United States Region 5 EPA-905/4-88-008
Environmental Protection 230 South Dearborn Street December 1988
Agency Chicago, Illinois 60604
&EPA Risk Management
Recommendations For
Dioxin Contamination At
Midland, Michigan
Final Report
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EPA-905/4-88-008
DECEMBER 1988
RISK MANAGEMENT RECOMMENDATIONS
FOR
DIOXIN CONTAMINATION AT MIDLAND, MICHIGAN
FINAL REPORT
Chicao. I 60604-3590
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION V
CHICAGO, ILLINOIS 60604
A 4,
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ACKNOWLEDGEMENTS
The Michigan Dioxin Studies and the resulting risk assessment and risk
management recommendations have been conducted and developed under the auspices
of the United States Environmental Protection Agency (USEPA) Region V Dioxin Task
Force. David Stringham was chairman of the Dioxin Task Force from its inception
in 1983 until 1986, when Howard Zar assumed the chair. Gary Amendola was USEPA's
project manager for the Michigan Dioxin Studies.
Amendola was the principal author of this report. Zar and Jonathan Barney
collaborated with Amendola in developing and refining the risk management
recommendations. Section III, a summary of the risk assessment, was initially
prepared by ICF-Clement Associates, Inc., and edited by Barney. Zar provided
Regional policy guidance and coordinated the extensive reviews by Region V, USEPA
Headquarters, and the Agency for Toxic Substances Disease Registry (ATSDR). This
report was reviewed by the following Region V staff: David Barna, Daniel
Bicknell, Donald Bruce, Dr. J. Milton Clark, David DeVault, Cynthia Fuller,
Carlton Nash, Walter Redmon, Vacys Saulys, Martin Trembly, and Carol Witt.
Comments were also received from Dr. Donald Barnes, Office of Pesticides and
Toxic Substances; from David Cleverly, Office of Research and Development (ORD);
and from other USEPA staff in ORD and the Office of Solid Waste, as well as from
ATSDR.
Many other current and former Region V staff have contributed or
participated in the investigations of dioxin contamination in the Midland,
Michigan, area over the past ten years. These include Curtis Ross, Director,
Central Regional Laboratory; Charles Elly, Marcia Kuehl, Francis Thomas, and
Kevin Bolger of the laboratory staff; and Charles Beier, Karl Bremen, Thomas
Daggett, Larry Fink, David Dolan, Philip Gehring, Joseph Good, Willie Harris,
John Perrecone, Vanessa Musgrave, and William Reynolds. Staff in a number of
USEPA laboratories have contributed to the development of analytical results.
Included are Robert Harless at the Environmental Monitoring Systems Laboratory,
Research Triangle Park, North Carolina; Dr. Douglas Kuehl and Brian Butterworth
at the Environmental Research Laboratory, Duluth, Minnesota; and Dr. Aubry Dupuy
and Danny McDaniel at the Pesticides Monitoring Laboratory, Stennis Space Center,
Mississippi. The staffs of the Michigan Departments of Natural Resources and
Public Health contributed significantly to the planning and implementation of
many aspects of the investigative programs.
USEPA acknowledges the cooperation and assistance of local government
officials, notably Mayor Joseph Mann and City Manager Clifford Miles, City of
Midland; the many citizens of Midland and surrounding communities who cooperated
in the studies and provided thoughtful comments; and the Dow Chemical Company in
conducting the field studies and for providing analytical services when
requested. Finally, USEPA wishes to acknowledge the efforts of Emilia Parker and
the staff of the Midland Public Library, Kurt Shaffner of Ingersoll Township, and
Winifred Oyen of the Midland County Health Department, who have maintained
information repositories for this undertaking.
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TABLE OF CONTENTS
I. INTRODUCTION 1
II. SUMMARY OF ENVIRONMENTAL AND POINT SOURCE INVESTIGATIONS ... 5
III. SUMMARY OF USEPA RISK ASSESSMENT 9
A. Hazard Identification 9
B. Dose-Response Assessment for 2378-TCDD 10
C. Dose-Response Assessment for CDD/CDF Mixtures 12
D. Exposure Assessment 12
1. Exposure to Ambient Air 12
2. Exposure to Contaminated Soil 12
3. Exposure Through Consumption of Contaminated Fish 13
4. Other Possible Routes of Exposure 13
E. Risk Characterization 15
IV. RISK MANAGEMENT 25
A. Point and Nonpoint Source Controls at Dow Chemical .... 27
1. Wastewater Discharges 27
2. Incinerator Emissions 29
3. Dust Suppression Program 29
4. Ground Water Contamination 30
B. Precautionary Measures Recommended to the Public 30
1. Tittabawassee River Fish 31
2. City of Midland Surface Soils 32
C. Point Source and Environmental Monitoring Programs .... 33
1. Dow Chemical Point Source Monitoring 33
a. Wastewater discharge monitoring 33
b. Incinerator emission testing 33
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TABLE OF CONTENTS (continued)
2. Proposed Supplemental Environmental and 34
Food Chain Monitoring Programs
a. Environmental Monitoring Programs 34
(1) Ambient air monitoring program 34
(2) Soil and dust monitoring program 34
(3) Tittabawassee River sediments 34
b. Food Chain Monitoring Program 35
(1) Tittabawassee River fish 35
(2) Other aquatic life, avian, and 35
animal monitoring program
(3) Dairy sampling 35
(4) Garden vegetable sampling 35
REFERENCES 37
APPENDICES
A. Response to Public Comments
B. 1988 Tittabawassee River Fish Monitoring Program
C. 1987 Midland Vegetable Sampling Program
VI
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I
INTRODUCTION
Environmental Risk Assessment is a scientific process in which facts and
assumptions are integrated and used to estimate the potential for adverse effects
on human health or the environment that may result from exposures to specific
pollutants. The risk assessment protocol followed by the United States
Environmental Protection Agency (USEPA) includes the following components (USEPA
1986):
o Hazard Identification
o Dose-Response Assessment
o Human Exposure Assessment
o Risk Characterization
The hazard identification is a qualitative risk assessment, establishing the
potential toxicity or hazard of a particular substance. The dose-response
assessment defines the relationship between the dose of a substance and the
probability of induction of adverse health effects. The human exposure
assessment is conducted to estimate, in a specific situation or setting, what are
the probable and maximum human exposures to a substance (i.e., dose rates),
including evaluations of potential high risk groups. In risk characterization,
the results of the dose-response and human exposure evaluations are combined to
estimate potential adverse health impacts, with a review of the uncertainties in
the overall analysis. The risk assessment for dioxin contamination in and around
Midland, Michigan, is fully described in a companion report to this document,
Risk Assessment for Dioxin Contamination at Midland. Michigan (USEPA 1988a),
referred to hereafter as the Risk Assessment.
Risk management, on the other hand, is a decision-making process which can
involve much more than consideration of the results of a risk assessment. Often,
such factors as technological feasibility, economic information about costs and
benefits, statutory requirements, and public concerns can heavily influence risk
management. This report sets out risk management recommendations for
contamination with 2,3,7,8-tetrachlorodibenzo-p-dioxin (2378-TCDD) and other
polychlorinated dibenzo-p-d1oxins (CDDs) and polychloMnated dibenzo-furans
(CDFs) in and around Midland, Michigan (see Figure 1-1).
On April 28, 1988, USEPA conducted a public meeting in Midland to present,
and accept public comment on, the results of the risk assessment and a series of
proposed risk management actions. The public comment period extended until June
3, 1988. This report has been revised to include a summary of the public
comments and responses (Appendix A); recent information regarding contaminant
levels in game fish from the Tittabawassee River (Appendix B); limited data for
homegrown vegetables in Midland (Appendix C); revised risk estimates based upon
the recent fish contaminant levels; and final risk management recommendations.
The outline and content of this report are similar to those in the public review
draft report, Proposed Risk Management Actions for Dioxin Contamination at
Midland. Michigan (USEPA 1988b).
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Dow Midland Site
Figure 1-1
Midland, Michigan Area and
Dow Midland Facility
Sources: USGS (1973), DOW (1984)
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The reader should keep in mind that CDD/CDF contamination at Midland is not
a new issue. Many of the remedial actions necessary to minimize human exposures
to CDDs and CDFs have already been taken, or are being taken, by Dow Chemical in
compliance with various statutory or regulatory requirements. Accordingly,
factors such as economic costs and benefits have not been considered in great
detail since most of the costs to Dow Chemical have been, or are being,
incurred. There are, however, questions of technical achievability, regarding
certain additional remedies, for which there are currently no answers. In these
circumstances the risk management recommendations outline a process to develop
the necessary information to answer questions about technical achievability and
related costs.
USEPA developed the final risk management recommendations presented in this
report taking into account the Risk Assessment, all of the public comments, the
current status of ongoing remedial actions, and the recent fish contaminant data
presented in Appendix B. We believe that these are reasonable and necessary
measures which can be implemented through existing regulatory mechanisms at the
state and federal levels. USEPA believes that the measures relating to the Dow
Chemical plant can most effectively be implemented through existing air, solid
waste, and water pollution control programs managed by MDNR and USEPA Region V.
Measures relating to fish consumption advisories can most effectively be managed
through the existing framework established by the Michigan Department of Public
Health.
This document provides: (1) a brief summary of the results of a number of
studies undertaken by the USEPA, the State of Michigan, and Dow Chemical Company;
(2) a summary of possible health risks to Midland area residents resulting from
exposures to CDDs and CDFs; (3) actions for minimizing emissions and discharges
to the environment from Dow Chemical; (4) recommendations for people living in
the Midland area on how to minimize their exposures to CDDs and CDFs, and thus
the possible health risks associated with those exposures; and (5) additional
monitoring programs, some of a continuing nature, for the purposes of
establishing long-term trends in emissions and discharges of CDDs/CDFs, and to
document changes in environmental contamination for the more significant human
exposure routes. As noted above, a summary of public comments and responses for
the Risk Assessment and proposed Risk Management Actions is presented in
Appendix A.
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II
SUMMARY OF ENVIRONMENTAL AND POINT SOURCE INVESTIGATIONS
Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (CDDs
and CDFs, respectively) are closely-related families of highly toxic and
persistent organic chemicals which have been formed as unwanted by-products in
some commercially significant chemical reactions, during high temperature
decomposition and combustion of certain chlorinated organic chemicals, and
through other reactions involving chlorine and organic materials.
Dow Chemical has manufactured over 1,000 different inorganic and organic
chemicals at the Midland facility. The manufacture of chlorinated phenols and
herbicides, and the formulation of pesticides and other products derived from
them have been major operations at the Dow Midland facility for many years.
Commercial production of chlorinated phenols began in the 1930's and continued at
substantial levels into the late 1970's. Dow Chemical reports that only two
chlorinated phenolic products—2,4-dichlorophenol and 2,4-dichlorophenoxyacetic
acid (2,4-D)—are currently manufactured at Midland (Dow 1984). Incineration has
been practiced since at least the 1930's with varying levels of emission
controls. Currently, Dow Chemical operates a rotary kiln incinerator for
combustion of both hazardous and non-hazardous wastes. Prior to 1980, a "tar
burner" was also operated at the site to dispose of still bottoms and other
hazardous chemical residuals (Dow 1988a).
In June 1978, Dow Chemical informed the Michigan Department of Natural
Resources (MDNR) and USEPA that rainbow trout exposed to a mixture of Dow
Chemical's treated effluent prior to discharge from outfall 031 to the
Tittabawassee River accumulated significant levels of 2,3,7,8-tetrachloro-
dibenzo-p-dioxin (2378-TCDD), the most toxic of the CDD/CDF compounds (Dow 1978).
Supplemental analyses of edible portions of Tittabawassee River catfish,
previously collected in 1976 downstream of the discharge from the Dow Chemical
facility, showed concentrations of 2378-TCDD ranging from 70 to 230 parts per
trillion (ppt). Dow Chemical also reported 2378-TCDD analyses for catfish, carp,
rock bass, crappie, and perch collected in 1977. The results of these studies
prompted the Michigan Department of Public Health (MDPH) to issue a formal
advisory in June 1978 warning against consumption of any fish collected from the
Tittabawassee River downstream of Dow Dam (MDNR 1978). The advisory remained in
effect until March 1986, when the MDPH modified it to apply only to catfish and
carp, after reviewing 1985 monitoring data showing that walleyes and other game
fish were contaminated at levels below a 10 ppt criterion established by MDPH
using its own risk assessment/risk management methodologies. (The advisory has
since been strengthened twice, in April and December 1988. See section IV(B)(1)
below.)
In response to the Dow Chemical findings, the MDNR and USEPA, Region V
undertook a number of investigations during the period 1978-1981 to determine
whether, or to what extent, the Dow Chemical operations at Midland contributed to
2378-TCDD contamination in Tittabawassee River fish. These investigations
included a caged fish bioaccumulation study and an experimental large volume
wastewater effluent sampling program conducted in September 1981. The results of
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those studies conclusively demonstrated that the Dow Chemical wastewater effluent
was a significant source of 2378-TCDD to the Tittabawassee River. The
preliminary results from those studies were released in March 1983 with a series
of recommendations for more comprehensive CDD/CDF studies in Midland and
elsewhere (USEPA 1983a). Most of those recommendations were subsequently
incorporated into USEPA's Dioxin Strategy and National Dioxin Study (USEPA 1983b
1987a).
Also, in March 1983, the State of Michigan made a formal request to the then
acting administrator of USEPA for assistance in conducting a comprehensive
multi-media investigation of CDD/CDF emissions and discharges from Dow Chemical
and CDD/CDF contamination in the Midland area (MDNR 1983). In the spring and
summer of 1983, USEPA collaborated with the Michigan Departments of Agriculture,
Natural Resources, and Public Health, and the Michigan Attorney General's Office
in planning for the requested studies. At about the same time, local
environmental groups petitioned USEPA pursuant to Section 21 of the Toxic
Substances Control Act for broad scale toxic pollutant investigations of an
eight-county area in mid-Michigan including Midland County (ECOMM and Foresight
1983). Although USEPA subsequently denied that petition, some of the requested
investigations were within the scope of those being planned by Region V and the
State agencies for the Midland area (USEPA 1983c).
The studies conducted by USEPA and the State were formally called the
Michigan Dioxin Studies and included the following major elements:
1. Supplemental fish and sediment sampling in the Tittabawassee River.
2. Surface soil sampling at Dow Chemical, in the city of Midland, and at
comparison sites.
3. Evaluation of public and private potable water supplies and Dow Chemical
brine operations.
4. Supplemental Dow Chemical wastewater and sewer system sampling.
5. Incinerator emissions testing and limited ambient air monitoring.
These investigations included analyses of CDDs and CDFs and other toxic
pollutants that might be present, and were consistent with the then-evolving
USEPA Dioxin Strategy. Since the Dow Chemical Plant was considered to have
operations within Tiers 1, 2, 3, 4, and 6 of the Dioxin Strategy, funding for the
studies was provided principally through the Comprehensive Environmental
Response, Compensation and Liability Act (CERCLA or Superfund) program. All Tier
1 and 2 facilities in the Dioxin Strategy were studied through Superfund.
In 1983, Dow Chemical initiated its own independent point source investi-
gation of CDDs and CDFs at the Midland Plant. That work included comprehensive
surface soil sampling at the plant, untreated and treated process wastewater
sampling, incinerator emissions testing and limited ambient air monitoring (Dow
1984). Dow Chemical has also conducted supplemental incinerator emissions
testing in 1987 (Dow 1987a), supplemental monitoring of Tittabawassee River fish
in response to a consent order with USEPA (U.S. v. Dow 1984), and twice-monthly
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monitoring for 2378-TCDD in the treated process wastewater discharge to the
Tittabawassee River (Dow 1984-1988).
Studies by Dow and USEPA revealed widespread contamination of the surface
soil at the Midland facility (on the average, less than 0.5 ppb 2378-TCDD)
(Dow 1984, USEPA 1985a). Several small areas within the facility were found to
be more highly contaminated (2-50 ppb). USEPA studies indicated lower-level
contamination of the soils throughout the community with CDDs/CDFs (average
<0.1 ppb 2378-TCDD) (USEPA 1985a). Since these studies were undertaken, Dow has
been ordered to remediate areas of high on-site contamination to prevent the
spread of contaminated soil (USEPA 1985c). The sources of the on-site soil
contamination appear to have been leaks or fugitive emissions from one or more of
the production processes discussed above and fallout from the waste incinerator.
The off-site soil contamination has been attributed to airborne emissions of
CDDs/CDFs from the waste incinerator, wind-borne transport of contaminated soil
from the facility, and possibly past fugitive emissions from production
operations.
Studies by Dow Chemical indicate the hazardous waste incinerator is the most
significant current air emission source at the Midland Plant (Dow 1984).
Emissions testing by USEPA in 1984 (Trembly and Amendola 1987) and Dow Chemical
in 1987 (Dow 1987a) indicated substantially reduced emission levels from those
measured in 1983 by Dow.
Significant levels of CDDs/CDFs have also been detected in the effluent from
the Dow wastewater treatment system to the Tittabawassee River (0.01-0.05 ppt
2378-TCDD in 1984; <0.002 to 0.008 ppt 2378-TCDD currently) (Dow 1984-1988). The
current lower levels are the direct result of the 1984 Final Order of Abatement
issued by the Michigan Water Resources Commission (MWRC) and the MDNR, requiring
Dow Chemical to install a final effluent filtration system and implement a
plant-wide program to reduce CDDs/CDFs (MWRC 1984). Studies conducted by USEPA,
the U.S. Food and Drug Administration (USFDA), the MDPH and MDNR, and Dow
Chemical between 1979 and 1985 revealed that 2378-TCDD persisted at levels of
concern in Tittabawassee River fish, despite shutdown of the Dow Midland
production facilities for the manufacture of 2,4,5-trichlorophenol, the
derivative 2,4,5-T herbicide, and pentachlorophenol, chemicals known to be
contaminated with CDDs and CDFs. Sampling and analysis of Tittabawassee River
sediments in 1978 and 1984 failed to detect 2378-TCDD, but did establish the
presence of a number of other CDDs and CDFs in patterns indicating Dow Chemical
as the most probable source. The levels found were not judged high enough to
warrant removal of sediments, but the extent of the data was not sufficient to
rule out the possibility of more highly contaminated areas elsewhere. (Amendola
and Barna 1986).
Recent data collected by the MDNR, MDPH, USEPA and Dow (MDNR 1988, USEPA
1988c, Dow 1988c) indicate 2378-TCDD levels in game fish have declined from
levels found in 1983-1985 (see Appendix B). Data collected in 1985 and 1988 also
show that Tittabawassee River fish collected downstream of Dow Chemical are
contaminated with several other organic chemicals, the most significant being
PCBs. Dow Chemical is not believed to be a significant source of PCBs.
Chemicals other than CDDs/CDFs were not found in any other media (air, soil,
etc.) at levels that would warrant specific consideration in this report.
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The USEPA has compiled the data from its testing programs (USEPA 1985a,
Barna and Amendola 1985, Amendola and Barna 1986, Trembly and Amende!a 1987) and
all available data from other investigations and has prepared a comprehensive
Risk Assessment (USEPA 1988a) for individuals living in the Midland area. A
summary of the Risk Assessment, with revised risk estimates based upon the recent
fish contaminant data, is presented in Section III.
