Concentrate Aqueous Low-Level Radioactive Waste Into A Disposable Dry Solid With RadAway

What do I do with aqueous low-level radioactive waste? As a radiation safety officer for a small biotechnology company, I found solving that problem to be the most difficult and time-consuming aspect of my job. Faced with limited access to disposal sites, budget-busting costs, and a small waste storage room, I've had to rely completely on decay-in-storage to cope with low-level radioactive waste. Typically, we hold radioactive waste with half-lives less than 90 days for a period equal to 10 half-lives. This allows the waste to decay to background radiation levels before it is disposed of as normal trash or released into the sanitary sewer. Of course, I thoroughly monitor and inspect the waste before releasing it. RadAway from Naiad Technologies For an isotope like 32P, 10 half-lives works out to 140 days, or about 5 months. In practice, I've found storing waste for 6 months to a year to be very manageable. On the other hand, isotopes such as 125I and 35S have decay-in-storage periods of 20 months and 2.5 years, respectively. While storing these isotopes' dry waste for those time periods has presented few problems, the storage of their aqueous waste causes some concern. In particular, the threat of leaks and spills always lurks in the background. Even though we use secondary containers and adsorbents, an accidental release of aqueous waste in storage carries a certain risk. In addition, the fear of running out of space also complicates storage matters. As an alternative to storage, the Code of Federal Regulations (10 CFR 20.2003) permits a licensee to annually dispose of, by release through the sanitary sewer, 5 Ci of 3H, 1 Ci of 14C, and 1 Ci of all other radioactive materials combined. In other words, it is legal to dump aqueous radioactive waste down the sink under the proper conditions. For a number of good reasons, however, my company prohibits this practice. So, what to do with that aqueous low-level radioactive waste? Naiad Technologies, Inc., of Portland, Ore., now offers a unique solution called RadAway. Based on technology originally developed by Oregon Health Sciences University, the RadAway system consists of a disposable 50 ml cartridge housed within a reusable plastic filter apparatus. The cartridge, which is slightly larger than a D-cell flashlight battery, contains a proprietary mixture of filtration materials. Aqueous low-level radioactive waste is poured into the top of the filter unit and pulled through the cartridge under vacuum. Suggested flow rates are 1 to 2 liters per hour. The radioactive molecules, in addition to most of the other compounds in solution, are bound up inside the cartridge as the liquid passes through it. The filter waste is held within a collection bottle. After the cartridge is saturated, it is removed, capped, and set aside for decay or disposal as a dry solid. A new cartridge is then placed inside the filter unit. According to Naiad, RadAway binds 3H, 14C, 32P, 33P, 35S, 45Ca, 51Cr, and 125I when these isotopes are incorporated into nucleotides, nucleic acids, amino acids, peptides, proteins, neurotransmitters, some drugs, some antibiotics, calcium chloride, sodium iodide, and inorganic phosphate. In fact, the company reports the likelihood of all charged and highly aromatic molecules binding to RadAway, especially those in low-salt, no-detergent buffers. The cartridges have applications for removing radioactive compounds from everything from DNA sequencing gel buffers to tissue culture media. Typically, a cartridge will process about 1 liter of waste, but the actual amount depends on the waste composition and the amount of radioactivity. For example, tissue culture media tend to saturate a cartridge faster than gel buffers do. At the extreme end of the scale, as explained by Kelly Dunlap, product manager for Naiad, some users have processed 3-4 gallons of sequencing gel buffer with a single cartridge and yet maintained a greater than 95% removal of their radioactive compounds. I liked the idea of converting aqueous waste into a small, very manageable solid, so I tested the RadAway system with a 1 X TBE gel buffer solution containing about 83,000 cpm per ml of 35S-dATP. I processed two 1-liter batches by attaching the RadAway unit to the house vacuum. For the first batch, filtered under continuous vacuum, the treated liquid contained 2,200 cpm per ml. By turning the vacuum on and off during the processing of the second batch, I improved the result to 1,875 cpm per ml. Overall, the RadAway system captured 97.5 percent of the 35S-dATP present in that waste sample while reducing its volume 20-fold. My results were right in line with the greater than 95 percent binding capacity indicated by Naiad. The "clunk" I heard when the saturated cartridges hit the bottom of the dry-waste barrel reinforced the relief I felt at no longer worrying about 2 liters of liquid waste sitting around for nearly three years. For researchers dealing with larger volumes of aqueous low-level radioactive waste, Naiad manufactures the RadAway LVS-ATM. This system features a 15 x 17.5 x 30 cm cartridge that binds the same isotopes and compounds as the smaller, benchtop RadAway. According to Dunlap, the LVS-A System is also more efficient because of the increased residence times inherent to the system. The RadAway Benchtop Kit, consisting of a filter unit, stand, and two cartridges, costs $275. A six-pack of replacement cartridges sells for $210. Naiad, whose name is taken from the mythological nymphs that protected waterways, also sells similar products for dealing with hazardous waste. DabOut removes diaminobenzidine (DAB) from aqueous waste generated during manual IHC staining, and FluorAway binds up ethidium bromide and other fluorescent dyes from aqueous solutions. SolvCycle extracts stains, dyes, and cellular debris from alcohols used for staining procedures in clinical histology and cytology labs. For more information, contact Naiad Technologies, Inc., at (888) 296-2423, or visit the company's web site at www.naiadtech.com. The author, Michael Brush can be reached at mdbrush@compuserve.com.

Concentrate Aqueous Low-Level Radioactive Waste Into A Disposable Dry Solid With RadAway

Interested in reading more?

Become a Member of