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.