Agronomics Management for Arsenic Stress Mitigation

Arsenic (As) accumulation in rice is considered as a new recognized disaster in Southeast Asia regions like Vietnam, Bangladesh, China, etc., where rice is considered as staple food. Rice cultivation required a huge volume of water for irrigation purposes. In Bangladesh and West Bengal, India, rice cultivation is mostly dependent on shallow contaminated groundwater tube well. Rice accumulates more As compared to other plants because they are grown mostly in flooded/anaerobic conditions. Rice accumulates As from the contaminated soil and also from the groundwater used for irrigation purpose. Exposure of high concentration of As through ingestion (mainly drinking water and eating contaminated rice) for long time span may affect the human health including cancers, melanosis, hyperkeratosis, lung disease, peripheral vascular disease, hypertension, and heart diseases. About one-third of the population of these regions is affected and suffers from various diseases. Widespread use of groundwater for irrigation suggests that ingestion of crops so produced could be a major source of As poisoning. Arsenic uptake by the rice plants via root tissues enters into plant body and edible parts (grains). Previous findings had reported rice grain samples with As accumulation much higher than the permissible limit (1 ppm) recommended by WHO. Arsenic uptake by rice plants depends on the plant species, physiochemical properties of the soil, redox conditions, and fertilization methods. Increase in concentration of phosphate in the soil through fertilization or by any other method could result in lower arsenate uptake by the plants because phosphate and As compete for the same transport protein (OS PHF1), and this results in competitive inhibition. Similarly, the use of silicon fertilizers results in lower arsenite uptake by the plants. In agricultural fields, providing aerobic conditions at regular intervals, selection of As-resistant rice varieties, and adoption of proper mitigation measures can reduce the bioaccumulation of As in rice plants.