[Effect of Graphene Oxide on Algal Toxicity of Dibutyl Phthalate]

Marine microalgae, Platymonas helgolondica var. tsingtaoensis, were used as experimental subjects to study the acute toxic effects of graphene oxide (GO) and dibutyl phthalate (DBP), both individually and together. The growth of algae cells, production of photosynthetic pigments, cell permeability, and oxidative stress were investigated. The effects of GO on the algal toxicity of DBP were evaluated. The results showed that low concentrations of GO (0.1-10 mg·L^-1) had no significant effect on algae density and chlorophyll production of Platymonas helgolondica var. tsingtaoensis (P<0.05). However, the algae cell permeability increased significantly with GO concentration (P<0.05) and reached 2.2 times that of the control group at 10 mg·L^-1. The EC_{50, 96 h} value of DBP for Platymonas helgolondica var. tsingtaoensis was (11.14±0. 80) mg·L^-1, which, in terms of toxicity, was much higher than that of GO (EC_{50, 96 h}>100 mg·L^-1). At a GO concentration of 1 mg·L^-1, the EC_{50, 96 h} value of DBP decreased to (4.93±2.14) mg·L^-1, showing that low concentrations of GO enhanced the algae toxicity of DBP. When 1 mg·L^-1 of GO was added, low concentrations of DBP (0.1-2 mg·L^-1) did not have any significant effect on algae density, chlorophyll production, cell permeability, ROS, and SOD. However, the inhibitory effects of high concentrations of DPB (4 mg·L^-1) on algae density and chlorophyll production were enhanced by GO, thereby increasing the average ROS and SOD in algae cells by 21% and 7%, respectively. SEM images showed that GO was the primary factor responsible for increasing the coverage and packing of, and the aggregation effect on, algae cells, which could be the reasons for the increased toxicity of DBP. The results of our study can provide data to reveal the risk of novel carbon nanomaterial pollutants to marine organisms.