Anca Melintescu PhD

       “Horia Hulubei” National Institute for Physics and Nuclear Engineering, Bucharest-
                                       Magurele, ROMANIA

2nd Meeting of the EMRAS II Working Group 7, “Tritium”, Chatou, France, 28–29, September
    Simplified models and experimental data base

•   Models in use are schematic and non-validated or are empirically derived
    and cannot be used out of initial data set;
•   Use one compartment for OBT with halftime given by total organic carbon
•   Animal products contribute significantly to the diet - reliable dynamical
    models are needed;
•   Sparse experimental data - old experiments insufficiently reported;
•   BUT very good experimental data and model for rat (experiments done by H.
    Takeda, NIRS, Japan);
•   Need a different approach based on comparative metabolism and OBT-C
                                    Animals bioenergetics
•   Review of past results of 3H and 14C transfer modelling                     1 dE 1 dM
    in mammals → necessity to have a common approach             E=mc2 →            
    based on energy needs and on the relation between                           E dt M dt
    energy and matter (well established in Atomic and
    Quantum Physics)
•   Knowledge on animal metabolism and nutrition
                                                              GE in food
•   Metabolism = countless chemical processes going on
    continuously inside the body that allow life and normal                 GEf
•   These processes require energy from food                     DE
•   Energy is derived from the digestion of several
    compounds, including carbohydrates and fats. Excess                      GEug
    dietary protein can also be used as an energy source,
    but it is a costly practice.
•   Gross energy, Digestible energy, Metabolisable                         Basal Met.
    Energy, Net energy                                                                        Maint. Met.
•   Maintenance metabolism (basal+heat of digestion),                      Heat of Dig.
    lost as heat
                                                                             Cold Therm.
•   Heat needed for cold thermogenesis, activity and
    losses in processes of growth, production and
                                                                            Used for work,
    reproduction                                                            Growth, re-prod
•   Energy stored (deposited, retained) in the products of
    growth, lactation (egg) and reproduction                     NE
•   Daily Energy Expenditure (Field Metabolic Rate)
•   Food must include maintenance protein
•   Field Metabolic Rate (FMR, MJ kg-1 d-1) = the net daily energy expenditure of
            - depends on the level of nutrition, taxon, diet, environment
     FMR= a*BWb ? b ~0.75 or 0.67 or ?
     BW – body weight (kg)
     a, b – scaling coefficients
•   Specific Metabolic Rate (SMR, MJ kg-1 d-1) = the daily energy expenditure per unit
    fresh body mass
•   Relative Metabolic Rate or the energy turnover rate (ReMR, d-1) = ratio of SMR
    and the energy content of the body, determined by the body composition (protein,
    lipids, and carbohydrates):
                          FMR      SMR
              Re MR             
                        EBW * BED BED

           ReMR - used also for loss rate of organic matter (as in ontogenetic growth)
    EBW - the empty body mass (kg) defined as the live-weight less the mass of the
    gastrointestinal contents;
    BED - the body energy density (MJ kg-1 fw)
         - depends on body composition
Body Size : Surface Area Ratio and Energy Demand Comparison of
                                                                                    Allometric relation

  Mass-specific metabolic rate (ml O2/gram/hour)





                                                               Harvest mouse

                                                                     Flying squirrel
                                                   1                         Bat     Cat        Dog       Human   Horse    Elephant
                                                       0.01           0.1      1           10             100     1000    10,000
                                                                                   Mass (kg)
     Derivation of a generic model based on energy
          metabolism tested with experiments

