Environmental Engineering Reference
In-Depth Information
15.4.2 Selection of Assessment Tools
The application of the Triad approach comprises the selection of tools which:
(1) fit in the specific tier of interest (from screening-level to highly sophisticated
tools);
(2) cover all three lines of evidence;
(3) effectively address the selected end-points.
The final suite of selected tools should allow for dealing with and ultimately
reducing uncertainty in ERA. A tool is defined as an instrument for quantification
of a specified aspect of the ecosystem. The outcome must ultimately be expressed
in a one dimensional number indicating the level of ecological effect on the uniform
scale. Tools range from very simple (a screening level bioassays or a concentra-
tion plus literature toxicity data) to highly sophisticated and integrated (results from
BLM modeling, maturity index of nematodes or a food web stability index). Any
tool must be based on site-specific information through modeling and/or measure-
ments and on information from literature data and ecotoxicological reasoning for
interpretation of the data on the uniform effect scale (see below for an explanation
in Section
15.4.3
).
Elaborating on the three issues for selecting tools (see former paragraph):
•
Sub 1 (tiers). With respect to the tailoring of the specific tier of interest, standard-
ization and costs of analysis are important issues for selection of tools, especially
in the lower tiers. Yet, even screening tools should be sufficiently reliable and
sensitive to demonstrate effects of contaminants under field realistic conditions.
Finally the tools should be relevant for the ecosystem under investigation. More
sophisticated and elaborated tools are used for improving site specificity in the
higher tiers of the ERA.
•
Sub 2 (lines of evidence). Each tier of the Triad approach should cover three
independent types of assessment tools, representing three different lines of evi-
dence. This requires at least one tool for a chemical based assessment (
chemical
characterization
), at least one bioassay (
determination of toxicity
), and at least
one type of on-site ecosystem observation, which can be related to effects of con-
tamination (
ecological observations
). When the different lines of evidence are
comparable in terms of effort and matching level of insight, a balanced weight-
ing between the lines of evidence can be applied (see below for more details on
weighting of the results).
•
Sub 3 (addressing selected end-points). The appropriateness of respective tools
to serve as indicators for selected endpoints is the third and last issue. The tools
should provide insight about compliance of end-points with respect to the poten-
tial effects of the contamination at the site. Many ecologically relevant end-points
cannot be directly assessed, because of imperfect knowledge and lack of tools.
Instead models or surrogate systems are used to extrapolate from the assessment
tools to real world situations. Confirmation of ecological significance of the indi-
vidual test systems originates from track records or literature evidence of the
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