Dietary risk assessment of fluoride, lead, chromium, and cadmium through consumption of Tieguanyin tea and white tea

Overview

This study reports concentrations of fluoride, lead, chromium, and cadmium in 112 Camellia sinensis tea samples drawn from the major production counties of Fujian Province, China, and uses transfer-rate-adjusted infusion exposures to compute hazard indices and target cancer risks for adult tea consumers. It is routeable for lead (Pb), chromium (Cr), and cadmium (Cd) occurrence evidence on Camellia sinensis tea (oolong-class Tieguanyin and unfermented white tea) in a Chinese production-region market.

Key numbers

• Sample design: 112 samples total — 40 Tieguanyin from Anxi, 32 Tieguanyin from Hua’an, and 40 white tea from Fuding, all sampled by county agricultural bureaus. Each lot was collected at 500 g per sample; a 200 g subsample was then ground and passed through a 200 µm polyethylene sieve. All concentrations reported on a dry-weight (DW) basis.
• Lead, dry tea (mg/kg DW, mean ± SD; range): Tieguanyin Anxi 0.91 ± 0.41 (0.31–2.00); Tieguanyin Hua’an 0.81 ± 0.24 (0.40–1.28); white tea Fuding 0.65 ± 0.37 (0.18–1.69); pooled mean 0.79 ± 0.34. Per Table 2, Anxi Tieguanyin Pb was statistically higher than the other two strata at p<0.05.
• Chromium, dry tea (mg/kg DW, mean ± SD; range): Tieguanyin Anxi 0.58 ± 0.30 (0.11–1.38); Tieguanyin Hua’an 0.54 ± 0.27 (0.18–1.20); white tea Fuding 0.73 ± 0.52 (0.14–2.30); pooled mean 0.62 ± 0.39. White-tea Cr was higher than Hua’an Tieguanyin Cr at p<0.05; the paper does not speciate Cr-III vs hexavalent chromium (Cr-VI), so all Cr values are total Cr.
• Cadmium, dry tea (mg/kg DW, mean ± SD; range): Tieguanyin Anxi 0.04 ± 0.03 (0.01–0.11); Tieguanyin Hua’an 0.02 ± 0.01 (0.01–0.05); white tea Fuding 0.03 ± 0.01 (0.01–0.07); pooled mean 0.03 ± 0.02. Anxi Tieguanyin Cd was statistically higher than the other two strata at p<0.05.
• Fluoride, dry tea (mg/kg DW, mean ± SD; range): Tieguanyin Anxi 190 ± 78 (73–350); Tieguanyin Hua’an 188 ± 101 (89–580); white tea Fuding 142 ± 87 (48–290); pooled mean 173 ± 83. Tieguanyin F was significantly higher than white-tea F at p<0.05.
• Infusion transfer rates assumed in the dietary model (% from dry leaf to brewed infusion, Table 4): Tieguanyin F 94, Pb 50.1, Cr 47.5, Cd 52.7; white tea F 100, Pb 7.1, Cr 12.4, Cd not detected. The white-tea rates for Pb, Cr, and Cd were borrowed from previously reported green-tea transfer rates because no white-tea-specific values were available.
• Adult exposure model (Table 4): 10 g dry tea per day, 60 kg body weight. Chronic daily intakes (CDI, µg/kg bw/day): Tieguanyin F 29.68, Pb 7.19×10⁻², Cr 4.46×10⁻², Cd 2.82×10⁻³; white tea F 23.68, Pb 7.73×10⁻³, Cr 1.52×10⁻², Cd not computed.
• Target hazard quotient (THQ, dimensionless): Tieguanyin F 7.42×10⁻³, Pb 2.02×10⁻², Cr 1.49×10⁻², Cd 2.82×10⁻³; white tea F 5.92×10⁻³, Pb 2.17×10⁻³, Cr 5.05×10⁻³. Combined hazard index HI = 4.53×10⁻² for Tieguanyin and 1.31×10⁻² for white tea, both well below the action threshold of 1.
• Carcinogenic risk (lifetime probability, dimensionless): for the three carcinogen-relevant analytes (Pb classed by USEPA as probable carcinogen; Cd and Cr as carcinogenic), individual TR values for Tieguanyin gave Cr the highest TR at 2.23×10⁻⁵, followed by Cd, then Pb. Total target cancer risk TR_total = 4.01×10⁻⁵ for Tieguanyin and 7.64×10⁻⁶ for white tea — both within the USEPA-acceptable 10⁻⁶ to 10⁻⁴ range.
• Metal-to-metal Pearson correlations in dry tea (r at α=0.95, Table 3): Tieguanyin Pb/Cd r=0.392 (p<0.01) and Cr/Cd r=−0.297 (p<0.05), with Pb/Cr non-significant (r=0.173); white tea Pb/Cr r=0.350 (p<0.05), with Pb/Cd (r=−0.150) and Cr/Cd (r=−0.276) non-significant. The authors interpret the positive Pb/Cd pair in Tieguanyin tea and the positive Pb/Cr pair in white tea as evidence that those metals share a common pollution source within each tea type.

