Tea is enjoyed by millions of people every day, but tea leaves can also accumulate traces of persistent environmental pollutants during cultivation and production. A new nationwide study provides one of the most comprehensive assessments to date of polychlorinated biphenyls (PCBs) in commercial tea produced across China.
Researchers analysed 192 tea samples covering all six major tea categories and 16 Chinese provinces, testing for 18 PCB compounds, including six indicator PCBs and 12 dioxin-like PCBs. Although PCBs were detected in all samples, the health risk assessment found that exposure from drinking Chinese tea is unlikely to pose an appreciable health risk to consumers.
“Tea leaves have a long journey from the field to the cup, and contaminants can potentially enter at several stages,” said corresponding author Wenfeng Zhou. “Our study provides a national baseline that helps us understand where PCBs occur in tea, how processing may influence their levels, and what those concentrations mean for consumers.”
Total concentrations of the 18 PCBs ranged from 9.36 to 4,490 picograms per gram (pg/g) of dry tea, with substantial differences among tea types. Dark tea had the highest average concentration at 549 pg/g, followed by oolong tea at 241 pg/g, while yellow tea recorded the lowest average concentration at 93.3 pg/g.
Geographic variations were also observed. Tea produced in Guangdong had the highest average PCB concentration at 505 pg/g, followed by Yunnan, Chongqing, Guangxi and Shaanxi. Researchers suggest these differences could reflect local environmental contamination, historical industrial activities and variations in tea production practices. Analysis of the chemical profiles showed that lower-chlorinated PCBs were dominant, with CB-28 and CB-52 contributing substantially to the overall PCB profile.
The researchers also examined whether tea processing itself could affect PCB concentrations by comparing fresh green tea leaves with tea made from the same batch. Total PCB levels increased from 51.2 to 63.7 pg/g after processing, largely because of increases in indicator PCBs. However, the difference was not statistically significant, suggesting that processing was not a major source of PCB contamination in this experiment.
For consumers, the health risk assessment offered reassuring results. Using World Health Organization toxic equivalency factors and typical tea consumption rates, researchers estimated exposure to dioxin-like PCBs. Green tea produced the highest estimated weekly intake because it is consumed in larger quantities, but estimated exposure remained well below established tolerable intake thresholds.
The authors caution that their assessment considers PCB exposure from tea alone rather than a person’s total dietary exposure. Because PCBs persist in the environment and can accumulate through food chains, continued monitoring is important. The study establishes a national baseline for PCBs in Chinese commercial tea, providing evidence that could strengthen food safety surveillance and help identify opportunities to reduce contamination throughout the tea production chain.
More information: Xingyi Wu et al, Profiling of polychlorinated biphenyls in Chinese tea: national distribution, variety-specific variations, and the impact of processing, New Contaminants. DOI: 10.48130/newcontam-0026-0019
Journal information: New Contaminants Provided by Shenyang Agricultural University Collaborative Journals
