Arsenic trioxide (CAS 1327-53-3): storage and disposal

In a school it usually sits in the prep room poison cupboard, often in an older bottle bought long before current staff arrived. That cupboard should be locked and carry a stock record, and the shelf should hold nothing else that looks similar, since this white powder can pass for an ordinary salt if a label falls off. Secure a loose label straight away, and do not rely on bottle position to identify it. Acids and oxidisers are stored somewhere else. Food and drink areas are out of the question. A dental practice is more likely to find small pots of old devitalising paste in a surgery drawer, and these need the same locked store and a label naming arsenic, as many will have no modern hazard wording.

Label and closure are the real test on this stock. A faded or peeling label on a white powder is a serious fault, because nothing about the contents will identify them. Old school bottles may have a crumbling cap, a failed seal or powder traces in the thread, and those need recording. The solid itself gives few visible signs of age, and a little caking says little either way. Dental pots may hold a paste, which can dry out, crack or change colour over time, so describe what you see without opening them. Unlabelled white powder found beside arsenic stock should be treated as an unknown until someone competent has looked at it. A missing stock record matters here as much as any visible change.

We arrange this by specialist collection. We do not publish a drain or general waste route for any chemical. It is normally packed in a toxic laboratory pack with compatible chemicals.

What must not be done comes first: no sink, no drain, no general waste bin, no skip, and no attempt to treat it or tip several part bottles together. Tipping removes the record of what each one was and raises dust from a powder that may cause cancer. Instead, specialist collection takes each container as it stands. List the name as labelled, the size and how full it is. Note any lost label as unidentified white powder found with arsenic stock, not as arsenic by assumption. A dental practice should mention that the item is old devitalising material, since a paste is grouped differently from a loose solid, and its usual code is 18 01 06*, though the producer classifies the waste. School and university stock normally goes in a lab pack under 16 05 06*.

Usually held as: legacy stock, legacy dental devitaliser.

Tell us the container size and how many you hold. An estimate is enough to start with, and some items cannot be priced until someone has looked at them.