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

Zinc sulfate (CAS 7733-02-0): storage and disposal

Zinc sulfate usually arrives as the heptahydrate, a white crystalline solid held on school and college shelves, in university teaching stores and in some pathology and pharmacy cupboards. It is classified as harmful if swallowed, as causing serious eye damage and as very toxic to aquatic life. The aquatic classification is what makes it a hazardous waste even though it looks like a plain salt.

CAS number
7733-02-0
Form
Solid
Storage class
General
Signal word
Danger
Usual EWC code
16 05 06*
  • Corrosive pictogramCorrosive
  • Harmful or irritant pictogramHarmful or irritant
  • Hazardous to the environment pictogramHazardous to the environment

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

In a school prep room this belongs on the general salts shelf, but the eye hazard argues for a low shelf so that a dropped jar is never at face height. A pharmacy or pathology store should keep it with the other inorganic salts, labelled by its full name and form, and not mixed in with ready-to-use solutions. Because it is held as the heptahydrate, the crystals carry their own water and are sensitive to warm, dry air as well as to damp, so a cupboard next to a radiator or heating pipe is a poor choice. Keep the lid screwed down and keep a stock record, since small amounts bought for one experiment tend to be left behind.

How to tell it has deteriorated

Heptahydrate crystals give themselves away by their surface. In dry or warm conditions they can lose water and develop a dull white powdery coating, while in a damp store they can clump and stick to the glass. Either way the crystals no longer look like the glossy, separate pieces that were put in the jar. Look also for a label stained from the inside, a crust round the thread, and a cap that has become hard to turn. This salt does not break down into anything dramatic with age, so the condition of the container and the clarity of the label usually tell you more than the contents do.

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.

Never wash it down a sink, however clean the crystals look, because very toxic aquatic effects are the reason it is a hazardous waste. It is not safe to bin either. A laboratory pack uses 16 05 06*, discarded stock that is not part of a laboratory pack uses 16 05 07*, and a hospital pharmacy or pathology lab in a human healthcare setting uses 18 01 06*. Record the container size, the form as heptahydrate and whether it is a solid or already in solution, then request a specialist collection. UN 3077 is the transport entry, and the stock is packed in a compatible group.

Waste codes and transport details for Zinc sulfate
EWC code, laboratory chemicals16 05 06*
Discarded inorganic chemical, not a laboratory pack16 05 07*
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: heptahydrate.

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.
  • H318 Causes serious eye damage.
  • H410 Very toxic to aquatic life with long lasting effects.
Precautionary statements
  • P264 Wash hands and exposed skin thoroughly after handling.
  • P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
  • P270 Do not eat, drink or smoke when using this product.
  • P273 Avoid release to the environment.
  • P280 Wear protective gloves, protective clothing, eye protection and face protection.
  • P301+P317 IF SWALLOWED: Get medical help.
  • P305+P354+P338 IF IN EYES: Immediately rinse with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
  • P317 Get medical help.
  • P330 Rinse mouth.
  • P391 Collect spillage.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.

Substance as classified, dilutions may differ.

Questions

Is zinc sulfate really hazardous waste when it looks like plain salt?

Yes. It is classified as very toxic to aquatic life with long lasting effects, and as causing serious eye damage, so it is treated as hazardous waste whatever it looks like. It goes for specialist collection.

Why has the surface of our crystals turned powdery?

The heptahydrate can lose some of its water in dry or warm storage and leave a dull white coating. Nothing needs doing beyond recording the change and keeping the lid tight until collection.

Which waste code applies in a hospital pharmacy?

A human healthcare setting uses 18 01 06*. A laboratory pack elsewhere uses 16 05 06*, and discarded stock outside a lab pack uses 16 05 07*. Tell the collector which setting you are in.

What should happen to leftover solution from a teaching practical?

It must never be poured away. A dilute solution may be less hazardous than the solid, but it still contains zinc and counts as chemical waste. Collect it in a labelled container and include it in the enquiry.

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 O4SZn. EC number 231-793-3.

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