This article was downloaded by: [University of Calgary] On: 21 October 2014, At: 22:52 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Food Additives & Contaminants: Part B: Surveillance Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tfab20
Lead, cadmium, arsenic, mercury and copper levels in Chinese Yunnan Pu’er tea a
b
a
a
Pengbo Ning , Chunmei Gong , Yanming Zhang , Kangkang Guo & Juan Bai
b
a
College of Veterinary Medicine, Northwest A & F University , Yangling, Shaanxi 712100, China b
College of Life Sciences, Northwest A & F University , Yangling, Shaanxi 712100, China Published online: 24 Feb 2011.
To cite this article: Pengbo Ning , Chunmei Gong , Yanming Zhang , Kangkang Guo & Juan Bai (2011) Lead, cadmium, arsenic, mercury and copper levels in Chinese Yunnan Pu’er tea, Food Additives & Contaminants: Part B: Surveillance, 4:1, 28-33, DOI: 10.1080/19393210.2011.551945 To link to this article: http://dx.doi.org/10.1080/19393210.2011.551945
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Food Additives and Contaminants: Part B Vol. 4, No. 1, March 2011, 28–33
VIEW DATASET Lead, cadmium, arsenic, mercury and copper levels in Chinese Yunnan Pu’er tea Pengbo Ninga, Chunmei Gongb, Yanming Zhanga*, Kangkang Guoa and Juan Baib a
College of Veterinary Medicine, Northwest A & F University, Yangling, Shaanxi 712100, China; College of Life Sciences, Northwest A & F University, Yangling, Shaanxi 712100, China
b
Downloaded by [University of Calgary] at 22:52 21 October 2014
(Received 18 September 2010; final version received 2 January 2011) The Yunnan region of China produces a distinctive variety of Pu’er tea, which is consequently labeled as a Chinese geographic indication product. In this study, the safety of Chinese Yunnan Pu’er tea with regard to heavy metal content was evaluated in 30 different brands of Pu’er tea, including 150 commercial samples. Metal levels in the Pu’er tea samples followed the order: copper (12–22 mg/g) 4 lead (0.26–3.2 mg/g) 4 arsenic (0.035–0.24 mg/g) 4 cadmium (0.0059–0.085 mg/g) 4 mercury (50.010 mg/g). Mercury was not detected in 17 of the brands of Pu’er tea. Metal-to-metal correlation studies showed that there were no significant correlation between metal pairs. Based on current safety standards, the low levels of metals detected in these Pu’er tea samples mean they are safe for human consumption. Keywords: heavy metals; arsenic; cadmium; mercury; lead
Introduction As the most widely consumed beverage, next to water, tea is an important agricultural crop for the Chinese economy. All varieties of tea are produced from the leaves of Camellia sinensis. Yunnan Province (Southwest China) is an important area for global Camellia sinensis production, most of which is sold as Pu’er tea. Yunnan Pu’er tea is very distinct and is labeled with its Chinese geographic indication. The Pu’er tea trade has been active in Yunnan for at least a millennium, and this area now boasts the largest production and marketing base in the world. Pu’er tea brings huge economic and social benefits to Yunnan, and tons of Pu’er teas are sold in China, South-east Asian, and other overseas markets every year. Most Chinese believe that Pu’er tea can reduce blood lipids, lower blood pressure, and aid digestion. They also believe that the quality of the tea increases with its age and, consequently, aged tea commands a higher the price. Recent research has shown that tea contains specific antioxidants and compounds that can lower the risk of heart disease (Hakim et al. 2003), and have anticarcinogenic (Kuroda and Hara 1999) and antimutagenic (Wu et al. 2007) effects. However, bioaccumulation of trace metals in plant foliage and branch tips presents a potential health risk to humans (Peralta-Videa et al. 2009). During the growth
*Corresponding author. Email: [email protected] ISSN 1939–3210 print/ISSN 1939–3229 online ß 2011 Taylor & Francis DOI: 10.1080/19393210.2011.551945 http://www.informaworld.com
(Han et al. 2006a) and processing of tea (Han et al. 2006b; Qin and Chen 2007), contamination with heavy metals can occur. This is second only to pesticide residues in its potential to adversely impact human health. Consumers are likely at risk of heavy metal exposure and accumulation through drinking Pu’er tea (Shen and Chen 2008). Consequently, many studies have focused on tea safety. Metals, such as lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and copper (Cu), are physiological and neurological toxins and could affect kidney (Lee and The0 venod 2008) and liver (Sa´nchez-Chardi et al. 2009) function, the embryo (Thompson and Bannigan 2008), and other organs or systems in the human body (Al-Saleh et al. 2008; Rana 2008). Considerable research has been conducted on the heavy metal content of green, red and other tea varieties available on the international market (Nookabkaew et al. 2006; Ashraf and Mian 2008). However, limited information is available for Chinese Pu’er tea. We believe a detailed investigation of the heavy metal content of Pu’er tea is important for evaluation of its quality and safety, and to guard against adverse effects on human health. In this study, we analyzed 30 representative Pu’er tea brands, including 150 samples from the Yunnan markets, for Pb, Cd and Cu by atomic absorption spectroscopy (AAS). As and Hg were determined by atomic fluorescence spectroscopy (AFS).
