Concerns have been raised over the recycled carbon often used to house breakfast cereals, after a study showed mineral oils present in the packaging could pass through it and into the food.

Dr Koni Grob, of the Food Safety Laboratory in Zurich, said toxicologists had linked the oils to inflammation of internal organs and even cancer, though he stressed individual meals would contain only a tiny dose of chemicals, according the Press Association.

The researchers discovered that the oils, found in the printing ink of recycled newspapers used in the cardboard, could even pass through the protective inner plastic bags.

The Swiss study analysed 119 products bought from German supermarkets last year and found that a large majority contained traces of mineral oils higher than the agreed level.

Research also showed that products such as paper and bags made of polyethylene and polypropylene were ineffective as a barrier from mineral oils, but aluminium foil was effective, said Grob.

A spokesperson for United Biscuits said the firm was aware of the recent concerns of the presence of mineral hydrocarbons in food packaging. “At UB we do not use recycled cardboard for any packaging that is in direct contact with the product and, to maintain freshness and food safety, we will normally have a film wrap between the product and any cardboard as a barrier to contamination.”

She added that findings on this issue were relatively new, and United Biscuits was in the process of gathering and analysing information from its packaging suppliers, so that it could consider any alternative packaging that may be advisable.

Breakfast cereal company Jordans has stopped using recycled cardboard, while a spokesperson for Kellogg’s said: “While experts tell us there’s no immediate health concern, we are looking at our packaging.”

Kellogg’s added that is working with its suppliers on new packaging, which allows it to meet its environmental commitments, but will also contain significantly lower levels of mineral oil. “We are also looking at alternative inner liners for our packets.”

Barbara Gallani, director of food safety and science, at the Food and Drink Federation (FDF), commented: “We are aware of recent studies looking at the potential presence of mineral hydrocarbons in food from recycled cardboard used in food packaging. We understand that the information currently available is limited and we are working with the Food Standards Agency, food manufacturers, retailers and the packaging supply chain to gather more information.”

She added: “The Food Standards Agency has indicated that there is not a need for immediate action. It is carrying out a survey of food packaging materials, including recycled cardboard, and will report back in the summer. In the meantime, FDF has revised guidance for food manufacturers on recycled carton board in food packaging.”