Chronic toxic effects of polystyrene micro-plastics, DCOIT and their combination on marine Chlorella sp.

Polystyrene (PS) is one of the most dangerous polymers, mainly because of the mutagenic or carcinogenic risk of the monomers used to produce it. Sea-Nine 211 is a commercial antifouling agent; its active ingredient is the biocide 4,5-dichloro-2-octyl-4-isothiazolinone-3-one (DCOIT). Micro- and nano-plastics have different synergistic effects on marine organisms together with organic pollutants. To understand the toxic effects of DCOIT and PS alone and in combination, marine Chlorella sp was selected as the experimental organism. The exposure concentration of DCOIT was set at 50 μg/L, and that of PS was set at 10 μg/L. The results show that all exposed groups promoted the growth of marine Chlorella sp in the late stage of exposure, and the recovery time of marine Chlorella sp in the exposed group containing PS was earlier. Changing trend of chlorophyll a was consistent with the growth trend. On the 15th day of exposure, the gene expression of the photosynthesis system in the combined exposed group showed a significant difference, and the cells produced oxidative stress. Scanning electron microscope observation shows the algae adhered to each other. The volume of algae cells in DCOIT and PS exposed groups decreased, and the internal structure of algae cells in each exposed group was damaged.