Evaluation of Digestion Methods in Microplastic Recovery from Mussels (Mytilus galloprovincialis) for a Standardised Microplastic Isolation Protocol

Although microplastics are known as bivalve mollusc contaminants, the standardisation of isolation protocols hasn't been developed yet. This study aims at assessing the best microplastic recovery rates and digestion efficiencies, applying two chemical reagents (10% KOH and 30% H2O2) across a wide range of known temperatures, on mussels (Mytilus galloprovincialis) contaminated with virgin microplastic standards. Both reagents provided good digestion efficiencies, but microplastic recovery was optimised employing 30% H2O2 at 50-60 °C, which also preserved polymer integrity. Indeed, recovery rates ranged from 88.75 to 91.86% at 50 and 60 °C, respectively, whereas 85.8 and 99.4% were the values of the digestion efficiency at 50 and 60 °C, respectively. Flotation and supernatant fractionation were found to be decisive parameters in maximising microplastic recovery; therefore, they shouldn't be overlooked. These findings lay the foundations for standardising microplastic isolation protocol from mussels, allowing for the reproducibility of data and consequently the comparison of different laboratories' results in order to concretely assess the risk for consumer health and lead to determining the benchmarks for food safety policymaking. Further studies are needed to standardise the method for the detection of microplastics from other foods.