Arsenic in paddy soils of Bangladesh: levels, distribution and contribution of irrigation and sediments

Arsenic is widely distributed in nature. It is associated with igneous and sedimentary rocks, particularly with sulphide ores. Natural phenomena such as weathering, biological activity, and volcanic activity, together with anthropogenic inputs, are responsible for the emission of arsenic into the atmosphere, where from it is distributed on the earth’s surface by rain and dry fall out. Bangladesh is currently facing the challenge of high arsenic concentration in shallow aquifers (Nickson et al., 1998). A large number of hand and shallow tube wells (STW) in some of the localities of 59 districts out of 64 districts have been identified to have arsenic (As) concentration above the Bangladesh standard of 0.05 As mg l 1 (Alam et al., 2002). To meet up the growing demand for food, the farmers had to cultivate high yielding varieties of Boro rice, which requires a large volume of irrigation water. Irrigation with arsenic contaminated groundwater to rice increases its concentration in soil (Jahiruddin et al., 2000; Meharg and Rahman, 2003; Ali et al., 2003), and eventually arsenic enters into food chains through crop uptake and poses long term risk to human health ((Duxbury et al., 2003; Islam et al. 2004a ) But detailed study on the levels and distribution of arsenic in irrigated paddy soils, and contribution of different sources of arsenic on build up of soil arsenic levels are still lacking in Bangladesh. This paper presents the levels and distribution and also quantifies the contribution of different sources of As on build up of As in paddy soils of five upazilas of Bangladesh.