A few weeks ago, I set 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?

The challenge came out of an article from FoE on nanomaterials and sunscreens, which I subsequently critiqued on 2020 Science.  Georgia Miller and Ian Illuminto from FoE kindly responded to my challenge – not by rising to it as such, but by fleshing out the justification for the position that they take on nanomaterials and sunscreens.

That post led to a useful discussion on the issues, with comments from the NGO community, regulators and respected scientists – it’s one that I would highly recommend anyone interested in nanomaterials and sunscreens reading.

To wrap things up (for the time being), I thought it would be worth reflecting on some of the issues raised by Georgia and Ian in their response, and the ensuing discussion:

Getting nanomaterials’ use in context. First, Georgia and Ian, very appropriately in my opinion, brought up the societal context within which new technologies and products are developed and used:

“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.”

This is a legitimate issue, and one that is touched on by a number of people in the comments.  Decisions on what is developed, what people are exposed to, who decides what is appropriate and what is not, and who pays the consequences while who reaps the benefits, go far beyond the science and technology itself.  This is touched on by Jennifer Sass from NRDC:

I strongly support a dialogue that has space for both scientific calculations and values and perceptions of risk. We need to make that dialogue public, inclusive, transparent, and thoughtful. Risk is more than a number – its a face, a person, a community.

Guillermo Foladorio also touches on this broader societal context:

We have here 2 kind of issues. One is the “scientific” knowledge (are nano-sunscreens harmful?). This is a never endend issue. Science is a process and not a fact. The other issue, although hidden, is of great importance: focusing on a never ended scientific discussion is the field that corporations like, in the meanwhile the market of such products grows and consolidates, aside from any wondering of the needs for such new stuff; or better which percentage of the population will benefit in the case.

I would suggest that forcing a technology on society has never been acceptable behavior.  But it has certainly been easier to do in the past.  These days though, we live in a much more crowded, resource-constrained and interconnected world than ever before.  Which means that the consequences of ill-conceived technology implementation are magnified, and the dynamics of introducing new – and possibly beneficial – technologies – are far more complex than they were in the past.

This means that we need to think critically about the broader societal issues associated with technology innovation, and we need to push the dialogue further upstream in the development process – a point Jeff Morris from EPA makes.  This means rethinking how we make decisions in partnership across society, and how we begin to apply ideas like the precautionary principle in a complex world – a point eloquently made by Richard Jones.

But it also means that we need to think carefully about how we use scientific knowledge and data – “evidence” – in making decisions.

Evidence-informed decision-making. At some point, decisions need to be based on information, and in the long run you cannot get away with making that information up!  It’s one thing to evaluate critically the current state of evidence in making decisions, but quite another to preferentially select evidence that supports a predetermined position.  Yet the latter is often the default position when it comes to influencing decisions – whether by policymakers or consumers.

Having worked at the heart of science-based policy in the US for a number of years, I’m all too familiar with the line of argument that goes “what do we want to achieve?” followed by “what evidence can we find that supports us?”.  Yet this is an approach that ultimately devalues the importance of evidence in making decisions, one that can have serious adverse consequences when decisions are made on dodgy information, and one that is patently unsustainable in the long run.

My original critique of FoE’s article challenged their use of “evidence” in supporting the position they took.  To me, they showed a tendency to use selective pieces of information to sow seeds of doubt in the mind of the reader, rather than to empower the reader to make informed decisions. The social agenda was a laudable one – the use of selective science sound-bytes, less so.

This begins to come out when you read the comments on Georgia and Ian’s response from three scientists who have worked on nanoscale materials on the skin.  Despite FoE’s implications that nanoparticles in sunscreens might cause cancer because they are photoactive, Peter Dobson points out that there are nanomaterials used in sunscreens that are designed not to be photoactive. Brian Gulson, who’s work on zinc skin penetration was cited by FoE, points out that his studies only show conclusively that zinc atoms or ions can pass through the skin, not that nanoparticles can pass through.  He also notes that the amount of zinc penetration from zinc-based sunscreens is very much lower than the level of zinc people have in their body in the first place.  Tilman Butz, who led one of the largest projects on nanoparticle penetration through skin to date, points out that – based on current understanding – the nanoparticles used in sunscreens are too large to penetrate through the skin.

These three comments alone begin to cast the potential risks associated with nanomaterials in sunscreens in a very different light to that presented by FoE.  Certainly there are still uncertainties about the possible consequences of using these materials – no-one is denying that.  But the weight of evidence suggests that nanomaterials within sunscreens – if engineered and used appropriately – do not present a clear and present threat to human health.

Yet, because there are uncertainties still, we cannot afford to be complacent here.

Handling uncertainty. And this brings me to the thorny issue of uncertainty.  When we are lacking absolute evidence on safety or risk, what do we do – do we halt progress until we are sure about how safe something is, or do we muddle along until more information is available?

This question is becoming increasingly important as the rate of technology innovation – and the complexity of emerging technologies – accelerates.  Consumers, regulators, businesses and others are being forced more and more to make decisions in the face of increasing uncertainty.  At the same time, we are dependent on technology innovation as a global society – although the idea of “going back to basics” is an attractive one, it’s not going to help the marginalized in an overcrowded and resource-constrained world.  Rather, we need new ideas on how to use science and technology in ways that ensure as many people as possible have an acceptable quality of life.

