Qualitative assessment of microplastic extraction from the natural and artificial salt marsh sediments of the Venice Lagoon: methodological insights

Microplastics (MPs) are emerging contaminants in aquatic ecosystems, capable of bioaccumulation, trophic transfer, and chemical transport. Salt marshes, which stabilize sediments and filter pollutants, may be understudied sinks for MPs, particularly in artificial systems created for restoration. The Venice Lagoon, the largest in the Mediterranean, has lost much of its natural marsh area, leading to the construction of artificial marshes using dredged sediments and stabilizing structures (fascines, gabions, etc.). The contribution of these artificial edge structures to microplastic inputs remains unexplored. This study refined the methodological approach for extracting MPs from sediments aiming to develop a protocol to compare their occurrence in natural and artificial salt marshes of the southern Venice Lagoon. Two extraction methods were tested: density-based and oleophilic separation. High organic matter and fine-grained sediments created significant challenges. Hydrogen peroxide (30%) removed most organic material without altering MP morphology at 50°C, though adjusting process conditions, such as increasing temperature or reducing dilution (by adding less water), may improve organic matter removal. Oleophilic extraction reduced filtration volume but left oil residues that interfered with FTIR and Raman analyses of MP. Despite this, oil-based separation was more effective than density-based extraction for isolating a wider size range of MPs. Oleophilic separation combined with manual sorting and supported by Raman spectroscopy, proved most reliable for confirming MP presence. Fibers, such as polyethylene (PE), polyvinyl chloride (PVC), and polyamide (PA) were present in both natural and artificial marshes; likely sourced from fishing, aquaculture, and urban runoff. Preliminary evidence suggests that artificial edge materials may also contribute to MPs. Overall, this work underscores methodological challenges and current limitations when investigating silty–clayey sediments and the need for standardized, site-adaptable protocols. Future studies should expand to multiple marshes, refine oil-removal procedures, and improve recovery of smaller MPs to better assess ecological risks and inform marsh management.