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Determination of lead, cadmium and chromium in the tissue of an economically important plant grown around a textile industry at Ibeshe, Ikorodu area of Lagos State, Nigeria.

Introduction

Pollution is correlated with the degree of industrialization and the intensity of chemical usage. Past and present industrial activities have often resulted in the pollution of underlying soils where these activities take place, either by leaching of water from landfills or direct discharge of industrial wastewater into soil [6]. These industrial wastewaters are produced mainly and in large quantities by textile industries [11], due to the nature of their operations, which require high volume of water that eventually results in high wastewater generation. The most common toxic soil pollutants include heavy metals and their compounds, organic chemicals, oils, tars and pesticides [20]. Soil pollution by heavy metals such as mercury, cadmium, chromium and lead are of great concern to public health [12]. The source of heavy metal in plant is the environment in which they grow and their growth medium (soil) from which heavy metals are then taken up by roots or foliage of plants [19]. Plants growing in polluted environment can accumulate heavy metals at high concentration causing serious risk to human health when consumed . Moreover, heavy metals are [4,23,6] dangerous because they tend to bioaccumulate in plants and animals thereby causing deleterious effects, bioconcentrate in the food chain or attack specific organs in the body [8].

Ingesting large amount of heavy metal like chromium, cadmium and lead can cause reduced litter size and weight, liver and kidney damage [7]. Cadmium can also accumulate in kidney where it damages filtering and causes excretion of essential proteins and sugar from the body [7]. In herbaceous plants, roots and leaves retain higher metal concentration of heavy metal than stems and fruits [19]. Therefore, there is need to know the concentration of heavy metals in crops particularly leafy vegetables which are consumed by humans. Over time, the soils within the vicinity of a textile industry in Ikorodu area of Lagos State in Nigeria have been used by residents for the cultivation of vegetables. This is probably due to the high volume of wastewater generated from the industry, which serves as a means of irrigation for their vegetable gardens. This is because the vegetable growers believe wastewaters from industries contain a lot of nutrients that can support and promote a high yield of vegetables. Talinum triangulare is an herbaceous perennial plant which is an all season vegetable and it is extensively grown in Nigeria. It serves as a nutritious source of food for both man and livestock because it contains vitamins A, C and mineral like calcium. Though it is consumed most times without consideration of its medicinal values, Talinum triangulare is medicinal and can be used for the treatment of diuretic and stomach problems [22] .

In this study, Talinum triangulare which is the dominant leafy vegetable in the gardens around the textile industry was used to determine the level of heavy metal pollution that might have been caused by the operations of the textile industry.

Materials and methods

The sampling was done around the surrounding of United Nigeria Textile PLC (UNT), which is located in Ibeshe town near Ikorodu, Lagos state. The textile industry occupies a large expanse of land in the vicinity while banks and residential houses occupy the neighboring land. The industry is located along a major express road. Very tall palm trees and vegetable gardens abound within the surrounding of this industry. The industry produces large amount of wastewater and this water flows through the soil to the surrounding gardens.

Description of sampling points

Three different points (A, B and C) 50 M around the textile industry were sampled for soil and plant while the fourth sampling point is located in a non-industrial area about 500 M away from the industry. The samples from this point served as control and the point was designated as D. A map of the different sampling points is shown in Figure 1.

Collection of plant and soil samples

Two soil and plant samples each were collected from points A, B, C and D. Plant samples were collected carefully using hand trowel to dig the soil around the plant and the plants were pulled out carefully, ensuring that no part of the root was lost. The different plant samples were kept in different polythene bags and properly labeled.

Soil samples were collected from the same point where the plant samples were uprooted. The soil samples were collected to a depth of 15cm using a soil auger. The soil samples were kept in polythene bags and labeled to avoid a mix-up of the different soil samples. The plant and soil samples were brought to the Environmental Biology laboratory and kept in the fridge prior to analysis for heavy metals.

Sample preparation

Each plant sample was separated into leaves, roots, and stems and then dried at 50[degrees]C for 8 hours using an oven. The dried plant samples were milled using a laboratory blender and kept for digestion. Unwanted materials such as stones, leaves and debris were removed from the soil samples by hand-picking. The soil sample was further broken down into finer particles using a laboratory mortar and pestle. The soil samples were dried for 8 hours at 80[degrees]C using an oven.

Sample digestion

Soil and plant samples were digested before analysis to reduce organic matter interference and allow for the conversion of the metal into a form that can be analyzed by the Atomic Absorption Spectrophotometer (AAS).

