Phenylthiocarbamide (CAS 103-85-5): storage and disposal
Phenylthiocarbamide, often called PTC, is the compound behind the classic genetic taste test in school and college biology. Prep rooms may hold paper strips in a tube, and sometimes an older pot of the white solid itself. The substance is classified as fatal if swallowed, so the form it is in, the amount and whether anyone has kept a record of it decide what happens next.
- CAS number
- 103-85-5
- Form
- Solid
- Storage class
- Toxic
- Signal word
- Danger
- Usual EWC code
- 16 05 06*
Acute toxicity
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
Most prep rooms meet it as a small tube of taste test papers, filed with biology practical kits rather than with the chemicals. That filing is the thing to correct. A pot of the solid belongs in a locked cabinet with a stock record, away from acids and oxidisers, and well clear of the kettle and mugs that end up in many prep rooms. Papers carry far less than a pot of neat solid, but they were made to go in a mouth and they should not be loose in an open drawer where a pupil could pocket them. Keep them in their labelled tube with the date on it, and list them on the same record.
How to tell it has deteriorated
A sound pot holds a white or off-white crystalline solid, and test papers look like plain strips of paper, so neither gives much away. This substance shows few visual signs with age. Caking, a colour change, staining around the cap or a failed seal are worth writing down. With papers, the real trouble is the label. Once it has faded or come away, a strip looks like any other test paper in the room and could be mistaken for a control strip. Nobody should try to identify old stock by tasting it. An undated tube or a pot missing from the stock record is reason enough to retire it.
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.
Packing puts it with other organic toxic solids in a lab pack, away from oxidisers, under 16 05 06* in most school and college clearances. List papers and any pot as separate lines, because a tube of strips and a pot of neat solid are very different quantities for the packer. Say which department holds them, as biology stock is often missed when chemistry runs a store clearance. Unused strips should not go into a classroom bin, and the powder must never be tipped into general waste or down a sink. Keep everything in its original container so that the name stays with it until collection.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded organic chemical, not a laboratory pack | 16 05 08* |
| 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: taste test paper, legacy stock.
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
- H300 Fatal if swallowed.
- H317 May cause an allergic skin reaction.
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.
- P272 Contaminated work clothing should not be allowed out of the workplace.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P301+P316 IF SWALLOWED: Get emergency medical help immediately.
- P302+P352 IF ON SKIN: Wash with plenty of water.
- P321 Specific treatment (see supplemental first aid instruction on this label).
- P330 Rinse mouth.
- P333+P317 If skin irritation or rash occurs: Get medical help.
- P362+P364 Take off contaminated clothing. And wash it before reuse.
- 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 still use an old tube of PTC paper in a genetics practical?
An undated or unlabelled tube should not be used, because nobody can say what is on the strips or how old they are. Whether the activity should run at all is a question for your science advisory service and your own risk assessment.
Are the paper strips as dangerous as the powder?
The fatal if swallowed classification describes the substance itself, and a strip carries much less than a pot of solid. That does not make strips safe to treat casually. They remain a chemical waste and should be described as papers on your list.
Our pot has PTC handwritten on it and nothing else. What should we do?
Lock it away if it is not already, and treat it as unidentified until someone competent has looked at the records. Those letters are used for other things in chemistry too, so tell us exactly what the label says and which department it came from.
Does skin contact matter when sorting through old stock?
It can. The substance may cause an allergic skin reaction, so a broken pot or spilled crystals should not be gathered up with bare hands. Leave a damaged pot where it is, keep pupils away and ask for advice on how it should be collected.
