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Numerical benchmarks: proposed levels and underlying reasoning

Numerical benchmarks: proposed levels and underlying reasoning. Objectives. ”Derive and propose numerical target values for an extended list of ecological targets and protection levels,

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Numerical benchmarks: proposed levels and underlying reasoning

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  1. Numerical benchmarks: proposed levels and underlying reasoning

  2. Objectives ”Derive and propose numerical target values • for an extended list of ecological targets and protection levels, • designed to assure compliance with environmental protection goals that resonate with protective goals set up for releases of hazardous substances in general

  3. Protection Goal • Level of protection? • (all) individuals • (all) populations • (all) ecosystems (structure, function of)

  4. To protect the sustainability of populations of the vast majority of all species and thus ensure ecosystem function now and in the future. Special attention should be given to keystone species and other species of particular value.

  5. Ways to assess goal achievement • Biological surveillance, e.g. monitor population parameters like population density, age distribution, sex ratio, biodiversity index. • Monitor media concentrations

  6. Types of values • Generic screening value • Predicted no effect • Generic (conservative) • Values triggering regulatory action • Probable significant harm

  7. Sensitivity: acute doses Unscear, 1996

  8. NCRP 1991 It appears that a chronic dose rate of no greater than 0.4 mGy h-1 to the maximally exposed individual in a population of aquatic organisms would ensure protection for the population. If modelling and/or dosimetric measurements indicate a level of 0.1 mGy h-1, then a more detailed evaluation...should be conducted.

  9. IAEA (1992) It would appear that there are unlikely to be any detrimental long term effects on plant communities in which the maximum dose rate is on the order of 10 mGy/d or less Irradiation at chronic dose rates of 1mGy/d or less does not appear likely to cause observable changes in terrestrial animal populations It appears that limitation of the dose rate to the maximally exposed individuals in the population to <10 mGy/d would provide adequate protection for the population

  10. UNSCEAR (1996) Chronic dose rates less than 400 µGy/h (10 mGy/d) would have effects, although slight, in sensitive plants but would be unlikely to have significant deleterious effects in the wider range of plants present in natural plant communities For the most sensitive animal species, mammals, there is little indication that dose rates of 400 µGy/h to the most exposed individual would seriously affect mortality in the population. For dose rates up to an order of magnitude less (40-100 µGy/h), the same statement could be made with respect to reproductive effects. For aquatic organisms, the general conclusion was that maximum dose rates of 400µGy/h to a small proportion of the individuals and, therefore, a lower average dose rate to the remaining organisms would not have any detrimental effects at the population level.

  11. Environment Canada (2003) An assumption is made that a radiation dose level can be defined, an environmental no effects value (ENEV), where the probability of an effect is so low that the population of organisms will not be affected. The ENEV is thus intended to represent effect thresholds for sensitive endpoints that clearly have ecological relevance. In this assessment the ENEV was set with as much rigor as possible (i.e., small application factors; minimal conservatism).

  12. ICRP (2008 draft) The Derived Consideration Levels are NOT intended to be regarded as dose limits, or ‘substitute’ values for them. They are zones of dose rates at which, with respect to the Reference Animals or Plants, or types similar to them, a more considered level of evaluation of the situation would be warranted. It does not imply that higher dose rates would be environmentally damaging, nor that lower dose rates were in some way ‘safe’ or non-damaging. But they are dose rates that could be used in any management action or decision-making process, in terms of being starting points from which further, auditable, information could be appended in order to justify or optimise any subsequent action that was taken

  13. Thompson et al., 2005 The LEL [Lowest Effect Level] represent the contaminant concentration below which harmful effects on benthic invertebrates are not expected. Benthic communities were considered to be not adversely affected if there was less than a 20% reduction in abundance and species richness relative to the reference.

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