Heavy metals in selected vegetables from markets of Faisalabad ...

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Heavy metals in selected vegetables from markets of Faisalabad, Pakistan. 1. Running title: Assessment of heavy metals in vegetables. 2. Shahzad Zafar Iqbal.
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Heavy metals in selected vegetables from markets of Faisalabad, Pakistan

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Running title: Assessment of heavy metals in vegetables

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Shahzad Zafar Iqbal a,b†, Jinap, S.c,d, Zaka Ullah a, Muhammad R. Asi e, Muhammad Tauseef Sultan f, Noeen Malik g

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a

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Pakistan

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b

Department of Applied Chemistry, Government College University Faisalabad, 38000,

Department of Plant Biology, Rutgers, The State University of New Jersey, NJ, 08901-

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8520, USA

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c

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43400, Malaysia

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d

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Malaysia, Serdang, 43400, Malaysia

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e

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38950, Pakistan

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f

Institute of Food Science & Nutrition, BZU Multan, Pakistan

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g

Department of Radiology, School of Medicine, New York University, USA

Institute of Tropical Agriculture and Food Security, Universiti Putra Malaysia, Serdang,

Department of Food Science, Faculty of Food Science and Technology, Universiti Putra

Food Toxicology Lab, Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad-

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*Corresponding Authors: [email protected] (Iqbal, S.Z.), [email protected]

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(Jinap, S.)

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Abstract

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A total 210 samples of selected vegetables (okra, pumpkin, tomato, potato, eggplant, spinach

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and cabbage) from Faisalabad, Pakistan were analyzed for the analysis of heavy metals

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(Cadmium (Cd), Lead (Pb), Arsenic (As), and Mercury (Hg)). Inductively Coupled Plasma

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Optical Emission Spectrometry (ICP OES) was used for the analysis of heavy metals. The

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mean levels of Cd, Pb, As, and Hg were 0.24, 2.23, 0.58 and 7.98 mg/kg, respectively. The

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samples with 27% (Cd), 50% (Pb) and 63% (Hg) were exceeding the maximum residual

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levels (MRL) set by European Commission. The mean levels of heavy metals in current study

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are high and may pose significant health concerns for consumers. Furthermore, considerable

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attention should be paid to implement comprehensive monitoring and regulations.

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Keywords: heavy metals; vegetables; ICP OES

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Heavy metal contamination is considered as a serious source of pollution in food and it is

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potentially growing environmental as well as human health concern. Particularly, in

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developing countries like Pakistan, these concerns have given urgent attention (2). Both

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natural processes (weathering, volcanic eruptions and atmospheric deposition etc.) and

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anthropogenic activities (sewage disposal, use of agrochemicals, mining, manufacturing,

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combustion of fossil fuels and composts application) are the main sources of these toxic

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metals to enter in the environment (13, 16, 18). It has been reported that almost 2 million

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people per year of which majority are children, die as a result of diseases caused by the

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consumption of contaminated food or water (3). The climatic conditions are conducive to the

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growth of a wide spectrum of fruits and vegetables in Pakistan. The Agriculture sector plays

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an important role in Pakistan’s Economy and it contributes almost 21% share in gross

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domestic product (4). Pakistan produces thousands of tons of vegetables like potato, okra,

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bitter melon, eggplant, tomato, cucumber, bell pepper, spinach, cauliflower, pumpkin, carrots

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etc. Vegetables contain protein, vitamins, carbohydrates, iron, calcium and other nutrients are

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therefore considered an important part of human diet (7). In developing countries especially

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in Asia, people consume more vegetables than meat and the intake of vegetables becomes the

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main source of nutrients. However, recently, concerns have been raised about the possible

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heavy metals contamination in vegetables, fruits, soil and water.

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Previous studies have shown that vegetables are contaminated with heavy metals in various

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ways, such as irrigation water, industrial emissions, the harvesting process, storage or at the

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point of sale. In developing countries, the industrial emissions and waste might be the

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primary pollution pathway (8). The reports have revealed that once the heavy metals, such as

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Cd and Pb were dispersed into water, soil and air, they could be accumulated by the crops (6).

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Considering the above mentioned facts and the current study has initiated with basic purpose

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to assess the level of toxic metals in vegetables. The main objectives of study are to

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investigate the presence of heavy metals (Cd, Pb, As, Hg) in selected vegetable (okra,

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pumpkin, tomato, potato, eggplant, spinach and cabbage) from Faisalabad, Pakistan. The

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results will be useful to implement strict regulations by food authority in Punjab and to create

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awareness among traders, farmers and consumers about the current level of these toxic metals

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in vegetables.

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Materials and methods

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Sampling. Total 210 samples (30 each) of selected vegetables (okra, pumpkin, tomato,

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potato, eggplant, spinach and cabbage) were collected directly from farmers, markets and

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superstores of Faisalabad, Pakistan. The sample size of each vegetable was at least of 1 kg.

