Anthropogenic 129I Traced in Environmental Archives by ...172268/FULLTEXT01.pdf · ACTA UNIVERSITATIS UPSALIENSIS UPPSALA 2008 Digital Comprehensive Summaries of Uppsala Dissertations

ACTA

UNIVERSITATIS

UPSALIENSIS

UPPSALA

2008

Digital Comprehensive Summaries of Uppsala Dissertationsfrom the Faculty of Science and Technology 448

Anthropogenic 129I Traced inEnvironmental Archives byAccelerator Mass Spectrometry

EDVARD ENGLUND

ISSN 1651-6214ISBN 978-91-554-7238-2urn:nbn:se:uu:diva-8989

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List of Papers

This thesis is based on the following papers:

I E. Englund, A. Aldahan, G. Possnert, V. Alfimov (2007). A routinepreparation method for AMS measurement of 129I in solid material.Nucl. Instr. Meth. B 259: 365 - 369

II A. Aldahan, E. Englund, G. Possnert, I. Cato, X. L. Hou (2007). Iodine-129 enrichment in sediment of the Baltic Sea. Appl. Geochem. 22: 637-647

III E. Englund, A. Aldahan, G. Possnert (2008). Tracing anthropogenic nu-clear activity with 129I in lake sediments. J. Environ. Radioact. 99: 219- 229

IV E. Englund, A. Aldahan, G. Possnert, X. Hou, I. Renberg, T. Saarinen.Modeling fallout of anthropogenic 129I submitted to Environ. Sci. Tech-nol. April 2008

V E. Englund, A. Aldahan, X. Hou, G. Possnert. Time series of 129I inaerosols, manuscript

Reprints were made with permission from the publishers.

In paper I, my part of the work includes installation and purchase of the laboratory forcombustion and chemical treatment, design of the combustion system and introduc-tion of new routines for the extraction procedure, as well as writing of the paper. Inpaper II, part of the laboratory work as well as interpretation was done by me. In paperIII, my part includes laboratory work, data processing and calculations, interpretationof the data and writing. In paper IV, I introduced the concept of signal processing tointerpret the 129I data in sediment archives, and did the laboratory work and writing.In paper V, I did laboratory work, data processing, interpretation and writing.

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Iodine in the environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Natural and anthropogenic sources of 129I . . . . . . . . . . . . . . . . 4

2 Sampling and analytical procedures . . . . . . . . . . . . . . . . . . . . . . . . 72.1 Sampling sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2 Aerosols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.3 Lake and Baltic Sea sediments . . . . . . . . . . . . . . . . . . . . . . . . . 92.4 Extraction of iodine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.4.1 The Uppsala accelerator mass spectrometry system . . . . . 122.4.2 Measuring procedure of 129I by AMS . . . . . . . . . . . . . . . . 13

3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.1 Sample preparation method . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.2 Chronology of the sediment profiles . . . . . . . . . . . . . . . . . . . . . 183.3 Iodine in sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.4 Aerosols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4 Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 Summary in Swedish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

1. Introduction

Since the beginning of the nuclear era, starting during the 1940s, largeamounts of radioactivity have been released into natural environments. Besideconcerns about hazards effects, radioactive isotopes associated with theseemissions provide opportunities as anthropogenic tracers of environmentalprocesses. Anthropogenic contributions of the long-lived isotope 129I (T1/2 =15.7 Myr) have been studied in fresh and marine water and sediment of northEurope [Rucklidge et al., 1994; Szidat et al., 2000; Buraglio et al., 2001ab;Alfimov et al., 2004; Gallagher et al., 2005; Michel et al., 2005; Aldahanet al., 2007a]. However, a continuous record covering the entire emissionperiod is lacking. Sediments have in general provided high resolution andcontinuous annual archives for environmental analysis. The small amount ofsediment that can be recovered on an annual scale for 129I extraction has untilrecently been a limiting factor restricting the utilization of 129I as a tracer.Accordingly, development of a standard method for extraction of 129I fromsmall amount of solid materials was needed in order to expose details ofpast anthropogenic emission of 129I. This thesis deals with the tracing of129I emissions over Scandinavia and Finland since the early 1940s throughthe use of sediment archives. In addition, atmospheric transport pathwaysand fallout modes (wet and dry) of 129I are elucidated through analysis ofaerosols samples and modeling.

1.1 ObjectivesThe objectives of this thesis include:• Development of a routine sample preparation procedure suitable for extrac-tion of 129I from small amount of solid material.

• Tracing variability in 129I in northern Europe since the beginning of thenuclear era by using a combination of lake and Baltic Sea sediments.

• Providing new data about 129I concentration in aerosols, that together withavailable data in precipitation are used to evaluate transport pathways andemission sources in northern Europe.

• Depicting relative contributions from the different anthropogenic sourcesof 129I by numerical modeling.

Before presenting results and discussion related to the above mentioned ob-jectives, a summary of the occurrence of iodine in the environment is given inthe next sections.

1

1.2 Iodine in the environmentThe ocean, atmosphere, terrestrial and biosphere form mobile iodine pools(Figure 1.1), which are included in a global box model for estimation of totalinventories and major circulation patterns among the different compartments[Kocher, 1981] (Figure 1.2). A major part (> 99%) of the iodine is containedin the oceans as iodide (I−) and iodate (IO−3 ). Iodine is accumulated in marinealgae and phytoplancton, which are linked to the iodine transfer from ocean toatmosphere [Fenical, 1981; Singh et al., 1983; Class and Ballschmiter, 1988].It is hence concluded that iodine transfer mainly occurs at the biologicallyactive areas of the oceans [Carpenter et al., 1999]. Phytoplancton occurs bothat open seas and particularly at the coasts, whereas macro algae are strictlylimited to coast areas, which covers only ∼0.5% of the oceans.

Ocean Land

IO3- I-

Organically mediated

Sea spray

I–, IO3–

Residence time in

Atmosphere ~2 weeks

WetDry

Washout

I–, IO3– , (particles)

ParticulateOrganic

Metal oxides

Dissolved salts I–, IO3–

In soils:

Organic iodine:

CH3I, CH2I2, CH2ClI, ...

Photodissociation (~1 Week):

I

Inorganic species,

I2, HI, HOI,...

Aerosols

Figure 1.1: Iodine in the upper ocean, atmosphere and terrestrial compartment, mod-ified after Aldahan et al. [2006]

Among marine areas with highly elevated concentrations of iodine, con-siderable amounts of alkyl iodides have been identified in the atmosphere.These species, mainly methyl iodide, CH3I but also for example CH2I2, C3H7Iand CH2ClI undergo photodissociation at a time scale of a few days and pro-duce elemental iodine, I, which in turn rapidly reacts with the surroundings toform a variety of inorganic species [Vogt et al., 1999; Carpenter et al., 1999].The behavior of iodine in the atmosphere is complex, and more than 200 re-actions, particularly transitions between the different phases are considered

2

[Vogt et al., 1999]. All of the listed iodine species are chemically unstablewith the exception of particular bounded iodate. Although gaseous iodine isdominant in the atmosphere, the fraction of particulate and gaseous iodinevaries with geographical locations [Rahn et al., 1976; Kitto et al., 1988;Wer-shofen and Aumann, 1989; Gäbler and Heumann, 1993]. Special interest hasbeen devoted to iodine in the atmosphere, for its role in the destruction ofozone [Chameides and Davis, 1980; Barrie et al., 1988; Solomon et al., 1994]and cloud formation [Saiz-Lopez et al., 2006].Removal of iodine from the atmosphere occurs through dry and/or wet

deposition. The considered pathways are (1) fallout through precipitation(wet deposition), either below cloud level (i.e. washout) or by incorporationinto water droplets at cloud level, or (2) direct deposition of aerosol particles(dry deposition) [Whitehead, 1984; Baker et al., 2001; Buseck and Schwartz,2003]. The residence time of iodine in the atmosphere is estimated to be afew weeks [Rahn et al., 1976; Kocher, 1981].

