Introduction
Atmospheric input of anthropogenic radionuclides to the ocean has been
regarded as one of the most important of the various input sources such as
river input, discharges from nuclear industrial activities and accidents, etc.
For this reason, in order to study the ?uxes of anthropogenic radionuclides,
their biogeochemical behaviour and the high scavenging rates of transuran-
ics in the Mediterranean Sea, as well as for monitoring possible accidental
discharges of radionuclides to the sea, we regularly collected rainwater
(wet and dry deposition) to estimate the amounts of delivery and to mea-
sure the concentrations of anthropogenic radionuclides.
Methods and Materials
Precipitation was collected monthly in a 2.35 m
2
plastic container
placed on the roof of the building which houses IAEA-MEL in Monaco.
Preconcentration of radionuclides in rainwater, radiochemical separation,
purification steps and
a
-spectrometry measurements have been described
elsewhere [1].
Results and discussion
Radionuclide concentrations in precipitation and monthly deposition
rates are presented in Table 1 and Figure 1, respective
ly. The monthly depo-
sition of radionuclides into the northwestern Mediterranean Sea shows that
a significant amount was delivered from September to October when high
precipitation rates were observed. A strong spring peak observed in prev
i-
ous studies [2] was not observed in the recent study; only a small sub-peak
was noted at this time. The annual delivery of anthropogenic radionuclides
into the Sea was calculated to be 0.51 ± 0.06 mBq m
-2
for
238
Pu, 16.5 ± 0.4
mBq m
-2
for
239,240
Pu, 6.8 ± 0.4 mBq m
-2
for
241
Am and for
137
Cs 1.17 ±
0.12 Bq m
-2
. These amounts correspond to 8% for
238
Pu, 6% for
239,240
Pu
and 32% for
241
Am of those measured previously by Thein et al.[2] in
Monaco during 1978-79.
These results demonstrate that the transport of anthropogenic radionu-
clides from the stratosphere to the troposphere and then to the sea, which
was observed previously, has been replaced by resuspension of radionu-
clides from soil and their wash-out from air to seawater.Therefore, at pre-
sent, delivery patterns of radionuclides are dependent on the amounts of
precipitation. The recent annual discharges of radionuclides to the
Mediterranean Sea through the adjacent rivers are poorly known and only
approximate data and gross activities have been reported [3, 4]. If we
assume that the same amounts of radionuclides as estimated by Fukai et al.
[3] are discharged into the Mediterranean Sea (in reality, the present
amounts should be lower), the observed deposition amounts of
239,240
Pu
and
241
Am are slightly higher than annual discharges by rivers. The
observed deposition amounts are only 4% for
239,240
Pu and 5% for
241
Am
of the mean annual transuranic loss in surface waters measured in the
northwestern Mediterranean [5]. Therefore, the total inputs from both the
atmosphere and rivers are less than 10% of the annual loss in surface water
of the northwestern Mediterranean.
The activity ratios of
238
Pu/
239,240
Pu show that plutonium in total depo-
sition originates mainly from global fallout. Noticeable exceptions are in
January, March and November and the high deviations from the global fall-
out ratio (0.024) for these months will require careful interpretation when
additional results become available. The
241
Am/
239,240
Pu ratios (weighted
mean 0.38), do not reveal any signature of a special input source compared
to that of global fallout (0.37). The observed mean activity ratio of
239,240
Pu/
137
Cs is 0.015. When taking decay correction into account, our
result is in good agreement with that (0.023) of Theinet al. [2].
References
[1] - La Rosa J., Burnett W., Lee S-H., Levy I., Gastaud J. and Povinec P.P.,
(in print). Separation of actinides, caesium and strontium from marine samples
using extraction chromatography and sorbents. J. Radional. Nucl. Chem.
[2] - Thein M., Ballestra S., Yamato A. and Fukai R., 1980. Delivery of
transuranic elements by rain to the Mediterranean Sea. Geochim et
Cosmochimica Acta., 44: 1091-1097.
[3] - Fukai R., Ballestra, S., Thein M. and Guion, J., 1981. Input of
transuranic elements through rivers into the Mediterranean Sea. Report SM-
248/125,In: Impact of radionuclide release into the marine environment.
