Arch Environ Contam Toxicol (2011) 61:1–13
DOI 10.1007/s00244-010-9636-9
Baseline Ecological Risk Assessment of the Calcasieu Estuary,
Louisiana: Part 1. Overview and Problem Formulation
Donald D. MacDonald • Dwayne R. J. Moore • Christopher G. Ingersoll •
Dawn E. Smorong • R. Scott Carr • Ron Gouguet • David Charters •
Duane Wilson • Tom Harris • Jon Rauscher • Susan Roddy • John Meyer
Received: 23 November 2009 / Accepted: 20 December 2010 / Published online: 26 March 2011
Springer Science+Business Media, LLC (outside the USA) 2011
Abstract A remedial investigation/feasibility study (RI/
FS) of the Calcasieu Estuary cooperative site was initiated
in 1998. This site, which is located in the southwestern
portion of Louisiana in the vicinity of Lake Charles,
includes the portion of the estuary from the saltwater barrier on the Calcasieu River to Moss Lake. As part of the RI/
FS, a baseline ecological risk assessment (BERA) was
conducted to assess the risks to aquatic organisms and
aquatic-dependent wildlife exposed to environmental contaminants. The purpose of the BERA was to determine if
adverse effects on ecological receptors are occurring in the
estuary; to evaluate the nature, severity, and areal extent of
any such effects; and to identify the substances that are
causing or substantially contributing to effects on ecological receptors. This article describes the environmental
setting and site history, identifies the chemicals of potential
concern, presents the exposure scenarios and conceptual
Electronic supplementary material The online version of this
article (doi:10.1007/s00244-010-9636-9) contains supplementary
material, which is available to authorized users.
D. D. MacDonald (&) D. E. Smorong
MacDonald Environmental Sciences Ltd., Nanaimo,
BC V9T 1W6, USA
e-mail: mesl@shaw.ca
D. R. J. Moore
Intrinsik Environmental Sciences, Inc., New Gloucester,
ME 04260, USA
C. G. Ingersoll
Columbia Environmental Research Center, United States
Geological Survey, Columbia, MO 65201, USA
R. S. Carr
Columbia Environmental Research Center, United States
Geological Survey, Corpus Christi, TX 78412, USA
model for the site, and summarizes the assessment and
measurement endpoints that were used in the investigation.
Two additional articles in this series describe the results of
an evaluation of effects-based sediment-quality guidelines
as well as an assessment of risks to benthic invertebrates
associated with exposure to contaminated sediment.
In response to concerns regarding environmental contamination, a remedial investigation/feasibility study (RI/FS)
was conducted in the Calcasieu Estuary. As part of the RI/
FS, studies were designed and implemented to support a
baseline ecological risk assessment (BERA) of the Calcasieu Estuary. The BERA was conducted in accordance with
the Ecological Risk Assessment Guidance for Superfund:
Process for Designing and Conducting Ecological Risk
Assessment (United States Environmental Protection
Agency [USEPA] 1997). The objectives of the BERA were
to estimate the risks posed by environmental contamination
to ecological receptors in the Calcasieu Estuary as well as
R. Gouguet
Windward Environmental LLC, Seattle, WA 98119-3958, USA
D. Charters
United States Environmental Protection Agency, Edison,
NJ 08837-3679, USA
D. Wilson T. Harris
Louisiana Department of Environmental Quality, Baton Rouge,
LA 70884-2178, USA
J. Rauscher S. Roddy J. Meyer
United States Environmental Protection Agency, Dallas,
TX 75202-733, USA
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provide the information needed by risk managers to make
decisions regarding the need for remedial actions.
This article is the first in a series that describe the BERA
that was conducted for the Calcasieu Estuary. It describes
the environmental setting and contamination history,
identifies the chemicals of potential concern (COPCs),
presents the exposure scenarios and conceptual model for
the site, and summarizes assessment and measurement
endpoints that were used in the investigation. As such, this
article provides an overview of the problem formulation
that was conducted for the BERA. Two additional articles
in this series describe the results of an evaluation of effectsbased sediment quality guidelines and the ecological risks
to benthic invertebrates associated with exposure to
Fig. 1 Map of the Bayou
d’Inde, Middle Calcasieu
Estuary, and Upper Calcasieu
River AOCs showing major
industrial facilities
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Arch Environ Contam Toxicol (2011) 61:1–13
contaminated sediments. This series of articles is based on
the BERA report that was published by the USEPA
(MacDonald et al. 2002).
Study Area
The Calcasieu River is one of the largest river systems in
southwest Louisiana (LA). From its headwaters in the
vicinity of Kisatchie National Forest (in Vernon Parish),
the Calcasieu River flows some 260 km to the Gulf of
Mexico near Cameron, LA (Fig. 1). Although much of the
Calcasieu River system is relatively uncontaminated, the
portion of the watershed from the saltwater barrier near
Arch Environ Contam Toxicol (2011) 61:1–13
Lake Charles, LA, to the Intercoastal Waterway has
undergone extensive industrial development during the
past seven decades. These developmental activities have
resulted in widespread contamination of sediment in the
estuarine portion of the watershed, particularly in the
bayous within the upper portion of the estuary (Curry et al.
