***Q. For the SCEM a view in the future is required. Which time fame makes
sense, is possible or common, related to contaminant transport and accumulation
in organisms?
A. Good question. I am currently working with a risk assessment for an underground
nuclear test site that should consider the next 10,000 years. The scope of the
risk assessment is a risk management decision. Many contaminants fade with time
(natural attenuation) so there is a time in the not too distant future where
they will not be a problem and that defines a logical time to end the assessment.
***Q. I'm not sure I understand the difference between Exposure Assessment
vs. Risk Assessment as described in the RAIS tutorial. It seems like both assessments
analyze the same types of hazards.
A. That's not the best part of RAIS. The Risk Assessment is summed up in the
Risk Characterization. That Risk Characterization is based on two things, a
Dose-response Evaluation and an Exposure Assessment. See
http://www.faculty.uaf.edu/ffrap/ENVE_651/Module01/1B_Risk_and_Safety/RiskandSafety3.html
***Q. Do risk assessment professionals always or generally always perform a
CSM? Is this standard practice or is it really established for public presentations
etc
after the fact?
A. You must do one, at least on the back of an envelope, to define the situation.
Sometimes, especially for emergency situations, there is a release, transport
path and receptor that are obvious and must be addressed first.
**Q. The Tox Tutor identified lifestyle choices as the primary cause of cancers.
I have always been taught that while the lifestyle choices most certainly will
affect the occurrence of cancer, it cannot occur without a genetic predisposition.
This was touched on briefly, but never really stated in the tutor. Do you believe
that the two are mutually exclusive?
A. Not exclusive. But lets clarify terms. At conception, a conceptus starts
with a genome from its parents. That could be called the "heredity"
of the conceptus. Cancer involves a change to a cell's "genome." If
you assume that it takes 8 mutations to cause cancer, the conceptus might "start
out" with two of them by heredity, then it would be that much easier for
cancer to occur. Some of the 8 mutations could be caused by lifestyle and some
by workplace exposures, and some by radiation, none are exclusive. There are
some forms of cancer that almost completely hereditary. These are very rare
cancers, but have been heavily studied to try to understand the genetic process
of cancer.
**Q. Why is Oak Ridge considered the "background" levels for so many
sights? When we accept these numbers are we saying that background levels in
fertile organic soil in Tennessee is the same as in Phoenix Arizona?
A. I think that is just a DoE system. But it is hard to find a true background.
You need to find a nearby site that is similar in every way, except for the
contamination, but this never really possible. It can be informative, though,
for example in Nome, there are very high levels of arsenic in the soil in many
places. It's hard to label a site "contaminated" if you cannot find
an uncontaminated site nearby.
Q. "Some epithelia are relatively impermeable; others are readily crossed.
This epithelial barrier can be damaged in response to various toxins".
This statement was directly taken from the Tox Tutor. Of the classified epithelial
tissue, which of the tissue is the least penetrable? Is there an index of permeability
for certain epithelia in relationship to others? I am speculating that if one
truly wanted a detailed account of exposure to an organ, the permeabilities
of all the epithelia that a chemical would have to cross could be of concern.
A. Since epithelial tissue lines everything, a chemical molecule must cross
many epithelial barriers to get to a target tissue. Two examples where damage
is important are skin and the glomeroulus of the nephron. It is seldom practical
to measure tissue transport that way, although I have tried. Usually the absorption
is determined by measuring the mass in the target organ or assumed by measuring
the blood concentration there.
Q. At http://www.nsc.org/library/chemical/Pentachl.htm is mentioned: PCP (not
the drug). What drug is it?
A. It is a "recreational drug," actually it is tranquilizer used for
livestock, pigs primarily, and it is dangerous.