Osmium and Platinum Decoupling in the Environment: Evidences in Intertidal Sediments (Tagus Estuary, SW Europe)

Catalytic converters in automobiles have significantly increased the input of platinum group elements (PGE) to the environment, and their coupled geochemical behavior has been proposed. To check this hypothesis, Pt and Os concentrations and ¹⁸⁷Os/¹⁸⁸Os ratios were determined in sediment cores and interstitial waters from the Tagus Estuary (SW Europe) affected by different traffic pressure. Platinum concentration in surface sediments nearby the high traffic zone (up to 40 ng g^–1) indicated severe contamination. Although lower than Pt, Os enrichment was also observed in surface sediments, with lower ¹⁸⁷Os/¹⁸⁸Os ratios than in deeper layers. Dissolved Pt and Os in interstitial waters, 0.1–0.7 pg g^–1 and 0.03–0.10 pg g^–1, respectively, were higher than in typical uncontaminated waters. Results indicate two sources of Pt and Os into the Tagus Estuary salt marshes: a regional input associated with industrial activities, fossil fuel combustions, and regional traffic and a local source linked to nearby traffic density emissions. Estimations of Os and Pt released by catalytic converters support this two-source model. Differences in geochemical reactivity and range of dispersion from their sources lead to a decoupled behavior of Os and Pt, questioning the use of Os isotopes as proxies of PGE sources to the environment