Table of Contents
- Properties of Hexavalent Chromium
- Hexavalent Chromium in Electronics
- Toxicity of Hexavalent Chromium
- RoHS: Restriction of Hazardous Substances
- Alternatives to Hexavalent Chromium
- Hexavalent Chromium-Limiting Legislation
Hexavalent chromium is a heavy metal used in the manufacturing of many electronic devices. Hexavalent chromium’s use is limited by the European Union’s RoHS directive due to its high toxicity.
Properties of Hexavalent Chromium
Hexavalent chromium is a heavy metal used in electronics. Heavy metals are metals with relatively high density that are toxic at low concentrations, meaning even a small amount of the metal is toxic.
Chromium is a naturally occurring element found in the earth’s crust, and is most commonly produced in South Africa and Kazakhstan. Hexavalent chromium is a chromium ion (an electrically charged chromium atom) that has the ability to pair with six other atoms. The chemical symbol for hexavalent chromium (sometimes referred to as chromium hexavalent) is Cr(VI). Hexavalent chromium is not found in nature and must be industrially produced.
Chromium exists in other forms as well. However, not only is hexavalent chromium the most common form of chromium in industrial settings, it is also the most toxic.
Hexavalent chromium is popular in electronics manufacturing due to its highly anti-corrosive properties.
Hexavalent Chromium in Electronics
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 hexavalent chromium salts are added to a metal in an electronic device. For example, many circuit boards are coated with hexavalent chromium.
The process of passivation also helps other coatings like paint and enamel stick better, so many steel and aluminum components have a thin layer of hexavalent chromium added before paint is added on top.
Chromium-coated metal is used in many products and components, including nuts and bolts, electric switches, and antennae.
Hexavalent chromium is also used to produce pigments that coat plastics on switches or fuses, or wire and cable insulation.
Toxicity of 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 inhaled 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 toxic.
Hexavalent chromium is particularly dangerous because it is very water soluble. When hexavalent chromium comes into contact with a water source, it spreads widely and quickly. Proper disposal of electronics containing hexavalent chromium is important to avoid the breakdown of electronics in landfills that release chromium into soil or water sources.
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). All EEE products sold in the EU must comply with RoHS.
RoHS restricts the use of ten hazardous substances in electronics, including hexavalent chromium. Electronic devices may only contain these substances in amounts lower than 1000 ppm. The allowable amount for cadmium is 100 ppm.
The materials include:
- Cadmium (Cd)
- Mercury (Hg)
- Lead (Pb)
- Hexavalent Chromium (Cr VI)
- Polybrominated Biphenyls (PBB)
- Polybrominated Diphenyl Ethers (PBDE)
- Bis(2-Ethylhexyl) phthalate (DEHP)
- Benzyl butyl phthalate (BBP)
- Dibutyl phthalate (DBP)
- Diisobutyl phthalate (DIBP)
Any manufacturer, importer, or distributor of electronic and electrical equipment (EEE) sold on the EU market must be compliant with RoHS.
EEE regulated under RoHS includes a wide variety of electronic products separated into eleven categories, ranging from large household appliances to medical devices. The eleventh category is all-encompassing, as it includes any EEE not covered in the previous ten categories.
Read more about how to ensure compliance with RoHS: What is ‘RoHS Compliant’?
RoHS Hexavalent Chromium Exemptions
While alternatives to hexavalent chromium coatings exist and are in the process of being refined, exemptions do exist under RoHS for the use of hexavalent chromium in certain applications and electronic categories. For example, exemptions exist for the use of hexavalent chromium in spare parts for x-ray systems. These exemptions are given a date upon which they expire, and will no longer be exempt from RoHS unless an extension is granted.
Visit the European Chemicals Agency website for a full list of hexavalent chromium exemptions.
Alternatives to Hexavalent Chromium
RoHS works to reduce the risk of hexavalent chromium exposure by limiting the amount of hexavalent chromium used in electronic devices.
As a result of RoHS legislation, many electronics manufacturers no longer use hexavalent chromium. RoHS pushes industry to innovate substitutions for restricted hazardous materials. Many manufacturers and scientists are researching and using alternatives to hexavalent chromium.
One of the most promising alternatives is another ion of chromium, trivalent chromium. Trivalent chromium is much safer both for human health and the environment. Some manufacturers resist using this alternative due to concerns that the coating it produces is of a lower quality and will increase costs. However, use of trivalent chromium will decrease waste treatment costs that manufacturers must pay when using hexavalent chromium.
Hexavalent Chromium-Limiting Legislation
RoHS is the main legislation that limits hexavalent chromium in electronics. However, other regulations have been passed that focus on occupational exposure to hexavalent chromium.
In the U.S., the Occupational Safety and Health Administration (OSHA) created standards limiting workplace exposure to hexavalent chromium. OSHA’s regulation is one of the strictest hexavalent chromium exposure limits internationally.
OSHA’s Standard 1910.1026 creates a permissible exposure limit (PEL) to hexavalent cadmium for workers in all non-exempt industries. Employers must ensure that none of their employees are exposed to airborne hexavalent chromium in amounts larger than 5 micrograms per cubic meter of air in an 8 hour work day.