Civil Engineering Reference
In-Depth Information
The presence of agents of disease
•
The concentration of the agent or the dose
•
The dose response
•
The host contact
•
A number of bacterial diseases have been associated with the consumption of sew-
age contaminated water, including typhoid fever, salmonellosis, shigellosis, cholera,
and infections due to enterocytopathic
Escherichia coli
and
Yersina entercolitica.
Dur-
ing the period 1969-74, the majority of waterborne outbreaks of bacterial disease in
the United States were due to
Shigella
sp., followed by
Salmonella
sp., typhoid fever,
and pathogenic
Escherichia coli.
Less than 10 percent of the cases of these diseases
in the United States were waterborne.
19
The waterborne parasitical diseases commonly associated with contaminated water
are amoebic dysentery,
Cryptosporidiasi
s and
Giardiasis,
both protozoan diseases.
There are at least 101 types of viruses that may find their way into water via fecal
contamination. Of these, the most serious threat to the public health (in terms of disease
severity) is the virus of infectious hepatitis (hepatitis A). Less than 1 percent of the
reported cases of hepatitis in the United States are attributable to contaminated drinking
water. A large proportion of cases were associated with the consumption of contami-
nated shellfish.
Infectious disease agents have traditionally been monitored in water using a sur-
rogate parameter, the coliform or fecal coliform test. The presence of these bacteria
in water is indicative of the presence of fecal material and thus the potential presence
of pathogenic enteric organisms. Through the years this test has been effectively used
in the quality control of finished drinking water. However, the absence of the latter
organisms in finished drinking water may not guarantee the absence of enteric viruses,
Giardia
or
Cryptosporidium
.
Fate of Contaminants in Streams
There are many factors that affect contaminants in streams. Contaminants may be
contributed to streams from a number of sources, including:
Soil and rock
•
Waste discharges
•
Storm runoff
•
Precipitation and atmospheric fallout
•
Biological organisms
•
Flowing streams are dynamic systems, whose chemical and biochemical reaction
rates are such that equilibrium conditions are only slowly, if ever, attained. The organic
and inorganic chemicals of concern in water supply interact with one another and with
other materials and organisms in various chemical and biochemical reactions. Reac-
tions that can take place in streams to decrease, or in some cases increase, the con-
centration of contaminants include:
Precipitation
•
Complexation
•
