vvEPA
United States
Environmental Protection
Agency
Great Lakes
National Program
77 West Jackson Bob. ard
Chicago, Illinois 60604
_ A905-R92-008
December 1992
Assessment and Remediation
Of Contaminated Sediments
(ARCS) Program
BASELINE HUMAN HEALTH
RISK ASSESSMENT:
SAGINAW RIVER, MICHIGAN,
AREA OF CONCERN
United States Areas of Concern
ARCS Priority Areas of Concern
PBIHTED ON RECYCLED PAPEB*
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BASELINE HUMAN HEALTH RISK ASSESSMENT:
SAGINAW RIVER, MICHIGAN, AREA OF CONCERN
by
Judy L. Crane
AScI Corporation
Athens, Georgia 30613
Project Officer
Robert B. Ambrose, Jr.
Environmental Research Laboratory
Athens, Georgia 30613
ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ATHENS, GEORGIA 30613
U S Environmental Protection Agency
Region 5, Library (PI-12J)
77 West Jackson Bcuicw.ia, 12th floor
Chicago, it 60604-3590
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DISCLAIMER
The information in this document has been funded wholly or in part by the
United States Environmental Protection Agency. It has been subject to the
Agency's peer and administrative review, and it has been approved for publication
as an EPA document. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use by the U.S. Environmental
Protection Agency.
11
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PREFACE
This risk assessment was prepared as part of the Assessment and
Remediation of Contaminated Sediments (ARCS) program coordinated by the U.S.
EPA Great Lakes National Program Office. The work by AScI Corporation was
completed under contract no. 68-C1-0012 with the U.S. EPA Environmental
Research Laboratory-Athens by Dr. Judy Crane under the supervision of Dr.
James L. Martin, P.E., AScI Site Manager. This work was performed through the
U.S. EPA Center for Exposure Assessment Modeling, Mr. Robert Ambrose, Jr.,
P.E., Manager.
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FOREWORD
Risk assessment has been denned as the characterization of the probability
of adverse effects from human and ecological exposures to environmental hazards.
Risk assessments are quantitative, chemical-oriented characterizations that can
use statistical and biological models to calculate numerical estimates of risk to
human health or the environment. The concept of risk assessment is a
cornerstone on which the U.S. Environmental Protection Agency builds programs
to confront pollution problems in air, water, and soil under the direction of
Congressional mandates. One such mandate is the Clean Water Act, which
includes a directive to the Agency to study the control and removal of toxic
pollutants in the Great Lakes, with emphasis on removal of contaminants from
bottom sediments. Charged with performing this study is EPA's Great Lakes
National Program Office (GLNPO) located in Chicago, IL. GLNPO administers
the Assessment and Remediation of Contaminated Sediments (ARCS) program to
examine the problem of contaminated sediments using a multidisciplinary
approach involving engineering, chemistry, toxicology, modeling, and risk
assessment.
In support of the GLNPO, the Environmental Research Laboratory-Athens
began a series of studies under the ARCS program that will culminate in a
baseline risk assessment for each of five Great Lakes Areas of Concern (AOC)~
Buffalo River, NY, Grand Calumet River/Indiana Harbor Canal, IN, Saginaw
River, MI, Ashtabula River, OH, and Sheboygan River, WI. This report describes
a baseline human health risk assessment for the population within the Saginaw
River AOC. The assessment, which is based on available environmental data, is
designed to provide a conservative estimate of carcinogenic and noncarcinogenic
risks to human health under the baseline, no-action alternative.
Rosemarie C. Russo, Ph.D.
Director
Environmental Research Laboratory
Athens, Georgia
IV
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ABSTRACT
The Assessment and Remediation of Contaminated Sediments (ARCS)
program, a 5-year study and demonstration project relating to the control and
removal of contaminated sediments from the Great Lakes, is being coordinated
and conducted by the U.S. Environmental Protection Agency's (EPA) Great Lakes
National Program Office (GLNPO). As part of the ARCS program, baseline
human health risk assessments are being performed at five Areas of Concern
(AOCs) in the Great Lakes region. The Saginaw River, located in east-central
Michigan, is one of these AOCs.
In this report, exposure and risk assessment guidelines, developed for the
EPA Superfund program, have been applied to determine the baseline human
health risks associated with direct and indirect exposures to contaminated
sediments in the lower 8 km of the Saginaw River. These risks were estimated for
noncarcinogenic (e.g., reproductive toxicity, teratogenicity, liver toxicity) and
carcinogenic (i.e., probability of an individual developing cancer over a lifetime)
effects.
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TABLE OF CONTENTS
DISCLAIMER ii
PREFACE iii
FOREWORD iv
ABSTRACT v
LIST OF FIGURES viii
LIST OF TABLES ix
ACKNOWLEDGMENTS xi
1. EXECUTIVE SUMMARY 1-1
1.1 OVERVIEW 1-1
1.2 STUDY AREA 1-1
1.3 EXPOSURE ASSESSMENT 1-2
1.4 RISK ASSESSMENT 1-3
1.4.1 Determination of Risk 1-3
1.4.2 Noncarcinogenic Risks 1-5
1.4.3 Carcinogenic Risks 1-6
1.4.4 Uncertainties 1-7
2. INTRODUCTION 2-1
3. LOWER SAGINAW RIVER AREA OF CONCERN 3-1
3.1 ENVIRONMENTAL SETTING 3-1
3.2 WATER QUALITY PROBLEMS 3-1
3.3 RECREATIONAL USES 3-4
3.4 WATER SUPPLY 3-5
3.5 CONTAMINATION OF FISH 3-6
3.5.1 Routes of Contamination 3-6
3.5.2 Fish Advisories 3-8
4. RISK ASSESSMENT FRAMEWORK 4-1
4.1 CONCEPT OF RISK 4-1
4.2 RISK FRAMEWORK 4-2
5. EXPOSURE ASSESSMENT 5-1
5.1 INTRODUCTION 5-1
5.2 EXPOSURE PATHWAYS 5-1
5.3 DATA USED IN THE EXPOSURE ASSESSMENT 5-4
5.3.1 Data Sources 5-4
5.3.2 Data Review 5-5
5.3.3 Data Sets 5-5
VI
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TABLE OF CONTENTS
5.4 EXPOSURE ASSESSMENT 5-9
5.4.1 General Determination of Chemical Intakes 5-9
5.4.2 Intakes: Ingestion of Contaminated Fish 5-11
5.4.3 Intakes: Ingestion of Contaminated Waterfowl 5-12
6. TOXICITY ASSESSMENT 6-1
6.1 TOXICITY VALUES 6-1
6.2 LIMITATIONS 6-1
7. BASELINE RISK CHARACTERIZATION FOR THE LOWER SAGINAW
RIVER 7-1
7.1 PURPOSE OF THE RISK CHARACTERIZATION STEP 7-1
7.2 QUANTIFYING RISKS 7-1
7.2.1 Determination of Noncarcinogenic Risks 7-1
7.2.2 Determination of Carcinogenic Effects 7-2
7.3 HUMAN HEALTH RISKS IN THE LOWER SAGINAW RIVER . . 7-2
7.3.1 Typical and Reasonable Maximum Exposures 7-2
7.3.1.1 Noncarcinogenic Risks 7-2
7.3.1.2 Carcinogenic Risks 7-3
7.3.2 Subsistence Food Pathways 7-4
7.3.2.1 Subsistence Anglers 7-4
7.3.2.2 Subsistence Hunters 7-4
7.3.3 Additive Risks 7-5
8. CHARACTERIZATION OF QUALITATIVE UNCERTAINTIES 8-1
8.1 INTRODUCTION 8-1
8.2 QUALITATIVE LIST OF UNCERTAINTIES 8-1
8.2.1 Data Compilation and Evaluation 8-1
8.2.2 Exposure Assessment 8-2
8.2.3 Toxicity Values 8-3
8.2.4 Risk Characterization 8-3
8.2.5 Summary g-4
REFERENCES 9-1
APPENDDI A: Importance of Other Complete Exposure Pathways in
the Saginaw River Area of Concern A-l
APPENDDI B: Human Toxicity Estimates for Contaminants Present in
the Saginaw River Area of Concern B-l
Vll
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LIST OF FIGURES
Figure Page
2.1 Map of ARCS priority Areas of Concern (USEPA, 1990) 2-2
2.2 Location of the Saginaw River/Bay Area of Concern 2-3
3.1 Map of the Saginaw River 3-2
3.2 Map of the Saginaw River in the vicinity of Bay City, MI 3-3
4.1 Components of baseline human health risk assessments 4-3
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LIST OF TABLES
Table Page
1.1 Amount of Fish Assumed To Be Consumed per Person per Day
from the Saginaw River for each Exposure Scenario 1-4
1.2 Amount of Waterfowl Assumed To Be Consumed per Person
per Year from the Saginaw River Area for each Exposure
Scenario 1-5
1.3 Estimated Noncarcinogenic and Carcinogenic Risks to People
Residing in the Lower Saginaw River Area 1-6
5.1 Potential Pathways by which People May Be Exposed to
Contaminants from the Lower Saginaw River 5-2
5.2 Complete Exposure Pathways in the Lower Saginaw River 5-3
5.3 Mean Contaminant Concentrations in Walleyes (Skin-On-
Fillets) Collected from the Mouth of the Saginaw River . . . 5-7
5.4 Mean Contaminant Concentrations in Carp (Skin-Off-Fillets)
Collected from the Mouth of the Saginaw River 5-8
5.5 Mean Contaminant Concentrations in Waterfowl Collected
from the Saginaw River Area 5-9
5.6 Generic Equation for Calculating Chemical Intakes (USEPA,
1989a) 5-10
5.7 Equation Used to Estimate Contaminant Intakes Due to
Ingestion of Fish or Waterfowl 5-12
5.8 Parameters Used in Estimating Contaminant Intakes Due to
Ingestion of Fish in the Lower 8 km of the Saginaw
River 5-13
5.9 Parameters Used in Estimating Contaminant Intakes Due to
Ingestion of Waterfowl in the Lower Saginaw River
Area 5-14
6.1 EPA Weight-Of-Evidence Classification System for
Carcinogenicity (USEPA, 1989a) 6-2
6.2 Human Health Risk Toxicity Data for Chemicals of Interest
in the Lower Saginaw River 6-2
7.1 Risk Associated with the Consumption of Walleye from the
Lower Saginaw River Based on Typical Exposure Levels . . 7-6
7.2 Risk Associated with the Consumption of Carp from the
Lower Saginaw River Based on Typical Exposure Levels . . 7-6
7.3 Risk Associated with the Consumption of Waterfowl from the
Lower Saginaw River Based on Typical Exposure Levels . . 7-7
7.4 Risk Associated with the Consumption of Walleye from the
Lower Saginaw River Based on Reasonable Maximum
Exposure Levels 7.7
IX
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LIST OF TABLES
Table
7.5 Risk Associated with the Consumption of Carp from the
Lower Saginaw River Based on Reasonable Maximum
Exposure Levels 7-8
7.6 Risk Associated with the Consumption of Waterfowl from the
Saginaw River Area Based on Reasonable Maximum
Exposure Levels 7-8
7.7 Risk Associated with the Consumption of Walleye from the
Lower Saginaw River for Subsistence Anglers 7-9
7.8 Risk Associated with the Consumption of Carp from the
Lower Saginaw River for Subsistence Anglers 7-9
7.9 Risk Associated with the Consumption of Waterfowl from the
Saginaw River Area for Subsistence Hunters 7-10
7.10 Summary of Noncarcinogenic and Carcinogenic Risks in the
Lower Saginaw River 7-10
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ACKNOWLEDGMENTS
Several people provided helpful information about the Saginaw River area
including: Greg Goudy (MDNR), Allan Brouillet (MDNR), Tim Kubiak (U.S. Pish
and Wildlife Service), Mardi Klevs (U.S. EPA, Region V), Doug Bell (East Central
Michigan Planning and Development Region), and John Giesy and Dave
Verbrugge (Michigan State University). We especially thank Greg Goudy,
Saginaw River/Bay RAP Manager, for providing Michigan DNR data on
contaminant levels in sediment, water, and fish collected from the Saginaw
River/Bay. Tim Kubiak supplied data on contaminant levels in waterfowl.
Members of the ARCS Risk Assessment and Modeling Work Group have also
provided useful feedback. The constructive review comments of James Martin
(AScI Corporation) and Bill Sutton (ERL-Athens) were much appreciated.
XI
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CHAPTER 1
EXECUTIVE SUMMARY
1.1 OVERVIEW
The Assessment and Remediation of Contaminated Sediments (ARCS)
program, a 5-year study and demonstration project relating to the control and
removal of contaminated sediments from the Great Lakes, is being coordinated
and conducted by the U.S. Environmental Protection Agency's (EPA) Great Lakes
National Program Office (GLNPO). As part of the ARCS program, baseline
human health risk assessments are being performed at five Areas of Concern
(AOCs) in the Great Lakes region. The Saginaw River, located in east-central
Michigan, is one of these AOCs.
In this report, exposure and risk assessment guidelines, developed for the
EPA Superfund program, have been applied to determine the baseline human
health risks associated with direct and indirect exposures to contaminated
sediments in the lower 8 km of the Saginaw River. These risks were estimated for
noncarcinogenic (e.g., reproductive toxicity, teratogenicity, liver toxicity) and
carcinogenic (i.e., probability of an individual developing cancer over a lifetime)
effects.
1.2 STUDY AREA
This risk assessment covers an area adjacent to the lower 8 km of the
Saginaw River as it passes through Bay City, Essexville, and parts of Hampton
and Bangor townships before entering Saginaw Bay. This area has a history of
water quality problems due to point (i.e., industrial and municipal discharges) and
nonpoint (e.g., upstream agricultural runoff) sources of nutrients and
contaminants. The extent of contamination and eutrophication in the entire
Saginaw River/Bay region led to the International Joint Commission's (IJC)
decision to designate this region as a Great Lakes AOC. In response, the
Michigan Department of Natural Resources (MDNR) has completed one phase of a
remedial action plan (RAP) to identify and implement pollution abatement
measures for the Saginaw River/Bay AOC (MDNR, 1988).
High levels of nutrients, heavy metals, polychlorinated biphenyls (PCBs),
and in some areas, dioxins, have been measured in different compartments of the
Saginaw River (e.g., sediments, water column, and fish). Concentrations of PCBs
in excess of 1 mg/kg have been measured in sediments, hi addition, fish
advisories have been issued against consuming carp and channel catfish from the
Saginaw River because of excessive levels of PCBs and dioxins. The transport of
these contaminants into Saginaw Bay is of concern, and the Michigan DNR has
conducted widespread sampling in the Bay to determine contaminant
1-1
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concentrations in the sediments and fish. However, it was beyond the scope of
this risk assessment to estimate human health risks to people using the Bay.
PCBs and other contaminants have been detected in fish (e.g., walleye,
yellow perch, carp, and catfish) collected from both the Saginaw River and Bay.
Since many species of fish travel between the river and bay, there is some
uncertainty as to where the fish accumulated their contaminant burden. Fish
collected from the mouth of the Saginaw Eiver during the late 1980s contained
higher contaminant concentrations than for similar fish species collected from
different points in the Bay. For the purpose of this risk assessment, it was
assumed that fish collected from the mouth of the river accumulated most of their
contaminant burden from the lower Saginaw River.
Several contact and noncontact recreational activities take place along the
Saginaw River, with fishing and boating being the most popular pastimes.
Fishing occurs by boat and from shore in the Bay City area; ice-fishing is also a
common activity during wintertime. Hunting is another popular sport, with
waterfowl hunting taking place in several wildlife refuges near the river.
