EFFECTS OF RADIATION ON BIOTA AND SETTING

BENCHMARKS

Radiation Protection of the Environment (Environment Agency Course, July 2015)

• Understand how radiation affects biological systems

• Put effects information into context for wildlife radiation protection

• Know how a benchmark is derived

• Be aware of how benchmarksare used in assessments

By the end of the presentation and practical you should….

Ionization

Ionization occurs when energy is sufficient to eject an electron – importance of DNA

The radiation emitted from radioactive atoms can be of sufficient energy to cause ionization of other atoms.

base lossbase change

single stand break

double stand break

interstrand crosslinks

O OHH

H

Feinendegen, Pollycove. J. Nucl. Medicine. 2001. V.42. p. 17N-

27N

Different kinds of DNA damage induced by γ-radiation per 0.01 Gy

Free Radicals (unstable molecule that loses one of its electrons)

DNA damage and repair

Fate of MutationsFate of Mutations

SomaticCells

SomaticCells

GermCells

GermCells

Decrease in number and quality of gametes

Decrease in number and quality of gametes

Increased embryo lethality

Increased embryo lethality

Alteration to

offspring

Alteration to

offspringCell

DeathCell

DeathCancerCancer

For humans, risk of hereditary effects in offspring of exposed

individuals is about 10% of the cancer risk to the exposed parents (UNSCEAR, 2001)

For non-human biota the risk of hereditary effects is unknown

Fate of mutations in non-human biota

Mutation

Cell

Confer a selective

advantage

Confer a selective

advantage

Deleterious mutations

Deleterious mutations

Neutral mutationsNeutral

mutations

Spread in the population

Spread in the population

Remove from the populationRemove from the population

Persist over many generations

Persist over many generations

Data Base of Knowledge on Effectsof Radiation Exposure on Biota

FREDERICA (www.frederica-online.org)

– An online database of literature datato help summarise dose-effect relationships

– FREDERICA can be used on its own;or in conjunction with the ERICA assessment tool(for conducting risk assessments of wildlife exposed to ionising radiation)

(> 1500 references; 26 000 data entries)

Radiation Effects on Non-Human Biota

Early Mortalitypremature death of

organism

Early Mortalitypremature death of

organism

Morbidityreduced physical well being including effects

on growth and behavior

Morbidityreduced physical well being including effects

on growth and behavior

Reproductive Success

reduced fertility and fecundity

Reproductive Success

reduced fertility and fecundity

These categories of radiation effects are similar to the endpoints that are often used for risk assessments of other environmental stressors, and are relevant to the needs of nature conservation and other forms of environmental protection

Reproduction is thought to be a more sensitive effect than mortality

Fundamental Differences In Human and Ecological Risk Analyses

Type Unit of Observation Endpoint Dose-Response Human individual lifetime cancer relationships risk established

Ecological varies varies not established population,

community,ecosystem

> mortality,

< fecundity,sublethaleffects

for chronic,low level exposure

to radiation, alone, ormixed with other

contaminants

Populations are resilient

Indirect effects often occur that are unpredictable

Blaylock (1969) studies at Oak RidgeDIRECT EFFECT: Increased mortality of fish embryos exposed to 4 mGy / dCOMPENSATING MECHANISM: Fish produced larger brood sizesNET RESULT: No effect to population

Compensating mechanisms exist

Predicting radiological effects to wildlife is complicated because:

Pika

LD50 in captivity: ~ 5.6 GyLD50 in the wild: ~ 3.8 Gy

(Markham, et al. 1974)

Responses of Animals to Radiation Are Complicated by:

- other stresses (chemical, physical, biological)

- life cycle stage and physiological condition

- environmental variables

26 April 1986

Exclusion Zone 3,500 km2

116,000 people relocated

Radioactive releases for 10 days

CHERNOBYL

Wildlife Defies Chernobyl Radiation

By Stephen Mulvey BBC News

“It contains some of the most contaminated land in the world, yet it has become a haven for wildlife - a nature reserve in all but name”.