1997). Based on the results of a screening-level ecological
risk assessment (SLERA), the portion of the Calcasieu
Estuary from the saltwater barrier to Moss Lake was
identified as the area in which environmental contamination posed the greatest potential risks to ecological receptors and, as such, was designated as the primary study area
(CDM 1999). To facilitate the RI/FS, this study area was
divided into three subareas (i.e., areas of concern [AOCs]),
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including the Upper Calcasieu River, Bayou d’Inde, and
Middle Calcasieu River (Fig. 1). Several reference areas
were also identified in the lower estuary and in the vicinity
of Sabine Lake to support the interpretation of the data
generated during the remedial investigation (RI; Fig. 2).
The upper Calcasieu River AOC (easting [x] =
476447.604; northing [y] = 3344135.439) includes the
portion of the watershed from the saltwater barrier to the
Highway 210 bridge, a distance of approximately 11 km
(Fig. 1). This portion of the river system consists of several
readily identifiable water bodies, including the following:
the upper Calcasieu River mainstem from the saltwater
barrier to Lake Charles, Lake Charles, Calcasieu Ship
Channel from Lake Charles to the Highway 210 bridge,
Fig. 2 Map of the study area,
showing the areas selected to
represent reference conditions
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Clooney Island Loop, Contraband Bayou, Coon Island
Loop, and Bayou Verdine.
Bayou d’Inde is one of the major tributaries to the
Calcasieu River. From its headwaters near Sulphur, LA,
Bayou d’Inde flows in a southeasterly direction approximately 16 km to its confluence with the Calcasieu Ship
Channel (Fig. 1). Over that distance, Bayou d’Inde is
joined by several tributaries, the largest of which is Maple
Fork. The lower portions of the bayou are characterized by
hydraulic connections with a great deal of off-channel
wetland habitat, the largest of which is the Lockport Marsh.
The Bayou d’Inde AOC (x = 471011.9724; y =
3341929.799) encompasses all of the aquatic habitats from
the headwater areas to the Ship Channel, including offchannel wetland.
The middle Calcasieu River AOC (x = 470168.0462;
y = 3336193.002) comprises the portion of the watershed
from the Highway 210 bridge to the outlet of Moss Lake
(a distance of approximately 11 km), excluding Bayou
d’Inde (Fig. 1). The primary physiographic features in this
portion of the study area include the Calcasieu Ship
Channel, Prien Lake, the original Calcasieu River channel,
and Moss Lake. For the purposes of this assessment, the
Indian Wells Lagoon and Bayou Olsen were also included
in the middle Calcasieu River AOC.
A total of five areas were selected to represent reference
conditions within the Calcasieu River watershed and surrounding environments. These areas included (1) Bayou
Choupique (x = 463827.1136; y = 3329317.306), (2) Grand
Bayou (x = 480233.0779; y = 3304222.294), (3) Bayou
Bois Connine (x = 480029.4149; y = 3309241.132), (4)
Willow Bayou (x = 425138.2076; y = 3304669.905), and
(5) Johnson Bayou (x = 425867.4187; y = 3300104.113;
Fig. 2). Bayou Choupique is located southwest of Moss Lake
and flows approximately 8 km from its headwaters to the
confluence with the Intracoastal Waterway northwest of
Ellender, LA. Grand Bayou and Bayou Bois Connine are
tributaries to Calcasieu Lake, both of which empty into the
lake along its eastern shore. Willow Bayou and Johnson
Bayou are tributaries to Sabine Lake and discharge into the
lake along its southeastern shoreline. All five of these reference areas are relatively pristine and have been virtually
unaffected by industrial activities (Ramelow et al. 1989).
Arch Environ Contam Toxicol (2011) 61:1–13
discharges, spills associated with production and transport
activities, and deposition of substances that have been
released into the atmosphere.
Industrial activities have been ongoing in the Lake
Charles area since the turn of the 20th century. However,
construction of the Calcasieu Ship Channel in 1937 transformed Lake Charles into a deep-water port. This attribute,
in conjunction with the ready availability of oil in the
region, set the stage for rapid industrial development in the
region. Today, the results of [70 years of industrial
development are evident in the number of sites within the
study area that are subject to some form of environmental
control or enforcement under federal and state regulatory
programs. In 1996, the National Oceanic and Atmospheric
Administration commissioned a study to evaluate the
extent of environmental contamination in the Calcasieu
Estuary (Curry et al. 1997). The results of this investigation
indicated that 12 major industrial facilities and two municipal wastewater treatment plants are within the study area.
The locations of the major industrial and municipal facilities that discharge wastewaters into the Calcasieu Estuary
are shown in Fig. 1.
Problem Formulation
The process of defining the questions addressed during a
BERA is termed ‘‘problem formulation.’’ Problem formulation is a systematic planning process that identifies the
factors to be addressed in a BERA and consists of five
major activities (USEPA 1997), including (1) refinement of
the preliminary list of COPCs at the site; (2) further
characterization of the potential ecological effects of the
COPCs at the site; (3) review and refinement of the
information on the fate and transport of COPCs, on
potential exposure pathways, and on the biota potentially at
risk; (4) development of a conceptual model with testable
hypotheses (or risk questions) that the site investigation
will address; and (5) selection of assessment and measurement endpoints. At the conclusion of the problem
formulation, there is a scientific/management decision
point, which consists of agreement on four items: the
assessment endpoints, the exposure pathways, the risk
questions, and the conceptual model that integrates these
components (USEPA 1997).
