Toxicology is both the scientific study and direct application of principles regarding xenobiotics (foreign chemicals). Earth is a chemical environment exposing humans to various harmful substances through ingestion, inhalation, and contact. Toxins are naturally occurring substances, whereas toxicants are human-produced substances. Both have the potential to cause death or disease.
Chemicals may be classified according to target organ (central nervous system, liver, etc), use (solvent, herbicide, etc.), source (animal, metal, etc), or effects (cancer, birth defects, etc). Chemicals might be classified by their physical state (gas, particulate, etc), their chemical makeup, labeling requirements, potential for poisoning, or the biochemistry within life-forms.
In addition to defining and identifying possible poisons or the exposure point of drugs, pesticides, chemical weapons, synthetic fibers, and industrial chemicals, toxicologists study toxic effects at the cellular, biochemical, and molecular levels and determine the probability of the toxic effect as well as safe versus toxic levels in animals, plants, and the environment.
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.
Within the science of toxicology are many distinct specialties and disciplines that utilize detection, identification, scientific inquiry, assessment, and measurement of the presence and adverse effects of xenobiotics or foreign substances on living organisms—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.
Analytical toxicology detects, identifies, and measures chemicals through testing for safety, clinical manifestations of deleterious effects from chemicals, and a chemical’s toxicity to fish, birds, plants, and the effect on an ecosystem. From the social standpoint, the work of analytical toxicologists is used to test for alcohol and drugs to determine driving under influence and to analyze urine samples for drugs and their metabolites for legal liability issues.
Mechanistic toxicology involves chemical action within living organisms from exposure to a foreign substance through biotransformation, elimination, and the effects and health outcomes. Observation in laboratory animals can be extrapolated to human potential toxicity. The difference between efficacy and the point where toxicity and adverse reaction occurs is evaluated to determine relative safety of a chemical.
Clinical toxicology applies analytical and mechanistic principles to determine cause of disease in living subjects with focus on emergency, palliative care, and treatment of poisoned patients. Within this biomedical arena is a subspecialty of pharmaceutical development and testing to determine safe and therapeutic levels of medication.
Forensic toxicology uses analytical and standard toxicology principles to determine cause of death or the harmful effects of exposure to hazardous substances. Tests run from sample tissues check for a standard array of possible toxins to determine cause of death or possible poison as cause of disease.
Environmental toxicology focuses on xenobiotic effect on the environment and ecosystems from impact from chemical pollution and the disposal of chemical and hazardous waste.
Regulatory toxicology as a science uses data collected from other fields of toxicology and outside sources to determine policy on approval or restriction of chemicals, pharmaceuticals, pesticides, and the cleanup of contaminated sites. They are responsible for determining appropriate action to protect the public from hazardous substances and to inform the public of health threats.
In the United States, Poison Control Centers respond to questions regarding poisons 24 hours a day, provide information in the event of accidental poisoning, and refer persons for emergency care or proper medical treatment as needed.
The National Toxicology Program was established in 1978 and is under the auspices of the Department of Health and Human Services. The impetus for the creation of the program was the belief that many human diseases were caused by direct or indirect chemical exposure. Made up of the National Institute for Environmental Health of the National Institutes of Health, the National Institute for Occupational Safety and Health of the Centers for Disease Control and Prevention, and the National Center for Toxicological Research of the Food and Drug Administration, the program coordinates federal toxicology programs and provide information to the public, regulatory agencies, and the scientific and medical communities.
The Agency for Toxic Substances and Disease Registry serves as an information resource and participates in policy development relating to toxic substances in the environment. The International Programme of Chemical Safety of the World Health Organization, publishes Toxicology and Poisoning information, including basic analytical techniques to identify the most common poisoning substances.
As a global issue, developing countries need improved access to toxicology education, poison control centers equipped to provide information and care with respect to regional variations in types of poisoning.
Agency for Toxic Substances and Disease Registry (ATSDR); Asbestos/Asbestosis; Drug Industry; Environmental Protection Agency (EPA); Environmental Toxicology; Pesticides; Pharmacology; Poisoning.
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