Titanium: Metal of the future or an emerging environmental contaminant?

Naturally occurring and anthropogenic sources, such as ore (minerals), waste disposal, and mine tailings, can introduce titanium (Ti) into both soils and aquatic environments. Ti is the ninth most abundant element in nature (0.63% w/w) and is found in igneous rocks. Major Ti-bearing minerals include rutile, brookite, anatase, ilmenite, and titanite. Among Ti compounds, Ti dioxide (TiO2) is of particular environmental and health concern. It is classified as potentially carcinogenic to humans (Group 2B) by the International Agency for Research on Cancer. Ti is increasingly used in aviation and aerospace fields and has important biomedical applications, including in joint replacements and dental implants. TiO2 nanoparticles (NPs) are one of the most important Ti compounds, entering the environment through various pathways, including biosolid applications, and have been shown to cause deleterious effects on soil microorganisms and, consequently, on soil functioning and health. Excessive Ti uptake can cause toxicity in plants, soil microorganisms, aquatic organisms, animals, and humans. Dust inhalation of TiO2 NPs by humans may cause chest pain, coughing, and breathing difficulty, while dermal contact may cause irritation. To control the main anthropogenic input sources of Ti in the environment, it is critical to develop affordable technologies for Ti removal during wastewater treatment. This comprehensive review examines the presence, sources, biogeochemical behavior, and potential risks of Ti in the environment and provides an in-depth outline of the network visualization bibliography to graphically represent the relationships between key publications, research areas, and authors. Additionally, future research priorities are suggested for the sustainable management of Ti contamination.