Radioactive Sewer Disposal

Liquid Waste

There are two main types of liquid radioactive wastes generated by research laboratories. The most common liquid waste is aqueous, in which the waste materials are dissolved in water. Such waste may be disposed of by dispersal into the sewage system if concentration limits are low enough. Designate and label a sink for this purpose. The pH range of any aqueous waste shall be adjusted to between 6.8 and 8.0. Aqueous wastes shall not exceed the following concentrations:

Radionuclide                      Concentration (μCi/ml)

H-3                                   1 x 10-2

C-14                                  3 x 10-4

P-32                                  9 x 10-5

P-33                                  8 x 10-4

S-35                                  1 x 10-3

I-125                                  2 x 10-5

I-131                                  1 x 10-5

Other radionuclide concentration limits can be found in Title 10, Code of Federal Regulations, Part 20, Appendix B, Table 3. 

Aqueous waste disposals into a laboratory drain should be recorded in the laboratory waste logs.  Information that should be recorded includes the date, isotope, activity and volume of dilution water used.  Alternately this information should be logged into the Division of Research Safety (DRS) database for recording and radiological inventory adjustment.

To initiate a sewer disposal request, fill out the Sewer Disposal Request form.

The other, less common form of liquid radioactive waste is composed of volatile, flammable, toxic or organic material that cannot be disposed of through the sewage system. Water insoluble organic solvents shall not be released into the sewage system under any circumstances. (Toluene and xylene-based liquid scintillation cocktails and some HPLC fluids fall into this category. Users are advised to use water-soluble fluids whenever possible). Non-aqueous waste shall be free of all filterable solids. For filtering liquid scintillation waste, a 60-mesh metal screen is recommended. Organic, water-insoluble liquid waste is then collected by DRS personnel for disposal. Non-aqueous waste shall be stored in spill-proof, unbreakable plastic containers of either six or ten liter capacities.  

Liquid wastes that do not fit into the above categories must be treated on a case-by-case basis. See also Section 8.7 of the Radiation Safety Manual.


Problems involving chemical reactions between mixtures of liquid wastes may occur. Disposing of cyanides in acidic liquid waste will produce hydrogen cyanide, a very toxic gas. Special care must be taken when disposing of tissue that has been digested in nitric acid, as oxides of nitrogen may be formed that could cause the waste container to explode.  The Principal Investigator must ensure that chemical reactions will not occur in liquid waste containers.

DRS reserves the right to refuse to accept any materials if, in its opinion, the materials have been improperly prepared or packaged or if they think that the movement of the materials would pose an unacceptable hazard to workers, other members of the campus community, or the public.

Each container of liquid waste should have a waste tag attached to it. Procedures for completing waste tags can be found in Appendix B of the Radiation Safety Manual.

Last Update: 5/27/2014