How does exposure to heavy metal occur?

Updated: Dec 31, 2020
  • Author: Adefris Adal, MD, MS; Chief Editor: Sage W Wiener, MD  more...
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Answer

Exposure to metals may occur through the diet, from medications, from the environment, or in the course of work or play. Where heavy metal toxicity is suspected, time taken to perform a thorough dietary, occupational, and recreational history is time well spent, since identification and removal of the source of exposure is frequently the only therapy required.

A full dietary and lifestyle history may reveal hidden sources of metal exposure. Metals may be contaminants in dietary supplements, or they may leach into food and drink stores in metal containers such as lead decanters. Persons intentionally taking colloidal metals for their purported health benefits may ultimately develop toxicity. Metal toxicity may complicate some forms of drug abuse. Beer drinker’s cardiomyopathy was diagnosed in alcoholics in Quebec, and later Minnesota, during a brief period in the 1970s when cobalt was added to beer on tap to stabilize the head. More recently, a parkinsonian syndrome among Latvian injection drug users of methcathinone was linked to manganese toxicity.

Classic examples of environmental contamination include the Minimata Bay disaster and the current epidemic of arsenic poisoning in South East Asia. In the 1950s, industrial effluent was consistently dumped into Japan’s Minimata Bay, and methylmercury bioaccumulated to exceedingly high concentrations in local fish. Although some adults did develop signs and symptoms of toxicity, the greatest impact was on the next generation, into which many were born with severe neurologic deficits.

Currently, millions of people living in and around Bangladesh are at risk for organ dysfunction and cancer from chronic arsenic poisoning from the water supply. In an effort to bypass ground water sources rife with bacterial contamination, tube wells were sunk throughout that area, deep into the water table. [4]  Unfortunately, the bedrock in that part of the world is rich in arsenic, giving these deeper water stores—and the crops they irrigate—a high concentration of arsenic, and toxicity is epidemic throughout the area. Childhood lead poisoning linked to the ingestion of old paint chips in North America is another good example of environmental contamination.

Metals have been used with malicious intent as poisons. Arsenic is perhaps more rightly classified as a metalloid, but it is consistently the single substance most commonly thought of as a poison. Metals have also been used in warfare as chemical weapons. Again, arsenic was the primary component of the spray known as Lewisite that was used by the British during trench warfare in World War I. Exposure produced severe edema of the eyelids, gastrointestinal irritation, and both central and peripheral neuropathies.

The first antidote to heavy metal poisoning, and the basis for chelation therapy today, was British Anti-Lewisite (BAL, or dimercaprol), a large molecule with sulfhydryl groups that bind arsenic, as well as other metals, to form stable covalent bonds that can then be excreted by the body. BAL was developed by the British during World War II in anticipation of a reinitiation of chemical warfare as had been waged earlier in the century.

In total, however, occupational exposure has probably accounted for the vast majority of heavy metal poisonings throughout human history. Hippocrates described abdominal colic in a man who extracted metals, and the pernicious effects of arsenic and mercury among smelters were known even to Theophrastus of Erebus (370-287 BC).


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