Environmental degradation of carbon nanomaterials and related degradation mechanisms

Carbon nanomaterials (CNMs) with unique physicochemical properties are widely applied in various fields, thus inevitably being released into the environment and posing threat to organisms and human beings. Simultaneously, CNMs in the environment could be degraded under natural conditions, and the toxicity of CNMs to organisms will be altered because of the changes in the structural and surface properties of CNMs. Therefore, a systematical summarization on the environmental degradation of CNMs is in urgent need. In this review, degradation routes of CNMs were addressed by dividing into biodegradation and abiotic degradation. Biodegradation included enzymatic degradation, microbial degradation, and cell degradation, while abiotic degradation included photodegradation and chemical (photochemical) degradation. All the above degradation routes were elaborated in the present review. The degradation of CNMs in different natural conditions was thoroughly summarized, and the degradation mechanisms were also concluded. In addition, current challenges on the investigations of CNMs degradation were prospected. The review could provide important information for better understanding the environmental fates and biological effects of CNMs.