The concentration and health risk of potentially toxic elements in black and green tea—both bagged and loose-leaf

Heshmati Ali1, Mehri Freshteh1*, Karami-Momtaz Javad1, Khaneghah Amin Mousavi2*

1Nutrition Health Research Center, Hamadan University of Medical Sciences, Hamadan, Iran;

2Department of Food Science, Faculty of Food Engineering, University of Campinas (UNICAMP), São Paulo, Brazil


The concentration of potentially toxic elements (PTEs), including lead (Pb), cadmium (Cd), arsenic (As), zinc (Zn), and copper (Cu), among 160 samples of black and green tea—both bagged and loose-leaf—in Iran was determined using a graphite furnace atomic absorption spectrophotometer (GF-AAS). Besides, the transfer rate of PTEs from made tea into tea infusion was investigated, and the related health risk for consumers was assessed. According to the results, the content of the PTEs is dependent on the type of tea (black or green), the place of cultivation (Iran or India), and the supplied form (both bagged and loose-leaf). The concentration of Pb, Cd, and As in green tea was significantly lower than black tea (P-value < 0.05). On the other hand, the contents of Zn and Cu in green tea were higher than the corresponding values for black tea. The mean concentration of Pb, As, and Zn in bagged tea samples was significantly higher than those of loose-leaf tea, while the Cd and As levels in Iranian tea samples were significantly lower than the Indian samples. Generally speaking, the mean concentration of Pb, Cd, As, Zn, and Cu were 0.59 ± 0.12, 0.12 ± 0.06, 0.16 ± 0.12, 14.23 ± 4.90, and 11.10 ± 2.49 mg kg−1, respectively. The mean transfer rates of Pb, Cd, As, Zn, and Cu were 7.78, 6.29, 9.27, 12.91, and 13.08%, respectively. The estimated daily intake (EDI) and noncarcinogenic quotient (target hazard quotient [THQ]) due to the ingestion of PTEs besides the carcinogenic risk of As and Cd were considered as acceptable.

Key words: PTEs, Iran, green tea, risk assessment, black tea

*Corresponding Authors: Freshteh Mehri, Nutrition Health Research Center, Hamadan University of Medical Sciences, Hamadan, Iran. Email: [email protected]; Amin Mousavi Khaneghah, Department of Food Science, Faculty of Food Engineering, University of Campinas (UNICAMP), Rua Monteiro Lobato, 80. Caixa Postal: 6121.CEP: 13083-862, Campinas, São Paulo, Brazil. Email: [email protected]

Received: 28 May 2020; Accepted: 08 September 2020; Published: 23 September 2020

DOI: 10.15586/qas.v12i3.761

© 2020 Codon Publications

This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0). License (


Tea prepared from Camellia sinensis leaves is the most popular nonalcoholic beverage among the global population (Atasoy et al., 2019). Tea is cultured in many countries, and China and India are the leading producers of tea (Karak and Bhagat, 2010). Moreover, the black and green tea variants are the most consumed (Pourramezani et al., 2019; Sun et al., 2019). It is assumed that 18–20 million cups of tea are consumed globally each day (Chang, 2015). The annual per capita consumption of tea in Iran is 1.3 kg (3.56 g day−1) (Falahi and Hedaiati, 2013). Tea consumption is noticeably increasing due to the reported positive effects on human health, including the reduction in blood cholesterol, improvements in immune system, antiaging properties, and the prevention of several types of diseases, such as cardiovascular diseases, Alzheimer’s disease, diabetes, and different types of cancers (Khan and Mukhtar, 2019; Prasanth et al., 2019; Xu et al., 2020). Tea consumption offers some antioxidant compounds, such as flavonols and polyphenolic compounds, with therapeutic properties (Abass et al., 2019; Amiri et al., 2018; Benjakul et al., 2018; Hussain et al., 2019; Szymczycha-Madeja et al., 2012).

Recently, the contamination of tea by some of the potentially toxic elements (PTEs), such as lead (Pb), cadmium (Cd), and arsenic (As), has attracted global attention (Brzezicha-Cirocka et al., 2016; Falahi and Hedaiati, 2013; Hu et al., 2014; Zhang et al., 2018a). Exposure to Pb may affect the central nervous system, resulting in memory disorder and delay in response time (Abass et al., 2019). Chronic exposure to As may lead to cancer of the kidney and the lung, and skin lesions (Heshmati et al., 2017, 2020). Cd is a very toxic element that can accumulate in the kidney and the bone (Saini and Dhania, 2020).

The accumulation of PTEs in tea depends on some factors, including the methods used for production, processing, and storage. At the same time, the natural occurrences of PTEs in different soils and geographical areas; the type of pesticides and fertilizers utilized in tea production; and anthropogenic sources, such as mining, traffic emissions, and industrial activities, are also among the crucial factors that have a bearing on the concentrations of PTEs in the different types of tea (Gu et al., 2014; Pourramezani et al., 2019; Zhang et al., 2018a).

