Journal of Nuclear and Radiochemical Sciences, Vol. 10, No. 2, pp. 1-5, 2009

ArticlesRadioactivity of 137Cs in Papers and Migration of the Nuclide in the Environment
Asaya Kobashi*
Department of Chemistry, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033,
Japan
Received: March 16, 2009; In Final Form: September 1, 2009
The 137Cs contents of papers such as magazines and newspapers printed in Japan were determined by gamma-ray
spectrometry. The average 137Cs content of weekly general interest magazines was 0.95 Bq kg-1 and far higher thanthose of other kinds of samples. The result of phloroglucinol color test showed that the main printed pages of theweekly general interest magazines were chiefly made of mechanical pulp. Possibly the pages held 137Cs brought bywood, raw material of paper, and that accounted for the high 137Cs content of the magazines. The experimental
result suggested that 137Cs was removed from wood into aqueous solution in the production of chemical pulp.
Cesium-137 radioactivity removed during paper manufacturing in the year 2000 in Japan was estimated to be 15
GBq, and the influence of paper manufacturing on the migration of 137Cs in the environment was discussed.

1. Introduction
In the previous researches1-4 the author analyzed naturally
occurring radionuclides (226Ra, 228Ra, 228Th, and 40K) and a fallout nuclide 137Cs (half-life 30.07 y) in papers such as books,
magazines, and newspapers and elucidated the radioactivity
levels and the sources of the nuclides in the samples.
A large amount of paper are produced, consumed, discarded,
and recycled in developed countries. In Japan, 3.11×1010 kg of
paper and paperboard was produced, and 1.88×1010 kg of waste
paper was recycled in the year 2006.5 Raw materials of paper,
paper, and waste paper migrate in the environment with theseprocesses. As a result, radionuclides contained in the raw
materials, paper, and waste paper also migrate in the environment with the processes.
The author1-3 has shown that the source of 137Cs contained in
papers is plants used as raw material of pulp. Cesium-137 ispresent in the environment mainly as a product of nuclear
weapon tests. A part of the 137Cs is taken in plants and thenincorporated into paper making, discarding, and recycling processes. How the radionuclide behaves in the environment withthe processes is not clear at all. The analysis of 137Cs in various
paper samples may give a clue to the elucidation of the behavior of the nuclide. In this article, the author reports the resultof measurement of 137Cs radioactivity in paper samples and discusses the influence of paper manufacturing on the migrationof 137Cs in the environment.
2. Experimental
2.1. Sample description. Pocket-sized books, weekly photomagazines, magazines full of color pages, weekly general interest magazines, weekly comic magazines, and newspapers
printed between 1999 and 2000 in Japan were examined in thiswork. Printing papers, copying papers, and notebooks soldbetween 1999 and 2000 in Japan were also examined in thiswork. The details of the samples are as follows:(A) Pocket-sized book. The samples were pocket-sized books
issued from five different large publishing companies. The
jacket covers were removed, and so the samples were made up
of printed pages and a cover. The weight percentage of printed*Corresponding author. E-mail: kobashi@chem.s.u-tokyo.ac.jp