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The samples were collected in plastic bags and stored at -4 °C in freezer and analyzed within

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24 h.

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Analysis conditions. The concentrations of Cd, Pb, As, and Hg were tested as

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described by Huang et al. (6). The samples were digested by taking 5-10 g sample in a 100

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mL round bottom flask. Then, 10 mL concentrated nitric acid was mixed in the sample and

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heated at 120 °C in hot plate (Perkin Elmer, USA) for 6 H. About 1 mL of hydrogen peroxide

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was periodically added, until a clear solution was reached. After digestion, the solution was

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diluted up to a 50 mL in a volumetric flask with distilled water. The open system digestion

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was carried out because it provide recovery more than 95% of the volatile analyte like Cd, As

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and Hg. The solution was analyzed by ICP OES (Optima 2100-DV) Perkin Elmer (Waltham,

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Massachusetts, United States) and radio frequency power of 1300 Watts. ICP-OES has dual

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view, radial and axial and carried in robust conditions. The plasma formed and then the

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individual metals give following wavelengths, Pb 220.3 nm, Cd 228.8 nm and As 193.6 nm.

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Nitrogen 99.9 % and argon 99.9 % gases were used. Plasma flow 15 L/min, Auxiliary flow

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0.2 L/min and Nebulizer flow 0.80 L/min.

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Quality control parameters. The method was verified by analysis of fortified

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concentration in non-contaminated potato samples with 0.24 ± 0.11, 0.33 ± 0.08, 0.12 ± 0.003

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and 0.14 ± 0.007 mg/kg level of Cd, Pb, As and Hg from certified reference materials

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(CRMs, Sigma-Aldrich, Germany) as shown in Table 1. Quantitative results (within 10% of

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the certified value) were obtained for each metal in potato sample. Recoveries were ranged

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between 83 to 103% with relative standard deviation (RSD) ranged from 7 to 14%. BEC

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(background equivalent concentration) of As, Cd, Hg and Pb were 0.004, 0.002, 0.008 and

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0.004 mg/kg, respectively.

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Statistical analysis. The data of heavy metals concentrations were analyzed statistically and

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presented as mean ± standard deviation (SD) and coefficient of determination (R2) was

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determined by regression/correlation analysis using SPSS software (IBM, PASW Statistics

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22, USA).

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Results and discussions

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Total 210 samples of vegetables from Faisalabad were analyzed for the presence of toxic

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metals in present study. The concentrations of Cd, Pb, As and Hg in selected vegetables are

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presented in Table 2. The highest mean level of 7.98 ± 2.19 mg/kg of Hg was found in

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selected vegetables, ranged from 4.3 to 9.8 mg/kg. Furthermore, the results have shown that

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63% samples of selected vegetables were found contaminated with Hg greater than the EU

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maximum residual limit (MRL) of 0.1 mg/kg. The number of samples exceeding the MLR

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level of other heavy metals were 27% for Cd, 50% for Pb, however no MRL level was

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established for As.

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The average levels of Cd, Pb, As, and Hg in different vegetables are shown in Figure 1. The

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results have shown that each vegetable has different absorption ability for each metal.

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Spinach has showed the highest mean level of Cd (0.38 mg/kg) and potato has shown the

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highest mean level of Pb 7.375 mg/kg. Furthermore, pumpkin has shown the highest mean 5

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level of 0.7 mg/kg, while no sample of eggplant and cabbage was found to be contaminated

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with As. High level of 9.8 mg/kg of Hg was found in cabbage.

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In another study from Khyber Pakhtunkhwa (Pakistan), the mean concentrations of Zn was

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reported ranged from 9.07 to 44.6 mg/kg, the mean level of Cu was ranged from 2.94 to 19

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mg/kg, the mean level of Ni was ranged from 1.01 to 28.6 mg/kg and the mean level of Cr

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was ranged from 0.65 to 26.6 mg/kg in selected vegetables (14), are higher as compare to the

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results of present study due to difference in sampling area. In same sampling city, the level of

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Pb and Cd were determined in ground water near the industrial waste water derange. The

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level of Pb was found to be in the range of 0.20 to 0.49 mg/L, 0.13 to 0.25 mg/L, 0.05 to 0.14

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mg/L in Paharang drain (Faisalabad), textile effluents and ground water, respectively,

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whereas these values for Cd were 0.25 to 0.39 mg/L, 0.25 to 0.34 mg/L and 0.10 to 0.23

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mg/L in Samana Main Drain (Faisalabad), connected textiles units and ground water,

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respectively (12).

