There's been an outpouring of anger and disgust since the reports of animal and human experiments came to light.

European Commission spokesman Margaritis Schinas said the EU was "shocked." German Chancellor Angela Merkel strongly condemned the tests.

"The indignation felt by many people is completely understandable," Merkel's spokesman, Steffen Seibert, said. "These tests on monkeys or even humans are in no way ethically justified."

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However, scientists contacted by DW say there's nothing unusual about using humans and animals in experiments to test the impacts of diesel fumes.

"Such studies have been performed for decades," says Flemming Cassee, an inhalation toxicologist from the Dutch National Institute for Public Health (RIVM). "And not only in the Netherlands, but worldwide, including in Germany."

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Human and monkey experiments

The recent uproar stems from reports in the Süddeutsche and Stuttgarter Zeitung dailies that a lobby group funded by Volkswagen, Daimler and BMW commissioned a study in Germany that involved 25 human volunteers inhaling nitrogen oxide gases for three hours.

That report came after the New York Times detailed how the same organization — the now-dissolved European Research Group on Environment and Health in the Transport Sector (EUGT) — locked 10 monkeys in airtight chambers in 2014 and made them breathe in diluted diesel exhaust fumes from a VW Beetle for four hours.

VW reportedly commissioned the study to show how the diesel technology in its cars was succeeding in controlling harmful emissions. The vehicle used in the monkey study was also reportedly rigged to make the fumes seem less polluting than they were in reality. VW admitted to manipulating millions of its diesel cars in this way in 2015, leading to a global scandal.

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Strict regulation

The methodology and results of the two studies have not been made public. But Cassee stresses that they would have been subject to approval by "a fully independent medical-ethical committee."

For the record, the US-based Lovelace Respiratory Research Institute, which conducted the VW-funded monkey study for EUGT, which was disbanded last year, said in a statement emailed to DW that it was "committed to the humane and ethical treatment of animals" and that it had complied with animal regulations in carrying out the tests.

It added that it was not initially aware the car's engine had been rigged, but when it learned "of this deception, we determined the study was compromised," and did not meet standards for peer-reviewed publication.

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The university hospital in the western German city of Aachen, which conducted the EUGT-commissioned tests using 25 human volunteers, said the study had also been approved by the hospital's ethics commission.

'Overblown' response?

The fact that the tests were sponsored by automakers, however, does raise some questions about potential conflicts of interest.

Mark Miller, a senior research scientist at the University of Edinburgh's Center for Cardiovascular Science, told DW that there's "a feeling that it has commercial benefit and it's been linked to a car company that has been in the headlines for other malpractices," but added that it was difficult to comment further without having seen the studies.

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Still, Miller said he felt the public outcry over the tests "has been overblown."

"What people have to remember is experiments of this type cannot go ahead without the strictest ethical standards. There is no work — either on animals or on man — that would not go through a huge review process to make sure it's safe."

Cassee and Miller have performed a number of similar studies themselves in which human volunteers were made to breathe in diluted emissions from a diesel engine for a few hours — the aim being to test the impact of road traffic and air pollution for governments and other public bodies.

Crucial data

Miller says these clinical experiments don't pose any health risks to volunteers, who would be exposed to pollution levels comparable to "cycling to work behind the bus."

They use specialized scientific technology that can detect "very slight changes in blood pressure, the way blood vessels react, various or small changes in the lung." From this information they then draw conclusions about health impacts or diseases that could develop from long term exposure to air pollution over decades.

According to Cassee, it's thanks to experiments of this nature that policy makers are aware of how harmful air pollution and exhaust fumes are. This data is used by bodies like the World Health Organization to set air quality guidelines, and drives government policy changes like enforcing low-emission zones in cities.

Scientists are working on ways to use stem cell culture for this kind of research in the future, but we're not quite there yet, Cassee says.

"In the meantime, studies in humans will be needed to gain insight in causal relationships between pollutants and health effects."