pages ranged from 97 to 98%.
(B) Weekly photo magazine. The samples were weekly or
biweekly magazines with a large circulation from different four
publishing companies. They were composed of a cover andphoto pages made of coated paper printed in a single color ormany colors.
(C) Magazine full of color pages. The samples were monthly
magazines published from different publishing companies.
They were mainly made of coated paper printed in many colors.
(D) Weekly general interest magazine. The samples wereweekly general interest magazines with a large circulation fromfour different large publishing companies. They consisted of acover, pages printed in many colors, monochrome photo pages(coated paper was used for the above parts), and main printed
pages made of low-grade paper. The proportions of the above
four parts were similar among the four samples. The weightpercentage of the main printed pages ranged between 55 and
63%.
(E) Weekly comic magazine. The samples were four weekly
comic magazines for boys with a large circulation from different publishing companies. They consisted of a cover, pages
printed in many colors (coated paper was used for the above
two parts), and main printed pages made of low-grade paper.
The proportions of the three parts were similar among the four
samples. The weight percentage of the main printed pages
ranged from 95 to 96%.
(F) Printing paper. The samples were two kinds of printing
paper prepared by different paper manufacturers.
(G) Copying paper. The samples were three kinds of PPC
paper prepared by different paper manufacturers.
(H) Notebook. The samples were four kinds of notebooks
made by different companies. Three of them were ordinary
notebooks with a thin cover whereas the other was a loose-leaf
notebook without a cover.
(I) Newspaper. The samples were three newspapers issued
from major newspaper publishing companies.
2.2. Gamma-ray spectrometry. The size of each sample
was adjusted to 210 mm long, 150 mm wide, and 30 mm thickby cutting and stacking the paper sheets forming the sample.
In case of a sample which was composed of different kinds ofpaper, the paper sheets of different kinds were arranged to beuniformly distributed in the sample. The samples were sealed© 2009 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 11/11/2009

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KobashiJ. Nucl. Radiochem. Sci., Vol. 10, No. 2, 2009

in two nylon bags to prevent contamination of the gamma-ray
spectrometer used for the measurement.
Gamma-ray spectrometry was made by using a Canberra
GC-series gamma-ray spectrometer equipped with a pure germanium detector of effective volume of 100 cm 3 and a 4096
channel pulse-height analyzer. The detector was placed in ashielding box made up of layers of 50-mm lead, 50-mm copper,and 2-mm acrylic resin. The spectrometer was placed in a wellventilated, air conditioned room to ensure low backgroundcounts. For each sample, measurement was made for 3 days.
Cesium-137 was determined by the intensity of 662 keVgamma-rays. The details of the method were described in theprevious paper.3 The 137Cs analysis was carried out simultaneously with the analysis of naturally occurring radionuclides.
The results of analysis of naturally occurring radionuclides
were reported in the author’s other article.4
2.3. Phloroglucinol color test. Paper is mainly made ofpulp. More than 99% of papermaking pulp has been preparedfrom wood for 50 years in Japan. The major components ofwood are cellulose, hemicellulose, and lignin. Cellulose andhemicellulose are fibrous materials, whereas lignin not. Woodalso contains inorganic constituents, resin and so on as minor
components.
Papermaking pulps are classified into mechanical pulp andchemical pulp according to their preparation method.
Mechanical pulp is prepared by grinding wood by a machine.
On the other hand, chemical pulp is prepared by cooking woodin aqueous solution such as NaS-NaOH mixture solution andthen by eliminating lignin and other useless constituents chemically to obtain fibrous component. However, there are intermediate pulps between mechanical pulp and chemical pulp,
and there are papers which are prepared by mixing mechanicalpulp and chemical pulp. Phloroglucinol reacts with lignin anddyes it reddish purple, and the reagent is used to detect lignin
in paper and to estimate lignin content of paper.6 The test using
the reagent is not a quantitative method but makes it possible toknow the extent of purification of pulp.

