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Assessment of the Impact of Arsenic Containing Irrigation Water on Soil Contamination and Plant Uptake

M A Mazid Miah
Soil Science Division, Bangladesh Rice Research Institute, Gazipur 1701

Z U Ahmed
Soil Science Division, Bangladesh Rice Research Institute, Gazipur 1701

M S Rahman
Soil Science Division, Bangladesh Rice Research Institute, Gazipur 1701

H M Khaled
Soil Science Division, Bangladesh Rice Research Institute, Gazipur 1701

Abstract/ Executive Summary:

A study was conducted to assess the quality and impact of As contaminated irrigation water on agricultural soils and crop uptake and to know the spatial variability of As in soil, water and rice. One hundred and five shallow tube wells (STW) were selected in Tala thana of Satkhira district in southwestern Bangladesh during boro, 2003. As content in water, soil and plant parts were determi ned by hydride generation - atomic absorption spectrophotometer (HG AAS). The mean val ue of As in the irrigation water samples was 150 µg/L Water As content was weakly to moderatel y correlated with electrical conductivity (EC), P, K, Mg, Na and Mn content in water. The mean soil As content was 19.37 mg/kg. The concentration of As in soil was influenced by water-As, P, Na, Ca, Mg and Fe and soil organic carbon, clay, exchangeable K, Ca and Mg contents. The mean As concentration in rice grain was 0.328 mg/kg, which was much below the maximum permissible limit (I mg/kg). The contents of As in straw were several folds higher than in grain and increased with increasing As contents in water and soil. Contents of organic carbon, exchangeable Mg and silt in soil and Fe in water significantly influenced the uptake of As by rice. A well-developed spatial variability of As content in irrigation water, soil and rice grain was observed in the studied area resulting from differences in soil and land type.

Keywords: Impact, As contaminated water, Crops, Uptake

Location: Tala thana of Satkhira district

Start Date: 00-01-2003

End Date: 00-05-2003

Program Area: Crop-Soil-Water Management

Commodity: Contamination of soil

Objectives:

1. To assess the quality of As-contaminated irrigation water, its impact on soil contamination and plant uptake and to determine the spatial variability of water, soil and rice As concentration.

Methodology:

A total of 105 STWs were randomly selected from Tala thana of Satkhira district during Boro, 2003. The sampling points were distributed throughout the Tala thana representing all land types used for irrigated boro rice. All selected locations were geo referenced by a global positioning system (GPS). Water samples were collected through membrane fil ter (0.45 µm) 10-15 minutes after the starting of the selected shallow tube wells and were acidified with 0.2M HCI. Water pH, electrical conductivity (EC) and dissolved oxygen (DO) were determined and recorded on the spot wi th portable pH (Hanna Instru ments), EC and DO meters (YSI Instru ments) . The water samples were brought to laboratory and immediately analyzed for As, B, P, K, Ca, Mg, Na, Fe, Mn, A L Cu, Zn, Mo and Ni. Composite soil samples from the plough layer (0-15 cm) were collected from the STW sites at the harvest of rice. The samples were dried, crushed, sieved (0.5 mm) and preserved before analysis. Rice straw and grain samples were collected at the time of harvest. The samples were oven dried at 70°C and finely grou nd prior to analyses. Soil pH was measured in water at 1:2.5 ratio. Soil organic carbon (SOC) was determi ned by Walkley-Black wet oxidation method. Soil texture was determined by hydrometer method. Total As, P, Fe and Mn was determined after digestion in perchloric and nitric acid. Available As was extracted by sodium bi-carbonate and ammoni um oxalate. The concentration of As i n the digest, sodium bi-carbonate and oxalate extract and i n the irrigation water was determined by a flow-injection hydride generation atomic absorption spectrophotometer (Fl-HG-AAS) (Perkin-Elmer Analyst 100) after red uci ng the sample in potassium iodide and concentrated HCl . Hydride of As (AsH₃) was generated using sodium borohydride. Total and NaHC03-extractable P was determi ned by vanado-molybdate yellow colour method and molybdate-ascorbic acid blue colour method, respecti vely accordi ng to Olsen and Sommers. Total Fe and Mn in the acid digest were determi ned directly in AAS. Rice straw and grain samples were also digested by perchloric-nitric acid mi xture. The digest was analysed for the mentioned properties following the same methods used for soil. Oxalate extractable soil-Fe and -Mn were determi ned by extracting the soil in a mixture of 0.2 M ammoni um oxalate and 0.2 M oxalic acid. Statistical analysis was performed usi ng standard statistical software. To evaluate the spatial variability of the soil properties; semivariogram was prepared usig GS+ 5.3.2.

Source of Information: Bangladesh J. Sci. Res. 21 (1&2), 35-41, 2008 (December)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The arsenic (As) content in the agricultural soil is influenced by its content i n irrigation water. The content of As in rice straw is much higher than that in grain. Accumulation of A$ in rice grain was limited, and was much less than that of maxi mum permissible limit of 1 mg/kg . In As contaminated area, the presence of very high concentrations of As in rice straw may pose a potential health hazard to the cattle population because rice straw is used as cattle feed in Bangladesh. The As status in rice varies widely from place to place. This variation probably results from differences in As availability depending on soil and land types. Irrigation with high-As water increased the As content i n all plant parts including edible parts such as grains and straw. The implication is that, continuing high As water irrigation over a long time without taking any mitigation measure could increase phyto-availability of As in the soil to such a limit where As uptake by plants and accumulation in the edible parts could become human health hazard .

Knowledge Management: Journal