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Multi-level toxicity assessment of polylactic acid (PLA) microplastics on the cladoceran Daphnia magna
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Researchers tested the toxicity of microplastics made from polylactic acid (PLA), a common bioplastic marketed as an eco-friendly alternative, on water fleas over 21 days. The PLA microplastics caused oxidative stress, depleted energy reserves, and reduced reproduction, though effects were generally milder than those reported for conventional plastics. This study challenges the assumption that bioplastics are harmless once they break down in the environment.
The accumulation of plastics waste in the environment has raised a worrisome concern, moving the society to seek out for sustainable solutions, such as the transition from the use of fossil-based, conventional plastics to bioplastics (BPs). However, once in the environment bioplastics have the same probability to accumulate and experience weathering processes than conventional plastics, leading to the formation of microplastics (MPs). However, to date the information on the potential toxicity of MPs originated from the weathering of bioplastics is limited. Thus, this study aimed at investigating the adverse effects induced by the exposure to MPs made of a bioplastic polymer, the polylactic acid (PLA), towards the freshwater cladoceran Daphnia magna. Organisms were exposed for 21 days to three concentrations (0.125 µg/mL, 1.25 µg/mL and 12.5 µg/mL) of PLA microplastics (hereafter PLA-MPs). A multi-level approach was performed to investigate the potential effects through the biological hierarchy, starting from the sub-individual up to the individual level. At the sub-individual level, changes in the oxidative status (i.e., the amount of reactive oxygen species and the activity of antioxidant and detoxifying enzymes) and oxidative damage (i.e., lipid peroxidation) were explored. Moreover, the total caloric content as well as the content of protein, carbohydrate and lipid content assess were used to investigate the effects on energy reserves. At individual level the changes in swimming activity (i.e., distance moved and swimming speed) were assessed. Our results showed that the exposure to PLA-MPs induced a slight modulation in the oxidative status and energy reserves, leading to an increase in swimming behavior of treated individuals compared to control conspecifics. These results suggest that the exposure to MPs made of a bioplastic polymer can induce adverse effects similar to those caused by conventional polymers.
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Scientists compared the toxicity of biodegradable PLA (polylactic acid) microplastics with conventional polyethylene microplastics on water fleas, a key species in aquatic food chains. The biodegradable PLA microplastics were actually more acutely toxic than conventional ones, partly because their higher density led to greater accumulation in the organisms. UV weathering further increased the toxicity of PLA microplastics, challenging the assumption that biodegradable plastics are automatically safer for the environment.
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Researchers exposed Daphnia magna to PET and PLA microplastics at three concentrations over 21 days, assessing biochemical endpoints including oxidative stress markers, antioxidant enzymes, lipid peroxidation, energy reserves, and swimming behavior. Both fossil-based PET and biobased PLA microplastics induced measurable stress responses at sub-individual and individual levels, demonstrating that bioplastics do not necessarily present a safer environmental profile than conventional polymers.
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