Title:

Microplastic extraction methods in complex water samples- effects on aged and pristine microplastics

Abstract:

Harmonized methods for optimal extraction of microplastics (MP) from surface waters containing considerable complex natural organic matter are needed that also consider aged in addition to pristine MP. We report on a systematic study of extraction procedures to effectively remove unwanted organic matter (OM) while balancing the retention of aged and pristine MP. Sequential combinations of oxidative-alkaline protocols (e.g., potassium hydroxide, hydrogen peroxide, Fenton’s reagent) were applied to polymeric particles (olefins, polystyrene, polyamide, polyesters, tire rubber) of various shapes and sizes from 63 to 1000 μm with and without OM. Recoveries of MPs from digested water samples depended on the polymer type, aging, and shape. Recoveries of easily degraded aged particles (e.g., polyurethane and polystyrene foams, polyester fibers) were up to 6 times lower than that of their pristine version after applying the same digestion method (2-35% vs. 12-79% after alkaline-oxidative digestion without OM). A Response Optimization Model indicated that, for OM concentrations <2 g/L, using a single-step digestion method can minimize MP losses while effectively digesting OM. Samples with OM concentrations exceeding 10 g/L require a sequential combination of two or more digestion solutions to balance efficiency and effectiveness while minimizing MP losses, especially for the highly weathered MP. Adding recovery spikes of known MP with OM prior to digestion is highly recommended, while both chemical characterization and morphometric methods are recommended to evaluate the MP degradation