Mercury: safe storage and disposal
Mercury (CAS 7439-97-6) is a dense silver liquid metal, and it is still found in many older stores. Bottles of the metal itself are now uncommon. Thermometers, barometers, manometers and old blood pressure instruments are far more likely, along with mercury salts in chemistry stock. Its GHS signal word is Danger. The hazard statements are H330 Fatal if inhaled, H360D May damage the unborn child, H372 Causes damage to organs through prolonged or repeated exposure and H410 Very toxic to aquatic life with long lasting effects.
The danger is mostly vapour. Liquid mercury gives off vapour at room temperature, and you cannot see or smell it. A small amount trapped under a bench or in a floor joint can go on releasing it for a long time.
- CAS number
- 7439-97-6
- Form
- Liquid
- 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 of mercury in a school or lab
Hold mercury in the toxic class, under lock, with restricted access. Keep it low in the store, where a fall is short and a leak stays contained. Sound containers should sit inside a second, sealed, unbreakable container, with enough capacity to catch the contents. A tray alone will not contain vapour.
Avoid warm places. Vapour release rises with temperature, so a shelf near a heater or in full sun is a poor location. Check that the storage area has its ventilation working, and that it is not somewhere people work all day.
Mercury instruments are the usual weak point. A thermometer loose in a drawer or a barometer on a corridor wall can be broken by anyone. If a school department is no longer using them, a planned collection removes the risk altogether. We suggest listing each item, as well as anything with an old mercury tilt switch.
How to tell mercury has deteriorated
Mercury metal does not expire. The surface may dull with a grey skin of oxide and dust, and the liquid itself remains just as hazardous. What fails is its container.
Look for cracks in glass, a loosened stopper, or fine silver beads on the shelf, in a drawer or around a box. Any residue at the bottom of an old instrument case is a warning sign, as is corrosion on metal fittings nearby, because mercury forms amalgams with several metals. Mercury salts may be found in old, poorly labelled bottles. They have a separate hazard profile, so treat them with equal care.
How mercury must be disposed of
Mercury goes by specialist collection. Waste metallic mercury has its own List of Wastes entry, 16 03 07*. It must not go down any drain, or into clinical, general or recycling waste. Broken instruments, contaminated gloves and spill debris are hazardous waste too, and go for specialist collection described as what they are.
| Setting | Usual List of Wastes code | Hazardous |
|---|---|---|
| Metallic mercury | 16 03 07* | Yes |
| Laboratory chemical containing mercury, including school and university | 16 05 06* | Yes |
| Discarded inorganic mercury compound, not in a laboratory pack | 16 05 07* | Yes |
| Human healthcare setting | 18 01 06* | Yes |
Dental amalgam has its own entry, 18 01 10*, and is covered in our article on dental amalgam waste. For transport, elemental mercury is UN 2809, packing group III. Mercury contained in manufactured articles, including some thermometers, barometers and manometers, is covered by UN 3506. Mercury compounds may have different UN classifications.
Larger holdings and older instruments are the core of mercury and heavy metal disposal. Treatment normally aims at recovering the metal. Ask where your mercury will go before it leaves.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| 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 mercury with
- Nitric acid reacts with mercury, giving mercury nitrates and toxic nitrogen oxides.
- Ammonia solution and ammonia gas can form unstable compounds with mercury.
- Picric acid and fixatives containing it, such as Bouin's fluid, form shock-sensitive metal picrates with metals. This matters particularly in an old store.
- Aluminium powder forms amalgams with mercury, and bromine reacts with it.
- Hydrogen peroxide breaks down faster around metals, releasing oxygen and building pressure.
- Sodium azide forms shock-sensitive metal azides with lead, copper, brass and similar metals, so keep it away from mercury as well.
Keep it away from all oxidisers and acids as storage classes.
- 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.
- Aluminium powderMercury forms amalgams or unstable compounds with these materials.
- Ammonia gasMercury forms amalgams or unstable compounds with these materials.
