Differing effects of inorganic and organic arsenic on uptake and distribution of multi-elements in Rice grain

Arsenic (As) pollution can lead to an element imbalance in rice. A hydroponic study was carried out to examine the influence of inorganic (arsenate) and organic (dimethylarsinic acid (DMA)) arsenic compounds on the concentration and distribution of iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), nickel (Ni), carbon (C), nitrogen (N), and sulfur (S) in rice caryopsis at maturity using laser confocal microscopy and synchrotron X-ray fluorescence (SXRF). Results showed that treatments with inorganic (iAs) and organic (DMA) arsenic did not change the distribution characteristics of the above elements in rice grains. Fe, Mn, and iAs were mainly limited to the ventral ovular vascular trace, while Cu, Zn, and DMA extended into the endosperm. This implies that milling processes are likely to remove a majority of Fe, Mn, and iAs, but not Cu, Zn, and DMA. With regard to the average fluorescent intensity of the rice endosperm, iAs exposure caused significant reductions in Mn (53%), Fe (40%), Cu (27%), and Zn (74%) while DMA treatments decreased Mn (49%), Fe (37%), and Zn (21%). Compared with DMA, iAs exerted more influence on the reduction of these elements in rice caryopsis. In addition, the elemental analysis revealed a significant 12.7% increase for N and 8% reduction for S in DMA-treated rice caryopsis while a significant decrease of 24.0% for S in iAs-exposed rice caryopsis. These findings suggest that Cu, Zn, and S are more easily impacted by iAs, while N is mostly affected by DMA.