Aging Enhances the Ecotoxicological Effects of Biobased Microplastic Poly(Lactic Acid) and Its Adsorbed Tris(1-chloro-2-propyl)phosphate on Mussels

The biodegradable plastic poly-(lactic acid) (PLA) has been widely used to reduce plastic pollution in the environment, but PLA does not readily degrade completely and is more prone to form microplastics (MPs) and age. In this study, MP-PLA was aged by simulating the behavior of the marine environment and combined with plastic additive tris-(1-chloro-2-propyl)-phosphate (TCPP) according to their susceptibility to adsorb environmental pollutants. Mussels were the exposed subjects, and exposure concentrations of MPs and TCPP were set at 0.2 mg/L, 1 mg/L, and 0.5 μg/L, respectively. The ecotoxicity of PLA, aged-PLA, TCPP, and TCPP+aged-PLA was compared based on the result that aged-PLA could adsorb more TCPP. Biomarker assays revealed that mussels ingesting and accumulating contaminants underwent a severe oxidative (ROS) and immune stress response in the organism, with disruption of energy metabolism for energy supply, leading to apoptosis, resulting in tissue damage, and disruption of the homeostasis of the symbiotic intestinal microbiota. Comparisons showed that aging enhanced the adverse effects of PLA and ecotoxicological effects are further exacerbated by the adsorption of TCPP on aged-PLA. Therefore, with the widespread use of degradable plastics, long-term environmental impacts such as incomplete degradation and release of additives must be a concern.