24 november 2015

INFORMATION NOTE

Realistic dose reconstruction for non-human species to assess theecological consequences of chronic exposure to ionizing radiationin the contaminated territories after the Fukushima accident
Several field studies dedicated to consequences of nuclear accidents on wildlife reportsignificant deleterious effects for dose rates of ionising radiation estimated so low that
their conclusions clearly challenge the basic knowledge in radiobiology.
On the basis of ecological data describing the bird community in the Fukushima area, apublication from IRSN in collaboration with two renowned ecologists highlights that abetter dosimetric estimation reconciles in situ observed effects with scientificknowledge of dose-effect relationships.
IRSN has just published in collaboration with two world renowned ecologists Anders Møller (CNRS,
laboratoire d’écologie, systématique et évolution, France) and Timothy Mousseau (University ofSouth Carolina, USA) in Scientific Reports (NPG) a new analysis of the ecological dataset describing
the abundance of birds in the Fukushima area. This dataset reports breeding bird censuses at 300
sampling sites visited once a year at the beginning of July during a 4-year period 2011-2014, after
the Fukushima nuclear accident. The dataset is composed of specific abundances for 57 species ofbirds using the standardized point count census method, along with various environmental
descriptors (e.g., the time of day at the start of counts at each point, cloud cover, temperature,wind force, type of habitats). Absorbed dose rates were reconstructed for individual birds of each of
the 57 species observed over 300 sites and during 4 years (2011-2014), by combining radionuclide
measurements in soils (134Cs, 137Cs, 131I) and models.
Radiological dose reconstruction for birds allows to take into account the spatial heterogeneityof radioactive deposits in the Fukushima area along with the influence of the species’ mode oflife on its exposure level.
Until this study, the deleterious effects on species diversity and abundance were linked to theambient dose rate measured on observation sites, and as such were analyzed as a weakness by thescientific community of radioecologists. The reconstructed absorbed radiological dose or dose rate
is likely the most appropriate variable reflecting the intensity of the radiological exposure andtherefore using this metric ensures the scientific credibility of the outcoming relationships between
absorbed doses and observed biological/ecological responses.
In the present study, a dose rate reconstruction work made it possible to take into account theexternal and internal radiation pathways, and the exposure characteristics of birds depending on
their lifestyle. Thus, the reconstructed dose rates can be higher to a factor of 20 than the measured
ambient radiation level using a hand-device. Moreover, for a given site, the reconstructed doserates vary by a factor of 8 between the 57 species examined. Finally, for a given specie,reconstructed dose rates vary 44-fold among the 300 observation sites.
This clearly demonstrates the need to take into account these two factors (location and species) for
dose reconstruction.

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Cumulative probability (Number of exposed species/total number of species)

Comparing these reconstructed exposure levels for birds with knowledge on their relationships withpotential induced effects as published by the International Commission of Radiation protection(ICRP, 2008), the study found that 90% of the 57 species constituting the observed bird community
were likely chronically exposed at a dose rate that could potentially affect their reproductive
success (Figure 1). This is consistent with conclusions published by Møller et al. (2015) regarding
the link between the exposure level and the deleterious effects on bird abundance and species
diversity.

Range of variation of theambient dose rate

(300 sites x 4 years)

Low
probablityof effect4,242

Potential for
reducedreproductive success

Up to420

Maximum total dose rate to adult bird (µGy h-1)
Figure 1- Simplified representation of the variation of the maximum exposure levels for adultbirds (expressed in µGy/h) for the 57 species composing the bird community observed over 300
sites and 4 years (2011-2014). Comparison with the range of variation (in blue) of the ambient
dose rate measured on sites and range of variation (in red) corresponding to various effects inbirds published by ICRP (2008) (modified from Garnier-Laplace et al., Sci. Rep., on line).

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Radiological dose reconstruction for birds reconciles outcomes of Fukushima regarding thedeleterious effects observed on bird individual abundance with knowledge of dose-effectrelationships.

