Enhancing microplastic monitoring with ships of opportunity to determine baselines: Methodological design matters

). No correlations were observed between seasonality, environmental parameters and microplastic concentration, indicating that while baseline levels were established, hotspots or environmental drivers could not be identified within this dataset. The study shows how methodological choices - such as spatial coverage, sampled volume, filter mesh size, and laboratory processing protocols - influenced reported concentrations and data comparability. Despite these limitations, resulting concentrations were within the same order of magnitude as other subsurface pump-based investigations, supporting the reliability of the approach. The FerryBox proved versatile and affordable, demonstrating its potential for integration into monitoring programmes. To maximise value of such databases, future efforts should prioritise methodological harmonisation and validation, as inconsistent sampling and analytical protocols currently limit cross-study comparability and hinder detection of broader regional trends. Addressing these issues will ensure datasets are fit-for-purpose and support robust regional and international comparisons.