Except for the printing paper, copying paper, and newspaper
samples, more than one kind of paper were used for the samples tested in this work. Each sample was divided after the
gamma-ray spectrometry into parts based on the difference of
paper used for the parts. The weight of each part was measured, and the weight percentage of each part was calculated.
A piece of paper was cut from each part. Each part was
assumed to be uniform in chemical composition, and the piece
cut from it was assumed to be representative of the whole part.
A drop of phloroglucinol solution was placed on the piece, andthe degree of reddish purple coloration was checked. The
details of the phloroglucinol color test were described in theprevious paper.1 The intensities of reddish purple color of thetested pieces were mutually compared by naked eyes. The
intensity varied from dark reddish purple to colorless, and it
was possible to classify the tested pieces into six groups
depending on the color intensity. Based on the result of thecomparison, the lignin content of each part was evaluated to be
one of the six levels as follows: very high, high, medium, low,
very low, and not detected.
3. Results and Discussion
3.1. Cesium-137 contents of the paper samples. The resultof gamma-ray spectrometry is shown in Figure 1. The 137Cs
contents were corrected for the decay to January 1, 2000. The
errors in the 137Cs contents shown in the figure are standard
deviations estimated on the counting statistics.
As shown in Figure 1, 137Cs is detected in the weekly generalinterest magazines, weekly comic magazines, and newspapers,
whereas the radionuclide is not detected in the other kinds ofsamples. The average concentrations of the weekly generalinterest magazines, weekly comic magazines, and newspapers
are respectively 0.95, 0.06, and 0.11 Bq kg-1. It is evident thatthe weekly general interest magazines contain far more 137Cs
than the other kinds of samples.
As already mentioned, most of pulp have been preparedfrom wood for many years in Japan. It is reasonable to assume

2.5
Cs-137

Cs-137 content (Bq/kg)

2

1.5

1

0.5

0

-0.5
A1 A2 A3 A4 A5 B1 B2 B3 B4 C1 C2 C3 D1 D2 D3 D4 E1 E2 E3 E4 F1 F2 G1 G2 G3 H1 H2 H3 H4 I1 I2 I3

Sample number
Figure 1. Concentration of 137Cs in paper samples. Kinds of samples are as follows: A, pocket-sized book; B, weekly photo magazine; C, magazine full of color pages; D, weekly general interest magazine; E, weekly comic magazine; F, printing paper; G, copying paper; H, notebook; I,
newspaper. The 137Cs concentrations have been decay corrected to January 1, 2000.

Radioactivity of 137Cs in Papers and Migration of the Nuclide

J. Nucl. Radiochem. Sci., Vol. 10, No. 2, 2009that the raw material for pulp of the paper samples tested inthis work is wood. Several works7-10 were done to investigate
137
Cs concentration in rings of trees that experienced the timeof fallout due to nuclear weapon tests. The data of the works
are summarized in Table 1. As shown in Table 1, the 137Cs content depends on the species of trees and the localities of trees.
The 137Cs content of whole wood of each tree was estimated byaveraging the 137 Cs contents of all the tree rings, and theobtained value was corrected for the decay to January 1, 2000.
The result of the estimation is also shown in Table 1. As canbe seen from Table 1, the 137Cs content of whole wood varies
from 0.01 to 4.1 Bq kg-1, and the average of all the 137Cs contents of whole wood is 0.88 Bq kg-1. The 137Cs contents of theweekly general interest magazines examined in this work arecomparable to the average 137Cs content of whole wood thus
obtained.
The remarkable difference in 137Cs concentration between
the weekly general interest magazines and the other kinds ofsamples can be interpreted as follows: the greater part of 137Cs
brought by material wood remained in the weekly generalinterest magazines while the nuclide was little left in the otherkinds of samples.

