Methods for the extraction of microplastics in complex solid, water and biota samples

The widespread distribution of plastics, their persistence and ability to act as a vector of toxic chemicals has rendered them concerning emergent pollutants. The quantification of these contaminants is highly relevant for the evaluation of anthropogenic impacts on aquatic and terrestrial ecosystems and dependent of the efficacy of methods to separate microplastics from environmental matrices. Little information is available about the microplastic extraction methods on complex samples - i.e. samples with multiple types of matrices. Herein, methods for the separation of microplastics from complex samples are summarized and discussed based on their advantages and drawbacks focused on a comparative analysis of their efficiency on organic matter removal, polymer recovery and preservation of plastic integrity. The efficiency on microplastic recovery and organic matter reduction, as well as the examination of the effects of treatments on plastics are closely linked to the density and digestion approaches selected, the polymer features and the environmental matrix analyzed. High density salt solutions are more effective for density separation, while oxidative methods have recurrently shown better rates of organic matter reduction (particularly in vegetal-rich samples) and plastic recovery, with little impact on plastics, while 10 % KOH has been described as highly efficient in samples containing animal organic matter. This comparative analysis highlights the benefits and limitations of different approaches for the analysis of microplastics in complex samples which may be helpful for the optimization and harmonization of the methods.