Spot checks conducted in 2011 found “isolated examples” of genetically modified plants near research laboratories and a station in different places in Switzerland.
The Federal Environment Office said on Friday that the plants had been dug up immediately, and there had been no contamination.
The plants found near laboratories belonging to the universities of Lausanne, Basel and Zurich were thale cress (Arabidopsis thaliana), which is often used in studying plant biology, since any changes in it are easily observed.
The universities were informed and asked to discover how the plants got out.
Genetically modified rape was found at the station in Lugano. The canton was asked to discover where it came from.
A statement by the environment office said the discoveries were “no great surprise”.
“Laboratories and communications routes are possible ways in which genetically modified plants are spread,” it pointed out.
They were detected by a monitoring system set up by the office to discover any early release of such plants into the environment. The system is being introduced ahead of the planned lifting of a moratorium on growing genetically modified crops in November 2013.
swissinfo.ch and agencies