Particulate distribution of plutonium and americium in surface waters from the Spanish Mediterranean coast

Measurements of the paniculate distribution of plutonium and americium in Spanish Mediterranean coastal waters have been carried out. Plutonium-239, 340 and 241Am concentrations have been measured in suspended particulate matter by filtering (< 0.22 μm) large volume (200–300 litres) sea water samples. Results indicate that paniculate plutonium constitutes on average 11 ± 4% of the total concentration in sea water. In the case of americium, this percentage rises to 45 ± 14%. From the 241Am/239, 240Pu activity ratios it is clear that suspended particulate matter is enriched in 241Am relative to 239,240Pu by a factor 8 ± 4. Plutonium and americium in surface Mediterranean coastal waters appear to be fractionated as they present a different transfer rate to the particles. Our measurements allowed us to estimate sediment-water distribution coefficients (Kd), which are a key parameter to interpret differences observed between the behaviour of plutonium and americium in sea water. Distribution coefficients Kd have been estimated to be (1.4 ± 0.5) × 105 litres kg−1 for plutonium and (0.9 ± 0.5) × 106 litres kg−1 for americium in surface Mediterranean coastal waters.