Finding traces of a potentially harmful chemical in food can sound alarming. But whether that chemical actually poses a health concern depends heavily on how much people are exposed to.
That distinction is central to a new study of commercial tea produced in China. Researchers detected polychlorinated biphenyls, or PCBs, in every sample they analyzed, with concentrations varying considerably among tea types and growing regions. Yet when they estimated how much consumers would actually be exposed to through tea consumption, the amounts remained far below established tolerable intake thresholds.
The study, published in New Contaminants, analyzed 192 commercial tea samples representing six major tea categories and 16 Chinese provinces. Researchers measured 18 different PCBs, a group of long-lasting environmental pollutants that can accumulate in food and the environment.
“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.”
PCB concentrations varied substantially among the samples. Dark tea had the highest average concentration, followed by oolong tea, while yellow tea had the lowest average level.
Location mattered as well. Tea produced in Guangdong had the highest average PCB concentration, followed by samples from Yunnan, Chongqing, Guangxi and Shaanxi. The researchers said differences in local environmental contamination, past industrial activity and tea production practices could potentially contribute to those patterns.
But higher concentrations in dry tea did not necessarily translate into the highest estimated exposure for people drinking it.
Green tea produced the highest estimated weekly PCB intake because it is consumed in larger quantities. Even so, researchers calculated that exposure from green tea and the other tea categories remained well below the tolerable intake levels used in their risk assessment.
That distinction is important when interpreting studies that detect contaminants in food. Modern laboratory methods can identify chemicals at extremely small concentrations, but detecting a substance does not by itself establish that people are receiving enough of it to pose a meaningful health risk.
The researchers also looked at whether tea processing might add PCBs. They compared fresh green tea leaves with tea made from the same batch and found PCB concentrations rose somewhat after processing. However, the difference was not statistically significant, meaning the experiment did not provide strong evidence that processing itself substantially increased contamination.
The study also cannot determine a person's total PCB exposure. Tea is only one possible dietary source, and the researchers noted that PCBs can persist in the environment and accumulate through food chains.
The findings are also specific to commercial tea produced in China and should not be assumed to represent PCB concentrations in tea grown elsewhere.
For consumers, however, the study's risk assessment was reassuring. Although researchers were able to measure PCBs across every tea category they examined, their calculations suggest that the amount associated with typical tea consumption is unlikely to pose an appreciable health risk.
The broader findings may be most useful for food safety monitoring. By showing how PCB concentrations differ among tea varieties and regions, researchers have established a baseline that could help identify changes over time and guide efforts to limit contamination before tea reaches consumers.
The study was supported by the National Technology Innovation Center for Dairy and Agricultural Science and the Technology Innovation Program.