MIKRONOR 2024 Monitoring of microplastics and tyre wear particles in the Norwegian environment

Summary

The 2024 MIKRONOR campaign, coordinated by NIVA and NILU on behalf of the Norwegian Environment Agency, signifcantly expanded the national monitoring framework for microplastics (MPs) to encompass diverse environmental compartments, including surface waters (Oslofjord and Lake Mjøsa), urban runoff, marine sediments, atmospheric deposition, and coastal beach sediments. Urban stormwater runoff was identifed as a predominant source of MPs, particularly tyre wear particles (TWP). Sediment samples from stormwater traps in Oslo exhibited high TWP concentrations up to 240 mg/g, constituting approximately 25% of the total sediment mass. Corresponding runoff water samples revealed MP concentrations as high as 733 ± 142 particles/L, indicating substantial episodic fuxes of MPs into receiving aquatic or marine systems. Inner Oslofjord sediments contained 0.6–3.5 % TWP by mass, confrming the high levels found in 2023. Microplastic concentrations in surface waters were generally low, ranging from 0 to 0.6 MP/m³. However, two hydrodynamic accumulation zones within the Oslofjord exhibited anomalously high concentrations, with levels approximately two orders of magnitude greater than outside the accumulation zones. One net tow recovered >7,000 fragments of expanded polystyrene, highlighting localized retention. Atmospheric deposition peaked in urban Sofenbergparken (1514 µg/m²/d; 68 % TWP) and showed a clear urban-to-remote gradient. Beach sediments at Akerøya remained low in MPs, with most samples below detection limits. The findings highlight urban runoff, especially TWP, as a dominant source to the Oslofjord, and reveal critical hotspots in both water and air pathways.