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Ill
SUMMARY OF USEPA RISK ASSESSMENT
In keeping with guidelines established by USEPA and by the National Academy
of Sciences and other scientific advisory bodies, USEPA's Risk Assessment for
Midland, Michigan, involved four distinct activities: hazard identification,
dose-response assessment, exposure assessment, and risk characterization. As
noted earlier, the first step, hazard identification, defines the basic
toxicologic properties of CDDs/CDFs and identifies the most important toxic
effects observed both in studies of animals exposed to these compounds and in
human epidemiological studies. Dose-response assessment, the second step,
consists of further review and analysis of these studies in order to develop an
understanding of the relationships between the amount of CDOs/CDFs to which
humans may be exposed and the likelihood and severity of adverse health effects.
The exposure assessment consists of a review of the available data regarding
the levels of CDDs/CDFs found in and around Midland and the development of
quantitative estimates of the amount of CDDs/CDFs to which Midland area residents
may be exposed. Finally, risk characterization involves the combination of the
dose-response information and the exposure estimates to derive an assessment of
the levels of risks faced by the various exposed populations in Midland.
Also included in the Risk Assessment are discussions of the extent of
uncertainty associated with the exposure and risk estimates. For each route of
exposure (inhalation of ambient air, contact with contaminated soils, etc.) more
than one exposure scenario was developed using ranges of assumptions about
environmental levels of CDDs/CDFs and exposure-related behavior of the exposed
populations.
A. HAZARD IDENTIFICATION
Chlorinated dibenzo-p-dioxins (CDDs) and dibenzofurans (CDFs) constitute a
family of over 200 related chemical compounds (congeners) with varying chemical,
physical, and toxicologic properties. The congener that appears to be the most
toxic and has generally raised the greatest health concerns is 2,3,7,8-tetra-
chlorodibenzo-p-dioxin, abbreviated as 2378-TCDD.
Experimental studies with 2378-TCDD in animal systems have demonstrated a
variety of toxic effects resulting from exposure to this compound (USEPA 1985b).
These effects include carcinogenesis, cancer promotion, reproductive and
teratogenic effects, immunotoxic effects, thymus atrophy, liver damage, and
effects on the skin and thyroid. Limited toxicological testing of other
CDDs/CDFs has demonstrated that several of these compounds cause similar
toxicological effects, but that higher doses are generally required to cause
effects of comparable magnitude to those induced by 2378-TCDD.
USEPA has determined that the critical end points of concern for purposes of
assessing risks associated with exposure to CDDs/CDFs in the Midland area are
cancer and reproductive and teratogenic effects. In addition, under certain
conditions, toxic effects on the liver and immune system may also be significant
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in risk assessment. The evidence for these health effects is discussed in more
detail in Chapter II of the Risk Assessment.
B. DOSE-RESPONSE ASSESSMENT FOR 2378-TCDD
The evidence for the carcinogenic (cancer-causing) action of 2378-TCDD is
provided mainly by several long-term studies of laboratory animals exposed to the
substance. On the basis of these animal studies and associated factors, USEPA
has concluded that 2378-TCDD is an animal carcinogen and should be regarded as a
probable human carcinogen (USEPA 1986). Applying its established procedures,
USEPA used the experimental animal data to estimate an upper bound on the cancer
potency factor (referred to as "qi*") for 2378-TCDD of 1.6 x 1CT4 (pg/kg/day)""1
over a 70-year lifetime. Note: "pg" stands for picogram = lO"*2 gram.
While the above value remains USEPA's current position on the potency of
2378-TCDD, and, therefore, was the one used in preparing the Risk Assessment, a
formal reassessment of its derivation is under way (USEPA 1988d). Final results
of that reassessment are not expected for at least several months.
2378-TCDD has been shown to be teratogenic and to cause adverse reproductive
effects in a number of animal species, including subhuman primates (USEPA 1985b).
USEPA has examined the data in detail and has selected a value of 1 pg/kg/day as
the Reference Dose (RfD) for 2378-TCDD (USEPA 1987b). This value is used in the
risk assessment to evaluate the potential for non-cancer effects resulting from
long-term exposures to CDDs/CDFs. USEPA is also concerned about doses which
pregnant women might ingest over a short period at a critical time in the
development of the fetus. USEPA therefore has adopted a "health advisory" (HA)
dose-level of 300 pg/kg/day for protection against teratogenic effects. This HA
dose-level is appropriate for comparison with single-dose or single-day
exposures, whereas the RfD of 1 pg/kg/day is more appropriate for comparison with
long-term or lifetime exposures.
Although USEPA has determined that reproductive/teratogenic effects are the
critical noncarcinogenic toxic effects for dose-response assessment of 2378-TCDD,
based upon a review of several animal studies, USEPA has concluded that the RfD
of 1 pg/kg/day also is appropriate to protect against possible liver damage in
all populations experiencing long-term exposures to CDDs/CDFs (USEPA 1985b). For
short-term exposures (a few days to a few weeks), the animal data support an HA
for liver effects of 28 pg/kg/day, and, for single-dose or single-day exposures,
an HA of 280 pg/kg/day has been adopted, which is close to the single-dose HA
derived for reproductive/teratogenic effects. The toxicologic parameters used in
the Risk Assessment are summarized in Table III-l.
The RfD, which is used for assessing toxic effects other than cancer, can
be defined as an estimate (with uncertainty spanning perhaps an order of
magnitude) of the daily exposure (daily dose, e.g., in pg/kg/day) of a human
population (including sensitive subpopulations) that is likely to be without an
appreciable risk of adverse health effects even if exposure occurs daily during a
lifetime.
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TABLE III-l
TOXICOLOGIC PARAMETERS FOR CDDs/CDFs
USED IN THE MIDLAND, MICHIGAN, RISK ASSESSMENT
Toxicologic End Point
Type of Parameter
Parameter Value
Cancer
Teratogenesis/Reproductive
Effects:
Dose-Response Slope
Parameter (95%
upper confidence
limit)
1.6xlO~4
(pg/kg/dayT1
C"B2"]*
long-term exposures
single-dose exposures
Hepatotoxicity (liver
effects):
long-term exposures
short (10-day) exposures
single-dose exposures
RfD
HA
RfD
HA
HA
1 pg/kg/day
300 pg/kg/day
1 pg/kg/day
28 pg/kg/day
280 pg/kg/day
*In USEPA's weight-of-evidence classification system for carcinogens, B2
indicates that the evidence for carcinogenicity in animals is "sufficient",
while the human evidence for carcinogenicity is "inadequate." B2 is placed in
quotation marks, because the classification was for 2378-TCDD alone, whereas
total TEQs are being evaluated here, in accordance with USEPA interim science
policy.
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All of the toxicological dose-response estimates described above—cancer
potency, Reference Dose, and Health Advisory—were derived by extrapolating
animal test results to humans through the use of mathematical models and/or
application of uncertainty factors. This approach is necessary because accurate
data on human exposures to CDDs/CDFs, and on the resulting toxic effects, are not
available. USEPA believes that its methods for dose-response assessment are
conservative, and that the estimates so derived are unlikely to be exceeded when
humans are exposed to CDDs/CDFs. The Agency recommends that the estimates be
used for assessing risks and for decision-making related to the protection of
human health, keeping in mind the uncertainties inherent in their derivation.
C. DOSE-RESPONSE ASSESSMENT FOR CDD/CDF MIXTURES
Studies have generally shown that most CDDs and CDFs cause similar effects
to those caused by 2378-TCDD in the same bioassay systems, but that 2378-TCDD is
the most potent. USEPA has adopted as interim science policy the "toxicity
equivalence factor (TEF)" approach for use until sufficient additional data are
available to derive a more accurate procedure that can be scientifically
validated (USEPA 1987c). The TEF approach uses correlations between structure
and chemical activity to estimate the toxicity of any CDD/CDF mixture with regard
to both carcinogenic and noncarcinogenic endpoints. The result is expressed as
an equivalent amount of 2378-TCDD.
The TEF approach was used in the Risk Assessment to convert reported
quantities of CDDs/CDFs in environmental samples to "2378-TCDD toxicity
equivalents" (TEQs), which were then treated as if they were concentrations of
2378-TCDD. The TEF approach and its limitations are discussed in more detail in
Part II.C of the Risk Assessment.
D. EXPOSURE ASSESSMENT
Quantitative estimates were developed for the significant routes of exposure
to CDDs/CDFs in the Midland area as outlined below.
1. Exposure to Ambient Air
Two scenarios were developed to estimate exposures of Midland area residents
to CDDs/CDFs in ambient air. The "fenceline case" represents exposure for a
hypothetical individual residing near the Dow Chemical plant boundary at a
location downwind (according to the prevailing wind direction) from the
incinerator and production areas; the "residential area case" represents
exposures further away from the plant, in the more densely populated areas of
Midland to the north of the facility. For each scenario, average exposure (dose
rate) estimates were derived for four specific age ranges as well as for an
entire lifetime. The procedures used to develop the air exposure estimates and
their limitations and associated uncertainties are described in detail in Section
III.B of the Risk Assessment.
2. Exposure to Contaminated Soil
The "lower estimate" and "upper estimate" of exposure were developed using
lower and higher estimates for (1) the frequency of exposure, (2) the amounts of
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soil ingested as a result of outdoor activities, and (3) the fraction of
CDDs/CDFs absorbed into the body from the ingested soil. Individual lifetime
segment and lifetime average estimates of exposure/dose rates were derived as for
air. The methods used to derive these estimates and their limitations and
associated uncertainties are discussed in detail in Section III.C of the Risk
Assessment.
3. Exposure Through Consumption of Contaminated Fish
The five exposure scenarios which have been developed (see Table III-2) vary
with regard to the amounts and types of fish consumed (all fish is assumed to
come from the Tittabawassee River except for half of the fish eaten by the
"general consumer"). Long-term consumption rates were used to estimate 70-year
lifetime CDD/CDF ingestion or dose rates to assess excess cancer risks and for
comparison with the RfD for non-cancer effects. Single-meal COD/CDF ingestion
rates also were developed to compare with the short-term HA values. Note that
the 1988 fish contaminant data indicate a decline in the 2378-TCDD TEQ
concentration exceeding 50 percent from the average value for game fish collected
in the 1983-1987 period (see Appendix B).
The exposure assessment established that consumption of contaminated fish
was clearly the dominant route of CDD/CDF exposure for some populations, with
exposure and intake levels being as much as several orders of magnitude higher
than those associated with other exposure routes. The methods used to develop
these estimates and their limitations and associated uncertainties are described
in detail in Section III.E of the Risk Assessment.
4. Other Possible Routes of Exposure
Several other possible routes of human exposure were evaluated in the Risk
Assessment (Section III.F). Consumption of ground water or surface water were
found unlikely to be associated with CDD/CDF exposure. Other routes that were
considered were exposure to potentially-contaminated house dust and exposure of
infants through breast milk.
Since no measurements were available of the levels of CDDs/CDFs in household
dust in Midland, no quantitative estimates of exposure through this route could
be conducted. It was concluded, however, based upon studies of other situations
where exposures to toxic pollutants in house dust had been measured, that this
route of exposure could be comparable to some of the other exposures that were
quantifiable.
Similarly, CDD/CDF levels in breast milk from the Midland area have not been
measured. However, a simple pharmacokinetic model (Smith 1987) was employed to
estimate intakes for nursing infants.
Finally, sufficient data are not available which would allow a quantitative
assessment of the exposures from consumption of CDDs/CDFs contained in or
deposited on home-grown vegetables. An initial sampling program by USEPA in the
fall of 1987 did not indicate uptake of CDDs/CDFs by root crops grown in Midland
soils, but neither the range of vegetables sampled nor the overall number of
samples was large enough to yield final conclusions.
13
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TABLE III-2
FISH CONSUMPTION SCENARIOS
FOR TITTABAWASSEE RIVER, MICHIGAN
Scenario
Consumption Rate
Type of Fisha
Plausible Maximum Consumer
High Sports Fisherman
Long-term: 100 g/dayb
(6.7 Ibs/month)
Single Meal: 255 gc
50% Bottom feeders
t 50% Game fish
Great
Genera
-- Level 1
-- Level 2d
Lakes Consumer^
1 Consumer
Long-term: 100 g/dayb
(6.7 Ibs/month)
Single Meal : 255 gc
Long-term: 48 g/daye
(3.2 Ibs/month)
Single Meal: 113 gf
Long-term: 16 g/dayn
(1.1 Ibs/month)
Single Meal : 113 gf
Long-term: 7.8 g/dayi
(0.52 Ibs/month)
Single Meal : 113 gf
100% Game fish
100% Game fish
100% Game fish
50% Game fish
+ 50% Clean fish
aAll fish are assumed to be from the Tittabawassee River except "clean" fish
which are assumed to be free from COD/COF contamination. The fish tissue
concentrations used in the Risk Assessment (1983-1987 data) and those found in
the most recent sampling are provided below (all are means):
Type of Fish
Partial TEQs (ppt)
1983-1987 Data
TEQs (ppt)
1988 Data
Bottom feeders 58
Game fish 13
Clean fish (by definition) 0
(Only game fish sampled)
5.7
0
b90th percentile consumption rate for a cohort of Lake Michigan sports fishermen
who ate more than 24 Ibs of fish per year (Humphrey et al. 1976).
C90th percentile fish meal size (USDA 1982).
dReferred to in Risk Assessment as "Median Sports Fisherman."
eMedian for a cohort of Lake Michigan sports fishermen who ate more than 24 Ibs
of fish per year (Humphrey 1983).
fMedian fish meal size (USDA 1982).
SAdded following completion of Risk Assessment, using the information and
procedures contained in that document.
hFDA-estimated upper 90th percentile consumption rate of freshwater fish in the
Great Lakes area (USEPA 1984a).
^Average consumption of "finfish other than canned, dried, and raw" (USDA 1982).
Figures for Tittabawassee River fish only would be 3.9 g/day and
0.26 Ibs/month).
14
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E. RISK CHARACTERIZATION
Quantitative estimates of the risks associated with CDD/CDF exposures by the
routes just discussed were developed by combining the exposure and intake
estimates with the toxicologic parameters discussed in the Dose-Response
Assessment. For long-term exposures to air and soil contamination, two measures
of risks were developed, an upper-bound estimate of the additional cancer risks
associated with lifetime exposures at the predicted levels, and a Hazard Index
(HI) for non-carcinogenic effects.
For a given exposure scenario, an HI of less than 1.0 indicates that
exposures are not likely to be associated with adverse non-cancer effects
(reproductive toxicity, teratogenicity, or liver toxicity). If the HI 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, HI 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).
The risk levels predicted for each of the three major exposure routes are
summarized in Tables 111-3 through 111-6. For air exposures, (see Table 111-3)
the predicted incremental, lifetime cancer risks (upper bound) range from 5 x
10~6["B2"] to 6 x 10~5["B2"], depending upon the exposure scenario and the method
used to calculate TEQs. Many of the His for the various age groups and scenarios
are less than 0.1, and all but one are less than 1.0.
The upper-bound excess cancer risk estimates associated with exposures to
contaminated soil (see Table 111-4) are slightly lower than those for the air
route; estimated lifetime risks are 5 x 10~7 ["B2"] for the "lower estimate"
scenario and 1 x 10~5 ["B2"] for the "upper estimate". The His for non-cancer
effects are likewise lower than for air exposures.
Both the cancer and non-cancer risks calculated for CDD/CDF exposures via
contaminated fish are much greater than for the other two pathways (see Table
111-5). For comparison purposes, risk estimates are presented for the 1983-1987
fish contaminant data used in the Risk Assessment and for the walleye data
collected in 1988. Generally speaking, the 2378-TCDD TEQ concentrations for the
walleyes have decreased by somewhat more than half. Thus, the risk estimates are
reduced by about a factor of two, assuming the same consumption patterns.
Upper-bound estimates of incremental lifetime cancer risks range from 6 x 10~5
["B2"] for the "general consumer" (1988 walleye data) to as high as 1 x 10 ^
C"B2"] for the "plausible maximum consumer" (1983-1987 carp and catfish data).
Although 1988 catfish and carp data are not available, it is likely that the
concentrations of 2378-TCDD TEQs are lower than those measured in 1983-1987. The
estimated risks would be reduced accordingly. The His approach or exceed 10 for
several of the scenarios, based upon the 1988 walleye data and taking into
account the estimated increased exposures of small children and breast-fed
*Defined as the ratio of the estimated average daily dose to the previously
defined RfD (or HA for single or short-term exposures).
15
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TABLE 111-3
RISK CHARACTERIZATION FOR INHALATION OF CDOs/CDFs
IN AMBIENT AIR IN MIDLAND, MICHIGAN
(September 1984 Samples)
Upper-Bound Cancer Riskb Hazard Indexc(Lona Terrrn
Exposure Scenario3 A-Methodd B-Methodd A-Methodd B-Methodd
1. Fenceline Case:
Infants 0-1 year — — 0.4 0.1
Children:
1-6 years — — i o.4
6-12 years — — 0.7 0.3
Adults (12-70) -- - 0.3 0.1
Lifetime 6xlO~5["B2"]e 2xlO~5["B2"]
2. Residential Area
Infants 0-1 year — — 0.05 0.02
Children:
1-6 years — — 0.2 0.08
6-12 years — — 0.1 0.06
Adults (12-70) — — 0.05 0.02
Lifetime lxlO~5["B2"] 5xlO~6 ["B2"]
aFrom Section II.B.6*. All exposure estimates assume 24 hr/day exposure to
outdoor concentrations, long-term residence (lifetime for cancer risks).
bUpper-bound estimate of additional lifetime cancer risk, obtained by multiplying
exposure estimate in Table 111-12* by cancer potency factor of 1.6 x 10~4
(pg/kg/day)"1 and multiplying by relative bioavailability factor of 1.8 (see
Section IV.C*).
cRatio of exposure estimate in Table 111-12* to RfD of 1 pg/kg/day, multiplied by
relative bioavailability factor of 1.8, for exposures lasting several months or
more. Shorter exposures (a few days to a few weeks) would yield indices about
28-times lower.
dA-Method assumes all Pe-, Hx- and Hp-CDDs and CDFs are 2378-substituted.
B-Method assumes all congeners within these groups are equally prevalent (see
Part II*).
eln USEPA's weight-of-evidence classification system for carcinogens, B2 indi-
cates that the evidence for carcinogenicity in animals is "sufficient", while
the human evidence for carcinogenicity is "inadequate." 82 is placed in
quotation marks, because the classification was for 2378-TCDD alone, whereas
total TEQs are being evaluated here, in accordance with USEPA interim science
policy.
*In Risk Assessment
16
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TABLE 111-4
RISK CHARACTERIZATION FOR INGESTION OF CDDs/CDFs
IN SOIL IN MIDLAND, MICHIGAN
(October 1983 Samples)
Upper-Bound Lifetime Hazard Indexc
Exposure Scenario3 Cancer Riskb (Long Term)
Lifetime Average Exposure:
1. Lower Estimate:
Infants 0-1 year — 0.02
Children:
1-6 years — 0.03
6-12 years — 0.009
Adults (12-70) — 0.0003
Lifetime average 5xlO~7["B2"]d
2. Upper Estimate:
Infants 0-1 year — 0.5
Children:
1-6 years — 0.6
6-12 years — 0.2
Adults (12-70) — 0.01
Lifetime average lxlO~5["B2"]
Assumptions and parameters are listed in Table 111-19*. Note that the estimates
do not include children with pica. Individuals with this disorder could incur
risks 10-fold higher.
