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EXTERNAL AND INTERNAL CONTAMINATION Radioactive sources Radioactive sources are present in the sealed (normally non spreadable) and unsealed form (spreadable): Gammagraphy essentially uses as sources iridium-192 and sometimes cobalt-60 Neutrongraphy uses sources of neutrons like californium-252 or an americium/beryllium couple. Betagraphy uses beta sources like carbon-14. Chemical and biological radiation-treatment uses gamma radiation sources cobalt-60 or caesium-137. Radioactive sources in medicine In medicine there are three uses for non-sealed radioactive nuclides: Biological analyses: radio-markers have been replaced progressively by non-radioactive markers. Medical imaging: nuclear medicine department use radio-pharmaceuticals for diagnostics, which are ingested by the patient to obtain an image of the tissue or organ while it is functioning. Therapy: radio-pharmaceuticals can constitute the treatment itself, for example iodine 131 for the treatment of thyroid cancer. Contamination risk Contamination sources reactor accidents involving damage to the core leading to combined inhalation-peroral entry into the body of a mixture of fission products (primarily of volatile caesium and iodine isotopes) accidental violation of the regulations or procedures governing work with radioactive substances, especially in form of powder or solution accidents involving leaking or damaged sealed sources (i.e. 192Ir, 137Cs, 60Co, 226Ra) errors in dosage of radionuclides used for diagnostic and therapeutic purposes accidents involving the fabrication and reprocessing of nuclear fuels and the transportation and disposal of radioactive waste Chernobyl accidents Goiania accident Area of contamination – 4 000 000 m2 249 contaminated (137Cs) persons, 129 with internal contamination, 4 deaths Contamination sources in nuclear accidents External radionuclide contamination External contamination: radioactive materials in form of dust, solid particles, aerosols or liquid, become attached to skin or clothes External contamination The risks linked to external exposure of the skin differ according to the type of radiation: alpha emitting radio-elements do not a priori present any risk by external contamination, beta emitting radio-elements do present a special risk because they entail exposure which is almost exclusively of the skin, gamma emitting radio-elements pose the same problems by external contamination as in external exposure, external contamination by a neutron emitting radioelement is impossible. External contamination reveals a secondary potential risk of internal contamination by inhalation, ingestion or breaking and penetration of the skin. People involved in the Chernobyl accident in 1986 The Chernobyl accident, 26 April 1986, involved the very serious irradiation and contamination of a number of people working in the power station and those who immediately intervened, it provides a good example of external contamination. More than 200 patients were hospitalized in the hours following the catastrophe. Before this massive flood of victims, the initial efforts to manage the situation were limited to treatment of the symptoms a full assessment of lesions, treatment of traumatic lesions and summary external decontamination. The latter fact was revealed to be particularly damaging as all the patients had external contamination by fission products, such as Cs-137, Sr-90, or I-131, all of them being beta and some gamma emitters. Beta emitters on the skin caused severe radiological burns with complex development. It is estimated that 5 of the 28 premature deaths following the accident were attributable in part to radiological burns. These 5 deaths, and perhaps others, could doubtless have been avoided if good external decontamination of all the exposed subjects had been carried out in the shortest time. External contamination triage Triage following known or suspected radiation accidents includes both medical and radiological considerations Medical triage should be based upon local procedures for medical management of persons involved in accidents with radioactive materials and on considerations dependent on the severity of injuries. Treatment in life threatening conditions has priority over considerations for exposure to or contamination with radioactive materials. Following medical stabilization of the patient’s condition, careful radiological assessment can be directed to determining the presence of both external and internal contamination. External contamination measurement Proper monitoring of patient can detect and measure alpha, beta or gamma emitters; radiation type depends on isotope in contaminant Alpha monitor Radiological survey Initial external contamination survey (of skin, eyes, lips) should be made with instruments adequate for the particular situation The results of the radiological survey should be recorded on an anatomical chart and made a part of the patient's medical record Quick `frisk’ 112 000 persons monitored in Goiania at olympic stadium Decontamınatıon Decontamination