Dynamic changes of leachates of aged plastic debris under different suspended sand concentrations and their toxicity

Plastic pollution in aquatic environments poses significant ecological risks, particularly through released leachates. While traditional or non-biodegradable plastics (non-BPs) are well-studied, biodegradable plastics (BPs) have emerged as alternatives that are designed to degrade more rapidly within the environment. However, research on the ecological risks of the leachates from aged BPs in aquatic environments is scarce. This controlled laboratory study investigated the leachate release processes and associated toxicity of traditional non-BPs, i.e., polyethylene terephthalate (PET) and polypropylene (PP) and BPs, i.e., polylactic acid (PLA) combined with polybutylene adipate terephthalate (PBAT) and starch-based plastic (SBP) under different aging time and suspended sand concentrations (0, 50, 100, 250, and 500 mg/L). The results indicated that BPs release significantly higher levels of dissolved organic carbon (DOC) than those of non-BPs, particularly at elevated suspended sand concentrations. The DOC concentrations in PLA+PBAT leachate reached 2.69 mg/L, surpassing those of PET and PP. Additionally, BPs released organic matter of larger molecular weight and protein-like substances. Toxicity tests showed that leachates from BPs inhibited the activity of Daphnia magna more than those from non-BPs. At a suspended sand concentration of 500 mg/L, PLA+PBAT leachate caused a 30 % inhibitory rate of Daphnia magna. Despite enhanced degradability, leachates from BPs may pose increased environmental risks in ecosystems with high suspended sand concentrations. Comprehensive ecological risk assessments are essential for effectively managing and mitigating these hazards of plastic pollution.