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OSWER 9200.3-56
PUBLIC REVIEW DRAFT
DRAFT RECOMMENDED INTERIM PRELIMINARY REMEDIATION GOALS
FOR DIOXIN IN SOIL AT CERCLA AND RCRA SITES
Prepared by:
U.S. Environmental Protection Agency
Office of Superfund Remediation and Technology Innovation
Washington, D.C.
December 30, 2009
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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LIST OF ACRONYMS AND ABBREVIATIONS
ARAR Applicable or Relevant and Appropriate Requirement
ATSDR Agency for Toxic Substances and Disease Registry
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
CSF Cancer Slope Factor
ECEH European Centre for Environmental Health
EPA U.S. Environmental Protection Agency
HAD Health Assessment Document
HEAST Health Effects Assessment Summary Table
HI Hazard Index
HQ Hazard Quotient
IPCS International Programme on Chemical Safety
IRIS Integrated Risk Information System
LOAEL Lowest-Observed-Adverse-Effect-Level
MCL Maximum Contaminant Level
MRL Minimal Risk Level
NAS National Academy of Sciences
NCEA National Center for Environmental Assessment
NCP National Contingency Plan
NOAEL No-Observed-Adverse-Effect-Level
NPL National Priority List
NTP National Toxicology Program
ODW Office of Drinking Water
OEM Office of Emergency Management
ORD Office of Research and Development
OSRTI Office of Superfund Remediation and Technology Innovation
OSWER Office of Solid Waste and Emergency Response
OW Office of Water
PCB Polychlorinated biphenyl
PCDD Polychlorinated dibenzodioxin
PCDF Polychlorinated dibenzofuran
pg Picogram (10"12 grams)
PM2.5 Particulate material less than 2.5 um
PM10 Particulate material less than 10 um
POCD Program Operations and Coordination Division
ppb Parts per billion
PPRTV Provisional Peer Reviewed Toxicity Value
ppt Parts per trillion
PRG Preliminary Remediation Goal
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AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
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LIST OF ACRONYMS AND ABBREVIATIONS - continued
PTMI Provisional Tolerable Monthly Intake
PWG Pathology Working Group
RAGS Risk Assessment Guidance for Superfund
RB A Relative Bioavailability
RCRA Resource Conservation and Recovery Act
RfD Reference Dose
ROD Records of Decision
RSC Relative Source Contribution
STSC Superfund Technical Health Risk Support Center
TCDD 2,3,7,8-Tetrachlorodibenzo-p-dioxin
TDI Tolerable Daily Intake
TEF Toxicity Equivalency Factors
TEQ TCDD Toxic Equivalent
WHO World Health Organization
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
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PUBLIC REVIEW DRAFT
DRAFT RECOMMENDED INTERIM PRELIMINARY REMEDIATION GOALS
FOR DIOXIN IN SOIL AT CERCLA AND RCRA SITES
OVERVIEW
In May 2009, the U.S. Environmental Protection Agency's (EPA) Administrator Lisa P.
Jackson decided that EPA needs to accelerate work underway to reassess the human
health risks from exposures to dioxin. EPA's Science Plan for Activities Related to
Dioxins in the Environment (EPA 2009a) details a plan, with interim milestones, for
completion of the Agency's dioxin reassessment and other efforts related to dioxins in the
environment. In a letter dated May 26, 2009, to the community of the Tittabawassee
River/Saginaw River and Bay Contamination Site in Michigan, the Administrator stated:
"As we move forward to develop remediation strategies at this site, the science on
dioxin's health and ecological effects will obviously play an important role in our
decisions. Although EPA scientists, supported by external peer review bodies, have
invested considerable time and effort in evaluating the scientific literature on dioxin,
we need to be sure that EPA's assessment of dioxin's risks to people and the
environment is brought to bear at this and other dioxin-contaminated sites in a timely
manner. Accordingly, I am, in parallel with this letter, announcing a commitment to
accelerate our scientific work on dioxin. Our goal is to issue a final dioxin
assessment by the end of 2010. In addition, our Office of Research and Development
and Office of Solid Waste and Emergency Response will review current dioxin
cleanup guidance set by the Agency and the States with the aim of recommending
interim preliminary remediation goals informed by the latest science and the work of
state agencies. We will announce these interim PRGs by the end of the year."
