Mechanisms involved in the impact of engineered nanomaterials on the joint toxicity with environmental pollutants

Emerging nanoscience and nanotechnology inevitably facilitate discharge of engineered nanomaterials (ENMs) into the environment. Owing to their versatile physicochemical properties, ENMs invariably come across and interact with various pollutants already existing in the environment, leading to considerable uncertainty regarding the risk assessment of pollutants. Nevertheless, the underlying mechanisms of the complicated joint toxicity are still largely unexplored. This review aims to aid in understanding the interaction of ENMs and pollutants from the perspective of ecological and environmental health risk assessment. Based on related research published from 2005 to 2018, this review focuses on summarizing the effect of ENMs on the toxicity of pollutants both in vivo and in vitro. Physicochemical interaction appears as a main factor affecting ENMs-pollutants joint toxicity, with the mechanisms and the resultants for ENM-pollutant adsorption been illustrated. Cellular and molecular mechanisms involved in the joint toxicity of ENMs and pollutants are discussed, including the effect of ENMs on the bioaccumulation, biodistribution, and metabolism of pollutants, as well as the defense responses of organisms against such pollutants. Future in-depth investigation are suggested to focus on further exploring biological mechanisms (especially for the antagonized effect of ENMs against pollutants), using more advanced mammalian models, and paying more attention to the realistic exposure scenarios.