Food Additives and Contaminants: Part B Materials and methods
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Preparation of materials Five commercial Pu’er tea samples were collected from each of 30 different brands (150 samples in total), which were both produced and marketed in Yunnan, China. Depending on the processing technique, Pu’er tea can be classified as either raw or ripened, and half the samples collected were from each class. All glassware was cleaned by soaking in dilute HNO3 and was rinsed with ultrapure water (Milli-Q, Millipore, MA, USA). For wet digestion of samples for determination (Chinese Ministry of Health 2003a–e), portions (2.00 g) of each tea sample were accurately weighed into the dry beakers and digested using a solution of 8 ml HNO3 and 2 ml HClO4 overnight. Afterwards, the solution was gently heated until it became transparent, then filtered and transferred to a 25-ml volumetric flask that had been rinsed many times with a small amount of ultrapure water. Pb, Cd, As and Cu were determined after the flask was shaken to ensure homogeneity of the solution. For Hg, 0.50 g of each ground sample was accurately weighed and digested by microwave digestion (Chinese Ministry of Health 2003e). Each sample was transferred to a Teflon canister. After added 4 ml of HNO3 solution and 1 ml of H2O2 solution, the Teflon canister was maintained as a close system to minimize loss of mercury during the digestion procedure. The mixture was submitted to a three-step program: 200 W (5 min), 350 W (7 min), and 450 W (7 min). After digestion and cooling, the volume of the sample was calibrated to 25 ml with HNO3 (1:9, v/v) solution. Blank samples were prepared in the same way for each selected digestion procedures. All reagents were purchased from Sigma (SigmaAldrich, St. Louis, MO, USA). Trace metal standard solutions (1000 mg/ml) were provided by the National Analysis Center for Iron and Steel (Beijing, China). A certified reference material for tea (GBW10016; Institute of Geophysical and Geochemical Exploration, Langfang, China) with certified Pb (1.5 0.2 mg/g), Cd (0.062 0.004 mg/g), As (0.09 0.01 mg/g), Hg (0.0038 0.0008 mg/g) and Cu (18.6 0.7 mg/g) concentrations were included for quality control.
Methods and measurements An atomic absorption spectrometer (Solar M6, Thermo Electron, USA) was used for determination of Pb, Cd and Cu according to a previously published method (Chinese Ministry of Health 2003b–d). The operating parameters are detailed in Table 1. As and Hg were analyzed using an atomic fluorescence spectrometer (AFS-8220; Titan Instruments, China) by a previously published method
29
(Chinese Ministry of Health 2003e). Optimal parameters for this instrument were: negative voltage (400 V for As, 240 V for Hg), lamp current (35 mA for As, 30 mA for Hg), atomizer temperature (300 C for As, 200 C for Hg), and height of atomizer (7.0 mm for As, 8.0 mm for Hg).
Quality control A series of (more than 10) negative blank samples (a sample containing no analyte but with a matrix identical to that of the average sample analyzed) were tested and the mean blank values and the standard deviations (SD) were calculated. The limit of detection (LOD) and limit of quantification (LOQ) were defined as the mean value of the negative blind controls plus 3 SD and 10 SD of the mean, respectively (Armbruster et al. 1994). Repeated analysis (n ¼ 7) of the reference material gave the mean concentration and the relative standard deviation (RSD) of each heavy metal: Pb for 1.5 0.04 mg/g and 3.0%, Cd for 0.062 0.001 mg/g and 1.6%, As for 0.09 0.003 mg/g and 3.7%, Hg for 0.0038 0.0002 mg/g and 4.2%, Cu for 18.6 0.16 mg/g and 0.8%. Recoveries were calculated by spiking with aliquots of metal standards and then analyzing them as usual, according to the original concentrations of the spiked samples (Burns et al. 2002). Acceptable recoveries of 96.7–102.8, 97.2–104.2, 96.8–103.3, 97.5–104.5 and 98.3–103.9% were obtained for externally added Pb, Cd, As, Hg and Cu, respectively. We included at least one laboratory duplicate for each Pu’er tea sample, and the result for each brand was the mean of the five samples analyzed.
