All 60 teas met Chinese limits for the harmful elements tested, but conservative risk modeling highlighted cadmium as the main contributor to elevated carcinogenic-risk estimates, while likely overstating real-world exposure.

Study: Pollution, risk and containment of harmful elements in the best-selling tea sold online. Image Credit: Anna_Kim / Shutterstock

In a recent study available as an 'Article in Press' in the journal npj Science of Food, a group of researchers assessed harmful-element contamination, pollution status, and noncarcinogenic and carcinogenic health risks associated with best-selling tea sold online (BSTSO) in China.

Background

What happens when a daily cup of tea also contains trace amounts of harmful elements? Tea is widely consumed in China and worldwide, while online purchasing has become increasingly common. Tea plants are often cultivated in acidic soils, where hazardous elements may be present and can accumulate in tea leaves.

Research shows that hazardous and toxic elements pose various health risks, including carcinogenic, mutagenic, and teratogenic effects. A national soil survey in China identified standard exceedances for arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), and lead (Pb), with cadmium showing the highest exceedance rate among these six elements. Further research is needed to clarify the risks posed by harmful elements in increasingly popular online tea products.

About the study

In 2022, researchers purchased 60 online tea samples in China, comprising 10 varieties each of black, white, dark, yellow, oolong, and green tea, with tea types classified according to the International Organization for Standardization (ISO) 20715. Ground tea powder (0.5 g) was microwave-digested using a nitric acid-perchloric acid mixture, with additional concentrated nitric acid added, diluted to 50.0 mL, and analyzed.

Quality control included six duplicate samples, three reagent blanks, three blank spikes, and three sample spikes. Accuracy and quality criteria were validated using certified reference material (CRM) GBW10052. The six harmful elements, As, Cd, Cr, Hg, Cu, and Pb, were measured using inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS). Recovery, limit of detection (LoD), and limit of quantification (LoQ) complied with the national standard GB 5009.268-2016.

The pollution index (Pi) and Nemerow synthetic pollution index (NSPI) were utilized to evaluate pollution levels. Non-carcinogenic risk was assessed using hazard quotient (HQ) and hazard index (HI) for youth aged 18- 44 years, middle-aged adults aged 45- 59 years, and adults aged 60 years or older.

Carcinogenic risk was assessed using incremental lifetime carcinogenic risk (CRi) and total carcinogenic risk for As, Cd, Cr, and Pb, following United States Environmental Protection Agency (USEPA) protocols. The exposure parameters used in this risk assessment are intake rate, exposure frequency, exposure duration, and body weight.

The oral reference dose (RfD), benchmark dose lower confidence limit (BMDL), and carcinogenic slope factor (SF) were used in risk calculations. The risk calculations used total element concentrations measured in digested tea leaves rather than concentrations measured in brewed tea infusions.

Study results

Among the 60 samples collected in total, the maximum concentrations of As, Cd, Cr, Cu, Hg, and Pb did not exceed Chinese standards. Mean concentrations were 0.28 mg/kg for As, 0.35 mg/kg for Cd, 1.18 mg/kg for Cr, 13.2 mg/kg for Cu, 0.004 mg/kg for Hg, and 0.65 mg/kg for Pb.

As concentrations were below the Canadian limit in all samples, 91.7% were at or above the Iranian limit. Cd concentrations were at or above the Canadian limit in 65.0% and at or above the Iranian limit in all samples. Cr was below the Canadian limit in 95.0% of samples, and Pb was below the Canadian limit in all samples, while 23.3% exceeded the Iranian limit.

Under Chinese standards, the levels of the pollution index (Pi) for all six harmful elements and the Nemerow synthetic pollution index (NSPI) were considered safe for the six types of tea.

Under Canadian standards, Cd indicated light pollution in green, yellow, and dark tea and alert levels in oolong and white tea, while Cr indicated alert levels in green and dark tea. According to Iranian standards, Cd and NSPI indicated heavy pollution in green and yellow tea, while Cd indicated heavy pollution in dark tea.

Average Pi values ranged from 0.01 (Hg) to 0.44 (Cu). NSPI was safe under Chinese standards, alert under Canadian standards, and medium under Iranian standards.

The lowest average hazard index (HI) was found in black tea (0.47), while dark tea had the highest HI (0.74). Mean HI values for young people (0.61), middle-aged individuals (0.59), and individuals aged 60 and above (0.62) were also reported.

All HI values remained below 1, indicating that adverse noncarcinogenic effects were considered unlikely under the study's risk model. As contributed most to HI (29.0%), followed by Cd (20.9%), Cu (20.7%), Pb (16.9%), Cr (12.1%), and Hg (0.4%).

Modeled carcinogenic risk was highest for yellow tea (4.4E-4) and lowest for black tea (1.5E-4), with values of 3.9E-4 for green tea, 3.4E-4 for dark tea, 2.6E-4 for white tea, and 2.3E-4 for oolong tea. Mean carcinogenic risk values were 4.06E-4 for youth, 2.17E-4 for middle-aged adults, and 2.77E-4 for elderly adults.

All three age-group mean values exceeded the acceptable upper limit of 1.0E-4 under the study's risk classification. Cd contributed most to CR, ranging from 77.2% in black tea to 88.4% in yellow tea; Cr contributed 10.0% and As 7.4% on average.

However, the model conservatively assumed complete digestion and 100% absorption of the harmful elements, which the authors said substantially overestimated actual health risks.

Conclusions

Analysis found that harmful-element concentrations in best-selling online teas were, on average, below Chinese national standards, but comparisons with Canadian and Iranian standards revealed additional pollution concerns.

Noncarcinogenic risk remained below the thresholds across youth, middle-aged, and elderly tea drinkers, whereas conservative modeled carcinogenic-risk estimates exceeded the acceptable upper limit. As was the largest contributor to non-carcinogenic risk, while Cd was the dominant contributor to carcinogenic risk.

Yellow tea had the highest carcinogenic risk, and dark tea had the highest noncarcinogenic risk. The authors recommended stronger controls during tea cultivation, production, packaging, logistics, and sales, particularly for As, Cd, and Cr, to reduce potential health risks among tea drinkers.

They also noted that incomplete solubilization and absorption meant the model likely overestimated actual health risks by more than fourfold, and that the health benefits of tea meeting food-safety standards may outweigh these risks, particularly for black tea, while weaker tea was associated with lower modeled risk.

Journal reference:

• Wu, Y., Qiao, N., Sun, Y., Chen, H., Zeng, T., Meng, Y., Ni, Y., Han, X., Wang, A., Qu, W., & Wang, Z. (2026). Pollution, risk and containment of harmful elements in the best-selling tea sold online. npj Science of Food. DOI:10.1038/s41538-026-01047-4. https://www.nature.com/articles/s41538-026-01047-4