Environmental Engineering Reference
In-Depth Information
carbon (TOC), acid volatile sulfi des (AVS), and so
on, to interpret the results from sediment bioassays.
In addition, further considerations for spiking sedi-
ments are the equilibration times of pore water
metals, temperature, contaminant loss due to tank
wall adhesion and degradation, the use of carrier
solvents and carrier controls (in the case of organics),
and mixing techniques (ASTM 1990; Hartl
et al.
2000; Northcott & Jones 2000; Simpson
et al.
2005).
Table 6.7 contains a selection of procedures for
spiking marine and freshwater sediments with
organic compounds and various inorganic metals.
et al.
2003); (3) the addition of powdered coconut
charcoal to sequester polycyclic aromatic hydrocar-
bons (PAHs), polychlorinated biphenyls (PCBs), and
pesticides, thus reducing toxicity (Ho
et al.
2004).
The strength of whole-sediment toxicity bioassays
lies in the realistic route of exposure making the
data more ecological relevant than tier 1 acute
tests alone. However, inconsistencies between the
results of bulk and sediment extract bioassays,
probably caused by differing routes of exposure,
mean that more developmental work in this area is
necessary to standardize procedures making data
more comparable.
6.2.2.2.3 Control and reference sediments.
Control
sediments, by defi nition, are contaminant-free, apart
from any solvents used in spiked sediments, but oth-
erwise comparable to the test sediment. This allows
for the distinction between effects of the sediment or
solvent themselves and the pollutant(s) of interest
(ASTM 1994a,b). However, in many cases it has
become increasingly diffi cult to fi nd sediments free
of pollutants, in relative proximity to the test site,
with comparable geochemical characteristics. To
fulfi ll these criteria, reference sediments (ASTM
1994b), which are relatively clean sediments with
similar physical properties to the test sediments, are
increasingly complementing or even replacing the
traditional control sediment in ecotoxicological
studies (Coughlan
et al.
2002; Hartl
et al.
2007).
6.2.2.2.2 Spiking sediments.
To establish causality
in toxicological bioassays, sediments can be spiked
to create controlled sediment conditions, which
allow the empirical unraveling of the mechanisms
involved in sediment-chemical-organism interac-
tions (Lamberson & Swartz 1992). Although eco-
logical relevance may be compromised, owing to
extensive handling of sediment, the route of expo-
sure is still maintained and can provide valuable
information on contaminant fait modeling.
Furthermore, spiked sediments can be used to check
the recovery of analytes for quality assurance
purposes.
The American Society for Testing and Materials
(ASTM) has defi ned spiking as “the experimental
addition of a test material, such as a chemical or
mixture of chemicals, sewage sludge, oil, particulate
matter or highly contaminated sediment, to a clean
negative control or reference sediment to determine
the toxicity of the material added. After the test
material is added, sometimes with a solvent carrier,
the sediment is thoroughly mixed to evenly distribute
the test material throughout the sediment” (ASTM
1993). Spiking can avoid possible additive, synergis-
tic, or antagonistic effects of complex chemical mix-
tures commonly found in natural sediments so that
the fate of specifi c compounds can be studied, which
is also useful for generating sediment quality criteria.
Furthermore, spiked sediments can be used for mod-
eling pore water conditions for use in
in vitro
studies
(Ni Shuilleabhain
et al.
2003).
Regardless if formulated or natural sediment is
used, spiking invariably involves major changes to
sediment properties. It is therefore vital to monitor
all relevant parameters, such as pH,
E
h
, total organic
6.2.2.3 Tier 3 tests
As can be seen from the above analysis of tier 1 and
2 tests, laboratory-based bioassays can be very useful
tools for rapidly generating general toxicity data,
establishing cause and effect and organism-contam-
inant-interaction models, and for method develop-
ment. As outlined above, chronic sediment toxicity
tests with long-lived organisms are often unsuitable
for tier 1 and 2 laboratory application. The toxicol-
ogy of contaminants may require bio- or photoacti-
vation and/or biomagnifi cation, and their toxicity
would thus be underestimated in short-term labora-
tory experiments. To an extent, this may be taken
into account by testing only the most sensitive species
of a certain ecosystem and applying appropriate
safety factors (Boxall
et al.
2002). They are, however,
limited in their ecological relevance, because expo-
sure dynamics and interactions occurring in the fi eld
