BERLIN—When German carmaker Volkswagen acknowledged last year that it was guilty of cheating on diesel emissions tests, the fallout cost the company over $25 billion. But the full extent of the company’s willingness to sideline ethics concerns to increase profits is still emerging. Three German carmakers appear to have commissioned or supported a study in 2014 which exposed monkeys and humans to exhaust fumes and nitrogen dioxide, according to German media reports on Monday.

The study by the European Research Group on Environment and Health in the Transport Sector (EUGT) was never published and the research institute overseeing it has since been dissolved. All three carmakers involved in the study — Daimler, BMW and Volkswagen — distanced themselves from the research over the weekend.

“We are shocked by the extent and application of the studies ... We condemn the experiments in the strongest terms,” carmaker Daimler wrote. The statement, released at a time when only experiments with monkeys but not humans were publicly known, accused the researchers of having violated ethics rules and company values, even though an ethics commission had approved the study. Daimler and BMW said they had no knowledge of the Volkswagen-led study.

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Meanwhile, Volkswagen blamed the “mistakes and misjudgments of individuals.”

In one of the experiments, monkeys were forced to inhale exhaust fumes from a Volkswagen Beetle car and an older pickup truck for several hours, in an attempt to prove the Beetle’s clean emission standards. The monkey experiments were first reported by the New York Times last week and are shown as a re-enactment in the new Netflix series “Dirty Money.”

Plans to also carry out the exhaust fumes experiments with humans were initially scrapped.

Human test subjects were still involved in a separate emissions study which also appears to have been encouraged by the three German carmakers, however. Germany’s Sueddeutsche Zeitung and Stuttgarter Zeitung newspapers reported on Monday that healthy test subjects were asked to inhale nitrogen dioxide (NO2), a gas that is primarily emitted through traffic. Even short-term inhaling of the gas can have serious health repercussions, according to the Environmental Protection Agency.

“Breathing air with a high concentration of NO2 can irritate airways in the human respiratory system. Such exposures over short periods can aggravate respiratory diseases, particularly asthma, leading to respiratory symptoms (such as coughing, wheezing or difficulty breathing), hospital admissions and visits to emergency rooms,” the EPA writes on its website.

The human experiments appear to have been conducted between 2012 and 2015 and there were no reports of subsequent injuries related to them. A researcher involved in the study acknowledged the experiments’ existence on Monday but cautioned that the deployed nitrogen dioxide levels resembled those found in normal work spaces. He added that the three carmakers were aware of the human experiments but had no say over them. They appear to have been disconnected from emissions tests.

But the research institute behind the controversial tests was founded by Daimler, BMW, Volkswagen and automotive components supplier Bosch, which has raised questions over the extent to which the experiment with humans was backed by the three major carmakers, too.

Nitrogen dioxide was the gas at the centre 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 last year. According to the DOJ, Volkswagen installed devices in its diesel engine vehicles that obscured the amount of emitted nitrogen dioxide.

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The devices and software that accompanied it allowed the German carmaker to evade U.S. regulators for years. Overall, the evasion efforts affected 11 million vehicles across the globe and over 500,000 in the United States.

Last year, federal U.S. prosecutors indicted six Volkswagen executives in connection with the emissions scandal. Only one executive ended up being charged in the United States; the others escaped arrest. The pursuit of the six top people at the time was nevertheless a rare occurrence among big companies, whose executives hardly ever face time in jail.