20 April 2006

Sergey Gaschak

Chernobyl ‘Shows Insect

Decline'

By Victoria Gill,Science Reporter, BBC NEWS18 March 2009

“Two decades after the explosion at the Chernobyl nuclear power plant, radiation is still causing a reduction in the numbers of insects and spiders”.

A. Moller and T. Mousseau

Pre-Chernobyl…

wealth of data about the biological effects of radiation on plants and animals

early data came from…• laboratory exposures• accidents (Kyshtym, 1957)• areas of naturally high background• nuclear weapons fallout • large-scale field irradiators

Increasing Sensitivity Decreasing SensitivityLarge nucleus Small nucleus

Large chromosomes Small chromosomes

Acrocentric chromosomes Metacentric chromosomes

Low chromosome number High chromosome number

Diploid or haploid High polypolid

Sexual reproduction Asexual reproduction

Long intermitotic time Short intermitotic time

Long dormant period Short or no dormant period

Factors Influencing the Sensitivity of Plants to Radiation

(Sparrow, 1961)

• minor effects (chromosomal damage; changes in reproduction and physiology)

Effects from Short Term Exposures (5 to 60 d)

Pre-Chernobyl…

• intermediate effects (selective mortality of individuals within a population)

Within Chernobyl’s 30-km zone

0

20

40

60

80

100

0.1 1 10 100

months post accident

Rel

ati

ve

Co

ntr

ibu

tio

n

D

ose

(%

)

I II III

• Environmental effects were specific to 3 distinct time periods

• Biota were exposed to a diverse group of radioisotopes

• Tremendous heterogeneity and variability (in all parameters)

• Accident occurred at a period of peak sensitivity for many biota

0.001 0.01 0.1 1 10 100 1000Gy / d

• Acute adverse effects within 10-km zone

• Mortality to most sensitive plants and animals

• Reproductive impacts to many species of biota

First Phase

Dose rates from gamma exposures

ranged from0.02 to 20 Gy / d

Dose dominated by short-lived isotopes 99Mo; 132Te/I; 133Xe; 131I; 140Ba/La

Second Phase

0

20

40

60

80

100

0.1 1 10 100

months post accident

Rel

ati

ve

Co

ntr

ibu

tio

n

Do

se (

%)

II

• Decay of short-lived isotopes

• Radionuclide migration

• β to δ ~ 6:1 to 30:1 with > 90 % of dose from β

Third and Continuing Phase

0

20

40

60

80

100

0.1 1 10 100

months post accident R

ela

tiv

e C

on

trib

uti

on

Do

se (

%)

III

• Dose rates are chronic, < 1% of initial

• 137Cs and 90Sr dominate dose

• Beta to gamma contributions more comparable, depends on bioaccumulation of Cs

• Indirect effects dominate

• Genetic effects persist; although some results are controversial

• Shift in ecosystem structure: Deceased pine stands

were replaced by grasses, with a slow invasion of hardwoods• Genetic effects extended in time

1993, pines of 5 to 15 Gy had 8 X greater cytogentic damage than controls

General Effects to Plants

• Morphological mutations 1 to 15 Gy (e.g. leaf gigantism)

• Hardwoods more radioresistant

• Evidence of adaptive response

• Growth and developmental problems

Twisted needles

0.001 0.01 0.1 1 10 100 1000

Gy / d

0.3 Gy / dGeneral Effects to Plants

• Inhibition of photosynthesis, transpiration

• Short term sterility

• Chromosome aberrations in meristem cells

• High mutation rates in wheat due to non-targeted mechanisms

• 60 to 90% of initial contamination captured by plant canopies

• Majority washed off to soil and litter within several weeks

• Populations of soil invertebrates reduced 30-fold, reproduction strongly impacted

General Effects to Soil Invertebrates

• 30 Gy altered community structure (species diversity) for 2.5 years

• Dose and effects to invertebrates in forest litter were 3- to 10-fold higher than those in agricultural soils

