Response of Rice Genotypes to Arsenic Contaminated Field Condition during Kharif and Boro Season

Arsenic is a naturally occurring toxic metalloid and widely distributed in the soil, water, air and all living matters. Anthropogenic activities, including metal smelting, coal combustion, dyes, and hide tanning wastes, chemical weapons and arsenic pesticides have contributed to elevated arsenic in the environment. Large areas of Bangladesh, West Bengal, northwest China and Vietnam have to rely on arsenic-contaminated ground-water for irrigation of staple crops such as rice (Berg et al. 2001, Abedin et al. 2002) and the extensive use of arsenic contaminated groundwater for crop irrigation in the arsenic affected areas as the cause of arsenic poisoning, and possibility of a build-up of arsenic in soils and agronomic and/or horticultural produce, that acts as a conduit for the passage of the toxicant to human population via food-web. Out of the twenty countries in different parts of the world where ground water arsenic contamination and human suffering from there have been reported so far, the magnitude is considered to be the highest in Bangladesh, followed by West Bengal, India. The wide spread arsenic contamination in groundwater in different parts of West Bengal, distributed over 111 blocks, located primarily in twelve districts in West Bengal. The distribution pattern of arsenic among various plant parts is highly variable. Excessive pumping of ground water has increased arsenic toxicity in West Bengal, Bangladesh and many other Asian countries. The arsenic concentration tends to build up from the contaminated groundwater, via the soil, to the crop, irrigated with such water. Adak and Mandal (2000) stated that among the plant parts, arsenic concentration was higher in roots, followed by stems and leaves, in that order, while the economic or edible parts recorded the lowest concentration of the toxin. Phosphorus (P) is one of the essential major plant nutrients for plant growth. Because As and P are both placed in group Vb, the interaction of As and P in soil-plant system is an important issue in respect of arsenic mobilization. Several workers showed that the presence of phosphate caused a reduction in arsenate adsorption, and that the reduction was much greater for the competitive effects of arsenate on phosphate adsorption by soil minerals, although a large variation in the degree of competition between these two oxyanions has also been reported (Kuo and McNeal, 1984; Mukhopadhyay and Sanyal, 2002). Inorganic arsenic is highly toxic to plants because it uncouples phosphorylation and inhibits phosphate uptake. Arsenate is taken up by plants via the phosphate (Pi) transport systems because of similarity between arsenate and Pi and after entering plant; arsenate might interfere the phosphate metabolisms and caused toxicity of plant (Dixon, 1997) In the above circumstances the present study was undertaken to see the concentration of arsenic in different parts and genotypes of rice and the relationship between arsenic in different parts and grain phosphorus.