Heavy Metal Hyper-accumulation in Plants and Metal Distribution in Soil on Tannery and Dying Industries Polluted Area in Bangladesh

 

Mohammed Mahabubur Rahman ^1*, L Haoliang² , Y Chongling², Sirajul Hoque ³

(1 Department of Botany, Dhaka Imperial College, 28 Mirpur Road, Dhaka 1205, Bangladesh; 2 School of Life Sciences, Xiamen University, 361005, P.R.China, 3 Dr. Sirajul Hoque in Department of Soil water and Environment University of Dhaka )

(* author for correspondence. Email: t_mahabub@yahoo.com  Phone and Fax number: 88028016202)

Abstract

The unplanned discharge of all the by-products, garbage, pollutants and effluents from tannery, and dying industries are caused serious pollution problems in environment. A study was conducted to investigate the indigenous plant species which are well adopted to the polluted environment as effected by industrial effluents which can accumulate higher concentration of heavy metals of dying and tannery industries around Dhaka city in Bangladesh. The pollutants in both contaminated soils were also compared. The results showed that concentrations of Lead（Pb）and Cadmium (Cd）were ranged from 219.183-2.673 ppm and 1.343-0.316 ppm, respectively, in seven plants samples Enhydra fluctuans Lour, Ipomoea aquatica Forsk, Colocasia esculenta L., Spilanthes acmella L., Polygonum hydropiper L., Cyperus rotundus L., Echinochloa colonum L. Exceptionally high value of 219.18 ppm was found in Ipomoea aquatica. The Lead concentration in other plants species ranged between 26.07 and 36.61 ppm. Our results indicated that Ipomoea aquatica may be acted as a Pb hyper-accumulator.

The concentration of nutrients and heavy metals of N, K, S, P, Pb and Cd ranged from, 388.90-10032.00, 992.90-2642.10, 2797.00-9762.00, 18.60-932.50, 8.52-32.88 and 0.28-1.85 ppm in soil, respectively among the industrial sites. Polluted soil contained considerable higher amount of heavy metal in tannery than dying. There are no significant differences (P>0.05) of pollutants distribution between two sites.

Keywords: Dying; Hyper-accumulator; Ipomoea aquatica Forsk.; Metal Pollution, Tannery

1.      Introduction

The Industrial wastes and effluents are increased sharply in recent years in Bangladesh, and discharging of all by products, wastage and effluents on soil, canals, rivers and water course along the road sides caused serious environmental pollution. They pollute productive soils, natural water systems as well as ground water (Kashem and Singh; 1998). The industrial by product, wastes, effluents contain high level of heavy metals such as As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn (Larsen et al., 1975; Arora et al., 1985). High amount of Lead and Cadmium is very dangerous for human body, children, and plant also. Heavy metal tolerance is a relatively rare trait found only in a few highly adapted plant species. These plants are capable of growing especially at sites with normally or artificially elevated levels of heavy metals. Some plant species are not only tolerant to Zn, Cd and Ni but they are also able to accumulate these metals in the shoots. Significant progress in phytoremediation has been made with metals and radionuclides. This process involves rising of plants hydrophobically and transplanting them in to metal polluted waters where plants absorb and concentrate the metals in their roots and shoots. Most researchers believe that plants for phytoremediation should accumulate metals only in the roots several aquatic species have the ability to remove heavy metals from water, viz., water hyacinth (Eichhornia crassipes (Mast.) Solms) pennywort (Hydrocotyle umbellata L.) and duckweed (Lemna minor L.). The roots of Indian masters are effective in the removal of Cd, Cr, Cu, Ni, Pb and Zn and sunflower removes Pb, U, 137Cs and 90Sr from hydrophobically solutions. Hyperaccumulators accumulate appreciable quantities of metals in their tissue regardless of the concentration of metal in the soil, as long as the metal in question is present. The phytoextraction process involves the use of plants to facilitate the removal of the metal contaminants from a soil matrix. Several researchers have screened fast growing high-biomass-accumulating plants, including agronomic crops for their ability to tolerate and accumulate metals in their shoots. About 400 plants that hyperaccumulate metals are reported （Majeti and Helena, 2003）Some species can hyperaccumulate a particular metal. While some others can hyperaccumulate more than one metal. Plants that hyper-accumulate metals have tremendous potential for application in remediation of metals in the environment.

