EPA/600/R-06/162
ERASC-011
External Review Draft
January 2007
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
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NOTICE
This report is an external draft for review purposes only and does not constitute Agency
policy. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
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TABLE OF CONTENTS
AUTHORS, CONTRIBUTORS AND REVIEWERS iv
ACKNOWLEDGMENTS iv
INTRODUCTION 1
STATE OF PRACTICE 3
Invertebrate Risk Assessment 3
OVERVIEW OF PAH EXPOSURE TO INVERTEBRATES 4
Use of Equilibrium Partitioning (EqP) to Predict Exposure 4
EqP Model Assumptions 5
Definition of Total PAHs and Recommended Analytical Method 6
OVERVIEW OF PAH EFFECTS TO INVERTEBRATES 7
Use of Narcosis Model to Predict Effects 7
Examples of EqP Approach in Use 9
PAH Datasets 11
Model Assumptions 12
SUMMARY 12
REFERENCES 13
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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
REVIEWERS
Robert Ozretich
U.S. Environmental Protection Agency
Office of Research and Development
National Health and Environmental Effects Research Laboratory
Western Ecology Division
Corvallis, OR 97330
Walter Berry
U.S. Environmental Protection Agency
Office of Research and Development
National Health and Environmental Effects Research Laboratory
Atlantic Ecology Division
Narragansett, RI 02882
ACKNOWLEDGMENTS
Programmatic review of the document was conducted by Venessa Madden of EPA
Region 7, a Trichair of EPA's Ecological Risk Assessment Forum.
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1 INTRODUCTION
2 In March 2004, ORD's Ecological Risk Assessment Support Center (ERASC) received a
3 request from the Ecological Risk Assessment Forum (ERAF) relating to the evaluation of
4 ecological risk to vertebrate and benthic invertebrate receptors from polycyclic aromatic
5 hydrocarbon compounds (PAHs) in sediment at hazardous waste sites. This paper only addresses
6 risks to benthic invertebrates because reaching a consensus scientific position on vertebrate risk
7 issues is a longer-term prospect. Benthic invertebrates are an important component of the biotic
8 integrity of the nation's waters. The PAHs addressed in this paper are composed of carbon and
9 hydrogen and do not include any heterocyclic atoms like oxygen, sulfur or nitrogen, or functional
10 groups such as nitro or hydroxyl.
11 Due to the use of fossil fuels in industrialized societies and subsequent transport via
12 atmospheric and aquatic pathways, PAHs are among the most widely distributed organic
13 pollutants. Furthermore, because of their presence in petrochemical substances ranging from
14 petroleum to creosote, they are found in concentrations of parts per million (ppm) in heavily
15 industrialized sites, while in areas remote from human activity they occur in parts per trillion
16 (ppt).
17 PAHs in the environment are known to originate from two sources: petrogenic and
18 pyrogenic. Petrogenic PAHs originate from petroleum sources including different types of oils,
19 coals and organic shales. Their introduction to the environment is frequently through spillage of
20 oils during transport. Pyrogenic PAHs are produced when fossil fuels are oxidized during
21 combustion. They are, therefore, released into the environment via the atmosphere, often
22 associated with different forms of soot or black carbon. Eventually, these PAHs are removed
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1 from the air phase through association with aerosols which then settle into terrestrial and aquatic
2 environments.
3 There are two basic types of PAHs: parent and alkylated. These classifications involve
4 the chemical structure of PAHs. Parent PAHs consist of only benzene rings fused together.
5 Conversely, alkylated PAHs have various levels of alkyl substitutions added to the fused ring
6 structure. Because of the different sources and types of PAHs, the pyrogenic parent PAHs are
7 ubiquitous while petrogenic alkylated PAHs are more likely to be found associated with point
8 sources like oil spills.
