Antagonistic effects of copper and microplastics in single and binary mixtures on development and reproduction in the freshwater cladoceran Daphnia carinata

The combined effect of microplastics (MPs) and other contaminants such as trace metals is largely unknown although MPs can act as a vector for other contaminants. The present study investigated the impact of a single and mixture of MPs and a common trace contaminant, copper (Cu) on the Australian freshwater cladoceran Daphnia carina. No acute value was recorded when D. carinata was exposed to clear polyethylene size of 1–10 μm with the concentration ranging from 5, 25, 50, 100, 200 and 300 mg/L during 48 h of exposure. D. carinata showed a tendency to utilize MPs from the surrounding environment to prolong their life when the food was scarce. When D. carinata were exposed to environmentally relevant concentrations of Cu: 1 and 3 μg/L or MPs concentration of 0.25 and 1 mg/L for 21 days, no effects on reproduction was recorded. The impacts of Cu and MPs on molting frequency in the mixture treatments were less than in the single contaminant treatments. D. carinata juveniles were more sensitive to Cu than the adults regardless of the presence or absence of MPs. The findings highlight the importance of clarifying the interaction between traditional and contaminants of emerging concern for effective risk assessment.