United States Region 5 EPA-905/4-88-006
Environmental Protection 230 South Dearborn April 1988
Agency Chicago, Illinois 60604
x°/EPA Proposed Risk
Management Actions
for Dioxin Contamination
Midland, Michigan
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PROPOSED RISK MANAGEMENT ACTIONS
FOR DIOXIN CONTAMINATION AT MIDLAND, MICHIGAN
APRIL 14, 1988
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION V
CHICAGO, ILLINOIS 60604
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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,
outputs from 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 1988), referred to hereafter as the Risk Assessment.
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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 USEPA's proposed risk
management actions for contamination with 2,3,7,8-tetrachlorodibenzo-p-dioxin
(2378-TCDD) and other polychlorinated dibenzo-p-dioxins (CDDs) and
polychlorinated dibenzo-furans (CDFs) in and around Midland, Michigan (see
Figure 1-1). The principal purpose of this document is to present to the
people of the Midland area and to its institutions, both public and private, a
summary of the Risk Assessment and an outline of the proposed risk management
actions USEPA believes are appropriate.
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 here since most of the costs to Dow
Chemical have been, or are being, incurred. There are, however, questions of
technical achievability, regarding additional remedies, for which there are
currently no answers. In these circumstances the proposed risk management
actions outline a process to develop the necessary information to answer
questions about technical achievability and related costs.
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*•?•" •-TtJL*'"n
- Facility Boundary
Midland, Michigan Area and
Dow Midland Facility
Seal* in Fut
0 1000 2000 3000
Sources: USCS (1973),
Dow (1984)
-3-
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USEPA developed the proposed risk management actions presented in this
report taking into account the Risk Assessment and the current status of
ongoing remedial actions. We believe that these proposed actions are
reasonable and necessary measures which can be implemented without major
disruptions. For the most part, USEPA believes that the measures relating to
the Dow Chemical plant can most effectively be implemented through existing
regulatory mechanisms including the air, solid waste, and water pollution
control programs managed by MDNR and USEPA Region V. Members of the public,
and public and private institutions, in the Midland area are invited to comment
on the Risk Assessment and the proposed risk management actions.
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) proposed 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) proposed 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.
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11. Summary of Past 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 emissions
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.
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-
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dibenzo-p-dioxin (2378-TCDD), the most toxic of the COD/CDF compounds
(Dow 1978). Supplemental analyses of edible portions of Tittabawassee River
native 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). 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 lower levels.
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 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).
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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, Region V 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 8(e) 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 native 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 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
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operations within Tiers 1, 2, 3, 4, and 6 of the Dioxin Strategy, funding for
the studies was provided principally through the 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
investigation 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 monitoring for 2378-TCDD in the treated process
wastewater discharge to the Tittabawassee River (Dow 1984-1987).
Studies by Dow and USEPA revealed widespread contamination of the surface
soil at the Midland facility (average of 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 contamina-
tion 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 contamina-
tion 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
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from the facility, and possibly past fugitive emissions from production
operations.
Studies by Dow Chemical indicated the hazardous waste incinerator to be
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 significantly 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; <0.005 ppt 2378-TCDD currently)
(Dow 1984-1987). 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 MONR, 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 native
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
(Amendola and Barna 1986).
However, the most recent data indicate 2378-TCDD levels in native fish may
be declining. Data collected in 1985 show that native Tittabawassee River fish
collected downstream of Dow Chemical are also contaminated with several other
organic chemicals, the most significant being PCBs. Dow Chemical is not
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believed to be a significant source of PCBs. Generally speaking, chemicals
other than CDOs/CDFs were not found in other media (air, soil, drinking water)
at levels that would warrant specific consideration in this report.
The USEPA has compiled the data from its testing programs (USEPA 1985a,
Barna and Amendola 1985, Amendola and Barna 1986, Trembly and Amendola 1987)
and all available data from other investigations and has prepared a
comprehensive Risk Assessment (USEPA 1988) for individuals living in the
Midland area. A summary of this document is presented in Section III.
III. Summary of USEPA's 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
CDDs/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
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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 CODs/CDFs and exposure-related behavior of the exposed
populations.
A. Hazard Identification
Chlorinated dibenzo-p-dioxins (CDOs) 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-tetrachlorodibenzo-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
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toxicological effects, but that higher doses of these compounds are generally
required to cause effects of comparable magnitude to those induced by 2378-
TCOD.