The concentration of PTEs in tea consumed in Iran and other countries were investigated (Falahi and Hedaiati, 2013; Karimi et al., 2008; Lisia et al., 2019; Martín-Domingo et al., 2017; Nkansah et al., 2016; Polechońska et al., 2015; Shekoohiyan et al., 2012; Shi et al., 2007; Zhang et al., 2018b). However, very little information was found about the concentration of PTEs in black and green tea—both loose-leaf and bagged. Therefore, the main aims of the current study were to measure and compare the concentrations of Cd, As, Pb, Zn, and Cu in green and black tea, supplied as loose-leaf and bagged, and to assess the potential health risks for consumers due to ingestion of PTEs via tea consumption.

Material and methods

Tea samples

A total of 160 tea samples were collected from different supermarkets located in Hamadan city, Iran, between December 2017 and March 2018. Tea samples were divided into two groups, that is, black and green. Samples of each tea were supplied in two forms, that is, bagged and loose-leaf. As for the location of cultivation, tea samples were produced in Iran or imported from India.

Chemical reagents

All chemical reagents, including PTEs, nitric acid, and other analytical grade chemicals, were purchased from Darmstadt, Germany. The plastic vessels were washed several times with tap water and were then soaked in 20% (v/v) nitric solution for the whole night. Subsequently, samples were washed with double distilled water to remove physical contamination.

Infusion preparation

Tea infusion samples were prepared according to common procedures in Iran for tea brewing; 2.00 g of each tea sample was added to 100 mL of boiling distilled water. After 10 min of brewing, the tea infusion was filtered by Whatman No. 42 filter paper to obtain a final clear solution for further processing. The concentration of PTEs in tea infusion was measured according to the described method. The transfer rate percentage (T) of each PTE from made tea samples into the infusion tea was estimated using the following equation (1):

T%C1×0.1×100C2×0.002     Equation (1)

where T is the transfer rate (%); C1 and C2 present the level of the metal in the brewed tea (µg L−1) and made tea (mg kg−1), respectively.

Sample digestion

Before analyzing the PTEs, in order to optimize digestion conditions, oven-dried tea samples were powdered. Then 2.00 g of each sample was poured into a digestion vessel. Afterward, 25 mL of the mixture (3:1 v/v) of HNO3 (65%) and H2O2 (35%) was added. The sample digestion was carried out with the aid of a microwave digestion system (Topex, Preekem Scientific Instruments Co., Ltd., Shanghai, China).

The digestion consists of five stages—stage 1 (2 min at 250 W), stage 2 (2 min at 0 W), stage 3 (2 min at 250 W), stage 4 (5 min at 400 W), and stage 5 (5 min at 600 W). Thus, the extracted sample was dissolved in 10 mL of distilled water; after dilution, it was filtered using filters of 0.45 µm pore size before analysis by an atomic absorption spectrophotometer with a graphite furnace (Thermo Scientifics’ CE 3300, Waltham, MA, USA). All digestions were repeated in triplicate. The used experimental conditions for graphite furnace atomic absorption spectrophotometer (GF-AAS) were demonstrated in Table 1. The data were presented as the average of three repeated measurements.

Table 1. The used Graphite furnace atomic absorption spectroscopy conditions.

Parameter Pb Cd As Zn Cu
Wavelength (nm) 217 228.8 193.7 213.9 324.8
Slit width (nm) 0.5 0.5 0.2 0.2 0.5
Sensitivity (µg ml−1 ) 2.5 0.8 6 0.25 2.5
Lamp current (mA) 10 8 12 6 5

Quality assurance and quality control for the data analysis

Quality assurance and quality control (QA/QC) were ensured based on previous studies (Heshmati et al., 2017; Martín-Domingo et al., 2017), and different factors, including recovery, the limit of detection (LOD) of the method, the limit of quantification (LOQ) of the method, and linearity were measured. The amount of LOD and LOQ were estimated using equations of 3 s/m and 10 s/m, respectively, where “s” expressed the standard deviation of five replicate detections of the blank sample, and m defined the slope of the standard curve for the studied PTEs. The recovery was determined by spiking the tea samples with the known concentrations of 1 mg kg−1 for Pb, 0.1 mg kg−1 for Cd, 0.15 mg kg−1 for As, 25 mg kg−1 for Zn, and 50 mg kg−1 for Cu, with analytical standards into the pre-analyzed tea samples (Nkansah et al., 2016). The calibration curves, linearity equations, regression coefficient (R2), LOD, LOQ, and recovery of studied PTEs in made tea and infusion are indicated in Table 2.

Table 2. The calibration curves, linear regression equations, regression coefficient (R2), the limit of detection (LOD), the limit of quantification (LOQ), and recovery of studied metals in tea.

