129I/127I as a new environmental tracer or geochronometer for biogeochemical or hydrodynamic processes in the hydrosphere and geosphere: the central role of organo-iodine

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Abstract

Iodine is a biophilic element, with several short-lived isotopes (e.g. 131I, t1/2=8 days), one long-lived isotope, 129I (t1/2=15.6 million years) and one stable isotope, 127I. The inventory of 129I in surface environments has been overwhelmed by anthropogenic releases over the past 50 years. Iodine and its isotopes are important for a number of reasons: (1) The largest fraction of the short-term and long-term dose from accidental releases and fallout from atomic bomb tests was from iodine isotopes. (2) 129I is one of the two long-lived nuclides with highest mobility in stored radioactive waste. (3) 129I could provide the scientific community with a new geochemical tracer and new geochronological applications in environmental science. (4) A better assessment of iodine deficiency disorders, mineralization in exploration geochemistry, and the transfer of volatile organic greenhouse-active and ozone-destroying iodine species from the oceans to the atmosphere is needed. One of the most promising future applications for the 129I/127I ratio is not only as a new geochronometer, but also as a new source tracer for terrestrial organic matter with ages of 50 years or less. This is especially attractive, since radiocarbon can be, at times, an ambiguous chronometer for the 50-year time-scale, whereas 129I concentrations during this time are overwhelming previous levels by orders of magnitude. Iodine is to a significant extent involved in the cycle of organic matter in all surface environments. Its biophilic nature is demonstrated by a relative enrichment of iodine in seaweed and dissolved macromolecular organic matter. Because of the close coupling of iodine and organic carbon cycles, our understanding of the underlying molecular mechanisms of the processes regulating iodination reactions in aquatic systems is still limited. The binding of iodine by organic matter has the potential to modify the transport, bioavailability and transfer of iodine isotopes to man. Equilibration times for 129I in many reservoirs are likely long enough that 129I could be used as a new source tracer for organic matter of terrestrial origin, and as a geochronometer. Current tracer applications of 129I are limited by our knowledge of the effects of UV-radiation, microbial activity and geochemical redox conditions on organo-I compounds and overall iodine speciation. The biogeochemical behavior of iodine and its isotopes appears to be different in North America and European waters, possibly due to climatic, source and speciation differences.

Introduction

Iodine is a biophilic element with several short-lived isotopes (e.g. 131I, with t1/2 of 8 days), one long-lived isotope, 129I (t1/2=15.6 million years) and one stable isotope, 127I. 129I is an emitter of low energetic beta, gamma and X-rays, and measured most accurately by accelerator mass spectrometry (AMS) (e.g. Fehn et al., 1986), but in the past, was also determined by neutron activation analysis (NAA) (e.g. Hou et al., 2000). A better understanding of the biogeochemistry of iodine and its isotopes in the environment is important for iodine deficiency disorders, mineralization in exploration geochemistry, migration of radionuclides from the nuclear industry and the transfer of volatile organic greenhouse-active and ozone-destroying iodine species from the oceans to the atmosphere.

129I: The inventory of natural 129I from cosmic ray-induced spallation of Xe in the atmosphere and spontaneous fission of 238U in the earth's crust is ∼100–260 kg (Fabryka-Martin et al., 1985). Atmospheric bomb testing (1945–1970s) added approximately 50–150 kg to this inventory (USA: approx. 4 kg) (UNSCEAR, 1982, Raisbeck et al., 1995, Eisenbud and Gesell, 1997); while the Chernobyl reactor accident (1986) contributed only ∼1.3 kg (Paul et al., 1987). The atmospheric releases by Hanford (1944–1972) added ∼260 kg (Hanford website, cited in Schnabel et al., 2001). Fuel reprocessing from France (La Hague) and England (Sellafield), however, exceeds all these sources, having provided ∼2600 kg (460 Ci) to the ocean (Raisbeck and Yiou, 1999, Schnabel et al., 2001), and about ∼6 kg/year to the atmosphere between 1991 and 1996 (Schnabel et al., 2001). As is evident from Fig. 1, the nuclear fuel reprocessing discharges to the ocean have increased greatly over the past decade (Raisbeck and Yiou, 1999), while releases to the atmosphere have remained nearly constant (Szidat et al., 2000, Schnabel et al., 2001).

