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CHEMICAL TOXICOLOGY OVERVIEW
Dose-Response RelationshipsThe toxicity of a chemical is defined by the amount (dose) of the chemical that will produce a response. The
greater the dose, the more severe the response will be. Routes of Entry into the Body There are three main routes by which hazardous chemicals enter the body:
- Absorption through the respiratory tract via inhalation.
- Absorption through the skin via dermal or eye contact
- Absorption through the digestive tract via ingestion. (Ingestion can occur through eating or smoking with contaminated hands or in contaminated work areas.)
NOTE: Exposure via injection (such as by needle sticks or broken glass) is possible but not a very common route of exposure to
chemicals. Examples of substances where skin absorption may be a significant factor include: pesticides, carbon disulfide, carbon tetrachloride,
dioxane, methanol, acetonitrile, organo metallic compounds, thallium compounds, xylene and hydrogen cyanide.
Types of Effects
- Acute poisoning is characterized by sudden and severe exposure and rapid absorption of the substance. Example - Carbon monoxide poisoning
- Chronic poisoning is characterized by prolonged or repeated exposures of a duration measured in days, months or years. Example - Lead poisoning
- A local effect refers to an adverse health effect that takes place at the point or area of contact. Example - Strong acids or bases.
- A systemic effect refers to an adverse health effect that takes place at a location distant from the body's initial point of contact
.
Example - Benzene affects the bone marrow.
Cumulative poisons are characterized by materials that tend to build up in the body as a result of numerous chronic exposures. Example - heavy metals
Substances in combination: This is called a synergistic effect in which exposure to a substance can increase the toxic effect of another substance. Example - smoking and asbestos exposure
Other Factors Affecting Toxicity
- Rate of entry and route of exposure; that is, how fast is the toxic dose delivered and by what means.
- Age can effect the capacity to repair tissue damage.
- Previous exposure can lead to tolerance, increased sensitivity or make no difference.
- State of health, physical condition and life style can affect the toxic response.
- Pre-existing disease can result in increased sensitivity.
- Environmental factors such as temperature and pressure.
- Host factors including genetic predisposition and the sex of the exposed individual.
Physiological Classifications
Irritants are materials that cause inflammation, reddening and swelling of the eyes, skin, nose and respiratory system.
Examples include:
- Ammonia
- Alkaline dusts and mists
- Arsenic trichloride
- Diethyl/dimethyl sulfate
- Halogens
- Hydrogen chloride
- Hydrogen fluoride
- Nitrogen dioxide
- Ozone
- Phosgene
- Phosphorus chlorides
Irritants can also cause changes in the mechanics of respiration and lung function.
Examples include:
- Acetic acid
- Acrolein
- Formaldehyde
- Formic acid
- Iodine
- Sulfur dioxide
- Sulfuric acid
Long term exposure to irritants can result in increased mucous secretions and chronic bronchitis.Asphyxiants Simple
asphyxiants are gases that displace oxygen.This can result in loss of consciousness and death.
Examples include:
- Carbon dioxide
- Nitrogen
- Sulfur hexafluoride
Chemical asphyxiants reduce the body's ability to absorb, transport, or utilize inhaled oxygen. They are often active at very low
concentrations (a few ppm). This can result in loss of consciousness and death.
Primary Anesthetics Primary anesthetics have a depressant effect upon the
central nervous system, particularly the brain.
Hepatotoxic Agents Hepatotoxic agents cause damage to the liver.
Examples include:
- Carbon tetrachloride
- Nitrosamines
- Tetrachloroethane
Nephrotoxic AgentsNephrotoxic agents damage the kidneys.
Examples include:
- Halogenated hydrocarbons
- Uranium compounds
Neurotoxic Agents Neurotoxic agents damage the nervous system. The nervous system is especially sensitive to organometallic compounds and certain sulfide compounds.
Examples include:
- Carbon disulfide
- Methyl mercury
Other Agents of Concern Some toxic agents act on the blood or
the blood forming (hematopoietic) system. The blood cells can be affected directly or the bone marrow (which produces the blood cells) can be damaged.
There are toxic agents that produce damage of the pulmonary tissue (lungs) but not by immediate irritant action. Fibrotic changes (a reduction in the
elasticity of the lungs) can be caused by free silica and asbestos. Other dusts can cause a restrictive disease called pneumoconiosis.
Allergens and SensitizersAllergens and
sensitizers are chemicals that can cause an allergic reaction after repeated exposure to the chemical. The reaction may be as mild as a rash (allergic dermatitis) or as serious as anaphylactic shock. This is
an often severe and sometimes fatal reaction when a sensitivie individual is exposed to a material such as wasp venom or penicillin.
Examples include:
- Chromium compounds
- Epoxies
- Nickel compounds
- Isocyanates
Particularly Hazardous SubstancesThese include select carcinogens, reproductive
toxins, and substances with a high degree of acute toxicity. If you are required to work with one of these chemicals, be certain
that you are thoroughly familiar with the chemical's physical and health hazards. If you have any questions, contact your supervisor or an
EH&S Industrial Hygienis
t
to make certain that the appropriate controls are in place and that you are properly prepared to work with the chemical. Carcinogens These are agents that cause neoplasms
(tumors) in humans and/or animals. Select carcinogens are a special class of chemicals identified by OSHA that are strongly implicated as a cause of cancer in humans and include:
Lists of carcinogens are available at the web links listed above. Reproductive Toxins These are chemicals that affect the reproductive system of both men and
women. They can cause chromosomal damage (mutations) and produce effects on fetuses (teratogenesis).
A list of reproductive toxins is available at the
California Prop 65 Web Site.
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