Is pigment grade titanium dioxide likely to contain any impurities that are toxic? I have a bag of titanium dioxide of pigment quality, unknown source. I am curious to know if the manufacturing process of titanium dioxide makes it likely that it contains any toxic by products / impurities.

Would it for example be safe to use pigment grade titanium dioxide to manufacture sunblock?
According to the MSDS for titanium dioxide, the substance itself is suspected of causing cancer. See, for example, this link.

My opinion is that, in general, it's not a good idea to use reagents from unknown sources for any purpose, especially something like sunblock.