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Toxic heavy metal
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Toxic heavy metal
A toxic heavy metal is a common but misleading term for a metal-like element noted for its potential toxicity. Not all heavy metals are toxic and some toxic metals are not heavy. Elements often discussed as toxic include cadmium, lead, and mercury all of which appear in the World Health Organization's list of 10 chemicals of major public concern. Other examples include chromium, nickel, antimony, arsenic, bismuth, thallium, and tin.
These toxic elements are found naturally in the earth. They become concentrated as a result of human caused activities and can enter plant and animal (including human) tissues via inhalation, diet, and manual handling. Then, they can bind to and interfere with the functioning of vital cellular components. The toxic effects of arsenic, mercury, and lead were known to the ancients, but methodical studies of the toxicity of some heavy metals appear to date from only 1868. In humans, heavy metal poisoning is generally treated by the administration of chelating agents. Some elements otherwise regarded as toxic heavy metals are essential, in small quantities, for human health.
The International Union of Pure and Applied Chemistry (IUPAC), which standardizes nomenclature, says the term "'heavy metals' is both meaningless and misleading". The IUPAC report focuses on the legal and toxicological implications of describing "heavy metals" as toxins when there is no scientific evidence to support a connection. The density implied by the adjective "heavy" has almost no biological consequences and pure metals are rarely the biologically active substance. This characterization has been echoed by numerous reviews. The most widely used toxicology textbook, Casarett and Doull's Toxicology, uses "toxic metal" not "heavy metals". Nevertheless many scientific and science related articles continue to use "heavy metal" as a term for toxic substances.
Metals with multiple toxic effects include arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and nickel (Ni).
Elements that are nutritionally essential for animal or plant life but which are considered toxic metals in high doses or other forms include cobalt (Co), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), selenium (Se), and zinc (Zn).
Toxic metals are found naturally in the earth, and become concentrated as a result of human activities, or, in some cases geochemical processes, such as accumulation in peat soils that are then released when drained for agriculture. Common sources include fertilisers; aging water supply infrastructure; and microplastics floating in the world's oceans. Arsenic is thought to be used in connection with coloring dyes. Rat poison used in grain and mash stores may be another source of the arsenic.
The geographical extent of sources may be very large. For example, up to one-sixth of China's arable land might be affected by heavy metal contamination.
Lead is the most prevalent heavy metal contaminant. As a component of tetraethyl lead, (CH
3CH
2)
4Pb, it was used extensively in gasoline during the 1930s–1970s. Lead levels in the aquatic environments of industrialised societies have been estimated to be two to three times those of pre-industrial levels. Although the use of leaded gasoline was largely phased out in North America by 1996, soils next to roads built before this time retain high lead concentrations. Lead (from lead(II) azide or lead styphnate used in firearms) gradually accumulates at firearms training grounds, contaminating the local environment and exposing range employees to a risk of lead poisoning.
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Toxic heavy metal
A toxic heavy metal is a common but misleading term for a metal-like element noted for its potential toxicity. Not all heavy metals are toxic and some toxic metals are not heavy. Elements often discussed as toxic include cadmium, lead, and mercury all of which appear in the World Health Organization's list of 10 chemicals of major public concern. Other examples include chromium, nickel, antimony, arsenic, bismuth, thallium, and tin.
These toxic elements are found naturally in the earth. They become concentrated as a result of human caused activities and can enter plant and animal (including human) tissues via inhalation, diet, and manual handling. Then, they can bind to and interfere with the functioning of vital cellular components. The toxic effects of arsenic, mercury, and lead were known to the ancients, but methodical studies of the toxicity of some heavy metals appear to date from only 1868. In humans, heavy metal poisoning is generally treated by the administration of chelating agents. Some elements otherwise regarded as toxic heavy metals are essential, in small quantities, for human health.
The International Union of Pure and Applied Chemistry (IUPAC), which standardizes nomenclature, says the term "'heavy metals' is both meaningless and misleading". The IUPAC report focuses on the legal and toxicological implications of describing "heavy metals" as toxins when there is no scientific evidence to support a connection. The density implied by the adjective "heavy" has almost no biological consequences and pure metals are rarely the biologically active substance. This characterization has been echoed by numerous reviews. The most widely used toxicology textbook, Casarett and Doull's Toxicology, uses "toxic metal" not "heavy metals". Nevertheless many scientific and science related articles continue to use "heavy metal" as a term for toxic substances.
Metals with multiple toxic effects include arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and nickel (Ni).
Elements that are nutritionally essential for animal or plant life but which are considered toxic metals in high doses or other forms include cobalt (Co), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), selenium (Se), and zinc (Zn).
Toxic metals are found naturally in the earth, and become concentrated as a result of human activities, or, in some cases geochemical processes, such as accumulation in peat soils that are then released when drained for agriculture. Common sources include fertilisers; aging water supply infrastructure; and microplastics floating in the world's oceans. Arsenic is thought to be used in connection with coloring dyes. Rat poison used in grain and mash stores may be another source of the arsenic.
The geographical extent of sources may be very large. For example, up to one-sixth of China's arable land might be affected by heavy metal contamination.
Lead is the most prevalent heavy metal contaminant. As a component of tetraethyl lead, (CH
3CH
2)
4Pb, it was used extensively in gasoline during the 1930s–1970s. Lead levels in the aquatic environments of industrialised societies have been estimated to be two to three times those of pre-industrial levels. Although the use of leaded gasoline was largely phased out in North America by 1996, soils next to roads built before this time retain high lead concentrations. Lead (from lead(II) azide or lead styphnate used in firearms) gradually accumulates at firearms training grounds, contaminating the local environment and exposing range employees to a risk of lead poisoning.
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