Environmental Engineering Reference
In-Depth Information
Assemble sediment toxicity data
DQOs
not met
Evaluate sediment toxicity data
using data quality objectives in
quality assurance project plan
Repeat necessary components of
sampling and analysis plan
DQOs Met
Not
toxic
Compare sediment toxicity data
to negative control
Sediments likely not
signifigantly toxic
Toxic
Not
toxic
Compare sediment toxicity data
to reference station(s)
a
Sediments unlikely to be toxic
relative to reference conditions
Toxic
Sediments are toxic to sediment-
dwelling organisms
Consider sediment toxicity data
with other data
a
Comparison to reference sites is only appropriate if reference sites have been
well charactized and satisfy criteria for negative controls (i.e., response in
reference sediments should not be significantly different from that in negative
controls).
Fig. 7.3
Recommended procedure for assessing sediment toxicity data.
pore-water toxicity tests have been identifi ed, includ-
ing responsiveness to hydrogen sulfi de and ammonia,
and depletion of hydrophobic organics during the
course of the test. However, a recent evaluation of
data from multiple studies showed that ammonia
and hydrogen sulfi de were rarely confounding factors
for pore-water toxicity tests with the sea urchin
Arbacia punctulata
(Carr
et al
. 2006). Elutriate tox-
icity tests are considered more relevant for assessing
the effects of open-water disposal of dredged materi-
als than evaluating the toxicity of in-place sediments.
Neither solid-phase nor aqueous-phase toxicity tests
with the bacterium
Vibrio fi sheri
(i.e., Microtox®)
are currently recommended for assessing contami-
nated sediments at marine or estuarine sites, as these
tests provide an indication of exposure to contami-
nants rather than specifi c measures of effects on
benthic organisms.
The recommended procedures for assessing sedi-
ment toxicity data are presented in Fig. 7.3.
Importantly, evaluation of the usability of the data
represents the fi rst step in this process. Comparison
of the results to negative control data and the refer-
ence envelope provides a basis for designating
samples as toxic or non-toxic (MacDonald
et al.
2002c). Such designations of toxicity are useful for
evaluating sediment quality conditions on a sample-
by-sample basis and for deriving concentration-
response relations for the site as a whole (Fig. 7.4)
(MacDonald
et al.
2008).
7.3.3 Selection of metrics for benthic
invertebrate community assessment
Benthic communities are assemblages of organisms
that live in or on the bottom sediment. Because most