Metal Range of linearity1 Regression linear equation Regression coefficient LOD1 LOQ1 Recovery ± RSD
Made tea
Pb 2.5–1000 Y = 0.00826x + 0.0146 0.9673 0.310 0.930 96.84 ± 1.34
Cd 2.5–1000 Y = 0.02021x − 0.0161 0.8966 0.170 0.510 108.91 ± 1.16
As 2.5–1000 Y = 0.00972x − 0.0056 0.9947 0.200 0.600 93.21 ± 1.28
Zn 2.5–1000 Y = 0.01487x − 1.3228 0.9991 1.703 5.101 98.43 ± 1.62
Cu 2.5–1000 Y = 0.04476x + 0.0015 0.9426 1.501 5.001 103.06 ± 1.92
Tea infusion
Pb 0.1–50 Y = 0.00733x + 0.0126 0.9681 0.015 0.046 100.84 ± 2.32
Cd 0.1–50 Y = 0.01043x − 0.0151 0.8943 0.008 0.020 98.21 ± 1.51
As 0.1–50 Y = 0.00512x − 0.0051 0.9921 0.011 0.040 107.00 ± 1.52
Zn 0.1–50 Y = 0.03467x − 1.3028 0.987 0.085 0.255 93.21 ± 1.31
Cu 0.1–50 Y = 0.02473x + 0.0115 0.9433 0.025 0.075 113.61 ± 1.22

1µg kg−1 for made tea and µg L−1 for tea infusion.

The LOQ of Pb, Cd, As, Zn, and Cu were 0.930, 0.510, 0.600, 5.101, and 5.001 µg kg−1 in made tea, and 0.046, 0.020, 0.040, 0.255, and 0.075 µg L−1 in tea infusion, respectively. The average recovery was in the range of 93.21–108.91% in made tea and 93.21–113.61% in tea infusion. The RSD percentage estimated for PTEs was lower than 2%. While the LOQ of PTEs was lower than the permissible values in tea, the validated method was sensitive and suitable to determine the PTEs in made tea and also the tea infusion.

Health risk assessment

Calculation of noncarcinogenic risk assessment

For noncarcinogenic health risk assessment, the estimated daily intake (EDI) (mg kg−1 bw day−1), the target hazard quotient (THQ), and the hazard index (HI) were determined according to the following equations (Heshmati et al., 2019; Nkansah et al., 2016; USEPA, 2001):

EDI=C1×M×Tbw,   Equation (2)

where C1, M, T, and bw are the mean PTE concentration (mg kg−1) of made tea, the mean daily consumption of tea (3.56 g day−1), the transfer rate (%) of PTE from made tea to infusion, and the average body weight of an adult (60 kg), respectively.

THQ=EDIRfD   Equation (3)

In this equation, reference dose (RfD) is the standard RfD suggested by the US Environmental Protection Agency (USEPA) (USEPA, 2001). Rfd of Pb, Cd, As, Zn, and Cu were 0.0036, 0.001, 0.0003, 0.3, and 0.04 mg kg−1 day−1, respectively (Antoine et al., 2017; USEPA, 2001; Zhang et al., 2018a)

HI=ljTHQi    Equation (4)

HI shows the sum of each of the THQs of the whole PTE analyzed in each product (Antoine et al., 2017). If THQ and HI were lower than 1, the level of health hazard was considered acceptable for health human (Qin et al., 2015).

Carcinogenic risk assessment

The International Agency for Research on Cancer considered As and Cd as potential carcinogenic PTEs, while Zn, Cu, and Pb were considered to be noncarcinogenic (IARC, 2011; Zeng et al., 2015). Carcinogenic risk (CR) of As and Cd was computed according to the following equation (Saha and Zaman, 2013; USEPA, 2017):

CR=EDI×SF,     Equation (5)

where CR is the carcinogenic rate per lifetime, and SF is the slope factor of cancer. According to the USEPA guidelines, CR in the range of 10−6 to 10−4 is acceptable. SF for Cd and As was 15 and 1.5 mg kg−1 day−1, respectively (Zeng et al., 2015).

Statistical analyses

In this study, the results are shown as mean ± SD. The statistical investigation was conducted using SPSS version 21 (SPSS Inc., Chicago, IL, USA). A sample t-test was employed to compare the mean concentrations of PTEs in different tea samples with the allowable limits of the Iranian National Standardization Organization (INSO, 2014a). The difference among the mean heavy metals of various samples was determined by one-way ANOVA, and the post-doc test was done using the Duncan’s new multiple range test. Statistically, a P-value of < 0.05 was considered as statistically significant.


The comparison between black and green tea with regard to heavy metals

The results obtained for each of the PTEs in tea samples are shown in Tables 3 and 4. The concentration of Pb, Cd, and As in green tea was significantly lower than that in black tea (P-value < 0.05). On the other hand, the concentrations of Zn and Cu in green tea were higher than that in black tea, although the difference was not significant (P-value < 0.05).

Table 3. The PTEs level (mg kg−1) among analyzed tea samples.

