Abstract
Nanotechnologies have been advantageous in many sectors and gaining much concern due to the unique physical, chemical and biological properties of nanomaterials (NMs). We have surveyed peer-reviewed publications related to "nanotechnology", "NMs", "NMs water treatment", "NMs air treatment", and "NMs environmental risk" in the last 23 years. We found that most of the research work is focused on developing novel applications for NMs and new products with peculiar features. In contrast, there are relatively few of publications concerning NMs as environmental contaminants relative to that for NMs applications. Thus, we devoted this review for NMs as emerging environmental contaminants. The definition and classification of NMs will be presented first to demonstrate the importance of unifying the NMs definition. The information provided here should facilitate the detection, control, and regulation of NMs contaminants in the environment. The high surface-area-to-volume ratio and the reactivity of NMs contaminants cause the prediction of the chemical properties and potential toxicities of NPs to be extremely difficult; therefore, we found that there are marked knowledge gaps in the fate, impact, toxicity, and risk of NMs. Consequently, developing and modifying extraction methods, detection tools, and characterization technologies are essential for complete risk assessment of NMs contaminants in the environment. This will help also in setting regulations and standards for releasing and handling NMs as there are no specific regulations. Finally, the integrated treatment technologies are necessary for the removal of NMs contaminants in water. Also, membrane technology is recommended for NMs remediation in air.