The Effects of Road Transport on Freshwater and Marine Ecosystems

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5 PATHWAYS & FATE OF CONTAMINANTS
EMITTED FROM TRANSPORT SOURCES
5.1 Introduction
<strong>The</strong> fate <strong>of</strong> contaminants emitted from motor vehicles influences both their concentrations in the
receiving environment and the ensuing load entering the environment in the short and the long term.
Both load and concentration have a role in the possible effects that contaminants may have in
freshwater and marine ecosystems. In a simplistic sense, the contaminants can be partitioned into
compartments in terms <strong>of</strong> assessing their fate. <strong>The</strong> principle pathways and compartments being:
1. <strong>The</strong> atmosphere.
2. <strong>The</strong> road surface, collection and discharge system.
3. <strong>The</strong> freshwater receiving environment.
4. <strong>The</strong> estuarine and marine receiving environment.
Within these compartments, the physical and chemical processes that determine fate are complex.
<strong>The</strong> number <strong>of</strong> different contaminants derived from motor vehicles also means that the contaminants
are involved in a range <strong>of</strong> different physical, chemical and biochemical processes. In this section <strong>of</strong>
the report, these processes are overviewed to provide an introduction to the factors that influence the
fate <strong>of</strong> contaminants and their potential effects within freshwater and marine ecosystems. <strong>The</strong> key
issues and questions examined include:
<strong>Transport</strong>:
<strong>Transport</strong> and deposition <strong>of</strong> airborne particulate matter.
Physico-chemical processes on the street surface.
Physico-chemical effects in stormwater receiving water systems.
Fate:
Fate in freshwater receiving environments.
Fate in estuarine and marine receiving environments.
5.2 <strong>Transport</strong> and Deposition <strong>of</strong> Airborne Particulate
Matter
5.2.1 Introduction
<strong>The</strong> emission <strong>of</strong> particulates (from exhaust, tyres and other sources) to the atmosphere and their
subsequent transport away from the point <strong>of</strong> emission allows road vehicle emissions to potentially
have effects within environments adjacent to and remote to the source. As a result vehicle emissions
can result in:
Deposition into soils adjacent to or remote from the source.
Secondary transport <strong>of</strong> vehicle derived contaminants (deposited to roadway surfaces and soil)
to waterways (through erosion, flood transport).
Deposition <strong>of</strong> airborne particulates and gaseous pollutants onto freshwater.
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