Availability of arsenic in rice grains by in vitro and in vivo (humans) assays.

Background: Rice grains are consumed by approximately half of the world's population. This cereal has higher arsenic (As) concentrations in grains than wheat or barley. Arsenic determination in food and/or in vitro studies are important for risk assessment; however, it is not enough to assess the real human exposure.

Method: In vitro bioaccessibility was carried out in husked-rice using gastric and intestinal solutions similar to humans. Also, As naturally found in husked-rice was evaluated by in vivo bioavailability in humans. For this purpose, diets from the 1 and 2 days were free of foods known to be high in As; 3 and 4 days the diets were composed by rice and water and; 5 and 6 the diet was similar the 1 and 2 days. During all experimentation, a representative aliquot of each meal, blood and urine were collected for total As (t-As) determination. Arsenic species were determined in the urine.

Results: t-As in husked rice varied from 157.3 ± 30.6 to 240.2 ± 85.2 μg kg. The in vitrobioaccessible fractions ranged from 91 to 94%. Inorganic As (i-As) ranged from 99.7 ± 11.2 to 159.5 ± 29.4 μg kg. For the in vivo assay, t-As concentrations in the woman and man blood were about 3 μg mL from the 1 to 6 day. Arsenic from the rice ingested was excreted by urine about 72 h after ingestion. The t-As and dimethyl As (DMA) in urine ranged from 3.59 to 47.17 and 1.02 to 2.55 μg g creatinine for the volunteers, indicating a two-fold DMA-increase in urine after ingestion of husked-rice.

Conclusion: After rice ingestion, As was quickly metabolized. The higher As concentrations were found in urine 72 h after rice ingestion. The main As-specie found in urine was DMA, indicating that methylation of As from rice followed by urine excretion is the main biological pathway for As excretion.