Arsenic

Arsenic is one of the most notorious elements in the periodic table, known since ancient times as a powerful poison. Its name comes from the Syriac word zarnikh, meaning "yellow" or “gold colored,” referring to a yellow mineral, orpiment, that contains arsenic. In ancient societies, the arsenic-bearing mineral was highly desired as a pigment. The Ancient Egyptians even used arsenic to gild metals.

In ancient times, arsenic had a number of practical uses, but it also gained a dark reputation. During the Bronze Age, it was mixed with copper to create arsenical bronze, a strong metal used for tools and weapons. However, arsenic's real claim to fame was its use as a poison. Because it was tasteless, odorless, and caused symptoms that resembled common illnesses, it earned the nickname "king of poisons" and "the inheritance powder." Arsenic poisoning would remain undetectable until the development of the Marsh test in the 1830s.

Although arsenic has been around for thousands of years, it wasn’t recognized as an element until much later. In 1250, Albertus Magnus, a German Dominican friar, philosopher, and scientist, isolated the element by heating soap with an arsenic compound. This marked the first step toward understanding arsenic as a separate element. In 1649, the German chemist Johann Schröder published two methods for preparing arsenic, describing more clearly how to purify the element. Even though arsenic had been known and used in different forms for thousands of years, these scientists' work that helped distinguish arsenic as its own chemical element, setting the stage for its later uses in medicine and industry.

In the 19th century, arsenic was widely used in products like green dyes for wallpaper, and in insecticides to kill pests in crops. The popular dyes Paris Green and Scheele’s Green, which contained arsenic, were eventually replaced as people learned more about how dangerous arsenic could be. By the 1940s, arsenic-based insecticides were phased out in favor of safer alternatives.

Arsenic is a metalloid, meaning that it has some qualities that are like those of a metal and some qualities that aren’t. Arsenic comes in three allotropes, or forms. The first, commonly called grey arsenic, is the most stable: it’s grey and metal-like, although it’s also brittle and relatively soft. The second, yellow arsenic, is soft and waxy, and it’s also unstable and toxic. The last form, black arsenic, is brittle and glassy.

Because arsenic isn’t a metal, it doesn’t melt when heated, but sublimes (meaning that it turns directly from a solid into a gas, without becoming a liquid first).

In the past, arsenic was used in pesticides or herbicides, but regulations have reduced this use. Arsenic continues to be an important component of the chemicals used to treat wood. Today, arsenic is often mixed into lead alloys, which are used in everything from bullets to car batteries, semiconductors, electrical circuits, and light-emitting diodes (LEDs).

Although arsenic is often thought of as a poison, small amounts of the element can act as a stimulant on the human nervous system. That’s part of the reason that the element has been used, at times, as a medicine. Recent studies have found that arsenic nanoparticles may be effective at attacking cancer cells!

Chromated copper arsenate is often used to make wood repellant to termites, fungi, and other pests. Gallium arsenide is used in semiconductors and other electronics.

Arsenic has one stable (non-radioactive) isotope, arsenic-75. At least 33 synthetic (laboratory-made) arsenic isotopes have been identified. The most stable of these, arsenic-73, has a half-life of a little over 80 days. Twenty-eight arsenic radioisotopes have half-lives of less than one day.

You’ll find arsenic in minerals, with arsenopyrite being the most common. Today, most of the world’s arsenic is produced as a byproduct from processing lead, copper, cobalt, and gold ores. The United States stopped producing arsenic in 1985. In 2022, Peru was the world’s top arsenic producer, followed by China and Morocco.

Research has found that many groundwater sources around the world have dangerously high levels of arsenic. This arsenic comes from human and from natural sources. Around 150 million people around the world are now thought to be exposed to arsenic-laced drinking water, which can cause all kinds of health issues.