Arsenic compounds in leaves and roots of radish grown in soil treated by arsenite, arsenate and dimethylarsinic acid†

The effect of arsenite [arsenic(III)], arsenate [arsenic(V)] and dimethylarsinic acid (DMA) on the growth of radish and the concentration of arsenic compounds in the roots and leaves of radish were investigated. Radish was grown in pots on Luvisols individually amended with arsenic concentrations of 20 mg kg -1 in the form of arsenic(III), arsenic(V), and DMA. In untreated soil, arsenate was the dominant arsenic compound; arsenite and DMA were also present. Arsenic(III) added to the soil was oxidized to arsenic(V), so that no differences between arsenic(III) and arsenic(V) soil treatments were observed. On DMA treatment, this compound remained in soil in high concentration in soluble and plant-available states, and the sum of arsenic(III), arsenic(V) and methylarsonic acid (MA) reached only 30% of water-extractable arsenic content. A low portion of soil arsenic added as DMA was immobilized, via adsorption, compared with inorganic compounds. Arsenic(III) was the dominant compound in radish roots planted in the untreated soil, whereas in leaves most of the arsenic present was arsenic(V). DMA was also detected in both plant tissues. A similar distribution of arsenic compounds was also found on arsenic(III) and arsenic(V) treatments. On DMA treatment, this compound showed high stability and the DMA concentration exceeded the sum of the remaining arsenic compounds [arsenic(III), arsenic(V) and MA] in both roots and leaves of radish.