Environmental Engineering Reference
In-Depth Information
7.3.1 Selection of metrics for whole-
sediment chemistry and pore-water
chemistry
reported on a dry weight basis, based on the results
of total extraction of sediment samples. However,
several other measures of sediment chemistry have
also been used in various assessments. For example,
the concentrations of non-ionic organic contami-
nants may be normalized to TOC concentrations in
sediment (Swartz
et al.
1987; Di Toro
et al.
1991;
USEPA 2003). In addition, AVS-normalization pro-
cedures may be used to interpret data on the levels
of simultaneously extracted metals (SEMs) (Di Toro
et al.
1992; Ankley
et al.
1996; USEPA 2005).
Furthermore, chemical concentrations can be nor-
malized to percent fi nes. These normalization proce-
dures are intended to defi ne better the bioavailable
fraction of the substance under consideration.
Pore water is the water that occupies the spaces
between sediment particles. It can be isolated from
the sediment matrix to conduct toxicity testing or to
measure the concentrations of chemical substances.
ASTM (2008a) and USEPA (2000a) describe proce-
dures for isolating pore water from whole-sediment
samples. Evaluation of the concentrations of COPCs
in pore water is important because sediment-dwelling
organisms are directly exposed to the substances that
occur in this sediment phase. For this reason, pore-
water assessments can provide useful information on
the potential effects of sediment-associated contami-
nants, particularly on infaunal species (i.e., those
species that use habitats within the sediment matrix).
Importantly, the toxicity of sediments to aquatic
organisms has been correlated to the concentrations
of COPCs in pore water (Di Toro
et al.
1991; Ankley
et al.
1996; USEPA 2003, 2005). COPCs in pore
water also represent hazards to water-column species
because these substances can be transported into
overlying waters through chemical partitioning, dif-
fusion, bioturbation, or resuspension processes.
However, data on the concentrations of chemicals in
pore water may not fully represent the total exposure
of sediment-dwelling organisms to sediment-associ-
ated contaminants, particularly for compounds with
higher octanol-water partition coeffi cients (
K
ow
) that
bind strongly to organic carbon in the sediment
(Harkey
et al.
1994). For this reason, pore-water
chemistry alone should not be used to evaluate total
exposure to sediment-associated COPCs.
Selection of appropriate metrics for pore-water
chemistry should be consistent with the process used
to select the metrics for whole-sediment chemistry.
Several types of information can be used to support
the selection of appropriate metrics for sediment
chemistry. First, current and historic land and water
use activities in the vicinity of the site should be deter-
mined. Historical data should include information on
the nature and location of industrial developments
(and associated management practices that could lead
to releases of chemical substances) and municipal
infrastructure (combined sewer overfl ows, sewage
treatment plants), on the nature and location of any
spills that have occurred, and on the nature and
general location of non-point pollution sources. In
addition, information on the location, composition,
and volumes of stormwater and effl uent discharges is
useful for identifying the chemicals that have been or
may have been released into surface waters near the
site. Evaluation of the environmental fate of these
chemicals provides a basis for identifying the sub-
stances that are likely to partition into sediments.
Finally, existing sediment chemistry data should be
assembled and used to identify the chemicals that
have been measured at elevated levels (i.e., through
comparisons with sediment quality guidelines
(SQGs)) in surfi cial (i.e., top 10 cm) and deeper sedi-
ments. Together, this information can be used to
develop a list of COPCs for the site. This list of
COPCs can then be used to establish the primary
metrics for sediment chemistry at the site. Additional
metrics, such as total organic carbon (TOC), grain
size, acid volatile sulfi des (AVS), ammonia, and
hydrogen sulfi de should also be included to support
interpretation of the resultant data for the primary
metrics. The fi nal list of chemical analytes to be meas-
ured is also infl uenced by the equipment, technology,
facilities, and funds that are available for the project.
The chemicals that are typically analyzed in whole-
sediment samples collected near urbanized and
industrial areas include trace metals, PAHs, PCBs,
and various other organic constituents (for example
PCDDs/PCDFs; chlorophenols, and phthalates). In
areas that may be affected by inputs from agricul-
tural activities, it may be appropriate to measure the
concentrations of pesticides (such as OCs, car-
bamates, and organophosphates) in sediment
samples. Chemical concentrations are generally
