RADINUCLIDES IN THE OCEANS:RADINUCLIDES IN THE OCEANS:a tool for understandinga tool for understanding

the ecosystems functioningthe ecosystems functioning

Roberta DelfantiRoberta DelfantiENEA – Marine Environment Research Centre, La SpeziaENEA – Marine Environment Research Centre, La Spezia

IAEA Regional Training Course on Sediment Core Dating Techniques. RAF7/008 Project

CNESTEN, Rabat, 5 – 9 July 2010

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1.1. Sources of anthropogenic and natural Sources of anthropogenic and natural radionuclides to the oceans.radionuclides to the oceans.

2.2. Radionudlides behaviour in the marine Radionudlides behaviour in the marine environment.environment.

3.3. The “tracer” concept.The “tracer” concept.

RADIONUCLIDES IN THE OCEANSRADIONUCLIDES IN THE OCEANSOUTLINEOUTLINE

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Sources of radionuclides Sources of radionuclides to the marine environmentto the marine environment

Cosmic radiation.Cosmic radiation.

In environmental studies:In environmental studies: 33H,H, 7 7Be, Be, 1414CC

formed by neutron capture in the atmosphere.formed by neutron capture in the atmosphere.

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Sources of radionuclidesSources of radionuclidesto the marine environmentto the marine environment

Primordial radionuclidesPrimordial radionuclides

Series Series 238238U U tt1/21/2 = 4.5 x 10 = 4.5 x 1099 a a

232232ThTh tt1/21/2 = 1.4 x 10 = 1.4 x 101010 a a235235UU tt1/21/2 = 7.1 x 10 = 7.1 x 1088 a a

They decay, through a long series of radionuclides,They decay, through a long series of radionuclides,to stable isotopes of Pb.to stable isotopes of Pb.

4040KK tt1/21/2 = 1.3 x 10 = 1.3 x 1099 a a

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Anthropogenic radionuclides:Anthropogenic radionuclides:

• Fallout from atmospheric weapons testingFallout from atmospheric weapons testing• Chernobyl accidentChernobyl accident• Nuclear IndustryNuclear Industry• Nuclear accidentsNuclear accidents

Sources of radionuclidesSources of radionuclidesto the marine environmentto the marine environment

Global falloutGlobal fallout Trinity test, AlamogordoTrinity test, AlamogordoJuly 16, 1945July 16, 1945Nuclear tests ban treatyNuclear tests ban treaty

19631963

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Fission yield curves for Fission yield curves for 235235U and U and 239239PuPu

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Fallout radionuclides Fallout radionuclides still present in the environment:still present in the environment:

137137CsCs fissionfission tt1/21/2 30.2 years 30.2 years9090SrSr fissionfission tt1/21/2 28.6 years 28.6 years1414C (n,p) + cosm C (n,p) + cosm tt1/21/2 5730 years 5730 years 33HH fuel residue + cosm.fuel residue + cosm. tt1/21/2 12.3 years 12.3 years238238PuPu fuel residue/prod fuel residue/prod tt1/21/2 87.7 years 87.7 years 239239PuPu fuel residue/prod fuel residue/prod tt1/21/2 24119 years 24119 years240240PuPu fuel residue/prod fuel residue/prod tt1/21/2 6570 years 6570 years

To the oceans: 380 PBq of To the oceans: 380 PBq of 9090Sr and 660 PBq of Sr and 660 PBq of 137137CsCs9

Hamilton, 2004

Atmospheric nuclear detonationsAtmospheric nuclear detonations

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Global Global falloutfalloutlatitudinal latitudinal depositiondeposition

Modified from Hamilton, 2004 10

The Chernobyl The Chernobyl accidentaccidentApril 26,April 26,19861986

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The Chernobyl The Chernobyl AccidentAccident

Simulation of theSimulation of thedispersion dispersion of theof theChernobyl plumeChernobyl plume

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137137Cs input to the oceans: 16 PBqCs input to the oceans: 16 PBq

Chernobyl Chernobyl 137137Cs deposition in Europe (kBqmCs deposition in Europe (kBqm-2-2) )

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Atmospheric Flux of Atmospheric Flux of 137137CsCs

La Spezia (NW Italy), 1957 – 2009 La Spezia (NW Italy), 1957 – 2009 14

Nuclear Industry:Nuclear Industry:Reprocessing Reprocessing plantsplants

Sellafield

La Hague

137137Cs input to the ocean: 40 PBqCs input to the ocean: 40 PBq

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Waste disposal (sea dumping)Waste disposal (sea dumping)

Linsley et al., 2004

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Nuclear Accidents

Linsley et al., 2004

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Summary Summary sources anthropogenic radionuclidessources anthropogenic radionuclides

• NUCLEAR WEAPON TESTINGNUCLEAR WEAPON TESTING

• NUCLEAR REPROCESSINGNUCLEAR REPROCESSING

• CHERNOBYLCHERNOBYL

ALL OTHER SOURCES ALL OTHER SOURCES CONTRIBUTE ORDERS OF MAGNITUDE LESS TOCONTRIBUTE ORDERS OF MAGNITUDE LESS TOTHE CONTAMINATION OF THE WORLD OCEANTHE CONTAMINATION OF THE WORLD OCEAN

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Conservative, like Cs (in open sea), H, Sr: Conservative, like Cs (in open sea), H, Sr: soluble, pathway related to water movements.soluble, pathway related to water movements.

Non conservative, like Pu, Th, Pb,Non conservative, like Pu, Th, Pb,high affinity for particles, settle with them.high affinity for particles, settle with them.

Radionuclide behaviourRadionuclide behaviourin the marine environmentin the marine environment

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Transported by the oceanic Transported by the oceanic currents….currents….

