"We are appalled by the extent of the studies and their implementation", Daimler said Monday in an emailed statement, adding it didn't have any influence over the study and promised an investigation.
"We strongly condemn the tests", the company said, insisting it was not involved in choosing testing methods that were "against Daimler's values and ethical principles". A Netflix investigative series Dirty Money has also documented the experiments, landing the carmaker into a fresh soup, even as it still struggles to recover from the 2015 emissions fiasco. Daimler and BMW said they had no knowledge of the Volkswagen-led study.
In a statement over the weekend, Volkswagen apologised for the misconduct and lack of judgment shown by individuals.
The 10 monkeys were placed in sealed chambers in front of TVs showing them cartoons, as Volkswagen Beetles drove on a treadmill, and their diesel fumes were pumped into the breathing spaces.
The goal was to compare the results of the Beetle emission to those of a 1999 Ford diesel pickup and debunk a World Health Organization report that claimed diesel exhaust is a carcinogen.
Plans to also carry out the exhaust fumes experiments with humans were initially scrapped.
"After the matter has been cleared up there will also be the question of who was personally responsible", he told journalists at a news conference on Monday. Even short-term inhaling of the gas can have serious health repercussions, according to the Environmental Protection Agency.More news: Candid digicam: Dutch hacked Russians hacking DNC, together with safety cameras
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It says exposure is "linked to premature mortality... from cardiovascular and respiratory diseases". They have not yet responded to the news of the human experiments.
Amal Johal, director of consumer action and group litigation specialists Your Lawyers, said: "How does a global corporation think it can continue to get away with another act of fraud?" McDonald did not know when the tests were conducted that the vehicle's emissions were rigged.
Doctors at an Aachen-based university hospital then examined 25 people after they inhaled varying concentrations of the gas over several hours.
Nitrogen dioxide was the gas at the center of Volkwagen's emissions cheating scandal, which led to the Department of Justice (DOJ) charging the company with conspiring to defraud the government and violate environmental regulations past year.
The devices and software that accompanied it allowed the German auto maker to evade USA regulators for years.
Regulations are more permissive in the United States, where tens of thousands of nun-humane primates are used in experiments each year, according to the U.S. Department of Agriculture.
Last year, federal US prosecutors indicted six Volkswagen executives in connection with the emissions scandal. The pursuit of the six top people at the time was nevertheless a rare occurrence among big companies, whose executives nearly never face time in jail.