Optimized Extraction Methods for Pristine and Aged Microplastics from Complex Water Samples

Efficient and replicable extraction of microplastics (MPs) and other anthropogenic particles from complex environmental matrices remains challenging. We tested and optimized the extraction of water samples with and without organic matter (OM) spiked with 9 MP polymers with 16 different morphologies and/or colors, that were pristine (63-1000 μm) and aged (300-1000 μm). Statistical analyses showed that OM presence most significantly influenced MP (300-1000 μm) recoveries, followed by the strength of digestion reagents, temperature, and exposure time. Optimal recovery of MPs in a matrix with OM of <2 g/L can be obtained with a single-step digestion of Fenton's reagent. A sequential combination of two or more digestion solutions (e.g., Fenton's reagent +10% potassium hydroxide) is recommended when OM >10 g/L. Recoveries of aged MPs susceptible to degradation were up to 6 times lower than those of their pristine version after applying the same digestion method. Thus, while the digestion method may be nondestructive for pristine MPs, weathered MPs could be partially or completely digested. We recommend that the characteristics of the spiked MPs closely match those of the targeted particles in real samples during quality control tests, which allows for the generation of robust and reliable monitoring data sets.