Short- and medium-term effects of biodegradable microplastics (PLA and PHB) on earthworm development and reproduction

Microplastics derived from biobased and biodegradable materials will increase their presence in soils as their use becomes more widespread. Research into their effects on soil fauna will help to ensure a better understanding of their environmental impacts. The aim of this work was to study the effects on the development of the earthworm Eisenia andrei (ingestion capacity, survival, growth, cocoon, and hatchling production), earthworm lysosomal stability through the neutral red retention time (NRTT), and substrate enzymatic activity of dehydrogenase (DHA) and fluorescein diacetate-hydrolysing activity (FDA) in the presence of polylactic acid (PLA), polyhydroxybutyrate (PHB) and polyethylene (PE) microplastics in laboratory tests. Three different tests were designed, one feeding test of 4 days, and two medium-term tests with 49 and 112 days. The 4-day test and the 49-day growth test were carried out using OECD artificial soil, while in the 112-day growth test, vermicompost was used as the substrate. PLA and PHB particle ingestion was demonstrated. No concentration or polymer-dependent lysosomal damage or effects on earthworm growth were observed. However, reproductive effects, such as a decrease in cocoon production and the number of juveniles, were reported upon exposure to PE and PLA during medium-term assays. These findings indicated that the toxicity of PLA bioplastic exposure is comparable to that of conventional plastic PE concerning the negative effects on the reproductive efficiency of the detritivorous earthworm E. andrei.