The most important documented sources of 129I have been and still are La Hague and Sellafield;, however, other 129I sources, such as those from the former Soviet Union, have also been identified. Estimated 129I fluxes in the Siberian rivers, Ob and Yenisei, which drain former nuclear-weapons-test sites, amount to less than 0.3 kg/year (Cochran et al., 2000, Moran et al., 2002), but are considerably higher than 129I fluxes in other European and US rivers (Table 1).

These sources of artificial 129I are important for several reasons: (1) The largest fraction of the short-term and long-term dose from accidental releases and fallout from atomic bomb tests was from iodine isotopes. If all the 2500 Ci of 129I produced by the nuclear power industry up to year 2000 would disseminate in the environment, the collective dose equivalent to the world's population will be large, approximately 108 person-thyroid rem (106 person-thyroid Sv) (Eisenbud and Gesell, 1997). (2) 129I is one of the two (the other is 99Tc) long-lived nuclides with highest mobility in stored radioactive waste (Eisenbud and Gesell, 1997). (3) 129I could provide the scientific community with a new geochemical tracer and geochronometer.

Because the atmospheric residence time of emitted iodine species is about 2 weeks, it can easily travel around the globe. In fact, anthropogenic 129I from reprocessing releases is currently found in rainwater (Moran et al., 1999a, Moran et al., 1999b, Lopez-Gutierrez et al., 2000) and river water of the Northern Hemisphere (Schink et al., 1995a, Oktay et al., 2001, Moran et al., 2002), not only in Western Europe, but also in the USA, where known atmospheric releases currently are negligible, as well as in the Southern Hemisphere (Fehn and Snyder, 2000).

127I: Reasons for studying the biogeochemical cycling of 127I in the environment include iodine deficiency disorders, mineralization in exploration geochemistry and the transfer of volatile organic greenhouse-active and ozone-destroying iodine species from the oceans to the atmosphere. Atmospheric and terrestrial sources of 127I (Fig. 2) are aerosols formed from the sea spray (inorganic iodide or iodate (Heumann, 1993) or from the emission of volatile organic iodine (VOI) compounds (Kolb, 2002, O'Dowd et al., 2002, Baker, 2002, Baker et al., 2000). Bacteria and phytoplankton are thought to convert the most thermodynamically stable form of iodine in the sea, iodate (IO3) to iodide (I). In turn, macroalgae and seaweed use I in the production of alkyl iodides or VOI, which are thought be emitted as a defense mechanism. The VOI in the surface oceanic microlayer are easily photolyzed into reactive iodine species. The most important of the VOI are CH2I2, CH2BrI and CH2ClI, each of which are found at the boundary layer in concentrations up to 1 ppt, with photolytic lifetimes of 5 min, 45 min and 10 h, respectively (Stutz, 2000). Even more significant is the VOI species CH3I, which is found in concentrations of 1–30 ppt (Stutz, 2000) and has the longest photolytic span of approximately 14–18 days (Moran et al., 1999a, Moran et al., 1999b). Once photolyzed, the VOI form a reactive pool of iodine oxides, i.e. HOI, I2O2, IO2, which either form condensable vapors as nuclei for aerosols, or which react with ozone (Kolb, 2002, O'Dowd et al., 2002), or perhaps cycle as short-term intermediates which re-form VOI, predominantly as CH3I.

It has also been suggested that at the sea surface microlayer, ultraviolet radiation causes formation of ozone and peroxide, which are strong enough oxidants to abiotically form the reactive intermediates HOI and I2 (Luther et al., 1995, Wong, 1991). These products in turn would be reduced back to I, form organic iodine species or be volatilized to the atmosphere as CH3I, HOI and I2 (Luther et al., 1995).