wood because it is made simply by grounding wood. On theother hand, almost no 137Cs will remain in chemical pulp, especially in high-grade chemical pulp, because chemical pulp is
prepared by eliminating lignin and other useless constituentsfrom wood in aqueous solution to obtain pure fibrous material.
Therefore, the lignin content of paper is a good measure of137
Cs left in pulp and paper.
Another important factor affecting 137Cs radioactivity left inpaper is deinking process in recycling paper. Deinked pulp is
produced by taking waste paper apart in aqueous solution andremoving ink from the waste paper chemically. Deinking is akind of chemical treatment, and 137Cs will be lost from thewaste paper owing to the treatment. In the deinking process, asmall proportion of ink inevitably remains in pulp as flakes
adhered to pulp fibers. Therefore, flakes of residual ink arecharacteristic of deinked pulp.
The result of the phloroglucinol color test is shown in Figure
2. As seen from Figure 2, a part exhibiting high or very highlignin content is present in each of weekly general interest
magazines (D1-D4). The part is the main printed pages of themagazines. Evidently the pages are chiefly made of mechanical pulp. The pages were observed by a microscope to examine
the presence of flakes of residual ink. Such flakes were notfound in the pages, showing that the pages are chiefly made ofvirgin mechanical pulp. Therefore, the main printed pages
hold most of 137Cs brought by wood. Because the proportionsof the main printed pages are more than a half (55-63%), the137
Cs contents of the weekly general interest magazines arehigh (Figure 1).
Figure 2 shows that the main printed pages of two weekly
comic magazines (E3 and E4) contain high concentration oflignin. The figure also shows that all the newspaper samples(I1-I3) contain medium concentration of lignin. Cesium-137
was detected in the two weekly comic magazines and the newspapers (Figure 1). The result of the phloroglucinol color test
indicates that considerable amount of mechanical pulp is present in the weekly comic magazines and newspapers, and that is
the reason why 137Cs remained enough to be detected in these

3.2. The behavior of 137Cs in the production of paper. It
is necessary to verify the above interpretation. Cesium is analkali metal element and has the property of dissolving easily
in water. It is likely that 137Cs contained in wood is dissolved
in aqueous solution by chemical treatment done to wood in
production of paper. Potassium is also an alkali metal element,
and it is contained in wood because it is essential to plants.
The author4 already studied the 40K contents of the paper samples tested in this work, and the result of the study suggested
the dissolution of 40K in the production of paper.
The most important factor affecting 137Cs radioactivity left
in paper is the intensity of chemical treatment in preparation of
pulp. In preparation of pulp, a part of 137Cs contained in woodis dissolved in aqueous solution while the rest of 137Cs is left in
pulp. Mechanical pulp will hold most of 137Cs contained invery highhighPercentages of parts exhibiting eachlignin content level3

mediumlow

very low
not detected

100

80

60

40

20

0

A1 A2 A3 A4 A5 B1 B2 B3 B4 C1 C2 C3 D1 D2 D3 D4 E1 E2 E3 E4 F1 F2 G1 G2 G3 H1 H2 H3 H4 I1 I2 I3

Sample number
Figure 2. Lignin content and weight percentage of each part of paper samples. Kinds of samples are as in Figure 1. The lignin contents were
evaluated into six levels on the basis of the result of phloroglucinol color test.

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KobashiJ. Nucl. Radiochem. Sci., Vol. 10, No. 2, 2009137

samples. However, the Cs contents of the samples are much
lower than those of weekly general interest magazines (Figure1). Oji Paper Co. Ltd.11 reported that main printed pages ofJapanese weekly comic magazines were made of nearly 100%
deinked pulp. Takeshita12 reported that about 45% of pulp used
for recent Japanese newspapers was deinked pulp. Possibly
waste paper containing much mechanical pulp was the raw
material of the deinked pulp used for the weekly comic magazines and newspapers tested in this work. The main printed
pages of the weekly comic magazines and newspapers examined in this work were observed by a microscope. Many flakesof residual ink were found on the samples. Thus it is confirmedthat deinked pulp is used for the samples, and that explains thereason for the lower 137Cs contents of the weekly comic magazines and newspapers compared with the weekly general interest magazines. Another reason for the lower 137Cs contents of
the newspapers is the lower proportions of mechanical pulp in
the newspapers as compared with the weekly general interest
magazines.
As can be seen from Figure 2, all the samples other thanweekly general interest magazines, weekly comic magazines,
and newspapers are composed of parts of lignin content lower
than medium level except for B2 sample. Although a part ofB2 sample exhibits medium level of lignin content, the weightpercentage of the part is 25%. Consequently, the lignin content
of the whole B2 sample is low level. Judging from the result of
the phloroglucinol color test, all the samples other than generalinterest magazines, weekly comic magazines, and newspapers
are essentially made of chemical pulp. This is in agreementwith the result that 137Cs was not detected in these samples(Figure 1).
The above discussion clearly accounts for the difference in137
Cs concentration between the weekly general interest magazines and the other kinds of samples.

