Despite the positive effects of tea drinking – the three-person team from the Universities of Alberta in Canada and Luleå in Sweden led by Dr. Gerry Schwalfenberg cites cardiovascular benefits, positive anti-cancer, weight loss and diabetes effects – they warn about the risk of heavy metal contamination via groundwater, air, soil and rain.
“The literature is replete with [links between heavy metals and] many common disease processes such as carcinogenesis, insulin resistance, neuro-degeneration and immune dysregulation,” Schwalfenberg et al. write in the peer-reviewed, open-access journal.
“Toxic contamination by heavy metals was found in most teas sampled. Some tea samples are considered unsafe…Public health warnings or industry regulation might be indicated to protect consumer safety,” they conclude in their abstract.
Tea Association of Canada: 'We conform to regulations'
But Louise Roberge, president of the Tea Association of Canada insists that her industry conforms to Canadian regulations.
She says her association was works with the Pest Management Regulatory Agency (PMRA), the Canadian Food Inspection Agency (CFIA) and within the framework of the Food Safety Action Plan to improve Canada’s food safety system.
Health Canada continues to monitor the concentrations of various chemicals in foods through its ongoing Total Diet Study surveys, she adds, and also conducts targeted surveys of other contaminants in specific foods.
"In the executive summary of a recent publication from the CFIA (Food Safety Action Plan Report 2009-2010), it is stated that 'tea is not expected to pose a human health concern to consumers," Roberge tells this website.
'Unacceptable' levels of lead and aluminum
In this study, 30 tea bags with 2-3g of tea – green, oolong and black in standard and organic varieties, and organic white (brands unnamed) - bought from Canadian supermarkets and health food stores, were boiled in Pyrex using 250ml of water then allowed to stand in fine bone china cups.
Samples of each were taken after three to four minutes brewing and 15-17 minutes.
Schwalfenberg et al. report. that only two of the teas had aluminum limits above acceptable levels after three minutes of brewing, but at 15-17 minutes six had levels greater than the general acceptable daily limit of 7,000 μgm/L (micrograms/liter).
“In regard to toxic elements only aluminum and lead had levels that were unacceptable. Unacceptable aluminum levels were found in 7% of teas brewed for three minutes and 20% of teas brewed for 15 minutes,” they write.
Lead levels posed a “significant concern” for pregnant women, they add, since 73% of the samples brewed for three minutes and 83% of samples brewed for 15 minutes had levels above 0.5μgm/L, the acceptable limit for reproductive health, while organic teas had significantly higher lead levels at 15+ minutes brewing.
Cadmium and arsenic raise long-term concerns
Smaller amounts of cadmium and arsenic in samples were within acceptable limits, but the scientists say they have concerns about the risk of long-term bioaccumulation of these heavy metals.
Schwalfenberg et al. advise that the public and officials alike pay greater attention to limiting exposure to toxic elements from all sources – given that heavy metals such as cadmium and lead have long half lives.
Routine inspection and testing of food and beverages could help identify tainted products, they add, while original source labeling would help consumers, since some regions have greater problems with contamination.
Study limitations include its confinement to teas on sale in Canada alone, Schwalfenberg et al. write, while it does not measure levels of fluoride, pesticides, herbicides and other organic contaminants.
Title: ‘The Benefits and Risks of Consuming Brewed Tea: Beware the Toxic Element Contamination’
Authors: Schwalfenberg, G., Genuis, S.J., Rodushkin, I.
Source: Journal of Toxicology, Accepted September 9, http://dx.doi.org/10.1155/2013/370460