Effect of microplastics on growth and biochemical composition of microalga Acutodesmus obliquus

Microplastics have been widely detected in different aquatic ecosystems. The toxicity of microplastics has been extensively evaluated on aquatic animals; however, there is limited information on their influence on microalgal growth and metabolism. This study investigates the effect of different concentrations (0, 5, 10, 15, 25, 100, 125, 200, and 250 mg L⁻¹), of microplastics namely high-density polyethylene, polypropylene, and polyvinyl chloride exposure on growth, photosynthesis, and biochemical composition of Acutodesmus obliquus. The highest growth inhibition ratio of 42.7% was observed for high-density polyethylene (250 mg L⁻¹) supplemented medium followed by polyvinyl chloride (41.6%) and polypropylene (37.7%) microplastics. The results revealed that during the early log phase, the photosynthetic efficiency (Fᵥ/Fₘ) decreased at higher concentrations on microplastics exposure. However, the microalga was able to adapt to the microplastics supplemented medium and did not show any significant effect on Fᵥ/Fₘ in the late-log phase. There was no significant effect on the lipid (14.6–17.9%) and carbohydrate (14.59–18.24%) content for all types of microplastic treatments as compared to the control growth medium. Protein content was observed to decrease significantly at higher concentrations of microplastics (100–250 mg L⁻¹). Scanning electron microscopy investigations revealed the microplastic aggregates on the algal surface. The effect on cellular metabolites composition of A. obliquus with different microplastics was also analyzed using infrared spectroscopy. The present study showed that microalga A. obliquus has the ability to adapt in the microplastics supplemented medium, however, higher concentrations could exert metabolic changes in the organism. The findings of the present study could form the basis for future investigations on the exploration of mechanisms of the microplastic toxicity and adaptation in microalgal species.