Terrestrial biosphere

113.0 x 10 g

Land atmosphere

Surface soil region

Shallowsubsurface

region

Deep subsurface region

5.7 x 10

4.2 x 10

1.4 x 10

1.1 x 10

9

14

13

13 g

g

g

g

Ocean Atmosphere

Ocean mixed layer

Deep ocean

Recent oceansediments

8.3 x 10

1.4 x 10

8.1 x 10

8.9 x 10

10

15

16

17 g

g

g

g

1.2 x 1011

2.0 x 1010

5.7 x 1010

5.7 x 109

5.7 x 1010

5.7 x 1010

2.9 x 108

1.5x 10101.5 x 1010

2.9 x 108

2.0 x 10121.9 x 1012

7.2 x 1013 7.2 x 1013

1.8 x 10111.8 x 1011

1.0 x 1011

g/yr

g/yr

g/yr

g/yr

g/yr

g/yrg/yr

g/yrg/yr

g/yr

g/yr

g/yrg/yr

g/yr

g/yr

g/yr

g/yr

Figure 1.2: The compartment model of global iodine cycle [Kocher, 1981]

The major pool of iodine on land is soils with concentrations varying be-tween 0.5 and 40 mg kg−1. Within the soils the organic fraction is the maincarrier of iodine [Sutcliffe and Davidson, 1979; Whitehead, 1979; Wenlocket al., 1982]. Soil iodine has a tendency to volatilize under certain conditions,e.g. if there is a low pH and low content of organic material or otherwise low

3

biological activity [Whitehead, 1984]. Concentrations of iodine in the soil arefurthermore influenced by proximity to the sea and weathered parent material.The iodine concentration of soils may also show a decreasing trend with depthsuggesting removal through leaching [Ernst et al., 2003].

1.3 Natural and anthropogenic sources of 129I129I is produced spontaneously in nature by spallation of xenon in the up-per atmosphere under influence of cosmic rays, and as a fission product of238U in the earth’s crust [Fabryka-Martin et al., 1985]. Before the nuclear era,which started with the Manhattan project in the 1940s, the natural ratio of129I/127I was in spatial and temporal equilibrium at∼ 10−12, corresponding toa total amount of about 100 kg of 129I (Table 1.1). Presently, the reprocessingplants in Sellafield (UK) and La Hague (France) are by far the most significantglobal sources of 129I. The total amount of liquid released 129I is estimated to∼5000 kg (Irish Sea and English Channel), and 230 kg as gaseous releases (tothe atmosphere) by the year 2006 [Aldahan et al., 2007a].Anthropogenic 129I has during the last decades increased the natural

129I/127I ratio to as much as 8 orders of magnitude in the vicinity of thereprocessing plants [Rucklidge et al., 1994]. The nuclear weapon tests arebelieved to have contributed with 50 - 150 kg 129I, during the 1950s and1960s. In addition to the above mentioned globally relevant sources of 129I,the Chernobyl accident in 1986 affected parts of Europe. The amount of 129Ireleased was relatively small, about 6 kg, and the fallout was well defined inboth time and space.For details and comprehensive description of the distribution of 129I in the

environment the reader is referred to the following references [Chamberlain,1991; Raisbeck and Yiou, 1999; Aldahan et al., 2007a].

4

Source 129I (kg) Release form Referenceb

Natural ∼100 - 1Nuclear weapons testing 1945 - 1980 50 - 150 Gaseous 1, 2, 3Chernobyl accident, 1986 2 - 6 Gaseous 4, a

Nuclear reprocessing facilities:Hanford, 1944 - 1972, USA 260 Gaseous 5Marcoule, 1988 - 1997, France 68 Gaseous 6Sellafield, 1952 - 2006, UK 157 Gaseous 7, 8, 9

1420 Liquid 7, 8La Hague, 1966 - 2006, France 70 Gaseous 7, 10

3320 Liquid 7, 10Others (Russia, Japan, India, China) Published data

not found-

a Estimated by data of 129I/131I from Mironov et al. [2002] and the released 131I from UN-SCEAR [2000]b References: 1. Raisbeck and Yiou [1999], 2. Eisenbud and Gesell [1997], 3. Wagner et al.[1996], 4. Paul et al. [1987], 5. Hanford [1997], 6. Cogema [1997], 7. Lopez-Gutierrez et al.[2004], 8. RIFE [2001 - 2006], 9. Reithmeier et al. [2006], 10. Cogema [2001 - 2006]

Table 1.1: Amount of 129I and release form from nuclear sources, modified after Al-dahan et al. [2007a].

5

2. Sampling and analytical procedures

Materials used in this study include sediment cores taken from three lakesand the Baltic Sea, as well as aerosol samples (Figure 2.1). Site description,sampling procedures and analytical techniques are presented in this section.

La Hague

Sellafield

Chernobyl

A

CSweden

Finland

ED

F

G

B

Figure 2.1: The map shows sampling sites, major 129I sources and general route of129I in the North Sea and Baltic Sea. Triangular dots mark lake or marine sedimentsites, circular dots mark aerosol sampling stations. Individual sampling sites are A -Lake Nylandssjön, B - Lake Lehmilampi, C - Lake Loppesjön, D - Baltic Sea, core 1,E - Baltic Sea, core 2, F - Kiruna, G - Ljungbyhed.

7

2.1 Sampling sitesSediment cores were collected from two lakes in Sweden and one in Finland,details of each site are given in Table 2.1. These sites were selected for theirundisturbed sediment sections, relatively high sedimentation rates and definedchronology. Two of the sites, Lake Nylandssjön and Lake Lehmilampi havevarved sediment sequences (Figure 2.2).The varve structure typically consists of an organic rich part deposited dur-

ing the biologically active seasons (spring, summer and autumn) associatedwith a higher mineralogical content during spring and autumn floods. At win-ter, fine grained material is dominating showing dark color and different tex-ture.

Figure 2.2: Varved sediment from Lake Nylandssjön

Lake Nylandssjön Lake Lehmilampi Lake Loppesjön

Coordinates 62◦ 57’ N, 18◦ 17’ E 63◦ 37’ N, 29◦ 6’ E 61◦ 42’ N, 16◦48’ EAnnual precipitation 800 mm 700 mm 500 mmLake area 0.28 km2 0.15 km2 0.28 km2

Drainage area 0.95 km2 ∼1 km2 4.1 km2

Max depth 17.5 m 11.6 m 14 mAltitude a.s.l. 34 m 150 m 97 m

Table 2.1: Site information of the studied lakes

Sediments cores were collected from two locations in the Baltic Sea at coor-dinates (59◦ 4’N, 19◦7’ E) and (59◦ 13’ N, 18◦40’ E). The Baltic Sea receivesits marine input through the Skagerrak and Kategatt basins that modulate wa-ter exchange between the North and the Baltic Seas (Figure 2.1).Aerosol filters from two stations, one from northern Sweden (Kiruna, 67◦

50’ N, 20◦ 20’ E) and the other from southern Sweden (Ljungbyhed , 56◦ 5’N, 13◦ 14’ E) were provided by the Swedish defense research institute (FOI).The station in northern Sweden is located at an altitude of 408 m a.s.l. and ischaracterized by mountainous topography and sparse vegetation. The stationin southern Sweden (altitude 43 m) is located in an agricultural and forested

8

area. There is a large difference in the climate between the two stations wherearctic conditions dominate at the northern station while temperate conditionsare found in southern Sweden.

2.2 AerosolsCollection of air filters has been conducted since 1957 as part of the Swedishsurveillance program for radioactivity in airborne particulate matters. The fil-ters, made of glass fiber with a total area of 0.58 m×0.58 m, were exposedat ground level to a daily air flow of ∼24000 m3 (flow rate = 84 cm s−1) andwere changed once per week [Vintersved and De Geer, 1982]. A 4 cm2 to16 cm2 of the aerosol filters were used in this study at selective years between1983 and 2000 with ∼4 samples for each year. Filters were stored in closedenvelopes in ∼ 14×14 cm2 pieces at +4◦C.Visual inspection of filters shows that those from southern Sweden were

brown-black in color, while the filters from northern Sweden were white tolight gray. Collection efficiency for the used filters indicate that > 99% ofsmall particles ( ∼ 0.3μm) is captured at a flow rate between 10 and 300 cms−1 [Suchny, 1968, the filter of this study is labeled FOA-1-484].