EPA's Office of Research and Development (ORD) expects to complete the dioxin
reassessment by the end of 2010, subject to further consideration of the science and the
scope and complexity of the revisions that will need to be made. ORD will be
responding to all National Academy of Sciences (NAS) comments received on EPA's
draft 2003 dioxin reassessment.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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EPA's Office of Solid Waste and Emergency Response (OSWER) has developed draft
recommended interim Preliminary Remediation Goals (PRGs) for dioxin in soil,
informed by the best available science and work of state agencies at this time. On
October 13, 2009, EPA posted a proposed plan for developing the interim PRGs,
(available at:
www.epa.gov/superfund/policv/remedv/sfremedv/remedies/dioxininterimplan.html)
and requested comments on the proposed plan. EPA has taken these comments into
account, establishing a docket (available at: http://www.regulations.gov and go to Docket
No. EPA-HQ-SFUND-2009-1002) where comments received to date can be found. EPA
has considered these comments in formulating the draft recommended interim PRGs
(available at: http://www.regulations.gov and go to Docket No. EPA-HQ-SFUND-2009-
0907).
EPA expects to finalize these draft recommended interim PRGs for soil in June 2010
after receipt and evaluation of public comments on all aspects of this draft interim
guidance. Until these draft recommended interim PRGs are finalized, EPA will continue
to use the 1998 recommended interim PRGs (EPA 1998). The finalized recommended
PRGs are intended for interim use until EPA issues its final dioxin reassessment
(hereafter "recommended interim PRGs" refers to PRGs that once finalized are to be used
in the interim until EPA issues its final dioxin reassessment). At that time, EPA intends
to issue updated recommended PRGs based on the final dioxin reassessment. Also at that
time, EPA intends to re-evaluate cleanup decisions at Comprehensive Environmental
Response, Compensation, and Liability Act (CERCLA) and Resource Conservation and
Recovery Act (RCRA) sites that were based on the 2010 recommended PRGs to ensure
that cleanups remain protective for human health.
PURPOSE
The purpose of this guidance is two-fold:
1. To recommend the use of PRGs to protect against cancer and non-cancer effects
associated with human exposure to dioxin in soil at CERCLA and RCRA sites,
and,
2. To discuss the interim use of these recommended PRGs for soil at CERCLA and
RCRA sites
These draft recommended interim PRGs are intended for use in evaluating dioxin
(2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) and other dioxin-like compounds in soil.
Dioxin-like compounds, including other polychlorinated dibenzodioxins (PCDDs),
dibenzofurans (PCDFs) and biphenyls (PCBs) may collectively be evaluated using the
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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recommended PRGs for dioxin after adjustment to account for relative toxicity using
toxicity equivalency factors (TEFs) to calculate dioxin toxicity equivalent (TEQ)
concentrations. EPA recommends the use of the TEFs developed by the World Health
Organization (WHO) (van den Berg et al. 1998, 2006) based on review of the
toxicological literature. For example, if a soil contained 10 ppt of dioxin (i.e, TCDD) and
also contained 20 ppt of some other dioxin-like chemical that was 1/10 as toxic as dioxin,
the toxicity equivalent concentration for the other dioxin-like compound would be 2 ppt,
and the total TEQ concentration for the soil would be 10 + 2= 12 ppt dioxin TEQ. The
total dioxin TEQ concentration would then be compared to the recommended PRG. EPA
acknowledges that there is uncertainty associated with risk estimates based on TEQs.
Therefore, risk assessors should identify the fraction of the TEQ attributable to dioxin
and to each chemical class of dioxin-like compounds (i.e., PCDDs, PCDFs, and PCBs).
