Dimethyl sulfoxide (CAS 67-68-5): storage and disposal

Dimethyl sulfoxide, usually called DMSO, is a clear solvent held as a neat liquid in school, college, university, pathology and pharmacy stores. It is not normally classified as hazardous, but it remains a chemical waste that needs an accurate description. Two things shape the shelf: it takes up water from the air, and it can set solid in a cold room.

CAS number: 67-68-5
Form: Liquid
Storage class: General
Usual EWC code, laboratory stock: 16 05 09

What to do this week

Without moving anything that looks damaged, check the label is readable and write down the opened date if it is not already there.
Check it is stored as general stock, and apart from anything listed under "Do not store with" on this page. If nothing is listed, that does not prove it is safe with everything.
If you no longer need it, add it to your disposal list so it can be included in a collection.

Safe storage in a school or lab

Nitric acid reacts violently with organic solvents and can ignite them or build pressure in waste bottles, and perchloric acid forms explosive mixtures with organic material, so both are kept away from DMSO. Put it in a dry, labelled, well organised store, dated on arrival. Keep the cap tight, because the liquid draws water out of the air, and a bottle opened often will gradually become wetter. A cold prep room or an unheated store can make it freeze, and a frozen bottle is best left as it is. Keep it apart from food grade supplies. DMSO passes through skin readily and can carry dissolved substances with it, so skin contact matters most with used solvent.

How to tell it has deteriorated

A bottle in a cool store may be part or fully solid, and that is a normal physical change, not spoilage. The slower change is water pickup, which does not show by eye, so look at the container instead: how often the bottle has been opened, whether the cap seals, how the level compares with the record, and whether the label is stained or peeling. Look for a cracked bottle after a freeze, a damp neck, and a missing receipt date. A bottle with no readable label, or one that has been topped up from another, is treated as unknown stock.

How it is disposed of

We arrange this by specialist collection. We do not publish a drain or general waste route for any chemical. It is normally packed in a non-regulated or low hazard laboratory pack with compatible chemicals.

It leaves the site by specialist collection, packed with compatible organic liquids in a lab pack. It is not normally classified as hazardous, so neat DMSO is usually described under waste code 16 05 09, or 18 01 07 in a human healthcare setting such as a pharmacy or pathology laboratory, subject to the producer's own classification, and the movement is recorded on a waste transfer note. The record that matters is whether the bottle is neat DMSO or has been used to dissolve something else, because the dissolved substance changes the description. It does not go into a sink, a bin or a skip.

Waste codes for Dimethyl sulfoxide
Usual EWC code, laboratory stock	16 05 09
Human healthcare setting	18 01 07
Usually classed as hazardous waste	No

The code depends on where the waste came from and what it contains, and classifying it is the producer's duty. Use the waste code finder to see why.

Do not store with

Named chemicals to keep apart

Nitric acidNitric acid reacts violently with organic solvents and can ignite them or build pressure in waste bottles.
Perchloric acidPerchloric acid forms explosive mixtures with organic material.

Common quantities

Usually held as: neat.

Tell us the container size and how many you hold. An estimate is enough to start with, and some items cannot be priced until someone has looked at them.

Where it is commonly held

Questions

Is DMSO hazardous waste?

It is not normally classified as hazardous, but it remains a chemical waste that must be described accurately. If it has been used to dissolve another substance, the contents may change the description, so say what it held.

Our DMSO has frozen solid. Is it spoiled?

No, it is a physical change that happens in a cold store. Leave the bottle closed and upright, check the glass for cracks once it is back at room temperature, and record that it was found frozen.

Can we pour old DMSO away because it is not classed as hazardous?

No. It stays a chemical waste and must not go down a sink or into the bin. Keep it in its labelled bottle and arrange specialist collection.

Which code does a hospital laboratory use?

A human healthcare setting may be described under 18 01 07, while a school or university store would normally use 16 05 09. Tell the collector what type of site you are and what the bottle contains.