Toxic heavy metals cadmium, mercury, lead, chromium, and arsenic are elements known for high density and toxicity even in small amounts. These five are notorious for adverse health effects and environmental impacts. They're used in paint pigments through history.
1. Cadmium
Discovery
Cadmium is discovered1817 by Swedish chemist Friedrich Strohmeyer as a byproduct of zinc processing. Cadmium is a common impurity of zinc compounds, though often found only in minute quantities.
Formation
Cadmium is typically formed from the weathering of zinc ores, primarily sphalerite, through both natural and anthropogenic processes.
Mining and Extraction
Cadmium is mainly extracted during the smelting of zinc, where it occurs in trace amounts in zinc ores. The process involves crushing and roasting the ore, followed by extensive refining.
Historical Use
Historically, cadmium was used in batteries (especially nickel-cadmium batteries), pigments, and coatings to prevent corrosion.
Role in Nature
In nature, cadmium can be found in low concentrations in soils, plants, and water, largely as a result of human activity.
Toxic Effects & Hazards
Cadmium is a known carcinogen and can cause kidney damage, lung cancer, and bone disease. Exposure often occurs through contaminated food, water, or inhalation of fumes.
Use in Paint Pigments
Cadmium-based pigments, like cadmium red and cadmium yellow, are valued for their vibrancy and stability by the French Impressionists and later artists. They're now replaced with non-toxic versions and remain some of the brightest colors available.
Other Uses
Besides pigments and batteries, cadmium is used in metal plating and in some types of solar cells.
2. Mercury
Discovery
Mercury, the only metal that is liquid at room temperature, has been known since ancient times, with its use going back to at least 1500 BCE in Egypt. In China it comes to prominence after the unification of the Warring States when First Emperor Qin seeks the Elixir of Life.
Formation
Mercury forms mostly through volcanic eruptions and the weathering of natural deposits, primarily from cinnabar (HgS), its principal ore.
Mining and Extraction
Mercury is extracted from cinnabar ore through roasting, which converts it into elemental mercury as vapor that can be condensed back into liquid form. Mercury mining and processing leads to slow terrifying death.
Historical Use
Historically, mercury is used in medicine, for dental amalgams, and as a preservative in vaccines before its toxic effects were understood. The toxic effects of mercury are understood by the Romans, who send convicted criminals and troublesome slaves to the mercury mines.
Its effects are also understood by physicians and alchemists such as Paracelsus, during the German Renaissance. He believes a small amount of toxin can be medicinal although a large amount is lethal, and prescribes it for syphilis, a terrible plague covering the body in sores.
People rub mercury over their entire bodies or bathe in mercury to combat syphilis, negating the concept of Paracelsus. It's thought during the Renaissance about one in seven people suffer from syphilis.
A cure is not found until the 20th century, with penicillin. Historically mercury is also widely used in thermometers, hat making, and early photography.
Role in Nature
Mercury naturally occurs in air, soil, and water. Its bioaccumulation in aquatic life poses significant ecological risks.
Toxic Effects & Hazards
Mercury is extremely toxic to the nervous system, leading to neurological disorders, respiratory failure, and even death in high doses.
Use in Paint Pigments
Mercury is used in paint and gold-plating by the Romans. Mercury processing yields the toxic scarlet pigment vermillion.
Other Uses
Current uses of mercury include thermostats, fluorescent light bulbs, and some types of electrical switches.
3. Lead
Discovery
Lead has been known since ancient times and is used by ancients c. 3000 BCE.
Formation
Lead primarily forms in mineral deposits through geological processes, often found in conjunction with zinc and silver.
Mining and Extraction
Lead is extracted via smelting, where ores containing lead (like galena) are crushed, roasted, and then treated to separate the lead.
Historical Use
Lead's historical uses include pipes, paints, and gasoline additives. Many of these applications have been reduced or eliminated due to health risks.
The oldest known lead-containing object made by human hands is a small statue found in Turkey, from 6,500 BCE. Egyptians between 3,000 and 4,000 B.C. use lead to glaze pottery and in construction.
Role in Nature
In low concentrations, lead can be found naturally in soil and rocks; however, human activities have elevated its levels significantly.
Toxic Effects & Hazards
Lead poisoning can cause severe health issues, particularly in children, including developmental and learning disabilities, as well as damage to the nervous system.
Use in Paint Pigments
Lead-based paints were famous for their durability and color, particularly in vibrant hues, before being banned in many countries. Lead white and minium red (roasted lead white) are particularly favored in early years due to their excellent coverage and brilliance.
Minium red is often used in illuminated manuscripts to paint robes or decorations. Illuminated manuscripts are generally small, and paintings made with minium red known as miniatures. Later the term broadens to include any small work.
Other Uses
Today, lead is used in electric car batteries, along with sulfuric acid and arsenic. It's a component of radiation shielding, and some types of glass.
4. Chromium
Discovery
Chromium is discovered in 1797 by French chemist Louis Nicolas Vauquelin. He isolates it from a red lead ore from Russia, crocoite.
Formation
Chromium typically forms as chromite ore, a result of igneous processes in the Earth’s crust.
Mining and Extraction
Chromium is extracted from chromite via a process of roasting and reduction in electric furnaces.
Historical Use
Historically, chromium is famous for its use in stainless steel and chrome plating, and dyes.
Role in Nature
Chromium exists in various oxidation states, with chromium (VI) being particularly toxic. In smaller quantities, chromium is essential for human metabolism.
Toxic Effects & Hazards
Chromium (VI) is known carcinogenic and can cause respiratory issues, skin ulcers, and other health problems upon exposure.
Use in Paint Pigments
Chromium compounds, such as chromate, are used in various pigments known for their bright colors and stability. Toxic elements are usually replaced with safer synthetics.
Other Uses
Chromium is widely used in the production of stainless steel, dyes, and anti-corrosion coatings.
5. Arsenic
Discovery
Arsenic has been known since ancient times, with documented use dating back to around 1250 BC in various cultures.
Formation
Arsenic is found in nature primarily in sulfide ores and can be formed from both volcanic activity and human mining practices.
Mining and Extraction
Arsenic is usually extracted from copper and lead ores but is often recovered as a byproduct in refining copper and gold.
Historical Use
Historically, arsenic was used in pesticides, herbicides, and even as a poison due to its toxicity. It's desirable as a preservative of wood. Less toxic substances are used today.
Role in Nature
Arsenic occurs naturally in soil and water, often as a contaminant from mining and industrial activities.
Toxic Effects & Hazards
Arsenic is highly toxic, known for causing cancer, skin lesions, and various organ diseases, particularly affecting the liver and kidneys.
Use in Paint Pigments
Arsenic compounds are once used in pigments, like Scheele’s green, Paris green, orpiment yellow and realgar red. Many are acclaimed by Renaissance and later artists.
Due to toxicity they're eventually replaced with non-toxic synthetic paints. Arsenic in historical artists' paint often darkens to an unpleasant shade of green or brown.
Other Uses
Today, arsenic is used in some alloys, semiconductors, and for the treatment of specific medical conditions, although its use is heavily regulated.