Evaluation of trace metal and polychlorinated biphenyl levels in tea brands of different origin commercialized in Italy

Influence of geographical location on the distribution of heavy metals in dairy cattle feeds sourced from two South African provinces

The contamination of feed and food by heavy metals represents a significant concern for the health of both animals and humans. This study investigates the impact of geographical location on heavy metal distribution in dairy cattle feeds sourced from Free State and Limpopo, South Africa (SA). A total of 70 feed samples (40 from Free State and 30 from Limpopo) were collected from 2018 to 2019 and analyzed for heavy metals, including cadmium (Cd), arsenic (As), copper (Cu), zinc (Zn), lead (Pb), and chromium (Cr), using inductively coupled plasma mass spectrometry (ICP-MS). Our findings revealed the presence of Cr, Cu, and Zn in the feeds, but at levels below the FAO/WHO permissible limits. Additionally, As, Cd, and Pb concentrations in the feeds were below the Limit of Detections (LODs). Generally, Cr concentrations (0.032-0.454 mg/kg) identified in the Free State samples were lower than those found in Limpopo (0.038-1.459 mg/kg), while the levels of Cu (0.092-4.898 mg/kg) and Zn (0.39-13.871 mg/kg) recorded in the Free State samples were higher than those from Limpopo [(0.126-3.467 mg/kg) and (0.244-13.767 mg/kg), respectively]. According to independent sample t-tests, Cu and Zn levels were substantially higher (p ≤ .05) in Free State feeds compared to Limpopo, while Limpopo feeds exhibited significantly higher (p ≤ .05) Cr concentrations than Free State feeds. Despite the low recorded heavy metal levels, regular monitoring of these elements in cow diets across all SA provinces is essential for ensuring the well-being of animals and humans.

Dietary Exposure and Health Risk Assessment of Polycyclic Aromatic Hydrocarbons in Black Tea Consumed in Taiwan

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds found in many foods and drinks, and there have been some concerns over these compounds due to their carcinogenic nature. This study evaluated the concentrations of PAH4 (BaP, BaA, BbF, and CHR) in different black tea infusions and drinks based on the origin of the tea. The release of PAH4 from tea leaves to tea infusions was significantly low, with the highest transfer being 25.81%. The mean concentrations of BaP and PAH4 in tea infusions were used to conduct a risk assessment for the Taiwanese population, which showed that the 19-65 age group had the highest estimated intake of PAH4 and BaP among all age groups. These results, however, also showed margin of exposure (MOE) values well above the benchmark of 10,000. This indicated that PAH exposure from black tea consumption for the Taiwanese population constitutes a low-level health concern.

Uptake and translocation of organic pollutants in Camellia sinensis (L.): a review

Camellia sinensis (L.) is a perennial evergreen woody plant with the potential for environmental pollution due to its unique growth environment and extended growth cycle. Pollution sources and pathways for tea plants encompass various factors, including atmospheric deposition, agricultural inputs of chemical fertilizers and pesticide, uptake from soil, and sewage irrigation. During the cultivation phase, Camellia sinensis (L.) can absorb organic pollutants through its roots and leaves. This review provides an overview of the uptake and translocation mechanisms involving the absorption of polycyclic aromatic hydrocarbons (PAHs), pesticides, anthraquinone (AQ), perchlorate, and other organic pollutants by tea plant roots. Additionally, we summarize how fresh tea leaves can be impacted by spraying pesticide and atmospheric sedimentation. In conclusion, this review highlights current research progress in understanding the pollution risks associated with Camellia sinensis (L.) and its products, emphasizing the need for further investigation and providing insights into potential future directions for research in this field.

Comparison and Risk Assessment of Macroelements and Trace Metals in Commercial Teas from Different Regions of China

