EPA/600/R-06/162F
ERASC-011F
October 2009
EVALUATING ECOLOGICAL RISK TO INVERTEBRATE RECEPTORS
FROM PAHS IN SEDIMENTS AT HAZARDOUS WASTE SITES
by
Robert M. Burgess
U.S. Environmental Protection Agency
Office of Research and Development
National Health and Environmental Effects Research Laboratory
Atlantic Ecology Division
Narragansett, RI 02882
Ecological Risk Assessment Support Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH
-------
NOTICE
This document has been subjected to the Agency's peer and administrative review and has
been approved for publication as an EPA document. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
This is contribution AED-05-030 of the Office of Research and Development National
Health and Environmental Effects Research Laboratory's Atlantic Ecology Division.
This report should be cited as Burgess, R.M. 2009. Evaluating Ecological Risk to Invertebrate Receptors from
PAHs in Sediments at Hazardous Waste Sites. U.S. Environmental Protection Agency, Ecological Risk Assessment
Support Center, Cincinnati, OH. EPA/600/R-06/162.
11
-------
TABLE OF CONTENTS
AUTHORS, CONTRIBUTORS AND REVIEWERS iv
ACKNOWLEDGMENTS iv
PURPOSE OF THIS DOCUMENT 1
INTRODUCTION 2
STATE OF PRACTICE 5
Invertebrate Risk Assessment 5
OVERVIEW OF PAH EXPOSURE TO INVERTEBRATES 6
Use of Equilibrium Partitioning (EqP) to Predict Exposure 6
Equilibrium Partitioning (EqP) Model Assumptions 7
Definition of Total PAHs and Analytical Methods 8
OVERVIEW OF PAH EFFECTS TO INVERTEBRATES 9
Use of Narcosis Model to Predict Effects 9
Examples of Equilibrium Partitioning (EqP) Approach in Use 12
PAH Datasets 13
Model Assumptions and Uncertainties 14
SUMMARY 15
REFERENCES 15
111
-------
AUTHORS, CONTRIBUTORS AND REVIEWERS
AUTHOR
Robert Burgess
U.S. Environmental Protection Agency
Office of Research and Development
National Health and Environmental Effects Research Laboratory
Atlantic Ecology Division
Narragansett, RI 02882
CONTRIBUTOR
Michael Kravitz
U.S. Environmental Protection Agency
Office of Research and Development
Cincinnati, OH 45268
REVIEWERS
Susan B. Kane Driscoll
Exponent, Inc.
Maynard, MA01754
Roman P. Lanno
Ohio State University
Columbus, OH 43210
Charles A. Menzie
Menzie-Cura & Associates Inc.
Severna Park, MD 21146
ACKNOWLEDGMENTS
The first draft of this document was internally (within EPA) reviewed by Robert Ozretich
and Walter Berry (EPA Office of Research and Development, National Health and
Environmental Effects Research Laboratory (ORD/NHEERL). Programmatic review was
conducted by Venessa Madden of EPA Region 7, a Trichair of EPA's Ecological Risk
Assessment Forum.
IV
-------
PURPOSE OF THIS DOCUMENT
In March 2004, ORD's Ecological Risk Assessment Support Center (ERASC) received a
request from the Ecological Risk Assessment Forum relating to the evaluation of ecological risk
to vertebrate and benthic invertebrate receptors from polycyclic aromatic hydrocarbon
compounds (PAHs) in sediment at hazardous waste sites. This paper only addresses risks to
benthic invertebrates because reaching a consensus scientific position on vertebrate risk issues is a
longer-term prospect. Benthic invertebrates are an important component of the biotic integrity of
the nation's waters.
Like the U.S. EPA Equilibrium Partitioning Sediment Benchmark (ESB) for PAH
mixtures document (U.S. EPA, 2003a) that this white paper is based on, this report is meant as
technical information. To cite selected text from the recently released ESB for Tier 2 nonionic
organic chemicals (U.S. EPA, 2008):
This document provides technical information to EPA Program Offices, including
Superfund, Regions, States, the regulated community, and the public. Decisions
about risk management are the purview of individual regulatory programs, and
may vary across programs depending upon the regulatory authority and goals of
the program. For this reason, each program will have to decide whether the
equilibrium partitioning (EqP) approach is appropriate to that program and, if so,
how best to incorporate this technical information into that program's risk
assessment process. At the same time, the ESBs do not substitute for the Clean
Water Act or other EPA regulations, nor are they regulation. Thus, they cannot
impose legally binding requirements on EPA, States, or the regulated community.
EPA and State decision makers retain the discretion to adopt approaches on a
case-by-case basis that differ from this technical information where appropriate.
It is recommended that the ESBs not be used alone but with other sediment
assessment methods to make informed risk management decisions.
In other words, the approach described in this white paper is simply a tool to be applied to the
greater problem of assessing risk, in this case, risk associated with PAHs in sediments at
hazardous waste sites. As discussed below, the use of the EqP approach discussed here as part of
a tiered risk assessment is one way that an assessment could be performed. At sites where the
assumptions of EqP are violated because of site-specific conditions, approaches like solid phase
microextraction (SPME) may be necessary to attain accurate measures of PAH exposure
concentrations. Furthermore, as discussed below, risk assessors may choose to formulate a risk
assessment strategy using EqP for screening purposes to be followed in a secondary tier with the
1
-------
measurement of PAH bioavailability using SPME and/or toxicity testing. It is from this
perspective with the objective of describing one tool in the risk assessment tool box that the
following technical information is provided.
