Two digestion methods were excluded from further experiments: H2O2 due to excessive foaming and therefore possible sample losses and Proteinase-K due to its cost. The trypsin protocol could not be optimised to 25-μm filtration. However, its efficacy was assessed on M. gigas, filtering over 63-μm mesh. This was done because of the negligible damage of enzymes to microplastics in the digestion process (see references in Table 1). Tissue digestions were performed in triplicate. Reagent controls were run alongside to establish effects on filters. The KOH protocol was applied to M. gigas, O. edulis and R. philippinarum. Digestates were filtered over pre-weighed filters (Table 2), rinsed with ultrapure water, dried overnight at 60 °C and re-weighed at room temperature. Efficacy was calculated by comparing the relative removal of organic material: