However, this approach is likely not to recover a large portion of microplastics. Avio et al(2015), using NaCl flotation followed by H2O2 digestion, successfully extracted microplastics from fish GITs, obtaining recovery rates of around 80 to 90% depending on particle size classes. However, it should be noted that they dosed samples with lower density polymers polyethylene and polystyrene only. Optimisation of an existing Proteinase-K approach would have resulted in unacceptable costs. Since previous studies digested only 0.2 g of tissue with Proteinase-K, the cost of digesting tissue of entire oysters would likely have increased fourfold or more (Table SI.2). Adjusting the tissue sample amount to suit the existing protocol is not advisable, as this would lead to sample heterogeneity. So far, most studies on European bivalves reported <1 microplastic/g w.w..