BayCEER Workshop 2026

Microplastic particles (MPP) are ubiquitous pollutants, and studies have shown potentially harmful effects on human health and marine ecosystems, with growing attention now directed towards terrestrial ecosystems.

P 6 in Posters

Microplastic particles (MPP) are ubiquitous pollutants, and studies have shown potentially harmful effects on human health and marine ecosystems, with growing attention now directed towards terrestrial ecosystems. Major input pathways of MPP into agricultural soils include mulch films, sewage sludge, compost and atmospheric deposition. In soil, MPP can be colonised by bacteria and may thereby alter microbial communities. Particle size is considered a key property, as it influences the transport, interactions and potential biological effects of MPP. This ecotoxicology study aimed to assess whether MPP affect the growth of a soil-relevant bacterium, and whether such effects depend on polymer type, particle size and concentration.

In this work we used a high-throughput 96-well microplate growth-inhibition assay with Pseudomonas putida, a soil-relevant, Gram-negative heterotroph and the test species of ISO 10712. PLA and PS were tested in three nominal size fractions (< 20, 20–75 and 125–200 µm), and PET and PA66 in the two coarser fractions, each at four nominal concentrations (50, 250, 500 and 1000 mg L⁻¹). Two endpoints were determined: the specific growth rate (µ) and the yield-based percentage inhibition, following the endpoint definitions of OECD Test Guideline 201. Preliminary results indicate that effects differed between polymers and size fractions, with the most pronounced, concentration-dependent inhibition of growth yield observed for the smallest PS fraction, and that growth rate alone may underestimate inhibition that is evident in growth yield. The analysis is currently being extended to the Gram-positive soil bacterium Arthrobacter globiformis.

Keywords: Microplastics; Pseudomonas putida; Particle size; Polymer type; Growth inhibition; ecotoxicology