John Cardarelli II, Captain US Public Health Service Officer, Cincinnati, OH, USA, Brant Ulsh, M. H. Chew & Associates, Livermore, CA, USA: The USEPA uses the linear no-threshold (LNT) model to estimate cancer risks and determine cleanup levels in radiologically contaminated environments. The LNT model implies that there is no safe dose of ionizing radiation; however, adverse effects from low dose, low-dose rate (LDDR) exposures are not detectable.