Effect of microplastics PAN polymer and/or Cu2+ pollution on the growth of Chlorella pyrenoidosa

Polyacrylonitrile polymer (PAN), a common representative textile material and a microplastic, has significant influence on phytoplankton algae, especially with co-exposure with other pollutants, e.g. Cu2+. In the present study, we carried out experiments to reveal the population size variation trends of Chlorella pyrenoidosa over time (during a whole growth cycle of 6 days) under PAN and/or Cu2+. The levels of pigments (chlorophyll a, b, total chlorophyll and carotenoids), chlorophyll a fluorescence parameters, and other physiological and biochemical indices, containing total protein measurements of H2O2, catalase (CAT), and malondialdehyde (MDA) under different treatment groups were measured to explain the physio-ecological mechanism of the effect of PAN and/or Cu2+ on the growth of C. pyrenoidosa. The results showed that PAN, Cu2+ and the combination of PAN and Cu2+ inhibited the growth of C. pyrenoidosa. Chlorophyll a and b decreased significantly with increasing levels of pollutants (PAN and/or Cu2+); however, the carotenoid levels increased with increasing levels of pollutants (PAN and/or Cu2+) for the first three cultivation days. The oxygen-evolving complexes (OECs) of C. pyrenoidosa had been damaged under Cu2+ pollution. The results also showed that CAT activity, MDA content and H2O2 activity of C. pyrenoidosa increased with increasing levels of pollutants (PAN and/or Cu2+); however, total protein content decreased with increasing levels of pollutants (PAN and/or Cu2+) at the first cultivation day. These results indicate that pollutants (PAN and/or Cu2+) are harmful to the growth of the C. pyrenoidosa population and negatively affect the levels and function of the pigments in C. pyrenoidosa by decreasing chlorophyll a and b levels, increasing carotenoid levels, and increasing antioxidant enzyme activity.