The Effects of Road Transport on Freshwater and Marine Ecosystems

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2.4.3 Brake Pads
Brake pads contain a complex range <strong>of</strong> organic compounds as a result <strong>of</strong> the inclusion <strong>of</strong> a range <strong>of</strong>
resins, binders and fillers in the pads. <strong>The</strong> general composition <strong>of</strong> pads is provided by Kennedy et al.
(2002). Specific information is available on the concentration <strong>of</strong> some key organic compounds based
upon the examination <strong>of</strong> a limited number <strong>of</strong> New Zealand brake pad samples (Gadd & Kennedy
2000). Key organic compound groups present include phenols, phthalates, amines and amides and
benzothiazoles amongst others.
2.4.4 Tyres
Tyres are composed <strong>of</strong> synthetic and natural rubbers. Kennedy et al. (2002) provides information on
the general composition <strong>of</strong> tyres and reviews what is known about the composition <strong>of</strong> tyres in New
Zealand and overseas. <strong>The</strong> New Zealand tyre information comes from analytical data presented in
Gadd & Kennedy (2000). That data showed that tyre particulates are dominated by n-alkanes and
alkanoic acids and natural resins. PAHs are relatively important constituents with other compound
groups such as benzothiazoles, aromatic and heterocyclic amines and phenols also contributing
significantly.
2.4.5 <strong>Road</strong> surface wear
Most road surfaces in New Zealand are composed <strong>of</strong> bitumen (and aggregate). Kennedy et al. (2002)
provide background information on the nature <strong>of</strong> road surfaces in New Zealand and summarise the
results <strong>of</strong> bitumen analysis presented in Gadd & Kenendy (2000). Bitumen is dominated by n-alkanes
with the bulk being >C 29 . Bitumen and asphalt contains a range <strong>of</strong> biological markers. <strong>The</strong>se
compounds include terpanes which comprise cyclic compounds such as hopanes and steranes.
Bitumen contains PAHs but typically only at low concentrations. Total PAH concentrations appear to
be in the order <strong>of</strong> 10 mg/kg with concentrations <strong>of</strong> many individual PAHs being in the range 1-3 mg/kg.
Concentrations <strong>of</strong> organic compounds are low with a nominal concentration <strong>of</strong> 10 mg/kg <strong>of</strong> total PAH
identified (Gadd & Kennedy 2000). Takada et al. (1990) found that the PAH concentration <strong>of</strong> asphalt
was found to be lower than that measured in Tokyo street dusts.
2.5 Summary
Motor vehicles are relatively complex emissions sources. Firstly they comprise multiple sources with
their own contaminant signatures (tyres; brake pad wear; exhaust emissions; oil, grease and collant
losses etc.,). Secondly for many <strong>of</strong> the sources there is considerable variability in the contaminants
emitted and the amount emitted as there are a large number <strong>of</strong> different manufacturers involved in the
production <strong>of</strong> motor vehicles and their parts. For some emission sources there are hundreds <strong>of</strong>
different types <strong>of</strong> a particular component many <strong>of</strong> which have different contaminant signatures. This
results in potential for considerable variation between countries and over time in contaminant
emissions from some sources
For inorganic contaminants (e.g., the trace elements including the heavy metals), there is a
reasonable understanding <strong>of</strong> what elements are present in the sources and in emissions. <strong>The</strong>re is a
degree <strong>of</strong> uncertainty in relation to the variability <strong>of</strong> some elements that are key constituents <strong>of</strong> some
sources (e.g., Cu in brake pads). This uncertainty arises because <strong>of</strong> the variation in brake pad
specifications between manufacturers. <strong>The</strong>re is less information on the variability in the concentration
<strong>of</strong> some elements for whose presence in emission sources has only relatively recently been
confirmed.
For organic compounds there is a less clear picture as to what is emitted from the various emission
sources. For exhaust emissions, there is a large body <strong>of</strong> published research data that examines the
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