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Chemical collection and stock control for UK schools, universities and hospitals

X-gal (CAS 7240-90-6): storage and disposal

X-gal is the pale powder that gives blue colonies in blue-white cloning screens, held in university labs as dry solid and as stock dissolved in dimethylformamide. The recorded hazards are harm if swallowed, in contact with skin and if inhaled. When it is held in solvent the label of the solvent also matters, and stock in tubes often outlasts the project it was bought for.

CAS number
7240-90-6
Form
Solid
Storage class
General
Signal word
Warning
Usual EWC code
16 05 06*
  • Harmful or irritant pictogramHarmful or irritant

What to do this week

  1. Check the label is readable and write down the opened date if it is not already there.
  2. Check it is stored as general stock and apart from the items listed under "Do not store with".
  3. 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

Dry X-gal belongs in a closed bottle on a general shelf, kept dry and out of light, with the opening date written on the label. Stock in dimethylformamide is a different item. It sits in small tubes or bottles, usually foil wrapped, inside a rack or box that names the contents, and the solvent changes how the item is described, so the label and supplier sheet for each tube decide. Keep solution tubes upright in a sealed secondary container, so a split cap does not wet neighbouring items. In a university cloning lab these tubes tend to be unlabelled shorthand, so add the full name, solvent and date.

How to tell it has deteriorated

Fresh X-gal powder is white to off-white. A change of colour in the powder or in the stock solution is the sign to look for, because the compound is a colour-forming substrate and it can start to break down on the shelf. Any blue, pink or darker tint in what should be a pale solid or pale liquid suggests this has begun. Solutions may also lose volume if the cap seal has failed, leaving crust round the thread. Tubes wrapped in foil can hide a label that has smudged. An unlabelled, undated tube is the usual problem, since nobody can say what solvent it holds.

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 non-regulated or low hazard laboratory pack with compatible chemicals.

Say whether you hold dry powder, solution in dimethylformamide or both, because they are packed separately. The code in a research lab is 16 05 06*, with 16 05 08* used where it is a discarded organic chemical outside a pack. Powder bottles go into a lab pack with compatible organic solids, and solution tubes go upright into the liquids section in a sealed secondary container. Give the approximate volume and name the solvent from the label. Agar plates and culture media containing X-gal are a separate biological waste stream. Leftover stock must not be tipped into a sink or drain, and no one should try to deactivate it.

Waste codes and transport details for X-gal
EWC code, laboratory chemicals16 05 06*
Discarded organic chemical, not a laboratory pack16 05 08*
Hazardous wasteYes

The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.

Common quantities we collect

Usually held as: solid, in dimethylformamide.

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

  • H302 Harmful if swallowed.
  • H312 Harmful in contact with skin.
  • H332 Harmful if inhaled.
Precautionary statements
  • P261 Avoid breathing 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.
  • P301+P317 IF SWALLOWED: Get medical help.
  • P302+P352 IF ON SKIN: Wash with plenty of water.
  • P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
  • P317 Get medical help.
  • P321 Specific treatment (see supplemental first aid instruction on this label).
  • P330 Rinse mouth.
  • P362+P364 Take off contaminated clothing. And wash it before reuse.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.

Substance as classified, dilutions may differ.

Questions

Our X-gal tube has turned pinkish. Does that matter?

A tint in what should be a pale solution suggests the compound has started to break down, so the stock may no longer work in screens. Record the tube, keep it sealed and arrange collection if it is not needed.

Does X-gal in dimethylformamide go in with the powder?

No. Dry powder and solution are packed separately, and the solvent decides how the solution is described. Name the solvent from the label and keep the tubes upright in a sealed secondary container.

What do the X-gal hazard statements say?

The recorded statements are harmful if swallowed, harmful in contact with skin and harmful if inhaled. They are why the powder is handled with care and why spent stock is collected as a hazardous chemical waste.

Guidance only. Check your own risk assessment and your supplier's safety data sheet.

Hazard data source: PubChem GHS Classification, retrieved 31 Oct 2026. Formula C14H15BrClNO6. EC number 230-640-8.

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