MAGENTC - MAmmal GENeral Tritium and Carbon transfer
• Complex dynamic model developed by us in the last four years in an
  international collaboration for H-3 and C-14 in mammals
• full description given in:
  D. Galeriu, A. Melintescu, N. A. Beresford, H. Takeda, N.M.J. Crout,
  “The Dynamic transfer of 3H and 14C in mammals – a proposed
  generic model”, Radiation and Environmental Biophysics, (2009)
• A key element in any model of radionuclide transfer in animals is the
  loss rate (half-time) from the body or organs;
• There are too few experimental data for 14C and 3H from which one
  could derive these values, and we therefore advance the working
  hypothesis that the loss rate of organic compounds (organic carbon,
  OBH or OBT) from the body or organs can be linked with the energy
  turnover rate.
•   The model has 6 organic compartments and
    distinguishes between organs with high transfer
    and metabolic rate (viscera), storage and very
    low metabolic rate (adipose tissue), and
    „muscle‟ with intermediate metabolic and
    transfer rates.
•   Some organs have high metabolic activities
    and will therefore have high 3H and 14C transfer
•   Liver, kidney, heart, and the gastrointestinal
    tract use about 50 % of the basal metabolic
    requirements whilst typically contributing less
    than 10 % of the body mass; these organs are
    included as a combined “viscera” compartment.
•   Blood is separated into red blood cells (RBC)
    and plasma as plasma is the vector of
    metabolites in the body (and also as a
    convenient bioassay media).
•   The remaining tissues are bulked into one
    model compartment („remainder‟) in order to
    achieve mass balance.
•   The organic compounds of 3H and 14C enter
    the body via the stomach and they are mostly
    absorbed from the small intestine and a
    simplified transfer through gastrointestinal tract
    is used to reproduce the delay between intake
    and absorption.
•   The stomach and small intestine compartment
    refers to the content, as an input pathway,
    whilst the stomach and small intestine walls are
    included in the viscera, having high metabolic
                             Modelling approaches
•   The metabolisable fraction of dietary intakes of organic tritium and carbon are transferred
    to systemic body compartments; the remainder is excreted. In the case of dietary tritium,
    the exchangeable fraction is transferred directly to body water and only the non-
    exchangeable fraction enters blood plasma;
•   Ingested HTO is assumed to be immediately mixed in the body water compartment
•   The transfer rates between compartment and blood plasma are given by RMR. The
    transfer rates from blood plasma to model compartments are assessed using the mass
    balance of the stable analogues (include net growth);
•   Transfers include the net flux after the digestion and transformation of dietary compounds
    in protein, lipids or carbohydrates;
•   Transfer rate to urine (organic) given by mass balance (urine dry matter production,
    plasma organic content);
•   Transfer rate between body HTO and plasma OBT given by hydrogen metabolism
    (equilibrium value of OBH derived from free H);
•   Transfer rate for respiration (or body HTO) by mass balance of stable nuclide: intake
    assumed correlated with energy needs;
•   Organ composition assumed similar to humans (cf. Geigy tables and other models)
•   Plasma composition (OBC,OBT) same for all mammals (cf. Baldwin 1995);
•   All model compartments have a single component (no fast-slow distinction)
   Model tests with experimental data on rats

• Complete database for 3H and 14C transfer, obtained from
  experiments with Wistar strain rats thanks to H. Takeda (NIRS,
• Studies included:
   – continuous 98 days intakes of 14C and OBT contaminated food
      or HTO;
    - acute intakes of HTO or 14C and 3H labelled glucose, leucine,
  glycine, lysine, and oleic and palmitic acids.
• Available data include 14C, OBT and HTO measurements in visceral
  organs, muscle, adipose tissue, brain, blood and urine.
• For the acute studies data on labelled organic compounds in
  proportions typical of normal rat food were combined.
• Model parameters not obtained from the study were estimated from
  the literature:
  - organ mass,
  - whole body and
  - organ energy expenditure.
• The intakes of OBT (metabolisable and non-exchangeable fractions)
  and organic 14C were estimated from the known food composition.
Results of model test with rat data (no calibration)
 Average and standard deviation of predicted to observed ratios in rat viscera,
 muscle, blood, adipose tissue and whole body (except bone and skin) for the six
 forms of intake

  Organ      14C   chronic   14C   acute     OBT          OBT          HTO         HTO acute
                                            chronic       acute       chronic

 Viscera     1.12 ± 0.15     0.51 ± 0.4    1.06 ± 0.15    0.67 ±     0.43 ± 0.07   0.87 ± 0.34

  Muscle     1.25 ± 0.14      0.81 ±       1.23 ± 0.21    0.90 ±     0.40 ± 0.09   1.02 ± 0.38
                               0.29                        0.37
 Adipose     1.11 ± 0.15      0.61 ±       0.97 ± 0.2     0.75 ±      0.3 ± 0.1    1.33 ± 0.3
                               0.12                        0.13