9 The prevalent mechanism of PAH toxicity to invertebrates is narcosis, which results in
10 the degradation of cell membranes. This degradation can result in mild toxic effects or mortality
11 depending upon the exposure. Some PAHs also demonstrate photoactivated toxicity. This form
12 of toxicity can cause mortality at very low concentrations of PAHs but requires direct exposure
13 of organisms to ultraviolet (UV) radiation in sunlight. Further, water strongly attenuates UV
14 radiation; thus, relatively shallow overlying water will protect benthic organisms from adverse
15 effects. The UV radiation causes the chemical bonds in the PAHs to excite and form high energy
16 radicals, which, for a very brief time period, oxidize the tissue of exposed organisms.
17 Carcinogenicity and teratogenicity have also been reported to occur due to exposure to certain
18 PAHs (e.g., benzo(a)pyrene), but there are limited data with regard to benthic invertebrates. In
19 general, unless conditions result in elevated UV levels, narcosis is the most common mode of
20 action of concern with PAHs in sediments.
21 Each of the above characteristics results in factors contributing to the nature of the PAH
22 exposure and kinds of PAH toxic effects. In this white paper, equilibrium partitioning (EqP) is
23 recommended for use in predicting PAH exposure concentrations, and narcosis theory is applied
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1 to determine whether or not sufficient PAHs are present to cause adverse effects. A selection of
2 PAHs defined as "total PAH" is also provided as well as an analytical method for measuring
3 PAHs. This white paper summarizes an approach for evaluating ecological risk to benthic
4 invertebrate receptors from PAHs in sediments at hazardous waste sites. This approach is based
5 heavily upon the recently published EqP Sediment Benchmark (ESB) for PAH mixtures
6 document prepared by the U.S. EPA (2003). Consequently, this white paper should be used in
7 conjunction with U.S. EPA (2003).
8 STATE OF PRACTICE
9 Invertebrate Risk Assessment
10 A brief and limited survey of project managers, scientists and risk assessors at sites
11 around the country, including the Pine Street Bridge Canal, Hocomonco and Beard Maguire sites
12 in Massachusetts (Region 1), the Ashland site in Wisconsin (Region 5) and Lower Duwamish in
13 Washington State (Region 10), indicated several characteristics of how PAH risk to invertebrates
14 is assessed currently at contaminated sediment sites. First, there is no "standard state of practice"
15 per se, rather, assessments are addressed on a site-by-site basis. Secondly, because of the
16 metabolism of PAHs by many organisms at various levels of the food web, there is no clear
17 relationship between body burdens of PAHs and effects, and hence tissue residues are seldom
18 used as measures of exposure. Thirdly, as a consequence of PAH metabolism, exposure and
19 effects measurements are most often assessed in the benthos, where acute and sublethal toxicity
20 may be observed. Specifically, sediment or interstitial (pore) water measures of PAHs are used
21 to quantify exposure while toxicity to benthic organisms is applied as a measure of effects. In
22 some instances, benthic community composition and condition are used to assess effects.
23 Sediment quality guidelines including empirical (Long et al., 1995; Field et al., 2002) and
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1 consensus (Swartz, 1999; MacDonald et al., 2000) approaches as well as the mechanistic ESBs
2 (U.S. EPA, 2003, 2005) are also used as complementary and predictive tools for assigning risk.
3 In a few rare cases, photo-enhanced toxicity caused by PAHs has also been used to assess risk.
4 OVERVIEW OF PAH EXPOSURE TO INVERTEBRATES
5 Use of Equilibrium Partitioning (EqP) to Predict Exposure
6 To determine the exposure invertebrates experience in contaminated sediments it is
7 necessary to measure or predict the concentrations of bioavailable PAHs. For hydrophobic
8 organic contaminants like PAHs, under equilibrium conditions, the interstitial water
9 concentration of PAH is the most accurate indicator of the bioavailable exposure concentration.
10 The interstitial water concentration can be measured empirically using several methods (U.S.
11 EPA, 2001). However, the results may be affected by manipulation of the sediment and
12 interstitial water, and the methods may be logistically impractical and expensive. Measurement
13 of the interstitial water concentration of PAHs has the additional challenge of assessing the effect
14 of dissolved organic carbon (DOC) on bioavailability. The presence of DOC has been shown to
15 reduce PAH bioavailability.
