Documents of the NRPB: Volume 16, No. 3

Synopsis

Generalised Derived Limits for Radioisotopes of Hydrogen, Carbon, Phosphorus, Sulphur, Chromium, Manganese, Cobalt, Zinc, Selenium, Technetium, Antimony, Thorium and Neptunium

This report reflects the understanding and evaluation of the current scientific evidence as presented and referenced in the full report.

Generalised derived limits (GDLs) are intended for use as convenient reference levels against which the results of environmental monitoring can be compared. Generalised derived limits have been calculated in various environmental materials for the radiologically significant isotopes of hydrogen, carbon, phosphorus, sulphur, chromium, manganese, cobalt, zinc, selenium, technetium, antimony, thorium and neptunium, derived from the annual effective dose limit of 1 mSv. The most recent age-dependent dosimetric models have been applied and the methods are generally as used in calculating GDLs for radioisotopes of other elements, such as caesium and polonium, published previously. However, for the first time exposure of the fetus has been taken into account in calculating the GDLs using the fetal dose coefficients recently published by ICRP.

Generalised derived limits are calculated using deliberately cautious assumptions and are based on the assumption that the level of environmental contamination is uniform over a year. If a measured environmental concentration exceeds about 10% of the GDL then the doses should be examined more closely, taking account of site-specific factors and the length of time for which the measured level is likely to be maintained.

Last reviewed: 22 October 2009