Ecotoxicological Health Risk Analysis of Toxic Heavy Metals Accumulation in Surface Water of the Upper Genale Dawa River Basin, Ethiopia

Abstract

Due to their toxicity, non-biodegradability, bioaccumulation, environmental stability, and persistence in nature, heavy metals (HMs) currently become pollutants of global concern. Either acutely or chronically exposed marine lives and human beings can result in severe damage to the structure and function of vital organs such as kidney, liver, and brain. Water quality is negatively affected by HMs released into the river ecosystem. This study, therefore, investigates the levels of HMs in surface water of the Upper Genale Dawa River Basin to assess water quality and associated ecotoxicological health risks at the study site. The mean levels of HMs (mg/L) in surface water followed the pattern: Hg (0.029) > Mn (0.028) > Cu (0.022) > Pb (0.022) > Ni (0.021) > As (0.021) > Co (0.019) > Cd (0.017) > Fe (0.017) > Zn (0.016) > Cr (0.016) > Se (0.014). Primarily, areas close to significant pollution sources exhibited higher concentrations of HMs. Water quality index (WQI) values for drinking water [(Heavy Metal Pollution Index, HPI =1958.40) and (Heavy Metal Evaluation Index, HEI = 35.10) indicated the quality of water was compromised. The HI values of the HMs for both children and adults via ingestion of drinking water were 7.83 and 5.76, respectively; and its values via dermal exposure in both children and adults were found to be 1.91 and 1.01, indicating intolerable noncarcinogenic health risks to the community as HI > 1 poses non-carcinogenic risks to the exposed populations. The ecotoxicological risk indices that account the synergetic impacts of multiple-metals [Ecological Risk Index, ERI = 492.59; Degree of Contamination, CD = 34.85; modified Degree of Contamination, mCD = 2.90; and Pollution Load Index, PLI = 0.34)] indicated the overall contamination of the river water by HMs considered in this study.  The CR values of the HMs for both children and adults via ingestion of drinking water were 6.44*10^-2 and 4.74*10^-2, respectively; and its values via dermal exposure in both children and adults were found to be 5.01*10^-4 and 2.65*10^-4, implying the potential carcinogenic health risks to the community as CR > 1*10^-4 poses carcinogenic risks to HM exposed groups. This research highlights the urgent need for monitoring and intervention strategies to mitigate HM pollution at Genale Dawa River Basin to prevent community health and the safety of the riverine ecosystem.