Silver-containing Waste: Spent X-ray Fixer Solution
The x-ray fixer is typically a weak acid solution. During the fixing process, light-sensitive silver-halide crystals present on radiographic films are released as silver-thiosulfate. The concentration of silver in spent fixer solutions is in the range of 3,000 to 8,000 mg/L, while the regulatory level of silver is 5 mg/L.17 In the environment, free-ionic silver acts as an enzyme inhibitor by interfering with metabolic processes within organisms.
On-site treatment of spent fixer solutions minimizes the risk of toxicity. The best option for an average practice is the use of a Chemical Recovery Cartridge (CRC). CRCs are canisters filled with another metal, usually steel wool. The iron dissolves in the fixer solution and interacts with the silver, i.e., the silver plates-out on the iron. To minimize the amount of silver from spent fixer from entering sanitary sewer or septic systems follow best management practices (Box E).
Box E. Best management practices for the disposal of spent x-ray fixer solution17
- Use a CRC to capture silver from the spent fixer solution and collect the silver-iron residue in a container. A. Label the hazardous waste container “Hazardous Waste – Silver Residue.” i. Once the container is full, have an approved hazardous waste transporter deliver it to an approved hazardous waste management facility. a. DO NOT DISCARD SPENT FIXER INTO SANITARY SEWER OR SEPTIC SYSTEMS. b. DO NOT PLACE CRC INTO MUNICIPAL GARBAGE.
- The de-silvered fixer solution can be diluted with water and disposed of in sanitary sewer or septic systems. A. The x-ray developer is an aqueous solution with a slightly basic pH due to the presence of potassium hydroxide. Environmental risks are minimal unless exposure is to concentrated solution. i. The spent developer may be mixed with the de-silvered fixer, diluted with water, and discharged into sanitary sewer or septic systems.
- Many cleaner solutions for x-ray developer systems contain chromium (D007), a toxic substance. A. DO NOT DISCHARGE CHROMIUM-CONTAINING CLEANERS INTO SANITARY SEWER OR SEPTIC SYSTEMS. i. Ask the supplier for a cleaner that is chromium-free.