Thiomersal (CAS 54-64-8): storage and disposal
Also spelt thimerosal, thiomersal is an organic mercury preservative held in university, pathology and pharmacy stock, as a pale powder or as an ingredient of preserved solutions. As classified it is fatal if swallowed, in contact with skin or if inhaled, and very toxic to aquatic life. It remains a mercury compound however dilute, so tracking down where it has been used decides much of how it is handled.
- CAS number
- 54-64-8
- 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
On a university bench it usually sits as a small bottle of cream coloured powder, with its traces spread across labelled buffers and antibody solutions in the nearest fridge. The powder belongs in a locked cabinet with a stock record, out of light, and clear of acids and oxidisers. The preserved solutions are the harder part: a dilute buffer may be less hazardous than the solid, but it remains a mercury compound however dilute, and its label may mention the preservative only in small print. Keep those bottles separate from food and drink, on a tray of their own, with the preservative named on the label. Pathology and pharmacy holders should treat preserved reagents the same way and keep them out of general stock rotation.
How to tell it has deteriorated
Sound stock is a white to cream powder, or a clear solution if it has been made into a preserved reagent by a supplier. Light is the main thing that affects it, so a powder that has yellowed or darkened where light reaches it has probably been kept in the wrong place. Otherwise thiomersal gives few visible signs. Mostly the warning comes from the container: a faded label, staining around the cap, a failed seal or a missing stock record. With solutions, a crust around the neck means water has been lost and what remains is no longer the labelled strength, which is worth noting. An unchanged look is no proof of quality, and any bottle that puzzles you should stay closed.
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.
The code follows the setting. Hospital pathology and pharmacy stock falls under 18 01 06*, the entry for human healthcare, while a university lab pack uses 16 05 06*. Each still means hazardous waste, and the mercury stays in the record however weak the solution. For a request, list the powder separately from any preserved solutions, with volumes and the wording on each label. Grouping depends on this, because organic mercury in a water based buffer is packed differently from a dry solid. There is no alternative to specialist collection. It never goes in a sink, drain, general waste bin or skip, and preserved reagents should not be mixed together or treated to reduce their volume.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded organic chemical, not a laboratory pack | 16 05 08* |
| Human healthcare setting | 18 01 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 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: preservative.
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.
Substance as classified, dilutions may differ.
Questions
Our buffer only contains a trace of thiomersal. Is it still mercury waste?
Yes. It remains a mercury compound however dilute, even though a weak buffer may be less hazardous than the powder. Describe it accurately with the preservative named, give the volume, and keep it out of routine waste streams until it can go by specialist collection.
How do we clear out-of-date preserved reagents from a pathology fridge?
Make a list from the labels first, since preservative wording is easily missed, then ask for a specialist collection and give the volumes. Keep each bottle closed and in its own container. Do not combine them, because mixing unknown reagents removes the record of what each one was.
Our bottle of powder has yellowed. Can it still be kept for use?
Yellowing suggests light has reached it and the condition is now uncertain. Age does not remove the mercury, so an old or discoloured bottle is better classed as waste. Keep it closed and locked away from light, and record the colour on the collection request.