What's The Story with Nanoparticulate Zinc Oxide?

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What's The Story with Nanoparticulate Zinc Oxide?

In recent years it has become possible to create high quality elegant and high SPF sun protection products using physical sun blockers actives such as zinc oxide and titanium dioxide. In the short period of time that these products have been available we have come to rely on this 'invisible' protection believing it to be more environmentally responsible, safer (for us than chemical filters) and more natural - a physical barrier rather than a mini-chemical reaction. However, one of the key scientific advancements that made this technology possible has its self come under the microscope as a potential risk to both the environment and our health. What we are talking about are nanoparticles or microscopically tiny little particles which can be as small as one millionth of a millimetre to 100 times that large (which is still very tiny).


To give you some idea of how small we are talking, the average human hair has a diameter of between 50-100,000 nanometers! Before we get any further it is important to understand that humans didn't 'invent' nanoparticles, nature spews them into the atmosphere with every volcano , forest fire or ocean mist. Us humans have created nanosized zinc oxide particles and these have been steadily making their way into our sunscreens and anti-ageing products over the last few years in a (rather successful asthetically speaking) attempt to give us, the public, high SPF sun protection without the ghosting. So, what is the problem with that?

Our understanding of how nanoparticulate zinc behave in biological and environmental systems is growing thanks to a global funding push in the consumer nanoparticle-based product arena. This, along with the work carried out by various private groups, non-government organisations and interested individuals is adding to our understanding. So, is there anything in this flood of information to raise alarm bells about the safety of all things nano? The answer is yes and no.

Man-made zinc oxide nanoparticles are a relatively new kid on the cosmetic chemistry block - a new kid that has become, alongside its micronized sisters very popular and that is what causes some of the problem. This nano-technology has blasted onto the cosmetics scene too quickly for some raising questions about its safety both for the individual applying the products and the environment that the product eventually gets washed into. With humans the concern is that nanoparticles will find their way into the bloodstream where they may affect any one of a myriad of biological processes. Environmentally speaking nanoparticulate zinc oxide has been found to be particularly toxic to marine organisms under some circumstances and as we all share the same planet, what is bad for one must indeed bare consequences for the other.

As far as evidence goes the scientific world is still a long way off having all of the answers and to some people that immediately rings alarm bells justifying the 'precautionary approach' - avoid, avoid, avoid! While this is understandable at an individual level, the potential benefits of getting zinc nanotechnology right are worth a closer look. In addition it is worth mentioning that no amount of science can prove a negative. i.e: it is impossible to state that anything is unequivocally safe, we can only prove safety in an applied way - at THAT concentration when delivered in THIS type of base under THESE conditions. It is this complex and somewhat endlessly variable equation that makes science nonsensical to many people and non-sensational for the majority of journalists or activists. You simply can't make an emotive, short sentence upon which to hand a campaign in which the words 'maybe, possible, under-these-circumstances, depending' feature!

There is mounting evidence to show that nanoparticulate zinc oxide can assert a toxic effect to various organisms including the zebra fish, daphnia, microalgae, bacteria and mice. The particles have also been shown to assert a toxic effect in human epidermal cells (cell culture) under the right conditions. Some of these studies also demonstrated a potential for nanoparticulate zinc oxide to bioaccumulate when ingested by aquatic microorganisms - something that has implications throughout the food chain. Based on the body of evidence thus far there is little doubt among the chemical industry that nanoparticulate Zinc Oxide should be handled with upmost care to prevent it from entering the environment or the body through inhalation or direct skin absorption - through contact with the raw material. However, all of the above trials stress the relationship between the toxicity and persistence of zinc oxide to the solubility of the metal in the given environment - in some cases nanoparticulate zinc oxide was no more toxic than straight zinc oxide, indeed many of the studies don't even give comparative data on big zinc VS micro zinc Vs nano zinc Vs the Zinc Oxide ions. This is significant as it is necessary in order for us to be able to understand the relative toxicity of nano zinc particles vs other forms of zinc pollution.

Based on the above revelation it would be easy to conclude that nano zinc oxide is akin to environmental suicide but that is not necessarily the case - once a risk is identified it can be managed. Further, the conclusions reached above have, in each case been based on very specific environmental conditions. These may or may not bare comparison to situations found outside of the laboratory and on that note it seems right to get back to our sunscreen Zinc Oxide.

A few years ago one of Australia's top sunscreen manufacturers Hamilton Laboratories carried out a test on their range of sunscreens with a view to finding out what happened to the nanoparticulate zinc active. While all of the six sunscreens tested had nanoparticles going into the formulation (particles less than 100nm), none of the finished products contained detectable nanoparticles. Indeed, the smallest detected zinc oxide aggregate was over 500nm putting it well into the micronized end of town. This is not surprising given the strong particle-particle attraction between zinc oxide molecules - an attraction that far exceeds the energy excerted in the manufacturing process. In addition, the results of this study may shed some light on the results of a 2009 study carried out by Macquarie University and the CSIRO. This study showed that small quantities of zinc (1/1000th higher than baseline levels) got into the blood stream of the panel over the period of the trial. The experiment took two groups - a non-nano zinc oxide and a nano zinc oxide sunscreen group and traced the passage of zinc through the body with a rare isotope. The fact that both groups experienced the same degree of absorption of zinc could be evidence that the nano zinc had agglomerated to an extent that made it biologically similar to the micronized zinc. Alternatively maybe it was just a small trace of nano in both that got through. Either way, this study showed that a small amount of zinc got through but as the trial didn't analyse the form that the absorbed zinc was in we can't tell what form the zinc was in. This one study begs a number of questions, especially in light of the fact that the sunscreens tested perform well in terms of looks and UV performance. So are nanoparticles necessary in sun care?

The Hamiltons study does, to some degree prove that the sunscreen world could probably maintain the products elegance with particulates of over 200nm (into the micron range), especially as it is unlikely that many finished products contain nanoparticles once manufactured. This would seem like a wise move in light of the fact that nanoparticulate zinc oxide has the potential to cause environmental damage under the right conditions. Further, the increase in minimum particle size for the sunscreen industry would help to avoid any negative effects caused by Zinc Oxides potential to become a photocatalyst as that function is very much dependent on the zinc particle size with 33nm thought to be the optimum (Dodd, A.C., Mckinley, A.J., Saunders, M. & Tsuzuki, T. (2006). Effect of particle size on the photocatalytic activity of nanoparticulate zinc oxide. Journal of Nanoparticle Research, 8(), 43-51). These two benefits seem worth pursuing from a logical and an ethical standpoint especially as there seems to be no pay-off at the customer end.

There is no doubt that the area of cosmetic nanotechnology is fraught with emotion and intrigue as the public and scientists around the world try to get to grips with a potentially powerful and valuable new branch of chemistry (or is it physics?). With facts and evidence looking to support a cautious approach to nano-adoption mounting it is also understandable that regulators such as those in the EU have chosen to 'let the public decide' if they want to buy into nano or not - products containing nanoparticles will soon have to be labelled as such. However, the jury is still out on how useful and effective that piece of label information will be!

So, while the world is making up its mind on all things nano what is New Directions doing?

At New Directions we understand that while potentially interesting, nanoparticles are still something that many of you wish to avoid or can't include (as is the case for Organics). For that reason we choose ingredients that comply with the definition of micronized or larger particles. This is particularly relevant for our Zinc Oxide, titanium dioxide and some new generation actives.

Create with confidence at New Directions, naturally forward!

Amanda Foxon-Hill

27 June 2011

More about: Skincare, Zinc Oxide

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