182
ENVIRONMENT, POLLUTION, DEVELOPMENT: THE CASE OF UZBEKISTAN
Furthermore, the illness was observed
not only in the people,
but also in those pets who consume fish – cats. These animals were
recorded with behavioral problems – they had lost the aversion to
water inherent to cats.
Minamata disease symptoms appeared at a mercury con centra-
tion of 10 mg/kg of edible fish. Numerous studies have found that
dangerously high contamination with methylmercury has also been
registered in other parts of the world, including the northern coast
of the Mediterranean Sea, NE Atlantic and the Baltic Sea. Entry of
mercury compounds in the Baltic Sea mainly takes place with river
water (8-44 t/year) and precipitation (4-29 t/year) they reach the
sea in significantly smaller amounts by the waste water of the cities
and factories located on the coast. Marine organisms accumulate
methylmercury. The biggest concentrations of mercury are found at
the highest stages of marine ecological food chain – the bodies of
seals, and the concentration increases significantly with age.
The human health hazard lies in the increased consumption
of the marine animal products containing
growing quantities of
mercury. The organisms of the predatory fish living and feeding in
the Baltic Sea coastal area contain methylmercury concentrations
exceeding 0.5 mg/kg. In the Mediterranean Sea high mercury
content was found in swordfish. Frequent intake of mercury-
contaminated fish may cause health disorders. Particularly sensitive
to contamination are the human foetus and growing child’s body.
One of the indicators that can be used to characterize the
received doses of mercury in the body at different periods of human
life is the content of this metal in hair. Studies in Japan have shown
that the mercury concentration in the hair of the people who
regularly, for several days a week had consumed seafood products,
exceeded that of the people in the control group 5 to 10 times.
However, in accordance with scientific findings, also the people of
the studied control group, although to a much lesser extent, were
exposed
to mercury pollution, which was contained in the consumed
agricultural production. Mercury compounds enter the agricultural
products as a result of applying mercury-containing grain fungicide
treatment substances. The chemical composition analysis of hair
carried out on the citizens of European countries, showed that
the mercury concentration there was similar to that found in the
control group of Japan. It indicates that
in this region there is
also a heightened background of mercury pollution. Data from
these studies at the end of 1960s prompted a number of European
governments to adopt more stringent regulatory measures for
mercury compound use in industry and agriculture.
Ecologically no less dangerous are the cadmium compounds.
Cadmium is one of the most mobile and biochemically active heavy
8. WATER POLLUTION
183
metals. It accumulates in the kidney cortex, causing hemorrhages.
When ingested, cadmium binds itself to proteins and accumulates in
the kidneys and liver. In the Baltic Sea cadmium, similar to mercury,
is brought mainly by river water and atmo spheric precipitation.
The concentrations of this metal in fish here range from 2 to
200 µg/kg, and in molluscs – 1300 to 10 800 µg/kg of the body
weight. Cadmium, like many other polluting elements, tends to
accumulate in the ecological food chain.
Threat to human health is
posed by increased accumulation of cadmium in those links of food
chain – marine organisms widely used in food. One of these fish
species is herring, in whose body an increase in cadmium content
has recently been observed.
One of the heavy metals of greatest ecological importance and
toxic to living organisms is lead. In the last century large quantities
of lead came into the sea and ocean ecosystem with industrial
effluents and emissions of tetraethyllead used in road transport.
Due to stricter environ mental legislation,
waste water treatment
technology improvements and the introduction of unleaded
automotive fuel, since 1980s the lead concentrations in the have
been decreasing, as shown by the analysis of fish and molluscs.
Biological pollution of waters is caused by inflow of untreated
municipal or industrial wastewater from industrial plants and
residential areas. Biological pollution consists of pathogens – viruses,
bacteria and microscopic fungi, as well as a variety of organic
substances subject to fermentation processes. Biological pollution
also manifests itself as the appearance of
species not characteristic
of specific water bodies – the so-called invasive species. Pathogenic
microorganisms cause public health and hygiene problems in
bathing places. This contamination is evaluated according to the
presence of intestinal bacillus
Escherichia coli in the water sample.
In itself, this bacillus is harmless to humans, they live as symbionts
in the human intestinal tract and as a result of their life processes
produce physiologically
important substances, including vitamin
B12. However, the presence of
Escherichia coli serves as a faecal
contamination indicator, but this contamination may conceal a
number of pathogenic microorganisms, incl. infectious hepatitis,
cholera, typhoid and dysentery agents, as well as staphylococci,
streptococci, and pathogenic fungi.
Humans become infested with
these microorganisms while swimming in biologically contaminated
water, so the most popular swimming sites on sea coast, including
seaside, in summer season are regularly monitored regarding
biological contamination and, if
Escherichia coli in water sample
exceeds a certain level, vacationers are warned not to go swimming.
Water contamination with pathogenic
microorganisms also
makes the produce of mollusc farms – oysters and other edible
Do'stlaringiz bilan baham: 