USEPA has determined that the critical end points of concern for purposes
of assessing risks associated with exposure to CDDs/COFs 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 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 "ql*") for 2378-TCDD
of 1.6 x 10*4 (pg/kg/day)~l. Note: "pg" stands for picogram = 10~12 gram.
While the above value remains USEPA1s 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. 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
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(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 intakes or short-term exposures lasting a few days, whereas the RfD
of 1 pg/kg/day is more appropriate for comparison with long-term or life-time
exposures.
Although USEPA has determined that reproductive/teratogenic effects are
the critical 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, 1988).
For short-term exposures (single dose), the animal data support an HA for liver
effects of 280 pg/kg, 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.
All of the toxicological dose-response estimates described above—cancer
potency, Reference Dose, and Health Advisory--were derived by extrapolating
*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
Dose-Response Slope
Parameter (95%
upper confidence
limit)
Teratogenesi s/Reproducti ve
Effects:
long-term exposures
single-dose exposures
Hepatotoxicity (liver
effects):
long-term exposures
short (10-day) exposures
single-dose exposures
RfD
HA
RfD
HA
HA
1.6xlO-4
(pg/kg/day)'1
["B2"]*
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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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 actual 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" 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-TCDO 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.
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0. 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, nearer the higher-population-
density areas in 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 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.
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3. Exposure Through the 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"). The long-term consumption rates were used to develop
CDD/CDF ingestion or dose rates to assess cancer risks and for comparison with
the RfD for non-cancer effects. Single-meal CDD/CDF ingestion rates also were
developed to compare with the short-term Health Advisory (HA) values.
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 Routes of Exposure
Several other potential 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
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TABLE 111-2
FISH CONSUMPTION SCENARIOS
FOR TITTABAWASSEE RIVER, MICHIGAN
Scenario Consumption Rate Type of Fish3
Plausible Maximum Consumer Long-term: 100 g/dayb 50% Bottom feeders
Single Meal: 255 gc -t- 50% Game fish
High Sports Fisherman
— Level 1 Long-term: 100 g/dayb 100% Game fish
Single Meal: 255 gc
-- Level 2d Long-term: 48 g/daye 100% Game fish
Single Meal: 113 g?
Great Lakes Consumer9 Long-term: 16 g/day^ 100% Game fish
Single Meal: 113 g?
General Consumer Long-term: 7.8 g/dayi 50% Game fish
Single Meal: 113 gf + 50% Clean fish
aAll fish are assumed to be from the Tittabawassee River except "clean" fish
which are assumed to be free from COD/CDF contamination. The following fish
tissue concentrations are used in the Risk Assessment (1983-1987 data):
Type of Fish Partial TEQs (ppt)
Bottom feeders 58
Game fish 13
Clean fisn 0
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).
9Added following completion of Risk Assessment, using the information and
procedures contained in that document.
"FDA-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).
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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 model was employed to estimate intakes
for nursing infants.
Finally, while no data were available which would allow a quantitative
assessment of the exposures from consumption of CDDs/CDFs contained in or
deposited on home-grown vegetables, a small number of samples are currently
being analyzed by USEPA, and the results should be available soon.
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 0.1 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
*Defined as the ratio of the estimated average daily dose to the previously
defined RfD (or HA for single or short-term exposures).
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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 III-3 through III-6. For air exposures, (see Table III-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 cancer risk estimates associated with exposures to
contaminated soil (see Table III-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 CDH/CDF exposures via
contaminated fish are much greater than for the other two pathways (see Table
111-5). Upper-bound estimates of incremental lifetime cancer risks range from
1 x 10-4 ["B2"] for the "general consumer" to 1 x 10'2 C"B2"1 for the
"plausible maximum consumer". The His also exceed 10 for two of the scenarios.
The estimated single-meal CDD/CDF intake levels result in His greater than 10
for meals comprising the maximum concentration bottom feeder (see Table III-6).
All other single meal His are less than 1.0. Note that the risk levels
presented in Tables III-5 and III-6 are for consumption of Tittabawassee River
fish contaminated with CDDs and CDFs. Native fish from the river also are
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TABLE 111-3
RISK CHARACTERIZATION FOR INHALATION OF CDOs/COFs
IN AMBIENT AIR IN MIDLAND, MICHIGAN
Upper-Bound Cancer Riskb Hazard Indexc(Long Term)
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 — -- 1 0.4
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"] SxlO'6 ["82"]
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 lifetime cancer risk, obtained by multiplying exposure
estimate in Table 111-12* by cancer potency factor of 1.6 x 10~* (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
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-TCDO alone, whereas
total TEQs are being evaluated here, in accordance with USEPA interim science
policy.
