Researchers in Singapore (Nanyang Technological University and the National University of Singapore) have published a study suggesting that nano zinc oxide, found in some sunscreens, may potentially cause cancer. The Nov. 29, 2011 news item on Nanowerk provides this detail,
The chemical, Zinc Oxide, is used to absorb harmful ultra violet light. But when it is turned into nano-sized particles, they are able to enter human cells and may damage the cells’ DNA. This in turn activates a protein called p53, whose duty is to prevent damaged cells from multiplying and becoming cancerous. However, cells that lack p53 or do not produce enough functional p53 may instead develop into cancerous cells when they come into contact with Zinc Oxide nanoparticles. [emphases mine]
I was able to access the study and while I’m not an expert by any means I did note that the study was ‘in vitro’, in this case, the cells were on slides when they were being studied. It’s impossible to draw hard and fast conclusions about what will happen in a body (human or otherwise) since there are other systems at work which are not present on a slide.
A few items I was not able to determine (it’s in the study but I don’t understand the term ‘sonicate’ or others the researchers used),
- were the concentrations of nano zinc oxide used in the research the standard concentrations one would find in a sunscreen, and
- were the cells continuously exposed to nano zinc oxide, e.g. sitting in a bath of the chemical, or were the cells exposed in the way cells in a body would be exposed
I ask these questions not to so much to expose my ignorance but to point out how difficult it is draw conclusions from a study when you don’t have the training for it. In fact, if you read the news item on Nanowerk or the study (The role of the tumor suppressor p53 pathway in the cellular DNA damage response to zinc oxide nanoparticles [article behind paywall]), you’ll notice that even the researchers have phrased their findings very carefully.
You’ll also notice that there is another agenda (from the news item on Nanowerk),
The breakthrough also validated efforts by Asst Prof Loo and Asst Prof Ng to pioneer a research group in the emerging field of nanotoxicology, which is still very much in its infancy throughout the world.
The research team would also like to work with the European Union to uncover the risks involving nanomaterials and how these materials should be regulated before they are made commercially available. Asst Prof Joachim Loo, who received his Bachelor and Doctorate degrees from NTU, was the only Singaporean representative in a recent nanotechnology workshop held in Europe. At the workshop, it was agreed that research collaborations in nanotoxicology between EU and South-east Asia should be increased.
Another research study on nano zinc oxide was released last year (it was not cited in the references for the latest Nov. 2011 study). From the Aug. 20, 2010 news item on physorg.com,
A technique developed by Macquarie University has proven for the first time that a tiny amount of zinc from sunscreens is absorbed through the skin into the human body, but is not yet able to discern whether the zinc is in nanoparticle form.
Professor Brian Gulson of Macquarie University conducted the research – published online in the current edition of the journal Toxicological Sciences – with collaborators in CSIRO and the Australian National University and the Australian Photobiology Testing Facility. The research was widely reported on in February 2010 following a presentation by Gulson at a scientific conference.
The team traced the skin absorption of a highly purified and stable isotope which allowed them to distinguish the zinc from the sunscreen from that which is naturally present in the body or environment. Zinc is absolutely essential to bodily functions.
The researchers suggest that follow-up studies from the scientific community with different formulations over longer periods of time are essential, but that until evidence to the contrary is obtained, people spending time outdoors should continue to use sunscreens.
Getting back to that question about the concentration of the nano zinc oxide solution used in the most recent studies in Singapore, here’s what Brian Gulson had to say about nano zinc oxide concentrations in his work and about a shortcoming in his study (from an Australian Broadcasting Corporation [ABC] Feb. 25, 2010 interview with Ashley Hall,
BRIAN GULSON: I guess the critical thing was that we didn’t find large amounts of it getting through the skin. The sunscreens contain 18 to 20 per cent zinc oxide usually and ours was about 20 per zinc. So that’s an awful lot of zinc you’re putting on the skin but we found tiny amounts in the blood of that tracer that we used.
ASHLEY HALL: So is it a significant amount?
BRIAN GULSON: No, no it’s really not.
ASHLEY HALL: But Brian Gulson is warning people who use a lot of sunscreen over an extended period that they could be at risk of having elevated levels of zinc.
BRIAN GULSON: Maybe with young children where you’re applying it seven days a week, it could be an issue but I’m more than happy to continue applying it to my grandchildren.
ASHLEY HALL: This study doesn’t shed any light on the question of whether the nano-particles themselves played a part in the zinc absorption.
BRIAN GULSON: That was the most critical thing. This isotope technique cannot tell whether or not it’s a zinc oxide nano-particle that got through skin or whether it’s just zinc that was dissolved up in contact with the skin and then forms zinc ions or so-called soluble ions. So that’s one major deficiency of our study.
Of course, I have a question about Gulson’s conclusion that very little of the nano zinc oxide was penetrating the skin based on blood and urine samples taken over the course of the study. Is it possible that after penetrating the skin it was stored in the cells instead of being eliminated?
It seems it’s not yet time to press the panic button since more research is needed for scientists to refine their understanding of nano zinc oxide and possible health effects from its use.
Final note: The researchers listed on the Singapore study are: Kee Woei Ng, Stella P.K. Khoo, Boon Chin Heng, Magdiel I. Setyawati, Eng Chok Tan, Xinxin Zhao, Sijing Xiong, Wanru Fang, David T. Leong, and Joachim S.C. Loo