Toxicology

Exposure to Harmful Substances

The potential for toxicity and adverse effects from chemicals introduced into a human or living organism depends on the route and site of exposure, the duration and frequency of exposure, and other chemical interactions (intentional or unintentional) introduced by other chemicals or the breakdown of the chemical into metabolites. Considerations of exposure include:

• Route and Site—chemicals enter the body by ingestion, inhalation, and direct contact. Direct injection into the bloodstream causes the highest and most immediate toxic effect. Localized or systemic effects depend on the chemical and biochemical transformation to more toxic products or reaching target organs.
• Duration and Frequency—the chemical stays in a poisonous state or is transformed to a toxin within a living system. Acute exposure is a single occurrence, exposure, or multiple exposures within 24 to 48 hours often occur within a work setting. Chronic exposures occur over a longer period of time and are often environmental. Delayed toxicity might not be noticed at the time of exposure and the effects occur in the future.
• Chemical interactions—a single chemical may not cause a toxic reaction, but when combined with other chemicals, it produces toxicity. When two or more chemicals combine, the additive effect means individual toxicities create a sum of all effects and the synergistic effect means the chemicals create a greater effect than either one individually or added together.

Antagonistic effects or chemical inactivation are the basis for antidotes. The antagonist effect means one chemical is used to counterbalance another by interfering with the other's chemical action. A functional antagonist effect means one chemical produces opposite effects on the same physiologic function. A chemical antagonist inactivates the first chemical through biotransformation distribution and excretion to alter the concentration or duration of time in the system.

Three potential paths of toxicity post exposure to a chemical, include causing immediate damage at the site of exposure, cellular dysfunction and injury once the chemical interacts with target the response or exceeding the system's ability to fight off or repair damage caused by the chemical.

Areas of Specialty

Within the science of toxicology are many distinct specialties and disciplines that utilize detection, identification, scientific inquiry, assessment, and [Page 1674]measurement of the presence and adverse effects of xenobiotics or foreign substances on living organ-isms—humans, animals, plants, and the environment. Toxicologists determine acceptable exposure levels and therapeutic application of potentially poisonous substances and study the effects of pollution and contamination of air, water, and soil.

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