Journal of Nuclear and Radiochemical Sciences, Vol. 9, No.1, pp. 13-18, 2008

Seasonal Variation of Iron Speciation in a Pearl-Raising Bay Sediment by Mössbauer
Spectroscopy
Akihito Kuno,*,a Motoyuki Matsuo,a Satoshi Chiba,b and Yoichi YamagatacaGraduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan
Faculty of Environmental and Information Sciences, Yokkaichi University, Kayouchou, Yokkaichi, Mie 5128512, JapancFisheries Research Division, Mie Prefectural Science and Technology Promotion Center, Agochou, Shima, Mie
519-3602, Japanb

Received: December 27, 2007; In Final Form: January 25, 2008
Ago Bay in Mie Prefecture, central Japan, is world-famous for the site of Mikimoto pearl culture, but recently the
production of pearls has considerably declined. Environmental deterioration of the bay is suspected of having
caused the decline. The periodic investigation into iron speciation of the bay sediment by 57Fe Mössbauer spectroscopy revealed its high pyrite (FeS2) content from the surface to the 20-cm depth. The pyrite in the surface
sediment decreased only in spring, three months after the dissolved oxygen in the bottom water was at maximum.
Such oxygen-consuming material as pyrite accumulated through long-term biotic activity is a most-likely explanation for the prolonged environmental deterioration of the bay, which appears in the high chemical oxygen demand(COD) of the sediment.

1. Introduction
Ago Bay in Ise-Shima National Park, central Japan (Figure1), is one of almost-enclosed bays that have been endangeredby human’s economic activities and therefore have collectedmuch attention in environmental studies.1-3 The bay is famous
for the cultivation of pearl oysters, Pinctada fucata, because itis the place where Kokichi Mikimoto started the artificial culture of pearls in 1890, and the pearl culture has continued formore than 100 years. However, mass mortality of the oysters
has often occurred in this bay.4 Even though the bay’s narrow
channel to the open sea keeps high waves off the rafts for cultivation, it makes the seawater change sluggish and accelerates
the water shifting toward under reducing condition.5 Organic
matter loading from the pearl culture to the water system further enhances reducing condition; feces of the pearl oysters andsewage from shell washing contain substantial amounts of

Sea ofJapanorganic matter, which promptly settles down onto the sediment.
Thirty thousand people live in the water catchment area of Ago
Bay and their domestic wastewater is another source of organic
matter. Thus it is highly plausible that the released organic
matter has broken the natural balance between its input andoutput. Harmful phytoplankton blooms called red tides havecaused serious social problems and heavy damage to fisheries
throughout the world.6 Such algal blooms are often blamed oncoastal pollution and eutrophication. Ago Bay has sufferedfrequent outbreaks of red tides.7
Tategami-ura is located in the inner part of Ago Bay (Figure1). Chemical oxygen demand (COD) of the surface sedimentcollected at Tategami-ura (water depth of 10 m) in August has
gradually increased since the annual measurement began in
1981 (Figure 2).8 A linear regression gives an increase rate of
2.12 mg g–1 year–1, and now the COD greatly exceeds 30 mg g–1,
the regulation limit for aquaculture. The COD of the surface

34°18’N

Tategami-ura

Ago Bay

Takonobori

Japan

Pacific
Ocean

34°15’N
136°46’E

136°49’E

Figure 1. Sampling locations in Ago Bay, central Japan.
*Corresponding author. E-mail: kuno@dolphin.c.u-tokyo.ac.jp.
Fax: +81-3-5454-6566© 2008 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 02/25/2008

Kuno

J. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008
29

80

28

COD/mg g

-1

70

27

60
50

26

40

25

30
20

24

10

102

23
2004

2002

2000

1998

1996

1994

1992

1990

1988

1986

1984

1982

1980

1978

1976

0

Relative intensity/%90

Average T in August/°C

14High-spin Fe(II)High-spin Fe(III)Low-spin Fe(II)

101
100
99
98
97
96
95
-10

-8

-6

-4

-2

0

2

4

6

8

10

-1

Velocity/mm s

Year

Figure 2. Time series of the average atmospheric temperature inAugust and the dry weight-based COD of the surface sediment collected at Tategami-ura and Takonobori. The COD was also measured
in August and lacked in 1986, 1988, 1991, and 1992. The averagetemperature in August was measured in Minami-Ise, adjacent to AgoBay. Open circles, COD at Tategami-ura; solid circles, COD at
Takonobori; solid diamonds, average temperature in August.