With these views in mind, the present work aim was to find out indigenous plant species which can accumulate higher concentration of heavy metals and for future cultivate for remediate the pollutants.

2. Methodology

2.1 Collection and Preparation of soil

Study sites are located at two main polluted areas of Dhaka districts, namely Tannery polluted area of Hazaribagh and Dye polluted area of Bamoil, Demra. Hazaribagh is at the western periphery of the city and Bamil Demra is 15 Km away from the city.

Five soil samples were collected from Hazaribagh tannery area. Five water samples were also collected from the watercourse of same area. The collection of samples was carried out at an interval of 0.25 Km, and no plant species were found to grow on the bank of watercourse. Consequently, it was not possible to collect plant species from this area. Soil samples were denoted symbols as TS₁, TS₂, TS₃, TS₄, TS₅ while for water samples TW₁, TW_2, TW_3, TW_4, TW₅ symbols are used.

Dye polluted area of Bamoil, Demra is highly polluted with dye stuffs. There are 5-10 textile dying factories present in this area. All the byproducts containing pollutants are discharged into a canal.

Five soil samples were collected from the bank of canal with an interval of 0.25km corresponding water samples were also collected from Dye polluted area of Bamoil, Demra.     

Plant samples were found to grow on the both sides of the canal. Soil samples were donated symbols as DS₁ , DS₂ , DS₃ , DS₄ , DS₅  while water samples were DW₁, DW₂, DW₃, DW₄, DW₅. Plant samples were marked as P₁(Enhydra fluctuans Lour), P₂ (Ipomoea aquatica Forsk), P₃ (Colocasia esculenta L.), P₄ (Spilanthes acmella L.), P₅(Polygonum hydropiper L.), P₆(Cyperus rotundus L.), P₇ (Echinochloa colonum L.) for laboratory analysis plant samples were taxonomically identified by prior to drying and grinding. All the samples were collected at the middle of the May 2005.

2.2 Processing of soils

Soil samples were dried in air and grind with a motor and pestle. Then soil samples were sieved with 1 mm sieve and before grain dying plants debris and other undesirable materials were removed by hand, then preserved in plastic bottles for chemical analysis.

2.3 Processing of Plant Samples

Plant species were dried at 80℃ for 24 h before grinding. Ground plant samples were preserved for chemical analysis.

2.4 Chemical Analysis

Electrical conductivity (EC) of the water samples and EC of the soil samples were determined from saturation extract by conductivity meter. Measurement of pH of the water and soil samples were done (soil and water ratio 1:25) were done with help of a glass electrode pH meter. Plant, water and soil samples were digested for the determination of total Nitrogen (N₂) following Kjeldahl’s method as described by Jackson (1973). For the determination of Sulfur (S), Potassium (K), Phosphorus (P), Chromium (Cr), Lead (Pb) and Cadmium (Cd). Plant samples were digested with Nitric Acid (HNO₃) – Perchloric Acid (HClO₄) mixture (2:1) in a closed system. Phosphorus contents of samples were determined by Vanadomolybdate yellow color method as described by Jackson. Sulfur contents of the samples were determined by the method of Hunt (1981).Potassium contents of the samples were determined by Flame photometer.  Lead and cadmium were determined by atomic absorption spectrophotometer.

2.5 Statistical Analysis

The results were statistically evaluated by T-test in SPSS 13.0 (SPSS Inc., Chicago,USA.) and Microsoft Excel software.

