Damages of aged-PVC microplastics exceed the enhanced resistance of chlorella pyrenoidosa induced by phosphorus...

Phytoplankton could adapt to multiple natural stresses. However, few have explicitly explored their complex adaptation patterns to emerging chemical contaminants (ECCs), such as microplastics (MPs), under nutrient-limited conditions. Here, we experimentally investigated the patterns of Chlorella pyrenoidosa responding to aged polyvinyl chloride (aged-PVC) and their leachate with a series of concentrations (0-20 mg/L) under phosphorus (P) repletion conditions (7.14 mg P/L) and P limitation conditions (0.1 mg P/L). Results revealed that C. pyrenoidosa displayed comparable patterns in response to aged-PVC treatments, regardless of P availability, showing significant decreases in growth rate but increases in photosynthetic efficiency (1.7%-39.6%), and the early-stage growth stimulation (day 2-14) may be attributed to the leachate. Moreover, cells of C. pyrenoidosa under both P availability elevated their cellular P quotas at the stationary phase under the low aged-PVC concentration (0.1 mg/L). These are significantly inconsistent with the responses of phytoplankton to multiple natural stresses, where phytoplankton typically enhance their resistance to environmental stresses under nutrient-limited conditions. This can be attributed to the stronger chemical toxicity of aged-PVC on enzymes and physical damage to the cell membrane. These findings suggest that cellular adaptive mechanisms of phytoplankton to natural stresses may fail against chemical contaminants, therefore providing crucial insights into the threshold dynamics of ecosystem resilience.