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Effects of Arsenic on the Mineral Nutrition of Rice Plant

I.JAHAN
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

S. M. ULLAH
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

S. HOQUE
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

T. K ULLAH
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

The response of rice (Oryza sativa L.) plants to different levels of arsenic (As) treatments was investigated. The accumulations of arsenic in rice plants and its effects on nutrient uptake (N, P, K, S, Ca, Fe and Zn) were also studied. Pot experiment was performed with seven levels of As (0, 10, 20, 30, 40, 50 and 60 mg/kg soil) to ascertain toxic levels and nutrient uptake in rice plants grown on silty clay loam soil. Arsenic was added as sodium arsenite (NaAs0₂) in soil. In rice plants, arsenic content increased with the increase in concentrations of arsenic in soil. In rice root, content of arsenic was higher than that of shoots. At the highest treatment. the concentrations of As were 6.20, 5.40 and 4.20 mg As/kg roots , shoots and grains, respectively showing that arsenic translocation from roots to shoots was restricted and roots were severely injured . It was observed that arsenic resulted in decreasing the uptake of most of the plant nutrients. An increasing effect of As was observed only with iron. Generally, arsenic toxicity symptoms started from 20 mg As/kg soil treatment in rice variety BR26.

Keywords: Toxicity, Arsenic, Mineral nutrition, Rice plant

Location:

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Rice

Objectives:

To investigate the toxic concentrations in soil and the effect of As on the mineral nutrition of rice plants.

Methodology:

Collection and preparation of soil : A pot experiment with silty clay loam soil of Chiatta series was carried out to assess the effects of arsenic on nutrient uptake and also to determine the toxicity limit of arsenic in rice plants. Uncontaminated soil sample was collected from Jhanjar in Gazipur district from a depth of 0-15 cm on the basis of composite sampling method. Soil samples were dried in the air after being transported to the laboratory. After air-drying, a portion of the larger and massive aggregates was broken by gentle crushing with a hammer. Dry roots, grasses and other particulate materials were discarded from the soil sample. A portion of the sample was passed through a 2.0 mm sieve for physical analysis, and for chemical analyses soils were ground as per requirement. The rest of the sample was processed for pot experiment. Six kilogram soil was taken in each 10 kg capacity earthen pot.Arsenic application : Arsenic was added in solution form to the pot as sodium arsenite at the rate of 0, 10, 20, 30, 40, 50 and 60 mg As/kg soil. Nitrogen, phosphorus, potassium, sulfur and zinc were applied at the rate of 110, 25, 60, 15 and 1kg/ha soil, respectively. A high yielding rice variety, BR26 was transplanted to soil to investigate the effect of arsenic on growth, yield, nutrient uptake and arsenic toxicity level in rice plant in kharif-1 season. The treatments were arranged in a completely randomized design with three replications for each treatment. Two seedligns of 30 days old and of uniform size were transplanted in a hill and the number of hills were two per pot.Collection of plant samples : Plant samples were collected at 45 days after transplantation ( DAT) and at maturity (M). The shoots and roots were collected separately. Shoots were harvested just above the soil surface level. Roots were collected carefully and washed thoroughly with distilled water to remove adhering soil particles. The shoots were also washed to remove dust particles. Plant samples were dried at 65°C for 72 hours, weighed, ground and were stored for chemical analyses. Plant analysis: Plant nitrogen (root and shoot) was determined by micro Kjeldahl's distillation method as described by Jackson.m After digestion with nitric acid : perchloric acid (5 : 1) mixture in a closed system, the total contents of P, K, S, Ca, Fe, Zn and As were determined in the plant samples. The total phosphorus of plant was determined after developing yellow colour with ammonium metavanadate as described by Jackson. Potassium was determined by Flame Photometer. Calcium, iron, zinc, and arsenic in the digest were determined by AAS. Sulphur was determined turbidimetrically. Statistical analysis : The experimental data were statistically evaluated. Analysis of variance (AVOVA) was done. The test of significance of different treatment means was computed by Duncan's Multiple Range Test (DMRT) at 5% level of significance.

Source of Information: Dhaka Univ. J. Biol. Sci. 12(2): 165-175, 2003 (July)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The results showed that arsenic had decreasing effects of N, P, S, K, Ca and Zn, while it had increasing effect on iron uptake into rice plants. Such effects were mainly evident from 30 mg As/kg soil. Arsenic contents in rice plants (roots, shoots and grains) increased with the increase in applied arsenic concentrations in soils. Roots accumulated more arsenic than shoots and grains accumulated the least amount of arsenic. Arsenic concentrations in shoots were beyond the permissible limits for animal food (> 2 mg As/kg) and above the permissible limits in grains for human consumption (> 1 mg As/kg grains).

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