Median concentration levels of 127I in environmental reservoirs, determined mostly by ICP-MS, are 10–200 nM in freshwaters (Oktay et al., 2001, Moran et al., 2002, Schwehr and Santschi, 2003), ∼600 nM in seawater (Schwehr and Santschi, 2003, and references therein), and 30–400 pmole m−3 in the atmosphere (Table 2); earlier results of 127I concentrations are likely low by a factor of approximately 2, as they did not quantitatively include organo-iodine in their determination of total iodine concentrations. Assessments of organo-iodine quantitation found discrepancies of up to 40% (Wong and Cheng, 2001) or higher (Schwehr, 2003), depending on methods.

For 129I, ranges in concentrations in aquatic systems are even larger. 105–109 atoms l−1 in freshwaters (summarized in Snyder and Fehn, 2003), 105–1012 atoms l−1 in seawater (higher values calculated from seaweed; data summarized in Raisbeck and Yiou, 1999), 106–1010 atoms m−3 and 106–1010 atoms l−1 in the atmosphere or rainwater, respectively, depending on location (Tsukada et al., 1991, Lopez-Gutierrez et al., 1999, Moran et al., 1999a, Moran et al., 1999b, Szidat et al., 2000, Schnabel et al., 2001, and references therein). Problems of organo-iodine-129 determination might be similar to those of 127I.

Chemical Speciation of Iodine isotopes: New applications for using 129I/127I ratios as a source tracer or as a geochronometer will require a better understanding of the chemical speciation, i.e. I, IO3, and especially, organo-iodine, for both 129I and 127I. Chemical speciation schemes for both fresh and marine waters have only recently been reported (Krupp and Aumann, 1999, Hou et al., 2001, Wong and Cheng, 2001, Farrenkopf and Luther, 2002, Schwehr and Santschi, 2003). Organo-iodine species can be expected to be important, based on the biophilic nature of iodine. Indeed, in oxic surface water on land and in the ocean, organo-iodine species have been found to be important (Fig. 3; Schwehr and Santschi, 2003). For these oceanic water samples, our total inorganic iodine (TII) values corresponded very closely to salinity-corrected total iodine (TI) values of other investigators (Schwehr and Santschi, 2003), thus demonstrating the difficulties of accurately assessing DOI values. In groundwaters where the near-surface soils retain colloidal organo-iodine species, however, DOI is likely the least important species, while the most mobile species is expected to be iodide (Santschi et al., 1999, Schwehr et al., 2003).

Interactions between water and soil, however, play a key role in the terrestrial iodine cycle. This is the most complex, and least well studied part of the cycle. The chemical forms of iodine in soils and soil water are especially poorly known, but have great bearing on retention vs. mobility of both stable I and 129I.

129I: 129Iodine released to atmosphere from nuclear fuel reprocessing facilities at La Hague and Sellafield is thought to be in the form of CH3I, which is relatively inert enough (or repeatedly cycles through photolytically-formed reactive intermediates back to CH3I) that it may be transported globally in the troposphere within approximately 14 days (Moran et al., 1999a, Moran et al., 1999b). In this form it may even be long lived enough to be transported to the stratosphere (Wayne et al., 1995). Within the troposphere the chemistry may involve complex cycling due to photolysis and reactions with atmospheric volatile active radicals, i.e. peroxides, hydroxides, ozone, activated oxygen, which form iodine oxides. It is here that we note that both iodine isotopes are following similar chemical pathways, although the concentrations of total 129I are much lower than those of 127I.

127I: Iodine in the atmosphere occurs in both gaseous and particulate (bound to aerosols) forms. While there is no study documenting the speciation of radioiodine in the atmosphere, that of 127I is reasonably well documented (Table 2). Data given in Table 2 show that the organic iodine fraction is an important reservoir. For example, Yoshida and Muramatsu (1995) and Baker et al. (2000) emphasize that almost 75–90% of the atmospheric iodine is in a gaseous form, in which the largest pool is organic.

