Research on the toxicity of PVC before and after aging

This study exposed Paramecium caudatum to aqueous solutions with varying PVC mass concentrations (0.00, 0.03, 0.06, 0.09, and 0.12 g/L) before and after aging for 15 days. Compared to blank controls, it was observed that PVC exposure influenced the growth patterns of Parame- cium caudatum larvae, showing an initial increase followed by a decrease. Meanwhile, the number of mature Paramecium caudatum initially rose and then stabilized. Over time, in the experimental groups exposed to PVC, the number of Paramecium caudatum was consistently higher than in the control group without PVC exposure. This phenom- enon may be attributed to the degradation of MPs, which potentially provides additional carbon sources for Paramecium caudatum, thus

supporting increased proliferation in the later stages. However, limited living space and nutrients meant that exponential growth of Paramecium caudatum could not be sustained indefinitely (Fig. 10).
In both aged and unaged experimental groups, larvae and adults showed slow growth in the first three days, possibly due to Paramecium caudatum ingesting small MPs or toxic substances produced by micro- plastic degradation, triggering a stress response in Paramecium cauda- tum, affecting their growth and reproduction. Similar conclusions were drawn in previous studies on water fleas exposed to polystyrene (PS) (De Felice et al., 2019). With time, Paramecium caudatum adapted to PVC, enhancing resistance, leading to a significant increase in adult popula- tion. However, larvae exhibited lower resistance to PVC, resulting in slow proliferation over time, and due to greater toxicity, their numbers

decreased later. As time progressed, resistant Paramecium caudatum survived, gradually increasing the adult population. These results sug-gest that the presence of MPs may inhibit the proliferation of Parame- cium caudatum, but due to MPs degradation, more carbon sources may be available for their proliferation later on. However, due to constraints in living conditions and the dual effects of MPs toxicity, Paramecium caudatum growth in later stages exhibited a suppressed phenomenon.