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Toxicity comparison of polylactic acid and polyethylene microplastics co-exposed with methylmercury on Daphnia magna
Summary
Researchers compared the toxicity of biodegradable polylactic acid microplastics with conventional polyethylene microplastics, both alone and in combination with methylmercury, on water fleas. The biodegradable microplastics caused greater harm, significantly reducing survival and reproduction while also increasing mercury accumulation in the organisms. The findings challenge the assumption that biodegradable plastics are always safer for the environment, suggesting they may actually enhance the toxicity of co-occurring pollutants.
The prevalence of microplastics (MPs) in aquatic ecosystems has become a significant environmental concern due to their persistence and potential toxicity. Although bioplastics, such as polylactic acid (PLA), are promoted as eco-friendly alternatives to conventional plastics, their toxicity remains poorly understood. This study compares the toxicity and pollutant vector roles of polar PLA-derived bio-microplastics (bio-MPs) with apolar low-density polyethylene (LDPE) MPs, both individually and in combination with methylmercury (MeHg), in Daphnia magna. PLA bio-MPs, both alone and in combination with MeHg, significantly reduced survival rates and reproduction while inducing oxidative stress. Additionally, PLA bio-MPs increased Hg accumulation and negatively impacted acetylcholinesterase activity and vitellogenin gene expression compared to LDPE MPs. The findings of this study suggest that PLA bio-MPs, despite being in vivo biodegradable, may pose similar or even greater environmental risks than fossil fuel-based MPs, particularly due to their potential to enhance the bioaccumulation and toxicity of coexisting pollutants.