Photo story

Microplastics in Postojna Cave: Another Month of Monitoring

4 September 2026 Postojna Cave, Slovenia CavesPostojnaNature

On Friday, 4 September, I joined Raffaele Bruschi, Dr Blaž Kogovšek and Dr Magdalena Aljančič for a morning of work in Postojna Cave. As part of his PhD, Raffaele is investigating how microplastics reach caves through the air, move through them and settle. This visit was for collecting the samples and preparing the samplers for another month of measurements.

Magdalena Aljančič, Blaž Kogovšek and Raffaele Bruschi sit in the yellow carriages of the Postojna Cave train. — Magdalena, Blaž and Raffaele aboard the cave train.

In their fluorescent-orange coveralls, Raffaele and Blaž looked ready to film a new season of Prison Break in Postojna Cave. The coveralls are made from pure cotton and limit the introduction of synthetic fibres from their everyday clothes. The bright orange colour also makes any stray cotton fibres from the coveralls easier to recognise in a sample.

The cave train was part of our journey, and also one of the questions behind the research. Raffaele is looking at particles that go unnoticed on an ordinary cave visit. He wants to know whether their deposition differs between areas with a train, crowds of visitors and almost no regular tourist traffic.

Blaž Kogovšek and Raffaele Bruschi carefully pour a sample between glass vessels, wearing orange cotton coveralls and blue gloves in Koncertna dvorana (Concert Hall) in Postojna Cave. — Blaž and Raffaele changing a sample in Koncertna dvorana (Concert Hall) in Postojna Cave.

Another month in the glass collectors

Blaž helped Raffaele change the water in the samplers and pack the collected samples. They arranged the glass containers beside the stands and got to work. In the light of their headlamps, even pouring water from one container into another showed how much care the job required.

An elevated glass deposition sampler stands beside the path in Postojna Cave, with Blaž Kogovšek approaching in orange coveralls.

Raffaele Bruschi checks a glass container by headlamp, with sample jars arranged at his feet in the dark Koncertna dvorana (Concert Hall) in Postojna Cave.

Raffaele Bruschi and Blaž Kogovšek crouch beside a sampling stand, their headlamps lighting the containers on the cave floor in Koncertna dvorana (Concert Hall) in Postojna Cave.

Blaž Kogovšek bends over the glass containers while Raffaele Bruschi handles a sample beneath the raised collectors in Koncertna dvorana (Concert Hall) in Postojna Cave.

Blaž Kogovšek reaches toward the elevated collectors while Raffaele Bruschi kneels beside the sample containers below a cave wall in Koncertna dvorana (Concert Hall) in Postojna Cave.

They also used powder-free nitrile gloves. These are made from synthetic rubber and help limit contamination while handling the samples. Their composition is known, so the laboratory can use infrared analysis (µ-FTIR) to check whether a suspect particle’s spectrum matches the glove material.

The coatings inside bottle caps can also contain plastic and introduce particles into a sample. Aluminium foil helps protect the samples from this contamination. Particles identified during analysis as coming from the cap coating can be excluded when interpreting the environmental sample.

Control samples, known as blanks, also help reveal contamination introduced during handling, transport and laboratory processing. Without these checks, particles from clothing, equipment or the sampling process itself could easily be mistaken for particles from the cave environment.

A close view of blue-gloved hands pouring water from a large glass collector into a smaller sample container in Postojna Cave.

Raffaele Bruschi labels a glass sample container with tape and a marker under his headlamp so the samples can be identified.

Raffaele Bruschi and Blaž Kogovšek stand on either side of a deposition sampler in Plesna dvorana, with glass jars on the ground.

Raffaele Bruschi looks up at the glass collectors on a metal stand beside the railway in Plesna dvorana.

The passive samplers catch particles as they settle out of the air, recording deposition over time. Air currents can carry particles through the cave, while people and trains can stir settled particles back into the air. Apparently, even underground, dust does not necessarily get a quiet life.

