Determination content of heavy metals in tea samples in Moc Chau district, Son La province, Viet Nam

127 HNUE JOURNAL OF SCIENCE DOI: 10.18173/2354-1059.2018-0080 Natural Sciences 2018, Volume 63, Issue 11, pp. 127-134 This paper is available online at DETERMINATION CONTENT OF HEAVY METALS IN TEA SAMPLES IN MOC CHAU DISTRICT, SON LA PROVINCE, VIETNAM Le Sy Binh 1 , Dao Van Bay 2 and Vu Duc Loi 3 1 Tay Bac University 2 Faculty of Chemistry, Hanoi National University of Education 3 Institute of Chemistry, Vietnam Academy of Science and Technology Abstract. Moc Chau is a large tea material area of Son La province. The analysis of heavy metal content in Moc Chau tea contributed to the evaluation of tea quality. The total concentrations of Iron, Zinc and Copper in tea samples from Son La province in Vietnam were determined using flame atomic absorption spectrometry (FAAS) after dry digestion. The proposed method shows satisfactory recovery, detection limits and standard deviation for trace metal determination in tea samples. The concentrations of Fe, Zn and Cu in the tea samples were in the range of 48.65 - 86.55 mg/kg, 23.47 - 52.30 mg/kg and 10.84 - 18.05 mg/kg, respectively. Keywords: Tea sample, Moc Chau, iron, zinc, copper, FAAS, dry digestion. 1. Introduction The tea tree was first described in 1753 by Carl Linnaeus in the book Species Plantarum. The tea tree is scientifically named Camellia Sinensis (L.), which is native to North India and South China. Tea cultivation areas include Southwest region of China (Yunnan, Sichuan, Guangxi, Guizhou), Northern Laos, Vietnam, Myanmar, Cambodia and Northern India. In addition, tea plants are also grown in regions such as Eastern China, Japan, South Korea, Thailand and Taiwan. Nowadays, tea is cultivated mainly in high elevation areas in the tea belt and in other tropical, sub-tropical and temperate some regions like Sri Lanka, Indonesia, Central African countries, Turkey, Argentina and Russia [1]. Tea leaves contain catechins, is a flavan-3-ol polyphenolic group and their gallate derivatives have beneficialeffects on human health such as antioxidant and antimicrobial, for example [2]. Susanne M. Henning et al. (2003) identified Epicatechin gallate (ECG), Epicatechin (EC), Epigallocatechin gallate (EGCG), gallic acid (GA), caffeine, Gallocatechin gallate (GCG), and catechin gallate (CG) in eleven black tea samples and eight green tea samples. The flavanol content ranged from 59.3 to 103.2 mg/g in green tea and from 21.2 to 68.3 mg/g in black tea. The content of flavanol in black tea is less than in green tea [2]. Received October 16, 2018. Revised November 16, 2018. Accepted November 23, 2018. Contact Dao Van Bay, e-mail address: daobaydhsphn@gmail.com Le Sy Binh, Dao Van Bay and Vu Duc Loi 128 Among the minerals and essential trace elements, Ca, Na, K, Mg, and Mn are present in tea leaves at g/kg level, while Cr, Fe, Pb, Ni, Cu, Zn are present at mg/kg level [3]. B. Srividhya et al. have determined the content of some metals in tea samples consumed in India. The results showed that the mean level of metals were Cu 14.34 ± 0.49 mg/kg, Ni 11.34 ± 0.63 mg/kg, Pb 2.31 ± 0.13 mg/kg, Cd 0.89 ±0.10 mg/kg, Zn 25.39 ± 0.59 mg/kg, Mn 709.0 ± 14.18 mg/kg and Cr 704.0 ± 14.18 mg/kg for black tea and Cu 11.28 ± 0.08 mg/kg, Ni 9.09 ± 0.75 mg/kg, Cd 1.59 ± 0.26 mg/kg, Zn 26.39 ± 0.92 mg/kg and Mn 508.0 ± 44.03 mg/kg for green tea. The contents of Pb and Cr in green tea were lower the quantification limit [4]. Saad Antakli et al. were used FAAS method to determine five elements in tea leaves consumed in Syria for 39 tea samples after microwave digestion. The obtained concentrations of copper, iron, manganese, nickel and zinc varied between 10.6 - 54.4 (µg/g), 74.8 - 854.9 (µg/g), 225.1 - 1633.1 (µg/g), 1.1 - 16.3 (µg/g) and 18.0 - 44.2 (µg/g), respectively [5]. 