^Upper-bound estimate of additional lifetime cancer risk, obtained by multiplying
lifetime average TEQs dose rate from Table II1-20* by cancer potency factor of
1.6 x 10~4 (pg/kg/day)~i, and multiplying by relative bioavailability factor of
1.8 (see Section IV.C*).
cRatio of adult TEQs dose rate from Table 111-20* to RfD of 1 pg/kg/day,
multiplied by relative bioavailability factor of 1.8.
dln USEPA's weight-of-evidence classification system for carcinogens, B2
indicates that the evidence for carcinogenicity in animals is "sufficient",
while the human evidence for carcinogenicity is "inadequate." B2 is placed in
quotation marks, because the classification was for 2378-TCDD alone, whereas
total TEQs are being evaluated here, in accordance with USEPA interim science
policy.
*In Risk Assessment
17
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TABLE III-5
RISK CHARACTERIZATION FOR INGESTION OF CODs/COFsa
IN FISH FROM THE TITTABAWASSEE RIVER, MICHIGAN
Long-Term Exposures
Exposure Scenario^
Plausible Maximum Consumer
(bottom + game fish)n
High Sports Fisherman
(game fish only)
-- Level 1
-- Level 2
Great Lakes Consumer
(game fish only)
General Consumer
(game + clean fish)
Upper-Bound Cancer Riskd»e
1983-1987 Data 1988 Data
lxlO~2["B2"]9 NA
Hazard Indexb»e.f
4xlO~3["B2"]
2xl
-------
infants (see footnote b, Table 111-5). The estimated single-meal CDD/CDF intake
levels result in His approaching 10 for meals comprising the maximum
concentration bottom feeder from the 1983 fish collection (see Table III-6). (It
is not likely that carp or catfish in the Tittabawassee River now contain
concentrations of that magnitude.) All other single meal His are less than 1.0.
Note that the risk levels presented in Tables 111-5 and 111-6 are for
consumption of Tittabawassee River fish contaminated with CDDs and CDFs. Fish
from the river also are contaminated with other toxic chemicals, most
importantly PCBs. Table III-7 presents a summary of estimated, upper-bound,
excess, lifetime cancer risks resulting from 2378-TCDD TEQs and PCBs using the
Sports Fisherman, Great Lakes Consumer, and General Consumer fish consumption
scenarios set out in Table III-2. These data indicate that the risks associated
with consumption of Tittabawassee River fish are dominated by PCBs as opposed to
CDDs and CDFs. The estimated additional lifetime cancer risk (upper bound) for a
person eating a single quarter-pound meal_ger month of game fish from the
Tittabawassee River would be about 5 x 10~^ (1 in 2,000). The estimated cancer
and non-cancer risks associated with the other contaminants found in the fish are
not significant when compared to those associated with the PCBs and CDDs/CDFs.
The cancer risk estimates calculated for all of the exposure routes are
summarized in Table III-8, and the His for non-cancer effects are summarized in
Table III-9 (CDDs/CDFs only). Because of the overall uncertainty in the exposure
and risk estimates, cancer risk estimates are displayed only to the nearest order
of magnitude. Non-cancer hazard indices less than 0.1 are rounded to "<0.1" in
order to simplify the table. As previously noted these estimates are upper-bound
values that are unlikely to be exceeded by actual risks to humans.
19
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TABLE 111-6
RISK CHARACTERIZATION FOR INGESTION OF CDDs/CDFsa
IN FISH FROM THE TITTABAWASSEE RIVER, MICHIGAN
Single Meal (Bolus) Exposures5
Fish Meal Size
255 g (9 oz)
Tvoe of Fish
Bottom-feeder
(catfish/carp)
— maximum
— mean
TEOsc
1983-1987
Data
690 ppt
58 ppt
1988
Data
NAf
NA
Hazard Indexd»e
1983-1987 1988
Data Data
8 NA
0.7 NA
Game Fish
(walleye, etc.)
— maximum 39 ppt 16 ppt 0.5 0.2
— mean 13 ppt 5.7 ppt 0.2 <0.1
113 g (4 oz) Bottom-feeder
(catfish/carp)
— maximum 690 ppt NAf 4 NA
— mean 58 ppt NA 0.3 NA
Game Fish
(walleye, etc.)
— maximum 39 ppt 16 ppt 0.2 <0.1
— mean 13 ppt 5.7 ppt <0.1 <0.1
aPCBs, found in the fish, add to the Hazard Index values (see Appendix B*).
bFrom data in Section III.E.2* and Tables 111-30*, 111-31*, and 111-32*. Also see
Table 111-2 in this document.
cNote that for 1983-1987 data, all estimates of intake are "partial TEQs,"
including only 2378-TCDD, other TCDDs, HxCDDs, HpCDDs, and 2378-TCDF (1983-1987
data). For 1988 data, estimates are based upon complete TEQs.
dRatio of bolus dose from Table 111-32* to single-dose HA of 300 pg/kg/day.
eNote that Hazard Indices will be about 2-3 times higher for small children (Table
111-33*).
f!988 carp and catfish contaminant data not available.
*In Risk Assessment
20
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TABLE 111-7
COMPARISON OF RISKS FROM INGESTION OF CDDs/CDFs AND PCBsa
IN FISH FROM THE TITTABAWASSEE RIVER, MICHIGAN
(Fish Collected in 1988)
Long-Term Exposures
Exposure Scenario13 Upper-Bound Cancer Riskc>d
CDDs/CDFs PCBs
High Sports Fisherman
(game fish only)
— Level 1 2xlO~3["B2"] lxlO~2[B2]
-- Level 2 8xlO"4["B2"] 6xlO~3[B2]
Great Lakes Consumer 3xl(T4["B2"] 2xlO~3[B2]
(game fish only)
General Consumer 6xlO-5["B2"] 5xl(T4[B2]
(game + clean fish)
aSum of Aroclors 1248 and 1254.
bFrom data in Section III.E.2* and Tables 111-30* and 111-31*. Also see
Table 111-2 in this document.
cValues for CDDs/CDFs from Table 111-5 (1988 data). For data on PCBs, see
Appendix B. Upper-bound estimates of additional lifetime cancer risk for
PCBs obtained by multiplying dose rate (consumption rate from Table III-2
multiplied by mean 1988 concentration of 0.81 ug/g and divided by human body
weight of 70 kg) by cancer potency factor of 7.7 x 10~3 (ug/kg/day)"1 and
multiplying by a factor of 1.3 to incorporate contribution of higher intakes
in childhood to average lifetime intake.
^In USEPA's weight-of-evidence classification system for carcinogens, B2
indicates that the evidence for carcinogenicity in animals is "sufficient,"
while the human evidence for carcinogenicity is "inadequate." B2 is placed
in quotation marks for the CDDs/CDFs, because the classification was for
2378-TCDD alone, whereas total TEQs are being evaluated here, in accordance
with USEPA interim science policy.
*In Risk Assessment
21
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TABLE II1-8
SUMMARY OF UPPER BOUND CANCER RISK ESTIMATES
FROM EXPOSURE TO CDD/CDF CONTAMINATION IN MIDLAND, MICHIGAN
Exposure Route Upper Bound Cancer Risk (Exposure Scenario)
Higher Estimate Lower Estimate
Fish 10~2 (plausible maximum 1(T4 (Great Lakes
consumer) consumer)
10~3 (high sports 1CT4 (general consumer)
fisherman—level 1)
Soil 10~5 (upper estimate) 10~6 (lower estimate)
10~4 (child with pica)
Air 10~4 (fenceline) 1CT5 (residential area)
Notes: (1) 10~2, 10~3, 10~4, etc., indicate risks of 1 in 100, 1 in 1,000, 1 in
10,000, etc.
(2) Other contaminants such as PCBs, found in the fish, add to the risk
from that exposure route (see text and Appendix B in the Risk
Assessment.
(3) Sources: Tables III-3, III-4, and III-5. Risks for fish consumption:
plausible maximum consumer based upon 1983-1987 data; others based
upon 1988 data.
(4) USEPA is currently Devaluating the cancer potency factor for
2378-TCDD; a final determination will not be available for at least
several months.
22
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TABLE 111-9
SUMMARY OF HAZARD INDICES FOR NON-CANCER EFFECTS
FROM EXPOSURE TO CDD/CDF CONTAMINATION IN MIDLAND, MICHIGAN
Exposure
Route
Exposure Scenario
Hazard Index (HI)a
Lonq-Term Short-Term
Fish^ Plausible maximum consumerc
High sports fisherman—level 1
Great Lakes consumer
General consumer
50
8
1
0.3
5
0.7
0.3
0.2
Soil
Upper estimate
— with pica
— normal
Lower estimate
Upper estimate
young child
young
adult
child
6
0.6
0.2
Aird
Infant at fenceline
Child at fenceline
Child in residential area
Adult in residential area
4
1
0.2
0.1
aHazard Index is the ratio of intake dose to:
— RfD (1 pg/kg/day) for long-term exposures (several months or more)
— 10-day HA (28 pg/kg/day) for short-term exposures (few days to few weeks)
bSmall child could be at 2-3 times higher risk than adult. Breast-fed infant
could be at 10-times higher risk than mother. Other contaminants such as PCBs,
found in the fish, add to the Hazard Index values (see text and Appendix B of
the Risk Assessment).
"-Long-term and short-term hazard indices for plausible maximum consumer based
upon 1983-1987 fish contaminant data for catfish, carp, and walleyes
(substitution of 1988 walleye data does not change His). Hazard indices for
other consumers based upon 1988 fish contaminant data for walleyes. Soil and
air estimates based upon Midland field measurements during 1983-1984 period.
dAll HI values calculated using the
exposure from breast-feeding.
"A method." Infant exposure includes
Note: See Table III-6 for His for single meal (bolus) exposures.
23
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IV
RISK MANAGEMENT
Collectively, the point source and environmental studies conducted by USEPA,
the State of Michigan, and Dow Chemical over the past several years clearly
indicate that the Dow Chemical Michigan Division plant at Midland has been the
most significant, if not the only significant, source of CDD/CDF contamination of
the plant site and the general Midland area environment. As a result of these
investigations Dow Chemical has undertaken several actions, some unilaterally,
some required by environmental permits or administrative orders issued by the
State of Michigan or USEPA, to minimize emissions and discharges of CDDs and
CDFs and other toxic pollutants. Dow Chemical has completed or is implementing
the following actions:
o Terminated production of chlorinated benzenes, and most chlorinated
phenols, including 2,4,5-trichlorophenol and derivatives and pentachloro-
phenol (late 1970s).
o Installed a riverbank revetment system to collect contaminated ground
waters from a significant portion of the plant site (1979-1981);
additional sections of the riverbank have undergone similar treatment
(1984-1987).
o Upgraded air emission controls on the hazardous waste incinerator (late
1970s); landfill ing rather than incinerating contaminated wastewater
treatment sludges; upgrading operational controls and practices at the
hazardous waste incinerator.
o Undertook extensive point source and underground investigations of CDD/CDF
contamination plant site (1983-1987).
o Installed a wastewater effluent filtration system for the entire
wastewater discharge to the Tittabawassee River (1985).
o Replaced open wastewater ditches on the plant site with enclosed sewers.
Isolated high contamination areas of the plant sewerage system from the
wastewater treatment system (1986-1987).
o Implemented plant-wide dust-suppression program (1986).
o Capped areas in the plant with high levels of surface soil contamination;
limited access to an area on the plant boundary with moderate levels of
CDD/CDF contamination (1986).
o Provided preliminary treatment of incinerator scrubber waters prior to
commingling with other process wastewaters (1987).
Recent data are beginning to show reduced incinerator emissions, reduced
wastewater effluent discharge levels, and reduced fish contamination levels.
Overall, it appears conditions have improved significantly over the last ten
25
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years. Nevertheless, the levels of discharge and environmental contamination as
depicted by point source and environmental data collected during the past five
years, including the fish data collected in 1988, indicate that further remedial
work at the plant site and actions by the public to minimize exposures could be
helpful in reducing the possible public health risks described earlier.
The estimated risk levels presented in the Risk Assessment and summarized in
Section III are upper-bound cancer risks and upper-bound risks of non-cancer
health effects based upon conservative assumptions regarding the toxicological
effects of 2378-TCDD, the possible toxicological effects of other CDDs and CDFs
which have not been studied to the same extent as 2378-TCDD, and the exposures of
Midland area residents to 2378-TCDD and other CDDs and CDFs in their environment.
Thus, the actual risks to Midland area residents are not likely to be higher than
those presented here, and they could be significantly lower. However, USEPA
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~° range, and when non-cancer health effects are estimated
to be significant through the use of a hazard index or other such measures for
comparing estimated exposures with reference doses and health advisories.
As highlighted in the preceding section, the greatest potential public
health risks (cancer and non-cancer health effects) are associated with
consumption of contaminated fish from the Tittabawassee River. Possible public
health risks associated with ambient air contamination from current Dow Chemical
incinerator emissions are estimated to be less significant. Possible risks
associated with exposure to contaminated soils in the community, which are
related to current and past incinerator emissions, past process emissions, and
windblown dusts from the plant site, are estimated to be less than estimated
risks from consumption of fish or from exposure to contaminated ambient air.
Even if USEPA adopted for use in risk assessments a carcinogenic potency
factor for CDDs/CDFs an order of magnitude lower (less conservative), the
estimated cancer risks associated with the higher levels of fish consumption
would still be quite high (10~3 to 10~5). Furthermore, the estimated risks
associated with the PCB contamination of the fish, as discussed above, would not
change. If one were to employ such a lower cancer potency factor in evaluating
the other routes of exposure, estimated risks for air and soil would be at or
below 1CT6 for all exposed groups except children with pica, for whom the
estimated risk would be about 10~5. The estimated non-cancer health effects,
which would not be affected by a change in the USEPA cancer potency factor for
2378-TCDD, are clearly of concern for children, pregnant women, and women of
child-bearing age, as well as for others with high rates of fish consumption;
the non-cancer health effects also could be of marginal concern for some
worst-case air exposures. (These worst-case air exposures are unlikely to
occur.) Actions to minimize risk for fish consumers are thus the highest
priority, based upon this risk assessment.
Presented below are USEPA's final risk management recommendations for dioxin
contamination at Midland, Michigan. These actions include point and nonpoint
controls by Dow Chemical, recommended precautionary measures that can be
implemented by the public to minimize exposures and possible risks, and a series
of point source and environmental monitoring programs. These mitigative measures
26
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are essentially the same as those presented in the public review draft of this
report (USEPA 1988b).
A. POINT AND NONPOINT SOURCE CONTROLS AT DOW CHEMICAL
1. Wastewater Discharges
Figure IV-1 presents a summary of monthly average Dow Chemical wastewater
discharges of 2378-TCDD for the period July 1984 to August 1988. Dow Chemical
began full scale operation of the final effluent mixed-media filtration system in
November 1985 and began full-scale operation of an incinerator wastewater
pretreatment system in July 1987 (Dow 1988a). The level of discharge was
initially reduced by about 75 percent upon operation of the mixed-media
filtration system. Another significant reduction has been realized after
preliminary treatment for incinerator wastewaters was instituted. Overall, the
average mass discharge has been reduced by nearly 90 percent from 1984 and 1985
levels. The level of discharge remains above the level deemed necessary by the
MDNR for protection of public health (0.1 ppq) (MDNR 1987b). That level is not
detectable with current sampling and analytical methodologies. Computer modeling
studies conducted at the direction of USEPA indicate that 2378-TCDD levels in
Tittabawassee River fish are mostly related to Dow Chemical wastewater discharges
as opposed to less significant sources including runoff from city soils and air
emissions (GSC 1987).
Given the complexity of the wastewater treatment system and the sources and
sinks of 2378-TCDD and other CDDs and CDFs at Dow Chemical, it is not possible to
predict to what extent further progress in reducing the discharge will occur
without additional remedial actions. USEPA has evaluated alternate end-of-pipe
wastewater treatment technologies and supplemental in-plant controls for
additional treatment of 2378-TCDD at Dow Chemical and concluded there are no
available performance data for the treatment systems considered and it is not
possible to predict discharge reductions for either the treatment systems
considered or possible in-plant controls. Accordingly, USEPA recommended to MDNR
a series of special NPDES permit conditions for the next NPDES permit for Dow
Chemical (1987d). These include:
o Feasibility and end-of-pipe wastewater treatability studies for CDDs and
CDFs.
o An assessment of the amount of 2378-TCDD in tertiary pond sediments and a
study to determine to what extent resuspended sediments containing CDDs
and CDFs pass through the filtration system.
o An evaluation of the effectiveness of the performance of the incinerator
wastewater pretreatment system.
The proposed NPDES special conditions set out in the above-referenced report
have been included by MDNR in the NPDES permit and accompanying administrative
order for Dow Chemical (MWRC 1988). The results from these special conditions
should allow a proper assessment of the extent to which additional controls can
be installed to further reduce discharge levels. Any further regulatory actions
would be implemented through the NPDES or RCRA permit programs.
27
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FIGURE IV - 1
2378-TCDD DISCHARGES
DOW CHEMICAL - MIDLAND PLANT
ro
00
Kg/day (E-07)
24 -
22 -
20 -
18 -
16 -
14 -
12 -
10 -
B
0
II
I
OPERATION OF
EFFLUENT
FILTRATION
SYSTEM
OPERATION OF
INCINERATOR
TREATMENT
SYSTEM
••..••••••••I
ItV
7/84
1/86
7/86 1/86 7/88 1/87 7/87
MONTHLY AVERAGE MASS LOADINGS
1/88
7/88
-------
2. Incinerator Emissions
The limited data available for Dow Chemical hazardous waste incinerator
emissions from 1978 through 1987 indicate that the emission rates of CDDs and
CDFs are considerably lower today than in the late 1970's. Emissions testing by
USEPA in 1984 (Trembly and Amendola 1987) and Dow Chemical in 1987 (Dow 1987a)
indicate emission rates of 2378-TCDD (Partial TEQs) have been reduced by more
than 90 percent from emission levels measured by Dow Chemical in 1983 (Dow 1984).
The investigations of air emission sources at the Midland plant conducted by
Dow Chemical clearly show the incinerator was the most significant point source
at that time (Dow 1984). However, estimated cancer and non-cancer risks for air
exposures in the Risk Assessment are related more to the actual measured ambient
air concentrations than to the estimates of ambient air concentrations resulting
from dispersion modeling of the incinerator emissions. These results suggest
historical deposition from past incinerator emissions, possible process
emissions, and windblown dusts from the plant site impact the ambient air around
the perimeter of the plant and, to some extent, out in the community more than
the current incinerator emissions.
Based upon the above considerations and the estimated health risks
associated with incinerator emissions alone, there does not appear to be
sufficient justification for recommending major changes in incinerator operations
at this time (e.g., change in waste feeds, installation of additional emission
control technology), although improvements might be required in the future by new
regulations. On the other hand, additional measures to optimize combustion
conditions within the incinerator and to optimize operation of the existing
emission controls should be pursued to further reduce emissions below current
levels to the extent possible.
At the present time it appears that the results from supplemental monitoring
of incinerator emissions and ambient air as described in Section IV.C are
necessary to determine whether, or to what extent, additional incinerator
emission controls are necessary. The RCRA permit for the Midland plant includes
the recommended incinerator emissions testing and ambient air monitoring programs
(USEPA 1988e).
3. Dust Suppression Program
A considerable portion of the Dow Chemical Midland plant site is either
paved roadway, paved open areas around process buildings, or paved parking lots.
