OUTDOOR AIR POLLUTION

Air pollution is a serious problem in the United States and many other industrialized countries. In the United States, the Environmental Protection Agency is charged with identification and

regulation of pollutants in the ambient air that may cause adverse health effects. The current National Ambient Air Quality Standards for the six major pollutants are listed in Table 9-9 .

Despite federal and state regulations, many cities and regions in the United States currently do not meet these primary standards. Epidemiologic research, human clinical studies, and

animal toxicologic studies continue to provide evidence for adverse health effects of ambient air pollutants, even at exposure levels below the current standards. The major sources of

ambient air pollutants are:

• Combustion of fossil fuels. These are divided into mobile sources such as motor vehicles, stationary sources such as power plants and factories, and other sources such as

barbecues and fireplaces. Tailpipe emissions from motor vehicles are a complex mixture of carbon monoxide, oxides of nitrogen, hydrocarbons, diesel exhaust particles, and other

particulates including lead oxide from tetraethyl lead contained in leaded gasoline.

• Photochemical reactions. Oxides of nitrogen and volatile hydrocarbons interact in the atmosphere to produce ozone (O3 ) as a secondary pollutant.

• Power plants. These release sulfur dioxide (SO2 ) and particulates into the atmosphere. Coal and oil contain sulfur, leading to atmospheric formation of sulfates. Automobiles

release oxides of nitrogen, leading to atmospheric formation of nitrates. Aerosolized acid sulfates contribute to acid rain.

• Waste incinerators, industry, smelters. These point sources release acid aerosols, metals, mercury vapor, and organic compounds that may be hazardous for human health. One

example of the numerous hazardous chemicals emitted by these sources is methyl isocyanate that was accidentally released at Bhopal in India in 1984, resulting in 3000 deaths due

to pulmonary edema. Some of the air toxins, such as polycyclic aromatic hydrocarbons, are known carcinogens.[34]

Lungs are the major target of common outdoor air pollutants; especially vulnerable are children, asthmatics, and people with chronic lung or heart disease, as summarized in Table 9-10 .

The serious toxicity associated with lead exposure is discussed subsequently under Industrial Exposures. The major air pollutants and the mechanisms responsible for their adverse health

effects are summarized briefly.[34]

Ozone.

Ozone is a major component of smog that accompanies summer heat waves over much of the United States. Exposure of exercising children and adults to as little as 0.08 ppm produces

cough, chest discomfort, and inflammation in the lungs. Asthmatics are especially sensitive and require more frequent visits to emergency rooms and more hospitalizations during smog

episodes. It is not known whether these acute changes lead to chronic, irreversible lung injury. Ozone is highly reactive and oxidizes polyunsaturated lipids to hydrogen peroxide and lipid

aldehydes. These products act as irritants and induce release of inflammatory mediators,

TABLE 9-10-- Health Effects of Outdoor Air Pollutants

Date: 2016-04-22; view: 563