16 An alternative approach for determining exposure is to predict PAH interstitial water
17 concentrations. The use of EqP is recommended for making such predictions. In a sediment
18 system, the predominant phases involved in EqP include the sediment organic carbon and
19 dissolved phase (i.e., interstitial water) (see Figure 1). Based on EqP, if the sediment
20 concentration of PAH and concentration of sediment organic carbon (foc) are known, the
21 interstitial water concentration of PAH can be predicted. As discussed above, because the
22 interstitial water concentration of PAH is the primary exposure concentration, knowing this
23 concentration allows for an assessment of potential risk to benthic invertebrates.
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Sediment
Organic
Carbon
Phase
Equilibrium
(KporKoc)
Interstitial
Water
Phase
(including
DOC)
Benthic
Organism
FIGURE 1. Diagram of Important Sediment Phases
Affecting the Unavailability of PAHs in
Sediments
*The larger arrow indicating exposure between "Interstitial Water Phase" and "Benthic Organism" signifies this is a
dominant exposure route.
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. Recent studies demonstrate that other forms of
carbon, specifically black carbon present in soots, fly ash and chars, can very strongly associate
with PAHs and alter their geochemical behavior as compared to "regular" organic carbon (e.g.,
Accardi-Dey and Gschwend, 2002). If black carbon is suspected to be present in the sediments
of interest, a site-specific prediction or measure of PAH bioavailability is necessary (Section 6.8
of U.S. EPA, 2003 discusses black carbon in detail).
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1 Definition of Total PAHs and Recommended Analytical Method
2 The term total, when discussing PAHs is misleading. There are tens of thousands of
3 possible PAH structures ranging from the smallest PAH naphthalene to the largest forms like
4 coronene. Alkylation, especially in petrogenic PAHs, contributes several thousand or more
5 varying structures of PAHs. Current technology does not allow for the direct analytical
6 measurement of all these PAHs. Early methods for measuring PAHs focused on the 13 priority
7 pollutant PAHs identified by the U.S. EPA. Since the mid-1980s, for NCAA's National Status
8 and Trends Program, 23 PAHs are routinely analyzed. Currently, the U.S. EPA's Ecological
9 Monitoring and Assessment Program (EMAP) measures up to 34 PAHs. Also, the U.S. EPA
10 PAH mixtures benchmark document (U.S. EPA, 2003) recommends these 34 PAHs be analyzed
11 when assessing the risk represented by PAHs in contaminated sediments. For the purposes of
12 this white paper, these 34 PAHs are recommended for analysis in order to capture PAHs
13 constituting an operational definition of "total PAHs."
14 The 34 PAHs are listed in Table 1. Although this list is far from comprehensive, it does
15 incorporate many of the most common parent PAHs and many alkylated PAHs frequently found
16 in PAH mixtures. Often, a major limitation in the analysis of PAHs is the availability of
17 standards, especially for the alkylated PAHs. As methods improve for measuring PAHs and
18 standards become available, the list presented in Table 1 may expand to include more PAH
19 molecules. Further, as the list of PAHs increases in number of analytes, uncertainty in method
20 predictions will decrease. The level of uncertainty is likely to never be negligible but will decline
21 as the most common PAHs are included in the analysis. For example, predictions made using the
22 list of 34 PAHs will have less uncertainty than estimates using only 13 PAHs. An analytical
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1 method for performing the analysis of the 34 PAHs defined above is provided in Lauenstein and
2 Cantillo(1998).
3 OVERVIEW OF PAH EFFECTS TO INVERTEBRATES
4 Use of Narcosis Model to Predict Effects
5 As discussed above, the principal form of toxicity elicited by PAHs to benthic
6 invertebrates is narcosis. Narcotic toxicants frequently demonstrate additive toxicity; that is, the
7 effects of narcotic toxicants can be added together to summarize the total amount of toxicity
8 present in a mixture of such chemicals (as occurs in sediments). Figure 2 illustrates the approach
9 used in U.S. EPA (2003) and discussed in Di Toro and McGrath (2000), Di Toro et al. (2000) and
10 Mount et al. (2003) for predicting toxicity to benthic organisms caused by PAHs.
11 Using contaminated site sediment data, including PAH concentrations and sediment
12 organic carbon content, EqP is used to predict the bioavailable concentrations of the 34 PAHs. As
13 discussed in U.S. EPA (2003), the bioavailable concentration of each PAH is then converted to
14 toxic units based on narcosis theory. The effects endpoint used to calculate toxic units in U.S.
