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Arsenic Accumulation in Crops in Relation to Their Water Requirement

Sharmin Sultana
IMMM, BCSIR, Joypurhat, Bangladesh.

Md. Harunur Rashid
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000 Bangladesh.

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

Abstract/ Executive Summary:

A pot experiment was conducted to study the transfer of arsenic (As) from soil to plant and to know the relation between arsenic accumulation and water requirement. The plants BR-29, BR-28, Red amaranthus (Lalshak) and Ipomoea aquatica (Kalmishak) were selected for this experiment. The control pots were irrigated with tap water and the treatment pots were irrigated with arsenic contaminated water. Different plant parts such as roots, straw, leaf and seeds of rice and roots, shoots, leaves of Lalshak and Kalmishak were analyzed. It was found that arsenic concentration was higher in the plants that were irrigated with arsenic contaminated water. Maximum arsenic concentration was found in roots and the minimum in leaves. The arsenic accumulation depended on the type of crops and varieties. The present study revealed that arsenic accumulation is higher in those plants that have higher water requirement. BR-29 needs more water than BR-28 and as a result BR-29 accumulated more arsenic than BR-28. Similarly Ipomoea aquatica accumulated more arsenic than Red amaranthus. From the experiment it was concluded that if irrigation is continued with arsenic contaminated water for a long time, arsenic may enter into the food chain beyond permissible limit and may cause human health risk.

Keywords: Arsenic, Water requirement, Root zone, Arsenic uptake

Location: Department of Soil, Water and Environment, University of Dhaka.

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Groundwater, Contamination, Rice, Red amaranth

Objectives:

To study the transfer of arsenic (As) from soil to plant and to know the relation between arsenic accumulation and water requirement.

Methodology:

Soil samples were collected from a cultivated land with the geo reference of the sampling spot 23^o54.776`N and 90^o10.938`E. The soil thus selected belongs to the soil series-Dhamrai; general soil type-non-calcareous grey floodplain soil (GST No.6); USDA soil taxonomy -typic Endoaquepts mixed, Non-acid and FAO (UNESCO Legend)- Chromi -Eutric Gley sol. The bulk of soil samples representing 0-15 cm depth from the surface were collected by composite soil sampling method as suggested by the soil survey staff of the USDA (1951). The collected soil samples were processed for chemical analyzes. A pot experiment was carried out in the net house of the Department of Soil, Water and Environment, University of Dhaka. Water containing As (III) was used to irrigate the crops. The salt used for making the solution was sodium meta arsenite (NaAsO₂). The application rate was 1 ppm of arsenic. All experiments were done in triplicates. The pots were arranged in a systematic way in the net house. Two verities of rice seeds BR-28 and BR-29 were collected from the Bangladesh Rice Research Institute (BRRI). The variety of Red amaranthus seeds, namely BARI lalshak-1 was collected from the Bangladesh Agriculture Research Institute (BARI) and the variety of Kalmishak seeds Ipomoea aquatica were also collected from the same source. The background level of As in soil was 4.68 mg/kg. This was taken as control. There were a total of 6 pots for each crop. Thus a total of 24 pots were used for this experiment. Earthen pots of 5 liter sizes were taken having no holes on the bottom. Each pot was filled with 4 kg soils. The control pots were irrigated with tap water only. The treatment pots were irrigated with As contaminated water. The whole of phosphorus, potassium and nitrogen doses except for rice as estimated for the soil were mixed with the soil. The sources of N, P and K were urea, TSP and MP. Seeds of BR-28 and BR-29 were dipped in water and kept overnight and then sown in a seed bed for germination. When the seedlings became about 10 cm high, then these were sown directly in the pots. Six seedlings were sown in each pot. One-third of the required dose of urea was applied after 35 days and the final one-third was applied during panicle initiation stage of rice plant. Cultural operations were made whenever necessary. Weeds were removed manually. Agronomic characters like plant height, tiller numbers, panicle numbers, leaf color etc. were observed during the growth period. Seeds of BARI- Lalshak - 1 were dipped in water and kept overnight and then sown directly in the pots and allowed to germinate under the hood of net house. After germination, when the seedling started to appear, the pots were then taken into the selected place of net house. The population was thinned to 10 plants after the seedlings were established. The same method was applied to Kalmishak. In case of Kalmishak, thinning was made to 5 plants after seedlings were established. Cultural operations and agronomic characters were maintained as it was for rice. Plants of BR-28 and BR-29 were harvested by uprooting at the age of 120 and 130 days respectively. The harvested roots were washed with de-ionized distilled water three times to remove ion from the ion free space as well as to dislodge any adhering particles on the root surface. The upper parts of plants were also cleaned. The plant (rice) samples were separated into four parts: root, leaf, straw and grain. After taking fresh weight the collected plant samples were air dried and then oven dried at 70^oC for 48 hours and the dry weight of plant samples were noted. The dried plant samples were then ground and were sifted through a 0.2 mm sieve. The ground plant samples of the two varieties were preserved separately. After harvesting, soil samples in each pot were collected. The same harvesting and preserving methods were followed for Lalshak and Kalmishak. These plant samples were separated into 3 parts as root, shoot and leaf. The soil samples were analyzed in the laboratory for their physical, chemical and physicochemical properties following procedure as described. The arsenic from the plant samples was extracted with HNO₃ and from the soil (both pre- and post experiments) with aqua -regia solution. The As in the extract was estimated by Hydride Generation -Atomic absorption spectrophotometer (HG-AAS). For every 10 samples a certified reference material (CRM) was included to ensure QC. Statistical analysis of all collected data of the experiment was made by using commonly used statistical software Minitab14.2. The amount of As uptake (mg/100 plants) by different plant parts and the plant as a whole were calculated. The uptake was calculated using the As concentration in the dry matter and the dry weight of plant parts and the result was expressed as mg/100 plants: Uptake (As) = Concentration (As) in dry matter × dry weight of plant part.

Source of Information: Bangladesh J. Sci. Res. 28(2): 171-180, 2015 (December)

Article Link (Online Journal): http://dx.doi.org/10.3329/bjsr.v28i2.26789

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The present study revealed that arsenic accumulation is higher in those plants that have higher water requirement. BR-29 needs more water than BR-28 and as a result BR-29 accumulated more arsenic than BR-28. Similarly Ipomoea aquatica accumulated more arsenic than Red amaranthus. From the experiment it was concluded that if irrigation is continued with arsenic contaminated water for a long time, arsenic may enter into the food chain beyond permissible limit and may cause human health risk.

Knowledge Management: Journal