General Effects to Soil Invertebrates

General Effects to Rodents• During Fall 1986, rodents population < 2- to 10-fold, dose

rates 1 to 30 Gy/d (δ & β)

0.001 0.01 0.1 1 10 100 1000

Gy / d

• Dose-rate dependent increase in reciprocal translocations

• Increased mortality of embryos

• Numbers of mice recovered within 3 years (immigration), but cytogenetic effects persisted

• At ~ 0.1 Gy/d temporary infertility, reduced testes mass

• ~ 30 to 40 generations post-accident • lower dose rates • chronic exposures• inadequate dosimetry • sample size and technique sensitivity• indirect effects (immigration)• interpretation of results from new

methods (microsatellites)

From virtually no effect….… to significantly elevated mutation rates

Effects Data from RodentsCollected in Phase III Are

Ambiguous and Controversial

4 km N of Reactor50,000 people

PripyatAbandoned

Indirect Effects of Human Abandonment

116,000 people and 60,000 cattle evacuated initially

Dozens of towns and villages deserted

Przewalski Horses

Russian Boar

Wolves

With the removal of humans, wildlife around Chernobyl are flourishing48 endangered species listed in the international Red Book of protected animals and plants are now thriving in the Chernobyl Exclusion Zone

Barn Swallows at Chernobyl

• partial albinism as a phenotypic marker for mutations ( ↑ 10x)

• carotenoids used for free-radical scavenging…rather than plumage coloration

• reduced levels of antioxidants in blood

• increase in abnormal sperm • elevated mutation rates in

microsats• partial albinism correlated to

reduced mating success• clutch size, brood size and

hatching success reduced

0.001 0.01 0.1 1 10 100 1000Gy / d

d

Gy

Gy

Gyx

d

hx

h

Gy0000024.0

10241.0

6

0.000001

IAEA Guidelines1 & 10 mGy / d

PNEDR for ecosystems

• Poor dosimetry can cause misinterpretation of data

• Spatial heterogeneity of exposure; free-ranging wildlife

• Confounding variables and indirect effects

• Questionable statistical analyses

• Lack of analogous controls

• What constitutes a “significant effect”??

• Adaptation to generations of chronic exposure

Potential Causes for Controversial Data

BENCHMARKS

The need for a benchmark...

... a retrospective screening model example

Fundamental to this approach is the necessity for the dose estimate to be

conservative

A Tier-1 screening model of risk to fish living in a radioactively contaminated

stream during the 1960s

This assures the modeler that the PREDICTED DOSES are LARGER

than the REAL DOSES

1) SOURCE TERM: used 1964 maximum release as a mean for calculations

2) EXPOSURE: assumed fish were living at point of discharge

3) ABSORPTION: assumed allfish were 30 cm in diameter

which maximized absorbed dose

4) IRRADIATION: behavior offish ignored, assumed theyspent 100% of time on bottom

sediments where > 90% of radionuclides are locatedCONTAMINATED

SEDIMENTS

54 59 64 69 74 79 840

1000

2000

3000

4000

5000To

tal 1

37

-Cs

Re

lea

sed

(G

Bq

)

Year

Conservative Assumptions forScreening Calculations

Resulting Dose Rates (mGy y-1)

…a BENCHMARK value

We need a point of reference; a known value to which we can compare…

Benchmarks values are concentrations, doses, or dose rates that are assumed to be safe based on exposure – response

information. They represent « safe levels » for the ecosystem

Benchmarks values are concentrations, doses, or dose rates that are assumed to be safe based on exposure – response

information. They represent « safe levels » for the ecosystem

Benchmarks are numerical values used to guide risk assessors at various decision points in a tiered approach

The derivation of benchmarks needs to be through transparent, scientific reasoning

