New Delhi: The pre-packaged bread may be a silent killer as it is laced with chemicals suspected to cause cancer, a new study has warned. Most of the breads made by the Indian companies are found to contain potassium bromate and potassium iodate -- chemicals banned in many countries for their adverse effects on human health, a study conducted by the Centre for Science and Environment (CSE) said. Potassium bromate is a powerful oxidizing agent, use of which makes bread fluffy, soft and gives it a good finish. The food safety regulations of India allow use of potassium bromate as flour treatment agent in bread and other bakery products. However, several bread companies and fast food chains have denied using these chemicals. "The use of these chemicals in the bread-making sector has been banned in many countries because they are listed as hazardous for public health: One is a category 2B carcinogen and the other could trigger thyroid disorders," the CSE report said. The CSE tested 38 commonly available branded varieties of pre-packaged breads, 'pav' and buns, ready-to-eat burger breads and ready-to-eat pizza breads of popular fast food outlets from Delhi. "We found 84 percent samples positive with potassium bromate or iodate. We re-confirmed the presence of chemicals in a few samples through an external third-party laboratory. We checked labels and talked to industry and scientists," CSE's deputy director general Chandra Bhushan said. In 1999, the International Agency for Research on Cancer (IARC) classified potassium bromate as possibly carcinogenic (cancer causing) to humans. It was found to cause tumours of the kidney, thyroid and cancer of the abdominal lining in laboratory animals. The European Union had banned its use in 1990. The other countries which have banned potassium bromate include Britain, Canada, Australia, New Zealand, China, Sri Lanka, Brazil, Nigeria, Peru and Columbia. "Globally, potassium bromate was allowed to be used on the assumption that the bromate residues would not be present in the end product. This assumption failed across the world. Residues were being detected even after reducing the permissible limits of use, and therefore countries started banning it," Bhushan said. "Our study confirms that residues of potassium bromate are present in bread sold in India," he added. Interestingly, only one company was found to be labelling the use of potassium bromate on its pre-packaged products. The CSE results showed high levels of potassium bromate or iodate in sandwich bread, 'pav', bun and white bread. Products of Harvest Gold, Britannia and Perfect Bread were those with higher levels, according to CSE. "Of these, only Perfect Bread labels the use of potassium bromate. No maker among those tested labels potassium iodate. Only Britannia denied use of potassium bromate or iodate," the study said. "Products of all five popular multinational fast food outlets selling pizza and burger were found positive with potassium bromate/iodate. These include KFC, Pizza Hut, Domino’s, Subway and McDonald’s. Except Domino’s, others have denied use in a response to CSE,” it added. Samples of two other fast food outlets -- Nirula’s and Slice of Italy -- also tested positive for potassium bromate/iodate. Slice of Italy denied use of the chemicals to CSE.