Variable Pb Cd As Zn Cu
Tea type Green 0.54 ± 0.12 0.07 ± 0.04 0.10 ± 0.05 14.66 ± 5.74 11.96 ± 2.79
Black 0.65 ± 0.10 0.17 ± 0.01 0.22 ± 0.15 13.80 ± 4.76 10.25 ± 2.18
P-value 0.033 0.015 0.038 0.084 0.068
Tea production origin Iran 0.59 ± 0.09 0.10 ± 0.07 0.13 ± 0.06 14.84 ± 6.92 12.74 ± 1.40
India 0.61 ± 0.17 0.14 ± 0.04 0.19 ± 0.16 13.62 ± 2.68 9.46 ± 2.31
P-value 0.092 0.043 0.023 0.081 0.07
Consumed form Loose leaf 0.69 ± 0.08 0.12 ± 0.06 0.22 ± 0.14 16.08 ± 5.51 10.17 ± 2.79
Bagged 0.50 ± 0.07 0.12 ± 0.04 0.10 ± 0.07 12.39 ± 4.08 12.04 ± 2.09
P-value 0.013 1.15 0.043 0.012 0.064

Table 4. Level of PTEs in made tea and tea infusion.

Heavy metal type Tea type Culture place Form Mean ± SD(mg kg−1) inmade tea Range(mg kg−1)in made* No. upper ofIranian standard (%) Mean ± SD(µg L−1) in teainfusion Transfer rate (%)
Pb Black India Bagged 0.79 ± 0.4a** 0.12–1.51 3 (15) 2.5 ± 0.21a 5.82 ± 0.12
Loose leaf 0.53 ± 0.4b 0.02–1.21 3 (15) 0.82 ± 0.01ab 7.74 ± 1.21
Iran Bagged 0.69 ± 0.2a 0.42–1.32 2 (10) 1.1 ± 0.22a 7.79 ± 0.89
Loose leaf 0.58 ± 0.3b 0.04–1.08 3 (15) 0.76 ± 0.02ab 8.64 ± 1.02
Green India Bagged 0.69 ± 0.43a 0.22–2.00 6 (30) 1.31 ± 0.02a 8.23± 2.12
Loose leaf 0.41 ± 0.34c 0.03–1.20 3 (15) 0.52 ± 0.11b 6.43 ± 0.68
Iran Bagged 0.59 ± 0.27b 0.10–1.03 3 (15) 1.1 ± 0.10a 9.32 ± 1.45
Loose leaf 0.48 ± 0.33bc 0.03–1.06 2 (10) 0.78 ± 0.09ab 8.13 ± 1.35
Total 0.59 ± 0.12 0.02–2.00 24 (15) 1.11 ± 0.61 7.78 ± 0.98
Cd Black India Bagged 0.18 ± 0.23a 0.21–0.35 13(65) 0.21 ± 0.01a 5.53 ± 0.87
Loose leaf 0.16 ± 0.09a 0.07–0.39 10 (50) 0.22 ± 0.02a 6.88 ± 1.05
Iran Bagged 0.11 ± 0.09a 0.03–0.38 6 (30) 0.35 ± 0.03a 5.91 ± 0.35
Loose leaf 0.04 ± 0.01b 0.01–0.09 0 (0) 0.08 ± 00.20b 6.25 ± 0.81
Green India Bagged 0.17 ± 0.11a 0.02–0.37 14 (70) 0.1 ± 0.01b 5.00 ± 0.28
Loose leaf 0.15 ± 0.08a 0.05–0.33 10 (50) 0.22 ± 0.5a 6.47 ± 1.20
Iran Bagged 0.11 ± 0.09a 0.02–0.35 8 (40) 0.21 ± 0.01a 7.00 ± 1.03
Loose leaf 0.03 ± 0.03b 0.01–0.09 0.16 ± 0.09ab 7.27 ± 0.84
Total 0.12 ± 0.06 0.01–0.39 61 (76.25) 0.19 ± 0.08 6.29 ± 0.45
As Black India Bagged 0.42 ± 0.5a 0.10–1.83 10 (50) 0.67 ± 0.01a 7.98 ± 0.59
Loose leaf 0.20 ± 0.3 b 0.07–1.21 3 (15) 0.36 ± 0.03ab 9.00 ± 1.56
Iran Bagged 0.20 ± 0.3b 0.05–1.32 2 (10) 0.44 ± 0.01a 11.00 ± 1.32
Loose leaf 0.07 ± 0.04c 0.11–0.16 2 (10) 0.14 ± 0.01b 9.50 ± 1.65
Green India Bagged 0.10 ± 0.02bc 0.04–0.17 4 (20) 0.21 ± 0.02ab 10.00 ± 1.85
Loose leaf 0.05 ± 0.01c 0.03–0.09 0.09 ± 0.01c 9.00 ± 0.96
Iran Bagged 0.17 ± 0.21bc 0.03–1.09 3 (15) 0.28 ± 0.07ab 8.24 ± 0.58
Loose leaf 0.09 ± 0.02c 0.06–0.13 0.17 ± 0.01b 9.44 ± 0.23
Total 0.16 ± 0.12 0.03–1.83 24 (0.3) 0.3 ± 0.19 9.27 ± 1.09
Zn Black India Bagged 11.52 ± 1.90bc 8.34–15.00 23.44 ± 1.61c 10.17 ± 2.01
Loose leaf 15.16 ± 3.03b 12.08–22.00 41.35 ± 2.61b 13.64 ± 2.21
Iran Bagged 8.76 ± 3.21cd 4.70–16.50 22.49 ± 3.01c 12.84 ± 1.68
Loose leaf 19.77 ± 4.50a 11.8–25.00 48.10 ± 0.13b 12.16 ± 1.52
Green India Bagged 11.20 ± 2.70bc 8.30–18.80 37 ± 0.22b 16.09 ± 2.41
Loose leaf 16.60 ± 2.93ab 14.10–25.60 58 ± 0.05a 17.79 ± 2.05
Iran Bagged 9.02 ± 1.24cd 8.14–12.22 12.2 ± 0.14d 16.29 ± 2.03
Loose leaf 21.82 ± 4.50a 16.4–34.01 62.2 ± 0.01a 14.27 ± 2.12
Total 14.23 ± 4.90 4.70–34.01 38.10 ± 17.80 12.91 ± 1.59
Cu Black India Bagged 7.5 ± 3.5bc 2.2–13.2 23.14 ± 1.21bc 14.43 ± 2.01
Loose leaf 9.7 ± 1.4ab 7.4–12.6 30.05 ± 0.01b 11.90 ± 2.45
Iran Bagged 12.6 ± 1.2a 9.3–16.9 37.76 ± 0.06a 12.92 ± 2.00
Loose leaf 11.2–2.5ab 6.6–15.8 28.33 ± 0.4b 11.28 ± 1.67
Green India Bagged 8.02 ± 4.90b 2.2–16.00 29.12 ± 3.41b 19.33 ± 2.13
Loose leaf 12.63 ± 3.15a 8.21–19.50 25.18 ± 2.13bc 12.83 ± 2.63
Iran Bagged 12.56 ± 4.38a 6.6–19.80 33 ± 3.31ab 14.73 ± 2.08
Loose leaf 14.61 ± 2.55a 10.05–19.20 18 ± 1.15c 7.14 ± 0.65
Total 11.10 ± 2.49 2.2–19.80 28.07 ± 6.06 13.08 ± 1.11

