Heavy Metals in Edible Vegetables

The levels of four different heavy metals [cadmium (Cd), lead (Pb), chromium (Cr) and copper (Cu)] were determined in various vegetables [leek (Allium ampeloprasum), sweet basil (Ocimum basilicum), parsley (Petroselinum crispum), garden cress (Lepidium sativum) and tarragon (Artemisia dracunculus)] cultivated around Sanandaj City. The contributions of the vegetables to the daily intake of heavy metals from vegetables were investigated. One hundred samples (20 samples per month) were collected for five months. Atomic absorption spectrometry was used to determine the concentrations of these metals in the vegetables. The average concentrations of each heavy metal regardless of the kind of vegetable for Pb, Cu, Cr and Cd were 13.60 ± 2.27, 11.50 ± 2.16, 7.90 ± 1.05 and 0.31 ± 0.17 mg/kg, respectively. Based on the above concentrations and the information of National Nutrition and Food Research Institute of Iran, the dietary intake of Pb, Cu, Cr and Cd through vegetable consumption was estimated at 2.96, 2.50, 1.72 and 0.07 mg/day, respectively. It is concluded that the vegetables grown in this region are a health hazard for human consumption. a wide range of concentrations (Bahemuka and Mubofu, 1999). Metals, such as lead, chromium, cadmium and copper are cumulative poisons. These metals cause environmental hazards and are reported to be exceptionally toxic (Ellen et al, 1990). Contamination of vegetables with havey metal may be due to irrigation with contaminated water, the addition of fertilizers and metal-based pesticides, industrial emissions, transportation, the harvesting process, storage and/or at the point of sale. Human beings are encouraged to consume more vegetables and fruits, which are a good source of vitamins, minerals, fiber and are beneficial for health. However, these plants contain both essential and toxic metals over a wide range of concentrations. It is well known that plants take up metals by absorbing them from contaminated soil as well as from deposits on parts of the plants exposed to the air from polluted environments (Khairiah et al, 2004; Chojnacka et al, 2005). Publicity regarding the INTRODUCTION Food safety is a major public concern worldwide. During the last decades, the increasing demand for food safety has stimulated research regarding the risk associated with consumption of foodstuffs contaminated by pesticides, heavy metals and/or toxins (D’Mello, 2003). Vegetables constitute essential components of the diet, by contributing protein, vitamins, iron, calcium and other nutrients which are usually in short supply (Thompson and Kelly, 1990). Vegetables also act as buffering agents for acidic substances obtained during the digestion process. However, these plants may contain both essential and toxic elements, such as heavy metals, at SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH 336 Vol 39 No. 2 March 2008 high level of heavy metals in the environment has created apprehension and fear in the public as to the presence of heavy metal residues in their daily food. The public is confused and alarmed about their food safety. Keeping in mind the potential toxicity and persistent nature of heavy metals, and the frequent consumption of vegetables and fruits, it is necessary to analyze these food items to ensure the levels of these contaminants meet agreed internat ional requirements (Radwan and Salama, 2006). Lead and cadmium are among the most abundant heavy metals and are particularly toxic (Radwan and Salama, 2006). Excessive content of these metals in food is associated with a number of diseases, especially of the cardiovascular, renal, nervous and skeletal systmes (WHO, 1992, 1995; Steenland and Boffetta, 2000; Jarup, 2003). These heavy metals are also implicated in carcinogenesis, mutagenesis and teratogenesis (Radwan and Salama, 2006). Other metals, such as copper and zinc are essential for important biochemical and physiological functions and necessary for maintaining health throughout life (Prentice, 1993; ATSDR, 1994; Linder and Azam, 1996). The aim of this study was to determine the concentrations of heavy metals in selected edible vegetables grown in the main farmlands (along the banks of the Gheshlagh River) around Sanandaj City, and to estimate their contribution to the daily intake of the metals. MATERIALS AND METHODS Samples of the edible vegetables were randomly collected from the main farmlands around the city. The samples were collected from these growing areas over a period of five months during the cultivation season (MaySeptember) during the year 2005. A total of 100 samples of five vegetables [leek (Allium ampeloprasum ) , sweet basi l (Ocimum basi l icum ) , and pars ley (Petrosel inum crispum), garden cress (Lepidium sativum) and tarragon (Artemisia dracunculus)] were collected (four composite samples of each kind of vegetable during each month). All samples were collected and stored in polythene bags according to their type and brought to the laboratory for preparation and treatment. For lead, cadmium, chromium and copper analyses, vegetable samples were washed with distilled water to eliminate suspended particles. The leafy stalks were removed from all samples and these were sliced and dried on a sheet of paper to eliminate excess moisture. Once dried, each sample was weighed and oven-dried at 60oC to a constant weight. Each oven-dried sample was ground in a mortar until it could pass through a 60 mesh sieve. The samples were stored in clean, dry, high density polyethylene bottles of 100 ml capacity with screw caps. Bottles were prewashed with nitric acid, rinsed with de-ionized water, dried and tested for contamination by leaching with 5% nitric acid. The bottles contained no metal liners that could contaminate the samples. Samples were precisely weighed (2 grams each) and ground in a mortar followed by wet digestion with HNO3:HClO4 (2:1) in a conical flask for 2-3 hours on a sand bath. Some 10 ml of HCl was added. Digested samples were filtered with 0.45 μm pore size cel lu lose nitrate membrane f i l ter paper (Millipore) and the volume was increased to 100 ml with distilled water and bottles were stored until flame atomic absorption spectrophotometry was performed. The samples were analyzed by an atomic absorption spectrophotometer (ALPHA 4, Chem Tech Analytical, England) using a nitrous oxide-acetylene flame for As and an air-acetylene flame for the four heavy metalsPb, Cd, Cr and Cu, using at least two standard solutions for each metal. A certified standard reference material (AlphaLine, Chem Tech Analytical, England) was used to ensure accuracy, and the analytical values were within the range of certified valHEAVY METALS IN EDIBLE VEGETABLES Vol 39 No. 2 March 2008 337 ues. All recoveries of the metals studied were greater than 95%. The mean (±SD) concentrations for each heavy metal regardless of the kind of vegetable (the means of twenty replicates for each element in mg/kg by dry weight) were calculated and a comparison of this data in the selected vegetables was studied, and compared with the permissible levels set by the FAO and WHO. Based on the average concentration and the average consumption of edible vegetables, estimates of the amount of each heavy metal consumed were calculated. Analysis using the Kruskal-Wallis test was carried out to examine the statistical significance of differences in the mean concentration of metals between groups of vegetables using SPSS, version 11. A probability level of p<0.05 was considered statistically significant.