Gregory M. Morrison

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.

Development of a novel passive sampling system for the time-averaged measurement of a range of organic pollutants in aquatic environments.

A new sampling system has been developed for the measurement of time-averaged concentrations of organic micropollutants in aquatic environments. The system is based on the diffusion of targeted organic compounds through a rate-limiting membrane and the subsequent accumulation of these species in a bound, hydrophobic, solid-phase material. It provides a novel and robust solution to the problem of monitoring in situations where large temporal fluctuations in pollutant levels may occur. Accumulation rates are regulated by choice of diffusion-limiting membrane and bound solid-phase material and have been found to be dependent on the physico-chemical properties of individual target analytes. Two separate prototype systems are described: one suitable for the sampling of non-polar organic species with log octanol/water partition coefficient (log P) values greater than 4, the other for more polar species with log P values between 2 and 4. Both systems use the same solid-phase material (47 mm C18 Empore disk) as a receiving phase but are fitted with different rate-limiting membrane materials (polysulfone for the polar and polyethylene for the non-polar analytes). The two systems complement each other and together can be used for sampling a wider range of organic analytes than generally possible using current passive sampling techniques. Calibration data are presented for both devices. In each case, linear uptake kinetics were sustained, under constant conditions, for deployment periods of between 1 and 9 days. The effects of water temperature and turbulence on sampling rates have been quantitatively assessed. The performance of the system was further investigated by means of field exposures for one and two weeks in marine environments where calibrated samplers were used to determine the time-averaged concentrations of the polar biocides diuron and irgarol 1051. The quantitative results obtained using the passive sampler were compared with those obtained using spot sampling.

A life cycle assessment based procedure for development of environmental sustainability indicators for urban water systems

Environmental sustainability is a concern and stated objective for municipalities and organisations, but is often vaguely defined and clear measurement procedures are lacking. An iterative procedure for the selection of indicators, which reflects the environmental sustainability of urban water systems, is presented. The analytical basis for selecting indicators is life cycle assessment (LCA), which provides a stringent assessment of environmental sustainability. The indicators were evaluated in Case Studies in a developed and a developing region. The iterative procedure allows refinement/replacement of indicators through Case Studies and further LCA.

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.

Platinum in road dusts and urban river sediments

Platinum concentrations in road dusts and urban river sediments were analysed by dry-ash digestion followed by adsorptive stripping voltammetry. The analysis gave a detection limit of 0.5 ng/g, with up to 85% recovery of added platinum and a standard deviation of ±2.2%. A comparison of platinum concentrations in size-fractionated road dusts collected in 1984 and 1991 showed average increases in all fractions: <63 μm, 3.0–8.9 ng/g; 63–125 μm, 1.5–3.6 ng/g; and 125–1000 μm, <0.5–2.8 ng/g. Present-day surface loadings of platinum were calculated for a car park (26 ng/m2) and a kerbside (1.28 μg/m2), and mean event platinum concentrations in highway run-off were calculated to be 0.1–0.7 ng/l. Concentrations of platinum in urban river sediments varied from <0.5 to 2.2 ng/g.

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.

Platinum analysis and speciation in urban gullypots

Concentrations of platinum in the <-μm fraction of some Swedish road sediments have been shown to increase from 3.0 ng n−1 in 1984 to 8.9 ng g−1 in 1991. Road sediments contained 39–88% more Pt than gullypot sediments and sequential extraction showed a distinct shift from predominantly inorganic Pt on the road surface to wholly organic Pt in the gullypot. Dissolved Pt concentrations in disturbed gullypot liquor were within the range 1.7 ng 1−1 to 3.8 ng 1−1 and are explained by bacterial action in teh gullypot sediment mobilizing organically bound dissolved Pt forms.

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.

Performance optimisation of a passive sampler for monitoring hydrophobic organic pollutants in water

The performance of an integrative passive sampler that consists of a C18 Empore disk sorbent receiving phase fitted with low density polyethylene membrane was optimised for the measurement of time-weighted average concentrations of hydrophobic micropollutants in water. A substantial improvement of sampling characteristics including the rate of sampling and the sampling precision was achieved by decreasing the internal sampler resistance to mass transfer of hydrophobic organic chemicals. This was achieved by adding a small volume of n-octanol, a solvent with high permeability (solubility [times] diffusivity) for target analytes, to the interstial space between the receiving sorbent phase and the polyethylene diffusion-limiting membrane.

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.