The question is, how do we do this when we cannot be sure of how safe or dangerous a new technology is?

The Precautionary Principle is one approach – and a very misunderstood and misused one – to addressing this, and one brought up by FoE and others in the context of sunscreens.  It has many formulations – it’s not a hard and fast principle.  But it is currently described in the European Union in this way:

The precautionary principle should be informed by three specific principles:

• implementation of the principle should be based on the fullest possible scientific evaluation. As far as possible this evaluation should determine the degree of scientific uncertainty at each stage;
• any decision to act or not to act pursuant to the precautionary principle must be preceded by a risk evaluation and an evaluation of the potential consequences of inaction;
• once the results of the scientific evaluation and/or the risk evaluation are available, all the interested parties must be given the opportunity to study of the various options available, while ensuring the greatest possible transparency.

Besides these specific principles, the general principles of good risk management remain applicable when the precautionary principle is invoked. These are the following five principles:

• proportionality between the measures taken and the chosen level of protection;
• non-discrimination in application of the measures;
• consistency of the measures with similar measures already taken in similar situations or using similar approaches;
• examination of the benefits and costs of action or lack of action;
• review of the measures in the light of scientific developments.
• The burden of proof

This is a pragmatic principle, that looks to using evidence and an evaluation of consequences in making informed decisions in the face of uncertainty.  It certainly does not preclude the development or implementation of a new technology until there is certainty on safety.

The emphasis on the potential consequences of inaction are particularly relevant to today’s world, where we are stuck on a technological tight-rope, and where the consequences of not doing something may be more harmful than taking action.  Richard Jones picked up on this in his suggestion for a more relevant application of the Precautionary Principle to emerging technologies:

what are the benefits that the new technology provides – what are the risks and uncertainties associated with not realising these benefits?

what are the risks and uncertainties attached to any current ways we have of realising these benefits using existing technologies?

what are the risks and uncertainties of the new technology?

This seems a useful place to start from when faced with the reality of having to make the best possible decisions in the face of uncertainty, and where inaction isn’t a option.

But to make decisions – even when there are gaping holes in the data – you need something to go on.

So why did I pose the challenge in the first place? Despite suspicions from some that I was merely being provocative with this question, I asked it in all seriousness.  In the face of uncertainty, playing out different potential scenarios is a powerful tool in helping identify the magnitude and nature of the consequences of different choices.

When it comes to using nanomaterials in sunscreens, I genuinely would like to know whether in the worst case we are looking at mass illness and death, isolated cases of skin rashes, or something in between.  Because the likely implications of the use of such materials in the future have profound implications on the actions we take now.

If decisions are made now on futures that are unlikely to be realized, not only do we waste resources and effort, but we potentially endanger people’s lives through ill-informed choices.  This cuts both ways – if TiO2 and ZnO nanomaterials in sunscreens are likely to harm a significant number of people to a significant degree, action should be taken to avoid this as soon as possible.  But if the benefits are positive and the impacts likely to be inconsequential, inhibiting the use of such materials could cost lives.

Using the best available information to work through possible scenarios provides insight into which futures are more likely, and where efforts are best focused.  This isn’t about setting exposure levels or conducting quantitative risk assessments – it’s about helping people making informed choices.

And who should do this?  I think any group that has a stake in how contemporary decisions affect future outcomes has a part to play.  I focused on FoE because they were pushing the issue.  And I think they have sufficient people they can draw on to make a stab at working through some scenarios and estimating likely impact.

But at the end of the day, this is something that all stakeholders should be involved in.

Because these are decisions that we are all going to have to live with the consequences of.

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
http://nano.foe.org.au
http://www.foe.org/healthy-people/nanotechnology-campaign

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.

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.

Friends of the Earth (FoE) do not like nanoparticle-based sunscreens.  This has been evident for some years – back in 2006 the organization published the report Nanomaterials, Sunscreens and Cosmetics: Small Ingredients, Big Risks, and every year since then they have had something to say on the subject.

This year’s web-based piece leaves now doubt about FoE’s stance on nanotechnology-enabled sunscreens.  The recently posted article starts:

While you’re planning your summer vacation and thinking about what to pack, don’t forget the sunscreen — but make sure it doesn’t have manufactured nanoparticles in it!

But what is the reasoning behind this stance?  Helpfully, FoE have also posted six cases of what they describe as evidence “of risks from manufactured nanomaterials in sunscreen.”

As these are evidence-based statements, I thought it would be worth while going through them, and taking a look at the evidence they are based on:

FoE: “Manufactured nanomaterials used in sunscreens (such as zinc oxide and titanium oxide) can Damage human colon cells: A study from the University of Utah showed that nano zinc oxide is toxic to colon cells even in small amounts. The scientists called for more research and warned that the evidence is especially concerning for children who are more likely to accidently ingest sunscreen. The colon is vital because it eliminates food waste and absorbs important nutrients.”

This was a study that looked at interactions between zinc oxide (ZnO) particles and cells derived from the human colon, and was carried out in vitro (i.e. in a cell culture rather than in animals or people).  It did indeed indicate that nanometer scale ZnO particles were around twice as potent as larger ZnO particles in their ability to kill these cells under idealized conditions.  But the research also emphasized that direct contact with the cells was needed for a nanoscale particle-related effect.  In fact, the title of the paper was “ZnO Particulate Matter Requires Cell Contact for Toxicity in Human Colon Cancer Cells,” emphasizing this point above the higher potency of the more finely structured particles.