- Ammonia solutionMercury forms amalgams or unstable compounds with these materials.
- Ammonium picratePicric acid forms shock sensitive metal picrates with metals.
- BromineMercury forms amalgams or unstable compounds with these materials.
- 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.
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- Hydrogen peroxideMetals speed the breakdown of hydrogen peroxide, releasing oxygen and pressure.
- Nitric acidMercury forms amalgams or unstable compounds with these materials.
- Picric acidPicric acid forms shock sensitive metal picrates with metals.
- 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.
- Sodium azideAzides form shock sensitive metal azides with lead, copper, brass and similar metals.
- Sulfuric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Common quantities of mercury collected
Most finds are small. A school might hold a few thermometers, a box of spares or a part-filled bottle left from an old physics or chemistry demonstration. A hospital or clinic may find older instruments in a store cupboard. Universities can hold larger volumes for older equipment. Every one of these needs careful description, because the weight is much higher than the size suggests.
Usually held as: liquid metal, thermometers, barometers.
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.
Mercury in different sectors
Schools and colleges. Physics stores, old barometers and thermometer sets are the usual sources. Include mercury salts and any manometer tubes in your stock check, and ask your advisory service, CLEAPSS or SSERC, about activity-specific matters.
Hospitals and clinics. The healthcare waste guidance places hazardous chemicals under 18 01 06*. Old sphygmomanometers sometimes appear when a department closes. They should not enter the sharps or clinical stream.
Dental practices. Amalgam waste is hazardous and is handled separately. HTM 07-01 describes its containers and marking. Any jar of elemental mercury from before the days of encapsulation should be left closed and passed to a specialist.
Hazard data from PubChem GHS classification, retrieved 31 October 2026. Guidance only. Check your own risk assessment and your supplier's safety data sheet.
Hazard statements
- H330 Fatal if inhaled.
- H360D May damage the unborn child.
- H372 Causes damage to organs through prolonged or repeated exposure.
- H410 Very toxic to aquatic life with long lasting effects.
Precautionary statements
- P203 Obtain, read and follow all safety instructions before use.
- P260 Do not breathe dust, fume, gas, mist, vapours or spray.
- 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.
- P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
- P316 Get emergency medical help immediately.
- P318 If exposed or concerned, get medical advice.
- P319 Get medical help if you feel unwell.
- P320 Specific treatment is urgent (see supplemental first aid instruction on this label).
- 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
Why can we not vacuum up a few beads of mercury?
A vacuum cleaner warms the metal and blows it through the machine and into the room as fine droplets and vapour. The cleaner is then contaminated too. Brushes break beads up and spread them further. A spill needs a mercury kit and a competent person.
Can a mercury barometer stay on the wall until it is collected?
Yes, if the glass is sound and nothing is leaking, because taking it down is the moment most likely to spill it. Mention it when arranging collection, so the removal can be planned. A cracked tube or beads below it need a competent person straight away.
Does old mercury go off or become less hazardous with age?
Age does not reduce the hazard. The metal may gather a grey film, but it still gives off toxic vapour under that film. Old bottles matter more because seals and labels fail over time, so the real questions are what has escaped and whether the container still holds.
A thermometer broke in a drawer years ago. Is there anything left to deal with?
Quite possibly. Beads can sit in drawer corners and joints long after the glass has gone, and they still give off vapour. Ask a competent person with a mercury kit to look, and treat whatever they recover, along with the broken device, as mercury waste for collection.
If mercury is spilled or a bottle is damaged
This does not call for improvisation.
Move people out and close the door. Do not vacuum, sweep or use a cloth, as those actions spread the droplets and raise the vapour. Do not walk the contamination out on your shoes. Do not try to pick up visible beads with anything to hand. Use the emergency procedure in your risk assessment, and tell your manager. Your COSHH emergency arrangements should already say who deals with spillages and what happens to the waste they create.
Get specialist advice on anything beyond a very minor incident already covered by your plan. If anyone has been exposed or feels unwell, get medical advice. Call 999 if there is immediate danger.