For CERCLA and RCRA sites, Regions generally should consider using the
recommended interim PRGs in this guidance as a starting point for residential and
commercial/industrial soil cleanup levels. EPA encourages State and Tribal programs
that do not use PRGs to consider the recommended interim PRGs as starting point
concentrations to develop cleanup levels.
This guidance supersedes OSWER's previous PRG guidance for dioxin in soil (EPA
1998). These draft recommended interim soil PRGs are national levels protective for
cancer and non-cancer effects from human exposure by ingestion and dermal contact with
surface soils. Inhalation exposure is not included for the draft recommended interim
PRGs, because at present, there is no available inhalation unit risk value for dioxin that
has been derived in accordance with current guidance for inhalation risk assessment
(EPA 2009d). However, inhalation exposure to dioxin (particulates and vapor) is
expected to be low (< 2.4%) compared to oral exposure in most cases (see Attachment 1).
Therefore, risks due to inhalation of particulates and vapors are expected to be minimal.
Regions should continue to develop PRGs on a site-specific basis for other media (e.g.,
sediments, which involve biotransfer and bioaccumulation through indirect pathways)
and for ecological assessments.
This guidance is consistent with OSWER's guidance (EPA 2003a) on using a hierarchy
of existing chemical toxicity value sources; it does not represent a new or independent
review of dioxin toxicity, which ORD is currently conducting as part of the final dioxin
reassessment. As a result, there is uncertainty associated with these draft recommended
interim PRGs because they do not take into account peer review comments on the new
science that was reviewed by the NAS, and new science that was released since the NAS
review. A final dioxin reassessment is still under development.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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This draft guidance presents current OSWER technical and policy recommendations
regarding PRGs for soil contaminated with dioxin. While OSWER developed this draft
guidance for facility response actions under CERCLA and RCRA corrective action, other
regulators, including the States, may find it useful in their programs, although they may
choose to use alternative assessments consistent with their own programs and policies. In
addition, EPA may use and accept other technically sound approaches after appropriate
review, either at its own initiative or at the suggestion of other interested parties. This
draft guidance does not impose any requirements or obligations on EPA, the States, other
Federal agencies, or the regulated community. It is important to understand that this
document does not substitute for statutes that EPA administers or their implementing
regulations, nor is it a regulation itself. Thus, this document does not impose legally
binding requirements on EPA, the States, or the regulated community, and may not apply
to a particular situation based upon the specific circumstances. Rather, the document
suggests approaches that may be used at particular sites as appropriate, given site-specific
circumstances.
BACKGROUND
Description of PRGs
Consistent with CERCLA and the National Contingency Plan (NCP), protection of
human health and the environment is a requirement for selected remedies (see 40 CFR
§300.430(f)(l)(i)(A)). In the CERCLA remedy selection process, PRGs typically are
used when developing cleanup levels. At CERCLA sites, PRGs typically are "specific
statements of desired endpoint concentrations of risk levels (55 FR 8713, March 8, 1990)
that are conservative, default endpoint concentrations used in screening and initial
development of remedial alternatives before consideration of information from site-
specific risk assessments". In accordance with the NCP (see 40 CFR
§300.430(e)(2)(i)(A)), PRGs are generally at the low end of the risk range and typically
are used in screening and initial development of remedial alternatives before
consideration of more detailed information from the site-specific risk assessment.
The NCP (40 CFR §300.430(e)(2)(i)(A)) states:
"Remediation goals shall establish acceptable exposure levels that are protective
of human health and the environment and shall be developed by considering the
following:
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(A) Applicable or relevant and appropriate requirements (ARARs) under federal
environmental or state environmental or facility siting laws, if available, and the
following factors:
(7) For systemic toxicants, acceptable exposure levels shall represent
concentration levels to which the human population, including sensitive
subgroups, may be exposed without adverse effect during a lifetime or part
of a lifetime, incorporating an adequate margin of safety;
(2) For known or suspected carcinogens, acceptable exposure levels are
generally concentration levels that represent an excess upper bound
lifetime cancer risk to an individual of between 10"4 and 10"6 using
information on the relationship between dose and response. The 10"6 risk
level shall be used as the point of departure for determining remediation
goals for alternatives when ARARs are not available or are not sufficiently
protective because of the presence of multiple contaminants at a site or
multiple pathways of exposure;
(3) Factors related to technical limitations such as detection/quantification
limits for contaminants;
(4) Factors related to uncertainty; and
(5) Other pertinent information."
