In recent years increasing amounts of metals have been discharged into the environment by industrial establishments and out of this mercury has been one of the worst offenders as a dangerous pollutant.
It has been responsible for several deaths in Sweden and Japan, and has caused the Minamata disease in Japan. Various Swedish rivers and lakes have already become heavily polluted by the widespread use of mercury compounds as fungicides and algicides in paper making and pulp lumber industries.
Effluent from about 150 km along the Swedish coast has raised the methylmercury content of the Baltic seawater to such an extent that fishing had to be banned in about one per cent of Sweden’s commercial take and coastal fisheries. If one were to enforce the permissible residue limit for mercury in human food as approved by World Health Organization, fishing in all Swedish fishing areas would have to be banned!
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Ackefors (1971) has studied the problem of mercury pollution in Sweden with particular reference to conditions in the aquatic habitat. Fishes have been found to absorb and concentrate mercury, in the form of methylmercury, to dangerous levels.
The aquatic invertebrate Esox lucius (pike) has been observed to act as a good indicator of mercury contamination, its mercury content reflecting the level of contamination in water. It can concentrate mercury by a factor of several thousand times.
Methylmercury is a highly persistent kind of pollutant that accumulates in food chains. Its half-life in human beings has been estimated at about 7 days (Ramel, 1974). It shows a fairly wide range and spectrum of undesirable effects including genetic changes. So far, most investigators have concentrated on its toxicology rather than mutagenicity.
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However, it is now known (se. Ramel, 1974) that certain mercury compounds can act on the spindle fibres in Allium tests at very low concentration—far lower than effective in tin colchicine test. Work done on Drosophila has shown that treatment with methylmercury can lead to chromosomal nondisjunction in the gametes Organic mercury has also been shown to react with DNA. Swedish fish eaten have been found to have high mercury content in their blood and they exhibited a significantly higher frequency of chromosomal breakage in then lymphocytes than control subjects with low mercury levels.
Exports of alkylmercury-treated seeds from America to Iraq, Pakistan and Guatemala have caused certain mass intoxication epidemics in which many persons got poisoned inadvertently by such seeds (see Ramel, 1974). In Sweden, mercury content of freshwaters (arising from leaching and runoff of fungicides, etc.) is still increasing even though the agricultural use of mercury compounds was banned some ten years ago. Neurological disorders involving cerebellar and visual pathway damage have grossly incapacitated human beings who happened to ingest shellfish and grain contaminated with methylmercury.
Japan has enacted legislation to control mercury pollution. Its Environmental Agency issues regulations or standards for effluent control, and its Ministry of the Interior, Trade, and Industry issues guidelines for effluent control. Table 8.11 lists standards applicable to all industrial discharges of mercury.
Chlor-alkali plants seem to be chief sources of mercury containing effluents. Certain paper and pulp companies in Japan, Canada and elsewhere have also contributed to mercury pollution.
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The Japanese Solid Waste Control Law prescribes that sludges and muds with a mercury content of less than 0.005 ppm may be used as landfill whereas those having more than 0.005 ppm must be mixed with concrete. Sludges and muds with less than 0.005 ppm of mercury may be disposed of at sea where the depth is more than 3,500 metres. Those with mercury content of more than 0.005 ppm must be mixed with concrete and the blocks may be dumped in areas with low currents and scarce fish. Any liquid or sludge with mercury content more than 2.0 ppm must be incinerated or chemically treated.