1
Heavy metals in selected vegetables from markets of Faisalabad, Pakistan
2
Running title: Assessment of heavy metals in vegetables
3 4
Shahzad Zafar Iqbal a,b†, Jinap, S.c,d, Zaka Ullah a, Muhammad R. Asi e, Muhammad Tauseef Sultan f, Noeen Malik g
5 6 7
a
8
Pakistan
9
b
Department of Applied Chemistry, Government College University Faisalabad, 38000,
Department of Plant Biology, Rutgers, The State University of New Jersey, NJ, 08901-
10
8520, USA
11
c
12
43400, Malaysia
13
d
14
Malaysia, Serdang, 43400, Malaysia
15
e
16
38950, Pakistan
17
f
Institute of Food Science & Nutrition, BZU Multan, Pakistan
18
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-
19 20 21 22 23 24
*Corresponding Authors:
[email protected] (Iqbal, S.Z.),
[email protected]
25
(Jinap, S.)
26
1
27
Abstract
28
A total 210 samples of selected vegetables (okra, pumpkin, tomato, potato, eggplant, spinach
29
and cabbage) from Faisalabad, Pakistan were analyzed for the analysis of heavy metals
30
(Cadmium (Cd), Lead (Pb), Arsenic (As), and Mercury (Hg)). Inductively Coupled Plasma
31
Optical Emission Spectrometry (ICP OES) was used for the analysis of heavy metals. The
32
mean levels of Cd, Pb, As, and Hg were 0.24, 2.23, 0.58 and 7.98 mg/kg, respectively. The
33
samples with 27% (Cd), 50% (Pb) and 63% (Hg) were exceeding the maximum residual
34
levels (MRL) set by European Commission. The mean levels of heavy metals in current study
35
are high and may pose significant health concerns for consumers. Furthermore, considerable
36
attention should be paid to implement comprehensive monitoring and regulations.
37
Keywords: heavy metals; vegetables; ICP OES
38 39 40 41 42 43 44 45 46 47 48 49 50 51
2
52
Heavy metal contamination is considered as a serious source of pollution in food and it is
53
potentially growing environmental as well as human health concern. Particularly, in
54
developing countries like Pakistan, these concerns have given urgent attention (2). Both
55
natural processes (weathering, volcanic eruptions and atmospheric deposition etc.) and
56
anthropogenic activities (sewage disposal, use of agrochemicals, mining, manufacturing,
57
combustion of fossil fuels and composts application) are the main sources of these toxic
58
metals to enter in the environment (13, 16, 18). It has been reported that almost 2 million
59
people per year of which majority are children, die as a result of diseases caused by the
60
consumption of contaminated food or water (3). The climatic conditions are conducive to the
61
growth of a wide spectrum of fruits and vegetables in Pakistan. The Agriculture sector plays
62
an important role in Pakistan’s Economy and it contributes almost 21% share in gross
63
domestic product (4). Pakistan produces thousands of tons of vegetables like potato, okra,
64
bitter melon, eggplant, tomato, cucumber, bell pepper, spinach, cauliflower, pumpkin, carrots
65
etc. Vegetables contain protein, vitamins, carbohydrates, iron, calcium and other nutrients are
66
therefore considered an important part of human diet (7). In developing countries especially
67
in Asia, people consume more vegetables than meat and the intake of vegetables becomes the
68
main source of nutrients. However, recently, concerns have been raised about the possible
69
heavy metals contamination in vegetables, fruits, soil and water.
70
Previous studies have shown that vegetables are contaminated with heavy metals in various
71
ways, such as irrigation water, industrial emissions, the harvesting process, storage or at the
72
point of sale. In developing countries, the industrial emissions and waste might be the
73
primary pollution pathway (8). The reports have revealed that once the heavy metals, such as
74
Cd and Pb were dispersed into water, soil and air, they could be accumulated by the crops (6).
75
Considering the above mentioned facts and the current study has initiated with basic purpose
76
to assess the level of toxic metals in vegetables. The main objectives of study are to
3
77
investigate the presence of heavy metals (Cd, Pb, As, Hg) in selected vegetable (okra,
78
pumpkin, tomato, potato, eggplant, spinach and cabbage) from Faisalabad, Pakistan. The
79
results will be useful to implement strict regulations by food authority in Punjab and to create
80
awareness among traders, farmers and consumers about the current level of these toxic metals
81
in vegetables.