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The results of current study were higher as compared to Huang et al. (6) from China. They

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have analysed 343 samples of vegetable and found mean levels of As 0.009, Cd 0.015, Hg

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0.003 and Pb 0.022 mg/kg. In another study, Wang et al. (17) have investigated heavy metals

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Cu, Zn, Pb, Cd, Hg, and Cr in vegetables and fish and found the level of Pb 0.2-0.3 µg/g, Cd

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0.1-0.5 µg/g and Hg 0.002-0.003 µg/g in locally produced vegetables from China. From

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Pakistan, Mahmood and Malik, (11) have analyzed heavy metals in vegetables and reported

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the mean level of Pb ranged from 0.01 to 0.93 mg/kg, Cd from 0.01 to 1.5 mg/kg and Cr from

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0.35 to 3.98 mg/kg.

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In some reports the average levels of heavy metals, such Cd and Pb were more than 0.2

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mg/kg in vegetables (15, 19). However, high level of heavy metals were reported by Luo et

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al. (2011) with a level of Pb (0.38 mg/kg) in lettuce and Cd (0.79 mg/kg) in broccoli grown in

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a contaminated soil from electronic waste processing site from China. Gupta et al. (5) have

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observed 17.79 mg/kg of Cd and 57. 63 mg/kg of Pb in radish, collected from wastewater

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irrigated suburban area from Titagarh, India, (the levels are comparable to present study). Li

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et al. (9) have analysed heavy metals in cucumber and tomato harvested in greenhouse (GH)

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and open field (OF) cultivation. The results of Cd, Mn and Zn levels have found in the most

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tissues of the vegetables in GH were significantly higher than those in OF. The reduction in

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the levels of Fe was observed in all parts of GH plants, however Pb content was decreased

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only in aboveground parts of GH plants. Ali and Al-Qahtani (1) have analysed leafy

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vegetables for the presence of heavy metals and found the highest metals values, especially in

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parsley (543.2 and 0.048 µg/g of Fe and Hg, respectively), Jews mallow (94.12 and 33.22

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µg/g of Mn and Zn, respectively), spinach (4.13 µg/g of Cd). While peas in legumes group

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have maintained the highest level of Zn 71.77 µg/g and cucumber had shown the highest

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level of Pb 6.98 µg/g on dry matter basis.

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In present study, heavy metal concentrations are found higher in vegetables as compared to

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MRL level of EU. The variation in the heavy metal concentration may be due to factors like

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heavy metal concentration in soil; wastewater used for irrigation, atmospheric deposition as

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well as the plant’s capability to uptake and accumulates heavy metals.

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Conclusions. The results of heavy metals (Cd, Pb, As and Hg) in selected vegetables

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from Faisalabad are much higher than the recommended limits as regulated by European

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Union. The levels of these toxic metals in vegetables might be due to the unprocessed waste

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of industries, which might contaminate soil and groundwater. Urgent attention is required for

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Punjab Food Authority to implement strict regulations and conduct comprehensive

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monitoring for these toxic metals in food on regular bases.

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Acknowledgements. The authors are highly grateful to appreciate the financial funding

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provided by the Higher Education Commission, (Project No; IPFP/HRD/HEC/2011)

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Islamabad, Pakistan and the analytical facilities provided by NIAB, Faisalabad, Pakistan.

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References

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1. Ali, M.H.H. and K.M. Al-Qahtani. 2012. Assessment of some heavy metals in

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Figure 1 251

0.4

Mean level (mg/kg)

Cd 0.35

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0.3

253

0.25

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0.2 0.15

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0.1

256

0.05

257

0 Lady Pumpkin Tomato finger

Potato

Brinjal Spinach Cabbage 258

259 260 261 262 8

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7 Mean level (mg/kg)

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Pb

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265

5

266

4 3

267

2

268

1

269 270

0 Lady Pumpkin Tomato finger

Potato

Brinjal Spinach Cabbage

271 272 273 274 275 276

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277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 12

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Table 1: Determination of recoveries using certified reference material (n = 8) Potato Certified mg/kg

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Cd 0.25 ± 0.005 Pb 0.33 ± 0.08 As 0.12 ± 0.003 Hg 0.14 ± 0.007 RSD= relative standard deviation

Measured mg/kg

Recovery %

RSD %

0.22 ± 0.007 0. 34 ± 0.15 0.10 ± 0.006 0.13 ± 0.08

88 103 83 93

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306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 13

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Table 2: The concentration of heavy metals in selected vegetables from Faisalabad, Pakistan (mg/kg) Element

n ˃ MRL

Mean

Range

MRL

(mg/kg)

(mg/kg)

(mg/kg) *

Cd

0.24 ± 0.11

BEC- 0.38

0.05-0.2

(27)

Pb

2.24 ± 2.61

BEC-7.375

0.1

(50)

As

0.58 ± 0.56

BEC-0.70

----

---

Hg

7.98 ± 2.19

BEC-9.80

0.1

(63)

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*Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain

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MRL; maximum residual limit

contaminants in foodstuffs

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