Elusive knowledge about the smallest particles
Toxicologist Hanna Karlsson investigates the health effects of the tiniest particles in the air. Those found in Barcelona’s harbour appear to be more inflammatory than others.
Text Annika Lund, first published in Medicinsk Vetenskap nr 2 2025
How did you come to this conclusion?
“We collected and analysed ultrafine particles, smaller than 0.1 micrometres. The sampling was done in harbours, at airports, on roads, and in underground stations in four different cities - Barcelona, Milan, Stockholm and Thessaloniki - during both summer and winter. The ultrafine particles from Barcelona’s harbour had the most negative impact on cells, regardless of the season. Milan airport also ranked high. The study was part of an EU-funded project that ran from 2022 to 2024. We are now compiling the results."
How did you assess how inflammatory the particles are?
“First, we collected them from each site using filters. Then we extracted the particles from the filters and exposed cultured cells to the same dose, regardless of where they were collected. We then measured how much inflammationmarkers the cells released. Based on that, we assigned toxicity scores to the particles. Many of the diseases caused by particles have inflammatory components. These include cardiovascular disease, cancer and asthma."
Why are the particles from Barcelona more inflammatory?
“We do not have an answer to that yet. It could be due to the types of fuel used. Or it might relate to the levels of so-called endotoxins, toxic substances from bacteria. There could be other explanations as well."
What did the samples collected in Sweden show?
“In Stockholm, we collected particles from a traffic junction in Hallunda, from the underground station at Tekniska Högskolan and in the Söderled tunnel. The traffic-related particles were more inflammatory than those from the underground, but not at the same levels as in Spain."
Is it difficult to research this?
“Yes, there are challenges. The particles are extremely small and weigh very little, so it is difficult to collect a large enough quantity to conduct many experiments."
Hanna Karlsson leads a research group at the Institute of Environmental Medicine at Karolinska Institutet.
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