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

Abstract

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.

Keywords: Bio-based plastics; Germination; Growth inhibition; Growth stimulation; Petroleum-derived plastics; Phytotoxicity.