The Effects of Road Transport on Freshwater and Marine Ecosystems

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that “concentrations <strong>of</strong> Zn in 20-50 years will exceed the sediment quality guidelines at which biological
effects are expected to widely occur”.
<strong>The</strong> predictions, presented in Williamson et al. (1999) and detailed in Vant et al. (1993), Snelder (1995)
and Snelder & Trueman (1995) are based upon a series <strong>of</strong> scenarios. <strong>The</strong> detailed calculations <strong>of</strong> which
can be found in Appendix 3 <strong>of</strong> Vant et al. (1993).
<strong>The</strong> predicted increases in total metal concentrations identified by Williamson et al. (1999) and earlier
reports are based upon ‘urban’ stormwater run<strong>of</strong>f, a proportion <strong>of</strong> which is contributed by road transport.
<strong>The</strong> available data has already indicated that contaminant concentrations in urbanised estuaries are at
levels with the potential to create adverse effects on biota. However, the direct comparison <strong>of</strong>
concentrations with guidelines such as the ER-L <strong>of</strong> Long et al. (1995) and the ANZECC sediment quality
triggers (refer Section 5), does not confirm that adverse effects have and are occurring as a consequence
<strong>of</strong> the elevated concentrations <strong>of</strong> the contaminants. In addition, any comparison does not take into
account changes in the geochemistry <strong>of</strong> the contaminant over time (i.e., the potential toxicity may
decrease). <strong>The</strong>se factors all add to the difficulty in making such predictions.
Examination <strong>of</strong> sediment quality adjacent to North Shore City <strong>of</strong>f the East Coast Bays has shown that
sediments contain elevated concentrations <strong>of</strong> elements such as Pb. Concentrations <strong>of</strong> Pb are about
100% higher than would be expected as a result <strong>of</strong> historical contributions <strong>of</strong> Pb from motor vehicle
emissions and other sources (Kingett Mitchell 2003c). <strong>The</strong> concentrations in muddy sediments (about 22
mg/kg) are lower than the ANZECC ISQG-low trigger <strong>of</strong> 50 mg/kg however.
In New Zealand and internationally there appears to be little data on the distribution <strong>of</strong> other elements in
the marine environment that have been identified as being emitted from motor vehicles (e.g., Mo, Sb
etc.,). In relation to the PGEs, Tuit et al. (2000) reported on Pt and Pd in Boston Harbour sediments. <strong>The</strong>
study reported that concentrations had increased about five times above background. Both Pt and PD
are released to the environment from a number <strong>of</strong> sources. Tuit et al. (2000) described the
anthropogenic sources <strong>of</strong> both elements as being derived from sewage, sewage sludge, medical and
dental, chemical and the jewellery industry. <strong>The</strong> use <strong>of</strong> Pt in catalytic converters has been the major
consumer <strong>of</strong> Pt (>60%) since 1973. Until 1993 when Pb was phased out <strong>of</strong> petrol in the US, catalytic
converters only accounted for 10% <strong>of</strong> Pd use. Subsequently Pd use in catalytic converters has increased
to about 40% <strong>of</strong> the demand. <strong>The</strong> Boston study didn’t specifically identify the proportion <strong>of</strong> Pd and Pt in
sediments attributable to vehicle emissions however. It is likely that it will be at least equal to or greater
than the amount <strong>of</strong> those elements used in catalytic converters as the other consumers practise some
element recovery.
Examination <strong>of</strong> contaminant concentrations immediately around the discharge points for stormwater
run<strong>of</strong>f from roads and urban areas shows that concentrations <strong>of</strong> contaminants in sediments are elevated.
Concentrations in both intertidal and subtidal sediments can rise above sediment quality guidelines and
triggers. For most smaller discharge points haloes <strong>of</strong> metal concentrations are generally restricted to 10-
20 m. In the wider urban and estuary and harbour context it is evident that sediments <strong>of</strong>ten contain
elevated concentrations <strong>of</strong> metals and organic contaminants. In locations such as the Waitemata
Harbour it is evident that all <strong>of</strong> the surface sediments in the Harbour are contaminated to some degree.
In depositional environments the concentration <strong>of</strong> elements such as Cu can exceed sediment quality
guidelines. Within New Zealand such effects are likely to be restricted principally to depositional
environments adjacent to urban areas. However, stormwater discharges from roads and smaller urban
centres to smaller estuarine will have comparable effects but on a smaller scale.
Overall, the contribution that motor vehicles have to sediment contamination is identifiable where the
discharge is derived from an isolated road. In urban areas, the contribution from vehicles to sediment
contamination adjacent to outfalls and within estuaries and harbours will be dependent upon the ratio <strong>of</strong>
the loads contributed by vehicle sources and other urban sources and activities. This ratio has not been
clearly quantified to-date.
Kingett Mitchell Ltd
Resource & Environmental Consultants