The content of lead (Pb), copper (Cu), zinc (Zn), cobalt (Co), nickel (Ni), and cadmium (Cd) in some selected fruits and vegetables from the Misurata City Market, Libya, were measured using atomic absorption spectrophotometry. The results of this study showed that the average concentrations detected ranged from 0.02 to 1.824, 0.75 to 6.21, 0.042 to 11.4, 0.141 to 1.168, 0.19 to 5.143, and 0.01 to 0.362 mg/kg for Pb, Cu, Zn, Co, Ni, and Cd, respectively. The highest mean levels of Pb, Cu, Zn, Co, Ni and Cd were detected in mango, melon, spinach, banana, mango, and mango fruits, respectively. The levels of these metals found in our study are compared with those reported for similar fruits and vegetables from some other parts of the world. The daily human intakes of Pb, Cu, Zn, Co, Ni, and Cd ascribed to a diet of fruits and vegetables in this region have also been estimated.
The effect of heavy metal contamination of fruit and vegetables cannot be underestimated as these foodstuffs are important components of human diet. Fruit and vegetables are rich sources of vitamins, minerals, and fibers and also have beneficial antioxidative effects. However, the intake of heavy metal-contaminated fruit and vegetables may pose a risk to human health; hence the heavy metal contamination of food is one of the most important aspects of food quality assurance [
Demirezen and Aksoy [
Based on their persistence and cumulative behavior as well as the probability of potential toxicity effects, the absorption of heavy metals in human diets as a result of the consumption of vegetables and fruits means that there is a requirement for the analysis of food items to ensure that the levels of trace heavy metals meet the agreed international standards. This is particularly important for farm products from parts of the world where only limited data on the heavy metal content are available. Knowledge of the contamination of fruit and vegetables with heavy metals from the Misurata areas of Libya has not yet been established; therefore, the present study was undertaken with the aim to compare and investigate the concentration of some specific heavy metals (Pb, Cd, Zn, Cu, Co, and Ni) found in some selected fruit and vegetables from this region.
Safe values for copper, lead, and cadmium in fruit and vegetables recommended by the WHO/FAO are 40, 0.3, and 0.2 mg/kg, respectively [
A total of 250 samples of fruit and vegetable produce were purchased from several local suppliers and markets in Misurata City, Libya, during 2010. The sampling comprised 2 kg for each commodity sold in each district and was considered to be quite representative since the districts were scattered randomly throughout the city; for the analysis, only the edible portions of each fruit and vegetable were included, and additionally the bruised or rotten parts were removed.
Subsamples (each of 1 kg) were taken at random from the composite sample (10 kg) and were processed for analysis by the dry-ashing method. The samples were first oven-dried at 105°C for 24 h. The dried samples were then powdered manually in a grinder and were subjected to analysis for their heavy metal content.
Powdered samples (14 g each), with three replicates taken for each food item, were accurately weighed and placed in a silica crucible, and few drops of concentrated nitric acid were added to the solid as an aid to ashing. The dry-ashing process was carried out in a muffle furnace by stepwise increase of the temperature up to 550°C and the samples left to ash at this temperature for 6 h [
The ash was kept in desiccators and then rinsed with 3 N hydrochloric acid. The ash suspension was filtered into a 50 mL volumetric flask through Whatman No. 1 filter paper, and the volume was made up to the mark with 3 N hydrochloric acid.
Standard solutions of the heavy metals, namely, lead (Pb), cadmium (Cd), copper (Cu), cobalt (Co), nickel (Ni), and zinc (Zn), were provided by Merck (Darmstadt, Germany). The standards were prepared from the individual 1000 mg/L standards (Merck) supplied in 0.1 N HNO3. A series of working standards were prepared from these standard stock solutions.
Appropriate quality assurance procedures and precautions were taken to ensure the reliability of the results. Samples were carefully handled to avoid cross-contamination.
Glassware was properly cleaned, and reagents used were of analytical grades. Deionized water was used throughout the study. Reagent blank determinations were used to apply corrections to the instrument readings. For validation of the analytical procedure, repeated analyses of the samples against internationally certified plant standard reference material (SRM) of the National Institute of Standard and Technology were used, and the results were found to lie within ±1% of the certified values.
The daily intake of heavy metals through the consumption of fruit and vegetables tested was calculated according to the equation [
Analysis for the heavy metals of interest was performed using atomic absorption spectrometry (180–30 Hitachi spectrometer). Measurements were made using standard hollow cathode lamps for Pb, Cd, Zn, Cu, Co, and Ni. The limit of detection (LOD) of the analytical method for each metal was calculated as being triple the standard deviation of a series of measurements for each solution, the concentration of which is distinctly detectable above the background level. These values were 0.001, 0.001, 0.001, 0.003, 0.001, and 0.002 mg/kg for Pb, Cd, Zn, Cu, Co, and Ni, respectively. Also, the limit of quantification (LOQ) of the element was determined; these were calculated as 0.003, 0.003, 0.003, 0.01, 0.003, and 0.007 mg/kg for Pb, Cd, Zn, Cu, Co, and Ni, respectively. The standard operating conditions for the analysis of heavy metals using atomic absorption spectrometry used in our experiments are given in Table
Standard operating conditions for the analysis of heavy metals using atomic absorption spectrometry.