Plant sample digestion

Plant samples were digested following the method of Allen et al., 3g of the milled plant sample were weighed into a conical flask using a digital weighing balance. 3 ml of 60% hydrochloric acid and 10 ml of 70% nitric acid were added to the weighed milled plant sample. The conical flask was then placed on a laboratory hot plate for digestion until the white fume evolving from the conical flask turned brown. The digest was allowed to cool and then filtered through a Whatman's filter paper, leaving a whitish residue. The filtrate was then made up to 50 ml using distilled water and kept for further analysis.

[FIGURE 1 OMITTED]

Soil sample digestion

The same procedure for the digestion of plant sample was used according to the method of Allen et al.

Determination of Heavy Metals in the Digested Samples using Atomic Absorption Spectrometer (AAS)

The digested plant and soil sample were analyzed for lead (Pb), cadmium (Cd) and chromium (Cr) using Atomic Absorption Spectrometer (AAS).

The readings were taken from the equipment and the results were converted to actual concentration of metals in the samples using the equation;

Concentration [micro]g/g = Extract volume Calibration reading x--Sample weight

Where calibration reading is the value of the reading obtained from the AAS equipment Extract volume is the final volume of the digest used for spectrometric analysis

Sample weight refers to the weight of the sample used. After which the mean of the heavy metal concentrations in soils from the industrial and non-industrial sites were then calculated.

The Multiplication Coefficient (MC) or Bioconcentration Fa ctor (BCF) according to Joonki et al, was also calculated using the equation:

Concentration of R ([micro]g/g)/ Concentration in S ([micro]g/g)

Where concentration of heavy metal in R is the concentration of heavy metal in the roots and concentration of heavy metal in S is the concentration of heavy metal in soil.

Determination of Soil pH

The soil pH was determined following the method of Eckerts and Sims. The soil samples were first air-dried and 5 g of the air-dried soil was mixed with 5 ml of distilled water and stirred. The mixture was allowed to stand for thirty minutes to allow it to settle. The slurry was decanted into a test tube.

The electrode of a pH meter was put into the slurry and the pH read off.

Results and discussion

Results

The results of the chemical analysis of lead (Pb), cadmium (Cd), and chromium (Cr) in soil and plant samples collected are presented in Table 1. The pH of soils from both industrial (5.92[+ or -]0.02) and non-industrial (6.02[+ or -]0.01) areas are slightly acidic. The concentrations of lead, cadmium and chromium are higher in soil samples obtained from the textile industry area when compared with those obtained from the non-industrial area. Lead and cadmium concentrations of the soil from the industrial area were significantly higher than those of the non-industrial area (Table 1). But generally the concentrations of the three heavy metals are low as it has been previously reported for soils in Nigeria [3,4]. Table 2 shows the concentrations of the heavy metals in the tissue of the plant. The concentrations of the heavy metals in the plant tissue were higher in the industrial area than the non-industrial area however chromium was not detected in the tissue of plants from non-industrial area. The concentrations of the three heavy metals in plant tissues from the industrial area were also higher than from non-industrial area at P<0.05 (Table 2). Table 3 shows the rate at which the roots of T. triangulare bi-accumulates these heavy metals as shown by the Multiplication Coefficient (MC) or Bio-concentration Factor (BCF). The soils of both industrial and non-industrial areas have more of the heavy metals than the roots of the vegetable except for cadmium concentration in the roots of vegetables from the industrial area. The MC or BCF for Pb and Cr in both study areas are less than one, while that for Cd in the industrial area is greater than one, with MC or BCF value of Cd from the industrial area being the highest. Generally, these MC/BCF values are low because of low levels of the heavy metals in the roots (Table 3).

