be treated before drinking.

© 2025. The Author(s).

In plain English

This study tested rainwater collected in Enugu State, Nigeria, between April and July 2018, in an urban area (Okpara Avenue, Enugu North) and a rural area (Olido village, Enugu-Ezike). Thirty-six samples were taken from the runoff of five roof types, including asbestos roofs, and directly from the sky as a control. The authors measured acidity, dissolved solids, nitrate, alkalinity, E. coli bacteria and metals including lead, chromium and iron. They also dissolved pieces of each roof to measure its metal content. The article does not report any measurement of asbestos fibers. No E. coli was found. For metals, rainwater from asbestos roofs showed no statistically significant difference from the control. Urban asbestos-roof runoff did differ significantly from the control in alkalinity. On a water quality index, asbestos-roof rainwater scored 3.00 (excellent) in the urban area and 78.44 (very poor) in the rural area. The authors concluded that roof materials do not readily leach into rainwater except on extended contact with acid rain. They also concluded that harvested rainwater must be treated before drinking.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Environmental field sampling and laboratory analysis of harvested rainwater, with roof runoff compared against rain collected directly from the sky (control)
• Who was studied: 36 harvested rainwater samples from an urban area (Okpara Avenue, Enugu North local government area) and a rural area (Olido village, Enugu-Ezike, Igbo-Eze local government area), Enugu State, Nigeria, collected during the rainy season, April to July 2018
• Exposure: Rainwater running off five roof types (long span aluminium, asbestos, corrugated iron, stone-coated tiles and Cameroun zinc), compared with rain collected directly. The measurements were physico-chemical, metal and bacterial. The article does not report measuring asbestos fibers or naming an asbestos fiber type.
• Main results:
  • For heavy metals, rainwater from asbestos roofs showed no statistically significant difference (p greater than 0.05) from the direct-rain control samples.
  • Alkalinity of runoff from asbestos roofs in the urban area differed significantly (p less than 0.05) from the control samples. Table 4 lists the urban asbestos-roof alkalinity as 48.67 ± 3.06 mg/L.
  • Water quality index for asbestos-roof rainwater: 3.00, rated excellent, in the urban area (RWEDU) and 78.44, rated very poor, in the rural area (RWEDR).
  • Rainwater from long-span aluminium and corrugated iron roofs in both areas, and from asbestos roofs in the rural area, was rated very poor. All other samples were rated excellent.
  • Digested asbestos roof material contained (mg/kg): lead not detected, aluminium 2.90, iron 51.64, zinc 0.78 and chromium 1.87.
  • Asbestos-roof runoff was slightly alkaline, as were the control samples, while runoff from the other roof types was slightly acidic.
  • E. coli was not found in any sample.
  • Heavy metal values met the NSDWQ, WHO and USEPA drinking water limits, except for a few samples.
  • The authors interpreted their results to mean that roof components do not readily leach into rainwater except on extended contact in the presence of acid rain.
• The authors' conclusion: The authors concluded that harvested rainwater can be suitable for other domestic purposes but must be treated before drinking.

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