Evaluation of some physicochemical parameters and health risks associated with potentially toxic elements (PTEs) in agricultural soils from the southwest region of Ethiopia

• A total of 13 potentially toxic elements were analyzed in six agricultural soil samples. • Some important physicochemical parameters were studied in agricultural soil samples. • For adults, both THQ and HI of all PTEs were less than unity. • ILCR values of toxic PTEs in Bure soils were slightly exceed USEPA threshold limit. • According to One way ANOVA test, there was a significant variation in all PTEs. In this study, soil samples collected from Burusa and Bure agricultural sectors were analyzed for their physicochemical parameters and potentially toxic elements (Fe, Mn, Zn, Cu, Co, B, Se, Ni, Cr, Pb, Cd, As, and Hg). Physicochemical parameters were analyzed according to AOAC methods. For quantification of PTEs, the soil samples were digested by using aquaregia (HCl: HNO 3 ; 3:1) and 5 mL of H 2 O 2 (30%) at a digestion temperature of 250°C for 3 hours prior to ICP-OES analysis. The percent recoveries (%R) and relative standard deviation (%RSD) of this method ranged from 83 to 106% and 0.39 to 9.2%, respectively. The LODs and LOQ values were in the range of 4.3 × 10 -4 -5.3 × 10 -2 mg/L and 1.4 × 10 -3 -1.76 × 10 -1 mg/L, respectively. The analyzed mean values of physicochemical parameter including pH, temperature, electrical conductivity, moisture, organic matter and nitrogen content were found in the range of 4.85-6.47, 20.5-21.4°C, 101.6-230.7 µS/cm, 8.67-20.7%, 0.677-1.81% and 5.81-6.85%, respectively. The average amount of potentially toxic elements found in the soil samples were ranged as 57073-81279, 1185-3255, 41.0-72.2, 12.6-29.2, 18.8-50.8, 25.0-40.5, 42.2-60.8, 13.6-34.5, 41.9- 67.2, 25.0-59.4, 9.92-13.3, 0.933-1.12 and 4.97-8.63 in mg/kg for Fe, Mn, Zn, Cu, Co, B, Se, Ni, Cr, Pb, Cd, As and Hg, respectively. The highest concentrations of among the entire PTEs were recorded for Fe, followed by Mn, in the analyzed soil samples. All the studied elements are below the FAO/WHO permissible limit except Fe, Se, Cd, and Hg for all analyzed soil samples and Mn for the Bure soil sample. The target hazard quotient (THQ) and hazard index (HI) values are <1, suggesting an insignificant non-carcinogenic risk of the heavy metals to the adults via ingestion, inhalation, and dermal contact exposure of agricultural soils. Likewise, the individual element incremental lifetime cancer risk (ILCR) occurrence for all studied soil samples is below 1 × 10 -4 . The total ILCR of potentially toxic heavy metals (Ni, Cr, Pb, Cd and As) resulting from ingestion, inhalation, and dermal contact exposure of agricultural soil by an adult population indicate a slightly higher potential cancer risk (> 1 × 10 -4 ) for soil samples obtained from Bure S1, Bure S2, and Bure S3. Therefore, continuous monitoring of these harmful elements should be made by agricultural sectors and responsible government regulatory authorities are crucial to prevent PTEs related to agricultural soils in Ethiopia.