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Cerium oxide nanoparticles (CeO 2 -NPs) are widely utilized in several areas such as; engineering, energy and biomedicine due to the redox properties (Ce +3,+4,+5 ) indicating a reducing potential to oxidative stress in organisms. Thus, conflicting articles on the ecotoxicity of CeO 2 -NPs have been published in recent years, demonstrating a protective effect of oxidation on organisms. To analyze and investigate the possible reasons, a comprehensive study of CeO 2 -NPs with several variables and aquatic, terrestrial and flyers organisms was realized. Also, CeO 2 -NPs did not demonstrate a ecotoxicity against organisms (aquatic, terrestrial, and flyers) compared to the current permitted legislation. At the same time, microorganisms such as algae (Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata) showed an inhibitory effect on growth, possibly due to the redox properties of CeO 2 -NPs causing an imbalance of reactive oxygen species in the solutions. Moreover, factors and parameters that affect the ecotoxicity of CeO 2 -NPs are denoted, such as; concentration, exposure time, organisms, solution pH and properties (surface area and positive or negative charge). It is assumed that CeO 2 -NPs more used and investigated and analyzed in aquatic, terrestrial and flyers environments using different organisms and comparing them, as well as using tracking methods to understand and study ecotoxicity processes involving metallic nanoparticles and organisms.

Contamination of wastewater for dyes; such as Rhodamine B (RhB), Methylene Blue (MB), and Methyl Orange (MO), has caused environmental problems, such as an imbalance in the aquatic ecosystem and a decrease in photosynthetic activity. Thus, for the treatment of waste in water, advanced oxidative process (AOPs) is used, such as the heterogeneous photocatalysis, in which they have been used in the photodegradation of organic pollutants, enabling the use of alternative materials (nanocatalysts). Titanates (TiO 2 X) have opticalelectronic properties, such as the absorption of a wide range of light and semiconductor behavior, presenting catalytic activity. The analysis of this review in the ScienceDirect and Scopus databases (2017 -Nov 2022) allowed us to demonstrate the different types of titanates with Al +2 , Bi +4 , Na +2 , and W +4 ions for photodegradation of dyes resulting in high percentages of degradation (>80%) mainly due to the formation of free radicals ((•OH) and (•O)) causing oxidation processes in organic compounds. Moreover, properties directly affected the degradation results, such as surface area (allowing an increase in interactions with organic compounds) and band gap energy (allowing the application under visible light). The tendency is that different types of titanates (with metallic ions) are more researched and investigated mainly for photocatalytic applications, allowing the understanding of the synergism mechanism between Ti and metallic ions, to meet sustainable development and the generation of clean energy.

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