The Green party made their warning after testing the breast milk of 16 women from a variety of German regions.

Traces of glyphosate, a chemical used in weed-killers, amounting to between 0.210 and 0.432 nanograms per mililitre were recorded.

In drinking water a quantity of no more than 0.100 nanograms of the substance is allowed.

Irene Witte, professor of toxicology at the University of Oldenburg described the findings as “intolerable.”

“I would never have guessed that the quantities are so high,” she said.

Witte warned that no conclusions should be drawn from tests on 16 women, but added that this was a first indication that there is a problem. She called for the tests to be broadened to included a larger sample set of breast-feeding women.

The extent to which glyphosate is harmful to one’s health is still contested, but in March the World Health Organisation’s cancer research programme designated the substance as “likely carcinogenic.”

Witte said that if the chemical is proven to be carcinogenic then any exposure could be dangerous.

“There is not upper limit you can then put on the quantity. Every molecule could cause cancer.”

The chair of the Environmental Committee in the Bundestag (German parliament) Bärbel Höhn of the Green Party, called for government action.