Distribution of Lanthanides in Mediterranean Coastal waters

Distribution and behaviour of the whole lanthanide series and yttrium in both seawater column and suspended particulate matter were investigated in coastal water located in the Central Mediterranean Sea. An area characterized by high anthropic pressure, atmospheric fallout and river input due to drainage of little local watersheds was selected. Water masses were discriminated with respect to both surrounding and depth and in relation to the processes occurring at the solid-liquid interface. We found that yttrium and Rare Earth Elements in the labile fraction of the suspended particulates result from the mixing between lithogenic material from the Sicilian basin and detrital material of Sahara origin. Y/Ho and Ce/La ratios, Ce anomalies, shape and amplitudes of tetrad effects calculated in both dissolved phase and suspended matter indicates that heavier Rare Earth (from Dy to Lu) mainly occur as organic complexes in near shore waters whereas, light and intermediate Rare Earths (From La to Ho) in the outer waters are ruled by scaveging processes onto surface of suspended matter. The behaviour of these trace elements is explained in terms of lanthanides sorption into Mn-Fe oxyhydroxide surfaces and under solution complexation. In particular, for deep water layers the found low apparent distribution coefficients for the heaviest REE and high dissolved organic matter concentration indicate surface complexation processes according to an outer sphere coordination mechanism.