## 4 Critical Discussion of Environmental and Economic Indicators  
Based on the previous extensive literature review (Section 3), as well as considering European standards (EN15804:2012+A2:2019 [128]; EN15643 [129] and international databases for conventional materials, the most relevant contributions of NMs to environmental, social, and economic impacts were identified. Based on these data, environmental, human health, and economic indicators were proposed and are summarized in Table 2.  
Figure 3: Evolution of peer-reviewed papers (number per year) on nanomaterials and their impact on human health and the environment (timespan 2011–2022). Concerning the economic indicators, it is suggested to include not only the initial costs of the different NMs (in EUR/unit), but also further costs related to operation and maintenance (repair or replacement) and eventual deconstruction. Additionally, at the end of the life of NMs, costs related to their transport, waste processing for re-use, recovery and/or recycling should also be considered. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Impact Category** & **Indicator Name** & **Indicators** & **Functional Unit** & **Referenced * & **Refs.** \\ \hline Depletion of abiotic resources, minerals, and metals & Abiotic depletion & ADP-minerals resources & kg Sb eq. & \\ \hline Depletion of abiotic resources, fossil fuels & Abiotic depletion for fossil resources & ADP-fossil & MJ & \\ \hline Acidification & Acidification potential, accumulated exceedance & AP & mol H+ eq. \\ \hline Ozone depletion & Depletion potential of the stratospheric ozone layer & ODP & kg CFC-11 eq. \\ \hline Photochemical ozone & Formation potential of tropospheric ozone & POCP & kg NMVOC eq. \\ \hline Water use & Water (user) deprivation potential, deprivation weighted water consumption & WDP & m\({}^{3}\) world eq. deprived & AqNPs CuO \\ \hline Climate change, total & Global warming potential, total & GWP-total & kg CO\({}_{2}\) eq. \\ \hline Climate change, fossil & Global warming potential, fossil & GWP-fossil & kg CO\({}_{2}\) eq. \\ \hline \multirow{4}{*}{Ectotoxicity (freshwater) effects} & Potential incidence of disease due to PM emissions & PM & Disease incidence \\ \cline{2-5}  & Potential comparative toxic unit for ecosystems & ETP-fw & CTUe \\ \hline Human toxicity, cancer effects & Potential comparative toxic unit for humans & HTP-c & CTUh \\ \hline Human toxicity, non-cancer effects & Potential comparative toxic unit for humans & HTP-nc & CTUh \\ \hline Land-use-related impacts/Soil quality & Potential soil quality index & SQP & (dimensionless) \\ \hline \multirow{4}{*}{Cost} & Initial costs & IC & & \\ \cline{2-5}  & & Operation and maintenance & OM & \\ \cline{2-5}  & & Repair & RE & EUR/unit \\ \cline{2-5}  & & Replacement & REP & & \\ \cline{2-5}  & & Deconstruction & DE & & \\ \cline{2-5}  & & Transport & T & EUR/m\({}^{2}\) & \\ \cline{2-5}  & & End of life & EoL & EUR/m\({}^{2}\) & \\ \cline{2-5}  & & Waste processing for re-use, recovery, and/or recycling & W & EUR/m\({}^{2}\) & \\ \cline{2-5}  & & Recycling & REC & EUR/m\({}^{2}\) & \\ \hline \hline \end{tabular}
* * Referenced NMs—includes the NMs that were most cited in the literature review for those impacts.  
\end{table} 
Table 2: Environmental, human health, and economic indicators proposed for nanomaterials. When an analysis of the environmental impacts of nanomaterials is carried out, we strongly recommend that the proposed environmental and human health indicators for NMs should be mandatory. In fact, there are significant concerns about the long-term effects on humans, both through inhalation and contact, and on ecosystems, especially for those NMs identified as being more toxic to human health, as in the case of CNTs, TiO\({}_{2}\), AgNPs, and Al\({}_{2}\)O\({}_{3}\). In fact, CNTs and TiO\({}_{2}\) nanoparticles are among the most widely studied NMs due to their potential hazardous effects. TiO\({}_{2}\) can cause inflammation, cytotoxicity, and damage to the DNA of mammalian cells due its photoactivity.