Site History and Sources of Contamination
COPCs
There are a number of anthropogenic sources of toxic and
bioaccumulative substances in the Calcasieu Estuary. The
primary sources of COPCs in the estuary include industrial wastewater discharges, municipal wastewater-treatment plant discharges, stormwater runoff, surface water
recharge by contaminated groundwater, non–point source
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The identification of COPCs represents an essential element of the problem-formulation process (USEPA 1998).
To initiate this process, CDM Federal Programs Corporation (CDM 1999) conducted a SLERA of the Calcasieu
Estuary in 1999 to assess the potential for adverse
Arch Environ Contam Toxicol (2011) 61:1–13
biological effects on ecological receptors associated with
either direct or indirect exposure to contaminated environmental media in the Calcasieu Estuary. The SLERA
was conducted by comparing the maximum concentration
of each chemical of interest (COI) in water or sediment
samples with conservative benchmarks (i.e., toxicity
screening values) for that COI. Substances with maximum
concentrations in excess of the selected benchmarks were
identified as COPCs. The results of the SLERA indicated
that the preliminary COPCs in the Calcasieu Estuary
included the following: metals, polycyclic aromatic
hydrocarbon (PAHs), polychlorinated biphenyls (PCBs),
organochlorine and other pesticides, polychlorinated
dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDDs/
PCDFs) chlorophenols, chlorinated benzenes, chlorinated
ethanes, phthalates, cyanide, and acetone (Table 1). This
list of preliminary COPCs was refined to include those
substances that were measured in environmental media at
levels greater then selected environmental-quality criteria
and guidelines (MacDonald et al. 2002).
Based on the results of these evaluations, the following
substances were identified as the primary water-borne
COPCs in the Calcasieu Estuary: metals (copper and mercury), 1,2-dichloroethane, and trichloroethane (Table 1). By
comparison, the sediment-associated COPCs included the
following: metals (copper, chromium, lead, mercury, nickel,
and zinc), PAHs (acenaphthene, acenaphthylene, anthracene, fluorene, 2-methylnaphthalene, naphthalene, phenanthrene, benz(a)anthracene, benzo(a)pyrene, chrysene,
dibenz(a,h)anthracene, fluoranthene, pyrene, total PAHs,
and other PAHs), PCBs, PCDDs/PCDFs, chlorinated benzenes (hexachlorobenzene [HCB], hexachlorobutadiene
[HCBD], and degradation products), phthalates (bis-2-ethylhexyl phthalate [BEHP]); carbon disulfide, unionized
5
ammonia, hydrogen sulfide, acetone, and organochlorine
pesticides (aldrin and dieldrin; Table 1).
The substances of greatest concern to aquatic-dependent
wildlife were those that are persistent and bioaccumulative.
The COPCs identified for water and sediment included all
of the persistent and bioaccumulative substances (e.g.,
PCBs, PCDDs/PCDFs, HCB, HCBD, and organochlorine
pesticides) that had been regularly detected in monitoring
studies of the Calcasieu Estuary (Table 1).
Potential Ecological Effects of COPCs in the Calcasieu
Estuary
A stressor is any physical, chemical, or biological entity
that has the potential to cause a change in the ecological
condition of the environment (USEPA 2000a). Accurate
identification of the stressor or stressors that are causing or
substantially contributing to biological impairments in
aquatic ecosystems is important because it provides a basis
for developing strategies that are likely to improve the
quality of aquatic resources (USEPA 2000a). In this way,
limited human and financial resources can be directed at
the challenges that are most likely to maintain or restore
beneficial uses.
The RI of the Calcasieu Estuary was focused on the
identification of the chemical stressors that are posing
potential risks to ecological receptors. Many physical–
chemical (e.g., water temperature, salinity, dissolved oxygen, erosion and sedimentation, habitat degradation, and
pH) and biological (e.g., introduced species, recreational
and commercial fishing, disease) factors also have the
potential to adversely affect aquatic organisms and aquaticdependent wildlife species. However, quantification of the
effects of these factors on key ecological receptors was
Table 1 Overview of key exposure routes for various classes of chemicals of potential concern in the Calcasieu Estuary
Classification
Chemicals of potential concern
Exposure route: aquatic
Contact
Ingestion
Exposure route: wildlife
Inhalation Contact Ingestion
Bioaccumulative substances
Mercury, PAHs, PCBs, PCDDs/PCDFs, HCB,
HCBD, aldrin, dieldrin
*
*
*
Toxic substances in sediments
Copper, chromium, lead, mercury, nickel, zinc,
PAHs, PCBs, HCB, HCBD, BEHP, aldrin and
dieldrin, carbon disulfide, acetone, unionized
ammonia, hydrogen sulfide
*
*
*
Toxic substances in surface water Copper, mercury, 1,2-dichloroethane,
trichloroethane
*
Toxic substances in surface
microlayer
*
Metals, VOCs, SVOCs
*
*
PCBs polychlorinated biphenyls, PAHs polycyclic aromatic hydrocarbons, PCDD polychlorinated dibenzo-p-dioxins, PCDF polychlorinated
dibenzofurans, VOCs volatile organic chemicals, SVOCs semivolatile organic chemicals, HCB hexachlorobenzene, HCBD hexachlorobutadiene,
BEHP bis-2-ethylhexyl phthalate, * indicates potentially complete exposure route
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outside the scope of the BERA. The strategy for addressing
this apparent limitation of the BERA involved assessing
risks to ecological receptors in the study areas relative to
the comparable risks to those receptors in nearby reference
areas with similar biological and physical conditions. In
this way, the incremental risks posed by COPCs, greater
then those posed by physical and biological stressors in the
reference systems, could be estimated. In addition, any
unaccounted effects for of such factors on the measurement
endpoints could be addressed in the associated uncertainty
analysis (MacDonald et al. 2002). Although the identity,
fate and transport, toxicity, and bioaccumulation of the
COPCs described in the SLERA (CDM 1999; Goldberg
2001) were summarized in the problem formulation for the
site (MacDonald et al. 2001), space limitations preclude
presentation of this information in this article.
