Effects of petroleum-based and biodegradable bio-based microplastics versus natural control particles on Paramecium caudatum, combined with in situ Raman spectroscopic detection

The impacts of microplastics (MPs) are becoming increasingly concerning. Although many ecotoxicological studies have examined potential effects of MPs on organisms, most have tested only a limited range of pristine plastic types, which do not reflect the properties of environmentally conditioned plastics. This limits the extent to which the results can be applied to real-world situations. Additionally, understanding the ecological impact of MPs requires studies that begin at the lower levels of the food web. In freshwater ecosystems, unicellular ciliophora are a key part of these trophic levels. Studying the effects of MPs on this group is essential for understanding their overall impact on the ecosystem. This study aimed to address both issues by examining MP uptake and the impact of environmentally conditioned MPs on the ciliophora Paramecium caudatum. A 72-hour exposure was conducted using six petroleum-based (PB-) and four biodegradable bio-based (BB-) MP types at three concentrations, albeit higher than those found in the environment, along with three types of particle controls. All particles were incubated in ultrapure and freshwater to compare the effects of pristine versus environmentally conditioned MPs. Verification of particle uptake was performed with µ-Raman spectroscopy, confirming particle uptake without the need for fluorescent dyes, except for two control particles. The exposure experiments showed increased reproduction in all treatments with BB-MPs and control particles, except for one, whereas results for PB-MPs were inconsistent. No significant differences were observed between different particle incubation conditions. Our findings indicate that MP effects depend on plastic type, regardless of environmental conditioning, and that uptake by P. caudatum alters the Raman spectra of BB-MPs and PET particles.