There have been some recent mentions of nano-toxicity as being nanotechnology safety. There are Government requests for review of proposed documents regarding either nano-safety or nano-toxicity. The way these items are stated could lead a casual reader to the conclusion that the terms are identical.
The field of nano(technology or materials) toxicity relates to investigations into the impact of nanomaterials on humans or the environment that can create undesirable and/or unwanted effects. Some of the effects are known to possibly occur after years of exposure or occur years after exposure. Whether due to initial exposure or long-term exposure, the resulting harm can have a serious impact and the exposure needs to be eliminated or the effects mitigated.
Nano-toxicity investigates the impact through testing, which normally requires exposure to the substance in question and observations of the resultant effects on subjects. In many cases these are done post-mortem. Consequently, substitutes are employed to represent the impact on humans. In order to expedite the evaluation, high dosages may be employed to imply the impact of smaller doses over a longer period of time. A potential issue is that certain materials, like arsenic, may be acceptable at doses of low parts per million (ppm) but deadly at higher concentrations. Large doses of inorganic arsenic containing 60 ppm or 60,000 parts per billion is toxic. Smaller doses of 30 ppm will cause sickness along with other effects. (These dosages are more than 10,000 times the amount found in most drinking water in the United States.) The nature of arsenic has been known since ancient times [1]. There are some known long-term effects due to exposure. Consequently, testing of arsenic effects does not increase the amount of exposure to shorten the time to determine its impact.
The methodology for testing creates an interesting situation. If one assumes that creating a higher dosage will equate to the same effects as a lower dosage over a longer time, then increasing the arsenic dosage would correlate to a lower dosage over time. From the report cited above, if one wanted to test the effect of 15 ppm and shorten the test duration, one could increase the dosage to 60 ppm or 75 ppm. Obviously, this is not done because we have knowledge that the higher dose is fatal. BUT, what if we don’t know the long term effect? Can one safely assume that increasing the quantity of carbon nanotubes in the test animal provides an indication of long term effects of a lower dosage? Or, does the dosage cross a threshold quantity that becomes detrimental? In many cases we can not answer that question. Correlations are made to provide justifications for assumptions, but the absolute answer is not known.
In order to reduce the amount of testing, the use of grouping materials may be employed to determine its impact. An early consideration, and still in use by many, is that any substance that was 100nm and smaller was considered nano. In previous blogs, I have mentioned the reactive nature of aluminum nanoparticles. There is a threshold that once crossed yields material that is highly reactive. At 50 nm, the main concern of exposure to the aluminum nanoparticles is from the dust being inhaled. However, at 30 nm, the same material becomes highly reactive and will explode in exposure to oxygen. If I have a batch of aluminum nanoparticles that has a mean of 40 nm, what will happen? It the half-width of the distribution is 1 nm, the results can be predicted. If the half-width is 15 nm, it probably will have a different reaction. But, both can be classified as a 40 nm particle distribution. The ability to determine the half-width is not readily available.
Nano-toxicity is about the impact of nanomaterials on people and the environment. It can not be all inclusive due to the immense number of possible combinations of materials. The obvious question is: How do we handle the material? That is not nano-toxicity. Nano-Safety is.
Nano-Safety focuses on the measures, training, and procedures to create an environment where researchers/workers are able to evaluate situations and determine proper actions to mitigate potential dangers in the creation and handling of nanomaterials. The next blog will address some of the progress that has been made in our Nano-Safety efforts.
References:
[1] http://www.atsdr.cdc.gov/phs/phs.asp?id=18&tid=3