Ecological Receptors Potentially at Risk
A critical element of the problem-formulation process is
the identification of the receptors at risk that occur within
the study area. USEPA guidance is available to help
identify receptors at risk (USEPA 1989, 1992, 1997). The
guidance states that receptors at risk include the following:
(1) resident species or communities exposed to the highest
chemical concentrations in sediments and surface water;
(2) species or functional groups that are essential to, or
indicative of, the normal functioning of the affected habitat; and, (3) federal- or state-designated threatened or
endangered species.
In the Calcasieu Estuary, the ecological receptors
potentially at risk include the plants and animals that use
aquatic, wetland, and terrestrial habitats within the watershed. Based on the results of the SLERA (CDM 1999), the
ecological receptors that are potentially at risk due to historic and ongoing discharges of COPCs into surface waters
are those species that use habitats within aquatic and
wetland ecosystems. These groups of organisms include
microorganisms, aquatic plants, benthic macroinvertebrates, zooplankton, fish, reptiles and amphibians, and
aquatic-dependent birds and mammals. The focal species
selected to evaluate risks to these ecological receptors are
identified with the assessment endpoints. Although other
groups of ecological receptors are known to occur within
this ecosystem (e.g., terrestrial insects, terrestrial plants),
risks to terrestrial organisms were not evaluated in the
aquatic risk assessment and may be addressed in the future.
Key Exposure Pathways for Ecological Receptors
Evaluation of the risks posed by COPCs in the estuary
requires a detailed understanding of the pathways through
which ecological receptors are exposed to these substances.
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In turn, the identification of key exposure pathways
requires an understanding of the sources and releases of
environmental contaminants and the environmental fate of
these substances. MacDonald et al. (2002) provides
descriptions of the sources and releases of COPCs within
the study area.
On release into aquatic ecosystems, COPCs partition
into environmental media (i.e., water, sediment, and/or
biota) in accordance with their physical and chemical
properties and the characteristics of the receiving water
body (Table 1). As a result of such partitioning, COPCs
can occur at increased levels in surface water, sediments,
and/or the tissues of aquatic organisms. To facilitate the
development of conceptual models that link stressors to
receptors, the COPCs can be classified into three groups
based on their fate and effects in the aquatic ecosystem,
including (1) bioaccumulative substances, (2) toxic substances that partition into sediments, and (3) toxic substances that partition into water (including the surface
microlayer; Table 1).
Once released to the environment, there are three pathways through which ecological receptors can be exposed to
COPCs. These routes of exposure include (1) direct contact
with contaminated environmental media, (2) ingestion
of contaminated environmental media, and (3) inhalation
of contaminated air. The exposure routes that apply to each
of the categories of COPCs are described in Table 1 and
later in the text.
Bioaccumulative Substances
Aquatic organisms and aquatic-dependent wildlife species
can be exposed to bioaccumulative substances by way of
several pathways. First, direct contact with contaminated
water or sediment can result in the uptake of bioaccumulative substances through the gills or through the skin of
aquatic organisms. This route of exposure is particularly
important for sediment-dwelling organisms because most
of the bioaccumulative COPCs tend to accumulate in
sediments on release into the environment (CDM 1999).
Ingestion of contaminated sediments and/or prey species
also represents an important route of exposure to bioaccumulative substances for aquatic organisms, particularly
for sediment-dwelling organisms, carnivorous fish,
amphibians, and reptiles (CDM 1999).
For aquatic-dependent wildlife species, ingestion of
contaminated prey species represents the principal route of
exposure to bioaccumulative substances (Moore et al.
1997; 1999). The groups of wildlife species that are likely
to be exposed to bioaccumulative substances through this
pathway include insectivorous birds, sediment-probing
birds, carnivorous-wading birds, piscivorous birds, and
omnivorous and piscivorous mammals (Table 2; Fig. 3).
