Editing Titanium dioxide (section)

===Environmental waste introduction===
Titanium dioxide (TiO₂) is mostly introduced into the environment as [[nanoparticle]]s via wastewater treatment plants.<ref name=":5">{{cite journal |last1=Tourinho|first1=Paula S.|last2=van Gestel|first2=Cornelis A. M.|last3=Lofts|first3=Stephen|last4=Svendsen|first4=Claus|last5=Soares|first5=Amadeu M. V. M.|last6=Loureiro|first6=Susana|date=2012-08-01|title=Metal-based nanoparticles in soil: Fate, behavior, and effects on soil invertebrates|journal=Environmental Toxicology and Chemistry|language=en|volume=31|issue=8|pages=1679–1692|doi=10.1002/etc.1880|pmid=22573562|s2cid=45296995 |issn=1552-8618|doi-access=free|bibcode=2012EnvTC..31.1679T }}</ref> Cosmetic pigments including titanium dioxide enter the wastewater when the product is washed off into sinks after cosmetic use. Once in the sewage treatment plants, pigments separate into sewage sludge which can then be released into the soil when injected into the soil or distributed on its surface. 99% of these nanoparticles wind up on land rather than in aquatic environments due to their retention in sewage sludge.<ref name=":5"/> In the environment, titanium dioxide nanoparticles have low to negligible solubility and have been shown to be stable once particle aggregates are formed in soil and water surroundings.<ref name=":5"/> In the process of dissolution, water-soluble ions typically dissociate from the nanoparticle into solution when thermodynamically unstable. TiO<sub>2</sub> dissolution increases when there are higher levels of dissolved organic matter and clay in the soil. However, aggregation is promoted by pH at the isoelectric point of TiO<sub>2</sub> (pH= 5.8) which renders it neutral and solution ion concentrations above 4.5 mM.<ref name=":0">{{cite book|title=Kirk-Othmer Encyclopedia of Chemical Technology|last=Swiler|first=Daniel R.|date=2005|publisher=John Wiley & Sons, Inc.|isbn=978-0-471-23896-6|language=en|chapter=Pigments, Inorganic|doi=10.1002/0471238961.0914151814152215.a01.pub2}}</ref><ref>{{cite journal |last1=Preočanin|first1=Tajana|last2=Kallay|first2=Nikola|year=2006|title=Point of Zero Charge and Surface Charge Density of TiO<sub>2</sub> in Aqueous Electrolyte Solution as Obtained by Potentiometric Mass Titration|journal=Croatica Chemica Acta|volume=79|issue=1|pages=95–106|issn=0011-1643}}</ref>