The Science of the Total Environment 311 (2003) 233–245 0048-9697/03/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0048-9697(03)00053-6 Concentrations of plutonium and americium in plankton from the western Mediterranean Sea Joan-Albert Sanchez-Cabeza *, Juan Merino , Pere Masque , Peter I. Mitchell , a, a a b ´ L. Leon Vintro , William R. Schell , Lluısa Cross , Albert Calbet b c d d ´ ´ ¨ Insitut de Ciencia i Tecnologia Ambiental-Departament de Fısica, Universitat Autonoma de Barcelona, 08193 Bellaterra, a ` ´ ` Barcelona, Spain Department of Experimental Physics, University College Dublin, Dublin 4, Ireland b Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA c Institut de Ciencies del Mar, Pg. Marıtim Barceloneta, 37-49 08003, Barcelona, Spain d ` ´ Accepted 11 January 2003 Abstract Understanding the transfer of radionuclides through the food chain leading to man and in particular, the uptake of transuranic nuclides by plankton, is basic to assess the potential radiological risk of the consumption of marine products by man. The main sources of transuranic elements in the Mediterranean Sea in the past were global fallout and the Palomares accident, although at present smaller amounts are released from nuclear establishments in the northwestern region. Plankton from the western Mediterranean Sea was collected and analyzed for plutonium and americium in order to study their biological uptake. The microplankton fractions accounted for approximately 50% of the total plutonium contents in particulate form. At Garrucha (Palomares area), microplankton showed much higher Pu activity, indicating the contamination with plutonium from the bottom sediments. Concentration 239,240 factors were within the range of the values recommended by the International Atomic Energy Agency. Continental shelf mesoplankton was observed to efficiently concentrate transuranics. In open seawaters, concentrations were much lower. We speculate that sediments might play a role in the transfer of transuranics to mesoplankton in coastal waters, although we cannot discard that the difference in species composition may also play a role. In Palomares, both Pu and Am showed activities five times higher than the mean values observed in continental shelf 239,240 241 mesoplankton. As the plutonium isotopic ratios in the contaminated sample were similar to those found in material related to the accident, the contamination was attributed to bomb debris from the Palomares accident. Concentration factors in mesoplankton were also in relatively good agreement with the ranges recommended by IAEA. In the Palomares station the highest concentration factor was observed in the sample that showed predominance of the dynoflagellate Ceratium spp. Mean values of the enrichment factors showed, on average, discrimination rather than enrichment in the primary producer trophic chain.  2003 Elsevier Science B.V. All rights reserved. Keywords: Plutonium; Americium; Plankton; Mediterranean Sea; Palomares; Environmental radioactivity *Corresponding author. Tel.: q34-93-581-1915; fax: q34-93-581-2155. E-mail address: joanalbert.sanchez@uab.es (J.-A. Sanchez-Cabeza).