A multi-criteria weight of evidence approach for deriving ecological benchmarks for radioactive substances

Abstract

Dose rate benchmarks are required in the tiered approaches used to screen out benign exposure scenarios in radiological ecological risk assessment. Such screening benchmarks, namely the predicted no-effect dose rates (PNEDR), have been derived by applying, as far as possible, the European guidance developed for chemicals. To derive the ecosystem level (or generic) PNEDR, radiotoxicity EDR(10) data (dose rates giving a 10% effect in comparison with the control) were used to fit a species sensitivity distribution (SSD) and estimate the HDR(5) (the hazardous dose rate affecting 5% of species with a 10% effect). Then, a multi-criteria approach was developed to justify using an assessment factor (AF) to apply to the HDR(5) for estimating a PNEDR value. Several different statistical data treatments were considered which all gave reasonably similar results. The suggested generic screening value of 10 microGy h(-1) (incremental dose rate) was derived using the lowest available EDR(10) value per species, an unweighted SSD, and an AF of 2 applied to the estimated HDR(5). Consideration was also given to deriving screening benchmark values for organism groups but this was not thought to be currently appropriate due to few relevant data being currently available.

Derivation of regional hazardous doses for amphibians acutely exposed to ionising radiation

“…In such frameworks, the risk level is judged by comparing dose rates to non-human biota with effect benchmark values. Some trials have been, therefore, made for estimation of benchmark values for ionising radiation [7][8][9][10]. These trials have been based on the species sensitivity distribution (SSD) approach.…”

“…It has been used to estimate 5% hazardous concentrations of chemicals (HC 5 s), at which only 5% species are affected and the other 95% species are protected in the environments. However, most of 5% hazardous dose rates (HDR 5 s) estimated for ionising radiation are generic, e.g., for the whole ecosystems (terrestrial + freshwater + marine ecosystems) [8,9], terrestrial or freshwater ecosystems [7] and vertebrates or invertebrates [10]. Currently it is difficult to estimate HDR 5 specific to each taxonomic group by SSD, because there is the limited number of effects data available to each group [8,10].…”

“…Since there is a large difference in radiosensitivity among taxonomic groups [11], generic benchmark values will be too strict for radioresistant groups and too generous for radiosensitive groups. It is, therefore, required to derive benchmark values specific to each taxonomic group such as family or class, which corresponds to each ICRP Reference Animal and Plant [3], as Garnier-Laplace et al [9] pointed out.…”

Impact assessment of long-term chronic radiation exposure on plant populations

“…To properly understand the effect of normal, real-world contaminant exposures, one must consider actual field conditions. However, for most wildlife groups and endpoints studies that link accumulation, chronic exposure and biological effects in natural settings are scarce [1]. These data gaps imply that the protection of the environment from ionizing radiation will require more experimental data related to effects of chronic low-level exposure to radionuclides at the population level.…”

The transfer of radionuclides to wildlife

“…However, to enable consideration of the wide range of radionuclides and wildlife species that may need to be considered in assessments, it currently represents a pragmatic approach that meets the needs of 'prospective' and 'current' exposure (ICRP 2007) assessments. The estimation of whole-body activity concentrations and, consequently, whole-body dose rates (rather than consideration of target tissues) also enables comparison with the available effects data, which originate from studies of external gamma exposure (Garnier-Laplace et al 2010).…”