The Dublin city air may be famous for the smell of hops brewing, and the aroma of the Liffey, but these days it also contains cannabis, magic mushrooms and disease-causing agents.
The findings, based on analysis of bits of DNA floating in air samples, were made by Dr David Duffy, an Irish scientist at the University of Florida (UF) .
Dr Duffy got his science degree at TCD, his PhD in NUI Galway, and worked at UCD and the University of Limerick before moving to Florida.
He is an expert in the use of environmental or eDNA. These are the small pieces of DNA scientists can recover from samples of air, water or soil, to find out what plants, animals, viruses and bacteria live at given locations.
This eDNA is constantly shed by living organisms into its environment.
“You can think of it as forensics for wildlife and all animals, plants, fungi, viruses and microbes,” said Dr Duffy, who is Assistant Professor of Wildlife Genomics at the UF Whitney Laboratory for Marine Bioscience.
“All species shed trace amounts of DNA. For example, through the shedding of hair and skin cells, release of bodily fluids during excretion and even when exhaling.”
Air samples seeking eDNA were taken at the Zoology Department in Trinity College Dublin, the Wildlife Rehabilitation Ireland offices in Duleek, Co Meath, at a private residence in Co Wicklow, and in a Florida forest.
“Between the Irish sites, we chose those locations as we wanted a contrast between the sites – city, mountainside and estuary – and as they were sites that facilitated repeat sampling across weeks and years,” Dr Duffy said.
“The Irish sites provided an interesting contrast to the sites in Florida. Temperate climate versus sub-tropical. This allowed us to confirm that our approach works well in different locations.”
In the Dublin samples, Dr Duffy said, there were eDNA traces from drugs, diseases, DNA from humans and animals, allergens and pollen.
“Dublin city was high in rat, dog, human and human pathogen DNA compared to the other sites.”
The capital also had the highest level of pig and cow eDNA, Dr Duffy said, probably explained by food products bought and consumed in the city.
The traces of human eDNA also showed that Dublin had more people from more parts of the world living there, than in the site in Florida.
“Dublin city air contained eDNA from a broader range of genetic ancestry than the Florida forest air,” it said.
The Florida air recorded the presence of eight shared, inherited human genetic characteristics, or haplogroups, while Dublin contained 87 such groups.
At the Irish sites, Dr Duffy and his team used filters that were attached to a vacuum pump, and air was filtered, sampled and collected for one week.
The scientists also used a lower-tech approach, taking swabs of surfaces like windowpanes and leaves, and this performed almost as well as the filter in terms of the number and variety of plant and animal species detected.
“Most of the DNA recovered from the swabs is eDNA that has settled on the surfaces,” Dr Duffy said. “This means every windowpane in the world essentially acts as an air eDNA sampler.”
eDNA can reveal what species are present in a given location, but also where the animal originated from
In future, eDNA could be used to track emerging diseases, control pandemics, identify endangered wildlife, track narcotics, identify antimicrobial resistance and measure allergens like pollen in the air.
“While we aren’t there yet, we are moving ever closer to the pathogen and lifeform detection capabilities envisaged in the fictional Star Trek Environmental Tricorder,” Dr Duffy said.
As Trekkies might recall, the Tricorder had three functions; sensing, recording and computing, and were often used to detect the presence of life on new planets that the cosmic explorers had landed on.
The use of eDNA sampling can prove vital for biologists seeking to preserve endangered species, Dr Duffy said, as it can reveal what species are present in a given location, but also where the animal originated from.
“The level of information that’s available in eDNA is such that we’re only starting to consider what the potential applications can be, from humans, to wildlife to other species that have implications for human health,” he said.
An air filter left running can pick up signs of nearly every species that grows or wanders nearby
The air we breathe is full of genetic material that can be easily sampled by scientists. A simple air filter left running for hours, days or weeks, Dr Duffy said, can pick up signs of nearly every species that grows or wanders nearby.
“In the Florida air we found bobcat, alligator, bird, sea turtle, bat, butterfly, snake and squirrel eDNA, as well as tree, vine and fungus eDNA, and many more animals and microbes.
“It opens up huge possibilities to study all the species in an area simultaneously, from microbes and viruses all the way up to vertebrates like bobcats and humans, and everything in between.”
The findings were reported in the journal, Nature Ecology and Evolution.
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