Some portions of the plant site are capped landfills with grass cover. The
remainder of the site is occupied by buildings or is unpaved dirt or gravel
covered open areas. Surface soil sampling conducted by Dow Chemical and USEPA
indicate the entire plant site is contaminated with 2378-TCDD (and other CDDs and
CDFs) with a mean surface soil 2378-TCDD concentration of less than 0.5 ppb (Dow
1984, USEPA 1985a). During dry weather periods, vehicular traffic through the
plant has been observed to raise considerable particulate matter from roadways.
Wind-blown dusts have undoubtedly contributed some CDDs and CDFs to ambient air
within the plant and around the plant perimeter. Impacts on nearby commercial
and residential areas are determined by wind direction and velocity.
29
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In 1986, Dow Chemical began implementing a fugitive dust suppression control
program which calls for regular flushing of paved roads and parking lots,
application of chemical dust suppressants to unpaved roads, and controls for
storage piles and loading and unloading of materials from pollution control
equipment (Dow 1988b). This program was revised in 1987 and appears to address
most sources of fugitive dusts from the plant site that may be contaminated with
CDDs and CDFs. The effectiveness of this program will be evaluated through the
ambient air monitoring program presented in section C.2.C below. Depending upon
the results, all or some combination of the following actions, or similar
measures, could be implemented to further minimize worker exposure levels and
migration of CDDs and CDFs from contaminated soils within the plant:
o Paving or planting grasses over some of the remaining sand and gravel
areas.
o Modified road dust suppression program or paving program for unpaved
roads. Modified spraying and sweeping programs for paved roadways to
further minimize fugitive particulate emissions.
4. Ground Water Contamination
Ground water and subsurface soil sampling conducted by Dow Chemical at the
Midland plant pursuant to Resource Conservation and Recovery Act (RCRA) require-
ments, revealed contamination with 2378-TCDD at a number of locations (Dow
1987b). Areas near former trichlorophenol production facilities were found to be
the most highly contaminated. USEPA sampling of sediments from a riverbank
revetment system collection sump revealed contamination with 2378-TCDD and other
CDDs and CDFs (Amendola and Barna 1986). Also, ground water monitoring by Dow
Chemical near the Poseyville Road landfill has demonstrated certain hazardous
constituents emanating from the landfill and migrating north to northeast (Dow
1987b). (CDDs and CDFs have not been studied in the ground water.) Dow Chemical
has installed a purge system to collect the release, and constructed a slurry
wall at the landfill to prevent future releases.
The contaminated ground water at the plant is largely contained within the
site. There are no potable ground water wells within the immediate area of the
plant and monitoring of both public and private potable ground water wells near
the plant and near Dow Chemical landfills showed no detectable CDDs or CDFs
(Barna and Amendola 1985). The RCRA permit for the Dow plant has as a principal
focus the issue of ground water contamination at the plant and at nearby
landfills. Accordingly, additional point or non-point source controls beyond
those required under the RCRA permit for the protection of ground water do not
appear necessary to protect public health.
B. PRECAUTIONARY MEASURES RECOMMENDED TO THE PUBLIC
Although operations at Dow Chemical have caused widespread contamination of
the Midland area with 2378-TCDD and other CDDs and CDFs, USEPA believes that the
levels of contamination, with the exception of the Tittabawassee River fish, do
not present unacceptable or unmanageable health risks to the Midland community.
USEPA does not believe that massive remedial measures such as those implemented
at Times Beach, Missouri, or Newark, New Jersey, are warranted in Midland. There
30
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are, however, a number of actions people can take to minimize exposures, and thus
minimize possible health risks associated with CDOs and CDFs. Most of these
recommendations focus on avoiding or minimizing ingestion of materials that
contain 2378-TCDD and other CDDs and CDFs.
1. Tittabawassee River Fish
In Michigan, legal responsibility for the evaluation of health risks and
issuance of health advisories resides with the Michigan Department of Public
Health (MDPH). Prior to April 1988, MDPH had in place a fish consumption
advisory warning against consumption of catfish and carp taken from the
Tittabawassee River (MDNR 1987a). These fish contain high levels of 2378-TCDD
and other organic chemicals. As shown in the Risk Assessment, regular
consumption of even relatively small amounts of these fish over the long term may
pose substantial risks of cancer. Also, long-term consumption or, in certain
circumstances, short-term consumption of these fish may pose significant risks of
adverse impacts other than cancer.
The Risk Assessment highlights possibly significant risks from consumption
of game or sports fish (e.g., walleye, northern pike, smallmouth bass, and white
bass) by children and women of childbearing age, related to possible
reproductive effects, teratogenic effects, liver damage, and cancer. These risks
may be associated with both short-term and long-term consumption. Risks from
consumption of game or sports fish for other less sensitive groups are also
presented in the Risk Assessment and summarized in Section III. Note that the
risks associated with PCB contamination of Tittabawassee River walleyes exceed
those associated with CDDs/CDFs. In April 1988, as an interim, precautionary
measure, the MDPH modified its fish consumption advisory to warn pregnant women
and women of childbearing age against consuming more than one meal per month of
Tittabawassee River walleye. MDPH further strengthened the advisory in December
1988, adding that no one should eat large quantities of any species from the
river (MDPH 1988). USEPA supports Michigan Department of Public Health actions
to make the fish consumption advisory for the Tittabawassee River more
restrictive.
Individuals who choose to consume fish caught in the Tittabawassee River
should clean them in accordance with MDPH recommendations to minimize contaminant
levels. Fillets should be skinned, with all visible traces of surface fat
removed. All belly fat from the fillet should be removed, as well as the dark
tissue along the lateral line on each fillet. Certain cooking methods that
permit fats and juices to drain from the fish can result in lower contaminant
levels in the cooked fish.
The 1988 fish contaminant data for spring walleyes developed by MDNR, MDPH,
Dow Chemical, and USEPA are presented in Appendix B. These data indicate a
relationship between 2378-TCDD and PCB concentration and size class:
31
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CDDs/CDFs and PCBs in Tittabawassee River Walleyes (1988^
2378-TCDD TEQs
Concentration
PCB*
Concentration
Lenath
15"
18"
22"
- 18"
- 22"
- >26"
Average
Wei ant
1.6
3.1
5.8
Ibs
Ibs
Ibs
2
3
4
Ranae
.0-3.9
.0-7.4
.1-15.9
Mean
ppt
ppt
ppt
3.1
4.9
8.2
PPt
ppt
ppt
Ranae
0.26-0.64 ppm
0.36-1.2 ppm
0.48-2.2 ppm
Mean
0.43
0.72
1.2
ppm
Ppm
ppm
*Sum of results for Aroclors 1248 and 1254.
These results indicate that smaller walleyes are likely to contain less CDDs/CDFs
and PCBs than larger fish. Thus, for those who choose to eat fish from the
Tittabawassee River, ingestion of contaminants can be reduced by eating only the
smaller fish caught.
2. Citv of Midland Surface Soils
The overall estimated cancer and non-cancer risks from exposures to surface
soils in Midland are not considered to be significant except possibly for
children with pica. Children with pica are those who intentionally consume
inordinate amounts of soil. Pica, considered a medical disorder, is believed to
affect an average of about 1 in 200 children.
Some possible routes of exposure to 2378-TCDD and other CDDs and CDFs in
city of Midland soils include direct ingestion by children at play outdoors;
ingestion of soil attached to home-grown vegetables, whether or not the contami-
nants were absorbed or transported into the edible portion of the plant;
absorption through the skin which comes in contact with the soil through play,
gardening, or other activities; inhalation of contaminated particulates from the
soil; and ingestion of household dusts which may be contaminated from outdoor
soils. Note that the results of the USEPA soil study showed that 2378-TCDD (and
other CDDs and CDFs by inference) tend to concentrate in areas near roof
downspouts or driplines (USEPA 1985a).
Although currently available information indicates that only children with
pica are at possibly significant risk from the soil contamination in Midland, the
commonsense practices presented below are recommended as generally useful for
minimizing exposure to soil contamination or bacteria, whether the soil is found
in Midland or elsewhere:
o Children at play, particularly toddlers and children with pica, should be
encouraged to keep soil or dirt out of their mouths. Areas near
downspouts and roof driplines are likely to have higher levels of
2378-TCDD and other CDDs and CDFs than open yard areas.
o Children and adults should wash their hands after exposure to outdoor
soils, particularly before meals.
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o Home-grown vegetables, both leafy vegetables and root crops, should be
thoroughly washed prior to consumption to remove soil particles. Peeling
root crops might be helpful in removing 2378-TCDD which may be in soil on
the skins or absorbed into the skins.
o Household interiors should be regularly cleaned to minimize contaminated
dusts which can be inhaled or ingested.
C. POINT SOURCE AND ENVIRONMENTAL MONITORING PROGRAMS
As noted earlier, there have been many remedial actions taken over the past
few years to minimize emissions and discharges of CDDs and CDFs from the Dow
Chemical Midland plant. The limited data collected recently indicate contaminant
levels outside the plant may be declining. Presented below are a series of
proposed point source and environmental monitoring programs designed to document
the effectiveness of the remedial programs and to characterize or evaluate other
possible, but less likely, routes of exposure which were not evaluated initially
as part of the Michigan Dioxin Studies. Some of the proposed monitoring programs
are current requirements of Dow Chemical environmental control permits or orders;
others are new programs that have been included in the RCRA permit or could be
required under other existing regulatory mechanisms. Final decisions regarding
implementation of these proposed monitoring programs will be made as part of the
permit issuance processes for the NPDES, RCRA, and other permits for the Dow
Chemical Midland plant.
Each required or proposed program is described in the following sections.
Study designs and sampling and analytical protocols would be approved by MDNR,
MDPH, and/or USEPA Region V.
1. Dow Chemical Point Source Monitoring
a. Wastewater discharge monitoring
Dow Chemical currently monitors the outfall 031 wastewater discharge to the
Tittabawassee River twice per month for 2378-TCDD as required by NPDES permit
MI0000868. The current discharge levels reported by Dow Chemical are in the
range of less than 1 to 8 parts per quadrillion (ppq or pg/1). Data collected
for the last six months of 1987 indicate the discharge had been fairly stable
from month to month remaining less than 3 ppq. However, data collected in May,
June and July of 1988 showed a few concentrations in the 4 to 8 ppq range. MDNR
has determined that 0.1 ppq of 2378-TCDD in Dow Chemical's effluent would be
protective of human health, by minimizing bioaccumulation of 2378-TCDD in fish
(MDNR 1987b). Dow Chemical should conduct experiments to determine what measures
might be feasible to attain analytical method detection levels of 0.1 ppq for
2378-TCDD (e.g., larger sample size, enhanced sample cleanup, high resolution
mass spectrometry).
b. Incinerator emissions testing
Over the past few years Dow Chemical has been modifying the operation of its
hazardous waste incinerator to optimize combustion conditions and minimize
emissions of 2378-TCDD and other CDDs and CDFs. The most recent stack tests were
33
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conducted by Dow Chemical during June 1987 (Dow 1987a). In Section IV.A.2, USEPA
proposes that Dow Chemical continue efforts to optimize incinerator emissions.
At some point over the next two years, preferably during the warm, dry-weather
seasons of 1988 or 1989, another series of stack tests should be performed to
characterize the emissions of 2378-TCDD and other CDDs and CDFs, and to determine
the particle size distribution of the stack emissions. The particle size data
are useful for estimating incineration emissions deposition for purposes of
exposure assessments and for distinguishing the incinerator emissions from other
sources of CDD/CDF contamination in the ambient air. Ideally, the incinerator
emissions testing would be conducted concurrently with the ambient air monitoring
program proposed below. These efforts should be coordinated with the incinerator
emissions trial burns for 2378-TCDD required for RCRA permitting.
2. Proposed Supplemental Environmental and Food Chain Monitoring Programs
a. Environmental Monitoring Programs
(1) Ambient air monitoring program
Concurrent with the incinerator emissions testing noted above, a limited
ambient air monitoring program should be conducted to determine particle size
distribution, particulate levels, and current concentrations of 2378-TCDD and
other CDDs and CDFs. A network of at least seven monitoring sites (one upwind of
plant, three downwind near the fence!ine, three downwind in the community) would
be necessary. Two of the downwind sites should be located in the vicinity of the
estimated point of maximum ground level impact of the incinerator emissions. An
extended particulate monitoring program should be conducted over a period of a
few months. CDD and CDF determinations should be made on at least three separate
days with wind blowing from the upwind monitors toward the downwind monitors.
Analyses of CDDs and CDFs under other conditions could also be considered. The
specific monitoring protocols should be developed by the MDNR and Region V air
and waste management programs in consultation with Dow Chemical.
(2) Soil and dust monitoring program
Surface soil sampling near each air monitoring station (10-15 samples,
total) should be conducted to reveal the presence of contaminated soils that
could influence the particulate samples through resuspension. Limited surface
soil sampling throughout the community (20 samples) also should be conducted to
document current surface soil concentrations in Midland. Selected sites sampled
in the 1983 USEPA survey should be resampled to measure changes that may have
occurred. Appropriate control sites should be established for this effort.
Collection and analysis of a limited number of household dust samples would
permit evaluation of the significance of this route of exposure.
(3) Tittabawassee River sediments
Tittabawassee River sediments and the river flood plain, from upstream of
Dow Chemical to about five miles downstream from outfall 031, should be
thoroughly surveyed, evaluated, and classified in order to locate any pockets of
organic contamination or deposition zones containing clay, silt, or other fine
particles of a type with the potential to adsorb CDDs/CDFs. The survey should
34
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include extensive grab and/or core sampling with visual evaluation of the samples
by an experienced sediment classifier, supplemented by the appropriate use of a
gross measure of organic material such as TOC (total organic carbon). Samples
with relatively high organic content or other indications of potential
contamination (e.g., large amounts of fine particles) would be analyzed for
2378-TCDD, other CDDs and CDFs, and other contaminants to determine whether or to
what extent sediment removal might be appropriate.
b. Food Chain Monitoring
(1) Tittabawassee River fish
Dow Chemical is currently required by the terms of a consent order with
USEPA to conduct monitoring of Tittabawassee River fish every two years through
1991 (U.S. v. Dow 1984). The MDNR has proposed to modify that program by
requiring fish monitoring every two years during even-numbered years (MDNR
1988). The MDPH, MDNR, Dow Chemical, and USEPA collaborated in developing an
expanded fish monitoring program for 1988. The results from that program are
presented in Appendix B and were reviewed above.
(2) Other aquatic life, avian. and animal monitoring program
A limited monitoring program should be conducted in 1988 or 1989 for
bivalves or gastropods present in the Tittabawassee River as well as for turtles,
fish-eating birds that nest in the vicinity of the river, and fish eating mammals
such as the muskrat and raccoon. About 20 samples should be adequate for
screening these organisms for 2378-TCDD and other CDDs and CDFs.
(3) Dairy sampling
A limited screening sampling program (10 to 15 samples) should be conducted
at dairy operations that may be located within 10 to 15 miles of the Dow Chemical
plant. Samples of whole milk, milk fat, and cheese should be collected and
analyzed for 2378-TCDD and other CDDs and CDFs.
(4) Garden vegetable sampling
Although preliminary monitoring by USEPA did not indicate uptake of
CDDs/CDFs by the root crops sampled, additional data are needed to confirm this
conclusion and to test for uptake in other crops. A limited garden vegetable and
garden soil sampling program (20 to 30 samples) should be conducted in 1988 to
supplement the limited data collected by USEPA for 1987 samples. These data
would be used to document whether, or to what extent, migration of 2378-TCDD and
other CDDs and CDFs occurs from contaminated soil into (or onto) garden
vegetables.
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study: Tittabawassee River sediments and native fish. Environmental
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BARNA, D.R., and AMENDOLA, G.A. 1985. Screening survey of surface water
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V, USEPA, Westlake, Ohio. October 20.
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Services, Michigan Division, Dow Chemical U.S.A., Midland, Michigan, to G.A.
Amendola, Environmental Sciences Division, Region V, USEPA, Westlake, Ohio.
March 15.
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DOW CHEMICAL COMPANY (Dow). 1988c. Letter from J.E. Garvey, Environmental
Specialist, Environmental Services, Michigan Division, Dow Chemical U.S.A.,
Midland, Michigan, to L. Duling, Surface Water Quality Division, Michigan
Department of Natural Resources, Lansing, Michigan. June 23.
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Hernandez, Acting Administrator, USEPA, Washington DC. March 16.
GENERAL SCIENCES CORPORATION (GSC). 1987. GEMS multi-media modeling of
2378-TCDD at Midland, Michigan. Prepared for Office of Pesticides and Toxic
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June 19.
HUMPHREY, H.E.B. 1983. Population studies of PCBs in Michigan residents. In
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HUMPHREY, H.E.B., RICE, H.A., and BUDD, M.L. 1976. Evaluation of changes of the
level of polychlorinated biphenyls (PCB) in human tissue. Final Report to
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MICHIGAN DEPARTMENT OF NATURAL RESOURCES (MDNR).
Lansing, Michigan.
1978. Michigan fishing guide.
MICHIGAN DEPARTMENT OF NATURAL RESOURCES (MDNR). 1983. Letter from H.A. Tanner,
Director, Lansing, Michigan, to J.W. Hernandez, Acting Administrator, USEPA,
Washington DC. March 23.
MICHIGAN DEPARTMENT OF NATURAL RESOURCES (MDNR).
Lansing, Michigan.
1987a. Michigan fishing guide.
MICHIGAN DEPARTMENT OF NATURAL RESOURCES (MDNR). 1987b. Public Notice of
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MICHIGAN DEPARTMENT OF NATURAL RESOURCES (MDNR). 1988. [Results of chemical
analysis of Tittabawassee River fish collected April 12, 1988.] Transmitted
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MICHIGAN DEPARTMENT OF PUBLIC HEALTH (MDPH). 1988. Public health advisory.
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Attorney General. Lansing, Michigan. May 17.
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MICHIGAN WATER RESOURCES COMMISSION (MWRC). 1988. NPDES permit no. MI0000868
(Michigan Division, Dow Chemical Company, Midland, Michigan). Lansing,
Michigan. September 15, 1988.
SMITH, A.H. 1987. Infant exposure assessment for breast-milk dioxins and
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viduals: Amount per day and per eating occasion. By Poa, E.M., Fleming,
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U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1987c. Interim procedures for
estimating risks associated with exposures to mixtures of chlorinated
dibenzo-p-dioxins and dibenzofurans. Risk Assessment Forum, Washington DC.
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U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1987d. Technical support document
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NPDES permit conditions, NPDES permit MI0000868, Dow Chemical, Midland
plant, outfall 031. Environmental Sciences Division, Region V, Westlake,
Ohio. August.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1988a. Risk assessment for dioxin
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Illinois. April. EPA 905/4-88-006.
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Butterworth, Environmental Research Laboratory, Duluth, Minnesota, to
Howard Zar, Region V, Chicago, Illinois. May 26.
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dose estimate for 2378-TCDD. Office of Health and Environmental Assessment.
Washington DC. EPA 600/6-88-007Aa. June. (External review draft).
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1988e. Resource Conservation and
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Illinois. September 30.
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U.S.A., Michigan Division, Defendant. March 30.
