FRANKFURT — Three major German carmakers that financed the researchers who used monkeys to test the health effects of diesel exhaust struggled to contain harsh criticism from animal rights activists and a wave of negative media coverage after details of the tests emerged.
News of the research — reported by The New York Times on Thursday and portrayed by an episode of the documentary “Dirty Money” that began airing on Netflix on Friday — quickly developed into a public relations disaster for the companies: Volkswagen, Daimler and BMW. It is also likely to intensify a backlash against diesel in Europe, where, until recently, it was the most popular engine option.
The research was intended to show that modern diesel technology had solved the problem of excess emissions linked to a range of lung ailments and blamed for tens of thousands of premature deaths. Instead, it has shed unwelcome light on the methods that the carmakers had used to influence political debate.
The experiments — carried out in 2014, a year before Volkswagen was caught using software to cloak excess diesel emissions — involved exposing a group of monkeys to exhaust from a late-model diesel Volkswagen, while another group was exposed to exhaust from an older Ford diesel pickup. After breathing diluted exhaust for four hours, the monkeys were examined and researchers took samples of lung tissue to check for inflammation. The research did not kill the monkeys, but it was unclear what happened to them afterward.
People for the Ethical Treatment of Animals, an animal rights group that claims 6.5 million supporters, wrote a letter to Volkswagen protesting what it said was the cruel mistreatment of the cynomolgus macaque monkeys used in the tests.
“There is nothing fair about condemning these complex, sensitive animals to suffer physical suffering and psychological torment in laboratories where they are caged and deprived of fresh air, sunshine, freedom of movement, the companionship of others, and just about everything else that makes any life worth living,” Harald Ullmann, a PETA vice president, wrote in a letter dated Friday to Matthias Müller, the chief executive of Volkswagen.
The monkey experiments also provided another example of how Volkswagen used software to conceal emissions of nitrogen oxides that were far above limits allowed by law. The Beetle provided by Volkswagen for the tests had been fitted with software that caused it to produce far less pollution in the lab than the car would have produced on the road. In other words, the results were deliberately manipulated.
The experiments were commissioned by the European Research Group on Environment and Health in the Transport Sector, known by its German initials E.U.G.T. The organization received all of its funding from Volkswagen, Daimler and BMW. It contracted the Lovelace Respiratory Research Institute in Albuquerque to carry out the tests.
The research group commissioned numerous studies on topics related to diesel, such as studies shedding doubt on whether restricting diesel vehicles in urban areas led to better air quality. The organization shut down last year amid controversy over its work, before the results of the Albuquerque study could be published.
The carmakers said the research group was independent and overseen by reputable scientists. But the studies it commissioned invariably supported the industry’s pro-diesel agenda. Diesel is particularly important to luxury carmakers like BMW, Daimler’s Mercedes unit and Volkswagen’s Audi division. It would be much harder to sell big cars in Europe without the fuel economy provided by diesel.
Carmakers expressed contrition about the experiments.
“The scientific methods used to conduct the study were wrong,” Volkswagen said in a statement. “Animal testing is completely inconsistent with our corporate standards. We apologize for the inappropriate behavior that occurred and for the poor judgment of individuals who were involved.”
Daimler distanced itself from the study and the E.U.G.T. “We will clarify how the L.R.R.I. study came about and have launched an investigation,” the company said in a statement, referring to the Albuquerque lab. “Daimler does neither tolerate nor support unethical treatment of animals. The animal experiments in the study are superfluous and repulsive.”
BMW said in a statement on Sunday that it “does not carry out any animal experiments,” adding, “The BMW Group did not participate in the mentioned study and distances itself from this study.”
News of the monkey experiments intensified criticism of how the auto industry has used its political clout to preserve tax breaks that make diesel fuel cheaper than gasoline in Europe.
“The lobbying practices of the industry need to be thoroughly examined, as painful as that might be,” the Stuttgarter Zeitung, a daily newspaper, said in an editorial on Sunday.