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Adsorbed onto particles in costal areas……..

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Scavenged by particles in the open sea……..

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Stocker et al., 2010

Taken up by organisms……..

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Bathimetry of the Mediterranean SeaBathimetry of the Mediterranean Sea

Continental shelves only 10% of its surfaceContinental shelves only 10% of its surface24

Spring climatological map of SeaWiFS derived chlorophyll concentration

(D’Ortenzio, 2003)

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The Med Sea is oligothrophic, characterised byThe Med Sea is oligothrophic, characterised bylow particle population.low particle population.

Saharan dust, although sporadically important, Saharan dust, although sporadically important, does not transfer to the sea bottom does not transfer to the sea bottom significant quantities of radionuclides.significant quantities of radionuclides.

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Inventory of Inventory of 137137CsCs and and 239,240239,240Pu Pu in the Mediterranean Sea (2010)in the Mediterranean Sea (2010)

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Radionuclides Radionuclides concentrationconcentrationin surface water in surface water of the of the world seasworld seas(IAEA, 2005)(IAEA, 2005)

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Natural radionuclides and their behaviourNatural radionuclides and their behaviour

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i) ti) t1/2 1/2 of progenitor >> tof progenitor >> t1/21/2 daughters daughters

ii) time from beginning of progenitor’s decay >> ii) time from beginning of progenitor’s decay >> t ½ daughterst ½ daughters

all radionuclides in the series have the same activityall radionuclides in the series have the same activity

Secular equilibriumSecular equilibrium

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IsotopeIsotopeDaughterDaughterHalf-life Half-life

(yr)(yr)

Surface Surface WaterWaterConc. Conc.

(Bq/m(Bq/m33))

238238UU parentparent 4040234234ThTh 0.0660.066 3838234234UU 248248 4747

230230ThTh 75,275,2 2 x 102 x 10-4-4

226226RaRa 16201620 11222222RnRn 0.0100.010 11210210PbPb 22.322.3 33210210PoPo 0.380.38 22

Approximate activities of Approximate activities of 238238U series isotopesU series isotopesin surface seawaterin surface seawater

Broecker and Peng, 1982, modified 31

Atmosphericparticles

RiverineParticlesMarine

biogenic Particles

Degradation of organic matter

Sedimentaccumulation

In the water column:In the water column:deficiency of deficiency of particle-associated particle-associated radionuclides with radionuclides with respect to their parentsrespect to their parents

In sediments: excess of In sediments: excess of particle-associated particle-associated radionuclides with respect radionuclides with respect to their parentsto their parents

Radionuclides interaction with particlesRadionuclides interaction with particles

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The tracer conceptThe tracer concept

Particle reactive nuclides produced in situ by decay of their parents.

Production rate determined by measuring parent’s conc.

Comparing concentrations of parent and daughter we can show whether the daughter is being removed ontoparticles, but also the rate at which this occurs.

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Knowing: ◊ input function (time and space) ◊ chemical/biological behaviour◊ evolution of their distributions within the sea

The tracer concept

}} Soluble radionuclidesSoluble radionuclides

Particle-reactive Particle-reactive RadionuclidesRadionuclides { 34

The tracer conceptThe tracer concept

Radionuclides as tracers of marine processes

Swimmingradionuclides

Ra-226, Ra-228, H-3 (C-14)

Running radionuclidesU-Th series Diving radionuclides

Th-234, Th-228, Th-230,Pb-210

Sediments: C-14, Pb-210, Th-234

Ra-226, Ra-228, Ra-222

Flying radionuclides

(Radon Rn-222)

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210210Pb as tracer of sedimentation processesPb as tracer of sedimentation processes

Rn-222 Pb-210

Pb-210

Pb-210 exU-238 Pb-210 matrix +

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210210Pb as sedimentation tracerPb as sedimentation tracer

The fraction of 210Pb reaching the sediment in association with settling particles, the so-called excess 210Pb, IS NOTin secular equilibrium with its parent 226Ra and decays with its own half-life (22 yr).

Its vertical profile in the sediment depends on physical decay and sediment accumulation rate.

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Vertical profile of 210Pb and 226Ra

in a sediment core

0

10

20

30

40

0 50 100 150 200

Ra-226 Pb-210 (Bq/kg)

Prof

. (cm

)

The levels of anthropogenic radionuclides The levels of anthropogenic radionuclides in the marine envirnment are presently low in the marine envirnment are presently low and will decrease in the future and will decrease in the future (except in a few hot spots)(except in a few hot spots)due to the decrease in the input.due to the decrease in the input.

In conclusion:In conclusion:

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In conclusion..

Doses to man Doses to man from from anthropogenianthropogenic c radionuclidesradionuclidesare generally are generally lower than lower than those deriving those deriving from natural from natural radionuclidesradionuclides(in the marine (in the marine environment environment mainly mainly 210210Po).Po).40

Dose rates to the world population Dose rates to the world population from marine radifrom marine radioactivity

Linsley et al., 2004

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Dose rates to the crtical groupsDose rates to the crtical groupsfrom marine radifrom marine radioactivity

Linsley et al., 2004

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Radionuclides are powerful tools to define the rates Radionuclides are powerful tools to define the rates of oceanographic process, that often can not be of oceanographic process, that often can not be derived in any other way.derived in any other way.

RADINUCLIDES IN THE OCEANS:RADINUCLIDES IN THE OCEANS:a tool for understandinga tool for understanding

the ecosystems functioningthe ecosystems functioning

They have produced essential information on They have produced essential information on water circulation, particle dynamics andwater circulation, particle dynamics andpollution studies and are a foundamental tool to pollution studies and are a foundamental tool to validate models. validate models.

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