Levels and health risk assessment of potentially toxic elements in rice (Oryza sativa) and soil from Ashanti Region.

Abstract

Anthropogenic activities release potentially toxic elements into the environment, which contaminate the food chain. The main objective of this research was to evaluate heavy metal exposure and potential health risk of consuming heavy metals in rice cultivated in the Asante Akim area. The levels of potentially toxic elements; As, Cd, Cr, Hg and Pb, in soil and rice samples were assayed using Agilent 7700 Series Inductively Coupled Plasma-Mass Spectrophotometer and compared with that of the WHO/FAO recommended levels. The mean heavy metal content in soil was 7.5 mg/kg, 0.52 mg/kg, 0.47 mg/kg, 1.30 mg/kg and 8.69 mg/kg for As, Cd, Cr, Hg and Pb, respectively. Mean levels of the elements in rice were 0.082 mg/kg, 0.27 mg/kg, 0.48 mg/kg, 0.028 mg/kg and 0.14 mg/kg for As, Cd, Cr, Hg and Pb, respectively. Soil pollution indices showed that the soils are unpolluted with the potentially toxic elements studied. The concentrations of the potentially toxic elements in rice were below the Maximum Allowable Concentration (MAC) recommended by Codex Alimentary Commission except Cd which was marginally higher than the MAC. Dietary exposure of the elements to consumers was assessed by comparing the estimated daily intake (EDI) to the Provisional Tolerable Daily Intake (PTDI). The estimated daily intake values for As, Cd, Cr, Hg and Pb were 1.45×10-4, 4.8×10-4, 8.5×10-4, 4.95×10-5 and 2.4×10-4 respectively. The non-carcinogenic health risk was assessed using Hazard Quotients (HQ). The HQ for all the potentially toxic elements were less than the USEPA permissible value of 1, suggesting that the consumption of rice from the study area constitutes no potential health risk to the population. Although the current levels of the potentially toxic elements in rice is low, it is recommended that, regular monitoring studies be conducted to ascertain the levels of heavy metals in rice cultivated in the area, since heavy metals can accumulate and the concentrations could go up with time.