Terrestrial Isopods as Biotic Generators of Microplastics Following Chronic Exposure to Weathered Low-Density...

Terrestrial detritivores such as isopods and springtails play a vital role in cycling nutrients through soil ecosystems. Microplastics (MPs, < 5 mm) are increasingly recognized as contaminants of terrestrial soils, yet little is known about whether soil invertebrates themselves are impacted by consuming these plastics or if they can generate MPs from larger plastic debris. This study investigated the ability of three isopod species (Porcellio laevis, Porcellio scaber, and Porcellionides pruinosus) to fragment weathered low-density polyethylene into MPs and assessed the impact on isopod survival and growth. Weathered polyethylene fragments were provided to isopods and replaced weekly over a 28-day exposure; MPs generated in the sand substrate were recovered by hydrogen peroxide digestion, filtration, and microscopy, while survival and growth were also monitored throughout. All three species foraged on the fragments and produced MPs throughout the experiment (min.-max. values: P. laevis = 88.3-1676.0 μm; P. scaber = 82.5-940.4 μm; and P pruinosus = 75.0-823.1 μm). The mean size of MPs generated differed significantly among species and was positively correlated with isopod body size. Weekly MP production did not differ significantly among species, though P. scaber and P. pruinosus varied significantly across weeks; total MP production over the 28 days did not differ among species. No significant effects on isopod survival or growth were observed. These findings indicate that terrestrial isopods can generate substantial quantities of MPs from macroplastic debris without apparent adverse effects on their own survival or growth, underscoring their potential role as biotic generators of secondary MPs in terrestrial ecosystems.