The radionuclide content dependency of on the season, location, type of sediment and type of algae and the comparison of radionuclide content in bottom
sediments and algae from one and the same sampling location gives information
for the mechanisms of radionuclide transfer from the sediments to biota as well as
the trend of the potential hazard for the marine ecosystems.
18.2.4.1 Radionuclides in Bulgarian Black Sea Sediments
A major part of the distribution and migration of long lived nuclide contaminants
(mainly
137 Cs,
90 Sr) are not only the hydrophysical processes but also the
biosedimentation and sorption on bottom sediments and concentration by biota. It
is known that
137 Cs and
90
Sr fallout are found in sea water mainly in soluble forms
and are weakly affected by biological migration (contrary to other nuclides as
141
Ce,
144 Ce,
103 Ru,
95 Zr etc.). Chernobyl radionuclides are characterised by a higher
content of nonsoluble forms (even “hot” particles) which are part of the reactor fuel.
These peculiarities affect the behaviour of the Chernobyl nuclides in sediments and
in their accumulation in biota. The contamination of sea bed sediments by
137 Cs and
90 Sr had a “spot” character which was due to the way Cs entered the environment at
the beginning – mainly airborne on different particles.
Cesium penetrated rather quickly the water depths – in 1987 Cs was measured up
to 120 m, while in 1988 it reached 200–250 m. The observed phenomenon of “self
decontamination” of Black Sea waters was due to the radioactivity spots dilution
and secondly to interaction of dissolved Cs with the bottom sediments.
The association of radionuclides with sediments in coastal and estuary areas
makes the sediments a large reservoir for radionuclides affecting significantly
specific marine ecosystems. As the sea water is constantly in contact with organic
and inorganic matter from sea bed sediments, the first necessary step in the
estimation of radionuclide migration is the measurement of radionuclide content
in sea bed sediments (as a first stage in food chain towards man) and set up a data
base for radioisotope content in the Black Sea.
The measurement of technogenic and natural radionuclides in sea bed sediments
was carried out in each season of every year after 1991 – spring, summer and
autumn, because in this way the estimation of concentration variations of the
contaminants, their accumulation and influence on marine ecosystems can be
followed. The intercomparisson between the data for the technogenic and natural
radionuclides gives the whole picture of isotope impact at a chosen reference point.
Many authors – Russian and Ukrainian scientists, (Polikarpov et al. 1988, 1989),
Turkish – Topcuoglu et al. (2001a, b), Guven et al. (1992), Bulgarian (Strezov et al.
1996, 1998, 1999), Romanian – Bologa and Patrascu (1996) have performed
measurements in the Black Sea. The impact of Chernobyl on marine ecosystems
was intensively studied and much data were published in recent years. Many
authors investigated the distribution of Chernobyl radionuclides and their accumulation in lake sediments as well as in sea bed sediments.
18 Radioecology of the Black Sea
311
sediments and algae from one and the same sampling location gives information
for the mechanisms of radionuclide transfer from the sediments to biota as well as
the trend of the potential hazard for the marine ecosystems.
18.2.4.1 Radionuclides in Bulgarian Black Sea Sediments
A major part of the distribution and migration of long lived nuclide contaminants
(mainly
137 Cs,
90 Sr) are not only the hydrophysical processes but also the
biosedimentation and sorption on bottom sediments and concentration by biota. It
is known that
137 Cs and
90
Sr fallout are found in sea water mainly in soluble forms
and are weakly affected by biological migration (contrary to other nuclides as
141
Ce,
144 Ce,
103 Ru,
95 Zr etc.). Chernobyl radionuclides are characterised by a higher
content of nonsoluble forms (even “hot” particles) which are part of the reactor fuel.
These peculiarities affect the behaviour of the Chernobyl nuclides in sediments and
in their accumulation in biota. The contamination of sea bed sediments by
137 Cs and
90 Sr had a “spot” character which was due to the way Cs entered the environment at
the beginning – mainly airborne on different particles.
Cesium penetrated rather quickly the water depths – in 1987 Cs was measured up
to 120 m, while in 1988 it reached 200–250 m. The observed phenomenon of “self
decontamination” of Black Sea waters was due to the radioactivity spots dilution
and secondly to interaction of dissolved Cs with the bottom sediments.
The association of radionuclides with sediments in coastal and estuary areas
makes the sediments a large reservoir for radionuclides affecting significantly
specific marine ecosystems. As the sea water is constantly in contact with organic
and inorganic matter from sea bed sediments, the first necessary step in the
estimation of radionuclide migration is the measurement of radionuclide content
in sea bed sediments (as a first stage in food chain towards man) and set up a data
base for radioisotope content in the Black Sea.
The measurement of technogenic and natural radionuclides in sea bed sediments
was carried out in each season of every year after 1991 – spring, summer and
autumn, because in this way the estimation of concentration variations of the
contaminants, their accumulation and influence on marine ecosystems can be
followed. The intercomparisson between the data for the technogenic and natural
radionuclides gives the whole picture of isotope impact at a chosen reference point.
Many authors – Russian and Ukrainian scientists, (Polikarpov et al. 1988, 1989),
Turkish – Topcuoglu et al. (2001a, b), Guven et al. (1992), Bulgarian (Strezov et al.
1996, 1998, 1999), Romanian – Bologa and Patrascu (1996) have performed
measurements in the Black Sea. The impact of Chernobyl on marine ecosystems
was intensively studied and much data were published in recent years. Many
authors investigated the distribution of Chernobyl radionuclides and their accumulation in lake sediments as well as in sea bed sediments.
18 Radioecology of the Black Sea
311