Tea is enjoyed by millions of people every day, but its leaves can also collect traces of persistent pollutants from the environment and during production. A new nationwide study has provided the most comprehensive picture to date of polychlorinated biphenyls, or PCBs, in commercial tea produced across China.
Researchers analyzed 192 tea samples representing all six major tea categories and 16 Chinese provinces, examining 18 PCB compounds, including six indicator PCBs and 12 dioxin-like PCBs. The study found measurable PCBs in all samples, but health risk calculations indicated that PCB exposure from drinking Chinese tea is currently 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."
The total concentration of the 18 PCBs ranged from 9.36 to 4,490 picograms per gram of dry tea. Among the six tea categories, dark tea had the highest average concentration at 549 pg/g, followed by oolong tea at 241 pg/g. Yellow tea had the lowest average level at 93.3 pg/g.
Geographic differences were also evident. Tea produced in Guangdong had the highest average PCB concentration at 505 pg/g, followed by Yunnan, Chongqing, Guangxi and Shaanxi. The researchers suggest that these differences may reflect a combination of local environmental contamination, historical industrial activity and differences in tea production methods.
The chemical fingerprints of the contaminants offered additional clues. Lower-chlorinated PCBs were dominant, particularly trichlorobiphenyls. Two compounds, CB-28 and CB-52, contributed strongly to the overall PCB profile, and similar contamination patterns appeared across most tea-producing regions.
To investigate whether manufacturing itself could contribute to PCB levels, the researchers compared fresh green tea leaves with tea produced from the same batch. Total PCB concentrations increased from 51.2 to 63.7 pg/g after processing, largely because indicator PCBs increased. However, the difference was not statistically significant, indicating that processing was not a major source of PCB contamination in this experiment.
For consumers, the most reassuring result came from the health risk assessment. The researchers calculated PCB exposure using World Health Organization toxic equivalency factors and typical tea consumption rates. Even green tea, which produced the highest estimated weekly intake because it is consumed in larger quantities, remained far below established tolerable intake thresholds.
The authors caution that the assessment covers PCB exposure from tea alone and does not represent total exposure from an individual's entire diet. Because PCBs persist in the environment and can accumulate through food chains, continued monitoring remains important.
The study establishes a national baseline for PCBs in Chinese commercial tea and identifies both geographic location and processing as factors worth monitoring. The findings may help guide future food safety surveillance and support efforts to reduce contaminant entry throughout the tea production chain.
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Journal reference: Wu X, Xin J, Fan Y, Zhang S, Han X, et al. 2026. Profiling of polychlorinated biphenyls in Chinese tea: national distribution, variety-specific variations, and the impact of processing. New Contaminants 2: e021 doi: 10.48130/newcontam-0026-0019
https://www.maxapress.com/article/doi/10.48130/newcontam-0026-0019
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About the Journal:
New Contaminants (e-ISSN 3069-7603) is an open-access journal focusing on research related to emerging pollutants and their remediation.
