LAUSR

The effects of combined exposure to microplastics and contaminants are still not completely understood. To fill this gap, we assessed the effects of polyethylene terephthalate microplastic fibers (MF) (100 mg/L; 360 µm average length) on the toxicity of AgNP (32 nm) and AgNO3 (0.1 - 10 µg Ag/L) to Daphnia magna. Acute immobilization (EC50) and cellular energy allocation (CEA; ratio between available energy and energy consumption) were determined in neonates (<24 h) and juveniles (7 d old), respectively. The 48h-EC50 for AgNP and AgNO3 (2.6 and 0.67 µg Ag/L, respectively) was not affected by MF presence (2.2 and 0.85 µg Ag/L, respectively). No decrease in the available energy was observed, as lipid, carbohydrate, and protein contents were unaffected. However, a significant increase in energy consumption was observed in animals exposed to AgNO3 (250% compared to control) and to the combination of MF with AgNP (170%) and AgNO3 (260%). The exposure to MF alone or in combination with both Ag forms decreased the CEA (values were 55-75% of control values). Our results show that upon short-term exposure (48 h) MF increased Ag toxicity at a subcellular level (i.e., CEA), but not at the individual level (i.e., immobilization). These results highlight the importance of combining different levels of biological organization to fully assess the ecotoxicological effects of plastics in association with environmental contaminants. This article is protected by copyright. All rights reserved.