India's health ministry Tuesday ordered an investigation after a study found samples of top bread brands with toxic chemicals that could lead to thyroid disorders and cancer.

Products of five popular multinational fast-food outlets, selling pizza and hamburgers - KFC, Pizza Hut, Domino's, Subway and McDonald's were also found to contain the chemicals, the study by the Delhi-based Centre for Science and Environment said.

Eighty-four per cent of 38 samples picked from outlets in the Indian capital were found positive with potassium bromate, a possible cancer-causing chemical and potassium iodate, which contributes to thyroid-related diseases, CSE's deputy director general Chandra Bhushan said.

‘We will come out with a report very soon,’ Health Minister JP Nadda said. ‘I have asked my officials to report to me on an urgent basis. There is no need to panic’.

Potassium bromate and potassium iodate are used to treat flour for baking.

‘After warnings from the World Health Organization, many countries including China and those in EU, but barring US and India, have banned their use,’ Bhushan said.

The All India Bread Manufacturers Association said domestic food regulations permitted the use of the additives, which were safe under particular levels.

‘We are just following norms that permit use of potassium bromate and or potassium iodate at 50 parts per million maximum for bread and 20 ppm for bakery purposes,’ association president Ramesh Mago said.

‘These levels are considered safe. Advanced countries like US allow up to 75 ppm levels in bread.’