2.3 Lake and Baltic Sea sedimentsThe sampling devices utilized for sediment coring were (1) gravity corer inLake Loppesjön and the Baltic Sea, and (2) freeze corer in Lake Nylandssjönand Lake Lehmilampi. After slicing, the sediments were dried and measuredfor 137Cs. Selective samples were set aside for isotopic and lithological mea-surements described in the following sections.Sediment cores have been collected continuously from Lake Nylandssjön

since the 1970s for environmental and paleoclimatic purposes. Samples usedin this study for 129I and total iodine were cored in winter 2007 at a waterdepth of 17.5 m, with a core length of 20 cm and an area of ∼ 10 cm2. Slicingof the core was performed in a freeze room after removing the outer partswith a hand plane, making the varves clearly visible. Individual varves werethereafter cut with a scalpel with a varve thickness typically 3 - 4 mm. Inaddition to varve counting, the chronology of the sediments has been verifiedby X-ray imaging analysis as well as direct control of annual sedimentationof cores taken in previous years.Sediment cores were collected from Lake Lehmilampi in winter 2006. The

same sampling procedure applied for cores of Lake Nylandssjön was also usedfor the sediments from Lake Lehmilampi. About 50 - 100 mg of sediment wassampled, covering 1 - 5 years for each subsample, down to the year 1968.Sediment cores from Lake Loppesjön, each 30 cm long and ∼6 cm in di-

ameter, were collected in winter 2004 from the deepest part of the lake (13.5 -14 m). A total of six cores were collected. The sediments had silt-clay texture

9

with a dark grayish-brownish color without visible laminations. Slicing of thecores was done either in the field or in the laboratory with a resolution of 0.3- 1 cm. The pore water was extracted by centrifugation of 3 cm thick intervals(i.e. 3 adjacent slices).The two sediment cores from the Baltic Sea , were 55 cm and 50 cm long

and were collected at depths of 144 m and 78 m respectively, during autumn1997 by the Geological Survey of Sweden. The sediment cores were sliced atinterval of 1 cm and stored in a freezer immediately after the collection. Thetopmost sediment was comprised predominately of black, homogeneous postglacial clay while the deeper part exhibited gradual color change from gray toblack.Additional analyzes were performed on the sediments, which include or-

ganic matter content in Lake Loppesjön, Lake Nylandssjön and the Baltic Seaand grain size analysis, 210Pb and 14C in Lake Loppesjön.

2.4 Extraction of iodineSummary of the procedure used for extraction of iodine from small solid ma-terial is shown in Figure 2.3 [Englund et al., 2007]. A mixture of a knownamount of iodine carrier (∼2 mg) and sample material was combusted at800◦C in a stream of oxygen (in case of total iodine measurements the carrierwas omitted). The liberated iodine was collected in a trapping solution andprecipitated as silver iodide, which was mixed with niobium (Figure 2.4) forthe accelerator mass spectrometry (AMS) at the Uppsala facility.

Considering that some supplementary 129I is added during the chemicalprocedure, the resulting 129I/127I ratios of the AMS-targets (Figure 2.4) canbe described from intrinsic, carrier and background iodine according to

129Itarget127Itarget

=129Iintrinsic +129 Ibackground

127Iintrinsic+127 Icarrier

Assuming that the amount of intrinsic iodine (127Iintrinsic) in samples is muchless than the iodine added from carrier, the above ratio can be approximatedby

129Itarget127Itarget

≈129Iintrinsic127Icarrier

+129Ibackground

127Icarrier

This approximation is adequate when 2 mg (2000 μg) of iodine carrier isadded to samples that contains less than 20 μg of intrinsic iodine, which applyto conditions in this study. The last term is approximated by procedural blankvalues and is further described in section 2.4.2.Extraction of 129I from pore and lake water was done according to the pro-

cedure in Buraglio et al. [2000]. For extraction of 129I from the aerosol sam-ples, the filters were mixed with 35 ml of 0.5 M KOH and 0.05 M Na2SO3

10

O

Pump

Sample + carrier

Quartz wool Furnace

Trapping solution2

Bypass connection

Thermal ribbons

Figure 2.3: Principal sketch of the combustion system.

100 – 1500 mg dried and

pulverized sample + 2 mg

dissolved iodine carrier

Stepwise heating:

200° – 300° C, 45 – 120 min.

680° C, 15 min.

800° C, 30 min.

Collection of iodine in

trapping solution (KOH + Na2SO3)

Acidification to pH 2,

Precipitation of AgI by

AgNO3

AMS-targets, AgI + Nb

Figure 2.4: Flow chart of the combustion procedure.

11

solution together with 1 - 2 mg of iodine carrier, and stirred for ∼2 days. Themixture was filtered and iodine was precipitated as AgI.Procedural blank values of (2− 5)× 10−13 in 129I/127I were at least three

times lower than the ratio of 10−12 to 10−10 measured in sediments, waterand aerosol samples. A summary of measured samples for 129I is given in(Table 2.2).

Site Material Interval Resolution

Lake Nylandssjön Sediment 1942 - 2007 1 year, annual tobiannual

Lake Nylandssjön Lake water 2 - 15 m 2 samplesLake Lehmilampi Sediment 1968 - 2006 1 - 5 years, entire

intervalLake Loppesjön Lake water 0.5 m - bottom 4 samples

core 1 Sediment 0 - 30 cm 1 cm, entire intervalcore 2 Sediment 0 - 17 cm 0.3 - 1 cm, 21 samplescore 3 Pore water 0 - 24 cm 3 cm, 3 samples

Baltic Seacore 1 Sediment 0 - 51 cm 1 cm, 12 samplescore 2 Sediment 0 - 45 cm 1 cm, 11 samples

Kiruna Aerosols 1983 - 2000 ∼4 weeks/year,10 selective years

Ljungbyhed Aerosols 1983 - 2000 ∼4 weeks/year,7 selective years

Table 2.2: Data related to the measured 129I samples.

Measurement of total iodine in sediments was carried out at the UniversityCollege Dublin following the procedure of Ohashi et al. [2000] and at theRisø National Laboratory for Sustainable Energy, Denmark, using the ICP-MS method. For aerosol and water samples only the ICP-MS method wasemployed.

2.4.1 The Uppsala accelerator mass spectrometry systemThe Uppsala tandem accelerator facility used for the measurements of 129I isshown in (Figure 2.5). The injector is equipped with a Cs+ sputter ion sourcefor negative ion production that can be loaded with up to 20 samples, a 90◦double-focusing electrostatic deflector and a 90◦ double-focusing sector mag-net. The vacuum chamber in the injector magnet is electrically isolated andan external power supply is applied for generating square-type voltage pulsesfor rapid interval selection of the 127I and 129I isotopes (∼10 Hz). Ion beamacceleration is achieved by using a 5 MV tandem accelerator (NEC 15SDH-2 Pelletron�). The analyzing and switching magnets at the high energy sidemakes separation of heavy elements feasible. A dedicated AMS beam line islocated after the switching magnet followed by a quadrapole doublet magnetic

12

lens, +20◦ electrostatic deflector and energy defining slits in front of a gas ion-ization energy detector. Setups for beam diagnostics consist of a Faraday cups,beam profile monitors and viewers in order to tune and optimize the ion beamtransport.

01

10 m

Acc

eler

ato

r tan

kIn

ject

or f

or I

-129

AM

S b

eam

line

Post

acc

eler

ato

r an

alyz

ing

mag

net

Swit

chin

g m

agn

et

Ion

so

urc

e

Elec

tro

stat

ic

def

lect

or

Mag

net

icd

efle

cto

r

Elec

tro

stat

ic d

efle

cto

r

Gas

ion

izat

ion

d

etec

tor

Figure 2.5: The Uppsala tandem accelerator.

2.4.2 Measuring procedure of 129I by AMSThe measuring scheme includes measurements of 5 - 10 samples followed bya measurement of a standard sample with a known isotopic ratio of 1.05×

13

10−11 (±3%), obtained from dilution of the standard material NIST SRM4949C. This sequence is repeated a number of times until required accuracy isachieved, normally 1 to 4 repetitions. In order to obtain standard and Poissonerrors for 129I/127I ratios, the time interval for a single sample measurement,normally 300 seconds, is partitioned into 10 second subintervals. In the pre-sentation of 129I/127I ratio and error estimation, the following notation are used

Sample cycle Time interval for a single sample measurement, nor-mally 300 s.

Sample subcycle A sample cycle is partitioned in time intervals of10 s.

Standard cycle The sequence of 5 - 10 sample cycles, initialized andterminated with measurement of a standard sample.

Ratio and error over a sample subcycle is expressed as

Ri =Nri

Qsi σRi =

√Nrii

Qsi

where Nri describes the number of 129I atoms detected (ri = rare isotope) andQsix represents the integrated current of 127I (si = stable isotope). The standard

deviation, σRi , is obtained by Poisson statistics. Consequently, ratio R over asample cycle, containing i sample subcycles, is obtained by the formula

R =∑ik=1Nri

k

∑ik=1 Qsi

k

The corresponding Poisson and standard error is calculated as

σPoissonR =

√∑ik=1Nri

k

∑ik=1 Qsi

kσStandardR =

√∑ik=1(Rk−R)2

(i−1)(2.1)

In following calculations, error for a sample cycle is taken as the maximum ofthe Poisson and standard error

σRsmp = max(σPoissonR ,σStandard

R )

Sample ratios (i.e. 129I/127I ratio obtained during a sample cycle) are nor-malized with standard 129I/127I ratios, which are obtained by time interpolatedvalues of the standard samples that initiate and terminates a standard cycle.Hence, the sample ratio R for a single standard cycle is achieved as

R =Rsmp

w1Rstd(i)+w2Rstd(i+1),

14

with

w2 =start time of Rsmp

total time of the standard cyclew1 = 1−w2

The error associated with the time interpolated standard value, σinterpl, is

σinterpl = max(σPoissonRstd(i)

, σPoissonRstd(i+1), σStandard

Rstd(i), . . .

