The research example that I used in part 1 of Sunscreen and nano time, again focused on zinc oxide but Andrew Maynard offers analyses of all the studies (in this blog posting at 2020 Science which includes the portion I excerpted in part 1)  cited specifically by Friends of the Earth (FOE) on their newly published nanosunscreen page where they renew their warning against nanotechnology-enabled sunscreens. Andrew also challenges FOE with a question,

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.

He’s asking for more than a number to represent probability (or absolute risk—the definition is in part 1), he wants to know how the number has been derived and that is the real challenge. I’ve suggested previously (in part 1) that there isn’t enough data yet but if there is a way to do it, I’d love to learn more.

It should be noted that the Environmental Working Group reluctantly gave nanosunscreens a passing grade last year (more about that on this blog here) after performing a meta analysis of the research available and I notice that they have not changed their stance this year. From Andrew’s June 8, 2010 blog posting,

… the Environmental Working Group (EWG) – recently recommended a range of nanoparticle-based sunscreens. In fact, in a recent review EWG stated

Our top-rated sunscreens all contain the minerals zinc or titanium. They are the right choice for people who are looking for the best UVA protection without any sunscreen chemical considered to be a potential hormone disruptor. None of the products contain oxybenzone or vitamin A and none are sprayed or powdered.

You can find EWG’s sunscreen report here. I find it interesting that even though EWG recommends certain sunscreens they do so in a very measured fashion (from the EWG’s  Sunscreens Exposed: 9 surprising truths page,

The ideal sunscreen would completely block the UV rays that cause sunburn, immune suppression and damaging free radicals. It would remain effective on the skin for several hours and not form harmful ingredients when degraded by UV light. It would smell and feel pleasant so that people use it in the right amount and frequency.

Unsurprisingly, there is currently no sunscreen that meets all of these criteria. [emphasis mine] The major choice in the U.S. is between “chemical” sunscreens, which have inferior stability, penetrate the skin and may disrupt the body’s hormone systems, and “mineral” sunscreens (zinc and titanium), which often contain micronized- or nano-scale particles of those minerals.

A June 2, 2010 article on AOL News stands in stark contrast to the EWG’s more measured approach to nanosunscreens. Typically, the author makes claims such as this,

France, Germany, the U.K. and the European Parliament have moved rapidly to require everything from safety testing and mandatory labeling of nanoparticles to even the outright ban of these engineered chemical creations in many sunscreen and cosmetic products.

Unfortunately no supporting citations or links are provided. I did find this (from the European Commission website page on cosmetics and nanomaterials),

What specific measures has the Commission taken to address the safety of insoluble nanoparticles?

Insoluble nanoparticles in cosmetic products are essentially used as UV-filters. Some minerals, if used in a nanoscale, become invisible but still absorb UV radiation. These UV-filtering substances are increasingly used in order to have a broad-band sun protection including UVA radiation (more information on the need to ensure efficient sunscreen products). Moreover, the advantage of mineral UV-filters is that they usually do not cause cutaneous adverse effects such as contact allergies.

Up until now, the Commission has permitted one mineral UV-filter which is usually used in its nanoscale in sunscreen products (titanium dioxide). [emphasis mine]

Another substance at nanoscale, zinc oxide, has been assessed by the SCCP in 2003 in view of permission as UV-filter. The SCCP, in its opinion SCCNFP/0649/03 , concluded that the safety of zinc oxide as UV-filter had not been sufficiently demonstrated. Consequently, zinc oxide has not been permitted by the European Commission as UV-filter.

In the above-mentioned opinion of December 2007, the SCCP suggested a re-evaluation of titan dioxide in order to address in particular abnormal skin conditions as well as the possible impact of mechanical effects (eg flexing) on skin penetration. This opinion is being followed-up actively by the Commission as risk-manager.

The page was last edited on Dec. 12, 2009 so “up until now” means that  Europeans are still allowing the use of titanium dioxide in sunscreens as the other information on the page does not provide any indication that the status has changed although its use is being reassessed.