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Air pollution and Covid-19: an explosive combination for our health?

This picture shows the air pollution at the City Life district of Milan, Italy, February 3, 2020.
This picture shows the air pollution at the City Life district of Milan, Italy, February 3, 2020. © Miguel Medina, AFP

Recently published studies have explored the possibility of a link between pollution levels and the lethality of Covid-19. While initial observations suggest that the virus is more dangerous in heavily polluted areas, more work is needed to prove this conclusively.

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The most polluted regions of Europe are also those where Covid-19 kills the most. A total of 78 percent of coronavirus deaths in Europe are concentrated in the five most-polluted areas of mainland Europe, according to Yaron Ogen, a researcher at the Institute of Earth Sciences at Martin Luther University in Halle, Germany, in a preliminary study published in the journal Science of Total Environment on April 20.

Ogen’s analysis attempts to establish a link between exposure to nitrogen dioxide, a pollutant generated mainly by diesel car exhausts, and the deadliness of the virus in France, Italy, Germany and Spain. His findings are powerful. The two areas with the highest concentration of nitrogen dioxide – the Po plain in northern Italy and around Madrid, the Spanish capital – also happen to be the areas with the highest number of Covid-19 victims.

Does pollution weaken our defence?

These regions have particularly toxic environments due to the presence of large cities with a lot of vehicular traffic, such as Milan, Turin and Madrid, surrounded by mountain ranges that prevent the pollution from dispersing.

"I decided to investigate nitrogen dioxide because its harmful effects on health are already well documented and the statistical data is easy to find," explained Ogen to FRANCE 24. Prolonged exposure to this pollutant can cause lesions similar to those considered to be factors of the coronavirus, such as lung damage, respiratory problems and heart failure.

Pollution may therefore have already "weakened the respiratory system, which is then less well equipped to fight the virus," noted the German-based researcher. For him, this could explain why people with no apparent prevailing conditions find themselves struggling to survive against the coronavirus.

"These environmental factors may also need to be taken into account in determining who is most at risk," said Ogen.

Environmental alarm bell

Ogen is not the only one sounding the environmental alarm bell. At the time of the Sars epidemic between 2002 and 2004, Chinese researchers had already pointed out that the most polluted cities also had the highest number of deaths due to this predecessor of Covid-19.

A British study, put online Tuesday in pre-publication and similar to the one conducted by Ogen, arrived at the same conclusion. In the United Kingdom, Covid-19 has claimed more victims in areas where fine particle pollution is highest, scientists at Cambridge University have found, reported British daily The Guardian.

The same is true in the United States, where "a very small increase in the concentration of fine particles in an area is associated with a 15 percent increase in coronavirus fatality”, observed researchers from the Harvard University School of Health in Boston in a study published on April 7.

Pollution is not the only possible explanation

But all these researchers also stress that we must be careful not to draw hasty conclusions from these initial observations. "The correlation found does not necessarily indicate a causal link," said Ogen. Other factors could also explain why these highly polluted regions concentrate the greatest number of deaths due to Covid-19.

For example, pollution levels are generally higher in the most densely populated areas and "population density favours the spread of the virus since it makes social distancing more difficult," noted Rosie Cornish, a researcher at Bristol Medical School in the UK.

In addition, Northern Italy and Madrid are among the first regions in Europe where the Covid-19 epidemic broke out. It is not surprising that the number of victims was higher in these regions, since the virus was present there for a longer period of time before being detected.

Local analysis required

An analysis of pollution by region may not be the most relevant for making this kind of comparison either.

"A more local level of observation is generally preferred because exposure to air pollution can vary greatly from one address to another in the same city, depending on whether you live near a major road or on the edge of the countryside," said Anna Hansell, Professor of Environmental Epidemiology at the University of Leicester, UK.

"In order to establish a real causal link, more than 20 serious studies would be needed," Mark Goldberg, an epidemiologist at McGill University in Montreal, Canada, told The Guardian.

Ogen does not disagree. "All I hope is that my study and others will encourage more researchers to take a closer look at this possible connection,” he said. 

For him, finding an answer to the question of causality could prove critical to preventing future epidemics. Indeed, at the very least, it should push the authorities to put in place special protection measures for populations living in the most polluted areas.

Ogen believes that if it is proven that the intensity of the virus is influenced by the level of pollution, “perhaps the whole model of economic development needs to be reinvented to make it less dependent on polluting activities".

As such, coronaviruses would be added to the ever-growing list of reasons for implementing greener development policies.

This article has been translated from the original in French.

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