  Whole      1.12 ± 0.27     0.4 ± 0.1     0.88 ± 0.12    0.38 ±     0.37 ± 0.09   0.62 ± 0.18
  blood                                                    0.03

Whole-body   1.18 ± 0.08     0.7 ± 0.1     1.08 ± 0.11   0.8 ± 0.1   0.36 ± 0.08   1.09 ± 0.18

                        Data error ?!
         Representative results, no calibration

Model predictions and experimental observations for rat muscle
following acute intakes of food labelled with 14C or OBT
    Model tests with cow data (no
• Several exposures
  – Single HTO intake
  – Continuous HTO intake
  – Continuous OBT intake
• Cow mass, feed and water intake, milk
  and urine production taken from
• All other model parameters taken from
  literature – no calibration with tritium data
Results of model test with cow data (no calibration)

   Model performance for dairy cow; NA: not calculated/available

     Experiment   R2        Milk total 3H           Milk OBT            Urine HTO

                                            Mean  standard deviation P/O
                                            (range presented in parenthesis)

     Cow_P        0.97      2.60 ± 1.7              1.68 ± 0.8             2.90 ± 2.34
                            (0.8 -1.9)              (0.5 - 2)

     Cow_C        0.89      0.97 ± 0.08             0.73 ± 0.17            0.97 ± 0.06
                            (0.9 -1.4)              (0.65 - 1.7)

     Cow_H3       0.67      1.02 ± 0.15             0.49 ± 0.12            1.36 ± 0.42
                            (0.9 - 1.5)             (0.4 - 0.9)

     Cow_H        0.88      1.45 ± 0.59             1.86 ± 0.38            NA
                            (0.6 - 2.3)             (0.55 - 2.12)
                                    Representative results, no calibration
Experimental data and model predictions for OBT in milk after OBT fed
for 26 days. Experimental data were reported only after stop dosing

      milk OBT concentration BQ/L

                                    10000                         milk_OBT_exp


                                             0   50                100               150
                                                      tim e (d)
    Model tests on sheep data (no calibration)
• Scottish Blackface female sheep – acute intake of 14C- and 3H-
  labelled glucose and acetate
• The experiment provides approximate information on the transfer
  from feed to organs.
• We added a sub-model for growth (from 27 kg at the beginning of
  exposure to 47 kg after one year)
        - Organs‟ masses growth were taken from experiment and
• The model considered normal marked food intake: protein + fat +
  carbohydrates (not only carbohydrates as in experiment);
• The study did not include labelled protein, although production of
  protein by rumen bacteria may have led to some labelled protein
  being present
• Model results are sensitive to the growth rate in the day of intake
                                     Representative results, no calibration
                           Dynamics of organic 14C (left) and OBT (right) in sheep muscle
                           after an intake of labelled glucose and acetate.

                           0.006                                                                      1.00E-02
                                                             predicted                                                                     predicted

                                                                           normalised concentration
normalised concentration

                                                             observed                                                                      observed
                           0.004                                                                      1.00E-03

                           0.002                                                                      1.00E-04

                               140    240    340       440           540
                                                                                                              140   240    340       440          540
                                            time (d)                                                                      time (d)
   Model tests with pig data (no calibration)
• Data on organ OBT concentrations are available for a gestating sow
  fed OBT for 84 days and who died before delivery.

   Results of model test with pig data (no calibration)

         Organ          P/O
         blood          1.17
         muscle         1.7
         viscera        1.4
• Initial body composition was adjusted to be close to
lean or fat genotype considering the lipid content of muscle
according with experimental information on inter-muscular
fat for the contrasting genotype PP, SL and MS.
• The results show a clear distinction between meat
concentrations of genotypes at the time of killing,
the fat MS genotype having the highest value and PP the

                       OBT concentration                                   0.6

           0.9                                                             0.5                          SLmuscle_conc

           0.6                                                             0.3
                                                 musSL                                                  MSmuscle_con

