Effects of HDPE and PBAT microplastics on growth and fatty acid profile of Nannochloropsis sp.

In this study, the effects of high-density polyethylene (HDPE) and polybutylene adipate terephthalate (PBAT) microplastics on the growth performance and physiological responses of the marine microalga Nannochloropsis sp. were evaluated under batch culture conditions. Cultures were exposed for 21 days to 5, 10, 50, and 100 mg/L of each polymer, and responses were assessed in terms of final medium pH, dry biomass, growth kinetics, and biomass fatty acid profile. Exposure to both HDPE and PBAT caused a slight but significant decrease in the final pH of the culture medium relative to the control, although pH remained within a range considered suitable for Nannochloropsis growth. In contrast, clearer inhibitory effects were observed on biomass accumulation and growth kinetics. Dry biomass was significantly reduced, particularly at concentrations ≥50 mg/L, while growth curve analysis revealed a progressive divergence from the control from approximately day 6 onward. The specific growth rate (μ) decreased from 0.090 day −1 in the control to approximately 0.069 day −1 and 0.064 day −1 under HDPE and PBAT exposure, respectively, indicating an overall growth inhibition of about 24–29% (based on μ). In addition, both polymers were associated with changes in fatty acid profile of Nannochloropsis sp., with PBAT showing the larger apparent change. Overall, the results indicate that both conventional and biodegradable microplastics can negatively affect the growth and fatty acid profile of Nannochloropsis sp., with the biodegradable PBAT producing effects more pronounced than the conventional HDPE. These findings highlight the potential ecological and biotechnological implications of microplastic contamination for marine microalgal systems.