## 5 Conclusions  
Nanomaterials have been increasingly used and investigated by the scientific community, leading to a wide range of applications. The number of scientific reports hassignificantly increased in recent years, with several publications focusing on the synthesis, incorporation, or application of nanomaterials (NMs) in the construction sector. On the other hand, the keyword bibliometric network on NMs indicates that terms such as nanotoxicity, environmental risk, risk assessment, and human health risks are scarce in the literature. This work intended to address the current concerns, evaluate the sustainability (environmental, social, economic) and viability, and thus contribute to the implementation of regulations on NMs, which are often commercialized and categorized similarly to regular construction materials. Based on an extensive literature review for nanomaterials and European standards for regular building materials, environmental, human health, and economic indicators were proposed as mandatory for nanomaterials to be applied in the construction sector. A particular focus on toxicity (ecotoxicity and human toxicity), soil impacts (land-use-related impacts/soil quality), and emissions into the air (particulate matter emissions) was identified. The use of these indicators should be considered for nanomaterials such as copper, aluminum oxide, titanium nanoparticles, or carbon nanotubes which have significant levels of toxicity and are widely used in the construction sector. Regarding the economic indicators, it was concluded that the evaluation of the cost impact throughout the various stages of the whole life cycle is essential, focusing not only on the initial cost but also on optimizing the less economically viable stages. These indicators would be particularly relevant for nanomaterials which are generally incorporated in large quantities (e.g., silica-aerogel in thermal insulation composites) and may cause economic problems during recycling processes. Furthermore, the lack of data on durability and end-of-life processes hinders the applicability on a larger scale of nanomaterials such as carbon nanotubes, iron oxide, and graphene oxide. These proposed indicators could be a good basis for their integration into a risk assessment framework of nanomaterials to be applied in construction. Limitations of the proposed indicators can be identified in terms of their applicability to certain nanomaterials, functionalized and designed according to specific applications, presenting different physicochemical properties and thus environmental risks. Although the evaluation of the physicochemical properties of nanomaterials that may affect human health, and aquatic and terrestrial ecotoxicology, has been widely debated, the categorization of a small number of nanomaterial groups was identified, which often resulted in specific tests being waived, creating consistent data gaps. Further research on the in-service life of constructive solutions with the incorporation of nanomaterials and nanoparticles, as well as on end-of-life processes, is necessary. A proper evaluation of these impacts is critical, especially considering that landfill is a common final destination, by using appropriate methods. A deeper knowledge of toxicity-associated properties for nanomaterials in construction (i.e., size, shape, chemical composition, surface properties, agglomeration and/or aggregation state, and biodegradability) is needed, as well as a hazard ranking for each nanomaterial (e.g., the higher toxicity of nano-ZnO is closely associated with its dissolution into toxic Zn\({}^{2+}\), in contrast to insoluble nano-TiO\({}_{2}\) and the nontoxic degradation products of nano-SiO\({}_{2}\)). Similarly, when assessing the potential toxicity of nanoparticles in aquatic environments, several critical parameters, e.g., the size, crystal structure, surface charge, morphology, surface coating, presence of co-pollutants in the aquatic environment, duration of exposure, concentration, and any photoactive effects, should be considered.