Silver, in the form of silverthiosulfate, is found in high concentrations in fixer solutions and rinses from x-rays. Light-sensitive silver-halide crystals present on the x-ray film are released as silverthiosulfate during the fixing process. Used x-ray fixer is regulated as a hazardous waste because of the high silver content. In the environment, free-ionic silver acts as an enzyme inhibitor by interfering with the metabolic processes of organisms.

Spent x-ray fixer exceeds the local wastewater authority limits for silver throughout most of the state. The North Carolina Sewer Use Ordinance template recommends a limit for silver of 0.005 mg/L. Some sewer authorities require installation of silver recovery equipment: the local wastewater authority will provide applicable information. Dischargers of any x-ray wastewater to a septic tank must obtain a permit from the local health department and approval of wastestreams and pretreatment facilities by the On-Site Wastewater Engineering Branch of the Division of Environmental Health ((919) 715-3270). A permit is required under North Carolina General Statute 130A-336 because x-ray waste is not considered part of typical residential sewage. A list of companies offering silver recovery systems is below.

X-Ray Waste Pollution Prevention Opportunities

• Silver Recovery Units. A silver recovery unit will remove the silver from spent fixer and permit the remaining effluent to be discharged to the drain. Most small systems utilize metallic replacement with a steel wool medium. When silver from the fixer comes in contact with the iron on the steel wool, the more active iron ions are displaced, and the silver ions are retained on the wool. The remaining solution can then be discharged to the drain.

Basic silver recovery units start at around $50. Maintenance and operating costs are less than $100 per year. Cartridges are replaced when they become saturated by the silver. Vendors claim that the replacement cartridges typically last about one year. Depending on the size of the dental operation, the system may actually turn a profit from the sale of the reclaimed silver.

Closed loop electrolytic recovery systems range in price from one thousand to several thousand dollars. These closed loop systems extract the silver from the fixer and enable the fixer to be reused. Vendors claim that fixer consumption is reduced by up to 70 percent. This reduced fixer consumption and the resale of the reclaimed silver provide a payback of 6 months to a year.

Pick-up service: Other companies charge a fee to periodically come to an office and remove the spent fixer.

Chemical suppliers often have a program to pick up the spent solution at no extra charge. They will then arrange for silver recovery.

Photolaboratories: Most professional photolabs operate a silver recovery/extraction system. Some photolabs will accept the spent fixer for free and run it through their recovery system.

• Waste x-ray film and old x-rays contain silver and are a recyclable resource. A list of companies that recycle x-ray film and x-rays is below.
  
• X-Ray Cleaner Some x-ray developing system cleaners contain chromium; a cleaner's material safety data sheet will indicate its chrome content, if any. Chromium solutions above 5 mg/L are regulated as a hazardous waste. However, discharge to the sewer is allowed for this material in many areas, and the local wastewater authority can provide applicable regulations. Dischargers to a septic tank need to contact the local health department to determine discharge requirements. One pollution prevention option is to request a chrome-free alternative from the x-ray chemical supplier.
  
• Lead Foil. Lead is used in the foil that shields x-ray film. Lead is a heavy metal that affects neurological development and functions and can potentially leach from landfills into the environment. Foil may be characteristically toxic for lead and, thus, be regulated as a hazardous waste. As explained in the Solid Amalgam Waste section above, hazardous waste cannot be disposed in municipal solid waste. Therefore, no form of lead should be placed in the solid waste (trash). Many companies recycle lead foil. Contact local metal recycling compnaies or DPPEA at (800) 763-0136 or nowaste@p2pays.org.
  
  Eastman Kodak at (800) 933-8031 coordinates a recycling program for dentists. For under $20, which includes all shipping and handling, Kodak will send a small container that will hold 7 to 9 pounds of foil, about one year's supply. When the container is full, an express courier returns the foil to the company for recycling. Eastman Kodak or your film supplier will provide lead foil recycling information.
  
  A list of Silver Fixer Recovery System Vendors is below.

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