Radionuclide Impact on Sediments and Algae form Black Sea Marine
Ecosystems
Аlexander Strezov
Institute for Nuclear Research and Nuclear Energy
Bulgarian Academy of Sciences
72 blvd. Tzarigradsko shossee, Sofia, BULGARIA
Introduction
Radionuclide metals are the major part of anthropogenic fallout pollutants in the
Black Sea marine ecosystems. Massive amount of industrial effluents is transported
by the big rivers that enter the Black Sea (Danube, Dnyepr, Dnester, etc) as well. The
complex analysis of pollutant concentrations is a major concern for modern ecology in
obtaining reliable information about the type and quantities of substances entering the
marine environment.
Marine macroalgae are important factor for nuclides accumulation in marine
ecosystems. Radionuclides affect the living organisms both as heavy metals and by
their radiation. They participate in radionuclide transfer to the biosphere and man as
elements of the food chain of marine biota.
The ecological conditions at the Black Sea littoral zone vary depending on the
location and depth. The seasonal change in macrophytic species is determined by
the season, temperature and light regime. Some algae species are adaptive to
contamination but some species react quickly to the environmental changes
especially to the chemical contaminants.
This paper deals with the problem of transboundary pollution in the Black Sea
and asks whether cooperation is needed to agree on an optimal level of pollution. The
Black Sea is the largest semi-enclosed anoxic basin in the world. In this sea, the most
significant pollution problem has been identified as the eutrophication 1 phenomenon.
This problem affects Romania and Ukraine, more than the other coastal countries
(Bulgaria, Russia, Georgia and Turkey). The eutrophication of the Black Sea due to
excessive loads of nutrients via the rivers and coming directly from the coastal
countries has led to radical changes in the ecosystem since the 1960s. Oxygen
deficiency (hypoxia or anoxia) and mass mortality caused by eutrophication have
become a permanent feature in the north-western shelf area where anoxic zones have
expanded from covering 3500 km2 in 1973 to 40,000 km2 in 1990. This has had a
major transboundary impact on biological diversity and human use of the sea,
including fisheries, tourism and recreation.
Aquatic ecosystems including streams, rivers, lakes, and estuaries have been
subjected to increasing anthropogenic stress over the past several decades. Aquatic
organisms can experience a number and variety of natural and man-induced stressors
which vary both spatially and temporally. These organisms are typically subjected to
variations in physicochemical factors (varying hydraulic, temperature, and salinity regimes),
changes in food and habitat availability, exposure to contaminants, and increases in
nutrient (eutrophication) inputs. For example, agricultural practices can have adverse
impacts on the health of aquatic systems through contaminant and nutrient increases
and through modifications in vegetative cover which can result in altered hydrodynamic
regimes and sediment loading to these systems. Contaminants and nutrients pose a
significant concern to water quality and to the health of aquatic systems because of not
only the varied types of pollutants that impact these systems, but also because of the
many ways pollutants can effect the health of aquatic systems. While impacts on
aquatic systems from point-source pathways are relatively straightforward to assess
using standard toxicological and ecotoxicological approaches, effects from non-point
sources are much more difficult to assess and quantify primarily due to multiple stressor
effects. In recent years eutrophication of aquatic systems from non-point sources such as
agricultural runoff and atmospheric deposition, in particular, has become an increasing
concern.
Radionuclide Content in Black Sea Sediments
The data for technogenic (mainly
137Cs)
and natural radionuclides were
determined in the sediment samples collected along the Bulgarian Black Sea coast
(Fig 1). The measured levels correspond to those cited in the literature for background
levels, showing no additional anthropogenic contamination.
The highest measured cesium content on the Bulgarian Black Sea coast is at the
north locations with slime sediments - Kaliakra and Kavarna. The increase in
137Cs
concentration in slime sediments and sorption on fine particles leads to cesium
The beach matrix and the near shore sediments at these locations are mainly
sand (sandy) and the data are within a close range:
137Cs
- (3.2 - 5.6) Bq/kg at Sunny
Beach, Albena (3.4 - 5), Balchik (4.6 - 7.8), Primorsko (4.0 - 5.6), Tulenovo (4.0-7.1)
Kamen Briag (4.0-6.6).
