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Is your lab storing long-lived radioactive material? We understand researchers sometimes need to store radio-labeled cells or keep stock vials of long-lived radioactive material (think H-3 and C-14) for future use. However, this can be problematic for the research lab. First, the viability of the material may degrade with time. Although the radioactivity is long-lived, the ligand or compound may not be. An Amersham safety sheet notes, “Chemical decomposition occurs as a natural process in all compounds during storage. However, this type of decomposition may be accelerated by free radicals which are formed as a result of the energy released in radioactive decay." DRS recommends you become aware of the practical limitations of storing your research products. Safety guidance additionally cautions that microbial contamination is a possibility once the vial has been opened. 

Second, there can be significant issues with H-3 (and to a lesser extent, C-14) compounds seeping through the plastic or glass of the container itself, leading to contamination of your freezer or refrigerator over time. This is especially true for H-3 atoms, which although are just hydrogen, inter-changes with hydrogen atoms of the plastic polymer—and then freezer frost and ice—during long-term storage. When defrosted, the freezer will spread the contaminated water throughout the appliance and onto lab surfaces. The longer the storage time, the more the opportunity for atoms to migrate increases. This could become a real headache when it is time to decommission your lab! Double-containment of all H-3 and C-14 containers, especially if they are to be held for long-term storage, is essential. 

Improper storage of radiolabeled compounds can include:

• Centrifuge tubes not stored in racks which eventually tip sideways and its contents eat through the caps, followed by the shelving materials (steel, wood, plastic)
• Similarly, scintillation vial lids are likely not compatible with the chemicals used and may become completely dissolved, whereupon vial contents will eat surrounding materials, run down shelving, and soak into anything porous
• Highly volatile materials will seep/weep out of vials and containers, spreading contamination 
• Plastic vials containing H-3 compounds will eventually develop tritium contamination on the external surface, spreading contamination

A third problem of long-term storage is a practical one: the longer a source vial is stored, the greater the chances it has of being forgotten. Authorized Users are accountable for inventory of their radioactive materials. No one wants the hassle of a potentially lost item on their watch!

DRS encourages you to dispose of radioactive samples and vials you no longer need. The longer you store a sample, the more likely it is to degrade and lead to contamination issues. Use the annual inventory time as an opportunity to assess your radiological needs. To request disposal of any radioactive sample (even if after many half-lives) call the Radwaste Service at 301-496-4451. ​​​