Studying microplastics: Lessons from evaluated literature on animal model organisms and experimental approaches

Although we are witnesses of an increase in the number of studies examining the exposure/effects of microplastics (MPs) on different organisms, there are many unknowns. This review aims to: (i) analyze current studies devoted to investigating the exposure/effects of MPs on animals; (ii) provide some basic knowledge about different model organisms and experimental approaches used in studying MPs; and to (iii) convey directions for future studies. We have summarized data from 500 studies published from January 2011 to May 2020, about different aspects of model organisms (taxonomic group of organisms, type of ecosystem they inhabit, life-stage, sex, tissue and/or organ) and experimental design (laboratory/field, ingestion/bioaccumulation/effect). We also discuss and try to encourage investigation of some less studied organisms (terrestrial and freshwater species, among groups including Annelida, Nematoda, Echinodermata, Cnidaria, Rotifera, birds, amphibians, reptiles), and aspects of MP pollution (long-term field studies, comparative studies examining life stages, sexes, laboratory and field work). We hope that the information presented in this review will serve as a good starting point and will provide useful guidelines for researchers during the process of deciding on the model organism and study designs for investigating MPs.