Biodegradable polymers boost reproduction in the earthworm Eisenia fetida

Area of Science:

• Environmental Science
• Ecotoxicology
• Soil Science

Background:

• Microplastic contamination poses a global threat to terrestrial ecosystems, impacting soil health and organisms.
• The environmental effects of biodegradable polymers, increasingly used as alternatives to conventional plastics, are not well understood.
• Earthworms are crucial soil ecosystem engineers, sensitive to environmental changes.

Purpose of the Study:

• To investigate the effects of conventional (polystyrene, PET, PP) and biodegradable (PLLA, PCL) microplastics on the earthworm Eisenia fetida.
• To assess impacts on earthworm weight gain, reproductive success, and gut microbial community.
• To evaluate changes in soil properties, specifically pH and cation exchange capacity.

Main Methods:

• Earthworms (Eisenia fetida) were exposed to artificial soil amended with conventional and biodegradable microplastics at 1% and 2.5% (w/w) for eight weeks.
• Direct effects on earthworm weight and reproduction (cocoons, juveniles) were measured.
• Indirect effects, including gut microbial composition and short-chain fatty acid production, were analyzed.
• Soil pH and cation exchange capacity were determined.

Main Results:

• Biodegradable polylactic acid (PLLA) and polycaprolactone (PCL) significantly increased cocoon production (135% and 54%, respectively) and hatched juveniles.
• PLLA and PCL altered earthworm gut microbial beta-diversity and increased lactate production.
• Polypropylene (PP) positively affected earthworm body weight and reproductive success.
• Soil pH decreased by approximately 1.5 units in the presence of PLLA and PCL.
• No adverse effects were observed for any microplastic type on the studied endpoints.

Conclusions:

• Microplastic effects are polymer-type dependent, with biodegradable polymers showing beneficial or neutral impacts on earthworms.
• Earthworm gut microbiota may enhance the degradation of biodegradable polymers, potentially utilizing them as a carbon source.
• Further research is needed to fully understand the long-term implications of biodegradable microplastic interactions within soil ecosystems.