Adaptation of Lemna Minor To Stress Induced by Biodegradable and Conventional Microplastics

Microplastics, widespread contaminants of the environment, are raising growing ecological concerns. To address this, efforts are being made to replace conventional plastics with biodegradable alternatives, designed to break down more easily in the environment. However, the degradation of these alternatives relies on specific conditions, such as temperature, pH, humidity, and the presence of microorganisms, which are not always met in natural ecosystems. As a result, biodegradable plastics can fragment and generate microplastics. So far, only a few studies have been conducted on the effect of biodegradable microplastics on freshwater plants and have included only short-term exposure. Therefore, in this study, we investigated the long-term effects (for 12 weeks) of poly-3-hydroxybutyrate (P3HB) and polyethylene terephthalate (PET) particles < 63 μm in concentration 100 mg/L on the growth, root length, photosynthetic pigment concentration, total antioxidant capacity, electron transport system and concentration of carbohydrates and proteins in fronds of freshwater plant Lemna minor. Most of the monitored parameters were not statistically significantly affected throughout the experiment. However, both types of microplastics induced significant root elongation, which may be related to nutrient depletion, similarly to what has been observed in short-term experiments. The effect was more pronounced with P3HB, and plant growth adaptation took longer than with PET. These results suggest that biodegradable microplastics may pose more severe stress to aquatic plants than conventional plastics and influence nutrient cycling and plant-microbe interactions. These findings highlight the need for long-term, plant-based ecotoxicological assessments when evaluating the environmental safety of biodegradable plastic materials. Neither P3HB nor PET microplastics affected the measured molecular markers in 12 weeks. Both P3HB and PET microplastics induced root elongation caused by nutrient loss. P3HB microplastics had a more pronounced effect on root elongation compared to PET. Lemna minor shows resilience and adaptability to chronic microplastic exposure.