Toxins | Research & Encyclopedia Articles

Toxins

A toxin is a substance that is harmful to living organisms. Toxic effects can be the result of exposure to toxins. Since World War II, the use of chemicals, especially synthetic ones, has increased tremendously in our society. Consequently, people have become concerned about the toxic effects of those chemicals, and the relatively new area of science known as toxicology was developed. Toxicologists study the harmful effects of chemicals on plants, animals, and humans.

It is a common misconception that natural chemicals are safe while synthetic (human-made) chemicals are not. The origins of chemicals do not determine their toxicity. Toxins include naturally occurring substances as well as hundreds of thousands of human-made substances. For example, heavy metals such as cadmium, lead, mercury, and nickel are naturally occurring. We encounter them in our everyday lives yet they are dangerous toxins. We eat foods that contain natural toxins. Aflotoxins occur naturally in peanut butter and cause severe reactions in some people. Potatoes, peppers and tomatoes contain a toxin called alkaloid solanine, which some people must avoid. Human-made toxic chemicals in our environment include pesticides such as DDT (dichlorodiphenyltrichloroethane) and PCBs (polychlorinated biphenyls) found in industrial wastes. Many plastics made from petroleum are toxins. The toxicity of a chemical depends on the dose and an individual's susceptibility. An individual's susceptibility varies depending on his or her genetic background, age, weight, gender, overall health, and previous exposure to the toxin.

The effects of toxins are classified according to three time-based categories: acute, subacute, and chronic. Acute effects are those that show up immediately. If the effects appear over weeks or months they are called subacute effects. Damage to organs such as lungs is often acute or subacute. Effects that appear gradually and last over extended periods (even a lifetime and possibly, but not always, leading to death) are called chronic effects. Examples of chronic effects include carcinogenesis (cancer), teratogenesis (birth defects), and mutagenesis (changes in genetic material).

Since the early 1970s, the United States government and all fifty states have passed hundreds of statutes designed to control toxins in our environment. Most environmental protection laws in the United States are enforced by the federal Environmental Protection Agency (EPA) and its state-level counterparts. Toxins found inside the workplace are regulated by the federal Occupational Safety and Health Administration (OSHA) and its state level counterparts. Administrative agencies have made thousands of regulations that help implement the statutes passed by legislators.

Before administrators can make regulations banning a chemical, limiting its use, or controlling its storage or disposal, they need information on which to base their decisions. Toxicologists provide such information by performing tests and compiling toxicity assessments based on the results of those tests. Most testing is done on animals. It is done using massive single doses to determine what is a lethal dose (a dose that kills) or using lower doses for long periods of time to determine effects other than death. Another type of testing is through epidemiology. In an epidemiological study, a group of human beings in the general population is studied over a long period in an attempt to discover links between exposure to a chemical and a specific effect such as cancer. Asbestos provides a good example of how a toxin is regulated. Asbestos is a naturally occurring substance that was used extensively as insulation up until the 1970s. As a result of animal tests and epidemiological studies, most scientists agree that inhalation of asbestos fibers causes asbestosis (a disease in the lining of the lungs) as well as lung cancer. Therefore, OSHA developed regulations limiting the number of asbestos fibers that can be in air breathed by workers. In addition, the federal EPA regulated the use of asbestos in buildings.

There are hundreds of thousands of synthetic chemicals in our environment, yet it is estimated that only about twenty percent have been thoroughly tested for toxic effects, and about a third have not been tested at all. Furthermore, even when toxicity testing is conducted, the results represent scientific estimates and do not provide clear answers. Whenever scientists use animal testing, they must make assumptions as to how humans would react to the same chemical. Epidemiological studies are limited in that scientists can only observe what happens to humans, as it is considered unethical to deliberately expose human beings to measured doses of specific chemicals in order to study the effects of those chemicals. Therefore, during the twenty-first century, federal regulators and the scientists who work with them face massive tasks as they try to identify toxins and make regulations designed to protect us from their harmful effects.