INTRODUCTION
In principal, there are many ways to attempt to address the risk to invertebrates associated
with PAHs in sediments and whenever possible the use of multiple lines of evidence to conduct a
risk assessment is recommended (Adams et al., 2005). For example, Table 1 lists several
approaches for quantifying exposure and effects of PAHs, as well as other organic contaminants,
in sediments. These include the use of analytical chemistry on whole sediments and interstitial
waters to derive protective guidelines (e.g., U.S. EPA, 2003a, 2005, 2008; Long et al., 1995;
Swartz, 1999; Fairey et al., 2001; Field et al., 2002), application of recently developed passive
sampler technologies to measure bioavailable concentrations (e.g., Hawthorne et al., 2005),
conducting acute and chronic sediment and interstitial water toxicity tests (ASTM, 1998a,b,c;
U.S. EPA, 1994, 2000, 2001a) and performance of bioaccumulation studies (U.S. EPA, 1993,
2000) to demonstrate contaminant bioavailability and biological effects. How these approaches
are used is also a topic of debate; for example, Figure 1 presents a conceptual model using the
methods listed above to address the question of whether a sediment is likely to cause adverse
effects. The approach discussed in this white paper uses data resulting from the chemical
analysis of whole sediments, mechanistic partitioning, and additive narcosis mode of action
models to predict adverse toxicological effects. In Figure 1, this approach is used in the first tier
of the assessment to screen for the likelihood of adverse effects. In other conceptual models, for
example, the approach discussed here could be applied in a diagnostic mode later in the
assessment process to determine if adverse effects are likely to be due to PAHs. The PAHs
addressed in this paper are composed of carbon and hydrogen and do not include any heterocyclic
atoms like oxygen, sulfur or nitrogen, or functional groups such as nitro or hydroxyl.
Due to the use of fossil fuels in industrialized societies as well as biomass fuels in
developing countries (including forest fires) and subsequent transport via atmospheric and
aquatic pathways, PAHs are among the most widely distributed organic pollutants. Furthermore,
because of their presence in hydrocarbon-based substances ranging from petroleum to creosote,
-------
TABLE 1. Examples of Approaches for Determining Exposures and Effects of PAHs
Approach
Analytical Chemistry
Toxicity Testing
Bioaccumulation Studies
Specific Method or
Technique
Mechanistic Guidelines
Empirical Guidelines
Passive Samplers
Acute and Chronic
Standard 2 8 -day
Examples
Equilibrium Partitioning
Sediment Benchmarks
(ESBs)
Effects-Range Limit (ERL)
and Effects -Range
Median (ERM)
Sediment Quality Guideline
Quotient (SQGQ1)
Logistic Regression Models
(LRM)
Consensus
Solid Phase Microextraction
(SPME)
-
-
References
U.S. EPA, 2003a,b,c,
2005, 2008
Long et al., 1995, 2000
Fairey et al, 2001
Field et al., 2002
Swartz, 1999; MacDonald
et al., 2000
Hawthorne et al., 2005
ASTM, 1998a,b,c; U.S.
EPA, 1994, 2000, 2001a
U.S. EPA, 1993,2000
Assessment of
PAH Bioavailability
Based on
Toxicity Testing
(e.g., Amphipod toxicity tests)
Assessment of
PAH Bioavailability
Based on Analysis
of Interstitial Waters
(e.g., SPME)
Yes
Significant
Bioavailable
Concentrations
Detected?
No
->• STOP
Assessment of
PAH Bioavailability
Based on Analysis
of Whole Sediments
(e.g., EqP, empirical guidelines)
Yes
Is Guideline Exceeded?
No
—•• STOP
FIGURE 1. Conceptual Model for Applying Various Sediment
Assessment Approaches in a Tiered System to Determine
the Risk of Adverse Effects Due to PAHs in Sediments.
-------
they are found in concentrations of parts per million (mg/kg) in heavily industrialized sites, while
in areas remote from human activity they occur in parts per trillion (ng/kg).
PAHs in the environment are known to originate primarily from two sources: petrogenic
and pyrogenic (biogenic PAHs make a very small contribution). Petrogenic PAHs originate from
petroleum sources including different types of oils, coals and organic shales. Their introduction
to the environment varies from industrial production, refining and transport, to spills and waste
site releases, and natural seeps and outcrops. Pyrogenic PAHs are produced when fossil fuels are
incompletely oxidized during combustion. They are, therefore, frequently released into the
environment via the atmosphere, often associated with different forms of soot or black carbon.
Eventually, these PAHs are removed from the air phase through association with aerosols which
then settle into terrestrial and aquatic environments. Pyrogenic PAHs can also be associated with
specific industrial sources (e.g., manufactured gas plants).
There are two basic types of PAHs: parent and alkylated. These classifications involve
the chemical structure of PAHs. Parent PAHs consist primarily of benzene rings fused together.
Conversely, alkylated PAHs have various levels of alkyl substitutions added to the fused ring
structure. Because of the different sources and types of PAHs, determining the specific sources
of PAHs in the environment is often complex; for example, combustion-related pyrogenic parent
PAHs are frequently ubiquitous while alkylated PAHs from both pyrogenic and petrogenic
sources may be more localized.
The prevalent mechanism of PAH toxicity to invertebrates is narcosis, which results in
the alteration of cell membrane function. This alteration can result in mild toxic effects or
mortality depending upon the exposure. Some PAHs also demonstrate photoactivated toxicity.
