Last week, I posed Friends of the Earth a challenge – “What is your worst case estimate of the human health risk from titanium dioxide and/or zinc oxide nanoparticles in sunscreens?”  Georgia Miller of FoE Australia and Ian Illuminato of FoE in the US have kindly provided a detailed response.  Rather than just keep this as a comment on the original blog, I thought it deserved a wider airing – and so am posting it here.

I will respond to the response in a few days time.  In the meantime, I would be extremely interested in what others think of the use of nanoparticles in sunscreens, based on my original piece and Georgia and Ian’s piece below.  Please do comment – this seems to be an area that desperately needs some good and open discussion.

Andrew – thanks for the invitation to perform some complex risk assessment using several poorly understood variables. However we do have to point out that the world’s best minds don’t yet have enough information even to design reliable nanomaterial risk assessment processes, let alone to come up with a single ‘worst case scenario’ figure for long term health impacts of using nano-sunscreens.

The huge knowledge gaps plaguing nanomaterials toxicity and exposure assessment (along with preliminary studies suggesting the potential for serious harm) are key reasons for calls by Friends of the Earth Australia and United States for a precautionary approach to management of nanotoxicity risks.

We explain below why your risk assessment challenge is impossible given these data gaps. We also point out that given that different people with different skin types are likely to experience different exposure levels, positing any single ‘worst case scenario’ figure is inappropriate. Obviously you are aware of these serious limitations. This does prompt us to question the intent of your challenge.

Further, we strongly suggest that your challenge is directed to the wrong people. Why not demand that the manufacturers of nano-sunscreens provide you with the data to demonstrate that their products are safe? Why not challenge the regulators to explain their failure to keep nanomaterials that behave as extreme photocatalysts out of sunscreens?

Better yet, why not support a discussion about the role of the precautionary principle in the management of uncertain new risks associated with emerging technologies? Why not explore the importance of public choice in the exposure to these risks? Why not contribute to a critical discussion about whose interests are served by the premature commercialisation of products about whose safety we know so little, when there is preliminary evidence of risk and very limited public benefit? Transparent micron-particle sized zinc oxide sunscreens are commercially available; a recent article suggests most titanium dioxide nano-sunscreens on the market could be doing more harm than good. No-one need use nanoparticles in order to produce a cosmetically and functionally acceptable sunscreen.

Andrew, we respectfully suggest that someone of your expertise and stature could play a more constructive role in these debates – debates which should not be limited to a question of technical risk assessment.

Georgia Miller and Ian Illuminato
Friends of the Earth Australia and United States

Why determining a single figure for ‘worst case scenario’ health harm associated with using nano-sunscreens is not possible

In 2004 the UK’s Royal Society recommended that nanoparticles be treated as new chemicals, subject to new safety testing before they could be used in products, and face mandatory labelling. Six years on, none of those things have happened.

The development and validation of nano-specific risk assessment processes may take years. As the European Food Safety Authority pointed out last year in relation to the risk assessment of nano-foods: “Although, case-by-case evaluation of specific ENMs [engineered nanomaterials] may be currently possible, the Scientific Committee wishes to emphasise that the risk assessment processes are still under development with respect to characterisation and analysis of ENMs in food and feed, optimisation of toxicity testing methods for ENMs and interpretation of the resulting data. Under these circumstances, any individual risk assessment is likely to be subject to a high degree of uncertainty. This situation will remain so until more data on and experience with testing of ENMs become available” (EFSA 2009, p2-39).

When it comes to sunscreens, a key component of risk assessment – determining likely exposure – is not yet possible because we do not yet understand what quantities of nanomaterials may be absorbed into the skin from sunscreens and in what circumstances. Skin penetration studies to date have largely failed to look at important variables such as skin condition (including damage through sunburn, injury or eczema, or thin skin present in the young or elderly), skin flexing (eg through exercise) and the role of substances in sunscreens that can act as penetration enhancers by increasing skin permeability. Further, most skin penetration studies have used excised skin in in vitro studies which is likely to underestimate actual penetration.