82
Materials and methods
83
Sampling. Total 210 samples (30 each) of selected vegetables (okra, pumpkin, tomato,
84
potato, eggplant, spinach and cabbage) were collected directly from farmers, markets and
85
superstores of Faisalabad, Pakistan. The sample size of each vegetable was at least of 1 kg.
86
The samples were collected in plastic bags and stored at -4 °C in freezer and analyzed within
87
24 h.
88
Analysis conditions. The concentrations of Cd, Pb, As, and Hg were tested as
89
described by Huang et al. (6). The samples were digested by taking 5-10 g sample in a 100
90
mL round bottom flask. Then, 10 mL concentrated nitric acid was mixed in the sample and
91
heated at 120 °C in hot plate (Perkin Elmer, USA) for 6 H. About 1 mL of hydrogen peroxide
92
was periodically added, until a clear solution was reached. After digestion, the solution was
93
diluted up to a 50 mL in a volumetric flask with distilled water. The open system digestion
94
was carried out because it provide recovery more than 95% of the volatile analyte like Cd, As
95
and Hg. The solution was analyzed by ICP OES (Optima 2100-DV) Perkin Elmer (Waltham,
96
Massachusetts, United States) and radio frequency power of 1300 Watts. ICP-OES has dual
97
view, radial and axial and carried in robust conditions. The plasma formed and then the
98
individual metals give following wavelengths, Pb 220.3 nm, Cd 228.8 nm and As 193.6 nm.
99
Nitrogen 99.9 % and argon 99.9 % gases were used. Plasma flow 15 L/min, Auxiliary flow
100
0.2 L/min and Nebulizer flow 0.80 L/min.
4
101
Quality control parameters. The method was verified by analysis of fortified
102
concentration in non-contaminated potato samples with 0.24 ± 0.11, 0.33 ± 0.08, 0.12 ± 0.003
103
and 0.14 ± 0.007 mg/kg level of Cd, Pb, As and Hg from certified reference materials
104
(CRMs, Sigma-Aldrich, Germany) as shown in Table 1. Quantitative results (within 10% of
105
the certified value) were obtained for each metal in potato sample. Recoveries were ranged
106
between 83 to 103% with relative standard deviation (RSD) ranged from 7 to 14%. BEC
107
(background equivalent concentration) of As, Cd, Hg and Pb were 0.004, 0.002, 0.008 and
108
0.004 mg/kg, respectively.
109
Statistical analysis. The data of heavy metals concentrations were analyzed statistically and
110
presented as mean ± standard deviation (SD) and coefficient of determination (R2) was
111
determined by regression/correlation analysis using SPSS software (IBM, PASW Statistics
112
22, USA).
113
Results and discussions
114
Total 210 samples of vegetables from Faisalabad were analyzed for the presence of toxic
115
metals in present study. The concentrations of Cd, Pb, As and Hg in selected vegetables are
116
presented in Table 2. The highest mean level of 7.98 ± 2.19 mg/kg of Hg was found in
117
selected vegetables, ranged from 4.3 to 9.8 mg/kg. Furthermore, the results have shown that
118
63% samples of selected vegetables were found contaminated with Hg greater than the EU
119
maximum residual limit (MRL) of 0.1 mg/kg. The number of samples exceeding the MLR
120
level of other heavy metals were 27% for Cd, 50% for Pb, however no MRL level was
121
established for As.
122
The average levels of Cd, Pb, As, and Hg in different vegetables are shown in Figure 1. The
123
results have shown that each vegetable has different absorption ability for each metal.
124
Spinach has showed the highest mean level of Cd (0.38 mg/kg) and potato has shown the
125
highest mean level of Pb 7.375 mg/kg. Furthermore, pumpkin has shown the highest mean 5
126
level of 0.7 mg/kg, while no sample of eggplant and cabbage was found to be contaminated
127
with As. High level of 9.8 mg/kg of Hg was found in cabbage.
128
In another study from Khyber Pakhtunkhwa (Pakistan), the mean concentrations of Zn was
129
reported ranged from 9.07 to 44.6 mg/kg, the mean level of Cu was ranged from 2.94 to 19
130
mg/kg, the mean level of Ni was ranged from 1.01 to 28.6 mg/kg and the mean level of Cr
131
was ranged from 0.65 to 26.6 mg/kg in selected vegetables (14), are higher as compare to the
132
results of present study due to difference in sampling area. In same sampling city, the level of
133
Pb and Cd were determined in ground water near the industrial waste water derange. The
134
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
135
mg/L in Paharang drain (Faisalabad), textile effluents and ground water, respectively,
136
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
137
mg/L in Samana Main Drain (Faisalabad), connected textiles units and ground water,
138
respectively (12).
