Congo red (CAS 573-58-0): storage and disposal
Congo red is a red dye with two lives. Histology and pathology staff use it to stain amyloid in tissue sections, and schools and colleges hold it as an old indicator that turns blue in strong acid. The recorded hazards are H350, may cause cancer, and H361d, suspected of damaging the unborn child, so the powder belongs in restricted storage.
- CAS number
- 573-58-0
- Form
- Solid
- Storage class
- Toxic
- Signal word
- Danger
- Usual EWC code
- 16 05 06*
Serious health hazard
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
Keep the bottle in a locked or restricted cupboard with a stock record, apart from the general indicator shelf where school and college stores usually put dyes. In a histology lab it sits with the other stains, and the same restriction applies there. Keep it away from food and drink areas, and segregate it from acids and oxidising agents to prevent contamination and incompatible contact. The fine powder is the main route of exposure, so close the lid fully after every use, keep it low, and do not weigh it on a shared open bench. Staff who are pregnant or planning a pregnancy should not handle open stock. Date the bottle on opening.
How to tell it has deteriorated
A deep red powder that marks every surface it touches gives the first sign on an old bottle is red staining around the cap, label and shelf. A fine red dust on the shelf below is more significant here than for most dyes because of the cancer statement, so do not sweep or blow it away. Caking, a damp surface and clumping show moisture has entered. A stain solution kept in a Coplin jar or bottle may form a dark crust or sediment as it ages. Because the dye turns blue with acid, a bottle with blue-violet patches has met acid. A bottle with no date or stock record is the usual problem.
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 in a research or school lab is 16 05 06*, a pathology, histology or human healthcare setting uses 18 01 06*, and 16 05 08* applies to a discarded organic chemical outside a lab pack. Say which fits, and record the powder weight, any stain solutions held and the cabinet they came from, and keep the register updated until collection. Bottles go into a lab pack, kept apart from acids and oxidising agents. Slides and tissue stained with it follow your clinical or biological route, not this one. It must never go to a sink or drain, and the H350 statement should be on the record.
| 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: solid, amyloid staining.
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
- H350 May cause cancer.
- H361d Suspected of damaging the unborn child.
Substance as classified, dilutions may differ.
Questions
Why is Congo red stored in a restricted cupboard?
It carries H350, may cause cancer, and H361d, suspected of damaging the unborn child. A locked cupboard with a stock record keeps it away from the general indicator shelf and limits who can open it.
Do stained histology slides go in the same pack as the powder?
No. Slides and tissue follow your clinical or biological waste route. The dry powder and any liquid stain are the chemical items for specialist collection, and they are listed separately on the record.
Our school still has an old bottle of Congo red indicator. What should we do?
Leave it closed, move it to restricted storage if it is not already there, and record it for collection. Do not open it to check the contents, as the fine dust is the problem, and avoid sweeping spilt powder.
Why did part of our Congo red turn blue?
The dye turns blue-violet in strong acid, so blue patches suggest contact with acid from a neighbouring bottle or a contaminated spatula. The bottle should be recorded and kept away from acid stock.