The maximum level of Pb, Cd, As, and Cu (in black tea), and Cu (in green tea) according to Iran standard was 1, 0.1, 0.15, 50, and 150 mg kg−1, respectively.

**Different letters indicated a significant difference among average values within each column (P < 0.05).

The comparison of metals between bagged and loose-leaf tea

The results indicated that the concentration of PTEs differed among tea samples supplied in the form of a tea bag or loose leaf, while the mean concentrations of Pb, As, and Zn in bagged tea samples were significantly higher than that in loose-leaf tea (Table 3).

The comparison of PTEs between Indian and Iranian tea

The levels of Cd (0.10 ± 0.07 mg kg−1) and As (0.13 ± 0.06 mg kg−1) in Iranian tea samples were significantly lower than that in Indian samples (Cd: 0.14 ± 0.04 mg kg−1 and As 0.19 ± 0.16 mg kg−1). However, no significant differences were noted in Pb, Zn, and Cu contents between Iranian and Indian tea (Table 3).

The transfer rate of PTE based on the infusion

In this study, the transfer rates of Pb, Cd, As, Zn, and Cu ranged from 5.82–9.32, 5–7.27, 7.98–11.00, 10.17–17.79, 7.14–19.33%, respectively, while the means were 7.78, 6.29, 9.27, 12.91, and 13.08%, respectively (Table 4). The level of Pb, Cd, As, Zn, or Cu in brewed tea samples differed, while this index is dependent on the initial level of PTEs in making tea. However, there is significant difference between each PTE transfer rate from various tea samples into the infusion.

The risk assessment of PTE intake through tea infusion

The health risk based on PTE intake (Pb, Cd, As) through tea infusion consumption among the Iranian people is shown in Table 5. The results indicated that the EDI of Pb, Cd, and As was lower than the EDI specified by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) (JECFA 1993). Besides, THQ and HI amounts calculated for the above-mentioned toxic metals were lower than 1, indicating that the levels of PTEs mentioned in tea samples are acceptable. According to Table 6, the CR of Cd and As was lower than the standard limit (10−6–10−4), indicating that Cd and As toxicity through the consumption of green and black tea samples pose no problem and could be considered as safe for the consumer (JECFA 1993).

Table 5. The estimated daily intake (EDI), the total hazard quotient (THQ), and hazard index (HI) for heavy metal intake through tea consumption.

Heavy metal Black tea Green tea
EDI (mg kg−1 bw day−1) THQ EDI (mg kg−1 bw day−1) THQ
Pb 3.00E–06 8.33E–04 2.49E–06 6.92E–04
Cd 6.34E–07 6.34E–04 2.61E–07 2.61E–04
As 1.21E–06 4.03E–03 5.50E–07 1.83E–03
Zn 1.06E–04 3.52E–04 1.12E–04 3.74E–04
Cu 7.95E–05 1.99E–03 9.28E–05 2.32E–03
HI = 7.84E–03 HI = 5.48E–03

Table 6. Carcinogenic rate (CR) of As and Cd intake through tea consumption.

