| In Canada, regulations developed under the
Nuclear Safety and Control Act require that license applicants describe the
effects on the environment of the nuclear facility to be licensed. For the
purpose of assessing risks to the environment, the Canadian Nuclear Safety
Commission recommends the use of an ecological risk assessment approach. It
is based on toxicity benchmarks from chronic exposure studies of
reproduction and survival in sensitive species. For mammals, an Expected
No-Effects Value of 3 mGy·d-1
has been derived from limiting studies on fertility effects in squirrel
monkeys exposed to tritium. This benchmark is adequate for regulatory
purposes relative to data on wild populations of small rodents living in
contaminated areas, or in areas artificially exposed to high levels of gamma
radiation. At least for short-lived, prolific species of mammals, it has
been impossible to define a Lowest-Observed-Effects-Level for population
effects at chronic dose rates up to about 100 mGy·d-1
for lifetime doses up to about 10 Gy. Refinement of taxa-specific benchmarks
to an appropriate level of conservatism will require more research on
long-lived, slowly-reproducing species. |