1. RADINUCLIDES IN THE OCEANS:
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

2. RADIONUCLIDES IN THE OCEANS OUTLINE
Sources of anthropogenic and natural radionuclides to the oceans.
Radionudlides behaviour in the marine environment.
The “tracer” concept.

3. Sources of radionuclides to the marine environment
Cosmic radiation.
In environmental studies:
3H, 7Be, 14C
formed by neutron capture in the atmosphere.
High energy protons alpha particles nuclei of some elements
they interact in the high atmosphere producing secondary particles (neutrons, protons)
and gamma radiations.

4. Sources of radionuclides to the marine environment
Primordial radionuclides
Series 238U t1/2 = 4.5 x 109 a
232Th t1/2 = 1.4 x 1010 a
235U t1/2 = 7.1 x 108 a
They decay, through a long series of radionuclides,
to stable isotopes of Pb.
40K t1/2 = 1.3 x 109 a

5. Sources of radionuclides to the marine environment
Anthropogenic radionuclides:
Fallout from atmospheric weapons testing
Chernobyl accident
Nuclear Industry
Nuclear accidents

6. Global fallout Trinity test, Alamogordo July 16, 1945
Nuclear tests ban treaty
1963

7. Fission yield curves for 235U and 239Pu8

8. Fallout radionuclides still present in the environment:
137Cs fission t1/ years
90Sr fission t1/ years
14C (n,p) + cosm t1/ years
3H fuel residue + cosm. t1/ years
238Pu fuel residue/prod t1/ years
239Pu fuel residue/prod t1/ years
240Pu fuel residue/prod t1/ years
To the oceans: 380 PBq of 90Sr and 660 PBq of 137Cs 9

9. Atmospheric nuclear detonations
Hamilton, 2004

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

11. The Chernobyl
accident
April 26,
1986 11

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

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

14. Atmospheric Flux of 137Cs
La Spezia (NW Italy), – 2009

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

16. Waste disposal (sea dumping)
Linsley et al., 2004
Since countries, including Italy, have used more than 80 sites to dispose approximately 85 PBq of radioactive waste. 53% lowlevel packaged solid waste, mainly in NE Atlantic. CRESP. Only in 1992 enhanced levels of 238Pu in bottom waters indicated leakage.
43%disposal of reactors with spent fuel (Kara Sea). Even here slightly enhanced levels of Co Cs and Pu Isotopes, no radiological significance.

17. Nuclear Accidents Linsley et al., 2004
6 nuclear submarines lost since 1963 at various sites in Atlantic Ocean, below 1500 m.
At present no elevated levels above fallout except for some Co in sediments close to US submarines.
Thule and Palmares

18. sources anthropogenic radionuclides
Summary
sources anthropogenic radionuclides
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, pathway related to water movements.
Non conservative, like Pu, Th, Pb,
high affinity for particles, settle with them.

20. Transported by the oceanic currents….
Carries warm surface waters from the tropics northward. At high latitudes, the waters cool, releasing heat to the atmosphere and moderating wintertime climate in the North Atlantic region. The colder (and denser) waters sink and flow southward in the deep ocean to keep the conveyor moving.

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. Bathimetry of the Mediterranean Sea
Continental shelves only 10% of its surface

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

26. The Med Sea is oligothrophic, characterised by
low particle population.
Saharan dust, although sporadically important,
does not transfer to the sea bottom
significant quantities of radionuclides.

27. in the Mediterranean Sea (2010)
Inventory of 137Cs and 239,240Pu
in the Mediterranean Sea (2010)
Compartment
137Cs
PBq
% of
delivery
239,240Pu
TBq
Water column m
6.1
90% 75
47%
Sediment shelf
0.2 3% 40
25%
Sediment deep sea
6.9 4%
TOTAL MEDITERRANEAN
6.5
96%
122
76%

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

29. Natural radionuclides and their behaviour
The marine geochemistry of daughter products of U and Th series is quite complex. As shown in this table, the activities of successive daughter products of a given decay series are far from equal, as radioactive equilibrium would dictate. The isotopes of particle-reactive elements generated within the sea become rapidly attached to particles and removed from the upper water column in association with them. So Th234 conc. is lower than that of 238U. 222Rn is a gas and diffuses out of surface water, so its activity is lower than that of its parent 226Ra.
The particle reactive nuclides are produced in situ by the decay of their immediate parents. This production rate can be determined by measuring the concentration of this parent in the water mass of interest. By comparing the in situ conc of the daughter isotope with that of its parent, we not only can show whether the daughter is being removed onto particulate matter, but also at what rate this removal occurs.