           0.5                                   viscSL                                                 c
                                                 adipMSC                   0.2
           0.3                                   viscMSC                   0.1
           0.2                                   musPPM                     0
           0.1                                   viscPPM
                                                                                 0   50     100   150
                                                                                     body mass
                 0    50           100     150
                     empty body mass kg
         Conclusions for MAGENTC
•   Despite simplifications, the model tests are encouraging for tissues and milk
    for a range of animals.
•   Without parameter optimization, the model predictions are within a factor of
    3 of the reported values in all cases.
•   Some improvements could be made to the model in the future, in order to
    increase the predictive power:

    1. Incorporation of an understanding of ruminant digestion to clarify the
    exchangeable fraction of net organic intake;
    2. Incorporation of fast and slow compartments for each organ/organs
    group, if a general rule can be obtained from animal science and physiology
    3. Inclusion of up-to-date knowledge on organ specific metabolic rate (in
    vivo) for animals; there has been considerable progress in the use of
    modern noninvasive techniques such as Positron Emission Tomography
    (PET) and Magnetic Resonance Imaging (MRI) for metabolic studies.
    Extension of the current model to wild mammals and
    • Full description is given in:
      A. Melintescu, D. Galeriu, “Using energy metabolism as a tool for modelling the transfer of 14C and
     3H in animals”, submitted to Radiation and Environmental Biophysics

Extension to wild mammals
•    Clear need to explicitly consider non-human biota within radiological
     assessments (ICRP 2007);
•    ICRP proposes the use of Reference Animals and Plants;
•    We have past experience to assess the concentration ratio for specific
     animals for tritium and 14C in the frame of European projects (EPIC,
     FASSET) for routine emissions; full details are given in:
     D. Galeriu, N.A. Beresford, A. Melintescu, R. Avila, N.M.J. Crout, “Predicting tritium and
     radiocarbon in wild animals”, International Conference on the Protection of the Environment on the
     Effects of Ionising Radiation, Stockholm, Sweden, 6 –10 Oct. 2003, P. 186-189, IAEA-CN-109/85
•    Data for radionuclides in wild animals are sparse and a number of
     approaches including allometry have been proposed to address this issue
•    Unlike to laboratory or housed farm animals, wild mammals and birds are
     subjected to large environmental and dietary variability for which they must
•    Our definition of biological halftime has been used in order to explore the
     range for wild mammals; full details given in:
     D. Galeriu, A. Melintescu, N.A. Beresford, N.M.J. Crout, H. Takeda, “14C and tritium dynamics in
     wild mammals: a metabolic model”, Radioprotection, Suppl. 1, Vol. 40 (2005), S351-S357, May
  • There are many studies demonstrating allometric (mass dependent) relations for basal
     metabolic rate, daily energy expenditure and organs‟ masses.
  • For DEE there is considerable evidence of taxon specific allometric relationships, but
    dietary habits can still have a large influence for rodents with herbivorous, omnivorous or
    granivorous diets.
  • DEE depends on environmental temperature (small mammals in the Arctic have a 2 fold
     higher DEE for the same body mass compared with animals in Mediterranean climates).

  Visceral percentage of body mass

                                                                                                 granivore       omnivore
                                                                                                 herbivore       Rodentia

                                                                     DEE (kJ d-1)
                                     15                                              100
                                     0                                                10
                                      0.01   1         100   10000                          10           100            1000   10000
                                             Body mass kg                                                    Body mass (g)

Variation with body mass in the mass of                               DEE (kJ d-1) for granivorous, carnivorous,
visceral organs expressed as a percentage of                          and herbivorous diets, compared with an allometric
whole body mass.                                                      relationship for rodents.
• The biological halftime does not only depend on animal mass but also on taxon either.

• For the same body mass, taxon and diet may affect the biological half time
  with a factor 2.

