Recent advances in arsenic bioavailability, transport, and speciation in rice

Abstract

Widespread arsenic (As) contamination in paddy rice (Oryza sativa) from both geologic and anthropogenic origins is an increasing concern globally. Substantial efforts have been made to elucidate As transformation and uptake processes in rhizosphere and metabolism in rice plant, which provides an essential foundation for the development of mitigation strategies. However, a range of crucial mechanisms from As mobilization in rhizosphere to transport to grains remain poorly understood. To provide new insight into the underlying mechanisms of As accumulation in rice, a range of new perspectives on As bioavailability, transport pathways, and in situ speciation are reviewed here. Specifically, the prominent effects of water regime, Fe plaque, and biochar on As mobilization in rice rhizosphere are discussed critically. An updated understanding of arsenite (AsIII) and methylated As transport from root to vascular bundle and grain is integrated and discussed in detail. Special attention is given to As speciation and distribution in rice grain with potential coping strategies being provided and discussed. Future research priorities are also identified. The new insight into As bioavailability, transport and speciation in rice would lead to a better understanding of As contamination in rice. They would also provide useful strategies from agronomic measures to genetic engineering for more effective restriction of As transport and accumulation in food chain.

Arsenic Accumulation in Rice and Probable Mitigation Approaches: A Review

“…However, the application of silica gel (10 g kg −1 of soil) was much more effective to decrease the arsenic concentration in flag leaf, straw, husk, and grains of rice as suggested by some authors [132,160]. Approximately 33% reduction of As III concentration in polished rice was found as a consequence of~50% reduced vascular transportation of arsenic after silicon application under flooded condition of paddy field [128,160].…”

“…The processes of bioavailability, root uptake, rhizosphere, transport, accumulation, and grain unloading of arsenic are imperative aspects of research to alleviate arsenic in rice [42,128,129].…”

Arsenic speciation in locally grown rice grains from Hunan Province, China: Spatial distribution and potential health risk

“…However, the iAs concentrations in two rice samples, one from Changsha (A2) and the other from Xiangtan (C1), exceeded the threshold value, which might pose serious health risk to population consuming the rice. Besides As concentration in cultured soil, there are many other factors, including soil properties, As bioavailability, distribution of As species, agricultural conditions and rice processing methods, could influence As concentrations in rice grains (Amaral et al, 2013;Naito et al, 2015;Wang et al, 2015). Therefore, large coefficients of variation were observed in As(V), MMA and DMA, which indicated wide variation of As concentrations in rice samples.…”

“…Furthermore, As content and species in rice also vary extensively with agricultural conditions and rice processing methods (Halder et al, 2014;Naito et al, 2015;Wang et al, 2015). For instance, As in intermittently flooded conditions was decreased by 41% in rice grains compared to the continuous flooded plots (Somenahally et al, 2011).…”

Advances in research on the use of biochar in soil for remediation: a review

“…This observation was made by Pan et al (2015) and Yokoyama et al (2012) who noticed that the ratio of the coefficients of distribution of As(III) and As(V) on calcite (KAs(V)/KAs(III)) at neutral pH was larger than 2100. Wang et al (2015b) also had similar observations but added that the relatively easy removal of As(V) from the environment is also attributable to its higher mobility.…”