Size- and shape-dependent effects of microplastic particles on adult daggerblade grass shrimp (<i>Palaemonetes pugio</i>)

The incidence of microplastics in marine environments has been increasing over the past several decades. The objective of the present 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 2000 particles/400 mL (= 50 000 particles/L) for 3 h. Following exposure, grass shrimp were monitored for survival, ingested and ventilated microplastics, and residence time. Mortality ranged from 0% to 55%. Spheres and fragments <50 μm were not acutely toxic. Mortality rates in experiments with spheres and fragments >50 μm ranged from 5% to 40%. Mortality was significantly higher in the exposure to 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 to 75 h, with an average of 43.0 ± 13.8 h. Within the gills, the residence time ranged from 27 to 45 h, with an average of 36.9 ± 5.4 h. The results suggest that microplastic particles of various sizes and shapes can be ingested and ventilated by adult daggerblade grass shrimp, resulting in acute toxicity. Environ Toxicol Chem 2017;36:3074-3080. © 2017 SETAC.