is the study of the nature and action of poisons.
is the ability of a chemical substance or compound to produce injury once it reaches a susceptible site in, or on, the body.
A material's hazard potential is the probability that injury will occur after consideration of the conditions under which the substance is used.
The potential toxicity (harmful action) inherent in a substance is exhibited only when that substance comes in contact with a living biological system. The potential toxic effect increases as the exposure increases. All chemicals will exhibit a toxic effect given a large enough dose. The toxic potency of a chemical is thus ultimately defined by the dose (the amount) of the chemical that will produce a specific response in a specific biological system.
There are three main routes by which hazardous chemicals enter the body:
Most exposure standards, such as the Threshold Limit Values (TLV's) and Permissible Exposure Limits (PEL's), are based in the inhalation route of exposure. These limits are normally expressed in terms of either parts per million (ppm) or milligrams per cubic meter (mg/m3) concentration in air. If a significant route of exposure for a substance is through skin contact, the MSDS, PEL, and/or TLV will have a "skin" notation. Examples of substances where skin absorption may be a significant factor include: pesticides, carbon disulfide, carbon tetrachloride, dioxane, mercury, thallium compounds, xylene and hydrogen cyanide.
Gas applies to a substance which is in the gaseous state at room temperature and pressure.
A Vapor is the gaseous phase of a material which is ordinarily a solid or a liquid at room temperature and pressure.
When considering the toxicity of gases and vapors, the solubility of the substance is a key factor. Highly soluble materials, like ammonia irritate the upper respiratory tract. On the other hand, relatively insoluble materials, like nitrogen dioxide, penetrate deep into the lung. Fat-soluble materials, like pesticides, tend to have longer residence times in the body and be cumulative poisons.
An aerosol is composed of microscopic solid or liquid particles dispersed in a gaseous medium.
The toxic potential of an aerosol is only partially described by its airborne concentration. For a proper assessment of the toxic hazard, the size of the aerosol's particles must be determined. A particle's size will determine if a particle will be deposited within the respiratory system and the location of deposition. Particles above 10 micrometers tend to deposit in the nose and other areas of the upper respiratory tract. Below 10 micrometers particles enter and are deposited in the lung. Very small particles (<0.2 micrometers) are generally not deposited but exhaled.
Irritants are materials that cause inflammation of mucous membranes with which they come in contact. Inflammation of tissue results from exposure to concentrations far below those needed to cause corrosion. Examples include:
Irritants can cause changes in the mechanics of respiration and lung function. Examples include:
Long term exposure to irritants can result in increased mucous secretions and chronic bronchitis.
A primary irritant exerts no systemic toxic action either because the products formed on the tissue of the respiratory tract are non-toxic or because the irritant action is far in excess of any systemic toxic action. Example:
A secondary irritant's effect on mucous membranes is overshadowed by a systemic effect resulting from absorption. Examples include:
Asphyxiants have the ability to deprive tissue of oxygen. Simple asphyxiants are inert gases that displace oxygen. Examples include:
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). Examples include:
Primary anesthetics have a depressant effect upon the central nervous system, particularly the brain. Examples include:
Hepatotoxic agents cause damage to the liver. Examples include:
Nephrotoxic agents damage the kidneys. Examples include:
Neurotoxic agents damage the nervous system. The nervous system is especially sensitive to organometallic compounds and certain sulfide compounds. Examples include:
Some toxic agents act on the blood or hematopoietic system. The blood cells can be affected directly or the bone marrow (which produces the blood cells) can be damaged. Examples include:
There are toxic agents that produce damage of the pulmonary tissue (lungs) but not by immediate irritant action. Fibrotic changes can be caused by free silica and asbestos. Other dusts can cause a restrictive disease called pneumoconiosis. Examples include:
A carcinogen is an agent that can initiate or increase the proliferation of malignant neoplastic cells or the development of malignant or potentially malignant tumors. Known human carcinogens include:
A mutagen interferes with the proper replication of genetic material (chromosome strands) in exposed cells. If germ cells are involved, the effect may be inherited and become part of the genetic pool passed onto future generations.
A sensitizer is a chemical which can cause an allergic reaction in normal tissue after repeated exposure to the chemical. The reaction may be as mild as a rash (allergic dermatitis) or as serious as anaphylactic shock. Examples include:
The following is a categorization of target organ effects, which may occur from chemical exposure. Signs and symptoms of these effects and examples of chemicals, which have been found to cause such effects, are listed.
|Toxins||Target Organs||Signs and Symptoms||Example Chemicals|
|Hepatotoxins||Liver||Jaundice, Liver Enlargement||Nitrosamines, Chloroform, Toluene, Perchloroethylene, Cresol, Dimethyl Sulfate|
|Nephrotoxins||Kidneys||Edema, Proteinuria||Halogenated Hydrocarbons, Uranium, Chloroform, Mercury, Dimethyl Sulfate|
|Neurotoxins||Nervous System||Narcosis, Behavior Changes, Decreased Muscle Coordination||Mercury, Carbon Disulfide, Benzene, Carbon Tetra-chloride, Lead, Nitrobenzene|
|Hematopoietic Toxins||Blood and Blood Forming Tissues||Cyanosis, Loss of Consciousness||Carbon Monoxide, Cyanides, Nitrobenzene, Arsenic, Benzene, Toluene|
|Pulmonary Toxins||Irritate or Damage the Lungs||Cough, Chest Tightness, Shortness of Breath, Cancer||Silica, Asbestos, Ozone, Hydrogen sulfide, Chromium, Nickel, Alcohols|
|Reproductive toxins||Reproductive Organs||Birth Defects, Decreased Fertility||Lead, Dibromodichloropropane|
|Skin Hazards||Dermal Layer||Defatting of Skin, Rashes, Irritation||Ketones, Phenol, Chlorinated Hydrocarbons, Alcohols, Nickel, Trichloroethylene|
|Eye Hazards||Eyes or Optic Nerve||Conjunctivitis, Corneal Damage||Acids, Bases, Cresol, Butyl Alcohol, Methyl Alcohol, Organic Solvents|
TLV: The threshold limit value is a recommended occupational exposure guideline published by the American Conference of Governmental Industrial Hygienists. TLV's are expressed as parts of vapor or gas per million parts of air by volume (ppm) or as approximate milligrams of particulate per cubic meter or air (mg/m3).The TLV is the average concentration of a chemical that most people can be exposed to for a working lifetime with no ill effects. The TLV is an advisory guideline. If applicable, a ceiling concentration (C), which should not be exceeded, or a skin absorption notation (S) will be indicated with the TLV.
PEL: The permissible exposure limit is a legal standard issued by OSHA. Unless specified, the PEL is a time weighted average (TWA).
TWA: Most exposure standards are based in time weighted averages. The TWA is the average exposure over an eight-hour workday. Some substances have ceiling (C) limits. Ceiling limits are concentrations that should never be exceeded.
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