The emission of the platinum group elements Pt, Pd and Rh (PGE) from automobile
catalytic converters has led to rapid increases in Pt, Pd and Rh concentrations in roadside
media. The vast majority of previous research examining autocatalyst-derived PGE
in the urban environment has been performed in Europe or North America. Although
catalytic converters became mandatory on all new cars sold in Australia from 1986, no
prior studies have focussed on urban platinum group element (PGE) concentrations in
Australian environments.
In general, the results of previous studies suggest a limited post depositional
mobility of catalyst derived PGE. However, these findings are from research conducted in
cool-temperate climate zones with regular rainfall and from environments where soils and
sediments differ from the typically coarse grained, sandy soils with low levels of organic
matter found in Perth. The relevance of European and North American findings to other
regions with different climates and soils is therefore unclear and where the climate regime
and properties of soils and sediments are not comparable to those previously studied, the
potential exists for different geochemical behaviour of autocatalyst-derived PGE. Through
investigations of spatial and temporal distribution and the identification of some of the
main factors controlling transport and fixation, the principal aim of the research presented
in this thesis was to elucidate aspects of the post depositional geochemical behaviour of autocatalyst derived PGE in selected roadside environments in Perth, Western Australia.
The quality of some of the reported PGE data has been questioned by a number of
workers. Possibly the most intractable diffculty in the determination of low concentrations
of PGE in environmental samples by ICP-MS is the control of interferences from common
matrix components. To ensure accurate and reliable data in this research, prior to
the analysis of environmental samples, the optimal instrumental conditions for PGE
determination and two commonly applied matrix separation methodologies (tellurium
coprecipitation and ion-exchange) were investigated. The most effective matrix separation
technique for the accurate determination of PGE in the environmental samples applicable
to this study, such as road dusts and roadside soils, was found to be cation exchange.
The lack of knowledge regarding urban PGE concentrations in an Australian context
was addressed through examinations of PGE levels in road dusts, roadside soils and
infiltration basin and wetland sediments. Data show significant elevation of all three
PGE above local background and average upper crust values. PGE ratios in surface road
dusts and soils were consistent with known catalytic converter compositions and while Pt
and Rh concentrations are comparable with European studies, Pd levels were generally
higher in these Australian samples.
The effect of climate on PGE levels in roadside environments was investigated by
repeat sampling of road dusts and roadside soils over a twelve month period. Both
sample media exhibited seasonal variations. The presence of seasonal variability in
PGE concentrations in roadside soils suggests that this environmental compartment
does not represent a long term accumulative matrix for autocatalyst-derived PGE.
Further examination of spatial distribution revealed that the PGE exhibit greater vertical mobility in the soils of Perth than has previously been reported, with elevations above
local background concentrations occurring at depths of 14-20cm. Neither small scale
spatial variability nor vertical mobilisation were of su±cient magnitude to explain the
observed temporal variability. Based on the pattern of seasonal PGE distribution and
that of rainfall, temporal fluctuations are attributed to transport by stormwater. The
mobilisation of PGE by stormwater is thought to occur principally via the water-mediated
transport of PGE bearing particulates. However, PGE fractionation leading to a
greater post-depositional mobility of Pd may occur during transport through the urban
stormwater system.
In the urban environment of Perth, infiltration basin and wetland sediments represent
a sink for autocatalyst-derived PGE. Based on the examination of PGE ratios, and the
vertical distribution of PGE in infiltration basin sediments, Pt and Rh remain associated,
whereas Pd may be differentially mobilised. For both soils and infiltration basin sediments,
variation in pH was limited and does not show any correlation with vertical profiles of PGE,
suggesting that pH does not act as a major control on PGE mobility. The role of organic
matter is less clear, and although no straightforward relationships were apparent, where
high levels of organic matter were present, profiles suggest an increased mobilisation of
Pd. This differential mobilisation of Pd may therefore be caused by the formation of an
organo-metallic species.
Temporal fluctuations in PGE levels in road dusts and roadside soils indicate that
inputs of PGE to aquatic environments are likely to occur as seasonal pulses. The routing
of road runoff into urban wetlands therefore represents a major pathway by which aquatic
ecosystems may be exposed to autocatalyst-derived PGE. The impact of such inputs is unclear, however, as other recent studies have shown that a portion of autocatalyst-derived
PGE, and especially Pd is bioavailable, the potential for ecosystem degradation due to
PGE contamination represents a major avenue for further research.
| Identifer | oai:union.ndltd.org:ADTP/225374 |
| Date | January 2004 |
| Creators | Jason D. Whiteley |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Jason D. Whiteley |
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