Overview of Metal Poisoning, Its Types and Instances in History

Metal poisoning or metal toxicity is the harmful effects caused due to specific metals in specific forms. It is a common misconception that all toxic metals are heavy metals but even lighter metals like Beryllium is listed as Category 1 Carcinogens by The International Agency for Research on Cancer. And not all heavy metals are toxic, example Nickel which promotes cell growth. The reason for the toxic effects of these metals is due to the ability to imitate as other metals and cause malfunction of human body. Example Beryllium has the same properties as Magnesium and it displaces it from enzymes and becomes malfunctioned. Thus they interfere with metabolic process and cause harm. The most common toxic metals are:

1. Metals which have no confirmed biological role such as Lead, Cadmium, Mercury etc.
2. Metalloids like Arsenic, Antimony.
3. Radioactive Metals that cause both radiation damage and chemical toxicity.
4. Abnormal forms of essential metals like Chromium (+3) has a role in action of insulin, whereas Chromium (+6) is a carcinogen.

The level of toxicity of metal depends on the ligand which it is attached to; example - Methyl Mercury is more toxic than elemental Mercury or its salts. The toxicity of a metal also depends on its solubility and absorbability. Bismuth is relatively less toxic than other heavy metals as its salts are less soluble making them common in number of medicines. The major Types of metal poisoning:

1. Arsenic poisoning: It is the poisoning caused due to higher levels of Arsenic in body. The causes are Drinking water (10-50 ppb is considered safe), Arsenate pesticides (although banned, its residues still remain), Copper smelting which produces Arsenic as by-product.
2. Beryllium poisoning: It is the toxic effect caused due to Beryllium and its compounds. It is a carcinogen.
3. Cadmium poisoning: Caused due Smoking, Industries that produce Cadmium-Nickel batteries. The maximum prescribed concentration of Cd in drinking water is 0. 005 ppm.
4. Argyria: It is a disease caused due to high exposure to Silver; it can be caused due to direct intake, or deposition of silver or silver sulphide on the skin. This picture shows the change in skin color due to Argyria in an old man who had been using nose drops which was contaminated with silver. The silver had deposited in the dermis changing the color.
5. Zinc Toxicity: Zinc becomes toxic by ingesting more than 225mg of Zinc, it may occur during galvanization. The maximum prescribed concentration of Zn in drinking water is 5. 0 ppm.
6. Lead poisoning: It occurs when blood lead concentration is above 10μg/dL. The reason for lead pollution is due to human activities such as lead-acid battery recovery facilities, use of Tetraethyl Lead as anti-knocking agents, Paints, Bullets. The main sources of absorption of inorganic lead are from ingestion and inhalation.
7. Mercury poisoning: Caused due to consumption of sea food like fishes (larger fishes like whales, tuna) contain high concentration of Methyl Mercury (formed from inorganic mercury by the action of microbes in lakes, rivers, open ocean. ), Inhalation of Mercury vapors. Mercury salts affect gastrointestinal tract and cause severe kidney damage too.

Metal Poisoning in Our History and Some Dreadful Instances:

Arsenic: The Greek geographer and historian wrote that only slaves were working in real mines and in space, because they would surely die from the poisonous effects of the poisonous fumes emitted from the ores. Arsenic-contaminated beer poisoned more than 6, 000 people in the Manchester area of England in 1900 and at least 70 people were believed to have been killed. Groundwater contamination with arsenic is a form of groundwater pollution. A 2007 study found that more than 137 million people in more than 70 countries are likely to be affected by arsenic poisoning from drinking water.

Dreadful Example for Mercury Poisoning: Minamata disease was first discovered in Minamata city in Kumamoto prefecture, Japan, in 1956. It was started due to the release of methylmercury in the industrial wastewater from the Chisso Corporation's chemical factory, which continued from 1932 to 1968. This highly bioaccumulative chemical in oysters and fish in Minamata Bay and the Shiranui Sea, eaten by the local population, causes mercury poisoning. While cats, dogs, pigs and human deaths continued for 36 years, the government and the company did much to prevent pollution. Animal relics were severe enough in cats called "dancer cats fever". In March 2001, 2265 of the victims were officially identified as having Minamata disease (1, 784 of who died). In 22 documented cases, pregnant women who ate contaminated fish showed mild or no symptoms but had children with severe developmental disabilities.

Lead poisoning: In the 2nd century BC the Greek botanist Nicander described the colic and paralysis seen in lead-poisoned people. Julius Caesar's engineer, Vitruvius, reported, "Water is much more wholesome from earthenware pipes than from lead pipes guidelines. The source of the contamination was attributed to "a combination of dilapidated drinking water infrastructure, including lead jointed pipelines, end-of-life polyvinyl chloride pipes and household plumbing".

Chromium poisoning: Chromium (III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium (VI) were horrible. In 1890, Newman explained the increased cancer risk of workers in a chromate dye company. Chromate-induced dermatitis was identified in aircraft workers during World War II. In 1963, an outbreak of dermatitis, ranging from erythema to exudative eczema, occurred amongst 60 automobile factory workers in England. The workers had been wet-sanding chromate-based primer paint that had been applied to automobile bodies. In Australia, chromium was released from the Newcastle Orica explosives plant on August 8, 2011. Up to 20 workers at the plant were exposed as were 70 nearby homes in Stockton.