Microplastics in sediments: A systematic review structured through reproducible analytical pipelines

Microplastic research has expanded rapidly, yet substantial methodological variability continues to limit comparability across sediment studies. To characterize current practice and identify priority areas for harmonization, we conducted a systematic literature review (SLR) of 3290 records, from which 37 sediment-focused studies (18 marine, 19 freshwater) met the inclusion criteria. Methods were analyzed using a Reproducible Analytical Pipelines (RAPs) framework encompassing sampling, preparation, detection, and polymer identification. Sampling approaches varied widely: grab samplers dominated (55% of marine and 42% of freshwater studies), while corers (28% and 16%) and manual tools (5% and 16%) were less frequently used. Lower size thresholds spanned <0.1-1mm, with <0.1 mm most common in marine studies (45%) and less so in freshwater systems (30%). Density separation was nearly universal (36 of 37 studies), with sodium chloride used in over 70% of workflows despite its limited ability to recover high-density polymers; denser media were employed in fewer than 25% of studies. Oxidative digestion was the dominant method for removing organic matter (81%). Polymer confirmation relied overwhelmingly on μFTIR (35 studies), whereas Raman spectroscopy appeared in only four studies, primarily for particles <0.1mm. Overall, the SLR reveals partial methodological convergence but persistent divergence in key analytical parameters, highlighting clear priorities for future harmonization efforts.