DIETARY ESTIMATES AND LEVELS OF TOXIC, ESSENTIAL ELEMENTS AND MICROBIAL LOAD OF LOCAL RICE

Abstract

This study investigated the levels of toxic elements: lead (Pb), arsenic (As), cadmium (Cd); essential micronutrients: chromium (Cr), zinc (Zn); and macronutrients: sodium (Na), calcium (Ca) and potassium (K) and the microbial load of locally cultivated rice consumed in Ondo and Ekiti states of Nigeria. The rice samples were obtained from six different towns namely Akure, Ondo, Ado, Igbemo, Ikole and Erinjiyan and their mineral profiles determined by either Atomic Absorption Spectrophotometric or Flame Photometric methods for heavy metals and macronutrients respectively. The rice samples were analysed for toxic metals (Pb, As, and Cd), essential micronutrients (Cr and Zn) and macronutrients (Na, Ca and K). The Estimated Daily Intake (EDI) of these elements were determined and compared to the Provisional Tolerable Daily Intake (PTDI) and Dietary Reference Intake (DRI) values set by Joint FAO/WHO and Institute of Medicine for PTDI and DRI respectively. The detected average mean levels of Pb, As, Cr, Cd, Zn, Na, Ca and K were 0.05 μg/g, 0.04 μg/g, 0.57 μg/g, 0.03 μg/g, 7.86 μg/g, 42.15 mg/kg, 337.11 mg/kg, and 2650.09 mg/kg respectively. The toxic elements were highest in rice from Erinjiyan (Pb=0.05 μg/g; Cd=0.04 μg/g) and Igbemo (As=0.06 μg/g) and lowest in rice from Ado (Pb=0.04 μg/g; Cd=0.02 μg/g) and Akure (As=0.03 μg/g). The average EDI contribution to the PTDI/DRI for Pb, As, Cr, Cd, Zn, Na, Ca and K were 3.29 μg/day, 2.87 μg/day, 39.90 μg/day, 1.82 μg/day, 0.55 mg/day, 2.95 mg/day, 23.60 mg/day and 185.51 mg/day respectively, which were all below the recommended levels except chromium. The total colony count showed that Akure had the highest bacterial count (1.25×104 cfu/g) while the highest fungal count was recorded in Erinjiyan (7.0×103 sfu/g). The least bacterial count was observed in Ikole and Igbemo (500 cfu/g), while the least fungal count was recorded in Igbemo (1.0×103 sfu/g). This study however showed that the consumption of these locally cultivated rice may pose a serious health risk unless they are supplemented with nutrient-rich supplements such as meats and eggs. High chromium observed in rice from Ekiti State (Ado, Erinjiyan, Igbemo and Ikole) may cause chromium toxicity if eaten for a prolonged period of time. More information are still required on the soil and water from this area in order to proffer bio-remediation techniques that would be needed to abate this problem.