France ordered an inquiry on Friday after scientists reported that a food additive widely used in Europe to whiten toothpaste and chewing gum could cause precancerous lesions in rats.
Researchers from France and Luxembourg gave the additive, called E171 in Europe and the United States, to lab rats in their drinking water for 100 days.
In 40 percent of the rodents exposed, they observed the development of "preneoplastic lesions" or precancerous growths, the team reported.
The additive also inhibited the immune systems of the rats and "accelerated" the growth of lesions induced for the experiment, France's INRA agricultural research institute, which took part in the study, said in a statement.
"These results demonstrate a role in initiating and promoting the early stages of colorectal cancer formation," it added, though it said no conclusion could be drawn about later phases of cancer, or of any danger to humans.
The results were published in the Nature journal published by Scientific Reports.
Reacting to the report, France's ministers of health, agriculture and economy instructed the country's food health and safety agency, Anses, to investigate whether the additive poses a risk for human health.
The agency must report its findings by the end of March.
E171 contains nanoparticles of titanium dioxide, a naturally occurring metal oxide. It is one of the five nanomaterials most commonly used in consumer products, including food, paints and cosmetics, according to the study.
E171 is commonly used as a whitening and brightening agent in candies, chewing gum, white sauces and cake icing.
The US Food and Drug Administration approved it in 1966 at levels of no more than one percent of a food product's weight.
But the study's authors said that in Europe, current regulations establish no daily intake limit.
The study was prompted by "growing concerns that daily oral... intake is associated with an increased risk of chronic intestinal inflammation and carcinogenesis", or cancer formation, they said.
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