|Mercury: Keep away from Toxic Heavy Metal
Pathology of Mercury Poisoning
Relationship between Mercury and Fish is complicated.
Interesting facts about Mercury:
-Sometimes called quicksilver, mercury is a silvery-white metal and a very unusual one because it is a liquid at ordinary temperatures.
-It does not become solid until frozen to -39 degree C and it boils at 357 degree C.
-It is more than 13 times heavier than water so that a 1 litre bottle of it would weigh about 13 kilograms-more than most people would care to lift.
-Unlike water or oil, mercury does not wet the walls of glass bottles or tubes, but leaves them perfectly clean as soon as it is emptied out of them, without any film or drops clinging to the surface.
-Mercury is usually found combined with sulphur in the red mineral cinnabar, found in Italy, Spain, Mexico and other countries where volcanoes have been active.
-The cinnabar is heated in a current of air to about 500 degree C, so that the mercury in it is turned to vapour, or gas.
The vapour is then condensed into little beads of liquids by being passed through a cooler, and the beads are strained through chamois leather in order to separate the mercury from the ashes and dirt.
-In ancient times cinnabar was used for making the red pigment (colour) called vermilion and as early as 415 B.C. mercury was used for gilding and in medicines.
-When the alchemists of the middle ages were trying to make gold they thought mercury was an almost magical material and often used it on their experiments.
-Mercury dissolves most other metals, forming a bright film or coating on them called amalgam.
Because of this, mercury is used for refining, or purifying, the precious metals. However, it does not form an amalgam with iron and is therefore stored in iron flasks.
-As it swells a good deal when heated, mercury is useful for thermometers, except those for measuring very cold temperatures.
-It is also used in some barometers.
-As mercury forms an easy path for an electric current, it is often used in switches for turning the current on and off.
If two metal rods called "contacts" are led into a glass tube with closed ends and half full of mercury, current can flow between the contacts through the mercury.
If, however, the tube is tilted so that the contacts are no longer bathed in the mercury, the current can no longer flow.
-Although mercury and its vapour are very poisonous, drugs and medicines are often made of its compounds.
-Fulminate of mercury, made by dissolving mercury in nitric acid and adding alcohol, explodes when heated or struck and is used in detonators for setting off other explosives.
-When electric current is passed through mercury vapour it gives off what are called ultraviolet rays.
Lamps of this kind are used in hospital for giving treatment.
Pathology of Mercury Poisoning:
At first, mercurialism (mercury poisoning) was mainly a disease of mercury miners.
In the 16th and 17th centuries, mercury poisoning was an occupational disease among gilders, of gold, silver, or copper, who used mercury in the process of preparing a surface to be decorated.
The phrase "mad as a hatter" arises from the use of mercury in the preparation of felt.
This clinical syndrome is popularized by Lewis Carroll, is a classic combination of emotional liability, depression, outbursts of anger, and insomnia.
In the last two decades it has become clear that mercury released into the environment may be bioconcentrated and enter our food chain.
Minamata disease (methylmercury poisoning) was first discovered in 1956 around Minamata Bay, Kumamoto Prefecture, Japan.
A second epidemic in Japan occurred in 1965 along the Agano River, Niigata Prefecture.
Epidemics of mercury poisoning have followed release of mercury into the environment from industrial activity, with uptake of methyl mercury from fish eating in Minamata Bay and uptake of both inorganic and methyl mercury following release of mercury vapour and deposition into waterways from gold recovery procedures in the Amazon basin.
In the early 1970s, there was a more extensive outbreak of mercury poisoning in Iraq resulting from the consumption of bread made from cereal grains that had been treated with organic mercury fungicides.
Six thousand people were affected, and 500 died.
Mercury vapour absorption occurs through the lungs, with about 80% of the inhaled vapour being absorbed by the lungs and rapidly entering the bloodstream.
Following distribution by blood circulation, mercury can enter and remain in certain tissues for longer periods of time, since the half-life of excretion is prolonged.
Toxic effect of mercury involve numerous organs and systems, but the two major target organs of concern are the kidney and central nervous system.
Kidney is primary target organ only for inorganic mercury.
In acute mercury poisoning, mercuric chloride is usually identified as causing the massive damage to proximal convoluted tubules that results in acute renal failure.
