Title: Environmental Protection: the Concept and Use of Reference Animals and Plants
1Environmental Protection the Concept andUse of
Reference Animals and Plants
2Report structure
- Preface
- Introduction
- Reference plants and animals
- Pathways of exposure
- Calculation of dose conversion factors for RAPs
- The effects of radiation and its relevance for
RAPs - Assessing effects in terms of derived
consideration levels - Applications and extrapolations
- Conclusions
- References
- Appendices
3Preface
- Timeline ? Developments at ICRP within the field
of environmental protection from ionising
radiation - Task Group set up in 2000
- Framework for Assessing the Impact of Ionising
Radiation on Non-Human Species, ICRP Publication
91, in 2003. - June 2005 Committee 5 established
- Task Group on Dosimetric modelling - 2006
- C5 members
- R. J. Pentreath (Chairman), C-M. Larsson
(Vice-chairman), K. A. Higley (Secretary), F.
Brechignac M. Doi (to 2006), G. Proehl, A.
Johnston (to 2007), A. Real, K. Sakai (from
2007), P. Strand.
4Introduction I
- New recommendations
- Planned, existing and emergency situations
- all of the environment needs to be considered,
including areas where humans are absent. - Aims of environmental protection now include
- Preventing or reducing the frequency of
deleterious radiation effects to a level where
they would have a negligible impact on the
maintenance of biological diversity, the
conservation of species, or the health and status
of natural habitats, communities, and ecosystems.
5Introduction II
- ICRPs approach to environmental protection
- Provide high levelguidance for demonstration of
compliance corresponding with existing/emerging
national and international legislation - Radiation one factor among many
- Compatible with other approaches to protect the
environment - Group biota effects in terms of early mortality,
or morbidity, or reduced reproductive success. - Provide a framework for more applied and specific
numerical approaches
Report - concept and use of Reference Animals and
Plants, serves as an introduction to this
complex subject
6Reference animals and plants
- Reference man of great utility use similar
approach for environment. - Limited group of biota for relating exposure to
dose and dose to effect for environmental
situations - Employ derived consideration levels
- Consequences for individuals or relevant
populations - Points of reference for drawing comparisons with
sets of information on other organisms - Not necessarily the direct objects of protection
- Allows more site-specific information (e.g.
secondary sets) to be compared and examined.
7Criteria for selection of RAPs
- Requirements
- To meet existing or expected legislation ?
vertebrates, wetland habitats - For environmental impact assessments ? animals
and plants relevant to practices such as
fisheries, agriculture, forestry - To achieve consistency in regulatory approaches ?
reasonable coverage of the major ecological
compartments of terrestrial and aquatic
ecosystems. - Pragmatism in selecting RAPs
- radiobiological information available amenable
to future research typical of particular
ecosystems likely to be exposed to radiation
exposure can be modelled and life-cycle relevant
for evaluating total dose and dose-effect
responses reasonable chance of identiying
effects in individuals political and public
resonance
8Appropriate level of generalization
- Animal kingdom Phyla, Classes, Orders, Families
(which share typical traits and features),
Genera, species. - no internationally accepted rules on
classification above Family (or Super Family)
level, and this has therefore been suggested as
the most suitable level of generalisation
9RAPs Definition
- A Reference Animal or Plant is a hypothetical
entity, with the assumed basic biological
characteristics of a particular type of animal or
plant, as described to the generality of the
taxonomic level of Family, with defined
anatomical, physiological, and life-history
properties, that can be used for the purposes of
relating exposure to dose, and dose to effects,
for that type of living organism.
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11Further notes on RAPs
- The set is essentially one of wild animals and
plants rather than domesticated ones - What RAPs are NOT intended to be
- Objects of protection
- Sentinel biota, i.e. such types are protected
then other types will also be protected - Biota that ICRP considers should be particularly
protected - Representatives of key links in food chains
- Representatives of key links in ecosystem
functioning
12The Individual Reference Animals and Plants
- Additional general information relating to RAP
biology and ecology provided in Appendix A,
general discussion on populations - Brief introduction and description of each RAP
type provided in main report - Which family, e.g. Deer Cervidae
- How many species make up the family
- Habitat
- Use as human resource
- Legislation
- Average life-span and information on reproduction
(how many offspring etc.)
