The environmental risks of nano pollutants have attracted extensive attention. Understanding the behaviors of nano pollutants is the pivotal premise to evaluate their environmental hazards. Due to their exceptional antibacterial and optical properties, silver nanoparticles (AgNPs) have wide applications in biomedicine and biosensing, leading to their inevitable release. In addition, it is evidenced that the released Ag+ ions majorly contribute to the toxicity of AgNPs. With the increasing multifarious plastics production, nanoplastics of diverse sizes and functionalities, degraded from plastic debris, have gained increased attention due to their durable properties and potential distribution in natural waters. Therefore, AgNPs and nanoplastics were chosen as the representative nano pollutants in the present dissertation to carry out research concerning their environmental behaviors. Natural organic matter (NOM) is ubiquitous in natural waters, and it can be categorized into two classes: autochthonous compounds, e.g., extracellular polymeric vii substance (EPS), and allochthonous compounds, e.g., humic acid (HA). The investigation of DOMs effect on the transformation of Ag+ ions and the behaviors of nanoplastics have become a hot spot in the field of Environmental Science. However, knowledge gaps still exist on formation kinetics and mechanisms of Ag+ ions transformation to AgNPs in the presence of DOM as regulated by environmental factors, such as omnipresent inorganic ions or light exposure, and the behaviors and biological response of nanoplastics with different surface characteristics as affected by the presence of DOM. Accordingly, the main objectives of my dissertation are to: Unravel the reduction mechanisms of Ag+ ions to AgNPs in the presence of Cl− ions and light exposure as facilitated by algal EPS. Expound the impact of particle size and surface functional groups of nanoplastics on their stability profiles and biological impacts when influenced by salinity and algal EPS. Uncover the mechanisms of biological responses induced by nanoplastics under nutritional stress as affected by the size of nanoplastics and the presence of HA.