3,3'-Diaminobenzidine (CAS 91-95-2): storage and disposal
Better known on the histology bench as DAB, 3,3'-diaminobenzidine is the chromogen behind brown immunohistochemistry staining. University, pathology and histology labs hold it as tablets, tetrahydrochloride powder or chromogen kits. It may cause cancer and is suspected of causing genetic defects. The amounts look small, but the volume of used solution, tips, filters and slides can build up quickly, and the form and quantity decide how it is handled.
- CAS number
- 91-95-2
- 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
Tablets in small dark bottles, weighed powder and multi-part chromogen kits are the usual forms, and kits are the ones that get lost: a box in the staining room refrigerator may hold a buffer, a substrate and the DAB concentrate side by side, and only the outer box carries the full label. Keep the parts together and do not assume an unlabelled small bottle is only buffer. Any stock that may cause cancer needs a stock record and locked or restricted storage, even if the working supply is cold-stored near the stainer. Separate it from oxidisers and acids, and do not store it next to bleach.
How to tell it has deteriorated
Damaged kit boxes, loose bottles and tablet containers that have lost their outer label come first, because a small dark bottle says very little on its own. Prepared solution darkens to brown as it oxidises, and old stock turns brown or purple. A pale powder or tablet that has taken on that colour has aged, often because air or light reached it, though that does not make it less of a concern. Brown staining on the bench or on a stainer drip tray comes from the same chemistry. Note any of these without opening the container, and record the date from the kit where it can still be read.
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.
A specialist collection is the only exit, and that applies to used chromogen as well as to unopened stock. Do not try to deactivate waste solutions with bleach, because oxidation can give hazardous by-products, and leave any such treatment to specialists. Never send it down a sink or drain, however pale the wash looks. Contaminated tips, filters and slides also count as chemical waste, so a separate labelled container at the stainer is worth having, with its contents written down. Hospital histology labs would normally see 18 01 06*, while a university group would see 16 05 06*. List tablets, powder, kits and used solution separately, and say roughly how many litres of waste the automated stainer generates between collections.
| 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: tablets, tetrahydrochloride powder, chromogen kits.
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
- H341 Suspected of causing genetic defects.
- H350 May cause cancer.
Precautionary statements
- P203 Obtain, read and follow all safety instructions before use.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P318 If exposed or concerned, get medical advice.
- 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
Our automated stainer produces DAB waste continuously. Where does it go if not the lab drain?
It goes to specialist collection, not to a drain, and the bleach treatment some older protocols mention is ruled out as well. Collect the waste in a sealed, labelled container set aside for chromogen, and mention how quickly it fills so that collection can be planned around that volume.
Our DAB tablets have turned brown. Should they be used, or disposed of separately?
Do not use them. Brown or purple colour is a typical sign of oxidised old stock. They can go with your other DAB stock on the collection list, provided the colour and the approximate number are mentioned. There is no need to open the bottle to count them precisely.
Do DAB-stained slides need to go as chemical waste?
Contaminated slides count as chemical waste, so unwanted ones should be gathered in a sealed container and described accurately, including how many there are. Keep them separate from sharps bins and general lab rubbish. Slides being retained for diagnostic or research records are outside this, until someone decides they are no longer needed.
