Membrane fingerprints and morphotype shifts in Phaeodactylum tricornutum co-exposed to cadmium and PBAT macroplastics as ecotoxicological indicators.

This study investigates the individual and combined effects of cadmium (Cd) and poly (butylene adipate-co-terephthalate) (PBAT), a biodegradable macroplastic, on the marine diatom Phaeodactylum tricornutum (P. tricornutum). Interestingly, co-exposure with PBAT mitigates Cd toxicity, except at high Cd concentrations. Using a non-invasive Fourier-transform infrared (FTIR) spectroscopy protocol with robust acquisition parameters and principal component analysis, specific biochemical changes in membrane composition were monitored, with notable decreases in carbohydrate and lipid contents, while protein levels remained unaltered. Morphological observations revealed a shift toward the oval morphotype under exposure to Cd and PBAT, alone and in combination, featuring a stress response. Additionally, the light-harvesting pigments, chlorophyll-a and fucoxanthin, increased in a dose-dependent manner upon Cd exposure, while no significant β-carotene changes were observed, except at high Cd concentrations in the presence of PBAT. This effect is further amplified under co-exposure conditions, the presence of PBAT leading to a marked increase in all three pigments, β-carotene included. The experimental protocol, which involved the aging of PBAT macroplastics in seawater for a short period, suggests that the degradation products of PBAT themselves are responsible for these observed biological effects. It is worth noting that morphotype shifts occur at lower Cd concentrations than those affecting photosynthesis and photoprotective systems. These findings highlight the potential of P. tricornutum membrane fingerprints and morphotype shifts as sensitive ecotoxicological indicators of metal and plastic pollution, particularly in relation to degradation by-products in marine environments.