Sebastien Rauch

Environmental risk of particulate and soluble platinum group elements released from gasoline and diesel engine catalytic converters

A comparison of platinum-group element (PGE) emission between gasoline and diesel engine catalytic converters is reported within this work. Whole raw exhaust fumes from four catalysts of three different types were examined during their useful lifetime, from fresh to 80,000 km. Two were gasoline engine catalysts (Pt-Pd-Rh and Pd-Rh), while the other two were diesel engine catalysts (Pt). Samples were collected following the 91441 EUDC driving cycle for light-duty vehicle testing, and the sample collection device used allowed differentiation between the particulate and soluble fractions, the latter being the most relevant from an environmental point of view. Analyses were performed by inductively coupled plasma-mass spectrometry (ICP-MS) (quadrupole and high resolution), and special attention was paid to the control of spectral interference, especially in the case of Pd and Rh. The results obtained show that, for fresh catalysts, the release of particulate PGE through car exhaust fumes does not follow any particular trend, with a wide range (one-two orders of magnitude) for the content of noble metals emitted. The samples collected from 30,000-80,000 km present a more homogeneous PGE release for all catalysts studied. A decrease of approximately one order of magnitude is observed with respect to the release from fresh catalysts, except in the case of the diesel engine catalyst, for which PGE emission continued to be higher than in the case of gasoline engines. The fraction of soluble PGE was found to represent less than 10% of the total amount released from fresh catalysts. For aged catalysts, the figures are significantly higher, especially for Pd and Rh. Particulate PGE can be considered as virtually biologically inert, while soluble PGE forms can represent an environmental risk due to their bioavailability, which leads them to accumulate in the environment.

Levels and risk assessment for humans and ecosystems of platinum-group elements in the airborne particles and road dust of some European cities

Traffic is the main source of platinum-group element (PGE) contamination in populated urban areas. There is increasing concern about the hazardous effects of these new pollutants for people and for other living organisms in these areas. Airborne and road dusts, as well as tree bark and grass samples were collected at locations in the European cities of Göteborg (Sweden), Madrid (Spain), Rome (Italy), Munich (Germany), Sheffield and London (UK). Today, in spite of the large number of parameters that can influence the airborne PGE content, the results obtained so far indicate significantly higher PGE levels at traffic sites compared with the rural or non-polluted zones that have been investigated (background levels). The average Pt content in airborne particles found in downtown Madrid, Göteborg and Rome is in the range 7.3-13.1 pg m(-3). The ring roads of these cities have values in the range 4.1-17.7 pg m(-3). In Munich, a lower Pt content was found in airborne particles (4.1 pg m(-3)). The same tendency has been noted for downtown Rh, with contents in the range 2.2-2.8 pg m(-3), and in the range 0.8-3.0 and 0.3 pg m(-3) for motorway margins in Munich. The combined results obtained using a wide-range airborne classifier (WRAC) collector and a PM-10 or virtual impactor show that Pt is associated with particles for a wide range of diameters. The smaller the particle size, the lower the Pt concentration. However, in particles <PM-10, some of the highest values correspond to the fraction <0.39 microm. Considering an average Pt content in all particles of approximately 15 pg m(-3), which is representative for all countries and environmental conditions, the tracheobronchial fraction represents approximately 10% and the alveolar fraction approximately 8% of the total particles suspended in air. However, from the environmental risk point of view, an exposure to PGEs in traffic-related ambient air is at least three orders of magnitude below the levels for which adverse health effects might theoretically occur (of approx. 100 ng m(-3)). Therefore, today inhalation exposure to PGEs from automotive catalysts does not seem to pose a direct health risk to the general population. Even though the data available today indicate no obvious health effects, there are still a number of aspects related to PGEs and catalysts that justify further research. First, continual monitoring of changes in PGE levels in air and road dust is warranted, to make sure that there is no dramatic increase from todays levels. Secondly, more detailed information on the chemical composition of the PGE-containing substances or complexes leaving the catalyst surface and the size distribution of the PGE-containing particles released during driving will facilitate a more in-depth human risk assessment.

Platinum-group elements: quantification in collected exhaust fumes and studies of catalyst surfaces

