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Photolytic degradation elevated the toxicity of polylactic acid microplastics to developing zebrafish by triggering mitochondrial dysfunction and apoptosis
Summary
Researchers found that biodegradable polylactic acid (PLA) microplastics become more toxic to zebrafish after being broken down by sunlight over 90 days. UV exposure shrank the particles and generated nanoplastics, which were harder for the fish to expel from their bodies compared to the original material. The degraded PLA triggered oxidative stress and mitochondrial damage in developing zebrafish, suggesting that the environmental breakdown of biodegradable plastics may actually increase their harmful effects.
Biodegradable plastics (BPs), as alternatives to conventional plastics, are increasingly consumed, but pose potential threats to aquatic ecosystems. In addition, the impact of natural aging on the toxicity of BPs is poorly understood. In this study, the photodegradation of polylactic acid (PLA, a typical BP) microplastics (MPs) under ultraviolet irradiation in water for 90 days was investigated, and the toxicities of virgin and degraded PLA to infantile zebrafish were compared. The results revealed that the size of MPs was reduced from ~25.56 to ~11.22 µm after degradation and nanoparticles were generated with a maximum yield of 7.13%. The formation of abundant oxygen-containing groups (i.e. C˭O and C-O-C) improved the hydrophilia and stability of MPs. Compared with pristine PLA, the efflux and detoxification of degraded PLA mediated by ABC transporters and P450 enzymes were slower, leading to higher bioaccumulation and skeletal development inhibition of zebrafish. Further, oxidative stress-triggered mitochondrial structural damage, depolarization, fission inhibition, and apoptosis were identified as crucial mechanisms underlying the elevated toxicity of PLA after degradation. These findings highlight the importance and necessity of considering natural degradation of BPs and related toxicity, which poses great implications for risk assessment and management of BPs.