In sand and sandy sediments Cs content does not change greatly while the
process of 137Cs accumulation is observed in slime and silt sediments.
The data show that the
226Ra/238U
238U
and
226Ra
values are close at most of the locations.
activity ratio (mean value) for sand and sandy sediments is in the range
0.55 - 0.85, meaning
226Ra
deficit while the values for
226Ra/238U
ratios in slime and
silt sediments are close to the equilibrium.
The obtained data show that radionuclide concentrations strongly depend on the
sediment nature. Results for sandy sediments are within close range, while those for
slime and silt vary to a much greater extent. The data for sand sediments are within a
close range while those for silt and slime ones are higher.
Bq/kg
Comparison of Natural nuclides in Shallow and Deepsea Sediments
The nuclide values for all sand sediments are combined in one cluster (from
Albena to Shabla max Euclidean distance 2.5). The second cluster includes locations
close in geographical position and sediment type (slime)- Tuzla, Kavarna and Tzarevo,
while Bjala, Chernomoretz and Kaliakra are completely separate from the rest.
Marine sediments are a very important abiotic element of water environment.
The determination of anthropogenic radionuclide and trace metal pollutants in
sediments is of great importance because their chemical compositions are a more
reliable indication of the marine environmental pollution.
N uc lide c onte nt in algae fr om B lac k Se a c oast loc ations
65
55
45
35
25
15
5
-5
S o zo p o l
R o sen etz
T za rev o
R ezo v o
Ravda
S in em o retz
M a slen n o s
K a lia k ra
S h a b la
A h to p o l
C s -1 3 7
T h -2 3 4
T h -2 3 2
R a -2 2 6
T u zla ta
B q /k g
(G a m m a S p ectroscop y)
The measured nuclide content in Black Sea algae can be used also as a
characterization of radionuclide level at different Bulgarian Black Sea coastal regions.
Ra and Pb quantity in seawater and sediments can be estimated by the results of
226Ra
210Pb
and
algae data analysis from the different geographical zones of the
Bulgarian Black Sea shore. Judging from the
226Ra
content in the red alga C. rubrum,
the studied locations can be arranged according the
226Ra
distribution model in the
following order:
Ravda < Maslen nos < Perla < Sinemoretz < Shabla < Ahtopol < Rezovo < Tuzlata
< Kaliakra
The highest measured natural nuclide concentrations are determined in the green
alga Bryopsis plumosa, which is one of the widespread Black Sea green macrophytes
and differs from the other studied algae because of its life cycle and maximum of
development in winter. This green alga seems to extract preferably some of
daughters -
226Ra, 210Pb
and
232Th
daughters -
228Ra, 228Ac, 208Tl, 212Bi, 212Pb
238U
from the
sea water up to 1000 – 2000 Bq/kg level i.e. approximately three orders of magnitude
higher than all other alga species, collected from the same site.
Tree D iagram fo r six B lack S ea alga sp ecies
W ar d`s m e tho d
C e r. rubrum
E nt. inte stina lis
C yst. c rinita
C yst. ba rba ta
U lv a rig ida
C la d. v a g a bunda
0 ,5
1 ,0
1 ,5
2 ,0
2 ,5
3 ,0
3 ,5
4 ,0
4 ,5
Eu clid ean d istan ces
The data for Black Sea algae were also treated statistically and the cluster tree
diagram of Black Sea algae demonstrates the liaisons of different algae depending on
the nuclide content.
In conclusion the obtained data show that there is no serious contamination with
radionuclides, which is normal as there is no nuclear facility at the Bulgarian coast to
release nuclides into the environment.
A database for the nuclide concentration values is created which will enable the
modeling of radionuclide transfers by estimation of their concentration variations,
accumulation and influence on the marine ecosystems.