**Q. Shouldn't natural bodily mitigation of substances be allowed for in the definition of toxicity? (i.e. urination of excess water) A. We'll spend a lot of time on that concept - the body's natural defenses. When a whole animal is tested, those natural defenses are integrated into the results.

** Q. What types of toxicity testing are performed on humans and why?
A. None, anymore. 50 years ago toxic effects were sometimes tested in volunteer prisoners, but this is now against the law. Drugs are tested for their beneficial effects in humans and toxic effects carefully noted, but it is considered unethical to test toxicity, as such, in humans. At least at levels where toxic effects are expected.

** Questions: Is my interpretation correct: i.e., Can LD50 be defined according to different scales (e.g., 96 hours, 14 days, etc.)? If so, how are different LD50's related to each other? Are they defined in terms of acute toxicity vs. 14 day lethality, etc.? And what would cause one to test in a time frame departing from the standard set by the CPSA?
A. It's easy for a scientist or engineer to make fun of the government. We are trying to find a truth about nature or design something, while they are trying to make a "bright line," i.e., an absolutely clear determination of what is legal and what is illegal. I'm guessing the 14 days was some sort of compromise long ago. It may, I'm guessing, give the animals a chance to die, but not enough time to build up defenses. But the variation of effects over time might be different for each and every of the 30,000 common chemicals or 2 million utilized chemicals, of which we have tested less than 500 in any detail. 96-hours is the standard for acute testing. Chronic testing usually lasts a lifetime, about two years for most lab animals. There are no rules, that I know about, that would let you compare a 96-hour test, with a 14 day test, with a 60 day test. They might all be very different.

* Q. What other means, besides radiation bombardment, lead to the creation of free radicals?
A. Many, both biological and chemical. Our bodies make a free radical, O2(dot)- (aka, superoxide anion) constantly, but they are in turn used in other processes, and if they get loose, there are enzymes to neutralize them. We will revisit radicals later.

* Q. How does an overabundance of water rupture the cell membrane?
A. The cell membrane of higher animals and plants passes water freely, but does not pass salt ions, except through channels. If you take such a cell out of the bod and place it in pure water, it will swell and burst because of osmotic pressure.