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Influence of Waste Water Irrigation on Heavy Metal Accumulation in Soil & Plant

M. G. KIBRIA
Professor
Department of Soil Science, University of Chittagong, Chittagong 4331, Bangladesh

M. ISLAM
Assistant Professor
Department of Soil Science University of Chittagong

M. ALAMGIR
Associate Professor
Department of Soil Science University of Chittagong

Abstract/ Executive Summary:

Soil and plant samples were collected from sixteen wastewater irrigated sites belonging four locations namely Syedpara, Hazipara, Jungalpara and Nazirpara and from another four sites belonging the location namely Chalidatoli selected as control location. Mean total Cd, Pb, Zn, Cu, Mn and Fe content in 0-15 cm depth of the study area ranged between 0.08 to 2.39, 13.96 to 50.29, 14.73 to 21.12, 27.07 to 59.13, 116.25 to 326.63 and 1523 to 2798 mg kg-1, respectively. The metals content in 15-30 cm depth was in the ranges 0.01 to 1.98, 8.96 to 33.29, 51.44 to 267.31, 18.63 to 43.79, 68.89 to 271.74 and 1126 to 2054 mg kg-1, respectively. Total and 0.1 N HCl extractable Cd, Pb, Zn, Cu, Mn and Fe contents of soils were significantly higher in wastewater irrigated location than those in the control location. Total Cd, Pb, Zn and Cu contents of surface soil in waste water irrigated locations were above the normal ranges of these metals for soils. Concentration of Cd, Pb, Zn, Cu, Mn and Fe in different plants (plant parts of rice, radish and aurum) varied from 0.02 to 16.65, 0.08 to 35.55, 0.84 to 102.75, 0.86 to.32.67, 0.95 to 185.50 and 3.23 to 485.23 mg kg-1, respectively.

Keywords: Wastewater, Soil, Plant, Heavy metal.

Location: Chittagong University

Start Date: 01-11-2010

End Date: 31-12-2011

Program Area: Crop-Soil-Water Management

Commodity: Contamination

Objectives:

(1) to assess the extent of heavy metal contamination (Cd, Pb, Zn, Cu, Mn etc) in waste water irrigated soils in Chittagong,

(2) to investigate the uptake of heavy metals in crop plants in order to establish advice regarding consumption of rice and vegetables grown in soils contaminated by heavy metals,

(3) to know the availability of heavy metals to plants and their accumulation in the food chain and

(4) to observe the bioaccumulation coefficient of heavy metals from soil to crops.

Methodology:

The study area (220–23/ N and 910–53/ E) was situated at the northern part of the Chittagong City Corporation Area . For soil and plant sampling, sixteen wastewater irrigated sites were selected belonging four locations namely Syedpara, Hazipara, Jungalpara and Nazirpara (4 sites in each location) along the canal at regular intervals which covered fully the distribution of irrigation water sampling points while another four sites for sampling belonging the location namely Chalidatoli was selected as control location, 1 km away from canal and that was neither irrigated nor overflowed by wastewater. Soil samples were collected from two depths of 0-15 and 15-30 cm in each site. Plant samples of each species (rice, aurum, and radish) were collected from the corresponding sites in the respective growing seasons. Soil samples were air dried and ground to pass through a 2 mm sieve for determining the following physical and chemical properties (i) Particle size distribution and textural classes, (ii) pH (iii) Organic matter (iv) Cation exchange capacity (v) Total contents of Cd, Pb, Zn, Cu, Mn and Fe (vi)0.1 M HCl extractable Cd, Pb, Zn, Cu, Mn and Fe. Collected plant samples were cleaned with tap water and then with distilled water. The samples were air dried in a dust free room and then dried at 650 for 72 hours and ground in a stainless steel mill to pass through a 0.5 mm sieve. Particle size distribution (percentage of sand, silt and clay) was determined by hydrometer method (Day, 1965). Soil textural classes were determined by using Soil Textural Triangle of Marshal. Soil pH was measured by a glass electrode pH meter using soil –water suspension at the ratio of 1:2.5. The potassium dichromate wet-oxidation method of Jackson (1973) was used for the determination of organic carbon followed by multiplying the values with 1.724 to calculate the organic matter contents. The cation exchange capacity was determined by saturation with 1N NH4OAc at pH 7.0 (Jackson, 1973). Total nitrogen was determined by micro - Kjeldahl method as described by Jackson (1973). The soil samples were digested with aqua regia (Jackson, 1973) on a sand bath for the determination of total Cd, Pb, Zn, Cu, Mn and Fe. In order to determine the mobility of heavy metals in the soils, the extractable amounts of the metals were determined after extraction with 0.1 M HCl (Sabienë and Brazauskienë, 2004). All the heavy metals (total and extractable) were measured by atomic absorption spectrophotometer (Varian spectra AA-220). To determine the plant contents of heavy metals (Cd,Pb, Zn, Cu, Mn and Fe) wet oxidation of plant samples were made with tri acid mixture (HNO₃, HClO₃ and H₂SO₄at the ratio of 5:1:2). After wet oxidation, all the elements were measured by using the procedure as described for soil analysis. The one way analysis of variance (ANOVA) was done followed by DMRT to evaluate differences in soil properties and heavy metal contents among the locations and depths. Pearson’s correlation coefficient was also estimated to test the relationship among various soil properties, between metal contents in soils and soil properties and between metal contents in soils and plants.

Source of Information: International Journal of Applied and Natural Sciences (IJANS) Vol.1, Issue 1 Aug 2012 43-54

Article Link (Online Journal):

Funding Source:

1.	Budget: 72500.00
2. University Grant Commission	Budget: 72500.00

Total Budget (Tk.) : 72500.00

Achievement/Findings:

The results of this study indicate anthropogenic inputs of heavy metals in agricultural soils associated with discharge of city wastewater near the area of investigation around Chittagong Municipality. The concentrations of heavy metals in soils in the investigated areas are high; especially Cd is above the worldwide natural background concentration of surface soils. Potential transfer of metals from soil to plants may be an especially important issue in areas where agricultural production has been pushed onto marginal lands. The distribution of heavy metals in various parts of crops implies that it would be a high risk to human health if paddy rice were grown in soils heavily polluted with Cd since a large proportion of this metal accumulated in the edible parts. The results of the present investigation highlight the need for establishing soil quality standards for heavy metals to predict human induced soil pollution. For further information about other areas of the Chittagong Municipality, the investigation should be expanded in the near future to enlarge and improve the basis for proposing agricultural soil quality standards at national levels.

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