Combined effects of polymethylmethacrylate microplastics with arsenic and copper on the euryhaline rotifer Proales similis

Aquatic organisms are typically exposed to chemical mixtures, including microplastics and metal(loid)s. However, most research has primarily focused on the toxicity of individual chemicals, potentially overestimating their risks to aquatic life. This study examined the combined effects of polymethylmethacrylate microplastics (PMMA-MPs) with As and Cu at environmentally relevant concentrations on the euryhaline rotifer Proales similis. The 48-h EC of PMMA-MPs (1.5-11.5 μm) was determined using concentrations from 1.0 to 100 mg/L. These concentrations were then combined with 0.41 mg/L As or 0.034 mg/L Cu. The combined effects of PMMA-MPs (0.031-1.0 mg/L) with As (0.025-0.2 mg/L) and Cu (0.0025-0.02 mg/L) at environmental concentrations were assessed through five-day chronic toxicity reproductive tests. The population growth rate was the endpoint for both acute and chronic testing. The EC of PMMA-MPs for P. similis was 44.0 mg/L, but this value significantly decreased when PMMA-MPs were co-exposed with the tested metal(loid)s. The tested mixtures of PMMA-MPs with As and Cu reduced growth rates by 13 - 48 % and 11 - 35 %, respectively, compared to the individual exposure to each chemical. This indicates that PMMA-MPs alter the toxic behavior of these metal(loid)s and vice versa. The present findings reveal that the combination of environmentally relevant concentrations of MPs (modeled as PMMA-MPs) with As and Cu can induce synergistic effects in marine rotifers. These results highlight the importance of investigating pollution in realistic scenarios that many aquatic invertebrates face.