Towards understanding uncertainties in the measurement of microplastic concentrations in river systems

This thesis investigates how methodological choices and regional context shape freshwater microplastic monitoring and risk assessment. It first evaluates key analytical parameters, showing that higher-resolution micro-FTIR objectives greatly increase detected particle numbers, while a 20 micro-m sieve can be sufficient for routine work. It then quantifies abundances, size spectra and polymer types in the Yangtze–Huangpu system and the Rhine–Meuse delta, revealing high contamination and region-specific polymer profiles. A systematic review of Yangtze studies, scored against updated QA/QC criteria, exposes substantial methodological gaps and likely underestimation of small particles, yet indicates that ecological thresholds are often exceeded. Finally, a detailed uncertainty analysis identifies sediment sampling, blank correction, and particle-to-mass conversion (including polymer density assumptions) as dominant error sources. Together, these components provide harmonized datasets, an uncertainty framework, and clear recommendations for standardized, quality-controlled monitoring to support more reliable freshwater microplastic risk assessments and management.