Figure 3. Mössbauer spectrum of the sediment collected from adepth of 0-0.5 cm at Tategami-ura on May 19, 2005. This was measured at 293 K. The guidelines at the top of spectrum show the positions of detected three doublets ascribable to paramagnetic high-spin
Fe(II), paramagnetic high-spin Fe(III), and diamagnetic low-spin
Fe(II) that corresponds to pyrite (FeS2). The dots are observed data,
and the solid line is the fit curve.

sediment collected at Takonobori (water depth of 25 m),located in the central part of Ago Bay, has not increased so
sharply. The production of pearls reached a peak in 1960s andhas decreased due to environmental deterioration, depression
on pearl markets, etc. The present annual production dropped
to less than 10,000 kg, about 20% of its maximum. In spite ofthe decreasing production of pearls, the COD of the surface
sediment in the inner bay has been increasing. On the other
hand, the average atmospheric temperature in August hasslightly increased with a rate of 0.035 °C year–1 while the timeseries COD also shows a similar increasing trend but one-yeardelayed cycles (Figure 2). The increasing trend in temperature
would be due to global warming. The correlation between
COD and temperature thus found may be best explained by thefact that increasing temperature more promotes biological production of organic matter. But why was the response of COD
delayed by one year? Is this delay the reason why the COD has
been still increasing despite smaller organic matter loading
than before?
To answer these questions, we have periodically investigatedthe vertical distribution of iron species in the sediments by 57Fe
Mössbauer spectroscopy. Mössbauer spectroscopy is one of
the most useful, nondestructive means for determining chemical states of iron and has been applied to the characterizationof a wide variety of environmental and geochemical samples.9,10

trometer using a 1.11 GBq 57Co/Rh source at 293 K and 78 K.
The curve fitting of the resulting spectra was performed with apersonal computer, assuming that the spectra were composedof peaks with Lorentzian line shapes. Half-widths and peakareas within each quadrupole doublet were constrained to beequal. Isomer shifts were expressed with respect to the centroid of the spectrum of metallic iron foil. Pyrite (FeS2) peak
positions were constrained (using values of δ = 0.307 mm s–1,
∆E Q = 0.610 mm s –1 at 293 K and δ = 0.405 mm s –1, ∆E Q =0.629 mm s–1 at 78 K) as in Manning and Ash,11 since the peak
positions of paramagnetic high-spin Fe3+ and pyrite containing
diamagnetic low-spin Fe2+ are in very close proximity. In addition to the measurements in the velocity range of –10.00 to
10.00 mm s –1, the spectra were also measured in the velocity
range of –3.33 to 3.33 mm s–1 for a better resolution. The total
iron contents of the sediments were determined by atomic
absorption spectrometry (AAS) after acid digestion.

2. Experimental
2.1. Sampling. Vertical sediment cores of about 10 cm inlength were collected at two stations every other month fromMay 2005 until May 2006. Tategami-ura is located in the innerpart of Ago Bay and Takonobori in the central part. At
Tategami-ura, the sample collection was continued until July
2007. The sediment cores were sometimes ca. 20 cm long.
The collected samples were cut at 0.5–2 cm intervals and porewater was extracted from the sediment by a pressure-filtration
technique (5 atm, N2).
2.2. Mössbauer Spectroscopy. Approximately 300 mg ofeach pressure-filtered sample was mounted in a sample holder(16 mm in diameter, 1 mm thick). Absorbers thus prepared
contained 5 mg cm–2 of Fe, a quantity low enough so to allow
relative peak areas to be used as a measure of the distributionof the corresponding Fe-bearing compounds. In order to avoid
air oxidation, the pressure-filtered sediments were purged withnitrogen gas in oxygen-impenetrable plastic bags. The spectra
were measured with an Austin Science S-600 Mössbauer spec-

