Mercury(II) oxide (CAS 21908-53-2): storage and disposal
Bottles of mercury(II) oxide, often labelled red mercuric oxide, remain in school, college and university stores, some bought for heating demonstrations that no longer run. It is classified as fatal if swallowed, in contact with skin or if inhaled, and very toxic to aquatic life. Repeated exposure may damage organs. Two behaviours decide how it is handled: light darkens it and heat releases mercury, so it must never be heated.
- CAS number
- 21908-53-2
- Form
- Solid
- Storage class
- Toxic
- Signal word
- Danger
- Usual EWC code
- 16 05 06*
Acute toxicity
Serious health hazard
Hazardous to the environment
What to do this week
- Check the label is readable and write down the opened date if it is not already there.
- Check it is stored as toxic stock and apart from the items listed under "Do not store with".
- If you no longer need it, add it to your disposal list so it goes on the next collection.
Safe storage in a school or lab
In a school it usually sits at the back of the locked prep room cabinet, a small bottle left from the days when heating it was a classroom demonstration. That cabinet is the right place, as long as it keeps the stock record current and stands well clear of radiators, ovens, sunny windows and any other source of heat or strong light. Heat is the deciding factor, because warming this oxide releases mercury and it must not be heated at all. Acids and oxidisers stay in a different store, and food and drink stay out of the room. With a classification of fatal by inhalation and through skin, the lid should stay on: there is no reason to tip out, scoop or sample a bottle kept only until it is collected.
How to tell it has deteriorated
Light slowly darkens this oxide, so a bottle that has stood where the sun reaches it may show a darker layer on the side facing the window. The powder is normally red or orange red, and there is also a yellow form of the same compound, so a yellow bottle is not in itself a fault. A darker surface says the stock has been exposed and may have started to break down, and it should be recorded, not investigated. Other visible changes are few. Fading on the label, staining around the cap, caking, a failed seal or a missing stock entry are the remaining things to look for from outside the bottle. Do not open it or sniff it to find out more, given that it is fatal if inhaled.
How it must be disposed of
By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a toxic laboratory pack with compatible chemicals.
List of Waste code 16 05 06* fits when this oxide travels in a lab pack, while 16 05 07* covers it as a discarded inorganic chemical outside one. In both cases the asterisk marks hazardous waste, so a consignment note is needed in England and Wales, or its special waste equivalent in Scotland. UN 1641 is the transport number. For the collection request, give the name as labelled, the colour seen, the amount and the state of the closure, because a cracked bottle of a powder that is fatal if inhaled changes how it is packed. It is grouped with compatible toxic solids, apart from acids and oxidisers. Specialist collection is the only route: it never goes into a sink, drain, general waste bin or skip, and nobody should heat or treat it first.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded inorganic chemical, not a laboratory pack | 16 05 07* |
| Hazardous waste | Yes |
The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.
Do not store with
- OxidiserToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- AcidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Named chemicals to keep apart
- Acetic acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Calcium hypochloriteToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Hydrochloric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Hydrogen peroxideToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Nitric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Potassium nitrateToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Potassium permanganateToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Sulfuric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Common quantities we collect
Usually held as: legacy stock.
Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.
Where it is commonly held
Hazard statements
- H300 Fatal if swallowed.
- H310 Fatal in contact with skin.
- H330 Fatal if inhaled.
- H373 May cause damage to organs through prolonged or repeated exposure.
- H410 Very toxic to aquatic life with long lasting effects.
Precautionary statements
- P260 Do not breathe dust, fume, gas, mist, vapours or spray.
- P262 Do not get in eyes, on skin, or on clothing.
- P264 Wash hands and exposed skin thoroughly after handling.
- P270 Do not eat, drink or smoke when using this product.
- P271 Use only outdoors or in a well-ventilated area.
- P273 Avoid release to the environment.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P284 In case of inadequate ventilation wear respiratory protection.
- P301+P316 IF SWALLOWED: Get emergency medical help immediately.
- P302+P352 IF ON SKIN: Wash with plenty of water.
- P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
- P316 Get emergency medical help immediately.
- P319 Get medical help if you feel unwell.
- P320 Specific treatment is urgent (see supplemental first aid instruction on this label).
- P321 Specific treatment (see supplemental first aid instruction on this label).
- P330 Rinse mouth.
- P361+P364 Take off immediately all contaminated clothing. And wash it before reuse.
- P391 Collect spillage.
- P403+P233 Store in a well-ventilated place. Keep container tightly closed.
- P405 Store locked up.
- P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
Substance as classified, dilutions may differ.
Questions
Can we use up the old bottle in a last oxygen demonstration?
No. Heating it releases mercury, and it must not be heated for any reason. It is also classified as fatal if inhaled, so a classroom is the wrong place for it. Treat the bottle as waste, keep it closed in the locked cabinet and arrange a specialist collection.
Does red or yellow mercuric oxide make any difference to disposal?
No. Red and yellow samples are the same compound in different particle sizes, and the classification and collection route are the same for both. Describe the colour you can see on the request, along with the wording on the label, so the record matches what the carrier finds.
Our bottle has gone darker than we remember. Does that change anything?
It changes the record, but not the route. Darkening comes from light, and it suggests the bottle has been stored somewhere too bright. Leave it closed, keep it in a dark part of the locked cabinet and mention the colour when you ask for a collection.
How should it be kept while we wait for collection?
Locked up with a stock entry, away from every heat source and strong light, and apart from acids and oxidisers. Keep the bottle upright on a tray in case of a cracked base. Do not open it to check the contents, as it is fatal if inhaled.