Current World Environment

Introduction

Vegetables are vital sources of minerals, vitamins, dietary fibers, antioxidants, protein and carbohydrate.^{1, 2} Whereas, both essential and lethal elements (metals) are present in vegetables. Heavy metals in vegetables mainly occurred due to contaminated soil and irrigation.³ Further, vegetables can easily absorb the metals accumulated on plant surfaces exposed to the tainted ambient.³ the existence of heavy metals in fertilizers enhance the probability of metal pollution for vegetables.⁴ Human activities like as farming, industrialization and urbanization amplify the level of heavy metal in the environment, as a result, elevate the metal concentration in the vegetables.⁵

Heavy metals from point sources, for instance metalliferous mining, smelting and industrial activities, on the other hand non-point source, for example fertilizers, pesticides, sewage sludge, organic manure and compost contribute to uplift the level of concentration in vegetables.⁶ Emission from the industries and vehicles may be stored heavy metals on the   vegetables surface during its production, transport and marketing. For instance, The level of heavy metals aggrandized into vegetables sold at Riyadh city in the Saudi Arabia due to atmospheric deposition.⁷ Another reference, the amount of heavy metals rise up in the vegetables sold at open market in the Varanasi ,India because of same cases.^8,9

Plants grown in contaminated environment can aggregate heavy metals at elevated concentration causing serious risk to human health when consumed. however, heavy metals are toxic because they tend to bio accumulate in plants and animals, bioconcentrate in the food chain and attack specific organs in the body.^10,11 Long time consumption of heavy metals through vegetables may causes disruption of numerous biochemical processes, Consequently occurred cardiovascular, nervous, kidney and bone diseases.^12,13 Despite trace quantities of certain heavy metals such as Cr, Co, Cu, Mn and Zn etcetera are essential micronutrients for human and plants growth but their high concentration may cause health problem.^4,15 Hence lot  of works have been carried out to assess heavy metals bioaccumulation in different vegetables and plants all over the world.^16,17

The uptake of heavy metals in vegetables is trendy to be higher and accumulation of these toxic metals in human body generated warning in the present days. The daily vegetables consumption by an adult of Bangladesh is 130gm.¹⁸ Varieties of vegetables are grown the whole year in tropical Bangladesh, but using little is known .about the heavy metal contents of vegetables.¹⁹ Few articles^{18, 19} are available reporting the heavy metals concentration in different vegetables grown in various parts of our country. But such researches are not conducted in the metropolitan city of Chittagong, Bangladesh. The present study was undertaken with the aim to investigate the concentration of some specific toxic metals (Mn, Cr, Pb, Cd, Cu and Co) and essential nutrients (K, Ca, Mg, Fe and Zn) in selected vegetables available in this region.

Materials and Method

Study area and sampling locations

The present study was carried out in the Chittagong metropolitan area of Bangladesh. Samples of vegetables were randomly collected from central whole sale market of Chittagong metropolitan city named Reazuddin bazar (figure 1). All the vegetables were collected from three different locations (south, medium, and north) to provide replicate samples of each vegetable. All samples were stored in clean polyethylene bag according to their type and transported to the laboratory for further processing. The scientific, common and family name of each studied vegetables are listed (table 1).

Sample Pre-treatment and Digestion

The collected vegetables samples were washed with distilled water to remove dust particles. The samples were then cut into nearly uniform size using clean knife. This was done to facilitate drying of the pieces at the same rate. After air drying the samples were placed in clean acid washed porcelain crucibles according to the label and oven dried at 105⁰ C for 24 hours until they were brittle and crispy. Now these dried samples of vegetables were grounded into fine particles using blender. The powdered samples were placed in labeled Petri dishes and dried to constant weight in desiccators until they acid digested. These samples were digested by using conc. H₂ SO₄ and 30% H₂O₂, in a three neck round bottom flask.
 

Figure 1: Map of the Chittagong metropolitan city Click here to View figure

Analytical technique

The samples were analyzed by an atomic absorption spectrophotometer (Thermo Scientific iCE 3300 AA Series Atomic Absorption Spectrophotometer), using an air acetylene flame. The analysis was carried out using hollow cathode lamps under standard instrument conditions.

Table 1: English name, Common name, scientific name and family name of different vegetables collected from Reazuddin bazar

Results and Discussion

All the twenty two vegetables sample contain more than 84% moisture except eddoe(68.35%), maximum amount of organic matter was found in eddoe (30.28%) due to presence of lots of carbohydrate whereas  inorganic matter varies from 0.12%-3.94% (Table 2).