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APPENDIX A
RESPONSE TO PUBLIC COMMENTS
0 N
RISK ASSESSMENT FOR DIOXIN CONTAMINATION
AT MIDLAND, MICHIGAN; EPA-905/4-88-005, APRIL 1988
AND
PROPOSED RISK MANAGEMENT ACTIONS FOR DIOXIN
CONTAMINATION AT MIDLAND, MICHIGAN; EPA-905/4-88-006, APRIL 1988
(PUBLIC REVIEW DRAFT)
DECEMBER 1988
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION V
230 SOUTH DEARBORN STREET
CHICAGO, ILLINOIS 60604
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PUBLIC COffOTS RECEIVED
1. April 28, 1988 Public Meeting, Midland, Michigan
Chairman
Howard Zar, Chairman, Dioxin Task Force
Water Division, Region V, USEPA, Chicago IL
Panel Members
Gary Amendola, Manager, MI Dioxin Studies
Eastern District Office, Region V, USEPA
Westlake OH
Donald Barnes, Ph.D., Chairman
Chlorinated Dioxins Workgroup
Office of Pesticides and Toxic Substances
USEPA, Washington DC
J. Milton Clark, Ph.D., Toxicologist
Pesticides and Toxic Substances Branch
Region V, USEPA, Chicago IL
Mark McClanahan, Ph.D., Toxicologist
Agency for Toxic Substances and Disease Registry
Atlanta GA
Ian C.T. Nisbet, Ph.D., Consultant
I.C.T. Nisbet and Associates
Lincoln MA
Commentors
Lawrence Chadzynski, M.P.H.
Michigan Department of Public Health
Diane Hebert
Midland, Michigan
John Hesse
Michigan Department of Public Health
Benjamin Johnson, M.D.
Michigan Department of Public Health
Appendix A
iii
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PUBLIC COtfCNTS RECEIVED (Continued)
Commentors (Continued)
Sandy Mannion
Hemlock, Michigan
Doug Martin
Terry Miller
Bay County
Pat Moore
Ingersoll Township
Wendell Mullison
Winifred Oyen
Midland County Public Health Department
John Pal urn
Harry Pine
Midland, Michigan
Several unidentified persons
2. May 30, 1988 Letter from Sandy Mannion, Hemlock, Michigan
3. June 1, 1988 Letter from R. M. Croyle, Dow Chemical Company,
Midland, Michigan
4. June 2, 1988 Letter from Barbara S. Glenn,
National Wildlife Federation, Ann Arbor, Michigan
Appendix A
iv
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INTRODUCTION
In April 1988, the United States Environmental Protection Agency (USEPA) released
a final risk assessment document entitled, Risk Assessment for Dioxin
Contamination at Midland. Michigan (USEPA 1988a) and a public review draft of a
risk management document entitled, Proposed Risk Management Actions for Dioxin
Contamination at Midland. Michigan (USEPA 1988b). Also issued in April 1988 was
a fact sheet entitled, Summary of Risk Assessment and Proposed Risk Management
Actions. Midland. Michigan. USEPA conducted a public meeting to discuss the risk
assessment and risk management documents on April 28, 1988, at the Northeast
Intermediate School in Midland. A panel of six experts, four from USEPA and one
each from a private consulting firm and the Agency for Toxic Substances and
Disease Registry, presented explanations of the procedures followed in the
Midland studies and subsequently responded to a number of questions and comments
from the audience. Written comments were solicited during the period from April
25 through June 3, 1988, and three letters were received, as indicated above.
The comments and suggestions received concerning the risk assessment and risk
management documents all have been noted and are greatly appreciated. An attempt
has been made to summarize and respond to all of the written comments received.
However, inasmuch as the risk assessment document is a final report that has gone
through Agency review procedures, no revisions currently are contemplated. The
draft risk management document, on the other hand, has been revised, and
appropriate changes have been incorporated therein (USEPA 1988c). With a few
exceptions, the comments received at the April 28, 1988, public meeting in
Midland were satisfactorily responded to during the meeting itself. However, a
few of the meeting comments and questions that were not covered in any of the
written comments or that appeared to call for expansion or clarification have
been included in this document (see Section II) along with the Agency's
responses. Transcripts of the meeting and copies of the written comments are
available for review at the Michigan Dioxin Studies document repositories in
Midland (see below).
Michigan Dioxin Studies Document Repositories
Grace A. Dow Memorial Public Library Ingersoll Township Hall
Emilia Parker Kurt Shaffner, Supervisor
1710 West St. Andrews Drive 4400 Brooks Road
Midland, Michigan 48640 Midland, Michigan 48640
(517) 835-7157 (517) 835-5289
Midland Health Department
Dr. Winifred Oyen, Director
125 Main Street
Midland, Michigan 48640
(517) 832-6655
Appendix A
v
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I.
COMMENTS RECEIVED IN WRITING
Comment: USEPA should not have split soil samples from the Midland area and
comparison sites with Dow Chemical. This allowed the company to determine the
validity of the data, damaging the credibility of the study. What other samples
from this study were split with Dow? Why? Why were Dow data and USEPA data
compared before completion of the study?
Response: The protocols for collection of soil samples, sample handling, and
analysis are fully described in the report for the soil study, Soil Screening
Survey at Four Midwestern Sites. EPA-905/4-85-005, June 1985, available for
review at the Michigan Dioxin Studies document repositories. As stated on
pages 8 and 9 of that report, samples were provided to USEPA and Dow Chemical
laboratories on a blind basis, and results were compared only after analyses
were complete. USEPA believes the results and conclusions from the study are
well supported by the high quality and comparable data generated by two
independent laboratories using different analytical techniques. At no time
during or after the soil study did USEPA allow Dow Chemical to determine the
validity of data.
All samples from this study were not split with Dow Chemical, and the company
did not analyze every split sample provided by USEPA. In addition to the soil
study samples, all samples collected inside the Dow plant, and some of the
potable water samples for dioxin analysis were split with the company. For
the soil study and part of the drinking water study, USEPA and Dow Chemical
results were compared prior to completion of the reports so that all relevant
data could be included in the final reports for those studies.
Comment: USEPA deliberately attempted to discourage reading and commenting or
questioning of data by citizens at opportune times such as public meetings.
Response: USEPA attempted to provide ample opportunity for public review and
comment on each aspect of the Michigan Dioxin Studies. Public meetings were
held in August and October 1983 to accept comment on the general study plans.
A public meeting was held in April 1985 to review the results of the soil
study, and small group meetings were held in December 1985 and July 1986 for
the drinking water and Dow Chemical wastewater characterization studies,
respectively. Finally, on April 28, 1988, USEPA conducted a public meeting to
review the results of USEPA's risk assessment and proposed risk management
actions for dioxin contamination in Midland. To the extent possible, public
information summaries and technical reports were distributed for review prior
to public or small group meetings. Also, USEPA has responded to numerous
public inquiries about various aspects of the studies and has been available
for additional small group meetings or meetings with individuals. USEPA has
not attempted to discourage or limit public review or questioning of data in
this matter.
Appendix
1
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Comment: The risk assessment incorrectly uses data from only the last five years
to calculate exposure rather than those from earlier years during which exposures
were likely to have been much higher.
Response: The primary purpose of the risk assessment was to determine current
risk levels in order to allow decisions to be made regarding the need for
further risk reduction measures. The calculations of current exposure levels
emphasized the last five years because this was the primary period for which
data were available, and also because estimates of current and future
exposures based on data from this period were expected to be conservative (due
to continuing clean-up work). Exposure levels are believed to have been
higher in prior years. The existence of this downward trend tends to support
the Agency's assumption that the calculations of current exposure are
conservative. Furthermore, underestimation of risk in this situation is made
even less likely by the assumption that the contamination will remain at
current levels over the next half century. The conservatism of the estimates
for exposure to fish contaminants has already been borne out in the most
recent analyses of Tittabawassee walleye samples obtained in the Spring of
1988. The average fish levels were found to be less than 50 percent of the
concentrations utilized in the risk assessment, which were based on data from
the 1983-1987 period.
Comment: Midland residents were not told that the soil screening survey
revealed that Midland soils contained considerably higher levels of dioxin than
either of the comparison community sites in the study. They were never told that
the concern over chlorinated dibenzofurans (CDFs) in the Midland environment is
nearly as great for 2378-TCDD.
Response: USEPA disagrees. The public information documents and the full
report of the soil study clearly state that Midland has higher dioxin soil
concentrations than any of the comparison sites. This fact was fully
discussed at the April 1985 and April 1988 public meetings. Also, with
respect to CDFs, all data were reported and considered in the risk assessment.
As noted in the risk assessment, 2378-TCDD is the most important compound,
accounting for 40% (fish) to 90% (soil) of the total 2378-TCDD toxicity
equivalents found.
Comment: The study was incomplete, because sampling of house dust, dairy
products, and breast milk was not done; vegetable samples had not yet been
analyzed; and air sampling was apparently flawed.
Response: The Midland study was an extraordinarily extensive environmental
study. The sampling and analytical techniques were state-of-the-art and were
implemented at considerable effort and cost. Sampling focussed on the issues
of highest priority in the opinion of USEPA and cooperating agencies. USEPA
agrees that further sampling would be helpful to quantify some of what are
believed to be less-significant exposure routes. The most significant
exposure routes, namely fish consumption, air inhalation, and soil ingestion,
were the principal focus of the Michigan dioxin studies. The draft risk
management document sets out the proposed further sampling programs to be
performed by Dow Chemical.
Appendix A
2
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Comment: Poseyville Landfill, a dioxin disposal site, is leaking. It is built
over an artesian system with private wells in close proximity. The draft risk
management document states (pages 36-37) that contaminants have migrated off
site, but that the groundwater is largely contained within the site. What data
are these conclusions based upon, what are the contaminants, and what does
"largely contained" mean? Why is this exposure in Midland declared acceptable?
Who will monitor the groundwater to make certain that private wells remain
uncontaminated?
Response: The Poseyville Road Landfill is an inactive landfill formerly used
by the Dow Chemical Company for disposal of solid wastes, some process
wastes, and rubble from building demolition. Some of these materials are
likely to be contaminated with dioxin. The proposed risk management report
(pages 36-37) indicates that ground water monitoring by Dow Chemical revealed
a plume of contamination emanating from the landfill in a north- to
northeasterly direction. The plume contains the following major
constituents:
1,1-Dichloroethane
Benzene
Chlorobenzene
Toluene
USEPA is not aware of any monitoring for 2378-TCDD or other CDDs/CDFs in the
ground water at the Poseyville Road Landfill. The artesian conditions
underneath the site may prevent downward migration of contaminants toward the
usable regional aquifer. Most of the private wells in the area are within the
deep regional aquifer or major sand seams in the till. A ground water purge
system was installed by Dow Chemical pursuant to an order issued by the
Michigan Department of Natural Resources (MDNR) to prevent flow towards
private wells. The containment of Poseyville Landfill will be addressed
further as a part of the Resource Conservation and Recovery Act (RCRA) permit
for the Dow facility, to assure long-term protection. Dow Chemical is
required to monitor the site, and the MDNR collects samples periodically to
confirm the company's testing. The USEPA has not sampled the site through the
RCRA program, but monitoring is required in the RCRA permit. The proposed
risk management report (page 37) indicates that contaminated ground water at
the plant (as opposed to Poseyville Road Landfill) is largely contained within
the site. This conclusion is based upon the installation of the riverbank
revetment collection system by Dow Chemical and analysis of the company's RCRA
permit application. Because of historical contamination at the facility, Dow
Chemical has been required, under the RCRA program, to study the ground water
flow paths beneath the entire 1900 acres of property. Although ground water
is known to flow towards the collection systems along the river, the study
will determine if there are any areas, not close to the river, where the flow
direction is toward the site boundary. Any such areas will be studied further
to determine if contaminants are migrating off-site. Any identified releases
will then be addressed through the HCRA program. USEPA and the MDNR will
monitor compliance with the study requirements and will sample occasionally
to cross check the company's results.
Appendix A
3
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Comment: PCB and 7 other carcinogens that were found in Tittabawassee River
walleyes along with the dioxins were not given adequate attention in the widely
distributed summary and were not fully evaluated in the risk assessment itself.
Response: USEPA agrees that PCB levels in Walleyes and their associated risks
may be of significant concern. The analysis of risks in Appendix B of the
risk assessment document indicated that, at the levels of PCBs and CDDs/CDFs
considered in the risk assessment, health risks associated with PCBs in fish
were probably similar to those from dioxins and furans that were the primary
subject of the study. The contributions of the other contaminants to the
total toxicity are negligible due to the small amounts found and the
relatively lower potencies and toxicities of these compounds. The tables in
the draft risk management document indicate that PCBs add to the risk.
If the conservative assumption were to be made that risks from CDDs/CDFs and
PCBs are additive, then estimates of the total risk of exposure to fish
contaminant levels found in the Tittabawassee River would increase by almost
an order of magnitude over the risk from CDDs/CDFs alone. Nevertheless, this
assumption would not appreciably change the advice given to fish consumers.
Inasmuch as dioxin risk is the primary issue addressed in the Midland study
and reports, the Agency chose to emphasize dioxin in the Summary. USEPA does,
however, agree with the commentor that PCBs deserve additional attention. The
discussion in the final risk management document has been expanded, using the
recently obtained analytical results on dioxin and PCBs in fish taken from
the Tittabawassee River in April 1988. A new Table III-7 compares the cancer
risks estimated on the basis of CDDs/CDFs and PCBs for the 1988 data. While
the PCB risks are dominant, no change in the risk management recommendations,
including the advice to the public, is called for.
Comment: The phrase "does not pose an unacceptable risk," referring to the
dioxin levels found in the study, should not have been used. It is awkward
English and is an attempt to divert attention from the actual meaning.
Response: The Agency concedes the awkwardness of the phrase in question,
which has become something of a standard expression in discussions of health
risk. However, USEPA does not believe that this interferes seriously with any
reader's comprehension of the Agency's conclusions concerning the air and soil
contamination. While estimates of the risks posed by exposure to Midland air
and soils can be calculated under the assumptions of the study, the resulting
numbers are so low as to be negligible in comparison to the health risks
Americans are comfortable about accepting as part of their daily lives. The
same cannot be said about consumption of fish from the Tittabawassee River.
Comment: The chairman of the April 28 public meeting discouraged questions from
the audience and was rude to citizens who posed questions.
Response: The chairman called on people from various parts of the audience.
generally limiting people to a few questions at a time. The intention was to
give everyone in the audience a fair opportunity to pose questions. While
this commentor apparently did not ask all the questions desired during the
Appendix A
4
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course of the meeting, it is true that the commentor was silent at the end of
the meeting when several last calls for questions were made.
Following the meeting, the commentor did advise the chairman that she had
unanswered questions. In consequence, the chairman telephoned the commentor
the following week to advise that additional opportunities could be made
available to her. First, that several USEPA personnel would be attending a
public meeting scheduled on May 12, 1988, by the Michigan Toxic Substances
Control Commission, and that questions on the documents could again be posed
at that time. Second, that a conference call could be arranged at government
expense for her to pose remaining questions to USEPA staff. The commentor
declined to pursue these opportunities.
The chairman handled the questions with reasonable fairness and without
intentional rudeness, despite numerous interruptions. Nevertheless, USEPA
regrets any impression of rudeness that the commentor may have received.
Comment: Has USEPA changed its opinion regarding the significance of windblown
dusts from the Dow plant as a source of contamination outside the plant?
Response: USEPA has not changed its view that windblown dusts from the Dow
Chemical plant site may have been a contributing source of off-site
contamination along with past and current hazardous waste incinerator
emissions and possible past process emissions.
Comment: Why was the final risk assessment done by USEPA contractors instead of
by USEPA staff such as Milton Clark? Is this normal procedure?
Response: USEPA frequently uses contractors to do risk assessments. The
contractor is able to focus extensive manpower and expertise on the problem in
a short period of time in a way that USEPA staff usually cannot. This is
particularly important in a situation such as Midland where a number of
different kinds of risk assessment must be made.
In the case of Midland, USEPA was fortunate to have a number of people on
staff, including Dr. Clark, Donald Barnes, and David Cleverly, who were able
to contribute to the risk assessment and who had done preliminary risk
assessments that the contractor could utilize. The combination of efforts
resulted in a strong document with which all of the authors and other
contributors are pleased.
Comment: Figure III-9 and page 111-61 in the risk assessment report indicate
TCDF analyses were not conducted for soil samples obtained inside the Dow
Chemical plant.
Response: Reference is made to page 3 of Appendix C, Quality Control Summary
in Soil Screening Survey at Four Midwestern Sites (USEPA 1985a), available
review at the Michigan Dioxin Studies document repositories. Analyses for
2378-TCDF were completed for the soil samples in question. However, the
analyses may not be isomer-specific, because sufficient reference standards
for the other tetrachTorodibenzofuran isomers (TCDFs) were not available ar
the time the analyses were undertaken. At this writing, the required
Appendix A
5
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standards still are not widely distributed among the analytical community.
The analyses for TCOFs as a homologue were attempted, but several of the
isomers could not be quantified, because they co-eluted with certain TCDO
isomers. Analysis of the TCDFs could have been completed using a separate
analytical procedure. However, owing to the relatively low toxicity
equivalence factor for TCOFs other than 2378-TCDF (0.001), the supplementary
analyses were not conducted.
Comment: Overall, the risk assessment is too conservative. All of the risk
estimates, both upper bound and lower bound, are based on worst-case potency
factors, and most are based on worst-case exposure values. The reader should not
be led to believe that the real world falls within the USEPA-derived scenarios.
Response: USEPA does not agree that the risk assessment is overly
conservative. Great care was taken in this effort to follow the procedures
specified in the Agency's Guidelines for Carcinogen Risk Assessment (USEPA
1986a), and this approach is consistent with that proposed by the National
Research Council of the National Academy of Sciences (NRC 1983) and with the
scientific principles of carcinogen risk assessment developed by the
President's Office of Science and Technology Policy (OSTP 1985).
Every attempt was made to base the exposure scenarios developed in the risk
assessment on realistic values, including the reasonable worst case scenarios.
The exposure ranges developed for air, soil, and fish were derived from the
literature, are consistent with USEPA policy and guidance, and were reviewed
and approved by the Agency's specialists in exposure assessment. USEPA
believes that most residents of Midland experience dioxin exposures and risks
from air and soil that fall within the ranges of estimates in the document.
Likewise, the Agency believes that the exposures and risks due to fish are
realistic for those who consume fish from the Tittabawassee River. (See also
the first comment and response in Section II below.)
Possible additive effects or synergism of mixtures of chemicals cannot be
assessed using current risk assessment methods, raising the possibility that
the risks are underestimated. Use of the upper 95 percent confidence limit on
the cancer potency factor is conservative by convention. Other factors,
however, discussed on pages 11-20 and 21 of the risk assessment indicate that
the Agency's approach may not be so conservative (e.g., the longer biological
half-life of dioxins in humans compared to animals and the internal exposure
from existing human body burdens of dioxins).
Comment: The risk assessment should have included a worst-case scenario for a
worker inside the Dow plant, who lived near the fence line and ate contaminated
fish from the river.
Response: USEPA generally does not assess risks to workers arising from their
exposures in the work place, as this falls under the purview of the
Occupational Safety and Health Administration (OSHA). It is likely that,
aside from any direct exposures to contaminated soils, wastes, or production-
related chemical mixtures, most workers' exposure levels would fall within the
conservative ranges for the fence-line scenarios. Except for a small group of
individuals who may have had significant direct exposures in the past, the
Appendix A
6
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greatest risk for Dow workers is expected to be consumption of Tittabawassee
River fish, just as it is for other Midland residents.
Comment: The statement on page 111-49 of the risk assessment, line 10, is
incorrect, since there are no residences located even close to the Dow fence line
in that area.
Response: Ambient air data collected at the fence line were pooled to
represent a "reasonable worst case" air exposure scenario. This is properly
characterized as such in the risk assessment and draft risk management
reports.
