How air pollution sensors can track wildlife

A new study finds that air pollution sensors are inadvertently capturing environmental DNA. Could this be a gamechanger for protecting biodiversity worldwide?

Tracking biodiversity worldwide is incredibly challenging; national monitoring programmes differ widely, the majority of collected data is erratic and little is shared publicly.

But scientists may have found a surprising solution: the filters already used around the world to monitor air pollution.

These devices have for decades been unintentionally capturing large amounts of environmental DNA from animals and plants. Scientists say this could be used to help us understand past, as well as future, changes in biodiversity.

A new study by Canadian and UK scientists found that stations monitoring air quality inadvertently collected a large array of DNA from animals and plants in 2021 and 2022. It says the captured data could be "an absolute game changer for tracking and monitoring biodiversity" worldwide.

In a test case, the scientists recovered environmental DNA from more than 180 different plants, fungi, insects, mammals and amphibians from air quality filters located in Scotland and London from September to October 2021 and April and May of 2022. Air monitoring infrastructure "may represent a tremendous opportunity to collect high resolution biodiversity data on national scales," the scientists conclude in the study.

"We were so surprised to successfully identify over 180 taxa from just two instruments," says Joanne Littlefair, one of the study co-authors and lecturer in biological sciences at Queen Mary University of London. The animals included little owls, smooth newts and 80 different types of trees and plants. The researchers did not identify any unusual species or population movements in their initial sampling. They say this shows that the DNA collected is local and "not blowing in from a different continent".  

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In the study, the scientists extracted airborne environmental DNA, shed in the form of skin cells, saliva, hair and faeces, from the filters and analysed specific primers, molecular tags, matching their results back to online reference libraries.

Elizabeth Clare, lead author of the study and assistant professor of molecular ecology at York University in Canada, says the findings are "really exciting" as they shows that existing infrastructure can be harnessed for biodiversity research.

"There's already infrastructure in place and we can collect material that's incredibly valuable as a byproduct of its operation," says Clare.

It means that existing and established air quality networks could be a huge untapped source of biodiversity data, according to Andrew Brown, principal scientist at the National Physical Laboratory, which manages the networks for the UK Environment Agency.

Around the world air quality stations collect data on a daily or weekly basis in a highly regulated and standardised way, says Brown – meaning they are "collecting exactly the same thing in exactly the same way day after day".

Mark McCauley, a researcher at the University of Florida, says the air filters not only help provide important information on which species are present in a specific location, but also allow scientists to analyse "how changes in these species occur on geographical and temporal scales that would have been unforeseen until recently".

The regular monitoring provided by air filters is "unheard of in biodiversity science" and crucial to understanding species changes as it enables scientists to study the dynamics of animal populations and see how they are changing over time, says Clare.

Unlike single samples, such repeated measurements can "provide a really complete picture of what is happening in the area", says Clare. "You might detect the migration of a [particular] population, the arrival of a new species or a shifting landscape [due to] climate change."

The problem with current biodiversity monitoring is that there is no systematic method for doing it, says Littlefair. In the UK, for example, scientists rely heavily on data collected by "citizen scientists" to monitor species. This works for "charismatic species", such as butterflies and birds, but there are poor records for other species, such as fungi and nocturnal animals, which are less popular and more difficult to identify, she says.

"The great thing about environmental DNA from these [air quality] networks is that we can use it to go and look for any taxonomic group we want," says Littlefair.

But Clare warns that there are still "many unknowns", such as the impact of body size and activity on the DNA sampling. However, the assumption is that all species shed DNA and that "we should have equal probability of detecting something if it is within range," she says.

The new study is not the first to look at whether airborne particles can help identify species. A 2022 study by Clare and other scientists found that air in a zoo contains enough environmental DNA to identify the animals residing there. They analysed airborne DNA shed by animals, including breath, saliva, fur and faeces, and managed to detect 49 vertebrate species at Copenhagen Zoo.

Airborne DNA is a helpful tool for scientists as it allows them to detect "species that we cannot see are there", Kristine Bohmann, the study's lead author and a molecular ecologist at the University of Copenhagen, said when the study was published. It is also less resource-intensive and expensive than other biodiversity monitoring methods, which involve setting up camera traps or tracking footprints, she said.

Matthias Obst, an associate professor at the University of Gothenburg in Sweden, says there are several limitations when it comes to tracking biodiversity using air filters. These stations are often not operational in biodiverse places, he notes, and there is likely to be a much higher rate of false positives than in the case of conventional methods. The filters could, for example, capture DNA from a bird passing by or dust blown there by the wind.

"We must not get ahead of ourselves," he says. "Environmental DNA methods have great potential but there is little evidence in this article for an “biodiversity monitoring infrastructure."

Clare says filters aren’t just located in urban environments, but often found in national parks and biodiverse regions. She hopes the study will incentivise countries to set up stations in new locations of "significant ecological interest" and to preserve and archive the DNA captured by air filters.

"In many places environmental DNA [captured by air filters] is thrown away almost immediately. With this pilot study we have shown the ecological value of these samples, so we hope the data will be archived and studied," she says.

It may, Clare adds, prove an incredible treasure trove.

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