Review of DWLs for radionuclides in environmental materials: interim guidance

The publication of a report entitled 'Criteria for controlling radiation doses to the public after accidental escape of radioactive material' (1975, UK Medical Research Council) has emphasized the need for a review of the recommendations on secondary standards applicable in normal, as distinct from emergency, situations. The basic standard used in the MRC report is the 'emergency reference level' (ERL) of dose equivalent. The secondary standards of derived ERLs, which are quoted for four radionuclides in air, in milk and on pasture, were based on new metabolic, dosimetric and other data. The basic standards applicable in normal situations are the ICRP dose limits, and the secondary standards of derived working limits (DWLs) are the obtained via appropriate models. The National Radiological Protection Board confirms the validity of the DWLs in milk for iodine-131 (400 picocuries per litre) and caesium-137 (30,000 picocuries per litre). The DWL of 800 picocuries strontium-90 per gram of calcium in milk should be retained pending development of a model which makes use of the substantial information now available, and used by the MRC, on radiostronitum metabolism and dosimetry in man. The NRPB is currently reviewing values of DWLs in environmental materials for a wide range of radionuclides which are, or may be, discharged to the atmosphere. (U.K.)