Namely
Titanium dioxide is a very abundant mineral on earth: it is the 9th most abundant chemical element in the earth's crust. It can be used in cosmetics as a UV filter or as a white dye. When it is a UV filter, it can be reduced in the form of nanoparticles: the CSSC has approved the use of titanium dioxide in the form of nanoparticles in sun creams from 2014, in concentrations of less than 25%. The EC regulation 2016/1143 of July 2016 released the use of titanium dioxide in this form in cosmetics. Titanium Dioxide reduced to the size of nanoparticles is allowed in Bio, and removes the unsightly whitish effect caused by this mineral filter when used in its micrometric state, i.e. in its original size. Please note that the manufacturer has the obligation to mention next to the name of the ingredient the mention (NANO) or [NANO] in the INCI list, when this is the case.
In 2006, the International Agency for Research on Cancer (IARC) classified titanium dioxide TiO2 in the group of substances "possible carcinogenic to humans" (group 2B): when inhaled regardless of the size of the nanoparticle or not. In 2016, ANSES submitted to ECHA (European Chemicals Agency) a proposal to classify titanium dioxide as an inhalation carcinogen (re-evaluation in category 1B).
As you have understood, the case of Titanium Dioxide, the only UV filter authorized in Bio with Zinc Oxide is very complex. Nevertheless, we note that it mainly raises questions and controversies when inhaled/swallowed and/or is used in nanoparticle form.