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.

Phytotoxicity assessment of biodegradable and non-biodegradable plastics using seed germination and early growth tests.

Global production of plastics remains at the high level despite the SARS-Cov-2 pandemic. These are primarily petroleum-derived plastics but the contribution of bio-based plastics estimated at the level of 1% in the plastic market in 2019 is expected to be increasing. Simultaneously, the significant part of plastic waste is still disposed improperly and pollutes the environment making a threat to all living organisms. In this work three plastic materials, two bio-based biodegradable: polylactide (PLA) and polyhydroxybutyrate (PHB), and one petroleum-derived non-biodegradable polypropylene (PP) were studied towards their effects on seed germination and early growth of higher plants. The following plants were used as bioindicators: monocotyledonous plant - Sorghum saccharatum and two dicotyledonous plants: Sinapsis alba and Lepidium sativum. Plastics did not affect seed germination of higher plants even at the highest concentration tested (11.9% w/w) but their presence in soil acted in various ways on growth of the plants. Either no or inhibitive or stimulation effects on growth of roots or stems were noticed. It depended on the concentration and chemical composition of the plastic tested, and plant species. PHB and PLA more often caused to the inhibition of root growth than PP did. This phenomenon was observed in particular with regard to the dicotyledonous plants. Moreover, in the tests with the dicotyledonous plants (S. alba and L. sativum) the dose-response relations were usually determined as statistically relevant. Among these plants cress (L. sativum) occurred to be more sensitive and allowed for obtaining the dose-response dependence for both root and stem length, and, what is important, it took place in the case of each of materials tested. Therefore, cress is recommended to be used as a bioindicator in the assessment of the effect of plastics (petroleum-derived and bio-based plastics) on the early stages of growth of higher plants.