σStandardRstd(i+1),

12[Rstd(i)−Rstd(i+1)]) (2.2)

Using the error propagation rule, the error for the sample ratio is expressed as

σR = R

√(σRsmp

Rsmp

)2+

(σinterpl

w1Rstd(i)+w2Rstd(i+1)

)2

Here, the σRsmp and σRstd are determined by the maximum error achieved inequation (2.1).The ratio of a sample over the entire measurement procedure is then sum-

marized as the weighted average of each R at the m times the sample is pro-cessed

R =

∑mk=1

Rkσ2

Rk

∑mk=1

1σ2

Rk

and the corresponding weighted Poisson and standard error are

σPoissonR

=1√

∑mk=1

1σ2

Rk

, σStandardR

=

√√√√√√ ∑mk=1

(Rk−R)2

σ2Rk

(i−1)∑mk=1

1σ2

Rk

Background correction is performed by use of procedural blank values Rbl(including the chemical procedure as well), to obtain the corrected ratios R

R = R−Rbl, σR =√σ2

R+σ2

Rbl

Consequently, sample 129I/127I ratio corrected for background is given as(129I127I

)smp

= R×

(129I127I

)std

15

The latter term is the 129I/127I ratio of the standard sample. Using the errorpropagation rule, the corrected error is

σ(129I127I

)smp

= R×

(129I127I

)std×

√√√√√√(σR

R

)2+

⎛⎜⎝σ(

129I127I

)std(

129I127I

)std

⎞⎟⎠

2

16

3. Results

The presentation of the results is divided into three sections, one devoted tothe experimental sample preparation methodology, the other to sediments (i.e.the profiles of lake sediments in Sweden, Finland as well as sediments fromthe Baltic Sea) and the third to aerosols.

3.1 Sample preparation methodThe sample preparation method has been tested for a variety of environmen-tal materials with a wide range of 129I concentrations (Figure 3.1) [Englundet al., 2007]. The preparation scheme was setup with frequently measurementsof blanks, which showed a negligible memory effect between preparations.Repeated combustions show reproducible concentrations and absolute con-centrations were validated by measurements of IAEA standard soil # 375.Results of five consecutive measurements of the IAEA standard soil samplewere (11.4± 0.4)× 108 atoms g−1, which is within the confidence intervalgiven from IAEA of (9.7−14.7)×108 atoms g−1[Strachnov et al., 1996].

106

107

108

109

1010

129 I a

tom

s g−1

Soil "sample 10"

Surface soilCentral Sweden

IAEA #375

Maple leaves

(a) Range and reproducibility for different ma-terials

nvbwgkmq nvbwgkmq nv wgkmq0

5

10

15

Nominal value

Laboratory code This study

Szidat et al.

129 I [

108 a

tom

s g−1

]

(b) IAEA standard soil # 375

Figure 3.1: Performance of the preparation method used in this study for differentmaterials (a) including standard soil IAEA # 375, maple leaves and soil "sample 10"from the interlaboratory comparison [Roberts et al., 1997]. (b) shows measurementof this study compared with data from the different AMS laboratories in [Roberts andCaffee, 2000]; the three clusters represent different chemical preparation procedures.

17

3.2 Chronology of the sediment profilesIn order to establish absolute chronologies of the sediment profiles, isotopicmeasurements were used together with the conventional varve counting. Sedi-ments of both Swedish lakes have a marked enhancement in 137Cs at the 1986year varve (Lake Nylandssjön) and at 9 cm depth (Lake Loppesjön), whichclearly are linked to the Chernobyl accident (Figure 3.2a-b). Total 137Cs in-ventory in the sediments are 4.6 Bq cm−2 in Lake Nylandssjön and 3.7 Bqcm−2 in Lake Loppesjön, which are 44% and 37% higher than the Chernobylfallout at the respective site, i.e. 3.2 Bq cm−2 and 2.7 Bq cm−2 respectively[Edvarson, 1991]. The 1986 137Cs peak in Lake Nylandssjön is higher thanin Lake Loppesjön, which reflects the higher activity of ∼50 Bq g−1 in LakeNylandssjön compared to ∼10 Bq g−1 in Lake Loppesjön. In contrast withthe Swedish lakes, the 137Cs profile in Lake Lehmilampi, Finland, shows con-stantly low values of < 2 Bq g−1 (Figure 3.2c), which is in accordance withthe low Chernobyl 137Cs fallout of <0.05 Bq cm−2 at the area [Paatero et al.,2007].

0 2 4 6 8 100

5

10

15

20

25

30

Dep

th [c

m]

137Cs [Bq g−1]

Core 1Core 2

(a) Lake Loppesjön

0 10 20 30 40 50 60

1930

1940

1950

1960

1970

1980

1990

2000

2010

137 [Bq g−1]

Dep

th [y

ear]

This studyAppleby 1994

(b) Lake Nylandssjön

0 1 2 3 4 5

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

137 [Bq g−1]

Dep

th [y

ear]

(c) Lake Lehmilampi

0 20 40 60 800

5

10

15

Dep

th [c

m]

137Cs [mBq g−1]

Core 1Core 2

(d) Baltic Sea

Figure 3.2: Concentrations of 137Cs in lake and marine sediments (dry weight). Mea-suring accuracy is within 5%.

18

The 137Cs profiles in the Baltic Sea exhibit a marked increase in concentra-tions from 14 cm to 12 cm and 13 cm to 11 cm in the two sediments cores re-spectively, corresponding to maximum values of∼ 0.08 Bq g−1 (Figure 3.2d).Activity at more recent sediments (above 11 cm), remains at a relatively highlevel, although decreasing towards the top to ∼ 0.04 Bq g−1. The 137Cs pro-files demonstrates impact from the Chernobyl accident (the single outstandingsource of 137Cs). Consequently, the layers at 11 cm and 13 cm respectively aredated to 1986.Carbon-14 activity associated with the atmospheric nuclear weapon tests

[Naegler and Levin, 2006] was traced in six samples from Lake Loppesjönin order to mark the increased signal around 1963-65 (Figure 3.3). The 14Cenhancement is clearly observed at 15 - 16 cm depth defining the absolutechronology at this interval. As a reference, measured 14C fallout in the atmo-sphere is shown in figure 3.4.

90 95 100 1050

5

10

15

20

Dep

th [c

m]

14C activity [pM]

Figure 3.3: 14C activity in sedimentsfrom Lake Loppesjön.

0 500 1000

1950

1960

1970

1980

1990

2000

D 14C (per mille)

Yea

r

Δ

Figure 3.4: Atmospheric 14C fallout[Levin et al., 1985].

3 3.5 4 4.5 5 5.5 60

5

10

15

20

25

30

log(210Pb) [mBq g−1]

Dep

th [c

m]

Figure 3.5: Excess 210Pb in sediments of Lake Loppesjön

Sediment accumulation rate in Lake Loppesjön was determined by the timemarker of 137Cs and 14C, associated to the Chernobyl accident in 1986 and

19

the nuclear weapon tests during the 1960s respectively. In addition, the 210Pb(Figure 3.5) was considered for determination of sedimentation rates by usingthe Constant Rate of Supply model (CRS) and Constant Initial Concentra-tion model (CIC) approaches of [Appleby and Oldfield, 1992]. The differentapproaches generated similar results of ∼50 mg (cm2 y)−1. Apparently, thesediment accumulation rate has relatively small variations with depth, since(1) the methods of the 210Pb dating show small variations with depth and (2)the time marker determinations results in similar accumulation rates.The sediment accumulation rates in Lake Nylandssjön vary between 16 and

37 mg (cm2 y)−1, whereas the variability in Lake Lehmilampi is 29 and 62mg (cm2 y)−1, but is associated with high uncertainty.

0 5 10 15 20 25

1920

1940

1960

1980

2000

129I [108 atoms g−1]

Dep

th [y

ear]

Core 1Core 2

(a) Lake Loppesjön

0 5 10 15 20 25

1940

1950

1960

1970

1980

1990

2000

2010

129I [108 atoms g−1]

Dep

th [y

ear]


0 5 10 15

1960

1970

1980

1990

2000

2010

129I [108 atoms g−1]

Dep

th [y

ear]

(c) Lake Lehmilampi

0 10 20 30 40 500

10

20

30

40

50

60

129I [108 atoms g−1]

Dep

th [c

m]

Baltic 1Baltic 2

(d) Baltic Sea

Figure 3.6: Concentrations of 129I in lake and Baltic Sea sediments.