This form of toxicity can cause mortality at very low concentrations of PAHs but requires direct
exposure of organisms to ultraviolet (UV) radiation in sunlight. Further, water strongly
attenuates UV radiation; thus, relatively shallow overlying water will protect benthic organisms
from adverse effects. However, it is possible that benthic organisms with a pelagic life stage
which includes swimming to the air-water interface may be exposed to elevated UV levels. The
magnitude of risk associated with this sort of exposure in combination with the bioaccumulation
of PAHs has not been studied extensively. The UV radiation causes the chemical bonds in the
PAHs to excite and form high energy radicals, which, for a very brief time period, oxidize the
tissue of exposed organisms. Carcinogenicity and teratogenicity have also been reported to occur
-------
in vertebrates (e.g., fish) (Hawkins et al., 1988) due to exposure to certain PAHs (e.g.,
benzo(a)pyrene), but there are limited data with regard to benthic invertebrates. In general,
unless conditions result in elevated UV levels, narcosis is the most common mode of action of
concern with PAHs in sediments.
Each of the above characteristics results in factors contributing to the nature of the PAH
exposure and kinds of PAH toxic effects. In this white paper, EqP is recommended for use in
predicting PAH exposure concentrations, and additive narcosis theory is applied to determine
whether or not sufficient PAHs are present to cause adverse effects. A selection of PAHs defined
as "total PAH" is also provided as well as an analytical method for measuring PAHs. This white
paper summarizes an approach for evaluating ecological risk to benthic invertebrate receptors
from PAHs in sediments at hazardous waste sites. This approach is based upon the ESB for
PAH mixtures document prepared by the U.S. EPA (2003a). Consequently, this white paper
should be used in conjunction with U.S. EPA (2003a). More recently, others have demonstrated
the usefulness of the EqP approach for understanding the bioavailability of PAHs in sediments
(e.g., Landrum et al., 2003; Barata et al., 2005; McGrath et al., 2005; Neff et al., 2005;
Hawthorne et al., 2006). This white paper does not address bioaccumulation or trophic transfer
of PAHs from contaminated sediments by aquatic organisms. Also, under site-specific
conditions it is possible for the assumptions used to predict risk associated with PAHs using EqP
to be violated (e.g., presence of black carbon or unusual carbon) (see U.S. EPA [2003a] for more
discussion). Under such conditions, site-specific predictions of the risk associated with PAHs
may be necessary using methods that directly measure interstitial water PAH concentrations (e.g.,
Hawthorne et al., 2005) or toxicity (U.S. EPA, 1994, 2000).
STATE OF PRACTICE
Invertebrate Risk Assessment
A brief and limited survey of project managers, scientists and risk assessors at sites
around the country, including the Pine Street Bridge Canal, Hocomonco, and Baird and McGuire
sites in Massachusetts (Region 1), the Ashland site in Wisconsin (Region 5), and Lower
Duwamish in Washington State (Region 10), indicated several characteristics of how PAH risk to
invertebrates is assessed currently at contaminated sediment sites. First, there is no "standard
state of practice" per se, rather, assessments are performed differently at each site using
-------
site-specific information. Secondly, because of the metabolism of PAHs by many organisms at
various levels of the food web, in general, there is no clear relationship between body burdens of
PAHs and effects, and hence tissue residues are seldom used as measures of exposure. Thirdly,
as a consequence of PAH metabolism, exposure and effects measurements are most often
assessed in the benthos, where acute and sublethal toxicity may be observed. Specifically,
sediment or interstitial (pore) water measures of PAHs are used to quantify exposure while
toxicity to benthic organisms is applied as a measure of effects. In some instances, benthic
community composition and condition are used to assess effects. Sediment quality guidelines
including empirical (Long et al., 1995; Field et al., 2002) and consensus (Swartz, 1999;
MacDonald et al., 2000) approaches as well as the mechanistic ESBs (U.S. EPA, 2003a,b,c,
2005, 2008) are also used as complementary and predictive tools for assigning risk. In a few rare
cases, photo-enhanced toxicity caused by PAHs has also been used to assess risk.
OVERVIEW OF PAH EXPOSURE TO INVERTEBRATES
Use of Equilibrium Partitioning (EqP) to Predict Exposure
To determine the exposure invertebrates experience in contaminated sediments it is
necessary to measure or predict the concentrations of bioavailable PAHs. For hydrophobic
organic contaminants like PAHs, under equilibrium conditions, the interstitial water
concentration of PAH is the most accurate indicator of the bioavailable exposure concentration.
The interstitial water concentration can be measured empirically using several methods
(U.S. EPA, 2001b). However, the results may be affected by manipulation of the sediment and
interstitial water, and the methods may be logistically impractical and expensive. Measurement
of the interstitial water concentration of PAHs has the additional challenge of assessing the effect
of dissolved organic carbon (DOC) on bioavailability. The presence of DOC has been shown to
reduce PAH bioavailability (e.g., McCarthy and Jimenez, 1985; Landrum et al., 1987). Recently,
new promising analytical techniques have been applied to directly measure interstitial water
concentrations of PAHs including SPME (Hawthorne et al., 2005). These methods also consider
the effects of DOC on PAH bioavailability.
An alternative approach for determining exposure is to predict PAH interstitial water
concentrations. The use of EqP is recommended for making such predictions. In a sediment
system, the predominant phases involved in EqP include the sediment organic carbon and
-------
dissolved phase (i.e., interstitial water) (see Figure 2). Based on EqP, if the sediment
concentration of PAH and concentration of sediment organic carbon are known, the interstitial
water concentration of PAH can be predicted. As discussed above, because the interstitial water
concentration of PAH is the most accurate indicator of the bioavailable concentration, knowing
this concentration allows for an assessment of potential risk to benthic invertebrates.
