Hans Urban

Geochemical behaviour of platinum-group elements (PGE) in particulate emissions by automobile exhaust catalysts: experimental results and environmental investigations

Abstract The increasing use of automobile catalysts leads to the emission of the platinum-group elements (PGE) platinum, rhodium and palladium into the environment. Experiments were conducted in order to assess the possibility of their mobility caused by species transformation. Soil material was contacted with a ground catalyst and, after varying parameters such as pH, chloride or sulfur concentration, the solubility of platinum and rhodium was measured. Laboratory results were compared with those from different environmental materials (soil, run-off sediments, surface waters, tunnel dust). Analytical techniques were GFAAS (after preconcentration by nickel sulfide fire assay), XRF, ICP-MS, AV, XPS and SIMS. Experimental results show that small, although significant, amounts of platinum and rhodium are adsorbed in soil or soluble in surface waters. Environmental materials exhibit a relatively constant Pt/Rh ratio of 5, which points to a common source, the automobile catalysts. A direct determination of PGE species by surface analysis is still not possible, due to low surface concentrations. As most of the PGE seem to behave in an inert manner and are immobile they do not constitute a hazard to health.

Konzentration und Verteilung von Platingruppenelementen (PGE) in Böden

ZusammenfassungDer zunehmende Einsatz von Abgaskatalysatoren in Kraftfahrzeugen könnte dazu führen, daß bei Abrieb des Katalysatormaterials eine erhöhte Platinmetall-Emission erfolgt und es damit zu einer Belastung der Umwelt mit Platingruppenelementen kommt.Um die derzeitigen Konzentrationen von Platingruppenelementen (PGE) in Böden zu ermitteln, wurden im Rahmen eines Forschungsprojekts des Instituts für Geochemie, Petrologie und Lagerstättenkunde der J. W. Goethe-Universität Frankfurt mit dem Thema „Bodenbelastung durch Platingruppenelemente entlang der Autobahnstrecke A66 Frankfurt-Wiesbade” systematisch 71 oberflächennahe Bodenproben entnommen und auf ihre PGE-Konzentrationen analysiert.Die Analysenergebnisse zeigen, daß die Platinkonzentrationen im Durchschnitt 10 μg/kg betragen. Sowohl für Palladium als auch für Rhodium liegen die Konzentrationen bei < 2 μg/kg und für Ruthenium bei 3 μg/kg. Ferner wurde festgestellt, daß mit zunehmender Entfernung vom Autobahnrand die PGE-Konzentrationen abnehment und in etwa 20 m Entfernung von der Autobahn mit dem angewandten Analysenverfahren nicht mehr nachzuweisen sind. Die Platingruppenelemente sind ausschließlich oberflächennah in den oberen 20 cm der Böden in meßbaren Konzentrationen vorhanden. Diese Ergebnisse zeigen bereits heute anormale PGE-Konzentrationen in den betroffenen Böden entlang der untersuchten Autobahnstrecke. Sie können dazu dienen, einen zu vermutenden weiteren Anstieg der PGE-Konzentrationen zeitabhängig zu kontrollieren.AbstractIn Germany automobile exhaust control by platinum-group element (PGE) loaded catalysts is now well established. By mechanical or chemical attrition, these catalysts could act as a potential source for a significant increase of PGE abundances in the environment. During a recent research program concentrations and distributions of PGE in different soils were measured along the highway A66 Frankfurt-Wiesbaden. 71 nearsurface soil samples were analysed by graphite furnace atomic absorption spectrometry (GFAAS). The results revealed average abundances of 10 ppb platinum and 3 ppb ruthenium. Palladium as well as rhodium were below the analytical detection limit of 2 ppb. With increasing distance from the highway edge PGE values gradually decreased. Only the upmost soil layer, down to 20 cm depth, contains measurable PGE concentrations. Results: There are irregular PGE concentrations of anthropogenic origin in different soils along the highway A66 Frankfurt-Wiesbaden possibly arising from automobile exhaust catalysts. Further monitoring could help to avoid potential environmental hazards. *** DIRECT SUPPORT *** A00HP020 00002

Sources of anthropogenic platinum-group elements (PGE): Automotive catalysts versus pge-processing industries

Soil samples from the area of Hanau (Hessen, Germany) were analyzed for anthropogenic platinum-group elements (PGE). The results confirm the existence of two different sources for anthropogenic PGE: 1. automotive catalysts, and 2. PGE-processing plants. Both sources emit qualitatively and quantitatively different PGE spectra and PGE interelemental ratios (especially the Pt/Rh ratio). Elevated PGE values which are due to automotive catalysts are restricted to a narrow-range along roadside soil, whereas those due to PGE-processing plants display a large-area dispersion. The emitted PGE-containing particles in the case of automotive catalysts are subject to transport by wind and water, whereas those from PGE-processing plants are preferably transported by wind. This points to a different aerodynamic particle size. Pt, Pd, and Rh concentrations along motorways are dependent on the amount of traffic and the driving characteristics.