3. Results and Discussion
Sediment cores were collected at Tategami-ura and
Takonobori every two months from May 2005 until July 2007
and May 2006, respectively. First, the 57Fe Mössbauer spectraof the sediments were measured in the velocity range of –10.00
to 10.00 mm s –1 at 293 K, and no significant magnetic sextet
was detected (Figure 3). The spectra measured at 78 K did notshow any sextet either, which indicates that the sediments did
not contain fine particles showing a doublet at 293 K and a sextet at 78 K by a superparamagnetic effect.12 Then, the samples
were measured in the velocity range of –3.33 to 3.33 mm s–1 fora better spectral resolution. Their Mössbauer spectra consistedof three doublets: one for paramagnetic high-spin Fe(III), paramagnetic high-spin Fe(II), and diamagnetic low-spin Fe(II)that corresponds to pyrite (FeS2). Table 1 lists the relative peakareas of iron components in the sediment cores. The paramagnetic high-spin Fe(III) would come from clay minerals andhydrated ferric oxides.13 The paramagnetic high-spin Fe(II) is
ascribable to clay minerals such as chlorite.14,15 Although vertical sediment cores of about 20 cm in length were sometimes
collected, the iron speciation in the sediment from a depth of
20 cm was not so different from that from a depth of 10 cm.
The relative distribution of iron components approximately
corresponds to the absolute distribution in this case because thetotal iron content of the sediment was almost constant throughout the core. The distribution of iron components did notchange vertically so much. In spring, however, pyrite decreasedin the near-surface sediment at Tategami-ura (Figure 4). The

Seasonal Variation of Iron Speciation in a Pearl-Raising Bay SedimentJ. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008

15

TABLE 1: Relative peak areas of iron components in the sediment cores collected at Tategami-ura and Takonobori in AgoBay