Arch Environ Contam Toxicol (2011) 61:1–13
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Table 2 Receptor groups exposed to various classes of chemicals of potential concern in the Calcasieu Estuary
Classification
Bioaccumulative
substances
Chemicals of potential concern
Ecological receptors
Mercury, PAHs, PCBs, PCDDs/PCDFs, HCB,
HCBD, aldrin, dieldrin
Aquatic organisms
Birds
Mammals
Benthic invertebrates,
carnivorous fish,
amphibians, reptiles
Insectivorous birds;
Piscivorous
sediment-probing birds,
mammals,
carnivorous-wading birds, omnivorous
piscivorous birds
mammals
Toxic substances Copper, chromium, lead, mercury, nickel, zinc, Decomposers, aquatic
Sediment-probing birds
in sediments
PAHs, PCBs, HCB, HCBD, BEHP, aldrin and plants, benthic
dieldrin, carbon disulfide, acetone, unionized
invertebrates, benthic
ammonia, hydrogen sulfide
fish, reptiles, amphibians
Toxic substances Copper, mercury, 1,2-dichloroethane,
in surface water trichloroethane
Aquatic plants, aquatic
invertebrates, fish,
amphibians
Toxic substances Metals, VOCs, SVOCs
in surface
microlayer
Aquatic invertebrates,
pelagic fish
Birds
Piscivorous
mammals
PCBs polychlorinated biphenyls, PAHs polycyclic aromatic hydrocarbons, PCDD polychlorinated dibenzo-p-dioxins, PCDF polychlorinated
dibenzofurans, VOCs volatile organic chemicals, SVOCs semivolatile organic chemicals, HCB hexachlorobenzene, HCBD hexachlorobutadiene,
BEHP bis-2-ethylhexyl phthalate
Sources of
Contaminants
COPCs
Piscivorous
Birds
Piscivorous
Mammals
Insectivorous
Birds
Omnivorous
Mammals
Aquatic
Plants
Carnivorous
Fish
Reptiles
Benthic
Invertebrates
Sedimentprobing Birds
Benthic
Fish
BIOTA
(Biota ingestion)
Aquatic
Invertebrates
Microbial
Community
Amphibians
Receptors
Carnivorous
Wading Birds
SEDIMENT
(Sediment contact,
sediment ingestion)
WATER
(Water contact)
Environmental Fate
SURFACE
MICROLAYER
(Water contact,
inhalation)
Pelagic
Fish
Decreased Survival, Growth and/or Reproduction
Risk Hypotheses
Decreased
Activity
Fig. 3 Conceptual model diagram illustrating exposure pathways and potential effects for all categories of COPCs
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Toxic Substances That Partition Into Sediments
Aquatic organisms and aquatic-dependent wildlife species
can be exposed to toxic substances that partition into sediments through several pathways. For aquatic organisms,
such as microbiota, aquatic plants, sediment-dwelling
organisms, benthic fish, and amphibians, direct contact
with contaminated sediment and/or contaminated pore
water represents the most important route of exposure to
toxic substances that partition into sediments (MacDonald
et al. 2002). However, ingestion of contaminated sediments
can also represent an important exposure pathway for
certain species (e.g., polychaetes) that process sediments to
obtain food (e.g., sediment-probing birds; Beyer et al.
1994). Direct contact with contaminated sediments also
represents a potential exposure pathway for reptiles; however, it is less important for reptiles than for other aquatic
organisms (MacDonald et al. 2002).
For aquatic-dependent wildlife species, ingestion of
contaminated sediments represents the principal route of
exposure to toxic substances that partition into sediments.
Of the wildlife species that occur in the Calcasieu Estuary,
sediment-probing birds are the most likely to be exposed
through this pathway (Tables 1, 2; Beyer et al. 1994).
Toxic Substances That Partition Into Surface Water
Aquatic organisms and aquatic-dependent wildlife species
can be exposed to toxic substances that partition into surface water through several pathways. For aquatic organisms—such as microbiota, aquatic plants, aquatic
invertebrates, fish, and amphibians—direct contact with
contaminated water represents the most important route of
exposure to toxic substances that partition into surface
water (MacDonald et al. 2002). This exposure route
involves uptake through the gills and/or through the skin.
For aquatic-dependent wildlife species, ingestion of
contaminated water represents the principal route of
exposure to toxic substances that partition into surface
water (Table 1). Although virtually all aquatic-dependent
wildlife species are exposed to toxic substances that partition into surface water, this pathway is likely to account
for a minor proportion of the total exposure to such
chemicals for most of these species (i.e., due to the lower
levels of COPCs in surface water compared with tissues
and due to the relatively low ingestion rates for brackish
water; MacDonald et al. 2002).
Toxic Substances That Partition Into the Surface
Microlayer
Aquatic organisms and aquatic-dependent wildlife species
can be exposed to toxic substances that partition into
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surface water through several pathways. For certain aquatic
organisms, such as aquatic invertebrates and pelagic fish,
direct contact with the contaminated surface microlayer
(i.e., the layer of water that is present at the water–air
interface) may represent an important route of exposure to
such toxic substances (MacDonald et al. 2002). This
exposure route involves uptake through the gills and/or
through the skin of aquatic organisms.
For aquatic-dependent wildlife species, inhalation of
substances that volatilize from the surface microlayer can
represent a route of exposure to toxic substances that partition into this environmental medium (Table 1). However,
this route of exposure is likely to be of relatively minor
importance under most circumstances (Moore et al. 1997,
1999). This pathway could become important during and
after accidental spills, when such substances are present as
slicks on the water surface.
Conceptual Model for the Calcasieu Estuary BERA
In accordance with USEPA guidance, the problem formulation for a BERA is intended to result in three main outputs: assessment endpoints, conceptual models, and a
risk-analysis plan (USEPA 1997, 1998). The conceptual
model represents a particularly important component of
problem formulation because it enhances the level of
understanding regarding the relations between human
activities and ecological receptors at the site under consideration. Specifically, the conceptual model describes
key relations between stressors and assessment endpoints.
In so doing, the conceptual model provides a framework
for predicting effects on ecological receptors and a template for generating risk questions and testable hypotheses
(USEPA 1997, 1998). The conceptual model also provides
a means of highlighting what is known and what is not
known about a site. In this way, the conceptual model
provides a basis for identifying data gaps and designing
monitoring programs to acquire the information necessary
to complete the assessment.