Results and discussion The results for heavy metal analysis of the 30 brands of Pu’er tea are shown in Table 2. Among the investigated metals, copper had the highest concentrations and mercury had the lowest. After copper, lead had the second highest concentrations, and this was followed by arsenic, then cadmium. Copper levels ranged from 12.22–22.22 mg/g among the 30 brands of Pu’er tea. The lowest and highest levels of copper were found in samples Gude B and Yuncha A, respectively. The copper content of the Pu’er tea samples was an order of magnitude greater than lead, and copper accounted for most of the total heavy metal content. While copper is an essential element in the human body, excessive copper consumption could impair human health. However, the copper levels detected in the Pu’er tea samples in this study were all below the upper limits imposed for tea by various countries: China (60 mg/g), Japan (100 mg/g), and the United States (150 mg/g). Our results compared well with the literature values reported for tea samples
30
P. Ning et al. Table 1. Operating parameters for the atomic absorption spectrophotometer. Parameter Wavelength (nm) Silt (nm) Lamp current (mA) Drying temperature ( C)/time (s) Ashing temperature ( C)/time (s) Atomization temperature ( C)/time (s)
Pb
Cd
Cu
283.3 0.7 6 120/30 450/20 1800/4
228.8 0.5 8 120/30 350/20 1800/4
324.8 0.5 6 120/30 800/20 2300/4
Table 2. Pb, Cd, As, Hg and Cu levels (mg/g) in Pu’er tea samples from Yunnan.
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Brand Yuncha A Yuncha B Dayi 7592 Dayi 0782 Bajiaoting A Bajiaoting B Mengku A Mengku B Linhao A Linhao B Longrun A Longrun B Gude A Gude B Heilongtan Jinhao Heilongtan 8817 Heilongtan Qizi Heilongtan Qiaomu Qingliangshan 0649 Qingliangshan 0419 Qingliangshan 0549 Qingliangshan 0329 Huanglipo A Huanglipo B Wuyi A Wuyi B Paka A Paka B Longsheng 0738 Longsheng B Mean SD
Pb
Cd
As
Hg
Cu
0.58 1.20 0.56 0.71 0.38 0.30 0.93 0.71 0.64 0.69 0.60 0.83 0.48 0.60 0.85 0.90 1.28 0.66 1.28 0.47 1.11 0.26 1.89 3.19 0.44 0.44 1.51 1.39 0.46 0.30 0.86 0.70
0.037 0.033 0.042 0.034 0.023 0.019 0.036 0.040 0.035 0.016 0.0059 0.012 0.0081 0.0076 0.045 0.042 0.057 0.040 0.052 0.053 0.055 0.054 0.080 0.085 0.025 0.066 0.075 0.075 0.078 0.070 0.043 0.024
0.092 0.096 0.083 0.077 0.099 0.068 0.18 0.10 0.13 0.056 0.064 0.13 0.094 0.062 0.24 0.12 0.21 0.24 0.075 0.060 0.15 0.097 0.11 0.066 0.13 0.041 0.15 0.076 0.052 0.035 0.11 0.059
0.0020 ND ND ND ND ND ND ND ND ND 0.0079 ND ND ND 0.0014 0.0011 0.00048 ND ND ND ND 0.00028 ND ND ND ND 0.010 ND ND ND 0.00079 0.0028
22.22 16.48 18.84 16.62 19.64 15.40 16.86 12.84 17.78 15.36 13.74 18.06 16.56 12.22 16.06 13.56 17.68 15.08 18.80 15.53 17.92 15.94 16.98 15.54 16.98 12.68 19.16 15.34 18.82 16.48 16.51 2.26
Notes: ND, not detected. The detection limits were: 5.0 ng/g for Pb, 0.1 ng/g for Cd, 0.01 mg/g for As, 0.15 ng/g for Hg, and 1.0 mg/g for Cu.
from markets in Saudi Arabia (Ashraf and Mian 2008), China (Han et al. 2005), United States (Kumar et al. 2005), and Turkey (Narin et al. 2004) (Table 3). The levels of lead in the Pu’er tea samples ranged between 0.26 and 3.19 mg/g. The lowest concentration of lead was found in sample Qingliangshan 0329. The highest lead concentration was in sample Huanglipo B, and may be attributed to dust particles in packaging. Table 3 shows the large variation in lead levels for teas from different international markets. Shen and Chen (2008) reported the mean concentration of lead in
green tea samples from Taiwan as 0.01 mg/g. The average level in black tea samples from Turkey was 17.9 7.1 mg/g, which may also be caused by dust particles during processing (Narin et al. 2004). Compared with other studies on tea from Chinese markets (Han et al. 2005), much lower levels of lead were detected in the Yunnan Pu’er tea samples in this study. Lead levels in all the Pu’er tea brands analyzed in this study were below the maximum permissible concentration of 5 mg/g (Chinese Ministry of Health 2005).
Species
Pb (mg/g)
Note: NA, not available; ND, not detected.