The research was interesting, but did not resolve whether zinc oxide particles could survive long enough in the gut to come into contact with cells lining the colon, whether interactions like those observed in the laboratory are plausible under real-world conditions, and what levels of exposure would be needed to cause significant harm.  The research also indicated that larger particles of zinc oxide – similar to particles that have been used in sunscreens and other topical creams for decades – were toxic to cells under the conditions of the study.

FoE: “Manufactured nanomaterials used in sunscreens (such as zinc oxide and titanium oxide) can Damage brain stem cells in mice: A study from China found that zinc oxide nanoparticles can damage the brains of mice by killing important brain stem cells. In another study, Japanese scientists injected pregnant mice with nano titanium dioxide and recorded changes in gene expression in the brains of their fetuses. These changes have been associated with autistic disorders, epilepsy and Alzheimer’s disease. Though more studies are necessary to know if this damage to would occur in humans, these studies with mice serve as important warnings. Such studies have encouraged scientists in the United Kingdom to explore the link between manufactured nanomaterials and Alzheimer’s disease. At the end of last summer, scientists at the University of Ulster were funded by the European Union to conduct more research.”

The China study was once again carried out using cell culture rather than in animals, and as a consequence the results are very hard to interpret.  What the researchers did find is that, under rather idealized conditions, it is possible to cause neural stem cells from mice to undergo apoptosis (controlled cell death) if they are exposed to enough zinc-containing material.  Importantly, the study did not indicate that cell death was associated with particle size – large particles, small particles and even dissolved Zinc all gave similar results.

The Japanese study on the other hand injected mice with extremely high concentrations of titanium dioxide (TiO2) particles – way, way higher than levels likely to get into people’s bloodstream.  Researchers saw qualitative changes in gene expression in fetuses and mice pups that are indicative of a number of disorders.  But – and this is important – there is no direct link between gene expression as measured in this study, and the onset of the neurological diseases mentioned above.  All this study indicates is that injecting TiO2 nanoparticles directly into the blood at extremely high levels causes brain cells in fetuses and pups to respond in some way.  Without knowing how those responses translate into disease (if they do at all), and what the relationship between dose and response is, this study does not provide information on the likelihood of TiO2 nanoparticles impacting the brain.

FoE: “Manufactured nanomaterials used in sunscreens (such as zinc oxide and titanium oxide) can Penetrate healthy adult skin: Isotope-labeled zinc used in nanosunscreens can potentially reach the blood stream and urine of humans, suggests an Australian study by Macquarie University’s Professor Brian Gulson. This study undermines claims that nanosunscreens will stay on the outer layers of dead skin.”

This study by Brian Gulson and colleagues has yet to be published, and so it is a little premature to draw conclusions from the findings.  However, from what has been discussed in the public sphere, the study does not show conclusively that manufactured nanoparticles used in sunscreens can penetrate healthy adult skin.  The study cleverly used sunscreens containing nanoparticles incorporating a stable isotope of zinc – one that is found naturally at very low concentrations.  This meant that, by applying the specially formulated sunscreens to volunteers and monitoring their blood and urine, researchers could tell conclusively whether the zinc from the sunscreen was getting into the body.  What they could not tell was whether it was particles or dissolved zinc getting through the skin.  And as zinc oxide is soluble, there’s a high chance that the very low levels of sunscreen-related zinc that were found in body fluid samples were associated with the stuff dissolving, rather than the penetration of nanoparticles.

We’ll have to wait for the paper to be published before any firm conclusions can be drawn from this work.  But if dissolution is the dominant mechanism here, it suggests that sunscreens relying on larger ZnO particles (and, coincidentally, recommended by Friends of the Earth), may lead to just as much zinc getting into the body as those using nanoscale ZnO particles.

It should also be noted that the results of this study are specific to ZnO – they cannot be extrapolated to other materials, such as TiO2.

FoE: “Manufactured nanomaterials used in sunscreens (such as zinc oxide and titanium oxide) can Travel up the food chain from smaller to larger organisms: A study by researchers at Arizona State University, the Georgia Institute of Technology, and Tsinghua University in China found through a dietary experiment that Daphnia (a “water flea” that provides important nutrition for aquatic life) can transfer nano titanium dioxide to larger organisms (in this case Zebrafish). This study is of great concern because it shows that manufactured nanomaterials with toxic properties could end up in the animal food chain at large.”

This is very true for the material that was the subject of the cited study – nanoscale TiO2 – although the results do not necessarily hold for other nanoscale materials.  At the same time, the study showed that the higher organisms in this case – zebrafish – accumulated more nanoscale TiO2 directly than they did through eating the lower organism – daphnia.

Where nanoscale materials used in sunscreens go in the environment, where they accumulate, and the impact they have, are all important questions.  But without information on toxicity and amounts of material potentially transferred, it is hard to say whether the transfer of these materials up the food chain is significant or not.

FoE: “Manufactured nanomaterials used in sunscreens (such as zinc oxide and titanium oxide) can Damage important microbes in the environment: Scientists at the University of Toledo found that nano titanium dioxide inhibited the function of bacteria after just an hour of exposure. Manufactured nanomaterials from sunscreens can easily wash off of the body in the shower and end up in wastewater and the wider environment, which could affect microbes that are helpful to ecosystems and sewage treatment plants.”

