Edouard Bastarache on wed 15 aug 01
Hello Matt,
Thank you for that information. I do appreciate your informative posts.
"Welcome"
It did seem surprising to me that silica was considered by the IARC as =
MORE
hazardous than mineral fibers. It appears there is still some =
disagreement
over the danger of these materials. The literature seems to run over a
fairly wide spectrum.
"Right, it seems to vary in time and space"
Perhaps risk assessment is like parenting... One can find books that
advise we never spank our children, while other books suggest that it is =
OK.
We can usually find an author who supports our initial predisposition.
"Good exemple but, I do not have kids.
-Great minds think alike and fools seldom differ-(Hehehe, Artimater's
influence)"
Yet we must all review the literature, make a rationale decision for
ourselves, and get on with our lives.
"Good thinking"
I am curious to find out how you regard these sorts of risks, in =
relation
to our everyday life. You seem very informed about hazardous materials.
You
seem interested in pottery. I am curious how you draw the line for
yourself when deciding what you will expose yourself to and how the risk
from such
exposure fits into the scope of the risks we all take every day. We =
drive
cars and fly in airplanes. We inoculate our children with new vaccines.
We get blood transfusions. We eat smoked sausage. We work on our tan =
in
the
summer. We are all going to die. Many of us will die from cancer. =
Maybe
in some real way, we must pick our poisons.
How do you make any sense of the risks we take each day?
"The good thing to do is to have access to decent information
and use "plain common sense" when it comes to evaluate your
personal exposure to any of the chemicals in a glaze lab or
elsewhere.
Considering ceramics raw materials since Clayart is for potters,
this may vary greatly depending on many factors such as your
status as a potter.
Are you a pottery factory worker, an arts teacher, a full-time
potter, a part-time one or only a dabbler like me( for 33 years now)?
It certainly depends on the intrinsic toxicological properties of each
material.
It may also depends on the state in which chemicals are, for instance.
wet glazes cannot be inhaled if you do not spray them. Particle size
distribution also very important. No one on this list is able to inhale
boulders, etc.
Everything boils down to your level of exposure and toxicological
properties of the different ceramics chemicals, to make things short.
As for crystalline silica, since it was much discussed recently:
The crystalline silica, alpha quartz, is the major cause of silicosis
worldwide.
Although the silica polymorphs, cristobalite and tridymite, prove more =
toxic
for cells and are highly fibrogenic under experimental conditions, these =
two
mineralogic variants are of more limited health variance.
Quartz particles in the occupational setting range widely in size, but =
those
less than 1 micron are believed to be the most pathogenic.
Since large particles impact and sediment in the nares and the major
airways, only relatively small particles enter the acini(lungs).
As a general rule, the smaller the diameter of particles, the more =
efficient
is the pulmonary clearance by the bronchi and acini.
The bronchial and alveolar retention of particles is the result of two
opposing factors, sedimentation and clearance. Retention of dust will be =
at
its peak,
depending on nature of dust, for the particles whose diameter ranges =
from
0.5 to 3 microns
The size of silica particles retained in the human lung is remarkably
constant, with median diameters ranging from 0.5 to 0.7 micron."
Permit one more question, if you don't mind. I have heard, as I =
mentioned
in another post, that the shape and size of mineral fiber particles as
important as their chemical composition. My old geology professor said
that some types of asbestos are much more dangerous than others, owing =
to
their
physical characteristics. She suggested to me that it was likely that
certain types of mineral fibers might be just as dangerous as asbestos =
for
this reason. Have you seem any information that implicates physical
characteristics so clearly?
1-"Indeed asbestos fiber morphology is important. In the case of =
asbestos-
related cancers, fiber characteristics, including durability, harshness,
surface chemistry, and dimensions appear to play a role in the
carcinogenic process.
Our experience with man-made fibers is relatively short, time-wise,
as compared to asbestos fibers and we already have data suggesting
somewhat similar toxicological properties, more especially with the
use of ceramic fibers."
2-"Here are Quebec's standards for asbestos fibers:
A-For actinolite, tremolite, antophyllite and chrysotile:
-1 fiber/cc (8 hours)
- 5 fibers/cc (15 minutes).
B-Amosite, crocidolite:
- 0.2 fiber/cc (8 hours)
-1.0 fiber/cc (15 minutes).
As you can see some asbestos fibers are intrinsically far more toxic =
than
others."
3-"A fiber may be defined as a lenghty particle whose lenght/diameter
ratio is equal or larger than 3. In order to reach the lung alveolar =
region
in man, a fiber must have an aerodynamic diameter of less than 10 =B5m.
When conducting occupational exposure studies to man-made fibers,
only fibers considered toxic to workers due to their granulometric
properties, are considered:
1-Lenght greater than 5 =B5m
2-Diameter less than 3 =B5m
3-Lenght/diameter ratio >3
Results are expressed as "number of fibers/millimeter of air"
A cumulative exposure index can also be computed like the one
for cigarette smoke exposure."
Hope this helps,
Edouard Bastarache
Irreductible Quebecois
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://www.absolutearts.com/portfolios/e/edouardb/
Matt MacIntire on thu 16 aug 01
Edouard,
I thank you for your very informative post.
When I was speaking with that Geology professor some years ago, the full
impact of what she was saying did not register fully. Your excellent
explanation filled in many gaps in my understanding of how and why the
mineral fibers are hazardous. I did not realize for example, that with
regards to asbestos fibers, the dangerous concentrations were so low.
Fortunately I don't work with asbestos, but it is instructive to make some
sort of interpolation with regard to levels of synthetic mineral fibers.
I especially appreciate learning that your basic approach is so rational.
You seem to have a perspective that acknowledges the risks, but takes into
account our need to actually work with some of these materials from time to
time. Acquire a basic understanding of the risks, and implement common
sense precautions. That seems like a prudent compromise.
Thanks again for your helpful explanations. It is great to have your voice
in with the rest of the crowd.
Matt
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