Methods

Tea samples were collected from major production counties in Fujian Province by the local agricultural bureaus at 500 g per lot; a 200 g subsample of each lot was then ground and passed through a 200 µm polyethylene sieve and stored in polyethylene at 4 °C until analysis. Fluoride was extracted with 0.2 M HCl for one hour, diluted with ionic-strength adjusting buffer, and measured by fluoride ion-selective electrode (INESA Scientific Instrument Co., Shanghai, China) following the China national standard for fluoride in food (Standardization Administration of China, 2003); recovery against the GBW10016 tea certified reference material was 94% with an 8% standard deviation. Lead, chromium, and cadmium were measured by inductively coupled plasma mass spectrometry on a Thermo Fisher XSERIES 2 ICP-MS after microwave digestion of 0.5 g tea with 5 mL of 65% HNO₃ in a TOPEX system (Preekem Scientific Instruments, Shanghai, China) at 800 psi and 170 °C for 10 minutes, then evaporation to near dryness and reconstitution in 25 mL of de-ionized water in PTFE bottles. Limits of detection were 0.005 mg/kg for Pb, 0.001 mg/kg for Cd, and 0.05 mg/kg for Cr; mean recoveries for Pb, Cd, and Cr against the GBW10016 CRM ranged from 90% to 115% with SD below 10%. Each sample was measured in triplicate with reagent blanks. The paper does not speciate Cr, so all reported Cr values are total Cr. Pearson correlation matrices and one-way ANOVA were computed in SPSS v20 (SPSS Inc., Chicago, IL, USA). The dietary risk model used USEPA reference doses (F 4000, Cr 0.5, Cd 1 µg/kg/day) and a provisional tolerable daily intake (Pb 3.57 µg/kg/day, FAO/WHO) for the THQ calculation, and USEPA slope factors (Pb 0.0085, Cr 0.5, Cd 6.1 mg/kg/day) for the cancer-risk calculation. The adult intake assumption was 10 g tea per day at 60 kg body weight; infusion transfer rates for Tieguanyin were quoted from Shokrzadeh et al. (2008), Shen and Chen (2008), and Koblar et al. (2012), and the green-tea transfer rates were used as the white-tea proxy for Pb, Cr, and Cd because white-tea-specific values were not available.

Implications

The source supports occurrence evidence for Pb, Cr, and Cd in Camellia sinensis dry leaf from a Chinese production-region market and provides an internally consistent adult dietary-exposure model for the Tieguanyin and white-tea production chain. The paper’s hazard-index and total-cancer-risk values fall within the USEPA-acceptable bands at the modelled 10 g/day adult intake; the paper itself cautions that the exposure model excludes other tea-borne elements such as inorganic arsenic, aluminium, and mercury, and that other exposure pathways (water, food, skin) are not captured. Pb is also higher in Anxi Tieguanyin than in Hua’an Tieguanyin or Fuding white tea (p<0.05), which the authors attribute to leaf-age differences in plucking standard (one bud and four or five leaves for Tieguanyin versus one bud and three leaves for white tea) rather than to formula or fermentation. White-tea Cr is higher than Hua’an Tieguanyin Cr (p<0.05), and the authors flag soil-Cr speciation and cultivar-specific uptake as candidate explanations. The Pearson correlations are consistent with a shared anthropogenic source for Pb–Cd and Pb–Cr in Tieguanyin tea but do not isolate that source. Cr values are total Cr, not Cr-VI, so no Cr-VI-specific routing applies. Cd transfer to the white-tea infusion was below detection, so the white-tea Cd CDI/THQ/TR is not computable in the exposure model.

Related evidence

• Camellia sinensis
• Tea
• Tea
• Tea Infusions
• True Tea (Camellia Sinensis)
• Lead
• Chromium
• Cadmium

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