A rapid method for extracting microplastics from oily food samples

The increasing evidence of microplastic (MP) contamination influence on aquatic organisms has been extensively reported globally. However, the discussions of extracting MPs from oily food samples are limited, highlighting the pressing need for effective and standardized analytical methods to extract MPs from oily food. Previous methods, such as using acid, alkali or oxidizing solutions as digestion reagents, usually take a long time to digest oily food, increasing the possibility of procedural contamination of MPs in food over time. The objective of this study was to develop a rapid, efficient, economical and simple analytical method to extract MPs from oily food samples. This innovative protocol combines the use of 4 : 1 HNO₃ : H₂O₂ as a digestion reagent to accelerate the digestion within 1 h at 50 °C and hexane as a washing solution to remove the oil adsorbed on the surface of MPs and membranes. Four common types of MPs, namely, polyethylene terephthalate, polyethylene, polystyrene and polypropylene of different sizes were added to oily flours to demonstrate this method. The mean recovery of MPs was 95% ± 2% (range: 93-98%), and no significant changes in color, particle size, surface area and spectrum features were found for all recovered polymers except for PS with minor changes in color and surface. The method was confirmed to be effective on rice, noodles, bean products and various meat samples. All in all, the present method can facilitate the observation and identification of characteristics of MPs, providing an innovative combination method for quantitative and qualitative analyses of MPs in oily food samples.