Tea (Camellia sinensis L.) is one of the most widely consumed non-alcoholic beverages worldwide. In the present study, 73 commercial tea samples were collected from tea plantations in the Southwest, South, Jiangnan, and Jiangbei regions of China. The contents of four macroelements (phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg)) and 15 trace metals (arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb), zinc (Zn), aluminium (Al), copper (Cu), manganese (Mn), iron (Fe), nickel (Ni), thorium (Th), thallium (Tl), rubidium (Rb) and barium (Ba)) in tea samples were determined. The mean concentrations of As, Cd, Cr, Hg, Pb, Zn, Al, Cu, Mn, Fe, Ni, Th, Tl, Rb and Ba were in the range of 0.02-0.61, 0.008-0.126, 0.09-1.12, 0.001-0.012, 0.07-1.62, 19.5-73.2, 170-2100, 5.9-43.3, 228-2040, 60-337, 2.09-17.95, 0.002-0.08, 0.004-0.409, 0-150.50 and 3.1-41.2 µg/g, respectively, which were all lower than the maximum permissible limits stipulated by China (NY/T 288-2012, NY 659-2003). The target hazard quotients of each heavy metal were lower than one, and the combined risk hazard index of all heavy metals for adults was in the range of 0.10-0.85; therefore, there was no significant carcinogenic health risks to tea drinking consumers under the current dietary intake. Significant differences were found in the content of trace elements (Zn, Cu, Fe, Ni, Th, Tl, Rb and Ba) (p < 0.05); however, no significant differences were found in the content of macroelements (P, K, Ca and Mg) and trace metals (As, Cd, Cr, Hg, Pb, Al and Mn) in teas from different regions. Therefore, the region did not affect the heavy metal exposure risk. Correlation coefficient and principal component analyses were performed to determine the source of the elements. Three principal factors were obtained: factor 1 was positively related to Ca, Mg, As, Cd, Cr, Hg, Pb, Al, Mn, Fe and Th (32.63%); factor 2 to P, Zn, Cu and Ni (18.64%) and factor 3 to K and Rb (10.10%). Thus, the elements in the same factor might originate from the same source. This study provides an essential basis to understand the variance and potential risks of different elements in tea from different regions of China.

Concentration and risk assessment of PCNs in green tea in different locations in China

Polychlorinated naphthalenes (PCNs) were added to the Stockholm Convention list of persistent organic pollutants in 2015. PCNs are mainly unintentionally produced during industrial processes nowadays, and can be widely found in environmental media and foodstuffs. Dietary intake is the primary pathway for human exposure to PCNs. PCNs in different categories of foodstuffs have been reported. However, little information on PCN concentrations in green tea, a popular beverage worldwide is available. In this study, all 75 PCN congener concentrations and distributions in green tea samples (n = 102) from 11 regions in China were determined, and risk assessment of human exposure to PCNs through tea consumption was conducted. The PCN concentrations in all the green tea samples were 3.62-175 pg/g dry weight (mean 36.1 pg/g dry weight). Similar PCN homolog and congener profiles were found in green tea samples from different areas. The dominant PCN homologs in all of the green tea samples were di-CNs, tetra-CNs, and tri-CNs. No direct relationships were found between PCN emission sources and PCN concentrations in the green tea samples. The brewing technique could affect the PCN concentrations and homolog profiles in tea leaves. PCNs in green tea from China were found to pose little risk to humans.

In-silico study of reducing human health risk of POP residues' direct (from tea) or indirect exposure (from tea garden soil): Improved rhizosphere microbial degradation, toxicity control, and mechanism analysis

The accumulation of potentially harmful substances in tea garden soils and tea leaves, especially persistent organic pollutants (POPs), is a special concern for tea consumers worldwide. However, their potential health and ecological risks in tea gardens have rarely been investigated. This study proposed measures to improve the degradation ability of POPs by the tea rhizosphere and to reduce the human health risks caused by POPs after tea consumption. In this study, the binding energy values of six types of POPs and the degraded protein were used to reflect the degradation ability and calculated using molecular dynamic simulations. The main root secretions (i.e., catechin, glucose, arginine, and oxalic acid) were selected and applied with a combination of tea fertilizer and trace element combination (i.e., urea, straw, and copper element), leading to an improved degradation ability (49.59 %) of POPs. To investigate the mechanisms of the factors that affect the degradation ability, molecular docking, tensor singular value decomposition methods, multivariate correlation analysis and 2D-QSAR model were used. The results showed that the solvation energy and solvent accessible surface area are the main forces, and the molecular weight, boiling point, and topological radius of the POPs were the key molecular features affecting their degradation ability. Based on the three key characteristics, a diet avoidance scheme (i.e., avoiding lysine, maslinic acid, ethanol, perfluorocaproic acid, and cholesterol with tea), which can reduce the binding ability of POP residues to aromatic hydrocarbon receptors by 506.13 %. This work will provide theoretical strategies to improve the quality and safety of tea production and reduce the potential risks of harmful substance residues in tea garden soils and tea leaves.

