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Spatial Variability of Arsenic in Soil and Rice in an Arsenic Contaminated Area of Bangladesh

MUHAMMAD SAJIDUR RAHMAN
Soil Science Division, Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh

MOHAMMAD ABDUL MAZID MIAH
Soil Science Division, Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh

ZIA UDDIN AHMED
Soil Science Division, Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh

HOSSAIN MOHAMMAD KHALED
Soil Science Division, Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh

GAZI HARUNUR RASHID
Department of Soil, Water & Environment, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

The spatial variability of arsenic (As) in soil and rice plants irrigated with As contaminated groundwater showed significant positive relation ships between soil As and rice straw and grain As. Most of the parameters exhibited strong spatial dependencies. The range of spatial dependence of the parameters varied from 24 to 135 m. Semivariogram of all of the parameters fitted best to spherical model. The kriged maps of the properties depicted different scales of spatial variability throughout the study area. The conspicuous differences found in the variability of the soil and plant As implied the effect of variable cultural and management practices on them.

Keywords: Arsenic contamination, Spatial variability, Rice soil

Location: Tala thana of Satkhira district

Start Date: 00-00-2003

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Arsenic

Objectives:

To characterize spatial variability of arsenic in soil and rice irrigated with As contaminated ground water from shallow tube-well (STW) and to detect autocorrelation among the soil and plant properties.

Methodology:

Experiments were carried out during the boro season, 2003 in Tala thana of Satkhira district of Bangladesh. A STW, that lifts As-contaminated. groundwater (250 µg As/L) for irrigation, was selected for the study. There were some slight depressions in the field away from the STW. The command area was grided by 20 m distance and the sampling points were geo-referenced by a GPS. Composite soil samples (0-15 cm) were collected from 59 locations before land preparation. Soil samples were air-dried, crushed, and sieved before analysis. Rice straw and grain samples were collected at the time of harvest and oven dried at 70°C for three days and finely ground prior to analyses. The soil samples were analyzed for pH (soil:water = 1 : 2.5), soil organic carbon (SOC) (wet oxidation method, NaHC0₃- extractable P, soil texture (hydrometer method). Total As, P, Fe and Mn both in soils and plants were determined after digestion with perchloric and nitric acids. Extractable As, Fe and Mn were determined after extracting the soil with buffered ammonium oxalate. The concentration of As in the digest, sodium bi-carbonate and oxalate extract and irrigation water was determined by a flow-injection hydride generation AAS ( FI-HG-AAS) (Perkin-Elmer AAnalyst 100) after reducing the sample with potassium iodide and concentrated HCl. Hydride of As (AsH₃) was generated using sodium borohydride. Statistical analysis was performed using standard statistical software. Semivariogram was prepared using geostatistical software GS + version 5.3.2 (Gamma Design Software, Michigan, USA) to evaluate the spatial variability of the soil properties . Maximum lag distance and lag interval for the semivariance calculation was determined iteratively to best fit the model having highest r² and lowest residual sum of squares (RSS) values.

Source of Information: Dhaka Univ. J. Biol. Sci. 14(1): 81-90, 2005 (January)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Rice straw and grain arsenic exhibited a good correlation with soil arsenic. The concentration of extractable As in soil is dependent on the concentrations of extractable Fe and Mn. Well-developed spatial variability was found in the distribution of soil and plant As in the contaminated irrigation command area. However, the concentration of As and other elements were not distributed in a pattern related to the source of As-contaminated ground water. The differences in spatial variability exhibited by the different soil and plant properties reflect the effect of management practices done by the farmers. Hence, different parts of a field may differ in their requirement of management practices. It is also clear from the high spatial variability of As in such a small field that the concentration of As in one location may not be well estimated by its concentration in the nearby locations.

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