Biochemical Alteration of Microalgae under Multiple Environmental Stressors: Insight into Interactions Between Nanoplastics and Aquatic Chemical Factors

While the combined presence of nanoplastics (NPs) and multiple stressors in freshwater ecosystems is obvious, the interactions between them are largely unknown. Here, we aim to understand how NPs will affect primary producers in concert with multiple stressors in freshwater ecosystems. The factorial design was employed to capture the complexity of interacting environmental stressors, including NPs, N, P, dissolved organic matter (DOM), pH, salinity and hardness. High and low levels of multiple environmental stressors were set based on the water quality parameters of Saskatchewan watershed to reflect the complexity and dynamics of realistic environmental levels. Biochemical responses of microalgae from cellular and molecular levels were revealed using flow cytometry and synchrotron-based Fourier transform infrared spectromicroscopy. Under 64 environmental conditions, it is found that the adverse effects of NPs on algal growth, cell size and lipid structure were significant. However, the most important factors are diverse for different biological response changes. Further, crucial interactions between NPs and various stressors were identified and found that the risks of NPs depend on local water quality conditions. NPs inhibited algal growth at 0.2 mg/L N while promoted at 22.5 mg/L N. In addition to quantity, the effect of NPs on algal quality (content, structure and composition of protein and lipids) also varied with N, P, DOM and pH levels. Our study highlights the coupled impacts of NPs and environmental stressors. It has important implications for the ecological risk assessment and management of NPs.