The link here is to a report from a presentation at an American Chemical Society meeting in 2009.  The full peer reviewed paper can be found here.  The published research indicates that nanoscale TiO2 can compromise the integrity of some (not all) bacterial cell membranes at certain concentrations under certain (laboratory) conditions.  The consequences of this are unknown, and it certainly isn’t possible to extrapolate from the research what the environmental impacts of nanoscale TiO2 releases might be, or at what concentrations in the environment an impact is likely.  More importantly, the published work showed no impact of nanoscale ZnO on bacteria at the concentrations used. In other words, the research does not show that nanoscale zinc oxide can damage important microbes in the environment.

FoE: “Manufactured nanomaterials used in sunscreens (such as zinc oxide and titanium oxide) can Travel from mothers to unborn fetuses: Nanoparticles up to 240 nm in size can cross into human placentas, meaning that the toxicity of manufactured nanomaterials could extend across generations.”

This is an important study, as it shows that particles of a specific type injected into the bloodstream can potentially cross over the placental barrier and into the fetus.  The research was carried out using human placenta, but outside the body and under laboratory conditions.  The particles used were polystyrene particles.  And the research was aimed at working out how to get beneficial drugs to the fetus.  The authors of the work note that high exposures were used, and that transport fro the placenta may well be influenced by particle composition and surface coating.  They go so far as to say that the research cannot be generalized across different types of nanoparticles.  In fact, while polystyrene particles up to 240 nm were observed to cross over the placental barrier in this study, the authors point out that in another study using the same system, polyethylene glycol coated gold particles up to 30 nm in diameter were not able to cross the placenta.

Each of the studies cited above is scientifically interesting.  But none of them seem to provide clear evidence that TiO2 or ZnO nanoparticles in sunscreens present a plausible risk to human health.  In many cases, they are associated with very artificial test systems that shed light on the science of how nanoparticles behave under certain conditions, but are far removed from real world situations.  Specifically, the studies do not shed light on whether nanoparticles in sunscreens can get into the body (the weight of scientific evidence is that they cannot get through the skin), whether the body’s defense mechanisms deal effectively with any nanoparticles that do get through (the evidence is that they can), and how much stuff is needed in the body to cause disease (a number of these studies indicate rather large quantities of material are needed).

In other words, the science is far from compelling in indicating that nanoparticles in sunscreens are a bad thing.  In fact, the current state of the science suggests that nanoparticles in sunscreens stay on top of the skin rather than penetrating it, are an effective and long lasting barrier against Ultraviolet radiation from the sun if applied correctly, and avoid some of the health concerns associated with non-nano sunscreens.  This is probably why another environment group – 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.

Part of the problem here is that there is a lot of speculation going on about the pros and cons of nanoscale TiO2 and ZnO in sunscreens, and not a lot of analytical thinking.  What would be really helpful is some numbers on how risky these products might be.  Of course, we don’t have the data to state conclusively what levels of nanoparticles in sunscreens are safe – and there is a compelling case for more research here.  But we should at least be able to guestimate the numbers for a worst case scenario, based on the current state of the science.

So here’s a question back to Friends of the Earth – based on the current state of the science, what number would you put on the risk to human health of using nanoparticle-based sunscreens under a plausible worst-case scenario?

I’ll reiterate this question in a follow-up blog.  But it strikes me that, if we can begin to get some numbers on the table – even if they are just rough estimates, we might be able to cut through some of the speculation here and open up a reasonable discussion on the safety or otherwise of nanotechnology-enabled sunscreens.

]]> http://2020science.org/2010/06/08/friends-of-the-earth-come-down-hard-on-nanotechnology-are-they-right/feed/ 10 http://2020science.org/2009/08/25/sunscreens-alzheimers/ http://2020science.org/2009/08/25/sunscreens-alzheimers/#comments Tue, 25 Aug 2009 14:26:31 +0000 Andrew Maynard http://2020science.org/?p=2089

Could using sunscreen lead to Alzheimer’s, Parkinson’s, or other neurodegenerative diseases?  The association seems far-fetched – given the amount of sunscreens, creams and lotions used every day, surely someone would noticed a link by now if it existed!  Yet a press release from the University of Ulster suggests the nanoparticles used in some sunscreens could potentially cause or exacerbate these diseases.  Drawing on the release, a number of media outlets are now running stories along the lines of “Sunscreen could cause Alzheimer’s” (this from The Daily Mirror in the UK).

This is a rather unfortunate case of a poorly conceived press release leading to sensationalist – and misleading – headlines… The press release is associated with new research funded under the umbrella of NeuroNano – a European project focused on developing nanoscale neuro-implants that will enhance the functioning of the brain.  However this new project, being led by Professors Vyvyan Howard and Dr. Christian Holscher at the University of Ulster, is focusing on how nanomaterials inadvertently entering the brain could cause damage.

The basis of their research is actually quite reasonable.  There is some evidence that exposure to specific types of nanometer-scale particles could lead to them entering the brain, either by traveling up the nerves connecting the nose to the brain, or by crossing over from the blood.  If insoluble nanoparticles do get into the brain they are likely to stick around for a while, as there are limited ways in which the body is able to get rid of foreign material from here.  While there, they could damage neurons by causing the release of reactive oxygen species (ROS) – highly active chemicals.  And there is also research showing that some nanoparticles can cause the type of protein misfolding that has been associated with neurodegenerative diseases like Alzheimer’s – although this was carried out outside the body, under conditions set up to favor misfolding.

