Spatial Distribution and Temporal Variability of Arsenic in Irrigated Rice Fields in Bangladesh. 1. Irrigation Water

Abstract

Around 38% of the area of Bangladesh is irrigated with groundwater to grow dry season crops, most importantly boro rice. Due to high As concentrations in many groundwaters, over 1000 tons of As are thus transferred to arable soils each year, creating a potential risk for future food production. We studied the reactions and changing speciation of As, Fe, P, and other elements in initially anoxic water during and after irrigation and the resulting spatial distribution of As input to paddy soils near Sreenagar (Munshiganj), 30 km south of Dhaka, in January and April 2005 and February 2006. The irrigation water had a constant concentration of 397 +/- 7 microg L(-1) As (approximately 84% As(III)), 11 +/- 0.1 mg L(-1) Fe, and 2 +/- 0.1 mg L(-1) P. During the fast flow along the longest irrigation channel (152 m) As, Fe, and P speciation changed, but total concentrations did not decrease significantly, indicating that As input to fields was independent of the length of the irrigation channels. In contrast, during slow water flow across the fields, As, Fe, and P concentrations decreased strongly with increasing distance from the water inlet, due to formation and settling of As- and P-bearing Fe aggregates and by adsorption to soil minerals. Total As concentrations in field water were approximately 3 times higher close to the inlet than in the opposite field corner shortly after irrigation, and decreased to below 35 microg L(-1) over the next 72 h. The laterally heterogeneous transfer of As, Fe, and P from irrigation waterto soil has important consequences for their distribution in irrigated fields and needs to be considered in sampling and in assessing the dynamics and mass balances of As fluxes among irrigation water, soil, and floodwater.

Evidence for the Root-Uptake of Arsenite at Lateral Root Junctions and Root Apices in Rice (Oryza sativa L.)

“…Briefly, rice (Oryza sativa L. cv. M206) was grown under flooded conditions in As-contaminated soil and irrigated with As-contaminated water at a ratio of 80% As(III) i and 20% As(V) i with total As concentrations of 4 µM, typical of paddy soil irrigated with moderately-contaminated groundwater [41]. Plants were grown to maturity in a controlled environment with 12 h light and dark cycles with maximum photosynthetic photon flux density of 600 µmol m −2 s −1 and temperatures ranging from 25 • C to 28 • C. At harvest, roots were removed from soil, washed gently with 18 MΩ·cm distilled deionized (DDI) water, and placed in an anoxic chamber to dry under anoxic conditions.…”

Mobilisation of arsenic in soils and in rice (Oryza sativa L.) plants affected by organic matter and zinc application in irrigation water contaminated with arsenic

“…A consistent increase in the concentration of arsenic due to submergence might result from varying intensity of reduction of arsenate to arsenite. Retention or mobility of As under varying redox conditions is based on the interaction of the aqueous phase with different mineral phases in the soil sediments (Bhattacharya et al 2002, Roberts et al 2007). The application of organic matter to the soil very frequently interacts with different inorganic pollutants including applied arsenic rendering the latter unavailable to plants.…”

Effects of water management on arsenic and cadmium speciation and accumulation in an upland rice cultivar

“…Cd is a highly toxic heavy metal which can readily accumulate in crops and thus lead to chronic toxicity diseases in livestock and humans. Contamination of agricultural soils by Cd and As has become an important issue as a result of industrial activities in the proximity of agricultural areas, excessive application of contaminated fertilizers, manures and sewage sludges, and irrigation with water contaminated with metal(loid)s (Roberts et al, 2007;Chen et al, 2008;Williams et al, 2009;Arao et al, 2010). Rice, the most important staple food in Asia, is considered to be a major source of Cd and As in the human diet in some parts of Japan, India and China (Tsukahara et al, 2003;Mondal and Polya, 2008;Liang et al, 2010).…”