Comparison of Some Radionuclides in the Marine Coastal Environment of the Black Sea and the Mediterranean

Abstract

Ten types of sea algae distributed along the Bulgarian coast have been collected and
analyzed for radioactivity content in the period 1996 - 2004. Results have shown that 37Cs
concentrations in all analyzed samples were relatively low (less than 10 Bq kg-1 dry weight)
while the levels of naturally occurring radionuclides, such as 226Ra and 2l0Pb, were found to be
higher in most samples; the highest observed value (896 Bq kg-1
dry weight for 226Ra and 68 Bq
kg-1 for 2l0Pb was in the green Bryopsis plumosa alga.
In addition, most alga species were also found to accumulate 2l0Pb, which indicates their
selectivity to this isotope. On the other hand, brown algae (Cystoseira barbata & crinita) have
shown a clear selectivity for some nuclides, this selectivity may encourage their use as a
biomonitor for pollution by nuclides. Moreover, the red alga species were found to contain the
highest levels of Cs.
The coastal areas far from rural settlings were chosen as control sites to evaluate
soluble and total metal concentrations and to gain additional information on both the
environmental conditions of the area and possible bioaccumulation patterns.
Data from this study were also compared with those previously obtained from neighboring
Mediterranean Sea. The results clearly show differences between these two marine
ecosystems. Nuclide concentrations recorded along the Bulgarian coast may be used for
background levels for intraspecific comparison within the Black Sea area, which information is
still very scarce.