Environmental Engineering Reference
In-Depth Information
Contaminated sediments represent an important
environmental concern for several reasons. First,
contaminated sediments have been demonstrated to
be toxic to sediment-dwelling organisms and fi sh. As
such, exposure to contaminated sediments can result
in decreased survival, reduced growth, or impaired
reproduction in benthic invertebrates and fi sh.
Additionally, certain sediment-associated contami-
nants (termed bioaccumulative substances) are taken
up by benthic organisms through a process called
bioaccumulation. When larger animals feed on these
contaminated prey species, the pollutants are taken
into their bodies and are passed along to other
animals in the food web in a process called biomag-
nifi cation. As a result, benthic organisms, fi sh, birds,
and mammals can be adversely affected by contami-
nated sediments. Contaminated sediments can also
compromise human health owing to direct exposure
when wading, swimming, or through the consump-
tion of contaminated fi sh and shellfi sh. Human uses
of aquatic ecosystems can also be compromised by
the presence of contaminated sediments through
reductions in the abundance of food or sportfi sh
species or by the imposition of fi sh consumption
advisories. As such, contaminated sediments in
aquatic ecosystems can pose potential hazards to
sediment-dwelling organisms (i.e., epibenthic and
infaunal invertebrate species), aquatic-dependent
wildlife species (i.e., fi sh, amphibians, reptiles, birds,
and mammals), and human health.
Although contaminated sediment does not repre-
sent a specifi c use impairment, a variety of benefi cial
use impairments have been documented in associa-
tion with contaminated sediments. For example, the
imposition of fi sh consumption advisories (i.e.,
resulting from the bioaccumulation of sediment-
associated contaminants) has adversely affected com-
mercial, sport, and food fi sheries in many areas. In
addition, degradation of the benthic community (i.e.,
resulting from direct exposure to contaminated sedi-
ments) and other factors have contributed to the
impairment of fi sh and wildlife populations.
Furthermore, fi sh from areas with contaminated
sediments have been observed to have higher inci-
dences of tumors and other abnormalities than fi sh
from reference areas (i.e., because of exposure to
carcinogenic and teratogenic substances that accu-
mulate in sediments). Contaminated sediments have
also threatened the viability of many commercial
ports through the imposition of restrictions on
dredging of navigational channels and disposal of
dredged materials (IJC 1997). A summary of use
impairments and how they can be affected by con-
taminated sediments is presented in Table 7.1.
7.3 Indicators of sediment
quality conditions
Owing to the potential effects of contaminated sedi-
ments on aquatic organisms, aquatic-dependent
wildlife, and human health and well-being, regula-
tory agencies require information on sediment
quality conditions. As comprehensive monitoring
programs to assess sediment quality can be resource
intensive, investigators often select one or more indi-
cators of sediment quality conditions to obtain the
requisite information in a cost-effective manner.
Several factors need to be considered in the selection
of indicators for assessing sediment quality condi-
tions. First, the indicators that are selected must be
related to the ecosystem goals and objectives estab-
lished for the body of water under investigation
(Environment Canada 1996). Second, a suite of indi-
cators should be selected to reduce the potential for
errors in decisions that are made based on the results
of sediment quality monitoring programs
(Environment Canada 1996). Third, the selection of
indicators should be guided by selection criteria that
refl ect the stated purpose of the monitoring program
(as described in Table 7.2).
Relative to sediment contamination, chemicals of
potential concern (COPCs) can be classifi ed into two
general categories based on their potential effects on
ecological receptors, including toxic substances and
bioaccumulative substances. For toxic substances
that partition into sediments, evaluation of direct
effects on sediment-dwelling organisms is likely to
represent the primary focus of sediment quality
investigations. For bioaccumulative substances,
sediment quality assessments are likely to focus on
evaluating effects on aquatic-dependent wildlife (i.e.,
fi sh, amphibians, reptiles, birds, and mammals) and
on human health. In this way, such investigations
can provide the information needed to evaluate
attainment of the sediment management objectives
for the site and the objectives that have been recom-
mended for soft-substrate habitats in freshwater
ecosystems.