Conceptual models consist of two main elements: (1) a
set of hypotheses that describe predicted relations between
stressors, exposures, and assessment endpoint responses
(along with a rationale for their selection) and (2) diagrams
that illustrate the relations presented in the risk hypotheses.
The sources and releases of COPCs, the fate and transport
of these substances, the pathways by which ecological
receptors are exposed to the COPCs, and the potential
effects of these substances on the ecological receptors that
occur in the Calcasieu Estuary are described in MacDonald
et al. (2001). Similarly, the hypotheses that provide predictions regarding how ecological receptors will be
exposed to and respond to the COPCs is presented in
MacDonald et al. (2001). Food web dynamics in the
Level 1
Level 2
Level 3
Level 4
Arch Environ Contam Toxicol (2011) 61:1–13
Piscivorous Mammals
Mink, River Otter, Dolphins
BI/IH
Omnivorous Mammals
Raccoon, Black Bear
BI
9
Piscivorous Birds
Osprey, Kingfisher, Pelicans,
Terns
BI
Carnivorous-wading Birds
Great Blue Heron, Great Egret,
Snowy Egret
BI/IH
Insectivorous Birds
Purple Martin, Swallows
BI
Sediment-probing Birds
Roseate Spoonbill, Willet,
Stilts, Ibis, Ducks
BI/SI/IH
Benthic Invertebrates
Oysters, Mussels, Clams, Sponges,
Penaeid Shrimp, Blue Crabs,
Bivalves, Aquatic Worms,
Amphipods, Sea Urchins, Other
Crabs
BI/SC/SI/WC
Aquatic Invertebrates
Copepods, Mysid Shrimp,
Crabs, Emergent Insects,
Water Striders
BI/WC
Aquatic Plants
Algae (periphyton, phytoplankton), Macrophytes
WC/SC
Reptiles
Mississippi Green Water
Snake, American Alligator,
Yellowbelly Water Snake
BI/SC
Amphibians
Bull Frog, Leopard Frogs,
Toads, Salamanders
BI/SC/WC
Carnivorous Fish
Redfish, Black Drum, Spotted
Seatrout, Gar, Chain Pickerel
BI/WC
Omnivorous Fish
Spot, Pinfish, Atlantic Croaker,
Hardhead Catfish, Gafftopsail Catfish,
Naked goby
BI/SI/WC
Herbivorous/Planktivorous Fish
Gulf Killifish, Sheepshead Minnow,
Inland Silverside, Gulf Menhaden,
Striped Mullet
BI/WC
Decomposers
Bacteria, Fungi, Protozoa
SC/WC
Water and Sediment
Nutrients, Detritus
Principal Exposure Routes (note: surface waters tend to have high salinity, reducing the potential for water ingestion by ecological receptors): BI = Biota Ingestion;
WC = Water Contact; WI = Water Ingestion; SC = Sediment Contact; SI = Sediment Ingestion; IH = Inhalation
Fig. 4 The Calcasieu Estuary food web showing the principal routes of exposure to contaminated water, sediment and biota
Calcasieu Estuary are presented in Fig. 4. In addition, a
conceptual model diagram that illustrates exposure pathways and potential effects for bioaccumulative substances,
toxic substances that partition into sediments, toxic substances that partition into overlying water, and toxic substances that partition into the surface microlayer, is
presented in Fig. 3.
Selection of Assessment and Measurement Endpoints
An assessment endpoint is an ‘‘explicit expression of the
environmental value that is to be protected’’ (USEPA 1997,
p. 4-2). The selection of assessment endpoints is an
essential element of the overall BERA process because it
provides a means of focusing assessment activities on the
key environmental values (e.g., reproduction of sedimentdwelling organisms) that could be adversely affected by
exposure to COPCs. Assessment endpoints were selected
based on the ecosystems, communities, and species that
occur, have historically occurred, or could potentially
occur at the site (USEPA 1997). The following factors
were considered during the selection of assessment endpoints (USEPA 1997): the COPCs that occur in environmental media and their concentrations; the mechanisms of
toxicity of the COPCs to various groups of organisms; the
ecologically-relevant receptor groups that are potentially
sensitive or highly exposed to the contaminant based on
their natural history attributes; and the presence of potentially complete exposure pathways. Thus, the fate, transport, and mechanisms of toxicity for each COPC or group
of COPCs was considered to determine which receptors are
likely to be most at risk. This information included an
understanding of how the adverse effects of the COPC
could be expressed (e.g., eggshell thinning in birds) and
how the form of the chemical in the environment could
influence its bioavailability and toxicity. Integration of
these various types of information provided a means of
developing a conceptual model of the site that identifies
linkages between contaminant discharges and effects on
key ecological receptors (Fig. 3). The resultant conceptual
site model and associated information provided the basis
for selecting the assessment endpoints that were most
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Arch Environ Contam Toxicol (2011) 61:1–13
relevant for the Calcasieu Estuary BERA. The assessment
endpoints and associated focal species (for which exposure
was evaluated or modeled) that were selected for consideration in the BERA included the following:
•
•
•
Activity of the microbial community (focal species =
Microtox);
Survival, growth, and reproduction of aquatic plants
(focal species = alga [Ulva fasciata]);
Survival, growth, and reproduction of benthic invertebrates (focal species = amphipods [Hyalella azteca
and Ampelisca abdita] and sea urchin [Arbacia
punctulata]);
•
•
•
Survival, growth, and reproduction of benthic and
pelagic fish (focal species = redfish [Sciaenops
ocellatus]);
Survival, growth, and reproduction of aquatic-dependent bird species (focal species = great blue heron,
osprey, kingfisher, roseate spoonbills); and,
Survival, growth, and reproduction of aquatic-dependent mammalian species (focal species = raccoon,
river otter, mink).
