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.