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

Phenol red (CAS 143-74-8): storage and disposal

Phenol red is the pH dye that turns cell culture and microbiology media red in neutral conditions and yellow when they go acid, so it appears in school and college practicals and in university and pathology tissue culture rooms. It is held as powder and inside media. The recorded hazards are skin irritation, serious eye irritation and respiratory irritation.

CAS number
143-74-8
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

The dye itself is a fine powder that stains and irritates, so keep it in a closed bottle on a general shelf below eye level, with the opening date on the label. Culture media containing phenol red are a different stock. They are mixtures made by someone else, and the label of each bottle describes the contents, which the dye's classification does not. Keep powder stock away from acids and alkalis, whose drips change its colour and stain the shelf. In a tissue culture room, powder and prepared media are often kept near each other, so label them clearly to avoid mix-ups between a reagent and a ready-to-use bottle.

How to tell it has deteriorated

In a bottle of media the dye is also an alarm. Red or pink media is normal, while media that has gone yellow suggests acid, usually from contaminating microbes, and a very purple or pink tinge points to alkali. Cloudiness and floating growth go with it. The powder is a deep red to orange fine solid, and the first sign on an old jar is stain on the cap and shelf, with clumping if damp. Faded labels and dried dye rings around the thread are common. Opened media with no date should be recorded, because nobody can say how long it has been open.

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.

A bottle of pink liquid should not be mistaken for a drink or a food ingredient. With skin, eye and respiratory irritation on record, the dye is collected as hazardous waste, and used culture media that has grown microbes belongs to the biological waste route instead. A research or school lab uses 16 05 06*, a pathology or human healthcare setting uses 18 01 06*, and 16 05 08* applies to a discarded organic chemical outside a lab pack. Bottles go upright into a lab pack. A sink or drain is not a route for the dye or unused media.

Waste codes and transport details for Phenol red
EWC code, laboratory chemicals16 05 06*
Discarded organic chemical, not a laboratory pack16 05 08*
Human healthcare setting18 01 06*
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, culture media.

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

  • H315 Causes skin irritation.
  • H319 Causes serious eye irritation.
  • H335 May cause respiratory irritation.
Precautionary statements
  • P261 Avoid breathing dust, fume, gas, mist, vapours or spray.
  • P264 Wash hands and exposed skin thoroughly after handling.
  • P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
  • P271 Use only outdoors or in a well-ventilated area.
  • P280 Wear protective gloves, protective clothing, eye protection and face protection.
  • P302+P352 IF ON SKIN: Wash with plenty of water.
  • P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
  • P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
  • P319 Get medical help if you feel unwell.
  • P321 Specific treatment (see supplemental first aid instruction on this label).
  • P332+P317 If skin irritation occurs: Get medical help.
  • P337+P317 If eye irritation persists: Get medical help.
  • P362+P364 Take off contaminated clothing. And wash it before reuse.
  • 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

Our phenol red media has turned yellow. Why?

The dye is yellow in acid, so media that has gone yellow has probably become acid, often from microbial growth. Check for cloudiness, take the bottle out of use and record it for the correct waste route.

Does phenol red in culture media follow the same route as the powder?

No. Media is a mixture described by its label, and used media that has grown microbes goes to the biological waste route. The powder is the dry dye, which is collected as a hazardous chemical waste.

What hazards are recorded for phenol red?

Skin irritation, serious eye irritation and respiratory irritation. They explain why the powder is kept in a closed bottle, below eye level, and why dust should not be swept dry.

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 C19H14O5S. EC number 205-609-7.

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