3.3 Iodine in sedimentThe distribution of 129I in the sediment profiles from the Swedish lakes, LakeNylandssjön and Lake Loppesjön (Figure 3.6) exhibits similar patterns. Inboth profiles, there appears a constantly low 129I concentrations ∼ (0.2−0.3)× 108 atoms g−1 that continue until ∼1960. This trend is followed by

20

a gradual increase until 1986 where a marked enhancement in concentrationsover a narrow interval is observed. In the succeeding interval 129I of LakeLoppesjön shows an approximately constant level of 10× 108 atoms g−1,whereas the profile of Lake Nylandssjön is varying at (14−24)×108 atomsg−1. At the topmost part of the sections, 129I concentrations increase towardthe sediment-water interface in both lakes.The sediment section in Lake Lehmilampi, Finland, exhibits a general in-

crease in the 129I concentrations throughout the profile, with maximum a valueobserved at the top of the section (Figure 3.6). The pre-1986 129I concentra-tions of (2− 3)× 108 atoms g−1 are in fair agreement among all the threelakes. There is, however, no corresponding increase in 129I concentrations inthe Finnish lake as is seen in the Swedish lakes around 1986.Similar to the trends observed in the lake sediment profiles, the 129I concen-

trations in the Baltic Sea sediments show the lowest values at the bottom ofthe cores and an increasing signal towards the sediment-water interface (Fig-ure 3.6), with exceptions at depths of ∼17 cm and the topmost layer. The 129Iconcentrations are generally higher than in lake sediments, ranging between(0.5−45)×108 atoms g−1.The amount of 129I in pore water in sediments of Lake Loppesjön ranged

at ∼ (17− 30)× 105 atoms ml−1 at three depth intervals between the topand 24 cm depth (Table 3.1). By calculating concentrations in atoms (ml wetsediment)−1, the pore water 129I concentrations vary between 1% at top and28 % at bottom at the respective depths in sediment (Table 3.2). The amountof 129I in the pore water is, however, negligible compared to the integratedamount of 129I in the sediment.

Volume (wet sed.) Volume (pore water) 129I in Pore water/lake water

[ml] [ml] [105 atoms ml−1]Lake water

0.5 m 1.8±0.18 m 2.0±0.313 m 1.7±0.2Bottom 7.6±0.3

SedimentTop water 19.8±0.70 - 3 cm 94 36 29.6±1.310 - 13 cm 94 35 27.0±1.021 - 24 cm 94 30 16.9±1.1

Table 3.1: 129I in lake water and pore water in Lake Loppesjön.

The 129I concentrations in the lake water, ∼ 2× 105 atoms ml−1 in LakeLoppesjön and ∼ 5×105 atoms ml−1 in Lake Nylandssjön, are considerablyless than in the pore water (Figure 3.7). Bottom water in Lake Loppesjön

21

129I in pore water Partition

Interval in sediment [106 atoms (ml wet sediment)−1]

0 - 3 cm 1.1±0.1 1%

10 - 13 cm 1.0±0.1 12%

21 - 24 cm 0.5±0.05 28%

Table 3.2: Amount of 129I contained in the pore water and related sediments of LakeLoppesjön.

(accumulation bottom) also shows enhanced concentrations relative to the lakewater.

0 5 10 15 20 25 30 35

21−24

10−13

0−3

13 m

8 m

0.5 m

~1 cm above bottom

~1 dm above bottom

105 atoms (ml of WATER)−1

Dep

th in

sed

imen

t [cm

]D

epth

in la

ke w

ater

Water−sediment interface

(2 m)

(15 m)

Lake LoppesjönLake Nylandssjön

Figure 3.7: 129I concentration in lake water and pore water of the sediment in LakeLoppesjön together with lake water concentrations in Lake Nylandssjön.

Total iodine (127I) concentration is higher in Lake Nylandssjön compared toLake Loppesjön (Figure 3.8). The iodine concentration in the sediments fromthe Baltic Sea range between 40 and 80 μg g−1, comparable with the con-centrations in Lake Nylandssjön. Total organic content varies between 11%and 22% in Lake Nylandssjön, 8% - 12% in Lake Loppesjön and 4% - 10%in the Baltic Sea . Despite visual correlation between total iodine and organiccontent, only the data from Lake Nylandssjön permit estimation of a reliablecorrelation coefficient of r2 = 0.85.

22

0 5 10 15

0

5

10

15

20

25

30

Carbon content [%]

Dep

th [c

m]

0 2 4 6 8 Total iodine [ μg g−1]

Carbon, core 1Carbon, core 2T. iodine, core 3

(a) Lake Loppesjön

0 5 10 15 201940

1950

1960

1970

1980

1990

2000

2010

Carbon content [%]

Dep

th [y

ear]

0 10 20 30 40 50 60 70Total iodine [ μg g−1]

Total iodineCarbon


0 2 4 6 8 10

0

10

20

30

40

50

60

Carbon content [%]

0 20 40 60 800

10

20

30

40

50

60

Total iodine [ μg g−1]

Dep

th [c

m]

Carbon, core 1Carbon, core 2T. iodine, core1

(c) Baltic Sea

Figure 3.8: Total iodine and carbon contents in sediments from Swedish lakes andBaltic Sea.

23

3.4 AerosolsThe concentrations of total iodine in aerosols vary between 0.34 and 2.31 ngm−3 (median 0.58 ng m−3) in southern Sweden and between 0.14 and 0.49 ngm−3 (median 0.29 ng m−3) in northern Sweden. The data do no show anyclear temporal trends (Figure 3.9) considering the annual standard deviationof 0.45 ngm−3 and 0.1 ngm−3 for southern and northern Sweden respectively.

1985 1990 1995 20000

0.5

1

1.5

2

2.5

ng m

−3

Year

(a) Southern Sweden (Ljungbyhed)

1985 1990 1995 20000

0.1

0.2

0.3

0.4

0.5

ng m

−3

Year

(b) Northern Sweden (Kiruna)

Figure 3.9: Total iodine in aerosols in southern and northern Sweden

The concentrations of 129I in aerosols show a higher range in southern(4−203)×104 atoms m−3compared to northern (0.7−39)×104 atoms m−3Sweden (Figure 3.10). Despite differences in amplitude, mean annual concen-trations at the two sampling sites are correlated, r2 = 0.68.

1985 1990 1995 20000

50

100

150

200

250

Year

104 a

tom

s m

−3

WinterSummer


1985 1990 1995 20000

10

20

30

40

50

Year

104 a

tom

s m

−3


Figure 3.10: 129I in aerosols in southern and northern Sweden

Isotopic ratios of 129I/127I [atoms/atoms] varied between 1.3× 10−8 and23.9×10−8 (median 5.9×10−8) in southern Sweden and between 0.6×10−8and 7.1×10−8 (median 2.3×10−8) in northern Sweden (Figure 3.11).

24

1985 1990 1995 20000

5

10

15

20

25

30

129 I /

127 I 1

0−8 [a

tom

s/at

oms]

Year


1985 1990 1995 20000

1

2

3

4

5

6

7

8

9

129 I /

127 I 1

0−8 [a

tom

s/at

oms]

Year


Figure 3.11: 129I/127I ratios in aerosols at southern and northern Sweden

25

4. Modeling

The 129I distribution patterns in the lake sediment archives were used to nu-merically model the contributions of the different sources to the studied re-gions. Modeling of 129I fallout was accomplished by taking into account rela-tive influence from emission rates, possible transport pathways and the influ-ences of the lake system. Major sources of emission were considered to be: 1)Liquid and gaseous releases from the reprocessing facilities in Sellafield andLa Hague. The two facilities are here regarded as a single source, althoughdifferent modes of release form (gaseous or liquid) is addressed. 2) Falloutfrom the Chernobyl accident in 1986 and 3) Fallout from the nuclear weapontests during the late 1950s and early 1960s. A comprehensive description ofthe model is provided in Paper IV.Influences from the different sources are described by the vectors in Ta-

ble 4.1.

