Zeitschrift für Umweltanalytische Chemie

Levels of selected essential and non-essential metals in rice and the underlying soil in major rice-growing areas of Ethiopia

Abstract

Abebe D Abitew* and Biruk B Yimam

The concentrations of essential metals (Ca, Mg, Cr, Cu, Fe, Mn, Ni, and Zn) and non-essential metals (Cd and Pb) were determined in Ethiopian white rice cultivated in Fogera, Metema, and Pawe areas with their corresponding growing soils. The amounts of metals in rice and soil were determined by flame atomic absorption spectrometry, after digesting the powdered rice and soil samples with a mixture of HNO₃, HClO₄, and H₂O₂. The accuracy of the digestion procedure was assessed using the spiking method, where an acceptable percentage metal recovery was obtained in the range of 86.6%-106.7% and 87.15%-112.8% for rice and soil, respectively. The concentrations (mg/kg) of metals found in rice and soil, respectively, were in the ranges of Mg 414.28-560.89, 618.70-709.43; Fe 49.36-167.95, 11673.60-12916.67; Ca 45.21-57.71, 281.60-655.20; Mn 27.40-57.71, 168.60-416.60; Cu 12.01-61.19, 59.98-139.66; Zn 24.19-28.07, 26.59-55.85; Cr 17.65-27.45, 12.75-12.76; Ni 3.16-8.61, 2.07-11.87; Cd 1.08-1.55, 1.08-3.43 and Pb 1.08-1.55, 4.17-9.38. The pH of the studied soil farms was in the range of 5.30-5.95. Among the analyzed metals Cr showed the maximum transfer factor from soil to rice grain. Pearson correlation indicated a strong correlation for some elements between or within rice and soil samples. One way analysis of variance results indicated that for all metals in rice, the difference between means in the three sampling sites was insignificant (p>0.05), while the significant difference among soil samples was observed only for Mg, Zn, Mn, and Cd. Except for Cr, Cd, and Pb in rice and Cu and Cd in metema soil, the determined concentrations of metals were below the world health organization allowed limit.