Encyclopedia of Environmental Science and Engineering, Volume I and II

42 AIR POLLUTANT EFFECTS

types of cancer. They found 175 deaths from mesothelioma,

a cancer rarely found in the general population, and 168 from

asbestosis, a form of pneumoconiosis characterized by fibro-

sis of the lung that often continues after exposure ceases.

Cigarette smoking was found to have a strong multiplica-

tive effect when combined with exposure to asbestos. Based

upon a mortality rate of 1 for a nonsmoking, nonexposed

comparison group, the mortality ratio for nonsmoking asbes-

tos workers, nonexposed cigarette smokers, and workers

exposed to asbestos who also smoked were 5, 11, and 53.

The methods of asbestos analysis differed in that occu-

pational exposures were originally measured by counting

the number of fibers longer than 5 m in a given volume

of air using optical microscopy. In the ambient air the sub-

microscopic fibers, called “fibrils,” which are the ones that

can penetrate deeply into the respiratory system, had to be

measured; therefore, the Environmental Science Laboratory,

led by Irving Selikoff, at Mount Sinai School of Medicine

developed an electron-microscopy method that measured the

mass of fibrils per cubic meter of air.

Asbestos air concentrations are now reported in terms of

nanograms per cubic meter—asbestos background concen-

trations are usually in the range of 0 to 10 ng/m^3.

Asbestos in schools has been a major concern because

of the prevalence of its use and the nature of the popula-

tion involved. A study of chrysotile asbestos in schools

known to contain damaged asbestos insulation measured

FIGURE 5 Percentage of plant species visibly injured as a function of peak 1-hour and 3-hour SO 2 concentrations.

Source: McLaughlin and Lee (1974); McLaughlin (1980). (Air Quality Criteria for Particulate Matter and Sulfur

Oxide, 1981.)

peak

Species

Affected

(%) Peak

SO 2 Concentration

SO 2 concentration (ppm)

20%

10%

1.20

1.00

0.65

0.45

0.35

0.28

1.0 2.0 3.0 4.0

0

20

40

60

80

100

percentage of total species injured

1-hour

3-hour

1h 3h

9 to 1950 ng/m^3. Measurements in schools selected at

random found a mean of 179 ng/m^3 , compared to average

outdoor concentrations of 6. The excess risk of death from

lung cancer caused by asbestos exposure is proportional to

the intensity of the exposure and its duration. One estimate

of the cancer-incidence rate from asbestos reported by the

EPA was that continuous exposure to 0.01 fibrils per ml

(about 300 ng/m^3 ) will cause 28 mesotheliomas per mil-

lion females and 19 per million males, and 5 excess lung

cancers per million females and 17 per million males.

PLANT EFFECTS

The effects upon the plant surfaces of the contact of vegeta-

tion by suspended particulate matter via dry or wet deposi-

tion are not well documented. Direct entry of sulfur-dioxide

gas molecules through the plant stomata, on the other hand,

produces effects that are better understood and appear

to depend, to a great extent, upon the rate of conversion

to sulfate, a natural plant nutrient. As might be expected,

the response of a plant to a particular exposure incident is

dependent upon the concentration and duration of exposure

and, because of the opening and closing patterns of stomata,

also on the time in its daily cycle that exposures occur. Data

on the injury threshold of 31 species of forest and agricul-

tural plants were plotted to show their relative sensitivity to

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