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Toxicology is the branch of pharmacology that encompasses the deleterious effects of chemicals on biologic systems. A number of chemicals in the environment (eg, atmosphere, home, workplace) pose important health hazards.


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BioaccumulationThe increasing concentration of a substance in the environment as the result of environmental persistence and physical properties (eg, lipid solubility) that leads to accumulation in biologic tissues
Endocrine disruptorsChemicals in the environment that have estrogen-like or antiandrogen activity or disrupt thyroid function. There is concern that exposure to endocrine disruptors may increase reproductive cancers, impair fertility, and have teratogenic effects
Environmental toxicologyThe area of toxicology that deals with the effects of agents found in the environment; regulated by the Environmental Protection Agency (EPA) in the United States
Occupational toxicologyThe area of toxicology that deals with the toxic effects of chemicals found in the workplace; regulated by the Occupational Safety and Health Administration (OSHA) in the United States
Threshold limit valueThe amount of exposure to a given agent that is deemed safe for a stated time period. It is higher for shorter periods than for longer periods

Classification and Prototypes

The major air pollutants in industrialized countries include carbon monoxide (which accounts for about 50% of the total amount of air pollutants), sulfur oxides (18%), hydrocarbons (12%), particulate matter (eg, smoke particles, 10%), and nitrogen oxides (6%). Air pollution appears to be a contributing factor in bronchitis, obstructive pulmonary disease, and lung cancer.

Carbon Monoxide

Carbon monoxide (CO) is an odorless, colorless gas that competes avidly with oxygen for hemoglobin. The affinity of CO for hemoglobin is more than 200-fold greater than that of oxygen. The threshold limit value of CO for an 8-h workday is 25 parts per million (ppm); in heavy traffic, the concentration of CO may exceed 100 ppm.


CO causes tissue hypoxia. Headache occurs first, followed by confusion, decreased visual acuity, tachycardia, syncope, coma, seizures, and death. Collapse and syncope occur when approximately 40% of hemoglobin has been converted to carboxyhemoglobin. Prolonged hypoxia can result in irreversible damage to the brain and the myocardium.


Removal of the source of CO and 100% oxygen are the main features of treatment. Hyperbaric oxygen accelerates the clearance of carbon monoxide.

Sulfur Dioxide

Sulfur dioxide (SO2) is a colorless, irritating gas formed from the combustion of fossil fuels.


SO2 forms sulfurous acid on contact with moist mucous membranes; this acid is responsible for most of the pathologic effects. Conjunctival and bronchial irritation (especially in individuals with asthma) are the primary signs of exposure. Presence of 5–10 ppm in the air is enough to cause severe ...

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