Automotive catalytic converters, in which Pt, Pd and Rh (platinum-group elements; PGEs) are the active components for eliminating several noxious components from exhaust fumes, have become the main source of environmental urban pollution by PGEs. This work reports on the catalyst morphology through changes in catalyst surface by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) and laser-induced breakdown spectrometry (LIBS) from fresh to aged catalytic converters. The distribution of these elements in the fresh catalysts analysed (Pt-Pd-Rh gasoline catalyst) is not uniform and occurs mainly in a longitudinal direction. This heterogeneity seems to be greater for Pt and Pd. PGEs released by the catalysts, fresh and aged 30,000 km, were studied in parallel. Whole raw exhaust fumes from four catalysts of three different types were also examined. Two of these were gasoline catalysts (Pt-Pd Rh and Pd-Rh) and the other two were diesel catalysts (Pt). Samples were collected following the 91,441 EUDC driving cycle for light-duty vehicle testing. The results show that at 0 km the samples collected first have the highest content of particulate PGEs and although the general tendency is for the release to decrease with increasing number of samples taken, exceptions are frequent. At 30,000 km the released PGEs in gasoline and diesel catalysts decreased significantly. For fresh gasoline catalysts the mean of the total amount released was approximately 100, 250 and 50 ng km(-1) for Pt, Pd and Rh, respectively. In diesel catalysts the Pt release varied in the range 400-800 ng km-1. After ageing the catalysts up to 30,000 km, the gasoline catalysts released amounts of Pt between 6 and 8 ng km(-1), Pd between 12 and 16 ng km(-1) and Rh between 3 and 12 ng km(-1). In diesel catalysts the Pt release varied in the range 108-150 ng km(-1). The soluble portion of PGEs in the HNO3 collector solution represented less than 5% of the total amount for fresh catalysts. For 30,000 km the total amount of soluble PGEs released was similar or slightly higher than for 0 km.

Bioaccumulation of palladium, platinum and rhodium from urban particulates and sediments by the freshwater isopod Asellus aquaticus

The three-way catalytic converters introduced to oxidize and reduce gaseous automobile emissions represent a source of platinum group elements (PGEs), in particular platinum, palladium and rhodium, to the urban environment. Abrasion of automobile exhausts leads to an increase of the concentration of PGEs in environmental matrices such as vegetation, soil and water bodies. The bioaccumulation of Pd, Pt and Rh by the freshwater isopod Asellus aquaticus was studied in natural ecosystems and under laboratory conditions. Owing to the low concentration level (ng g(-1)) of PGEs in the animals studied. analyses were performed with a quadrupole inductively coupled plasma mass spectrometry (ICP-MS) and hafnium, copper, yttrium, rubidium, strontium and lead were monitored for spectral interference correction. Asellus aquaticus collected in an urban river showed a content (mean +/- s) of 155.4 +/- 73.4, 38.0 +/- 34.6, and 17.9 +/- 12.2 ng g(-1) (dry weight) for Pd, Pt and Rh, respectively. The exposure of Asellus aquaticus to PGE standard solutions for a period of 24h give bioaccumulation factors of Bf: 150, 85, and 7 for Pd, Pt and Rh, respectively. Exposure of Asellus aquaticus to environmental samples for different exposure periods demonstrated that PGE bioaccumulation is time dependent. and shows a higher accumulation for the materials with a higher PGE content. While all three elements have the same uptake rate for exposure to catalyst materials, for exposure to environmental materials they havc a different uptake rate which can be attributed to transformations of the PGE species in the environment.

Bioelectrochemical recovery of Cu, Pb, Cd, and Zn from dilute solutions

In a microbial bioelectrochemical system (BES) living microorganisms catalyze the anodic oxidation of organic matter at a low anode potential. We used a BES with a biological anode to power the cathodic recovery of Cu, Pb, Cd, and Zn from a simulated municipal solid waste incineration ash leachate. By varying the control of the BES, the four metals could sequentially be recovered from a mixed solution by reduction on a titanium cathode. First, the cell voltage was controlled at zero, which allowed recovery of Cu from the solution without an electrical energy input. Second, the cathode potential was controlled at -0.51 V to recover Pb, which required an applied voltage of about 0.34 V. Third, the cathode potential was controlled at -0.66 V to recover Cd, which required an applied voltage of 0.51 V. Finally, Zn was the only metal remaining in solution and was recovered by controlling the anode at +0.2V to maximize the generated current. The study is the first to demonstrate that a BES can be used for cathodic recovery of metals from a mixed solution, which potentially could be used not only for ash leachates but also for e.g. metallurgical wastewaters and landfill leachates.

Platinum uptake by the freshwater isopod Asellus Aquaticus in urban rivers

Platinum has been increasing in the environment as a result of emissions from catalytic converters. The platinum emitted is principally located in the vicinity of roads but might be transported to urban rivers through highway and urban run-off water. Platinum concentrations in the freshwater isopod Asellus aquaticus were measured for two urban rivers and a stormwater detention pond. Concentrations ranged from 0.04 to 12.4 micrograms g-1 for direct analysis and from 0.16 to 4.5 micrograms g-1 after depuration. Analyses of water, pore water and sediments indicate that platinum in urban rivers is mostly found in the sediments and these provide the major contribution of platinum to Asellus aquaticus. Exposure experiments showed the importance of platinum speciation for uptake.

