Getting to General Principles: Are We Making Progress?

Cal Baier-Anderson, Ph.D., is a Health Scientist.

With conventional chemicals, experience has allowed us to articulate general criteria based on chemical properties that identify chemicals of greatest concern.  For example, persistent and bioaccumulative chemicals are assigned a high priority, whereas chemicals that quickly degrade and don’t build up in blood or tissue are, as a rule, likely to be of lower priority.

Concerns about nanomaterials arise from observations that properties that emerge or are greatly enhanced at the nanoscale can alter behavior, including biological activity.  These properties make such materials different from conventional forms of the same chemicals.  But can a general principle that nanomaterials pose a greater concern than their conventional counterparts be supported? 

Some nanomaterials have been found to have hazardous properties, while others appear benign, at least under the tested conditions.  The major challenge is how to go about identifying the general principles that govern whether a given nanomaterial falls into one or the other category.  That is, what key properties of nanomaterials determine whether they are “safe” or “risky”?  Is it their size, their large surface area, their surface charge, their shape, some other property or some combination?

At the Society of Toxicology’s annual meeting in Seattle last month, the huge diversity of nanomaterial properties was on full display, a dazzling illustration of how complex this new field of study is, how little we really know and understand, and how far we are from uncovering general principles that can be used to guide our decisions.

Various short-term studies found that certain nanomaterials can translocate from the lungs to the brain, blood, and heart (nano gold); can move from the lungs to the interstitial space, but not the blood (single-walled carbon nanotubes); and either trigger a strong immune response (multi-walled carbon nanotubes) or do not (nano zirconium oxide).  One study found that, in the blood, silicon-based nanoparticles become coated with proteins, altering the proteins’ shape and increasing the likelihood that the immune system will recognize it as damaged.  These are just a few indications of the wide range and nature of biological responses to nanomaterials that complicate our ability to understand and predict their behavior in biological systems.

My take-home message:  We’re nowhere near to deriving general principles.  And we still have a lot of hard work to do to get there:  Fully characterize the physical and chemical properties of each assessed nanomaterial and examine a broad range of potential biological effects based on all reasonably expected routes of exposure.  Only in that way can we begin to correlate nanomaterials’ key physical and chemical properties with their biological properties.  The more data we generate – and the more that is made publicly available for scrutiny and evaluation by the larger nanotoxicology community – the sooner we’ll get to the general principles we need going forward.