Guidance Info
S35 Reference Sheet
Handling Precautions: Sulfur-35
- Half-life: 87.2 days
- Type of Emitter: Beta
- Beta Energy: 0.167 MeV
- Travel Distance in Air: 25.4cm: 10.2 inches
- Travel Distance in Plexiglass/Lucite: 0.025cm : 0.01 inches
Annual Intake Limits
- Inhalation: 2,000 µCi
- Ingestion: 6,000 µCi
Concerns
Concerns
Some 35S labeled compounds may migrate through gloves and skin. 35S compounds should be handled with gloved hands, and in some cases, with double gloves. Change gloves often. One should be careful not to contaminate the skin as some 35S beta particles penetrate the dead layer of the epidermis. Some 35S compounds may be incorporated in the skin causing very large skin doses and a pathway into the body. 35S methionine, cysteine and Translabel® are volatile and should be used in a fume hood. Activated charcoal is effective in helping reduce contamination due to volatility.
Tools and equipment, such as incubators, should be checked for contamination after using 35S-methionine or other volatile compounds. Excessive contamination can be found on the inside surfaces and in water reservoirs of incubators used for 35S work. Most notable surface contamination can be found on rubber seals (rubber stoppers, gaskets or o-rings) of incubators and centrifuges.
Shielding
None required.
Survey meters with a GM probe have a low efficiency for 35S, usually 4 - 8% (under ideal conditions). A pancake probe may be sensitive if used within a ½ inch of the surface. However, covering the window with plastic wrap or paraffin film will stop most or all of their betas from entering the detector.
Wipe tests should be taken and counted in a Liquid Scintillation Counter for greatest sensitivity when detecting removable surface contamination.
Follow General Safety Precautions for all isotopes.
Specific Recommendations: While Working
- Suitable traps may be necessary if large gas or vapor releases are anticipated, to reduce the releases to the environment. It may be necessary to incorporate activated charcoal into experiments involving volatile forms of 35S.
- Screw top tubes with rubber seals are recommended for storage of single-use aliquots of volatile 35S material. Open tubes in a fume hood with appropriate precautions. Allow sufficient time for frozen stock solutions to thaw before withdrawing an aliquot. If you are working with 35S-methionine, cysteine and Translabel® see the related worksheet on 35S volatility.
Specific Recommendations: Post Use
- Take wipes of work areas and equipment surfaces and count them in a Liquid Scintillation Counter.
- Segregate 35S waste and keep separate from 32P, 125I and other radioactive waste (with the exception of dual label experiments). Consolidate and store the waste in an isolated spot away from work and high traffic areas.
- Dispose of 35S waste according to the waste disposal guidelines. If by sink disposal, ensure that it is soluble in water and does not exceed the posted limit (100 µCi daily, if only one radionuclide is being disposed of). Do not exceed this limit, unless otherwise authorized by the Radiation Safety Committee in the permit.
General Radiation Safety Information
Radiolysis of 35S labeled amino acids may lead to the release of 35S labeled volatile impurities. Delivery vials and thawed materials should be opened in a fume hood. Vials of 35S labeled cysteine and methionine should be opened and used in ventilated enclosures (exhaust hoods). The addition of stabilizers (buffers) will reduce (not prevent) the evolution of 35S volatiles from tissue culture media. Vent 35S amino acid stock vials with an open-ended charcoal-filled disposable syringe.
Radiolytic breakdown may occur during freezing processes, releasing as much as 1 uCi of 35S per 8.0 mCi vial of 35S amino acid during the thawing process. Place an activated carbon or charcoal canister, absorbent sheet, or tray (50-100 grams of granules evenly distributed in a tray or dish) into an incubator to passively absorb 35S vapors. Discard absorbers in the solid radioactive waste.
Information about 35S Volatility
35S labeled amino acids (methionine, cysteine, and translabelled) appear to have a volatile radioactive component. There is some indication that amount of volatilization is amino acid dependent with 35S-cysteine being less volatile than 35S-methionine.
When a fresh 8 mCi vial of 35S-methionine is thawed without a lid in a large open container, approximately 0.01% was released. This may be due to product breakdown during freezing (a physiochemical breakdown). There also appeared to be some volatilization when 35S amino acids are initially introduced to cell culture medium at 37C. Therefore it can be reasoned that the release in not metabolic in nature.
It is believed that the 35S contamination is due to either SO2 or CH3SH. The volatile component is water-soluble and contributes to contaminating equipment. Using a liquid scintillation counter, 300,000 cpm was detected in 500 ml of water after a container with 2.5 mCi of 35S-methionine was incubated for 6 hours (0.00635%).
What to look out for:
- Incubators - walls of the incubator generally will become contaminated with 35S
- Freezers - When defrosting freezers that stored 35S, the water may be contaminated.
Recommendations for Researchers Using 35S Amino Acids to Reduce Potential Contamination Due to Volatility:
- Thaw 35S amino acids in a fume hood. Use a needle and rubber septum to aliquot the material, if multiple experiments are going to be conducted using the same stock solution. This eliminates multiple thaw- freeze cycles with the stock vial.
Store aliquots in screw top tubes ( example: NUNC tubes VWR Catalog) - Consider incorporating charcoal paper into procedure. Line incubators and storage boxes with activated charcoal paper. Contact Atlantic Nuclear for prices 617-828-9118.
- Change the incubator water after each labeling.
Remember to survey yourself, and work area thoroughly after using 35S amino acids or any radioactive material.
Email radiation_protection at harvard dot edu to send comments and suggestions to the Radiation Protection Office
