Behavior of platinum during estuarine mixing (Pontevedra Ria, NW Iberian Peninsula)

The concentrations of Pt in sediments, water and suspended particulate matter (SPM) were determined in the Lérez River estuary (Pontevedra Ria, NW Iberian Peninsula) on two sampling dates in 2008 and 2011, by means of catalytic adsorptive stripping voltammetry. Average concentrations in sediments (1.2 ± 0.5 ng g− 1; n = 13) corresponded to an enrichment factor of 2–4 compared to background values, and were in the range of those found in the SPM during the 2011 sampling (2.1 ± 2.4 ng g− 1; n = 15), but significantly lower than those in 2008 SPM (8.0 ± 4.4 ng g− 1; n = 15). Higher dissolved Pt concentrations were also found in 2008 (0.21 and 0.62 pM in the freshwater and seawater end-member) compared to the 2011 campaign (0.03 — freshwater and 0.40 pM — seawater end-member). Concentrations in the seawater end-members exceed those of typical North Atlantic waters, suggesting inputs of this element within the estuary. The extremely low value for the freshwater end-member in 2011 appears to be among the lowest Pt concentrations ever reported in the literature. Non-conservative behavior of Pt during estuarine mixing was observed on both sampling dates. Particle–water distribution coefficients (KD) show a decrease with salinity, in agreement with speciation calculations, which predict a transfer from neutral Pt(II) (as Pt(OH)2) in freshwater to negatively charged Pt(IV) (as PtCl5(OH)2 −) species in seawater. Such behavior during estuarine mixing can play an important role in Pt mobilization from contaminated particles discharged into estuaries and coasts.

► Estuarine concentrations of Pt in sediments, particulate suspended matter and water were determined.
► Concentrations are significantly lower than those previously reported for estuarine waters.
► Non-conservative behavior of Pt during estuarine mixing was observed.
► Speciation calculations predict a change in Pt redox state from fresh to sea water.
► A decrease of Pt particle-reactivity with salinity agrees with the predicted speciation.