Environmental Engineering Reference
In-Depth Information
2.7 New protocols
A number of new sediment testing protocols have recently been published
that are designed to produce better information on recalcitrant compounds'
sediment-pore water partitioning, bioaccumulation potential, exposure
potential, and toxicity. These approaches have been reviewed from a toxico-
logical perspective (Condor et al., 2002). In evaluating these approaches, it
is important to realize that whereas some of them are designed to provide
better information on the chemical partitioning of recalcitrant compounds
between sediment and pore water, others are designed to produce better
data on the transfer of recalcitrant compounds from sediment into biota. All
of these approaches have their respective merits and disadvantages. For
example, Kelsey and Alexander (1997) compared mild solvent extractions
(e.g., butanol) to contaminant bioaccumulation. Although the procedure was
simple and fast, no single solvent extraction system produced a reasonable
correlation to empirically measured BASF when different soils and test
organisms were used. Weston and Maruya (2002) have suggested that stom-
ach fluids from deposit-feeding animals are an appropriate extraction fluid
for benthic animals that accumulate contaminants via their digestional
tracks. Standardizing this assay presents some technical challenges, and it
may not be the most appropriate approach for hydrophobic/lipophilic con-
taminants that are also taken up through the skin and gills. Concurrent
USACE Long Term Effects of Dredging Operations (LEDO) work units led
by Dr. Jim Brannon, Dr. Vic McFarland, and Dr. Todd Bridges are focused
on evaluating these approaches.
Karickhoff's (1979) original assumption was that pore water was the
major exposure pathway associated with sediments and derived K oc as a
means to predict recalcitrant compounds' levels in pore water. The low
volume of pore water recoverable from most sediments, coupled with the
low levels of recalcitrant compounds in most pore waters, presents an ana-
lytical challenge with respect to recalcitrant compound detection limits and
the precision and accuracy of the data. A series of studies has shown that
the rapidly desorbing fraction of sediment-bound recalcitrant compounds
was the most likely to become accumulated into biomass (Landrum, 1989;
Robertson and Alexander, 1996, 1998; Tang et al., 1998; Cornelissen et al.,
1998; Rockne et al., 2002; Kraaij et al., 2002; McGroddy et al., 1996; Talley et
al., 2002; Weber et al., 2002). Kraaij et al. (2002) demonstrated that pore water
recalcitrant compound concentration was a far superior predictor of bioac-
cumulation potential than levels of recalcitrant compounds extractable with
organic solvent from the bulk sediments (Figure 2.4). Kraaij's prediction
method is independent of bulk sediment measures. This approach shows
promise because it is a simple model that also appears to accurately predict
recalcitrant compounds' bioaccumulation potential.
A number of analytical solutions based on solid phase extraction tech-
nologies have been proposed to measure the rapidly desorbed recalcitrant
compounds' fraction, if not the actual recalcitrant compounds' pore water
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