0.0-0.5
1.0-1.5
3-4
8-10

Paramagnetic
Fe(III)/%
49.6
45.3
36.1
39.7

Paramagnetic
Fe(II)/%
39.0
36.5
34.4
34.0

Jul 7, 2005

0.0-0.5
1.0-1.5
3-4
8-10

33.4
38.2
41.5
34.2

41.2
37.3
30.1
32.3

25.4
24.5
28.4
33.5

Sep 21, 2005

0.0-0.5
1.0-1.5
3-4
8-10

39.4
39.3
36.0
36.1

31.4
32.5
27.6
32.9

29.2
28.2
36.4
31.0

Dec 14, 2005

0.0-0.5
1.0-1.5
3-4
8-10

35.9
34.1
39.2
35.8

36.6
32.5
29.1
27.9

27.5
33.4
31.7
36.3

Jan 17, 2006

0.0-0.5
1.0-1.5
3-4
8-10

36.9
44.2
42.5
38.7

36.1
34.5
29.5
29.3

27.0
21.3
28.0
32.0

Apr 20, 2006

0.0-0.5
1.0-1.5
3-4
8-10
20-22

43.8
45.9
38.2
36.0
32.1

38.2
28.2
31.4
29.8
38.0

18.0
25.9
30.4
34.2
29.9

May 29, 2006

0.0-0.5
1.0-1.5
3-4
8-10

41.3
48.2
38.9
30.6

35.3
32.2
30.7
33.5

23.4
19.6
30.4
35.9

Jul 13, 2006

0.0-0.5
1.0-1.5
3-4
8-10
20-22

32.0
41.7
40.5
31.3
43.1

39.9
33.5
29.7
29.3
36.0

28.1
24.8
29.8
39.4
20.9

Sep 7, 2006

0.0-0.5
1.0-1.5
3-4
8-10
20-22

34.5
35.6
30.8
38.0
39.1

38.2
39.8
31.1
33.8
37.6

27.3
24.6
38.1
28.2
23.3

Nov 9, 2006

0.0-0.5
1.0-1.5
3-4
8-10
20-22

41.0
41.7
42.1
42.4
35.0

38.2
38.5
32.4
31.1
38.6

20.8
19.8
25.5
26.5
26.4

Jan 17, 2007

0.0-0.5
1.0-1.5
3-4
8-10
20-22

44.3
37.1
38.2
38.1
32.3

30.6
30.3
28.2
33.6
36.0

25.1
32.5
33.6
28.3
31.7

Mar 7, 2007

0.0-0.5
1.0-1.5
3-4
8-10
20-22

48.3
36.6
39.3
36.5
36.6

33.2
34.6
31.1
32.2
36.9

18.5
28.8
29.6
31.3
26.5

Site

Date

Depth/cm

Tategami-ura

May 19, 2005

Pyrite/%
11.4
18.2
29.4
26.3

16

Kuno

J. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008

TABLE 1: Continued

0.0-0.5
1.0-1.5
3-4
8-10
20-22
30-32

Paramagnetic
Fe(III)/%
47.3
41.4
36.0
33.4
42.8
49.4

Paramagnetic
Fe(II)/%
35.6
35.1
33.0
33.7
37.6
36.8

Jul 19, 2007

0.0-0.5
1.0-1.5
3-4
8-10
20-22

39.7
39.1
34.0
34.6
35.8

35.8
37.9
32.4
30.3
38.3

24.5
23.0
33.6
35.1
25.9

May 19, 2005

0.0-0.5
1.0-1.5
3-4
6-8

37.5
37.3
39.4
36.6

55.5
52.6
52.6
52.2

7.0
10.1
8.0
11.2

Jul 7, 2005

0.0-0.5
1.0-1.5
3-4
8-10

46.3
38.3
29.5
33.3

51.9
53.9
55.4
51.0

1.8
7.8
15.1
15.7

Sep 21, 2005

0.0-0.5
1.0-1.5
3-4
8-10

42.4
43.0
40.9
39.3

51.7
51.4
48.7
51.5

5.9
5.6
10.4
9.2

Dec 14, 2005

0.0-0.5
1.0-1.5
3-4
6-7

40.1
35.3
40.4
32.3

52.2
51.5
52.0
51.7

7.7
13.2
7.6
16.0

Jan 24, 2006

0.0-0.5
1.0-1.5
3-4
8-10

34.2
45.3
39.2
36.3

52.4
42.0
51.2
51.0

13.4
12.7
9.6
12.7

Apr 5, 2006

0.0-0.5
1.0-1.5
3-4
8-10

38.5
40.7
42.0
30.9

53.6
50.4
53.1
51.0

7.9
8.9
4.9
18.1

May 29, 2006

0.0-0.5
1.0-1.5
3-4
8-10

37.5
33.4
42.9
39.7

53.5
50.7
52.8
50.9

9.0
15.9
4.3
9.4

Site

Date

Depth/cm

Tategami-ura

May 23, 2007

Takonobori

paramagnetic high-spin Fe(III) varied complementarily topyrite and, therefore, would be converted to pyrite. Pyrite at
Takonobori was less abundant (Figure 5) than at Tategami-ura.
In contrast, the paramagnetic high-spin Fe(II) was more abundant at Takonobori. Since the total iron contents of the
Tategami-ura sediments were greater than those of the
Takonobori sediments, both the pyrite and paramagnetic highspin Fe(III) contents of the Tategami-ura sediments were also
greater than those of the Takonobori sediments. The difference in the total iron contents would be due to the geologicaldifference. The geology of this area mainly consists of eroded
sedimentary rocks of the late Cretaceous accretionary complex,
and the sand gravel layer after the late Pleistocene is observedat planation surfaces around the inner bay. Another possible
explanation is the difference in sedimentation environment
between the inner and central parts of the bay.
The Ago Bay Watch System has been monitoring the water

Pyrite/%
17.1
23.5
31.0
32.9
19.6
13.8

quality such as dissolved oxygen (DO) since 2003. These
parameters are automatically recorded every one-hour at fivestations within the bay and are accessible through the Web.16
The Tategami-ura and Takonobori monitoring stations arelocated at 34°17.642’N, 136°49.895’E and 34°17.098’N,
136°47.459’E, respectively. DO of the bottom water at
Tategami-ura decreases in summer due to thermal stratification(Figure 6), resulting in oxygen-deficient water mass on the seafloor through bacterial digestion of organic matter in the sediment.17,18 Red tides often occur when heating creates a
stratified surface layer above colder, nutrient-rich waters.6 The
dissolved oxygen in the bottom water of Takonobori showed asimilar seasonal variation, and therefore only that of Tategamiura is shown in Figure 6 for brevity’s sake. Pyrite in the surface sediment at Tategami-ura increased with decreasing DOin summer but did not decrease in autumn when the DO in thebottom water increased again. Decrease in pyrite became