Sediment
Organic
Carbon
Phase
Interstitial
Water
Phase
(including DOC)
Equilibrium
(KD or Koc)
Benthic
Organism
FIGURE 2. Diagram of Important Sediment Phases Affecting the
Unavailability of PAHs in Sediments Dominated by
Organic Carbon
Equilibrium Partitioning (EqP) Model Assumptions
Use of EqP to predict exposure concentrations comes with several assumptions: (1) the
environmental system and phases therein are at or approximating equilibrium, (2) interstitial
water is a good measure of bioavailable contaminant, and (3) the sediment organic carbon is the
primary partitioning phase for the contaminant. Quantitatively, we can represent the EqP
approach as follows:
•^Pl = foC ' KQC [1]
-------
where, KP1 is a one particulate phase partition coefficient (L/kg sediment [dry]), foc the fraction
organic carbon of the sediment (g organic carbon/g sediment [dry]), and KQC the organic carbon
normalized partition coefficient (L/kg organic carbon). Recent studies demonstrate that PAHs
can very strongly associate with other forms of carbon, specifically black carbon present in soots,
fly ash and chars, and alter their geochemical behavior as compared to partitioning to "regular"
organic carbon (e.g., Accardi-Dey and Gschwend, 2002). The influence of black carbon can be
shown as follows:
F - f y 4. f y f-t"-i m
P2 JOC OC J BC SC D 1^1
where, KP2 is the two particulate phase partition coefficient (L/kg sediment [dry]), fBC the fraction
black carbon (g black carbon/g sediment [dry]), KBC is the black carbon normalized partition
coefficient (L/kg black carbon), CD the dissolved phase concentration (ug/L) of the contaminant
of interest, and n a Freundlich coefficient used to consider non-linear sorption by the black
carbon. If black carbon is measured or suspected to be present in the sediments of interest, a
site-specific prediction using Equation 2 or measure of bioavailable PAHs may be necessary
(Section 6.8 of U.S. EPA, 2003 a discusses black carbon in detail).
Definition of Total PAHs and Analytical Methods
The term total, when discussing PAHs is misleading. There are tens of thousands of
possible PAH structures ranging from the smallest PAH naphthalene to the largest forms like
coronene. Alkylation, especially in petrogenic PAHs, contributes several thousand or more
varying structures of PAHs. Current technology does not allow for the direct analytical
measurement of all these PAHs. Early methods for measuring PAHs focused on the 13 priority
pollutant PAHs identified by the U.S. EPA. Since the mid-1980s, for NOAA's National Status
and Trends Program, 23 PAHs are routinely analyzed. Currently, the U.S. EPA's Ecological
Monitoring and Assessment Program (EMAP) measures up to 34 PAHs. Also, the U.S. EPA
PAH mixtures benchmark document (U.S. EPA, 2003a) recommends these 34 PAHs be analyzed
when assessing the risk represented by PAHs in contaminated sediments. For the purposes of
this white paper, these 34 PAHs are recommended for analysis in order to capture PAHs
constituting an operational definition of "total PAHs."
-------
The 34 PAHs are listed in Table 2. Although this list is far from comprehensive, it does
incorporate many of the most common parent PAHs and many alkylated PAHs frequently found
in PAH mixtures. Often, a major limitation in the analysis of PAHs is the availability of
standards, especially for the alkylated PAHs. As analytical methods improve for measuring
PAHs and standards become more readily available, the list presented in Table 2 may expand to
include more PAH molecules. For example, recent work by Hawthorne et al. (2005, 2006)
discusses approaches using alkylated standards to more effectively quantify PAH concentrations.
Further, as the list of PAHs increases in number of analytes, uncertainty in method predictions
will decrease. The level of uncertainty is likely to never be negligible but will decline as the
most common PAHs are included in the analysis. For example, predictions made using the list of
34 PAHs will have less uncertainty than estimates using only 13 PAHs. Examples of analytical
methods for the analysis of the 34 PAHs are provided in Lauenstein and Cantillo (1998) and
Hawthorne et al. (2005). For the analysis of total organic carbon, methods discussed in
U.S. EPA (200Ib) and Ryba and Burgess (2002) are recommended. Black carbon analysis using
a thermal oxidation method is described in Gustafsson et al. (1997) and Acardi-Dey and
Gschwend (2002).
OVERVIEW OF PAH EFFECTS TO INVERTEBRATES
Use of Narcosis Model to Predict Effects
As discussed above, the principal form of toxicity elicited by PAHs to benthic
invertebrates is narcosis. Narcotic toxicants frequently demonstrate additive toxicity; that is, the
effects of narcotic toxicants can be added together to summarize the total amount of toxicity
present in a mixture of such chemicals (as occurs in sediments). It has been observed that this
additivity can occasionally over-estimate toxicity (i.e., result in a conservative and
overly-protective estimate of risk). Figure 3 illustrates the approach used in U.S. EPA (2003 a)
and discussed in Di Toro and McGrath (2000), Di Toro et al. (2000) and Mount et al. (2003) for
predicting toxicity to benthic organisms caused by PAHs.
