How healthy are urban soils in the south of Ireland?
This has been the question on Hannah Binner's mind over the past few years.
Hannah is an environmental geochemist with iCRAG in University College Cork. As part of her PhD research, she is assessing metal concentrations in urban soils in parks and playgrounds in the south of Ireland.
Her research has given her a special appreciation for soil. "We take soil for granted," she says.
"Soil is needed to grow our food, filter our water, store carbon, and there's so much life in it - one handful of soil has more living organisms in it than there are people on Earth.
"But soil is a non-renewable resource. It takes hundreds of years for a few centimetres of soil to form, and it's facing multiple pressures," she warns. One such pressure is the accumulation of metals in the soil.
When we burn fires or release exhaust fumes when driving, this causes metals to rise into Earth's atmosphere. When rain washes them down as part of the water cycle, they can end up in soil and water. When metals accumulate in soils, they can linger there for centuries, with little horizontal or vertical movement.
We need to be aware of metal concentrations in our soils, explains Hannah, so that, if levels of a metal become much higher than natural ones, people can be informed and potential action can be taken. This is particularly important when speaking of metals such as arsenic and lead, which can have negative impacts on human health.
In the context of climate change, Ireland is likely to experience hotter and wetter days. "Hotter days are associated with more dust, with potential for dust inhalation, while wetter days are associated with more flooding and perhaps more runoff - with potential for horizontal movement of metals through soil." This makes understanding metal concentrations in soils all the more pressing, she says.
Soils in the city
As part of her PhD research, Hannah compared samples of soil from ten parks in Cork city and ten parks across Wexford, including Wexford town, smaller towns and rural areas.
Her sampling efforts took her to some of the most popular parks in Cork city, including Lough Park, Fitzgerald's Park, Glen Park and Tramore Valley Park.
Using a circular shovel called an auger, she sampled the top 20 centimetres of soil at 15 sites in each park. After measuring pH, soil moisture and organic levels in the samples, she used XRF (X-ray fluorescence) to detect which metals were present and how much of them.
The five parks in Cork city centre had much higher levels of lead, copper and zinc than the five parks on the outskirts of the city, she found.
"The presence of lead is clearly linked to historical use of leaded gasoline, with copper and zinc possibly coming from brake linings and other car parts," she explains. These metals may also come from industry and domestic coal burning, she adds.
The same pattern was evident in Wexford, with soils in Wexford town displaying higher levels of man-made metals compared to those in some of the more rural parts of Wexford.
Overall, Cork soils contained evidence of much more human impact compared to Wexford soils.
Aside from metals, some of the samples were polluted with plastic, bottle caps, bits of glass, and tabs from cans.
"We need to start appreciating our soils," says Hannah. Before this research, Dublin and Galway were the only areas where researchers had investigated urban soils. Now the national picture is becoming clearer.
Making a difference
Hannah's work is already informing policy. In 2022, she co-authored an EPA policy report that provides an evidence-base for new policy on soil. The report, based on an analysis of 260 papers, will help Ireland meet its commitments to both national and EU soil strategies.
Although the research found that certain metal levels are above what we would consider natural for Ireland, there are currently no guidelines that would allow researchers to say whether the soils are polluted, contaminated or require remediation.
"We need legislation with clear guidelines on this, so that if a metal is elevated in an area, remediation can take place," says Hannah.
One way of remediating soils is to add fresh soil on top of contaminated soil to dilute it; another is to use specific plant species that are capable of taking up certain metals in the soil, she explains.
Hannah has always been interested in the environment, and is driven by the idea that her research can have an impact and "help improve something".
One way of doing this is by working with people to help them better understand soil science, and science in general. Hannah has nicely dovetailed this into taking on a new position in iCRAG as Education and Public Engagement Officer (maternity cover).
As she moves her hands through the soil of the raised beds in her urban garden in Cork, she hopes that one day it will be possible for everyone to get their soil tested in a lab for free.
Hannah's garden: in one of the raised beds, she grows catmint for her two cats, Smudge and Voidling.
Hannah is a PhD student with iCRAG in UCC. Her research is funded by iCRAG and Geological Survey Ireland.