        Biological half times for Carbon (and OBT) units days

         Mass (kg)      0.03    0.1      1       5       10     30     300
           Animal                       Biological half-times
         Terrestrial     3.1    4.8    11.1    19.8     25.4    37.8    -
        Mesic rodents    2.8    4.1     8.4    13.7       -      -      -
         Carnivores      5.5    6.7     9.4    12.0     13.3    15.7
         Granivores      4.9    10.0     -       -        -      -      -
         Herbivores      3.1    4.8    10.8    19.2     24.5    36.2   81.8
        Insectivores     3.8    6.1    14.6    26.8       -      -      -
         Omnivores       3.7    5.4    11.4    19.2       -      -      -
• Our model needs as input the Basal Metabolic Rate (BMR), the field energy expenditure
  (FMR), organ mass and organ Specific Metabolic Rate (SMR).
• Body mass is not the only predictor of BMR, but body temperature, taxon, diet and
  climate are also important;
• A gap in the database for wild animals is the assessment of maintenance energy needed
  per kg tissue and time unit, the so called specific metabolic rate (SMR) for organs in
  basal and active states.
• Due to adaptation to various environmental constraints it is possible that the organ
  metabolism of wild mammals to differ from domesticated ones.
• The organ mass for wild mammals also is less documented than for farm animals and
  the intraspecific variability can be higher. This explains why our predicted BMR values
  are sometimes close to observed values, but there are cases of 50 % discrepancies.
• In practice we have considered the relative contribution of organs to whole body BMR
  and use the experimental BMR in the model input values.

Species                    Mass (kg fw)   Measured BMR (MJ d-1)   Estimated BMR (MJ d-1)

Hare (Lepus carpensis)         2.9                0.78                     0.79
Jackal (Canis mesomelas)       2.8                 0.7                     1.05
Racoon (Procyon lotor)         2.2                 0.5                     0.76
Puma (Felis capensis)          9.6                 1.9                     1.5
Wild cat (Felis ocreata)       2.7                 0.5                     0.52
Chipmunk (Tamias             0.0075               0.045                    0.07
We reassessed all input data and also select red deer as a large herbivore.
We include two rodents (lemming and chipmunk), a small herbivore - rabbit and a carnivore –
red fox.
The lemming from Arctic regions is modelled with enhanced energy needs.
As much as possible input data correspond to same habitat, diet, temperature and subspecies
for each considered mammal.
The effect of a coherent selection of model parameters is exemplified for chipmunk, for which
we considered mixed literature data but also measured BMR and FMR of the same population
(Quebec - personal data from Careau).
     Model inputs

  Animal     Latin name     Mass (kg)     BMR                Mass fractions            BMR          FMR
                                        (MJ day-1)                                   (MJ day-1)   (MJ day-1)
                                                     adipose    muscle    viscera
 lemming       Lemmus         0.06        0.045       0.35       0.28         0.15     0.042         0.19
 chipmunk      Tamias         0.096       0.052       0.15        0.4         0.22     0.081         0.12
 chipmunk      Tamias        0.0915      0.0675       0.15        0.4         0.22     0.078         0.17
     C         striatus
  rabbit        Lepus          1.8         0.57        0.1       0.43         0.13     0.573         1.3
  red fox   Vulpes vulpes      6           1.1        0.15       0.45         0.13      1.43         4.5
 red deer      Cervus         107          11.7        0.1       0.43         0.12      12.4         24.5
   (elk)       elaphus
                                             Model results

 Animal       Mass      Fast half-    Slow half-          Fast         Effective half-   Transfer factor
              (kg)         time       time (day)     contribution in     time (day)        (day kg-1)
                          (day)                         retention
lemming        0.06           4.2         52               0.8              5.2              36.88
chipmunk      0.096           4.4        69.3             0.91              4.76             47.75
chipmunk      0.0915          3.1        55.4             0.926             3.32              34.6
 rabbit        1.8            7.4        79.8             0.87              8.44              3.35
 red fox        6             8.1       147.6             0.91              8.76              1.51
red deer       107        25.2          227.2             0.83              29.6              0.21

  Concentration ratios in different model compartments

   Animal           whole body       adipose    muscle     viscera     remainder

  lemming              0.70           1.38         0.32     0.28         0.79
  chipmunk             0.48           1.26         0.32     0.28         0.76
 chipmunkC             0.49           1.34         0.32     0.28         0.76

    rabbit             0.44           1.19         0.32     0.28         0.57
   red fox             0.38           1.03         0.24     0.21         0.50
   red deer            0.45           1.28         0.32     0.28         0.55
   Short term dynamics of 14C in whole body (generalised coordinates)


                     norm whole conc

                                              1   2   3   4     5     6   7   8   9     10

          Generalised coordinates:
          Normalised concentration=Whole body conc *Mature mass
          T*RMR – non-dimensional time = time * mature RMR

