What are radionuclides and what reporting requirements apply to their release?
A radionuclide is a type of atom with an unstable nucleus. The atom releases energy by a process of decay called radioactivity. There are approximately 1,500 known radionuclides.
All radionuclides are hazardous substances because they are designated generically as hazardous air pollutants by CAA section 112 and CERCLA section 101(14)(E) defines the term "hazardous substance" to include CAA hazardous air pollutants. Even though the source of their listing is the CAA, releases of radionuclides to all media - not just to air - are covered by CERCLA's reporting requirements.
On May 24, 1989, EPA issued a final regulation adjusting the statutory RQ for radionuclides. The adjusted RQs for radionuclides are in units of curies (Ci), which provide a measure of the amount of radioactivity emitted by a radionuclide. EPA established the adjusted radionuclide RQs in units of curies rather than pounds (like the RQs for other hazardous substances) because curies better reflect the intrinsic hazard posed by radionuclides and because the unit is more commonly used by people who handle radionuclides. The final radionuclide RQ adjustment rulemaking establishes seven RQ categories: 0.001, 0.01, 0.1, 1, 10, 100, and 1,000 Ci. A total of approximately 760 radionuclides are listed individually and assigned to one of these RQ categories. All other radionuclides not listed individually are assigned an RQ of 1 Ci.