In your earlier blog you point out that research by Professor Brian Gulson at Macquarie University and by scientists at Australia’s CSIRO which shows radio-isotope labelled zinc from sunscreens in the blood and urine of human volunteers is not yet published. True enough – also that these researchers are not yet able to say whether or not the absorbed zinc they detected is in particle or ionic form. Nonetheless, the results do show that zinc in sunscreens does not simply remain on the outer layers of dead skin cells, as some have claimed. Many questions remain: the one clear answer is that more research is required.

One interesting point about Brian Gulson’s study underscores the impossibility of determining any single ‘worst case scenario’ figure for health harm. Professor Gulson told the ICONN conference in Sydney this year that one woman with sensitive skin suspended her participation in the trial after four days due to an adverse reaction. The levels of isotope labelled zinc in her blood were also substantially greater than that of other people in the trial. Are people with sensitive skin more likely to experience substantially greater skin penetration by nano-ingredients in sunscreens? Could this put a minority of the population at greater health risk? We don’t yet know.

A further constraint on calculating your requested ‘worst case scenario’ figure is the paucity of long-term and multi-generational nanotoxicity studies. This is a very serious limitation. Potential health harm from exposure to many nanomaterials may be more likely to manifest in the long term, rather than immediately. This point was made in 2004 by global reinsurance giant Swiss Re (2004). Swiss Re emphasised that as with asbestos, the significant time lag between exposure to nanomaterials and the onset of health harm is the greatest challenge for insurers attempting to calculate risk.

You ask for a ‘worst case scenario’. One worst case scenario is the accelerated development of skin cancer in people using nano-sunscreens, despite their wearing sunscreens for sun protection. We are copying below an extract of comments made by Dr Maxine McCall of the Australian CSIRO to the ABC’s 7.30 Report in late 2008.

“There’s the concern that there could be free radical generation on the skin, potentially damage, when the nano particles get into cells in the body if they don’t dissolve,” Maxine McCall, head of the CSIRO’s nano safety research, said. “Because they could interact with proteins in the cell or with DNA which codes – which has the genetic information – the worst case scenario, I suspect, could be development of cancer. We don’t know. That’s what we’re trying to find out.”

Dr McCall told the 7.30 Report that it would be two to three years before the CSIRO could reach a conclusion on nano sunscreens. “At the moment, we just don’t have enough information to make informed decisions,” she said.

Nanomaterials that behave as photocatalyts have been found in five of six Australian nano-sunscreens tested by Barker and Branch (2008). Sunscreens containing both nanoparticle titanium dioxide and zinc oxide were demonstrated to have a photocatalytic effect. Some of these photocatalysts were so extreme that they accelerated sun damage to pre-painted steel roofs by up to 100 times. Clearly the effects on human skin of nano-sunscreen use will differ from a pre-painted steel roof. Will these extreme photocatalysts penetrate human skin and persist in particulate form in sufficient quantities to cause long-term health harm? We don’t know.

Another worst case scenario is harm to the developing brains and reproductive systems of unborn babies, following maternal exposure to sunscreens. If nanoparticles from sunscreens are absorbed into a pregnant woman’s bloodstream, it is possible that they could pass across the placenta to the unborn baby. A recent study showed that polystyrene nanoparticles up to 240nm in size can be transported through a human placenta [note to Andrew: in your earlier blog you state that this “research was aimed at working out how to get beneficial drugs to the fetus”. The motivation of the study is arguably irrelevant. However in this instance the study is clearly designed to explore the potential for risky nanoparticle exposure in utero].

Animal studies have found altered gene expression, harm to the brains and reproductive systems and minor neuro-behavioural alterations in mice born to mothers exposed to titanium dioxide nanoparticles. Will nanoparticles of titanium dioxide be absorbed from sunscreens into the bloodstreams of pregnant women in sufficient quantities, and will they persist in particulate form in sufficient quantities, to harm unborn babies? Again, we don’t know. This will require much further research.

In the meantime, regulators faced with substantive knowledge gaps struggle to formulate an appropriate public policy response to uncertain but potentially serious risks. Challenging community groups to calculate the technical risk of a worst-case scenario of wearing nano-sunscreens to justify their asking product manufacturers to undertake basic safety research seems more than a little retrograde.