Table 2: Moisture content, organic and inorganic part of vegetables collected from Reazuddin bazar

Essential nutrients and Toxic metals (Table 3, Table 4) concentrations (mg/kg) of twenty two vegetables are depicted below. The potassium concentration in the vegetables samples varied from 572.64 mg/kg in green papaya to 4097.43 mg/kg in coriander leaf (Table 3).The concentration (mg/kg) of K is higher than the others essential nutrients because potassium is one of the main components of NPK fertilizer which is frequently used by farmer in cultivation field consequently vegetables under examination abundant with potassium since K can easily be absorbed by vegetables. Evidence Show that dietary potassium plays a role in decreasing blood pressure, controlling nerve and muscle function. Low potassium and high sodium level in food increase the probability of blood pressure.²¹

The concentration of calcium was found to be 4.99-242.56 mg/kg. All the vegetables except tomato contain reasonable amount calcium. Ca is essential for skeleton and central ion for vast range of biological process such as muscle contraction,glycolysis and gluconeogenesis ,ion transport ,cell division and growth.²² The Mg concentration (mg/kg) in most green vegetables is more than 150 mg/kg since Mg is the central element of chlorophyll structure. So that in leafy vegetables coriander leaf contain highest 4797.63 mg/kg of Mg. Lack of Magnesium can affect most of vital organ of human body. ²³ High content of iron were observed in cabbage (14.67mg/kg) since it is fully leafy vegetable .Iron is an inevitable element since it is the central ion for hemoglobin which is involved in oxygen and carbon dioxide transportation.²⁴ A deficiency of iron influence the formation of hemoglobin consequently limits the oxygen delivery to cells, resulting in fatigue, poor working efficiency and immunity. On the reverse side, excess iron can result in toxicity and even death.^{25, 26}

Table 3: Essential nutrients concentration (mg/kg) in different vegetables collected from Reazuddin bazar

*All the values of concentration are expressed in Average±SD

Cu, Mn, Cr, Pb, Cd and Co concentration (Table 4) of twenty two vegetables collected from Reazuddin bazar, central vegetables market, Chittagong metropolitan city, Bangladesh. The

average concentration of toxic metals estimated in twenty two vegetables ranged from 0.18-2.49 mg/kg for Cu, 0.04-3.92 mg/kg for Mn, 0.05-1.59 mg/kg for Cr, 0.04-2.97 mg/kg for Pb, 0.01-0.07 mg/kg for Cd, 0.02-0.35 mg/kg for Co. Heavy metals content in the examined vegetables found in the decreasing order as Mn>Cu>Pb>Cr>Co>Cd(Table 4).Though trace amount of Mn, Cu and Cr are accounted as important electrolyte for several biological processes in human body, but higher levels of these metals can affect the major organs on consumer health.¹³ Manganese plays major role in oxygen evolution catalyzed by the proteins of the photosynthetic reaction center and pyruvate carboxylase in human being and also involved in bone concentration, protein, lipid and metabolism.²² The Adequate Intake (AI) of Mn for adult men and women is 2.3mg/day and 1.8 mg/day respectively.²⁶ Copper plays an important role as biocatalyst in the body [13]. Generally soil contain inadequate amount of copper so that copper is provided to plants through artificial or organic fertilizers.²⁷ Further, the copper toxicity can induce lipid peroxidation, iron deficiency and destruction of cell wall [28]. The highest value of copper is found 2.49 mg/kg in string and lowest value is found 0.11mg/kg in tomato (Table 4). Chromium can cause ulceration, liver and kidney damage.^{27, 28} In addition, Chromium in trace amount controls the glucose level in blood.²⁸ Chromium concentration is highest in string bean (1.59 mg/kg) and lowest in radish (0.05 mg/kg).

When Pb is up taken by crops from soil, it’s mainly stay at root area as it cannot effectively transport the endodermis of roots whereas leaves can absorb vast quantities of Pb from the atmosphere.³⁰ Pb is toxic metals which have carcinogenic effects and teratogenic abnormalities in human, even at very low concentration.³¹ Pb has been reported as a severe aggregative body toxin which enters the body through food, air and water, cannot be eliminated through washing vegetables.^{32, 33} In our tested vegetables all the vegetables contain huge (more than 0.50 mg/kg) amount of Pb which is really a great concern for consumer health issue. The high concentration of Pb in all the vegetables might be due to contaminants in irrigation water, soil or industrial and vehicular emission as lead occurs in the fuel as anti knocking agents.³³ Artificial fertilizers are one of the major source of soil contamination by trace metals especially Cd, as it is naturally found as an impurity in phosphate rocks. ^{34, 35} It was found that FAO/WHO for 

Table 4: Toxic metals concentration in different vegetables collected from Reazuddin bazar

*All the values of concentration are expressed in Average±SD

The Cd concentration(Table 4) of all the vegetables were within the safe limit recommended by human consumption.³⁶ The Co found in most of the vegetables were within the limit recommended by WHO/FAO [36]. Among all the tested vegetables Co was found highest in Brinjal (0.35 mg/kg) and lowest in potato (0.001 mg/kg).

