Catchment characteristics and land-use influence on microplastics distribution in freshwater sediments

This study examines microplastic contamination in freshwater sediments from three urban creeks in Brisbane, Australia. A dual-density extraction method, validated by recovery experiment (85-100%), was used to extract microplastics, followed by identification via light microscope, micro- FTIR and SEM. Kedron Brook showed the highest median abundance (4400 items/kg), followed by Bulimba Creek (4100 items/kg) and Enoggera Creek (2800 items/kg). Site-wise assessment revealed three distinct spatial patterns among the creeks, likely reflecting differences in runoff dynamics, surrounding anthropogenic activities, catchment elevation profile, and land-use. Microplastics abundances were higher at downstream and estuarine sites, particularly within urbanised zones. Polymer analysis identified polyethylene (PE), polypropylene (PP) and Polymethyl methacrylate (PMMA) as the most dominant types. Linear mixed-effects modelling identified creek system (p = 0.018) and sampling round (p = 0.003) as significant predictors of microplastic abundance, while between-site variability was reflected by a site-level random-effect variance of 0.0116. Multivariate analyses revealed distinct land-use associations, with residential and commercial land-uses significantly associated with PP and polyester, and industrial land-use associated with PP, polystyrene (PS), and polyester, whereas natural land-use showed no significant associations with any polymer type. Overall, urban land-use types exerted a stronger influence compared to natural land-use on microplastic distribution in freshwater sediments.