1998 OSWER Guidance on PRGs for Dioxin in Soil
This draft interim guidance, when finalized, will supersede the 1998 OSWER directive
entitled "Approach for Addressing Dioxin in Soil at CERCLA andRCRA Sites " (EPA
1998). The 1998 OSWER directive recommended that a soil concentration of 1 part per
billion (ppb), which is equivalent to 1,000 parts per trillion (ppt) of dioxin (as TEQ) be
generally used as a starting point for developing cleanup levels for CERCLA removal
sites and as a PRG for CERCLA remedial sites for dioxin TEQ in surface soil involving a
residential exposure scenario. For commercial/industrial exposure scenarios, a soil
concentration within the range of 5 ppb (5,000 ppt) to 20 ppb (20,000 ppt) dioxin TEQ
was recommended as a starting point for developing cleanup levels for CERCLA sites. A
range in soil concentrations was recommended for commercial/ industrial soils due to the
greater variability in exposures associated with the commercial/industrial scenarios. The
PRGs were also generally recommended as a starting point for actions taken at RCRA
corrective action sites. These levels were recommended unless extenuating site-specific
circumstances warranted a different level.
Based on the oral cancer slope factor (CSF) developed by EPA (1985), EPA (1998)
estimated that the lifetime excess cancer risks to residents from oral exposure to dioxin in
soil at a PRG of 1,000 ppt dioxin TEQ was about 2.5E-04, and that lifetime excess cancer
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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risks to workers at a PRG of 5,000 ppt dioxin TEQ corresponds to a risk of about 1.3E-
04. Dermal exposure was not considered for either residential or commercial/industrial
land use. EPA (1998) noted that these risks were at the higher end of the range of excess
cancer risks.
Need to Update the 1998 OSWER PRGs
In developing this guidance, the Agency has evaluated several attributes of the current
PRGs for dioxin in soil that are not consistent with the best available science on dioxin.
These inconsistencies include the following:
• The derivation procedure did not consider potential non-cancer effects of dioxin
• The value for residents considered oral exposure only, and did not include dermal
exposure
• The value for workers is based on an indoor worker (oral exposure only), while
the most exposed worker is usually an outdoor worker with both oral and dermal
exposure
Based on a consideration of a number of factors, the Administrator has determined that it
is important to develop updated interim PRGs to be used until the release of the final
dioxin reassessment. The following sections describe the approach used by EPA to
provide and select new recommended interim PRGs for dioxin.
RECOMMENDATIONS
Recommended Toxicity Values
The most common health effect in people exposed to large amounts of dioxin is
chloracne. Chloracne cases have typically been the result of accidents or significant
contamination events. Chloracne is a severe skin disease with acne-like lesions that
occur mainly on the face and upper body. Other effects of exposure to large amounts of
dioxin include skin rashes, skin discoloration, excessive body hair, and possibly mild
liver damage.
One of the main concerns over health effects from dioxins is the risk of cancer in adults.
Several studies suggest that workers exposed to high levels of dioxins at their workplace
over many years have an increased risk of cancer. Animal studies have also shown an
increased risk of cancer from long-term exposure to dioxins.
Finally, based on data from animal studies, there is some concern that exposure to low
levels of dioxins over long periods (or high level exposures at sensitive times) might
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result in reproductive or developmental effects (FDA, 2008). Consequently, both a
cancer slope factor and a non-cancer toxicity value are used to derive PRGs for cancer
and non-cancer effects.