These tantalizing snippets of information are like a red rag to a bull as far as scientists go – they suggest there is new knowledge waiting to be discovered; knowledge that could help prevent some forms of brain disease.  Together, they form a sound reason for carrying out more research.

But in no way do they link sunscreens to Alzheimer’s!

The sunscreen link comes about because a number of these lotions use insoluble nanoparticles as the active ingredient.  The thought-process then goes something like this:

The nanoparticles of titanium dioxide or zinc oxide in a sunscreen could conceivably get into someone’s body, by passing through the skin, being eaten, or being inhaled.  Once there, they might be able to get into the blood.  From there, there is a chance that they could pass over into the brain.  Or they might even be inhaled and travel straight up the olfactory nerve and into the brain.  And once there, they could cause vital proteins to misfold that then lead to diseases like Alzheimer’s.

But while this makes an interesting story and a compelling grant proposal, it has little bearing on reality as we currently understand it:

• Most research suggests nanoparticles in sunscreens don’t pass through the skin.
• Even if you could snort sunscreens (a feat in itself), studies showing nanoparticles traveling from the nose to the brain have used rodents not humans – and human noses are very different; they don’t offer the same opportunities for significant exposure through this route.
• It takes a very special type of nanoparticle to cross the blood-brain barrier – you can’t get any old junk across it.
• And research into nanoparticle-induced protein misfolding is at a very preliminary stage – any associations between effects seen in test tubes and brain disease are little more than speculative.

More to the point, we are exposed to billions of nanoparticles each day in the air we breathe; from car exhausts, fires, even sea spray.  If any nanoparticles are going to find their way to our brains in large numbers, it will be these – not those used in some sunscreens.

This is not to detract from the importance of this new research project.  If there are links between nanoparticle exposure and neurodegenerative diseases, we need to know.

But linking sunscreens to Alzheimer’s in the absence of any hard scientific data?  Given what we currently know, that just seems irresponsible!

Update, 8/27/09.  Since posting the original press release, the University of Ulster have changed the headline – without, apparently, telling anyone.  What was “Groundbreaking Research Links Sunscreen and Alzheimer’s Disease” is now “Groundbreaking Research Into Nanoparticles And Alzheimer’s Disease.”

Makes you wonder how much of the sensationalist coverage could have been avoided with a bit of forethought, rather than post-thought.

Thanks to @silentypewriter for the archive link

For more information…

Information on the NeuroNano program can be found here

Nanoparticles traveling from the nose to the brain: There have been a number of studies showing that this is possible in rodents, although little is known about how many particles are likely to get to the brain after being inhaled.  Three useful papers are:

Oberdörster, G., Z. Sharp, V. Atudorei, A. Elder, R. Gelein, W. Kreyling and C. Cox (2004). “Translocation of inhaled ultrafine particles to the brain.” Inhal. Toxicol. 16(6-7): 437-445.

Elder, A., R. Gelein, V. Silva, T. Feikert, L. Opanashuk, J. Carter, R. Potter, A. Maynard, J. Finkelstein and G. Oberdorster (2006). “Translocation of inhaled ultrafine manganese oxide particles to the central nervous system.” Environmental Health Perspectives 114(8): 1172-1178. [PDF]

and

Oberdörster, G., V. Stone and K. Donaldson (2007). “Toxicology of nanoparticles: A historical perspective.” Nanotoxicology 1(1): 2 – 25.

For information on nanoparticles and protein misfolding, the following is a key paper:

Linse, S., C. Cabaleiro-Lago, W.-F. Xue, I. Lynch, S. Lindman, E. Thulin, S. E. Radford and K. A. Dawson (2007). “Nucleation of protein fibrillation by nanoparticles.” Proc. Natl. Acad. Sci. U. S. A. 104: 8691-8696.

The Mexico City study mentioned in the University of Ulster press release is:

Calderon-Garcidueñas, L., B. Azzarelli, H. Acune, R. Garcia, T. M. Gambling, N. Osnaya, S. Monroy, M. R. DEL Tizapantzi, J. L. Carson, A. Villarreal-Calderon and B. Rewcastle (2002). “Air Pollution and Brain Damage.” Toxicol Path 30(3): 373-389.

When it comes to crossing the blood brain barrier, there has been a lot of research on engineering nanoparticles to do exactly this – for delivering drugs.  Most research has shown that fancy materials science and chemistry are needed to engineer nanoparticles to move across the barrier – it’s pretty effective at keeping bad stuff out of the brain.  However, there are indications that small quantities of very small nanoparticles could inadvertently cross over from the blood – more more research is needed to understand whether early findings have any significance though.

Less is known about the possibility of ingested nanoparticles getting into the bloodstream.  Again, the barrier between the guts and the blood is a complex one, and it is unlikely that any old nanoparticle will be able to fool the body into getting where it isn’t wanted.  But this is an area where more research would be useful.

