Application of a small scale-terrestrial model ecosystem (STME) for assessment of ecotoxicity of bio-based plastics

In this work a small-scale terrestrial model ecosystem (STME) filled with 4 kg of soil mimicking the natural ecosystem was constructed, and then successfully applied to evaluate the effect of bio-based plastics on soil biota at the community level. It was inhabited by higher plants monocotyledonous (Sorghum saccharatum) and dicotyledonous (Lepidium sativum), and earthworms (Eisenia andrei). Two innovative bioplastics based on polylactic acid (PLA) were tested. This work is one of the first studies, in which potential impacts of bioplastic particles on soil organisms were determined at the community level. Owing to the application of the STME the ecotoxicity data for plants and earthworms were simultaneously collected and the mutual interactions might be taken into account. PLA-based plastics studied did not affect the percentage of seed germination of higher plants that was on average not lower than 88.9%. Neither the length nor fresh mass of shoots of cress were affected. One out of two PLA-based plastics (BPE-RP-PLA) inhibited sorghum growth so that it was statistically significant. PLA-based plastics did not cause to the mortality of earthworms as all ten organisms introduced to each STME survived each experiment. However, the presence of PLA-based plastic particles influenced the depth distribution of earthworms in the STMEs. Most of earthworms (60-70%) exposed to PLA-based plastics migrated downwards to the bottom soil zone, while 80% of the earthworms not exposed to PLA-based plastics lived in the top soil zone of the STME. This avoidance behaviour of earthworms known earlier for other contaminants (e.g. metals, pesticides) was for the first time reported with regard to bioplastic particles present in soil. It is a dangerous phenomenon not only for earthworms but also for the functioning and structure of terrestrial ecosystems. The STME proved to be an appropriate tool to detect it.