Conclusion

Though all the vegetables are great source of essential nutrients such as K,Mg,Ca,Fe and Zn but the average concentration of heavy metals especially Mn, Cr and Pb exceeding the recommended limits whereas Cu, Cd and Co level maintained within the safe limits in all the vegetables.  Consuming heavy metals contaminated vegetables for prolonged time might create different types of chronic diseases. Therefore regular monitoring of heavy metals in vegetables is crucial to avoid excessive uptake of these metals in the food chain and concern authority should take necessary steps to avoid heavy metals contamination in vegetables.

Acknowledgement

We are grateful to Bangladesh Council of Scientific and Industrial Research (BCSIR) and The Director of BCSIR Laboratories, Chittagong.

References

1. Abdulazeez, Z. M., and Aziz, J. M. A., Some of Heavy metals in some Green Leafy Vegetables in Sulaimani, Kurdistan-Iraq. International Journal of Multidisciplinary and current research, May/June (2014).
2. Sobukola, O. P., Adeniran, O. M., and Odedairo, O. E., Heavy metal levels of some fruits and leafy vegetables from selected markets in Lagos, Nigeria. African Journal of Food Science, 4(2): 389-393 (2010).
3. Sharma, R.K., Agrawal, M., and Marshall, F. M., Heavy metals in vegetables collected from production and market sites of a tropical urban area of India. Food and Chemical toxicology, 47: 583-591(2009).
   CrossRef
4. Yusuf, A. A., Arowolo, T. A., and Bamgbose, O., Cadmium, copper and nickel levels in vegetables from industrial and residential areas of Lagos City, Nigeria. Food and Chemical Toxicology, 41: 375-378(2003)
   CrossRef
5. Alegria, A.,Barberfi, R., Boluda, R., Errecalde, F., Farr, R., and Lagarda, M. J., Environmental cadmium, lead and nickel contamination: possible relationship between soil and vegetable content. Fresenius Journal of Analytical Chemistry, 339: 654-657(1991)
   CrossRef
6. Singh, B. Heavy metal in soils: sources, chemical reactions and forms. In Geo Environment. Proceedings of 2nd Australia and New Zealand Conference on Environmental Geotechnics: Newcastle, New South Wales’, 77-93(2001)
7. Al Jassir, M.S., Shaker, A., and Khaliq, M.A., Deposition of Heavy metals on green leafy vegetables sold on roadsides of Riyadh city, Saudi Arabia. Bulletin of Environment Contamination and Toxicology, 75: 1020–1027(2005).
   CrossRef
8. Sharma, R.K., Agrawal, M., and Marshall, F.M., Heavy metals (Cu, Cd, Zn and Pb) contamination of vegetables in Urban India: a case Study in Varanasi. Environmental Pollution 154:254-263(2008)
   CrossRef
9. Sharma, R.K., Agrawal, M., and Marshall, F.M., Atmospheric depositions of heavy metals (Cd, Pb, Zn, and Cu) in Varanasi city, India. Environmental Monitoring and Assessment 142 (1–3): 269–278 (2008)
   CrossRef
10. Akinola, M.O., Njoku, K.L., and Ekeifo, B.E., Determination of lead, cadmium and chromium in the tissue of an economically important plant grown around a textile industry at Ibeshe, Ikorodu area of Lagos State, Nigeria. Advances in Environmental Biology, 2(1): 25–30(2008)
11. Chatterjee, J., Chatterjee, F., Phytotoxicity of chromium, cobalt and copper in cauliflower. Environmental Pollution, 109: 69–74(2000)
12. WHO (World Health Organization). Cadmium. Environmental Health Criteria, 134 (1992)
    CrossRef
13. Jarup, L., Hazards of heavy metal contamination. British Medical Bulletin, 68: 167–182(2003).
    CrossRef
14. Yusuf, A. A., Arowolo, T. O. and Bamgbose, O., Cadmium, Copper and Nickel levels in vegetables from industrial and residential areas of Lagos city, Nigeria", Global Journal of Environmental Science, 1(1): 1 - 6(2002).
    CrossRef
15. Pandey, H.K., Gakhar, S., and Chawla, G., Heavy metal toxicity in ground water ofkhajuwala area Located in Bikaner division of western rajasthan. Current World Environment, 1(1): 41-44(2006).
16. Jacob, J.O., and Kakulu, S.E., Assessment of Heavy Metal Bioaccumulation in Spinach, Jute Mallow and Tomato in Farms within Kaduna Metropolis, Nigeria. American Journal of Chemistry, 2(1): 13-16 (2012).