In aquatic systems (including rain water), very few studies have used reliable procedures to determine the total iodine concentration including organo-iodine. In the absence of certified aquatic standard reference materials, only when using ICP-MS can we be certain that the total concentration is accurately measured. Recently, Schwehr and Santschi (2003) have presented a speciation scheme for iodine in aquatic samples that relies on HPLC measurements that have been compared to ICP-MS for total iodine determination. It is likely that many past iodine measurements have only quantified the inorganic speciation and concentrations of iodine, with uncertain results for organo-iodine concentrations. The main reason is likely that most methods rely on oxidation methods to decompose organic iodine compounds, such as UV irradiation, H2O2 or NaClO. However, such methods are also known to iodinate phenolic compounds or amino acids contained in natural organic matter. This practice illuminates the need for further studies of the biogeochemistry of iodine in the environment.

What is currently known about the chemical and physical behavior of iodine isotopes in two contrasting continents, North America and Western Europe, can be summarized as follows:

  • 1

    The atmospheric flux of 129I in Western Europe is ∼3×1012 at m−2 per year (approx. 760 g/year) (Schnabel et al., 2001), compared to a much smaller flux of approximately 1×1010 at m−2 per year (30 g/year) (Moran et al., 2002) to the contiguous USA (Fig. 4).

  • 2

    As a consequence of the transfer of 129I and 127I from air to water to soil to rivers to groundwater, and the longer time 127I had to equilibrate in environmental reservoirs, the present-day 129I/127I ratios in both USA and Western Europe decrease in the direction from rainwater>surface water>near-surface groundwater (Lopez-Gutierrez et al., 2000, Szidat et al., 2000, Schnabel et al., 2001, Buraglio et al., 2001, Moran et al., 2002, Schwehr et al., 2003). 127I concentrations generally decrease from seawater (approx. 600 nM)>freshwater (approx. 10–200 nM)>rainwater (approx. 20 nM).

  • 3

    129I concentrations in rainwater are higher than in river water in Western Europe due to iodine removal in soils and high local atmospheric source input. 129I concentrations in rain of USA, however, are much lower than in river water due to evapotranspirative concentration processes in catchments (Moran et al., 2002, Oktay et al., 2001).

  • 4

    In USA, 129I from bomb fallout still mainly resides in soils, while 129I in rivers is likely from reprocessing sources. In contrast, in Western Europe both sources of 129I reside mainly in soils. Positive correlations between 129I concentrations and chloride and DOC, DON or total phosphate concentrations in Swedish rivers suggest that 129I in rivers is from both atmospheric sources as well as from soil erosion (Kekli et al., 2003).

  • 5

    129I in European groundwater decreases, as expected, with water residence time of 1 day to 2 years. In USA, 129I concentrations decrease from surface to groundwater due to retention of macromolecular organic iodine, but increase in ground waters with water residence time of 0.1–7 years. The mechanism for this striking difference between European and USA groundwater is probably due to the more inert behavior of the predominant 129I species in USA rivers and semi-arid soils (see Fig. 5).

  • 6

    In the surface environment, it appears that there are contrasting physico–chemical responses in iodine isotopic behavior, e.g. 129I vs. 127I, and also different speciation behavior between 129I from bomb fallout (more reactive iodine) and 129I from nuclear fuel reprocessing (less reactive iodine) (Oktay et al., 2000, Oktay et al., 2001).

  • 7

    129I (Smith et al., 1998, Cooper et al., 1998, Cooper et al., 2002) and other radioisotopes (e.g. Baskaran et al., 1995, Baskaran et al., 1996) in Russian Arctic waters are mainly from the European reprocessing plants of La Hague and Sellafield. However, the amounts of 129I carried by the Ob River to the Arctic Ocean, due to releases from nuclear facilities in its drainage basin, are some of the highest of any world river (Table 1).