Using contaminated site sediment data, including PAH concentrations and sediment
organic carbon content, EqP is used to predict the bioavailable concentrations of the 34 PAHs. As
discussed in U.S. EPA (2003a), the bioavailable concentration of each PAH is then converted to
toxic units based on narcosis theory. The effects endpoints used to calculate toxic units in
-------
TABLE 2. List of PAHs Recommended for Analytical Measurement to Quantify "Total
PAHs" (from U.S. EPA, 2003a)
PAH
Naphthalene
C 1 -Naphthalenes
Acenaphthylene
Acenaphthene
C2 -Naphthalenes
Fluorene
C3 -Naphthalenes
Anthracene
Phenanthrene
Cl-Fluorenes
C4-Naphthalenes
C 1 -Phenanthrene/anthracenes
C2-Fluorenes
Pyrene
Fluoranthene
C2-Phenanthrene/anthracenes
C3-Fluorenes
C 1 -Pyrene/fluoranthenes
C3 -Phenanthrene/anthracenes
Benz(a)anthracene
Chrysene
C4-Phenanthrenes/anthracenes
C 1 -Benzanthracene/chrysenes
Benzo(a)pyrene
Perylene
Benzo(e)pyrene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
C2-Benzanthracene/chrysenes
Benzo(ghi)perylene
C3 -Benzanthracene/chrysenes
Indeno(l ,2,3-cd)pyrene
Dibenz(a,h)anthracene
C4-Benzanthracene/chrvsenes
CAS*
91203
-
208968
83329
-
86737
-
120127
85018
-
-
-
-
129000
206440
-
-
-
-
56553
218019
-
-
50328
198550
192972
205992
207089
-
191242
-
193395
53703
-
Molecular Weight (jug/mol)
128.17
142.20
152.2
154.21
156.23
166.22
170.25
178.12
178.23
180.25
184.28
192.26
194.27
202.26
202.26
206.29
208.30
216.29
220.32
228.29
228.29
234.23
242.32
252.31
252.31
252.32
252.32
252.32
256.23
276.23
270.36
276.23
278.35
284.38
* For C# PAHs CAS is not available.
10
-------
Measure 34 PAHs in Sediment
I
Use Equilibrium Partitioning to Estimate
Amount of Bioavailable PAH
Convert Bioavailable Concentrations
of PAHs to Toxic Units
I
Sum PAH Toxic Units
If Sum of PAH Toxic Units Exceeds
One, Toxicity May Occur
(Based on DiToro et al., 2000; DiToro and McGrath, 2000; U.S. EPA, 2003a)
FIGURE 3. Simplified Flowchart of Approach for Predicting
Toxicity of PAHs to Benthic Organisms
U.S. EPA (2003a) are the PAH final chronic values (FCVs). The FCVs for over 60 PAHs,
including the 34 PAHs discussed above in Table 2, are reported in Table 3-4 of U.S. EPA (2003a).
Because toxicity caused by narcotic chemicals has been demonstrated to be additive, these toxic
units are summed together and an estimate of whether or not toxicity may occur can be derived.
For example, if the sum of the toxic units exceeds a value of 1.0, toxicity to benthic invertebrates
may occur. It should be noted that estimates of the bioavailable amounts of PAHs in the interstitial
water can not exceed PAH solubility. If PAH solubility is exceeded, a non-aqueous phase liquid
may form and observed toxicity maybe due to other mechanisms including smothering. The
11
-------
organic carbon normalized maximum sediment concentration of a PAH (Coc PAHi MAXi) can be
calculated by multiplying the PAH solubility by the PAH KQC value (see U.S. EPA, 2003a). If the
organic carbon normalized sediment concentration, Coc PAHi, exceeds the maximum sediment
concentration, the Coc PAHi MAXi should be used for calculating actual toxic units in place of Coc PAHi
(the subscript i indicates the identity of a given PAH; for example, anthracene or pyrene).
Examples of Equilibrium Partitioning (EqP) Approach in Use
A simple example of this approach is provided below. For simplicity, three PAHs are
addressed in this example rather than the recommended 34. All the information needed to work
with this example, except sediment concentrations and sediment organic carbon (i.e., site data), is
available in U.S. EPA (2003a). As shown in Table 3, concentrations of the PAHs anthracene,
fiuoranthene and chrysene range from 3328 to 51896 ug/kg in a sediment with an organic carbon
content of 0.0202 goc/g- Dividing the PAH concentration by the sediment organic carbon (and
again dividing by 1000 to account for differences in units) results in the organic carbon normalized
PAH concentration (Coc PAHi) (the subscript i indicates the identity of a given PAH; for example,
anthracene or pyrene). This value is a more realistic indicator of the concentration of bioavailable
PAHs. Dividing the Coc PAHi by an organic carbon normalized toxicity value (Coc PAHi FCVi)
generates toxic units for each PAH. For this example, and as used in U.S. EPA (2003a), PAH
FCVs are applied to generate sediment toxicity values. These values, Coc PAHi FCVi (in ug/goc), for
individual PAHs are calculated by multiplying the PAH specific FCV (in ug/L) by the Koc for that
PAH (and again dividing by 1000 to account for differences in units); they are also reported in
Table 3-4 of U.S. EPA (2003a). As noted above, if the sum of the toxic units exceeds 1.0, there is
an elevated likelihood that toxicity to benthic organisms may occur. In the example above,
because of the high concentrations of fiuoranthene and chrysene in the sediments, the sum of the
toxic units easily exceeds 1.0 with a value of 5.17. These sediments are predicted to exhibit
chronic toxicity from PAHs. The same basic process is used when considering all the other PAHs.
