Microplastics in the Terrestrial Ecosystem: Implications forLumbricus terrestris(Oligochaeta, Lumbricidae)

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.

Modeling the Fate and Transport of Plastic Debris in Freshwaters: Review and Guidance

“…Model predictions suggest that currently over 5 trillion plastic particles float on the ocean surface [3] and that in 2010 alone between 4.8 and 12.7 million metric tons of plastic entered the ocean [4]. Plastics occur in a wide range of sizes, and particles can therefore be ingested by a variety of terrestrial [5] and aquatic species [6]. Ingestion of microplastics, particles <5 mm in length [1], can negatively affect hatching, growth rates, and food ingestion [7,8].…”

Effects of polystyrene microplastics on the fitness of earthworms in an agricultural soil

“…Especially in the 2% treatment, around 40 % of earthworms were dead due to the PS-MPs exposure, implying that PS-MPs could have a lethal effect on earthworms. These results could be attributed to the serious damage in the self-defense system of earthworms caused by the PS-MPs exposure at the high concentrations (≥ 0.5%) [8]. …”

Microplastic transport in soil by earthworms

“…refs 12, 16 and 17). In the experiment we used four adult, healthy earthworms with a body weight between 3 to 5 g each per experimental unit; the individuals were carefully washed, dried on filter paper and weighed prior to their addition to the experimental pots.…”

“…PE is among the major plastic types that are used worldwide 3 . We assumed, based on a previous study 12 , which also used PE, that earthworms might ingest and/or transport microparticles of different sizes to a different extent. For this reason, we used four commercially available different particle size ranges: 710–850 μm (PE-1), 1180–1400 μm (PE-2), 1700–2000 μm (PE-3) and 2360–2800 μm (PE-4).…”

“…Since microplastic could have potential adverse effects on soil biota, for example earthworms 12 , a critical research need relates to the incorporation of this material into the soil profile. Only when this material is transported into the soil can it be expected to lead to broad exposure of soil biota to these particles.…”