13Populations
- In some cases individual exposure is important
but in other cases, populations need to be
considered - A population
- group of individuals of the same species that
live in the same place at the same time - area for population sufficient for the
organisms to carry out their normal functions - group of genetically similar individuals that can
be characterised in terms of e.g. birth rate,
death rate, age structure etc. - Effects of radiation at a population level
requires information on - characteristics of the population being
considered, - the fraction of the population known or assumed
to be exposed to different dose-rates (? total
dose) - stages in the life cycle receiving the relevant
dose
14Basic populations characteristics of RAPs
15Pathways of exposure
- Useful to consider sources
- indicates any physical entity or procedure that
results in a potentially quantifiable radiation
dose. - Types of exposure situation
- Planned
- Emergency
- Existing
16Data needs with regard to different exposure
situations
- Direct measurements sometimes available
- Otherwise modelling approaches required (notably
in planned emergency situations) - Steady state (transfer factors, CFs relevant) or
Dynamic - Data often pertain to parts consumed by humans
- Data often lacking on parts of life-cycle
- Factors that may need consideration
- external exposure from contaminated soil,
sediment, or water - contamination of fur, feathers and skin
- inhalation of (re)suspended contaminated
particles or gaseous radionuclides - ingestion of radionuclides and
- the direct uptake from the water in the case of
aquatic organisms. - Subsequent report in relation to transfer in RAPs
17Dose conversion factors for RAPs
- Simplification whole organisms represented by
simple shapes - Uniform isotropic models, or simplified
analytical or semi-analytical methods sufficient
for aquatic environments - Large density differences require radiation
transport models (e.g. using Monte Carlo)
18Dosimetry dose-concept
- Basic unit absorbed dose (Gy) but
- Different types of radiation are known to produce
different degrees of effect in the same
biological tissue, for the same absorbed doses,
for many types of organisms. - Key quantity Absorbed fraction energy emitted
by a radiation source that is absorbed within the
target
19Dosimetric modelling assumptions
- Based on task group intercomparisons exercise
(details provided in Appendix B of report) - EPIC (Doses-3D), EA RD128, EDEN, RESRAD-BIOTA
and FASSET-ERICA. - FASSET-ERICA selected for reference DCF
derivation because of flexibility - Units of µGy day-1 per Bq kg-1.
20Dosimetry - Selected method
- A practical method to estimate absorbed fractions
for a wide range of ellipsoids and spheres has
been developed by Ulanovsky and Pröhl (2006) - computed using Monte Carlo code MCNP4C
- body composition four-component composition
from ICRU and body density of 1.0 g cm-3. - The organisms are assumed to be in an infinite
water medium. - The transport of electrons and photons simulated
to energy cut-offs of 1 keV for photons and 10
keV for electrons - The mass of the organisms considered covered a
range from 10-3 g to 106 g in steps of an order
of magnitude. - For both photons and electrons the energies
ranged from 10 keV to 5 MeV. re-scaling of the
absorbed fraction for tissues in water - A non-sphericity parameter ? is derived, to
adjust the absorbed fraction for organism shape.
Ulanovksy, A Pröhl, G., 2006. A practical
method for assessment of dose conversion
coefficients for aquatic biota. Radiation and
Environmental Biophysics, 45, 203-214.
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22DCF derivation
- Internal DCF
- External DCF (aquatic)
- For external terrestrial DCFs explicit MC
simulations for selected target-source
configurations see Taranenko et al. (2004). - To enable the use of specific weighting factors
absorbed dose that are due to different types of
radiation are also given in Appendix C. Split
into components of a, low (lt 10 keV) beta and
b-g.
