Following up from my previous post, here’s an open question to Friends of the Earth:

What is your worst case estimate of the human health risk from titanium dioxide and/or zinc oxide nanoparticles in sunscreens?

What I am interested in is a number – a probability of a specific human health impact being caused by using a given amount of nano-sunscreen over a certain amount of time.  Something like:

“In the worst case, it is estimated that using [number] grams per day of sunscreen comprising [percent] TiO2/ZnO nanoparticles over [number] days could lead to an [percent] risk of the user developing [disease].”

This can be based on an extrapolation of the current state of the science to a worst case scenario.  But it must be plausible.  And the calculations/sources to get to the end number must be transparent.

I’m asking because I am interested to see whether it is possible to place an upper bound on the safety of nanoparticle-based sunscreens, and whether this will be useful in moving the dialogue over nano-enabled sunscreens away from ungrounded speculation, towards evidence-based discussion.

So that’s the challenge.  I’m hoping my good friends at Friends of the Earth will rise to it.

Andrew Maynard