IAEA,Vienna, 3-14.
[4] - Martin J. M., and Thomas A. J., 1990. Origins, concentrations and
distributions of artificial radionuclides discharged by the Rhone river to the
Mediterranean Sea. J. Environ. Radioactivity, 11: 105-139.
[5] - Fowler S. W., Noshkin V. E., La Rosa J. and Gastaud, J., 2000. Temporal
variations in plutonium and americium inventories and their relation to
vertical transport in the northwestern Mediterranean Sea. Limnol. Oceanogr.,
45(2) 446-458.
Rapp. Comm. int. Mer Médit., 36,2001
142
ATMOSPHERIC INPUT OF RADIONUCLIDES TOTHE NORTHWESTERN MEDITERRANEAN SEA
Sang-Han Lee*, Pavel P. Povinec, Mai K. Pham
International Atomic Energy Agency, Marine Environment Laboratory, Monaco - S.Lee@iaea.org
Abstract
137
Caesium,
238
Pu,
239,240
Pu and
241
Am were determined in total monthly deposition (wet + dry) to elucidate the delivery behaviour of
anthropogenic radionuclides into the northwestern Mediterranean Sea. The results show that the concentrations of
239,240
Pu in
precipitation were similar to those found in Mediterranean surface water while the concentrations of
241
Am in precipitation were higher.
The annual contribution of transuranics from the atmosphere to northwestern Mediterranean was much lower than their mean annual loss.
However, many particles loaded in precipitation in February and August probably played important roles in enhancing the scavenging of
transuranics in the northwestern Mediterranean Sea.
Keywords: radionuclides, precipitation, atmosphere, Mediterranean Sea
Fig. 1. Monthly deposition (mBq m
-2
month
–1
) of radionuclides
and precipitation (fallout) into northwestern Mediterranean
MonthPrecipitation
238
Pu
239,240
Pu
241
Am
137
Cs
(mm)(µBq L
-1
)(µBq L
-1
)(µBq L
-1
)(µBq L
-1
)
January251.4 ± 0.34.9 ± 0.73.6 ± 0.71.9 ± 0.7
*February-116 ± 313300 ± 1801780 ± 130126 ± 1
March
252.1 ± 0.618 ± 25.8 ± 1.62.7 ± 0.7
April
1230.4 ± 0.24.7 ± 0.74.4 ± 0.71.3 ± 0.8
May
650.5 ± 0.123 ± 18.7 ± 0.71.7 ± 0.2
June
3.82.3 ± 0.6530 ± 3023 ± 27.4 ± 1.0
July
8.31.3 ± 0.342 ± 221 ± 25.6 ± 0.5
August7.57.4 ± 1.5280 ± 10105 ± 810 ± 1
September701.4 ± 0.670 ± 416 ± 12.6 ± 0.2
October275-16 ± 18.8 ± 1.20.9 ± 0.2
November482.6 ± 0.417 ± 16.7 ± 0.81.8 ± 0.1
December300.2 ± 0.17.0 ± 0.72.8 ± 0.30.29 ±
0.04
MonthPrecipitation
238
Pu/
241
Am/
(
239,240
Pu/
137
Cs)*
(mm)239,240
Pu
239,240
Pu1000
January250.286 ± 0.0810.73 ± 0.172.6 ± 1.0
*February-0.035 ± 0.0100.54 ± 0.0526.3 ± 1.5
March
250.119 ± 0.0360.33 ± 0.106.6 ± 1.9
April
1230.089 ± 0.0460.93 ± 0.203.7 ± 2.4
May
650.023 ± 0.0050.38 ± 0.0314 ± 2.0
June
3.80.044 ± 0.0110.44 ± 0.047.1 ± 1.0
July
8.30.031 ± 0.0080.49 ± 0.047.5 ± 0.7
August7.50.026 ± 0.0060.37 ± 0.0328 ± 2
September700.021 ± 0.0090.23 ± 0.0226 ± 2
October275
-0.54 ± 0.0819 ± 5
November480.155 ± 0.0250.39 ± 0.0510 ± 1
Table 1. Concentrations and activity ratios of anthropogenic
radionuclides in precipitation over Monaco, 1999.
