Manufacturers are now required to identify use of nano-particles, the extremely fine grains that are increasingly found in drugs and consumer products, in France.
Manufacturers must make a declaration if they used at least 100 grammes (3.52 ounces) of nano-particles in products that were imported, manufactured or distributed in France in 2012, the ecology ministry said on Thursday.
The rule took effect on January 1 following a government decree dated to last February 17.
It applies to particles with a diameter of between 1 and 100 billionths of a metre. Companies must make the declaration on a website, www.R-nano.fr, by May 1.
In its press release, the ministry said the requirement was a precautionary measure, given that "the risk profile (of nanomaterials) is still poorly understood."
Nano-particles are used increasingly in the form of titanium oxide or as aluminium silicates in pills to help ingestion of pills and in food, where they are used as stabilisers or anti-caking agents in fluids and creams.
Some research, including a study carried out on chickens in February last year, has suggested that the particles may be harmful for the gut, where they interact with intestinal processes.
However, these investigations are still small-scale and are far from conclusive.