STUDYING THE EFFECTS AND CHANGES OF LOCALIZATION AND SPECIATION OF ARSENIC IN COOKED RICE GRAINS USING µXRF AND XANES-ASSOCIATED HEALTH IMPACTS

Threats of Arsenic (As) through food uptake, via consumption of rice, is a potential pathway that presents a concern for the millions of inhabitants who live in river valleys and irrigate their soil with contaminated water, not to mention the global market. This study focuses on As-contaminated rice from India and Bangladesh grown in such soils, and the effect of boiling this rice with As-contaminated water in preparation for dietary intake. Husked and unhusked rice grains were boiled with >500 µg/L As-contaminated water from the field to simulate cooking methods. The resulting cooked water was analyzed using HR-ICP-MS to understand the changes in dissolved elemental concentrations before and after cooking, and HPLC was introduced to measure for changes in As speciation in the waters. The husks were then manually removed from the rice grain, and analysis of the husks and grains for both cooked and uncooked samples was undertaken. Using spectroscopic methods like Micro X-Ray Fluorescence (µXRF) mapping and micro X-ray Absorption Near Edge Structure (µXANES) spectroscopy, distribution and speciation changes of As in rice grains were followed. Further, with Linear Combination Fitting (LCF) of XANES spectra utilizing relevant reference compounds, we were able to determine organic and inorganic As species in rice grains. The results so far indicates inorganic As species (AsV, AsIII), with ~26% to 70% of As-sulfides, and some organic species (MMA and DMA) localized in areas of uncooked rice grains, typically in the outer aleurone layers. When analyzing the cooked rice grains, the speculation is that the speciation appears to be an unidentified As species, while the best LCF gives between 63% and 93% MMA and was found less localized throughout the grain but rather heterogeneously when compared to the uncooked samples. The analyses of boiled/cooked water results showed a drastic decrease in dissolved As post-cooking (~ 90%), but a subsequent increase in elements such as K, Na, Li, Mo, and La. The impact that this study portrays is consuming rice cooked by As-contaminated waters may not decrease the levels of As being consumed, but entitles further study on the specific health impacts that such cooked rice consumption could add to the community.