139
The results of current study were higher as compared to Huang et al. (6) from China. They
140
have analysed 343 samples of vegetable and found mean levels of As 0.009, Cd 0.015, Hg
141
0.003 and Pb 0.022 mg/kg. In another study, Wang et al. (17) have investigated heavy metals
142
Cu, Zn, Pb, Cd, Hg, and Cr in vegetables and fish and found the level of Pb 0.2-0.3 µg/g, Cd
143
0.1-0.5 µg/g and Hg 0.002-0.003 µg/g in locally produced vegetables from China. From
144
Pakistan, Mahmood and Malik, (11) have analyzed heavy metals in vegetables and reported
145
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
146
0.35 to 3.98 mg/kg.
147
In some reports the average levels of heavy metals, such Cd and Pb were more than 0.2
148
mg/kg in vegetables (15, 19). However, high level of heavy metals were reported by Luo et
149
al. (2011) with a level of Pb (0.38 mg/kg) in lettuce and Cd (0.79 mg/kg) in broccoli grown in
150
a contaminated soil from electronic waste processing site from China. Gupta et al. (5) have
6
151
observed 17.79 mg/kg of Cd and 57. 63 mg/kg of Pb in radish, collected from wastewater
152
irrigated suburban area from Titagarh, India, (the levels are comparable to present study). Li
153
et al. (9) have analysed heavy metals in cucumber and tomato harvested in greenhouse (GH)
154
and open field (OF) cultivation. The results of Cd, Mn and Zn levels have found in the most
155
tissues of the vegetables in GH were significantly higher than those in OF. The reduction in
156
the levels of Fe was observed in all parts of GH plants, however Pb content was decreased
157
only in aboveground parts of GH plants. Ali and Al-Qahtani (1) have analysed leafy
158
vegetables for the presence of heavy metals and found the highest metals values, especially in
159
parsley (543.2 and 0.048 µg/g of Fe and Hg, respectively), Jews mallow (94.12 and 33.22
160
µg/g of Mn and Zn, respectively), spinach (4.13 µg/g of Cd). While peas in legumes group
161
have maintained the highest level of Zn 71.77 µg/g and cucumber had shown the highest
162
level of Pb 6.98 µg/g on dry matter basis.
163
In present study, heavy metal concentrations are found higher in vegetables as compared to
164
MRL level of EU. The variation in the heavy metal concentration may be due to factors like
165
heavy metal concentration in soil; wastewater used for irrigation, atmospheric deposition as
166
well as the plant’s capability to uptake and accumulates heavy metals.
167
Conclusions. The results of heavy metals (Cd, Pb, As and Hg) in selected vegetables
168
from Faisalabad are much higher than the recommended limits as regulated by European
169
Union. The levels of these toxic metals in vegetables might be due to the unprocessed waste
170
of industries, which might contaminate soil and groundwater. Urgent attention is required for
171
Punjab Food Authority to implement strict regulations and conduct comprehensive
172
monitoring for these toxic metals in food on regular bases.
173
Acknowledgements. The authors are highly grateful to appreciate the financial funding
174
provided by the Higher Education Commission, (Project No; IPFP/HRD/HEC/2011)
175
Islamabad, Pakistan and the analytical facilities provided by NIAB, Faisalabad, Pakistan.
7
176
References
177
1. Ali, M.H.H. and K.M. Al-Qahtani. 2012. Assessment of some heavy metals in
178
vegetables, cereals and fruits in Saudi Arabian markets. Egyptian J. Aqu. Res. 38: 31–
179
37.
180 181 182
2. Atta, S, F. Moore, and S. Modaberri. 2009. Heavy metal contamination and distribution in the Shiraz Industrial Complex Soil. World. App. Sci. J. 6 (3): 412-424. 3. Food and Agricultural Organisation of the United Nations (FAO). 2014. Food safety:
183
A right or a privilege?
184
quality/events-projects/event/detail/en/c/266111/ (Accessed 09.06.17).
185
Available at: http://www.fao.org/food/food-safety-
4. Government of Pakistan (GOP). 2014. Economic Survey of Pakistan. 2013-14.
186
Islamabad:
187
http://www.finance.gov.pk/survey/chapters_14/Highlights_ES_201314.pdf
Economic
affairs
wing,
Finance
Division.
188
5. Gupta, N., D.K, Khan and S.C. Santra. 2008. An assessment of heavy metal
189
contamination in vegetables grown in wastewater-irrigated areas of Titagarh, West
190
Bengal, India. B. Environ. Contam. Toxicol. 80(2): 115-118.
