Environmental Engineering Reference
In-Depth Information
and tissues are analyzed after an established period
of exposure.
In some cases, semipermeable membrane devices
(SPMDs) are deployed in the fi eld for specifi ed
periods to simulate exposures of aquatic organisms
to COPCs (Williamson
et al.
2002).
Models that describe bioaccumulation are rela-
tively well developed both for organic and inorganic
contaminants (Thomann 1989; Luoma & Fisher
1997; ASTM 2008b). Toxicokinetic models have
a long history, as do simpler models of bioaccu-
mulation processes. Site-specifi c models predict
bioaccumulation based on laboratory-determined
characterization of biological processes in the species
of interest and fi eld-determined chemical measure-
ments at the area of concern. Some uncertainties
remain unresolved in most models and consensus
does not exist about the appropriate model to apply
for some (if not all) COPCs (Luoma & Fisher 1997).
Equilibrium models are commonly used in assess-
ments of bioaccumulation and are available for both
organic and inorganic COPCs (Di Toro
et al.
1991;
Ankley
et al.
1996). The models assume that the
concentrations of COPCs among all compartments
of the environment are controlled by thermodynam-
ics and at least approach equilibrium conditions. If
thermodynamic equilibrium exists and if one route
of uptake is known or can be predicted, overall bio-
accumulation is inferred. Recent applications use an
extension of the equilibrium models, termed kinetic
or pathway models (ASTM 2008b). These models
incorporate geochemical principles and address
uncertainties in the assumptions of equilibrium.
Kinetic models assume that routes of bioaccumula-
tion are additive and must be determined independ-
ently. Kinetic models and equilibrium models may
yield similar results if COPC distributions and con-
centrations in an environment are at equilibrium
(although not always), but can yield very different
results where environmental compartments are not
at equilibrium (for example if biological processes
control concentrations, speciation, or phase parti-
tioning of COPCs) (Ingersoll
et al.
1997).
Tissue residue guidelines for the protection of pis-
civorous wildlife species and/or human health repre-
sent candidate sediment-quality targets that are used
to interpret the results of bioaccumulation assess-
ments (Fig. 7.7). However, a variety of risk-based
procedures have also been developed to evaluate the
results of such assessments (i.e., by calculating
average daily doses of COPCs for specifi c receptor
groups and comparing them with no or lowest
observed effect doses). These tools can also be used
to back-calculate to the concentrations of COPCs in
sediment that will protect human health and ecologi-
cal receptors.
7.4 Integration of information on
multiple indicators of sediment
quality conditions
Sediment quality assessments are typically conducted
to determine if sediments have become contaminated
as a result of land- or water-use activities. When such
contamination is indicated, the results of sediment
quality assessments need to provide the information
required to evaluate the nature, severity, and areal
extent of sediment contamination. In turn, this infor-
mation can be used to identify actual and probable
use impairments in the assessment area. As indicated
previously, investigators can select a variety of indi-
cators for evaluating sediment quality conditions.
Data on such indicators can provide useful informa-
tion for assessing effects on aquatic life, wildlife, or
human health.
Although individual indicators of sediment quality
each have an inherent level of uncertainty associated
with their application, the uncertainty associated
with an overall assessment of sediment contamina-
tion can be reduced by integrating information from
each of these individual indicators. For example,
sediment chemistry, sediment toxicity, and benthic
community data can be used together in a sediment
quality triad assessment to establish a weight of evi-
dence linking contaminated sediments to adverse
effects on sediment-dwelling organisms (Table 7.6).
The integration of multiple tools using a weight-of-
evidence approach has the potential to reduce sub-
stantially uncertainty associated with risk assessments
of contaminated sediment and, thereby, improve
management decisions (Long & Chapman 1985;
Chapman 1992; Canfi eld
et al.
1996; Ingersoll
et al.
1997; Wenning & Ingersoll 2002).
The fi rst step in the evaluation of sediment quality
data should be to determine if individual indicators
exceed the established targets. For example, the fol-
lowing questions should be addressed:
