Recent reports have indicated that rice when grown under anaerobic flooded field conditions can accumulate high levels of grain arsenic (As). This is a public health concern due to the high daily consumption of rice by some populations. The As-based herbicide (monosodium methanearsonate, MSMA) has been used in USA rice breeding program to select for resistance to straighthead, a physiological disorder that results in reduced grain yields. We conducted this study to determine if there is a potential linkage between straighthead resistance and high grain-As concentrations in US-produced rice. We selected 41 cultivars from 10 countries, 28 resistant and 13 susceptible to straighthead, and conducted field evaluations in native soil with No MSMA and in soil amended with MSMA over three years. The total grain As (TGAs) in polished (white) rice was determined using inductively-coupled-plasma mass-spectroscopy (ICP-MS), and As species of organic dimethylarsinic acid (DMA) and inorganic arsenite (iAsIII) were determined using HPLC-ICP-MS. Our results demonstrate that under MSMA soil amended conditions that induced straighthead, i) the grain yield of resistant cultivars was 291% of that of susceptible ones; ii) the TGAs of the resistant cultivars was 83.5% of that of the susceptible ones; iii) the DMAsV
of resistant cultivars was 75.1% of that of susceptible ones; and iv) the iAsIII
of resistant cultivars was 80.0% of that of susceptible cultivars. However, in the No MSMA soil, there was no straighthead and no difference in grain yield, TGAs and DMA between the resistant and susceptible cultivars. Thus, selecting for straighthead resistance may be helpful in limiting grain As in rice. Our results show that DMA accounted for 78.8% and 52.4% of TGAs in the MSMA and No MSMA soils, respectively. iAsIII
accounted for 8.8% and 27.4% of TGAs in the MSMA and No MSMA soils, respectively. DMA was more variable than iAsIII
in responding to environment and genotype. Further, our results concur with other studies that have found the majority of arsenic in US produced rice, whether grown on MSMA amended or native soils, exists as the less-toxic organic species in contrast to rice produced in many other parts of the world.