15 EPA (2003) are the PAH final chronic values (FCVs). The FCVs for over 60 PAHs, including the
16 34 PAHs discussed above in Table 1, are reported in Table 3-4 of U.S. EPA (2003). These toxic
17 units are summed together and an estimate of whether or not toxicity is expected can be derived.
18 For example, if the sum of the toxic units exceeds a value of 1, toxicity to benthic invertebrates is
19 expected to occur.
20
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TABLE 1. List of PAHs Recommended for Analytical Measurement to Quantify "Total
PAHs" (from U.S. EPA, 2003)
PAH
Naphthalene
Cl -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
B enzo(k)fluoranthene
C2-Benzanthracene/chrysenes
Benzo(ghi)perylene
C3 -Benzanthracene/chrysenes
Indeno(l,2,3-cd)pyrene
Dib enz(a, h)anthracene
C4-Benzanthracene/chrysenes
CAS*
91203
-
208968
83329
-
86737
-
120127
85018
-
-
-
-
129000
206440
-
-
-
-
56553
218019
-
-
50328
198550
192972
205992
207089
-
191242
-
193395
53703
-
Molecular Weight (ug/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.
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Measure 34 PAHs in Sediment
Use Equilibrium Partitioning to Estimate
Amount of Bioavailable PAH
I
Convert Bioavailable Concentrations
of PAHs to Toxic Units
Sum PAH Toxic Units
If Sum of PAH Toxic Units Exceeds
One, Toxicity is Expected
(Based on Di Toro and McGrath, 2000; Di Toro etal., 2000; U.S. EPA, 2003)
FIGURE 2. Simplified Flowchart of Approach for Predicting
Toxicity of PAHs to Benthic Organisms
Examples of 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 (2003). As shown in Table 2, concentrations of the PAHs anthracene,
fluoranthene and chrysene range from 3328 to 51,896 u.g/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 (COCPAHl). This value is a more realistic indicator of the concentration of
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bioavailable PAHs. Dividing the Coc PAHl by an organic carbon normalized toxicity value
(Coc FAHipcvi) generates toxic units for each PAH. For this example, and as used in U.S. EPA
(2003), PAH FCVs are applied to generate sediment toxicity values. These values, COCPAHlFCVl (in
Hg/gocX f°r individual PAHs are calculated by multiplying the PAH specific FCV (in |ig/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 (2003). As noted above, if the sum of the toxic units exceeds
1.0, there is an elevated likelihood that toxicity to benthic organisms will occur. In the example
above, because of the high concentrations of fluoranthene 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.
TABLE 2. Example Calculation of Toxic Units Associated with a Sediment
Contaminated with Three PAHs
PAH
Anthracene
Fluoranthene
Chrysene
Concentration
(ug/kg)
3,328
51,896
21,453
Sediment Organic
Carbon (goc/g)
0.0202
0.0202
0.0202
COC,PAHI
fag/goc)
164.8
2569
1062
CoC,PAHi,FCVi
(ug/goc)
594
707
844
Toxic
Units
0.28
3.63
1.26
£ = 5.17
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) evaluate an early version of the approach, in which
toxic units of 13 PAHs based on sediment concentrations were used to successfully predict
observed sediment toxicity. In an extension of Swartz et al. (1995), Ozretich et al. (2000) included
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1 33 PAHs in his evaluation of this type of approach using contaminated sediments from Elliot Bay,
2 Washington. In that evaluation, the approach was generally successful in predicting observed
3 sediment toxicity (Ozretich et al., 2000). Further, Di Toro and McGrath (2000), Di Toro et al.
4 (2000) and Mount et al. (2003) describe in great detail the technical basis for the approach,
5 discussing its performance in comparison to the results of toxicity testing and EMAP benthic
6 analyses (Di Toro and McGrath, 2000).
