Protection Of Non-human Biota Research Articles

Regulatory experience in applying a radiological environmental protection framework for existing and planned nuclear facilities

Frameworks and methods for the radiological protection of non-human biota have been evolving rapidly at the International Commission on Radiological Protection and through various European initiatives. The International Atomic Energy Agency has incorporated a requirement for environmental protection in the latest revision of its Basic Safety Standards. In Canada, the Canadian Nuclear Safety Commission has been legally obligated to prevent unreasonable risk to the environment since 2000. Licensees have therefore been meeting generic legal requirements to demonstrate adequate control of releases of radioactive substances for the protection of both people and biota for many years. In the USA, in addition to the generic requirements of the Environmental Protection Agency and the Nuclear Regulatory Commission, Department of Energy facilities have also had to comply with specific dose limits after a standard assessment methodology was finalised in 2002. Canadian regulators developed a similar framework for biota dose assessment through a regulatory assessment under the Canadian Environmental Protection Act in the late 1990s. Since then, this framework has been applied extensively to satisfy legal requirements under the Canadian Environmental Assessment Act and the Nuclear Safety and Control Act. After approximately a decade of experience in applying these methods, it is clear that simple methods are fit for purpose, and can be used for making regulatory decisions for existing and planned nuclear facilities.

Radionuclide monitoring in molluscs inhabiting intertidal region near a nuclear installation, Gulf of Mannar, India

Protection of non-human biota from ionizing contaminants, especially in the vicinity of nuclear installations is a very important aspect for nuclear engineers and ecologists. In this view, a baseline data on the activity concentration of 210Po and 210Pb were quantified in different tissues of molluscs inhabiting the intertidal region along the coast of Kudankulam. The activity concentration was noticed higher in the organs associated with digestion and metabolism. Filter feeding bivalve molluscs registered the maximum activity of 210Po in their whole body compared to grazing gastropods. 210Po:210Pb ratio was calculated to be greater than unity in most of the analysed tissues. The ecological sensitivity of molluscs to the radiation exposure and the safeness of the environment was analysed by calculating the external and internal dose rate. The hazard quotient for molluscs was lesser than the global bench mark dose rate of 10μGyh–1.

External radiation doses from 137Cs to frog phantoms in a wetland area: in situ measurements and dose model calculations

For assessment of external radiation doses to frogs in a wetland area contaminated with (137)Cs, frog phantoms were constructed from polymethyl methacrylate (PMMA). The frog phantoms contained thermoluminescence (TL) chips and were used in situ at two study sites to measure doses. To test if higher doses are received by the sensitive skin of frogs, extra-thin TL chips were applied close to the surface of the frog phantoms. In addition, the measured doses were compared with those calculated on the basis of soil sample data from the wetland multiplied with dose-conversion coefficients from the US Department of Energy's RESRAD-BIOTA code and from the ERICA assessment tool. Measured doses were generally lower than those calculated to ellipsoids used to model frogs. Higher doses were measured at the frog phantoms' surfaces in comparison to inner parts at one of the two sites indicating that the frogs' thin skin could receive a higher radiation dose than expected. In the efforts to assure protection of non-human biota, in situ measurements with phantoms provide valuable dose information and input to dose models in site-specific risk assessments of areas contaminated with radionuclides.

Protection of non-human biota against radiation in freshwater—Effect of time dependence in tiered exposure assessment

The ERICA's European framework that have been proposed to assess the exposure of biota to radionuclides is based on tiered approach: the Tier 1 assessment is based on equilibrium assumptions (constant radioactive releases over time, equilibrium at the interfaces water-suspended matter and water-biota); the Tier 2 assessment allows to use time-dependent and site-specific data to perform a more precise evaluation. The objective of this paper was to compare these two tiers in the context of routine releases from nuclear power plants in freshwater ecosystem. The Loire River where 14 nuclear power plants (NPPs) operate was chosen as a case study and the transport of 60Co in the river, its partition between water and suspended particles and its bioaccumulation was calculated under equilibrium and time-dependent assumptions respectively. Using this case study allowed to quantify the overpredictions linked to conservatisms assumed in Tier 1. Recommendations were identified on when a Tier 2 approach is actually needed.

On the application of a radiation weighting factor for alpha particles in protection of non-human biota.

Radiation protection standards for non-human biota have been expressed in terms of absorbed dose. In calculating dose to biota, some investigators have modified the absorbed dose due to alpha particles by a factor of 20, based on the radiation weighting factor used in protection of humans, to account for the greater effectiveness of these radiations in producing biological damage. However, this value is intended to apply to stochastic health effects, primarily cancers, whereas deterministic effects have been the primary concern in protection of biota. Based on an analysis by the International Commission on Radiological Protection, the deterministic radiation weighting factor for alpha particles appears to lie in the range of about 5-10. Given the potential importance of this weighting factor in determining allowable levels of alpha-emitting radionuclides in the environment, regulatory authorities must be impressed with the need to develop an appropriate value for use in protection of biota. There also is a need to express doses and dose limits for biota in terms of a quantity other than absorbed dose and to develop an appropriate name for the biologically significant dose to biota.

Radiological dose conversion factors for generic non-human biota used for screening potential ecological impacts

Protection of non-human biota from radionuclides in the environment is an important aspect of many environmental assessments. Biosphere transport models can be used to estimate radionuclide concentrations in plants and animals, and the radiological dose is calculated as the product of concentration and a dose-rate conversion factor (DCF). Here, we calculate and present DCF values for 99 radionuclides that can be used in a generic sense to estimate the dose to a wide variety of plants and animals. DCF values for internally incorporated radionuclides are based on the absorption of all emitted radiations from within the body. DCF values for external exposures include immersion in air, water, soil/sediment and vegetation. We implicitly include the energy from the decay progeny if they have a half-life of less than 1 day, to be consistent with many biosphere transport models. The DCF values can be used for simple screening of potential doses in assessments where a specific target organism cannot be defined.