More complex examples of the use of this type of approach can be found in the scientific
literature (e.g., Swartz et al., 1995; Di Toro and McGrath, 2000; Di Toro et al., 2000; Ozretich et
al., 2000). In their study, Swartz et al., (1995) evaluated an early version of the EqP approach, in
which toxic units of 13 PAHs based on sediment concentrations were used to successfully predict
12
-------
TABLE 3. Example Calculation of Toxic Units Associated with a Sediment
Contaminated with Three PAHs
PAH
Anthracene
Fluoranthene
Chrysene
Concentration
(Jig/kg)
3328
51896
21453
Sediment Organic
Carbon (goc/g)
0.0202
0.0202
0.0202
c
*^OC,PAHi
0*g/goc)
164.8
2569
1062
c
*^OC,PAHi,FCVi
0*g/goc)
594
707
844
Toxic
Units
0.28
3.63
1.26
£ = 5.17
observed sediment toxicity. In an extension of Swartz et al. (1995), Ozretich et al. (2000) included
33 PAHs in his evaluation of this type of approach using contaminated sediments from Elliot Bay,
Washington. In that evaluation, the approach was generally successful in predicting observed
sediment toxicity (Ozretich et al., 2000). In their review of these data sets, Di Toro and McGrath
(2000) reported the EqP-based approach accurately predicted toxic or non-toxic effects in over
90% of sediments evaluated. Further, Di Toro and McGrath (2000), Di Toro et al. (2000) and
Mount et al. (2003), describe in great detail the technical basis for the EqP approach, discussing its
performance in comparison to the results of toxicity testing and EMAP benthic analyses (Di Toro
and McGrath, 2000).
Finally, in U.S. EPA (2003a) three 'real-life'-like examples are provided and discussed in
detail in Section 6.3. To enhance the realism of the examples, the authors include scenarios where
only 13 PAHs were measured as well as cases in which all 34 PAHs were quantified.
PAH Datasets
Frequently, especially in the case of older data sets, fewer than the 34 recommended PAHs
were measured. Under some conditions, the toxic units contribution of PAHs not measured can be
predicted using uncertainty factors (Section 6 in U.S. EPA, 2003a). In principle, the uncertainty
factor serves as a multiplier to convert the toxic units associated with 13 or 23 measured PAHs to
the toxic units of the desired 34 PAHs based on a selected confidence level (e.g., 95%). However,
due to the unique distribution of PAHs in contaminated sediments resulting from their original
source(s), uncertainty factors tend to be very site-specific. Consequently, the uncertainty factors in
13
-------
U.S. EPA (2003a) should only be used to provide a very general estimate of the toxic units
associated with 34 PAHs. Further, if only 13 or 23 PAHs have been measured in the contaminated
sediments of interest, the development of site-specific uncertainty factors using a subset of
sediments from the site is highly recommended. Site-specific uncertainty factors would provide a
cost-effective way to reduce the variability around the predicted toxic units at the contaminated site
(see U.S. EPA [2003a] and Mount et al. [2003] for a discussion of how to calculate site-specific
uncertainty factors). However, it is very strongly encouraged that whenever possible all 34 PAHs
are measured in sediment samples to avoid the need for generic or site-specific uncertainty factors.
Model Assumptions and Uncertainties
The approach described above for predicting risk to benthic invertebrates from sediment
PAHs also requires several assumptions including the following: (1) benthic invertebrates do not
appreciably metabolize PAHs, (2) the PAHs used to make predictions of toxicity are composed of
carbon and hydrogen and do not include any heterocyclic atoms like oxygen, sulfur or nitrogen, or
functional groups such as nitro or hydroxyl, and (3) the invertebrates for which risk is being
predicted are coupled to the benthic environment; that is, they are exposed to toxic chemicals
primarily via the sediment. See Di Toro and McGrath (2000), Di Toro et al. (2000), Mount et
al. (2003) and U.S. EPA (2003a) for further discussion of these assumptions.
It is worth noting that a sum of toxic units greater than 1.0 can occur without the occurrence
of significant benthic organism toxicity. This may happen if another sediment phase, like the black
carbon discussed earlier, is reducing PAH bioavailability. Further, sediment toxicity to benthic
organisms can occur if the sum of toxic units is less than 1.0, but this will most likely be due to the
presence of other toxicants including, possibly, unanalyzed PAHs.
Primary uncertainties associated with this approach include (1) analytical uncertainties,
including under-estimating the concentration of alkylated PAHs, which limits the accurate
measurement of all toxic PAHs contributing to toxicity, (2) uncertainties in the equilibrium
partitioning models resulting in over- and under-predictions of bioavailable PAH concentrations,
and (3) uncertainties in the narcosis model causing under- and over-predictions of toxicity. Some
of these uncertainties have been discussed already. Further, Sections 6 and 7 of U.S. EPA (2003a)
go into detail on the uncertainties with this approach, and it is recommended that the users of this
white paper refer to that document for more information.
14
-------
SUMMARY
This white paper provides an overview of an approach for assessing risk to invertebrate
receptors resulting from exposure to PAHs in contaminated sediments at hazardous waste sites.
PAHs are possibly the most widely distributed of anthropogenic organic pollutants. The approach
is based on the procedures described in U.S. EPA (2003a) and involves the use of EqP to
determine exposure/bioavailability and additive narcosis theory to estimate sublethal toxicity of
PAHs to benthic invertebrates. In an evaluation of over 30 sediments, this approach made accurate
predictions over 90% of the time. The white paper also provides examples of how to use this
approach with analytical data resulting from the analysis of contaminated sediments. The
approach, particularly when used with other contaminated sediment assessment methods, offers
risk assessors a useful tool for assessing the risk of PAHs to benthic invertebrates at hazardous
waste sites. As noted earlier, assessments of sediments are improved when multiple lines of
evidence are used (Adams et al, 2005). Finally, development of new technologies for measuring
bioavailable concentrations of PAHs in sediments, as well as advances in analytical methods for
PAH quantification, offer promising ways to supplement the EqP tool discussed in this white
paper.