Ei is the energy of component ltigt of emitted
radiation (MeV) yi is the yield of emitted
radiation of energy Ei (dis-1) ?T(Ei) is the
absorbed fraction in the target for energy
Ei 1.384x10-2 is the factor to account for
conversions of MeV to Joules and seconds to days
Taranenko, V., Pröhl, G. Gómez-Ros, J.M.(2004)
Absorbed dose rate conversion coefficients for
reference biota for external photon and internal
exposures. J. Radiol. Prot. 24 A35A62.
23Special note on reference Deer DCFs
- some preliminary considerations were also given
to the relative dosimetry of internal organs,
such as the liver and gonad, but essentially for
illustrative purposes rather than as definitive
models.
24Summary of exposure situation assumptions
25Effects of radiation and its relevance to RAPs
- Large data base on the effects of radiation on
plants and animal regularly reviewed (e.g.
UNSCEAR) - More systematic approach ? FREDERICA database.
- For individual studies, enormous variation in
- range of individual species studied
- mode of exposure,
- dose rates and
- selection of biological effects recorded.
26Current understanding of radiation effects in
general, and within the contextof the human
animal.
- The principal cellular target for biological
effects chromosomal DNA - Effects at a sub-cellular level
- a high proportion of radiation induced damage in
DNA is represented by the occurrence of complex
clusters of chemical alterations - Frequency and complexity of clusters depends on
LET - Error-prone repair of double strand breaks best
explains chromosome aberrations, gene mutation
and cell killing
27Current understanding of radiation effects II
- Compelling evidence that changes in DNA damage
response/repair and apoptotic/cell cycle control
are closely associated with tumor development - Recent radiobiological work on
- Induction of gene and chromosomal mutations at
low doses. - Genomic instability consequences expressed
after many post irradiation cell cycles
28Tissue and organ effects
- Stochastic effects
- Single cell death no consequences for tissues,
but mutation in a single cell ? tumorogenesis ?
cancer - No threshold, frequency related to dose
- Early or late tissue or organ reactions
- larger doses ? substantial amount of cell killing
? detectable tissue reactions - Structure of organs and tissue plays a role in
response - Reserve capacity in organs ? high tolerance to
partial irradiation - Radiation tumorogenesis
- Weak promoter of tumour development, likely
acts in earliest phase - Mutations causing heritable diseases
- Principal genetic effects in humans
multi-system developmental abnormalities rather
than single gene diseases.
29A special note on RBEs
- An approach to account for RBE is needed because
- RBE phenomenon exists in animals other than man
(most RBE studies are in fact for non-human
biota) - Naturally occuring alpha emitters ubiquitous in
bodies of plants and animals. Therefore useful to
apply weighing factors in attempting to normalise
radiation doses. - Many environmental problems concern releases of
alpha emitters therefore more damaging aspect
of these needs to be accounted for. - Subsequent report on issues relating to RBEs and
RAPs
30Radiation Effects in RAPs
- Effects of radiation take place at the level of
the individual BUT - useful to consider such effects in terms of how
they might effect populations early mortality,
reduced reproductive success, some forms of
morbidity and scorable cytogenetic effects - No attempt to interpret such effects at a
population level
31Summarised effects data
- In the report, pages 48-87 summarise effects
under the headings Mortality, morbidity, reduced
reproductive success and chromosomal damage for
each RAP group. - Mammals fish and conifers comprehensive data
coverage - Much fewer data for other categories, e.g. birds,
amphibians, insects and grasses - No data for macroalgae
32Discussion on Effects data
- Miscellaneous data sets
- Many data but little guidance on reliability,
consistency, interpretability, or utility. - Most data for acute exposure therefore of limited
relevance to environmental situations - Data often difficult to use because dose rates
averaged (arbitrarily) over periods of hours,
days, or years. - Data often organised in terms of exposure pathway
as oppose to phylogeny or biology - Many data on stochastic effects in mammals used
for improving human radiological protection have
been omitted.
