title: Uncertainties in dose coefficients for intakes of tritiated water and organically bound forms of tritium by members of the public.
abstract: The International Commission on Radiological Protection (ICRP) provides models for the calculation of doses from intakes of radionuclides, including intakes of tritium as tritiated water (HTO) or organically bound tritium (OBT). The ICRP models for HTO and OBT are explained and the assumptions made are examined. The reliability of dose estimates is assessed in terms of uncertainties in central estimates for population groups. The models consider intakes of HTO and OBT by ingestion and inhalation by adults and children and doses to the fetus following intakes by the mother. The analysis includes uncertainties in the absorption of OBT to blood, incorporation of tritium into OBT in body tissues, retention times in tissues, transfer to the fetus and the relative biological effectiveness (RBE) of tritium beta emissions compared with gamma rays. Heterogeneity of dose within tissues and cells is also considered. For intakes as HTO, dose is predominantly due to distribution and retention of HTO in body water and it was concluded that adult doses are reliable to within a factor of 2. For intakes of OBT, the extent of incorporation into OBT in body tissues results in greater uncertainties with estimates relying on animal data for selected compounds. The analysis indicated that adult doses from OBT can be considered to be known to within a factor of 3. Greater uncertainties in estimated doses for children and for in utero exposures were considered. Central values from the uncertainty analyses of doses for HTO and OBT were greater than the corresponding ICRP dose coefficients by about a factor of 2, mainly due to the inclusion of uncertainties in RBE for tritium. A detailed assessment of doses using appropriate parameters and considering uncertainties would be of particular importance in situations where the dose may approach dose limits or constraints. For exposures to known forms of OBT, specific dose assessments may be required.
authors.affiliation: National Radiological Protection Board, Didcot, Oxon, UK. johnd.harrison@nrpb.org.uk
authors.forename: J D
authors.initials: JD
authors.lastname: Harrison
authors.forename: A
authors.initials: A
authors.lastname: Khursheed
authors.forename: B E
authors.initials: BE
authors.lastname: Lambert
mesh_terms: D000328:Adult; D000375:Aging; D000818:Animals; D002648:Child; D002675:Child, Preschool; D004781:Environmental Exposure; D006801:Humans; D007223:Infant; D007700:Kinetics; D008954:Models, Biological; D011835:Radiation Protection; D011874:Radiometry; D013997:Time Factors; D014018:Tissue Distribution; D014316:Tritium / Q000737:chemistry* / Q000493:pharmacokinetics*; D014867:Water
chemical_list: D014867:Water; D014316:Tritium