Comment: The risk assessment should include the statement that the true value of
the risk to humans from dioxin exposure "is unknown and may be as low as zero,"
in accordance with USEPA policy. Considerable epidemiologic evidence collected
to date has not shown serious adverse effects — cancer, reproductive, or other
-- among humans exposed to dioxin at relatively high levels, some sufficient to
cause chloracne.
Response: Owing to incomplete exposure information and other well-established
constraints, human epidemiologic studies are inherently capable of detecting
only comparatively large increases in adverse effects. Negative results from
such studies cannot prove the absence of any effect. USEPA, based upon
review of all available human and animal cancer data, as reviewed in Health
Assessment Document for Polvchlorinated Dibenzo-p-dioxins. has concluded that
2378-TCDD is a probable human carcinogen:
2,3,7,8-TCDD has induced hepatocellular carcinomas in two strains of
female rats and both sexes of one mouse strain, along with the
induction of thyroid tumors, subcutaneous fibrosarcomas and tumors
of the lung, nasal turbinates/hard palate in male rats, and tongue
tumors in female rats. These effects notable occur at extremely low
doses. There is evidence that 2,3,7,8-TCDD is also a promoter and a
cocarcinogen. The evidence of carcinogen!city for 2,3,7,8-TCDD in
animals is regarded as "sufficient" using the EPA interim weight-of-
evidence classification system for carcinogens (USEPA 1984).
The human evidence for the carcinogenicity of 2,3,7,8-TCDD alone is
regarded as "inadequate" using the EPA classification criteria,
because of the difficulty of attributing the observed effects solely
to the presence of 2,3,7,8-TCDD that occurs as an impurity in the
phenoxyacetic acids and chlorophenols. However, the human evidence
for the carcinogenicity of chlorinated phenoxyacetic herbicides
and/or chlorophenols with chlorinated dibenzodioxin impurities is
judged to be "limited" according to the EPA criteria.
The overall evidence for carcinogenicity, considering both animal
and human studies, would place 2,3,7,8-TCDD alone in the 82 category
of EPA's classification scheme, and 2,3,7,8-TCDD in association with
the phenoxy herbicides and/or chlorophenols in the Bl category.
Chemicals in category B are regarded as being "probably"
carcinogenic in humans (USEPA 1985b).
Appendix A
7
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Moreover, given the frank teratogenic and liver effects of dioxin at low
doses, as demonstrated in a number of animal studies, it would be difficult to
conclude that substantial exposure to dioxin (e.g., via consumption of
Tittabawassee River fish) could result in a risk of zero for humans.
Consequently, USEPA did consider, but chose not to use, the phrase, "may be as
low as zero" to describe the risk of exposure to dioxin in the Midland risk
assessment. While this wording has been included in some previous USEPA
documents and appears in the Agency's Guidelines for Carcinogen Risk
Assessment (USEPA 1986a), it is by no means mandated by USEPA policy, and it
was judged inappropriate in this case. On the other hand, the uncertainties
and caveats involved in generation of the risk estimates are clearly and
thoroughly presented in the Midland document, including the statement, "...the
actual risk is not likely to be greater than these levels; the actual risks
could be significantly lower," which appears on pages IV-7, IV-10, and IV-18.
Comment: The statement on page 11-8 of the risk assessment that 2378-TCDD has
been shown to be teratogenic in rats does not appear to be correct based upon a
review of three studies.
Response: USEPA believes that 2378-TCDD has been clearly demonstrated to be
teratogenic in rats. A teratogenic effect is any structural or functional
defect in the offspring of exposed animals. Courtney and Moore (1971) found
kidney abnormalities in the fetuses of pregnant rats exposed to dosage levels
of 0.5 ug/kg-bw-day and 2 ug/kg-bw-day. Giavini (1982 and 1983) observed
cystic kidney anomalies and dilated renal pelvises in fetuses of exposed
Sprague-Dawley rats. Murray et al. (1979) observed increases in dilated renal
pelvises in the Fi generation of a 3-generational study of Sprague-Dawley
rats. These studies are discussed in further detail in the Health Assessment
Document for Polvchlorinated Dibenzo-p-dioxins (USEPA 1985b).
Comment: The statement on cancer promotion mechanisms at page 11-6 of the risk
assessment, tenth line from the bottom, reflects differences in scientific
opinion and is resolved by policy decision, not by scientific consensus. The
document also appears to contradict in several places the direction of the
ongoing internal Agency review of dioxin cancer potency.
Response: USEPA believes that scientific consensus is the preferred approach
to resolving disputes of this kind. The proposed new USEPA cancer potency
factor for dioxin has been a subject of debate among Agency scientists, and
differing points of view have been common. The proposed revision was
published in the Federal Register on June 28, 1988, for public review and
comment. All scientists now have the opportunity to provide their opinions,
which will help develop the basis for USEPA science policy on the issue, For
the purposes of the Midland risk assessment, the dioxin cancer potency factor
used was, properly, the value officially sanctioned by the Agency at that
time. The same potency factor is still in effect at this writing.
Comment: Following completion of USEPA's review of the carcinogenic potency of
2378-TCDD, will the Agency revise the Midland risk assessment?
Appendix A
8
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Response: The Agency currently has no plans to revise the risk assessment.
The estimated carcinogenic risks in the document would increase or decrease in
simple, direct proportion to any increase or decrease in the potency. If the
position of the Agency should change to such a degree that the risk management
conclusions were significantly affected, USEPA would consider reissuance of
the risk management document. A change of this magnitude is considered highly
unlikely.
Comment: Page 11-21 of the risk assessment indicates that the U.S. population
already has a substantial body burden of CDDs/CDFs. Why were existing body
burdens and the consequent internal dose levels not further considered in the
risk assessment, and why were human fat samples not analyzed to determine the
actual levels for Midland residents?
Response: By the cited discussion, the risk assessment acknowledges the
likelihood that prior exposures to dioxin have resulted in substantial body
burdens. Some Midland residents, particularly those who have eaten fish from
the Tittabawassee River, could have body burdens exceeding the national
average. USEPA's calculations suggest that the background body burden of
dioxin in U.S. residents, if incurred during the early life stages, would
yield estimated lifetime cancer risks in the 10~5 to 10~4 range.
Consequently, future exposures to air and soil in Midland would not be
expected to increase the total risk more than a negligible amount,
particularly if the early lifestage (background) risk was closer to 10 4. For
those Midland residents who have accumulated historical body burdens of dioxin
higher than the national average, the additional risks from exposure to
Midland soils and air would be even lower by comparison.
It is important to note that the risk assessment assumes lifetime exposure to
the currently measured concentrations of CDDs and CDFs in air, soil, and fish,
which is unlikely to occur. Remedial measures such as dust control, cessation
of chlorophenol production at the plant, improved incineration controls, and
general clean-up of the site should result in declines in air levels over
time. For soils, lifetime cancer risks may be closer to 10~6, based upon
lower measured soil intake rates reported in recent studies of children. The
risk management report also provides advice on ways to reduce exposures from
contaminated soils. CDD/CDF contamination in Tittabawassee River fish is
expected to decline at some unknown rate reflecting the decreases in the Dow
plant wastewater effluent and the results of the other remedial efforts.
Finally, sampling body fat in order to measure dioxin involves a surgical
procedure. USEPA does not believe that the results of such a study would
alter the proposed actions and advice already provided in the risk management
document.
Comment: Page 59 of the Ambient Air Study lists a number of data limitations,
and page 70 states that the analytical results should be considered minimum
values, as the air sampling method employed was not formally validated at the
time the study occurred. Please explain how the health risks from these emission
levels can be called acceptable in view of past higher emission levels, the
difficulty with the collection of samples, and the limited three-day sampling.
Appendix A
9
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Response: At the time the ambient air sampling study was conducted (September
1984), the monitoring system employed (modified high-volume air sampler with
standard high-volume glass fiber filter and extended throat with polyurethane
foam (PUF) plug) was believed to be the state-of-the-art with respect to
collection of PCDDs and PCDFs from ambient air. This monitoring system was
selected with advice and assistance from the USEPA Environmental Monitoring
Systems Laboratory located at Research Triangle Park, North Carolina. The
survey results demonstrated that more higher-chlorinated CDDs and CDFs were
captured on the glass fiber filter and more lower-chlorinated CDDs and CDFs
were captured on the PUF plug.
Although the collection efficiency of this system had not been fully validated
at the time of the survey, these data suggest that the combination of capture
devices is far more efficient than a glass fiber filter alone for sampling
tetra- through octa-CDDs and CDFs. Because it is possible that some fraction
of the CDDs and CDFs may have passed through the PUF plug, the report notes
that the results should be considered minimum values. It is important to note
that the "minimum" concentrations measured in ambient air were higher than
those estimated from the then current Dow Chemical incinerator emissions,
suggesting that soil particles contaminated by past incinerator emissions, and
contaminated windblown dusts from the plant site, may have been contributing
to the ambient air levels.
When conducting risk assessments, the cancer risk estimates are normally
expressed as "upper bounds." The "upper bound" designation derives from the
many conservative assumptions made regarding the toxicology of the pollutant
in question and the human exposure patterns considered in the analysis. Also,
as explained at the April 28, 1988, public meeting, the risk assessment
conducted for Midland was prospective; that is, it evaluated then-current
exposures and projected them forward — for 70 years, for example, for
estimating cancer risks. Finally, the excess lifetime cancer risks from air
exposures, or from any other exposures evaluated are nowhere described as
"acceptable." For the specific case of ambient air concentrations, which can
be influenced by incinerator emissions and windblown dusts from the Dow plant
site, the estimated cancer risks and non-cancer health impacts based upon 1984
data were not so high that additional remedial measures beyond those
implemented since 1984 (improved incinerator operations and plant-wide dust
suppression program) appeared warranted. This was a risk management
conclusion. To insure that this conclusion was appropriate, the proposed risk
management actions include follow-up ambient air monitoring to assess current
levels.
Comment: Why were immunotoxic effects not fully considered in the risk
assessment? It was noted in the report that animal studies suggest that
immunotoxic effects may occur at exposure levels lower than the Reference Dose
Appendix A
10
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(RfD)* of 1 pg/kg/day. This effect appears to be a more sensitive indicator of
toxicity for these compound than reproductive, teratogenic, or hepatic effects.
Response: Several studies have reported immunotoxic effects from dioxin in
animals at low doses. Clark (1981 and 1983) found that 0.004 ug/kg-bw-week or
0.6 ng/kg-bw-day caused replicative impairment of T-cells. This is very close
to the lowest observed adverse effect level (LOAEL) of about 1 to 1.5 ng/kg-
bw-day observed in the animal reproductive studies. As discussed in the
Midland risk assessment, an uncertainty factor of 1000 * is applied to derive
an RfD of 1 pg/kg-bw-day for long-term exposure. Applying the same procedure
to the Clark studies, which reported the lowest observed immunological effects
to date, an "RfD" of 0.6 pg/kg-bw-day would be derived — very similar to the
RfD based upon the reproductive studies. Therefore, 1 pg/kg-bw-day should be
protective of both immunological and reproductive effects.
USEPA and CDC have derived RfDs and Health Advisories (HAs) using studies
showing less equivocal, more serious effects, such as birth defects. The
significance for humans of T-cell replication impairment by dioxin at low
doses is unclear at this time, and there is no precedent or generally-accepted
procedure for the use of immunotoxicity data in establishing RfDs or HAs.
The Agency believes it is being most protective of human health by using the
data on adverse reproductive and liver effects caused by dioxin. Accordingly,
possible immunotoxic effects were not considered in a quantitative manner, as
were cancer and other, non-cancer health impacts.
Comment: Should ground water analysis have included furans to be complete and
accurate in the assessment of its safety for human consumption?
Response: CDFs and CDDs other than 2378-TCDD were not analyzed in the potable
ground waters or major potable surface water supplies included in the drinking
water portion of the Michigan Dioxin Studies. A more complete analysis of
additional CDDs and the CDFs was not considered necessary, owing to the
affinity of the CDDs and CDFs to solid particles and their general lack of
mobility in soils not affected by high levels of organic solvents.
Comment: Deer hunting is popular in and around Midland, and many deer are
probably consumed by residents. The risk assessment should have considered this
route of exposure, since soil levels lower than 1 part per billion (ppb) have
been cited as of concern for grazing animals.
*The RfD can be defined as an estimate (with uncertainty spanning perhaps an
order of magnitude) of the daily exposure of the human population (including
sensitive subpopulations) that is likely to be without an appreciable risk of
deleterious effect during a lifetime. The RfD supersedes, and is generally
equivalent to, the Acceptable Daily Intake (ADI) values previously used by USEPA
and other agencies to define dose levels for non-cancer endpoints.
**Includes subfactors of 10 because the lowest administered dose was not a
"no observed adverse effect level (NOAEL)," 10 to account for possible inter-
species differences in sensitivity, and 10 to account for possible inira-species
differences in sensitivity.
Appendix A
11
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Response: Given the low levels of dioxins and furans in soils off the plant
site, USEPA does not anticipate that concentrations of concern would
accumulate in deer. The company will be collecting soil samples from grazing
areas so that the potential for accumulation in deer or cattle can be
assessed. Unlike cattle, deer generally do not eat large amounts of grass and
other low-lying ground vegetation and, thus, are much less likely to consume
significant quantities of soil, which provides the main exposure route for
cattle. Finally, deer muscle (venison) contains significantly less fat
(marbling) than that of cattle (beef) and consequently would not tend to
contain as much dioxin, given equivalent levels in the animals' food.
Comment: In the potable well water analyses lab data, levels for calcium,
magnesium, sodium, and potassium are listed for private wells I through P, but
not for wells A through H.
Response: Calcium, magnesium, sodium, and potassium were not analyzed in
samples from wells A through I collected in August 1984. A sample from well G
was also collected in December 1984 and was analyzed for the elements noted
above. The results presented below were inadvertently omitted from the
drinking water report:
Well G -- December 1984
Magnesium 22.6 mg/L
Calcium 60 mg/L
Sodium 21.2 mg/L
Potassium 1.96 mg/L
These results are well within applicable drinking water criteria and have been
provided to the well owner.
Comment: The soil screening survey indicates that the laboratory analysis for
soil samples was conducted on a blind basis (page 9). Was the air sample
analysis also done on a blind basis?
Response: The analyses by USEPA's contract laboratory for the air study were
not conducted on a blind basis, as were those for the soil study. Since the
ambient air sampling and incinerator emissions testing were conducted only in
Midland, with no comparison sites, the source of the samples could not be
fully concealed as was done for the soil study.
Comment: In the soil screening survey report, an April 4, 1985, letter from
Donald Barnes to Michael Cook states that the CDDs/CDFs in the Midland soils
outside the Dow plant are below the 1 ppb CDC level of concern. However, page
111-53 of the risk assessment states that the majority of Midland soil samples
were analyzed for 2378-TCDD only. Please explain Dr. Barnes's conclusion given
the limited sampling analysis.
Response: The conclusion reached by Dr. Barnes regarding levels of CDDs/CDFs
in Midland soils is based upon a review of the 2378-TCDD data reported for all
soils analyzed in Midland and the 2378-TCDD toxicity equivalents for the
Appendix A
12
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smaller number of Midland soils analyzed for 2378-TCDD and other CDDs and
CDFs.
Comment: Is MR I a USEPA laboratory?
Response: MRI (Midwest Research Institute), is not a USEPA laboratory. MRI,
located in Kansas City, Missouri, is a private contract laboratory hired by
USEPA for analysis of certain samples from the Michigan Dioxin Studies.
Comment: Were deep core samples from the Dow plant ever analyzed? If so, what
were the results?
Response: 2378-TCDD analyses of soil core samples at several locations within
the Dow plant were conducted by Dow Chemical at the request of USEPA's
hazardous waste management program. The results were reported to the public
at an MDNR meeting in Midland on June 2, 1987, by Carol Witt of USEPA and also
were summarized in The National Dioxin Study Report to Congress (USEPA 1987b).
In a separate study, subsurface soil samples were collected and analyzed by
Dow Chemical from the two areas of high surface soil contamination in response
to a CERCLA (Superfund) Section 106 order issued by USEPA. The areas of
subsurface soil contaminated with 2378-TCDD (ranging in concentration from
below detection to 1500 ppb) were found to be isolated and confined to
locations where production-related spills or leaks had occurred in the past.
The highest concentrations were found in a small volume of soil 5 to 15 feet
below the surface near a former chlorophenols manufacturing operation. The
contamination in these areas has been, or is being, controlled in connection
with the RCRA permit for the facility. The analytical data are available upon
written request from the USEPA Region V Waste Management Division.
Comment: USEPA has made very little attempt to interpret the risks of fish
consumption for the public.
Response: USEPA strongly disagrees. Through a variety of reports and public
statements, Agency personnel and its contractors, both alone and in
conjunction with the staff of other agencies, have made a considerable effort
to advise the public of the risks of consumption of fish from the
Tittabawassee River. Chief among USEPA's efforts has been the publication and
dissemination of a series of documents which describe and interpret the risks
at varying levels of technical detail. Included are the risk assessment
document, which provides the background technical discussion; the draft risk
management document, which discusses the topic at a level of detail suitable
for a somewhat larger audience; and an eight-page summary or "fact sheet,"
which deals with the issue in concise fashion and has been widely distributed.
In addition, the Agency issued a press release, and Agency staff spent
considerable time discussing the matter with members of the press who were
preparing articles on the topic. Lastly, the Agency held public meetings in
April 1985 and April 1988, in which the risks of fish consumption were
discussed in considerable detail, and in which questions from the public were
answered by a number of experts brought in for the purpose.
Appendix A
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In all of these efforts, USEPA has consistently stated what the estimated
risks are for particular consumption patterns and exposure groups in the most
specific terms possible. The Agency has made it clear that these risks may be
significant, particularly for large-quantity consumers, children, pregnant
women, and women of child-bearing age.
USEPA has recommended that people follow the state's fish consumption advisory
and has assisted the state in further evaluation of the problem, in part by
chemical analysis of fish samples collected from the river in 1988.
Comment: An objective should be included in the monitoring program for
Tittabawassee River fish to better characterize the concentrations of penta-CDD
and CDFs in fish tissues.
Response: The 1988 fish collection program for the Tittabawassee River
described in the draft risk management document included analyses of
penta-CDOs and CDFs. These data are reported in the final risk management
report.
Comment: While the objective of the dioxin risk assessment is to report dioxin
levels and associated risks in Midland, Michigan, the document gives no
comparative data from other locations to put the dioxin issue in perspective.
The report should give a more general perspective, because it currently misleads
the reader into believing that dioxin contamination is only observed in Midland,
Michigan.
Response: While the risk assessment is specific to the environmental
contamination and human exposures for Midland, Michigan, environmental
contamination at other locations was described in other reports of the
Michigan Dioxin Studies. For example, data from several comparison sites were
presented in the soil study report, and contamination at several other
National Dioxin Study Tier 1 and 2 sites was described in the public
information documents accompanying the soil study report.
Comment: Much data on dioxin in fish has been collected over the past several
years, showing low levels of dioxin in many areas throughout the world. The risk
assessment document isolates the data on fish from the Tittabawassee River. The
discussion on fish in Section III should not be viewed in isolation relative to
other dioxin sources and other locations. The reader is led to believe that low
levels of dioxin are only seen in fish from the Tittabawassee River.
