Cross-posted from The Risk Science Blog

Several months ago, I was asked by a colleague if I fancied co-authoring a review on nanotoxicology for a copy of Toxicological Sciences celebrating the 50th anniversary of the Society of Toxicology (coming out later this year).

Fool that I am, I agreed.  Interestingly though, as I and my co-authors (Martin Philbert and David Warheit) grappled with a topic we were all, to be frank getting a little fatigued with, it became clear that “nanotoxicology” as it is currently understood is merely a step towards a much bigger field of the “new toxicology of sophisticated materials”

The review is currently available here as an Advance Access publication from Toxicological Sciences.  In it we start by reviewing the history of the emergence of nanotoxicology as an integral part of the field of nanotechnology, and continue to examine some of the key toxicology-based challenges presented by engineered nanomaterials.

Yet we conclude that, despite the current flurry of activity in researching the toxicity of nanomaterials, the field of nanotoxicology is suffering from something of an identity crisis:

“There is a strong sense that emerging, novel and complex materials that have been engineered at the nanoscale may exhibit unusual or unanticipated toxicity from a conventional perspective, and that research is needed to understand and address how these designed-materials might cause harm in ways that are not readily understood at present. This concern is supported by a growing body of research which indicates that some nanometer scale materials do demonstrate biological behavior that is mediated by physical form as well as chemical composition. Yet a clear identification and formulation of the problems being faced remain elusive.

For example, what is meant by the “nanoscale” is far from clear, meaning that there is considerable ambiguity over which materials are embraced by “nanotoxicology.” Widely accepted definitions of nanotechnology refer to a size range of approximately 1 – 100 nm “where unique phenomena enable novel applications”. Yet these are largely definitions of convenience, not of science. And while the definitions defining the field of nanotechnology have been important in driving new science and technology   innovation, it is not clear how they apply to a new material’s propensity to cause harm in unexpected ways.”

This is not to say that the questions and issues raised by nanotoxicology are not important.  On the contrary, we note that

“there is an array of increasingly sophisticated materials that are emerging from advances in science, technology and engineering that do demand careful consideration of the new risks they might pose.”

But we suggest that new thinking on how the potential safety challenges presented by these “sophisticated materials” is needed.

“In this respect a differential approach to toxicology studies is required – one which helps identify where emerging materials and products deviate from established ones in their potential to cause harm, and focuses research on narrowing the resulting knowledge gap.

Undoubtedly, materials intentionally designed and engineered to behave in specific ways because of their fine structure are at the forefront of the new challenges being faced in toxicology. These materials increasingly demonstrate biological behavior that results from a synergistic interaction between chemical composition and physical form. But whether these new challenges can be confined to a narrow size scale implied by “nanotoxicology” is debatable.

Rather, we would argue that a broader perspective is needed on the challenges presented by novel and functional materials, that captures the idea of “sophisticated materials.” These are substances that arise at the intersection of scientific disciplines and technology platforms, and demonstrate novel and even time and context-dependent functionality based on their engineered and increasingly complex physicochemical structure.

While many of these materials will depend on nanoscale engineering, decoupling the materials from the underlying technology – or technologies – is helpful in formulating science-based questions regarding their toxicity. In this respect, the toxicology challenge presented by sophisticated materials is to understand and address the hazards presented by materials that have the ability to enter the body, interact with it and elicit an adverse response in ways that are not adequately understood through a conventional and chemical composition-dominated perspective on toxicology.”

We conclude the review by suggesting that

We can now begin to appreciate the challenges presented by simple nanoscale materials such as TiO2, ZnO, Ag, carbon nanotubes and CeO2. But these simple materials are merely the vanguard of a new era of complex materials, where novel and dynamic functionality is engineered into multifaceted substances. If we are to meet the challenge of ensuring the safe use of this new generation of substances, it is time to move beyond “nano” toxicology and towards a new toxicology of sophisticated materials.

Maynard, A. D., D. Warheit and M. A. Philbert (2011). “The New Toxicology of Sophisticated Materials: Nanotoxicology and Beyond.” Tox. Sci. Advance Access.  DOI: 10.1093/toxsci/kfq372