For more info on nanoparticles and sunscreens, check out Industry critics give nanotechnology sunscreens the thumbs up

For more papers on nanoparticles and the brain, check out the nanoEHS Virtual Journal

]]> http://2020science.org/2009/08/25/sunscreens-alzheimers/feed/ 11 http://2020science.org/2009/07/03/nanotechnology-sunscreens/ http://2020science.org/2009/07/03/nanotechnology-sunscreens/#comments Fri, 03 Jul 2009 16:45:17 +0000 Andrew Maynard http://2020science.org/?p=1882

The Environmental Working Group (EWG) – a US-based non-profit organization committed to using public information to protect public health and the environment – has just released what is probably the most comprehensive evaluation to date of the safety and effectiveness of using titanium dioxide and zinc oxide nanoparticles in sunscreens.  And their conclusion?

On balance, EWG researchers found that zinc and titanium-based formulations are among the safest, most effective sunscreens on the market based on available evidence.

In other words, not only are zinc oxide and titanium oxide nanoparticle-based sunscreens OK, but they are safer and more effective than many non nanotechnology-enabled sunscreens.

What makes this statement so startling is that EWG is not known for treating regulators and industry with kid gloves.  This is how the organization describes it’s way of working:

Our research brings to light unsettling facts that you have a right to know. It shames and shakes up polluters and their lobbyists. It rattles politicians and shapes policy. It persuades bureaucracies to rethink science and strengthen regulation.

EWG is about as far as you can get from a bunch of industry lackeys.  Yet here they are endorsing one of the more controversial products of nanotechnology…

For the past few years, the safety of using nanometer-scale particles in sunscreens has been hotly debated.  As manufacturers have  turned increasingly to nanoscale mineral UV-blocking agents in place of more conventional chemicals, speculative questions over whether the nanometer-scale particles of titanium dioxide or zinc oxide being used could penetrate through the skin and harm people have been asked.  In the absence of conclusive safety-focused research, some groups have suggested that nanoparticle-based sunscreens should be avoided in favor of more conventional products, where there we have a clearer idea of the possible risks.  In 2007, Friends of the Earth published “A consumer guide for avoiding nano-sunscreens,” kicking off with:

Sun worshippers beware.  While slathering up with sunscreens to block dangerous ultra-violet (UV) rays you may be exposing yourself to a new danger.  Sunscreen manufacturers are adding nanoparticles to sunscreens to make sun-blocking ingredients like titanium dioxide and zinc oxide rub on clear instead of white. These nanoparticles are being added without appropriate labeling or reliable safety information.

Even EWG admit that their researchers were skeptical about the use of nanoparticles in sunscreens, and thought the organization would end up advising against their use.

Over the past few years, there has been a growing body of published data addressing the effectiveness and safety of nanoparticle-containing sunscreens.  EWG researchers ploughed through nearly 400 studies in their quest to assess what the upsides and downsides might be for consumers.  Importantly, they also compared these data to what is known about conventional UV-blocking agents like octinoxate and oxybenzone.

The result is a comprehensive, robust analysis that wouldn’t be out of place in a peer reviewed scientific journal.  The conclusions are highly relevant to consumers concerned over which sunscreens to use, companies paranoid over how they present their products, and governments wondering how to regulate nanotech-enabled sunscreens.  The report states:

Our study shows that consumers who use sunscreens without zinc and titanium are likely exposed to more UV radiation and greater numbers of hazardous ingredients than consumers relying on zinc and titanium products for sun protection. We found that consumers using sunscreens without zinc and titanium would be exposed to an average of 20% more UVA radiation — with increased risks for UVA-induced skin damage, premature aging, wrinkling, and UV-induced immune system damage — than consumers using zinc- and titanium-based products. Sunscreens without zinc or titanium contain an average of 4 times as many high hazard ingredients known or strongly suspected to cause cancer or birth defects, to disrupt human reproduction or damage the growing brain of a child. They also contain more toxins on average in every major category of health harm considered: cancer (10% more), birth defects and reproductive harm (40% more), neurotoxins (20% more), endocrine system disruptors (70% more), and chemicals that can damage the immune system (70% more) (EWG 2007).

We also reviewed 16 peer-reviewed studies on skin absorption, nearly all showing no absorption of small-scale zinc and titanium sunscreen ingredients through healthy skin. In a 2007 assessment the European Union found no evidence of nano-scale particles absorbing through pig skin, healthy human skin, or the skin of patients suffering from skin disorders (NanoDerm 2007). Overall, we found few available studies on the absorption of nano-scale ingredients through damaged skin, but nearly all other sunscreen chemicals approved for use in the U.S. also lack these studies.

In contrast to zinc and titanium, the common sunscreens octinoxate and oxybenzone absorb into healthy skin — in large amounts according to some studies. These 2 sunscreens can cause allergic reactions, can lead to hormone-driven uterine damage, and can act like estrogen in the body, raising potential concerns for breast cancer.

On balance, EWG researchers found that zinc and titanium-based formulations are among the safest, most effective sunscreens on the market based on available evidence. The easy way out of the nano debate would be to steer people clear of zinc and titanium sunscreens with a call for more data. In the process such a position would implicitly recommend sunscreen ingredients that don’t work, that break down soon after they are applied, that offer only marginal UVA protection, or that absorb through the skin.

EWG acknowledge that more research is still needed, alongside effective oversight, to ensure that nanotech-enabled sunscreens are as safe as possible.  But the key message is that the current balance of evidence supports their use as a safe and effective alternative to more conventional sunscreens.

