Acute Toxicity Effects of Aged Polyethylene and Polylactic Acid Microplastics on Microcystis aeruginosa: Growth and Oxidative Stress Response.

The usage of biodegradable plastics as a substitute for traditional plastics is increasing yearly. However, the toxicity of biodegradable microplastics to freshwater microalgae is still unclear compared to traditional microplastics; In addition, the toxic release effects of different aging methods on biodegradable plastics are also unknown. Taking polyethylene (PE) and polylactic acid (PLA) as the research objects, the acute toxicity (96 h) of Microcystis aeruginosa under high temperature aging (HT) and ultraviolet aging (UV) conditions was investigated. Results showed that more cracks appeared on the surface of aged PLA, and the inhibition effect on microalgae was greater than that of aged PE. Moreover, the inhibition rate of microplastics on microalgae after UV aging (PLA: 39.64%, PE: 32.66%) was higher than that of HT aging (PLA: 30.95%, PE: 26.36%). In addition, the reactive oxygen species (ROS) levels in the treatment groups subjected to UV aging (PLA: 7-45%, PE: 3-28%) increased more than those subjected to HT aging (PLA: 6-31%, PE: 2-20%). This study revealed the toxicity difference between PLA and PE on Microcystis aeruginosa under different aging conditions, which provided a theoretical basis for studying the effects of aging biodegradable plastics on freshwater microalgae.