7.2 Pollution of Water with Reference to Human Health: Bacterial Indicators of Fecal Pollution 157
(a) Use of bacteria
The use of bacteria to detect pollution is based on
the principle that when there is a high nutrient con-
centration the biological population is high and
diverse (i.e., a large number of a wide range of
bacteria are present) unless toxic materials are
present in the water or there is a shortage of some
key nutrients. This high bacterial population (apart
from using up the nutrients) uses up the oxygen
and hence creates anaerobic or near-anaerobic
conditions. The result is that many bacteria die
out, and only a few types will remain. This is even
accentuated by the grazing activity of protozoa.
In order to detect pollution changes it is neces-
sary to make observations at least from two different
points along the stream or to do so at some point at
two different occasions. By taking plate counts on
a variety of media and both under aerobic and
anaerobic conditions, it is possible to follow the
progress of pollution.
(b) Use of protozoa and other organisms
The types of organisms present besides the bac-
teria will indicate whether the water is just recei-
ving pollutants or is just recovering from them by
natural self-purification. If bacteria, protozoa of
group Sarcodina, flagellates, and free-swimming
ciliates are seen in that order of abundance, then
the pollution is fresh. On the other hand, if stalked
ciliates, free-swimming ciliates, and bacteria are
seen in that order of abundance, then the water is
recovering from pollution. A predominance of
insects and rotifers indicates that the pollution is
over as these organisms are encountered in bodies
of water low in organic matter.
7.2 Pollution of Water with Reference
to Human Health: Bacterial
Indicators of Fecal Pollution
Many parameters are used by different authorities as
indicators of water pollution. These parameters include
biological oxygen demand (BOD), dissolved oxygen
(DO), pH, specific conductance, water temperature,
and chemical constituents including nitrates and phos-
phates. BOD and DO will be discussed in Chap. 11.
The most widely used parameters are, however,
bacterial indicators of fecal pollution. The indicators
have been undertaken in order to protect human health.
They have been in use for over a 100 years and the pro-
cedures involved have become highly standardized.
Bacterial indicators are used to indicate if:
(a) Drinking water sources are fit for drinking.
(b) Treatment of drinking water has been adequate.
(c) Drinking water in the distribution system continues
to be protected.
(d) Recreational and shellfish waters are microbio-
logically safe.7.2.1 Microbiological Examination of
Water for Fecal ContaminationThe purpose of examining water microbiologically is to
help in the determination of its sanitary quality and its
suitability for general use. The sanitary quality of water
may be defined as the relative extent of the absence of
suspended matter, color, taste, unwanted dissolved
chemical, bacteria indicative of fecal presence, and other
“aesthetically offensive” objects or properties. In short,
the sanitary quality of water depends on its acceptability
for internal consumption and other uses in which water
comes directly or indirectly in contact with man.
The current bacterial indicator approaches have
become standardized, are relatively easy and inexpen-
sive to use, and constitute the cornerstone of many mon-
itoring and regulatory programs. Due to an increased
understanding of the diversity of waterborne pathogens,
including their sources, physiology, and ecology, a
growing understanding has occurred that the use of bac-
terial indicators may not be as universally protective as
was once thought. Thus, the greater environmental sur-
vival of pathogenic viruses and protozoa, when com-
pared with indicator bacteria (coliforms) has raised
serious questions about the suitability of relying on rela-
tively short-lived organisms as an indicator of the micro-
biological quality of water (Anonymous 2004, 2005 ).
The implication of this situation is that while the
presence of coliforms could still be taken as a sign of
fecal contamination, the absence of coliforms can no
longer be taken as assurance that the water is uncon-
taminated. Thus, existing bacterial indicators and indi-
cator approaches do not, in all circumstances, identify
all potential waterborne pathogens. Furthermore, recent
advances in microbiology, molecular biology, and
analytical chemistry make it necessary to reassess the
current reliance on traditional bacterial indicators for
waterborne pathogens.