Industrial processing contaminates tea

By Nisha P Lalu
Published: Tuesday 15 January 2008

The blades form layers of chro (Credit: RUHANI KAUR)your morning tea contains chromium, which may cause cancer and skin diseases. The heavy metal gets into the leaves when tea leaves are processed using the 'crush, tear and curl' (ctc) method, a study from Tamil Nadu said.

The tea industry has been using the ctc process since the 1950s. A series of stainless steel rollers with hundreds of small sharp blades turn tea leaves into granules making them easy to brew and bag. The rollers contain 17 per cent chromium, which combines with oxygen and forms a thin layer of oxide on it. As the rollers need to be sharpened periodically, the passive film is disrupted and leads to the release of chromium into the tea leaves that come into contact with the metal. The juices extruded by tea leaves during processing make contamination easier.

Such contamination is not found in the orthodox method--withering, rolling, fermentation, drying and sorting--because the rollers used in this process is made of gun metal, which has very little chromium.

The Pesticide Residue Laboratory of upasi Tea Research Foundation in Valparai first found chromium in tea leaves available in the market. It then conducted an indepth study to find its source. The scientists tested samples from the factory unit of the institute and a tea factory in Valparai. They detected higher amounts of chromium within two days of sharpening of the rollers at both the units. "We are yet to find out whether the chromium in the tea is trivalent or hexavalent. Hexavalent chromium poses serious health hazards," says Subbiah Seenivasan, the lead author of the study, which will be published in the February 2008 issue of the journal Food Chemistry.

There is no prescribed limit of chromium in marketable tea in India. "We are analysing the study. We will be keen on regulations because tea has an extensive market," says B Bera, director of research, Tea Board of India.

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