2. Content 2.1. Experiments * Reagents and solutions All of the chemicals used were of analytical reagent grade, free from Fe, Zn, Cu traces. The standard solution of 1000 mg/L of the analytical elements was used for the experimental process (Merck). Working standard solutions were prepared by stepwise diluting the stock solutions. The laboratory glassware was kept in 10% (w/w) nitric acid for at least 24 hours and subsequently washed three times with doubly deionized water. * Apparatus A ZEEnit Model 700 (Analytikjena, Germany) atomic absorption spectrometer equipped with deuterium background correction and hollow cathode lamp was used for Fe, Zn, and Cu determination. The elements were determined by flame atomic absorption spectrometer using air mixed with acetylene. Tea samples were dry digested by Vulcan Furnace model A-550 eqquiment. * Sample collected Moc Chau is the main tea cultivation area of Son La province, Vietnam. Eight green tea samples were collected from four communes: Nong Truong, Phieng Luong, Tan Lap and Chieng Son (Table 1). * Dry digestion After drying to a constant weight, the tea samples were ground into powder. At the next step, 0.5 g of dried samples was accurately weighed into a crucible, the crucible was then heated in muffle furnace at 350°C for one hour, and gradually heated to 550°C for seven hours in order to make the sample dry ashing. The ashed samples were digested with 4 mL of concentrated HNO3 and 1 mL concentrated H2O2, then the digestion solution was heated until evaporating to moist salt. The residue was filtered and transferred into a volumetric flask and made up to 25 mL with 2% HNO3. The blank digestion experiments were also carried out in the same way. The final solution was determined by FAAS. Determination content of heavy metals in tea samples in Moc Chau District, Son La Province, Vietnam 129 Table 1. Tea samples collected in Moc Chau district, Son La province Tea samples Location Coordinates, elevation 1 Sub-zone Che Den, Nong Truong town 20 o49’57 N; 104o41’41 E; 950 m 2 Sub-zone S89, Nong Truong town 20 o49’50 N; 104o42’48 E; 942 m 3 Muong village, Phieng Luong commune 20 o49’12 N; 104o44’16 E; 913 m 4 Suoi Khem village, Phieng Luong Commune 20 o50’34 N; 104o46’08 E; 809 m 5 Hoa village, Tan Lap commune 20 o56’51 N; 104o37’53 E; 844 m 6 Hoa village, Tan Lap commune 20 o57’10 N; 104o37’22 E; 799 m 7 Sub-zone 7, Chieng Son commune 20 o44’33 N; 104o37’17 E; 712 m 8 Sub-zone 2, Chieng Son commune 20 o46’08 N; 104o35’21 E; 712 m * Optimum conditions for analysis iron, zinc and copper using FAAS The optimum conditions for FAAS measurements for Fe, Zn and Cu were selected including wavelength, lamp current, slit width, Buner hight, Fuel flow (Table 2). Table 2.The optimum conditions for analysis Characteristics Element Fe Zn Cu Wavelength (nm) 248.3 213.9 324.8 Lamp current (mA) 6 4 3 Slit Width (nm) 0.2 0.5 1.2 Buner hight (mm) 6 6 6 Fuel flow (l/h) 80 75 90 2.2. Result