Yunnan Pu’er tea 0.86 0.70 Saudi Arabia Black tea 1.7 0.8 Taiwan Black, oolong, 2.01, 0.4 and 0.01 and green teas Thailand Green and other teas 3.93 China Black, green, Oolong, 2.7 (Han et al. 2006a) and other teas USA Black, green and other teas NA Japan Green and other teas 0.31 0.04 Turkey Black tea 17.9 7.1
Market
Table 3. Comparison of our results with other studies. As (mg/g)
Hg (mg/g)
Cu (mg/g)
Reference
0.09 0.26 NA NA NA
0.04 0.02 NA 0.0158 0.0036 2.3 0.4
NA NA NA
NA NA
12.3 4.8 NA 16.5 3.9
NA 18.33
Kumar et al. (2005) Wang et al. (2005) Narin et al. (2004)
Nookabkaew et al. (2006) Han et al. (2005)
0.043 0.024 0.11 0.059 0.00079 0.0028 16.51 2.26 This work 1.1 0.5 NA NA 18.1 6.9 Ashraf and Mian (2008) 0.07, 0.005 and ND 0.01, 0.005 and ND NA 0.3, 0.9 and 0.4 Shen and Chen (2008)
Cd (mg/g)
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Food Additives and Contaminants: Part B 31
32
P. Ning et al.
Table 4. Correlation coefficients between metal concentrations (r ¼ 95%).
Pb Cd As Hg Cu
Pb
Cd
As
Hg
Cu
1.000
0.205 1.000
0.011 0.000 1.000
0.116 0.033 0.039 1.000
0.002 0.000 0.019 0.003 1.000
lead, cadmium and copper by AAS, and arsenic and mercury by AFS. The results compared well with corresponding international data. Based on the data obtained and current safety standards, the brands of Pu’er tea in this study are safe for human consumption. Variation among the Pu’er tea brands in this study was not large enough to be of commercial significance.
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Acknowledgements Arsenic levels (0.035–0.24 mg/g) in the Pu’er tea samples in this study were lowest in sample Longsheng B and highest in samples Heilongtan Jinhao and Heilongtan Qiaomu. The mean arsenic content was 0.11 0.059 mg/g. A previous study found a mean arsenic concentration of 0.09 mg/g in teas from Thailand (Nookabkaew et al. 2006), which compared well with our results. Han et al. (2006a) found a mean arsenic concentration of 0.26 mg/g in various teas from China. However, Shen and Chen (2008) reported Taiwanese tea samples had arsenic concentrations an order of magnitude lower than our results. The concentration range for cadmium was 0.0059– 0.085 mg/g (mean: 0.043 0.024 mg/g). The lowest cadmium concentration was found in sample Longrun A, and the highest in sample Huanglipo 07516. Cadmium concentrations in the Yunnan Pu’er tea samples were similar to those in tea samples from Taiwan (Shen and Chen 2008), Thailand (Nookabkaew et al. 2006), China (Han et al. 2005), and Japan (Wang et al. 2005). However, the concentrations were lower than those in black teas produced in Saudi Arabia (Ashraf and Mian 2008) and Turkey (Narin et al. 2004) (Table 3). Minimal levels of the heavy metal, mercury, were found in the Pu’er tea samples in this study. Mercury could not be detected in 17 brands of Pu’er tea by AFS (0.15 ng/g of the detection limit). Mercury levels in the 13 brands of Pu’er tea ranged from 0.00028 to 0.010 mg/g. There was no recent data on Hg levels in other teas available for comparison. The maximum permissible concentrations of arsenic, cadmium and mercury in tea set by the Chinese Ministry of Agriculture are 2, 1 and 0.3 mg/g, respectively. Correlations coefficients between the metal concentrations (Table 4) in the Pu’er tea samples were calculated by statistical analysis of the entire data set. Metal-to-metal correlations for all samples were not significant, and each ion appeared independent from all the other elements except for lead/cadmium.
Conclusions Thirty different brands of Chinese Yunnan Pu’er tea, including 150 commercial samples, were analyzed for
The authors thank Northwest A & F University Testing Center and Kunlong XU for providing tea samples. This project was supported by Foundation of National Technology Support Project (2007BAD58B05-3).