Response: There have been several publications by USEPA describing dioxin
data in fish. Most notable among these are the following:
Polychlorinated Dioxins and Polvchlorinated Furans in Fish from
the Great Lakes and Midwest (DeVault 1984);
Dioxin in Great Lakes Fish (USEPA 1986b);
The National Dioxin Study. Tiers 3. 5. 6. ^nd 7 (USEPA 1987a); and
The National Dioxin Study Report to Congress (USEPA 1987b).
Comment: Because the analyses were not isomer specific, assumptions were made
with regard to the isomer distributions. This uncertainty could be significantly
Appendix A
14
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reduced by using the isomer distribution ratios found in Point Sources and
Environmental Levels of 2378-TCDD on the Midland Plant Site of the Dow Chemical
Company and in the City of Midland. Michigan (Dow 1984).
Response: To the extent possible, data from the above-cited report were
included in the derivation of the 2378-toxicity equivalents for Dow plant
emission sources that were used in the exposure assessment.
Comment: The conclusions of the risk assessment should be qualified to the
extent they are based upon analytical results reported as "not detected (NO)."
Response: The NO data exerted a significant influence only in the exposure
assessment for ambient air. The implications of the approach used to handle
these data in the Midland risk assessment are fully explored in the
discussions on pages 111-50 to 52 and IV-7.
Comment: A listing of comparative cancer risks could have been included in the
risk assessment to help the lay person put the estimated risks from dioxin
exposure in perspective (e.g., 3 in 10 overall average lifetime cancer risk and 1
in 8 risk from smoking cigarettes).
Response: Some comparative information was provided by the panel during the
public meeting in Midland on April 28, 1988. USEPA will consider adding such
a listing if the risk assessment document should be revised.
Comment: There is no mention in the study of Dow's massive cleanup efforts
before the sampling began. Soil was removed from the plant site, and the
incinerator was scrubbed.
Response: This comment is similar to one received by USEPA after the soil
study report was released, alleging that USEPA sampled "new dirt" inside the
Dow Chemical plant after a cleanup by Dow prior to the in-plant soil sampling
study. USEPA believes the soil study results clearly indicate that any
cleanup efforts that may have been undertaken by Dow Chemical did not
materially impact the conclusions of the study. 2378-TCDD was detected in
every targeted and random soil sample collected. These data were used by
USEPA to issue a CERCLA (Superfund) Section 106 order to Dow Chemical for
corrective actions at the plant.
Comment: Page 1-8, paragraph 2: The average represents an average of soil
suspected of being contaminated; i.e., the most highly contaminated areas were
sampled.
Response: The USEPA in-plant soil sampling program included both targeted an
-------
Comment: On page II-9 of the risk assessment, last paragraph, the teratology no
observed adverse effect level (NOAEL) is incorrectly used as a lowest observed
adverse effect level (LOAEL).
Response: As discussed in the text, there has been debate over whether the
Murray et al. (1979) study showed a NOAEL or a LOAEL. USEPA has concluded
that the lowest dose tested was a LOAEL.
Comment: On page 11-14 of the risk assessment, first paragraph, the comments
concerning the potential for risks existing below the RfDs and HAs appear to be
highly speculative. Is this consistent with Agency policy?
Response: USEPA policy on the use of immunotoxicity data for the development
of RfDs and HAs is currently under review. Because the studies cited on the
referenced page of the risk assessment indicate the possibility of toxic
effects below the current LOAEL, adoption of a procedure utilizing the
immunotoxicity data could lower the RfD and HAs.
Comment: On page 11-19 of the risk assessment, indent 2, there is a need for
greater emphasis on the limited information on carcinogen!city for some of the
isomers included in the TEF calculations.
Response: The Agency is aware of the assumptions made in developing the TEF
procedure which it has adopted as interim science policy, and it intends to
issue periodic updates. A complete discussion of this matter can be found in
Interim Procedures for Estimating Risks Associated with Exposures to Mixtures
of Chlorinated Dibenzo-p-Dioxins and -Dibenzofurans (CDDs and CDFs) (USEPA
1987c).
Comment: On page III-3 of the risk assessment, line 2, and page 111-15, line 3,
the word "significant" should be replaced with "detectable".
Response: USEPA agrees that the "significance" of the results reported here
is limited to the fact that CDDs/CDFs were detected.
Comment: On page 111-15 of the risk assessment, paragraph 2 and the section as a
whole assume that Site 1 is ambient and the other sites are influenced by the Dow
waste incinerator. Actually, Site 1 is also downwind of the heaviest
concentration of auto exhaust and home heating.
Response: Site 1 is described in the risk assessment and in the ambient air
study report as "upwind" not "ambient." This site was selected to distinguish
any additional dioxin contamination impacts on Sites 2 and 4, located
"downwind" of the incinerator and major production areas of the plant. Based
upon prevailing wind directions, Site 1 is not downwind of the heaviest
concentrations of auto exhausts. Also, since the ambient air study was
conducted during mid-September, home heating could not have had a significant
impact on the results, even if home heating were a significant source of COD
and CDF emissions, which the Agency believes is extremely unlikely.
Appendix A
16
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Comment: On page 111-16 of the risk assessment, paragraph 2, the Dow Point
Source Survey should be reflected in the statement concerning availability of
data.
Response: The Dow study is cited in line 6 of this paragraph as "Dow 1984."
While primary emphasis was placed upon the USEPA data for the reasons stated,
the Dow data were fully reviewed and considered in the preparation of the risk
assessment.
Comment: On page 1 1 1-35 of the risk assessment, third line from the bottom, the
downwind increment of 136 degrees (58 percent of the total time) seems very high.
There ought to be a profile giving time vs. percent of maximum on a more narrow
basis.
Response: USEPA agrees that the downwind increment selected (58 percent of
the time) is on the high side. However, this increment is supported by the
analysis of available meteorological data and is consistent with the
conservative nature of the risk assessment.
Comment: On page 1 1 1-37 of the risk assessment, the statement that monitoring
Site 3 was less downwind than Sites 2 and 4 is not correct. Air dispersion
modelling using USEPA' s ISCLT program with the FLINT77 STAR deck show that
maximum predicted concentrations are directly north of a source and fall off
equally on each side of north up to about 15 degrees off north. Therefore, Sites
2 and 3 were equally downwind, and Site 4 was less directly downwind.
Response: Based upon a review of the meteorological data obtained at the time
of the ambient air study, only those samples from Sites 2 and 4 collected on
the following dates were analyzed:
_ Date _ Average Wind
September 8-9, 1984 199 degrees, 6 mph
September 12-13, 1984 191 degrees, 6 mph
September 22-23, 1984 212 degrees, 5 mph
Accordingly, most of the data were collected when Sites 2 and 4 were, in fact,
more in the downwind direction than Site 3. The statement made on page 111-37
of the risk assessment is that Site 3 is "...less directly downwind of the
incinerator and major production area." Given the meteorology on the sampling
days, this statement is correct.
Comment: With regard to the statement on page 111-45 of the risk assessment,
line 8, it should be noted that there are no residences located at or near 0.6
miles north and northeast of the incinerator.
Response: The statement in question refers to the estimated location of
maximum annual average ground level concentrations of CDDs and CDFs, not trie
location of residences.
Appendix A
17
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Comment: On page 111-69, the assumption that exposure to soil is possible for
247 days per year is high for Midland. Snow-covered and frozen ground reduce the
number of days below 247.
Response: Recent studies by Clausing (1987) and Calabrese (1988), as well as
previous work (see Hawley 1985), indicate that young children may be exposed
to indoor dusts, which typically have the same contaminant concentrations as
soils found outside. Therefore, exposures may occur throughout the year.
Adults, too, could be exposed to indoor dusts on a daily basis. Because
ranges of the soil exposure parameters, from typical to worst-case, were used
in the assessment, the total number of days of exposure becomes less critical,
as does the issue of exposure to indoor dust.
Appendix A
18
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II.
COMMENTS RECEIVED AT THE PUBLIC MEETING
Comment: The fish consumption scenarios evaluated by USEPA in the risk
assessment are unrealistically conservative when considered in light of the
results of MDPH's recent creel survey of Tittabawassee River fishermen.
Response: Results from the MDPH creel survey (Smith and Enger 1988) for those
respondents who reported that they caught and consumed fish from the
Tittabawassee River (49 percent), in fact, tend to support the fish
consumption scenarios developed for the risk assessment . The consumption
rates presented below were developed from the creel survey data, making the
assumption that the size of a typical fish meal ranged from 113 to 255 grams,
or 4 to 9 ounces (the same assumption used in the risk assessment). The
principal focus of the risk assessment is on those people who actually eat
fish from the river.
COMPARISON OF TITTABAWASSEE RIVER FISH CONSUMPTION RATES
USEPA RISK ASSESSMENT*
TITTABAWASSEE RIVER CREEL SURVEY*"
Scenario
General Consumer
Great Lakes Consumer
High Sports Fisherman
Level 1
Level 2
Consumption
Rate
3.1 Ibs/yr
12.9 Ibs/yr
38.6 Ibs/yr
80.4 Ibs/yr
Results Reported for 343 Respondents
Who Catch and Eat Tittabawassee Fish
58% Eat Less Than 3.0 to 6.7 Ibs/yr
28% Eat About
3.0 to 6.7 Ibs/yr
Plausible Maximum Consumer 80.4 Ibs/yr
10% Eat About 12.9 to 29.2 Ibs/yr
4% Eat More Than 12.9 to 29.2 Ibs/yr
*From Table II1-2, Risk management document (USEPA 1988c)
**Annual consumption rate ranges based upon 4 oz to 9 oz meal sizes.
Appendix A
19
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The creel survey data also show that about 14% of 360 fishermen responding
process (clean and freeze for later consumption) from 24 to 59 Ibs/year of
game fish, and about 10% process more than 50 Ibs/year. There were seven
people reporting that they process from 24-49 Ibs/year of carp or catfish and
three people reporting processing more than 50 Ibs/year of carp or catfish. A
number of respondents reported sharing their catch with other family members
including children. Accordingly, Region V believes these data are consistent
with the fish consumption rates selected for the risk assessment.
Comment: Removal of fat according to the directions in the Michigan Fishing
Guide and cooking in ways that allow additional fat to drip away can reduce
contaminants in the fish actually eaten. According to new data from testing of
"restructured" carp fillets [surimi], combined trimming and cooking reductions
can amount to 90 percent, and charbroiling alone will produce a 40 to 70 percent
reduction. Why did USEPA do the risk assessment on uncooked, skin-on fillets?
Response: As a matter of policy, USEPA and the Great Lakes states provide
fish consumption advice based upon the analysis of edible-portion samples.
The Agency and the Great Lakes states have agreed that the best representation
of the edible portion is a skin-on fillet. Fish cleaning and cooking advice
is provided that, if followed, should result in some reduction in risk. The
extent of this reduction has never been well-documented and is variable,
depending upon the skill of the fish cleaner, the detailed cooking conditions,
and, probably, the fish species and the nature of the contaminants. There is
no generally-accepted value available for risk assessment calculations. The
following is a statement of the agreed policy for the Great Lakes area, as
published by Michigan (Humphrey and Hesse 1986):
It was agreed that all monitoring for Great Lakes fish shall be
done on a skin-on fillet basis, unless otherwise specified. No
adjustments should be made in risk estimations based on
anticipated reduction in contaminants from recommended trimming
and cooking techniques, although all agencies should broadly
publicize these methods as a means of further reducing one's
exposure to contaminants from fish consumption.
Comment: The U.S. Food and Drug Administration (FDA) permits fish to be sold
for consumption with higher levels of these pollutants—25 parts per trillion
(ppt) 2378-TCDD and 2 parts per million (ppm) PCBs—than are present in the
Tittabawassee River game fish.
Response: The FDA regulates fish in interstate commerce and has made clear
that its action levels are not directly applicable to consumption by sports
fishermen and other localized situations where specific subpopulations are
exposed to contaminants in fish. To accomplish its mission, the FDA uses
procedures and assumptions quite different from those of USEPA, making
comparisons of the "acceptable levels" difficult. For example, for 2378-TCDD,
FDA assumed that the average contaminant level in the fish was only one-third
of the guideline level cited (i.e., about 8 ppt). FDA further assumed that
the average person ate 15.7 g/day of fish, but that only 10 percent of these
fish were contaminated. Additional differences appear in the methods used to
Appendix A
20
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interpret the results of the critical animal tests and in the calculations
used to move from the animal model to humans. As explained above, USEPA has
carried out its Midland risk assessment in conformity with its established
procedures and policies for human health risk assessment (USEPA 1986a). The
protocols and assumptions utilized by USEPA have been set out in great detail
in the risk assessment document and herein. Ultimately, it is up to the State
to determine the levels of contaminants that are acceptable in the food supply
of its residents and at what point action should be taken to restrict
consumption.
Comment: Epidemiological studies of human populations exposed to dioxins,
including those at Seveso, Italy, and Times Beach, Missouri, have not shown
adverse reproductive effects attributable to the exposures.
Response: USEPA does not believe that the findings to date are conclusive
one way or the other. For additional detail, please refer to the response to
the second comment on page 7 of Section I, above.
Comment: Pica is not as uncommon a disorder as the risk assessment implies.
Response: Pica can be defined as consumption by children of soil at rates in
excess of the normal range of about 0.1 to 0.5 grams per day — often as much
as 10 grams per day or more. It occurs, on the average, in about 1 out of
every 200 children.
Comment: With regard to a sample collected at the Rockwell dump that had been
sent to USEPA's Minneapolis laboratory, why did Mr. Zar [the chairman of the
meeting] instruct Mr. Larry Fink, then an USEPA employee, not to discuss this
sample?
Response: Mr. Zar could not recall any such conversation at the time of the
meeting. However, he contacted Mr. Fink, who was no longer with USEPA, the
following day and was reminded of a conversation that took place at the
Agency's Duluth laboratory in August 1985, regarding a sample from the
Mapleton Public Well that had just been received by the laboratory. Mr. Fink
remembered Mr. Zar advising him in strong terms that it would be inappropriate
to discuss the sample publicly until final analytical results had been
obtained.
The sample in question subsequently was analyzed by the Duluth laboratory, and
by the Dow Chemical Company as well. Neither laboratory found 2378-TCDD in
the sample, although analysis of a previous sample had yielded an apparently
false positive at one of three participating laboratories. These results and
further discussion are presented on pages 23 and 25 of Michigan Dioxin
Studies; Screening Survey of Surface Water Supplies. Potable Ground Water, and
Dow Chemical Brine Operations (Barna and Amendola 1985), available for review
in the Michigan Dioxin Studies document repositories.
The results for the above sample and the other results published in the above-
cited report were the subject of a public meeting held by USEPA in Midland on
December 19, 1985, and were further discussed in a number of newspaper
articles during the next several days. USEPA is satisfied that the Mapleton
Appendix A
21
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well was adequately tested and that the results were fully reported to the
public.
Comment: What is an acceptable level of dioxin in the sediments of the
Tittabawassee River? What could be done about contaminated sediments?
Response: Currently there are no published criteria specifying safe levels of
dioxin in river, lake, or harbor sediments. USEPA's concern with regard to
the sediments is that remaining pockets of relatively highly contaminated
sediments might be contributing significant amounts of dioxins to the fish
either directly or via other organisms or the water column itself. The clean-
up of the water and the fish might be retarded by such a reservoir of
contaminants, even though the levels in wastewater and other external inputs
continue to drop. In the river studies performed to date, 2378-TCDD has not
been detected in the sediments, and the bottom of the river has appeared to be
composed rather uniformly of sand and gravel, which would not be conducive to
dioxin accumulation. Monitoring proposed in Section IV(C)(2)(b) of the risk
management document is aimed at confirming whether or not pockets of organic
sediments do exist downstream of the Dow Chemical plant and, if so, whether
they contain detectable levels of dioxins. If significantly contaminated
sediments were found and confirmed, serious consideration would be given to
removal by dredging or excavation.
Comment: What is the range of soil concentrations of concern, for the chemical
2378-TCDD.
Response: In his response to the previous comment at the meeting, Dr.
McClanahan indicated that the level of concern in a particular situation could
be in the neighborhood of 1 part per billion (ppb), but that the specifics of
the individual site would govern. Basically, one has to go through a site-
specific analysis of the kind that has been done for Midland. The levels
found in Midland residential and public use area soils were all well under
1 ppb, and USEPA's assessment indicates that the component of risk, to the
residents via this route of exposure is negligible, with the possible
exception of children who eat large amounts of soil due to the medical
disorder, pica.
Conroent: If no 2378-TCDD was found at the Saginaw Bay drinking water intake at a
detection limit of 5 to 10 parts per quadrillion (ppq), how does USEPA account
for the findings of high levels in common terns and tern eggs—-25 and up to 3763
parts per trillion (ppt), respectively—in the Saginaw River and Bay area?
Response: Terns are at the top of the aquatic food chain and are
extraordinarily efficient at concentrating chemicals such as dioxin. It is
not unusual to observe bioconcentration factors of 100 thousand or a million
between water and the tern eggs. Consequently, there is no inconsistency in
finding 2378-TCDD at hundreds or even thousands of ppt in tern eggs and not
finding it in the water at less than 10 ppq.
Comment: Were the contaminants other than dioxins that were found in the fish
considered in developing the fish consumption advisory?
Appendix A
22
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Response: Fish consumption advisories are the responsibility of the Michigan
Department of Public Health (MDPH). At the public meeting, John Hesse of the
MOPH responded that the other chemicals were considered individually as to the
need for an advisory. In addition, the "10-percent rule" was applied: if more
than 10 percent of the fish population were found to require advisories,
regardless of the contaminant, then an advisory was put in place.
Comment: Why did USEPA recommend that the 1988 walleye sampling be done in the
spring after the fish have been out in the bay all winter?
Response: It is the Agency's understanding that the fish are in the river and
the mouth for some time prior to the spring run. Samples collected in 1985
showed little difference in dioxin concentration between those caught in the
spring and those caught in the summer. Furthermore, the spring run is the
most heavily fished period of the year, so it is likely to be more
representative in terms of the fish that people are eating.
Comment: [By a resident of Ingersoll Township] Ingersoll Township has been in
favor of USEPA's involvement with the Oow Chemical Company Midland plant site
from the very beginning. The whole investigation process has been very
beneficial from the standpoint of the community and the company.
Response: USEPA acknowledges and appreciates the comment.
Comment: [By a representative of Dow Chemical Company] Dow would like to thank
USEPA for conducting the study and thank the community members for urging Dow,
through the years, to change the way it does business. The study was a positive
experience for Dow and is probably as comprehensive, substantive, and exhaustive
a study as has ever been done on any community. The study probably will serve as
a model for future USEPA efforts. Dow pledges its continued efforts to resolve
this problem.
Response: USEPA acknowledges and appreciates the comment.
Appendix
23
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REFERENCES
BARNA, D.R., and AMENDOLA, G.A. 1985. Screening survey of surface water
supplies, potable ground water, and Dow Chemical brine operations.
Environmental Services Division, Region V, USEPA, Westlake, Ohio.
CALABRESE, E. 1988. Preliminary results of University of Massachusetts,
Amherst, epidemiological soil and dust ingestion study. Presentation at
Colloquium on Oral and Dermal Exposure to Soil and Dust. Risk Assessment
Forum, USEPA, Washington D.C. March 23.
CLARK, D.A., GAULDIE, J., SZEWCSIL, M.R., and SWEENET, G. 1981. Enhanced
suppressor cell activity as a mechanism of immunosuppression by 2,3,7,8-
tetrachlorodibenzo-p-dioxin. Proc. Soc. Exp. Biol. Med., 168(2):290.299.