If certain conditions are met, 129I could be used as a new environmental radioactive tracer, i.e. as a process proxy or analogue. These conditions include: (1) 129I must trace a single environmental process with a defined time scale. (2) 129I must be equilibrated with the stable isotope, 127I. If not equilibrated, the extent to which this is the case needs to be defined. (3) The predominant chemical species of 129I and their geochemical properties must be known. These conditions appear to be met in some studies, where the different iodine species and isotopes have all similar properties (i.e. soluble and mobile), are equilibrated or have defined geochemical properties. 129I looks promising as a tracer for recent North Atlantic water and ocean mixing (Fig. 6), sedimentation (Fig. 7, Oktay et al., 2000), evapotranspiration (ET) in a large watershed (Fig. 8, Oktay et al., 2001), and as a tracer and dating tool of spreading of infiltrating river water in the near-surface infiltration zone (Fig. 5, Santschi et al., 1999, Schwehr et al., 2003).

One of the most promising future applications for the 129I/127I ratio is as a new source tracer and geochronometer for terrestrial organic matter with ages of 50 years or less. This is especially attractive, since radiocarbon can be, at times, an ambiguous chronometer for the 50-year time-scale, whereas 129I concentrations during this time are overwhelming previous levels by orders of magnitude.

Because Iodine has a 40 000 year mean oceanic residence time, and thus behaves almost ‘conservatively’ (Wong, 1991), it can be used as an oceanographic mixing tracer in the Northern Hemisphere (summarized in Raisbeck and Yiou, 1999) and to distinguish the contributions of different downwelling regions in the North Atlantic Ocean (e.g. Santschi et al., 1996) or large rivers in the Arctic Ocean. 129I is even moving with currents from the Northern to the Southern Hemisphere, where it has been recently detected as well (Fehn and Snyder, 2000). Despite its long mean residence in the ocean, from which one would expect that little 129I had been transferred from the surface ocean to underlying sediments, 129I has indeed been detected in ocean margin sediments (Fehn et al., 1986). In another study by Oktay et al. (2000), the presence of 129I and the profile of 129I/127I ratios in Mississippi delta sediments (Oktay et al., 2000) has been ascribed to close-in tropospheric particle-bound fallout, because of low 240Pu/239Pu ratios in that core, and 129I/127I ratios closely tracking 239,240Pu and 137Cs nuclides, without exhibiting any extra mobility. It should thus be possible to date North American aquatic sediments using iodine isotope ratios.

The behavior of 129I in other environmental archives is, however, not as straightforward, especially in Europe, as recent results have shown that 129I in glacier ice showed progressively increasing inputs rather than a bomb peak (see Fig. 9; Wagner et al., 1996), enhanced mobility of 129I in tree rings (Hauschild and Aumann, 1985, Rao et al., 2002), and significant offsets in 129I/127I ratios between bovine thyroids and vegetation or soils (e.g. Frechou et al., 2002).

While 129I profiles in European environmental archives, such as alpine glaciers (Wagner et al., 1996) or coastal sediments (Lopez-Gutierrez et al., 2000) are mainly marked by atmospheric nuclear fuel reprocessing emissions (Fig. 1), this is not the case in the USA. In the USA 129I from bomb fallout is likely of equal importance to the reprocessing signal. This is evident from a comparison of the 129I inventory in an undisturbed soil core of Marlin, TX, with that expected from bomb fallout (Santschi and Moran, Fig. 10, unpublished results).

The 129I inventory in the Marlin (TX) soil core is approximately 1×108 at/cm2, which is very similar to the inventory in the Mississippi river delta sediment core of Oktay et al. (2000). If extrapolated to the area of the contiguous USA, it would amount to a total of 2 kg of 129I, which compares favorably to approximately 4 kg from bomb fallout deposited over the USA. In many locales, regardless of soil type, climate or vegetation, one observes that there is a rapid decrease in 129I concentration with depth, such that a major fraction of the 129I inventory is found in the top 10 cm.

Iodine is to a significant extent involved in the cycle of organic matter in the surface environment. The biophilic nature of iodine is demonstrated by a high enrichment factor of 5×105 to 106 l/kg (Schink et al., 1995a, Hou et al., 1997, Oktay et al., 2001) in the environment, leading to high concentrations not only in seaweed (20–250 ppm) but also in detrital macromolecular organic matter (Oktay et al., 2001). Large fractions of 127I and 129I were found to be associated with organic matter in fresh, estuarine and surface ocean water (Krupp and Aumann, 1999, Szidat, 2000, Oktay et al., 2001, Schwehr and Santschi, 2003).