techniques Decontamination procedures Start with gentle stream of warm water Use mechanical action of flushing and/or friction of cloth, sponge or soft brush For showering, begin with the head and proceed to the feet Keep materials out of eyes, nose, mouth and wounds Use waterproof draping to limit spread Cover uncontaminated area with plastic sheet and tape edges Decontamination techniques and control • Use single inward movements or circular motion • Then rinse area with tepid water and gently dry using the same motions • After drying, premonitory skin to determine effectiveness of decontamination Decontamination procedures: body orifices Consideration: Orifices need special attention because absorption of radioactive material more rapid than through skin Mouth Nostrils Procedures: Oral cavity: brush teeth with toothpaste, frequently rinse mouth with 3% citric acid Pharyngeal region: gargle with 3% H2O2 Swallowed radioactive materials: gastric lavage Nose: rinse with tap water or physiological saline Decontamination procedures: body orifices Procedures: •Eyes: rinse by directing stream of water or physiological saline from inner to outer canthus while avoiding contamination of nasolacrimal gland •Ears: - rinse externally with water - rinse auditory canal using ear syringe Eyes Ears Useful therapeutic agents for skin decontamination Common soap or detergent solution for skin and hair; low acidity (pH ~5) recommended Chelating agents: solution of EDTA 10% for skin or hair contamination with transuranium, rare earth and transition metals DTPA 1% in aqueous acid solution (pH ~4) for washing skin after contamination with transuranics, lanthanides or metals (cobalt, iron, zinc, manganese) Useful therapeutic agents for skin decontamination Potassium permanganate 5% aqueous solution should be used carefully not recommended for face, natural orifices and genital regions use when conventional washing ineffective follow with application of reducing agent, then rinse with water Hydroxylamine or sodium hyposulfite 5% freshly prepared aqueous solutions reducing agents - apply after KMn04 or Lugol, then wash with water Useful therapeutic agents for skin decontamination Antiphlogistic topical ointment: To be applied for fixed contamination, especially useful for contamination of fingers Isotonic saline solution for eyes Isotonic 1.4% bicarbonate solution for removing uranium from body Lugol solutions for iodine contamination Acetic acid solution (pH 4 to 5) or simply vinegar for decontamination of 32P Internal contamination Occurs when people ingest, inhale or are injured by radioactive material. The most frequent points of entry are by inhalation and wounds. Metabolism of non-radioactive analogue determines radionuclide’s metabolic pathway. Paints for luminous watch faces In the 1920s and 1930s the clock making industry used radium 226 and 228 in radio-luminescent paint for watches. At this time, the risk from alpha emitting radio-elements was almost unknown. The workers who painted the luminous faces had the bad habit of tapering their brushes with their lips. Every time they did this they ingested several becquerels of radium. The fact that radium and calcium are chemical homologues, resulted in rare bone cancers appearing starting from the 20s, in the form of carcinoma of the sinus of the face. An epidemiological enquiry demonstrated the link between exposure to radium and the risk of bone cancer in 2,403 workers, whose ingestion of quantities of radium could be evaluated. 64 were suffering from osteosarcoma whereas 2 cases of this type of cancer would have been expected statistically. Extent of hazard Factors determining extent of contamination hazard: Amount of radionuclides Energy and type of radiation Biological and radiological half-life Critical organ Chemical and physical properties of radionuclide Intake routes In order of decreasing frequency, contaminants enter the body by four principle routes: Inhalation: Particularly likely with explosion or fire Particle characteristics important composition, solubility in body fluids) Ingestion: Critical for general public after accidental environmental release Wound contamination Absorption (size, chemical Inhalation Fate of inhaled particles dependent on physicochemical characteristics Soluble particles (3H, 32P, 137Cs) absorbed directly into circulatory system Insoluble particles (Co, U, Ru, Pu, Am) are cleared by lymphatic system or by mucociliary apparatus above alveolar level. Most secretions reaching pharynx swallowed, enter gastrointestinal system Deposition and clearance from respiratory tract Contaminant's particle size determines deposition in respiratory tract Particles <5 microns in diameter may reach alveolar area Particles >10 microns too large to pass into alveoli, deposited in upper airways Pulmonary effects Irradiated lung tissue Pulmonary fibrosis Ingestion All swallowed radioactive material enters digestive tract primarily from contaminated food and water secondarily from respiratory tract Absorption from the gastrointestinal tract depends on chemical make-up and