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.18 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).