Decorporation of Radionuclides

Metal radionuclides occur naturally in the environment, however, most radionuclides categorized as harmful are of anthropogenic origin, released from military, industrial, or medical processes. The uses of metal radionuclides for energy production, medicinal, industrial, and military purposes often generate waste with extensively long decay halftimes and potential for environmental pollution. Major pathways to hazardous radionuclides exposure are through inhalation, food contamination, and through occupational exposure at mining and processing sites. Accidents or low working standards at nuclear facilities can lead to contamination of employees with radionuclides due to ingestion, inhalation of gases or particulates, or contamination of skin or wounds, as well as contamination of the surroundings resulting in external γ-radiation exposure. The most frequent exposure situation is the contamination of skin or hair during work with radionuclides. Other potential sources for radionuclide exposure are terrorist actions via production of "dirty bombs" or deliberate contamination of infrastructure key facilities, for example, drinking water reservoirs, situations fortunately not realized yet but feared by authorities. Exposure can be to one main metal compound or to complicated mixtures. Due to decay of parent radionuclides, the effects of exposure are in some cases caused by combined effects of parent and daughter radionuclides. The health effects of metal radionuclides exposures are a combination of radiation increasing cancer risk in chronic exposure and toxicity of the metals. Acute health effects after extensive radiation exposure starts with nausea, vomiting, and headaches. Further exposure leads to weakness and fatigue, fever, hair loss, disorientation and dizziness, diarrhea with bloody stools, decreased blood pressure, and ultimately death. The main purpose of radionuclide decorporation is to minimize the radiation dose (eg, polonium) and chemical insult (eg, uranium) received by exposed individuals. Since some of the important metal radionuclides have very long biological half-times after deposition in bone, liver, or kidneys, rapid initiation of chelation treatment is imperative after a contamination event, to reduce uptake from skin or wounds, lungs, or gastrointestinal tract, and to promote excretion of circulating radionuclide in blood before tissue deposition. Two chelators are approved for radionuclide decorporation, diethylene triamine pentaacetic acid (DTPA), and Prussian blue. Several experimental chelators and drugs approved, for example, iron overload and Wilson's disease are being evaluated as potential actinide decorporating agents. New formulations of DTPA as prodrugs (eg, ethyl and pentyl diesters) are being developed for oral use. Chelators are being developed based on alginates, pectin, and other macromolecular compounds for wound and skin cleaning, for oral use, and for extracorporal chelation.