Water Pollution 167
of North Europe and North America. Apart from the damage it causes to
structures and terrestrial ecosystems, acid rain causes severe damage to
aquatic ecosystems. Trout and salmon disappeared from Swedish lakes and
watercourses in which the pH fell well below 5.
Chlorine, which is widely used to disinfect water, is a decisive factor in
dealing with infectious diseases. In water, however, it reacts with certain
organic substances to form some chlorinated organic compounds which may
be carcinogenic and teratogenic. Some regulations set the maximum permissible concentration of such compounds in drinking water at 100 μgr/L.
Underground as well as surface water is often loaded with dangerous
quantities of nitrates NO 3
– , originating from over-fertilisation of fields or
from urban, stock-raising and other wastes that end up in underground and
surface bodies of water. In the right conditions, which have been detected
mainly in the digestive system of very small children, nitrates are converted
biologically into toxic nitrites.
Finally, worth mentioning for its toxic effect on plants, is boron. Concentrations greater than 0.5 mg/L in water used for irrigation cause damage
to many plants, and only a few plants are able to withstand concentrations
higher than 2 mg/L.
8.6 OIL
In the 1980s, it was estimated that human activities introduced approximately 5 million tonnes of oil per year into the oceans. In a report published in
2002 by the National Research Council (NRC) of the US National Academy
of Sciences, the average total worldwide annual release of petroleum (oils)
from all known sources to the sea has been estimated at 1.3 million tonnes.
However, the range is wide, from a possible 470,000 tonnes to a possible
8.4 million tonnes per year. According to the report, the main categories
of sources include natural seeps (46%), discharges (operational discharges
from ships and discharges from land-based sources 37%), accidental spills
from ships (12%) and oil extraction (3%). Oil may enter the sea through
surface runoff, leaks and liquid urban and industrial waste. Another contributor is hydrocarbons that have evaporated on land and fall into the seas
along with rain. From the oil pollution due to the marine transport, only
a small part is due to oil tanker accidents, with the well-known dramatic
local polluting effects. A greater part results from the “normal” operation
of many ships and particularly from flushing out ballast consisting of seawater containing a small quantity of oil.
Apart from the well-known, extremely disagreeable effects of oil in
the form of tar on swimming beaches, there is a range of other negative
impacts. Some of the components of oil are indirectly toxic, whereas others
are known carcinogens. Fears have been expressed that the carcinogenic
of North Europe and North America. Apart from the damage it causes to
structures and terrestrial ecosystems, acid rain causes severe damage to
aquatic ecosystems. Trout and salmon disappeared from Swedish lakes and
watercourses in which the pH fell well below 5.
Chlorine, which is widely used to disinfect water, is a decisive factor in
dealing with infectious diseases. In water, however, it reacts with certain
organic substances to form some chlorinated organic compounds which may
be carcinogenic and teratogenic. Some regulations set the maximum permissible concentration of such compounds in drinking water at 100 μgr/L.
Underground as well as surface water is often loaded with dangerous
quantities of nitrates NO 3
– , originating from over-fertilisation of fields or
from urban, stock-raising and other wastes that end up in underground and
surface bodies of water. In the right conditions, which have been detected
mainly in the digestive system of very small children, nitrates are converted
biologically into toxic nitrites.
Finally, worth mentioning for its toxic effect on plants, is boron. Concentrations greater than 0.5 mg/L in water used for irrigation cause damage
to many plants, and only a few plants are able to withstand concentrations
higher than 2 mg/L.
8.6 OIL
In the 1980s, it was estimated that human activities introduced approximately 5 million tonnes of oil per year into the oceans. In a report published in
2002 by the National Research Council (NRC) of the US National Academy
of Sciences, the average total worldwide annual release of petroleum (oils)
from all known sources to the sea has been estimated at 1.3 million tonnes.
However, the range is wide, from a possible 470,000 tonnes to a possible
8.4 million tonnes per year. According to the report, the main categories
of sources include natural seeps (46%), discharges (operational discharges
from ships and discharges from land-based sources 37%), accidental spills
from ships (12%) and oil extraction (3%). Oil may enter the sea through
surface runoff, leaks and liquid urban and industrial waste. Another contributor is hydrocarbons that have evaporated on land and fall into the seas
along with rain. From the oil pollution due to the marine transport, only
a small part is due to oil tanker accidents, with the well-known dramatic
local polluting effects. A greater part results from the “normal” operation
of many ships and particularly from flushing out ballast consisting of seawater containing a small quantity of oil.
Apart from the well-known, extremely disagreeable effects of oil in
the form of tar on swimming beaches, there is a range of other negative
impacts. Some of the components of oil are indirectly toxic, whereas others
are known carcinogens. Fears have been expressed that the carcinogenic