The dose conversion coefficients can be used to estimate the unweighted absorbed dose rate from media and organism activity concentrations. For internal exposure the following equation can be used:

Dbnt = X Cb * DCCiui (5)

i

Where:

• Dbnt is the absorbed internal dose rate for reference organism b;

• Cb is the average concentration of radionuclide i in reference organism b (Bqkg-1 fw); and

• DCCbnt { is the radionuclide-specific dose conversion coefficient for internal exposure defined as the ratio between the average activity concentration of radionuclide i in the organism b and the dose rate to the organism (pGyh-1 per Bqkg-1 fw).

For external exposure the following equation can be used in terrestrial ecosystems:

D bxt = X vzY, Crzf * DCCbx

z

Where:

• vz is the occupancy factor, the fraction of time that organism b spends at a specified location z in its habitat;

• Crzf is the average concentration of radionuclide i in the reference media of a given location z (Bq kg-1 fw, soil); and

• DCCbbxtzi is the dose conversion factor for external exposure defined as the ratio between the average activity concentration of radionuclide i in the reference media corresponding to the location z and the dose rate to organism b (pGyh-1 per Bq unit media).

External DCCs from beta and alpha emitters are comparatively low and may be assumed to be zero for some radionuclides in some approaches.46

Weighted total dose rates (in pGyh-1) can be calculated as:

DCCint = wf lowp ‘ DCCint, lowP + wf p+g ■ DCCint, p+g + wf a ‘ DCCint, a (7)

DCCext = wf lowp ‘ DCCext, lowp + wf p+g ‘ DCCext, p+g (8)

Where wf are the weighting factors for various components of radiation (low energy p, p + g and a).

Although there is no agreement on wf for wildlife, currently most assessment approaches are using broadly similar values with default radiation weighting factors of 10-20 for alpha radiation and 1-3 for low beta radiation and 1 for beta-gamma radiation.13,14,47 For a-radiation weighting factors, these values are broadly consistent with the upper bound on the range of variation reported by Chambers et al.48 in relation to deterministic endpoints (mainly mortality). Currently, the estimated doses for wildlife do not take account of tissue weighting factors as used in human dosimetry.

The ICRP have derived dose conversion coefficients4 for 75 radionuclides for the Reference Animals and Plants using the methodology of Ulanovsky and Prohl49 developed for the ERICA Tool.13

Vives i Batlle et al.50 presents a comparison of unweighted whole-body dose rates from ten different approaches being used (or developed) to assess the exposure of wildlife to radiation.