Arsenic, cadmium, lead and chromium concentrations in irrigated and rain-fed rice and their dietary intake implications

Absorption of heavy metals and contaminants through a rice-based diet may have serious consequences for human health. The present study determined the levels of arsenic (As), cadmium (Cd), lead (Pb) and chromium (Cr) in 71 irrigated and rain-fed rice and assessed dietary (rice) exposure to the heavy metals. The concentration in rice grains were generally higher in the irrigated season which may be related to the use of contaminated irrigation water: As 0.153 ± 0.112 and 0.140 ± 0.080 mg kg^-1, Cd 0.073 ± 0.069 and 0.038 ± 0.032 mg kg^-1, Pb 0.264 ± 0.125 and 0.147 ± 0.077 mg kg^-1 and Cr 1.208 ± 0.913 and 0.986 ± 0.796 mg kg^-1 in irrigated and rain-fed rice, respectively. Elevated concentration of grain As was recorded for rice samples that were collected from the locations with As-contaminated groundwater used for irrigation. For Cd, Pb and Cr, relatively higher concentration was noted for the areas which could be linked to industrial effluent contamination. Daily intake of As and heavy metals from rice is estimated as 18.6-214 μg for As, 2.6-119 μg for Cd, 25.0-241 μg for Pb and 59.0-1846 μg for Cr, based on 400g daily rice consumption for 60 kg Bangladeshi adult people. The rice component of the diet alone may contribute up to 46%, 57%, 50% and 60% of the Maximum Tolerable Daily Intake (MTDI) for As, Cd, Pb and Cr, respectively, making it a more important factor in the dietary intake for these elements than other food stuffs and drinking water. Hence, heavy metals accumulation in rice grains is a big concern in south Asia where people's daily meal largely contains rice or rice based products.