Benchmarks correspond to screening values when they are used in screening tiers

Definition of benchmarks

Data on radiation effects for non-human species

Wildlife Group Morbidity MortalityReproductive

capacity Mutation

Amphibians

Aquatic invertebrates

Aquatic plants

Bacteria

Birds

Crustaceans

Fish

Fungi

Insects

Mammals

Molluscs

Moss/Lichens

Plants

Reptiles

Soil fauna

Zooplankton

No data

To few to draw conclusions

Some data

Approaches to derive protection criteria

Historic reviews

• From literature reviews• Earlier numbers derived by expert judgement

(different levels of transparency)• Later numbers, more quantitative/mathematical• Levels of conservatism?• Often “maximally exposed individual” not

population...• NCRP 1991 states use with caution if large number

of individuals in a population may be affected

Deriving benchmarks for radioecological risk assessments

i.e. screening values thought to be protective of the structure and function of generic

freshwater, marine and terrestrial ecosystems.

Adapting approaches used for chemical contaminants to estimate predicted no-effect

dose rate (PNEDR)

Best-Estimate Centile 5% Centile 95%

Vertebrates Plants Invertebrates

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.1 1 10 100 1000 10000 100000 1000000 10000000

Dose rate (µGy/h)

Percentage of Affected Fraction

5%

HDR5 = 17 µGy/h [2-211] PNEDR=10 µGy/h

(SF of 2)

EDR10 and 95%CI: Minimum value per species

Generic ecosystem SSD for chronic external γ-radiation (PROTECT)

…a BENCHMARK value

We need a point of reference; a known value to which we can compare…

10 μGy/h * 24 h / d = 240 μGy/d = 0.2 mGy /d

Reminders…

• The PNEDR:– is a basic generic ecosystem screening value– Can be applied to a number of situations requiring

environmental and human risk assessment• Be aware of:

– PNEDR was derived for use only in Tiers 1 and 2 of the ERICA Integrated Approach

– Use for incremental dose rates and not total dose rates which include background

Background radiation exposure for ICRP RAPs (weighted dose rates)

Marine organisms – 0.6 - 0.9 μGy/h (Hosseini et al., 2010)

Freshwater organisms – 0.4 – 0.5 μGy/h (Hosseini et al., 2010)

Terrestrial animals and plants – 0.07-0.6 μGy/h (Beresford et al., 2008)

Background radiation exposure for ICRP RAPs (weighted dose rates)

Marine organisms – 0.6 - 0.9 μGy/h (Hosseini et al., 2010)

Freshwater organisms – 0.4 – 0.5 μGy/h (Hosseini et al., 2010)

Terrestrial animals and plants – 0.07-0.6 μGy/h (Beresford et al., 2008)

ICRP Approach

Effects

• As part of ICRP 108, effects considered• No dose ‘limits’ but still need something to

compare to– …background– …derived consideration reference levels

DCRLs

• Derived Consideration Reference Levels

– “A band of dose rate within which there is likely to be some chance of deleterious effects of ionising radiation occurring to individuals of that type of RAP (derived from a knowledge of expected biological effects for that type of organism) that, when considered together with other relevant information, can be used as a point of reference to optimise the level of effort expended on environmental protection, dependent upon the overall management objectives and the relevant exposure situation.”

DCRLs

Series1

0.001

0.01

0.1

1

10

100

1000

Deer Rat Duck

Frog Trout Flatfish

Bee Crab Earthworm

Pine tree

Grass Seaweed

mG

y/d

Background level

Representative Organism

Reference Animals and Plants

‘Derived consideration reference levels’ for environmental protection

REPRESENTATIVE ORGANISMS

Radionuclide intake and external exposure

Planned, emergency and existing exposure situations

Environment Agency

• For doses to wildlife, if initial assessment outcome ≥ 1 μGy/hr = more detailed realistic assessment required before regulatory decision made

• EA must ensure integrity of Natura 2000 Habitat sites – Total dose below 40 μGy/hr (agreed with Natural

England)• Use Initial Radiological Assessment Tool (IRAT)

– Habitats component based on R&D128

Summary

• Range of methods for deriving benchmarks• Range of benchmarks proposed• Be careful with the wording around the

benchmark– What does it reflect?

• Look for clear, well documented benchmark values

• Watch this space for further developments!