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Food Additives and Contaminants: Part B Han WY, Shi YZ, Ma LF, Ruan JY. 2005. Arsenic, cadmium, chromium, cobalt, and copper in different types of Chinese tea. Bull Environ Contam Toxicol. 75:272–277. Han WY, Zhao FJ, Shi YZ, Ma LF, Ruan JY. 2006a. Scale and causes of lead contamination in Chinese tea. Environ Pollut. 139:125–132. Kumar A, Nair AGC, Reddy AVR, Garg AN. 2005. Availability of essential elements in Indian and US tea brands. Food Chem. 89:441–448. Kuroda Y, Hara Y. 1999. Antimutagenic and anticarcinogenic activity of tea polyphenols. Mutat Res. 436:69–97. Lee WK, The0 venod F. 2008. Novel roles for ceramides, calpains and caspases in kidney proximal tubule cell apoptosis: lessons from in vitro cadmium toxicity studies. Biochem Pharmacol. 76:1323–1332. Narin I, Colak H, Turkoglu O, Soylak M, Dogan M. 2004. Heavy metals in black tea samples produced in Turkey. Bull Environ Contam Toxicol. 72:844–849. Nookabkaew S, Rangkadilok N, Satayavivadm J. 2006. Determination of trace elements in herbal tea products and their infusions consumed in Thailand. J Agric Food Chem. 54(18):6939–6944. Peralta-Videa JR, Lopez ML, Narayan M, Saupe G, Gardea-Torresdey J. 2009. The biochemistry of environmental heavy metal uptake by plants: implications
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for the food chain. Int J Biochem Cell Biol. 41:1665–1677. Qin F, Chen W. 2007. Lead and copper levels in tea samples marketed in Beijing, China. Bull Environ Contam Toxicol. 78:128–131. Rana SVS. 2008. Metals and apoptosis: recent developments. J Trace Elem Med Biol. 22:262–284. Sa´nchez-Chardi A, Ribeiro CAO, Nadal J. 2009. Metals in liver and kidneys and the effects of chronic exposure to pyrite mine pollution in the shrew Crocidura russula inhabiting the protected wetland of Don˜ana. Chemosphere. 76:387–394. Shen FM, Chen HW. 2008. Element composition of tea leaves and tea infusions and its impact on health. Bull Environ Contam Toxicol. 80: 300–304. Thompson J, Bannigan J. 2008. Cadmium: Toxic effects on the reproductive system and the embryo. Reprod Toxicol. 25:304–315. Wang XP, Ma YJ, Itoh M. 2005. Analysis of 23 mineral elements in tea samples collected from China and Japan by using ICP–AES and ICP–MS combined with a closed decomposition (in Chinese). Spectrosc Spectral Anal. 25(10):1703–1707. Wu SC, Yen GC, Wang BS, Chiu CK, Yen WJ, Chang LW, Duh PD. 2007. Antimutagenic and antimicrobial activities of pu-erh tea. LWT Food Sci Technol. 40:506–512.
Food Additives & Contaminants: Part B: Surveillance Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tfab20
Lead, cadmium, arsenic, mercury and copper levels in Chinese Yunnan Pu’er tea a
b
a
a
Pengbo Ning , Chunmei Gong , Yanming Zhang , Kangkang Guo & Juan Bai
b
a
College of Veterinary Medicine, Northwest A & F University , Yangling, Shaanxi 712100, China b
College of Life Sciences, Northwest A & F University , Yangling, Shaanxi 712100, China Published online: 24 Feb 2011.
To cite this article: Pengbo Ning , Chunmei Gong , Yanming Zhang , Kangkang Guo & Juan Bai (2011) Lead, cadmium, arsenic, mercury and copper levels in Chinese Yunnan Pu’er tea, Food Additives & Contaminants: Part B: Surveillance, 4:1, 28-33, DOI: 10.1080/19393210.2011.551945 To link to this article: http://dx.doi.org/10.1080/19393210.2011.551945
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Food Additives and Contaminants: Part B Vol. 4, No. 1, March 2011, 28–33
VIEW DATASET Lead, cadmium, arsenic, mercury and copper levels in Chinese Yunnan Pu’er tea Pengbo Ninga, Chunmei Gongb, Yanming Zhanga*, Kangkang Guoa and Juan Baib a
College of Veterinary Medicine, Northwest A & F University, Yangling, Shaanxi 712100, China; College of Life Sciences, Northwest A & F University, Yangling, Shaanxi 712100, China
b
Downloaded by [University of Calgary] at 22:52 21 October 2014
(Received 18 September 2010; final version received 2 January 2011) The Yunnan region of China produces a distinctive variety of Pu’er tea, which is consequently labeled as a Chinese geographic indication product. In this study, the safety of Chinese Yunnan Pu’er tea with regard to heavy metal content was evaluated in 30 different brands of Pu’er tea, including 150 commercial samples. Metal levels in the Pu’er tea samples followed the order: copper (12–22 mg/g) 4 lead (0.26–3.2 mg/g) 4 arsenic (0.035–0.24 mg/g) 4 cadmium (0.0059–0.085 mg/g) 4 mercury (50.010 mg/g). Mercury was not detected in 17 of the brands of Pu’er tea. Metal-to-metal correlation studies showed that there were no significant correlation between metal pairs. Based on current safety standards, the low levels of metals detected in these Pu’er tea samples mean they are safe for human consumption. Keywords: heavy metals; arsenic; cadmium; mercury; lead
