The Effects of Road Transport on Freshwater and Marine Ecosystems

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on the nature <strong>of</strong> the particulate material transported by stormwater and distributed within the receiving
environment. In New Zealand there have been a number <strong>of</strong> investigations <strong>of</strong> urban gutter dust quality
but few <strong>of</strong> these studies have examined the general composition <strong>of</strong> gutter dusts. Overseas, Ellis
(1976) provided data on the gross composition <strong>of</strong> gutter dusts. In New Zealand, ARC (1992)
examined the material in gutter dusts in the suburbs <strong>of</strong> Pakuranga (low and high-density traffic
residential) and Southdown (industrial), Ng et al. (2003) in Auckland City and Kennedy & Gadd (2003)
in Waitakere City. Composition <strong>of</strong> the particulate matter in urban street gutters can be summarised as
follows:
Inorganic matter sourced from road and pavement materials and adjacent soils can make up to 45
to 70% <strong>of</strong> the mass <strong>of</strong> material present (Ellis 1976). ARC (1992) estimated that 15 - 60% <strong>of</strong> the
material present in the gutter dust samples collected in that study in Auckland was inorganic.
Rubber fragments from tyre wear are common.
Metal fragments, rust and other ferromagnetic materials are common (Fergusson et al. 1980).
Litter such as paper, glass, plastic and other debris is common (ARC 1992).
Organic debris from plants and lawn clippings may be present but the amount tends to be
seasonal and varies between areas depending upon landuse (e.g., residential streets, motorway
grass verges, median strips etc).
3.2.2 Particle sizes
<strong>The</strong> particle size distribution on the road surface is a function <strong>of</strong> a number <strong>of</strong> factors including the wear
and particle size <strong>of</strong> eroded materials from the road surface, external soil and dust sources and their
availability and the particle size <strong>of</strong> wear and emission products from motor vehicles. On the road
surface, sorting by wind and water would be expected to produce a log-normal distribution <strong>of</strong> particle
sizes amongst road surface particulates (Sartor & Boyd 1972, Shaheen 1975, Ellis & Revitt 1982).
ARC (1992) presented data on the grain size distribution <strong>of</strong> road gutter dust samples from Pakuranga
and Southdown in Auckland. Gutter sediments were dominated by particles in the range 0.12 to 1.0
mm (69% and 59% by weight respectively) with only 2.0-3.6% in the