Overview
Arsenic is a metalloid with a long and notorious toxicology. The element and many of its compounds are carcinogenic, which keeps it under firm regulatory control. Despite that, arsenic still has legitimate technical uses, most visibly in compound semiconductors and certain specialty glasses.
Where it's restricted
Several arsenic compounds appear on the SVHC Candidate List under REACH, and some have moved onto the Authorisation list, which means their use needs explicit permission. Others are caught by restrictions tied to REACH Annex XVII. The carcinogenicity of arsenic compounds is the common thread behind these controls.
Typical uses
In semiconductors, arsenic combines with gallium to form gallium arsenide, a compound used in high-frequency electronics, laser diodes and solar cells. Some specialty optical and technical glasses use arsenic oxides as fining agents to clear bubbles. Historically, arsenic compounds preserved timber against rot and insects, a use now largely withdrawn from consumer products.
Arsenic in a product is usually bound into a stable compound such as gallium arsenide or a glass matrix. The compliance question is which specific compound is present, since they sit at different points on the Candidate and Authorisation lists.