Environmental Engineering Reference
In-Depth Information
Ideal
test
In vitro tests
Monospecific
tests
Community
tests
Controlled
ecosystem tests
Field tests
Ecological relevance
Fig. 6.1 Relation between ecological relevance and procedural simplicity for various types of aquatic ecotoxicological test.
environmental variables (Hartl et al. 2005); these
may provide data for contaminant fate and impact
assessment models.
However, laboratory-based approaches to eco-
toxicology require procedures for collection, storage,
and preparation of sediments (ASTM 1990), which
all induce unavoidable geochemical changes, in par-
ticular to the pH and redox status ( E h ) after handling
(Luoma & Ho 1998; Hutchins et al. 2007). Natural
sediment deposits are structured systems of oxic sedi-
ments on top of anoxic ones (Fenchel 1969). The
depth of the oxic layer is a function of grain size,
sedimentation rate, and the biological oxygen
demand of the system (Aller 1978), the latter driven
in turn by the organic content of the sediment and
ambient temperature. The redox potential disconti-
nuity is the depth where oxygen demand begins to
exceed supply and separates the oxygenated from the
reduced sediment layers beneath (Elskens et al.
1991). Usually horizontally orientated, the redox
potential discontinuity can be complicated by the
burrows of invertebrate infauna, such as lugworms
and mudshrimps. The two zones display very differ-
ent chemical conditions (Machan & Ott 1972; Aller
1978): in oxidized sediments, iron and manganese
oxides occur mainly as reactive species. Under oxic
conditions, contaminants, such as other metals, will
bind to these and other available surfaces. In anoxic
sediments oxidized iron and manganese are rare. The
soluble reduced forms, together with other metal
sulfi des, are the dominant species and accumulate in
the pore water.
Therefore, before any sampling, several details of
the sampling procedure will need careful considera-
tion, as proper handling of samples during the col-
lection process is essential for maintaining quality
standards and avoiding distortion of analytical
results (Chapman 1989; ASTM 1990; Power &
Chapman 1992; US Environmental Protection
Agency 1992; Chapman & Wang 2001). Suitable
sampling methods will depend on site accessibility
and the type and amount of sediment required,
which are representative of the conditions at the site
and, where possible, the integrity of the sample is
maintained. The advantages and limitations of com-
monly used sampling methods have been extensively
discussed elsewhere: dredges (ASTM 1990), grabs
and box corers (Carlton & Wetzel 1985; Papucci
et al. 1986; Webb 1989; Weaver & Schultheiss 1990;
Flower et al. 1995; Santschi et al. 2001), mega
corers (Black et al. 2002), and hand-held corers or
scoops (Byrne & O'Halloran 1999; Coughlan et al.
2002).
A complete integrated ecotoxicology assessment
approach should include chemical analysis. Therefore
it is imperative that suitable containers are used to
collect environmental and biological samples, such as
high-density polyethylene or polytetrafl uroethylene
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