Heavy Metals: Definition & Examples

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, you'll learn what heavy metals are. After reviewing the definition, we'll look at four examples: lead, copper, mercury and arsenic. We'll cover where these elements are found and how they affect the environment and human health.

What Are Heavy Metals?

A group of citizens are protesting at their local school. The school was built in the 1800s and is a beautiful historical building. But the reason for the protests come from within the school's infrastructure. The pipes are made of lead, as was common in that time period. Lead is a heavy metal, a compound toxic to humans, especially children. The parents have every right to be upset as lead poisoning can lead to permanent, neurological damage.

Heavy metals are metallic, naturally occurring compounds that have a very high density compared to other metals--at least five times the density of water. Heavy metals are toxic to humans. Even small doses can have serious consequences. Today, we'll learn more about lead, like in the school, plus copper, mercury and arsenic.


Although once appealing for its pliability, high density and ability to absorb harmful radiation, lead has been taken out of use in many products. Lead is a soft, silver colored heavy metal naturally found in the Earth.

Naturally occurring lead and a lead cube

It is toxic to humans and builds up in the body over time. That means anytime you're exposed to lead, your body doesn't get rid of it. It sits there, accumulating and poisoning the body. Lead is toxic to the nervous system and can cause serious brain damage in children. Lead was used widely in the 1800s in makeup and persisted to 1978 as an additive in paint. Today, lead is used mostly in large batteries, as shields for X-rays, or insulation for radioactive material.

Lead bricks are used to shield radiation
lead shielding


As you enter the coffee shop to pick up your morning latte, the penny jar on the counter catches your eye. You remember pennies are made of copper, a reddish brown heavy metal. Although now most pennies are just plated with copper, it still has many other uses. Copper is still one of the best conductors of electricity and heat, and many electrical wires are made of copper and coated in plastic. Acute copper poisoning is rare, but like lead it can build up in the tissues, eventually leading to toxicity. People who are exposed to large amounts of copper or copper dust are at risk.

Copper conducts electricity well and is used in wires in the home
copper wire


Do you remember the Mad Hatter in the classic book Alice in Wonderland? It's not a coincidence the kooky character had a huge top hat. In 19th century England hat workers used mercury to make felt for the hats. The workers frequently came down with mercurial disease, characterized by tremors and the mental instability that created the nickname 'Mad-Hatter disease.' Mercury is toxic in any form and can even be absorbed through the skin. Mercury is a unique heavy metal, as it is liquid at room temperature and sometimes referred to as 'quick silver.'

Mercury is a liquid at room temperature

You might have seen quick silver in action in an older thermometer. Mercury is great in a thermometer because as a liquid it absorbs heat, changing volume with even the slightest difference in temperature. This allows the mercury to rise or fall in the glass thermometer tube. Since mercury is a potent neurotoxin, many companies are switching to alcohol based thermometers, which are colored red. So, if you break a red thermometer you should probably clean it up, but rest assured, you won't be going crazy from cleaning up the spill.

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