1.3 EXPOSURE ASSESSMENT
This assessment focused on two pathways by which residents of the lower
Saginaw River could be exposed to sediment-derived contaminants: 1) consumption
of contaminated fish (i.e., walleye or carp), and 2) consumption of contaminated
waterfowl (i.e., mallards and gadwalls). Other exposure pathways were
determined to be either incomplete (e.g., ingestion of sediments) or insignificant in
terms of risk (e.g., ingestion of surface water while swimming). Swimming does
not occur very often in the lower Saginaw River, and there are no beaches in the
area.
Only a few species of fish and waterfowl were included in the exposure
assessment because of the lack of data for many other species. Walleye were
chosen because they are the preferred sport fish in the Saginaw River and could
be used to represent a pelagic (open-water) species. Carp were selected because
they are generally the most contaminated fish in water bodies due to their benthic
feeding habits and high lipid content; carp were used to represent a benthic
species. Thus, by examining the estimated risk from consuming either carp or
walleye, a range of risk estimates could be determined for a variety of exposure
scenarios. In terms of waterfowl consumption, the only available data set
containing contaminant levels in wild waterfowl were for two mallards and six
gadwalls collected in 1985 from the Saginaw River area; these data sets were
combined and used in the exposure assessment.
Noncarcinogenic and carcinogenic risks were estimated for typical,
reasonable maximum, and subsistence exposures. Typical (i.e., average) exposures
were assumed to occur over a period of 9 years; reasonable maximum (i.e., the
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maximum exposure that is reasonably expected to occur at a site) and subsistence
exposures were assumed to occur over a period of 30 years (USEPA, 1989a).
These exposure durations were extrapolated over a period of 70 years for
estimating carcinogenic risks. The subsistence pathway was chosen for a small
segment of the population that may be relying on the consumption of fish or
waterfowl from the area for their main source of protein. For all three exposure
scenarios, exposures were determined for each chemical and added for each
pathway. In addition, exposures were added across pathways (i.e., consumption of
fish and waterfowl) for typical and reasonable maximum exposures; this was not
done for the subsistence scenario because subsistence anglers and waterfowl
hunters represent two sensitive subpopulations that should be considered
separately.
For each of these exposure scenarios, different consumption patterns of fish
and waterfowl were assumed to take place (Tables 1.1 and 1.2). These
consumptions patterns were based, in part, on recommended values given in EPA
Superfund guidance (USEPA, 1989a,b; 1991a) or else on study assumptions.
Several heavy metals and organic compounds were included in the exposure
assessment: arsenic, cadmium, copper, mercury, zinc, chlordane, dieldrin,
heptachlor epoxide, hexachlorobenzene, PCBs, p,p' dichlorodiphenyl dichloroethane
(DDD), p,p' dichlorodiphenyl dichloroethylene (DDE), p,p' dichloridiphenyl
trichloroethane (DDT), and styrene. This list was selected for those chemicals
detected in fish and waterfowl for which noncarcinogenic and/or carcinogenic
toxicity values were available.
1.4 RISK ASSESSMENT
1.4.1 Determination of Risk
Noncarcinogenic effects were evaluated by comparing an exposure level over
a specified time period with a reference dose (RfD)1 derived from a similar
exposure period (otherwise known as a hazard quotient (HQ)). Thus, HQ =
exposure level/RfD. An HQ value of less than 1 indicates that exposures are not
likely to be associated with adverse noncarcinogenic effects. HQ values between 1
and 10 may be of concern, particularly when additional significant risk factors are
present (e.g., other contaminants at levels of concern) (USEPA, 1988a). The sum
of more than one HQ value for multiple substances and/or multiple exposure
pathways is represented by the Hazard Index (HI). This assumption of additivity
1 The RfD provides an estimate of the daily contaminant exposure that is not
likely to cause harmful effects during either a portion of a persons' life or
their entire lifetime (USEPA, 1989a).
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TABLE 1.1. AMOUNT OF FISH ASSUMED TO BE CONSUMED PER
PERSON PER DAY FROM THE SAGINAW RIVER FOR
EACH EXPOSURE SCENARIO
Exposure Scenario
Typical
Reasonable Maximum
Subsistence Fishing
Ingestion
Rate*
(g/day)
19.2
54
132
x FI**
0.10
0.25
0.7
Amount of
Saginaw R.
Fish
= Consumed
(g/day)
1.92
13.5
92.4
* Sources: Typical (West, 1989); Reasonable Maximum (USEPA, 1991a); Subsistence [Pao
et al (1982) cited in USEPA (1989a)].
** FI = Fraction offish (i.e., walleye or carp) estimated to be ingested from the Saginaw
River (study assumption). Walleye represent skin-on-fillets, whereas carp
represent skin-off-fillets.
does not account for any synergistic or antagonistic effects that may occur among
chemicals.
Carcinogenic risks were estimated as the incremental probability of an
individual developing cancer over a lifetime as a result of exposures to potential
carcinogens. This risk was computed using average lifetime exposure values that
were multiplied by the oral slope factor2 for a particular chemical. The resulting
carcinogenic risk estimate generally represents an upper-bound estimate, because
slope factors are usually based on upper 95th percentile confidence limits.
Carcinogenic effects were summed for all chemicals in an exposure pathway as
well as for multiple pathways (i.e., ingestion of fish and waterfowl). This
summation of carcinogenic risks assumed that intakes of individual substances
were small, that there were no synergistic or antagonistic chemical interactions,
and that all chemicals caused cancer. The EPA believes it is prudent public
health policy to consider actions to mitigate or minimize exposures to
2 Slope factors are estimated through the use of mathematical extrapolation
models for estimating the largest possible linear slope (within 95%
confidence limits) at low extrapolated doses that is consistent with the data
(USEPA, 1989a).
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TABLE 1.2. AMOUNT OF WATERFOWL ASSUMED TO BE CONSUMED
PER PERSON PER YEAR FROM THE SAGINAW RIVER
AREA FOR EACH EXPOSURE SCENARIO
Exposure Scenario
Typical
Reasonable Maximum
Subsistence Hunting
Ingestion
Rate* x
(g/meal)
85
110
280
Number of
Meals x
per year**
3
16
16
FI***
0.33
0.5
1.0
Amount of
Saginaw R.
Waterfowl
Consumed
(s/yr)
84
880
4480
* Sources: Typical (University of Georgia Extension Service, personal communication,
1991); Reasonable Maximum and Subsistence [Pao et al. (1982) cited in
USEPA (1989a)].
** Study Assumption (see Chapter 5).
*** FI = Fraction of waterfowl (i.e., mallards and gadwalls) assumed to be ingested from
the Saginaw River area (study assumption). Waterfowl represents "roaster
ready" (i.e., plucked and eviscerated) birds.
contaminants when estimated, upper-bound excess lifetime cancer risks exceed the
10"5 to 10"6 range, and when noncarcinogenic health risks are estimated to be
significant (USEPA 1988a).
1.4.2 Noncarcinogenic Risks
Noncarcinogenic risks, as represented by HI, were less than 0.5 for all
exposure levels and pathways except for the subsistence consumption of walleye
(HI = 1) and carp (HI = 4) (Table 1.3). For the high consumption of walleye, the
noncarcinogenic risk was at a borderline level of concern and was due mostly to
the additive risk of methyl mercury and copper. For carp, only heptachlor epoxide
had a HQ value exceeding one; this chemical has been found to cause increased
liver-to-body weight ratio in both male and female beagle dogs. The rest of the
subsistence hazard index for carp was attributable to the combined risk resulting
from exposure to chlordane, dieldrin, and copper.
Although some of the chemicals detected in these animals do not presently
have RfD values (e.g., PCBs), it would be premature to state that no
noncarcinogenic risk exists from consuming fish or waterfowl from the lower
Saginaw River area under typical and reasonable maximum exposures. The
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TABLE 1.3.
ESTIMATED NONCARCINOGENIC AND CARCINOGENIC
RISKS TO PEOPLE RESIDING IN THE LOWER SAGINAW
RIVER AREA
Additive Risks
Type of
Risk and
Exposure*
Walleye
Individual
Carp
Risks
Waterfowl
Walleye +
Waterfowl
Carp +
Waterfowl
Noncarcinogenic (HI)
Typical 0.02
Reasonable Maximum 0.2
Subsistence 1
0.08
0.5
4
0.001
0.02
0.08
0.02
0.2
0.08
0.5
Carcinogenic
Typical 1E-05
Reasonable Maximum 2E-04
Subsistence 2E-03
1E-04
3E-03
2E-02
6E-06
2E-04
IE-OS
2E-05
4E-04
1E-04
3E-03
Noncarcinogenic risks were averaged over the same period as the exposure duration
while carcinogenic risks were averaged over a period of 70 years (i.e., average
lifetime of an individual).
noncarcinogenic risk reported here is an estimated risk based on currently
available data and toxicity information and should not be construed as an absolute
risk.
1.4.3 Carcinogenic Risks
The estimated, upper-bound carcinogenic risk levels for all pathways and
exposure scenarios were at or above concern levels (i.e., 10~5 to 10"6 range). In all
cases, PCBs accounted for nearly all of the carcinogenic risk. There is a possibility
that people who ingest, inhale, or have dermal contact with certain PCB mixtures
may have a greater chance of incurring liver cancer; however, this statement is
based on suggestive evidence rather than on verified data.
These risk estimates may have been overestimated because the only
available oral slope factor for PCBs was based on Aroclor 1260. The primary
Aroclor mixture detected in fish collected from the Saginaw River resembled
Aroclor 1254, while only total PCBs were reported for waterfowl. Since Aroclor
1260 contains more highly chlorinated congeners (as well as potentially toxic
coplanar congeners) than Aroclor 1254, these risk estimates may be overly
conservative.
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In comparison with the typical exposure scenario, carcinogenic risks
increased by approximately one order of magnitude for reasonable maximum
exposures and by two orders of magnitude for subsistence anglers or hunters. The
individual risks from consuming walleye or waterfowl were nearly equivalent for
each exposure scenario; in comparison, carp consumption increased carcinogenic
risks by an order of magnitude. Although walleye and waterfowl contributed
equally to the risks of consuming both of these items, the additive risk of
consuming carp and waterfowl was largely due to the risk level for carp.
1.4.4 Uncertainties
Several assumptions and estimated values were used in this baseline risk
assessment that contributed to the overall level of uncertainty associated with the
noncarcinogenic and carcinogenic risk estimates. As with most environmental risk
assessments, the uncertainty of the risk estimates probably varied by at least an
order of magnitude or greater. Uncertainties were addressed in a qualitative way
for those parameters and assumptions that appeared to contribute the greatest
degree of uncertainty. One of the greatest sources of uncertainty was the
assumption that exposure intakes and toxicity values would not change during the
exposure duration. This assumed that human activities and contaminant levels
would remain the same over the exposure duration, and that toxicity values would
not be updated.
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CHAPTER 2
INTRODUCTION
The 1987 amendments to the Clean Water Act, in Section 118(c)(3),
authorize the U.S. Environmental Protection Agency's (EPA) Great Lakes National
Program Office (GLNPO) to coordinate and conduct a 5-year study and
demonstration project relating to the control and removal of contaminated
sediments from recommended areas in the Great Lakes region. To achieve this
task, GLNPO has initiated the Assessment and Remediation of Contaminated
Sediments (ARCS) program. The overall objectives of the ARCS program (USEPA,
1991b), for selected Areas of Concern (AOCs), are to:
1. Assess the nature and extent of contaminated sediments,
2. Evaluate and demonstrate remedial options (e.g., removal,
immobilization, and advanced treatment technologies) as well
as the "no action" alternative,
3. Provide risk assessments for humans, aquatic life, and wildlife
exposed to sediment-related contaminants, and
4. Provide guidance on the assessment of contaminated sediment
problems and on the selection and implementation of necessary
remedial actions in the Areas of Concern and other locations in
the Great Lakes.
As one part of the ARCS program, baseline human health risk assessments
are being prepared for five AOCs: Ashtabula River, OH; Buffalo River, NY; Grand
Calumet River/Indiana Harbor Canal, IN; Saginaw River, MI; and Sheboygan
River, WI (Figure 2.1). The objectives of these risk assessments are to: 1)
estimate the magnitude and frequency of human exposures to contaminants in the
AOC, and 2) determine the risk of adverse effects resulting from both typical and
reasonable maximum exposures (i.e., the highest exposure that is reasonably
expected to occur at a site) to contaminants. Risk estimates are determined for
both noncarcinogenic (i.e., chronic or subchronic effects) and carcinogenic (i.e.,
probability of an individual developing cancer over a lifetime) effects resulting
from direct and indirect exposures to sediment-related contaminants.
This document presents a baseline human health risk assessment for one
portion of the Saginaw River/Bay AOC (Figure 2.2), the lower 8 km of the Saginaw
River. This section of the Saginaw River was chosen because: 1) the site is located
in an urban area (Bay City) bisected by the Saginaw River and lies adjacent to
Saginaw Bay; 2) several industrial and municipal wastewater treatment plants
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ARCS1 PRIORITY
AREAS OF CONCERN
GREAT LAKES AREAS OP CONCERN
1. SHEBOYGAN HARBOR
2. GRAND CALUMET/INDIANA HARBOR
3. SAGINAW RIVER/BAY
4. ASHTABULA RIVER
5. BUFFALO RIVER
* Assessment and Remediation of Contaminated Sediments
MO 5DO
I I
NUMCIBM
Figure 2.1.
Map of ARCS priority Areas of Concern (USEPA, 1991b).
2-2
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Source Area of Concern
Figure 2.2.
Location of the Saginaw River/Bay Area of Concern.
2-3
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discharge treated effluent into the river; 3) high levels of contaminants, especially
PCBs, have been measured in the river sediments; 4) several recreational areas
and marinas are located along the river; and 5) contaminant modeling for another
task of ARCS (i.e., the comparative risk assessment) is to be conducted in the
same region.
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CHAPTERS
LOWER SAGINAW RIVER AREA OF CONCERN
3.1 ENVIRONMENTAL SETTING
The Saginaw River, located in east central Michigan, is a short (35 km),
eutrophic river with a drainage basin of 671 km2 (Figure 3.1). This river receives
most of its flow from the Cass, Flint, Shiawassee, and Tittabawassee Rivers and in
turn provides approximately 75% of the tributary hydraulic input to Saginaw Bay.
The average discharge of the Saginaw River is 114 m3/sec, and flow reversals have
been observed as far upstream as river kilometer 35. During September 1986,
extreme flooding took place in the Saginaw, Tittabawassee, and Cass Rivers when
over 45 cm of rain fell during a 3-week period [F. Nurnberger, personal
communication cited in the Remedial Action Plan or RAP (MDNR, 1988)]. As a
result of this flooding, sediments may have been resuspended and transported as
far as the bay before settling out again. Consequently, the distribution of
contaminants in the sediments, water column, and biota of the Saginaw River may
have been altered after this flooding event.
The specific area of concern for this risk assessment is the lower 8 km of
the Saginaw River (i.e., from the Lafayette Street Bridge in Bay City to the mouth
of the river) (Figure 3.2). This area includes the towns of Bay City and Essexville
and part of Bangor and Hampton townships. Several industries are located along
the river and a navigation channel is maintained for shipping traffic. The dredged
sediments from the navigation channel have been stored in an offshore Confined
Disposal Facility (CDF) which is nearing its capacity; no plan has been made for
disposing of future dredged sediments.
3.2 WATER QUALITY PROBLEMS
The Saginaw River and Saginaw Bay have been listed as an AOC by the
International Joint Commission. This designation is given to areas where
environmental quality is degraded and designated uses of the water are impaired.