Metals | Wavelength (nm) | Lamp current (mA) | Flame | Slit width (mm) |
---|---|---|---|---|
Pb | 283.3 12 | 283.3 12 | Air-acetylene | 0.7 |
Cd | 228.8 6 | 228.8 6 | 0.7 | |
Cu | 324.8 30 | 324.8 30 | 0.7 | |
Zn | 213.9 20 | 213.9 20 | 0.7 | |
Co | 240.7 30 | 240.7 30 | 0.2 | |
Ni | 232.0 30 | 232.0 30 | 0.2 |
The present study reports on the heavy metal content of Pb, Cd, Zn, Cu, Co, and Ni determined in selected fruit and vegetables collected from production and market sites in the Misurata area of Libya. The observed concentrations of Pb, Cd, Zn, Cu, Co, and Ni in the fruit and vegetables were compared with the recommended limit as established by the FAO/WHO in 1999 to assess the levels of food contamination.
The mean concentrations and range of heavy metals found in fresh fruit and vegetables sampled from the local markets in Misurata City, Libya, are summarized in Table
Concentration of heavy metals (mg/kg or ppm) in fruits and vegetables.
Commodity | Moisture content (%) | Concentrations of metals | |||||
Pb | Cd | Zn | Cu | Co | Ni | ||
Fruits | |||||||
Banana | 75.0 | ||||||
Peach | 90.3 | ||||||
Orange | 88.5 | ||||||
Strawberries | 90.1 | ||||||
Watermelon | 95.4 | ||||||
Melon | 92.5 | ||||||
Apple | 85.0 | ||||||
Grape | 89.1 | ||||||
Mango | 82.1 | ||||||
Vegetables | |||||||
Tomatoes | 94.0 | ||||||
Onion | 86.4 | ||||||
Potatoes | 75.2 | ||||||
Green pepper | 91.3 | ||||||
Carrot | 85.6 | ||||||
Cucumber | 94.3 | ||||||
Spinach | 89.9 |
Concentration of pb, Cd, and ZN in fruits.
Concentration of Cu, Co, and Ni in fruits.
Concentration of pb, Cd, and ZN in vegetables.
Concentration of Cu, Co, and Ni in vegetables.
Within the selected fruit, the highest concentrations of Pb were noticed in mangos followed by strawberries, watermelons, grapes, peaches, melons, apples, and oranges in decreasing concentrations, whereas in the vegetables studied the highest concentration of Pb was found in tomatoes followed by green peppers, spinach, carrots, onions, and potatoes. The higher levels of heavy metal contamination found in some fruit and vegetables could be closely related to the pollutants in irrigation water, farm soil, and pesticides or alternatively could be due to pollution from traffic on the the highways [
Apart from its function as a biocatalyst, Cu is necessary for body pigmentation, for the maintenance of a healthy central nervous system, and for the prevention of anaemia, and it is interrelated with the function of Zn and Fe in the body [
Like Cu, Zn is an essential element for plants and animals, but only a small increase in its level may cause interference with physiological processes. The presence of Zn seems to be essential to neutralize the toxic effects of Cd. In this study, the maximum quantity of zinc was detected in melons (8.24 mg/kg) while mangos had the lowest concentration (0.635 mg/kg). Zn levels in this study showed a divergence from those reported in other countries; its levels were here found to be higher in vegetables and lower in fruits when compared with similar samples in other countries, as shown in Table
The exposure of consumers and the related health risks are usually expressed in terms of the provisional tolerable daily intake (PTDI) [
Estimation of heavy metal intake through consumption of fruits and vegetables in Misurata, Libya.
Foodstuffs (g/person/day) | Mean level (mg/kg) | |||||||||||
Pb | Intake | Cd | Intake | Zn | Intake | Cu | Intake | Co | Intake | Ni | Intake mg/day | |
Fruits (78) | 0.473 | 36.89 | 0.071 | 5.54 | 3.7 | 0.288 | 2.63 | 0.205 | 0.58 | 45.24 | 1.49 | 0.116 |
Vegetables (98) | 0.25 | 24.8 | 0.14 | 13.3 | 8.15 | 0.8 | 3.36 | 0.33 | 0.51 | 49.7 | 0.24 | 0.0231 |
Levels of metals in fruits and vegetables in previously published results from other parts of the world [
sample | Pb | Cd | Zn | Cu | Co | Ni |
---|---|---|---|---|---|---|
Banana | 7.46 | 13.36 | 45.64 | 14.19 | 25.40 | 8.90 |
Apple | 23.48 | 8.39 | 35.88 | 3.00 | 185.90 | 47.43 |
Mango | 67.20 | 16.9 | 18.29 | 6.34 | 6.23 | — |
Tomato | 0.26 | 0.01 | 7.69 | 1.83 | — | — |
Onion | 0.06 | 0.07 | 0.09 | 0.09 | — | — |
Potatoes | 0.009 | 0.031 | 2.10 | 0.64 |
It can therefore be concluded that our estimated daily intakes for the heavy metals studied here are below those reported by the FAO/WHO, which have set a PTDI limit for the heavy metal intake based on body weight for an average adult (60 kg body weight) for Pb, Cd, Cu, and Zn as 214
In conclusion, the results reported here confirm that the fruit and vegetables collected from chosen production and market sites in the Misurata area of Libya contained measured heavy metal contents within the safe limits prescribed by the WHO in 1999. This is an important result as human health is directly affected by ingestion of fruit and vegetables; the biomonitoring of trace elements in fleshy fruits needs to be continued because these are the main sources of food for humans in many parts of the world.