Assessment of organic and inorganic arsenic species in Sengcu rice from terraced paddies and commercial rice from lowland paddies in Vietnam

Abstract

As a toxic metalloid and nonthreshold carcinogen, arsenic in rice has become a serious concern worldwide due to the risks of chronic human exposure through food. In this study, we aimed to assess the variation in arsenic concentration between Sengcu rice planted in a mountainous terrain and lowland commercial rice available for sale in markets around Vietnam. An optimized protocol using microwave-assisted extraction in combination with an HPLC-ICP-MS/MS system was employed for species-specific arsenic extraction from rice samples, and experimental conditions were determined by response-surface methodology for optimal extraction of all arsenic species. Multivariate analysis with generalized linear models was performed to test the hypothesis of intergroup variation in arsenic concentration. Our method yielded high productivity for all arsenic species with >95% accuracy and <6.1% precision for the certified-reference NIST® SRM® 1568b material. The method determination limits for As(III), As(V), DMA and MMA were 0.1, 0.2, 0.5 and 0.1 μg kg−1, respectively, thus ensuring the concentration stability of each arsenic species. As(III) was the predominant species in both Sengcu and commercial rice, which may be due to its abundance in the aquatic environment of paddy fields, thus being readily absorbed by rice roots. In contrast, differences in irrigation practices, microbial activities of farming fields and soil properties may lead to variations in As(V) and DMA concentrations between Sengcu and commercial rice. A further detailed investigation is necessary to provide a comprehensive understanding of the effect of farming practices on arsenic assimilation in rice grains.