Anthropogenic emission of platinum-group elements (Pt, Pd and Rh) into the environment: concentration, distribution and geochemical behaviour in soils

The introduction of catalytic converters on cars in order to meet emission standards initiated the beginning of a sometimes controversial discussion on the probable immission of platinum-group elements (PGE) into, and their possible effects on the environment. The used PGE (platinum, palladium and rhodium) reduce by catalytic reactions hazardous components in engine emissions. However, the complex and often adverse working conditions (temperature changes, variations in gas composition and flow rate, and mechanical abrasion by vibrations) lead to a chemical and mechanical treatment of the catalytic converters, resulting in a loss and emission of PGE. In consequence, even only 15 years after the introduction of catalytic converters in Germany, one finds significantly elevated PGE contents in environmental compartments along roadsides. The geogenic background PGE concentrations are estimated to lie in untreated soil at ca. 1 µg/kg (Zereini et al. 1997a), whereas contaminated soils along roadsides show contents up to several hundred µg/kg (e.g. Cubelic et al. 1997; Claus et al. 1999; Beyer at al. 1999; Dirksen 1998; Helmers and Mergel 1997; Laschka et al. 1996; Zereini 1997; Zereini and Alt 1999). Whereas this trend is well proven, the environmental effects are still not understood and await further investigation.

Platinum, Lead and Cerium Concentrations of Street Particulate Matter (Frankfurt am Main, Germany)

Road dust samples were collected in and around various traffic areas in Frankfurt am Main, Germany and analyzed in terms of their chemical composition using ICP-MS, AV, XPS, TXRF and GF-AAS methods. Platinum (Pt), lead (Pb) and cerium (Ce) were the focus of analysis. Street particulate matter or dust is primarily composed of quartz, clay minerals, soot and organic substances and, through its transport by wind and precipitation, is a precursor for sediments and soils. Particle sizes are variable with the largest having a maximum diameter in the range of 10 to 25 µm. Sample locations included the A5/A67 Autobahn (i.e. highway), various inner city streets, two tunnels and three indoor car parks.The average Pt concentrations in the samples ranged from highest to lowest in the following order: Autobahn, inner city streets, indoor car parks and tunnels. Pb concentrations were found to display a similar trend. Ce concentrations, in contrast, exhibited a different pattern with the highest amounts being found in samples collected from the inner city.Pt concentrations in road dust appear to be positively related to both traffic density and speed of travel. Elevated Pt concentrations in particulate matter samples collected in indoor car parks, however, suggest that platinum metals can also be emitted at low speeds. The height at which samples are collected can also strongly influence the concentrations found. Specifically, samples taken at a height of <1.5 m generally display the highest concentrations. Surface particle analysis using XPS to determine the presence of Pt species could not be conducted for the two tunnel samples as concentrations fell below the detection limit. Our results, however, indicate the presence of elevated atmospheric Pt concentrations.

The determination of platinum-group elements (PGE) by nickel sulfide fire-assay: Coexisting PGE-phases in the nickel sulfide button

The chemical composition of phases in buttons obtained by nickel sulfide fire-assay during the determination of platinum-group elements (PGE) has been investigated by electron microprobe analysis. Different PGE-containing phases, due to varying flux constituents and species of added PGE, have been detected. By using sodium tetraborate as flux constituent and adding PGE as chlorides, in a cryptocrystalline Ni3S2 matrix with low PGE (mainly Rh and Ru) contents, Rh- and Ru-bearing nickel sulfides ((Ni7.68–7.80Ru0.84–0.90Rh0.35–0.43)9S8) and Ir alloys ((Ir,Pt,Os)0.56–0.62(Ru,Rh)0.25–0.28Ni0.12–0.19) are found. Treatment with lithium tetraborate leads to a Ni3S2 matrix exhibiting slightly higher Rh and Ru contents, with inclusions of nickel-rhodium sulfides (Ni8Rh4S9) and platinumnickel alloys (Pt0.45Ni0.36–0.39Ru0.11–0.14Rh0.05). Finely dispersed metallic colloidals from an automobile catalyst, with platinum and rhodium as main components, have given only platinum-nickel alloys (Pt1−xNix). Considerable losses of PGE during analytical steps following the fire assay are expected when their contents in sulfidic phases, which are more likely to be dissolved, are high.