Heavy metal type Black tea Green tea
Cd 6.34E–07 4.23E–08 2.61E–07 1.74E–08
As 1.21E–06 8.07E–07 5.60E–07 3.67E–07

The means of Cd and As were 0.07 ± 0.0 and 0.10 ± 0.05 mg kg−1 in green tea, and 0.17 ± 0.01 and 0.22 ± 0.15 mg kg−1 in black tea samples, respectively.

Discussion and Conclusions

In this study, the concentration of PTEs in tea samples consumed in western Iran was determined. The type of tea (black or green), the place of cultivation (Iran or India), and the supplied form (loose-leaf or bagged) were among the factors that were investigated.

The mean concentrations of Pb (0.59 ± 0.12 mg kg−1) and Cu (11.10 ± 2.49 mg kg−1) (Table 4) were lower than the maximum allowable limit according to Iranian standards (Pb: 1 mg kg−1, Cu: 50 and 150 mg kg−1 in black and green tea, respectively). The mean concentrations of Cd (0.12 ± 0.06 mg kg−1) and As (0.16 ± 0.12 mg kg−1) were higher than the acceptable values (0.1 mg kg−1 for Cd and 0.15 mg kg−1 for As), while no significant difference was noted (P-value > 0.05).

Some studies have reported lower levels of PTEs in green tea than black tea; our findings were in line with these studies (Barone et al., 2016; Podwika et al., 2018). The level of Pb in green tea samples (0.47 ± 0.07 mg kg−1) analyzed by Barone et al. (2016) was lower than that of black tea (0.55 ± 0.35 mg kg−1), although de Oliveira et al. (2018) reported higher Pb level in green tea (0.76 ± 0.12 mg kg−1) while compared with black tea (0.64 ± 0.11 mg kg−1) (Barone et al., 2016; de Oliveira et al., 2018). Besides, Zhong et al. (2018) reported that the Pb value of green tea samples from China (0.48–10.57 mg kg−1) was greater than that of black tea (1.88–5.63 mg kg−1) (Zhang et al., 2018b). It seemed that the transfer of PTEs through the industrial equipment used for black tea manufacturing, dust particles during processing, and also soldering being used in the packaging step could be accounted among the reasons for the higher level of PTEs while compared with green tea (Jin et al., 2008).

Our findings were in agreement with a study conducted by Dambiec et al. (2013), which reported that the Pb level of the bagged tea samples was significantly higher than that of loose-leaf tea (Dambiec et al., 2013). The discrepancy between PTE content of bagged and loose-leaf tea was related to the production processes and tea quality that were different for bagged and loose-leaf tea. The bagged tea generally had lower quality, compared with loose-leaf tea (Polechońska et al., 2015).

No significant difference was noted between PTE transfer rates in various kinds of tea, while Dambiec et al. (2013) found that the transfer rate of PTEs in bagged tea was higher than the corresponding values associated with loose-leaf tea. These authors believed that the orthodox process was utilized in leaf tea, causing less cellular damage than the CTC (crush, tear, and curl) process frequently utilized for bagged tea. Therefore, the leaves in bagged tea are crushed into tiny pieces, leading to a higher transfer rate of PTEs (Dambiec et al., 2013). The transfer rates of PTEs into infusion depended on the organic or inorganic form, the solubility of each PTE and their binding into tea leaves, brewing time, and temperature (Lin et al., 2006).

