Environmental and health risk assessment of heavy metal contamination from healthcare wastewater in the Akaki river catchment, Ethiopia

Abstract

Wastewater from municipality contains toxic heavy metals that are discharged into nearby rivers. This study evaluated heavy metals concentrations in vegetables and forages grown on wastewater-irrigated soils in the Akaki River Catchment (ARC), Addis Ababa, Ethiopia. Healthcare wastewater (HCWW), soils, vegetables, and forage samples were collected from three sites (Site 1, Site 2, and Site 3), representing healthcare waste outlets, animal grazing lands, and vegetable farms irrigated with wastewater. Among the vegetables tested, cabbage accumulated heavy metals at significantly higher levels compared to tomatoes, lettuce, beetroots, and carrots. Wastewater sample consistently exhibited the highest heavy metal pollution index (HMPI) values, with mean concentrations increasing progressively from Site 1 to Site 3. A significant variation difference in heavy metal levels concentration among sites (F = 77.033, P < 0.001), showed that identified wastewater as a primary reservoir and the principal driver of environmental contamination. All wastewater HMPI values far exceeded the safe threshold of 100, indicating severe serious health risks for humans and animals exposed to contaminated vegetables and forages. Grass samples presented the highest target hazard quotient (THQ) values, followed by soils and vegetables, with the order Site 1 < Site 2 < Site 3. Furthermore, total cancer risk (TCR) assessments demonstrated that lead (Pb), cadmium (Cd), and chromium (Cr) concentrations in vegetables and forages surpassed acceptable limits, posing substantial carcinogenic hazards. Overall, HCWW is among heavy metal pollution source in the catchment, particularly for Cd and Pb, resulting in severe bio-accumulation and posing an urgent public health concern.