High-Yield Terms to Learn

Bioaccumulation The 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 disruptors Chemicals 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 toxicology The 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 toxicology The 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 value The 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

Air Pollutants

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.

Effects

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.

Treatment

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.

Effects

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 persons with asthma) are the primary signs of exposure. Presence of 5-10 ppm in the air is enough to cause severe bronchospasm. Heavy exposure may lead to delayed pulmonary edema. Chronic low-level exposure may aggravate cardiopulmonary disease.

Treatment

Removal from exposure to SO2 and relief of irritation and inflammation constitute the major treatment.

Nitrogen Oxides

Nitrogen dioxide (NO2), a brownish irritant gas, is the principal member of this group. It is formed in fires and in silage on farms.

Effects

NO2 causes deep lung irritation and pulmonary edema. Farm workers exposed to high concentrations of the gas within enclosed silos may die rapidly of acute pulmonary edema. Irritation of the eyes, nose, and throat is common.

Treatment

No specific treatment is available. Measures to reduce inflammation and pulmonary edema are important.

Ozone

Ozone (O3) is a bluish irritant gas produced in air and water purification devices and in electrical fields.

Effects

Exposure to 0.01-0.1 ppm may cause irritation and dryness of the mucous membranes. Pulmonary function may be impaired at higher concentrations. Chronic exposure leads to bronchitis, bronchiolitis, pulmonary fibrosis, and emphysema.

Treatment

No specific treatment is available. Measures that reduce inflammation and pulmonary edema are emphasized.

Solvents

Solvents used in industry and solvents to clean clothing are a major source of direct exposure to hydrocarbons and also contribute to air pollution.

Aliphatic Hydrocarbons

This group includes halogenated solvents such as carbon tetrachloride, chloroform, and trichloroethylene.

Effects

Solvents are potent CNS depressants. The acute effects of excessive exposure are nausea, vertigo, locomotor disturbances, headache, and coma. Chronic exposure leads to hepatic dysfunction and nephrotoxicity. Long-term exposure to tetrachloroethylene or to trichloroethane has caused peripheral neuropathy.

Treatment

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