Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
PROTECT: First Proposed Levels for Environmental Protection against Radioactive Substances Definitions,Derivation Methods to Determine Thresholds, Available Effects Data, Preliminary Reasoning and Results
Reminder of PROTECT objective within WP3 • To derive and propose numerical target values for an extended list of ecological targets and protection levels,… explore the possibility for the application of advanced statistical methods that : (1) allow the best use of the available knowledge when this is represented by small data sets, (2) allow quantification of the associated uncertainty, (3) easily allow revision of resultant values when new knowledge becomes available.
Ecosystem: structure & function Definition Communities: Populations of species • Protection goals: For the ecological target(s) of interest, combination of : • the targeted level of biological organisation (e.g., a population of a given ecosystem, taxonomic group, species) (2) the targeted level of protection that may take into account legal requirements (e.g., each individual for an endangered species, 95% of species for a taxonomic group or a community) Species: Population Individual (sub) -> a range of protection goals can be listed -> a range of numerical thresholds can be derived to assure compliance to those environmental protection goals
Numerical Thresholds (1/3) Definition: a limit quantifying the interface between an acceptable stressor level (e.g., in a given medium, in biota)and an unacceptable level [« acceptable » being related to the protection goal] Applications : • EcologicalRisk Assessment – used as ScreeningValues, associated with a tiered RA scheme; Exceeding means « do more » to better understand the risk (e.g., the screening value in ERICA) (2)Regulation – used as Action Values, i.e. « legally » binding criteria (or standards) to meet the « legal » requirements; Exceeding means « act » (e.g., an EQS)
Numerical Thresholds (2/3) • Application: Planned and existing situations for which environmental impact/risk needs to be assessed (e.g., chronic (routine) releases). Existing situations such as contaminated sites, for which a threshold may be defined to identify serious risk level triggering an immediate action/intervention (e.g., clean up a site). • Unit : Dose Rates in Gy per unit time (e.g., µGy/h) that may be converted into activity concentrations in media (water, sediment, soil, air)
Numerical Thresholds (3/3)In Summary Screening Values-> to trigger further investigation in a tiered risk assessment Action Values-> to make a final decision about acceptability, trigger a regulatory action Both categories of thresholds may be: (1) Applied to the context of chronic radioactive substances releases due to planned or existing situations. (2) Designed to be protective at a pre-defined level, of different ecological targets that are potentially exposed to radioactive substances(ecosystems (terrestrial, marine and freshwater), communities or wildlife taxonomic groups, populations of a species, individuals of a specific population of a species).
Methods for deriving thresholds (1/5) • Existing (chemical) approaches are based on available critical ecotoxicity data, typically ED50 for acute exposure conditions (short-term) and EDR10 for chronic exposure conditions (long-term). Exposure-response relationship from ecotoxicity tests (stressor, species, endpoint) Effect (%) 100 % Observed data Regression model 50 % 10 % ED50 EDR50 Dose (Gy) Dose Rate (µGy/h) ED10 EDR10 EDR10: Dose Rate giving 10% effect in the exposed group in comparison to the control
Methods for deriving thresholds (2/5) • Methods recommended by EC for chemicals (Technical Guidance Document (2003)) – easily adaptable to radioactive substances when ED50 or EDR10 are available (1) The Assessment Factor Method for small data sets Case not used Problem of Unit
Calculation of a dose rate that is assumed to protect a given % of species In the Technical Guidance Document (2003): the agreed concentration is the hazardous concentration affecting 5 % of species to a 10%. When it remains other extrapolation issues, the TGD recommends to apply an additional AF (1-5) 5% HDR5% : Dose rate giving 5% of the species affected to a 10% effect Methods for deriving thresholds (3/5) (2) The Species Sensitivity Distribution (SSD) Method statistical extrapolation models to address variation between species in their sensitivity to a stressor. The species for which results are known are representative, in terms of sensitivity, of the totality of the species in the ecosystem. The endpoints measured in laboratory tests are indicative of effects on populations in the field. PAF (%) 100 80 EDR10 60 40 Dose Rate (µGy/h) 20 0 1 10 100 1000 10000
Methods for deriving thresholds (4/5) • (3) a weight of evidence approach using data from field exposures (field measurements of biodiversity indexes co-occurring with stressor(s) levels) • ->Concerning radioactive substances, such data series may be available for some specific sites • (e.g.,uranium mining sites and long-term ecological surveillance – SQGs for ERA of metals and radionuclides)
Methods for deriving thresholds (5/5) • In summary 3 main methodologies may be used (combined) for deriving thresholds (methods 1 & 2 reviewed/compared during ERICA): (1) the Assessment Factor method when few ecotoxicity data are available, or (2) the Species Sensitivity Distribution (SSD) approach associated with an arbitrary cut-off value, which is usually set at a protection level of 95% of the species when the available data set is more robust. (3) a weight of evidence approach using data from field exposures based on critical ecotoxicity values- i.e., stressor level in a given medium giving 10% effect in the exposed group in comparison to the control group for chronic exposure (or 50% effect for acute exposure conditions).
