Civil Engineering Reference
In-Depth Information
substantial gastrointestinal damage and cardiac abnormalities. Symptoms may be ev-
ident within 8 minutes if arsenic is ingested in a drink, but at up to 10 hours if it is
solid and taken with food. The acute fatal dose of arsenic trioxide for a human is in
the range of 70 to 180 mg, or 0.76 to 1.95 mg / kg of body weight for a 70 kg person.
There is a wide variation in toxicity of various arsenical formulations. The arsenic
compounds are listed below in descending order of toxicity:
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Arsines (trivalent, inorganic, or organic)
•
Arsenite (inorganic)
•
Arsenoxides (trivalent with two bonds to oxygen)
•
Arsenate (inorganic)
•
Pentavalent arsenicals, such as arsenic acids
•
Arsenium compounds (four organic groups with a positive charge on arsenic)
•
Metallic arsenic
•
Epidemiologic investigations have reported an association between arsenic exposure
in drinking water and cancer. Studies in laboratory animals have not demonstrated this
effect following ingestion exposures. Consequently, there is no comparable model sys-
tem for studying arsenic-induced carcinogenicity. Arsenic has been shown to be mu-
tagenic in several bacterial test systems, and sodium arsenate and arsenite have shown
teratogenic potential in several mammalian species. The EPA has classified arsenic as
a human carcinogen (Group A).
In addition to cancer, arsenic exposures have been reported to result in other adverse
health effects. These include thickening of the skin; effects on the nervous system,
such as tingling and loss of feeling in limbs; hearing impairment; effects on the heart
and circulatory system, diabetes; developmental effects; and effects on the gastroin-
testinal system and liver. Many of these effects are observed at concentrations where
cancer effects were observed in the epidemiology studies.
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Asbestos
Sources
Asbestos fibers enter surface waters from both natural and anthropogenic
sources. Large deposits of chrysotile and emphibole are found throughout North Amer-
ica (Fig. 2-1), and leaching from asbestos mineral deposits in contact with surface
water constitutes the major natural source. Asbestos also occurs in water exposed to
asbestos mining discharges, and in asbestos-cement pipe. Studies have also found that
precipitation may result in surface water contamination through scavenging of airborne
asbestos.
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Anthropogenic sources of asbestos fibers in water include mining operations and
use of products containing asbestos. Chrysotile and amphibole are commercially mined
to make over 3,000 products, including filters, auto brake and clutch linings, floor
covering, paper products, textiles, gasket materials, and asbestos cement pipe.
Occurrence
Asbestos levels are based on fiber counts rather than concentration by
weight. WHO reports that expected values of asbestos in raw water will vary from
less than 1 to as much as 10 million fibers per liter (MFL), with an average value of
1 MFL. EPA sampling of water distribution systems in 406 cities in 47 states reported
the following asbestos levels: 29 percent were below detection limits, 53 percent were