Mechanisms of iodination of organic matter: Iodination of organic matter can be accomplished in the laboratory by electrophilic substitution of benzene ring, phenol or alkenes by I+ (or H2OI+). These iodine species are produced by promoters such as hydrogen peroxide, H2O2 or CuCl2 (creates Cu+), chloramines or ICl (creates I+ and Cl). Also, iodine reacts in the laboratory with alpha-methylcarbonyl, which involves the initial conversion of the alpha-methylcarbonyl to the enol. The enol then reacts with IOH. Enolization of the alpha-methylcarbonyl is promoted by both H+ and OH.

In environmental systems, much less is known about iodination of natural organic matter. While it had been shown that humic matter could be iodinated by extracellular peroxidases, the exact mechanisms could not be unequivocally elucidated, as the reactions appeared to be only partly reversible at low, environmentally relevant concentrations of iodide (Christiansen and Carlsen, 1991). In seaweed, the majority of iodine appears to be in proteins (Hou et al., 2000). In humic acids, the majority of iodine appears to be in methoxy-phenols (Warner et al., 2000). In river water, the majority of I appears to end up in refractory high molecular weight organic matter after ∼2 months of exposure to I. Transitory low molecular weight organic matter species, however, occurred over the course of 1–2 months, especially when exposed to bacterial cultures (Rädlinger and Heumann, 2000).

While kelps and other algae can contain up to 90% of iodine in a water-soluble form, mainly as iodine ions, 5–37% can be present as organic iodine, of which approximately 50% can be in the form of iodo-amino acids (Hou et al., 1997). In Sargassum and Laminaria sp. thyroxin and triiodothyronine as well as monoidotyrosine and diiodotyrosine, have been found with monoidotyrosine levels reaching up to 0.1% dry weight of Sargassum (Nisizawa, 1979). Studies of Pacific seaweeds suggest that the mechanism of iodine enrichment is different for various algae and that its bioavailability also varies. The mechanisms by which seaweeds concentrate, store or use iodine from seawater are not well understood.

Macroalgae and phytoplankton produce volatile halogenated substances, such as iodomethane, diiodomethane, chloroiodomethane, propyl iodide or butyl iodide in the ocean (Schall et al., 1997). However, these volatile species are generally present at concentrations of considerably less than a few ng/l. Therefore, even though these species are important atmospheric gases exerting some control on climate and ozone layer, they constitute much less than 1 permil of the total iodine in seawater. According to Schall et al. (1997), the concentration of volatile organic iodine species do not relate well to chlorophyll a concentration, while those of organic bromine do. This might be due to the greater sensitivity of organo-iodine species to UV light transformation reactions.

Photochemical decomposition of dissolved organic iodine (DOI) in seawater has been shown to produce iodide (Wong and Cheng, 2001, Schwehr and Santschi, 2003). However, UV irradiation can also produce new organo-iodine species (e.g. Schwehr and Santschi, 2003). Photochemical processes can directly (photolyses) or indirectly (through radical formation) influence iodine speciation and transport. The photochemical formation of hydrogen peroxide (Zika et al., 1985) for example likely promotes the iodination of organic matter. While some organic iodine compounds in aquatic systems are likely destroyed by photolyses, others are newly formed upon UV radiation. While UV oxidation of natural water samples does not appear to totally destroy organo-iodine species, these species are, however, totally decomposed when using dehydrohalogenation (Schwehr and Santschi, 2003). Photochemical processes can be expected to have numerous effects on the speciation and transport of iodine within aquatic systems but also between the ocean and the atmosphere (e.g. Stutz, 2000, Kolb, 2002, O'Dowd et al., 2002). Our understanding of these processes is still very limited.

