German carmakers came under fire on Monday following revelations they helped finance experiments that saw humans and monkeys exposed to toxic diesel fumes that have been linked to asthma, lung diseases and heart attacks.
The disclosures sparked widespread outrage, led by Chancellor Angela Merkel who strongly condemned the latest controversy to engulf the nation's powerful but scandal-tainted auto industry.
"These tests on monkeys or even humans are in no way ethically justified," said Merkel's spokesman Steffen Seibert.
"The indignation felt by many people is completely understandable."
Earlier on Monday the Sueddeutsche
and Stuttgarter Zeitung
dailies reported that a research group funded by Volkswagen, Daimler and BMW had measured the effects of inhaling nitrogen oxide gases on 25 healthy human beings at a German university hospital.
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.
Several German cities grappling with air pollution are now mulling diesel bans.
All three German carmakers have distanced 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.
"The BMW Group did not participate in the mentioned studies," the luxury carmaker said in a statement.
"We are appalled by the extent of the studies and their implementation," a Daimler spokesman told AFP.
While 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 finally shut its doors last year.
'No significant effects'
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.
But Thomas Kraus, the head of the relevant department at the university hospital in Aachen, told German media the findings were limited as they weren't representative of the wider population and didn't take into account general air pollution.
The institute released a statement stressing the study had been approved by the university hospital's ethics commission.
The study was carried out before "dieselgate" erupted and was not linked to diesel emissions testing or to experiments involving monkeys, it added.
On its website the World Health Organisation points to "growing evidence" that nitrogen dioxide exposure "can increase symptoms of bronchitis and asthma, as well as lead to respiratory infections and reduced lung function and growth."
Exposure is "linked to premature mortality... from cardiovascular and respiratory diseases," it states.