Total Number of Birds

The statistical analysis based on the reconstructed dose reveals the overall abundance of birds at
Fukushima during 2011-2014 decreased significantly with increasing absorbed doses. More precisely,
we were able to quantify a loss of 22% of the total number of individuals over the four-year postaccident period in the study area (see Figure 2 where one can quantify a loss of 22% of individuals
when the absorbed dose increases e.g., from 10 to 100 mGy). On the basis of the present dataset
and the statistical model we implemented to represent the full dataset while taking into accountconfounding variables describing environmental conditions, we estimated that a total dose of
550 mGy reduced by 50% the total number of birds in the study area over 2011-2014.

Total Dose absorbed in Gray by adult bird (log10)

Figure 2- Total number of birds as a function of the total absorbed dose (log-10 transformed)
predicted by the best statistical model obtained to represent the ecological dataset. The slope(partial regression coefficient of the model) is statistically highly significant. It allows to estimate
the loss of the total number of birds according to the increase of the absorbed dose (e.g., loss of
22% when the dose increases from 10 to 100 mGy) (modified from Garnier-Laplace et al., Sci.
Rep., on line)
Combining dose reconstruction and advanced statistics to mathematically process ecological
data set is promising to improve the understanding of ecological consequences associated tochronic low dose exposure situations.
To conclude, this paper highlights the need to combine dose reconstruction for non-human species
of interest and statistical treatments to understand the key message from ecological datasets
acquired in territories impacted by a nuclear accident. After the two major nuclear accidents whichmarked the history of civil electronuclear energy (Chernobyl, Ukraine, 1986 and Fukushima, Japan,2011), ca. one hundred studies dealing with consequences on wildlife chronically exposed to ionising3

24 november 2015radiation and effects of “low doses” was published. These studies were carried out from year 2000
on wildlife in the Chernobyl Exclusion Zone and, from July 2011 within the 100-km area around thedamaged Fukushima Daiichi nuclear power plant. Their goal was to assess the health consequenceson populations of species composing the ecosystems impacted by the accidental releases ofradioactive substances and, to identify/understand their cause, and to quantify the intensity of theresulting effects. Except a very few of them, these studies have a common feature: the estimationof the radiological dose absorbed by the organisms according to their exposure conditions is either
missing or partial. IRSN is interested in analyzing these voluminous and precious datasets according
to the methods presented in this publication. This will help to improve knowledge on ecologicalconsequences of chronic exposure to ionising radiation, by analyzing dose-effect relationships
acquired in radioactively contaminated area for ecologically relevant endpoints, i.e. those withpotential consequences in terms of ecosystem structure and function and population demography.
Any dose-effect relationship is complex to understand in the field since it can be modified due tothe combination of radiotoxicity effects on growth rate/reproduction and of genetic diversity,competition, predation and changes driven by abiotic factors including other pollutants in addition
to radionuclides
References
ICRP. Environmental Protection – the Concept and Use of Reference Animals and Plants, ICRP Publication 108,Ann. ICRP 38 (4-6) (2008). http://www.icrp.org/publication.asp?id=ICRP%20Publication%20108
Garnier-Laplace J., Beaugelin-Seiller K., Della-Vedova C., Métivier J.M., Ritz C., Mousseau T. and Møller A.P.
Radiological dose reconstruction for birds reconciles outcomes of Fukushima with knowledge of dose-effectrelationships, Sci. Rep. on line. http://www.nature.com/articles/srep16594
Møller, A. P., Nishiumi, I. & Mousseau, T. A. Cumulative effects on interspecific differences in response of birds
toradioactivity
fromFukushima.
J.
Ornithol.
inpress(2015).
http://www.researchgate.net/publication/273770328_Cumulative_effects_of_radioactivity_from_Fukushima_on_the_abundance_and_biodiversity_of_birdsExternal collaborations
Anders Pape Møller, écologue, Laboratoire d'Ecologie, Systématique et Evolution, CNRS UMR 8079,
Université Paris-Sud, Bâtiment 362, F-91405 Orsay Cedex, France.
Timothy A. Mousseau, écologue, Department of Biological Sciences, University of South Carolina,
Columbia, SC 29208, USA.
Christian Ritz, biostatisticien, Department of Nutrition, Exercise and Sports Faculty of Science,
University of Copenhagen, Rolighedsvej 26 DK-1958 Frederiksberg C, Denmark.

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