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Toxicology is the branch of pharmacology that concerns the study, regulation, and treatment of adverse effects in humans resulting from exposure to chemicals encountered at work or in the general environment.



A. 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. Air contaminants are regulated in the United States by the Environmental Protection Agency (EPA).

B. 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 motor vehicle traffic, the concentration of CO may exceed 100 ppm.

1. 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. Exposure of a pregnant woman to elevated CO levels at critical fetal developmental periods may cause fetal death or serious and irreversible but survivable birth defects.

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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
Biomagnification Although the concentration of a contaminant may be virtually undetectable in water, it may be magnified hundreds or thousands of times as the contaminant passes up the food chain
Ecotoxicology Study of the toxic effects of chemical and physical agents on populations and communities of living organisms within defined ecosystems
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 (air, soil, water); regulated by the Environmental Protection Agency (EPA) in the United States. The FDA regulates exposure in food
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 ...

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