Page 148 - Materials Chemistry, Second Edition

L1644_C04.fm Page 123 Tuesday, October 21, 2003 3:13 PM

several ecological assessment endpoints — a very important point because the
different types of ecosystems have unique combinations of physical, chemical,
and biological characteristics and thus may respond to contamination in unique
ways. The physical and chemical structure of an ecosystem determines how con-
taminants affect its resident species and biological interactions may determine
where and how the contaminants are distributed in the environment and which
species are exposed to particular concentrations. The following ecosystems are
normally studied in an ERA:

• Terrestrial ecosystems are classified depending on the vegetation types
that dominate the plant community and terrestrial animals.
• Wetlands are areas in which topography and hydrography create a zone
of transition between terrestrial and aquatic environments.
• In freshwater ecosystems the dynamics of water temperature and move-
ment of water can affect the availability and toxicity of contaminants.
• Marine ecosystems are of primary importance because of their vast size
and critical ecological functions.
• Estuaries support a multitude of diverse communities and are important
breeding grounds for numerous fish, shellfish and bird species.
Assessment endpoints, mentioned in Chapter 3 with regard to life-cycle impact
assessment, are explicit expressions of the actual environmental value to be pro-
tected. The main criteria used in the selection of assessment endpoints include their
ecological relevance, their susceptibility to the stressor, and whether they represent
management goals (to include a representation of societal values). Ecological
resources are considered susceptible when they are sensitive to human-induced
stressors to which they are exposed. Delayed effects and multiple stressor exposures
add complexity to evaluations of susceptibility. Conceptual models need to reflect
these factors. If a species is unlikely to be exposed to the stressor of concern, it is
inappropriate as an assessment endpoint.
To evaluate every species that may be present at a locale affected by an envi-
ronmental contamination problem is not feasible. Therefore, the selected target of
indicator species will normally be chosen in an ERA study. Then, by using reason-
ably conservative assumptions in the overall assessment, it is rationalized that ade-
quate protection of selected indicator species will enable protection for all other
environmental species as well.
A guiding criterion for the selection of ERA target species considers if they are:

• Threatened, endangered, rare or of special concern
• Valuable for several purposes of interest to human populations (i.e., of
economic and societal value)
• Critical to the structure and function of the particular ecosystem that they
inhabit
• Indicators of important changes in the ecosystem
• Of relevance for species at the site and its vicinity

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