Effects of Two Cooking Methods on the Concentrations of Some Heavy Metals (Cadmium, Lead, Chromium, Nickel and Cobalt) in Some Rice Brands Available in Iranian Market

Dietary intake is the most important route of exposure to heavy metals for most people. Rice is a staple food for Iranians that, if polluted, threatens public health. Cooking process may affect heavy metals content of rice. In this study, concentrations of cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni) and cobalt (Co) were measured in 3 brands of imported rice available in Shiraz-Iran market. Two methods of cooking (Kateh and Pilaw) were applied for all brands. The heavy metals were detected in raw and cooked rice grains. The samples were analyzed by atomic absorption spectrometer. The mean concentrations of Cd, Pb, Cr, Ni and Co were 0.33, 1.75, 0.38, 0.89 and 0.20 µg/g in raw rice samples respectively, 0.10, 1, 0.29, 0.19, and 0.03 µg/g in Kateh rice samples and 0.10, 0.98, 0.28, 0.18 and 0.03 µg/g in Pilaw rice samples. Cooking rice grains reduced the content of heavy metals. Minimum cooking efficiency was for Cr. The effect of cooking methods was not significantly different in this study. The obtained concentrations were compared with the permitted values, published by Institute of Standards of Iran, for heavy metal contents in rice. Moreover, weekly intakes of the metals through rice were estimated and compared with the PTWI (Provisional Tolerable Weekly Intake) amounts determined by FAO/WHO.