and discussion 2.2.1. Characteristics of the method The freshly prepared working solutions (5.0 mg/L Fe, 2.5 mg/L Zn, 4.0 mg/L Cu) were diluted with 2% (w/v) HNO3 solution to obtain a series of working solutions for plotting the calibration curves: from 0.1 mg/L to 5.0 mg/L for Fe; from 0.25 mg/L to 4.0 mg/L for Cu; from 0.1 mg/L to 2.5 mg/L for Zn. The linear standard curves of the analyte metals have the correlation coefficient greater than 0.999 (Figures 1-3). Figure 1.The linear standard curves for iron Le Sy Binh, Dao Van Bay and Vu Duc Loi 130 Figure 2.The linear standard curves for zinc Figure 3. The linear standard curves for copper The limit of detection (LOD) is defined as the concentration equivalent to three times the standard deviation of 10 measurements of the blank and is the lowest analyte concentration that produces a response detectable above the noise level of the system. The limit of quantification (LOQ) is the lowest level of analyte that can be accurately and precisely measured. LOQ, defined as ten times the standard deviation of the blank [6, 7]. Table 3. Equations, LOD, LOQ and correlation coefficients for the standard curves of iron, zinc and copper Element Equation SD LOD (mg/L) LOQ (mg/L) R 2 Fe Abs = 0.03661CFe + 0.0023 0.0267 0.080 0.267 0.999 Zn Abs = 0.1013CZn + 0.0044 0.0239 0.072 0.239 0.999 Cu Abs = 0.05464CCu - 0.0010 0.0169 0.051 0.169 0.999 2.2.2. Repetition of the method To evaluate the influence of the entire procedure on the measured results, the recoveries of the three heavy metals were studied. Four quality control samples were prepared by adding various amounts (0 μL, 50 μL, 100 μL, and 150 μL) of the standard solution mixtures (containing 300 mg/L Fe, 200 mg/L Zn, and Cu) to quadruplication of tea sample 1 (0.5 g for each), respectively. The concentrations of the three heavy metals in QC samples were analyzed six times Determination content of heavy metals in tea samples in Moc Chau District, Son La Province, Vietnam 131 to determine the relative standard deviation and the recovery of the method. The recoveries ranged from 96.7% to 101.7% for Fe, from 95.0% to 100.8% for Zn, from 97.5% to 103.7% for Cu (Table 4). Performance recovery has ensured the requirement of AOAC [8]. Table 4. Addition-recovery test for tea sample 1 (n = 3) Element Added (mg/L) Determination (mg/L) Recovery (%) Fe 0 1.61 - 0.6 2.19 96.7 1.2 2.83 101.7 1.8 3.40 99.4 Zn 0 0.86 - 0.4 1.24 95.0 0.8 1.63 96.3 1.2 2.07 100.8 Cu 0 0.29 - 0.4 0.68 97.5 0.8 1.12 103.7 1.2 1.47 98.3 n: Number of measurements for every sample 2.2.3. Analysis of green tea samples The proposed dry digestion procedure was applied for determining iron, zinc and cooper in green tea samples in Moc Chau district, Son La province, Vietnam. The obtained results are shown in Tables 5 - 7. Table 5. Concentration of Cu in green tea samples in Moc Chau (n = 3) Sample Cu concentration (mg/kg) Average Feb. 2017 Apr. 2017 Jun. 2017 1 12.39 14.71 16.11 14.40 2 13.09 14.21 12.24 13.18 3 13.66 12.84 15.08 13.86 4 17.05 18.04 19.07 18.05 5 11.76 9.82 10.95 10.84 6 11.78 12.7 10.86 11.78 7 14.21 15.56 13.37 14.38 8 12.04 11.34 14.23 12.54 n: Number of measurements for every sample Le Sy Binh, Dao Van Bay and Vu Duc Loi 132 Table 6. Concentration of Fe in green tea samples in Moc Chau (n = 3) Sample Fe concentration (mg/kg) Average Feb. 2017 Apr. 2017 June. 2017 1 77.66 82.78 81.52 