Sodium metabisulfite (CAS 7681-57-4): storage and disposal

Usually a tub or glass jar of white powder or small crystals, this solid belongs on the general shelf only if that shelf is dry and well away from acids. A reaction with acid gives off sulfur dioxide, a sharp smelling gas, so keep the jar apart from acid stock in a prep room cupboard. Oxidising stock stays on a separate shelf too, because a sulfite is a reducing agent and the two should not share space. Histology and pharmacy holders tend to keep small amounts, while a school may have one old tub. Screw the cap down firmly after each use, date it on arrival and keep it off the floor where damp collects. Eye protection matters whenever it is handled, since the classification includes serious eye damage.

Left in a loosely closed jar, the powder slowly takes up oxygen and turns to sulfate, so the sharp smell fades and the stock loses its value as a reducing agent. Damp speeds this up and sets the powder into hard lumps or a solid cake at the base of the tub. Look too for a crust around the neck, a corroded metal cap, a cracked jar and a label that has faded or lifted. An old tub that gives off a strong sulfur smell on opening should be closed again straight away and reported. A pharmacy or histology jar with no date of receipt is treated as old stock, because nothing on the shelf shows how long the cap has been loose.

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.

Waste code 16 05 06* is the usual entry for this item, and the asterisk marks it as hazardous waste. A pharmacy or hospital store would use 18 01 06* instead, so say which setting the jar comes from. It does not go into a sink, a drain, a general waste bin or a skip, and nobody should try to treat it first. The powder travels in a lab pack with compatible stock and never beside acids, which matters more than the paperwork, since a leaking jar next to acid bottles would give off sulfur dioxide in transit. Record each container size and whether the seal is intact, and say if the powder has set into a lump. A consignment note is completed for the collection.

Usually held as: solid.

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.