title: Assessing the potential of inorganic anions (Cl-, NO3-, SO42-and PO43-) to increase the bioaccessibility of emitted palladium in the environment: Experimental studies with soils and a Pd model substance.
abstract: Palladium (Pd) emitted from vehicles equipped with exhaust catalytic converters has been accumulating at a greater rate relative to other platinum group elements (PGE) in the last 10-20 years. Little is known, however, regarding the various environmental factors and conditions which are likely to modulate the chemical behavior and bioaccessibility of this element post-emission. To meet data needs, soils and a Pd model substance were treated with solutions containing common anions (Cl-, NO3-, SO42-und PO43-) to shed light on the geochemical behavior of emitted Pd under ambient conditions. As part of this, the particle surface chemistry of treated residues (insoluble phase) and solutions (soluble phase) was examined using XPS to assess the chemical transformation of Pd in the presence of inorganic anions. The results show that Pd is the most soluble in the presence of anionic species, followed by rhodium (Rh) and platinum (Pt). Pd in field-collected samples was found to be considerably more soluble than the metallic Pd in the model substance, Pd black, when treated with anionic species. The results also demonstrate that the solubility of Pd black is strongly dependent on solution pH, concentration and the duration of reaction. The outer 3-4 atomic layers of metallic Pd was determined via XPS to be partially oxidized when treated with anion solutions, with the degree being dependent on anion type. The concentration of dissolved O2in solution was found to have little impact on the transformation of metallic Pd. Given the ubiquitous nature of the anions examined, we can expect that Pd will become more bioaccessible post-emission.
authors.affiliation: Institute for Atmospheric and Environmental Sciences, Department of Environmental Analytical Chemistry, Goethe University Frankfurt am Main, Frankfurt am Main, Germany.
authors.forename: Fathi
authors.initials: F
authors.lastname: Zereini
authors.affiliation: School of the Environment, Earth Sciences Centre, Rm. 1016V, 33 Willcocks St., University of Toronto, Toronto, Ontario, Canada M5S 3E8; Dalla Lana School of Public Health, University of Toronto, Toronto, Canada. Electronic address: clare.wiseman@utoronto.ca.
authors.forename: Clare L S
authors.initials: CLS
authors.lastname: Wiseman
authors.affiliation: Monheimer Str. 3, 53229 Bonn, Germany.
authors.forename: Jana
authors.initials: J
authors.lastname: Poprizki
authors.affiliation: Evonik Technology & Infrastructure GmbH, Hanau-Wolfgang, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Albers
authors.affiliation: Umicore AG & Co. KG, Hanau-Wolfgang, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schneider
authors.affiliation: Institute of Analytical and Bioanalytical Chemistry, Ulm University, Ulm, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Leopold
mesh_terms: D000838:Anions; D002384:Catalysis; D002713:Chlorine / Q000737:chemistry*; D004785:Environmental Pollutants; D052918:Environmental Restoration and Remediation; D009566:Nitrates / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D010984:Platinum; D012238:Rhodium; D012987:Soil / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*; D001335:Vehicle Emissions
chemical_list: D000838:Anions; D004785:Environmental Pollutants; D009566:Nitrates; D010710:Phosphates; D012987:Soil; D013431:Sulfates; D001335:Vehicle Emissions; D010984:Platinum; D002713:Chlorine; D010165:Palladium; D012238:Rhodium
keywords: Bioaccessibility; Geochemistry; Inorganic anions; Palladium; Platinum group elements