This AOC has a history of water quality problems due to agricultural runoff and
industrial and municipal discharges into the river and bay. Although conditions
in this AOC have improved over the past 20 years for some pollutants (e.g.,
phosphorus, suspended solids, oil and grease), problems remain for persistent
hydrophobic organic contaminants (e.g., PCBs) and some heavy metals. A RAP for
the Saginaw River/Bay AOC has been developed by the Michigan DNR to identify
and implement pollution abatement measures. The main objectives of the RAP
are to: 1) reduce contaminant levels in fish tissue to the point where fish
consumption advisories are no longer needed for any fish species in the AOC, 2)
reduce contaminant levels in the AOC to those of Michigan's water quality
standards, and 3) reduce eutrophication in Saginaw Bay to a level that will
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BAY CITY
LAUNCH
N
SAGINAV RfVER
Figure 3.1. Map of the Saginaw River.
3-2
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NORTH END COAST
GUARD STATION
INLET BUOYS
ESSEXVILLE
RAMP
D&M RAILROAD
BRIDGE
INDEPENDENCE
BRIDGE
SOUTH END
MIDDLE GROUNDS
ISLAND
SHADED AREAS ARE
SAGINAW
RIVER
NO WAKE
ZONES
N
t
Figure 3.2.
Map of the Saginaw River in the vicinity of Bay City, MI.
3-3
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support a balanced mesotrophic biological community (MDNR, 1990). The RAP
was the major source of information for this risk assessment.
There are a number of sources that continue to contribute contaminants to
the Saginaw River and Saginaw Bay including industrial and municipal
discharges, combined sewer overflows, contaminated sediments in the river and
bay bottom, urban and agricultural nonpoint runoff, waste disposal sites, and the
atmosphere (MDNR, 1988). The greatest water quality problems in the lower
Saginaw River have resulted from industrial and municipal wastewater treatment
plant (WWTP) discharges into the river. There are ten major dischargers to the
Saginaw River, of which three are located in the lower 8 km of the river: General
Motors Corp. (GMC) Powertrain Division (formerly known as GMC Chevrolet-
Pontiac-Canada (CPC) Group), Monitor Sugar Company, and the Bay City
Wastewater Treatment Plant (WWTP). Of these three industries, the GMC
Powertrain Division plant is the only company that lists PCBs in its NPDES
permit. The RAP contains additional information about the GMC plant as well as
other sources of pollution to the Saginaw River (MDNR, 1988).
As a result of inputs of contaminants into the Saginaw River, the sediments
have become contaminated with PCBs, heavy metals, and other compounds.
These sediments provide an additional source of contaminants to the water
column through processes such as resuspension events, bioturbation, and
equilibrium partitioning. Some of the highest concentrations of PCBs (i.e., >1
mg/kg) in the Saginaw River have been measured in the sediments below the
GMC Powertrain outfall (G. Goudy (MDNR), personal communication, 1991).
These contaminated sediments are of concern because of the potential health risk
to people resulting from direct (e.g., dermal contact with sediments) and/or
indirect (e.g., consumption of contaminated fish) exposures to sediment-derived
contaminants.
3.3 RECREATIONAL USES
The greatest recreational opportunities on the Saginaw River involve fishing
and boating. Four parks, seven marinas and yacht clubs, and three public boat
ramps are located in the lower 8 km of the Saginaw River. This river is a popular
site for fishing from shore and by boat. In addition, ice fishing is prevalent during
the winter. Walleye is the main sport fish, but yellow perch, largemouth bass,
smaUmouth bass, northern pike, crappie, and bluegill are also caught (MDNR,
1988). In addition, the Saginaw River supports spawning runs of salmonids, white
bass, and suckers. Waterfowl hunting also occurs in the Quanicasse Wildlife Area
bordering Saginaw Bay east of the Saginaw River.
The largest park in this region is Veterans Memorial Park located near
Veterans Memorial Bridge (Figure 3.2). Many noncontact recreational activities
(e.g., softball, volleyball, jogging/walking, picnicking, and swimming in an outdoor
pool) are available. In addition, this park is frequently used by anglers fishing
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from shore; a walkway and gazebo extending out into the middle of the Saginaw
River allows protected fishing for handicapped individuals. Veterans Memorial
Park is the site of a popular July 4th celebration that spans several days.
Fireworks are set off over the river and thousands of boaters come to view them.
Some people have been observed to jump off their boats and swim in the water
during the festivities (A. Brouillet (MDNR), personal communication, 1991). Other
parks, such as Essexville Park, are regularly used by anglers. Additional
recreational opportunities on the Saginaw River will be available when a crew
house is completed near the Lafayette Street Bridge.
The Bay City Chamber of Commerce is encouraging tourism in the area to
supplement its economic base, which has been weakened by industrial closures.
Bay City is becoming a popular place for people from Flint and Detroit to harbor
their boats (A. Brouillet (MDNR), personal communication, 1991). A new marina
recently opened to accommodate greater boat traffic on the river, partly from
people who use the river as an access point to Saginaw Bay.
No swimming areas or beaches exist along the lower 8 km of the Saginaw
River. The eutrophic water quality of the Saginaw River does not make it
aesthetically pleasing for swimming. In addition, the banks of the river are either
filled with rock and cement or else are walled off; thus it is not likely that anyone
would be exposed to contaminants through contact with river bank sediments.
Official swimming beaches are located along Saginaw Bay at Bay City State Park
and adjacent to private residences in Bangor township. Some sporadic swimming
may occur in the river from people jumping off their boats and swimming in the
water. The water is warm enough for swimming with an average summer (i.e.,
June - August) temperature of 22 °C (72 °F) (MDNR, 1988). People who use jet
skis on the river may be immersed in the water if their jet ski becomes
unbalanced. Although jet skiing occurs, water skiing is not likely to take place on
the lower Saginaw River because of the prevalence of no wake zones. Other
activities that may result in immersion in the water (e.g., wind surfing) are
unlikely to occur in the lower Saginaw River because of heavy boat traffic and flow
reversals in the surface water.
3.4 WATER SUPPLY
The Saginaw River is not used as a drinking water source by municipalities
in the region. Instead, the Bay City Water Supply System draws water from a
point on the bay just west of the mouth of the Saginaw River. This system serves
80,815 people and withdraws an average of 11.9 million gallons/day (Bendell, 1982
cited in MDNR, 1988). Raw water samples taken from this system did not exceed
primary drinking water standards during 1985 (USEPA, 1985 cited in MDNR,
1988).
3-5
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3.5 CONTAMINATION OF FISH
3.5.1 Routes of Contamination
One of the primary ways in which people in the Great Lakes region,
including the Bay City area, have been exposed to sediment-derived contaminants
is through the consumption of contaminated fish. The specific mechanisms by
which contaminants may be transferred from sediments to fish are still being
elucidated. Part of the problem with determining these mechanisms is that
different fish species occupy different habitats in the water column (e.g., benthic
(bottom) versus pelagic (open water) habitats) and their diet and metabolism may
change with age. This section will examine some of the ways in which fish
occupying a river/harbor area of the Great Lakes may accumulate contaminants,
assuming that the major source of pollutants comes from in-place contaminated
sediments. The next section will discuss specific fish advisories for the Saginaw
River AOC.
The group of contaminants that have been of major concern in the Great
Lakes are hydrophobic organic compounds (HOCs) such as PCBs and DDT. These
compounds are persistent in the environment, due to their physical-chemical
properties, and will preferentially accumulate in the lipids of organisms relative to
other compartments (e.g., muscle, bone). Many of the commercially exploited
Great Lakes fish have relatively high amounts of body fat (e.g., lake trout, lake
whitefish, and channel catfish), and thus would be expected to contain higher
levels of lipid soluble HOCs than species characterized by low body fat (e.g., yellow
perch and suckers) (Kononen, 1989).
The accumulation of contaminants in fish lipids can occur by two routes: 1)
diffusion across the gills into the body and 2) transfer from the gut into the body
after the consumption of contaminated food (Swackhamer and Kites, 1988). For
the first route, the uptake of contaminants from water is functionally dependent
on fish respiration and is related to the transfer of dissolved oxygen across the gill
surfaces (Weininger, 1978). For the second route, the flux of contaminant transfer
through feeding is dependent on the following factors: a) contaminant
concentration in food, b) rate of consumption of food, and c) degree to which the
ingested contaminant in the food is actually assimilated into the tissues of the
organism. The assimilation of pollutants is affected by the desorption and
excretion of contaminants from body tissues, and by the growth of the organism
(Thomann and Connolly, 1984).
There is some uncertainty as to whether compounds sorbed to sediment
particles will be available to fish for uptake. A chemical equilibrium model would
assume that contaminant concentrations in the fish and sediments would be in
equilibrium through their individual equilibrium coefficients with the water
column (Connor, 1984). Studies with marine bottom fish in urban bays seem to
indicate that the concentration of organic contaminants in the fish is correlated
3-6
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with the sediment concentration of those compounds (Connor, 1984; Mallins et al.,
1984). This correlation may depend on the area's physical flushing capacity
(residence time of water in a basin) and the metabolism of the organism (Connor,
1984). Similarly, a good correlation between the types of contaminants found in
sediments collected from areas of industrial and urban development with the types
of contaminants detected in freshwater carp from the same area has been made
(Jaffe et al., 1985). Carp tend to remain in a local territory and, for the most part,
are benthic feeders; thus, they would be expected to serve as a reasonable
barometer of the types of contaminants (especially organic compounds) found in
their aquatic environment. In another study, Brown et al. (1985) hypothesized
that PCB concentrations in pelagic consumers (i.e., pumpkinseed) of benthic-
feeding organisms in the Hudson River were largely controlled by PCB levels in
the surficial sediments. While the aforementioned studies seem to indicate some
causal linkage between contaminant concentrations in sediment and fish, there is
a degree of uncertainty associated with this linkage. One of the difficulties with
assessing the impacts of sediment contaminants on fish is that the factors
controlling their bioavailability are not well understood, nor is there a basic
understanding of trophic transfer from benthic to pelagic food chains (Bierman,
1990).
Due to the difficulty involved with assessing sediment-fish linkages in the
field, controlled laboratory experiments have been conducted. Seelye et al. (1982)
exposed young-of-the-year perch to a slurry of contaminated sediments for 10 days
to simulate the conditions these fish would encounter during dredging. Although
the perch accumulated organic compounds and heavy metals from the resuspended
sediments, it is not known whether the contaminants in the fish reached steady
state. In another experiment by Kuehl et al. (1987), carp exposed to Wisconsin
River sediment for 55 days accumulated 7.5 pg/g 2,3,7,8-TCDD; maintaining
exposed fish in clean water for an additional 205 days resulted in the depuration
of 32-34% of the accumulated 2,3,7,8-TCDD. The most likely uptake route for
2,3,7,8-TCDD in the carp was through the ingestion of contaminated sediments
while feeding (Kuehl et al., 1987). In another experiment, lake trout that were
exposed to Lake Ontario sediment and smelt in long term lab experiments
appeared to bioaccumulate 2,3,7,8-TCDD primarily through the food chain and
secondarily through contact with contaminated sediment (Batterman et al., 1989).
These lake trout did not bioaccumulate a significant concentration of 2,3,7,8-TCDD
from the water column, even under simulated equilibrium conditions and with low
suspended solids concentrations (Batterman et al., 1989).
Recent evidence indicates that concentrations of HOCs in fish are primarily
the result of food chain biomagnification and not equilibrium partitioning from the
sediments or water column (Oliver and Niimi, 1988; Batterman et al., 1989). In
Lake Ontario, samples from all trophic levels in the planktonic (water to plankton
to mysid to alewive/smelt to salmonid) and the benthic (water to bottom
sediment/suspended sediment to amphipod/oligochaete to sculpin to salmonid) food
chains showed classic biomagnification of PCBs between successive trophic levels
3-7
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(Oliver and Niimi, 1988). Thus, the rate at which contaminant concentrations
increase with body size will be a function of how efficiently the contaminant is
excreted after assimilation (Borgmann and Whittle, 1991). In turn, the
assimilation of contaminants in fish will be affected by declines in feeding and
clearance rates as growth occurs (Pizza and O'Connor, 1983). Temperature has
also been found to affect the accumulation of PCBs in certain adult species of fish
because temperature controlled food consumption, growth, and lipid content
(Spigarelli et al., 1983).
Other contaminants, such as mercury, are also of concern in the Great
Lakes. Unlike HOCs, mercury appears to accumulate in fish tissues through
direct uptake from the water column (Gill and Bruland, 1990). The major form of
mercury in the water column is the highly toxic methylated mercury species.
Because of the problem of mercury contamination in fish in the Great Lakes
region, fish advisories have been issued for certain size classes of sport fish.
3.5.2 Fish Advisories
The Great Lakes jurisdictions have issued consumption advisories for sport
fish since the late 1960s and early 1970s. These consumption advisories are based
on the relationship between tissue concentrations of contaminants in individual
size classes and species of fish and on specific trigger levels. When tissue
concentrations exceed some trigger level (usually Food and Drug Administration
action levels), consumption advice is issued by the states. The governors of the
Great Lakes states called for the uniform development of fish consumption
advisories by the states in the 1986 Great Lakes Toxic Substances Control
Agreement (Foran and VanderPloeg, 1989). However, this mandate has not been
followed by all states, and this inconsistent consumption advice may serve to
confuse the fishing public and those consuming Great Lakes sport fish.
The Michigan Department of Public Health (MDPH) has issued a fish
advisory for the entire Saginaw River. Carp and catfish should not be consumed
by anyone because they have been found to contain PCBs and dioxin. In addition,
the MDPH suggests that no one should eat large quantities of any species from
the Saginaw River. In particular, women who intend to have children should eat
no more than one meal per month of fish from this river. In addition, people
should restrict their consumption of lake trout, rainbow trout, and brown trout to
no more than one meal per week out of Saginaw Bay. Despite these warnings,
some anglers may not be aware of specific advisories or may choose to ignore them
(West et al., 1989).
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CHAPTER 4
RISK ASSESSMENT FRAMEWORK
4.1 CONCEPT OF RISK
People are subject to a number of risks throughout their day that may cause
them immediate or delayed harm. Some risks arise from personal choices (e.g.,
driving a car, participating in sports) while other risks may result from things
people have little control over (e.g., breathing urban air, being a victim of a
random crime). In terms of human health risks resulting from exposure to some
chemical, biochemical, or physical agent, risks are classified into two categories:
carcinogenic and noncarcinogenic risks.
Cancer is the leading cause of death for women in the United States, and
most cancers, for both men and women, are caused by factors resulting from life
style choices [e.g., smoking, drinking alcohol, consuming a diet high in animal fat,
being overweight, or staying out in the sun too long (ultraviolet light exposure)]
(Henderson et al., 1991). In particular, tobacco (alone or in combination with
alcohol) accounts for one of every three cancer cases occurring in the United States
today (Henderson et al., 1991). Occupational exposures to specific carcinogens
(especially asbestos) account for only about 4% of the cancers in the United States
(Henderson et al., 1991). Although nonoccupational exposures to environmental
contaminants probably cause an even smaller fraction of the cancers reported in
the U.S., it is important to safeguard the public's health from unnecessary and
involuntary risks. In addition, environmental contaminants may also pose a
noncarcinogenic risk to human health.
Noncarcinogenic risks include a variety of both chronic and subchronic
effects to people. Included in this risk category are birth defects, respiratory
diseases (e.g., asthma), liver diseases, learning disabilities, etc. One way to
examine for incidences of these risks in human populations is through
epidemiological studies. Three sets of studies of the impacts of human exposure to
PCB contaminated fish from the Great Lakes basin—the Michigan Sports
Fisherman Cohort, the Michigan Maternal/Infant Cohort, and the Wisconsin
Maternal/Infant Cohort were evaluated using epidemiologic criteria (Swain, 1991).
