What Is the Function of Heavy Metals in Electronics?

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Devices that consumers use every day, such as televisions and computers, contain heavy metals. This article explores why heavy metals are used in electronics and, as well as the toxic effects of those heavy metals.

What Are Heavy Metals?

There is no agreed upon definition of heavy metals. Instead, heavy metals have two definitions.

  1. Heavy metals are metals that have a high density (particles are packed closely together). 

Most heavy metals under this definition have a high atomic number (the number of protons in the nucleus of an atom) and a high atomic weight (the total weight of the atoms making up an element).

  1. Heavy metals are metals with relatively high density that are toxic at low concentrations, meaning even a small amount of the metal is toxic.

To be considered a heavy metal, the material must meet either of these definitions, but does not need to meet both. Some metals, such as mercury or lead, are both high density and toxic at low concentrations. Other metals may simply fit one of the definitions.

Many of the metals you’ve heard of, such as iron, copper, platinum, and gold, are heavy metals due to their high density. Some of these high density heavy metals, such as iron, cobalt, and zinc act as nutrients. Others, such as silver, are not toxic in small amounts, but can be toxic in higher amounts or different states.

Other heavy metals, such as hexavalent chromium and cadmium, are highly toxic in low concentrations and can cause severe health problems when a human is exposed.

Which Heavy Metals are Found in Electronics?

Heavy metals are necessary to create many of the electronic devices an average consumer uses every day. The following heavy metals, while not the only heavy metals used, perform important functions in a wide variety of electronics. 

Cadmium

Cadmium is a heavy metal used in electronics, and is popular due to its malleability. Cadmium selenide, a cadmium compound, is an easily shaped metal that is most often used as semiconductors. 

Semiconductors can conduct electricity in high heat, but not in low heat. Cadmium is a good semiconductor because it is highly resistant to high temperatures. Semiconductors like cadmium selenide have a conductivity (ability to conduct electricity) that lies in between a conductor (like metal) and a non-conductive insulator (like ceramic). As temperature rises, the conductivity of the semiconductor increases, and the cadmium material can act as a conductor. At low temperatures, the same material blocks the flow of electricity. 

Semiconductors are found in most electronic devices today. Semiconductors have an extremely wide variety of functions, but generally they work to amplify signals in a circuit, convert energy, and pass current in a specific direction.

Cadmium also is resistant to corrosion. This makes it a popular metal to use as a protective shield against corrosion in electronics.

Read more about cadmium in electronics: Cadmium

Mercury

Mercury is a heavy metal commonly used in LCD (liquid crystal display) screens. LCD screens use cold-cathode fluorescent lamps (CCFLs) that contain mercury. CCFLs include fluorescent tubes that work to backlight an LCD TV or monitor screen. The light is produced when electricity is used to excite (add energy to) mercury vapor. The vapor is discharged, which creates a fluorescent coating on the inside of the tube that emits light.

Mercury is also used in some laptop screen shutoffs. In a mercury tilt switch used in some laptops, mercury moves to the other side when the laptop is opened or closed. This shift turns the screen on or off.

Mercury was also used to create switches in televisions that were produced before 1991.

Read more about mercury in electronics: Mercury


Lead

Lead is considered one of the most important metals in electronic production. Lead is malleable, does not break easily, and, when combined with tin, has a low melting point, which means it can be worked with at a lower temperature and is less sensitive to variations in temperature.

The main use of lead in electronics is lead soldering. Lead-tin soldering is used to attach electronic components. The lead solder connects two metals securely, allowing an electric signal to pass through. For example, lead solder could attach a wire to a circuit board

Lead is also used in alloys (a mixture) with other metals, such as copper and steel, which expands the use of these metals. Lead alloy in steel is often used in electronic products.

Read more about lead in electronics: Lead

Nickel

Nickel is a heavy metal used in a variety of electrical equipment and devices. Pure nickel conducts electricity well, is magnetic, and is resistant to corrosion. Nickel is often used in electronic wiring. 

Nickel is often used in electronics in alloy form, particularly in heating coils of electric appliances like irons, toaster ovens, and grills. Nickel is also used in powder form in cell phone capacitors, a device that stores electrical energy. Nickel powder may also be mixed in with a non-conductive substance, such as silicone and rubber, to allow for conductivity through the substance. This technique is most frequently used in cell phone microphones.

Hexavalent Chromium

Hexavalent chromium is a form of the heavy metal chromium that is not found in nature, and is thus manmade. Hexavalent chromium is commonly used in anticorrosive coatings on metal parts in electronics or as a pigment or paint.

The process of protecting metal from corrosion using hexavalent chromium is called chromating or passivation. In passivation, a thin layer of chromium salts are added to a metal in an electronic device. Chromium-coated metal is used in many components, including nuts and bolts, electric switches, and antennae.

