Heavy Metals in Fish Muscle from an Ethiopian Rift-Valley Lake (Hawassa) and a Neighboring Stream (Boicha): Assessment of Human Health Risks

Concentrations of heavy metals (Cr, Co, Fe, Ni, Cu, Zn, As, Se, Pb and Hg) in muscle tissues of two fish species (Clarias gariepinus and Oreochromis niloticus) in an Ethiopian rift-valley lake (Hawassa) and a neighboring stream (Boicha) were determined. Target hazard quotients (THQ), hazard index (HI) and target cancer risk (TCR) were used as indices to evaluate potential human health risks from fish consumption. Average concentrations of metals decreased in the order Zn>Fe>Se>Cu>Hg>As>Ni>Cr>Co>Pb and Zn>Fe>Se>Cu>As>Hg>Cr>Ni>Pb>Co in muscle tissues of C. gariepinus and O. niloticus, respectively. Mean concentrations of Hg (0.34+0.04 mg kg-1) in muscle tissues of C. gariepinus from Lake Hawassa, and As (0.18+0.05 mg kg-1) as well as Hg (0.46+0.03 mg kg-1) in muscle tissues of C. gariepinus from Boicha stream were above the safety limits set by WHO/FAO. Likewise, mean concentrations of As (0.31+0.03 mg kg-1) and Hg (0.19+0.05 mg kg-1) in muscle tissues of O. niloticus from Lake Hawassa and Cr (0.19+0.03 mg kg-1), As (0.33 +0.04 mg kg-1), and Hg (0.34+0.09 mg kg-1) in O. niloticus from Boicha stream were also above safety limits. From the results of human health risk assessments it was concluded that Cr, Cu, Hg and As pose potential health risks due to consumption of the two fish species from both water bodies. Moreover, effects of all heavy metals put together may affect human health as indicated by the high HI. Effluents from industries are assumed to be the main sources of the heavy metals. Therefore, regular monitoring of the water bodies and policy interventions with respect to waste disposal are recommended to protect the health of the ecosystem and the public. Keywords: Fish consumption, health risk, heavy metals, Lake Hawass

Heavy Metals Contamination of Soil in the Vicinity of Hawassa Industrial Zone, Ethiopia

Industrial effluents, containing heavy metals, drain directly into downstream water sources within the Hawassa Industrial Zone. These, water  sources are used for irrigation, drinking water and other domestic purposes. The load of pollutants, environmental risks and potential human impacts are generally, unknown for soil in Ethiopia. Therefore, the aim of this study was to determine the extent of heavy metal pollution of soil within the Hawassa Industrial Zone and to evaluate environmental impacts using contamination factor (CF), degree of contamination (Cd), modified degree of contamination (mCd), ecological risk factor (Er), ecological risk index (ERI) and pollution load index (PLI) analyses. Seven heavy metals: Cr, Ni, Cu, Zn, As, Cd and Pb were determined in soil samples from three different sites by inductively coupled plasma mass spectrometry (ICP-MS). Average concentration of metals decreased in the order of Zn>Cu>Cr>Ni>Pb>As>Cd consistent with the normal order of abundance in non-polluted soils. One way ANOVA revealed significant differences (P<0.05) in the concentrations of Cu, As, Cd and Pb among the sampling sites. Pearson’s correlation, principal component and cluster analyses revealed that heavy metals are originating from different sources. Within the industrial area,  the CF increased in the order of Pb<Cd<Zn<As<Cu<Cr<Ni. The result of Cd revealed that there was considerable to very high contamination of the soil. The mCd index showed moderate contamination of the soils. The Er increased in the order of Zn<Cr<Pb<Cu<Ni<As<Cd and the result of the ERI value revealed considerable ecological risk for the soils. Overall, the study showed that the soils within the Hawassa Industrial Zone are highly contaminated with heavy metals. Therefore, regular monitoring of heavy metals concentration in soil and policy interventions with respect to waste disposal are recommended. Keywords: Heavy metals, potential ecological risks, pollution load index, soi