Discussion

The concentration of Pb, Cd and Cr in the soil was higher in soil samples from the industrial site compared with the non-industrial site. There is no doubt that heavy metals are present in soil naturally and non-degradable, and can be accumulated in the plant tissues [3,17] as shown by the concentrations of heavy metals obtained in soils from non-industrial site, but their concentrations can be increased by industrial activities [20]. In this case, chemicals such as dyes and other finishes used on the fabrics can lead to an increase in the concentration of heavy metals in the soils. This is similar to the observation of Abdulkaaheem and Singh [1] in which heavy metals like Cd, Cr, Cu, Pb and Zn in soil and plants samples around tannery and textile industries decreased as the distance from point of effluent diacharge increased. Fakayode and Onianwa [10] made similar observation noting that plant and soil samples from industrial sites contain more heavy metals than those from non-industrial sites. Moreover, direct and indirect discharges of industrial effluents, dumping of metallic products and atmospheric deposit can lead to high levels of heavy metals in soils and water bodies [2]. The high levels of heavy metals in the shoots of T. triangulare obtained in this study are similar to those observed by Akinola and Njoku [4]. This observation calls for caution because it is the shoot portion of this popular pot herb that is consumed by the people. Heavy metals are known to be biomagnified in the tissues of the consumers along the foodchain. Moreover, the short foodchain between plant and man as an herbivore makes the efficiency of transfer from plant to man very high [18]. Hence the level of heavy metals in man can easily increase. It is opined that cultivation of vegetables around industrial areas should be minimized and discouraged as much as possible. This is because of its implication to human health. For instance, lead has been found to be toxic to the red blood cell, kidney, nervous and reproductive systems [21]. Excess of cadmium has been reported to cause renal tubular dysfunction accompanied by osteomalacia (bone softening) and other complications which can lead to death [14]. Although the levels of the heavy metals in the tissue of T. triangulare in this study were less than the values recommended as the minimum intake values. However, continuous consumption of the vegetable from this site is not advisable. The quantity of the vegetable which is usually consumed is a lot more than the small quantity which is used for analysis of heavy metal concentrations. This implies that the heavy metal levels can be more in the quantity of the vegetable consumed. Furthermore, heavy metals are known to bio-accumulate in the tissue of organisms at higher trophic levels, so continuous consumption of the vegetable may lead to increase in the levels in humans. It has been noted that more heavy metals are absorbed by plants when pH is as low as 2-3 [9]. So the pH of near neutral recorded for the soils could be the cause of low uptake of Pb and Cr by the vegetable [15] thereby leaving a higher concentration of the two heavy metals in the soil than the concentration in the root. A high pH value has been found to cause immobilization of heavy metals in the soil[16]. This can further explain the low concentrations of these metals in the roots of the crops. But these concentrations become magnified as they move up from the roots to the shoot portion of the crops. This also explains the generally low magnification coefficients/bioconcentration factors (MC/BCF) recorded in this study.

Reference

[1.] Abdulkaheem, M.D. and B.R. Singh, 1999. Heavy metal concentration of soil and vegetation in the vicinity of industries in Bangladesh. Water, Air, and Soil pollution, 115(1-4): 347-361.

[2.] Ademoroti, C.M.A., 1996. Environmental Chemistry and Toxicology. Foludex press, Ibadan., pp: 215.

[3.] Adeyeye, E.I., 2005. Trace metals in soils and plants from Fadama farms in Ekiti state, Nigeria. Bulletin of Chemical Society of Ethiopia., 19: 23-24.

[4.] Akinola, M.O. and T.A. Ekiyoyo, 2006. Accumulation of lead, cadmium and chromium in some plants cultivated along the bank of river Ribila at Odo-nla area of Ikorodu, Lagos state, Nigeria. Journal of Environmental Biology., 27(3): 597-599.

[5.] Akinola, M.O. and K.L. Njoku, 2006. An assessment of heavy metal pollution on the cultivated mudflat of Abule-Ado flood plain in Amuwo-Odofin area of Lagos state, Nigeria. Journal of Science, Techno logy and Environment., 6(1-2): 88-95.

[6.] Alloway, B.J., 1990. Heavy Metal in Soils. 2nd ed. Glasglow Blackie and Son Publishers, England., pp: 339.

[7.] Blowes, D., 2002. Tracking hexavalent chromium in groundwater. Science., 295: 2024-2025. 8. Chatterjee, J. and F. Chatterjee, 2000. Phytotoxicity of Chromium, Cobalt and Copper in Cauliflower. Environmental Pollution., 109: 69-74.

[9.] Elliot, H.A., 1983. Adsorption behaviour of cadmium in response to soil surface charge. Soil Science., 136(5): 317-321.

[10.] Fakayode, S. and P. Onianwa, 2002. Heavy metal contamination of soil and bioaccumulation in guinea grass (Panicum maximum) around Ikeja industrial estate, Lagos, Nigeria. Journal of Environmental Geology, 43(1-2): 145-150.

[11.] Ghoreishi, S.M. and R. Haghighi, 2003. Chemical catalytic reaction and biological oxidation for treatment of nonbiodegradable textile effluent. Chemical Engineering Journal., 95: 163-169.

[12.] Goyer, R.A., 1996. Toxic and essential metal interaction. Annual Review of Nurition., 17: 37-50.

[13.] Lasat, M.M., 2002. Phytoextraction of toxic metals: A Review of Biological mechanisms. Journal Environment Quality., 31: 109-120.

[14.] Laws, E.A., 2000. Metals. In: "Aquatic pollution: An introductory text". pp: 369-429. John Wiley and Sons, Inc., New York.

[15.] Lee, S.Z., H.H. Yang, C.M. Chen and M.C. Liu, 1998. Absorption characteristics of lead onto soil. Journal of Hazardous Materials, 63: 37-49.

