Investigating Contamination Of Soils Of Auto-Garages By Selected Heavy Metals And, Physico-Chemicals Parameters, Associated Human And Ecological Risks In Ambo Town, Oromia Regional State, Ethiopia

Abstract

Auto-garages are seen currently as potential sources of heavy metal contamination to urban soil. This study aimed to investigate the contamination of soils in garage and auto-mechanical workshops by selected heavy metals and to evaluate associated human and ecological risks in Ambo town, Ethiopia. Risk assessment models were applied to measure the pollution levels of heavy metals and estimate of their health risk of human exposure. To achieve objectives, 24 soil samples (0–15 cm soil depth) were collected using soil auger from randomly selected seven (7) auto-garages and one references site in Ambo town, Ethiopia employing judgemental/purposive sampling technique. The reference soil samples were collected from uncontaminated or less disturbed sites. Wet digestion technique was employed to prepare the soil samples for the quantification of heavy metal levels using flame atomic absorption spectrometric (FAAS) technique. The optimum acid volume ratio was 2:2:1 for H2O2:HClO4 and aqua-regia, respectively with the digestion time of 3:30hrs and digestion temperature of 220 ˚C.The LOD and LOQ values lied in the range of 0.01– 0.1 mg.kg−1 and 0.02 – 0.34 mg.kg−1 , respectively. The observed relative standard deviation (%) and recovery (%) values for the samples ranged from 0.0002 to 1.89 and 90.55-99.98%, respectively. The average concentration of heavy metals found in the auto-garage soil samples were ranged as. 24.3-315.9,179.9-1438.8, 76.3-176.9, 485.3-1849.9, 25985.8-68064.6, 2342.9-6098.64, 70.79-1095.85, 187.7-1615.83,and 1275.59-41768 in mg/kg for Cd,Co,Cr,Cu,Fe,Mn,Ni,Pb,and Zn, respectively.These values exceeded the soil quality guidelines established by FAO/WHO and EU, except Cr,Fe and Ni at ABR.G,ABU.G and ISH.G site which is below the permissible limit. The results of pollution indexes such as contamination factor (CF), degree of contamination (CD), modified degree of contamination (mCd), enrichment factor (EF) and geo-accumulation (Igeo) indicated that the the studied auto-garage soils contamination status lied between moderate to severe contamination by the studied heavy metals. The results of the evaluated ecological risk indexes (ecological risk factor (ErF = 4.78 to 2181) and potential ecological risk index (PERI = 694 to 6392)) showed that there are slight risk to extremely strong risk due to individual metal elements and their mixture, respectively. The human health risk assessment results showed that lead (Pb; HQoral >1) and mixture of the studied metals (THI > 1) can pose non-carcinogenic health risk (HQoral >1) . Similarly, the carcinogenic risk assessment result indicated that Cd,Cr,Ni and Pb metals can pose slight to high cancer risk to adult population (total cancer risk (TCR) range from 1.42x10-5 to 3.3x10-3 ). The study highlights that open auto-garages in Ambo town are greatly contaminating their surrounding soils by the heavy metals and threating health of humans and the environment which necessitating immediate intervention to avert the problem.