Monitoring of radionuclide and heavy metals in sediments and macrophytes from Black Sea ecosystems

Full text: Data for natural and technogenic radionuclides content in three types of sediments (slime, silt and sandy) were obtained for 35 location at the Bulgarian Black Sea coast from the north border with Romania to the southern with Turkey. Radioecological investigations of who le Bulgarian Black sea coast were started in 1991. Contaminant behavior (nuclides and HM) was traced in the period 1991 - 2003 and tendencies for pollutant behavior and intercorrelations were evaluated and followed. It is considered that direct influence of Chernobyl accident has entered equilibrium after five years and monitoring this influence will enable modeling of ecological consequences for the marine environment. Radionuclides were measured by low level gamma spectroscopy and γ spectrometry measurements were carried out using HPGe detector with 35 % counting efficiency and energy resolution 1.8 KeV (1332 KeV). Heavy metals (HM) in algae were measured by Atomic Absorption spectrometry (AAS) - ETAAS (Perkin - Elmer Zeeman 3030 with graphite furnace) for Pb and Cd and flame AAS Pye Unicam SP 1950 for Fe, Mn and Cu. Certified reference material NIES-CRM-3 (Chlorella) was run with each sample series. Radionuclide and heavy metal content was determined in bottom sediments and ten macroalgae species (five green: Cladophora vagabunda, Ulva rigida, Enteromorpha intestinalis, Chaetomorpha gracilis and Bryopsis plumosa; two brown: Cystoseira crinita and Cystoseira barbata; three red: Ceramium rubrum, Callithamnion corymbosum and Corallina officinalis) from 12 reference locations. A comparative analysis of eco-toxicological state in the environment in different Bulgarian Black Sea geographic zones is made. The intercomparison of radionuclide content in bottom sediments and algae from one and the same sampling location can give information for mechanisms of radionuclide transfer from sediments to biota and give the trend of potential hazard of anthropogenic impact on marine ecosystems. Some alga species can be used as bio-monitors for the radioactive contamination along the Black Sea shore. Evaluation of the HM content added additional information to the data base for nuclide and HM accumulation, sorption and migration monitoring of the whole Bulgarian coastal zone that will help future assessment and modeling of contaminant transfer processes in environment and biosphere. The content of radionuclides in sediments depends on mineral type - slime sediments accumulate the highest content of technogenic (137Cs) and natural nuclides (U and Th series). Sand and sandy sediments are in the lower limit of radionuclide content - data for 137Cs content in sand sediments is within the range 2.1 - 9.6 Bq/kg and do not depend on the geographical position. Same is true for the main sea resorts and at places where sand sediments predominate at Bulgarian coast. Clear dependence of radionuclide content on sediment type was obtained - considerably low and in a narrow range of technogenic and natural nuclides while data for silt and slime vary more. Small seasonal changes of radionuclide concentration in sandy sediments were observed while greater variations in slime and silt ones occur. Data for natural radionuclides in sediments correspond to the cited in literature natural levels, showing no additional anthropogenic contamination. The obtained data for nuclide content in Black sea sediments show that highest content of Cs and some natural nuclides has been determined in the northern part of the Black sea coast. The content of radionuclides in the main Black Sea resorts where sand sediments predominate, is in the lowest limit of determined values. Data have been obtained based on the investigations for Fe, Mn, Cu, Pb and Cd content in the most widespread Black Sea green, brown and red macroalgae for the period 1996-2000. All the obtained results prove the dependence of heavy and toxic metal accumulation in green algae species on the location and sampling season. It can be concluded that Fe, Mn, Cu, Pb and Cd concentration in Black Sea green macroalgae decrease during the studied period. Ulva rigida species accumulates the lowest concentrations of the studied metals. The highest Fe, Mn, Pb and Cd content depending on the location, is in macrophytes from Tuzlata. High Cu concentration is observed in the southern coastal area- Ahtopol and Sinemoretz. This work establishes a database for heavy metal content in green macroalgae and their ecological impact on marine ecosystems along the Bulgarian Black Sea coast. The data obtained for the chosen locations for the six consecutive years indicate no serious artificial pollution along our shore. The obtained higher HM content (nuclides as well) can be attributed to the influence of the big rivers entering the northern part of the Black Sea - Danube, Dnyepr, Dnester. (author)