Effects of microplastics on key reproductive and biochemical endpoints of the freshwater microcrustacean Daphnia magna

Human activities have directly impacted the environment, causing significant ecological imbalances. From the different contaminants resulting from human activities, plastics are of major environmental concern. Due to their high use and consequent discharge, plastics tend to accumulate in aquatic environments. There, plastics can form smaller particles (microplastics, MPs), due to fragmentation and weathering, which are more prone to interact with aquatic organisms and cause deleterious effects, including at the basis of different food webs. This study assessed the effects of two microplastics (polyethylene terephthalate, PET; and polypropylene, PP; both of common domestic use) in the freshwater cladoceran species Daphnia magna. Toxic effects were assessed by measuring reproductive traits (first brood and total number of offspring), and activities of biomarkers involved in xenobiotic metabolism (phase I: cytochrome P-450 isoenzymes CYP1A1, 1A2 and 3A4; phase II/conjugation: glutathione S-transferases; and antioxidant defense (catalase)). Both MPs showed a potential to significantly reduce reproductive parameters in D. magna. Furthermore, PET caused a significant increase in some isoenzymes of CYP450 in acutely exposed organisms, but this effect was not observed in chronically exposed animals. Similarly, the activity of the antioxidant defense (CAT) was significantly increased in acutely exposed animals, but not in chronically exposed organisms. This pattern of effects suggests a possible mechanism of long-term adaptation to the presence of the tested MPs. In conclusion, the herein tested MPs have shown the potential to induce deleterious effects on D. magna mainly observed in terms of the reproductive outcomes. Changes at the biochemical level seems transient and are not likely to occur in long term, environmentally exposed crustaceans.