Ethidium bromide: safe storage and disposal
Ethidium bromide (CAS 1239-45-8), often written EtBr, is a nucleic acid stain used in gel electrophoresis. It binds to DNA, and that is what makes it both useful in the lab and a concern for anyone exposed to it. Stock comes as a dark red solid or as a ready-made solution, and it spreads quickly through a lab in gels, running buffer and gloves. Its GHS signal word is Danger. The hazard statements on our record are H302 Harmful if swallowed, H330 Fatal if inhaled and H341 Suspected of causing genetic defects.
Most guidance found online on this chemical comes from overseas universities. UK law on waste applies here, so a UK lab should start from its own classification duties and not from a protocol borrowed from a foreign institution.
- CAS number
- 1239-45-8
- Form
- Solid
- Storage class
- Toxic
- Signal word
- Danger
- Usual EWC code
- 16 05 06*
Acute toxicity
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 of ethidium bromide in a school or lab
Keep stock in the toxic class, under lock, in a closed and labelled container that is kept away from light. Buy ready-made solutions if you can, because powder carries a dust risk during weighing, and that is where the inhalation hazard is most relevant. Your COSHH assessment should cover substitution, which is a real option for this chemical, as well as the bench controls.
Set aside a marked area for gel work, with its own equipment. Comb trays, gel tanks and transilluminators are all commonly contaminated, so keep them inside that area and label them clearly. Stain and buffer bottles should be labelled at the point of filling, with dates.
How to tell ethidium bromide has deteriorated
Ethidium bromide is chemically stable, and it does not become unstable with age. That also means it does not simply go away. Old stain solution remains hazardous.
Look for container problems. Solutions may evaporate, concentrating the contents and leaving a red crust around the cap. Light-damaged labels, an unlabelled red solution in a lab fridge and an old stock bottle left behind by a past research group are common finds. Treat dried stain on a shelf as contamination. Do not wipe or brush it, as that raises dust.
How ethidium bromide must be disposed of
Ethidium bromide goes by specialist collection. Do not pour stain or running buffer containing it down a sink. Do not treat it with bleach, as sodium hypochlorite is listed as incompatible.
| Setting | Usual List of Wastes code | Hazardous |
|---|---|---|
| Laboratory chemical, including school and university | 16 05 06* | Yes |
| Discarded organic chemical, not in a laboratory pack | 16 05 08* | Yes |
| Human healthcare setting | 18 01 06* | Yes |
For transport, ethidium bromide is usually UN 2811 as a toxic solid, packing group I on our record. The contractor will confirm the entry for your solution or mixture.
Plan waste by stream, as each has different handling:
- Stock solid and concentrated solution. Keep in the original container and list by name.
- Gels. Collect in a sealed, leak-proof, labelled container, and do not let them dry out on the bench or in an open bin.
- Running buffers and stain baths. Collect in a labelled liquid container, with a closed lid and a secondary tray.
- Gloves, tips, tubes and paper. Use a labelled solid waste container, separate from general waste.
- Sharps. Contaminated sharps need a suitable rigid container, with its contents marked.
Keep each stream separate from other wastes, and do not put these into clinical bags unless the items are also infectious and your waste officer has agreed how they should go. Whole-lab clear-outs and regular streams come under laboratory chemical disposal.
| 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 ethidium bromide with
- Sodium hypochlorite and potassium permanganate are listed as specifically incompatible. Those two also feature in older decontamination recipes, which is a reason to be sceptical of them.
- Oxidisers in general, as toxic and oxidising stock are stored apart and a reaction could release toxic vapour.
- Acids in general, as toxic stock is kept separate from them.
- 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 permanganateReaction with these oxidisers can produce unknown hazardous products.
- Sodium hypochloriteReaction with these oxidisers can produce unknown hazardous products.
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- Sulfuric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Common quantities of ethidium bromide collected
Stock is usually small: a few grams of powder, or a few millilitres of solution. The waste is much larger in volume, since each stream of gels, buffers and contaminated plastics builds up week by week. Expect sealed tubs of gels and containers of contaminated consumables, with their weight mostly made up of agarose and plastic.
Usually held as: solid, 1% solution, 10 mg/ml solution.
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.
Ethidium bromide in different sectors
Universities and research. This is the main home of ethidium bromide. Group changes mean old stock is often found at the back of a fridge. Lab handover notes should record it. If you have moved to a safer stain, list your remaining ethidium bromide for collection and do not leave it in place as a backup. Note that a replacement has its own data sheet, and you should classify it on its own merits. Other molecular biology waste, such as phenol extractions, needs its own lines as well.
Hospital and pathology laboratories. The healthcare classification guidance gives 18 01 06* for hazardous chemicals. Yellow-bag clinical waste is for items that are both infectious and chemically contaminated, so agree with your waste officer how molecular work should be split.
Schools and colleges. It is rare in school science, as many schools use safer alternatives for gel work. An old bottle from a past project should be recorded and included in your next collection. Ask your advisory service, CLEAPSS or SSERC, if you are planning gel work.
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
- H302 Harmful if swallowed.
- H330 Fatal if inhaled.
- H341 Suspected of causing genetic defects.
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.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P284 In case of inadequate ventilation wear respiratory protection.
- P301+P317 IF SWALLOWED: Get medical help.
- 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.
- P320 Specific treatment is urgent (see supplemental first aid instruction on this label).
- P330 Rinse mouth.
- 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 run used gel buffer through a charcoal filter before collection?
Do not attempt it. Filtering, bleach and other ways of removing the stain are left to specialists, and a used filter would itself be contaminated waste. Keep the buffer sealed and labelled, and declare it as containing ethidium bromide with an approximate volume. That description is all that is needed from you.
How should we store stained gels until they are collected?
Use a sealed, labelled container set aside for ethidium bromide gels, kept away from bleach and other oxidisers. Note the approximate weight and any other stains or solvents present. Gels shed moisture and can leak, so a good lid and a tray beneath it are worth having.
The stock bottle has crystals in the cap. Is it still all right to use it?
Do not use it, and leave the cap where it is. Crystals show that the seal has failed and some solution has dried at the thread, and the dry material carries a fatal if inhaled classification. Keep the bottle upright and locked away, and mention the crystals in your request.