The results from comparing the studies against each other, and against
comparable data from other geographic locales, strongly suggest a causal
relationship between PCB exposure and alterations in both neonatal and early
infancy health status (Swain, 1991). However, there is no evidence that these
short-term effects lead to any chronic health effects (Bro, 1989). Possible
developmental effects in infants and children will not be addressed in this risk
assessment because complex pharmacokinetic models, which are not well
developed in the risk assessment field, would have to be used. Thus, it is beyond
the scope of the ARCS Program to address this issue in any great detail (USEPA, 1991b).
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4.2 RISK FRAMEWORK
Risks associated with environmental exposures to contaminants are difficult
to assess because: 1) the exposure itself is often difficult to document and 2) the
exposure does not always produce immediately observable effects. Due to these
difficulties, human health risks associated with exposures to contaminants must
often be estimated via scenarios using standard EPA exposure parameters.
The approach used for this baseline human health risk assessment followed
exposure and risk assessment guidelines established by the EPA for use at
Superfund sites (USEPA, 1988b; 1989a,b; 1991a). Although the Saginaw River is
not a Superfund site, the risk assessment procedures developed for the Superfund
Program can be applied to this site to estimate current risks to people residing in
the AOC. Unlike the Superfund risk assessments, this assessment did not
consider risks resulting from future scenarios (e.g., future risks associated with
turning a contaminated site into a playground). Instead, this risk assessment was
based on the most up-to-date information available to estimate current
noncarcinogenic and carcinogenic risks to human populations in the lower 8 km of
the Saginaw River.
The procedures used in this risk assessment are outlined briefly in Figure
4.1. The first step in the process was to obtain information about the Saginaw
River from documents such as the Remedial Action Plan or RAP (MDNR, 1988)
and ARCS "Information Summary" (Brandon et al., 1991). In addition, a search
for the latest data on contaminant levels in the environmental media of interest
was conducted to characterize the extent of contamination at the site. The next
step was to determine the exposure pathways by which people could come in
contact with sediment-derived contaminants from the river. The most complete
and current data sets were then evaluated to judge whether adequate QA/QC
protocols were followed. Next, based on the exposure pathways and sites of
exposures, the most current environmental data were used to determine
contaminant intake levels. Intake levels are essentially equivalent to
administered doses and are expressed in units of mg chemical per kg body weight
per day. These chemical intake levels were then integrated with noncarcinogenic
and carcinogenic toxicity data, obtained from verified and interim EPA sources, to
estimate the respective human health risks to people in the lower Saginaw River.
Finally, because of the number of assumptions that went into each step of the risk
assessment procedure, a qualitative listing of the uncertainties involved in these
assumptions was made.
4-2
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Site Character IzatI on
Determination of
Probable Exposure
Pathways
Rev I ew & Eva. I uat I on
or EX I st. I ng
Chemical Data
1
Tox1cIty Prof I Ies
Eva IuatI on of
Base I [ ne RI sks
Determination of
Exposure Point
Concentrations
I
DetermInatI on oT
Contamlnant
Intakes/Exposure
Risk/Hazard
Character IzatIon
Character IzatI on
of UncertaInty
Figure 4.1.
Components of baseline human health risk assessments.
4-3
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CHAPTER 5
EXPOSURE ASSESSMENT
5.1 INTRODUCTION
In this exposure assessment, the magnitude, frequency, duration, and route
of direct and indirect exposures of people to sediment-derived contaminants from
the Saginaw River AOC will be estimated. The transport of contaminants into
Saginaw Bay is also of concern, but it was beyond the scope of this risk
assessment to address human health risks in the entire bay.
5.2 EXPOSURE PATHWAYS
Exposures to contaminants in the Saginaw River can potentially occur via
three pathways: dermal contact, inhalation, and ingestion. Dermal contact
involves direct contact of the skin with either contaminated sediments, riverplain
soils, or overlying water. Inhalation of airborne vapors or dust may introduce
chemicals of potential concern into the respiratory system. Ingestion of
contaminants through the consumption of contaminated soils, sediment, or food
(e.g., fish, waterfowl) is potentially significant because of the direct transfer of
contaminants across the gut.
The lower 8 km of the Saginaw River was toured during 13-14 May 1991 to
observe firsthand how people may be exposed to sediment-derived contaminants
from the river. The weather was unseasonably warm (~32 °C or 90 °F) and partly
sunny during this period, and a number of outdoor activities were observed.
Informal conversations with local residents who were fishing, playing, or working
in the parks and marinas along the Saginaw River yielded helpful information
about how people utilize the river. In addition, a drive-by tour of the Saginaw
River from the city of Saginaw to the mouth of the river with Allan Brouillet,
MDNR, was particularly useful because he identified contaminated sites and
described industrial, municipal, and recreational uses of the river. Additional
conversations were held with Greg Goudy, RAP Manager (MDNR), Tim Kubiak
(U.S. Fish and Wildlife Service), John Giesy (Michigan State University), Mardi
Klevs, U.S. EPA Coordinator for the Saginaw Bay RAP (USEPA, Region V), and
Doug Bell (East Central Michigan Planning and Development Region) to obtain
information and/or contaminants data on the river.
The potential pathways by which people may be exposed to contaminants
from the lower Saginaw River are given in Table 5.1. These pathways were then
examined to determine whether they were complete or incomplete. A pathway is
complete if there is: 1) a source or chemical release from a source, 2) an exposure
point where contact can occur, and 3) an exposure route by which contact can
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TABLE 5.1. POTENTIAL PATHWAYS BY WHICH PEOPLE MAY BE
EXPOSED TO CONTAMINANTS FROM THE LOWER
SAGINAW RIVER
INGESTION OF CONTAMINATED:
- Surface Water
- Fish and Wildlife
- Drinking Water
- Sediments
- Contaminated Soils
DERMAL CONTACT WITH CONTAMINATED:
- Surface Water
- Sediments
- Soils
INHALATION OF AIRBORNE CONTAMINANTS
occur (USEPA, 1989a). Otherwise, the exposure pathway is incomplete if one of
these conditions is not met. Five pathways appear to be incomplete:
1) Ingestion of contaminated drinking water: the Saginaw
River is not used as a source of drinking water in the AOC.
Instead, the Bay City Water Supply System draws water from
a point 5.6 km out into Saginaw Bay just west of the mouth of
the Saginaw River. A study in 1985 indicated that the primary
drinking water standards were not exceeded for the raw water
supply for Bay City [USEPA (1985) cited in MDNR (1988)].
2) Ingestion of sediments: the ingestion of bottom sediments
does not appear to be occurring. Only the bottom sediments
near the shore would be accessible if, for example, a child
reached into the water and grabbed some sediments; however,
no evidence of this behavior was available.
3) Ingestion of contaminated soils: the ingestion of
contaminated soils from the river banks does not appear to be
occurring. The banks are either walled-off or are covered with
boulders and cement, thus limiting the opportunities for
human contact.
4) Dermal contact with contaminated soils: the river bank
soils are mostly inaccessible to people; thus, this pathway is
unlikely to be complete.
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5) Ingestion of certain types of wildlife: people are known to
consume snapping turtles and muskrats from the lower
Saginaw River area [T. Kubiak (U.S. Fish and Wildlife Service)
personal communication, 1991]. However, no data are
currently available on contaminant levels in these animals.
TABLE 5.2. COMPLETE EXPOSURE PATHWAYS IN THE LOWER
SAGINAW RIVER
• Ingestion of Contaminated Fish
• Ingestion of Contaminated Waterfowl
• Ingestion of Surface Water while Swimming or Playing in the
Water
• Dermal Contact with Water while Boating, Fishing, Swimming,
Wading, Jet-skiing, etc.
• Dermal Contact with Sediments while Entering or Leaving the
Water
• Inhalation of Airborne Contaminants
Although the six exposure pathways in Table 5.2 were considered complete
in the lower Saginaw River, not all of these exposure pathways may result in
significant human health risks. In particular, it was assumed that if insignificant
risks were associated with the ingestion of surface water while swimming, then
the risk associated with dermal exposure to surface water or sediments in the
Saginaw River would also be insignificant (see Appendix A for the reasons behind
this assumption). As described in Chapter 3, swimming does not occur frequently
in the Saginaw River. The estimated lifetime cancer risk for ingesting surface
water containing 1.72 x 10'5 mg/L PCBs from downstream of the Bay City WWTP
(~30 m upstream of the Bay Harbor Marina) was calculated as 2 x 10"10 (Appendix
A). This risk assumed that someone swam 3 days/yr for 0.5 hr/event over a period
of 30 years and ingested water at a rate of 5 x 10"2 L/hr. In addition, the cancer
risk was extrapolated over a period of 70 years to represent the estimated lifetime
carcinogenic risk to people. This risk estimate also assumed that PCBs were the
major source of carcinogenic risk. Based on this low carcinogenic risk estimate for
the ingestion of surface water, dermal exposures to water and sediments were also
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considered to be insignificant. A noncarcinogenic risk estimate could not be
calculated for this scenario because of the lack of an approved noncarcinogenic
toxicity value for PCBs.
In terms of inhaling airborne contaminants, it would be difficult to separate
out the contribution of contaminants from the river and that from industrial,
municipal, and background sources. In addition, the contribution of airborne
contaminants from the river may be small compared to other sources. Although
this exposure pathway may be complete, the currently available data set of
atmospheric contaminant levels in the Bay City area is inadequate to
quantitatively assess the risks to human health.
The only complete exposure pathways that will be considered for this risk
assessment are the consumption of fish and waterfowl. Noncarcinogenic and
carcinogenic risks will be determined for typical (i.e., average) and reasonable
maximum exposures (i.e., the maximum exposure that is reasonably expected to
occur at a site), as well as for exposures resulting from subsistence fishing and
hunting. The subsistence pathway was chosen because of anecdotal evidence
about people who consumed high quantities of fish or waterfowl. In one case, a
young woman in Veterans Park mentioned that her family ate fish from the river
nearly every day while she was growing up because they were poor. This
anecdotal evidence is supported by a fish consumption survey of Michigan anglers
during the off-season which showed that a small minority (<1%) of sample
household members consumed fish at subsistence levels (>132 g/day) (West et al.,
1989). In another case, T. Kubiak (U.S. Fish and Wildlife Service, personal
communication, 1991) knew of a man who consumed the breast meat of up to 60
ducks/year collected from the Saginaw River area. Thus, a small number of people
in the area may be relying on local fish and/or waterfowl for their main source of
protein.
5.3 DATA USED IN THE EXPOSURE ASSESSMENT
5.3.1 Data Sources
Data on contaminant levels in fish and waterfowl (ducks) were obtained
from the Michigan DNR and the U.S. Fish and Wildlife Service, respectively. In
addition, the water quality data used to determine the risk from ingesting surface
water also were obtained from the Michigan DNR. Other data containing
contaminant levels in water, sediment, and caged fish were obtained but not used
in this risk assessment. These data were not used because dermal exposure
pathways to surface water and sediment were not considered to be important, and
data from natural fish populations were used instead of short-term caged fish
exposures to the Saginaw River.
No assumptions about the temporal and spatial variability of contaminants
data in the Saginaw River will be made here. As mentioned in Chapter 3, heavy
5-4
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flooding occurred during the fall of 1986; this flooding may have scoured and
resuspended contaminated sediments in the river. Thus, pre- and post-1986 data
sets may differ due to this hydraulic event.
An effort was made to obtain data collected after the flood of 1986; however,
current data sets were not always available. The only waterfowl data (i.e.,
mallards and gadwalls) for the area were collected in 1985. The water quality
data used in the estimation of risk from ingesting surface water were collected at
a joint Michigan DNR/EPA sampling station from 7-9 August 1989. Two DNR
data sets were used to estimate contaminant levels in Saginaw River fish. Carp,
catfish, yellow perch, and walleye were collected from the mouth of the Saginaw
River on 17 May 1987 and were analyzed for mercury and organic contaminants.
A DNR data set for carp and walleye collected on 10 June 1986 (i.e., pre-flood)
were used for other metals. The DNR also collected fish samples from other
locations in Saginaw Bay, but these data were not used because the fish collected
at the mouth of the river contained higher concentrations of contaminants. Fish
have been collected from the Saginaw River for the ARCS program, and these data
may be incorporated into future updates of this risk assessment when they become
available.
5.3.2 Data Review
All of the data used in this risk assessment underwent a QA/QC review by
Lockheed Engineering and Sciences Company (Lockheed-ESC) under a contract
with the EPA Environmental Monitoring Systems Laboratory in Las Vegas, NV.
Lockheed-ESC could not conduct a complete review of the data because
insufficient QA/QC information was available. Thus, an assessment of the
accuracy of the data could not be made. All of the data used for this risk
assessment were either in the form of data sheets released from an analytical
laboratory (i.e., waterfowl data) or as a spreadsheet of contaminant concentrations
compiled by the Michigan DNR (i.e., fish and water quality data). Although
inadequate QA/QC information was available to fully assess the quality of the
data, the data were assumed to be of adequate quality for use in this risk
assessment.
5.3.3 Data Sets
Not all of the fish species sampled by the DNR for contaminants were used
in this risk assessment. Data were obtained for both bottom feeders (i.e., carp
and channel catfish) and open water feeders (i.e., yellow perch and walleye). Since
walleye are the preferred sport fish in the Saginaw River, this fish was selected
for inclusion in the risk assessment. Carp were also included since they generally
accumulate the highest levels of contaminants in water bodies due to their feeding
habits and high fat content. In addition, walleye and carp could be used to
generally represent pelagic and benthic fish species, respectively. The yellow
perch data were not used because all of the fish collected were very small (<0.1 kg)
5-5
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and would not be of an edible size. The channel catfish data were not used
because higher contaminant levels were observed in the carp. Thus, by
determining separate exposures for the consumption of carp and walleye, a range
of risk estimates could be determined for a variety of exposure scenarios.
The mean contaminant levels, number of samples, and standard deviations
of the walleye and carp data sets are given in Tables 5.3 and 5.4, respectively.
The walleye data were based on skin-on fillets, whereas the carp data were for
skin-off fillets. In cases where part of the sample set contained nondetected
values, one-half of the detection limit was used in determining the mean
concentration levels. Higher contaminant levels were observed in the carp as
would be expected for these benthic feeders.
Neither the carp or walleye were analyzed for 2,3,7,8-TCDD (dioxin),
another chemical of concern in the Saginaw River. The Tittabawassee River,
downstream of the Dow Chemical Company Midland facility, has been
contaminated with chlorinated dibenzo-p-dioxins and dibenzofurans (CDDs and
CDFs) (USEPA, 1988). Because the Tittabawassee River contributes about 50% of
the flow entering the Saginaw River, there is concern that fish could accumulate
CDDs and CDFs in the Saginaw River. The Michigan DNR set out cages
containing juvenile catfish to assess their uptake of 2,3,7,8-TCDD (MDNR, 1991a).
Twenty-one caged catfish that had been placed in the Saginaw River at Essexville
for 1 month during the summer of 1988 accumulated an average 2,3,7,8-TCDD
concentration of 3.1 ng/kg (MDNR, 1991a). The results of this caged fish study do
not indicate whether all contaminant concentrations reached equilibrium in the
fish tissue, nor does the study consider different uptake rates for different ages of
fish (e.g., juvenile versus adult). The uptake of PCBs did not appear to reach
equilibrium after 29 days (based on measurements taken after 4, 8, 16, and 29
days). Thus, other hydrophobic organic compounds, like 2,3,7,8-TCDD, may not
have reached equilibrium either. The caged fish study also does not take into
consideration that natural fish populations will be exposed to varying amounts of
contaminant concentrations in the water column as they travel through the river.
