Cadmium Bromide

OtherCdBr2CAS: 7789-42-6

Physical Properties

Also known as: CdBr2

Cadmium bromide (CdBr₂; CAS 7789-42-6) is a historical collodion-salting reagent — used in 19th-century wet-plate photography to form silver bromide in the collodion coating for improved emulsion speed and tonal rendering.[1] Modern collodion workers should not use this compound: cadmium is an IARC Group 1 human carcinogen, a kidney and bone toxicant, and an environmental hazard regulated under REACH Annex XVII and California Prop 65.[2] Safer bromide alternatives (potassium bromide, ammonium bromide) perform the same photographic function with dramatically lower health and regulatory burden.

This page exists primarily for historical reference and to document why cadmium bromide has been replaced.

Photographic uses (historical)

  • Wet-plate collodion salting: Dissolved in alcohol-water with potassium or ammonium iodide, cadmium bromide formed a mixed silver iodobromide in the collodion on contact with the silver nitrate bath. The bromide content boosted plate speed noticeably vs. iodide-only formulas.
  • Silver halide emulsion manufacture (industrial historical): Some pre-1970s commercial photographic emulsions used cadmium-containing stabilizers and sensitizers; largely eliminated by the 1980s due to environmental regulations.

Modern replacements

  • Potassium bromide for the bromide ion contribution in collodion salting.
  • Ammonium bromide for faster-dissolving alternative.
  • Zinc bromide for workers who specifically want divalent metal chemistry without cadmium toxicity.

All three replacement salts have negligible toxicity compared to cadmium bromide and produce essentially indistinguishable photographic results.

Regulatory status

Cadmium compounds are:

  • IARC Group 1 human carcinogen (lung, kidney, prostate)
  • REACH Annex XVII restricted — commercial sale in the EU requires authorization
  • California Proposition 65 listed as carcinogen and reproductive toxin
  • OSHA-regulated with a 5 µg/m³ workplace exposure limit (PEL) and separate action level[3]

These regulatory classifications are more restrictive than for hexavalent chromium, lead, or mercury. Workers should avoid cadmium bromide entirely unless a specific historical-accuracy demonstration requires it.

Related compounds

Potassium bromide is the non-toxic replacement. Cadmium iodide and cadmium chloride are related cadmium halides with identical regulatory concerns.

Safety Notes

Acute hazards

Cadmium bromide is among the most hazardous chemicals in this catalog — on par with selenium dioxide and formaldehyde:

  • Fatal if inhaled (H330): cadmium fumes and fine dust cause acute pulmonary edema.
  • Toxic if swallowed (H301).
  • Suspected of causing genetic defects (H341).
  • May cause cancer (H350): established IARC Group 1 classification for cadmium compounds.
  • May damage fertility (H360): reproductive toxicant.
  • Causes damage to organs through prolonged or repeated exposure (H372): kidney and bone damage cumulative.
  • Very toxic to aquatic life with long-lasting effects (H410).

Chronic hazards

  • Cadmium accumulates in kidneys with a biological half-life of 10–30 years. Single high exposures contribute to lifetime body burden.
  • Itai-itai disease: well-documented Japanese industrial-pollution case study of cadmium-induced bone-softening and kidney failure from environmental exposure. Not relevant at single-incident darkroom scale but illustrates the cumulative toxicity pathway.

Storage & handling

  • Personal protective equipment: Full respiratory protection (half-face or full-face respirator with P100 filter), butyl or nitrile gloves, safety goggles, long-sleeved chemical-resistant apron, closed-toe shoes. This is not a casual-handling chemical.
  • Ventilation: Required fume hood for any work with cadmium bromide. Do not work with it in a casually-ventilated darkroom.
  • Storage: Locked cabinet (to prevent unauthorized access), tightly sealed container, cool dark storage.
  • Disposal: Treat as hazardous waste exclusively. Do not drain, do not incinerate, do not landfill without formal hazardous-waste handling.
  • Strongly recommended alternative: Use potassium bromide or ammonium bromide instead. The historical-accuracy argument for cadmium bromide use is very rarely strong enough to justify the health and regulatory risk.

First aid

Consult the full Sigma-Aldrich Safety Data Sheet for authoritative first-aid instructions.[4]

  • Skin contact: Remove contaminated clothing. Flush with copious water for at least 20 minutes. Seek medical attention.
  • Eye contact: Flush with running water for at least 20 minutes, lifting the lids. Seek medical attention immediately.
  • Inhalation: Move to fresh air immediately. Seek emergency medical attention — acute cadmium inhalation causes chemical pneumonitis and pulmonary edema.
  • Ingestion: Do NOT induce vomiting. Rinse mouth. Seek medical attention immediately; cadmium ingestion is a medical emergency.

References

  1. BOOK Crawford, William. The Keepers of Light: A History and Working Guide to Early Photographic Processes 1st ed. Morgan & Morgan, 1979. ISBN 0-87100-158-6. ↩
  2. STANDARD European Chemicals Agency (ECHA). REACH Regulation (EC) No 1907/2006, Annex XVII – Restrictions on manufacture, placing on the market and use European Union. https://echa.europa.eu/substances-restricted-under-reach ↩
  3. STANDARD U.S. Occupational Safety and Health Administration. OSHA Permissible Exposure Limits – Table Z-1 (29 CFR 1910.1000) U.S. Department of Labor. https://www.osha.gov/annotated-pels/table-z-1 ↩
  4. WEB Sigma-Aldrich (Merck KGaA). Sigma-Aldrich Safety Data Sheets Sigma-Aldrich. https://www.sigmaaldrich.com/US/en/search/safety-data-sheets ↩

Reference databases

Last reviewed 2026-04-22