Environmental Engineering Reference
In-Depth Information
necessitates some form of enclosure, such as, micro-
or mesocosms (Graney
et al.
1997; Hartl & Ott
1999). Careful planning and experimental design is
needed to avoid or minimize handling stress of sen-
tinel organisms, and the installation and removal of
enclosures are possible sources of artifacts.
Furthermore, although general guidelines have
been developed, unlike tier 1 and tier 2 approaches,
there are no standardized procedures available for
in situ
experiments, partly because of site-specifi c or
temporal conditions (seasonal variations), thus
making inter-experimental comparative analyses
often diffi cult.
of integration to environmental sediment quality
assessments are presented in Table 6.9.
6.4 Conclusions
Variability in approach and resulting data signifi -
cantly contribute to the uncertainty in results of sedi-
ment toxicity testing. Efforts to standardize methods
for sediment sampling, handling, aqueous and
organic elutriation, and pore-water extraction
through inter-calibration exercises have led to
improvements in this area. Nevertheless, despite these
targeted initiatives and the establishment of interna-
tional working groups (SETAC, SEDNET), it would
appear that the science of sediment quality assess-
ment is still somewhat behind that of water or soil,
because there are relatively few recognized standard
test methods for evaluating sediment toxicity com-
pared with those established for water and soil.
The consensus within the scientifi c community
requires a sediment monitoring strategy to incorpo-
rate both chemical characterization and ecotoxico-
logical analysis in a balanced way without over
emphasizing one tier or single test result. Furthermore,
there is wide recognition that toxicity is not merely
a chemical property but rather a function of the test
organism and the test conditions. Consequently,
although sediments might contain relatively high
concentrations of contaminants, these may not nec-
essarily lead to adverse effects on test organisms.
Contaminant fate in a sediment-water system is
highly dependent on sorption behavior, which in
turn determines bioavailability and toxicity.
Therefore, quantitative chemical analysis in environ-
mental samples is not necessarily indicative of bio-
logical and ecological effects of identifi ed
contaminants, because the bioavailable fraction may
vary greatly, making toxicity predictions based on
chemical analysis alone diffi cult and unreliable.
Moreover, varying sensitivities displayed by different
species to a particular contaminant further highlights
the need for a battery-style bioassay approach within
a tiered ecotoxicological assessment. A battery of
toxicity tests for evaluation of sediment toxicity
should include representatives from different trophic
levels, because utilization of only a few test species
would clearly constrain contaminated sediment eval-
uations that rely solely on bioassay results. Test
species should have a wide geographic distribution
6.3 Integrated approaches to
environmental impact assessments
Policies governing environmental impact and man-
agement in general and sediment quality assessment
in particular increasingly require a shift from lower
level to more ecosystem-based, holistic approaches
incorporating chemical, biological, and ecological
objectives, with a focus on large-scale risk evaluation
and management (Hagger
et al.
2006; Apitz
et al.
2007).
As in any complex procedure, each level of a tiered
approach has its advantages and limitations; the
latter can be overcome or mitigated by the applica-
tion of multiple lines of evidence (LOEs) integrated
in a weight-of-evidence (WOE) approach (Hyland
et al.
1998; Neuparth
et al.
2005; Hagger
et al.
2006;
Pereira
et al.
2007). Such an integrated assessment
typically includes relevant bioassays within different
tiers, levels of biological organization, trophic com-
partments, as well as chemical analysis, and physico-
chemical characterization of the representative
sediment samples. This will address issues that arise
through complex biogeochemical properties of sedi-
ments, such as bioavailability and the route of expo-
sure of contaminants.
As risk is defi ned as the product of toxicity and
exposure, an isolated data input describing one or
the other would be insuffi cient for the purpose of an
ecological impact or quality assessment. In addition
to risk assessment, the information gained from an
integrated approach aims to provide insights into
sediment quality that allow conclusions to be drawn
that would otherwise not be supported by the data.
Several recent case studies applying various degrees