137

3.3. The radioactivity of Cs removed from wood intoaqueous solution during paper manufacturing in Japan.
The above discussion has revealed that most of 137Cs containedin material wood dissolves into aqueous solution in preparationof chemical pulp. This result makes it possible to estimate
137
Cs radioactivity removed from wood to aqueous solution in
paper manufacturing in Japan.
The weight percentages of pulps prepared in 2000 in Japan
were as follows: kraft pulp, 85.9%; half-chemical pulp, 0.9%;
mechanical pulp, 12.3%; others, 0.9%.13 Thus most of pulp
prepared in Japan is kraft pulp, a kind of chemical pulp. The
radioactivity A of 137Cs removed from wood into aqueous solution during paper manufacturing in Japan is calculated by thefollowing equation:
A=VrdC(1)where V is the volume of wood used for preparation of pulp, r
the proportion of wood used to prepare chemical pulp, d thedensity of the wood, and C the average 137Cs content of thewood. The consumption of pulp wood in 2000 in Japan13(3.76×107 m 3) is adopted as the value of V. The value of r is
estimated to be 0.93 based on the above pulp production data
and the data on yields of kraft pulp and mechanical pulp fromwood (45% and 91%, respectively14). On the basis of the dataon the density of typical woods used in Japan15, 500 kg m-3 isadopted as the value of d. The average 137Cs content of wood
estimated in Table 1 (0.88 Bq kg-1) is adopted as the value of C.
The radioactivity A of 137Cs removed from wood to aqueous
solution during paper manufacturing in the year 2000 in Japanis calculated to be 1.5×1010 Bq (15 GBq) by eq 1.
3.4. Migration of 137Cs in the environment. The environmental contamination with 137Cs began with the first nuclear
test in July 1945.16 It became global because many atmospherictests of nuclear weapons were done after the World War II.

TABLE 1: 137Cs concentration in wood

Tree

Locality

White oak
Massachusetts, USA
Red spruce
Tennessee, USA
Eastern hemlock
Tennessee, USA
Eastern white pine
Tennessee, USA
Hickory
Tennessee, USA
Elm
Tennessee, USA
American beech
Tennessee, USA
Sugar maple
Tennessee, USA
Yellow poplar
Tennessee, USA
Japanese cedar
Chiba Pref., Japan
Cypress
Ehime Pref., Japan
Japanese cedar
Tokyo, Japan
Japanese cedar
Kanagawa Pref., Japan

GrowthperiodRange of 137Csconcentration intree rings*(Bq kg-1)

1860-1967
1813-1987
1887-1986
1916-1987
1800-1987
1934-1987
1870-1987
1920-1987
1907-1987
1914-1979
1929-1979
1914-1982
1930-1982

0.94-9.3
4.4-7.2
1.4-4.7
0.07-0.36
0.16-0.67
0.08-0.27
0.8-2.8
0.0-0.35
0.0-0.05
0.07-1.48
0.44-1.73
0.09-0.63
0.26-1.07

Average 137Cs concentration in whole wood

137

Reference

Cs
concentration inwhole wood**(Bq kg-1)

Corrected 137Csconcentration inwhole wood***(Bq kg-1)

7)
8)
8)
8)
8)
8)
8)
8)
8)
9)
9)
10)
10)

3.8
5.5
2.9
0.22
0.27
0.15
1.8
0.09
0.02
0.78
0.96
0.33
0.48

1.8
4.1
2.1
0.16
0.2
0.11
1.3
0.07
0.01
0.49
0.6
0.22
0.32
0.88

* The original 137Cs data in the literatures were given in 137Cs concentration variation in tree rings at the time of felling down thetree.
** The 137Cs concentrations in this column are the 137Cs concentrations in whole wood obtained by averaging 137Cs cocentrations in
all the tree rings.
*** The 137Cs concentrations in this column are obtained by decay-correcting the 137Cs concentrations in the left column to January
1, 2000.