Introduction As the most widely consumed beverage, next to water, tea is an important agricultural crop for the Chinese economy. All varieties of tea are produced from the leaves of Camellia sinensis. Yunnan Province (Southwest China) is an important area for global Camellia sinensis production, most of which is sold as Pu’er tea. Yunnan Pu’er tea is very distinct and is labeled with its Chinese geographic indication. The Pu’er tea trade has been active in Yunnan for at least a millennium, and this area now boasts the largest production and marketing base in the world. Pu’er tea brings huge economic and social benefits to Yunnan, and tons of Pu’er teas are sold in China, South-east Asian, and other overseas markets every year. Most Chinese believe that Pu’er tea can reduce blood lipids, lower blood pressure, and aid digestion. They also believe that the quality of the tea increases with its age and, consequently, aged tea commands a higher the price. Recent research has shown that tea contains specific antioxidants and compounds that can lower the risk of heart disease (Hakim et al. 2003), and have anticarcinogenic (Kuroda and Hara 1999) and antimutagenic (Wu et al. 2007) effects. However, bioaccumulation of trace metals in plant foliage and branch tips presents a potential health risk to humans (Peralta-Videa et al. 2009). During the growth
*Corresponding author. Email: [email protected] ISSN 1939–3210 print/ISSN 1939–3229 online ß 2011 Taylor & Francis DOI: 10.1080/19393210.2011.551945 http://www.informaworld.com
(Han et al. 2006a) and processing of tea (Han et al. 2006b; Qin and Chen 2007), contamination with heavy metals can occur. This is second only to pesticide residues in its potential to adversely impact human health. Consumers are likely at risk of heavy metal exposure and accumulation through drinking Pu’er tea (Shen and Chen 2008). Consequently, many studies have focused on tea safety. Metals, such as lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and copper (Cu), are physiological and neurological toxins and could affect kidney (Lee and The0 venod 2008) and liver (Sa´nchez-Chardi et al. 2009) function, the embryo (Thompson and Bannigan 2008), and other organs or systems in the human body (Al-Saleh et al. 2008; Rana 2008). Considerable research has been conducted on the heavy metal content of green, red and other tea varieties available on the international market (Nookabkaew et al. 2006; Ashraf and Mian 2008). However, limited information is available for Chinese Pu’er tea. We believe a detailed investigation of the heavy metal content of Pu’er tea is important for evaluation of its quality and safety, and to guard against adverse effects on human health. In this study, we analyzed 30 representative Pu’er tea brands, including 150 samples from the Yunnan markets, for Pb, Cd and Cu by atomic absorption spectroscopy (AAS). As and Hg were determined by atomic fluorescence spectroscopy (AFS).
Food Additives and Contaminants: Part B Materials and methods
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Preparation of materials Five commercial Pu’er tea samples were collected from each of 30 different brands (150 samples in total), which were both produced and marketed in Yunnan, China. Depending on the processing technique, Pu’er tea can be classified as either raw or ripened, and half the samples collected were from each class. All glassware was cleaned by soaking in dilute HNO3 and was rinsed with ultrapure water (Milli-Q, Millipore, MA, USA). For wet digestion of samples for determination (Chinese Ministry of Health 2003a–e), portions (2.00 g) of each tea sample were accurately weighed into the dry beakers and digested using a solution of 8 ml HNO3 and 2 ml HClO4 overnight. Afterwards, the solution was gently heated until it became transparent, then filtered and transferred to a 25-ml volumetric flask that had been rinsed many times with a small amount of ultrapure water. Pb, Cd, As and Cu were determined after the flask was shaken to ensure homogeneity of the solution. For Hg, 0.50 g of each ground sample was accurately weighed and digested by microwave digestion (Chinese Ministry of Health 2003e). Each sample was transferred to a Teflon canister. After added 4 ml of HNO3 solution and 1 ml of H2O2 solution, the Teflon canister was maintained as a close system to minimize loss of mercury during the digestion procedure. The mixture was submitted to a three-step program: 200 W (5 min), 350 W (7 min), and 450 W (7 min). After digestion and cooling, the volume of the sample was calibrated to 25 ml with HNO3 (1:9, v/v) solution. Blank samples were prepared in the same way for each selected digestion procedures. All reagents were purchased from Sigma (SigmaAldrich, St. Louis, MO, USA). Trace metal standard solutions (1000 mg/ml) were provided by the National Analysis Center for Iron and Steel (Beijing, China). A certified reference material for tea (GBW10016; Institute of Geophysical and Geochemical Exploration, Langfang, China) with certified Pb (1.5 0.2 mg/g), Cd (0.062 0.004 mg/g), As (0.09 0.01 mg/g), Hg (0.0038 0.0008 mg/g) and Cu (18.6 0.7 mg/g) concentrations were included for quality control.
Methods and measurements An atomic absorption spectrometer (Solar M6, Thermo Electron, USA) was used for determination of Pb, Cd and Cu according to a previously published method (Chinese Ministry of Health 2003b–d). The operating parameters are detailed in Table 1. As and Hg were analyzed using an atomic fluorescence spectrometer (AFS-8220; Titan Instruments, China) by a previously published method
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(Chinese Ministry of Health 2003e). Optimal parameters for this instrument were: negative voltage (400 V for As, 240 V for Hg), lamp current (35 mA for As, 30 mA for Hg), atomizer temperature (300 C for As, 200 C for Hg), and height of atomizer (7.0 mm for As, 8.0 mm for Hg).
