166 Ecology and Applied Environmental Science
The main source of contamination of water bodies with pathogenic
microorganisms is urban and stock-raising wastewater, since it contains
human and animal excrement. The pathogens are present in water in very
low concentrations and are difficult to detect. For that reason coliform bacteria are used as indicators of contamination. Such bacteria are not generally
pathogenic but are excreted by humans in numbers of around 100 × 10 9 to
400 × 10 9 per person per day. One group of coliform bacteria , the fecal
coliform bacteria, grow only in the digestive system and thus their presence
in water indicates pollution with feces and therefore possible pathogenicity.
Another feature of coliform bacteria which makes them a suitable measure
to indicate pathogenicity is that they are generally harder to eliminate by
disinfecting water than are pathogenic bacteria. Thus eliminating coliform
bacteria ensures that pathogenic bacteria are also eliminated. The same is
not true of viruses, however, because coliform bacteria are not generally a
good viral indicator.
Sanitary ordinances set maximum permissible concentrations of coliform
bacteria in water according to what it is used for (drinking, swimming, etc.).
8.5 toxic watEr PollutantS
From an ecological or hygienic point of view, there are a great number
of toxic pollutants. All the important toxic pollutants, such as synthetic
organic compounds, lead, mercury, cadmium, nickel, chromium, arsenic,
selenium, compounds of fluorine, sulphur, cyanide, the various acids and
radioactive materials can be found in water, as well as in the air and the
soil. Depending on how toxic they are, they have adverse effects when their
concentrations in water exceed certain limits. Pollution may also be transmitted to humans in food through the phenomenon of biomagnification
(Chapters 4 and 7), e.g. in fish whose flesh contains high concentrations of
mercury that have been increased through the food chain.
Sources of toxic substances are many and varied. Agriculture is the
main source of pollution with synthetic organic toxic substances, which
are carried to water bodies by surface runoff or by air transfer. Industry
is frequently a source of toxic pollutants, which are transported to bodies
of water through direct drainage of liquid industrial waste, and gaseous
industrial waste, which falls to earth when it rains.
A large proportion of air pollutants originating from means of transport, central heating installations and industry end up in bodies of water.
A major part of the lead emitted into the atmosphere ends up in marine
ecosystems. Oxides of sulphur and nitrogen are converted in the atmosphere into sulphuric and nitric acid and return to the earth, to terrestrial
and aquatic ecosystems, in the form of acid rain (Chapter 9). During the
1980s, pH values lower than 4 were measured in rain over extensive areas
The main source of contamination of water bodies with pathogenic
microorganisms is urban and stock-raising wastewater, since it contains
human and animal excrement. The pathogens are present in water in very
low concentrations and are difficult to detect. For that reason coliform bacteria are used as indicators of contamination. Such bacteria are not generally
pathogenic but are excreted by humans in numbers of around 100 × 10 9 to
400 × 10 9 per person per day. One group of coliform bacteria , the fecal
coliform bacteria, grow only in the digestive system and thus their presence
in water indicates pollution with feces and therefore possible pathogenicity.
Another feature of coliform bacteria which makes them a suitable measure
to indicate pathogenicity is that they are generally harder to eliminate by
disinfecting water than are pathogenic bacteria. Thus eliminating coliform
bacteria ensures that pathogenic bacteria are also eliminated. The same is
not true of viruses, however, because coliform bacteria are not generally a
good viral indicator.
Sanitary ordinances set maximum permissible concentrations of coliform
bacteria in water according to what it is used for (drinking, swimming, etc.).
8.5 toxic watEr PollutantS
From an ecological or hygienic point of view, there are a great number
of toxic pollutants. All the important toxic pollutants, such as synthetic
organic compounds, lead, mercury, cadmium, nickel, chromium, arsenic,
selenium, compounds of fluorine, sulphur, cyanide, the various acids and
radioactive materials can be found in water, as well as in the air and the
soil. Depending on how toxic they are, they have adverse effects when their
concentrations in water exceed certain limits. Pollution may also be transmitted to humans in food through the phenomenon of biomagnification
(Chapters 4 and 7), e.g. in fish whose flesh contains high concentrations of
mercury that have been increased through the food chain.
Sources of toxic substances are many and varied. Agriculture is the
main source of pollution with synthetic organic toxic substances, which
are carried to water bodies by surface runoff or by air transfer. Industry
is frequently a source of toxic pollutants, which are transported to bodies
of water through direct drainage of liquid industrial waste, and gaseous
industrial waste, which falls to earth when it rains.
A large proportion of air pollutants originating from means of transport, central heating installations and industry end up in bodies of water.
A major part of the lead emitted into the atmosphere ends up in marine
ecosystems. Oxides of sulphur and nitrogen are converted in the atmosphere into sulphuric and nitric acid and return to the earth, to terrestrial
and aquatic ecosystems, in the form of acid rain (Chapter 9). During the
1980s, pH values lower than 4 were measured in rain over extensive areas