33General observations effects data
- For the higher vertebrates,
- there is little difference in response across a
range of dose rates for mammals, - Similar response for birds (although data
insufficient in this case to draw conclusions) - For the lower vertebrates,
- generalisations are difficult because allowance
has not usually been made for their lower
metabolic rates - if this fact accounted for, differences between
higher and lower vertebrates may be less than it
appears to be. - Invertebrates more radioresistant than
invertebrates - Mechanistic understanding missing
- eggs and larvae have usually been found to be
more radiosensitive, - Trees and plants
- Long time scales required for study (for effects
to appear) - Few controlled experiments and little data on
which tissues have received dose - No clear information on differences in effects of
radiation on plant and animal cells - WHAT CAN BE DONE WITH THIS INFORMATION IN A
STRUCTURED WAY ?
34Derived Consideration Levels
- Practical means required to make environmental
management decisions and judgements based on
knowledge of effects of radiation on different
types of biota - Useful comparator might be natural background
- Additional doses that were e.g. fractions of
normal background dose rates might be unlikely to
cause concern, whereas dose rates that were very
much higher, and in the region of expected
effects, would need to be considered further - bands of dose rates based on natural background
Derived consideration levels - Point of reference to summarise what is know
about effects on RAPs - Used in conjunction with other relevant
information, e.g. area affected - Information on natural background
- Typical background dose-rates cited from
published works
35Preliminary DCL values
- Extreme simplification of existing data
- Start point to stimulate development
- Derived Consideration Levels highlighted in
yellow - Dose-rates gt 1 Gy d-1 not relevant for
environmental management but considered for
completeness
36DCL further example frog, trout, flatfish
37DCLs - Matters for consideration
- DCLs NOT intended to be dose limits
- Values greater than DCLs not necessarily to be
considered as environmentally damaging - Values less than DCLs not necessarily to be
considered safe. - DCLs are the starting points to consider such
conclusions in the light of the local legislation
and local situation. - Management use other information to justify
action, e.g. - Exposure situation (existing, planned, emergency)
- Area where dose-rates occur
- Time over which dose-rates occur etc. etc.
- Issues
- Not considered appropriate to simplify tables
- Precautionary factors (e.g. safety factors) might
be applied but at least can be related to tables - Link between protection of individuals versus
populations still very uncertain
38Applications
- Environmental management requirements pollution
control, nature conservation, EIA, e.g. - compliance with national pollution control
licensing requirements - compliance with the requirements of specific
national wildlife and habitat protection
legislation. - Process of assessment key in all cases.
Assessment models exist - Exposure adaptation of existing human rad.
protection models - Consequences more problematic because
open-ended - Major requirement to make evaluations at
population or ecosystem level BUT focus on
radiation effects on the individual for purpose
of developing a framework - Consistent with assessment method for other
contaminants - Effects mediated via individuals
- Secondary sets of references organisms may
require development
39Extrapolations
- 3 extrapolation issues
- biology,
- dosimetry and
- effects
40Extrapolation differences in biology
- Awareness that biological objects of interest may
be different to RAPs and that - Differences in biology could make large
differences to estimates of exposure to certain
radionuclides via different pathways - Appendix A Biological background to reference
animals and plants cited as a supporting
document to assist in adapting approach to
specific case.
41Extrapolation differences in dosimetry
- Effects of changing various parameters considered
- Mass, energy, shape
- Configuration of target to source
- Task Group on more realistic dosimetry
- Explore above issue, including inhomogeneity of
contamination -
42Extrapolation differences in effects
- High acute dose rates (low LET ?- and X-rays) to
lower doses accumulated at lower dose-rates - Very few data on environmentally relevant
dose-rates over life-span of organisms - From one organism type to another
- Variation in radiosensitivity between and within
taxonomic groups lifestages - From individuals to populations and communities
- Including extrapolation from laboratory to field
43Conclusions
- Environmental protection complex and difficult to
articulate - Any approach should be compatible with other
approaches - ICRP will provide high-level guidance and advice
upon which regulators and operators may draw in
order to demonstrate compliance - Development of framework central
- Key feature Reference Animals and Plants
- RAP report serves as an introduction to this