REFERENCES
Accardi-Dey, A. and P.M. Gschwend. 2002. Assessing the combined roles of natural organic
matter and black carbon as sorbents in sediments. Environ. Sci. Technol. 36:21-29.
Adams, W.J., A.S. Green, W. Ahlf et al. 2005. Using sediment assessment tools and a
weight-of-evidence approach. In: Use of Sediment Quality Guidelines and Related Tools for the
Assessment of Contaminated Sediments, R.J. Wenning, G.E. Batley, C.G. Ingersoll and D.W.
Moore, Ed. Society of Environmental Toxicology and Chemistry, SETAC Press, Pensacola, FL.
ASTM (American Society for Testing and Materials). 1998a. Standard Guide for Conducting
Static Sediment Toxicity Tests with Marine and Estuarine Amphipods. E1367-92. In Annual Book
of Standards, Vol. 11.05, Philadelphia, PA, USA.
ASTM (American Society for Testing and Materials). 1998b. Standard Test Methods for
Measuring the Toxicity of Sediment-associated Contaminants with Freshwater Invertebrates.
E1706-95b. In Annual Book of Standards, Vol. 11.05, Philadelphia, PA, USA.
ASTM (American Society for Testing and Materials). 1998c. Standard Guide for Conducting
Sediment Toxicity Tests with Marine and Estuarine Polychaetous Annelids. E1611. In Annual
Book of Standards, Vol. 11.05, Philadelphia, PA, USA.
15
-------
Barata, C., A. Calbet, E. Saiz, L. Ortiz and J.M. Bayona. 2005. Predicting single and mixture
toxicity of petrogrenic polycyclic aromatic hydrocarbons to the copepod Oithona davisae. Environ.
Toxicol. Chem. 24:2992-2999.
Di Toro, D.M. and J.A. McGrath. 2000. Technical basis for narcotic chemicals and polycyclic
aromatic hydrocarbon criteria. II. Mixtures and sediments. Environ. Toxicol. Chem.
19(8):1971-1982.
Di Toro, D.M., J.A. McGrath and D.J. Hansen. 2000. Technical basis for narcotic chemicals and
polycylic aromatic hydrocarbon criteria. I. Water and tissue. Environ. Toxicol. Chem.
19(8):1951-1970.
Fairey, R., E.R. Long, C.A. Roberts et al. 2001. An evaluation of methods for calculating mean
sediment quality guideline quotients as indicators of contamination and acute toxicity to
amphipods by chemical mixtures. Environ. Toxicol. Chem. 20:2276-2286.
Field, L.J., D.D. MacDonald, S.B. Norton et al. 2002. Predicting amphipod toxicity from
sediment chemistry using logistic regression models. Environ. Toxcol. Chem. 21:1993-2005.
Gustafsson, O., F. Haghseta, C. Chan, J. MacFarlane and P.M. Gschwend. 1997. Quantification
of the dilute sedimentary soot phase: Implications for PAH speciation and bioavailability. Environ.
Sci. Technol. 31:203-209.
Hawthorne, S.B., C.B. Grabanski, D.J. Miller and J.P. Kreitinger. 2005. Solid-phase
microextraction measurement of parent and alkyl polycyclic aromatic hydrocarbons in milliliter
sediment pore water samples and determination of KDOC values. Environ. Sci. Technol.
39:2795-2803.
Hawthorne, S.B., D.J. Miller and J.P. Kreitinger. 2006. Measurement of total polycyclic aromatic
hydrocarbon concentrations in sediments and toxic units used for estimating risk to benthic
invertebrates at manufactured gas plant sites. Environ. Toxicol. Chem. 25:287-296.
Hawkins, W.E., W.W. Walker, R.M. Overstreet, T.F. Lytle and J.S. Lytle. 1988. Dose-related
carcinogenic effects of water-borne benzo[a]pyrene on livers of two small fish species. Ecotoxicol.
Environ. Safety 16:219-231.
Landrum, P.P., S.R. Nihart, B.J. Eadie and L.R. Herche. 1987. Reduction in bioavailability of
organic contaminants to the amphipod Pontoporeia hoyi by dissolved organic matter of sediment
interstitial waters. Environ. Toxicol. Chem. 6:11-20.
Landrum, P.P., G. R. Lotufo, D.C. Gossiaux, M.L. Gedeon and J. Lee. 2003. Bioaccumulation
and critical body residue of PAHs in the amphipod, Diporeia spp.: additional evidence to support
toxicity additivity for PAH mixtures. Chemosphere 51:481 -489.
16
-------
Lauenstein, G.G. and A.Y. Cantillo, Ed. 1998. Sampling and Analytical Methods of the National
Status and Trends Program Mussel Watch Project: 1993-1996 Update. NOAA Technical
Memorandum NOS ORCA 130. U.S. Department of Commerce, National Oceanic and
Atmospheric Administration, Silver Spring, MD. Available at
http://www.ccma.nos.noaa. gov/publications/techmemo 130 .pdf.
Long, E.R., D.D. MacDonald, S.L. Smith and F.D. Calder. 1995. Incidence of adverse biological
effects within ranges of chemical concentrations in marine and estuarine sediments. Environ.
Manage. 19:81-97.
Long, E.R., D.D. MacDonald, C.G. Severn and C.B. Hong. 2000. Classifying probabilities of
acute toxicity in marine sediments with empirically derived sediment quality guidelines. Environ.
