The Neighborhood Toxicologist: Length Matters: Nanotoxicity

Monday, April 02, 2007

Length Matters: Nanotoxicity

Obviously size matters for nanoparticles, or the world wouldn’t be making such a big deal of them. Size also matters when it comes to toxicity of nanoparticles. A recent study published in Advanced Materials (Length-Dependent Uptake of DNA-Wrapped Single-Walled Carbon Nanotubes) by Matthew Becker and others, emphasizes that size (such as length and diameter of particles) matters particularly when deciphering toxicity studies. One source of size variation suggests the authors is dispersion of single-walled carbon nanotubes (SWNT) used in toxicity testing.

According to the article:

“Given a constant dosage, differences in dispersion ranging from macroscopic aggregates to micrometer-scale clusters bundles of multiple nanotubes or individually dispersed nanotubes will dramatically affect the absolute size and amount of nanotube surface area to which the cells will be exposed.”

Surfactants are materials used to increase water solubility and in some cases dispersion of a material, and are commonly used in studies of nanoparticle toxcity. Becker’s group used DNA as a surfactant, because they noted,

“These dispersions, in the case of DNA, are even stable enough to allow for the separation of the dispersed material into well-defined subpopulations of the SWNTs.”

Using this method to test the toxicity of SWNTs of varying length to muscle cells, the authors concluded that, “The assays determined an approximate uptake threshold of approximately (189+17) nm. Indicating that nanotubes shorter than this are consumed and likely induce more toxicity.”

Though they note that identifying an upper threshold for toxicity of nanoparticles is nothing earth-shattering or new, they do suggest that such behavior is likely to be a “general phenomenon,” though the actual size threshold is likely to vary depending on the type of cell.

For more information check out: Length-Dependent Uptake of DNA-Wrapped Single-Walled Carbon Nanotubes, by Becker et al, Vol 19:939-945.

No comments:

Subscribe to: Post Comments (Atom)

Some history: Toxicology as a formally recognized scientific discipline is relatively new (mid 1900’s) although the science itself is thousands of years old. Consider the potential results of early trial and error experiences of hunter-gatherers for whom identifying a toxic plant or animal was a life or death situation. Some of the most poisonous substances known today are naturally produced chemicals including Ricin from castor beans or tetrodotoxin from the puffer fish. Early humans’ careful observation of plants or animals with toxic characteristics such as frogs containing curare, were put to use not only for avoidance of toxic substances but for weapons as well. Additionally, many naturally derived poisons were likely used for hunting, medicinals (the Egyptians were aware of many toxic substances such as lead, opium and hemlock as early as 1500 BCE), and eventually for the political poisonings practiced, for example, by the early Greeks and Romans.

As humans sought to better understand natural compounds that were both beneficial and harmful, there was very little if any clear understanding of the fundamental chemical nature of substances. That is, there was no connection between the ‘extract’ or ‘essence’ of a poisonous plant or animal and any one particular chemical that might cause toxicity. In fact, an awareness of chemistry in its modern form did not occur until the mid to late 1600’s[i]. So it is ironic that Paracelsus, a physician from the sixteenth century and one of the early “Fathers of Toxicology” had no clear understanding of chemistry as we know it today. He along with many others at that time apparently believed that all matter was composed of three “primary bodies” (sulfur, salt, and mercury)[ii]. Yet Paracelsus also coined the now famous (or infamous) maxim of the newly emerging discipline of toxicology:

“All substances are poisons, there is none which is not a poison. The right dose differentiates a poison from a remedy.” (Paracelsus,1493-1541)

This phrase and Paracelsus’ name are committed to memory by hundreds of new toxicology students each year and has become the ‘motto’ of toxicology. Interestingly, if one takes Paracelsus at face value, it appears he was referring to potential remedies. This is an important point, since in recent years some have turned this around to suggest that exposure to very small doses of highly toxic chemicals (such as dioxins) might not be an problem! These days most of us are well aware of the fact that overdosing can turn remedies to poisons, even with apparently innocuous drugs such as aspirin and Tylenol.

[i] Ball, P. 1999. Life’s Matrix: A Biography of Water. Farrar, Straus and Giroux, NY, NY.

[ii] Ball, 2001.