Evaluation of the impact of polylactide microparticles on soil biota

Polylactide (PLA) is a bioplastic produced in the largest quantities in the world in the recent years. The forecast of the global production capacities of bioplastics indicates that this phenomenon will be continued at least until 2028. Therefore, it is very important to extend the knowledge and collect the data about the possible impacts of PLA on the environment. In this work the ecotoxicity tests towards individual organisms and the multispecies tests in the small terrestrial model ecosystem (STME) were used in order to estimate the effect of PLA microparticles (MPs) on the biotic part of the terrestrial compartment. Earthworms and plants representing the most important functional groups of soil biota were employed as bioindicators in these tests. The mortality and body mass of the earthworm Eisenia andrei were not affected even at the concentration of PLA MPs equal to 12.5% w/w but its reproduction ability decreased by about half (from 50 to 51.8%) at the concentrations of PLA 2.5% w/w and 12.5% w/w in the soil. Cress was more sensitive than other plants used in the evaluation of the effect of microplastics on plant growth, and it is recommended to use cress in the future ecotoxicological studies on bioplastics. The application of the STME which mimics the functionality of the terrestrial ecosystem occurred to be the valuable development and supplementation of the basic ecotoxicological tests towards the individual species. In the STME tests containing PLA MPs at the concentration of 2.5% w/w, the avoidance behaviour of earthworms, i.e. the downward movement of most of them (from 60 to 80%), was observed. It indicates that the contamination of soil by microplastics implies dangerous effects on soil invertebrates.