Q. You discussed the FDA and their allowable risk. You went on to mention that carcinogens are not allowed in food. What about when you read a label and it says, "this product contains saccharin which has been linked to cancer in laboratory animals" or something to that effect?
A. This was a special law. Into the 1970's saccharin was the only artificial sweetener and was in very common use. When it was discovered that it caused cancer in rats, it would have been banned under the Delaney Clause in the Food and Drug Act. But the saccharin users threatened to riot and congress made a special exception for saccharin, and that is the verbiage you noted. However about that same time new sweeteners came onto the market, so saccharin lost market share. Aspartame, the sweetener in heaviest use, breaks down into methanol and phenylalanine in the liver. Methanol is very toxic to everyone; phenylalanine is very toxic to a few people. But they are not carcinogens. Drink up. (There is so little methanol produced it is really not an issue.)

Q. I would suggest that you make a distinction between 2 different types of guidances. There is guidance that is referenced in regulation, such as the Risk Assessment Procedures Manual, that has the weight of law due to the reference.
A. Good point. Regulations often reference test procedures and these are indeed incorporated in the regulations by reference. What happens if the test procedure changes after the regulation has been promulgated? The case you cited is not too common, citing a manual, but as you noted, it can happen.

Q. Then there is guidance that is not referenced by regulation and it therefore only policy, such as the Voluntary Cleanup Program. This guidance can be changed by the department at will and also is much more flexible in its implementation. The downside is that if the guidance were contested in a court, the department wouldn't have the backup of having it be law if it were trying to enforce the measures.
A. Yup.