Is nanotechnology safe?

I have a confession to make. I never thought, when I started our laboratory in 1998 at the medical school of Cornell University in New York, that I would ever be concerned about the possible toxic effects of exotic (and, back then, hardly invented) nanomaterials. I was a junior professor training clinical fellows, some of them from the critical care unit, others from surgical oncology, in basic research.

Most of these guys were primarily worried about their clinical duties, keeping as many of their intensive care patients alive as possible. Who cared whether exposure to quantum dots or liposomes would perhaps cause an adverse effect 30 years down the line? The breathing support monitors and their pagers were beeping! Patients had to be kept alive by all means available!

I believe the same even now - at least at an emotional level. Our lab is now across the street from Great Ormond Street Hospital in London and every time I see and interact with its young patients and their carers I get the same reaction. Why do we spend so much time, effort and resources in our laboratories trying to determine whether using carbon nanotubes to treat leukaemia or glioblastoma (an aggressive form of brain cancer) may increase the risk of another cancer? First, we are dealing with cancer patients already, second the worst case scenario is that carcinogenesis may occur to some of them decades hence. In the meantime there are all these so little guys, so badly sick right now.

In the context of medical applications of nanotechnology we primarily want to develop tools for clinicians to save lives. I do not think many people would dispute this as a worthwhile and urgent task. However, we also need to develop safe tools and medicines. No clinician, regulatory authority or sponsor will support a technology that is not "safe". That is why there are very strict rules that regulate the approval of new products for medical use. This is something that many of my colleagues who develop nanomaterials but are less involved with clinical development are liable to forget. The challenge then becomes who defines "safety" and how.

Generally, what is safe and what is not is a relative matter. For me bungee jumping is clearly not safe. For many others it is not only perfectly safe but also fun. In modern interventional medical practice almost every treatment strategy is "unsafe". Radiation therapy, surgery, laser ablation, chemotherapy, immunisation – all entail risks of serious adverse side-effects. But this is what we have available and what we learn to work with.

It is the famous risk-benefit balance that clinical practice is based on. When a patient walks into the clinic with severe pathological symptoms or has been diagnosed with a malignancy, the risk of killing healthy cells and collateral damage is immediately balanced by the benefit of eradicating the tumour. This is the reality that a lot of my colleagues in toxicology (usually environmental or occupational health) forget or ignore when they consider nanotechnology in medicine. This is why almost every time I give a lecture on the ways we are developing carbon nanotechnologies for the treatment of stroke or Parkinson's disease there are people in the audience who will vehemently criticise the technologies I describe as "unsafe', maybe even "daft" or "self-indulgent".

More than a decade ago a very experienced clinician told me: "Kostas, water can be an intoxicant, if you so wish to use and see it that way." That statement has resonated so vividly with me that since then I have tried many times to answer the question: "is water safe?" Well, the inhalation of excessive amounts of water can kill us. It is called drowning. The risk of drowning stands very high, typically in the UK at 450 deaths per year. Also, excessive oral intake of water can lead to water intoxication. Indeed, a medical condition known as dilutional hyponatremia results from drinking excessive amounts of water and can lead to brain damage and stroke.

So is water toxic? Surely it is not "safe". Should we ban or heavily regulate shipping or swimming or punting then, because the risk of drowning increases dramatically when on water. Should we regulate the accessibility of water in our homes, because it can potentially kill?

What if we then try to extrapolate about the safety of carbon nanofibres in our tennis rackets and bicycle frames? How toxic are they? Are we prepared to balance the risks from exposure to such new nanomaterials against the benefits from useful products we get in return?

Next time you hear or read about a nanoparticle being toxic, dangerous, unsafe, my advice is to ignore the sensationalism and focus on the use to which that material or technology will be put. If carbon or gold nanomaterials will be used in medicine, they will be subject to a battery of tests and a series of regulatory inspections and approvals to maximise protection of the patient. These will include clinical trials lasting around a decade to determine first and foremost the safety and efficacy of such technologies, so you can rest assured that most problems will become apparent.

Having said that, I believe patients in a critical condition might want to try less proven, riskier technologies, and if at all possible these should be made available to them. Extending the life of someone with a brain tumour by six months can be such a significant achievement it may justify the use of "unsafe" technologies. If on the other hand the same technology is used as a window cleaning product or as an additive in the fizzy drink our child likes to consume, then we may want to be more careful and minimise all potential risks. Better still, we might encourage them to give up fizzy drinks altogether.

One of the most difficult challenges of the human condition is sharing our different realities. What is safe for me may be very dangerous for you and vice versa. What may be unsafe for an NGO with an environmentalist "reality", may be a safe, essential tool for an oncologist or a neurosurgeon in their clinical "reality". Radiation is just such a case.

In a play called The Memory of Water, three sisters talking over the dead body of their mother (not killed by anything nano) exchange memories about the same past events, only to find that none of them perceived exactly the same thing. Despite sharing their childhood they cannot agree upon one unifying experience because each one experienced a different "reality". The result of this, as one character in the play puts it, is: "We don't argue, we bicker!"

By analogy, let's avoid bickering when it comes to discussions about the safety of nanotechnology, try to exchange realities and always remember that even water can intoxicate and kill. No nano-substance will ever be absolutely "safe". Whether we choose to use it will depend on the application.

Kostas Kostarelos is a professor of nanomedicine at the University of Manchester and director of the university's Nanomedicine Lab