Hierarchy for Selecting Interim Toxicity Values
OSWER has developed a recommended hierarchy (EPA 2003a) for the selection of
toxicity values, including those used in developing PRGs. As discussed in EPA (2003a),
the first tier of toxicological information is found in EPA's Integrated Risk Information
System (IRIS), and is developed by EPA's ORD National Center for Environmental
Assessment (NCEA). Generally, any values in IRIS are considered to be Tier 1. If no
data are available in IRIS, the next preference (Tier 2) is Provisional Peer Reviewed
Toxicity Values (PPRTVs) developed by EPA NCEA's Superfund Technical Health Risk
Support Center (STSC). If toxicity values are not available from either Tier 1 or 2, other
high quality sources of toxicity information can be used. These are considered Tier 3
values in this hierarchy.
As discussed in EPA (2003a), toxicity values generally are not appropriate for use as Tier
3 values until they have been through peer review, the peer review comments have been
addressed, and the analysis is made publicly available. Also, toxicity values should be
based on similar methods and procedures as those used for Tier 1 and Tier 2, and the
methods and processes used to develop the values should be transparent. It should be
noted that these procedures are specific to CERCLA/RCRA cleanup programs and are
not necessarily the approach taken by other EPA programs.
At present, EPA has not derived any Tier 1 or Tier 2 toxicity values for dioxin, either for
cancer or non-cancer effects. Consequently, for the purposes of providing these
recommended interim PRGs for dioxin, EPA reviewed available toxicity values to
identify the most appropriate Tier 3 values (EPA 2009b, 2009c). The recommended
interim Tier 3 toxicity values that are discussed in this guidance may be appropriate for
the Regions to use to assess human health risks until toxicity values for dioxin are
available in EPA's IRIS database or until further scientific analysis indicates that
alternate values should be used. When a new IRIS toxicity assessment is finalized, EPA
intends to review cleanup level decisions to ensure that sites addressed using these
interim toxicity values remain protective, given the revised toxicity values. If important
new scientific information becomes available before a new IRIS toxicity assessment is
finalized, EPA may issue additional guidance addressing the recommended interim
toxicity values discussed in this guidance.
Recommended Cancer Slope Factor
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
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Because EPA does not have a Tier 1 or Tier 2 cancer toxicity value for dioxin, EPA
reviewed available cancer slope factors for dioxin (EPA 2009b) to determine whether
they would meet EPA's Tier 3 criteria. Five primary candidate values were identified, as
follows:
• EPA's Office of Health and Environmental Assessment (EPA 1985) developed an
oral cancer slope factor of 1.56E-04 (pg-kg-day)"1. This was based on the
combined incidence of lung, palate, and nasal carcinomas, and liver hyperplastic
nodules or carcinomas in female rats in the study by Kociba et al. (1978).
. EPA (1997a) (EPA's Health Effects Assessment Summary Table, or HEAST)
included an oral CSF of 1.5E-04 (pg-kg-day)"1. The citation for the CSF in
HEAST lists EPA (1985) as one of the sources for the HEAST value.
• California (CalEPA) (1986, 2002) developed an oral cancer slope factor of 1.3E-
04 (pg/kg-day)"1. This is based on the occurrence of hepatocellular adenomas and
carcinomas in male mice in a study by the National Toxicology Program (NTP
1982).
• Michigan (MDEQ 1998) utilizes an oral cancer slope factor of 7.5E-05 (pg/kg-
day)"1, which is based on a re-analysis of the histological slides of livers from
female rats from the Kociba et al. (1978) study using the liver tumor classification
scheme proposed by NTP in 1986 (Maronpot et al. 1986, EPA 1990).
• Minnesota (MNDOH 2003) uses an oral cancer slope factor of 1.4E-03 (pg/kg-
day)"1, which is based on the draft re-evaluation of the exposure-response data for
liver cancer in female rats reported in the draft EPA (2003b) dioxin reassessment.
More detailed descriptions of these five alternative slope factors are presented in
Attachment 2.
The slope factor identified by Minnesota is not considered appropriate because it is based
on the 2003 EPA draft dioxin reassessment (EPA 2003b), which has not been finalized.