CLARK, D.A., SWEENEY, G., SAFE, S., HANCOCK, E., KILBURN, D.G., and GAULDIE, J.
1983. Cellular and genetic basis for suppression of cytotoxic T cell
generation by haloaromatic hydrocarbons. Immunopharmacology 6:143-153.
CLAUSING, P., BRUNEKREEF, B., and VAN WIJNEN, J.H. 1987. A method for
estimating soil ingestion by children. Int. Arch. Occup. Environ. Health
59:73-82.
COURTNEY, K.D., and MOORE, J.A. 1971. Teratology studies with 2,4,5-T and
2,3,7,8-TCDD. Toxicol. Appl. Pharmacol. 20:396-403.
DEVAULT, D. 1984. Polychlorinated dioxins and polychlorinated furans in fish
from the Great Lakes and Midwest. EPA-905/3-84-006. Great Lakes National
Program Office, USEPA, Chicago, Illinois. October.
DOW CHEMICAL. 1984. Point sources and environmental levels of 2378-TCDD
(2,3,7,8-tetrachlorodibenzo-p-dioxin) on the Midland Plant site of the Dow
Chemical Company and in the city of Midland, Michigan. Dow Chemical Company,
Midland, Michigan. November 5.
GIAVINI, E., PRATI, M., AND VISMARA, C. 1982. Effects of 2,3,7,8-
tetrachlorodibenzo-p-dioxin administered to pregnant rats during the
preimplantation period. Environ. Res. 29(1):185-189.
GIAVINI, E., PRATI, M., AND VISMARA, C. 1983. Embryotoxic effects of 2,3,7,8-
tetrachlorodibenzo-p-dioxin administered to female rats before mating.
Environ. Res. 31:105-110.
HAWLEY, O.K. 1985. Assessment of health risk from exposure to contaminated
soil. Risk Analysis 5:289-302.
Appendix A
24
-------
HUMPHREY, H.E.B., and HESSE, J.L. 1986. Sport-caught fish consumption
advisories: Philosophy, procedures and process. Draft procedural statement.
Center for Environmental Health Sciences, Michigan Department of Public
Health. November.
MURRAY, F.J., SMITH, F.A., NITSCHKE, K.D., HUMISTON, C.G., KOCIBA, R.J., and
SCHWETZ, B.A. 1979. Three-generation reproduction study of rats given
2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the diet. Toxicol. Appl.
Pharmacol. 50:241-251.
NATIONAL RESEARCH COUNCIL (NRC). 1983. Risk assessment in the Federal
Government: Managing the process. National Academy Press, Washington, D.C.
OFFICE OF SCIENCE AND TECHNOLOGY POLICY (OSTP). 1985. Chemical carcinogens: A
review of the science and its associated principles. Executive Office of the
President. February. Fed. Reg. 50:10371-10442 (March 14).
SMITH, B.F., and ENGER, E.D. 1988. A survey of attitudes and fish consumption
of anglers on the lower Tittabawassee River, Michigan. Under contract for
Center for Environmental Health Sciences, Michigan Department of Public
Health. April 26.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1984. Ambient water quality
criteria for 2,3,7,8-tetrachlorodibenzo-p-dioxin. EPA 440/5-84-007. Office
of Water Regulations and Standards. February.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1985a. Soil screening survey at
four midwestern sites. EPA 905/4-85-005. Environmental Services Division,
Region 5. Westlake, Ohio.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1985b. Health Assessment Document
for polychlorinated dibenzo-p-dioxins. EPA 600/8-84-014F. Office of Research
and Development. Washington, D.C.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1986a. Guidelines for carcinogen
risk assessment. 51 FR 33992-34003.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1986b. Dioxin in Great Lakes
fish. Great Lakes National Program Office and Region V, Chicago, Illinois.
May.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1987a. National dioxin study,
tiers 3, 5, 6, and 7. EPA-440/4-87-003. February.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1987b. National dioxin study
report to Congress. Office of Solid Waste and Emergency Response.
Washington, D.C. EPA/530-SW-87-025. August.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1987c. Interim procedures for
estimating risks associated with exposures to mixtures of chlorinated dibenzo-
p-dioxins and dibenzofurans. EPA/625/3-87/012. Risk Assessment Forum.
March.
Appendix A
25
-------
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1988a. Risk assessment for dioxin
contamination at Midland, Michigan. EPA-905/4-88-005. Region V. April.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 19885. Proposed risk management
actions for dioxin contamination at Midland, Michigan. EPA-905/4-88-006.
Region V. April.
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1988c. Risk management recom-
mendations for dioxin contamination at Midland, Michigan. EPA-905/4-88-008.
Region V. November.
Appendix A
-------
APPENDIX B
1988 TITTABAWASSEE RIVER FISH MONITORING PROGRAM
Twenty spring run, Tittabawassee River walleyes were collected near Midland
by the Michigan Department of Natural Resources on April 12, 1988. Skin-on
fillets from each fish were analyzed for PCBs, PBBs, chlorinated styrenes,
hexachlorobenzene, and several chlorinated pesticides and derivatives by the
Michigan Department of Public Health. Each sample was analyzed for 2378-TCDD by
Dow Chemical Company, and four samples were analyzed by both Dow Chemical Company
and USEPA for 2378-substituted CDDs and CDFs. The analytical results are
attached.
Presented below is a comparison of recent Tittabawassee River walleye (skin-on
fillet) monitoring data for 2378-TCDD and PCBs (all are mean concentrations):
2378-TCDD
PCBs
Tissue Cone.
Year
1983
1985
1987
1988
Number
of Fish
5
19
Tissue
Cone.
3.9 ppt
4.5 ppt
Number
of Fish
Aroclor
1254
Aroclors
1248+1254
3 1.3 ppt
20 3.1 ppt
14 0.59 ppm
20 0.57 ppm 0.81 ppm
These data indicate a decrease in 2378-TCDD levels in 1987-1988 walleye from
those measured in 1983-1985. This trend generally follows the reduction in
2378-TCDD discharge levels from the Michigan Division plant of Dow Chemical
Company. Comparison of the average PCB data indicates no change in fish
concentrations from 1985 to 1988. On the following page is a presentation of
the 1988 data for 2378-TCDD, 2378-TCDD TEQs, and PCBs by size class,
demonstrating higher contaminant levels in larger fish. A full listing* of the
analytical results is attached.
*[Results of chemical analysis of Tittabawas^ea River fish collected
April 12, 1988.] Transmitted by L. Duling, Fish Contaminant Monitoring Program,
Surface Water Quality Division, Michigan Department of Natural Resources, to
H. Zar, Water Division, Region V, USEPA, Chicago, Illinois. July 29, 1988.
Appendix
1
B
-------
TABLE B-l
CDDS/CDFS AND PCBS IN 1988 SPRING WALLEYE FRCM THE THTABAWASSEE RIVER
Number of
Fish Size Class Weioht
6
6
8
Ranae
15" - 18" 680-780
18" - 22" 1240-1640
22" - 26+" 2170-3660
(a)
703
1450
2650
2379-TCI'P (ipt)
Ranae x
1.1-2.1 1.7
1.6-4.0 2.7
2.2-8.6 4.4
2378-TCDD TEQs (ppt)
Ranae x
2.0-3.9 3.1
3.0-7.4 4.9
4.1-16. 8.2
PCBs (ppn)
Ranae x
0.26-0.64 0.43
0.36-1.2 0.72
0.48-2.2 1.2
Average (20 fish)
3.1
5.7
0.81
Notes: (1) Analyses by Michigan DNR; Dow Chemical Company; and USEPA, Duluth MN.
(2) 2378-TCDD TEQ estimated from four USEPA analyses with mean TEQ/2378-
TCDD ratio of 1.85 (range: 1.63 to 2.23).
(3) PCB values are the sum of measurements for Aroclors 1248 and 1254.
-------
FISH OMTAIUNANT NONITQR1N6 PRQ6RAH
HICH16A* DEPARTMENT OF NATURAL RESOURCES
Hittrbodyi
location:
[M
88001-01
88001-03
38001-03
38001-04
88001-09
38001-10
38001-13
88001-14
88001-15
38001-16
88001-17
38001-18
38001-22
88001-23
88001-24
88001-27
88001-28
88001-29
38001-30
88001-31
Tittabmsut
HidUnd
SpKIM
falltyt
ttalltyt
lUlltyt
Malltyt
fcHtyt
talltyt
IMlltyt
talltyt
tolltyt
lUlltyt
Ualltyt
Halltyt
tolltyt
Halltyt
Halltyt
tolltyt
Hilltyt
lalltyt
Mailiyt
Hilltyt
Rmr
Sti
N
H
N
H
H
K
N
N
N
If
H
F
N
N
F
F
H
R
F
F
STORE! Mo.: 560143 Collection Oite: 4/12/33
Srid No.: Lib : DM, EPA, HMM
ItnjtN Mtiqht Sup It I Fit
(in) llbi) Typt Z F«t (RtpiKJtt) CotMflts
16.54
17.13
17.13
17.13
16.93
17.52
20.87
21.06
21.26
20.47
21.06
21.46
23.62
23.23
23.20
26.77
25.20
24.02
24.02
24.02
1.32
1.52
1.30
1.34
1.72
1.50
3.02
3.20
3.17
2.73
3.04
3.62
5.18
5.07
6.15
6.13
5.64
4.78
5.69
8.07
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
f
r
1.2
1.4
1.8
1.6
2.7
1.6 1.6
2.2
2.0
1.8
1.25
2.65
1.2 1.2
5.00
2.95
2.25
1.35
3.1
2.3
2.4
1.6 1.7 Lvipocyiti)
F indicitM ikin-m filltt.
Ft indicittt itin-oM filltt.
E indicatH 199 saaplt only.
H indicatn rtolt *»§*•
0 indicatH othtr tuplt typt.
Appendix B
3
-------
FISM OMTMINMT HMITMIB P1NIRM
NIQIIiMI OEPMTKIT OF MTUML KSOUKCS
Natirkotfys
Location:
t-QiloNaM
IN
98001-01
88001-03
98001-05
88001-04
8M01-09
98001-10
•
8N81-13
•8001-14
98001-13
NOOI-I4
88001-17
08001-18
•
08001-22
81801-23
98001-2*
98001-27
98001-28
88001-29
•8001-30
88001-31
•
<•!/*!>
0.002
0.002
0.003
0.002
0.004
0.003
0.003
0.009
0.010
0.003
0.004
0.014
0.003
0.003
0.021
0.014
0.004
0.011
o.oa
0.029
0.004
0.009
0.010
TittaftaMSMt Rim
NitflaMl
cif- tram-
NMcklor NMCklor
y^.
0.001
O.OOIK
0.002
0.001
0.001
0.002
0.001
0.004
O.ON
0.003
0.003
0.009
0.002
0.003
0.004
0.004
0.002
0.004
0.021
0.024
0.004
0.009
0.009
(•f/kf)
0.002
0.001
0.002
0.001
0.002
0.001
0.081
0.003
0.084
0.007
0.004
0.018
0.004
0.004
0.019
0.012
0.003
0.011
0.042
0.099
0.008
0.018
0.011
toy
cklortfaM f-cklortfant
(•f/kf)
O.OOIK
O.OOIK
O.OOIK
O.OOIK
O.OOIK
O.OOIK
O.OOIK
0.003
0.004
0.002
0.001
0.087
O.OOIK
O.NIK
0.004
0.004
0.002
0.004
O.ON
O.N7
0.082
0.002
0.002
(M/kf>
O.N1
0.001
O.N2
0.001
0.002
0.001
O.NI
0.003
0.004
0.002
0.002
0.009
O.N2
O.N2
0.009
O.ON
0.001
0.009
0.010
0.009
O.NIK
0.009
0.009
CollKtion Battt 4/12/N
Huachlort- OctachHro- PMtackliri-
tttl im taunt styrMt ityrttt
(•f/kf)
O.NIK
O.NIK
O.NIK
O.OOIK
O.NIK
O.NIK
O.NIK
O.NIK
O.NIK
O.NIK
O.NIK
0.004
O.NIK
O.NIK
O.NIK
0.013
0.002
0.009
0.014
0.011
0.009
0.004
0.004
(•f/kf)
0.004
O.NI
O.NI
O.NI
O.NI
O.NI
O.NI
0.003
0.004
0.002
O.NI
0.002
O.N1
0.002
0.004
0.002
O.NI
O.NI
0.003
0.003
O.NI
0.009
0.009
(•f/kf) (M/kf)
0.003
O.NI
0.002
O.NI
O.N2
O.N2
0.002
0.002
0.003
0.083
O.N2
0.004
0.002
0.082
0.089
0.003
0.002
0.082
0.084
.004
.002
.009
.003
.004
.ON
.ON
.009
.084
.ON
.ON
.012
.089
.804
.012
.007
.003
.004
.010
O.N7 0.019
0.082 0.004
0.004 0.019
0.004 0.019
PCI PCI
ft-1248 ft-1254
(•f/kf)
0.17
0.21
0.37
0.22
0.33
0.23
0.22
0.20
0.37
0.43
0.24
0.99
0.22
0.23
0.87
0.02
0.03
0.02
0.10
0.09
0.04
0.07
0.04
tM/kf>
0.09
0.14
0.27
0.14
0.24-
0.17
0.18
0.39
0.42
0.39
9.27
0.41
0.14
0.14
0.99
0.97
0.43
0.7
1.84
2.N
0.39
0.39
0.33
K iMcitn •fcttctri at tte fetKtiM 1ml
Appendix B
4
-------
-•5
i
r*. —.
2*f
581
Z**
rJJE IP
3 =
g
ft
I
^^ ^cJ-:-^^^^,,,,.^^^^*' ~
2
ir §§§§ iiSSII issSssis^ 0000000 °o2 J6
§§!!
» *^- iisi §iii§§ iiiiisiii isn ?!"~
lit
1 ii"*
i nn mill sssssissi is»
f! Ml
v -S * X • £
• <• k ««.«•»» pi
iiii'ii'iii'iii'illi!"iii'
I
O.
-------
FISH CONTMIMNT MMITORIM PMGRM
lUOUMN BEMWKMT OF MTUML RESOURCES
TittasuufMt Rivir
Locations Hocjtiodi ftitflMtf CollKtiw Mn 4/12/88
1,2,3,7,8,9- 1,2,3,4,4,7,8- 2,3,7,8- 2,3,4,7- 3,4,4,7- 2,4,4,8- 1,2,3,7,8- 2,3,4,7,8- 2,3,4,4,7- 1,2,3,4,8-
feCH *CtO KM TC8F TC8F TC8F TC* fidf PtCIF PtdF ftC*
188
K irticatM mUbct* it tfet MictiM 1ml
88001-01
88001-03
88001-09
88001-04
•
88001-09
88001-10.
88001-13
88001-14
88001-19
t
88001-14
88001-17
88001-18
88001-22
88001-29
88001-24
88001-27
88001-21
1
•
88001-29
88001-30
88801-31
•
1.38K
IK
1.37K
IK
I.3BK
1.371
IK
1.38K
IK
U47K 3.20
3K
2.09K 99.40
2K
1.84K 1.2
2. Ill 3.38
3
3.4« 1.9
21
4.83 0.4K
8.9
12.87 O.S3K
19
14.12 0.94K
14.11 0.581
28
29.82 0.92K
29
0.4* 1.29
1.2
0.4* 0.40 3.U
1.4
0.4* 1.12 2.49
9.4* 0.93 3.03
2.2
0.4* 0.41 4.17
4.4
2.0X 1.04X
1.7
2.44 0.81
2.7
3.04 1.23
3.49 2.11
4.4
9.07 1.10
9.4
3.20
4.48
4.93
3.48
Appendix B
6
-------
*•
3
§*
si
fi
ft
•*
£:*!•
Si
3&~
,. *
•'jkff
B
*;-:
55
312
i
ig* mm
•» r+* • ^ •
BI B
B
II
ii
as
TTTT II III ill Illll III
liii Ii iii Hi iiiii iii
^^
1
-------
APPENDIX C
1987 USEPA PRELIMINARY VEGETABLE SAMPLING PROGRAM
In November 1987, Region V, with the cooperation of the Michigan Departments
of Agriculture, Health, and Natural Resources conducted a preliminary screening
program of home-grown vegetables from two gardens in Midland, Michigan, and a
control garden in Eagle, Michigan. Samples were collected by the Michigan
Department of Agriculture. Because the sampling was conducted after the end of
the growing season, certain vegetables were obtained from homeowners after they
had been cleaned and frozen. These were sent to the laboratory as obtained. The
others were collected directly from the gardens, rinsed off with tap water, and
sent to the laboratory. Composite soil samples from each garden, made up of six-
inch soil plugs, were obtained in the immediate areas where the vegetables were
grown.
Samples were analyzed for CDOs and CDFs at Triangle Laboratories, Research
Triangle Park, North Carolina, a contract laboratory for USEPA. A summary of the
results is presented in terms of 2378-TCDD and 2378-TCDD TEQs in the attached
table. The results indicate laboratory blank contamination at sub-part-per-
trillion levels for certain 2378-substituted CDDs and CDFs, and, in one blank
sample, for 2378-TCDD.
For Garden 1 (Midland), the soil contained 34 ppt 2378-TCDD (48 ppt 2378-
TCDD TEQs). There was no detectable 2378-TCDD in peeled carrots or onions, and,
given the low levels of blank contamination, there was no discernable uptake of
other CDDs and CDFs (expressed as 2378-TCDD TEQs) in these vegetables. The
laboratory solvent blank for analysis of a lettuce sample contained 0.3 ppt 2378-
TCDD and 2.1 ppt 2378-TCDD TEQs, indicating severe blank contamination, and
rendering the analysis of this sample unacceptable. The remaining sample volume
was insufficient for a reanalysis.
For Garden 2 (Midland), the soil contained 11 ppt 2378-TCDD (17 ppt 2378-
TCDD TEQs). An unpeeled beet sample contained less than 0.1 ppt 2378-TCDD and
2378-TCDD TEQs, indicating no significant contamination. For Garden 3 (Eagle -
Control), the soil contained less than 0.1 ppt 2378-TCDD and about 0.3 ppt
2378-TCDD TEQs. 2378-TCDD was not detected in unpeeled beets or carrots, and
there was no discernable uptake of 2378-TCDD TEQs.
In summary, the limited screening study did not indicate uptake of 2378-TCDD
or 2378-TCDD TEQs in root crops grown in Midland and a control site. Results
with respect to one lettuce sample grown in Midland were inconclusive due to
laboratory solvent blank contamination.
Appendix C
1
-------
TABLE C-l
USEPA PRELIMINARY GARDEN VEGETABLE SAMPLING
MIDLAND, MICHIGAN
NOVEMBER 1987
SAMPLE
Garden 1 - Midland
TLI Blank #7
Soil (3561E-6)
TLI Blank #1
Peeled Carrots (3561E-3)
Peeled Onions (3561E-5)
TLI Blank - Veg
Lettuce (3561E-4)
Garden 2 - Midland
TLI Blank #7
Soil (3561E-2)
SAMPLE TYPE
Garden/composite(20)
Frozen/composite(pkg)
Garden/composite(3)
Garden/composite(3)
Garden/composite(10)
2378-TCDD
(PPt)
ND«0.1)
34
ND«0.1)
ND(<0.1)
ND«0.1)
0.3
NA
ND«0.1)
11
TEOs
(PPt)
48 "
------- |