A measurement endpoint is defined as ‘‘a measurable
ecological characteristic that is related to the valued characteristic selected as the assessment endpoint’’ and is a
Table 3 Assessment endpoints, testable hypotheses and measurement endpoints for assessing risk to microbes, plants, and invertebrates
Assessment endpoint
Risk questions & testable hypotheses
Measurement endpoints
Activity of the microbial
community (e.g., rate of
carbon processing by
decomposers)
Is the metabolic rate of bacteria (i.e., the activity of Bioluminescence of bacterium Vibrio fisheri
aquatic microbiota) exposed to whole sediments
(Microtox; as a surrogate for bacterial metabolic
from the Calcasieu Estuary significantly lower
rate) in whole-sediment toxicity tests (Johnson
(p \ 0.1) than that for bacteria exposed to reference 1998; Johnson and Long 1998)
sediments?
Survival and growth of aquatic
plants
Is the survival and/or growth of aquatic plants
Germination, germling length, and cell number of the
exposed to pore water from Calcasieu Estuary
alga U. lactuca (as surrogates for survival, growth
sediments significantly lower (p \ 0.1) than that for and/or reproduction) in pore-water toxicity tests
aquatic plants exposed to pore water from reference (Hooten and Carr 1998)
sediments?
Survival, growth, and
reproduction of benthic
invertebrates
Are the levels of contaminants in whole sediments
Concentrations of contaminants in whole sediments
from the Calcasieu Estuary greater than the
(i.e., reported on a dry-weight basis relative to
sediment-quality guidelines for the survival, growth, sediment-quality benchmarks for survival, growth,
or reproduction of benthic invertebrates?
and/or reproduction of benthic invertebrates
expressed as mean sediment-quality guideline
quotients; USEPA 2000b; Long et al. 1995; Long
and Morgan 1991; MacDonald et al. 1996).
Are the levels of contaminants in pore water from
Calcasieu Estuary sediments greater than the
toxicity thresholds for survival, growth, or
reproduction of benthic invertebrates?
Concentrations of contaminants in pore water (i.e.,
relative to acute and chronic toxicity thresholds for
survival and/or growth of benthic invertebrates in
pore water; USEPA 1999)
Is the survival of benthic invertebrates exposed to
whole sediments from the Calcasieu Estuary
significantly lower (p \ 0.1) than that of benthic
invertebrates exposed to reference sediments?
Survival of the amphipod H. azteca in 10- to 28-day
whole-sediment toxicity tests (USEPA 2000b;
ASTM 2009a); survival of the amphipod A. abdita
in 10-day whole-sediment toxicity tests (ASTM
2009b); survival of the polychaete Nereis virens in
28-day whole-sediment toxicity tests (ASTM 2009c)
Is the growth of benthic invertebrates exposed to
whole sediments from the Calcasieu Estuary
significantly lower (p \ 0.1) than that of benthic
invertebrates exposed to reference sediments?
Growth of the amphipod H. azteca in 10-day wholesediment toxicity tests (ASTM 2009a; USEPA
2000b, 2000c)
Is the reproductive success of benthic invertebrates Fertilization and embryo development of the sea
exposed to pore water from Calcasieu Estuary
urchin A. punctulata (as a surrogate for reproductive
sediments significantly lower (p \ 0.1) than that of success in benthic invertebrates) in pore-water
benthic invertebrates exposed to pore water from
toxicity tests (Carr and Chapman 1992; Carr et al.
reference sediments?
1996a, 1996b, 1997)
Is the structure of benthic macroinvertebrate
Percent annelid abundance, percent arthropod
communities in Calcasieu Estuary sediments outside abundance, and index of contamination as
the normal range for benthic invertebrate
calculated from raw species counts (Gaston and
communities in reference sediments (i.e., 95%
Nasci 1988; Gaston et al. 1988; Gaston and Young
confidence interval)?
1992; Brown et al. 2000)
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11
Table 4 Assessment endpoints, testable hypotheses and measurement endpoints for assessing risk to benthic and pelagic fish
Assessment endpoint
Risk questions/testable hypotheses
Measurement endpoints
Survival, growth, and
Are the concentrations of contaminants in overlying water Concentrations of contaminants in overlying water (i.e.,
reproduction of benthic from the Calcasieu Estuary greater than the waterrelative to the water-quality criteria for the protection of
and pelagic fish
quality criteria for the survival, growth, or reproduction aquatic organisms; USEPA 1999)
of fish?
Are the concentrations of contaminants in pore water
Concentrations of contaminants in pore water (i.e.,
from Calcasieu Estuary sediments greater than the
relative to the water quality criteria for the protection of
water-quality criteria for the survival, growth, or
aquatic organisms; USEPA 1999)
reproduction of fish?
Is the survival of fish (as indicated by the survival of fish) Survival of redfish S. ocellatus larvae in 48-hour poreexposed to pore water from Calcasieu Estuary
water toxicity tests (Carr and Chapman 1992)
sediments significantly lower (p \ 0.1) than that of fish
exposed to pore water from reference sediments?
