DETERMINATION OF TOXIC HEAVY METALS IN KHAT AND ITS SUPPORT SOIL AND ASSOCIATED HEALTH RISK ASSESSMENTS IN ALGE SACHI WOREDA, ILUBABOR ZONE, SOUTHWEST ETHIOPIA

Khat (Catha edulis Forsk) is a stimulant plant that grows in certain areas of East Africa and the Arabian Peninsula. Heavy metal pollution has been a global concern due to its acute and chronic health effects and the major route of exposure is consumption of contaminated foods. In this study, determination and health risk assessment of heavy metals (Mn, Cu, Zn, Ni, Cr, Cd, and Pb) in khat and its support soil samples was carried out. The calibration curves of each analyte were linear in the concentration range of 0.3 - 10 mg/L with R2 > 0.99 and the detection limit and limit of quantification of the method were 0.0131 - 0.497 mg/kg and 0.016 - 0.1911 mg/kg; 0.0419 - 1.586 and 0.052 - 0.609 mg/kg for soil and khat, respectively. The percent recoveries and relative standard deviations were 93.07 - 101.59 and 0.007 - 5.1, respectively. The levels (mg/kg) of analytes in soil and khat samples were: Cu in soil (29.00+0.94); in Sembeto kebele ,in Chkorsa doyu (31.40+0.35); in Nado (35.80+0.88); and in khat (23.09+0.12) in Chokorsa doyu (25.68+0.49); in Nado (6.78+0.71) Mn in Senbeto kebele( 1724.60+0.52);in Chokorsa Doyu (1855.40+0.72);in Nado kebele (1197.60+0.48 );Zn in Sembeto kebele(4.30+0.65); in soil (199.02+0.73); in Chokorsa Doyu (87.90+0.19);in Nado( 87.66+1.42 );and in khat in Sembeto( 25.09+0.84); in Chokorsa Doyu (29.89+1.0);in Nado kebele Ni (6.37- 64.80); Cr (0.82-169.20); Cd (14.2-38.8) and Pb (Not Detected). Among the analyzed heavy metals in soil, Mn was the most abundant, followed by Zn, Cr, Cu, Ni, and Cd while that of Zn was the highest followed by Cu, Mn, and Cr in khat. The levels of Zn, Cr, and Cd in soil samples from all the study sites and detected concentrations of Cr in khat samples exceeded the recommended FAO/WHO levels. The hazard index (HI) of metals in khat from study areas was less than one indicating a less likelihood of noncarcinogenic toxicological health effects. However, the presence of these toxic chemicals in soil and khat indicates product contamination and needs extensive further investigation involving other heavy metals.