The average level of Pb in samples analyzed in our study (black tea: 0.65 ± 0.10 mg kg−1; green tea: 0.54 ± 0.12 mg kg−1) was higher than that reported in Italy (black tea: 0.55 ± 0.35 mg kg−1; green tea: 0.47 ± 0.07 mg kg−1) (Barone et al., 2016) and lower than that reported in Slovakia (black tea: 1.387 ± 0.54 mg kg−1; green tea: 0.875 ± 0.59 mg kg−1), China (green tea: 3.04 mg kg−1), Saudi Arabia (black tea: 1.7 ± 0.8 mg kg−1), Turkey (black tea: 8.3 ± 0.1 mg kg−1), Japan (black tea: 0.71 ± 0.02 mg kg−1), China (black tea: 3.30 ± 1.42 mg kg−1), and Iran (black tea:1.41 ± 0.72 mg kg−1) (Árvay et al., 2015; Fernández-Cáceres et al., 2001; Han and Li, 2002; Matsuura et al., 2001; Narin et al., 2004; Salahinejad and Aflaki, 2010). The transfer rate of Pb in this research (7.78%) was lower, compared with those explained by de Oliveira et al. (2018) (33% in green tea and 32.5% in black tea). The concentrations of Pb among the tea infusion samples ranged from 0.52 to 2.5 μg L−1, with a mean of 1.11 ± 0.61 μg L−1, which were lower in comparison with the limit (10 μg L−1) set by the World Health Organization for drinking water (WHO, 2011). The diversity observed in the Pb level in different studies may be related to various contaminant sources of Pb in tea crops, including deposits from the unclean air onto the leaves of the tea plants, the plant growth in different soils, and the geographical location (Han and Li, 2002). Cd’s range and mean concentration in all tea samples were reported as 0.01–0.0.39 and 0.12 ± 0.06 mg kg−1, respectively. Cd level in 61 (76.25%) samples was higher than the Iranian limit (0.1 mg kg−1) (INSO, 2014a, 2014b). The highest (0.18 ± 0.23 mg kg−1) and the lowest (0.03 ± 0.03 mg kg−1) mean Cd values were found in Indian bagged black tea and Iranian loose-leaf green tea, respectively. In comparison with other studies, the average concentration of Cd in our study (0.12 ± 0.06 1 mg kg−1) was higher than that reported by Han et al. (2005) in Japan (0.1 mg kg−1), Hosseni et al. (2013) in Iran (0.027 mg kg−1), Li et al. (2015) in China (0.05 mg kg−1) (Han et al., 2005; Hosseni et al., 2013; Li et al., 2015) and was lower than that reported by Yousefi et al. (2017) in Iran (0.19 mg kg−1), Moreda-Piñeiro et al. (2003) in India (2.01 mg kg−1), Saud and Oud (2003) in Japan (1.48 mg kg−1), Narin et al. (2004) in Turkey (2.0 mg kg−1), Ashraf and Mian (2008) in Saudi Arabia (0.49 mg kg−1 mg kg−1), Sofuoglu and Kavcar. (2008) in Turkey (0.19 mg kg−1), and Tsushida and Takeo (1977) in Japan (0.51 mg kg−1) (Ashraf and Mian, 2008; Moreda-Pineiro et al., 2003; Narin et al., 2004; Saud and Oud, 2003; Sofuoglu and Kavcar, 2008b; Yousefi et al., 2017). When compared with other analyzed PTEs, the transfer rate of Cd (6.29%) was lower, which might be related to the strong connection between Cd and the tea matrix (Matsuura et al., 2001). The results indicated that the mean level of Cd (0.19 μg L−1) in tea infusion was similar to a previous study (Sofuoglu and Kavcar, 2008) and lower than the maximum contaminant level in drinking water, that is, 3 μg L−1 (WHO, 2011). It should be mentioned that Cd is a hepatotoxic and nephrotoxic metal, and persistent exposure to it may negatively impact the proximal tubular cells related to the kidneys and lead to renal failure in humans (Byber et al., 2016; Heshmati and Salaramoli, 2015).

In the current investigation, seven (8.75%) green tea samples and 17 (21.25%) black tea samples had higher As content than the maximum limit (0.15 mg kg−1) per the INSO (2014a, 2014b). While the average As in the current study (0.16 mg kg−1) was lower than that demonstrated by de Oliveira et al. (2018) in the United States (green tea: 0.18 ± 0.07 mg kg−1 in; black tea: 0.22 ± 0.02 mg kg−1), Shi et al. (2007) in China (0.30 mg kg−1), Nejatolahi et al. (2014) in Iran (0. mg kg−1), Martín-Domingo et al. (2017) in Spain (0.20 mg kg−1), and Sofuoglu et al. (2008) in Turkey (0.21 mg kg−1), it was higher than the corresponding values reported by Milani et al. (2016) in Brazil (0.021 mg kg−1), Nookabkaew et al. (2006) in China (0.01 mg kg−1), Karimi et al. (2008) in Iran (0.11 mg kg−1), Zhelev et al. (2019) in India (0.05 mg kg−1), and Popović et al. (2017) in Belgrade (0.04 mg kg−1) (de Oliveira et al., 2018; Karimi et al., 2008; Martín-Domingo et al., 2017; Milani et al., 2016; Nejatolahi et al., 2014; Nookabkaew et al., 2006; Popovićet al., 2017; Shi et al., 2007; Sofuoglu and Kavcar, 2008b; Zhelev et al., 2019). As concentration in tea, infusion samples ranged from 0.09 to 0.67 μg L−1, while the recorded transfer rate was between 7.98 and 11.00%. Arsenic levels in all tea infusions were below the MRL (10 μg L−1) in drinking water (WHO, 2011). The mean As content in the tea infusion sample in our study was higher than that analyzed by Szymczycha-Madeja et al. (2012) and Sofuoglu and Kavcar (2008), and lower than samples investigated by Schwalfenberg et al. (2013) (Schwalfenberg et al., 2013; Sofuoglu and Kavcar, 2008). The discrepancies in different studies may be related to the ratio of pollution in various regions, the type of pesticides and fertilizers utilized in tea culture, the attributes of soils, the tea cultivars, and the brewing methods (Chen et al., 2006; Karak et al., 2016; Tokalıoğlu and Kartal, 2004). The exposure to a high level of As via daily consumption of tea could lead to different side effects, such as skin cancers and internal diseases. There are also reports of a significant association between exposure to As and cancer of the liver, prostate, and bladder (Hong et al., 2014).

