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Transfer of Arsenic from Groundwater and Paddy Soil to Rice (oryza Sativa L.) Grain:a Micro Level Study in Chandina, Comilla

Md. Habibur Rahman
Central Laboratory, Soil Resource Development Institute, Krishi Khamar Sarak, Dhaka-1215.

Md. Mohashin Farazi
Central Laboratory, Soil Resource Development Institute, Krishi Khamar Sarak, Dhaka-1215.

Kohinoor Begum
Dhamrai Government College, Dhaka.

Md. Serazul Islam
Chemist Agro-biotech Limited, Bangladesh.

Abstract/ Executive Summary:

Rice ( Oryza sativa L.) is one of the major food crops in many countries. As the cultivation of rice requires huge vol ume of water, long term use of Arsenic contaminated groundwater for irrigation may result in the increase of arsenic concentration in the agricultural soil and eventually accumulation in rice grains. A microlevel study was conducted to investigate the transfer of arsenic from irrigation water and soil to rice plants in the arsenic affected 8 unions of Chandina upazilla, Comilla district. The level of arsenic in irrigation water (0.12±0.08 and 0.67±0.07 mg l^{- 1} ) was much above the WHO permissible limit of 0.01 mg l^-1 for drinking water and FAO permissible limit of 0.10 mg l^-1 for irrigation water. The total soil arsenic concentrations ranged from 3.21±0.8 0 to 8.74±2.83 mg kg^-1 dry weight of soil, which was below the maximum acceptable limit for agricultural soil of 20.0 mg kg^-1 as recommended by the European Community. The accumulation of arsenic in the grain ranged from 0.12±0.04 to 0.58±0.06 mg kg^-1 in B oro and 0.16±0.04 to 1.06±0.20 mg kg^-1 in T. Aman. Except grain sample (T. Aman) of one union, the grains in both Boro and T. Aman of all unions did not exceed 1.0 mg kg^-1 dry weight of arsenic (the permissible limit of arsenic in rice according to WHO recommendation). Thus, till now rice has remained harmless for consumption in the study area. The results clearly showed that the arsenic content in the grains of Boro rice is correlated to the intensity of arsenic contamination of irrigation water and soil.

Keywords: Arsenic, Bioaccumulation, Groundwater, Rice, Irrigation water

Location: Mahichal, Gollai, Dollai Nawabpur, Madhaia, Joag, Borokorai, Maijkhar and Barera union in Chandina upazilla, Comilla district, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Arsenic

Objectives:

To understand the transfer of arsenic from irrigation water and paddy soil to the rice plant.

Methodology:

The present study conducted in the area where the level of Arsenic in ground water exceeded WHO permissible limit (0.01 mg l^-1) for drinking water and FAO permissible limit for irrigation water (0.10 mg l^-1). Thirty eight samples were collected from the eight unions of this upazilla namely Mahichal, Gollai, Dollai Nawabpur, Madhaia Joag, Borokorai, Maijkhar and Barera. Irrigation water samples were collected from the shallow and deep shallow tube well pumps which were used for irrigation in the study area. Prior to sample collection, the pumps were kept running for about 10-15 minutes in order to get a uniform rate of discharging water. Then the water samples were collected in the plastic bottles and preserved with 6 N HCl. Soil and rice samples were collected from the fields irrigated with the arsenic contaminated water and transferred to airtight polythene bags. Soil samples were also collected from 10-15 cm depth in using GPS reading. Rice grain samples were collected in the same position from where soil samples were collected during harvesting time both in Boro and Aman seasons. The irrigation water samples were filtered using Whatman Filter Paper No.42 and were kept inplastic bottle for analysis. The soil samples after collection were immediately dried. The dried soil samples were then grinded and passed through 2.0 mm pore sized sieve to get homogenized representative powder sample. Finally the samples were stored in airtight polyethylene bags at room temperature. The rice grain samples were dried in the Hot Air Oven at 60⁰C for 72 hours and were stored in airtight polyethylene bags at room temperature. Proper care was taken at each step to minimize any sort of contamination. Soil samples and grain portions of the rice samples were digested separately following heating block digestion procedure . About 1.0 gm soil sample and 2.0 gm rice grain sample were taken into clean dry digestion tubes and 10ml of concentrated HNO₃ was added to it. The mixture was allowed to stand overnight under fume hood. In the following day, the digestion tubes were placed on heating block and heated at 60⁰C for 2 hours. The tubes were then allowed to cool down at room temperature. About 5 ml of concentrated HClO₄ was added to the samples. Then the tubes were heated at 160⁰C for about 4-5 hours. The heating was stopped when the dense white fume of HClO₄ was emitted. The content was then cooled, diluted to 50 ml with de-ionized water filtered through Whatman No. 42 filter papers and finally stored in plastic bottles. Prior to sample digestion all glass goods were washed with 2% HNO₃ followed by rinsing with deionized water and drying. Total arsenic of the digested soil, rice grain and irrigation water samples were analyzed by flow injection hydride generation ICP-OES using external calibration through arsenate as standard. The optimum HCl concentration was 6 N and 3% NaBH₄ produced the maximum sensitivity. Pearson’s correlation coefficient (r) was carried out to find out the correlation among arsenic concentrations in irrigation water, irrigated field soil and rice grains (Boro and T. Aman) by SPSS software.

Source of Information: The Agriculturists 12(2): 74-82(2014) ISSN 2304-7321 (Online), ISSN 1729-5211 (Print), A Scientific Journal of Krishi Foundation

Article Link (Online Journal): http://banglajol.info/index.php/AGRIC/article/view/21734/14940

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The level of arsenic in irrigation water in the study area was very much above the WHO permissible limit of 0.01 mg l^-1 for drinking water and FAO permissible limit of 0.10 mg l^-1 for irrigation water. Soil gets contaminated with arsenic due to the irrigation with the arsenic contaminated water. Although it is got clear that the arsenic is transferred from irrigation water and paddy soil to grain of the rice plant with different pattern of distribution, the results suggest that irrigation with groundwater enriched in arsenic affects the rice grain quite limitedly. Except one, all of the studied samples the concentration of arsenic in rice grain exceeds the permissible limit of 1.0 mg kg^-1 dry weight (WHO recommendation). There may be a number of options for reducing inflow of arsenic in rice fields. The concentration of As in STW water decreases with increasing well depth therefore, pumping irrigation water from the greater depth might lead to decrease in the arsenic load to the rice fields. Another option is the economic use of irrigation water by reducing the depth of ponded water by alternate wetting/ drying practice for Boro rice cultivation.

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