Arsenic speciation in rice grain grown in microwave and biochar treated soil

Abstract

Since the toxicity of arsenic (As) depends on its forms, it is necessary to determine the As species to evaluate the associated risk. Therefore, in this study, the As speciation of rice grain samples was performed. Arsenic contaminated (0, 20, 40, 60, and 80 mg kg–1) soils were treated with microwave (MW) and biochar (BC) with MW irradiation for 0, 3 and 6 minutes and BC application of 0, 10, 20 t ha–1 as As alleviation techniques where soil could remain contaminated but result in less accumulation in the grain. Atomic Fluorescence Spectrometry (AFS) and High-Performance Liquid Chromatography coupled with Inductively Coupled Plasma Mass Spectrometry (HPLC-ICP-MS) techniques were used for the determination of total As and As species identification respectively. With increasing soil As concentration both the inorganic As [as arsenite; As(III)] and organic As (as dimethylarsinic acid; DMA) concentration in rice grains increased significantly. However, rice grain As(III) and DMA concentrations were up to 73.74 % lower in MW treatments (MW-3 and MW-6) compared to the untreated control (MW-0). In rice grain samples, As was present mainly as DMA (70.6 %) and the remainder was As(III), accounting for 29.4 % of the total As. In the case of BC treatments, compared to the untreated control (BC-0), rice grain As(III) rose in the BC treatments (BC-10 and BC-20). While, DMA concentration decreased in the BC-10 treatment, compared with the control (BC-0), it increased again at BC-20. Thus, MW could be a novel technique for plant As toxicity alleviation however, more detail investigation needed considering MW and BC effect on the different soil’s rhizosphere system in different variety of rice.