Despite these shortcomings, the results presented above are less uncertain than
for many other radionuclides and can provide useful results for biota radioprotection.
            Extension of the current model to birds
•   The model developed for mammals is based on energy metabolism and
    body composition with the assumption that the turnover rate of organics is
    linked to energy turnover rate.
•   There are not reasons to restrict the model to mammals, if the assumptions
    are qualitatively correct.
•   The allometry of basal metabolic rate of birds has close mass exponent to
•   After a selection of good data and correction for phylogenetic bias, we
           BMR = 303*M-0.33 (mass in kg and metabolic rate in kJ day-1).
•   There is no difference between passerine and non passerine and the higher
    values for birds comparing to mammals are explained by higher body
•   The scaling exponent of BMR in captive birds (0.670) is significantly lower
    than in wild-caught birds (0.744) due to phenotypic plasticity.
•   The scaling exponents of FMR for birds and mammals were not significantly
           birds: FMR = 1.02 M0.68,
           mammals: FMR = 0.68 M0.72
  Disregarding the effect of increased body temperature we compare our model BMR to
  experimental data

   Comparison between BMR model and experimental data for birds


          BMR calc/BMR exp





                                   0   0.1   0.2   0.3        0.4         0.5   0.6   0.7   0.8
                                                         Body mass (kg)

For small birds we under predict with 20-40 %.
With one exception (Arenaria interpres) all are passerine with higher body temperature than
other birds.
We conclude that our mammals SMR, corrected for body temperature, can help as a first attempt
to expand the model to birds.
  For food chain modelling, laying hens and broilers are of special concern and there are
  not experimental data for eggs or meat contamination with 3H and 14C.
  We considered a tritium intake (1 Bq day-1) for 60 days in both forms (HTO or OBT).

              Dynamics of tritium in eggs after HTO or OBT intake

         Concentration (Bq/kg)


                                  0.01                                       Total(HTO)

                                         0   50   100      150   200   250
                                                    Time (d)

OBT concentration in eggs is predicted to increase rapidly in the first 7 days corresponding to the
duration of egg formation, and slowly thereafter, due to contribution of recycled body OBT.
We observe that the OBT concentration in egg, after stop dosing decreases in the first days with
a half-time of about 5 days and slower later (halftime of about 40 days), due to contribution of
body reserves.
Total tritium in eggs is 2 times higher when the intake is OBT, but share of OBT is about 75 % for
OBT intake and only 9 % for HTO intake.
                In order to obtain directly the transfer factor, intake has been fixed at 1 Bq day-1, while for
                concentration ratio, intake was 1 Bq kg-1 dry matter or 1 Bq L-1 of water.

                                 Transfer factor for tritium in broiler                      Concentration ratio for tritium in broiler
                          100                                                                                         1
                                                                           OBT (HTO)
                                                                           T (HTO)
                                                                           OBT (OBT)
                                                                           T (OBT)
 Transfer factor (1/kg)

                                                                                              Concentration ratio
                                                                                                                                                                     OBT (HTO)
                            1                                                                                        0.1
                                                                                                                                                                     T (HTO)
                                                                                                                                                                     OBT (OBT)
                                                                                                                                                                     T (OBT)

                          0.01                                                                                      0.01
                                 0   20   40   60     80       100   120     140       160                                 0   20   40   60     80       100   120   140       160
                                                    Time (d)                                                                                  Time (d)

 In the case of fast growing broiler, at the market weight of about 2 kg (42 days old) the model
 predicts lower transfer factors (TF) than for the equilibrium case
 The predicted concentration ratios (CR) for our fast growing broiler are close to those
 obtained for “equilibrium” .
In absence of any experimental data or previous modelling assessments, our results give
a first view on the transfer of 3H and 14C in birds.
• We developed research grade model for plants and
  animals based on process level, pointing out that model
  inputs can be obtained using Life Science research in
  connection with National Research on plant physiology
  and growth, soil physics, and plant atmosphere
  interaction, as well as animal physiology, nutrition and
• We re-use these knowledge with a very low cost, but
  spending time to learn basics from these fields →
  Interdisciplinary Research;
• Classical compartmental models can be derived and
  appropriate parameters for each case can be obtained in
  this way.
Thank you!

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