Volkswagen has called a study which exposed monkeys to engine fumes "a mistake" amid revelations exhaust emissions were also tested on humans.
The New York times reported on the research, which had 10 monkeys inhaling diesel emissions from a Volkswagen Beetle. The Beetle was one of those 11 million vehicles installed with software which meant the cars wouldn't exceed test limits for emissions.
"We apologise for the misconduct and the lack of judgment of individuals," A spokesperson for Volkswagen said in a statement.
"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."
According to German newspaper Stuttgarter Zeitung, a study funded by Volkswagen Group, Daimler and BMW in 2007 had 25 people inhaling diesel exhaust fumes at a clinic used by the University of Aachen. Details about the study were revealed by the European Research Group on Environment and Health in the Transport Sector.
Daimler has quickly distanced itself from the tests, stating "We are appalled by the extent of the studies and their implementation. We condemn the experiments in the strongest terms."
Volkswagen shareholders are pushing for the automaker to make a statement regarding the tests on humans, with supervisory board member Stephan Weil telling Automotive News:
"At the end of the day, the purpose of such experiments is the decisive factor. If for example, safety and health in the workplace were being tested, as Aachen University has suggested, and ethical standards were adhered to, it is defensible."
"Where experiments served the purposes of marketing and sales, however, I cannot think of an acceptable justification for such an approach."