Due to these uncertainties in how representative the contaminants data from the
caged fish study corresponded to contaminant levels in natural fish populations in
the Saginaw River, the caged fish data for 2,3,7,8-TCDD were not used in this risk
assessment.
The waterfowl data for two mallards and four or five gadwalls were
combined to determine mean contaminant concentrations (Table 5.5); these data
were based on "roaster ready" (i.e., plucked and eviscerated) birds. Although these
waterfowl are migratory, they reside in the Saginaw River area from about April
through October-November. This area is on a major migratory flyway and several
waterfowl refuges are located near the Saginaw River and Bay; thus, it seemed
reasonable to assume that these waterfowl accumulated their greatest
contaminant burdens from the Saginaw River AOC, especially from their food
(e.g., invertebrates).
5-6
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TABLE 5.3.
MEAN CONTAMINANT CONCENTRATIONS IN WALLEYES
(SKIN-ON-FELLETS) COLLECTED FROM THE MOUTH OF
THE SAGINAW RIVER
Chemical
METALS
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Zinc
Mean
Cone. •
(mg/kg)
ND (0.010)
ND (0.100)
3 . OOE-01
ND (0.100)
1.22E-01
ND (0.100)
6.30E+00
N
3
3
3
3
9
3
3
SD
1.40E-01
7.68E-02
6.80E-01
AROMATIC HYDROCARBONS
Hexachlorobenzene
PCBs (total)*
ORGANOCHLORINE INSECTICIDES
Chlordane (total)**
Dieldrin
Heptacblor epoxide
p,p' DDD
p,p' DDE
p,p' DDT
PURGEABLES
Styrene (total)***
OTHER ORGANICS (NO TOXICITY VALUES)
Aldrin
beta-BHC
ci s—Nonachlor
trane-Konachlor
g-BHC (lindane)
Heptachlor
Heptachlorostyrene
Hexachlorostyrene
Mirex
Oct achlorostyrene
Oxy-chlordane
Pentachlorostyrene
PBB (Firemaeter BP-6)
PCS - A. 1242
PCB - A. 1248
PCB - A. 1254
PCB - A. 1260
Terphenyl
Toxaphene
1.06E-03
3.73E-01
6.33E-03
4.00E-03
ND (0.003)
1.53E-02
5.57E-02
4.11E-03
3.9SE-03
ND (0.005)
ND (0.005)
3.11E-03
5.78E-03
ND (0.005)
ND (0.005)
ND (0.001)
ND (0.001)
ND (0.005)
1.28E-03
ND (0.003)
2.67E-03
ND (0.005)
(0.025)
(0.0250
3.73E-01
ND (0.025)
ND (0.250)
ND (0.050)
ND
ND
1.21E-03
2.80E-01
2.30E-03
1.32E-02
4.53E-02
2.53E-03
2.53E-03
5.37E-03
1.09E-03
3.05E-03
2.80E-01
PCBs represent a group of 209 congeners that were manufactured by Monsanto under the
trade name Aroclor. Aroclors contain a mixture of congeners, and are named with numbers
which indicate the weight percent of chlorine in each mixture (e.g., Aroclor 1242 represents
42% chlorination of the biphenyl ring).
**
Total Chlordane was not reported; a-chlordane and g-chlordane were summed to represent
total chlordane.
**#
Total styrene was not reported; octachlorostyrene, pentachlorostyrene, hexachlorostyrene,
and heptachlorostyrene were summed to represent total styrene.
Detection limits reported in parentheses.
5-7
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TABLE 5.4.
MEAN CONTAMINANT CONCENTRATIONS IN CARP
(SKIN-OFF-FILLETS) COLLECTED FROM THE MOUTH OF
THE SAGINAW RIVER
Chemical
METALS
Chromium
Copper
Lead
Mercury
Nickel
Zinc
Mean
Cone.*
(mg/kg)
6.00E-03
ND (0.100)
4.40E-01
ND (0.100)
6.90E-02
ND (0.100)
1.30E+01
N
5
5
5
5
10
5
5
SD
2.00E-03
2.24E-01
4.01E-02
7.42E+00
AROMATIC HYDROCARBONS
Hexachlorobenzene
PCBs (total)
ORGANOCHLORINE INSECTICIDES
Chlordane (total) *
Dieldrin
Heptachlor epoxide
p,p' DDD
p,p' DDE
p,p' DDT
PDRGEABLES
Styrene (total)**
OTHER ORGANICS (NO TOXICITY VALUES)
Aldrin
beta-BBC
ci B-Nonachlor
trans-Nonachlor
g-BHC (lindane)
Heptachlor
Hept achl orosty rene
Hexachlorostyrene
Mirex
Octachlorostyrene
Oxy-chlordane
PentachlocoBtyrene
PBB (Firemaster BP-6)
PCS - A. 1242
PCB - A. 1248
PCS - A. 1254
PCB - A. 1260
Terphenyl
Toxaphene
5.35E-03
5.24E+00
4.23E-02
1.80E-02
1.53E-02
1.74E-01
7.47E-01
3.7SE-03
5.90E-02
ND (0.005)
ND (0.005)
1.94E-02
3.29E-02
ND (0.005)
ND (0.005)
2.40E-03
.65E-03
(0.005)
2.34E-02
5.70E-03
3.16E-02
(0.005)
(0.025)
(0.025)
.24E+00
ND (0.025)
ND (0.250)
(0.050)
1.
ND
ND
ND
ND
5.
ND
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
4.06E-03
3.89E+00
2.39E-02
1.11E-02
1.28E-01
6.00E-01
3.95E-03
1.84E-02
2.86E-02
1.87E-03
1.33E-03
1.24E-02
6.54E-03
2.31E-02
3.89E+00
Total Chlordane was not reported; a-chlordane and g-chlordane were summed to represent
total chlordane.
**
Total styrene was not reported; octachlorostyrene, pentachlorostyrene, hexachlorostyrene,
and heptachlorostyrene were summed to represent total styrene.
Detection limits reported in parentheses.
5-8
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TABLE 5.5.
MEAN CONTAMINANT CONCENTRATIONS IN
WATERFOWL COLLECTED FROM THE SAGINAW RIVER
AREA
Chemical
METALS
Arsenic
Cadmium
Lead
Mercury
Selenium
AROMATIC HYDROCARBONS
Hexacblorobenzene
PCBs (total)
ORGANOCHLORIKE INSECTICIDES
Dieldrin
Heptachlor epoxide
p,p' DDD
p,p' DDE
p,p' DDT
OTHER ORGANICS (NO TOXICITY VALUES)
cis-Nonacblor
trans-Konacblor
Endrin
Oct achl or o styrene
oxy— chlordane
Toxapbene
Mean
Cone. *
(mg/kg)
6.40E-02
4.10E-02
3.15E+00
4 . 80E-02
4 . 63E-01
ND (0.01)
1 . 73E+00
ND (0.01)
ND (0.01)
ND (0.01)
5 . 03E-01
ND (0.01)
ND (0.01)
ND (0.01)
ND (0.01)
ND (0.01)
ND (0.01)
ND (0.01)
N
6
6
6
6
6
7
7
7
7
7
7
7
7
7
7
7
7
7
SD
2.56E-02
4.16E-03
1 . 78E+00
1 . 92E-02
6.57E-02
9.50E-01
3.89E-01
Detection limits reported in parentheses. These birds were not analyzed for 2,3,7,8 TCDD.
5.4 EXPOSURE ASSESSMENT
5.4.1 General Determination of Chemical Intakes
Once the complete exposure pathways were identified and contaminant
concentrations for relevant media were obtained, an exposure assessment could be
conducted for each pathway. Exposures were normalized for time and body weight
to determine chemical "intakes," expressed in units of mg chemical per kg body
weight per day. For the ingestion of contaminated fish and waterfowl, intakes
represent the amount of chemical available for absorption in the gut. The general
equation for calculating chemical intakes is given in Table 5.6. Several variables
were used to determine intakes, including specific information about the exposed
population and the period over which the exposure was averaged.
Noncarcinogenic effects were averaged over the same time period as the exposure
duration [i.e., 9 years for typical exposures and 30 years for reasonable maximum
exposures (RME)]. Carcinogenic effects were averaged over a lifetime (i.e., 70
years). Intake variable values were selected so that the combination of all values
resulted in a conservative estimate of either the typical, reasonable maximum, or
subsistence exposure intakes.
5-9
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TABLE 5.6.
GENERIC EQUATION FOR CALCULATING CHEMICAL
INTAKES (USEPA, 1989a)
_ C X CR X EFD
BW X AT
where:
I
CR
EFD
BW
AT
Intake = the amount of chemical at the exchange boundary (mg/kg body weight-
day)
Chemical-Related Variables
Chemical Concentration = the average concentration contacted over the exposure
period (e.g., mg/L)
Variables that Describe the Exposed Population
Contact Kate = the amount of contaminated medium contacted per unit time or
event (e.g., L/day)
Exposure Frequency and Duration = how long and how often exposure occurs.
Often calculated using two terms, EF and ED, where
EF = exposure frequency (days/year)
ED = exposure duration (years)
Body Weight = the average body weight over the exposure period (kg)
Assessment-Determined Variables
Averaging Time = period over which exposure is averaged (days)
The contaminant intake levels were based on the consumption of raw fish
fillets and duck meat. At the present time, contaminant concentrations in raw
meat cannot be extrapolated to concentrations hi cooked products. For the past 20
years, Mary Zabik and coworkers from Michigan State University have been
investigating whether cooking methods can reduce pesticide and PCB residues in
meat and fish (Smith et al., 1973; Stachiw et al., 1988; Zabik, 1974, 1990; Zabik et
al., 1979, 1982). They found that PCB-contaminated chicken that had either been
stewed or pressure-cooked contained significantly lower PCB levels than raw meat
(Zabik, 1974), and roasting reduced the PCBs in contaminated turkey rolls by
5-10
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approximately 60% (Zabik, 1990). However, their results have not been consistent
between and within species of fish. In one instance, different cooking methods did
not result in significant changes in the level of PCBs, DDE, or DDT in cooked carp
fillets (Zabik et al., 1982). In another case, cooking resulted in reductions of
TCDD in restructured, deboned carp fillets (Stachiw et al., 1988).
In order to further assess how cooking techniques may alter the level of
contaminants in fish, the Michigan Department of Public Health and Michigan
State University have just begun a 2-year investigation (H. Humphrey, Michigan
Department of Public Health, personal communication, 1991). This study will be
done for a variety of sport fish in the Great Lakes (e.g., chinook and coho salmon)
for skin-on and skin-off fillets. The results of the Michigan study will be useful for
future human health risk assessments for determining better estimates of
contaminant levels in cooked fish. At the present time, the Michigan DNR
recommends that anglers use the following cooking techniques to reduce their risk
to contaminants: 1) trim fatty areas, 2) puncture or remove skin before cooking so
that fats drain away, or 3) deep-fry trimmed fillets in vegetable oil and discard the
oil (MDNR, 199 Ib). Some of these protocols could be applied to preparing ducks
too.
5.4.2 Intakes: Ingestion of Contaminated Fish
The equation used to estimate intakes of contaminants due to the ingestion
of contaminated fish is provided in Table 5.7. The parameter values used in that
equation are given in Table 5.8. Parameter values were obtained mostly from
recommended EPA sources. The exposure parameters used in the typical scenario
were assumed to be applicable to the general population of anglers and their
families in Bay City, whereas the reasonable maximum exposure scenario applied
to more recreational anglers and their families.
At the present time, specific information on fish consumption rates and
trends in the Saginaw River AOC is lacking. The Michigan Sport Anglers Fish
Consumption Survey, conducted by West and co-workers at the University of
Michigan, may give a better indication of ingestion rates of fish by Saginaw River
anglers than the default EPA parameter values that are applied to general
populations. West et al. (1989) found that, for their survey conducted during the
January-June 1988 time frame, the average fish consumption was 18.3
g/person/day with a standard deviation of 26.8 g/person/day; approximately 26% of
the sample household persons who ate fish consumed between 20-40 g/person/day,
whereas another 10% consumed between 40-75 g/person/day. From the survey
results, West et al. (1989) estimated a year-round average fish consumption rate of
19.2 g/person/day. This exposure assessment used a reasonable maximum
ingestion rate of 54 g/person/day; this number seems appropriate because it falls
within the upper 10% ingestion rate of the Michigan anglers. This exposure
assessment also assumed that the only contaminated fish ingested by local
residents came from the Saginaw River AOC. Because there was not any
5-11
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TABLE 5.7.
EQUATION USED TO ESTIMATE CONTAMINANT
INTAKES DUE TO INGESTION OF FISH OR WATERFOWL
intake = C x IR x FI X EF x ED
X AT
where:
Intake
C
IR
FI
EF
ED
BW
AT
Intake Rate (mg/kg-day)
Contaminant Concentration in Fish or Waterfowl (mg/kg)
Ingestion Rate Gig/day for fish; kg/meal for waterfowl)
Fraction Ingested from Contaminated Source (unitless)
Exposure Frequency (days/yr for fish; meals/yr for waterfowl)
Exposure Duration (yr)
Body Weight (kg)
Averaging Time (days)
quantitative information available on the fraction of fish ingested from the
Saginaw River (i.e., FI), conservative estimates were made. Chemical intake
values will be incorporated into the estimation of risk presented in Chapter 7;
thus, separate tables of intake values will not be presented here.
5.4.3 Intakes: Ingestion of Contaminated Waterfowl
The equation used to estimate ingestion of contaminated waterfowl is
provided in Table 5.7, and the parameter values used in that equation are given in
Table 5.9. More study assumptions were used with this exposure pathway than
for the consumption of fish. This is because fewer data are available on
consumption patterns of waterfowl than there are for fish. The exposure
frequency was based on the limited hunting season for ducks (6 October to 4
November 1990), the number of weekend days that someone might have time to go
hunting (11 days), the bag limit for ducks (3 ducks/day), and the portion of the bag
limit that a hunter would fill each day (assumed to be 50%). Thus, it was
assumed that a hunter would shoot and retrieve 16 ducks/season of which 8 ducks
would come from the Saginaw River area; this value was used for the reasonable
maximum exposure and subsistence hunting scenarios. Under typical exposures,
an individual was assumed to consume three servings of waterfowl per year of
5-12
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TABLE 5.8.
PARAMETERS USED IN ESTIMATING CONTAMINANT
INTAKES DUE TO INGESTION OF FISH IN THE LOWER 8
KM OF THE SAGINAW RIVER
Var.
IR
FI
EF
ED
BW
AT:
Units
kg/day
-
day/yr
yrs
kg
days
Value
Used
0.0192
0.054
0.13
0.1
0.25
0.7
350
9
30
70
3285
10950
25550
Comment
Typical: West et al. (1989)
Reasonable Maximum Exposure (RME): USEPA
(199 la)
Subsistence fishing: used the 95th percentile daily
intakes averaged over 3 days for consumers of fin
fish [Pao et al. (1982) cited in USEPA (1989a)]
Typical: study assumption
RME: study assumption
Subsistence fishing: study assumption
USEPA (1991a)
Typical: USEPA (1989a)
RME and Subsistence: USEPA (1989a)
50th percentile average for adult men and women
(USEPA, 1989b)
9 yrs x 365 days/yr (typical noncarcinogenic risk)
30 yrs x 365 days/yr (RME and subsistence
noncarcinogenic risk)
70 yrs x 365 days/yr (carcinogenic risk)
which one serving was assumed to come from the Saginaw River area. Chemical
intake values were calculated in the same manner as for the ingestion of fish.
5-13
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TABLE 5.9.
PARAMETERS USED IN ESTIMATING CONTAMINANT
INTAKES DUE TO INGESTION OF WATERFOWL IN THE
LOWER SAGINAW RIVER AREA
Var.