Raffaele and his collaborators are testing a new prototype adapted to cave conditions. Passage shape and ventilation can change considerably over a short distance, so a single sample can hardly tell the story of an entire cave. Comparing several positions helps make sense of those differences. The laboratory work will then establish which collected particles are plastic, what shapes they have and which polymers they consist of.

Blaž Kogovšek and Raffaele Bruschi carry equipment along the railway through a narrow, illuminated passage in Postojna Cave. — Carrying the equipment onward through the passage beside the tracks.

Three places in the same cave

Map of Postojna Cave marking the three monitoring sectors: Plesna dvorana, Pisani rov and Koncertna dvorana, with the Pivka River shown in blue. — The three monitoring sectors in Postojna Cave: 1 — Plesna dvorana (Dance Hall), 2 — Pisani rov, 3 — Koncertna dvorana (Concert Hall).

In Plesna dvorana, the Dance Hall, the samplers stand at different distances from the railway. Here the researchers are investigating the possible influence of the cave train and the air movement accompanying its passage. As we worked and I took photographs, yellow and red carriages carried visitors past us, while the collectors stayed in place.

The yellow cave train passes behind Raffaele Bruschi, Blaž Kogovšek and the glass sampling vessels in Plesna dvorana.

A wide view of Plesna dvorana shows the sampling stands spaced across the hall while Blaž and Raffaele work beside their equipment.

Blaž Kogovšek and Raffaele Bruschi stand beside a sampler as a train approaches through the tunnel into Plesna dvorana.

A yellow and red cave train enters Plesna dvorana beside the microplastic sampling station and two researchers in orange coveralls.

In Koncertna dvorana, the Concert Hall, the focus is on people walking and gathering in larger numbers. Pisani rov, a passage with almost no regular tourist traffic, provides a comparison with a less visited part of the cave. All three sectors belong to the same cave system, but the activity within them is quite different.

Visitors ride past the sampling equipment beneath the chandelier in Plesna dvorana, with Blaž and Raffaele standing beyond the carriages.

The cave train curves across the foreground beneath the bright chandelier, passing the researchers and collectors in Plesna dvorana.

A train filled with visitors crosses Plesna dvorana under its chandelier, with the monitoring station visible beside the railway.

Monitoring is still underway and there are no results yet. Raffaele hopes to establish whether the quantity and characteristics of deposited microplastic particles differ between these settings, and how far any differences can be linked to visitors and the train. The work will also show how well the prototype performs inside a cave. The findings could help with cave conservation and planning similar monitoring elsewhere.

Work on both sides of the border

A considerable amount of shared work went into the collectors on their stands. Manuela Bisiacchi, Renzo Crevatin and Elvio Merlach at the University of Trieste helped turn the idea into a working prototype. The project involves Prof. Lucia Gardossi, Prof. Monia Renzi and the BioScience Research Center, where the samples will be analysed in a laboratory specialising in microplastic identification.

Dr Tanja Pipan and the Karst Research Institute ZRC SAZU team contribute scientific expertise, knowledge of the cave and practical support. Dr Magdalena Aljančič and Dr Blaž Kogovšek were with us on this visit. Postojna Cave Park also provides essential support for the work inside the cave.

Sanela Čoralič also covered the research in Primorski dnevnik on 27 August: How do microplastics reach the karst underground? The article is in Slovenian.

Raffaele Bruschi stands beside the glass deposition collectors in Plesna dvorana as a yellow locomotive passes on the nearby track.

Blaž Kogovšek looks toward the elevated glass collectors, his headlamp shining beside the passing train in Plesna dvorana.

Most of the photographs were taken without posing this time too, even though we had time and everyone was more than willing to pose. I increasingly find that the candid, spontaneous moments are my favourites because they feel more real. Carefully placing people in the frame can soon start to feel a little artificial.

Raffaele, the pleasure is mine too. It is always enjoyable to work with motivated, creative people who carry an idea through to work in the field. Thank you for the invitation and the company — I would be happy to join you again.

Postojna Cave, Slovenia, 4 September 2026.