How are studies on environmental effects of chemicals conducted?

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Offline krool1969

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In a Naked Science Podcast a man was interviewed who worked on the effects of estrogen in fish. This is a world wide problem so I'm not sure it matters what species of fish he used, but Id does matter how the fish are exposed. Is he using real treated sewage or is he adding the chemicals directly.
I know in the 70's they were testing food additives in animals exposing them to thousands of times normal rates. Some of the animals developed cancer which lead to laws (at least in the States) requiring labels warning of the link. However the levels of food required to reach cancer thresholds would be so high as to lead to other health problems long before you got cancer.
A little later California passed a law requiring signs on buildings accessed by the public warning of chemicals that MAY cause cancer or birth defects. This was a boon to sign makers but not very helpful to the public. Now EVERY building has such a sign. No information is provided telling you about how much real risk you are exposed to, just that their MAY be some level of risk.
Things like this lead me to wonder how real these threats really are. Possibly also why so many people don't believe in global warming. "Wolf" has been cried far too many times.
« Last Edit: 04/12/2012 22:32:05 by chris »


Offline evan_au

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Traditionally, safety tests were conducted on lab animals such as mice. A critical measure of the toxicity is the LD50: the concentration of a substance which will kill 50% of the test animals. This can be extrapolated from a mouse to a human by expressing it as a dose as milligrams per kilogram of body mass.

Animal rights groups insist that these tests incur unnecessary suffering on the test animals with little benefit, so recently there has been a search for alternative ways to test for toxic effects.

One such test for cancer-causing chemicals is the Ames Test, which uses bacteria as the test subjects:

Due to genetic differences between species, a test on a chimpanzee is likely to be more applicable to humans than a test on mice or bacteria (but a lot more expensive, take a lot longer, and be considered more "inhumane"). But in the end, a new pharmaceutical must be tested on humans.

Some research groups use cultures of different human cells "in vitro" to search for side-effects from a new chemical, before tests on live humans.

But even amongst humans, genetic differences between individuals can mean that:
  • One person's liver breaks down the substance 10x slower than average, resulting in rapid buildup in the bloodstream to potentially lethal levels when given the standard dosage.
  • On the other hand, another person may break it down 10x faster than average, resulting in no therapeutic effect at the normal dosage.
  • Interactions between different substances are hard to evaluate, because the number of possible interactions grows rapidly with the number of chemicals considered.
  • Even natural substances like grapefruit juice can disable part of the digestive system, resulting in 3x the dose of a substance making it into the bloodstream. This affects many common pharmaceuticals.
  • Whenever something is being absorbed faster than your body can dispose of it, the substance will rapidly reach dangerous concentrations.
« Last Edit: 24/12/2012 09:18:10 by evan_au »