Seasonal Variation of Iron Speciation in a Pearl-Raising Bay Sediment

Relative content/%
0

60
0

1

1

2

2

3

3

4

4

6

7

7

8

8

9

9

10

10

10

12

5

14

0
2005

2006
Month and year

Ratio of pyrite/%

10

Jul

15

May

8

Jan

20

Mar

25

6

No v

4

Jul

30

Sep

2

May

35

Jan

0

May

obvious only in spring because it is rather chemically stable
and slowly degrades.19 The pyrite slightly decreased in
November 2006 but got back to a high content in January 2007in spite of the increasing DO. The total iron content of thesediment did not change seasonally so much. Therefore, theabsolute abundance of pyrite showed similar seasonal variation
to its relative abundance.
The pyrite at Takonobori in the central bay did not showmuch seasonal variation. The COD of the surface sediment at
Takonobori was also lower than that at Tategami-ura (Figure2), which suggests a relation to its lower pyrite content. The
pearl culture has shifted from the inner bay to the central bay
with increasing deterioration in the inner bay. Therefore, a difference in accumulation of organic matter is likely to bring thedifference in the COD and pyrite content between Tategamiura and Takonobori. The maximum production of pearls in
1960s has provided much organic matter to the sediment in the
inner part of Ago Bay. The recent utilization of tough ropes forthe cultivation rafts enabled a mass exodus of pearl oysters to
the central bay with relatively high waves. However, the environment of the central bay would also be deteriorated in several
years if much organic matter is accumulated in the sediment of
the central bay.
During summer, thermal stratification interrupts the supply
of dissolved oxygen to the bottom water and sulfate ion fromseawater is reduced to hydrogen sulfide, which reacts with ironcompounds to form iron sulfides in the sediment.20 Iron sulfides thus produced consist of acid-volatile sulfides (AVS) andpyrite. 21, 2 2 Pyrite is chemically more stable than AVS.
Therefore, pyrite is inclined to more remain in the surface sedi-

Figure 5. Vertical distribution of iron components in the sedimentcore collected at Takonobori on May 19, 2005. Circles, pyrite; triangles, paramagnetic high-spin Fe(II); squares, paramagnetic high-spin
Fe(III).

-1

Figure 4. Vertical distribution of iron components in the sedimentcore collected at Tategami-ura on May 19, 2005. Circles, pyrite; triangles, paramagnetic high-spin Fe(II); squares, paramagnetic highspin Fe(III).

60

40

5

Mar

6

20

N ov

5

Depth/cm

0

Jul

40

Sep

20

Relative content/%

Dissolved oxygen/mg L

Depth/cm

017

J. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008

2007

Figure 6. Time series of the dissolved oxygen in the bottom water ofTategami-ura and the ratios of pyrite in the surface sediment collected at Tategami-ura and Takonobori from May 2005 until July
2007. The sediment at Takonobori was collected until May 2006. The
dissolved oxygen was automatically measured and recorded every
one hour. The left ordinate is shown upside down for an easy comparison because less dissolved oxygen favors the production of pyrite.
Open circles, ratio of pyrite at Tategami-ura; solid circles, ratio of
pyrite at Takonobori; solid line, dissolved oxygen.

ment than AVS, thus carried forward to the next year eventhough vertical circulation of seawater resumes in winter.
These findings were obtained by both the periodic investigation into iron speciation of the sediment and the continuous
monitoring of dissolved oxygen. The pyrite accumulated inthis way is one of the major reasons for the fact that the COD

