Pak. J. Bot., 40(5): 2099-2106, 2008.
APPRAISAL OF HEAVY METAL CONTENTS IN DIFFERENT VEGETABLES GROWN IN THE VICINITY OF AN INDUSTRIAL AREA MUHAMMAD FAROOQ, FAROOQ ANWAR* AND UMER RASHID Department of Chemistry & Biochemistry, University of Agriculture, Faisalabad-38040, Pakistan Corresponding Author: E-mail.
[email protected] Abstract The contents of lead (Pb), copper (Cu), chromium (Cr), zinc (Zn) and cadmium (Cd) in various leafy vegetables viz., spinach, coriander, lettuce, radish, cabbage and cauliflower grown in an effluent irrigated fields in the vicinity of an industrial area of Faisalabad, Pakistan were assessed using atomic absorption spectrophotometer. The concentrations of Pb, Cu, Cr, Zn and Cd in the leaves, stems and roots of spinach, coriander, lettuce, radish, cabbage and cauliflower were found to be 1.1331−2.652, 1.313-2.161, 1.121-2.254; 0.252-0.923, 0.161-0.855, 0.221-0.931; 0.2170.546, 0.376-0.495, 0.338-0.511; 0.461-1.893, 0.361-0.874, 0.442-1.637; 0.033-0.073, 0.017-0.061, 0.011-0.052 mg kg-1 on dry matter basis, respectively. The contents of Cu, Zn, Cr, Pb and Cd were below the recommended maximum acceptable levels proposed by the Joint FAO/WHO Expert Committee on Food Additives. The leaves of spinach, cabbage, cauliflower, radish and coriander contained higher concentrations of Cu (0.923 mg kg-1), Cd (0.073 mg kg-1), Cr (0.546 mg kg-1), Zn (1.893 mg kg-1) and Pb (2.652 mg kg-1) as compared to other parts of each vegetable. High concentrations of heavy metals as analyzed in the present analysis of different parts of the vegetables might be related to their concentration in the soils irrigated with industrial waste water.
Introduction Wastewater irrigation is known to contribute significantly to the heavy metal contents of soils (Mapanda et al., 2005). Although problems occur in waterways when pollutants are leached out of the soil. If the plants die and decay, heavy metals taken into the plants are redistributed, so the soil is enriched with the pollutants. Uptake and accumulation of elements by plants may follow two different paths i.e., through the roots and foliar surface (Sawidis et al., 2001). The uptake of metals from the soil depends on different factors such as their soluble content in it, soil pH, plant growth stages types of species, fertilizers and soil (Sharma et al., 2006; Ismail, et al., 2005). Plant species have a variety of capacities in removing and accumulating heavy metals, so there are reports indicating that some species may accumulate specific heavy metals, causing a serious health risk to human health when plants based food stuff are consumed (Wenzel & Jackwer, 1999). Disposal of sewage water and industrial wastes is a great problem. Often it is drained to the agricultural lands where it is used for growing crops including vegetables. These sewage effluents are considered not only a rich source of organic matter and other nutrients but also they elevate the level of heavy metals like Fe, Mn, Cu, Zn, Pb, Cr, Ni, Cd and Co in receiving soils (Singh et al., 2004). As a result, it leads to contamination of the food chain, because vegetables absorb heavy metals from the soil polluted air and water. One important dietary uptake pathway could be through crops irrigated with
2100
MUHAMMAD FAROOQ ET AL.,
contaminated wastewater. Heavy metals are not easily biodegradable and consequently can be accumulated in human vital organs. This situation causes varying degrees of illness based on acute and chronic exposures (Demirezen & Ahmet, 2006). Vegetables are an important part of human’s diet. In addition to a potential source of important nutrients, vegetables constitute important functional food components by contributing protein, vitamins, iron and calcium which have marked health effects (Arai, 2002). Vegetables, especially those of leafy vegetables grown in heavy metals contaminated soils, accumulate higher amounts of metals than those grown in uncontaminated soils because of the fact that they absorb these metals through their leaves (Al Jassir et al., 2005). Demirezen & Ahmet (2006) investigated the concentrations of heavy metals such as Cd, lead (Pb), Zinc (Zn), Cu and Ni in different vegetables, grown in various parts of Turkey. The levels of heavy metals (lead, cadmium, copper and zinc) were examined in selected fruits and vegetables sold in the local markets of Egypt (Radwan & Salama, 2006). Fytianos et al., (2001) studied the contents of heavy metals in vegetables grown in an industrial area of North Greece. The present study was carried out around industrial areas of Faisalabad, Pakistan, where irrigation of vegetable crops with wastewater is a very common practice. Knowledge on the contamination of vegetables with heavy metals from industrial areas of Faisalabad is not yet established. Therefore the present study was undertaken with an aim to compare and investigate the concentration of heavy metals (cadmium, lead, zinc, copper and chromium) accumulation potential of the commonly grown leafy vegetables from sites having longterm use of industrial wastewater for irrigation of agricultural land. Materials and Methods Collection of samples: The samples of vegetables (spinach, coriander, lettuce, radish, cabbage and cauliflower) were randomly collected from effluent irrigated fields during 2006 in the vicinity of Sheikh Irfan Dying Industries Private Limited, Rehman Pura and ABC Road, Faisalabad, Pakistan. Leafy vegetables were preferred for sampling because previous researches indicate that they accumulate heavy metals at a greater capacity than other vegetables. The varieties of the vegetables collected were made sure. For this purpose, the samples of vegetables were further authenticated from the Department of Botany, University of Agriculture, Faisalabad, Pakistan. Pretreatment Washing of samples: The collected vegetable samples were washed with distilled water to remove dust particles. The samples were then cut to separate the roots, stems and leaves using a knife. Drying of samples: Different parts (roots, stems and leaves) of vegetables were air-dried and then placed in a dehydrator at 80 °C for 2-3 days and then dried in an oven at 100 °C. Grinding of samples: Dried samples of different parts of vegetables were ground into a fine powder (80 mesh) using a commercial blender (TSK- Westpoint, France) and stored in polyethylene bags, until used for acid digestion.
METAL CONTENTS IN VEGETABLES GROWN ON AN INDUSTRIAL AREA
2101
Heavy metal composition Preparation of samples / Wet digestion: Duplicate samples (0.5g) of each part (leaves, stems and roots) of each vegetable were weighed in digestion flasks and treated with 5 mL of concentrated HNO3. A blank sample was prepared applying 5 mL of HNO3 into empty digestion flask (Sahito et al., 2002). The flasks were heated for 2 hours on an electric hot plate (HP 220, UTEC Products Inc., Albany N.Y., USA) at 80-90oC and then the temperature was raised to 150oC at which the samples were made to boil. Concentrated HNO3 and 30% H2O2 were further added to the sample (3-5 mL of each was added occasionally) and digestion continued until a clean solution was obtained. After cooling, the solution was filtered with Whatman No. 42 filter paper and