Units
Value
Used
Comment
IR
kg/meal
0.085
0.11
0.28
Typical: recommended consumption of poultry
(University of Georgia Extension Service, personal
communication, 1991)
RME: 50th percentile value given for beef (assumed
equivalent to waterfowl) [Pao et al. (1982) cited in
USEPA (1989a)]
Subsistence hunting: 95th percentile value given for
beef (assumed equivalent to waterfowl) [Pao et al.
(1982) cited in USEPA (1989a)]
FI
0.33
0.5
1
Typical: study assumption
RME: study assumption
Subsistence hunting: study assumption
EF
meals/yr
3
16
Typical: study assumption
RME and Subsistence: study assumption
ED
yrs
9
30
Typical: USEPA (1989a)
RME and Subsistence: USEPA (1989a)
BW
70
50th percentile average for adult men and women
(USEPA, 1989b)
AT:
days
3285
10950
25550
9 yrs x 365 days/yr (Typical noncarcinogenic risk)
30 yrs x 365 days/yr (RME and subsistence
noncarcinogenic risk)
70 yrs x 365 days/yr (Carcinogenic risk)
5-14
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CHAPTER 6
TOXICITY ASSESSMENT
6.1 TOXICITY VALUES
Two types of toxicity values were used in combination with exposure
estimates (i.e., chemical intake values) to calculate noncarcinogenic and
carcinogenic health risks. One toxicity value, the reference dose (R£D), provides
an estimate of the daily contaminant exposure that is not likely to cause harmful
effects during either a portion of a persons' life or his/her entire lifetime. The RfD
is the toxicity value used in evaluating noncarcinogenic effects. The other toxicity
value, the slope factor, is used in risk assessments to estimate an upper-bound
lifetime probability of an individual developing cancer as a result of exposure to a
particular level of a potential carcinogen. In addition, the EPA weight-of-evidence
classification scheme indicates the strength of evidence that the contaminant is a
human carcinogen (Table 6.1). Slope factors are typically calculated for potential
carcinogens in classes A, Bl, and B2 as well as for class C on a case-by-case basis.
A more detailed description of these toxicity values, summarized from "Risk
Assessment Guidance for Superfund. Volume 1. Human Health Evaluation
Manual (Part A)" (USEPA, 1989a), is given in Appendix B.
Chronic oral RfD values and oral slope factors were used for the food
ingestion pathways examined in this risk assessment. Toxicity values, which had
undergone an EPA review process, were obtained from the EPA's Integrated Risk
Information System (IRIS) data base. For chemicals lacking a "verified value,"
interim toxicity values were obtained from the Health Effects Assessment
Summary Tables (HEAST), if available. Table 6.2 lists the toxicity data used for
the chemicals of interest. Although RfD values are provided for known
carcinogens, it does not imply that these levels are protective against
carcinogenicity. This table also includes the form in which the chemical was
administered to the test animal or patient (e.g., drinking water, diet, or gavage)
for determination of the oral RfD. The endpoints of concern for evaluating
noncarcinogenic risks are listed in Table B-l of Appendix B.
6.2 LIMITATIONS
This risk assessment was limited by the current availability of toxicity
information. In some cases, toxicity values were not available for some of the
chemicals (e.g., lead) detected in the lower Saginaw River. Toxicity values were
not available for individual types of styrenes (e.g., octachlorostyrene) and
chlordanes (e.g., a-chlordane) but were available for total styrene and chlordane.
Consequently, detected values of heptachlorostyrene, hexachlorostyrene,
octachlorostyrene, and pentachlorostyrene were summed and assigned the toxicity
values for total styrene. Similarly, detected values of a-chlordane and g-chlordane
6-1
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TABLE 6.1.
EPA WEIGHT-OF-EVIDENCE CLASSIFICATION SYSTEM
FOR CARCINOGENICITY (USEPA, 1989a)
Group
Description
Bl or
B2
C
D
E
Human carcinogen
Probable human carcinogen
Bl indicates that limited human data are available
B2 indicates sufficient evidence in animals and
inadequate or no evidence in humans
Possible human carcinogen
Not classifiable as to human carcinogenicity
Evidence of noncarcinogenicity for humans
TABLE 6.2.
HUMAN HEALTH RISK TOXICITY DATA FOR CHEMICALS
OF INTEREST IN THE LOWER SAGINAW RIVER
Chemical
"METALS"
Arsenic
Cadmium
Copper
Mercury, methyl
Zinc
"AROMATIC HYDROCARBONS'
Haxachlorobenzeae
PCBs
"ORGBNOCHLORINE INSECT]
Chlordane
Dieldrin
Heptachlor epoxlde
p,p' ODD
p,p' DDE
p,p' DDT
" PXJRGEABLES "
Styrene
Sources:
Oral RfD
{mg/kg/day)
3. OE-04
5. OE-04
1.3E-03
3 . OE-04 pa
2 . OE-01
8. OE-04
[CIDES"
6.0E-05
5 . OE-OS
1.3E-05
S. OE-04
2. OE-01
a: IRIS (current a.
b: USEPA (1989c)
c
Form Source
diet a
water a
b
isonings a
b
diet a
diet a
diet a
diet a
diet a
gavage a
3 of 1/28/92)
larcinogenlc
Height of
Evidence
Class
A
Bl
D
D
D
B2
B2
B2
B2
B2
B2
B2
B2
Source
a
a
a
a
a
a
a
a
Oral Slope
Factor
I/ (mg/kg/day) S
1.60E+00
7.70E+00
1.30E+00
1 . SOE+01
9 . 10E+00
2. 4 OE-01
3.40E-01
3.40E-01
Source
a
a
a
a
a
a
a
a
6-2
-------
were summed to represent total chlordane. In other cases, toxicity values were
available for a particular metal species rather than for the total metal (e.g.,
mercury). In particular, methyl mercury was assumed to be the major form of
mercury present in this system.
6-3
-------
CHAPTER?
BASELINE EISK CHARACTERIZATION FOR THE LOWER SAGINAW RIVER
7.1 PURPOSE OF THE RISK CHARACTERIZATION STEP
The purpose of the risk characterization step is to combine the exposure and
toxicity estimates into an integrated expression of human health risk. This
section presents the calculated potential human health risks associated with the
consumption of contaminated fish and/or waterfowl from the Saginaw River AOC
under the no-action alternative. It is important to recognize that these calculated
risk estimates are not intended to be used as actual values. Risk assessment is a
regulatory process that provides risk managers with quantitative estimates that
are to be used for comparative purposes only. These risk estimates must be
interpreted in the context of all the uncertainties associated with each step in the
process. Some of the major uncertainties in this risk assessment are addressed in
the following chapter.
Three means of expressing the carcinogenic and noncarcinogenic risks of
adverse health effects are presented in this chapter. First, chemical specific risks
were estimated for each exposure pathway. Secondly, chemical specific risks were
added to estimate a cumulative pathway specific risk. Finally, risks were added
across all chemicals and relevant pathways to estimate the total human health
risks to people residing in the lower Saginaw River AOC.
7.2 QUANTIFYING RISKS
7.2.1 Determination of Noncarcinogenic Risks
Noncarcinogenic effects are evaluated by comparing an exposure level over a
specified time period with a RfD derived from a similar exposure period [otherwise
known as the hazard quotient (HQ)]. Thus, HQ = exposure level (or intake)/R£D.
Hazard quotients are expressed to one significant figure in a nonprobabilistic way.
In this risk assessment, HQ values were expressed to two significant figures for
each chemical; this was done to reduce round-up error when HQ values were
summed for each pathway. An HQ value of less than 1 indicates that exposures
are not likely to be associated with adverse noncarcinogenic effects (e.g.,
reproductive toxicity, teratogenicity, or liver toxicity). As the HQ approaches or
exceeds 10, the likelihood of adverse effects is increased to the point where action
to reduce human exposure should be considered. Owing to the uncertainties
involved with these estimates, HQ values between 1 and 10 may be of concern,
particularly when additional significant risk factors are present (e.g., other
contaminants at levels of concern). However, the level of concern does not
increase linearly as the RfD is approached or exceeded because RfDs do not have
7-1
-------
equal accuracy or precision; nor are RfDs based on the same severity of toxic
effects (USEPA, 1989a).
In assessing health risks, all HQ values are representative of long term
chronic exposures (i.e., exposures assumed to occur over a period of 9 or 30 years).
The sum of more than one HQ value for multiple substances and/or multiple
exposure pathways is the Hazard Index (HI). This assumption of additivity does
not account for any synergistic or antagonistic effects that may occur among
chemicals. For this risk assessment, no attempt was made to distinguish between
risk endpoints (e.g., target organs and related effects) when calculating the HI.
Thus, this expression of total risk may be extremely conservative; it would be
better to refine the HI to specific endpoints for HQ values greater than one.
Additional limitations of HQ values and the segregation of hazard indexes have
been described elsewhere (USEPA, 1989a).
7.2.2 Determination of Carcinogenic Effects
Carcinogenic risks are estimated as the incremental probability of an
individual developing cancer over a lifetime as a result of exposure to the potential
carcinogen. This risk is computed using average lifetime exposure values that are
multiplied by the oral slope factor for a particular chemical. Slope factors are
used to convert estimated daily intakes averaged over a lifetime of exposure
directly to the incremental risk of an individual developing cancer. The resulting
carcinogenic risk estimate is generally an upper-bound estimate, because slope
factors are usually based on upper 95th percentile confidence limits. The EPA
believes it is prudent public health policy to consider actions to mitigate or
minimize exposures to contaminants when estimated excess lifetime cancer risks
exceed the 10~5 to 10"6 range, and when noncarcinogenic health risks are estimated
to be significant (USEPA, 1988a).
Carcinogenic effects are summed for all chemicals in an exposure pathway
as well as for multiple pathways. This summation of carcinogenic risks assumes
that intakes of individual substances are small, that there are no synergistic or
antagonistic chemical interactions, and that all chemicals produce the same effect
(i.e., cancer). The limitations to this approach are discussed in detail elsewhere
(USEPA, 1989a).
7.3 HUMAN HEALTH RISKS IN THE LOWER SAGINAW RIVER
7.3.1 Typical and Reasonable Maximum Exposures
7.3.1.1 Noncarcinogenic Risks
Based on typical and reasonable maximum exposure levels over a 9- and a
30-year period, respectively, estimated noncarcinogenic risks were below levels of
concern (i.e., <1) for the individual consumption of walleye, carp, and waterfowl
7-2
-------
(Tables 7.1-7.6). Since some of the chemicals (e.g., PCBs) detected in these
animals do not presently have RfD values, it would be premature to state that no
noncarcinogenic risk exists from consuming fish or waterfowl from the lower
Saginaw River. The noncarcinogenic risk reported here is an estimated risk based
on currently available data and toxicity information and should not be construed
as an absolute risk.
7.3.1.2 Carcinogenic Risks
The estimated carcinogenic risks resulting from the consumption of walleye,
carp, or waterfowl were 1 x 10~5, 1 x 10'4, and 6 x 10~6, respectively, for typical
exposures (Tables 7.1-7.3). Carcinogenic risks increased by about one order of
magnitude for reasonable maximum exposures (i.e., 2 x 10"4, 3 x 10~3, and 2 x 10"
4) for consuming walleye, carp, or waterfowl, respectively (Tables 7.4-7.6). PCBs
accounted for most of this risk, and all of these risk estimates were at or above
levels of concern (i.e., >10~6). However, these risk estimates may have been
overestimated because the only available oral slope factor for PCBs was based on
Aroclor 1260. Aroclor 1260 is not representative of the kinds of PCBs found in the
lower Saginaw River. The primary Aroclor mixture detected in fish collected from
the Saginaw River was Aroclor 1254, whereas only total PCBs were reported for
waterfowl. Since Aroclor 1260 contains more highly chlorinated congeners (as well
as potentially toxic coplanar congeners) than Aroclor 1254, these risk estimates
may be overly conservative.
The carcinogenic risk from consuming either walleye or waterfowl was
nearly equivalent under typical and reasonable maximum exposure scenarios.
This similarity in risk does not mean that these animals accumulated the same
amount of contaminants in their body tissues. Different assumptions about food
consumption went into each exposure assessment, and the outcome of similar risk
values may have been a coincidence. In addition, these ducks are migratory, and
it is not possible to determine the exact geographic location where they
accumulated contaminants. However, since the Saginaw River lies on a major
migratory flyway and several waterfowl refuges are located in the Saginaw River
area, it is plausible that these ducks accumulated most of their contaminant
burden from local sources.
Carp had the worst level of carcinogenic risk for the typical and reasonable
maximum exposure pathways, as would be expected for these bottom feeders. In
addition, carp are fatty fish and hydrophobic organic contaminants (e.g., PCBs)
will preferentially accumulate in their lipids. Although fish advisories are in
effect against consuming carp and catfish in the Saginaw River, people often
disregard these advisories. Consequently, it is not unreasonable to assume that
some people may consume carp out of the Saginaw River. In addition, food
scientists are examining ways in which carp flesh can be deboned and
restructured to form fabricated seafood products (Stachiw et al., 1988); this is of
7-3
-------
particular interest to Michigan firms as a way of exploiting an underutilized fish
in Saginaw Bay.
There is a possibility that people who ingest, inhale, or have dermal contact
with certain PCB mixtures may have a greater chance of incurring liver cancer;
however, this statement is based on suggestive evidence rather than on verified
data. Studies with three strains of rats and two strains of mice have verified the
carcinogenic toxicity of PCBs through the occurrence of hepatocellular carcinomas
(IRIS data base retrieval for PCBs, 1992). This evidence was used to classify
PCBs as a probable human carcinogen.
7.3.2 Subsistence Food Pathways
7.3.2.1 Subsistence Anglers
Subsistence anglers increased their risks to contaminants by an order of
magnitude over recreational anglers in the reasonable maximum exposure
scenario. Although it is unlikely that a subsistence angler would eat carp or
walleye exclusively, these species can be used to obtain a range of risk values
resulting from the subsistence fishing scenario. The noncarcinogenic hazard
indexes for walleye and carp were 1 and 4, respectively (Tables 7.7 and 7.8). For
walleye, the noncarcinogenic risk was at a borderline level of concern and was due
mostly to the additive risk of methyl mercury and copper. For carp, only
heptachlor epoxide had an HQ value exceeding one; this chemical has been found
to cause increased liver-to-body weight ratio in both male and female beagle dogs.
The rest of the hazard index for carp was attributable to the combined risk
resulting from exposure to chlordane, dieldrin, and copper. Carcinogenic risks
ranged from 2 x 10"3 to 2 x 10"2 for the consumption of walleye and carp,
respectively (Tables 7.7 and 7.8); the carcinogenic risk was driven by exposure to
PCBs. The risks from this exposure pathway will not be added to other pathways
because this scenario only applies to a subgroup of the population.
7.3.2.2 Subsistence Hunters
For the subsistence hunter scenario, only the consumption of mallards and
gadwalls was considered because of the lack of data for other waterfowl. Although
noncarcinogenic risks were below levels of concern (i.e., <1), the carcinogenic risks
due to PCBs and p,p' DDE resulted in an estimated lifetime cancer risk of 1 x 10~3
(Table 7.9). These risk estimates may be even higher for fish-eating waterfowl
because they are more likely to accumulate higher levels of contaminants through
the food chain.
Because the waterfowl data used in this risk assessment were collected in
1985, a more thorough and up-to-date study of the extent of contamination in
waterfowl is needed to determine whether contaminant levels have changed. In
addition, some estimate of the proportion of contaminants in ducks resulting from
7-4
-------
exposure to contaminants in the Saginaw River would be helpful. The results of
this kind of study could be used by the Michigan DNR to determine whether
consumption advisories are needed for waterfowl. In addition, there is a need to
monitor contaminant levels in other wildlife (i.e., muskrats and snapping turtles)
that people are known to consume in this region (Tim Kubiak, U.S. Fish and
Wildlife Service, personal communication, 1991).