80.65 2 75.17 80.12 79.08 78.12 3 82.24 76.46 78.82 79.17 4 81.37 85.63 83.43 83.48 5 75.35 82.86 86.95 81.72 6 84.24 88.65 86.76 86.55 7 46.08 49.53 50.34 48.65 8 63.76 56.77 59.98 60.17 n: Number of measurements for every sample Table 7. Concentration of Zn in green tea samples in Moc Chau (n = 3) Sample Zn concentration (mg/kg) Average Feb. 2017 Apr. 2017 Jun. 2017 1 40.08 43.16 46.13 43.12 2 23.27 27.13 24.69 25.03 3 50.19 53.88 52.88 52.32 4 49.87 47.92 56.38 51.39 5 35.32 37.18 40.7 37.73 6 55.13 49.71 51.85 52.23 7 20.65 22.92 26.84 23.47 8 29.05 30.14 34.26 31.15 n: Number of measurements for every sample The content of Cu was 10.84 - 18.05 mg/kg. The lowest content of Cu was found in sample 5 (Hoa village, Tan Lap), while the highest content was found in sample 4 (Suoi Khem village, Phieng Luong). The copper content of this study is similar to that of Saad Antakli et al. for seven Vietnamese green tea samples, consumed in Syria (from 10.72 µg/g to 18.54 µg/g) [5]. Renee Street et al. determined 21.4 mg/kg of Cu in Vietnamese tea. This figure is slightly higher than the content of Cu in tea sample in Moc Chau. Nguyen Dang Duc et al. reported that the Cu content in green tea from Thai Nguyen province in Vietnam ranged from 6.56 mg/kg to 12.43 mg/kg [9]. Average value of Cu content in this study is 13.63 mg/kg, similar to that found in green tea from Japan (13.40 mg/kg), lower than that found in green tea from China (19.7 mg/kg), India (17.7mg/kg), Sri Lanka (23.38 mg/kg) and Thailand (15.20 mg/kg) [10-12]. The Fe levels ranged from 48.65 mg/kg to 86.55 mg/kg and averaged at 74.79 mg/kg. The lowest content of Fe was found in sample 7 (Sub-zone 7, Chieng Son), while the highest content was found in sample 6 (Hoa village, Tan Lap). In the study of Saad Antakli, the Fe content of the seven Vietnamese tea samples was 104.41 - 347.16 mg/kg and averaged 221.71 mg/kg. The result of Determination content of heavy metals in tea samples in Moc Chau District, Son La Province, Vietnam 133 Saad Antakli is higher than those in this study [5]. The Fe content of Renee Street's study was 233 mg/kg, higher than this study [13]. The average value of Fe content in this study is 74.79 mg/kg, lower than those found in green tea from China (336 mg/kg), India (154mg/kg), Sri Lanka (480 mg/kg) and Thailand (167.1 mg/kg) [10-12]. The Zn contents ranged from 23.47 mg/kg to 52.32 mg/kg and averaged at 39.55 mg/kg. The lowest Zn content was found in sample 7 (23.47 mg/kg), while the highest was found in sample 3 (52.30 mg/kg). In the study of Saad Antakli, Zn contents ranged from 18.76 mg/kg to 38.50 mg/kg and averaged at 29.59 mg/kg [5]. The average value of Zn content in green tea is 39.55 mg/kg, similar to those found in green tea from China (36.9 mg/kg) and India (38.4 mg/kg), higher than those found in green tea from Japan (31.10 mg/kg), Sri Lanka (34.80 mg/kg) and Thailand (32.17 mg/kg) [10-12]. 