Chronic effects data from FREDERICA • To apply any of the methods in a robust way, comparable critical ecotoxicity endpoints are needed i.e. EDR10 for chronic exposure. • To meet this aim, a meta-analysis of effects data has been initiated and applied in ERICA to reconstruct dose-effect relationships exhibiting a logistic pattern. • Only data devoted to effects induced by external irradiation pathway were quantitatively adequate to be mathematically structured in terms of dose-effect relationships. • In Protect, we have included an analysis of dose-effects relationships exhibiting an hormetic pattern.
EDR10 = 123.14 EDR10 = 7.42 Dose-effect relationships reconstruction(examples) Sus scrofa (mammal, pig) Response : reproduction (number of germ cells in female %of control) (ID:629) Synechococcus lividus (Cyanobacteria) Response : growth (number of cells) (ID:804) Logistic Hormetic
Data set (EDR10 in µGy/h) obtained for chronic g external exposure Hormetic relationship
Chronic critical radiotoxicity valuesSummary and « possible » SSD-cases • Only obtained for g external exposure conditions • EDR10 – geometric means per species and effect category and per model (logistic/hormetic) Total number of EDR10 : 80 (logistic) + 8 (hormetic) Total number of geometric means: 24 + 6 Number of species: 18 + 3
First Proposed Thresholds & Reasoning for use PAF (%) 100 80 60 40 Dose Rate (µGy/h) 20 0 1 10 100 1000 10000 • Protection goals: • Ecosystem (structure & function) • 95% of species • + AF for a high degree of conservatism • Taxonomic groups (one or several) 95% of species • + AF for small datasets 5% HDR5%
Without the lowest data (n=29) HDR5 = 109 µGy/h CI 95% = [36;374] First Proposed Thresholds (1/3) • Ecological target : Ecosystem (structure & function) All data (n=30) HDR5 = 45 µGy/h CI 95% = [8.8;207] Proposed Screening value: Application of a max AF (5) -> 10 or 20 µGy/h
Taxonomic groups without enough chronic data First Proposed Thresholds (2/3) HDR5 (µGy/h) Best estimate and CI95% 800 700 600 500 400 300 200 100 0 Aquatic Plants Terrestrial Plants Aquatic Vertebrates Generic Ecosystem Aquatic Ecosystem Aquatic Invertebrates Terrestrial Vertebrates Terrestrial Ecosystem Terrestrial Invertebrates without the lowest data
First Proposed Thresholds (3/3) Lowest value included Action Values (AV) Application of AF (1-5) possible Screening Values (SV) Application of AF of 5
Issues for discussion (not exhaustive!) • Application of an additional AF to generate Screening values for ecosystems (SV<<AV) • Application of a taxonomic weight on Plants, Invertebrates and vertebrates to establish the SSD at the ecosystem-level • Use of extrapolation empirical models to fill the gaps for taxonomic groups (Acute-to-Chronic relationships on sensitivity distributions) • Use of other groupings (e.g., plants, invertebrates) • Use of an additional standard for « contaminated sites » to trigger a remediation action (i.e. HDR50% or dose rate affecting 50% of species to a 10% effect) e.g., HDR50 SSD-All EDR10 - Ecosystem = 4.2 mGy/h • …