BERLIN (Reuters) - A German environmental group said on Thursday it has found traces of the widely used weed-killer ingredient glyphosate in Germany’s 14 most popular beers, a potential blow to the country’s reputation for “pure” brewing.

Industry and government immediately sought to play down the report from the Munich Environmental Institute.

The Brauer-Bund beer association said the findings, which were based on a small number of samples, were not credible. Germany’s Federal Institute for Risk assessment said the levels did not pose a risk to consumers’ health.

“An adult would have to drink around 1,000 liters (264 U.S. gallons) of beer a day to ingest enough quantities to be harmful for health,” it said in a statement.

Under the “Reinheitsgebot”, or German purity law - one of the world’s oldest food safety laws and celebrating its 500th anniversary this year - brewers have to produce beer using only malt, hops, yeast and water.

Glyphosate was brought into global use by Monsanto in the 1970s and is used in its top-selling product Roundup as well as many other herbicides around the world.

The environmental group, an investigative body, said it had tested Germany’s 14 top-selling beer brands and said all showed traces above the 0.1 microgram limit allowed in drinking water. It added that no general conclusions about the contamination of certain brands of beer could be made.

Brauer-Bund said there were government controls in place in breweries to ensure that no harmful substances made their way into the production process. Its own monitoring system for malt has never detected levels of glyphosate that were above the permitted maximum limits, it added.

Hasseroeder, a beer brewed in Saxony-Anhalt in eastern Germany and owned by Anheuser Busch Inbev, contained the highest trace of glyphosate at 29.74 micrograms per liter, the institute said. The smallest amount, 0.46 micrograms per liter, was found in Augustiner, made in Munich.

Anheuser-Busch InBev said it questioned the scientific integrity of the tests due to the small number of samples. It d rejected the institute’s allegation that brewers were not adequately monitoring raw ingredients as “absurd and completely unfounded.”

European Union regulators are currently reviewing whether to renew approval for glyphosate. The World Health Organization’s cancer research committee has said glyphosate was probably carcinogenic to humans, but the European Food Safety Authority has said it is unlikely to cause cancer.

Germany is Europe’s biggest producer of beer and is home to more than 1,300 breweries which produce about 5,000 different beers.