Limitations for microplastic quantification in the ocean and recommendations for improvement and standardization

Microplastics (MPs) in aquatic ecosystems, especially in the marine environment, represent an environmental issue of increasing scientific and societal concern. MPs have widespread adverse effects to the marine environment. However, the ecological effects of marine MPs, at regional and global scales, have remained poorly understood, which is partly due to the inconsistency of methodologies employed. In this chapter, we summarize and compare the analytic approaches utilized by the scientific community for numerating MPs in marine environments. Based on commonly used procedures for quantification of MPs in different marine matrices, this chapter is structured in four sections: (1) sample collection, (2) separation, (3) analysis, and (4) quality assurance/quality control. Amid the specific challenges in these four steps, cost-effective recommendations are provided to accelerate method standardization and harmonization for measuring MPs in different marine environments. The reliable and consistent methods are the imperative prerequisite for clarification of crucial questions about MPs in seas and thus for future risk assessment and reduction strategies. Furthermore, the analytic techniques discussed here are also applicable to other aquatic environments, such as freshwater and estuarine systems.