191
6. Huang, Z., X.D. Pan, P.G. Wu, J.L. Han and Q. Chen. 2014. Heavy metals in
192
vegetables and the health risk to population in Zhejiang, China. Food Contr. 36: 248-
193
252.
194 195 196 197 198 199
7. Ivey, M.L.L., J.T. LeJeune and S.A. Miller. 2012. Vegetable producers’ perceptions of food safety hazards in the Midwestern USA. Food Contr., 26: 453-465. 8. Jiang, G.B., J.B. Shi, and X.B. Feng. 2006. Mercury pollution in China. Environ. Sci. Technol. 40(12): 3672-3678. 9. Li, F.L., W. Shi, Z.F. Jin, H.M. Wu and G.D. Sheng. 2017. Excessive uptake of heavy metals by greenhouse vegetables. J. Geochem. Explor. 173, 76–84.
8
200
10. Luo, C., C. Liu, Y. Wang, X. Liu, F. Li, G. Zhang. et al. 2011. Heavy metal
201
contamination in soils and vegetables near an e-waste processing site, south China. J.
202
Hazard. Mat. 186(1): 481-490.
203
11. Mahmood, A. and R.N. Malik. 2014. Human health risk assessment of heavy metals
204
via consumption of contaminated vegetables collected from different irrigation
205
sources in Lahore, Pakistan. Arabian J. Chem. 7: 91–99.
206
12. Noreen, M., M. Shahid, M. Iqbal, and J. Nisar. 2017. Measurement of cytotoxicity
207
and heavy metal load in drains water receiving textile effluents and drinking water in
208
vicinity of drains. Measurement 109: 88–99.
209
13. Oti, W.J.O. 2015. Pollution indices and bioaccumulation factors of heavy metals in
210
selected fruits and vegetables from a Derelict mine and their associated health
211
implications. Int. J. Environ. Sci. Toxic. Res. 3 (1): 9-15.
212
14. Rehman, Z.U., S. Khan, M.T. Shah, M.L. Brusseau, S. A. Khan, and J. Mainhagu.
213
2017. Transfer of Heavy Metals from Soils to Vegetables and Associated Human
214
Health
215
0160(17)60440-5.
Risk
in
Selected
Sites
in
Pakistan.
Pedosphere,
10.1016/S1002-
216
15. Singh, A., R.K. Sharma, M. Agrawal and F.M. Marshall. 2010. Health risk
217
assessment of heavy metals via dietary intake of foodstuffs from the wastewater
218
irrigated site of a dry tropical area of India. Food Chem. Toxicol. 48(2): 611-619.
219
16. Singh, R.B. 2001. Heavy metals in soils: sources, chemical reactions and forms.
220
proceedings of the 2nd Australia and New Zealand conference on environmental
221
geotechnics 8th October, 2000. Australian Geochemical Society, 77-93.
222
17. Wang, X., T. Sato, B. Xing and S. Tao. 2005. Health risks of heavy metals to the
223
general public in Tianjin, China via consumption of vegetables and fish. Sci. Total
224
Environ. 350: 28 – 37.
9
225
18. Waqas, M., G. Li, S. Khan, I. Shamshad, B.J. Reid, Z. Qamar and C. Chao. 2015.
226
Application of sewage sludge and sewage sludge biochar to reduce polycyclic
227
aromatic hydrocarbons (PAH) and potentially toxic elements (PTE) accumulation in
228
tomato. Environ. Sci. Pollut. Res. 22:7071-7081.
229
19. Zhuang, P., M.B. McBride, H. Xia, N. Li, and Z. Li. 2009. Health risk from heavy
230
metals via consumption of food crops in the vicinity of Dabaoshan mine, South
231
China. Sci. Total Environ. 407(5): 1551-1561.
232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249
10
250
Figure 1 251
0.4
Mean level (mg/kg)
Cd 0.35
252
0.3
253
0.25
254
0.2 0.15
255
0.1
256
0.05
257
0 Lady Pumpkin Tomato finger
Potato
Brinjal Spinach Cabbage 258
259 260 261 262 8
264
7 Mean level (mg/kg)
263
Pb
6
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
11
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
304
Table 1: Determination of recoveries using certified reference material (n = 8) Potato Certified mg/kg
305
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
9 14 8 7
306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 13
327 328
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)
329 330 331
*Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain
332
MRL; maximum residual limit
contaminants in foodstuffs
333 334
14