solubility of contaminant Parameters of ingestion Gastrointestinal absorption < 10 % for most elements Elements of high absorption: • radium (20%) • strontium (30%) • tritium (100%) • iodine (100%) • caesium (100%) Wound contamination Any wound considered contaminated until proven otherwise Open fracture demonstrates wound contamination with depleted uranium shrapnel Percutaneous absorption Generally, radionuclides do not cross intact skin, so uptake by this route does not occur Most important exceptions are: tritium, iodine, caesium Skin wounds, including acid burns, abrasive scrabbing, create portal for particulate contamination to subcutaneous tissue, bypassing epithelial barrier Distribution and deposition Iodine Uranium Metabolism Diagram of intake, metabolism and excretion of radionuclides Internal contamination measurement: direct methods Whole body counters Thyroid uptake system Indirect contamination measurement Indirect measurement of contamination includes nasal swipes to determine respiratory intake of radioactive aerosols, and also urine and faeces sampling to establish internal contamination Alpha and beta emitters, the most hazardous internal contaminants, detected through bioassay sampling Accurate bioassays require carefully executed sampling over time and knowledge of type and time of contamination Bioassay sampling Managment of internal contamination: First Action Life threatening conditions have priority over considerations of radioactive exposure or contamination. Attention to vital functions and control of haemorrhage take priority Contamination levels almost never serious hazard to personnel for time required to perform lifesaving measures and decontamination Treatment of internal contamination Treatment procedures: the sooner started – the more effective In practice, initial treatment decisions based on accident history rather than careful dose estimates Basic principles of treatment Reduce absorption and internal deposition Enhance excretion of absorbed contaminants Current methods of treatment of internal contamination - Saturation of target organ, e.g. potassium iodide for iodine isotopes - Complex formation at site of entry or in body fluids followed by rapid excretion, e.g. DTPA for Pu isotopes - Acceleration of metabolic cycle of radionuclide by isotope dilution, e.g. water for 3H - Precipitation of radionuclide in intestinal lumen followed by faecal excretion e.g. barium sulphate administration for 90Sr - Ion exchange in gastrointestinal tract, e.g. prussian blue for 137Cs Diluting agents: water for tritium - 3H Single exposures are treated by forced fluid intake: Enhanced fluid intake e.g. water, tea, beer, milk has dual value of diluting tritium and increasing excretion (accelerated metabolism) Biological half-life of tritium - 10 days Forcing fluids to tolerance (3-4 L/day) reduces biological half-life to 1/3-1/2 of normal value Ion exchange: prussian blue for 137Cs 137Cs - physical half-life Tp=30 years; biological half-life in adults average Tb=110 days, in children 1/3 of this Prussian blue effective means to reduce body's uptake of caesium, thallium and rubidium from the gastrointestinal tract Dosage of prussian blue: one gram orally 3 x daily for 3 weeks reduces Tb to about 1/3 normal value Chelation agents: DTPA for heavy metals and transuranic elements Ca-DTPA is 10 times more effective than Zn-DTPA for initial chelation of transuranics. Must be given as soon as possible after accident After 24 hours, Ca-DTPA and Zn-DTPA equally effective Repeated dosing of Ca-DTPA can deplete body of zinc and manganese Dosage of Ca-DTPA and Zn-DTPA 1 g iv. or inhalation in a nebulizer Initially: 1 g Ca-DTPA, repeat 1 g Zn-DTPA daily up to five days if bioassay results indicate need for additional chelation Pregnancy: First dose Zn-DTPA instead of Ca-DTPA Additional chelating agents Dimercaprol (BAL) forms stable chelates, and may therefore be used for the treatment of internal contamination with mercury, lead, arsenic, gold, bismuth, chromium and nickel Deferoxamine (DFOA) effective for chelation of 59Fe Penicillamine (PCA) chelates with copper, iron, mercury, lead, gold. Superior to BAL and Ca-EDTA for removal of copper (Wilson’s disease) Treatment of uranium contamination In any route of internal contamination, treatment consists of slow intravenous transfusion of 250 mL of isotonic 1.4 % sodium bicarbonate Local treatment: for skin contamination, wash with isotonic 1.4% solution of sodium bicarbonate Summary of lecture Attend to life-threatening injuries first Earlier skin decontamination decreases degree of beta burns, lowers risk of internal contamination, reduces chance of further contamination Goal of internal contamination treatment: decrease uptake into circulatory system, decrease deposition in critical organs, increase excretory rate contaminant Health physicists and medical specialists should advise on risks and benefits of decorporation Lecture is ended THANKS FOR ATTENTION In lecture materials of the International Atomic Energy Agency (IAEA), kindly given by doctor Elena Buglova, were used