Determination of palladium, platinum and rhodium concentrations in urban road sediments by laser ablation-ICP-MS

The introduction of catalytic converter technology to cars has alleviated gaseous exhaust emissions but in turn has resulted in emissions of the three platinum group metals (PGMs), Pd, Pt and Rh, contained in the automobile catalyst. The environmental effects of PGMs are still largely unknown and their accurate determination is particularly difficult because concentrations are at trace levels. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a direct trace element measurement technique and can be used for the rapid characterization of metals in solid environmental matrices. Here, the capability of LA-ICP-MS for the direct quantitative determination of PGMs in road sediments was assessed. Two Nd:YAG laser systems operating at 266 and 1064 nm, respectively, were coupled to an ICP-MS. Uncontaminated road sediments were spiked with PGMs, both as solution and as solid certified reference material, and used to assess the analytical performance of the technique and to calibrate the instrument. Interferences due to the formation of molecular ions and double charged ions were investigated. The LA-ICP-MS was then used to determine the concentration of PGMs in a recent urban road sediment and the results were compared with high resolution-ICP-MS measurements after microwave sample digestion with Aqua Regia. The LA-ICP-MS allows the quantitative analysis of Pd, Pt, and Rh in road sediments at sub microgram per gram levels with a relative standard deviation of 10% and with estimated detection limits in the lower nanogram per gram range. Good agreement between LA-ICP-MS and HR-ICP-MS analysis could be obtained for Pt and Rh (<3% R.S.D. at ca. 100 ng g−1) whereas the determination of Pd remains subject to interferences.

Environmental Relevance of the Platinum-Group Elements

It has recently been demonstrated that platinum group elements (PGE) are released from automobile catalysts into the environment, raising concern over ecological and human health risks. However, there is still a lack of knowledge regarding the dispersion and transformation of PGE in the environment and it is therefore difficult to assess potential risks. The research presented here focuses on the development and use of analytical procedures to investigate the environmental relevance of PGE. While PGE occur at low concentrations, increasingly sensitive analytical techniques allow their determination at environmentally relevant levels. Inductively coupled plasma-mass spectrometry (ICP-MS) is the method of choice for the determination of PGE in environmental samples, although interference is a severe obstacle when trace concentrations have to be determined. Several approaches to ICP-MS were assessed, including quadrupole ICP-MS with mathematical correction, sector field ICP-MS and sample introduction by laser ablation. Besides quantification, the coupling of a laser microprobe to ICP-MS allowed the investigation of PGE emission mechanisms and provided definitive fingerprints for tracking PGE containing particles in the environment. Palladium, platinum and rhodium were determined in exhaust fumes from representative catalysts and the impact of ageing on emissions was assessed for distances up to 80000 km. As a result of emission PGE were found in airborne particles, road sediments and river sediments. Further, bioaccumulation by the freshwater isopod Asellus aquaticus was investigated. Although PGE were previously believed to be relatively inert, this study shows the presence of bioavailable PGE species in the environment, with Pd presenting a higher bioavailability. Results show that PGE concentrations are low and might not present a direct human health risk. However, the occurrence of bioavailable PGE species raises concern about potential ecological risks. The present study provides information on PGE dispersion and evidence of their transformation into bioavailable species, although further studies are still needed to fully understand their environmental behaviour.

Scanning laser ablation-ICP-MS tracking of platinum group elements in urban particles

While it has now been demonstrated that platinum group elements (PGE) are released from automobile catalysts into the environment, less is known about the form in which they are emitted and transported. Here we show that scanning laser ablation-inductively coupled plasma-mass spectrometry (scanning laser ablation-ICP-MS) can identify and track individual particles released from automobile catalysts present in environmental particulates and sediments. Particles with high PGE concentrations were found in the exhaust of gasoline and diesel vehicles equipped with catalytic converters. The PGE-Ce association in individual particles provides a definitive fingerprinting for tracking catalyst particles in environmental compartments, while relative PGE signal intensity is an indication of the catalyst type. Scanning laser ablation-ICP-MS of road and aquatic sediments revealed a few PGE containing catalyst particles and it was possible to identify catalyst types for the origin of these particles.

Performance of an in situ passive sampling system for metals in stormwater

A passive sampler has been developed and is demonstrated in situ for urban runoff. The passive sampler is compared to conventional composite (time-dependent and flow-weighted) bottle sampling during and between storm events. The sampling was carried out at established stormwater stations; before and after a stormwater detention pond. In situ deployment of the passive sampler provides the metal concentrations, corresponding to the electrochemically available fraction of total metal, for time-dependent samples collected in parallel. The sampler provides improved accuracy compared to bottle sampling because contamination during sample transport and handling is minimised. Laboratory handling is reduced by direct analysis of the accumulated metals on the receiving membrane by laser ablation inductively coupled plasma mass spectrometry. Passive sampling also solves the problem of metal speciation change during transport to the laboratory, which is a potential problem for bottle samples. The low cost and convenience of the passive sampler and subsequent analysis should allow significantly more extensive spatial and temporal monitoring of metals in the aquatic environment than has previously been possible.