Read more about chromium in electronics: Hexavalent Chromium

Exposure to Heavy Metals

Some heavy metals used in electronics are toxic. Exposure to heavy metals used in electronics can cause serious environmental and health problems. 

Most people are not exposed to heavy metals when using electronics. For example, it is unlikely that you are frequently exposed to your phone’s circuit board or the inner workings of your LCD television screen. However, exposure may occur either during manufacturing of electronics or during recycling, when the parts are broken down and heavy metals are exposed.

According to a paper published at Stanford University in 2011, heavy metals can harm not only workers in the production and recycling phases, but also communities located near manufacturing plants (Nimpuno et al. 2011).

Additionally, if electronics are not recycled and are instead allowed to break down in a landfill, it is likely that heavy metals will eventually leak out. This not only creates a risk of toxic exposure for humans, but also has severe environmental impacts. Toxic substances can leach into water, soil, and air, harming not only human health, but other species.

Negative Impacts of Heavy Metals

Cadmium

Exposure to cadmium is most famous for causing a degenerative bone disease, Itai-itai disease. This disease was caused by cadmium poisoning contracted as a result of mining. Cadmium is highly water soluble, and so as mining byproducts, including cadmium, were released into a nearby river, cadmium pollution occurred. Eventually, cadmium was absorbed into crops irrigated by the river, causing widespread disease.

Cadmium can also soften the bones and cause kidney damage.

Mercury

Mercury exposure at high levels can cause a host of health impacts, including damage to the brain, heart, lungs, kidneys, central nervous system, and immune system. 

Mercury can be released into the air a number of ways, one of which is through burning of electronic products containing mercury. Mercury can be transported in the air for great distances before it is deposited in soil and water.

While mercury exposure is most common by eating seafood containing mercury, exposure to mercury vapor is also possible if an electronic device containing mercury breaks. For example, if an LCD screen containing cold-cathode fluorescent lamps (which contain mercury) breaks, toxic mercury dust or powder can be released.

Mercury can also cause significant environmental damage. When animals are exposed to mercury at high levels, death and reproductive damage can occur.

Lead

There is no safe exposure level to lead. When lead is swallowed or breathed in, or enters the body another way, it gets stored in blood, which can cause long-term harm.

 Lead exposure, particularly in children, can cause damage to the brain and nervous system, slowed growth, and problems with hearing and speech. Long term exposure in adults can also cause fertility problems, heart disease, and kidney disease.

Nickel

Industrial use of nickel has led to environmental pollution and has increased human exposure to the toxic heavy metal.

Nickel has a wide variety of health impacts caused by exposure, including allergy, headaches, cardiovascular and kidney diseases, lung fibrosis, lung and nasal cancer. While research is ongoing as to the mechanism for these diseases (how nickel acts in the body to cause the disease), inhalation is the clear route of exposure that causes respiratory tract cancer.

Hexavalent Chromium

Hexavalent chromium is carcinogenic and causes a wide range of health problems, particularly in people exposed to the metal in manufacturing.

If hexavalent chromium is breathed at high levels, it can cause lung cancer, damage to the respiratory tract, and damage to the eyes and skin (dermatitis). Prolonged exposure, such as working in a factory that uses hexavalent chromium to produce anti-corrosive coatings, is especially dangerous.

Solutions: Reducing the Risk of Heavy Metals in Electronics

Several countries have enacted legislation that aims to reduce the risks, both to the environment and human health, associated with heavy metals. The most impactful legislation in this area comes from the EU, in the form of RoHS and WEEE directives.

RoHS: Restriction of Hazardous Substances

RoHS stands for Restriction of Hazardous Substances. The RoHS directive, issued in the European Union, restricts the use of several hazardous materials in electronic and electrical equipment (EEE). 

Manufacturers may not use restricted substances in amounts above 1000ppm (cadmium’s limit is 100ppm). Restricted substances include heavy metals Cadmium (Cd), Mercury (Hg), Lead (Pb), and Hexavalent Chromium (Cr VI).

RoHS restrictions help reduce the risk of exposure to toxic heavy metals in electronics. For example, if those electronic devices were to break or be put in landfill, it is less likely that high amounts of toxic metals will leak out.

Read more: What is RoHS?

WEEE: Waste Electrical and Electronic Equipment

Waste Electrical and Electronic Equipment (WEEE) is an EU directive that aims to improve the collection, treatment, and recycling processes of electronic and electrical equipment (EEE) that is no longer in use. WEEE helps reduce the amount of electronic waste that ends up in landfills, and helps ensure proper, safe disposal of electronic waste.

Read more: What is WEEE?

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