[16.] Massey, H.F., 1972. pH and soluble copper, nickel and zinc in Eastern Kentucky coalmine spoil materials. Soil Science, 144: 217-221.

[17.] Nriagu, J.O., 1990. Global metal pollution: Poisoning the biosphere. Environment ENVTAR., 32(9): 7-11,28-33.

[18.] Odum, E.P. and G.W. Barrett, 2005. Fundamentals of Ecology 5 edn. Thomson th Brooks/Cole, Belmount, USA, pp: 108-121.

[19.] Okonkwo, N.C., J.C. Igwe and E.C. Onwuchekwa, 2005. Risk and health implications of polluted soils for crop production. African Journal of Biotechnology., 4(13): 1521-1524.

[20.] Singh, B., 2001. Heavy metals in soils: Sources, Ch emi c al Re a c t i o n s an d Fo rm s in Geoenvironment. Proceedings of the 2 Australia and New Zealand conference on environment geotechniques. New Castle, New South Wales.

[21.] Taupeau, C., J. Poupson, F. Nome and B. Lefevre, 2001. Lead accumulation in the mouse ovary after treatment-induced follicular atresia. Reproductive Toxicology., 15(4): 385-391.

[22.] Ukpong, I.E. and J.O. Moses, 2001. Nutrient requirement for growth of Waterleaf (Talinum triangulare) in Uyo metropolis, Nigeria. The Environmentalist, 21: 153-159.

[23.] Vousta, D., A. Grimanins and C. Samara, 1996. Trace elements in vegetables grown in an industrial area in relation to soil and air particulate matter. Environmental Pollution, 94(3): 325-335.

Akinola, M.O., Njoku, K.L. and Ekeifo, B.E.

Environmental Biology, Laboratory, Department of Cell Biology & Genetics, University of Lagos, Akoka, Lagos, Nigeria.

Corresponding Author

Akinola, M. O., Environmental Biology, Laboratory, Department of Cell Biology & Genetics, University of Lagos, Akoka, Lagos, Nigeria Email: tundeakin5@yahoo.com
Table 1: Mean concentration of heavy metals Lead, Cadmium and
Chromium ([micro]g/g) in soil samples.

Sampling Points Soil pH Lead (Pb)

Textile industry area 5.92 [+ or -] 0.02 10.89 [+ or -] 4.69
Non-industrial area 6.02 [+ or -] 0.01 2.33 [+ or -] 0.01

Sampling Points Cadmium (Cd) Chromium (Cr)

Textile industry area 0.81 [+ or -] 0.01 12.50 [+ or -] 3.18
Non-industrial area 0.65 [+ or -] 0.08 12.48 [+ or -] 1.21

Table 2: Mean concentrations of heavy metals ([micro]g/g) in
tissues of T. triangulare.

Heavy Metal Plant Sampling Site
 tissues
 Industrial area Non-industrial area

Lead Root 0.71 [+ or -] 0.59 0.60 [+ or -] 0.25
 Stem 0.23 [+ or -] 0.19 0.16 [+ or -] 0.01
 Leave 0.86 [+ or -] 0.68 0.74 [+ or -] 0.56

Cadmium Root 1.22 [+ or -] 0.32 0.63 [+ or -] 0.05
 Stem 1.21 [+ or -] 0.40 0.73 [+ or -] 0.05
 Leave 1.25 [+ or -] 0.37 0.86 [+ or -] 0.06

Chromium Root 1.51 [+ or -] 0.37 ND
 Stem 2.78 [+ or -] 0.48 ND
 Leave 65.60 [+ or -] 39.74 1.21 [+ or -] 0.12

ND--Not Detected

Table 3: The concentration of heavy metals in soils in relation
to its concentrations in plant roots as shown by the
multiplication coefficient/bio-concentration factor (MC/BCF).

Sampling Site Lead Cadmium

Industrial area Root 0.71 [+ or -] 0.59 1.22 [+ or -] 0.32
 Soil 10.89 [+ or -] 4.69 0.81 [+ or -] 0.01
 MC/BCF 0.07 1.51

Non-industrial Root 0.60 [+ or -] 0.25 0.63 [+ or -] 0.05
 area Soil 2.33 [+ or -] 0.01 0.65 [+ or -] 0.08
 MC/BCF 0.26 0.97

Sampling Site Chromium

Industrial area 1.51 [+ or -] 0.37
 12.50 [+ or -] 3.18
 0.12

Non-industrial ND
 area 12.48 [+ or -] 1.21
 0

ND- Not Detected
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Title Annotation:Original Article
Author:Akinola, M.O.; Njoku, K.L.; Ekeifo, B.E.
Publication:Advances in Environmental Biology
Date:Jan 1, 2008
Words:3180
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