7 Finally, in U.S. EPA (2003) three 'real-life'-like examples are provided and discussed in
8 detail in Section 6.3. To enhance the realism of the examples, the authors include scenarios where
9 only 13 PAHs were measured as well as cases in which all 34 PAHs were quantified.
10 PAHDatasets
11 Frequently, especially in the case of older data sets, fewer than the 34 recommended PAHs
12 were measured. Under some conditions, the toxic units contribution of PAHs not measured can be
13 predicted using uncertainty factors (Section 6 in U.S. EPA, 2003). In principle, the uncertainty
14 factor serves as a multiplier to convert the toxic units associated with 13 or 23 measured PAHs to
15 the toxic units of the desired 34 PAHs based on a selected confidence level (e.g., 95%). However,
16 due to the unique distribution of PAHs in contaminated sediments resulting from their original
17 source(s), uncertainty factors tend to be very site-specific. Consequently, the uncertainty factors in
18 U.S. EPA (2003) should only be used to provide a very general estimate of the toxic units
19 associated with 34 PAHs. Further, if only 13 or 23 PAHs have been measured in the contaminated
20 sediments of interest, the development of site-specific uncertainty factors using a subset of
21 sediments from the site is highly recommended. Site-specific uncertainty factors would provide a
22 cost-effective way to reduce the variability around the predicted toxic units at the contaminated
23 site.
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1 Model Assumptions
2 The approach described above for predicting risk to benthic invertebrates from sediment
3 PAHs also requires several assumptions including the following: (1) benthic invertebrates do not
4 appreciably metabolize PAHs, (2) the PAHs used to make predictions of toxicity are composed of
5 carbon and hydrogen and do not include any heterocyclic atoms like oxygen, sulfur or nitrogen, or
6 functional groups such as nitro or hydroxyl, and (3) the invertebrates for which risk is being
7 predicted are coupled to the benthic environment; that is, they are exposed to toxic chemicals
8 primarily via the sediment. See Di Toro and McGrath (2000), Di Toro et al. (2000), Mount et al.
9 (2003) and U.S. EPA (2003) for further discussion of these assumptions.
10 It is worth noting that a sum of toxic units greater than 1 can occur without the occurrence
11 of significant benthic organism toxicity. This may happen if another sediment phase, like the black
12 carbon discussed earlier, is reducing PAH bioavailability. Further, sediment toxicity to benthic
13 organisms can occur if the sum of toxic units is less than 1, but this will most likely be due to the
14 presence of other toxicants including, possibly, unanalyzed PAHs.
15 SUMMARY
16 This white paper provides an overview of an approach for assessing risk to invertebrate
17 receptors resulting from exposure to PAHs in contaminated sediments at hazardous waste sites.
18 PAHs are possibly the most widely distributed of anthropogenic organic pollutants. The approach
19 is based on the procedures described in U.S. EPA (2003) and involves the use of EqP to determine
20 exposure/bioavailability and narcosis theory to estimate sublethal toxicity of PAHs to benthic
21 invertebrates. The white paper also provides examples of how to use this approach with analytical
22 data resulting from the analysis of contaminated sediments. The approach, particularly when used
23 with other contaminated sediment assessment methods, offers risk assessors a useful tool for
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1 assessing the risk of PAHs to benthic invertebrates at hazardous waste sites. Whenever possible,
2 assessments of sediments are improved when multiple lines of evidence are used (Adams et al.,
3 2005).
4 REFERENCES
5 Accardi-Dey, A. and P.M. Gschwend. 2002. Assessing the combined roles of natural organic
6 matter and black carbon as sorbents in sediments. Environ. Sci. Technol. 36:21-29.
7
8 Adams, W.J., A.S. Green, W. Ahlf et al. 2005. Using sediment assessment tools and a weight-of-
9 evidence approach. In: Use of Sediment Quality Guidelines and Related Tools for the Assessment
10 of Contaminated Sediments, RJ. Wenning, G.E. Batley, C.G. Ingersoll and D.W. Moore, Ed.