I cannot emphasize enough how important this report is.  The analysis is credible and the conclusions drawn are supported by the current state of the science.  It should reduce consumer concerns over using nanoparticle-based sunscreens, and allow them to make informed decisions that will result in better UV protection.  It should also encourage companies developing and selling nanoparticle-enabled sunscreens to stop obscuring  the fact – either by avoiding any mention of nanoparticles, hiding behind silly euphamisms alike “micronized,” or coming up with elaborate explanations of why their product doesn’t actually contain any nanoparticles.  These are good products using an effective technology, and companies shouldn’t be shy to let people know!

That said, there is still work to be done.  There are gaps in our understanding of how titanium dioxide and zinc oxide nanoparticles behave on the skin and in the environment that it would be good to fill.  Approaches to testing these materials need to be fully evaluated. And regulators need to clarify the rules concerning the safe use of these materials.

Given what still isn’t known, EWG cautioned against the use of nanoparticles in cosmetics at the moment, where they are not being used to protect the wearer’s health.  But when it comes to protecting the skin the organization was clear – nanoparticle-based sunscreens.

End Notes

The full EWG report on “Nanotechnology & Sunscreens” can be read here.

This is part of a larger review of sunscreens, which is accessible here.

Something not covered in the EWG report is nanoparticle agglomeration.  Some companies have claimed that, while the basic size of titanium dioxide and zinc oxide particles they use is in the range of 1 – 100 nm, they form much larger agglomerates in the products and should therefore not be considered “nanoparticles.”  While this may be the case for some products, it isn’t universal, and there are still questions over whether large agglomerates could disaggregate when applied to the skin.  However, given the EWG’s findings and conclusions, the question of agglomeration doesn’t seem to be that important from a consumer’s perspective.

One concern over the use of titanium dioxide and zinc oxide nanoparticles in sunscreens is that these materials are photoactive, and could become more harmful when exposed to sunlight.  As the EWG report notes, most manufaturers treat the nanoparticles to supress their photoactivity.  Howere, there is some evidence that products containing photoactive particles could still be entering the market.   Whether this is important from a health perspective is unknown, although the indications are that it probably isn’t a significant concern when the particle-containing sunscreens are appolied to healthy skin.

]]> http://2020science.org/2009/07/03/nanotechnology-sunscreens/feed/ 16 http://2020science.org/2008/06/21/8621-nano-sunscreens-leave-their-mark/ http://2020science.org/2008/06/21/8621-nano-sunscreens-leave-their-mark/#comments Sun, 22 Jun 2008 00:57:05 +0000 Andrew Maynard http://2020science.wordpress.com/?p=247

Painted metal roofs are cheap, convenient, and usually very durable.  But over the past two years, a rash of accelerated ageing has blighted pre-painted steel roofing in Australia.  And intriguingly the ageing—which affects the coating—seems to be localized to small patches, taking on the form of fingerprints, handprints and even footprints.

The culprit it seems is sunscreen that is spilt or otherwise transferred to the roofing by construction workers during installation. And not any old sunscreen—this would appear to be a uniquely nano phenomenon.  But I get ahead of myself…

Pick up a bottle of sunscreen and there is a fair chance these days that it contains nanoparticles, engineered to absorb and reflect away harmful UV radiation.  Many manufacturers are introducing lines of nanoparticle-containing sunscreens as alternatives to those using more conventional organic chemicals, and it’s not hard to see why: the active ingredients in these nano sun blocks are generally more gentle on the skin than their non-nano counterparts; they are made to sit on the surface of the skin rather than penetrate into it; and if designed well, they continue to block UV radiation for several hours after application.  And of course, they go on clear, giving a product that works well and looks good.

But each year as the sun and the sunscreen come out, questions over the safety of nano-formulations are raised.  Can these nanoscale particles penetrate through the outer layers of the skin to the underlying living cells, and even the bloodstream? And if they get there, what harm could they cause?  So far, most studies suggest that nanoparticles in sunscreens stay where they are supposed to—on the skin, not in it.  Yet there is another question that has been bobbing along just under the surface for the past few years: could mixing nanoparticles, sun and moisture lead to a chemically corrosive mix that is bad for the skin?

The issue in question is photocatalytic activity.  Titanium dioxide, and to a lesser extent zinc oxide, are photoactive—they have the ability to absorb UV, and in the presence of moisture convert benign water molecules into chemically active hydroxyl free radicals.  These highly reactive chemicals could spell bad news for sunscreen users if they are generated in large amounts—eating away the components that hold the sunscreen together, and even possibly causing skin damage if they get below the surface and into cells.

Fortunately, manufacturers and users of titanium dioxide have long been aware of this propensity to generate free radicals, and have found ways of suppressing it in sunscreens. Photocatalytic activity depends on the crystalline structure of titanium dioxide.  Anatase and rutile forms of titanium dioxide have the same chemical formula but different crystalline structures. And, as it turns out, different properties. Make nanoparticles from anatase titanium dioxide, or a mix of anatase and rutile, and you have a powerful source of harmful hydroxyl radicals in the presence of water and UV. But make nanoparticles out of rutile titanium dioxide alone, and photocatalytic activity is reduced substantially.

However, even rutile titanium dioxide particles show some photocatalytic activity.  Early uses of rutile titanium dioxide as a white pigment in outdoor paint were plagued by the paint turning chalky after too much sun exposure. The problem was tracked down to hydroxyl radicals being produced and degrading the paint’s binder.  The solution: coat the particles with a material that prevents free radical formation—no more chalky paint, and coatings that will last for years in the fiercest sun.

