µPlastiTrap I Portable microplastic sampler

µPlastiTrap I is a portable microplastic sampler for small, shallow rivers developed by FVO. It was designed in response to the 2023 floods in the Savinja–Šalek region. In March 2026, the faculty received a special commendation at Slovenia’s national ED.VITA awards for the sampler.

The Savinja River after the 2023 floods.

Project at a glance

Coordinator	Faculty of Environmental Protection (FVO)
Partner	College of Industrial Engineering (VŠPI)
Developed under	the Interreg Europe PLASTIX project
Duration	March 2023 – June 2027
Project initiator and researcher	Anja Bubik, PhD, Assistant Professor
Study area	Paka and Savinja rivers, Savinja–Šalek (SAŠA) region
Recognition	2026 ED.VITA special commendation, Research and Innovation category

Challenge and solution

A sampler designed for small rivers

The 2023 floods left large amounts of plastic on the banks of the Paka and Savinja rivers. The plastic gradually breaks down and washes back into the water when it rains. Microplastics bind to pollutants and travel down rivers to the sea, but the region has not previously collected systematic data on them.

Conventional sampling requires boats, bridges or deep channels, which are unavailable along most stretches of the Paka and Savinja. µPlastiTrap I draws water directly from the bank and filters several thousand liters on site. It is portable, robust, affordable and simple enough for students and municipal staff to use.

How does sampling work?

PumpingČrpanje

A high-capacity portable pump draws water directly from the riverbank. The filtered water returns to the river through the outlet hose.

Pressure filtration

Pressurized water passes through a metal filter with 150 µm openings, which traps larger particles.

Flow measurement

An ultrasonic flow meter accurately measures the volume of filtered water, which is essential for calculating microplastic concentrations.

Concentrate

Several thousand liters of water yield around two liters of concentrated sample for laboratory analysis.

Laboratory analysis

We sieve the sample, break down organic matter and examine the particles under a stereomicroscope. We use FTIR spectroscopy to identify the polymers and report the result as particles per cubic meter of water.

Eight sampling sites

µPlastiTrap I sampling sites on the Paka and Savinja rivers
Code	Location	Why this site?
Paka
P1	Paka near Velenje	upstream of a major urban area, beside the Slovenj Gradec–Velenje main road
P2	confluence of the Paka and Bečovnica	downstream of Velenje and upstream of the Šalek Valley Central Wastewater Treatment Plant, near an industrial zone and farmland
P3	Penk – Mešič	uninhabited area downstream of the Šalek Valley Central Wastewater Treatment Plant
P4	Rečica ob Paki	just upstream of the confluence with the Savinja, where the Paka channel has been widened and deepened
Savinja
S1	Luče, upstream of the wastewater treatment plant	near the source and upstream of larger settlements, where human impact is still limited
S2	Melišče pri Grušovljah	downstream of the Luče wastewater treatment plant, beside farmland; the floods substantially widened the channel
S3	Nazarje, confluence with the Dreta	deepened and widened channel beside a footpath and the main road
S4	Soteska	downstream of all settlements in the region, near meadows, woodland and the main road

Sampling takes place seasonally. Source: Nika Kotnik’s undergraduate thesis (FVO, 2025).

Results and collaboration

Initial results (particles/m³): the Paka recorded 11 in fall 2024 and 7 in winter 2025; the Savinja recorded 4 in fall 2024 and 1 in winter 2025. The counts are low but concerning because both rivers are considered clean. The method can be used in other watercourses. Contact Assistant Professor Anja Bubik if you are interested in collaborating or writing a thesis on microplastics.