*ln Risk Assessment
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TABLE 111-4
RISK CHARACTERIZATION FOR INGESTION OF CDDs/COFs
IN SOIL IN MIDLAND, MICHIGAN
Upper-Bound Lifetime Hazard Index0
Exposure Scenario3 Cancer Risk^ (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["R2"]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 upper
estimate does not include children with pica. Individuals with this disorder
could incur risks 10-fold higher.
bUpper-bound estimate of lifetime cancer risk, obtained by multiplying lifetime
average TEQs dose rate from Table 111-20* by cancer potency factor of
1.6 x 10~4 (pg/kg/day)~l, 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.
^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.
*In Risk Assessment
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TABLE 111-5
RISK CHARACTERIZATION FOR INGESTION OF CHOs/COFs3
IN FISH FROM THE TITTABAWASSEE RIVER, MICHIGAN
Long-Term Exposures
Upper-Bound
Exposure Scenar1oc Cancer Riskd»e Hazard Index°»e»'
Plausible Maximum Consumer lxlO-2["B2"]9 50
(bottom + game fish)
High Sports Fisherman
(game fish only)
— Level 1
-- Level 2
Great Lakes Consumer
(game fish only)
General Consumer
(game + clean fish)
4xlO-3["B2"]
2xlO-3["B2"]
6xlO-4["B2"]
lxlO-4["B2"]
20
9
3
0.7
aOther contaminants such as PCBs, found in the fish, add to the toxicity
(see Appendix B*).
bNote that Hazard Indices will be about 2-3 times higher for small children
(Table 111-32*). Breast-fed infant could be 10-times higher than mother.
cFrom data in Section III.E.2* and Tables 111-30* and 111-31*. Also see
Table III-2 in this document. Long-term dose rate for Great Lakes Consumer
is 3.0 pg/kg/day.
^Upper-bound estimate of lifetime cancer risk, obtained by multiplying dose
rate from Table 111-31* by cancer potency factor of 1.6 x 10~4 (pg/kg/day)-l
and multiplying by a factor of 1.3 to incorporate contribution of higher
intakes in childhood to average lifetime intake in pg/kg/day (from data in
Table 111-33*).
eNote that all estimates of intake are "partial TEQs," including only
2378-TCDD, other TCDDs, HxCDDs, HpCDDs, and 2378-TCDF.
fRatio of dose rate from Table 111-31* to RfD of 1 pg/kg/day.
9ln USEPA's weight-of-evidence classification system for carcinogens, 82
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.
*Tn Risk Assessment
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TABLE 111-6
RISK CHARACTERIZATION FOR INGESTION OF CDDs/CDFsa
IN FISH FROM THE TITTARAWASSEE RIVER, MICHIGAN
Single Meal (Bolus) Exposures'3
Fish Meal Size Type of Fish Partial TEQsc Hazard Indexd»e
255 g (9 oz) Bottom-feeder
(catfish/carp)
— maximum 690 ppt 8
-- mean 58 ppt 0.7
Game Fish
(walleye, etc.)
— maximum 39 ppt 0.5
— mean 13 ppt 0.2
113 g (4 oz) Bottom-feeder
(catfish/carp)
— maximum 690 ppt 4
— mean 58 ppt 0.3
Game Fish
(walleye, etc.)
— maximum 39 ppt 0.2
-- mean 13 ppt <0.1
aOther contaminants such as PCBs, found in the fish, add to the toxicity
(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 all estimates of intake are "partial TEQs," including only
2378-TCDD, other TCDDs, HxCDDs, HpCDOs, and 2378-TCDF (1983-1987 data).
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*).
*In Risk Assessment
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contaminated with other toxic chemicals, including PCBs. The presence of the
other toxic chemicals would result in increased calculated risk levels from
those presented in Tables III-5 and III-6.
The cancer risk estimates calculated for all of the exposure routes are
summarized in Table III-7, and the His for non-cancer effects are summarized in
Table III-8. 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 the actual risks to humans.
