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RADINUCLIDES IN THE OCEANS: a tool for understanding the ecosystems functioning

IAEA Regional Training Course on Sediment Core Dating Techniques. RAF7/008 Project CNESTEN, Rabat, 5 – 9 July 2010. RADINUCLIDES IN THE OCEANS: a tool for understanding the ecosystems functioning Roberta Delfanti ENEA – Marine Environment Research Centre , La Spezia.

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RADINUCLIDES IN THE OCEANS: a tool for understanding the ecosystems functioning

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  1. IAEA Regional Training Course on Sediment Core Dating Techniques. RAF7/008 Project CNESTEN, Rabat, 5 – 9 July 2010 RADINUCLIDES IN THE OCEANS: a toolforunderstanding the ecosystemsfunctioning Roberta Delfanti ENEA – Marine EnvironmentResearchCentre, La Spezia

  2. RADIONUCLIDES IN THE OCEANS OUTLINE Sourcesofanthropogenic and naturalradionuclidesto the oceans. Radionudlidesbehaviour in the marine environment. The “tracer” concept.

  3. Sourcesofradionuclidesto the marine environment • Cosmicradiation. • In environmentalstudies: • 3H, 7Be, 14C • formedbyneutroncapture in the atmosphere.

  4. Sourcesof radionuclidesto the marine environment • Primordial radionuclides • Series238U t1/2 = 4.5 x 109 a • 232Th t1/2 = 1.4 x 1010 a • 235U t1/2 = 7.1 x 108 a • Theydecay, through a long seriesofradionuclides, • tostableisotopesofPb. • 40K t1/2 = 1.3 x 109 a

  5. Sourcesof radionuclidesto the marine environment • Anthropogenicradionuclides: • Fallout fromatmosphericweaponstesting • Chernobyl accident • NuclearIndustry • Nuclearaccidents

  6. Global fallout Trinity test, Alamogordo July 16, 1945 Nucleartestsbantreaty 1963

  7. Fissionyieldcurvesfor235U and 239Pu 8

  8. Fallout radionuclides stillpresent in the environment: 137Cs fission t1/2 30.2 years 90Sr fission t1/2 28.6 years 14C (n,p) + cosm t1/2 5730 years 3H fuel residue + cosm. t1/2 12.3 years 238Pu fuel residue/prod t1/2 87.7 years 239Pu fuel residue/prod t1/2 24119 years 240Pu fuel residue/prod t1/2 6570 years To the oceans: 380 PBqof90Sr and 660 PBqof137Cs 9

  9. Atmosphericnucleardetonations Hamilton, 2004

  10. Global fallout latitudinal deposition 10 Modified from Hamilton, 2004

  11. The Chernobyl accident April 26, 1986 11

  12. The Chernobyl Accident Simulationof the dispersion of the Chernobyl plume 12

  13. Chernobyl 137Cs deposition in Europe (kBqm-2) 137Cs input to the oceans: 16 PBq

  14. AtmosphericFluxof137Cs La Spezia (NW Italy), 1957 – 2009

  15. NuclearIndustry: Reprocessing plants 137Cs input to the ocean: 40 PBq Sellafield La Hague

  16. Wastedisposal (sea dumping) Linsley et al., 2004

  17. Nuclear Accidents Linsley et al., 2004

  18. Summary sourcesanthropogenicradionuclides • NUCLEAR WEAPON TESTING • NUCLEAR REPROCESSING • CHERNOBYL ALL OTHER SOURCES CONTRIBUTE ORDERS OF MAGNITUDE LESS TO THE CONTAMINATION OF THE WORLD OCEAN

  19. Radionuclide behaviour in the marine environment Conservative, like Cs (in open sea), H, Sr: soluble, pathwayrelatedto water movements. Non conservative, like Pu, Th, Pb, high affinityforparticles, settlewiththem.

  20. Transported by the oceanic currents….

  21. Adsorbed onto particles in costal areas……..

  22. Scavenged by particles in the open sea……..

  23. Taken up by organisms…….. Stocker et al., 2010

  24. Bathimetryof the MediterraneanSea Continental shelvesonly 10% ofitssurface

  25. Spring climatological map of SeaWiFS derived chlorophyll concentration (D’Ortenzio, 2003)

  26. The MedSeaisoligothrophic, characterisedby low particlepopulation. Saharandust, althoughsporadicallyimportant, doesnot transfer to the seabottom significantquantitiesof radionuclides.

  27. Inventory of 137Cs and 239,240Pu in the Mediterranean Sea (2010)

  28. Radionuclides concentration in surface water of the world seas (IAEA, 2005)

  29. Naturalradionuclides and theirbehaviour

  30. Secularequilibrium i) t1/2 ofprogenitor >> t1/2daughters ii) timefrombeginningofprogenitor’s decay >> t ½ daughters allradionuclides in the serieshave the sameactivity

  31. Approximateactivitiesof238U seriesisotopes in surfaceseawater Broecker and Peng, 1982, modified

  32. Radionuclidesinteractionwithparticles Atmospheric particles Riverine Particles In the water column: deficiencyof particle-associated radionuclideswithrespecttotheirparents Marine biogenic Particles In sediments: excessofparticle-associatedradionuclideswithrespecttotheirparents Sediment accumulation Degradation of organic matter

  33. The tracerconcept 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 onto particles, but also the rate at which this occurs.

  34. The tracer concept Knowing: ◊ input function (time and space) ◊ chemical/biological behaviour ◊ evolution of their distributions within the sea • Information on oceanographic processes. • Patterns and rates of • ◊ circulation • ◊ ventilation • ◊ sediment transport • ◊ particle (carbon) fluxes….. }Solubleradionuclides { Particle-reactive Radionuclides

  35. Flying radionuclides (Radon Rn-222) Running radionuclides U-Th series Diving radionuclides Th-234, Th-228, Th-230, Pb-210 Swimming radionuclides Ra-226, Ra-228, Ra-222 Ra-226, Ra-228, H-3 (C-14) Sediments: C-14, Pb-210, Th-234 The tracer concept Radionuclides as tracers of marine processes

  36. Rn-222 Pb-210 210Pb astracerofsedimentationprocesses Pb-210 U-238 Pb-210 matrix + Pb-210 ex

  37. 210Pb assedimentationtracer The fraction of 210Pb reaching the sediment in association with settling particles, the so-called excess 210Pb, IS NOT in 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.

  38. Ra-226 Pb-210 (Bq/kg) 0 50 100 150 200 0 10 20 Prof. (cm) 30 40 Vertical profile of 210Pb and 226Rain a sediment core

  39. In conclusion: The levelsofanthropogenicradionuclides in the marine envirnment are presently low and willdecrease in the future (except in a few hot spots) due to the decrease in the input.

  40. In conclusion.. Dosesto man fromanthropogenic radionuclides are generallylowerthanthosederivingfromnatural radionuclides (in the marine environmentmainly210Po).

  41. Dose ratesto the world population from marine radioactivity Linsley et al., 2004

  42. Dose ratesto the crticalgroups from marine radioactivity Linsley et al., 2004

  43. RADINUCLIDES IN THE OCEANS: a toolforunderstanding the ecosystemsfunctioning Radionuclides are powerfultoolstodefine the ratesofoceanographicprocess, thatoften can notbederived in anyother way. Theyhaveproducedessential information on water circulation, particledynamics and pollutionstudies and are a foundamentaltoolto validate models.

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