30. Secular equilibrium i) t1/2 of progenitor >> t1/2 daughters
ii) time from beginning of progenitor’s decay >> t ½ daughters
all radionuclides in the series have the same activity

31. Approximate activities of 238U series isotopes
in surface seawater
Isotope
Daughter
Half-life
(yr)
Surface Water
Conc.
(Bq/m3)
238U
parent 40
234Th
0.066 38
234U
248 47
230Th
75,2
2 x 10-4
226Ra
1620 1
222Rn
0.010
210Pb
22.3 3
210Po
0.38 2
The marine geochemistry of daughter products of U and Th series is quite complex. As shown in this table, the activities of successive daughter products of a given decay series are far from equal, as radioactive equilibrium would dictate. The isotopes of particle-reactive elements generated within the sea become rapidly attached to particles and removed from the upper water column in association with them. So Th234 conc. is lower than that of 238U. 222Rn is a gas and diffuses out of surface water, so its activity is lower than that of its parent 226Ra.
Broecker and Peng, 1982, modified

32. Radionuclides interaction with particles
Atmospheric
particles
Riverine
Particles
Marine
biogenic
Degradation of organic matter
Sediment
accumulation
In the water column:
deficiency of
particle-associated
radionuclides with respect to their parents
The particle reactive nuclides are produced in situ by the decay of their immediate parents. This production rate can be determined by measuring the concentration of this parent in the water mass of interest. By comparing the in situ conc of the daughter isotope with that of its parent, we not only can show whether the daughter is being removed onto particulate matter, but also at what rate this removal occurs.
In sediments: excess of particle-associated radionuclides with respect to their parents

33. The 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 onto
particles, but also the rate at which this occurs.
The particle reactive nuclides are produced in situ by the decay of their immediate parents. This production rate can be determined by measuring the concentration of this parent in the water mass of interest. By comparing the in situ conc of the daughter isotope with that of its parent, we not only can show whether the daughter is being removed onto particulate matter, but also at what rate this removal occurs.

34. } Soluble radionuclides {
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…..
} Soluble radionuclides {
Particle-reactive
Radionuclides

35. Running radionuclides
The tracer concept
Radionuclides as tracers of marine processes
Swimming
radionuclides
Ra-226, Ra-228,
H-3 (C-14)
Running radionuclides
U-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)
There are natural radionuclides for tracing almost any marine process, at any time scale, because they show all type of geochemical behaviour and half-lives.
Rn isotopes (gaseous) are used to study air-sea exchanges, Th and 210Pb for particle dynamics, Ra/Rn isotopes to follow groundwater discharges or mixing of shelf and open-sea waters.

36. 210Pb as tracer of sedimentation processes
Rn-222
Pb-210
Pb-210
U-238
Pb-210 matrix +
Pb-210 ex

37. 210Pb as sedimentation tracer
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. Vertical profile of 210Pb and 226Ra in a sediment core10 20 30 40 50
100
150
200
Ra-226
Pb-210 (Bq/kg)
Prof. (cm)
Vertical profile of 210Pb and 226Ra in a sediment core

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

40. In conclusion.. Doses to man from anthropogenic radionuclides
are generally lower than those deriving from natural radionuclides
(in the marine environment mainly 210Po).

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

42. Dose rates to the crtical groups from marine radioactivity
Linsley et al., 2004

43. RADINUCLIDES IN THE OCEANS: a tool for understanding
the ecosystems functioning
Radionuclides are powerful tools to define the rates of oceanographic process, that often can not be derived in any other way.
They have produced essential information on water circulation, particle dynamics and
pollution studies and are a foundamental tool to validate models.