7.3.3 Additive Risks
Risks were added along exposure pathways (i.e., consumption offish and
waterfowl) in order to determine cumulative risks under typical and reasonable
maximum exposure scenarios. Since subsistence anglers and waterfowl hunters
were considered as separate subpopulations, their individual risks were not added
together.
Based on typical and reasonable maximum exposure levels, noncarcinogenic
risk levels were below levels of concern for both scenarios of the consumption of
walleye and waterfowl or carp and waterfowl (Table 7.10). As mentioned
previously, the noncarcinogenic risk of exposure to PCBs could not be determined
since a RfD value has not been verified for it. Thus, this risk estimate will
probably change as verified toxicity information becomes available. Carcinogenic
risks for the same exposure scenarios were of concern for both typical and
reasonable maximum exposures. The additive, upper-bound carcinogenic risk of
consuming walleye and waterfowl was 2 x 10~5 for typical exposures and 4 x 10"4
for reasonable maximum exposures, whereas the risk of consuming carp and
waterfowl was 1 x 10~4 for typical exposures and 3 x 10"3 for reasonable maximum
exposures (Table 7.10). Based on these upper-bound risk levels, regular
monitoring of contaminants in fish and waterfowl from the Saginaw River area
should be done to track changes in contaminant levels.
7-5
-------
TABLE 7.1.
RISK ASSOCIATED WITH THE CONSUMPTION OF
WALLEYE FROM THE LOWER SAGINAW RIVER BASED
ON TYPICAL EXPOSURE LEVELS
Chemical
"METALS"
Copper
Mercury, methyl
Zinc
9 yr
HQ
(Intake/RfD)
6.1E-03
1 . 1E-02
8.3E-04
Lifetime
Cancer
Risk
Carcinogeni c
Height of
Evidence
Class
D
D
"AROMATIC HYDROCARBONS"
Hexachlorobenzene
PCBs
"ORGANOCHLORINE INSECTICIDES"
Chlordane
Dieldrin
p,p' ODD
p,p' DOE
p,p' DDT
"PURGEABLES"
Styrene
3.5E-05
2.8E-03
2.1E-03
2.2E-04
5.2E-07
5.7E-09
9.7E-06
2.8E-08
2.2E-07
1.2E-08
6.4E-08
4.7E-09
B2
B2
B2
B2
B2
B2
B2
TOTAL
0.02
IE-OS
TABLE 7.2.
RISK ASSOCIATED WITH THE CONSUMPTION OF CARP
FROM THE LOWER SAGINAW RIVER BASED ON TYPICAL
EXPOSURE LEVELS
Chemical
9 yr
HQ
(Intake/RfD)
Lifetime
Cancer
Risk
Carcinogen! c
Weight of
Evidence
Class
"METALS"
Cadmium
Copper
Mercury, methyl
Zinc
"AROMATIC HYDROCARBONS"
Hexachlorobenzene
PCBs
3.2E-04
8.9E-03
6.0E-03
1.7E-03
1.8E-04
2.9E-08
1.4E-04
Bl
D
D
B2
B2
"ORGANOCHLORINE INSECTICIDES"
Chlordane
Dieldrin
Heptachlor epoxide
p,p' DDD
p,p' DDE
p,p' DDT
"PURGEABLES "
Styrene
1.9E-02
9.5E-03
3.1E-02
2.0E-04
7.8E-06
1.9E-07
9.7E-07
4.7E-07
1.4E-07
8.6E-07
4.3E-09
B2
B2
B2
B2
B2
B2
TOTAL
0.08
1E-04
7-6
-------
TABLE 7.3.
RISK ASSOCIATED WITH THE CONSUMPTION OF
WATERFOWL FROM THE LOWER SAGINAW RIVER
BASED ON TYPICAL EXPOSURE LEVELS
Chemical
"MEIALS"
Arsenic
Cadmium
Mercury, methyl
9 yr
HQ
(Intake/RfD)
7.0E-04
2 . 7E-04
5.3E-04
Lifetime
Cancer
Risk
Car cinogeni c
Weight of
Evidence
Class
A
Bl
D
"AROMATIC HYDROCARBONS"
PCBs
"ORGftNOCHLORINE INSECTICIDES"
p,p' DDE
5.6E-06
7.2E-08
B2
B2
TOTAL
0.001
6E-06
TABLE 7.4.
RISK ASSOCIATED WITH THE CONSUMPTION OF
WALLEYE FROM THE LOWER SAGINAW RIVER BASED
ON REASONABLE MAXIMUM EXPOSURE LEVELS
Chemical
30 yr
HQ
(Intake/RfD)
Lifetime
Cancer
Risk
Carcinogenic
Weight of
Evidence
Class
"METALS"
Copper
Mercury, methyl
Zinc
"AROMATIC HYDROCARBONS"
Hexachlorobenzene
PCBs
"ORGANOCHLORINE INSECTICIDES"
Chlordane
Dieldrin
p,p' ODD
p,p' DDE
p,p' DDT
"FURGEABLES"
Styrene
4.3E-02
7.5E-02
5.8E-03
2.5E-04
2. OE-02
1.5E-02
1.5E-03
3.7E-06
1.4E-07
2.3E-04
6.5E-07
5.1E-06
2.9E-07
1.5E-06
1.1E-07
B2
B2
B2
B2
B2
B2
B2
TOTAL
0.2
2E-04
7-7
-------
TABLE 7.5.
RISK ASSOCIATED WITH THE CONSUMPTION OF CARP
FROM THE LOWER SAGINAW RIVER BASED ON
REASONABLE MAXIMUM EXPOSURE LEVELS
Chemical
"METALS"
Cadmium
Copper
Mercury, methyl
Zinc
30 yr
HQ
(Intake/RfD)
2 . 2E-03
6.3E-02
4 . 3E-02
1.2E-02
Carcinogen! c
Lifetime Weight of
Cancer Evidence
Risk Class
Bl
D
D
"AROMATIC HYDROCARBONS"
Hexachlorobenzene
PCBs
"ORGANOCHLORINE INSECTICIDES"
Chlordane
Dieldrin
Heptachlor epoxide
p,p' DDD
p,p' DDE
p,p' DDT
"PURGEABLES"
Styrene
1.2E-03
1.3E-01
6.7E-02
2.2E-01
1.4E-03
5.5E-05
7.2E-07
3.2E-03
4E-06
3E-05
1E-05
3E-06
OE-OS
l.OE-07
B2
B2
B2
B2
B2
B2
B2
B2
TOTAL
0.5
3E-03
TABLE 7.6.
RISK ASSOCIATED WITH THE CONSUMPTION OF
WATERFOWL FROM THE SAGINAW RIVER AREA BASED
ON REASONABLE MAXIMUM EXPOSURE LEVELS
Chemical
30 yr
HQ
(Intake/RfD)
Lifetime
Cancer
Risk
Carcinogeni c
Weight of
Evidence
Class
"METALS"
Arsenic
Cadmium
Mercury, methyl
"AROMATIC HYDROCARBONS"
PCBs
"ORGANOCHLORINE INSECTICIDES"
p,p' DDE
TOTAL
7.3E-03
2.8E-03
5.5E-03
0.02
2.0E-04
2.5E-06
2E-04
A
Bl
D
B2
B2
7-8
-------
TABLE 7.7.
RISK ASSOCIATED WITH THE CONSUMPTION OF
WALLEYE FROM THE LOWER SAGINAW RIVER FOR
SUBSISTENCE ANGLERS
Chemical
"METALS"
Copper
Mercury, methyl
Zinc
30 yr
HQ
(Intake/RfD)
2.9E-01
5.1E-01
4.0E-02
Lifetime
Cancer
Risk
Carcinogen! c
Weight of
Evidence
Class
D
D
"AROMATIC HYDROCARBONS"
Hexachlorobenzene
PCBs
"ORGANOCHLORINE INSECTICIDES"
Chlordane
Dieldrin
p,p' DDD
p,p' DDE
p,p' DDT
"PURGEABLES "
Styrene
1.7E-03
1.3E-01
1. OE-01
l.OE-02
2.SB-OS
9.2E-07
1.6E-03
4.5E-06
3.5E-05
2.0E-06
1.OE-05
7.6E-07
B2
B2
B2
B2
B2
B2
B2
TOTAL
2E-03
TABLE 7.8.
RISK ASSOCIATED WITH THE CONSUMPTION OF CARP
FROM THE LOWER SAGINAW RIVER FOR SUBSISTENCE
ANGLERS
Chemical
30 yr
HQ
(Intake/RfD)
Lifetime
Cancer
Risk
Carcinogenic
Weight of
Evidence
Class
"METALS"
Cadmium
Copper
Mercury, methyl
Zinc
"AROMATIC HYDROCARBONS"
Hexachlorobenzene
PCBs
" ORGANOCHLORINE
Chlordane
Dieldrin
Heptacblor epoxide
p,p' DDD
p,p' DDE
p,p' DDT
"PDRGEABLES"
Styrene
TOTAL
INSECTICIDES"
1.5E-02
4.3E-01
2. 9E-01
8.2E-02
8.5E-03
8.9E-01
4.6E-01
1.5E+00
9.5E-03
3.7E-04
4.6E-06
2.2E-02
3.OE-05
1.6E-04
7.6E-05
2.3E-05
1.4E-04
6.9E-07
2E-02
Bl
D
D
B2
B2
B2
B2
B2
B2
B2
B2
7-9
-------
TABLE 7.9.
RISK ASSOCIATED WITH THE CONSUMPTION OF
WATERFOWL FROM THE SAGINAW RIVER AREA FOR
SUBSISTENCE HUNTERS
Chemical
"METALS"
Arsenic
Cadmium
Mercury, methyl
30 yr
HQ
(Intake /RfD)
3.7E-02
1 . 4E-02
2.8E-02
Lifetime
Cancer
Risk
Carcinogenic
Weight of
Evidence
Class
A
Bl
D
"AROMATIC HYDROCARBONS"
PCBs
"ORGftNOCHLORINE INSECTICIDES"
p,p' DDE
1.OE-03
1.3E-OS
B2
B2
TOTAL
0.08
1E-03
TABLE 7.10
SUMMARY OF NONCARCINOGENIC AND CARCINOGENIC
RISKS IN THE LOWER SAGINAW RIVER
Type of
Risk and Exposure
Individual Risks
Additive Risks
Walleye Carp
Waterfowl
Walleye +
Waterfowl
Carp +
Waterfowl
Noncaxcinogenic (HI)
Typical 0.02 0.08 0.001
Reasonable Maximum 0.2 0.5 0.02
Subsistence 1 4 0.08
0.02
0.2
0.08
0.5
Carcinogenic
Typical IE-OS 1E-04 6E-06
Reasonable Maximum 2E-04 3E-03 2E-04
Subsistence 2E-03 2E-02 1E-03
2E-05
4E-04
1E-04
3E-03
7-10
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CHAPTERS
CHARACTERIZATION OF QUALITATIVE UNCERTAINTIES
8.1 INTRODUCTION
A number of assumptions and estimated values are used in baseline risk
assessments that contribute to the level of uncertainty about the risk estimates.
For most environmental risk assessments, the uncertainty of the risk estimates
varies by at least an order of magnitude or greater (USEPA, 1989a). In this
chapter, a qualitative listing of the uncertainties associated with each step in the
risk assessment process will be made in order to determine the impact of these
uncertainties on the final risk assessment results.
8.2 QUALITATIVE LIST OF UNCERTAINTIES
8.2.1 Data Compilation and Evaluation
The data compilation and evaluation step is one part of the risk assessment
process where uncertainties arise. These uncertainties are listed below for the
following assumptions and statements.
• The available data for contaminant levels in fish, waterfowl,
and water samples collected from the Saginaw River were
representative of the true distribution of contaminants in the
Saginaw River AOC. A moderate level of uncertainty is probably
associated with this assumption. Additional sampling over a longer
period of time would be needed to look for any temporal or spatial
variability in contaminant levels, and to obtain a more representative
profile of contaminant concentrations in the media of interest.
• Some data studies may have been missed in the data
compilation step. This is unlikely since the Saginaw River/Bay
RAP Manager and U.S. Fish and Wildlife supplied the most recent
data available. Other research investigations are currently underway
in the Saginaw River, but their data were not available for inclusion
in this risk assessment.
• A complete QA/QC review of the data reports obtained for this
risk assessment could not be made because of a lack of
information supplied with the reports. Therefore, no information
about the accuracy of the data could be obtained. The uncertainty
associated with using this data is unknown, but may have been
minimized by using more up-to-date monitoring studies that generally
have more rigorous QA/QC plans than older studies.
8-1
-------
• Contaminant burdens in fish and waterfowl may decrease
depending on how the meat is prepared and cooked.
Contaminant levels may be reduced 10-70% depending on how the
meat is prepared and cooked (H. Humphrey, Michigan Department of
Public Health, personal communication). Because of this wide range,
the uncertainty associated with the resulting overestimation of risk is
not well established.
8.2.2 Exposure Assessment
A number of assumptions were made in the exposure assessment step of
this baseline human health risk assessment.
• An adequate assessment of complete and incomplete exposure
pathways was made. There is a low uncertainty that some
exposure pathways were either not identified or else were incorrectly
classified as a complete or incomplete exposure pathway.
• The exclusion of some complete exposure pathways (i.e.,
dermal exposure to water and sediments) from the exposure
assessment was justifiable because of the low probability that
these pathways would result in significant human health
risks. The uncertainty associated with this assumption is probably
low because the carcinogenic risk from ingesting PCB contaminated
water while swimming (3 events per year) was low (4 x 10"10), and
this pathway usually results in greater risk than the dermal exposure
pathways (for similar exposure frequencies).
• The complete exposure pathways chosen for the exposure
assessment represent the primary pathways by which people
in the lower Saginaw River were exposed to contaminants.
The pathways chosen were based primarily on observed activities and
on the availability of data. Data on contaminant levels in other types
of waterfowl (e.g., geese) and wildlife (e.g., snapping turtles) were not
available and represent incomplete exposure pathways. A medium
level of uncertainty is probably associated with not being able to
include these incomplete exposure pathways.
• The assumptions made about exposure frequency and
duration variables, body weight, life expectancy, and
population characteristics were appropriate. Many of these
assumptions (e.g., body weight, life expectancy, exposure frequency)
were based on EPA guidance (USEPA, 1989a,b; 1991a) and probably
have a low to moderate level of uncertainty associated with them. A
similar level of uncertainty may be attributed to professional
8-2
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judgments about the fraction offish or waterfowl ingested from
contaminated sources.
8.2.3 Toxicitv Values
The toxicity values (i.e., oral RfDs and oral slope factors) used in this risk
assessment were either verified values obtained from IRIS or interim values
obtained from other sources. RfDs and slope factors are subject to change as a
result of new information and updates of the IRIS data base. In addition,
chemicals will be added to IRIS in the future to expand the data base. Thus, this
risk assessment is "dated" to the toxicity values available at the time it was
prepared. Listed below are the uncertainties associated with using these toxicity
values.
• RfD values and slope factors have a certain amount of
uncertainty associated with them. Uncertainty and modifying
factors are incorporated into the calculation of RfDs (see Appendix B)
and take into consideration factors such as extrapolating data from
long-term animal studies to humans, etc. In general, RfD values
have an uncertainty range of about one order of magnitude. Since
slope factors represent an estimate of an upper-bound lifetime
probability of an individual developing cancer, these values are
already conservative. Thus, the amount of uncertainty associated
with slope factor values may be minimized.
