Chemical toxicity of microplastics is stronger than particle effects in D. magna

Microplastics (MP) are ubiquitous environmental contaminants with diverse physicochemical characteristics. Many studies have shown that size, shape, and polymer type are responsible for their toxicity, but this also seems to differ among MP from the same plastic type. One parameter likely contributing to these differences is plastic chemicals, a broad class of compounds intentionally or unintentionally added to plastics during their production and manufacturing. However, knowledge on the composition of plastic chemicals and their effects remains scarce. Therefore, to elucidate the chemical aspect of MP toxicity, we exposed Daphnia magna individuals to MP (PET, PBS, and PDLLA), cellulose, extracted particles (eMP), and methanol-based extracts of these particles for 10 days. Chemicals within such extracts were analyzed via GC-MS. This study was conducted with reduced food availability to investigate plastic effects in an environmentally relevant scenario. The introduction of a high-food control suggests that a more realistic feeding regime might exacerbate the plastic effects of the selected treatments. Our results indicated that, depending on the polymer type, plastic chemicals determine MP toxicity, which varies according to the endpoint investigated (i.e., body length, reproduction, levels of ROS and LPO). Body length, in particular, was significantly impaired by PET and PDLLA extracts, whereas reproduction was affected by most treatments. The investigated biochemical parameters (ROS and LPO) were not affected by the exposure. These results suggest that MP toxicity strongly depends on their chemical composition, whereas adverse effects due to physical properties are present independently of chemical composition across all MP types.