Model vector Description

Chern(t) Influences from the Chernobyl accident in 1986NW (t) Influences from the nuclear weapon tests in late

1950s and early 1960sG(t) Influences from gaseous emissions from the

facilities in Sellafield and La HagueLΣ (t) Influences from the cumulative liquid emissions

from the facilities in Sellafield and La Hague

Table 4.1: Description of model vectors

Chern(t) is defined as a single spike with height 1 at the year t = 1986and zero elsewhere, and NW (t) is proportional to the modeled fallout valuesfrom the nuclear weapon tests at the late 1950s and early 1960s in centralEurope [Reithmeier et al., 2006]. G(t) is proportional to the summed gaseousreleases from the facilities in Sellafield and La Hague, and LΣ (t) describes thecumulative liquid emissions in the English Channel/ Irish Sea /North Sea, andis defined as follows. Let L′ (t) [kg] designate the liquid release rate of 129Iin absolute amounts [kg] (Figure 5.2). The parameter tlag corresponds to thetime interval when the emissions from the reprocessing facilities are supposedto affect the sampling sites. Accordingly, the total amount of liquid 129I that

27

will impact the investigated area at time t is described as

L′Σ (t) =

∫ t

τ=t−tlagL′ (τ)dτ [kg]

The modeling vector LΣ (t) is proportional to L′Σ according to the normaliza-tion described below.Fallout at the sampling sites are described as a weighted sum of the normal-

ized vectors (LΣ (t),G(t),Chern(t),NW (t)) multiplied with the fallout con-stant φF129

Fallout (t) =

φF129 [wLLΣ (t)+wGG(t)+wChernChern(t)+wNWNW (t)] , (4.1)

with the conditions

wL +wG +wChern +wNW = 1

and∑tLΣ (t) =∑

tG(t) =∑

tChern(t) =∑

tNW (t) = 1

so that LΣ (t) =L′Σ (t)

∑t L′Σ (t) and so forth. With this definition, the weights (wL, wG,wCh and wNW ) designate the total contribution (as a fraction between 0 and 1)of 129I in fallout from a specific source during the measured time interval.Influences from the lake system are described with the convolution

Dep(t) = φIF×n

∑i=−m

(ai f allout (t− i)) (4.2)

where the sequence {ai}ni=−m denotes the impact of the lake system on 137Csor 129I, stretching over a time interval of (m+n+1) years. The constant φIF(impact factor) denotes the relation between 129I fallout and deposition intothe sediments. In case of 137Cs, the values of the coefficients {ai}ni=−m areproportional to the 137Cs sediment profile itself and are calculated as

ai =Dep137(1986+ i)∑τ Dep137(τ)

,

m = 1986−1942= 44n = 2006−1986= 20

(4.3)

The response function,Φfallout→ sed, for 129I (Figure 4.1 and 4.2) is assumedto follow 137Cs and is hence expressed on basis of the coefficients ai in equa-

28

tion (4.3) as

Dep129(t) = φ IF129 ×min(n,2006−t)

∑i=−m̃

ai Fallout129(t− i) =

φ IF129 φF129︸︷︷︸CAmp

×min(n,2006−t)

∑i=−m̃

ai [wLLΣ (t− i)+wGG(t− i)+

wChernChern(t− i)+wNWNW (t− i)] (4.4)

Because of assumed impact from the nuclear weapon tests, the sequence aiwas here truncated for i > m̃ = 16, representing an effect from the year 1969and earlier in the 137Cs profile, and again normalized.

−15−10−5051015200

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

i

a i

(a) Lake Nylandssjön and Lake Lehmilampi

−15−10−5051015200

0.02

0.04

0.06

0.08

0.1

i

a i

(b) Lake Loppesjön

Figure 4.1: 129I response functions for Lake Nylandssjön, Lake Lehmilampi and LakeLoppesjön.

The relation between deposition at the lake bottom and concentration insediment with steady state diagenesis is assumed to (137Cs or 129I)

Dep(t− x) =Conc(x,t)× acc(t− x)

dia(x)(4.5)

wheret Time of samplingx Depth measured in yearsacc(t− x) Dry mass accumulation ratedia(x) Diagenetic influenceDep(t− x) DepositionConc(x,t) Concentration

The model was applied to 129I profiles of lake sediments at Lake Nylandssjön,Lake Lehmilampi and Lake Loppesjön. In case of the latter sampling site

29

0 1 2 3 4 5 6 7 8 9 100

2

4

6

8

10

12

14

16

18

20

A

B

C

Dep

th [y

ears

]

[Arbitrary unit]

FalloutTotal responsIndividual responses

Figure 4.2: Illustration of how three hypothetical point releases (A, B and C) aredistributed in the sediment according to the response function for Lake Nylandssjön.

(Lake Loppesjön), a time lag ρ = 3 years related to processes in the lake sys-tem was incorporated into the model, according to the observed shift of∼1 cmbetween the 129I and 137Cs profiles [Englund et al., 2008], and equation (4.4)transforms to

Dep129(t+ρ) = φ IF129 ×min(n,2006−t)

∑i=−m̃

ai Fallout129(t− i)

In case of Lake Lehmilampi, which lacks a clear 137Cs time marker from theChernobyl accident, the response function is approximated with that of LakeNylandssjön. This is motivated by the similar conditions at the two lakes withrespect to lake and drainage areas and the fact that both lakes has laminatedsediments. The diagenetic behavior of 129I is approximated by that of carbon,Closs, in Lake Nylandssjön [Gälman et al., 2008] in all sampling sites accord-ing to

dia(t) = 1−1.21

100Closs (t), (4.6)

The cumulative effect of the liquid 129I releases, determined by tlag, wasconstrained to an upper limit of 3 years related to the transit times between thereprocessing facilities and the North Sea/Norwegian coast waters boundary.The model parameters, CAmp, tlag, wL, wChern and wNW (the fourth weight,

wG, comes from the condition wL +wG +wChern +wNW = 1), have been opti-mized to minimize the objective function Q =∑y ε2t , with the norm εt definedas

ε (t) = log (Dep129 (t)measured)− log(Dep129 (t)modeled)

in order to meet the criteria [Fletcher, 2000; Xu, 2001]• {ε (t)} is independent of {ε (t+ k)}, for any k≥ 1

30

• {ε (t)} has no trend component and constant variance when plotted againsteither Dep129 (t) or t

In addition to the above criteria, the set of {ε (t)} is also normally distributed(Kolgorov-Smirnoff test), which allows to infer standard deviations of themodel parameters. The optimization is performed by the interior-reflectiveNewton method [Coleman and Li, 1994; Coleman and Yuying, 1996] used inthe MATLABTM environment.

31

5. Discussion

The sample preparation method presented has proven to be reproducible andis independently validated. However, to achieve a high chemical yield, specialprecautions have been taken regarding the combustion. Stepwise heating, slowoxygen gas flow rate and continuous warming of the whole system to avoidcondensation were among the critical processing steps of significance.

0 20 40 60 80

1950

1960

1970

1980

1990

2000

106 atoms (cm2 y)−1

Yea

r

(a)

Measured depositionModeled depositionLiquid derived falloutGaseous derived fallout

(a) Lake Nylandssjön

0 20 40 60 80

1950

1960

1970

1980

1990

2000


Yea

r

(b)

(b) Lake Lehmilampi

0 50 100

1950

1960

1970

1980

1990

2000


Yea

r

(c)

(c) Lake Loppesjön

Figure 5.1: Modeled and measured 129I deposition in lake sediments from Swedenand Finland

Despite different geographical location, drainage areas, lake surface areasand precipitation rates between the sites (Table 2.1), there is a rather similarrange in the 129I deposited within the sediment for the period 1950 to 1986(Figure 5.1). The profile of the pre nuclear era (before 1950s) is shown in Lake

33

Loppesjön and Lake Nylandssjön. This period is characterized by close tonatural background 129I concentrations. At the beginning of the 1950s, the 129Iflux to the sediments increases indicating contributions from anthropogenicemissions related to the Sellafield facility (Figure 5.2) and from atmosphericnuclear bomb tests [Schink et al., 1995;Oktay et al., 2000]. A further increasereflecting emissions from La Hague facility is also marked at the late 1960s.

0 100 200 300 400

1950

1960

1970

1980

1990

2000

Yea

r

Liquid 129I emissions [kg]

SellafieldLa HaugeTotal

0 2 4 6 8 10Gaseous 129I emissions [kg]

Figure 5.2: Historical liquid and gaseous emissions from the reprocessing facilities inSellafield and La Hague.

