Environmental Engineering Reference
In-Depth Information
These levels can reduce mental efficiency. The standard recommended by the
National Institute for Occupational Safety and Health is (NIOSH) 55 mg/m
3
(50 ppm) 8-hour time-weighted average. Carbon monoxide levels of 200 to
400 ppm may cause headache and levels of 800 to 1600 ppm unconsciousness;
even 50 ppm for 120 minutes has been shown to reduce exercise tolerance
in subjects with angina. Persons with cardiovascular diseases are sensitive to
concentrations of 35 ppm and as low as 10 ppm for extended periods.
Mercury Poisoning
Mercury poisoning in humans has been associated with the consumption of
methylmercury-contaminated fish, shellfish, bread, and pork and, in wildlife,
through the consumption of contaminated seed. Fish and shellfish poisoning
occurred in Japan in the Minamata River and Bay region and at Niigata between
1953 and 1964. Bread poisoning occurred as a result of the use of wheat seed
treated with a mercury fungicide to make bread in West Pakistan in 1961, Central
Iraq in 1960 and 1965, and Panorama, Guatemala, in 1963 and 1964. Pork poison-
ing took place in Alamagordo, New Mexico, when methylmercury-treated seed
was fed to hogs that were eaten by a family. In Sweden, the use of methylmer-
cury as a seed fungicide was banned in 1966 in view of the drastic reduction in
the wild bird population attributed to treated seed. In Yakima, Washington, early
recognition of the hazard prevented illness when 16 members of an extended
family were exposed to organic mercury poisoning in 1976 by the consump-
tion of eggs from chickens fed mercurytreated seed grain. The grain contained
15,000 ppb total mercury, an egg 596 and 1902 ppb, respectively, of organic and
inorganic mercury. Blood levels in the family ranged from 0.9 to 20.2 ppb in a
man who ate eight eggs per day. A whole-blood level above 20 ppb may pose a
mercury poisoning hazard.
It is also reported that crops grown from seed dressed with minimal amounts
of methylmercury contain enough mercury to contribute to an accumulation in
the food chain reaching humans. The discovery of moderate amounts of mercury
in tuna and most freshwater fish and relatively large amounts in swordfish by
many investigators in 1969 and 1970 tended to further dramatize the problem.
The organic methylmercury and other alkylmercury compounds are highly
toxic. Depending on the concentration and intake, they can cause fever, chills,
nausea, unusual weakness, fatigue, and apathy followed by neurologic disorders.
Numbness around the mouth, loss of side vision, poor coordination in speech
and gait, tremors of hands, irritability, and depression are additional symptoms
leading possibly to blindness, paralysis, and death. Methylmercury also attacks
vital organs such as the liver and kidney. It concentrates in the fetus and can
cause birth defects.
Methylmercury has an estimated biologicalhalf-lifeof70to74daysin
humans, depending on such factors as age, size, and metabolism, and is excreted
mostly in the feces at the rate of about 1 percent per day. Mercury persists in
large fish such as pike from 1 to 2 years.
