The incidence of microplastics in marine environments has been increasing over the past several decades. The objective of this study was to characterize the size and shape dependent effects of microplastic particles (spheres, fibers and fragments) on the adult daggerblade grass shrimp, Palaemonetes pugio. Grass shrimp were exposed to 11 sizes of plastic; spheres (30, 35, 59, 75, 83, 116, and 165 µm), fragments (34 and 93 µm), and fibers (34 and 93 µm) at a concentration of 20,00 particles/400 mL (= 50,000 particles/L) for three hours. Following exposure, grass shrimp were monitored for survival, ingested and ventilated microplastics, and residence time. Mortality ranged from 0-55%. Spheres and fragments under 50 microns were not acutely toxicity. Spheres and fragments greater than 50 microns had mortalities ranging from 5-40%. Mortality was significantly higher at 93 µm fibers than other sizes tested (p < 0.001). The shape of the particle had a significant influence on the number of particles ingested by the shrimp (p < 0.001). The residence time of particles in the gut ranged from 27-75 hours with an average at 43.0 ± 13.8 hours. Within the gills, the residence time ranged from 27-45 hours with an average of 36.9 ± 5.4 hours. Results from this study suggest that microplastic particles of various sizes and shapes can be ingested and ventilated by adult daggerblade grass shrimp, resulting in acute toxicity. This article is protected by copyright. All rights reserved

Plastic is a ubiquitous environmental contaminant, resulting in widespread exposure across terrestrial and marine spaces. In the environment, plastics can degrade into microparticles where exposure has been documented in a variety of fauna at all trophic levels. Human epidemiological studies have found relationships between inhaled microplastics and oxidative stress and inflammation. Previous studies of bottlenose dolphins (Tursiops truncatus) have reported prevalent exposure to plasticizing chemicals (e.g., phthalates) as well as particle loads in gastrointestinal tracts, but exposure from inhalation has not yet been studied. The objective of this study was to determine if inhalation is a viable route of microplastic exposure for free-ranging dolphins. Exhalation samples were opportunistically collected from dolphins residing in Sarasota Bay, Florida (n = 5) and Barataria Bay, Louisiana (n = 6) during catch-and-release health assessments to screen for microplastic particles. All dolphin samples contained at least one suspected microplastic particle, and polymer composition was determined for 100% of a subset (n = 17) of samples. Additional studies are warranted to better understand the extent of inhaled microplastics, as well as to explore impacts, given potential risks to lung function and health.