Section snippets

Conclusions

Research of interdisciplinary nature is recommended in the following areas:

  • 1

    Kinetics of equilibration with 127I and transformations of 129I: Our knowledge of the speciation and transport of 129I and 127I, which reflects differences in equilibration times within environmental archives, needs to be greatly improved. 129I appears to undergo a number of biological and physical transformations potentially changing from an organic to an inorganic form (or vice versa) several times. Over time scales of

Acknowledgements

We gratefully acknowledge the constructive reviews of Christoph Schnabel, who also provided the updated figure for the paper, and the financial support of the Texas Institute of Oceanography (TIO) and the Texas Water Research Institute (TWRI).

References (65)

  • G. Krupp et al.

    Iodine-129 in rainfall over Germany

    J Environ Radioact

    (1999)
  • J.M. Lopez-Gutierrez et al.

    Determination of 129I in atmospheric samples by accelerator mass spectrometry

    Appl Radiat Isot

    (1999)
  • J.M. Lopez-Gutierrez et al.

    129I/127I ratios and 129I concentrations in a recent sea sediment core and in rainwater from Sevilla (Spain) by AMS

    Nucl Instrum Methods Phys Res B

    (2000)
  • S.D. Oktay et al.

    The 129Iodine bomb pulse recorded in Mississippi river delta sediments: results from isotopes of I, Pu, Cs, Pb and C

    Geochim Cosmochim Acta

    (2000)
  • M. Paul et al.

    Measurement of 129I concentrations in the environment after the Chernobyl reactor accident

    Nucl Instrum Methods Phys Res, B

    (1987)
  • G.M. Raisbeck et al.

    129I in the oceans: origins and applications

    Sci Total Environ

    (1999)
  • G.M. Raisbeck et al.

    129I from nuclear fuel reprocessing facilities at Sellafield (UK) and La Hague (France): potential as an oceanographic tracer

    J Mar Syst

    (1995)
  • P.H. Santschi et al.

    Evidence for elevated levels of Iodine-129 in the deep western boundary current in the middle Atlantic Bight

    Deep-Sea Res I

    (1996)
  • D.R. Schink et al.

    Prospects for ‘Iodine-129’ dating of marine organic matter using AMS

    Nucl Instrum Methods Phys Res B

    (1995)
  • D.R. Schink et al.

    129I in Gulf of Mexico waters

    Earth Planet Sci Lett

    (1995)
  • K.A. Schwehr et al.

    A sensitive determination of iodide species in fresh and sea water samples, including organo-iodine, using high performance liquid chromotography and spectrophotometric detection

    Anal Chim Acta

    (2003)
  • J.N. Smith et al.

    129I and 137Cs tracer measurements in the Arctic Ocean

    Deep-Sea Res I

    (1998)
  • S. Szidat et al.

    Iodine-129: sample preparation, quality control and analyses of pre-nuclear materials and of natural waters from Lower Saxony, Germany

    Nucl Instrum Methods Phys Res B

    (2000)
  • H. Tsukada et al.

    Particle-size distributions of atmospheric I-129 and I-127 aerosols

    Atmos Environ

    (1991)
  • M.J.M. Wagner et al.

    Increase of 129I in the environment

    Nucl Instrum Methods Phys Res B

    (1996)
  • G.T.F. Wong et al.

    The formation of iodide in inshore waters from the photochemical decomposition of dissolved organic iodine

    Mar Chem

    (2001)
  • R.G. Zika et al.

    Spatial and temporal variations of hydrogen peroxide in Gulf of Mexico waters

    Geochim Cosmochim Acta

    (1985)
  • Baker AR. Air–sea exchange of iodine. Sch Environ Sci, University of East Anglia, United Kingdom, 2002; URL:...
  • T.M. Beasley et al.

    36Cl and 129I in the Yenisei, Kolyma and Mackenzie rivers

    Environment

    (1997)
  • N. Buraglio et al.

    129I from the nuclear reprocessing facilities traced in precipitation and runoff in Northern Europe

    Environ Sci Technol

    (2001)
  • Butler. Ph.D. Dissertation, University of Rhode Island, RI,...
  • J.V. Christiansen et al.

    Enzymatically controlled iodination reactions in the terrestial environment

    Radiochim Acta

    (1991)
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