Microplastics in the Terrestrial Ecosystem: Implications for<i>Lumbricus terrestris</i>(Oligochaeta, Lumbricidae)

TLDR

Plastic debris is widespread in the environment, but the effects of microplastics on terrestrial fauna are completely unknown. The study aimed to evaluate the survival and fitness of earthworms exposed to varying concentrations of microplastics in litter. Earthworms were exposed to polyethylene microplastics (<150 µm) at 7–60 % dry weight in litter, corresponding to 0.2–1.2 % in bulk soil after bioturbation. Higher microplastic concentrations (28–60 %) increased mortality and reduced growth, while microplastics were concentrated in casts and preferentially egested as particles <50 µm, indicating concentration‑transport and size‑selection mechanisms that could influence terrestrial microplastic fate.

Abstract

Plastic debris is widespread in the environment, but information on the effects of microplastics on terrestrial fauna is completely lacking. Here, we studied the survival and fitness of the earthworm Lumbricus terrestris (Oligochaeta, Lumbricidae) exposed to microplastics (Polyethylene, <150 μm) in litter at concentrations of 7, 28, 45, and 60% dry weight, percentages that, after bioturbation, translate to 0.2 to 1.2% in bulk soil. Mortality after 60 days was higher at 28, 45, and 60% of microplastics in the litter than at 7% w/w and in the control (0%). Growth rate was significantly reduced at 28, 45, and 60% w/w microplastics, compared to the 7% and control treatments. Due to the digestion of ingested organic matter, microplastic was concentrated in cast, especially at the lowest dose (i.e., 7% in litter) because that dose had the highest proportion of digestible organic matter. Whereas 50 percent of the microplastics had a size of <50 μm in the original litter, 90 percent of the microplastics in the casts was <50 μm in all treatments, which suggests size-selective egestion by the earthworms. These concentration-transport and size-selection mechanisms may have important implications for fate and risk of microplastic in terrestrial ecosystems.