Tea is one of the world’s most widely consumed beverages, associated with relaxation, cultural tradition and, increasingly, perceived health benefits. Yet the same leaves that absorb water and nutrients from their growing environment can also accumulate persistent environmental pollutants. A nationwide investigation of commercial tea produced across China has now delivered the most extensive assessment to date of polychlorinated biphenyls, or PCBs, in the country’s tea supply. The study detected measurable quantities of these industrial chemicals in every sample examined, but its risk assessment offered reassuring news for tea drinkers: exposure through ordinary tea consumption appears unlikely to pose an appreciable health risk at present.

PCBs are a family of 209 synthetic chlorinated compounds that were once used widely in electrical equipment, hydraulic fluids, paints, sealants and other industrial applications. Although production has been banned or heavily restricted in many countries, the chemicals are highly resistant to heat, chemical breakdown and biological degradation. Their persistence allows them to remain in soils and sediments for decades, while their tendency to accumulate in living organisms can move them through food webs. Some PCB congeners can interfere with endocrine and immune systems, and dioxin-like PCBs are evaluated for toxicity because they can activate the aryl hydrocarbon receptor, a cellular pathway linked to developmental and carcinogenic effects.

Researchers analyzed 192 tea samples collected from 16 Chinese provinces and representing all six major tea categories: green, black, oolong, white, yellow and dark tea. The investigation focused on 18 PCB congeners, including six indicator PCBs commonly used to describe overall contamination and 12 dioxin-like compounds with toxicological significance. Concentrations were reported on a dry-tea basis and varied widely, ranging from 9.36 to 4,490 picograms per gram. One picogram is equal to one trillionth of a gram, meaning that the measured quantities were extremely small, but still analytically significant because PCBs can persist and accumulate over long periods.

The results revealed clear differences among tea categories. Dark tea had the highest average total PCB concentration, at approximately 549 picograms per gram, followed by oolong tea at 241 picograms per gram. Yellow tea had the lowest average concentration, at 93.3 picograms per gram. These distinctions do not necessarily mean that one type of tea is inherently more dangerous than another. Tea categories differ in cultivar, growing region, harvesting conditions, leaf structure, fermentation or microbial transformation, drying temperature and storage practices. Dark tea, for example, undergoes post-fermentation and aging processes that may alter the distribution of hydrophobic contaminants on or within the leaf, although the study did not establish a single mechanism responsible for its higher average level.

Geography also played an important role. Samples from Guangdong showed the highest average PCB concentration, approximately 505 picograms per gram, followed by tea from Yunnan, Chongqing, Guangxi and Shaanxi. The researchers suggest that regional variation may reflect several overlapping factors rather than a single source of pollution. Historical industrial activity, atmospheric transport, contaminated soil or irrigation water, proximity to urban areas, and differences in local processing infrastructure could all influence the final chemical profile. Because PCBs can travel through the atmosphere attached to airborne particles and later settle onto vegetation or soil, even remote agricultural regions may receive residues originating far from the tea plantation itself.

The chemical signatures in the samples provided additional clues about how contamination may have occurred. Lower-chlorinated PCBs, especially trichlorobiphenyls, were dominant across the dataset. Two congeners, CB-28 and CB-52, contributed substantially to the overall PCB profile, and broadly similar patterns appeared across many tea-producing regions. PCB congeners differ in the number and position of chlorine atoms attached to their molecular structures. Lower-chlorinated compounds are generally more volatile and can migrate through the atmosphere more readily than highly chlorinated congeners, while highly chlorinated forms are often more strongly retained in soil and organic matter. The prevalence of lower-chlorinated compounds may therefore be consistent with atmospheric deposition as one pathway by which residues reach tea plants.

The study also examined whether the manufacturing process itself could increase PCB concentrations. Researchers compared fresh green tea leaves with tea made from the same batch after processing. Total PCB levels rose from 51.2 to 63.7 picograms per gram following production, with the increase driven mainly by indicator PCBs. However, the difference was not statistically significant. This finding suggests that, under the conditions tested, processing was not a major source of new PCB contamination. The apparent rise could instead reflect changes in moisture content, concentration effects caused by drying, redistribution of chemicals during heating or ordinary sample variation. Since tea manufacture involves multiple combinations of rolling, steaming, pan-firing, drying, fermentation and storage, the researchers emphasize that different production systems may require separate evaluation.

For consumers, the most important question was not simply whether PCBs could be detected, but whether the amounts found were likely to create a meaningful health risk. The researchers estimated exposure using World Health Organization toxic equivalency factors, which assign greater weight to PCB congeners with dioxin-like biological activity. They also incorporated typical tea consumption patterns and calculated estimated weekly intakes. Green tea generated the highest estimated intake in the analysis, largely because it is consumed in greater quantities than several other tea categories. Even so, the resulting exposure remained far below established tolerable intake thresholds. On the basis of tea consumption alone, the calculated risk was therefore considered low.

That conclusion does not mean that PCB contamination can be ignored. The assessment addressed exposure from tea, not the total amount of PCBs a person may encounter through fish, meat, dairy products, dust or other foods. PCBs are lipophilic, meaning they dissolve readily in fats and can accumulate in animal tissues, making dietary exposure from other sources potentially more important for overall intake. In addition, tea consumption varies sharply between individuals, and people who drink unusually large quantities or consume products from areas with elevated contamination may experience different exposure levels from the national average. Continued surveillance, improved tracing of regional sources and monitoring of raw leaves as well as finished products will therefore remain important.

The findings establish a national baseline for understanding PCBs in Chinese commercial tea and demonstrate how chemical analysis can reveal patterns invisible to consumers. Although the measured concentrations were low in health-risk terms, the wide range among samples highlights the value of tracking geography, tea variety and production practices together. The study also illustrates a broader challenge in food safety: pollutants that are no longer widely manufactured can continue to circulate through the environment long after their original use has ended. For now, the evidence indicates that ordinary tea drinking in China is unlikely to represent a significant PCB hazard, while systematic monitoring can help ensure that this reassuring picture remains accurate as environmental conditions and production systems change.

Subject of Research: Polychlorinated biphenyl contamination in Chinese commercial tea, including national distribution, tea-category differences, geographic variation and processing effects.

Article Title: Profiling of polychlorinated biphenyls in Chinese tea: national distribution, variety-specific variations, and the impact of processing

News Publication Date: 10-Jul-2026

Web References: https://doi.org/10.48130/newcontam-0026-0019; https://www.maxapress.com/newcontam

References: 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

Image Credits: Xingyi Wu, Jianing Xin, Yaqun Fan, Su Zhang, Xiaoxu Han, Jun Cao, Wenfeng Zhou, Haixiang Gao and Shujun Dong

Keywords: polychlorinated biphenyls, PCBs, Chinese tea, tea safety, food contaminants, environmental pollutants, dioxin-like PCBs, tea processing, geographic variation, chemical exposure

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