Environmental Engineering Reference
In-Depth Information
licenses (in the case of vertebrates
1
), and does not
lend itself readily to a rapid initial assessment of
potential sediment toxicity. Therefore, to generate
such data, tier 1 tests use various sediment phases:
(1) solid phase tests (Cook & Wells 1996; Côte
et al.
1998; Kemble
et al.
2000); (2) pore water or
interstitial water occupying the spaces between sedi-
ment particles. Contaminants present in pore water
represent the water-soluble, bioavailable fraction, a
major route of exposure to benthic organisms (see
Buffl ap & Allen 1995; Adams
et al.
2001; US
Environmental Protection Agency 2001b; Dalmacija
et al.
2006; Lewis
et al.
2006); (3) elutriates origi-
nally developed by Keely & Engler (1974) to deter-
mine the solubility of contaminants released during
physical disturbance, such as dredging operations
(Beg
et al.
2001; Doherty 2001; Casado-Martinez
et al.
2007; Losso
et al.
2007); (4) organic solvent
extraction procedures that liberate contaminants
that would otherwise not be found in elutriates or
pore water fractions (Looser
et al.
2000; Vella &
Adami 2001; Huang 2004), especially those that
simulate the release of organic compounds through
digestive processes in the guts of deposit feeding
invertebrates (see Nakajima
et al.
2006). The test
phase and extraction processes of choice will depend
on the type of sediment and the question being
addressed (Tables 6.1-6.5).
As the main concern of these tests is to establish
potential toxicity of sediment contaminants rather
than ecological relevance, many tier 1 tests use an
in vitro
approach to bioassays. These may include
various commercially available bacterial biolumines-
cence and invertebrate test kits as well as tissue cul-
tures allowing for standardized procedures with
highly reproducible results. Consequently, many tier
1 test systems have been accredited by governments
and regulatory bodies as monitoring tools for envi-
ronmental impact assessments contributing to rele-
vant legislation (US Environmental Protection
Agency 1977). Selected tier 1 tests, designed around
various extraction phases, are compared in Tables
6.2-6.5. A more in-depth discussion of acute and
in vitro
approaches to sediment toxicity assessment,
including details and an evaluation of fractionation
techniques, can be found in Ni Shuilleabhain
et al.
(2003).
6.2.2.2 Tier 2 tests
As with tier 1 tests, several standardized whole-sed-
iment bioassays using a variety of sentinel organisms
are well accepted by regulatory authorities in several
countries (Keddy
et al.
1995; Environment Canada
1997; US Environmental Protection Agency 2001a;
Simpson
et al.
2005) and may include the use of
outdoor simulated fi eld studies (Graney
et al.
1997);
the responses measured have in many cases been
successfully related to effects in the fi eld (Day
et al.
1995; Côte
et al.
1998).
As mentioned above, sediments are heterogeneous
systems. Accordingly, the distribution of sediment-
associated contaminants and their behaviour, in
terms of sorption expressed as particle-water parti-
tioning coeffi cient (
K
d
) and bioavailability, deter-
mined by zonation patterns of pH and redox potential
(
E
h
), are usually very patchy (Luoma & Ho 1998;
Simpson
et al.
2005). This can make the reproduci-
bility and the interpretation of data from exposure
experiments diffi cult. A tier 2 test system will there-
fore typically involve one of two or a combination
of both of the following approaches: whole homog-
enized sediment and spiked sediment formulations.
With both preparation methods, ecological rele-
vance is to varying degrees compromised in favor of
standardization, cause and effect relations, and
reproducibility (Luoma & Ho 1998).
6.2.2.2.1 Whole-sediment tests.
Toxicity bioassays
using whole sediment collected from the environ-
ment have been developed for many relevant taxa;
examples are given in Table 6.6. Whole sediment
toxicity bioassays using benthic fi sh as sentinel
organisms have been reviewed by Hartl (2002).
After collection, homogenization of the sediments
should be carried out as soon and as quickly as pos-
sible; prolonged mixing can change the particle size
distribution causing oxidation (Ankley
et al.
1996).
This can be avoided by restricting the sampling of
sediments, where possible to the oxidized layer, as
most macrofaunal species will only ingest or be
exposed to oxidized sediments (Coughlan
et al.
2002; Hartl
et al.
2007). This is not always practical
because of diffi culties in determining the depth of the
1
Regulations will vary from country to country and should
be consulted before starting any toxicology work.
