Synergetic and antagonistic effects of microplastics and perfluorooctanoic acid on constructive species in freshwater ecosystems

MPs and PFOA are widely found in water, and both are capable of causing different levels of damage to each organism. However, plant activities might alter the environmental behavior of MPs and PFOA during phytoremediation. In this study, based on Abotts equation and combined with correlation analysis, we evaluated the combined toxic effects and water purification capacity of predetermined concentrations of PS and PFOA on H. verticillata, and analyzed the adsorption kinetics of PS to PFOA. The results showed that PS and PFOA altered the biofilm permeability of H. verticillata and inhibited plant growth (synergistic). In contrast, at low concentration combinations, PS adsorption of PFOA reduced the utilization of PFOA by H. verticillata and weakened their respective inhibition of photosynthesis in H. verticillata (antagonistic). During this period, H. verticillata resisted PS and PFOA stress by activating CAT and APX, respectively, and reutilized nutrients for compensatory growth. This suggests that the combined effect of PS-PFOA co-pollutants is related to concentration ratio, site of action and species specificity. Meanwhile, H. verticillata synergized with the biological communities affected by the co-pollutant to purify the water and effectively remove PS and PFOA. This study provides new insights for assessing the ecological effects of MPs-PFOA co-pollution and provides a theoretical basis for improving phytoremediation.