Analysis of Conventional and Biodegradable Microplastics in Solid Sample Matrices: A Contribution to Method Standardization

Abstract

Microplastics are the new emerging pollutants ubiquitously detectable in aquatic and terrestrial ecosystems. Fate and behavior as well as ecotoxicity are of increasing environmental concern particularly in sediments and soils as natural sinks. For a global environmental risk assessment reliable and easy to apply analytical methods are mandatory to obtain comparable data. This is based on the isolation of microplastics out of the solid sample matrices prior to instrumental detection. Thus, this study provides a validated approach for density separation, which emerged from a comparative study using different salt solutions to isolate conventional and for the first time biodegradable microplastics from different solid sample matrices, i.e., sand, artificial soil, and compost. Four solutions (water, sodium chloride, sodium hexametaphosphate and sodium bromide) of different densities were applied followed by oxidizing digestion. Finally, the impact of the procedures on size and surface properties of microplastics was tested. Dependent on the sample matrix, highest recovery rates of 87.3-100.3 % for conventional polymers and 38.2–78.2 % for biodegradable polymers were determined with sodium bromide. It could be shown that the type of solid sample matrix influences the recovery rates and has to be considered when choosing a sample preparation technique.