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TABLE III-7
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 10~3 (Great Lakes
consumer) consumer)
10~3 (high sports 10~4 (general consumer)
fisherman—level 1)
Soil 10~5 (upper estimate) 10~6 (lower estimate)
ID'4 (child with pica)
Air 10~4 (fenceline) 10~5 (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 Appendix B in the Risk Assessment).
(3) Sources: Tables III-3, III-4, and III-5.
(4) USEPA is currently Devaluating the cancer potency factor for
2378-TCDD; a final determination will not be available for at least
several months.
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TABLE III-8
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
Long-Term Short-Term
Fishb
Plausible maximum consumer
High sports fisherman--!eve! 1
Great Lakes consumer
Genera! consumer
50
20
3
0.7
5
2
0.7
0.4
Soil
Upper estimate young child
— with pica
— normal
Lower estimate young child
Upper estimate adult
6
0.6
0.2
Airc
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)
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 toxicity (see Appendix B of the Risk
Assessment).
CA11 HI values calculated using the "A method." Infant exposure includes
exposure from breast-feeding.
Note: See Table III-6 for His for single meal (bolus) exposures.
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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
pentachlorophenol (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); landfilling 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 on the 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).
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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, to some extent, reduced fish contami-
nation levels. Overall, it appears conditions have improved significantly over
the last ten years. Nevertheless, the levels of discharge and environmental
contamination as depicted by point source and environmental data collected
during the 1983-1986 period indicate 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-TCDO 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 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 t0 ig-6 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.
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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 ai r.
Even if USEPA adopted for use in risk assessments a potency factor an order of
magnitude lower (less conservative), the estimated cancer risks associated with
certain levels of fish consumption would still be quite high (10~3 to 10~5).
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
10~6 for all groups except children with pica, for whom the estimated risk would
be about 10~5. Actions to minimize risk for fish consumers are thus the highest
priority.
Also, the estimated non-cancer health effects, which would not be affected
by a change in the USEPA cancer potency factor for 2378-TCDD, are at a level of
concern for most rates of fish consumption, and are of marginal concern for
some worst-case air exposures. (The worst-case air exposures are unlikely to
occur.)
Accordingly, it is logical to focus additional remedial measures, to the
extent they are necessary, on those point and nonpoint Dow Chemical sources
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having the greatest impacts on the environment outside the plant. Some of
these measures would be effective at reducing worker exposures in-plant as
well. These proposed measures are described below, followed by recommended
precautionary measures that can be implemented by the general public and a
review of proposed supplemental point source and environmental monitoring
programs associated with the proposed remedial measures.
A. Proposed 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 December 1987. 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 two-thirds upon operation of the
mixed-media filtration system. Another significant reduction (73%) has been
realized after preliminary treatment for incinerator wastewaters was
instituted. Overall, the average mass discharged has been reduced by about 93%
from 1984 and 1985 levels. The level of discharge for the past few months
(nominally
-------
CO
•a
CO
o
en
en
cd
O
H
I
00
r-
co
M
cd
24
22
20
18
16
14
12
10
8
6
4
2
0
FIGURE IV-1
Dow Chemical - Midland Plant
2378-TCDD Discharges
July 1984 - December 1987
I
1985
OPERATION OF
EFFLUENT
FILTRATION
SYSTEM
OPERATION OF
INCINERATOR
TREATMENT
SYSTEM
CD
r~
»—i
o
OJ i—i
ro m
i E:
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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.
Given the current levels of discharge of 2378-TCDD, the continued progress
made toward reducing the levels of discharge, and the need to achieve lower
levels of discharge as determined by MDNR, USEPA recommends that the proposed
NPDES special conditions included in the above-referenced report be implemented
through the NPDES permit program. The results from these special conditions
will 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.
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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% 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 incinerator emissions.
Based upon these considerations and the estimated risks associated with
incinerator emissions alone, there does not apppear to be sufficient
justification for requiring major changes in incinerator operations at this
time (e.g., change in waste feeds, installation of additional emission control
technology). However, additional measures to optimize combustion conditions
within the incinerator and to optimize operation of the existing emission
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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 program can require
various incinerator emissions testing and ambient air monitoring programs for
final RCRA permits.
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 about
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.