3. Results and Discussions

Soil pH values as affected by industrial effluents are presented in Table 1. It is revealed from the data that pH values did not show any definite trend in the variation with distance from the effluent sources. The values ranged from 6.67 to 7.55 in different sites along the watercourse of the Bamoil, Demra area as affected by the effluents of dyeing industries. In Rayer Bazar area under the influence of tannery industries, the pH values ranged between 7.30 and 7.94. Although the pH values of Hazaribagh area are slightly higher than those of Demra area, the two areas are mere or less identical. Similar results reported previously by Kashem and Singh (1998) in the same area.

The pH values of water samples varied between 6.81 and 8.17 in Demra area and between 7.17 and 7.30 in Hazaribagh area. Though variation existing in relation to distance from effluent sources in Demra area, there was no definite trend in the change of variation.

Table 1 Nutrient elements and Heavy metals concentration (For water parameter).

Sample no	pH	EC μs/cm	Total N ppm	K ppm	S ppm	P ppm	Pb ppm	Cd ppm
DW1	7.03	933	11.07	119.07	218.75	2.50	0.27	0.09
DW2	6.81	1788	10.96	109.96	984.35	13.12	0.22	0.03
DW3	8.17	1247	12.50	29.29	0992.12	6.25	0.15	0.06
DW4	7.19	1000	11.04	10.54	355.93	3.12	0.39	0.03
DW5	8.02	1017	10.39	18.42	515.62	4.75	0.20	0.43
TW1	7.17	160	11.52	13.69	226.30	1.75	0.63	0.05
TW2	7.18	114	11.35	11.47	725.00	1.87	0.65	0.06
TW3	7.17	105	14.30	10.34	734.3	2.25	0.58	0.05
TW4	7.30	96	13.20	10.22	375.00	3.00	0.67	0.06
TW5	7.25	1765	11.80	9.91	361.50	2.50	0.69	0.07

 

3.1 Electrical Conductivity (EC)

Electrical conductivity is a measure of the dissolved salts present in soil and water. The values of water EC varied in the range of 5.596 to 10.588 μs/cm in Bamiol, Demra area and from 0.956 to 10.588 μs/cm in Hazaribag area. Electrical conductivity values of saturation extract of soil varied between 1.780 and 4.228 μs/cm in Bamoil, Demra area and between 1.732 μs/cm to 7.330 μs/cm in Hazaribagh area. The EC values varied irregularly in relation to distance (Table 1) possibly because of the connection of different drainage systems originating from different sources to the main channel of watercourse.

3.2 Nutrient contents of the samples

Soil and water samples were analyzed for N, P, K and S which are essential for plant growth. Different kinds of plants were found to grow in Bamoli Dema area but along the watercourse of Hazaribagh area there was no plant growth at all. Total Nitrogen content of the water samples was more or less similar in both locations (Table 1). Soils from these areas however showed extreme variation in the total nitrogen contents of the soils. The nitrogen content varied between 388.90 and 2296.00 ppm in Bamoil, Demra area. On the other hand soils total nitrogen contents of soil samples varied between 418.90 and 10163.00 ppm in Hazaribagh area (Table 2). The higher contents of total nitrogen in soils are due to the accumulation of debris of leather under the influence of tannery industry.

Table 2 Nutrient elements and heavy metals concentration (For soil parameter).

Sample no	pH	EC μs/cm	Total N ppm	K ppm	S ppm	P ppm	Pb ppm	Cd ppm
DS1	7.46	705	1077.00	1790.70	7296.00	932.50	8.52	1.22
DS2	7.12	485	2296.00	1899.60	6620.00	736.80	23.53	1.85
DS3	7.30	705	755.00	992.90	4876.00	595.70	28.94	0.96
DS4	6.67	575	610.40	1853.60	4752.00	629.75	15.83	0.28
DS5	7.55	297	388.90	2642.10	3363.00	550.44	15.56	0.42
TS1	7.85	1222	4852.00	2369.00	4886.00	710.80	27.86	1.08
TS2	7.30	289	4834.80	2747.00	6448.00	919.00	32.88	1.38
TS3	7.55	1082	10163.00	1634.00	9762.00	18.60