Toxicology (from the Greek words toxicon and logos) is the study of the adverse effects of chemicals on living organisms. It is the study of symptoms, mechanisms, treatments and detection of poisoning, especially the poisoning of people. The chief criterion regarding the toxicity of a chemical is the dose, i.e. the amount of exposure to the substance. Almost all substances are toxic under the right conditions. As Paracelsus, the father of modern toxicology said, “Sola dosis facit venenum” (only dose determines the poison). Paracelsus, who lived in the 16th century was the first person to explain the dose-response relationship of toxic substances.

Many substances regarded as poisons are toxic only indirectly. An example is "wood alcohol" or methanol, which is not poisonous itself, but is chemically converted to toxic formaldehyde and formic acid in the liver. Many drug molecules are made toxic in the liver, a good example being acetaminophen (paracetamol), especially in the presence of alcohol. The genetic variability of certain liver enzymes makes the toxicity of many compounds differ between one individual and the next. Because demands placed on one liver enzyme can induce activity in another, many molecules become toxic only in combination with others. A family of activities that engages many toxicologists includes identifying which liver enzymes convert a molecule into a poison, what are the toxic products of the conversion and under what conditions and in which individuals this conversion takes place.

The term LD50 refers to the dose of a toxic substance that kills 50 percent of a test population (typically rats or other surrogates when the test concerns human toxicity). LD50 estimations in animals became obsolete in 1991 and are no longer required for regulatory submissions as a part of pre-clinical development package.

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Human & Experimental Toxicology current issue

Hormesis, non-linearity, and risk communication
Calabrese, E. Fri, 01 May 2009 00:00:00 -0000

Risk communication and non-linearity
Ropeik, D Fri, 01 May 2009 00:00:00 -0000
This article will consider non-linearity and hormesis from the perspectives of risk perception and risk communication. The observations that follow do not come from a scientist or researcher. (For a richer academic treatment of the issue of risk communication and nonlinearity, see BELLE, Vol. 11, Issue 1, 2002). I was for 25 years a journalist on television and in print, focusing on coverage of environmental issues. I then studied and taught risk perception and risk communication at the Harvard School of Public Health. I now independently consult in these areas. From the academic side, I have read a fair amount of the literature that helps explain what I call ‘The Perception Gap,’ the gap between our fears and the facts. And as a journalist and consultant I have witnessed in the real world, people’s relatively greater fear of lesser risks, and relatively lower fear of the risks the scientific data suggest they ought to worry about more. I offer the following perspectives based on those foundations.
Risk communication in precautionary culture-the precautionary coalition
Hanekamp, J., Pieterman, R Fri, 01 May 2009 00:00:00 -0000


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