Differential physiological response of microalgae exposed to petroleum- and bio-based microplastics

Petroleum-based plastic pollution has become a severe problem all over the world. Bio-based plastics have garnered the attention of researchers since their appearance because of their simple molecular structure and easier degradation compared to petroleum-based plastics. However, almost no studies have clearly compared the biological toxicity and environmental hazards of petroleum-based plastics and bio-based plastics to the organisms in the ecosystem. To fill this research gap, two different microalgae species (Chlorella pyrenoidosa and Tetradesmus obliquus) were selected and exposed to two types of microplastics. We compared polystyrene (PS), a petroleum-based plastic, and polylactic acid (PLA), a bio-based plastic. We hypothesized that microalgae would exhibit higher stress levels when exposed to PS than PLA, which means lower growth rates and photosynthesis activity levels and more antioxidant responses. The results indicated that the growth rates and photosynthetic activities of both microalgae decreased with increasing microplastic concentration when exposed to PS. Comparatively, the negative effect on microalgae growth in the PS-treated group is more significant than in the PLA-treated group. In addition, in both microplastic groups, the negative impacts were more profound on C. pyrenoidosa than on T. obliquus. The findings indicate that petroleum-based plastics like PS have a more detrimental effect on microalgae compared to bio-based plastics, likely due to differences in obstructing light absorption and causing oxidative damage and aggregation. Our study provides reliable data on the different impacts caused by two types of plastics and gives a potential way to reduce hazards caused by plastics by replacing petroleum-based plastics with bio-based plastics.