3. Conclusions Dry digestion and flame atomic absorption spectrometry are suitable for the analysis of Fe, Zn and Cu in tea leaves. The recoveries ranged from 96.7% to 101.7% for Fe, from 95.0% to 100.8% for Zn and from 97.5% to 103.7% for Cu. The results show that the content of heavy metals is in the order of Fe > Zn > Cu in the tea leaves. The concentrations of Fe, Zn and Cu in the samples were in the range of 48.65 - 86.55 mg/kg, 23.47 - 52.30 mg/kg and 10.84 - 18.05 mg/kg, respectively. According to the Health Ministry's regulation 46/2007/QD-BYT, the maximum Cu and Zn content in tea are 150 mg/kg and 40 mg/kg, respectively [14]. Thus, the content of Cu, Zn in tea samples collected in Moc Chau district to ensure requirements, does not affect the health of users. REFERENCES [1] Victor R. Preedy, 2013. Tea in Health and Disease Prevention, ISBN: 978-0-12-384937-3, Copyright 2013 Elsevier. [2] Seeram NP, Henning SM, Niu Y, Lee R, Scheuller HS, Heber D Susanne M. Henning, Claudia Fajardo-Lira, Hyun W. Lee, Arthur A. Youssefian,Vay L. W. Go, and David Heber, 2003. Catechin content of 18 teas and a green tea extract supplement correlates with the antioxidant capacity. Nutrition and Cancer, Vol. 45(2), pp. 226-235. [3] Lydia Ferrara, Domenico Montesano, Alfonso Senatore, 2001. The distribution of minerals and flavonoids in the tea plant (Camellia sinensis), Il Farmaco, Vol. 56, pp. 397-401. [4] B. Srividhya, R. Subramanian and V. Raj, 2011. Determination of lead, manganese, copper, zinc, cadmium, nickel, and chromium in tea leaves. International Journal of Pharmacy and Pharmaceutical Sciences, Vol. 3(4), pp. 257-258. [5] Saad Antakli, Nazira Sarkis and Ahmad Mahmod Al-Check, 2011. Determination of Copper, Iron, Manganese, Nickel and Zinc in Tea Leaf Consumed in Syria by Flame Atomic Absorption Spectrometry after Microwave Digestion. Asian Journal of Chemistry, Vol. 23(7), pp. 3268-3272. [6] Alankar Shrivastava, Vipin B. Gupta, 2011. Methods for the determination of limit of detection and limit of quantitation of the analytical methods. Chronicles of Young Scientists, Vol. 2(1), pp. 21-25. [7] International Conference on Harmonization (ICH) of Technical Requirements for the Registration of Pharmaceuticals for Human Use, Validation of analytical procedures: Text and Methodology. ICH-Q2B, Geneva; 1996. Le Sy Binh, Dao Van Bay and Vu Duc Loi 134 [8] AOAC Official Methods of Analysis, 2016. Guidelines for Standard Method Performance Requirements. [9] Nguyen Dang Duc, Le Thi Van , Nguyen To Giang, Do Thi Nga, 2013. Determination of Cu and Cr in green tea in Thai Nguyen. Journal of Science and Technology, Thai Nguyen University, Vol. 104(4), pp. 101-107. [10] Justyna Brzezicha-Cirocka, Małgorzata Grembecka and Piotr Szefer, 2016. Monitoring of essential and heavy metals in green tea from different geographical origins. Environmental Monitoring and Assessment, Vol. 188 : 183. [11] Augustine Donkor, Charles Kuranchiea, Paul Osei-Fosua, Stephen Nyarkoa and Louis Doamekpora, 2015. Assessment of Essential Minerals and Toxic Trace Metals in Popularly Consumed Tea Products in Ghana, A Preliminary Study. Research Journal of Chemical and Environmental Sciences, Vol. 3 (1), pp. 49-55. [12] Nookabkaew S, Rangkadilok N, Satayavivad J., 2006. Determination of trace elements in herbal tea products and their infusions consumed in Thailand. Journal of Agricultural and Food Chemistry, Vol. 54(18),pp. 6939-6944. [13] Renee Street, Jirina Szakova, Ondrej Drabek and Lenka Mladkova, 2006. The Status of Micronutrients (Cu, Fe, Mn, Zn) in Tea and Tea Infusions in Selected Samples Imported to the Czech Republic. Czech Journal of Food Sciences, Vol. 24(2), pp. 62-71. [14] Ministry of Health, 2007. Decision No: 46/2007/QĐ-BYT on promulgation “Regulations on maximum limit of biological and chemical pollution in food”. Ministry of Health, Vietnam (in Vietnamese).