***Q. There are people who want "zero tolerance" for contaminants in food, but don't discuss the fact that this is a global problem and even if Alaska became toxic free (I would applaud that), there are many factors that would enable toxics to enter the Alaskan environment. Water and air currents from other countries (Russia, China, etc.) bring these contaminants. If risk assessment is not the answer, then what is the solution?
A. Risk assessment just answers (or tries to) the question, "How dangerous is it?" It is very different from Risk management, which answers the question, "What are we going to do about it." At first risk management always answers that question by saying, "Right now, nothing." Then goes on from there, "When we get the money (or time, etc.) we propose to do this and/or that."

***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.