Quality control A series of (more than 10) negative blank samples (a sample containing no analyte but with a matrix identical to that of the average sample analyzed) were tested and the mean blank values and the standard deviations (SD) were calculated. The limit of detection (LOD) and limit of quantification (LOQ) were defined as the mean value of the negative blind controls plus 3 SD and 10 SD of the mean, respectively (Armbruster et al. 1994). Repeated analysis (n ¼ 7) of the reference material gave the mean concentration and the relative standard deviation (RSD) of each heavy metal: Pb for 1.5 0.04 mg/g and 3.0%, Cd for 0.062 0.001 mg/g and 1.6%, As for 0.09 0.003 mg/g and 3.7%, Hg for 0.0038 0.0002 mg/g and 4.2%, Cu for 18.6 0.16 mg/g and 0.8%. Recoveries were calculated by spiking with aliquots of metal standards and then analyzing them as usual, according to the original concentrations of the spiked samples (Burns et al. 2002). Acceptable recoveries of 96.7–102.8, 97.2–104.2, 96.8–103.3, 97.5–104.5 and 98.3–103.9% were obtained for externally added Pb, Cd, As, Hg and Cu, respectively. We included at least one laboratory duplicate for each Pu’er tea sample, and the result for each brand was the mean of the five samples analyzed.
Results and discussion The results for heavy metal analysis of the 30 brands of Pu’er tea are shown in Table 2. Among the investigated metals, copper had the highest concentrations and mercury had the lowest. After copper, lead had the second highest concentrations, and this was followed by arsenic, then cadmium. Copper levels ranged from 12.22–22.22 mg/g among the 30 brands of Pu’er tea. The lowest and highest levels of copper were found in samples Gude B and Yuncha A, respectively. The copper content of the Pu’er tea samples was an order of magnitude greater than lead, and copper accounted for most of the total heavy metal content. While copper is an essential element in the human body, excessive copper consumption could impair human health. However, the copper levels detected in the Pu’er tea samples in this study were all below the upper limits imposed for tea by various countries: China (60 mg/g), Japan (100 mg/g), and the United States (150 mg/g). Our results compared well with the literature values reported for tea samples
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P. Ning et al. Table 1. Operating parameters for the atomic absorption spectrophotometer. Parameter Wavelength (nm) Silt (nm) Lamp current (mA) Drying temperature ( C)/time (s) Ashing temperature ( C)/time (s) Atomization temperature ( C)/time (s)
Pb
Cd
Cu
283.3 0.7 6 120/30 450/20 1800/4
228.8 0.5 8 120/30 350/20 1800/4
324.8 0.5 6 120/30 800/20 2300/4
Table 2. Pb, Cd, As, Hg and Cu levels (mg/g) in Pu’er tea samples from Yunnan.
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Brand Yuncha A Yuncha B Dayi 7592 Dayi 0782 Bajiaoting A Bajiaoting B Mengku A Mengku B Linhao A Linhao B Longrun A Longrun B Gude A Gude B Heilongtan Jinhao Heilongtan 8817 Heilongtan Qizi Heilongtan Qiaomu Qingliangshan 0649 Qingliangshan 0419 Qingliangshan 0549 Qingliangshan 0329 Huanglipo A Huanglipo B Wuyi A Wuyi B Paka A Paka B Longsheng 0738 Longsheng B Mean SD
Pb
Cd
As
Hg
Cu
0.58 1.20 0.56 0.71 0.38 0.30 0.93 0.71 0.64 0.69 0.60 0.83 0.48 0.60 0.85 0.90 1.28 0.66 1.28 0.47 1.11 0.26 1.89 3.19 0.44 0.44 1.51 1.39 0.46 0.30 0.86 0.70
0.037 0.033 0.042 0.034 0.023 0.019 0.036 0.040 0.035 0.016 0.0059 0.012 0.0081 0.0076 0.045 0.042 0.057 0.040 0.052 0.053 0.055 0.054 0.080 0.085 0.025 0.066 0.075 0.075 0.078 0.070 0.043 0.024
0.092 0.096 0.083 0.077 0.099 0.068 0.18 0.10 0.13 0.056 0.064 0.13 0.094 0.062 0.24 0.12 0.21 0.24 0.075 0.060 0.15 0.097 0.11 0.066 0.13 0.041 0.15 0.076 0.052 0.035 0.11 0.059
0.0020 ND ND ND ND ND ND ND ND ND 0.0079 ND ND ND 0.0014 0.0011 0.00048 ND ND ND ND 0.00028 ND ND ND ND 0.010 ND ND ND 0.00079 0.0028
22.22 16.48 18.84 16.62 19.64 15.40 16.86 12.84 17.78 15.36 13.74 18.06 16.56 12.22 16.06 13.56 17.68 15.08 18.80 15.53 17.92 15.94 16.98 15.54 16.98 12.68 19.16 15.34 18.82 16.48 16.51 2.26
Notes: ND, not detected. The detection limits were: 5.0 ng/g for Pb, 0.1 ng/g for Cd, 0.01 mg/g for As, 0.15 ng/g for Hg, and 1.0 mg/g for Cu.
from markets in Saudi Arabia (Ashraf and Mian 2008), China (Han et al. 2005), United States (Kumar et al. 2005), and Turkey (Narin et al. 2004) (Table 3). The levels of lead in the Pu’er tea samples ranged between 0.26 and 3.19 mg/g. The lowest concentration of lead was found in sample Qingliangshan 0329. The highest lead concentration was in sample Huanglipo B, and may be attributed to dust particles in packaging. Table 3 shows the large variation in lead levels for teas from different international markets. Shen and Chen (2008) reported the mean concentration of lead in
green tea samples from Taiwan as 0.01 mg/g. The average level in black tea samples from Turkey was 17.9 7.1 mg/g, which may also be caused by dust particles during processing (Narin et al. 2004). Compared with other studies on tea from Chinese markets (Han et al. 2005), much lower levels of lead were detected in the Yunnan Pu’er tea samples in this study. Lead levels in all the Pu’er tea brands analyzed in this study were below the maximum permissible concentration of 5 mg/g (Chinese Ministry of Health 2005).