As shown in Table 4, Zn was the PTE identified the most in this current study. Zn is considered an essential element and has an important role in most of the metabolic activities (Abass et al., 2019; Heshmati et al., 2019). The insufficiency of Zn daily can lead to diminishing appetite, slowing growth, skin disorders, and immune system abnormalities (Salgueiro et al., 2000). Exposure to high amounts of Zn could lead to nausea, vomiting, diarrhea, and prostate cancer (Plum et al., 2010). Based on the recommended daily consumption (RDI) of Zn for adults (15 mg day−1), the maximum daily Zn intake through tea consumption was estimated at 0.1% of RDI for this element (Salgueiro et al., 2000; Zhang et al., 2018b). The average consumption of Zn (14.23 ± 4.90 mg kg−1) in our study was lower than the value described by Srividhya et al. (2011) in green tea (26.39 mg kg−1) of India, Podwika et al. (2018) in green tea (24.4 mg kg−1) of Poland, Falahi and Hedaiati, (2013) in black tea (28.8 mg kg−1) of Iran (Falahi and Hedaiati, 2013; Podwika et al., 2018; Srividhya et al., 2011).

Cu is one of the PTEs found in tea, which is a major element present in various polyphenol oxidase enzymes (Zhang et al., 2018b). According to the INSO (2014a, 2014b) , the permitted level for Cu in green and black tea are 150 and 50 mg kg−1, respectively. In the current study, the Cu level of all samples was less than the mentioned limits. Cu is an important element, and its presence in tea can be beneficial for human beings, although a high dose is toxic. Considering the daily consumption of made tea (3.56 g), the maximum Cu level in samples analyzed in the current study (19.80 mg kg−1), and the transfer rate of 13.08%, the daily Cu intake through tea among Iranian consumers was estimated to be 0.0092 mg, which is 0.46% of the RDI (2 mg) for this element in adults (Goldhaber, 2003). The maximum transfer rate of Cu in our study (19.33%) was less than the findings reported by Zhang et al. (2018b) in China (24%), Brzezicha-Cirocka et al. (2016) in different geographical areas of China (27%), Matsuura et al. (2001) in Japan (23%), and Street et al. (2006) in tea samples (30%) imported into China (Brzezicha-Cirocka et al., 2016; Matsuura et al., 2001; Street et al., 2006; Zhang et al., 2018b). The discrepancy between the present study data and the previous research was related to the existence of different contaminant sources of heavy metals in tea production areas, tea storage and processing procedures, and packaging (Han et al., 2006).

In the current study, EDI values of the mentioned PTEs in tea samples were reduced in the following order: Zn > Cu > Pb > As > Cd. Soliman (2016) indicated EDI levels of Cu and Pb in tea as 0.7 and 0.007 (mg day−1), respectively, which was higher than our findings (Soliman, 2016). In our study, the THQ level of metals in black tea and green tea was in the order of Pb > Cd > As > Zn > Cu and Pb > Zn > Cd > Cu > As. The THQ associated with PTEs in Sri Lankan and Indian black tea were reported as Cu > As > Pb > Cd > Hg and As > Cu > Pb > Cd > Hg, respectively (Pourramezani et al., 2019). In other investigations carried out by Gruszecka-Kosowska and Mazur-Kajta (2016) and Zhang et al. (2018), similar THQ and HI values were reported (Gruszecka-Kosowska and Mazur-Kajta, 2016; Zhang et al., 2018a).

In conclusion, in this study, the concentration of PTEs and the health risk of tea consumed in western Iran were investigated. Pb, Cd, As, Zn, and Cu content were compared between the tea variants (black or green) cultivated in two different places, that is, Iran or India, and supplied as loose-leaf or bagged tea. The mean Pb (0.59 ± 0.12 mg kg−1) and Cu (11.10 ± 2.49 mg kg−1) were lower than the maximum allowable limit according to the INSO (Pb: 1 mg kg−1, Cu: 50 and 150 mg kg−1 in black and green tea, respectively). The mean of Cd (0.12 ± 0.06 mg kg−1) and As (0.16 ± 0.12 mg kg−1) was higher than the acceptable value (0.1 mg kg−1 for Cd and 0.15 mg kg−1 for As), although no significant difference was noted. The statistical data showed that the level of Pb, Cd, and As in green tea was significantly lower than that of black tea (P-value < 0.05). Also, the mean Pb, As, and Zn in bagged tea samples was significantly higher than in loose-leaf tea. Furthermore, the Cd and As levels in Iranian tea samples were significantly lower than the Indian samples. The mean transfer rates of Pb, Cd, As, Zn, and Cu were 7.78, 6.29, 9.27, 12.91, and 13.08%, respectively. An estimate of the non-CR of whole metals and CR for As and Cd indicated that tea consumption posed no health risk to Iranian consumers.


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