In 1986, Dow Chemical began implementing a fugitive dust suppression
control program which calls for regular flushing of paved roads and parking
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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 CDOs and CDFs. It is proposed that the effectiveness of this program be
evaluated through the proposed ambient air monitoring program presented in
section C.Z.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)
requirements, 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
Mverbank 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
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water.) Dow Chemical has installed a purge system to clean up the release, and
a slurry wall was constructed 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 MDNR and USEPA Region V are currently
processing a RCRA permit for the Dow plant which 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 are, however, a number of actions people can take to minimize
exposures, and thus minimize possible health risks associated with CDDs and
CDFs. Most of these recommendations focus on avoiding or minimizing ingestion
of materials that contain 2378-TCDD and other CDDs and CDFs.
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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). At this writing the MDPH has 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 current Michigan
fish consumption advisory for catfish and carp is fully supported by the USEPA
studies.
The Risk Assessment also 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 childbean'ng 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.
The MDPH has been conducting a creel survey to better define fish
consumption patterns for Tittabawassee River fishermen and their families. The
MDPH also has been actively participating in ongoing discussions with the other
Great Lakes states, USEPA, and the Food and Drug Administration regarding
establishment of a uniform basis for fish consumption advisories. At this
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writing, the MDPH has decided to consider the results of its creel survey, the
findings from this report, new data from the 1988 fish monitoring survey, and
the aforementioned discussions prior to determining whether or to what extent
to modify its fish consumption advisory for the Tittahawassee River.
Individuals who choose to consume any fish caught in the Tittabawassee
River should clean them in accordance with MDPH recommendations to minimize
contaminant levels. Fillets should he 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 which permit fats and juices to drain from the fish may result in lower
contaminant levels in the cooked fish.
2. City 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 is considered a medical disorder.
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
contaminants 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
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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.
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. Proposed 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
other possible, but less likely, routes of exposure which were not evaluated
initially. Some of the proposed monitoring programs are current requirements
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of Dow Chemical environmental control permits or orders; others are new
programs that could be included in the RCRA permit now being developed or
required under other existing regulatory mechanisms.
Each proposed program is described in the following sections. In all
cases, USEPA proposes that these monitoring programs would be conducted by Dow
Chemical in response to specific requirements placed in environmental permits
or administrative orders issued under the Air, RCRA, or NPDES programs as
appropriate. 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 2 parts per quadrillion (ppq or pg/1). Data
collected for the last six months of 1987 indicate the discharge has been
fairly stable from month to month. 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). 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).
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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 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 these 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. Ambient Ecological Effects and Food Chain Monitoring
a. Tittabawassee River native 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 most recent data were collected in 1987
(Dow 1987c). The current sampling protocol calls for collection of three
bottom-feeding fish (carp or catfish) and three game or sports fish (usually
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walleye) downstream of the plant. The number of data points resulting from
this program is not sufficient to adequately characterize the fishery for
purposes of establishing appropriate fish consumption advisories. Accordingly,
the MDPH, MONR, and USEPA have collaborated in developing an expanded fish
monitoring program for 1988. That program will include analysis of 20 walleyes
in 4 size classes and 10 carp. The walleyes will be from the 1988 spring run,
and the carp will be collected during the summer. All of these fish will be
collected downstream of the former Dow Dam, preferably in the vicinity of
Smith's Crossing Road. A limited number of fish will also be collected
upstream. All of the fish will be analyzed for 2378-TCDD and PCBs. A limited
number will be analyzed for other CDDs and CDFs.
b. 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 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 and other CDDs and CDFs and other contaminants
to determine whether or to what extent sediment removal might be appropriate.
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c. 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-TCDO and
other CDDs and CDFs. A network of at least seven monitoring sites (one upwind
of plant, three downwind near the fenceline, 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. COD and CDF determinations should be
made on at least three separate days with wind blowing from the upwind monitors
toward the 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.
d. 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.
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3. Food Chain Monitoring
a. 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.
b. Garden vegetable sampling
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-TCDDs and other CDDs and CDFs occurs from
contaminated soil into (or onto) garden vegetables.
c. Aquatic life, avian, and animal monitoring program
A limited monitoring program should be conducted in 1988 or 1989 for
native bivalves or gastropods present in the Tittabawassee River as well as
for native 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.
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REFERENCES
AMENDOLA, G.A. and Barna, D.R. 1986. Dow Chemical Wastewater
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BARNA, D.R., and AMENDOLA, G.A. 1985. Screening survey of surface water
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March 15.
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ENVIRONMENTAL CONGRESS OF MID-MICHIGAN (ECOMM) and FORESIGHT SOCIETY
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U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1983b. Dioxin Strategy. Office
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