Species
Pb (mg/g)
Note: NA, not available; ND, not detected.
Yunnan Pu’er tea 0.86 0.70 Saudi Arabia Black tea 1.7 0.8 Taiwan Black, oolong, 2.01, 0.4 and 0.01 and green teas Thailand Green and other teas 3.93 China Black, green, Oolong, 2.7 (Han et al. 2006a) and other teas USA Black, green and other teas NA Japan Green and other teas 0.31 0.04 Turkey Black tea 17.9 7.1
Market
Table 3. Comparison of our results with other studies. As (mg/g)
Hg (mg/g)
Cu (mg/g)
Reference
0.09 0.26 NA NA NA
0.04 0.02 NA 0.0158 0.0036 2.3 0.4
NA NA NA
NA NA
12.3 4.8 NA 16.5 3.9
NA 18.33
Kumar et al. (2005) Wang et al. (2005) Narin et al. (2004)
Nookabkaew et al. (2006) Han et al. (2005)
0.043 0.024 0.11 0.059 0.00079 0.0028 16.51 2.26 This work 1.1 0.5 NA NA 18.1 6.9 Ashraf and Mian (2008) 0.07, 0.005 and ND 0.01, 0.005 and ND NA 0.3, 0.9 and 0.4 Shen and Chen (2008)
Cd (mg/g)
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Food Additives and Contaminants: Part B 31
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P. Ning et al.
Table 4. Correlation coefficients between metal concentrations (r ¼ 95%).
Pb Cd As Hg Cu
Pb
Cd
As
Hg
Cu
1.000
0.205 1.000
0.011 0.000 1.000
0.116 0.033 0.039 1.000
0.002 0.000 0.019 0.003 1.000
lead, cadmium and copper by AAS, and arsenic and mercury by AFS. The results compared well with corresponding international data. Based on the data obtained and current safety standards, the brands of Pu’er tea in this study are safe for human consumption. Variation among the Pu’er tea brands in this study was not large enough to be of commercial significance.
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Acknowledgements Arsenic levels (0.035–0.24 mg/g) in the Pu’er tea samples in this study were lowest in sample Longsheng B and highest in samples Heilongtan Jinhao and Heilongtan Qiaomu. The mean arsenic content was 0.11 0.059 mg/g. A previous study found a mean arsenic concentration of 0.09 mg/g in teas from Thailand (Nookabkaew et al. 2006), which compared well with our results. Han et al. (2006a) found a mean arsenic concentration of 0.26 mg/g in various teas from China. However, Shen and Chen (2008) reported Taiwanese tea samples had arsenic concentrations an order of magnitude lower than our results. The concentration range for cadmium was 0.0059– 0.085 mg/g (mean: 0.043 0.024 mg/g). The lowest cadmium concentration was found in sample Longrun A, and the highest in sample Huanglipo 07516. Cadmium concentrations in the Yunnan Pu’er tea samples were similar to those in tea samples from Taiwan (Shen and Chen 2008), Thailand (Nookabkaew et al. 2006), China (Han et al. 2005), and Japan (Wang et al. 2005). However, the concentrations were lower than those in black teas produced in Saudi Arabia (Ashraf and Mian 2008) and Turkey (Narin et al. 2004) (Table 3). Minimal levels of the heavy metal, mercury, were found in the Pu’er tea samples in this study. Mercury could not be detected in 17 brands of Pu’er tea by AFS (0.15 ng/g of the detection limit). Mercury levels in the 13 brands of Pu’er tea ranged from 0.00028 to 0.010 mg/g. There was no recent data on Hg levels in other teas available for comparison. The maximum permissible concentrations of arsenic, cadmium and mercury in tea set by the Chinese Ministry of Agriculture are 2, 1 and 0.3 mg/g, respectively. Correlations coefficients between the metal concentrations (Table 4) in the Pu’er tea samples were calculated by statistical analysis of the entire data set. Metal-to-metal correlations for all samples were not significant, and each ion appeared independent from all the other elements except for lead/cadmium.
Conclusions Thirty different brands of Chinese Yunnan Pu’er tea, including 150 commercial samples, were analyzed for
The authors thank Northwest A & F University Testing Center and Kunlong XU for providing tea samples. This project was supported by Foundation of National Technology Support Project (2007BAD58B05-3).
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