Scientists at Switzerland’s ETH Zurich (Swiss Federal Institute of Technology Zurich) note that cerium oxide nanoparticles do not degrade. From the May 21, 2012 article by Simone Ulmer on the ETH Zurich website,

Tiny particles of cerium oxide do not burn or change in the heat of a waste incineration plant. They remain intact on combustion residues or in the incineration system, as a new study by researchers from ETH Zurich reveals.

Over 100 million tons of waste are incinerated worldwide every year. Due to the increasing use of nanoparticles in construction materials, paints, textiles and cosmetics, for instance, nanoparticles also find their way into incineration plants. What happens to them there, however, had not been investigated until now. Three ETH-Zurich teams from fields of chemistry and environmental engineering thus set about finding out what happens to synthetic nano-cerium oxide during the incineration of refuse in a waste incineration plant. Cerium oxide itself is a non-toxic ceramic material, not biologically degradable and a common basic component in automobile catalytic converters and diesel soot filters.

Here’s their reasoning (from Ulmer’s article),

Experts fear that non-degradable nanomaterials might be just as harmful for humans and the environment as asbestos. As yet, however, not enough is known about the properties of nanomaterials (see ETH Life, 25 March 2010). One thing is for sure: they differ greatly from larger particles of the same material. Nanoparticles are more mobile and have a different surface structure. Knowledge of these properties is important with the increasing use of nanomaterials as, as they are transferred through incineration plants or sewage, and as they are absorbed by people in food (see ETH Life, 15 July 2008) and perhaps even through the skin and respiration, and can thus enter the body. [emphases mine]

Recent research suggests that there are many, many naturally occurring nanoparticles which we and other living beings have been innocently ingesting for millenia as noted in my Feb. 9, 2012 posting and my Nov. 24, 2011 posting. More recently, Dr. Andrew Maynard at his 2020 Science blog posted about carbon nanoparticles, which are  ubiquitous. From Andrew’s May 19, 2012 posting,

This latest paper was published in the journal Science Progress a few weeks ago, and analyzes the carbon nanoparticle content of such everyday foods as bread, caramelized sugar, corn flakes and biscuits.  The authors found that products containing caramelized sugar – including baked goods such as bread – contained spherical carbon nanoparticles in the range 4 – 30 nm (with size being associated with the temperature of caramelization).

Getting back to the cerium oxide project, here’s what the Swiss scientists found (from Ulmer’s article),

The researchers’ tests revealed that cerium oxide does not change significantly during incineration. The fly-ash separation devices proved extremely efficient: the scientists did not find any leaked cerium oxide nanoparticles in the waste incineration plant’s clean gas. That said, the nanoparticles remained loosely bound to the combustion residues in the plant and partially in the incineration system, too. The fly ash separated from the flue gas also contained cerium oxide nanoparticles.

Nowadays, combustion residues – and thus the nanoparticles bound to them – end up on landfills or are reprocessed to extract copper or aluminium, for instance. The researchers see a need for action here. “We have to make sure that new nanoparticles don’t get into the water and food cycle via landfills or released into the atmosphere through further processing measures,” says Wendelin Stark, head of the study and a professor of chemical engineering at ETH Zurich. Moreover, the fact that nanoparticles that could be inhaled if inadequate protection is worn might be present in the incineration system needs to be taken into consideration during maintenance work.

I have a couple questions for the researchers. First, is nanoscale cerium dioxide dangerous and do you have any studies?  Second, does anything ever degrade? As I recall (dimly), matter cannot be destroyed. Are they trying to break down the nanoscale cerium oxide to a smaller scale? And, what would the impact be then?

All in all, this is very interesting research to me as it has raised some questions in a way I had not previously considered. Thanks to Nanowerk where I found the May 24, 2012 news item that alerted me to the article.