Lead – Lead is a highly corrosion-resistant, machinable metal. Piping and paint symbolise some of its use cases. It was utilised as an anti-knocking delegate in gasoline. It was later discovered that its by-product could cause serious health complications. You will find lead in car batteries, ammunition, lifting weights, radiation protection, and cable sheathing.

Mercury – Mercury is a naturally-occurring chemical element found in rock in the earth’s crust, including in deposits of coal. On the periodic table, it has the symbol “Hg” and its atomic number is 80. It exists in several forms.

Elemental or metallic mercury is a shiny, silver-white metal, historically referred to as quicksilver, and is liquid at room temperature. It is used in older thermometers, fluorescent light bulbs and some electrical switches. When dropped, elemental mercury breaks into smaller droplets which can go through small cracks or become strongly attached to certain materials. At room temperature, exposed elemental mercury can evaporate to become an invisible, odourless toxic vapor. If heated, it is a colourless, odourless gas.

In its inorganic form, mercury occurs abundantly in the environment, primarily as the minerals cinnabar and metacinnabar, and as impurities in other minerals. Mercury can readily combine with chlorine, sulphur, and other elements, and subsequently weather to form inorganic salts.  Inorganic mercury salts can be transported in water and occur in soil. Dust containing these salts can enter the air from mining deposits of ores that contain mercury. Emissions of both elemental or inorganic mercury can occur from coal-fired power plants, burning of municipal and medical waste, and from factories that use mercury. Inorganic mercury can also enter water or soil from the weathering of rocks that contain inorganic mercury salts, and from factories or water treatment facilities that release water contaminated with mercury.

Although the use of mercury salts in consumer products, such as medicinal products, have been discontinued, inorganic mercury compounds are still being widely used in skin lightening soaps and creams. Mercuric chloride is used in photography and as a topical antiseptic and disinfectant, wood preservative, and fungicide. In the past, mercurous chloride was widely used in medicinal products, including laxatives, worming medications, and teething powders. It has since been replaced by safer and more effective agents. Mercuric sulphide is used to colour paints and is one of the red colouring agents used in tattoo dyes.

Human exposure to inorganic mercury salts can occur both in occupational and environmental settings. Occupations with higher risk of exposure to mercury and its salts include mining, electrical equipment manufacturing, and chemical and metal processing in which mercury is used. In the general population, exposure to mercuric chloride can occur through the dermal route from the use of soaps and creams or topical antiseptics and disinfectants. Another, less well-documented, source of exposure to inorganic mercury salts among the general population is from their use in ethnic religious, magical, and ritualistic practices and in herbal remedies.

When inorganic mercury salts can become attached to airborne particles. Rain and snow deposit these particles on land. Even after mercury gets deposited on land, it often returns to the atmosphere, as a gas or associated with particles, and then redeposits elsewhere.

As it cycles between the atmosphere, land, and water, mercury undergoes a series of complex chemical and physical transformations, many of which are not completely understood. Microscopic organisms can combine mercury with carbon, thus converting it from an inorganic to organic form. Methylmercury is the most common organic mercury compound found in the environment and is highly toxic.

Cadmium – Cadmium (Cd) is a soft, malleable, bluish white metal found in zinc ores, and to a much lesser extent, in the cadmium mineral greenockite. Most of the cadmium produced today is obtained from zinc by-products and recovered from spent nickel-cadmium batteries. First discovered in Germany in 1817, cadmium found early use as a pigment because of its ability to produce brilliant yellow, orange, and red colours. Cadmium became an important metal in the production of nickel-cadmium (Ni-Cd) rechargeable batteries and as a sacrificial corrosion-protection coating for iron and steel. Common industrial uses for cadmium today are in batteries, alloys, coatings (electroplating), solar cells, plastic stabilizers, and pigments. Cadmium is also used in nuclear reactors where it acts as a neutron absorber. While lithium-ion batteries have made significant gains in popularity for lightweight electronic devices, new market opportunities for industrial applications of Ni-Cd batteries will continue to fuel cadmium use.

Cadmium and its compounds are highly toxic and exposure to this metal is known to cause cancer and targets the body’s cardiovascular, renal, gastrointestinal, neurological, reproductive, and respiratory systems.

Others – Whilst the above are the most common forms of toxic metals there are plenty more out there, including Nickel, Chromium, Cobalt, Manganese, Beryllium and so on.

Rare Earth Metals

There are 17 different types of rare Earth metals and the most common one found is Neodymium, commonly found in older style hard drives and used predominantly in hybrid cars and guided missile systems. The whole list of rare metals is: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), and yttrium (Y).