Arsenic Fate and Transport in the Groundwater-Soil-Plant System: An Understanding of Suitable Rice Paddy Cultivation in Arsenic Enriched Areas

A. Mukherjee Department of Geology & Geophysics, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India Abstract Irrigation with arsenic (As)-rich groundwater in agricultural soil is one of the major causes for As contamination in rice. This can be observed in Bangladesh where the highest levels of As were reported in rice grains. However, As risk assessment in rice based on the As contaminated groundwater and soil can be misleading, since As accumulation in plant is controlled by a number of factors in the soil–rhizosphere system. In this chapter, we have discussed the impact of As-rich groundwater on rice cultivation, and the major factors which control the fate of As in the soil–rhizosphere–plant system. Soil parameters such as pH, redox potential, and concentrations of phosphorous, sulfur, silica, and iron affect the availability of As in the soil–rhizosphere zone, thus, should be considered in the assessment of As toxicity for rice. Concentration of silica and phosphate compete with arsenite and arsenate respectively during uptake by plants. Environmental factor such as soil flooding condition is also one of the potential factors influencing arsenic accumulation in rice by increasing As mobility in the soil–rhizosphere. In biological factors, rice genotype, which controls the root aeration, is significant in affecting accumulation of As. Therefore, selection of suitable rice genotype besides growing rice in aerobic conditions would be important to minimize As accumulation in rice. The translocation of As from roots to above-ground parts is dependent on As speciation. Although, organic As is more readily translocated, its uptake is much lower compared to inorganic As; thus, inorganic As predominates in grains.