Health Risk Assessment of Exposure to Trace Elements from Drinking Black and Green Tea Marketed in Three Countries

Although tea can be beneficial for our health, consuming excess trace elements in tea can be harmful. In this study, the carcinogenic and noncarcinogenic health risk for trace elements in tea influenced by the country of origin, tea type, and infusion process was assessed. Tea (Camellia sinensis) purchased from China, India, and the USA, including black and green tea, were analyzed for essential micronutrients (Cu, Se, and Zn) and nonessential trace elements (Ag, As, Ba, Cd, Cr, and Pb) in leaves and three types of infusions. The results showed that country of origin, tea type, and infusion process had a significant influence on the trace element contents in tea leaves and infusions, also on health risk. Country of origin had a significant influence on Ba, Cr, Pb, and Zn contents in tea leaves and on As, Ba, Cd, Cr, Pb, and Zn contents in tea infusions. Black tea had significantly higher (p < 0.05) Cr and Cu content in tea leaves than green tea, but only Cr content was significantly higher (p < 0.05) than that of green tea in tea infusion. The trace element contents were the highest in the first infusion and decreased as the number of infusion steps increased. The results showed that the consumption of tea infusion was not likely to cause noncarcinogenic risk. However, the carcinogenic risk for As was of concern. Our results indicate that avoiding drinking the first infusion can help to reduce both carcinogenic and noncarcinogenic health risks for trace elements.

Short- and medium-chain chlorinated paraffins in green tea from 11 Chinese provinces and their migration from packaging

Chlorinated paraffins (CPs) have been found to occur ubiquitously in foodstuff of both animal and plant origin. However, limited information is available on the content of CPs in green tea, one of the most commonly consumed beverages worldwide. Herein, 107 commercial green tea samples originating from 11 provinces of China, were collected to study the occurrence of short- and medium-chain chlorinated paraffins (SCCPs and MCCPs, respectively). The concentration of SCCPs in all green tea samples ranged from 4.99 to 717 ng/g (mean: 55.7 ng/g), while MCCPs ranged from 2.55 to 543 ng/g (mean: 33.5 ng/g). CP profiles in green tea samples from different provinces exhibited no regional differences. To identify the potential sources of CPs in green tea, 19 tea packaging samples were collected and analyzed, showing that SCCPs and MCCPs existed at much higher concentrations in the tea packaging material than in the teas. Migration tests indicated that CPs could migrate from packaging into teas during storage, with the migration velocity and efficiency of SCCPs being higher than MCCPs.

Risk assessment of heavy metals in rooibos (Aspalathus linearis) tea consumed in South Africa

A total of 80 rooibos tea samples from a range of brands were purchased from various registered retail shops in South Africa. The samples were bought during 2019 winter (40) and summer (40) period which are classified as 6 natural rooibos, 18 herbal rooibos samples, and 16 flavor rooibos samples and subjected for heavy metal analysis such as chromium (Cr), iron (Fe), arsenic (As), cadmium (Cd), and lead (Pb) using inductively coupled plasma mass spectrometer (ICP-MS). Human health risks were determined by estimating the daily intake non-cancer hazard quotient (THQ) and hazard index (HI) via oral exposure to toxic elements based on daily tea consumption. The concentration range of the determined heavy metals in rooibos tea samples were as follows: Cr (0.17-11.98 mg/kg), Fe (31-450 mg/kg), As (ND-0.51 mg/kg), Cd (0.09-0.17 mg/kg), and Pb (0.06-2.73 mg/kg). Cr was found in higher amount when compared to the World Health Organization (WHO) permissive limit (1.3 mg/kg). The concentrations of all studied heavy metals during winter and summer period were compared using two-way Anova, and no significant differences (p = 0.832) were observed for the two seasons. Both the target risk quotient (THQ) and the hazard index (HI) levels in all analyzed tea were well below 1, implying that intake of rooibos tea with analyzed heavy metals should not cause a threat to human health. On the other hand, the continuous intake due to the high concentrations of trace metals such as Cr may pose a serious chronic health risk due to accumulation in body tissues over time. The study, therefore, suggests constant monitoring of these heavy metals in teas in order to limit the risk of exceeding the permissive limits.

