"The indignation felt by many people is completely understandable."
Earlier Monday the Sueddeutsche and Stuttgarter Zeitung dailies reported that a research group funded by Volkswagen, Daimler and BMW had ordered a study in Germany measuring the effects of inhaling nitrogen oxide gases on 25 healthy human beings.
The revelation came just days after the New York Times wrote that the same organisation carried out tests on monkeys in the United States in 2014. According to the NYT article, the researchers locked 10 monkeys into airtight chambers and made them breathe in diesel exhausts from a VW Beetle while watching cartoons.
Volkswagen apologised for the animal testing at the weekend, saying the group "distances itself clearly from all forms of animal abuse". The German government has called a special meeting with the affected car companies to ask them to explain themselves, said acting transport minister Christian Schmidt.
"This has once again damaged trust in the auto industry," he said. It was VW's admission in 2015 that it had manipulated 11 million diesel cars with cheating software to make them seems less polluting than they were that brought close scrutiny to the industry, which had long touted diesels as better for the environment than gasoline-powered engines.
All three German carmakers scrambled to distance themselves from the research body in question - the now defunct European Research Group on Environment and Health in the Transport Sector (EUGT) - and promised to launch internal investigations.
"We are appalled by the extent of the studies and their implementation," a Daimler spokesman told AFP. "The BMW Group did not participate in the mentioned studies," the luxury carmaker said in a statement, while VW said the EUGT was set up to be an "independent" research body.
Although it was the EUGT that commissioned both tests, the organisation itself was financed by the trio of car giants hoping its research would defend diesel's green reputation - and the valuable tax breaks that go with it. The car companies decided in late 2016 to dissolve the EUGT, which shut its doors last year.
The tests involving 25 human volunteers were carried out at a university hospital in the German city of Aachen in 2013 and 2014. As part of the study, the participants were exposed for several hours to different levels of nitrogen dioxide (NO2) - the most toxic form of nitrogen oxide and commonly found in diesel exhausts. The researchers detected "no significant effects", according to a summary of the study.