The sharp increase in the 129I profile of both Lake Loppesjön and Lake Ny-landssjön during 1986 coincides with the Chernobyl accident. This pattern isnot observed in Lake Lehmilampi and thus clearly demonstrates the responseof the sediments to the varying intensity of the Chernobyl fallout over northEurope.Use of Chernobyl 137Cs distribution as a response function to model 129I de-

position seems to agree well with measured data. However, the mechanismsthat control 129I transport throughout the system (ocean/atmosphere/land) arenot directly described by the model parameterization. Accordingly, the mainoutcome of this approach is a quantification of the cumulative rather than in-dividual effects of each process.The positive correlation observed between 129I and carbon (r2 = 0.87) and

total iodine and carbon (r2 = 0.85), show that most of the 129I is associatedwith the organic material in the sediment. Despite these correlations the 129Iflux pattern cannot be explained by changes in the organic matter content, due

34

to the relatively much lower variation in the organic content (×2 difference)compared to 129I (×100 difference). The same argument can also be appliedto infer only small impact of diagenesis on the 129I flux pattern observed sincethe total iodine concentrations vary only by a factor of two (Figure 3.8).Post-Chernobyl 129I fluxes differ somewhat among the sites, (40− 60)×

106 atoms (cm2 y)−1 in Lake Nylandssjön, (60−80)×106 atoms (cm2 y)−1in Lake Loppesjön, and (20− 70)× 106 atoms (cm2 y)−1 in Lake Lehmil-ampi, without significant trend at the former two sites. The flux of 129I to thesediment depends on both dry and wet fallout of the isotope. Estimate of thewet 129I fallout was based on precipitation data from Uppsala (59◦ 51’ N,17◦ 38’ E) and Abisko (68◦ 21’ N, 18◦ 49’ E) [Persson, 2007]. The averageannual flux between 2001 and 2005 from precipitation data ranges between60×106 atoms (cm2 y)−1 and 30×106 atoms (cm2 y)−1, without significanttemporal trend. This implies that a major part of the 129I fluxes to the studiedsites is associated with wet fallout.

Lake Nylandssjön Lake Lehmilampi Lake Loppesjön

Liquid emissions 70±6% 71±18% 50±7%Gaseous emissions 16±7% 29±20% 28±9%Chernobyl accident 10±4% < 8% 21±6%Nuclear weapon tests 4±1% - 1±1%Liquid time delay (years) 1 l.b.∗∗ 3 u.b.∗ 1 l.b.∗∗∗ Upper boundary value∗∗ Lower boundary value

Table 5.1:Model outcome on the relative contributions of 129I from different sources,derived from the weights wL, wG, wCh and wNW in equation (4.1) and (4.4)

Modeled 129I deposition into the sediment archives at the three studied sites(Figure 5.1) depicts contribution from liquid emissions as the dominating fall-out source, accounting for 50% to 71% of the total inventories (Table 5.1). Atransfer rate of 129I from sea to atmosphere is derived for pertinent sea areas(English Channel, Irish Sea and North Sea) and is estimated at 0.04 to 0.21y−1. This range is higher than the 0.003 y−1to 0.01 y−1values previously de-rived by [Schnabel et al., 2001; Reithmeier et al., 2006] based on 127I. Thediscrepancy between the two estimates may be explained by different chemi-cal speciation of 129I and 127I and corresponding efficiency in sea-atmospheretransfer. A study of the surface waters in the North Sea clearly shows that 129Iand 127I occur in different chemical forms in the same water parcel [Hou et al.,2007].Dry deposition as well as washout of iodine is much dependent on the asso-

ciated particle size distribution. Estimating dry fallout based on average 129Iconcentrations in aerosols and using settling velocity within a range of 0.001m/s to 0.02 m/s [Baker et al., 2001], indicate values of (2−600)×105 atoms(cm2 y)−1and (5−900)×104 atoms (cm2 y)−1for southern and northern Swe-den respectively (during the years 1983 - 2000). In comparison with wet fall-

35

out during the period 2001 - 2005, which is estimated to 3×108 atoms (cm2

y)−1and 3× 107 atoms (cm2 y)−1for southern and northern Sweden respec-tively [Persson, 2007], the dry fallout constitutes at most 1/4 of the total 129Ifallout. However, the upper limit of the settling velocity (0.02 m s−1) reflectsparticles > 1μm in diameter, whereas the main atmospheric carrier of 129Iseems to be smaller particles [Wimschneider and Heumann, 1995; Vogt et al.,1999]. Hence, the contribution from dry fallout is relatively small, which isconsistent with the agreement between wet fallout and fluxes in sediment [Pa-per IV].There is a large difference in the concentration of both 129I and 127I in

aerosols with respect to the two samplings sites (Figure 3.9 and 3.10) wherethe higher values are found in southern Sweden. However, the difference iseven larger in the 129I values, ∼9 times, compared to ∼2 times in 127I con-centration. A possible explanation for this feature is the different distances tothe emission sources, regarding both the marine surface waters with high 129Iconcentrations and the reprocessing facilities (Sellafield and La Hague). Suchdifference in 127I concentration in the aerosol has also been observed in pre-cipitation [Persson, 2007]. The 129I/127I values in aerosols apparently followan increasing temporal trend during the years 1983-2000 (Figure 3.11) thatpartly reflect the liquid releases (Figure 5.2).The contribution of 129I atmospheric fallout to the Baltic Sea sediment is

negligible compared to the supply by sea current from the Kattegatt- Skager-rak [Aldahan et al., 2007b]. Accordingly, the lag time in the received liquidemissions to the studied sites in the Baltic Sea from the reprocessing facilitiesis expected to be considerably delayed in comparison to the releases occasion.This factor induces difficulties in linking the 129I trends found in the sedi-ments of the Baltic Sea with those of the lakes. Furthermore dilution of theChernobyl 129I contribution by the vast Baltic Sea basin may have caused therelatively weaker 129I signal in the sediments profiles compared to those ofthe lakes.

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6. Conclusions

The principal findings of this thesis are summarized as follows,

• A routine sample preparation procedure for extraction of 129I from smallamount (at mg level) of solid materials has been developed. The repro-ducibility and accuracy of the procedure were evaluated through measure-ments of international standard reference materials.

• The first documentation of anthropogenic 129I profiles in lake sedimentsfrom northern Europe and the Baltic Sea covering the last 80 years is pre-sented.

• Imprints of emissions from the nuclear fuel reprocessing facilities in Sell-afield (UK) and La Hague (France) are identified in the sediments since thestart of operation in 1952 and 1966 respectively.

• Signals of 129I introduced from the atmospheric nuclear weapon tests dur-ing the 1950s and 1960s are apparently mixed and overwhelmed in thestudied sediments by contributions from the reprocessing activity.

• The 129I associated with the Chernobyl accident is well identified in thesediments from the Swedish lakes, which are located in areas affected byhigh Chernobyl fallout. The Chernobyl 129I can also be traced in regionswith low fallout as shown by the sediment profiles from the Baltic Seaand Finland. The major pathway of 129I into the Baltic Sea goes throughcurrents from the North Sea and the associated liquid releases from thereprocessing facilities.

• Numerical modeling of the 129I deposition indicated that more than 50% ofthe total inventory of the lake sediments are related to the liquid emissionsfrom the reprocessing facilities. The modeling also reasonably simulatesthe contribution of the Chernobyl event to the total 129I flux.

• The novel time series from northern Europe on 129I in aerosols show aboutone order of magnitude higher concentration in northern Sweden comparedto southern Sweden. Estimate of 129I dry fallout based on the aerosol datasuggests <25% contribution of the total fallout.

• The distribution of 129I in the sediment archives demonstrates the potentialof the isotope as a new time marker for chronological and environmentalinvestigations.

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7. Acknowledgments

First of all, I want to thank my supervisors, Göran Possnert and Ala Aldahanfor supporting me in finishing this work. In particular, I want to express mygratitude for the intensive cooperation during the latest time, when both ofyou have spent a lot of time with me to achieve a satisfactory result. Göran,thanks for spending time listen to my ideas, and sharing your analytical skillswith me. Thanks Ala, for your enthusiasm, collaboration and response to allmy scientific writing stuff and also introducing a humoristic perspective of theworld of science.

I would like to express my gratitude to my co-authors Ingmar Renberg, Xi-aolin Hou and Timo Saarinen for a fruitful collaboration and constructivecomments.

Special thanks to Jan-Erik Wallin for the help with slicing sediments fromLake Nylandssjön.

Thanks Vasily, for introducing me to the laboratories at Geocentrum andÅngström, and for spending time on discussing my questions, despite thatyou had so many other things to do. Your friendly and never ending positiveattitude have encouraged me in my work.

I am also very thankful to you people who have supported me in all the prac-tical stuff concerning the experimental setup of the 129I extraction procedure.Thanks Inge, for constructing all my versions of the combustion furnaces.Sören, for helping me to improve the laboratory at Geocentrum, and Inger, forintroducing me to the chemical procedures concerning the 129I extraction.

Bengt and Rogerio, you have been excellent teachers at the tandem laboratory!

Thanks Susanna, my companion in the 129I research field, for great discussionsand being a nice friend.

I want to thank you all at the tandem laboratory and the Division of Ion Physicsfor nice company during my time here.

Thanks Geotryckeriet for the help with the printing of this thesis!

Finally, I want to thank my family for the encouragement during the years.