The ingestion of this material is usually associated with suicide or accidental death.
Autopsy findings reveal enlarged kidney with pale and swollen cortices. and dark and congested pyramids.
When death does not ensue until a period of 3 to 4 days has passed, the proximal convoluted tubules undergo extensive cellular necrosis.
The lumen is filled with eosinophilic debris.
The basement membrane of the nephron is intact.
The ascending limbs of distal convoluted tubules and collecting and collecting tubules contain casts.
Mercury poisoning: There is coagulative necrosis of the tubules
After approximately 8 days The proximal convoluted tubules are dilated.
The epithelium shows regeneration as indicated by presence of mitotic figures.
The necrotic debris from the tubular lumen disappear.
Mercury poisoning: There is regeneration of the tubular epithelial cells.
After about 14 days the epithelium of the proximal convoluted tubules return to normal appearance.
Healing is characterized by reabsorption of the interstitial edema fluid and repair of the tubular epithelium along the intact basement membrane.
In other cases the section of the kidney shows ischemic changes in which the basement membrane is fragmented and ruptured with disintegration of the tubular structure and leakage of the tubular contents into the interstitium.
This lesion is referred to as tubulorrhexis.
Due to ingestion of inorganic mercurial salt there is severe acute tubular nephrosis or necrosis and ischemic changes.
There is ulceration of colonic mucosa in severe mercury poisoning.
The clinical symptoms include severe diarrhea and fluid loss leading to hypovolumic shock and peripheral circulatory failure.
This leads to tubular damage of the kidney due to ischemia of hypovolumic shock and direct action of the mercury, the toxic agent.
Calcification particularly of the proximal convoluted tubules occur in a matter of a few days.
Mercury poisoning: Section of the kidney showing calcification of the renal tubules
In chronic industrial exposure of mercury there are reported cases of thickening of basement of the glomerular basement membrane leading to proteinuria.
With severe damage, the nephrotic syndrome may appear characterized by all the features of membranous glomerulonephritis with subepithelial electron-dense deposits, reminiscent of an immune complex deposition.
Central Nervous System:
Exposure to both mercury vapour and mercury compounds exerts a strong effect on the central nervous system.
In acute mercury poisoning the brain is characterized by necrosis of gray matter, hyalinization of vessels, proliferation of capillaries and astrocytic proliferation.
1) Acute mercury poisoning - Brain tissue: Necrosis of the the occipital cortex
2) Acute mercury poisoning - Brain tissue: Capillary proliferation and necrosis
3) Acute mercury poisoning - Brain tissue: Proliferation of the astrocytes
Mercury vapour effects are neuropsychiatric in nature and occur at relatively low levels.
Symptoms include excessive shyness, insomnia and emotional instability with depression and irritability.
Intention tremor occurs with both forms of mercury toxicity.
In contrast to mercury vapour toxicity, methyl mercury effects are largely sensorimotor in nature and include paresthesias, constriction of visual field, loss of hearing, loss of sense of smell and taste, incordination, paralysis and abnormal reflexes.
In addition, spontaneous fits of laughing and crying and intellectual deterioration occur only in methyl mercury poisoning.
Morphologically, in both forms of poisoning degenerative changes are widespread and include degeneration of both the plasma membrane and the myelin sheath.
Microscopic examination reveals both cerebral and cerebellum atrophy with involvement of the granular layer of the cerebellum being particularly prominent.
The Purkinje cells are intact.
Spongy degeneration of the white matter in the visual cortex and other cortical regions are present.
Prenatal exposure to mercury:
Mercury has a teratogenic effect on the fetus.
The abnormal changes include microcephaly, abnormal gyration patterns, gray matter heterotopias and disruption of cortical architecture.
Chronic instances of methyl mercury poisoning are reflected are reflected by gross atrophy of the calcarine cortex and cerebellum.
In the calcarine cortex there is considerable neuronal loss and gliosis.
The outer cortical layers and depths of sulci appear most effective.
In the cerebellum, internal granular cell neurons are lost along with small numbers of Purkinje cells.
The route of administration seems unimportant as both ingestion and intravenous administration as well as other routes result in similar morphological presentation.
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