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, slowlyreproducing species.
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