Makers of titanium dioxide-based sunscreens use a similar trick to retain the functionality of nanoparticles while avoiding the potentially harmful photocatalytic properties. For instance Optisol—a UV blocking agent made by the company Oxonica—incorporates a minute amount of manganese into the crystal lattice of rutile titanium dioxide nanoparticles.  This doping allows the absorbed UV energy to be dissipated while virtually eliminating the formation of free radicals.  Not only does this make sunscreens using Optisol potentially safer; they also last longer in the sun, as there are fewer free radicals to break down other ingredients in the product.

So all looks rosy for nano-enabled sunscreens.  At least, it did until the publication of a recent paper.  And this is where we get back to pre-painted steel roofs. Since mid 2006, researchers in New South Wales Australia have noticed unusual defects developing in newly installed pre-painted steel roofs.  The damage is typically localized to areas of pressure contact, often taking the form of fingerprints or shoe impressions.  And it results in accelerated weathering—in one example, patches of a roof appeared to age an equivalent of 15 years in only 18 months. The culprit?  Nanoparticle-containing sunscreens, which are accidentally transferred to the roof during installation by touching or splashing.

In the paper “The interaction of modern sunscreen formulations with surface coatings,” [Progress in Organic Coatings62: 313:320. 2008] authors Phil Barker and Amos Branch systematically track down the underlying cause behind the unsightly blemishes.  Out of ten sunscreens tested—four containing no nanoparticles, five containing titanium dioxide nanoparticles, and one containing zinc oxide nanoparticles—all but one of the nanoparticle-based sunscreens consistently degraded samples of pre-painted roofing surface exposed to sunlight for 12 weeks.  In contrast, the non-nano products had no obvious deleterious effect.  In the worst case, the roofing lost over 85% of its gloss (a measure of degradation) in just six weeks.

Digging a little deeper, Barker and Branch pinned the effect to nanoparticles in all but one sunscreen acting as photocatalysts, and generating hydroxyl radicals in the presence of UV radiation and water.  Despite assumptions that nanoparticles in sunscreens are engineered not to produce significant amounts of free radicals, these products were generating them fast enough to significantly damage roof coatings in a matter of weeks!

So have we had the wool pulled over our eyes?  Are these supposedly benign nano-sunscreens we are slathering on our skin adding to our wrinkle-count before our time, and perhaps more besides?

Before jumping to conclusions, it is worth taking stock of what is known, and what is not.  While the study showed all but one of the nanoparticle-based sunscreens had some adverse effects on the roofing, these effects varied greatly between products.  The sunscreen using nano-zinc oxide particles led to a 55% reduction in gloss over 12 weeks, while in the worst case, a sunscreen containing 4% titanium dioxide led to a 95% reduction in gloss over 12 weeks.  Assuming that the reduction in gloss is associated with the formation of hydroxyl radicals (and the evidence presented by Barker and Branch arising from a logical sequence of laboratory experiments is pretty convincing), there is still uncertainty over how harmful these would be when generated on the skin of a sunscreen-user.  To cause damage, the hydroxyl radicals would need to penetrate deep into the skin and into cells before loosing their potency, and if the nanoparticles stay on top of the skin where they are supposed to, significant penetration may not occur.

Then there is the anomalous nano-sunscreen that didn’t show an appreciable effect.  A nifty piece of X-ray diffraction analysis in the Barker and Branch paper showed that the titanium dioxide nanoparticles in the roof-damaging sunscreens were an anatase/rutile mix, while the nanoparticles in the benign sunscreen were comprised of rutile titanium dioxide alone.  Clearly crystalline form matters, as Oxonica realized when they selected the less-active rutile form of titanium dioxide as the basis for Optisol.

This study demonstrates that it is possible to create nanoparticle-based sunscreens that do not generate significant amounts of hydroxyl free radicals.  But the bottom line here is that some nano-based sunscreens are being sold (in Australia at least) that contain photoactive nanoparticles which generate hydroxyl radicals in the presence of water and sunlight.  This raises questions about the impact of these products on users over time and, perhaps more significantly, their impact on the environment.  A photocatalytic titanium dioxide particle released into the environment will continue to generate hydroxyl radicals as long as it is exposed to UV radiation—because this is a catalytic process, the particle is not destroyed in the process, but just carries on doing its stuff; day after day, year after year.

But perhaps the biggest question here is one of regulation.  In the US, the Food and Drug Administration does not currently discriminate between anatase and rutile titanium dioxide particles in sunscreens, or doped and un-doped particles [Sunscreen Drug Products For Over-The-Counter Human Use: Final Monograph.  May 21 1999.  PDF, 144 KB].   This may change following further consultation on the use of nanoscale titanium dioxide and zinc oxide in sunscreens [see Sunscreen Drug Products For Over-The-Counter Human Use; Proposed Amendment of Final Monograph; Proposed Rule.  August 27 2007.  PDF, 424 KB].  But in the meantime, what is to stop manufacturers using potentially harmful forms of titanium dioxide in sunscreens?  And how will consumers be able to distinguish between companies that have got it right, and those that have not?

It seems that if we are not careful, nano-sunscreens could be making their mark on more than just pre-painted steel roofing.

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This post first appeared on the SAFENANO blog in June 2008