Assessment of the impact of radionuclide releases from Canadian nuclear facilities on non-human biota

The radiological impact of radionuclides released from nuclear facilities is being assessed for regulatory purposes using an ecological assessment framework. Hazard quotients are determined by dividing an estimated exposure value (EEV) by an estimated no effect value (ENEV). Values less than one indicate that environmental harm is not likely, whereas in Tier 2 or Tier 3 assessments values greater than one indicate the potential for environmental harm. Radiation exposure values are calculated using annual mean radionuclide concentrations in water, sediment and biota, and either published screening DCFs or dosimetry equations taking into account the geometry and size of the organism. A relative biological effectiveness (RBE) weighting factor of 40 for alpha emitters and 3 for tritium is used in the dose calculations. When radionuclide concentrations are not measured in biota, they are estimated from published geometric mean concentration ratios. Radionuclide concentrations in benthic invertebrates are assumed to be equivalent to those in the sediment. The radiation dose is the sum of the internal and external doses, except for benthic invertebrates where the total radiation dose is assumed to be from internal radiation exposure. The ENEVs for the various taxonomic groups are determined from literature data using an ecotoxicological approach. The ENEVs derived for radiation effects on biota are: 0.2 Gy(.)a(-1) for fish, 2 Gy(.)a(-1) for both benthic invertebrates and terrestrial invertebrates, and 1 Gy(.)a(-1) for algae, macrophytes, mammals and terrestrial plants. The assessment conducted for uranium mines and mills is presented as a case study outlining the recommended approach. The results suggest that a probabilistic Tier 3 assessment may not be necessary when environmental data are readily available.