Environmental Engineering Reference
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oxidation-reduction conditions (expressed as redox
potential, E h ), which can differ greatly from those in
the overlying water (Brassard 1991).
There are a variety of dedicated sources that
address methods for the physical and chemical char-
acterization of sediments (Buchanan 1971; Horowitz
& Elrick 1988; ASTM 1990; US Environmental
Protection Agency 1992; Reynoldson & Rodriguez
1999; Rodriguez & Reynoldson 1999). These are
also discussed in detail in this volume (see Chapter 3).
1991), have been drawn up by several organizations
(US Environmental Protection Agency 1993; CCME
1995; OSPAR 1997). Detailed accounts of methods
for establishing sediment quality criteria have been
extensively reviewed elsewhere (Ingersoll 1995;
Simpson et al. 2005).
6.2 Approaches to assessing
sediment toxicity
6.2.1 General considerations
6.1.3 Signifi cance of sediments
in ecotoxicology
The purpose of sediment toxicity tests is to determine
whether sediments contain substances harmful to
benthic organisms. They can cover a range of issues,
including determining bioavailability of contami-
nants, the potential interaction among contaminants,
spatial and temporal distribution, and establishing
causality of observed effects. Furthermore, sediment
toxicity tests are used in tiered decision trees for the
assessment of contaminated sediments to earmark
areas for cleanup and to monitor the effectiveness of
remediation and management initiatives.
Clearly, the methods applied will depend on the
aims of a given study and can range from acute tests
that measure the effects of an individual contaminant
on a single species to complex chronic tests with an
increased level of ecological relevance that determine
effects of chemical mixtures on the structure and
function of communities and ecosystems. Accordingly,
the sediment phase examined can range from whole
sediment to pore water and elutriates of varying
volumina (Ni Shuilleabhain et al. 2003) and use test
organisms covering all trophic levels, including algae
and macrophytes, benthic invertebrates, pelagic
invertebrates with benthic life stages, and fi sh (Burton
1992).
Toxicity tests should ideally be simple, inexpen-
sive, have a rapid turnaround time, and a high level
of ecological relevance. As can be seen from Fig. 6.1,
this is very rarely realized, as the complexity and
cost of sediment toxicity tests increases with ecologi-
cal relevance, and thus large-scale integrated fi eld
tests, the most ecological relevant, are very rarely
performed. Consequently, there has been a rapid
development of laboratory-based tests using fi eld-
collected sediment samples, that present far fewer
logistical diffi culties and at the same time allow
for the control and correction of confounding
Many contaminants, especially less polar organic
compounds and the most toxic of the trace elements,
show a strong affi nity to suspended particulate
matter and are thereby sequestered from the water
column and incorporated into the sediment (Harris
& Cleary 1987; Ragnarsdottir 2000). Redox condi-
tions in sediments drive shifts in ion ratios that can
change the chemical speciation, sorption behavior
and partition coeffi cients of incorporated compounds
and trace elements, resulting in the pore water dis-
playing a very different natural chemical composi-
tion than the overlying water. Undisturbed sediments
accumulate chemical compounds and so can become
sinks and eventually reservoirs for contaminants
potentially toxic to aquatic organisms. The retention
capacity of sediments for many contaminants is,
however, reversible, owing to changes in salinity,
pH, E h or mechanical disturbance. Sediments there-
fore act not only as sinks, but also as secondary
sources of accumulated contaminants, directing
often highly concentrated pulses of toxic substances
at benthic organisms; that is, organisms that during
part or their life cycles are intimately associated with
sediments, as a source of food or refuge. Fine-
grained, organically rich sediments, therefore, play a
major role in the biogeochemical fate of chemicals,
both of natural and anthropogenic origin (Eggleton
& Thomas 2004; Atkinson et al. 2007).
Unlike water-quality criteria (WQC) that have
been implemented for some time (US Environmental
Protection Agency 1972, 1986), sediments have tra-
ditionally been regarded as a fi nal sink for many,
especially, non-polar pollutants. Guidelines for sedi-
ment quality criteria (SQC), mostly based on the
equilibrium partitioning approach (Di Toro et al.
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