Element 33 in our International Year of the Periodic Table series is arsenic. Well known for its use as a poison, compounds of arsenic are also used to treat wood, while other arsenic-containing substances were previously used in poultry feed.

Arsenic’s best-known use is as a poison. Most often arsenic trioxide was used for poisoning, a colourless compound which earned the name ‘inheritance powder’ for its use in bumping off relatives. As it is colourless and odourless, its addition to food of the victims was difficult to detect. Improvements in chemical detection methods, however, limit modern day usage of arsenic as a poison. Arsenic trioxide still finds use due to its toxicity, used in small quantities as part of the treatment of some types of leukaemia.

Another compound of arsenic, chromated copper arsenate, is used to treat wood and give it insecticidal properties, particularly for outdoor use. Concerns over the safety of this practice, due to the presence of both arsenic and chromium in the compound, have led to restrictions being placed on using it on wood destined for residential use.

Finally, arsenic compounds previously found another unlikely sounding use: in chicken feed. Roxarsone, an arsenic-containing organic compound, was added to chicken feed to promote weight gain and prevent parasitic infections. However, its use has been banned in the EU since 1999, and in the U.S. since 2013, due to concerns about the low but avoidable exposure to inorganic arsenic it led to in chicken meat and livers.

Remember, you can keep track of all of the previous entries in this series on the site here, or on the Royal Society of Chemistry’s dedicated page.