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Environmental Protection: the Concept and Use of Reference Animals and Plants

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Title: Environmental Protection: the Concept and Use of Reference Animals and Plants


1
Environmental Protection the Concept andUse of
Reference Animals and Plants
  • ICRP Committee 5

2
Report 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

3
Preface
  • 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.

4
Introduction 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.

5
Introduction 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
6
Reference 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.

7
Criteria 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

8
Appropriate 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

9
RAPs 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.

10
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11
Further 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

12
The 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.)

13
Populations
  • 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

14
Basic populations characteristics of RAPs
15
Pathways 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

16
Data 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

17
Dose 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)

18
Dosimetry 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

19
Dosimetric 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.

20
Dosimetry - 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.
21
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22
DCF 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.
23
Special 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.

24
Summary of exposure situation assumptions
25
Effects 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.

26
Current 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

27
Current 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

28
Tissue 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.

29
A 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

30
Radiation 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

31
Summarised 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

32
Discussion 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.

33
General 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 ?

34
Derived 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

35
Preliminary 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

36
DCL further example frog, trout, flatfish
37
DCLs - 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

38
Applications
  • 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

39
Extrapolations
  • 3 extrapolation issues
  • biology,
  • dosimetry and
  • effects

40
Extrapolation 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.

41
Extrapolation 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

42
Extrapolation 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

43
Conclusions
  • 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
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