Radioactivity in three species of eastern Mediterranean jellyfish

• Activity concentrations of 137Cs, 40K, 210Po, 210Pb, 234U and 238U were determined in three jellyfish species distributed along the Syrian coast.
• Rhopilema nomadica Galil, 1990 species can be used as biomonitor for 210Po and 210Pb in the marine environment.
• The obtained data can be considered the first reported baseline values for radioactivity in jellyfish.

Activity concentrations of 137Cs, 40K, 210Po, 210Pb, 234U and 238U were determined in umbrella and oral arms of three widely distributed jellyfish species; namely Rhopilema nomadica Galil, 1990, Aurelia aurita Linne, 1758 and Aequorea forskalea Péron & Lesueur, 1810 collected from February 2011 to January 2012 in four sampling locations along the Syrian coast (Eastern Mediterranean Sea). The results have shown significant variations in radionuclides activity concentrations amongst the species. The average activity concentrations of 40K, 210Po, 210Pb, 234U and 238U in the umbrella of R. nomadica species were higher than the average activity concentrations in the umbrella of A. aurita species by about 3.2, 1.4, 1.8, 3.2 and 3.2 folds, and A. forskalea species by about 45.5, 15.4, 19, 7.4 and 7.6 folds, respectively. The average activity concentrations of 40K, 210Po, 210Pb, 234U and 238U in oral arms of R. nomadica species were higher than the average activity concentrations in oral arms of A. aurita species by about 3.8, 1.7, 1.9, 2.8 and 2.9 folds, respectively. 137Cs activity concentrations were below the detection limit in all measured samples. In addition, activity concentrations of 137Cs, 40K, 210Po, 210Pb, 234U and 238U were also determined in 44 surface seawater samples and the activity concentrations ranged between 10.6 and 11.9 Bq l−1 for 40K, 1.1 and 1.4 mBq l−1 for 210Po, 0.5 and 0.7 mBq l−1 for 210Pb, 40.8 and 44.5 mBq l−1 for 234U, and 36.9 and 38.4 mBq l−1 for 238U, while 137Cs activity concentrations were below the detection limit in all measured samples. Moreover, the umbrella and oral arms readily accumulated 40K, 210Po, 210Pb, 234U and 238U above ambient seawater levels in the sequence of 210Po > 210Pb > 4 K > 234U and 238U. Concentration ratio (CR) values were relatively high for 210Po and 210Pb and reached 103 and 102, respectively for the jellyfish R. nomadica species compared to A. aurita and A. forskalea species. Therefore, R. nomadica can be used as biomonitor for these two radionuclides in the Eastern Mediterranean Sea. However, the obtained data can be considered the first reported baseline values for radioactivity in jellyfish.