The Effects of Road Transport on Freshwater and Marine Ecosystems

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by ARC (1994) indicated that TPH concentrations ranged from 1,000 up to about 4,000 mg/kg in the
different particle sizes examined
Williamson (unpublished data in NIWA 1996) measured PAH concentrations in suspended sediment
from Hillcrest (Hamilton) <strong>of</strong> 52 - 2,375 µg/kg. Hickey et al. (1997) examined PAH concentrations in
suspended stormwater particulates from Mt Albert in Auckland. <strong>The</strong> results indicated a total PAH
concentration <strong>of</strong> 972 µg/kg. Data for a total <strong>of</strong> 24 PAHs was reported ranging from 0.2 µg/kg for
napthalene, to 66 µg/kg for benzo(a)pyrene to 126 µg/kg for pyrene and 148 µg/kg for
benzo(ghi)perylene.
Stormwater from roads contains a wide range <strong>of</strong> organic compounds. Many contaminants are present
as a result <strong>of</strong> their emission from a number <strong>of</strong> sources associated with motor vehicles (e.g., tyre and
brake pad wear, exhaust emission). Compounds present on road surfaces and in stormwater include
volatile organic compounds and a wide range <strong>of</strong> semi-volatile organic compounds. <strong>The</strong> PAHs are the
most well understood group <strong>of</strong> SVOCs and have been measured in stormwater.
<strong>The</strong> amount <strong>of</strong> any particular organic compound present in the dissolved phase is dependent upon its
properties. A higher proportion <strong>of</strong> the concentration <strong>of</strong> low MW PAHs is present in the dissolved
phase compared to high MW PAHs which are almost entirely present in the particulate phase.
4.5 Other Constituents
Other Constituents in Particulate Matter
<strong>The</strong> particulate matter transported by stormwater carries a range <strong>of</strong> other constituents other than
metals and organic compounds. <strong>The</strong>se other constituents include nutrients and oxygen demanding
substances. ARC (1992, 1994) carried out an examination <strong>of</strong> the concentration <strong>of</strong> nutrients and their
constituents in the particulate matter transported from a residential catchment in Auckland.
Organic carbon concentrations in suspended solids in stormwater were found to be higher than those
measured in street gutter dusts (probably due to differential sorting <strong>of</strong> organic suspended solids).
Concentrations <strong>of</strong> up to 22% organic carbon were measured. Density separation may result in the
increase in concentration compared to the source. Increases were also noted in relation to total
Kjeldahl nitrogen (TKN) with concentrations <strong>of</strong> up to 0.09% being measured. In relation to both OC
and TKN, no assessment <strong>of</strong> the relative contribution <strong>of</strong> road transport to both constituents (from
hydrocarbon and NOx emissions) has been identified. However, although it has been assumed to be
low, the relative contribution between road transport and urban landscape and other sources is
expected to be highly variable.
ARC (1992) examined the phosphorus content <strong>of</strong> particulates in stormwater from residential and
commercial catchments in Auckland. <strong>The</strong> results showed that although total phosphorus
concentrations were high (typically >2,000 mg/kg), the available fraction was a very small part
(typically 2%). Concentrations in that study appeared to be greater than would be expected in local
soils (e.g.,