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8. Summary in Swedish

Allt sedan början av den nukleära tidsepoken, som startade under 1940-taletdå kärnvapenutvecklingen under andra världskriget initierades, har vår miljöbelastats med stora mängder radioaktivitet. 1950 och 1960-talen känneteck-nades av det kalla krigets kapprustning och ett antal atmosfäriska kärnvapen-testsprängningar utfördes som på ett dramatiskt sätt ökade radioaktiviteteni miljön främst i norra hemisfären. Under senare delen av 1900-talet är deti första hand den fredliga användningen av uran för energiproduktion i fis-sionsrektorer som dominerat bidragen av antropogen radioaktivitet, dels di-rekt genom utsläpp från reaktorbyggnaderna, dels indirekt vid hanteringen avdet utbrända reaktorbränslet. Av speciell betydelse är också haveriet i den sov-jetiska reaktorn i Tjernobyl 1986 eftersom utsläppet vid den händelsen är välkarakteriserat i både tid och rum.Den här avhandlingen är inriktad mot studier av den långlivade radioiso-

topen jod-129 (T1/2 = 15.7 miljoner år) som förekommer naturligt i mycketlåga koncentrationer till en följd av fission av uran i jordskorpan och kärnreak-tioner mellan den kosmiska strålningen och atmosfärens xenon. Idag har dockden mänskliga användningen av uran som kärnbränsle medfört att den naturli-ga förekomsten av jod-129 i stort sett är försumbar jämfört med den mängdsom introducerats i naturen från upparbetningen av kärnbränsle. De globaltsett mest relevanta utsläppskällorna i detta sammanhang är upparbetningsan-läggningarna i Sellafield (England) och La Hague (Frankrike) som togs i brukunder 1950 och 1960-talen. Merparten av det jod-129 som släppts ut är vätske-buren och utsläppen sker främst till Irländska sjön och Engelska kanalen (ca.5000 kg fram till 2006). En mindre del av den upparbetade aktiviteten avgesdirekt till atmosfären som gas (ca. 200 kg fram till 2006).Undersökningar av den stabila isotopen av jod (jod-127) som förekom-

mer i relativt stora mängder i havet visar att endast en liten del transporterasfrån havet till kontinenternas landområden via atmosfären och att inverkan avden biologiska aktiviteten hos alger och plankton i ytvattnet är av betydelse.Den biologiska påverkan tillsammans med att jod kan förekomma i ett antaletmöjliga oxidationstillstånd (-1 till +7) möjliggör en antal olika jodföreningar imiljön. Transportmekanismer och spridning av jod är därför komplicerad ochidag endast delvis kartlagd. Utöver den grundläggande geokemiska forsknin-gen om jod i miljön har bl.a. dess inverkan på klimatet i sambandmed nedbryt-ning av marknära ozon i atmosfären ägnats speciellt intresse, liksom dess pro-duktion av kondensationskärnor som har en central betydelse vid molnbild-ning.

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Det faktum att utsläppsfunktionerna av jod-129 är relativt kända ger en möj-lighet till en förbättrad förståelse av transportmekanismer för jod-129. Mer-parten av det globalt förekommande radioaktiva jod-129 återfinns i eller harpasserat Nordsjön. Detta innebär att undersökningar av förekomsten av ra-dioisotopen i norra Europa och inte minst Skandinavien har ett stort infor-mationsvärde vad gäller spridningen av jod-129 i miljön. Nedfall av jod-129 iEuropa har hittills undersökts främst genommätningar i nederbörd. Resultatenhar uppvisat en mycket hög varians från dag till dag. För att klarlägga bakom-liggande orsaker till denna variation krävs systematiska undersökningar avlängre tidsserier från de senaste 10 - 50 åren.Eftersom många av de naturliga långlivade kosmogena radionukliderna i

vår miljö, däribland även jod-129, förekommer i mycket låga isotopkocentra-tioner 10−7 till 10−17, krävs speciell mätteknik för att kunna detektera och ut-nyttja dessa som känsliga spårämnen. Acceleratormasspektrometrin (AMS) ären sådan ultrakänslig analysteknik för detektion av enskilda atomer i extremtlåga isotopkoncentrationer (> 10−16) som utnyttjats i de här presenteradestudierna av jod-129. Metoden har utvecklats ur forskning inom kärnfysikendär ett partikelacceleratorsystem utnyttjas som mätinstrument. Atomerna frånett prov joniseras, accelereras och separeras i elektriska och magnetiska fält,för att slutligen identifieras med hjälp av etablerade kärnfysiska detektions-metoder. Den grundläggande bakomliggande principen är således att enskildaatomer räknas direkt till skillnad mot den konventionella sönderfallsdetek-teringen som är beroende av radioaktiviteten och därmed mycket ineffektivför isotoper med långa halveringstider Den stora fördelen med AMS-metodenjämfört med den konventionella sönderfallsdetektionsmetoden är sammanfat-tningsvis att mycket små prover kan analyseras med relativt korta analystider.Det övergripande målet med denna studie är att öka förståelsen för sprid-

ning och transportmekanismer av jod-129.Mer specifikt så formulerades föl-jande delmål:

• att utveckla en metod för att extrahera jod-129 från fasta naturliga materialsom kan användas för analys med AMS-metoden.

• att bestämma koncentrationer av jod-129 i sjö- och marina sediment samti aerosoler för att rekonstruera isotopens nedfall över norra Europa under1900-talet.

Det första delmålet har uppnåtts genom utveckling av en reproducerbar ochkänslig förbränningsmetod som tillämpats och visats fungera på naturligaprover, och som kvalitetskontrollerats m.h.a. internationella referensmaterial.Metoden är anpassad för milligram-stora provmängder av fasta material, somär ett av kraven vid en undersökning av sedimentprover med årlig upplösning.Profiler av jod-129 i sedimentkärnor från tre sjöar, två i Sverige och en i

Finland, har mätts upp och använts för att återskapa en nedfallshistoria av jod-129 under 1900-talet. De olika källornas (atmosfäriska kärnvapentester, ut-släpp från upparbetningsanläggningarna, Tjernobylolyckan) inverkan har nu-

42

meriskt modellerats med hänsyn till storlek på utsläpp, transport i atmosfärenoch inverkan från sjösystemet. En förutsättning för en sådan rekonstruktionär att sedimentet kan dateras dvs. tilldelas en kronologi (djup-tidsaxel) ochatt det jod-129 som finns i sedimentet inte i någon större grad är mobilt efterdeponering. I två av sjöarna finns varviga avlagringar i sedimentet, dvs. attsediment som deponerats under olika årstider kan urskiljas genom färg- ochtexturförändringar. Här kan en tidsskala relativt enkelt erhållas enbart genomvisuell inspektion av kärnorna. Sediment från den tredje sjön har daterats medmetoder som använder sig av de radioaktiva isotoperna bly-210, caesium-137och kol-14 som förekommer i sedimentet.Profiler av jod-129 från två sedimentkärnor tagna från Östersjön har ock-

så mätts upp och undersökts. Dessa profiler återspeglar transport av jod-129 ihavsströmmar från Nordsjön-Västerhavet till Östersjön snarare än bidrag frånatmosfären och ger därmed speciell information angående vattenutbytet mel-lan Östersjön och Kattegat.Mätningar av jod-129 i aerosoler, samlade med luftfilter i norra och södra

Sverige, har utförts för utvalda tidpunkter under en 20-årsperiod. Då endastett fåtal liknande studier har presenterats för kortare tidsperioder från lokaleri Spanien och Tyskland är dessa data av stor betydelse vid förståelsen av denatmosfäriska transporten av jod-129. Resultaten visar på en storleksordninghögre koncentrationer i södra jämfört med norra Sverige och att merpartenav den totala atmosfäriska jod-129 depositionen hänför sig till nederbörden(> 75%) snarare än till torr partikulär deposition.De numeriska beräkningar som presenteras i denna studie skiljer sig från

tidigare uppskattningar som utgår ifrån mätningar i regn eller teoretiskaresonemang baserat på studier av stabilt jod. Den centrala slutsatsenbeträffande ursprunget till jod-129 nedfallet över Skandinavien och Finlandär att största delen (50% - 70%) är relaterat till de vätskeburna marinautsläppen av jod-129 från upparbetningsanläggningarna i Sellafield och LaHague.

43

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Acta Universitatis UpsaliensisDigital Comprehensive Summaries of Uppsala Dissertationsfrom the Faculty of Science and Technology 448

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A doctoral dissertation from the Faculty of Science andTechnology, Uppsala University, is usually a summary of anumber of papers. A few copies of the complete dissertationare kept at major Swedish research libraries, while thesummary alone is distributed internationally through theseries Digital Comprehensive Summaries of UppsalaDissertations from the Faculty of Science and Technology.(Prior to January, 2005, the series was published under thetitle “Comprehensive Summaries of Uppsala Dissertationsfrom the Faculty of Science and Technology”.)

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