• Toxicity values were not available for all of the chemicals
detected in the lower Saginaw River. For some chemicals, such
as lead, a risk characterization could not be done because toxicity
values have not been derived yet or else are under review by EPA
workgroups. In addition, a RfD value has not been listed yet for
PCBs in IRIS; thus, noncarcinogenic risks from exposure to PCBs
could not be determined. The uncertainty of not being able to include
some chemicals in this risk assessment is unknown.
• A conservative assumption for metal speciation in the lower
Saginaw River was made for mercury because toxicity values
for the total metal form were not available. Thus, toxicity
values for methyl mercury were used to represent the major form of
mercury. The use of this more toxic chemical species results in a
conservative estimate of risk. A moderate level of uncertainty is
probably associated with this uncertainty.
8.2.4 Risk Characterization
The uncertainties associated with the risk characterization step are listed
below.
8-3
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• Exposure intakes and toxicity values will remain the same
over the exposure duration. This assumes that human activities
and contaminant levels will remain the same over the exposure
duration, and that toxicity values will not be updated. A moderate to
high level of uncertainty is probably associated with this assumption
since it does not take into consideration the implementation of
remedial actions or the deposition of cleaner sediments over
contaminated sediments. Furthermore, toxicity values are frequently
updated in the IRIS data base as new information becomes available.
The level of uncertainty will probably increase with longer exposure
durations.
• Health risks are additive for both noncarcinogenic and
carcinogenic effects. The uncertainty associated with this
assumption is unknown. The toxicity exhibited by a mixture of
chemicals may involve synergistic and antagonistic effects. However,
no guidelines are available to judge the complex interactions a
mixture of contaminants may possess in terms of its potential toxicity
to humans. At the present time, standard risk assessment guidance
assumes that health risks are additive.
8.2.5 Summary
Based on the current information available, a complete description of the
level of uncertainty associated with all of the assumptions and data used in this
risk assessment cannot be made. This baseline human health risk assessment
was based on data and assumptions that, in reality, represent a snapshot in time.
One of the greatest sources of uncertainty in this risk assessment arises from
assuming that estimated risks will remain constant over the exposure duration
(i.e., 9 years for typical exposures and 30 years for reasonable maximum and
subsistence exposures). The overall uncertainty of the risk estimates probably
varies by over an order of magnitude. As additional data are collected from the
Saginaw River and as additional (or revised) toxicity values are generated, a
better estimate of human health risk can be determined for people living in this
area. Thus, updates of this risk assessment will probably reduce the level of
uncertainty associated with it.
8-4
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Bro, KM. 1989. Setting Priorities for Investigating Chemical Contaminants in
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Biphenyls in the Hudson River. Environ. Sci. Technol. 19:656-661.
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Foran, J.A. and D. VanderPloeg. 1989. Consumption Advisories for Sport Fish in
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Kononen, D.W. 1989. PCBs and DDT in Saginaw Bay White Suckers.
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Kuehl, D.W., P.M. Cook, A.R. Batterman, D. Lothenbach, and B.C. Butterworth.
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Dibenzofurans from Contaminated Wisconsin River Sediment to Carp.
Chemosphere. 16:667-679.
Malins, D.C., B.B. McCain, D.W. Brown, S-L. Chan, M.S. Myers, J.T. Landahl,
P.G. Prohaska, A.J. Friedman, L.D. Rhodes, D.G. Burrows, W.D. Gronlund,
and H.O. Hodgins. 1984. Chemical Pollutants in Sediments and Diseases
of Bottom-dwelling Fish in Puget Sound, Washington. Environ. Sci.
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Great Lakes and Environmental Assessment Section, Lansing, MI.
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Lansing, MI.
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August 1, 1988 to September 21, 1988. Michigan Department of Natural
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Oliver, B.G. and A.J. Niimi. 1988. Trophodynamic Analysis of Polychlorinated
Biphenyl Congeners and other Chlorinated Hydrocarbons in the Lake
Ontario Ecosystem. Environ. Sci. Technol. 22:388-397.
Pizza, J.C. and J.M. O'Connor. 1983. PCB Dynamics in Hudson River Striped
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Seelye, J.G., R.J. Hesselberg, and M.J. Mac. 1982. Accumulation by Fish of
Contaminants Released from Dredged Sediments. Environ. Sci. Technol.
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Concentrations of PCB and DDT Compounds in Chinook (Oncorhynchus
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Spigarelli, S.A., M.M. Thommes, and W. Prepejchal. 1983. Thermal and
Metabolic Factors Affecting PCB Uptake by Adult Brown Trout. Environ.
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p-dioxin Residue Reduction through Cooking/Processing of Restructured
Carp Fillets. J. Agric. Food Chem. 36:848-852.
Swackhamer, D.L. and R.A. Hites. 1988. Occurrence and Bioaccumulation of
Organochlorine Compounds in Fishes from Siskiwit Lake, Isle Royale, Lake
Superior. Environ. Sci. Technol. 22: 543-548.
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Outcome of Humans who Consumed Contaminated Great Lakes Fish: an
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Polychlorinated Biphenyl Levels in Turkey. School Food Service Res. Rev.
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Dieldrin and DDT in Lake Trout Cooked by Broiling, Roasting or
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APPENDIX A
IMPORTANCE OF OTHER COMPLETE EXPOSURE PATHWAYS IN THE
SAGINAW RIVER AREA OF CONCERN
The dermal exposure of people to water and sediments in the lower Saginaw
River was assumed to be insignificant based on the frequency with which these
exposures would take place and also in comparison to the estimated carcinogenic
risk from ingesting surface water while swimming or playing in the Saginaw
River. In this appendix, these assumptions and estimated risk estimates will be
described.
Dermal contact with Saginaw River sediments may occur infrequently
because there are no designated swimming areas along shore where someone could
wade into the water. Another place where dermal contact with sediments may
occur is at the boat ramps when people are putting in or taking out their boats;
however, most people would probably be wearing some kind of foot protection to
shield their feet from rocks, broken glass, etc. Dermal contact with water will
occur from a variety of activities in the river, especially boating and fishing.
Although dermal exposures to water and sediment appears to take place in
the Saginaw River, it is more difficult to determine the risks from these pathways
than from an ingestion or inhalation pathway. This is because toxicity values are
not developed specifically for dermal sorption, nor are absorption rates developed
well for contaminants. Thus, the estimation of exposure for the dermal pathway,
calculated as an absorbed dose, has a greater amount of uncertainty associated
with it than exposures that are based on an actual intake of contaminant into the
body. Based on dermal exposures calculated for other more contaminated ARCS
sites, dermal exposures to water and sediments in the Saginaw River are not
likely to result in significant noncarcinogenic and carcinogenic risks. In addition,
a greater risk is likely to be encountered due to the ingestion of surface water
from the Saginaw River than dermal exposures to it. This is because of the direct
intake of contaminants into the gut versus the absorption of contaminants (with
varying levels of permeability) across the skin interface.
The lifetime cancer risk for ingesting surface water from the lower Saginaw
River was estimated based on exposure and risk assessment guidance developed
for the EPA Superfund program (USEPA, 1989a). Based on the other carcinogenic
risk estimates determined in this report for the consumption of fish and/or
waterfowl, PCBs contribute nearly all of the risk. Consequently, PCBs were the
only contaminant chosen to estimate the carcinogenic risk from ingesting Saginaw
River water. The Michigan DNR and EPA sampled several stations in the
Saginaw River during 7-9 August, 1989 for water column PCBs (G. Goudy, MDNR,
personal communication, 1991). The surface water downstream of the Bay City
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WWTP (approximately 30 m upstream of the Bay Harbor Marina) contained 1.72 x
10 5 mg/L total PCBs. This concentration value was used in this risk estimate.
The carcinogenic risk estimate also assumed that a 70-kg person swam 3
days/year for 0.5 hr/event for 30 years and ingested water at a rate of 5 x 10"2
L/hr; the risk was then extrapolated over a 70-year period to represent a lifetime
carcinogenic risk. These assumptions were based, in part, on study assumptions
as well as on values recommended by the EPA Superfund program (USEPA,
1989a).
The estimated lifetime intake of ingesting PCBs in surface water under
these conditions was 2 x 10"11 mg/kg-day. This value multiplied by the oral slope
factor for PCBs (i.e., 7.7/mg/kg-day) yielded an estimated, upper-bound
carcinogenic risk of 2 x 10'10. The EPA believes it is prudent public health policy
to consider actions to mitigate or minimize exposures to contaminants when
estimated excess lifetime cancer risks exceed the 10"5 to 10"6 range (USEPA,
1988a). Based on this low carcinogenic risk estimate for the ingestion of surface
water, dermal exposures to water and sediments were assumed to be insignificant.
A noncarcinogenic risk estimate could not be calculated for this scenario because
of the lack of a RfD toxicity value for PCBs.
A-2
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APPENDIX B
HUMAN TOXICITY ESTIMATES FOR CONTAMINANTS PRESENT IN THE
SAGINAW RIVER AREA OF CONCERN
B.I TOXICITY ASSESSMENT
The toxicity assessment step is an integral part of the human health
baseline risk assessment. This step includes four tasks: 1) gather qualitative and
quantitative toxicity information for substances being evaluated, 2) identify
exposure periods for which toxicity values are necessary, 3) determine toxicity
values (i.e., reference doses (RfDs)) for noncarcinogenic effects, and 4) determine
toxicity values (i.e., slope factors) for carcinogenic effects (USEPA, 1989a). The
EPA has performed the toxicity assessment step for a limited number of chemicals
and these assessments have undergone extensive peer review. Therefore, the
toxicity assessment step of this study involves primarily a compilation of available
toxicity data.
Once a "verified" toxicity value is agreed upon by the EPA's toxicologists, it
is entered into the EPA's Integrated Risk Information System (IRIS) data base;
these values are updated as necessary. IRIS is the primary source of toxicity
information used in baseline risk assessments. The Health Effects Assessment
Summary Tables (HEAST) are the second most current source of toxicity
information and include both verified and interim RfDs and slope factors. Interim
values are used for chemicals that have not yet been approved by the EPA.
Specific EPA workgroups, such as the Carcinogen Risk Assessment Verification
Endeavor (CRAVE) and R£D Workgroups, are another source of interim toxicity
values. If toxicity values are not available in the aforementioned sources, then
interim values from other reports may be used.
This appendix summarizes pertinent toxicity information obtained from
IRIS and other sources for chemicals in the lower 8 km of the Saginaw River.
Also included in this appendix are brief descriptions of the most important toxicity
values used to evaluate noncarcinogenic and carcinogenic effects; these subsections
were summarized from the EPA guidance document: "Risk Assessment Guidance
for Superfund. Volume 1. Human Health Evaluation Manual (Part A)" (USEPA,
1989a).
B.I.I Noncarcinogenic Chronic Toxicitv
The RfD is the toxicity value used most often in evaluating noncarcinogenic
effects. The RfD is defined as an estimate of the daily exposure to the human
population that is likely to be without an appreciable risk of deleterious effects
during either a portion of the lifetime (i.e., subchromc RfD or "RfDs") or during the
B-l
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lifetime (i.e., chronic RfD or "RfD"). This toxicity value has an uncertainty range
of about an order of magnitude and includes exposures to sensitive subgroups in
the population. For each chemical, the RfD is calculated from the following
equation:
ofn _ NQAEL 01 LOAEL
RfD= UFXMF
where:
NOAEL = No-Observed-Adverse-Effect-Level
LOAEL = Lowest-Observed-Adverse-Effect-Level
MF = Modifying Factor
UF = Uncertainty Factor
The NOAEL and LOAEL are derived from dose-response experiments. The
NOAEL represents the highest exposure level tested at which no adverse effects
occurred (including the critical toxic effect), whereas the LOAEL represents the
lowest exposure level at which significant adverse effects occurred. Uncertainty
factors usually consist of multiples of ten, with each factor representing a specific
area of uncertainty included in the extrapolation from available data. An
uncertainty factor of ten is usually used to account for variation in the general
population so that sensitive subpopulations are protected. An additional ten-fold
factor is usually applied for each of the following extrapolations: from long-term
animal studies to humans, from a LOAEL to a NOAEL, and when subchronic
studies are used to derive a chronic RfD. A modifying factor, ranging from >0 to
10, is included as a qualitative assessment of additional uncertainties.
Table B-l includes the uncertainty and modifying factors, confidence
classifications, and critical effects of the contaminants examined for this risk
assessment. Uncertainty factors ranged from 3 to 1000, and either a low,
medium, or high level of confidence was given for these RfD values. Better
estimates of oral RfD values are needed to reduce these levels of uncertainty, and
IRIS is constantly being updated to refine RfD estimates.
B.1.2 Carcinogenicity
Human carcinogenic risks are usually evaluated for a chemical by using its
slope factor (formerly designated as a cancer potency factor) and corresponding
weight-of-evidence classification. These variables were listed in Table 6.2 for the
Saginaw River chemicals. Slope factors are estimated through the use of
mathematical extrapolation models, most commonly the linearized multistage
model, for estimating the largest possible linear slope (within 95% confidence
limits), at low extrapolated doses, that is consistent with the data. The slope
B-2
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TABLE B-l.
ORAL RfD SUMMARY FOR CHEMICALS LISTED IN IRIS AS
OF 28 JANUARY 1992
Chemical
UF
MF
Confidence
in Oral
RfD Critical Effects
"METALS"
Arsenic
Cadmium
Copper
Mercury, methyl
Zinc
3 1
10 1
10 1
Medium
High
Medium
Hyperpigmentation, keratosis, and possible
vascular complications in humans
Significant proteinuria in humans
Central nervous system effects in humans
"AROMATIC HYDROCARBONS"
Hexachlorobenzene 100 1
PCBs
"ORGANOCHLORINE INSECTICIDES"
Chlordane 1000 1
Dieldrin 100 1
Heptachlor epoxide 1000 1
p,p' ODD
p,p' DDE
p,p' DDT 100 1
"PURGEABLES"
Styrene 1000 1
Medium
Liver effects in rats
Low Regional liver hypertrophy in female rats
Medium Liver lesions in rats
Low Increased liver-to-body weight ratio in both male
and female dogs
Medium Liver lesions in rats
Medium Red blood cell and liver effects in dogs
factor is characterized as an upper-bound estimate so that the true risk to
humans, while not identifiable, is not likely to exceed the upper-bound estimate.
The weight of evidence classification for a particular chemical is determined
by the EPA's Human Health Assessment Group (HHAG). Chemicals are placed
into one of five groups according to the weight of evidence from epidemiological
studies and animal studies. These groups are designated by the letters A, B, C, D,
and E which represent the level of carcinogenicity to humans (see Table 6.1).
Quantitative carcinogenic risk assessments are performed for chemicals in Groups
A and B, and on a case-by-case basis for chemicals in Group C.
B.2 UNCERTAINTIES
A number of uncertainties are involved with using toxicity values for
estimating noncarcinogenic and carcinogenic risks. Some of these qualitative
uncertainties are listed below:
• Using dose-response information from healthy animal or human
populations to predict effects that may occur in the general
population, including susceptible subpopulations (e.g., elderly,
children),
• Using dose-response information from animal studies to predict
effects that may occur in human populations,
• Using NOAELs derived from short-term animal studies to predict
effects that may occur in humans during long-term exposures,
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Using dose-response information from effects observed at high doses
to predict the adverse health effects that may occur following
exposure of humans to low levels of the chemical in the environment,
and
Using a toxicity value derived from exposure to a particular chemical
mixture (e.g., Aroclor 1260) to represent the level of toxicity for other
similar chemical mixtures (e.g., Aroclor 1242, 1248, and 1254).
B-4
*D.S.GOVEBNMENT PRINTING OFFICE 1993 747-25O
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