An overview of recent advances in micro/nano beads and microfibers research: Critical assessment and promoting the less known.

Uptake and toxicity of microplastics (<5 mm) on organisms has merited substantial attention from scientific and research communities. Micro- (1-5000 μm) and nano- (<1 μm) beads have been recognized as promising polymeric particles globally to assess risks for organisms after ingestion. Microfibers (<5 mm) are abundant worldwide, but studies demonstrating their impacts on organisms are only emerging and remain poorly understood. The goal of this review is to facilitate the research of microfibers towards risk assessments and understanding of their health effects on organisms. This paper examines the abundance, size, shapes, colors, and polymer types of micro/nano beads and microfibers in different environments as well as summarizes the existing knowledge related to the potential effects on organisms demonstrated from laboratory-based studies. It therefore also reviews and compares current methodologies used to synthesize microfibers for ingestion studies and further, documents their effects on organisms, critically assessing the knowledge gaps that need urgent attention in this rapidly developing research field. Taking together, this article will be useful to the microplastic scientific community and provide helpful referential information to those currently engaged in this field.