11 Society of Environmental Toxicology and Chemistry, SET AC Press, Pensacola, FL.
12
13 Di Toro, D.M. and J.A. McGrath. 2000. Technical basis for narcotic chemicals and polycyclic
14 aromatic hydrocarbon criteria. II. Mixtures and sediments. Environ. Toxicol. Chem.
15 19(8):1971-1982.
16
17 Di Toro, D.M., J.A. McGrath and DJ. Hansen. 2000. Technical basis for narcotic chemicals and
18 polycylic aromatic hydrocarbon criteria. I. Water and tissue. Environ. Toxicol. Chem.
19 19(8):1951-1970.
20
21 Field, L. I, D.D. MacDonald, S.B. Norton et al. 2002. Predicting amphipod toxicity from
22 sediment chemistry using logistic regression models. Environ. Toxcol. Chem. 21:1993-2005.
23
24 Lauenstein, G.G. and A.Y. Cantillo, Ed. 1998. Sampling and Analytical Methods of the National
25 Status and Trends Program Mussel Watch Project: 1993-1996 Update. NOAA Technical
26 Memorandum NOS ORCA 130. U.S. Department of Commerce, National Oceanic and
27 Atmospheric Administration, Silver Spring, MD. Available at
28 http://www.ccma.nos.noaa.gov/publications/techmemol30.pdf.
29
30 Long, E.R., D.D. MacDonald, S.L. Smith andF.D. Calder. 1995. Incidence of adverse biological
31 effects within ranges of chemical concentrations in marine and estuarine sediments. Environ.
32 Manage. 19:81-97.
33
34 MacDonald, D.D., C.G. Ingersoll and T.A. Berger. 2000. Development and evaluation of
35 consensus-based sediment quality guidelines for freshwater ecosystems. Archives Environ.
36 Contam. Toxicol. 39:20-31.
37
38 Mount, D.R., C.G. Ingersoll and J.A. McGrath. 2003. Approaches to developing sediment quality
39 guidelines for PAHs. In: PAHs: An Ecotoxicological Perspective, P.E.T. Douben, Ed. John Wiley
40 and Sons Ltd., Chichester, UK.
41
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1 Ozretich, R.J., S.P. Ferraro, J.O. Lamberson and F.A. Cole. 2000. Test of ^polycyclic aromatic
2 hydrocarbon model at a creosote-contaminated site, Elliott Bay, Washington, USA. Environ.
3 Toxicol. Chem. 19:2378-2389.
4
5 Swartz, R.C. 1999. Consensus sediment quality guidelines for polycyclic aromatic hydrocarbon
6 mixtures. Environ. Toxicol. Chem. 18:780-787.
7
8 Swartz, R.C., D.W. Schults, RJ. Ozretich et al. 1995. £PAH: A model to predict the toxicity of
9 polynuclear aromatic hydrocarbon mixtures in field-collected sediments. Environ. Toxicol. Chem.
10 14(11):1977-1987.
11
12 U.S. EPA. 2001. Methods for Collection, Storage and Manipulation of Sediments for Chemical
13 and Toxicological Analyses: Technical Manual. U.S. Environmental Protection Agency, Office of
14 Water, Washington, DC. EPA-823-B-01-002. Available at
15 http ://www. epa.gov/waterscience/cs/collectionmanual .pdf.
16
17 U.S. EPA. 2003. Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks
18 (ESBs) for the Protection of Benthic Organisms: PAH Mixtures. U.S. Environmental Protection
19 Agency, Office of Research and Development, Washington, DC. EPA/600/R-02/013. Available at
20 http://www.epa.gov/nheerl/publications/files/PAFIESB.pdf
21
22 U.S. EPA. 2005. Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks
23 (ESBs) for the Protection of Benthic Organisms: Metal Mixtures (Cadmium, Copper, Lead, Nickel,
24 Silver, and Zinc). U.S. Environmental Protection Agency, Office of Research and Development,
25 Washington, DC. EPA/600/R-02/011. Available at
26 http://www.epa.gov/nheerl/publications/files/metalsESB 022405.pdf.
27
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