Is the reproductive success of fish exposed to pore water Hatching success of redfish S. ocellatus eggs in 24-hour
from Calcasieu Estuary sediments significantly
pore-water toxicity tests (Carr and Chapman 1992)
(p \ 0.1) lower than that of fish exposed to pore water
from reference sediments?
Table 5 Assessment endpoints, testable hypotheses and measurement endpoints for assessing risk to avian and mammalian wildlife
Assessment endpoint
Risk questions/testable hypotheses
Measurement endpoints
Survival and reproduction Do the daily doses of bioaccumulative COPCs received Concentrations of contaminants in the tissues of benthic
of aquatic-dependent
by sediment-probing birds due to the consumption of
invertebrates (i.e., as used to model daily doses of
bird species
the tissues of prey species from in the Calcasieu Estuary COPCs for selected focal species)
exceed the toxicity reference values for survival or
reproduction of birds?
Do the daily doses of bioaccumulative COPCs received Concentrations of contaminants in the tissues of benthic
by carnivorous-wading birds due to the consumption of invertebrates and fish (i.e., as used to model daily doses
the tissues of prey species from in the Calcasieu Estuary of COPCs for selected focal species)
exceed the toxicity reference values for survival or
reproduction of birds?
Do the daily doses of bioaccumulative COPCs received Concentrations of contaminants in the tissues of fish (i.e.,
by piscivorous birds due to the consumption of the
as used to model daily doses of COPCs for selected
tissues of prey species from in the Calcasieu Estuary
focal species)
exceed the toxicity reference values for survival or
reproduction of birds?
Survival and reproduction Do the daily doses of bioaccumulative COPCs received Concentrations of contaminants in the tissues of benthic
of aquatic-dependent
by omnivorous mammals due to the consumption of the invertebrates and pelagic invertebrates (i.e., as used to
mammal species
tissues of prey species from in the Calcasieu Estuary
model daily doses of COPCs for selected focal species)
exceed the toxicity reference values for survival or
reproduction of mammals?
Do the daily doses of bioaccumulative COPCs received Concentrations of contaminants in the tissues of
by piscivorous mammals due to the consumption of the invertebrates and fish (i.e., as used to model daily doses
tissues of prey species from in the Calcasieu Estuary
of COPCs for selected focal species)
exceed the toxicity reference values for survival or
reproduction of mammals?
measure of biological effects (e.g., mortality, reproduction,
growth; USEPA 1997; Tables 3 through 5). Measurement
endpoints are frequently numerical expressions of observations (e.g., toxicity test results, community diversity
measures) that can be compared with similar observations
at a control treatment and/or reference site. Such statistical
comparisons provide a basis for evaluating the effects that
are associated with exposure to a contaminant or group of
contaminants at the site under consideration. Measurement
endpoints can include measures of exposure (e.g., contaminant concentrations in water or sediments) or measures
of effects (e.g., survival or growth of amphipods in laboratory toxicity tests). The relation between an assessment
endpoint, a risk question, and a measurement endpoint is
described within the conceptual model and is based on
scientific evidence (USEPA 1997).
In the Calcasieu Estuary BERA, a series of risk questions were posed to support the identification of candidate
123
12
measurement endpoints that would provide relevant information for determining the status of the assessment endpoints. As it was recognized that it would not be practical
nor possible to incorporate all of the possible measurement
endpoints into the RI, the suite of candidate measurement
endpoints was refined to include those that would provide
the most useful information for evaluating the ecological
risks associated with exposure to environmental contaminants in the study area. This process culminated in the
selection of key measurement endpoints for inclusion in the
RI (i.e., for use in the sampling program; see Tables 3, 4,
5). The risk questions that link the assessment and measurement endpoints articulate how the data collected in the
sampling program would be used to characterize risks to
ecological receptors in the Calcasieu Estuary. The methods
that were used in the exposure assessment, effects assessment, and risk characterization for each receptor group are
described in MacDonald et al. (2002) and, for selected
receptor groups, in the subsequent papers in this series
(Table 4).
Conclusion
The problem-formulation stage represented an essential
element of the overall Calcasieu Estuary BERA. Importantly, the problem-formulation process led to the refinement of the preliminary list of COPCs at the site and
further characterization of the potential ecological effects
that are likely to be associated with exposure to COPCs at
the site. In addition, evaluations of the environmental fate
of the COPCs, of the potential exposure pathways at the
site, and of the aquatic and aquatic-dependent wildlife
biota that were potentially at risk were conducted as part of
the problem-formulation process. This information facilitated the development of a conceptual model for the site
and the testable hypotheses that would be addressed in the
site investigation. Finally, this process led to the selection
of assessment and measurement endpoints used to design
the sampling program and guide the risk characterization
phase of the BERA (MacDonald et al. 2002).
Acknowledgments The authors acknowledge a number of individuals who provided excellent technical reviews of the document,
including Paul Conzelmann (United States Parks Service), John Kern
(National Oceanic and Atmospheric Administration), Denise Sanger
(South Carolina Department of Natural Resources), Heather Findley,
John DeMond (Louisiana Department of Environmental Quality),
Barry Forsythe, and Buddy Goatcher (United States Fish and Wildlife
Service). Funding for the preparation of this document was provided
through a contract to CDM Federal Programs Corporation from the
USEPA. Any use of trade, product, or firm names is for descriptive
purposes only and does not imply endorsement by the United States
Government.
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Arch Environ Contam Toxicol (2011) 61:1–13
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