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