Toxicol. Chem. 19:2598-2601.
MacDonald, D.D., C.G. Ingersoll and T.A. Berger. 2000. Development and evaluation of
consensus-based sediment quality guidelines for freshwater ecosystems. Arch. Environ. Contam.
Toxicol. 39:20-31.
McCarty, J.F. and B.D. Jimenez. 1985. Reduction in bioavailability to bluegills of polycyclic
aromatic hydrocarbons bound to dissolved humic material. Environ. Toxicol. Chem. 4:511-521.
McGrath, J.A., T.F. Parkerton, F.L. Hellweger and D.M. Di Toro. 2005. Validation of the
narcosis target lipid model for petroleum products: gasoline as a case study. Environ. Toxicol.
Chem. 24:2382-2394.
Mount, D.R., C.G. Ingersoll and J.A. McGrath. 2003. Approaches to developing sediment quality
guidelines for PAHs. In: PAHs: An Ecotoxicological Perspective, P.E.T. Douben, Ed. John Wiley
and Sons Ltd., Chichester, UK.
Neff, J.M., S.A. Stout and D.G. Gunster. 2005. Ecological risk assessment of polycyclic aromatic
hydrocarbons in sediments: identifying sources and ecological hazard. Int. Environ. Assess.
Manag. 1:22-33.
Ozretich, R.J., S.P. Ferraro, J.O. Lamberson and F.A. Cole. 2000. Test of ^polycyclic aromatic
hydrocarbon model at a creosote-contaminated site, Elliott Bay, Washington, USA. Environ.
Toxicol. Chem. 19:2378-2389.
Ryba, S.A. and R.M. Burgess. 2002. Effects of sample preparation on the measurement of organic
carbon, hydrogen, nitrogen, sulfur and oxygen concentrations in marine sediments. Chemosphere
48:139-147.
Swartz, R.C. 1999. Consensus sediment quality guidelines for polycyclic aromatic hydrocarbon
mixtures. Environ. Toxicol. Chem. 18:780-787.
17
-------
Swartz, R.C., D.W. Schults, R.J. Ozretich et al. 1995. £PAH: A model to predict the toxicity of
polynuclear aromatic hydrocarbon mixtures in field-collected sediments. Environ. Toxicol. Chem.
14(11):1977-1987.
U.S. EPA. 1993. Guidance Manual: Bedded Sediment Bioaccumulation Tests. U.S.
Environmental Protection Agency, Office of Research and Development, Washington DC.
EPA/600/R-93/183.
U.S. EPA. 1994. Methods for Measuring the Toxicity of Sediment-associated Contaminants with
Estuarine and Marine Invertebrates. U.S. Environmental Protection Agency, Office of Research
and Development, Washington DC. EPA/600/R-94/025.
U.S. EPA. 2000. Methods for Measuring the Toxicity and Bioaccumulation of Sediment-
associated Contaminants with Freshwater Invertebrates. U.S. Environmental Protection Agency,
Office of Research and Development, Office of Water, Washington DC. EPA-600-R-99-064.
U.S. EPA. 2001a. Methods for Assessing the Chronic Toxicity of Sediment-associated
Contaminants with the Amphipod Leptocheirusplumulosus. U.S. Environmental Protection
Agency, Office of Research and Development, Office of Water, Army Corps of Engineers,
Washington DC. EPA-600-R-01-020.
U.S. EPA. 2001b. Methods for Collection, Storage and Manipulation of Sediments for Chemical
and Toxicological Analyses: Technical Manual. U.S. Environmental Protection Agency, Office of
Water, Washington, DC. EPA-823-B-01-002. Available at
http://www.epa.gov/waterscience/cs/collectionmanual.pdf.
U.S. EPA. 2003a. Procedures for the Derivation of Equilibrium Partitioning Sediment
Benchmarks (ESBs) for the Protection of Benthic Organisms: PAH Mixtures. U.S. Environmental
Protection Agency, Office of Research and Development, Washington, DC. EPA/600/R-02/013.
Available at http://www.epa.gov/nheerl/publications/files/PAHESB.pdf.
U.S. EPA. 2003b. Procedures for the Derivation of Equilibrium Partitioning Sediment
Benchmarks (ESBs) for the Protection of Benthic Organisms: Endrin. U.S. Environmental
Protection Agency, Office of Research and Development, Washington, DC. EPA/600/R-02/009.
Available at http://www.epa.gov/nheerl/publications/.
U.S. EPA. 2003c. Procedures for the Derivation of Equilibrium Partitioning Sediment
Benchmarks (ESBs) for the Protection of Benthic Organisms: Dieldrin. U.S. Environmental
Protection Agency, Office of Research and Development, Washington, DC. EPA/600/R-02/010.
Available at http://www.epa.gov/nheerl/publications/.
U.S. EPA. 2005. Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks
(ESBs) for the Protection of Benthic Organisms: Metal Mixtures (Cadmium, Copper, Lead, Nickel,
Silver, and Zinc). U.S. Environmental Protection Agency, Office of Research and Development,
Washington, DC. EPA/600/R-02/011. Available at
http://www.epa.gov/nheerl/publications/files/metalsESB 022405.pdf.
18
-------
U.S. EPA. 2008. Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks
(ESBs) for the Protection of Benthic Organisms: Compendium of Tier 2 Values for Nonionic
Organics. U.S. Environmental Protection Agency, Office of Research and Development,
Washington, DC. EPA/600/R-02/016. Available at http://www.epa.gov/nheerl/publications/.
19
------- |