Radioactivity of 137Cs in Papers and Migration of the Nuclide
137

The Cs contamination of the surface of the earth was causedby the deposition of the radionuclide from the air where thenuclide was produced by nuclear weapon testing or released
from nuclear facilities such as nuclear reactors. The depositionof 137Cs fallout on the surface of the earth had a peak in thefirst half of the 1960s and then has been decreasing except for
the temporary increase due to the Chernobyl accident.17 Fallout
137
Cs is adsorbed on the surface of plants and is graduallyabsorbed into the plant bodies. Plants have a tendency toabsorb more 137Cs from their parts in contact with the air suchas leaves than from their root.16 Therefore, the 137Cs content ofannual plants shows a time-dependent change similar to that of137
Cs fallout deposition on the earth surface.
As for annual plants, Komamura et al18,19 studied the 137Cs
contents of rice and wheat collected at a number of localities inJapan. Their result indicated that the 137Cs contents of rice andwheat were the highest for the samples collected in 1963. The
average 137Cs contents of rice and wheat samples collected in
1995 were respectively 0.046 and 0.018 Bq kg-1, and the values
were two or three orders of magnitude below the corresponding
values of samples collected in 1963.
Trees are perennial and live long lives. Therefore, trees
which grew after July 1945 hold 137Cs in their bodies. Man
uses wood, xylem part of trees, and 137Cs contained in wood
migrates in the environment with the activity of man. Wood
has been used as fuel, construction material, raw material for
pulp, etc. The volume of wood consumed as raw material for
pulp in the year 2000 in Japan13 was 3.76×107 m3. Thirty percent of it was domestic wood, while 70 per cent imported
wood. Other main uses of wood are lumber and plywood inJapan, and the volumes of wood used for lumber and plywood
in 2000 were 2.65×107 m3 and 5.4×106 m3, respectively.20
As a result, the volume of wood consumed in 2000 in Japanis estimated to be about 7×107 m3 (about 3.5×1010 kg).
Food is also contaminated with 137Cs. The amount of foodconsumed in Japan 21 was 1.21×1011 kg in 2000. This value
includes the amount of feed for domestic animals and fish.
Japan Chemical Analysis Center 22 analyzed 137Cs in a wide
variety of food samples purchased between 1989 and 1996 in
Japan. The number of samples tested was 337. The result
showed that 83% of the samples had concentrations below 0.2
Bq kg-1. The average 137Cs concentration of twenty four mushroom samples was 4.8 Bq kg-1 and was far higher than those of
the other kinds of samples. However, mushrooms comprised
only 0.4% of total food consumed in 2000 in Japan. 21
Therefore, to average the 137Cs contents of all the samples
except the mushrooms is adequate for the estimation of theaverage 137Cs content of foods consumed in Japan. The average
137
Cs content of foods estimated by this method is 0.15 Bq kg-1.
The amount of wood consumed in 2000 in Japan is about
one third of that of food. However, the estimated average 137Cs
content of woods (Table 1) is about six times as high as that offoods. Therefore, the 137Cs radioactivity contained in wood
consumed in recent Japan may be higher than that contained infood consumed in recent Japan. Paper manufacturing accounts
for a half of the use of wood in Japan, and it causes transfer ofhigh degree of 137Cs radioactivity from wood to aqueous solution as already explained. Consequently, paper manufacturing
may play an important role in the migration of 137Cs in and near
Japan.

J. Nucl. Radiochem. Sci., Vol. 10, No. 2, 20095

Acknowledgements. A part of this research was done inRadioisotope Center, The University of Tokyo. The author is
grateful to Prof. N. Momoshima, Kyushu University, for providing information on 137Cs contents of wood.
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