Journal of Radioanalytical and Nuclear Chemistry, Vol. 265, No. 1 (2005) 21–29 0236–5731/USD 20.00 Akadémiai Kiadó, Budapest © 2005 Akadémiai Kiadó, Budapest Springer, Dordrecht Radionuclide accumulation in green and brown macroalgae at the Bulgarian Black Sea coast A. Strezov,* T. Nonova Bulgarian Academy of Sciences, Institute for Nuclear Research and Nuclear Energy, 72, Tzarigradsko shossee, 1784 Sofia, Bulgaria (Received July 14, 2004) The concentration of technogenic and natural radionuclides were measured in brown and green macroalgae from the Bulgarian Black Sea coast for the period 1996 and 2003 using low-level gamma spectroscopy. Mean values and concentration range for the studied species enables the comparison of the nuclide content in macroalgae showing that brown algae accumulate the studied radionuclides to a higher extent. Introduction Compared with the Mediterranean the biodiversity of the Black Sea is confined due to its higher degree of geographical isolation which is manifested in lower water salinity and a lower seasonal water temperature. The main sources of radioactive pollution in the Black Sea are atmospheric fallout and the big river (Danube, Dnyeper, Dnester) runoffs as well as the local land- based outfalls. 1,2 The Bulgarian Black Sea coast received an impact of great amount of radionuclides during 1960’s and after 1986, because its close location to Chernobyl NPP. The increase of technogenic and natural nuclide concentrations in seawater leads to a change of the natural background of the marine environment and affects the living organisms. Therefore, a systematic monitoring of contaminant concentrations is important for the assessment of harmful anthropogenic impact in the marine environment. Bioaccumulation studies are an essential method for measuring the bioavailability of specific contaminants. Macroalgae being one of the primary stages of the trophic chain, often provide one of the first signals for the living status of marine ecosystems. Many radionuclides can be accumulated in certain marine macrophytes and affect their life cycles. Marine macroalgae can be used for studying the bioaccumulation because they are abundant, have a reasonable size and adequate tissue for analysis. 3 The determination of the proper species for bio-indication, is the way to control the impact of man’s activities on the environment and the radioecological situation of the marine ecosystem and to look for correlations of site contamination and the bioavailability of pollutants. 4,5 The radioactive contaminants, the migration of radionuclides and their biological effects in the * E-mail: strezov@inrne.bas.bg Black Sea marine environment have been studied by many authors. 6–12 However, the data for radionuclide contamination of waters, sediments and macroalgae from the Bulgarian section of the Black Sea coast are scarce. The macrophytic species from the phylum of Chlorophyta (green) and Phaeophyta (brown) are widely distributed in the coastal Black Sea ecosystem. Brown macroalgae as well as some of the common green species (Chaetomorpha and Cladophora) can be found mainly in clean and low contaminated areas. 13 Some green species (Ulva rigida and Enteromorpha intestinalis) demonstrate clearly marked ability for adaptation towards the changes in microelement concentrations. The main purposes of this investigation are to study the radionuclide accumulation in the Bulgarian Black Sea macroalgae during the period 1996–2003 and to compare the sensitivity and accumulation capacity of different algae species and their application as bio- indicators in marine ecological research studies. Experimental Two brown macroalgae species (Cystoseira barbata and Cystoseira crinita) and five green species (Ulva rigida, Enteromorpha intestinalis, Cladophora vagabunda, Chaetomorpha gracilis and Bryopsis plumosa) were analyzed for technogenic and natural radionuclide content. All the plants were collected in the period 1996–2003 at 0.5–2 m depth from eleven sites (Shabla, Kaliakra, Tuzlata, Ravda, Sozopol, Maslen nos, Perla, Varvara, Ahtopol, Sinemoretz and Rezovo) along the Bulgarian Black Sea coast (Fig. 1).