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

Abstract

Arsenic (As) exposure is a global public health concern affecting millions worldwide and stems from drinking water and foods containing As. Here, we assessed how agronomic practices and postharvest fermentation techniques influence As concentrations in rice bran, and calculated health risks from consumption. A global suite 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 the 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 dosage scenario for adults, children and infants exceeded THQ and LCR thresholds, and LCR was above threshold for median iAs-rice bran. This environmental exposure investigation into rice bran provides novel information with food safety guidance for an emerging global ingredient.

Methylation of arsenic in rice: Mechanisms, factors, and mitigation strategies

“…The mechanism is that aerobic conditions during the dry period of AWD promote the activity of As-methylating microorganisms in the soil, which preferentially methylate iAs to DMA over MMA. Weber et al [13] reported lower MMA (0.003 ± 0.004 mg kg −1 ) ( Table 1 ) in rice bran cultivated under AWD compared to that cultivated under CF (0.01 ± 0.006 mg kg−1). However contrary results have also been reported.…”

“…However contrary results have also been reported. For instance, Weber et al [13] also reported a much lower mean DMA (0.031 ± 0.010 mg kg −1 ) in rice bran under AWD compared to that under CF (0.149 ± 0.0622 mg kg −1 ) ( Table 1 ). In contrast, under CF, the anaerobic conditions in the soil promote the methylation of iAs to MMA.…”

“… Different microbial populations methylate AsV to MMA and DMA. [13] ARC ARC increases oxygen level in root zones Elevated oxygen levels fosters growth of different microbial populations Different microbial populations transform iAs into oAs species [101] SDI SDI induces variable oxygen availability Variable oxygen availability influence the activity of different microbial communities. Microorganisms variably impact As transformations.…”

“…In recent years, there has been a growing interest in understanding the mechanisms of methylation of As in rice [8] , [9] , [10] , [11] , [12] . As-methylation involves the addition of a methyl group (-CH 3 ) to an inorganic arsenic (iAs)-containing molecule, converting it into less toxic organic forms (the organic arsenic (oAs)) such as monomethylarsonous acid (MMA(III)), dimethylarsinous acid (DMA(III)), monomethylarsonic acid (MMA(V)) and dimethylarsinic acid (DMA(V)) [8] , [9] , [13] , [14] , [15] . Given that rice is a staple food for over 60% of the global population [16] , [17] , [18] , comprehending the processes that govern the methylation of iAs in rice is crucial for minimizing the health risks associated with rice consumption among consumers across the globe.…”

“…Numerous studies have highlighted As contamination in rice as a global issue, with varying levels of iAs detected in rice samples worldwide [2] , [8] , [9] , [13] , [14] , [19] , [20] , [21] , [22] . However, the extent of contamination depends on soil conditions and cultivation practices [8] , [10] .…”