Antidote or Trojan horse for submerged macrophytes: Role of microplastics in copper toxicity in aquatic environments

Due to their unique surface structures and physicochemical properties, microplastics (MPs) can adsorb other contaminants, thus impacting their toxicity and fate in aquatic ecosystems. In the present study, the adsorption and transportation of copper ions (Cu2+) in polyethylene (PE, 5 and 150 μm) and their combined effects on four submerged macrophyte species were assessed. Results demonstrated that the addition of PE reduced the Cu2+ concentration in copper sulfate (CuSO4) solution and the adsorption of Cu2+ in PE (10 mg/L) increased with CuSO4 concentration (100-600 μmol/L). PE alone exhibited no inhibitory effects on macrophytes, while Cu2+ showed fatal toxicity toward the macrophytes. However, the combination of PE and Cu2+ showed lower inhibitory effects on macrophytes and the toxicity attenuation varied among species. Additionally, PE may act as a carrier (like a Trojan horse) for the environmental transfer of Cu2+, thereby hosting Cu2+ toxicity against macrophytes in the imported environment. Our findings indicate that PE acts as both an antidote to and carrier of Cu2+ toxicity in macrophytes. This study should help in clarifying the combined effects and risk assessments of MPs and heavy metals in future studies.