18

J. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008of the sediment has been increasing even though organic matter loading has been decreasing. Generally, environmental
deterioration often persists after discharges from human activities are reduced (e.g., chlorofluorocarbons). The COD of thesediment in the inner part of Ago Bay is one of such examples.
It may gradually decrease in the future but may take time. Ago
Bay is one of enclosed coastal seas where much organic matterhas been discharged onto the seafloor sludge for many years.
In the future, similar phenomena may occur in other embayments that receive continuous loading of reducing materials
such as organic matter. Therefore, the prolonged environmental deterioration of Ago Bay is not only a crisis in the pearl
production but also a future threat to many people living
around enclosed coastal seas. The iron compounds in the sediment fix hydrogen sulfide and reduced sulfur compounds inthe form of iron sulfides. In other words, the iron compounds
suppress a much release of hydrogen sulfide that threatens thehealth of living organisms and is responsible for malodor.23
Further investigations and continued effort are necessary forthe remediation of the deteriorated environment.
4. Conclusion
By means of Mössbauer spectroscopy, the vertical distribution of iron species in the sediments collected from two stations in Ago Bay was clarified, and its seasonal variation wasinvestigated through periodic sampling. Three doublets ascribable to paramagnetic high-spin Fe(III), paramagnetic high-spin
Fe(II), and diamagnetic low-spin Fe(II) that corresponds topyrite were separated in their spectra. The pyrite in the surface
sediment of the inner bay decreased only in spring, threemonths after the dissolved oxygen in the bottom water was at
maximum. The delay would be caused by the stability of pyrite
and may be related to the prolonged environmental deterioration of the bay. Mössbauer spectroscopy was thus successfully
applied to the environmental monitoring of a bay with highorganic matter loading in order to elucidate the seasonal variation of iron speciation in the sediments.
Acknowledgements. We are indebted to Professor B.
Takano for constructive comments. This study was partly supported by the Mie Prefecture Collaboration of Regional Entities
for the Advancement of Technological Excellence.
References(1) H. S. Jensen, P. B. Mortensen, F. Ø. Andersen, E.

Kuno
Rasmussen, and A. Jensen, Limnol. Oceanogr. 40, 908(1995).
(2) M. M. Jensen, B. Thamdrup, S. Rysgaard, M. Holmer, and
H. Fossing, Biogeochemistry 65, 295 (2003).
(3) R. N. Glud, J. K. Gundersen, H. Røy, and B. B. Jørgensen,
Limnol. Oceanogr. 48, 1265 (2003).
(4) K. Nagai, Y. Matsuyama, T. Uchida, M. Yamaguchi, M.
Ishimura, A. Nishimura, S. Akamatsu, and T. Honjo,
Aquaculture 144, 149 (1996).
(5) S. Chiba, H. Okumura, T. Nishikawa, and Y. Yamagata,
Yokkaichi Univ. J. Environ. Inf. Sci. 8, 39 (2004).
(6) D. M. Anderson, Sci. Am. 271 (Aug), 62 (1994).
(7) T. Horiguchi, Phycol. Res. 43, 129 (1995).
(8) Council for Provision of Marine Pollution in Ago Bay,
Annual Report of Council for Provision of Marine Pollution
in Ago Bay (Council for Provision of Marine Pollution in
Ago Bay, Shima, 1976-2006).
(9) T. Tominaga and Y. Minai, Nucl. Sci. Appl. 1 , 749 (1984).
(10) A. Kuno, M. Matsuo, Q. Wang, and C. J. Zhang, Hyperfine
Interact. 166, 637 (2005).
(11) P. G. Manning and L. A. Ash, Can. Miner. 17, 111 (1979).
(12) W. Kündig, H. Bömmel, G. Constabaris, and R. H.
Lindquist, Phys. Rev. 142, 327 (1966).
(13) P. G. Manning, J. D. H. Williams, M. N. Charlton, L. A.
Ash, and T. Birchall, Nature 280, 134 (1979).
(14) M. Matsuo, T. Kobayashi, and M. Tsurumi, Hyperfine
Interact. 84, 533 (1994).
(15) I. König and R. Hollatz, Hyperfine Interact. 57, 2245
(1990).
(16) Mie Industry and Enterprise Support Center, Ago Bay
Watch System (http://www.agobay.jp/).
(17) H. Kawahata, M. Inoue, M. Nohara, and A. Suzuki, J.
Oceanogr. 62, 405 (2006).
(18) S. M. Libes, An Introduction to Marine Biogeochemistry,
John Wiley & Sons, New York, 1992.
(19) R. A. Berner, Early Diagenesis, Princeton Univ. Press,
Princeton, 1980.
(20) A. Kuno, M. Matsuo, and B. Takano, Hyperfine Interact.
C3, 328 (1998).
(21) C. Gagnon, A. Mucci, and É. Pelletier, Geochim.
Cosmochim. Acta 59, 2663 (1995).
(22) B. J. Presley and J. H. Trefry, Chemistry and
Biogeochemistry of Estuaries, Eds. E. Olausson and I.
Cato, John Wiley & Sons, New York, 1980, p 187.
(23) M. Matsuo, M. Kawakami, and K. Sugimori, Hyperfine
Interact. 126, 53 (2000).