Arsenic speciation in rice bran: agronomic practices, postharvest fermentation, and human health risk assessment across the lifespan

Authors: WEBER, ANNIKA - Colorado State University; BAXTER, BRIDGET - Colorado State University; McClung, Anna; LAMB, MOLLY - University Of Colorado; BECKER-DREPS, SYLIVIA - University Of North Carolina; VILCHEZ, SAMUEL - National Autonomous University Of Nicaragua Unan At Leon; KOITA, OUSMANE - University Of Sciences; WIERINGA, FRANK - University Of Montpellier; RYAN, ELIZABETH - Colorado State University

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2021
Publication Date: 8/12/2021
Citation: Weber, A.M., Baxter, B.A., McClung, A.M., Lamb, M.M., Becker-Dreps, S., Vilchez, S., Koita, O., Wieringa, F., Ryan, E.P. 2021. Arsenic speciation in rice bran: agronomic practices, postharvest fermentation, and human health risk assessment across the lifespan. Environmental Pollution. https://doi.org/10.1016/j.envpol.2021.117962.
DOI: https://doi.org/10.1016/j.envpol.2021.117962

Interpretive Summary: Most rice is consumed as a milled or polished grain which removes the outer bran layer. However, rice bran is rich in fatty acids, phytochemicals, B and E vitamins, and soluble and insoluble fibers and may have protective effects against colon cancer and enteric infections and diseases. The rice plant is unique in being able to thrive under flooded field conditions. However, these saturated soils result in an anaerobic environment that make some soil compounds, like arsenic (As), more available for plant uptake. Thus, rice can naturally accumulate higher levels of As than other cereal grains and the inorganic form of As, considered more toxic to humans than other forms, is primarily localized in the outer bran layer of the grain. Thus, globally there are concerns about possible dietary exposure of As from rice bran consumption. This study aimed to assess the impact of global production sites, irrigation management, soil treatments with an As-based herbicide, organic versus conventional management systems, and bran fermentation treatments on As contents found in rice bran. Bran samples (53) were obtained from 10 rice producing countries and were analyzed for As content. Wide variation was found in inorganic As concentrations (619 to 17 ppm) depending on where the bran was produced. Agronomic practices and soil conditions were identified as major influencers for As uptake into the grain. Water saving irrigation practices such as alternate wetting and drying allow for non-saturated conditions in the soil that may help reduce As accumulation in the grain. Application As to the soil resulted in higher levels of uptake to the bran. Rice bran sourced from organic production systems, which generally have higher soil organic matter and soil health, tended to have higher levels of As than conventionally produced sources, but this varied greatly among production sites. Post-harvest fermentation of bran had little effect on bran As contents. With the suite of health benefits associated with rice bran, it is imperative to better understand how various production and post-harvest processes can optimize health beneficial compounds while minimizing any non-desirable compounds.

Technical Abstract: Arsenic (As) exposure is a global public health concern affecting millions worldwide and stems from drinking water and foods. Here, we assessed how agronomic and postharvest techniques influence As concentrations in rice bran, and calculated health risks from consumption of three rice bran-As concentration scenarios. A total of 53 rice brans were tested for total As and speciation. Targeted quantification of inorganic As (iAs) concentrations in rice bran were used to calculate Target Hazard Quotient (THQ) and Lifetime Cancer Risk (LCR) across the lifespan. Mean iAs was highest in Thailand rice bran samples (0.619 mg kg-1) and lowest in Guatemala (0.017 mg kg-1) rice bran samples. When comparing monosodium-methanearsonate (MSMA) treated and Native-soil counterpart under the irrigation technique Alternate Wetting and Drying (AWD) management, the MSMA treatment had significantly higher total As (p=0.022), and iAs (p=0.016). No significant differences in As concentrations were found between conventional and organic production, nor between fermented and non-fermented rice bran. Health risk assessment calculations for the highest iAs-rice bran scenario for adults, children and infants exceeded THQ and LCR thresholds, and LCR was above threshold for median iAs-rice bran. This investigation provides novel information with food safety relevance of rice bran as an emerging food ingredient.