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Calcium carbonate nanoparticles (CaCO 3 NPs) derived from CO 2 are promising materials for different industrial applications. It is imperative to understand their toxicological profile in biological systems as the human and environmental exposures to CaCO 3 NPs increases with growing production. Here, we analyse the cytotoxicity of CaCO 3 NPs synthesized from a CaO slurry on two cell lines, and in vivo on zebrafish (Danio Rerio). Our results demonstrate the CaCO 3 NPs in vitro safety as they do not cause cell death or genotoxicity. Moreover, zebrafish treated with CaCO 3 NPs develop without any abnormalities, confirming the safety and biocompatibility of this nanomaterial., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

• CO2 utilization for nanoCaCO3 production as cement filler from cement flue gases. • Three scenarios for the synthesis of CaCO3 nanoparticles were assessed by LCA. • An improved cement filled with 2 wt% of this nanoCaCO3 was assessed. • The filled cement obtained environmental benefits with respect conventional Portland. CaCO 3 nanoparticles as filler have received considerable attention for the mechanical improvement that they provide to cements. However, their life-cycle impact on the environment remains almost unexplored, even if the cement industry is considered one of the largest CO 2 emitters. In this perspective, this research work assessed a novel method for using CO 2 from cement flue gases to produce nanoCaCO 3 as cement filler within the cradle to cradle thinking. For this purpose, two routes of CO 2 capture were assessed followed by the study of the synthesis of CaCO 3 through a mineral carbonation. Three scenarios for the synthesis of CaCO 3 nanoparticles were assessed targeting the use of waste or by-products as raw materials and recirculation of them to reduce any kind of emission. The three scenarios were evaluated by means of the Life Cycle Assessment methodology. Once the best considered route for nanoCaCO 3 production was determined, this research work examined the environmental effect of including 2 wt% of CaCO 3 nanoparticles into the cement. Closing the loop follows a circular economy approach since the CO 2 is captured within the same cement factory. The results were compared with conventional Portland cement. Regarding nanoCaCO 3 results, the scenario with simultaneous production of NH 4 Cl, and using as calcium source CaCl 2 deriving from the soda ash Solvay process, proved to be the best option. Moreover, when cement was filled with 2 wt% of this nanoCaCO 3 , the benefit in terms of emission reductions in the Climate Change category was higher than 60 % compared to the conventional Portland cement. [ABSTRACT FROM AUTHOR]