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Arsenic in Rice Grains at Sonargaon, Bangladesh

Abdul Aziz
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Shah Mohammad Ullah
Department of Soil Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh.

Md. Rafique Ullah
Department of Chemistry, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh.

Abstract/ Executive Summary:

Rice plants absorb substantial amount of arsenic when grown in rice field soil containing 3.21 mg/kg arsenic and irrigated with contaminated groundwater from a shallow tube-well having 476 ± 3 μg arsenic/l at Sonargaon, Bangladesh. It is revealed that highest total arsenic accumulation occurred in roots (5.790 ± 0.337 mg/kg) followed by shoots (3.766 ± 0.370 mg/kg) and brown-rice grains (2.552 ± 0.507 mg/kg). The concentration of total arsenic in rice grains was beyond permissible limit (1.00 mg/kg) for human consumption. At the time of harvest 4.90 ± 1.11 - 8.27 ± 1.35 mg As/kg soil remained in the rice field soil. However, majority of the soil arsenic is washed out by rain and flood water leaving more than 3.00 mg As/kg soil after flood period which along with high level of As contaminated groundwater for irrigation, elevated the level (up to 8.27 ± 1.35 mg As/kg soil) beyond permissible limit of e.g. in USA it is 5 mg/kg soils for agriculture use. To keep the environment clean, surface water for irrigation has been suggested.

Keywords: Rice, Arsenic, Heavy metal, Toxicity, Groundwater

Location: Sonargaon in Narayanganj district, Bangladesh

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Rice, Water management

Objectives:

To determine total As accumulation in rice grain grown in fields irrigated with arsenic contaminated groundwater.

Methodology:

High yielding boro-rice variety BR-28 was grown during lean period in a farmer’s field at village Sanmandi (23° 40´ 35? N, 90° 35´ 14? E), Nilkanda Union under P. S. Sonargaon in Narayanganj district, Bangladesh. The experiment was conducted in 19 × 19 m plots of five replicates arranged in a complete randomized block design. Recommended doses of NPK fertilizers at the rate of 45, 15 and 40 kg/ha, respectively were applied to all plots at the time of land preparation except N which was applied in two splits- 25 kg/ha at 15 DAT and 20 kg/ha before flowering. The boro-rice crop was irrigated once in a week with pond water (as control) and As contaminated (476 μg/l) groundwater from a STW. The soil textural class- silt clay, and contained 4.31% sand, 45.56% silt, 50.13% clay; having 6.35 pH, 200 μS/cm EC, 0.87% iron, 3.21 mg/kg arsenic, 1.85% organic matter, at Meghna Floodplain in Silmondi and Narailbag soil series. Soil particle size analysis was carried out by hydrometer method while organic carbon by wet oxidation method and soil pH from a solution of 1 : 2.5 of soil and water. Total As was determined by Atomic Absorption Spectrophotometer (AAS) after digestion with HNO₃- HCl at 5 : 1 in a closed system. Plant samples as roots, shoots and paddy grains were collected separately and dried at 70°C for three days, grounded and kept in poly-bags till analysis. Arsenic concentration in brown-rice grains was cross checked by Neutron Activation Analysis (NAA) using the 3 MW Research Reactor at Atomic Energy Research Establishment, Saver, Dhaka.

Source of Information: Bangladesh J. Bot. 44(1): 85-89, 2015 (March)

Article Link (Online Journal): http://www.banglajol.info/index.php/BJB/article/view/22728/15636

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The present study rice plants appeared not to absorb As (only insignificant amount by roots) at a concentration of (on an average) 2.50 mg As/kg soil or less. The presence of 3.21 mg/kg soil arsenic at the time of plantation of rice seedling compared to 8.27 ±1.35 at the time of harvest, indicates that during monsoon the rain and floodwater washed out the arsenic from the previous year’s rice-field soil to the surrounding environment. The total As in rice grains collected from an adjacent farmer’s field irrigated with the same groundwater was cross checked by NAA and was found to be 2.56 ± 0.20 mg/kg.

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