Are Disinfection Byproducts (DBPs) Formed in My Cup of Tea? Regulated, Priority, and Unknown DBPs

Globally, tea is the second most consumed nonalcoholic beverage next to drinking water and is an important pathway of disinfection byproduct (DBP) exposure. When boiled tap water is used to brew tea, residual chlorine can produce DBPs by the reaction of chlorine with tea compounds. In this study, 60 regulated and priority DBPs were measured in Twinings green tea, Earl Grey tea, and Lipton tea that was brewed using tap water or simulated tap water (nanopure water with chlorine). In many cases, measured DBP levels in tea were lower than in the tap water itself due to volatilization and sorption onto tea leaves. DBPs formed by the reaction of residual chlorine with tea precursors contributed ∼12% of total DBPs in real tap water brewed tea, with the remaining 88% introduced by the tap water itself. Of that 12%, dichloroacetic acid, trichloroacetic acid, and chloroform were the only contributing DBPs. Total organic halogen in tea nearly doubled relative to tap water, with 96% of the halogenated DBPs unknown. Much of this unknown total organic halogen (TOX) may be high-molecular-weight haloaromatic compounds, formed by the reaction of chlorine with polyphenols present in tea leaves. The identification of 15 haloaromatic DBPs using gas chromatography-high-resolution mass spectrometry indicates that this may be the case. Further studies on the identity and formation of these aromatic DBPs should be conducted since haloaromatic DBPs can have significant toxicity.

Persistent organic pollutants (PCBs and PCDD/Fs), PAHs, and plasticizers in spices, herbs, and tea - A review of chromatographic methods from the last decade (2010-2020)

Edible and highly demanded plant-derived products such as herbs, spices, and tea may be subjected to exogenous contamination of well-known chemical hazards such as persistent organic pollutants (POPs), and emerging ones such as plasticizers, affecting negatively the safety of these food commodities. This fact has led to the increasing analysis of exogenous compounds including priority POPs such as polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs), as well as highly persistent polycyclic aromatic hydrocarbons (PAHs). Currently, plasticizer residues are also considered an emerging issue because of the extensive use in food packaging and potential migration into foodstuffs. In this review, the studies published from 2010 to 2020 were discussed, including the main extraction methods applied for these contaminants from herbs, spices, and tea, and it was revealed the trend toward the use of less solvent-consuming and time-effective methods. Chromatographic methods were also described, which were mainly combined with detection techniques such as classical or mass spectrometry (MS) detection. Finally, a comprehensive overview of the occurrence of these selected exogenous compounds was presented in the studied matrices, showing that their monitoring should be further investigated to ensure food safety of highly consumed condiments and tea.

Distribution, accumulation, and potential risks of heavy metals in soil and tea leaves from geologically different plantations

Risk assessment regarding heavy metals in tea is crucial to ensure the health of tea customers. However, the effects of geological difference on distribution of heavy metals in soils and their accumulation in tea leaves remain unclear. This study aimed to estimate the impacts of geological difference on distribution of cadmium (Cd), lead (Pb), thallium (Tl), mercury (Hg), arsenic (As), antimony (Sb), chromium (Cr), nickel (Ni), and manganese (Mn) in soils and their accumulation in tea leaves, and further evaluate their health risks. 22 soils and corresponding young tea leaves (YTL) and old tea leaves (OTL), from geologically different plantations, were sampled and analyzed. Results showed that heavy metals concentrations in soils, derived from Permian limestone and Cambrian weakly mineralized dolomite, were obviously greater than those from Silurian clastic rock. The geological difference controlled the distribution of soil heavy metals to a large extent. Contents of Cd, Tl, and Mn in tea leaves mainly depended on their contents in soils. Soil Hg, Pb, As, and Sb contents may not be the only influencing factors for their respective accumulation in tea leaves. More attentions should be paid to soil acidification of tea plantations to ensure the tea quality security. Target hazard quotients (THQ) of Cd, Pb, Tl, Hg, As, Sb, Cr, and Ni and hazard index (HI) via tea intake were below one, indicating no human health risk. The non-mineralized Silurian area was less at risk of heavy metals accumulation in tea leaves than the Cambrian metallogenic belt and the Permian Cd-enriched zone. This study could provide an important basis to understand and mitigate the potential risks of heavy metals in tea.

