The levels of essential and non-essential metals and Proximate Composition in Rice from Central and South Gondar Zones, Ethiopia

Abstract

Rice is the most important staple food crop for more than half of the world’s population. In this study, proximate and elemental composition of rice collected from three study sites: West Dembia, East Dembia and Fogera districts in the Central- and South-Gondar Administrative Zones, Ethiopia, were analyzed. After proper sample pretreatment, a 0.5 g of oven-dried rice sample was digested with an optimized wet-digestion procedure using 3.5 mL of HNO3, 1.5 mL of HClO4 and 0.5 mL of H2O2 at 175 °C for 1:55 h; and validity of the procedure was evaluated by spiking experiments. The concentrations of essential- (Zn, Cu and Mn) and non-essential (Pb and Cd) metals were determined by flame atomic absorption spectrophotometer. Results of proximate analyses showed that moisture and ash contents varied from 11.1 to 12.3% and 0.96 to 1.77%, respectively. With respect to metal analyses, the percentage recoveries ranged from 92.5 to 98.0%, indicating good accuracy and repeatability of the optimized procedure. The concentrations of metals (mg/kg) in rice samples from the three study sites ranged from: Zn (50.5–52), Cr (19.9–30.5), Mn (21–22.6), Cu (1.22–1.49), Pb (1.24–1.49), and Cd (1.1–1.14). One-way ANOVA revealed significant differences (p < 0.05) among the mean concentrations of metals in all rice samples; while insignificant differences were observed for metal values among the three study sites, indicating absence of effect of geographic origin on the metal levels. The concentrations of metals observed were comparable with some of the reported values in the literature. The levels of Cr, Cd and Pb, were above the permissible limit set by WHO/FAO, except for Cr in rice samples from Fogera district. Thus, special concern should be paid on the consumption of rice from these study areas since they were found to contain higher levels of toxic metals, especially Cd and Pb. Hence, a complete risk assessment is required