The main method for measuring the nuclide content in sediments and algae was
the high resolution gamma spectroscopy performed on large high purity Ge semiconductor detectors with nuclear electronic tracts using sophisticated software.
The upper layer of sediments was collected from approximately 1 m
2 of the
bottom acquiring about 2–3 kg of solid phase plus several liters of aqueous phase.
The depth of the sample layer was maximal 3 cm to evaluate radionuclide content
on the surface of the sea bed. In this way the potential seasonal variations could be
estimated. The sample collection was performed by experienced scuba divers who
carefully selected the sample site to avoid or minimize the differences of samples in
particle size, depth and distance from shore, so that the comparison of the sea bed
samples of different seasons could be done with greater level of confidence,
reliability and accuracy.
Samples were also collected and data obtained for the main Black Sea resorts –
Albena, Golden sands, Sunny Beach etc. as well as for some of the main cities along
the Bulgarian Black Sea coast. These data were compared with samples taken from
definitely clean areas. The contribution of the inflowing rivers for radioisotope
content in the Black Sea was also studied sampling river’s estuaries and comparing
them with the inland sections of the same rivers. So the influence of the river on the
adjacent area was compared with that of the sea.
The obtained results (Fig. 18.4) for Black Sea sediment samples show that
radionuclide concentrations strongly depend on the nature of the sea bed sediments,
because the data obtained for sand sediments are within a close range while those
for silt and slime ones are higher and vary to a much greater extent.
The beach matrix from the near shore sediments at these locations is mainly sand
and
137 Cs data are within a close range: Sunny Beach – 3.2 – 5.6 Bq/kg, Golden
Sands – 1.8 – 6.9 Bq/kg, Albena – 3.4 – 7.3 Bq/kg, Tulenovo 4.0–7.1 Bq/kg, Kamen
Briag – 4.4–6.6 Bq/kg, Balchik – 4.6 – 7.8 Bq/kg, Primorsko 4.0–5.6 Bq/kg,
Sinemoretz – 3.6 – 7.8 Bq/kg. It should be noted that all sand sediment data fall
within 8 Bq/kg level except Albena, Golden sands, Ravda, Burgas and Sozopol
where nuclide content is higher.
The highest measured cesium content (Fig. 18.4) on the Bulgarian Black Sea
coast is at the north locations with slime sediments – Kaliakra (mean 89 Bq/kg),
Kavarna (mean 30 Bq/kg) and central Ravda2 (mean 65 Bq/kg). This fact can be
attributed to the influence of the big rivers Danube, Dnyepr, Dnester, entering the
northwest part of the Black Sea.
The increase in
137
Cs concentration in slime sediments and sorption on fine
particles leads to cesium scavenging and occurrence at greater depths, which is due
to physico-chemical interaction processes of the soluble Cs forms with the surrounding media. In sand and sandy sediments Cs content does not change greatly
while the process of
137 Cs accumulation is observed in slime and silt sediments.
Due to such a process, sea bottom sediments play a major role in radionuclide
redistribution between different components in the ecosystems, which change the
concentration of
137 Cs in the water as it is accumulated more in the sediments.
The observed dependence of radionuclide content on sediment type is valid also
for the natural nuclides in sediments. The lowest concentrations of natural nuclides
18 Radioecology of the Black Sea
313
the high resolution gamma spectroscopy performed on large high purity Ge semiconductor detectors with nuclear electronic tracts using sophisticated software.
The upper layer of sediments was collected from approximately 1 m
2 of the
bottom acquiring about 2–3 kg of solid phase plus several liters of aqueous phase.
The depth of the sample layer was maximal 3 cm to evaluate radionuclide content
on the surface of the sea bed. In this way the potential seasonal variations could be
estimated. The sample collection was performed by experienced scuba divers who
carefully selected the sample site to avoid or minimize the differences of samples in
particle size, depth and distance from shore, so that the comparison of the sea bed
samples of different seasons could be done with greater level of confidence,
reliability and accuracy.
Samples were also collected and data obtained for the main Black Sea resorts –
Albena, Golden sands, Sunny Beach etc. as well as for some of the main cities along
the Bulgarian Black Sea coast. These data were compared with samples taken from
definitely clean areas. The contribution of the inflowing rivers for radioisotope
content in the Black Sea was also studied sampling river’s estuaries and comparing
them with the inland sections of the same rivers. So the influence of the river on the
adjacent area was compared with that of the sea.
The obtained results (Fig. 18.4) for Black Sea sediment samples show that
radionuclide concentrations strongly depend on the nature of the sea bed sediments,
because the data obtained for sand sediments are within a close range while those
for silt and slime ones are higher and vary to a much greater extent.
The beach matrix from the near shore sediments at these locations is mainly sand
and
137 Cs data are within a close range: Sunny Beach – 3.2 – 5.6 Bq/kg, Golden
Sands – 1.8 – 6.9 Bq/kg, Albena – 3.4 – 7.3 Bq/kg, Tulenovo 4.0–7.1 Bq/kg, Kamen
Briag – 4.4–6.6 Bq/kg, Balchik – 4.6 – 7.8 Bq/kg, Primorsko 4.0–5.6 Bq/kg,
Sinemoretz – 3.6 – 7.8 Bq/kg. It should be noted that all sand sediment data fall
within 8 Bq/kg level except Albena, Golden sands, Ravda, Burgas and Sozopol
where nuclide content is higher.
The highest measured cesium content (Fig. 18.4) on the Bulgarian Black Sea
coast is at the north locations with slime sediments – Kaliakra (mean 89 Bq/kg),
Kavarna (mean 30 Bq/kg) and central Ravda2 (mean 65 Bq/kg). This fact can be
attributed to the influence of the big rivers Danube, Dnyepr, Dnester, entering the
northwest part of the Black Sea.
The increase in
137
Cs concentration in slime sediments and sorption on fine
particles leads to cesium scavenging and occurrence at greater depths, which is due
to physico-chemical interaction processes of the soluble Cs forms with the surrounding media. In sand and sandy sediments Cs content does not change greatly
while the process of
137 Cs accumulation is observed in slime and silt sediments.
Due to such a process, sea bottom sediments play a major role in radionuclide
redistribution between different components in the ecosystems, which change the
concentration of
137 Cs in the water as it is accumulated more in the sediments.
The observed dependence of radionuclide content on sediment type is valid also
for the natural nuclides in sediments. The lowest concentrations of natural nuclides
18 Radioecology of the Black Sea
313