The Effects of Road Transport on Freshwater and Marine Ecosystems

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one factor used to classify organic compounds emitted by vehicles as contaminants <strong>of</strong> potential
concern (COPC) in relation to potential environmental effects.
6.3.3.3 Stormwater Quality and Toxicity
In assessing the potential for adverse effects to arise from the discharge <strong>of</strong> stormwater to freshwater,
resource managers would in the first instance compare available stormwater data with the water
guidelines (Table 6.3) identified in the previous sections (e.g., the EMC data in Tables 4.5 to 4.7).
<strong>The</strong>re is a relatively significant body <strong>of</strong> stormwater quality data with which this comparison can be
made.
Cadmium
For cadmium, most stormwater data has not been obtained using sufficiently sensitive analytical
techniques. Cadmium concentrations in motorway run<strong>of</strong>f obtained using strong acid digestion are
<strong>of</strong>ten reported as exceeding USEPA acute criteria and the ANZECC (2000) trigger. Data such as that
reported by ARC (1992) are lower than the USEPA chronic criteria <strong>of</strong> 0.38 mg/m 3 at a hardness <strong>of</strong> 25
g/m 3 and the ANZECC (2000) trigger <strong>of</strong> 0.2 mg/m 3 . Although some reported data indicates that Cd
concentrations in road run<strong>of</strong>f might exceed chronic criteria and triggers, work such as that <strong>of</strong> ARC
(1992) suggests that it is likely that most road run<strong>of</strong>f in New Zealand would not exceed the cadmium
criteria.
Copper
Dissolved copper concentrations in motorway and road run<strong>of</strong>f (in New Zealand and overseas) exceed
USEPA acute and chronic criteria and ANZECC (2000) triggers (Tables 4.5-4.7). Comparison <strong>of</strong>
dissolved copper concentrations in New Zealand stormwater run<strong>of</strong>f and motorway run<strong>of</strong>f (refer Table
4.7) shows that ANZECC (2000) trigger values are exceeded in urban stormwater run<strong>of</strong>f. Figure 6.1
from Timperley (2002) illustrates the range in concentration versus the ANZECC (2000) trigger (for
95% protection).
Timperley (2002) has also shown that the concentrations are much higher in the first flush <strong>of</strong> urban
stormwater. Work by NIWA (Webster 2000) examined the influence <strong>of</strong> DOM on the bioavailability
(toxicity) <strong>of</strong> dissolved metals. <strong>The</strong> complexing ability <strong>of</strong> stormwater/stream waters is dependent upon
the availability <strong>of</strong> DOM. In catchments with negligible riparian vegetation there appears to be little
complexing ability. Increased inputs <strong>of</strong> DOM (e.g., humic and fulvic acids) result in greater ability to
complex metals such as Cu. In streams with a good supply <strong>of</strong> DOM, much <strong>of</strong> the dissolved Cu may be
complexed. This may mean that dissolved Cu in stormwater leaving roads entering streams and
drains may become complexed by DOM if there is sufficient present. Webster (2000) also noted that
the complexing ability is not directly related to the amount <strong>of</strong> DOC present as the source/composition
<strong>of</strong> the DOC may change. Initial work reported by Webster (2000) also showed that DOM from different
plants has different abilities to complex metals. Overall, although concentrations <strong>of</strong> dissolved Cu in
stormwater and urban stream water may exceed ANZECC (2000) triggers, the significance may vary
depending upon local water chemistry. Where there is a sufficient supply <strong>of</strong> DOM, the dissolved
copper may be complexed reducing its potential toxicity.
Lead
Initial examination <strong>of</strong> stormwater Pb data (e.g., the motorway data in Table 4.5) indicates that the
concentrations are well above USEPA acute and chronic criteria and ANZECC (2000) triggers.
However as described earlier in this report most Pb is present in the particulate phase. <strong>The</strong> higher
concentrations <strong>of</strong> Pb in the data tables are typically the result <strong>of</strong> analysis undertaken at times or in
locations where Pb was or is still used in petrol. In addition, the Pb presented in some studies may
also be the result <strong>of</strong> poor analytical detection limits. Recent data for stormwater from roads in New
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