Anthropogenic emission of platinum-group elements into the environment

This work represents a summary of our test results over emissions of platinum-group elements (PGE) in soils, which were won in the context of an interdisciplinary research project on ‘ecological future research’ sponsored by the Hessian government. Directly related to this investigation was the time-dependent entry of concentrations of PGE in soils along roadsides, their further rise in control and the investigation of the geochemical behaviour of these metals regarding their solubility and mobility in the soil.Soil samples were taken along the motorways of Frankfurt-Wiesbaden (A66), Frankfurt-Mannheim (A5/A67/A6), and the A3 and A45 in the area of Hanau, and the PGE were examined here. The test results do not leave a doubt that the increased PGE contents in the soils in the direct environment of the motorway are to be attributed to motor vehicles with catalysts. In sections of the soil samples of Hanau, Ir and Ru are also seen to occur beside Pt, Pd and Rh. Since these items are not constituents of the catalyst, their origin is possibly due to emissions from the precious metal-processing industry in Hanau.The highest concentrations of PGE in the soil occur directly at the edge of the motorway and decrease with increasing distance from the motorway. The PGE emissions depend on traffic volume and driving characteristics. Based on Pt concentrations found in soils near roadsides and observed traffic volumes, automotive catalytic converters are estimated to emit an average of 270 ng/km. Currently, the Pt and Rh deposited behave immobile in soils. At present, Pt and Rh from catalytic converters present no danger to the groundwater.Although platinum does not represent an acute danger, due to its low concentrations in the environment at the present, this rise in concentration may necessitate the use of routine checks in the future.

Platinkonzentrationen in Staubproben aus Frankfurt am Main und Umgebung

Nach der Einfuhrung des PGE-haltigen Katalysators zur Reduzierung der Schadstoffemissionen im Automobilabgas Anfang der 70iger Jahre in den USA wurde bald deutlich, das eine hohe Abrasionsrate des Katalysators zur Deposition der PGE in der naheren Umgebung der Verkehrswege fuhrte. In den USA wurden von Hodge u. Stallard (1986) erhohte Mengen Platin in Stauben auf breitblattrigen Pflanzen langs stark befahrener Strasen ermittelt. Schramel et al. (1995) konnten in einem Tunnelstaub Pt-Gehalte von 65,3 ± 8,4 μg/kg nachweisen. Untersuchungen von Wei u. Morrison (1994) und Farago et al. (1996a) ermittelten ebenfalls Pt-Konzentrationen in Strasenstauben. Die dabei angewandten Sammeltechniken lassen allerdings keinen direkten Vergleich zu. Die besser als Kehrgut zu bezeichnenden Proben enthielten unter 20 μg/kg Pt.

Platingruppenelemente (PGE) in Schlamm- und Abwasserproben aus Absetzbecken der Autobahnen A8 und A66

Die Platingruppenelemente Platin, Palladium, Iridium, Rhodium, Ruthenium und Osmium gehoren zu den seltenen Elementen des Periodensystems und sind am Aufbau der Erdkruste mit schatzungsweise 0,4 bis 5 μg/kg beteiligt (Hartley 1991). Bislang wurde ihnen keine umweltrelevante Bedeutung zugemessen. Dies konnte sich durch die generelle Ausrustung von Kraftfahrzeugen mit Abgaskatalysatoren in der Zukunft andern.

Mammalian target of rapamycin complex 1 activation sensitizes human glioma cells to hypoxia-induced cell death

Glioblastomas are characterized by fast uncontrolled growth leading to hypoxic areas and necrosis. Signalling from EGFR via mammalian target of rapamycin complex 1 (mTORC1) is a major driver of cell growth and proliferation and one of the most commonly altered signalling pathways in glioblastomas. Therefore, epidermal growth factor receptor and mTORC1 signalling are plausible therapeutic targets and clinical trials with inhibitors are in progress. However, we have previously shown that epidermal growth factor receptor and mTORC1 inhibition triggers metabolic changes leading to adverse effects under the conditions of the tumour microenvironment by protecting from hypoxia-induced cell death. We hypothesized that conversely mTORC1 activation sensitizes glioma cells to hypoxia-induced cell death. As a model for mTORC1 activation we used gene suppression of its physiological inhibitor TSC2 (TSC2sh). TSC2sh glioma cells showed increased sensitivity to hypoxia-induced cell death that was accompanied by an earlier ATP depletion and an increase in reactive oxygen species. There was no difference in extracellular glucose consumption but an altered intracellular metabolic profile with an increase of intermediates of the pentose phosphate pathway. Mechanistically, mTORC1 upregulated the first and rate limiting enzyme of the pentose phosphate pathway, G6PD. Furthermore, an increase in oxygen consumption in TSC2sh cells was detected. This appeared to be due to higher transcription rates of genes involved in mitochondrial respiratory function including PPARGC1A and PPARGC1B (also known as PGC-1α and -β). The finding that mTORC1 activation causes an increase in oxygen consumption and renders malignant glioma cells susceptible to hypoxia and nutrient deprivation could help identify glioblastoma patient cohorts more likely to benefit from hypoxia-inducing therapies such as the VEGFA-targeting antibody bevacizumab in future clinical evaluations.