Research Modul

Dimethylarsenate in rice

Aya Bouallegue (03/2018-03/2018)

Support: Britta Planer-Friedrich

Background. The new European limit for rice only considers inorganic As to be toxic, while methylated arsenates are regarded as non-toxic and exempt from the limit. There is therefore great practical interest in understanding what determines the share of methylated versus inorganic As in the rice grain. It is known by now that the rice plant itself cannot methylate As. The methylated As is produced by microorganisms in the paddy soil and then taken up by the plant. However, while the percentage of methylated arsenates in the soil is rather low (very few %) compared to inorganic As, in the rice grain especially dimethylarsenate can be the dominant species with more than 80% in total As. There are reports that show that the higher the total As concentration in the grain, the higher the share of dimethylarsenate. It is currently unclear whether a high share of dimethylarsenate in the rice grain is really always directly linked to high total As concentrations and what could be the reasons for such a correlation.

This research module will first be a literature study, compiling information on the following questions:

1. Does % grain DMA increase with increasing total As in grain?
2. Does % grain DMA change (increase?) with sulfate application?
3. Does DMA occurrence in soil correlate with DMA percentage in grain?
4. What promotes DMA formation in pore water?
5. Is there evidence for DMA demethylation?
6. Which bacteria methylate As?