Isotope tracers for lead and strontium sources in the Tieguanyin tea garden soils and tea leaves

The concentrations of Pb & Sr in Tieguanyin tea leaves and soils from 15 tea gardens of Anxi, China, were determined and the sources of Pb & Sr in soil and leaf samples were analysed using isotope tracing technology. The results showed pH in soils had significant correlations to both acid-extractable Pb & Sr in soils and new leaves. The Pb concentration in leaves was significantly lower than that in soils, especially the acid-extractable Pb in soils. The low Bio-concentration Factor (BCF) indicated the bioavailable Pb in soils could not easily be transferred to leaves. The contribution rates of parent material were 61%-100% and 45%-100% for total Pb isotope and acid-extractable Pb isotope in soils, respectively, indicating a low impact of human activity. A sizeable influence of parent material for leaves was also observed, suggesting that Pb may be present in the dust-fall. Although Sr concentrations in leaves were not high, they exceeded that in soils. The high BCF also indicated that tea has a high capacity to accumulate Sr, with the coincidence that Sr⁸⁷/Sr⁸⁶ in the acid-extractable isotope in soils were similar to new leaves. A Pb-Sr joint tracer indicated that Sr in old and new leaves may be influenced by parent material and anthropogenic sources, respectively.

Evaluation of heavy metal concentration in imported black tea in Iran and consumer risk assessments

Tea grows in the contaminated soils, absorbs the heavy metals, and enters them into the human food chain. The concentrations of Pb, Cd, Cu, As, and Hg of the imported black tea leaves to Hormozgan Province were evaluated by atomic absorption spectrometer. Then, the Hazard Quotient (HQ) and Hazard Index (HI) levels of heavy metal intakes were calculated to estimate the health hazard for consumers. The Pb, Cd, Cu, As, and Hg concentrations in the Sri Lankan and Indian blank tea were 0.14, 0.017, 11.29, 0.057, 0.0076 mg/kg, and 0.21, 0.02, 14.56, 0.067, 0.01 mg/kg, respectively. It was found that except for As concentration in Indian black tea were higher than Sri Lankan black tea. The HQ and HI levels of all studied metals were less than one, but they were higher in Indian black tea compared with the Sri Lankan black tea. The HI of Indian and Sri Lankan black tea samples were 0.061 and 0.048, respectively, which indicated no significant health hazard for tea consumers. The results showed that the consumption of the studied tea could not have any risk of heavy metal exposure.

Zn, Ni, Mn, Cr, Pb and Cu in soil-tea ecosystem: The concentrations, spatial relationship and potential control

Excessive accumulation of heavy metals in tea has certain health risk to the consumers. To discuss the spatial relationship between heavy metals in tea leaves and soil in a county scale, 74 samples of tea leaves and corresponding subsoil (15-30 cm) were collected in the tea plantations of Lishui, Nanjing, China. The total Zn, Ni, Mn, Cr, Pb and Cu in both tea leaves and soil samples, as well as pH value in soil were analyzed. The results of regression showed that the Mn and Cr in tea leaves were increased when the Mn and Cr in soil were at high levels, and higher pH decreased Zn, Ni, Mn and Cu contents in tea leaves. Moreover, distance to village and metal industry had negative impacts on the Mn level in soil. It is necessary to control the pH of soil in tea plantations which are close to villages or metal industries, as well as, to search more appropriate areas, where are far away from villages or metal industries, to plant tea should be taken into consideration. In addition, 17.57% of the samples have higher concentration of Pb than the maximum limits was found in tea plantation of Lishui. Heavy metals (Cr) standards regarding leafy vegetables is used for reference in this study, as there are no maximum levels of contaminants (MLC) in tea. It is significant to construct a targeted standard of heavy metals contents that could applicable throughout the world for reduce the health risks to the consumers.

Green Tea Quality Evaluation Based on Its Catechins and Metals Composition in Combination with Chemometric Analysis

Green tea infusions are one of the most popular beverages consumed across the world, especially is Asian countries. Green tea quality is primarily based on catechin content, however, the concentration of elements could also significantly influence its biological properties and thus quality and safety. The main purpose of the present study was the evaluation of catechin, antioxidant activity and metal content (K, Na, Ca, Mg, Fe, Mn, Cu, Zn, Cr, Pb, Cd and Ni) in different green tea types cultivated in Japan, Sri Lanka, South Korea, India, China and Japan. The chemical analysis of samples was performed using LC-ESI-Q-TOF-MS for organic constituents and atomic absorption spectrometry (flame and electrothermal) method for inorganic ones. The obtained results were subjected to chemometric elaboration. EGC (213 mg/100 mL of the tea infusion in South Korean Jeoncha) and EGCG (124 mg/100 mL in Japanese Sencha) were the dominant catechins in all green tea samples. Chinese and Indian green tea samples contained the highest concentration of toxic heavy metals, however these values were far below appropriate limitations for green teas. PCA revealed significant similarities between Japanese samples and Korean Jeoncha. In general the latter one was evaluated to have the best quality based on the investigated parameters.

