Environmental Engineering Reference
In-Depth Information
shown 0.05 to 0.7 ppm or more mercury, with the larger and older fish showing
the higher concentration.
There is no evidence to show that the mercury in the current daily dietary
intake has caused any harm, although this does not rule out possible nondetectable
effects on brain cells or other tissues. The general population should probably
not eat more than one freshwater-fish meal per week.
Since mercury comes from manmade and natural sources, every effort must
be made to eliminate mercury discharges into the environment. The general pre-
ventive and control measures applicable to chemical pollutants were summarized
previously under “Background,” but the goal should be “zero discharge.”
Habashi
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has summarized techniques for the removal of mercury at metal-
lurgical plants in the United States, Europe, and Japan. The author reports that
“the removal and recovery of traces of mercury from SO
2
gases or from sulfuric
acid has been proved to be technically and economically feasible.” Insofar as
water supply is concerned, approximately 98 percent of inorganic mercury may
be removed by coagulation and settling at a pH of 9.5 followed by filtration
through a granular activated carbon filter.
Illnesses Associated with Air Pollution— Lung Diseases
The particulate and gaseous contaminants in polluted air may irritate the eyes
and respiratory system or damage the clearance mechanism of the lungs, thereby
increasing susceptibility to upper respiratory diseases and aggravating existing
chronic illnesses. Diseases mentioned as
also
being associated with air pollution
include bronchial asthma (restriction of the smaller airways or bronchioles and
increase in mucous secretions), chronic bronchitis (excessive mucus and frequent
cough), pulmonary emphysema (shortness of breath), lung cancer, heart diseases,
and conjunctivitis (inflammation of the lids and coatings of the eyeballs) (also
with lead and carbon monoxide poisoning as previously discussed). In an example
of the built environment influencing health, one study found the higher prevalence
of asthma in poor neighborhoods of Hartford, Connecticut, to be due in large part
to a heavy burden of dust laden with cockroach antigen.
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A direct single cause-and-effect relationship is often difficult to prove because
of the many other causative factors and variables usually involved. Nevertheless,
the higher morbidity and mortality associated with higher levels of air pollution
and reported episodes are believed to show a positive relationship.
Certain air contaminants, depending on the body burden, may produce systemic
effects. These include arsenic, asbestos, cadmium, beryllium compounds, mercury,
manganese compounds, carbon monoxide, fluorides, hydrocarbons, mercaptans,
inorganic particulates, lead, radioactive isotopes, carcinogens, and insecticides.
They require attention and are being given consideration in the development of
air quality criteria.
Bronchial asthma
affects susceptible sensitive individuals exposed to irritant
air contaminants and aeroallergens. The aeroallergens include pollens, spores,
rusts, and smuts. There also appears to be a good correlation between asthmatic
attacks in children and adults and air pollution levels.