The slope factor identified by Michigan is based on an updated and peer-reviewed
evaluation of the Kociba et al. (1978) data using the updated NTP tumor classification
system. However, documentation of the slope factor of 75,000 (mg/kg-day)"1, including
its derivation, peer review and supporting information, is very brief and the information
that is publicly available is limited or not completely transparent. The slope factor listed
in HEAST of 1.5E-04 (pg/kg-day)"1 is slightly different from the slope factor listed in the
source document (EPA 1985) of 1.56E-04 (pg/kg-day)"1. Because of this, the HEAST
was not considered to be transparent as to the derivation of the CSF and how the value
came to be changed slightly from that listed in the source document. Of the two
remaining slope factors (EPA 1985, CalEPA 1986), both are publicly available,
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transparent as to their derivation, and were adequately peer-reviewed. However, the
slope factor of 1.56E-04 (pg/kg-day)"1 derived by EPA (1985) is preferred because it is
based on the incidence of all significant tumors combined, rather than the incidence of
liver tumors alone.
Recommended Non-Cancer Toxicity Factor
As noted above, EPA has not yet derived a Tier 1 or Tier 2 non-cancer toxicity value
(Reference Dose, or RfD) for dioxin. Therefore, EPA reviewed non-cancer toxicity
values developed by States, foreign countries, or other health agencies (EPA 2009b,
2009c). Based on a review of available documents, the following candidate values were
identified:
• A chronic oral Minimal Risk Level (MRL) value of 1 pg/kg-day developed by the
Agency for Toxic Substances and Disease Registry (ATSDR). This value is
based on behavioral effects in the offspring of female monkeys exposed to dioxin
in the diet for 16 months, including the period of gestation and lactation (ATSDR
1998).
• A chronic oral RfD value of 1 pg/kg-day developed by the EPA's Office of
Drinking Water (ODW) (EPA 1987) to support derivation of a lifetime health
advisory for TCDD. This value is based on the occurrence of reproductive effects
in animals.
• A range of Tolerable Daily Intake (TDI) values, ranging from about 1 pg/kg-day
to 4 pg-kg-day, developed by the WHO (WHO 1991, 1998; JECFA 2002). These
values are derived by identifying a no-effect tissue burden in exposed animals for
a range of non-cancer effects, and computing the average daily intake level that
would yield the no-effect tissue burden in humans.
Each of these approaches is described in greater detail in Attachment 2.
Of these values, OSWER recommends the chronic oral MRL value of 1 pg/kg-day
developed by ATSDR (1998) generally as the most appropriate value for use in the
development of non-cancer PRGs. This value is well documented and peer reviewed,
and qualifies as an OSWER Tier 3 toxicity value. This toxicity value is consistent with
the RfD of 1 pg/kg-day developed by EPA's ODW (EPA 1987), and is also consistent
with the low end of the range of TDI values developed by WHO (1991, 1998; JECFA
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AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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2002). Note that ATSDR (2008) has used the 1 pg/kg-day value to derive a soil
screening concentration of 50 ppt1 dioxin TEQ.
Recommended Exposure Pathways and Parameters
EPA provides guidance on the calculation of PRGs in two main documents, including
Risk Assessment Guidance for Superfund (RAGS) Volume I, PartB (Development of
Risk-Based Preliminary Remediation Goals) (EPA 1991) and Supplemental Guidance for
Developing Soil Screening Levels for Superfund Sites (EPA 2002a). For the purposes of
this effort, EPA has utilized default exposure equations and exposure parameters
discussed in the more recent EPA guidance (2002a) along with the RAGS dermal
guidance (EPA 2004). For workers, RAGS B recommends evaluating only indoor
workers, while EPA (2002a) recommends evaluating both indoor and outdoor workers.
Also, EPA (2002a) recommends evaluating non-cancer risk to a resident based on the soil
intake rate of a child, which is considered more protective of children than the approach
used in RAGS B (that uses a time-weighted average intake rate across childhood and
adulthood). Soil PRGs calculated using EPA 2002a equations are generally appropriate
provided that conditions at the site are the same as the conditions assumed in the
calculations. Site managers wishing to use PRGs developed with these protective
equations should consider whether it may be appropriate to modify any of the
assumptions in deriving site-specific PRGs.
