Assessment of the Effect of Artisanal Gold Mining on Heavy Metals Concentrations and Associated Potential Public Health Risk: The Case of May Sieley River of the Shire , Tigray, Region Ethiopia
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Date
2021-02-19
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Addis Ababa University
Abstract
Artisanal gold mining (AGM), in third world countries including Ethiopia has become a livelihood diversification strategy, which makes significant contribution to poverty alleviation. Although artisanal gold mining provides enormous economic benefits, the mining activities are carried out at the expense of the environment and public health due to pollution with heavy metals (HMs). The protection of public health and aquatic resources necessitates the availability of scientific information on pollution with heavy metals. The present study was, therefore, conducted to investigate the efffect of artisanal gold mining on the levels of selected heavy metals in May Sieley River (Tigray) and evaluate the potential human health risk. Surface sediment and water samples were collected from upstream, midstream and downstream sites (USS, MSS &DSS) respectively, during the dry and post-rainy periods and were analyzed for Pb, Cd, Cu, As, Cr, Hg, Ni, and Zn by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The concentrations of heavy metals in water samples were compared with WHO and Ethiopian standards for drinking water and assessment of human health risk was made following the guidelines provided by the US Environment Protection Agency. Temperature, pH and dissolved oxygen were measured insitu and were found to be within acceptable ranges and did not show large variations. The differences in HMs concentrations in water among sampling sites during both seasons were not marked except for Cu and Zinc in dry season, although Zn, Cu, Hg, Cd and Pb were higher at the MSS suggesting the association of their levels primarily with AGM. The differences in the concentrations of all HMs in water samples between seasons were marked. The concentrations of HMs in sediment samples varied markedly between the two seasons. The differences in HMs concentrations in sediments among sampling sites during dry seasons were marked for Cu, Zn, Pb and As while in post-rainy season, differences were not marked except for Ni and Pb. The concentrations of all HMs except Nickel in sediment samples of the dry season were higher at the MSS, while they were higher at USS during the post-rainy season. The present results suggest that both AGM and natural sources associated with the weathering of rocks have made contributions to the metal pollution of May Sieley River. Hg and As were above WHO and Ethiopian standards for drinking water in the dry season in all sampling sites, while Cr, Cd, Pb and As were above the same standards for drinking water in the post-rainy season in all sites, except Hg (in one sample of MSS) and Ni (in one sample of DSS). The HQ values for As, Pb, Hg and Cd for both age groups were at unacceptable non-carcinogenic potential health risk levels (HQ>1), while As and Cd for adults and As, Cd and Hg for children, are likely to have chronic effects (Q>10). The Sum of HQs (HI) of analyzed metals was far greater than 1 for both age groups, children being at greater risk. This raises concern about the non-carcinogenic adverse health effects of using the river water for drinking and other household purposes. The results of the ILCR assessment for Arsenic, Lead, Cadmium, Chromium and Nickel indicated that the carcinogenic effect associated with these metals is not acceptable. The study has revealed that the river water is not safe due to HMs pollution, AGM should be managed to reduce its contribution to the pollution of water bodies with heavy metals. The government needs to assist and empower the miners so that they can carry out their activities sustainably and in an environmentally friendly way. Further monitoring of the impact of traditional gold mining on HMs pollution by considering aquatic organisms in order to assess their biomagnification along the food chains is also recommended.
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Heavy Metals, Artisanal Gold Mining, May Sieley River, Human Health Risk