Here’s another blow to the embattled diesel engine. Reports have emerged about experiments that exposed people and monkeys to diesel fumes. The research was backed by the European Research Group on Environment and Health in the Transport Sector (EUGT), a lobby group set up by Volkswagen, Daimler, BMW and Bosch.

The New York Times reported that in 2014, a lab in Albuquerque, New Mexico conducted an experiment where 10 cynomolgus macaque monkeys inhaled fumes from a diesel Volkswagen Beetle (later found out to have been rigged with a ‘defeat device’ in Dieselgate) while watching cartoons for entertainment.

It said that German automakers had financed the study via EUGT in an attempt to prove that diesel vehicles with the latest technology were cleaner than old smoky ones. It was also meant to be a rebuttal to a 2012 finding by the World Health Organization that had classified diesel fumes as a carcinogen.

This has now come to light because of disclosures in a lawsuit brought against Volkswagen in the US.

Separately, there was an experiment that studied the health effects of emissions in the workplace, carried out at the University of Aachen in Germany and backed by EUGT. Stuttgarter Zeitung reported on a human trial at the university, citing EUGT annual reports.

The tests featured 25 volunteers at a clinic used by Aachen University, which said it had followed typical procedures, such as approval by an independent ethics commission as well as written consent from each participant. No tailpipe emissions here, but just nitrogen dioxide, with the conclusion that its participants suffered no detectable health impacts. The study ended before VW’s Dieselgate scandal surfaced.

German politicians condemned the experiments. The trials were “abhorrent and repulsive,” Stephan Weil, prime minister of Lower Saxony and a member of VW’s supervisory board, said. He has asked for an investigation and for management to explain the experiments. Germany’s transport minister Christian Schmidt said carmakers had further undermined trust in the industry while economy minister Brigitte Zypries said ethical boundaries mustn’t be violated.

The carmakers named have distanced themselves from the dubious research methods and Volkswagen has apologised. “We apologise for the misconduct and the lack of judgment of individuals. We’re convinced the scientific methods chosen then were wrong. It would have been better to do without such a study in the first place,” the Wolfsburg-based carmaker said in a statement.

Daimler said that it would start an investigation into the study ordered by EUGT, which was financed equally by the three carmakers. “We believe the animal tests in this study were unnecessary and repulsive. We explicitly distance ourselves from the study,” the maker of Mercedes-Benz cars said. “We are appalled by the extent of the studies and their implementation. We condemn the experiments in the strongest terms,” the company told Bloomberg.

BMW said it had taken no part in the study’s design and methods, but added – according to Bloomberg – that the assessment of the trial at Aachen University before an independent body with appropriate expertise (such as the ethics commission) should be taken into account.

The EUGT is now closed, and Bosch left the group in 2013. Volkswagen said that the controversial project was not completed.

This latest piece of unsavoury news would no doubt give the diesel engine – which is already down on the mat but not quite out yet – a hard kick. Once the default choice in Europe, oil burners are fast gaining pariah status in the continent because of the NOx they emit. Among the measures taken by cities and governments are bans and extra taxes on diesels. It’ll be a slow goodbye.