Understanding Toxicology
 The Dose Makes the Poison
An AO Primer
By Dr. Alice Ottoboni
Toxicologist, California State Department of Public Health (retired)
Edited by Sandra Blakeslee
Science Reporter, The New York Times
Toxicology is the science that studies the harmful effects of chemicals. Compared to its parent discipline of pharmacology – the science that emphasizes the medicinal effect of chemicals – toxicology is a young science that is exerting a growing influence on public policy and decision making.
Everything in our physical world is chemical. All matter is composed of chemical elements, 90 of which are stable and hence commonly found in nature. An individual unit of an element is called an atom. Atoms are the basic building blocks for all substances. When two or more atoms combine chemically, they form units called molecules (molecules are usually composed of atoms of different kinds of elements). Since the 90 elements can be combined ad infinitum, the kinds of molecules that can be formed are almost limitless. A substance composed of all the same kind of molecules is called a compound. A substance composed of atoms and molecules of different kinds is called a mixture. Almost all of the chemicals that we come into contact with in our daily lives are mixtures – that is, substances made up of combinations of different kinds of atoms and molecules.
All chemicals fall into one of two major categories: natural (made by natural processes) and synthetic (made by man). A great many chemicals fall into both groups; they are found in nature and they can be synthesized in the laboratory. However, some natural chemicals still defy man’s ingenuity at synthesis, and there are some synthetic chemicals that are not produced by any natural process.
Many people believe that while some chemicals may be good or bad for you, natural chemicals are “good” and man-made chemicals are “bad.” The fact is that a living organism cannot distinguish chemicals by their origin, be they from nature or the laboratory. It can only distinguish between chemicals it can use to make more of itself and chemicals it cannot use. The former are called biochemicals and the latter are called foreign (xenobiotic) chemicals. A biochemical for one organism may be a foreign chemical for another and vice versa. For example, strychnine is a biochemical for the nux vomica plant. But it is a foreign chemical for people – and a very deadly one at that.
Biochemicals may be natural or synthetic and foreign chemicals may be natural or synthetic. The laws and principles of toxicology and pharmacology apply equally to all chemicals whether they be natural or synthetic, biochemical or foreign. In other words, from the organism's point of view neither goodness nor badness has anything to do with chemical origins.
Poisonous vs. therapeutic chemicals
For purposes of regulation, chemicals are categorized by use. Foods are regulated by food laws, drugs by drug laws, cosmetics by cosmetics laws, etc. The category most feared by the public is pesticides. This is probably because pesticides are used to kill things (insects, rodents, weeds, etc.) and because of the tremendous amount of media attention given to their use and – in tragic instances – misuse. The public, however, often views all pesticides as being toxic chemicals. The fact is that many pesticides are no more toxic than many non-pesticide chemicals that we encounter in our daily lives.
For example, a number of chemicals used as pesticides are also used for other purposes, such as drugs or industrial chemicals. The laws that apply in the regulation of a chemical depend upon the use to which the chemical is put, and not upon its toxicity. For example, boric acid is regulated as a drug when used as an antiseptic eye wash, as a household product when used in laundry detergents, as an insecticide when used to kill roaches, as an herbicide when used to kill weeds and as a flame retardant when used to fireproof fabrics. The toxicity of a chemical is independent of the category in which it is placed.
Chemicals may harm us in a number of different ways. They may injure us as a result of their explosive properties. They may cause thermal burns as a result of their flammability. They may destroy tissue by virtue of their corrosiveness, or they may injure tissue because of their irritant properties. Some chemicals cause sensitization (allergic) reactions, and others may harm us because of their toxic properties. Some chemicals possess only one harmful property and others two or more.
The word “hazard” is commonly misused to mean “toxicity.” Hazard is much more complex, referring to the chance that something (in this case, a chemical) will be harmful. Chemical hazard has two components: one, the chemical can inherently do harm, and two, the chemical and the object of concern can all too easily come into contact with each other. No chemical is so toxic that it cannot be used without presenting a hazard, even if it means extremes of personal protection.
The toxicity of a chemical refers to its ability to do systemic damage – namely, damage somewhere else in the body at a site removed from the site of contact. For example, a chemical can damage the kidneys after being absorbed through the lungs or damage the liver as a result of being eaten. The toxicity of chemicals is the subject of this study guide.
Next Page >
Be the first to comment on Understanding Toxicology
|
