Human exposure to arsenic and methods for reducing it through the food chain in West Bengal, India

Resumen

The world's worst mass arsenic poisoning is located in Bangladesh and West Bengal (India). Only in West Bengal, it is estimated that 26 million people are potentially at risk from drinking arsenic contaminated water (above 10 ¿g As/L). The aim of the current Ph.D. dissertation was to assess the human exposure to arsenic and to recommend simple and sustainable methods for reducing it through the food chain in West Bengal. Rice is an important source of arsenic for the Bengali population, because cooked rice is their staple food and it accumulates higher levels of arsenic (339 ¿g As/kg) than other vegetables (75 ¿g As/kg) and spices (91 ¿g As/kg). It was estimated that the daily arsenic intake of this population is 1.5, 6.8 and 13.3-fold the Provisional Tolerable Daily Intake (2.14 ¿g i-As/day/kg body weight) when cooking and drinking water contained 50, 250 or 500 ¿g As/L, respectively. Cooked rice itself represented by up to 45 % of the total daily arsenic intake. Rice accumulates high levels of arsenic because of its cultivation system (flooding) and arsenic biogeochemistry. Arsenic is highly available for plant uptake at low pH (pH 5.5) and under moderately anaerobic conditions (between +50 mV and -150 mV). The two most popular methods of dehusking rice changed the arsenic concentration in the commercial rice in West Bengal (atab and parboiled rice). Atab rice, obtained from the dry dehusking procedure, showed lower arsenic concentration (290 ¿g As/kg) than parboiled rice (332 ¿g As/kg), obtained from the wet dehusking procedure. The cooking process increased the arsenic concentration in the cooked rice up to 874 and 1642 ¿g As/kg when cooking raw rice (247 ¿g As/kg) with water containing 250 or 500 ¿g As/L, respectively. However, the arsenic concentration in cooked rice (227 ¿g As/kg) was reduced up to 30 % when the cooking water had 50 ¿g As/L. The cooking method affected significantly the arsenic concentration in the cooked rice. The cooked rice contained 258, 365 and 387 ¿g As/kg when it was cooked following the traditional, intermediate and contemporary method along with cooking water with 40 ¿g As/L. Besides, atab rice always showed lower levels of arsenic (283 ¿g As/kg) than parboiled rice (390 ¿g As/kg) independently of the cooking method used. It is recommendable to obtain atab rice after dehusking process and to cook it in excess of water after washing (traditional method) if water free of arsenic is not available. This way the arsenic exposure can be reduced by up to 20 % or 30 % when rice plus drinking water (40 ¿g As/L) or only rice are used to estimate the daily arsenic intake, respectively.