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Retention of Irrigation Water Arsenic in Different Horizons of a Soil Profile

Apu Biswas
Bangladesh-Aushtralia Centre for Environmental Research, Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000

J C Joardar
Bangladesh-Aushtralia Centre for Environmental Research, Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000

A F M Manzurul Hoque
Bangladesh-Aushtralia Centre for Environmental Research, Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000

S M Imamul Huq
Bangladesh-Aushtralia Centre for Environmental Research, Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000

Abstract/ Executive Summary:

A field-cum-laboratory experiment was carried out to find the fate of arsenic applied through irrigation in a soil profile. The main objective of the experiment was to see whether portion of As applied through irrigation water is moved down to the ground water. From the field observations, it is clear that the irrigation water As leached down the soil profile which was evidenced from the presence of more As in the lower horizons of soil profile at the end of irrigation (after crop harvest). In the laboratory, soil monoliths of the same soil profile were irrigated with simulated irrigation water. Similar trend of As movement in the monoliths was noticed as for the field. The leachates draining out of the soil profile contained a fraction of added arsenic indicating a probable recharge of ground water with As from irrigation water.

Keywords: Irrigation water; Arsenic retention, Soil profile

Location: Faridpur Sadar Upazila, Faridpur, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Contamination

Objectives:

To see whether portion of As applied through irrigation water is moved down to the ground water.

Methodology:

A farmer's field at Doyarampur village under Gerda union of Faridpur Sadar Upazila was selected for sampling site. It is located in an area where As contaminated groundwater has been used for- irrigation. Characteristically, the soil belongs to Grey Calcareous Floodplain Soil and the soil series is Ishuardi. It is taxonomically referred to as Aerie Endoaquept. Samples were collected from specific geographic location (23°33.289' N; 89°54.638' E). The soil is poorly drained, flooded up to 0.61-0.91 m for about 3 to 4 months, remains unsaturated for about 7-8 months in the dry season. After opening up of the soil profile the individual horizons were delineated and soil samples from different horizons were collected periodically in three phases: irrigation, during irrigation and the end of irrigation. Three undisturbed soil monoliths (representative soil profile) were also collected at the time of first sampling in rectangular shaped mild steel boxes (100 cm x2S cm x 15 cm) and were carried to the laboratory to study the fate of As resulting from the movement of irrigation water As through the same profile. Soil and plant samples were collected at three pha ses. Shallow tube-well water (STW) that was used for irrigation was also collected three times. Procedures of sampling and preservation of samples were followed. Leachates were collected from the day of plantation to the day of harvest. Rice plants were harvested after 105 days of transplantation. After crop harvest, soil samples were collected from the different horizons of the soil monoliths. The collected soil samples from field and net-house experiment were air dried, and visible roots and debris were removed. The soil aggregates were ground to pass through a 0.5 mm sieve. Plant roots were washed with deionized water The rice plant was separated into root and straw. These samples were oven dried at 70°1 : 5°C for 48 hours and the dry weights were recorded. The dry plant samples were ground and sieved through a 0.2 mm sieve. Some routine analyses of the soils were done in the laboratory following the methods as described. Soil arsenic was extracted by digestion with aqua-regia (HCI : HN0₃, 3: I) whereas the plant arsenic was extracted by digestion with concentrated nitric acid (HN0₃). All the extracted soil , plant and water samples as well as the leachates from the soil monoliths were analyzed for total arsenic by hydride generation atomic absorption spectrometry (HG AAS). Certified reference materials were used through the digestion and analyzed as a part of the quality assurance/quality control protocol. Reagent blanks and internal standards were used where appropriate to ensure accuracy and precision of As analysis. Each batch of 10 samples was accompanied with reference standard samples to ensure strict QA/QC procedures. The experimental data were statistically analyzed by using the statistical software MINITAB 13.0.

Source of Information: Bangladesh J. Agric. and Environ. S. (2):53-61, December 2009

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The above observation indicates clearly that the percolation of As through the soil profile may provide a substantial pathway for the temporary loss of As by various adsorption processes. Adsorption is totally irreversible and desorption of As back into solution is a distinct possibility. Indeed, desorption of As from the solid phase of the soil could probably be considered a prerequisite for the long-term loss of As from soils by leaching. However, A s leaching is a complex process and the rates and amounts of As lost from soils by leaching depends on many factors. The potential for As leaching has been demonstrated in both field and laboratory studies. However, the issue relating to As build-up of soil through irrigation requires careful study .

Knowledge Management: Journal