The equations and exposure assumptions recommended by EPA (2002a, 2004) for oral
and dermal exposure of residents and workers (both indoor and outdoor workers) to soil
are provided in Tables 1 to 4. In brief, some of the key exposure assumptions for these
populations are as follows:
• Residents and outdoor workers are assumed to be exposed by both oral and
dermal exposure
1 AT SDR's soil screening levels are calculated in accordance with ATSDR's Public Health
Assessment Guidance Manual (ATSDR 2005). The dioxin soil screening level is based on
ATSDR's chronic oral MRL value of 1 pg/kg-day, assuming a soil intake rate of 0.2 g/day by a
10-kg child. Dermal exposure is not included. The assumption of a body weight of 10 kg is
consistent with previous exposure factor recommendations from EPA, while EPA currently
recommends a body weight of 15 kg for a child. Moreover, the 50 ppt screening level is not
intended for use as a PRO, or to serve as a remedial goal. Rather, ATSDR uses the soil screening
concentration as an initial comparison value for health assessments and to make public health
recommendations, such as community health education or site access limitations..
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• Indoor workers are assumed to be exposed by oral exposure only, as no
significant dermal exposure is expected.
• Inhalation exposure is not included for any population because at present, there is
no available inhalation unit risk value for dioxin that has been derived in
accordance with current guidance for inhalation risk assessment (EPA 2009d).
• Inhalation exposure to dioxin (particulates and vapor) is expected to be low (<
2.4%) compared to oral exposure in most cases (see Attachment 1).
• For evaluation of cancer PRGs, residential exposure is assumed to begin at birth
and extend for 30 years. This includes exposure for 6 years as a child and 24
years as an adult. Worker exposures are assumed to occur for 25 years, but only
as an adult.
• For non-cancer PRGs, exposure as a resident is assumed to occur only as a child.
This assumption is thought to be generally conservative (EPA 2002), since
exposure to soil is higher for a child than for an adult resident. For workers,
exposure is assumed to occur only as an adult.
The equations shown in Tables 1 to 4 include two additional terms not explicitly
included in the equations recommended by EPA (2002a):
• RBA. Relative bioavailability (RBA), for purposes of this guidance, is the ratio
of the absorption of dioxin from soil compared to the absorption that occurred in
the study used to derive the oral cancer slope factor or the oral reference dose for
dioxin. For the calculations included in this document, the value of RBA is
assumed to be 1.0 (i.e., dioxin absorption is the same as that occurring in the
study.) This is an appropriate assumption for establishing a default PRO because
use of a RBA factor of 1.0 will ensure protectiveness. However, this assumption
may need to be revisited when performing site-specific assessments.
• RSC. The Relative Source Contribution (RSC) is the amount of a daily safe
intake for non-cancer effects that is "allocated" to soil. RSCs should be applied
only for effects that have a non-zero threshold, and are used mainly by EPA in
developing water standards (EPA 2000). In cases where other sources (e.g., the
diet) contribute a substantial fraction of the ingestion exposure, then the RSC term
may be set to some lower value. The national average dioxin contribution from
diet is estimated to be more than 90% (from beef, pork, poultry, other meats,
dairy, eggs, milk, and fish). If we accounted for this 90% contribution from food,
then the RSC would be 0.1 and the PRG would be one-tenth of the non-cancer
PRO value that we are currently recommending. However, an RSC adjustment for
soil is not often used at Superfund sites, where soil is an exposure source for the
following reasons. The available dietary data are for adults, but the PRGs are
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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developed for children who are exposed to lower concentration levels in the
current food supply. In addition, EPA's responsibilities are to evaluate and
manage only contaminant sources related to the site. For those individuals near
Superfund sites, the contribution of soil derived dioxin exposures relative to food
derived exposures is expected to be much greater than the national average.
