Characterizing microplastic ingestion, transformation, and excretion in insects using fluorescent plastics

Plastic pollution is a growing threat to our natural environment. Plastic waste/pollution results from high emissions of both macro (> 5 mm) and microplastics (MPs; < 5 mm) as well as environmental fractioning of macroplastics into microplastics. Microplastics have been shown to have a range of negative impacts on biota. Harmonized methods to accurately measure and count MPs from animal samples are limited, but what methods exist are not ideal for a controlled laboratory environment where plastic ingestion, transformation, and elimination can be quantified and related to molecular, physiological, and organismal traits. Here we propose a complete method for isolating and characterizing fluorescent MPs by combining several previously reported approaches into one comprehensive workflow. We combine tissue dissection, organic material digestion, sample filtering, and automated imaging techniques to show how fluorescently-labelled MPs provided to animals (e.g. in their diet) in a laboratory setting can be isolated, identified, and quantified. As a proof of concept, we fed crickets (Gryllodes sigillatus) a diet of 2.5% (w/w) fluorescently-labelled plastics and isolated and characterized plastic particles within the gut and frass.