# Potassium dithionite or Potassium hydrosulfite · USPS — Mailing and air-carriage restrictions by item category

For Potassium dithionite or Potassium hydrosulfite · USPS, item category is Potassium dithionite or Potassium hydrosulfite; carrier is USPS; restriction type is prohibited; scope is domestic mail (air and surface); conditions is Hazard class 4.2, UN1929, packing group II; domestic mail air: Prohibited; domestic mail surface: Prohibited, recorded from its source on 2026-08-30.

- **Item category:** Potassium dithionite or Potassium hydrosulfite _(verified: appears in the quote below)_
- **Carrier:** USPS _(our reading, not quoted from the source)_
- **Restriction type:** prohibited _(our reading, not quoted from the source)_
- **Scope:** domestic mail (air and surface) _(our reading, not quoted from the source)_
- **Conditions:** Hazard class 4.2, UN1929, packing group II; domestic mail air: Prohibited; domestic mail surface: Prohibited

## What the source says

> Potassium dithionite or Potassium hydrosulfite 4.2 UN1929 II Prohibited Prohibited

## Source

- https://pe.usps.com/cpim/ftp/pubs/pub52/pub52.pdf

Last verified: 2026-08-30. Review by: 2027-08-30.
Part of [Mailing and air-carriage restrictions by item category](https://referencesource.org/shipping-restrictions-by-class/).