Aluminum and Heavy Metal Accumulation in Tea Leaves: An Interplay of Environmental and Plant Factors and an Assessment of Exposure Risks to Consumers

Environmental and plant factors (soil condition, variety, season, and maturity) and exposure risks of aluminum (Al), manganese (Mn), lead (Pb), cadmium (Cd), and copper (Cu) in tea leaves were investigated. The concentrations of these metals in tea leaves could not be predicted by their total concentrations in the soil. During any one season, there were differences in Al, Mn, and Cd levels between tea varieties. Seasonally, autumn tea and/or summer tea had far higher levels of Al, Mn, Pb, and Cd than did spring tea. Tea leaf maturity positively correlated with the concentrations of Al, Mn, Pb, and Cd, but negatively with Cu. The calculated average daily intake doses (mg/ [kg•d]) for these metal elements were 0.14 (Al), 0.11 (Mn), 2.70 × 10^-3 (Cu), 2.80 × 10^-4 (Pb), and 2.88 × 10^-6 (Cd). The hazard quotient values of each metal were all significantly lower than risk level (=1), suggesting that, for the general population, consumption of tea does not result in the intake of excessive amounts of Al, Mn, Pb, Cd, or Cu. This study identified the factors that can be monitored in the field to decrease consumer exposure to Al and Mn through tea consumption.

PRACTICAL APPLICATION

Environmental and plant factors influence aluminum and heavy metal accumulation in tea leaves. Consumers of tea are not ingesting excessive Al, Mn, Pb, Cd, or Cu. Trackable factors were identified to manage exposure levels.

Evaluation of Macro- and Microelement Levels in Black Tea in View of Its Geographical Origin

The aim of this study was to evaluate the elemental composition of black tea samples and their infusions in view of their geographical origin. In total, 14 elements were analyzed, 13 (Ca, K, Mg, Na, Mn, Fe, Zn, Cu, Cr, Ni, Co, Cd, and Pb) by flame atomic absorption spectrometry, and P by UV-Vis spectrometry, after mineralization of samples. It was found that K was the most abundant macroelement in the analyzed samples, whereas among microelements, the highest concentration was found for Mn. Based on the obtained data, the percentage of elements leached into the infusions as well as the daily elemental intake from tea were calculated. The daily intake from tea was compared to the recommended daily allowances (RDAs), and the highest percentages of the RDAs were found for Mn (15 %) and Co (10 %). To study the relations between elemental composition and country of origin of samples, factor analysis and cluster analysis were applied. These multivariate techniques proved to be efficient tools able to differentiate samples according to their provenance as well as plantation within the common regions.

Determination of heavy metals in the soils of tea plantations and in fresh and processed tea leaves: an evaluation of six digestion methods

Background

The aim of this study was to determine the levels of cadmium (Cd), chromium (Cr), lead (Pb), arsenic (As) and selenium (Se) in (1) fresh tea leaves, (2) processed (black) tea leaves and (3) soils from tea plantations originating from Bangladesh.

Methods

Graphite furnace atomic absorption spectrometry (GF-AAS) was used to evaluate six digestion methods, (1) nitric acid, (2) nitric acid overnight, (3) nitric acid–hydrogen peroxide, (4) nitric–perchloric acid, (5) sulfuric acid, and (6) dry ashing, to determine the most suitable digestion method for the determination of heavy metals in the samples.

Results

The concentration ranges of Cd, Pb, As and Se in fresh tea leaves were from 0.03–0.13, 0.19–2.06 and 0.47–1.31 µg/g, respectively while processed tea contained heavy metals at different concentrations: Cd (0.04–0.16 µg/g), Cr (0.45–10.73 µg/g), Pb (0.07–1.03 µg/g), As (0.89–1.90 µg/g) and Se (0.21–10.79 µg/g). Moreover, the soil samples of tea plantations also showed a wide range of concentrations: Cd (0.11–0.45 µg/g), Pb (2.80–66.54 µg/g), As (0.78–4.49 µg/g), and Se content (0.03–0.99 µg/g). Method no. 2 provided sufficient time to digest the tea matrix and was the most efficient method for recovering Cd, Cr, Pb, As and Se. Methods 1 and 3 were also acceptable and can be relatively inexpensive, easy and fast. The heavy metal transfer factors in the investigated soil/tea samples decreased as follows: Cd > As > Se > Pb.

Conclusion

Overall, the present study gives current insights into the heavy metal levels both in soils and teas commonly consumed in Bangladesh.