Chemistry Reference
In-Depth Information
Table 3.11
Concentrations of the main radionuclides in
seawater
Radiation causes ion and free radical formation in
tissue, which can lead to cell death or mutation. This
in turn can lead to a range of short-term and long-
term effects to the exposed individual (somatic) and
potentially through chromosomal aberrations to suc-
ceeding generations (genetic). For the short-term
effects to become apparent a fairly high threshold
dose is necessary but for longer term somatic and for
genetic effects there is theoretically no threshold.
Discharges from the nuclear fuel cycle peaked in
the 1970s and early 1980s and now, under the effects
of stricter legislation, have fallen to about 1.5% of
the peak levels for beta-emitting nuclides and 0.15%
for the alpha-emitters.
Sections of the Irish Sea adjacent to the Sellafield
site of British Nuclear Fuels Limited (BNFL) have
received some of the highest discharges of radioac-
tivity in the world. Sampling of seawater close to the
site shows alpha levels of 7 Bq kg
-1
and beta/gamma
levels of 10 Bq kg
-1
from anthropogenic sources [27].
This may be compared with the natural background
level in seawater of 12 Bq l
-1
.
To illustrate the effects of legislation in this area
the concentration of
137
Cs, a typical long-lived
beta/gamma emitter, has fallen steadily, reflecting
the reduced discharges, and currently stands at
0.3 Bq kg
-1
(1% of peak levels).
Radionuclide
Concentration (Bq kg
-
1
)
Potassium-40
11.
8
4
Rubidium-
8
7
1.07
Tritium
Up to 0.11
Uranium-234
0.05
Uranium-23
8
0.04
Carbon-14
0.007
Less than 10
-
2
Radium-226
Less than 10
-
2
Radium-222
Less than 10
-
2
Potassium-210
Less than 10
-
2
Thorium isotopes
Source: Ref. 26.
Seawater has a natural radioactivity of 12.6 Bq l
-1
(a bequerel (Bq) is one disintegration per second)
and marine sediments are in the range 200-1000 Bq
kg
-1
(see Table 3.11).
Anthropogenic sources are mainly from atmos-
pheric nuclear weapons testing (which has declined
sharply since the Test Ban Treaty in 1963) and
nuclear power generation operations. The latter
include fuel fabrication, electrical power generation,
reprocessing and waste management. Biologically
significant nuclides from weapons testing are
14
C
(half-life 5730 years),
137
Cs (30.07 years),
89
Sr (50.53
days),
90
Sr (28.79 years) and
131
I (8.02 days). Chronic
discharges from power production are dominated by
85
5 Conclusion
'The world can only be grasped by action not by
contemplation. The hand is the cutting edge of the
mind.'
Kr (10.76 years) and from reprocessing by
14
C,
60
Co
(5.27 years),
90
Sr,
99
Tc (211 000 years),
106
Ru (373.6
days),
Jacob Bronowski (1908-1974)
Ag (249.8 days),
137
Cs and
239
Pu (24 110
years),
241
Pu (14.35 days),
237
Np (2.144 million years)
and
241
Am (432.2 years).
Acute radioactive discharges from reactor acci-
dents tend to be dominated by the volatile radioiso-
topes of I and Cs, although significantly increased
106
110m
If pollution, and particularly chemical pollution, did
not exist it is doubtful whether the study of the envi-
ronment and its chemistry would have reached the
intensity it has at the turn of the millennium. Inter-
vention to minimise and remediate environmental
pollution effects should be on the 'if it ain't broke
don't fix it' principle. However, in places the envi-
ronment is broken and we must intervene immedi-
ately to fix it. Exactly where and how it can be fixed
needs careful study
and
action. It is hoped that this
book will help to point the way.
Ru (367 days) levels in fish also were detected fol-
lowing Chernobyl.
Radionuclides, of course, behave chemically iden-
tically to their stable isotopes. Radiation of marine
organisms occurs internally from ingestion and
absorption and externally from immersion. Little
evidence exists for biomagnification and doses are
almost exclusively sub-lethal, the one exception
being carnivorous fish in the Marshall Islands due to
131
I from weapons testing fall-out.
References
1.
Brimblecombe, P.
Air Composition and Chemistry
, 2nd
edn. Cambridge University Press, Cambridge, 1996.
