Determination Of Levels Of Major Rock Forming Oxides, Selected Trace Heavy Metals And Human Health Risk Assessments In Ambo Sandstones, Ethiopia

Abstract

The sandstones deposited around Ambo district have gained a widespread recognition for their extensive utilization as a construction material within and around Ambo town, but detailed studies on mineral composition and heavy metals contents is lacking. The purpose of this study is therefore to determine the levels of major rock forming oxides (SiO2, Al2O3, Fe2O3, MnO, MgO, CaO, Na2O, K2O, TiO2 and P2O5), trace heavy metals (As, Cd, Cu, Pb, Zn, Hg, Co, Ni and Cr) and human health risks in the sandstone sample from the two main quarry sites of Aleltu and Senkelle areas of Ambo districts, West Shewa, Ethiopia. Fusion sample decomposition technique was employed to prepare sample for the determination of major rock forming oxides by FAAS and an optimized wet acid digestion with a mixture of HNO3, HClO4, HF and aquaregia were used prior to trace metal analysis via ICP-OES. The result of the study shows that the sandstone sample were predominantly composed of SiO2 (65.12-66.12%), followed by Al2O3 (13.26- 15.26%), Na2O (3.25-4.25%), Fe2O3 (1.83-2.63), K2O (1.25-2.79%), MgO (0.12-0.32%), CaO (0-22%) and MnO (0.003-0.027%). TiO2 and P2O5 were found to be below the method detection limit. Geochemical results of Ambo sandstones indicate that they are mineralogically immature and classified into Greywacke. The mean concentrations of analyzed heavy metals in Aleltu and Senkelle sampling sites were found to be: 10.89±2.28 and 25.93±2.97, 9.48±0.33 and 19.17±0.92, 1.87±0.14 and 7.97±0.28, 14.78±1.12 and 12.20±1.16, 6.07±1.64 and 13.59±2.77, and 103.49±4.48 and 123.36±16.01 in mg/kg for Pb, Zn, Cd, Cu, Ni and Cr, respectively. The levels of As, Hg and Co were found to be below the method detection limits. All the detected trace heavy metals are accumulated in higher concentrations in the Senkelle sites except for Cu. The non-carcinogenic health risk assessment from the exposure of trace heavy metals were calculated as HQ for individual toxicants and HI for combined effects of toxic agents were both <1, suggesting no adverse health effects. However, the evaluated total cancer risk due to exposure to Cd, Ni, Cr and Pb for sandstone obtained from Aleltu and Senkelle sampling sites are above the tolerable value of cancer risk (1.08×10-4) and (1.92×10-4), respectively, signifying strict regulatory control is required by all stakeholders to mitigate the health risk