    CrossRef
17. Vandana, P., Murthy, N.N., Saxena R.P., Assessment of heavy metal contamination in soil around hazardous waste disposal sites in Hyderabad city (India): natural and anthropogenic implications, E3 Journal of Environmental.
18. Islam, M. R., Hoque, M. E., Jahiruddin, M., and Islam, M., Heavy metal contamination of vegetables grown in Chapainawabganj, Bangladesh and its implication to daily intake for human health, Bangladesh Journal of Agricultural Research 1(1): 37-48(2005)
19. Alam, M.G.M., Snow, E.T., and Tanaka, A., Arsenic and heavy metal contamination of vegetables grown in Samta village, Bangladesh. Science of the Total Environment. 308: 83-96(2003)
    CrossRef
20. Huq, S.M.I., and Alam, M.D., A hand book on analyses of soil, plant and water, University of Dhaka, Bangladesh , 246 (2005).
21. Anderson, J. Young, L., and Long, E., Potassium and Health, Food and Nutrition series, Health,Fact sheet no 9.355,Link:http://www.ext.colostate.edu/pubs/foodnut/09355.html
22. Ivano, B., Bioinorganic Chemistry, Viva books private limited; New Delhi (2007).
23. Baker, S. M., Magnesium and Trace Elements, 10, 251-262(1991-1992).
24. Das,J., Das, S., Bakar, A. M., Biswas, A., Uddin, M., Evaluation of essential and toxic metals in bakery foods consumed in Chittaqgong(Bangladesh). Analytical Chemistry an Indian Journal, 13(3): 118-125(2013)
25. Dietary Supplement Fact Sheet: http://ods.od.nih.gov/factsheets/Iron-health professional/
26. Institute of Medicine ,Food and Nutrition Board,Dietary Reference Intakes for Vitamin A,VitaminK,Arsenic,Boron,Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, silicon, Vanadium and Zinc.,National Academy ress,Washington,DC,Link:http://www.nap.edu/catalog.php?record_id=10026#toc;(2001).
27. Chen,Y.,Wu, P., Shao, Y., and Ying, Y., Health risk assessment of heavy metals in vegetables grown around battery production area. Scientia Agricola, 71 (2): 126-132, March/April (2014).
28. Mollazadeh, N., Metals health risk assessment via consumption of vegetables. International Journal of Agriculture and Crop Science, 7(8): 433-436(2014)
29. Sardar,K., Ali, S., Hameed, S., Afsal,S., Fatima, S., Shakoor, M.B., Bharwana, S.A., and Tauqeer, H.M., Heavy Metals Coatamination and what are the impacts on Living Organism. Greener journal of Environment Management and public safety, 2(4): 172-179(2013)
30. Domergue, F.L., and Vedy, J. C., Mobility of heavy metals in soil profiles. International Journal of Environment and Analytical Chemistry, 46: 13-23 (1992).
    CrossRef
31. Kananke, T., Wansapala, J., and Gunaratne, A., Heavy Metal Contamination in Green Leafy Vegetables Collected from Selected market Sites of Piliyandala Area, Colombo District, Sri Lanka. American Journal of Food and Technology, 2(5): 139-144(2014)
    CrossRef
32. Abbas, M., Parveen, Z., Iqbal, M., Riazuddin, Iqbal, S, Ahmed, M., and Bhutto, R., Ahmed M., and Bhutto R., Monitoring of toxic metals (Cadmium, Lead, Arsenic and Mercury) in vegetables of Sindh, Pakistan. Kathmandu University Journal of science, Engineering and Technology, 6(2): 60-65(2010)
    CrossRef
33. Zamora, P.W., Jesus, J.D., Su,G.S., Ragragio, E., Su, M.L.S., and Villanueva, S., Assessing Lead Concentrations in Leafy Vegetables in selected private Markets in Metro Manila, Philippines. Journal of Applied Technology in Environmental Sanitation, 2(3): 175-178(2012)
34. Nazar, R., Iqbal, N., Masood, A., Khan, M.I.R., Syeed,S., and Khan, N. A., Cadmium toxicity in plants and role of mineral nutrients in its alleviation. American journal of plant sciences, 3: 1476-1489(2012)
    CrossRef
35. Bakhshayesh, B.E., Delkash M., and Scholz, M., Response of Vegetables to Cadmium-Enriched Soil. Water, 6(5): 1246-1256(2014)
    CrossRef
36. Nankishore, A., Heavy metal levels in leafy vegetables from selected markets in Guyana. Journal of Agricultural Technology, 10(3): 651-663(2014)