Therefore, for all PRG calculations performed in this document, the value of RSC
is set to 1.0.
Draft Interim Recommended PRGs for Dioxin in Soil
Cancer PRGs
Based on the recommended oral cancer slope factor of 1.56E-04 (pg/kg-day)"1 discussed
above, recommended interim soil PRGs for protection against cancer effects at the 1E-06
risk level may be computed in accordance with current EPA equations and default
exposure assumptions shown in Table 1 and Table 2. The results are shown below:
Potential Soil PRGs for Dioxin Based on Cancer (1E-06 Risk Level)
Land Use
Residential
Commercial/
Industrial
Receptor
Resident
Indoor Worker
Outdoor Worker
PRG
(pptTEQ)
3.7
37
17
All PRGs are shown to two significant figures
Non-Cancer PRGs
Based on the recommended oral non-cancer interim toxicity value of 1 pg/kg-day
selected above, recommended interim non-cancer PRGs for residential and
commercial/industrial land use that correspond to a Hazard Quotient (HQ) of 1 may be
calculated in accordance with current EPA equations and default exposure assumptions
shown in Table 3 and Table 4. These results are shown below:
Potential Soil PRGs for Dioxin Based on Non-Cancer Effects (HQ of 1)
Land Use
Residential
Commercial/
Industrial
Receptor
Resident
Indoor Worker
Outdoor Worker
PRG
(pptTEQ)
72
2,000
950
All PRGs are shown to two significant figures
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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Draft Recommended Interim PRGs
Based on consideration of oral and dermal exposures to dioxin and other dioxin-like
compounds in soil, EPA recommends the interim PRGs for dioxin in soil calculated
based on non-cancer effects: 72 ppt dioxin TEQ in residential soil and 950 ppt dioxin
TEQ in commercial/industrial soil. EPA believes that these recommended interim PRGs
generally provide adequate protection against non-cancer effects. In addition, they
generally are protective for cancer effects at approximately the IE-OS risk level, which is
within EPA's protective risk range of 1E-04 to 1E-06 (see 40 CFR §300.430(e)(2)(i)(A)).
It should be noted that because these recommended interim PRGs correspond to a HQ of
1, they limit the upper bound cancer risk level to IE-OS rather than the typical upper limit
of 1E-04. These recommended interim PRGs are set at a more protective cancer risk level
than the 1998 PRGs, which reflect a cancer risk level of 2E-04. These draft
recommended interim PRGs are expected to be higher than typical background levels for
residential and most commercial/industrial soils, respectively (ATSDR 1998).
Land Use
Residential
Commercial/Industrial
PRO (ppt TEQ)
72
950
All recommended PRGs are shown to two significant figures
EPA believes the draft recommended PRGs described above if finalized would be
appropriate for use on an interim basis until EPA releases its final dioxin reassessment.
However, EPA is also considering an alternative concentration of 3.7 ppt dioxin TEQ in
residential soil and 17 ppt dioxin TEQ in commercial/industrial soil as the point of
departure for determining PRGs. These alternative draft PRGs are at the 1E-06 risk level
and therefore are also consistent with the NCP provision for PRGs (see 40 CFR
§300.430(e)(2)(i)(A)(2)), which states 1E-06 is the point of departure for determining
remediation goals. These alternative values are protective for non-cancer as well as
cancer effects. EPA notes that PRGs based on a 1E-06 cancer risk level would likely be
within or possibly below background concentrations of dioxins in U.S. soils. A recent
EPA report found mean rural soil concentrations ranging from 0.2 to 11.4 ppt dioxin TEQ
(EPA 2007). Generally, it is OSWER policy to not set site specific cleanup levels at
concentrations below site specific natural background levels (EPA 2002b). Thus, if EPA
were to finalize these alternative values, soil background levels would need to be
identified at CERCLA sites in order to develop appropriate cleanup levels. While EPA is
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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taking comments on all aspects of this draft guidance, EPA is particularly interested in
comments on the utility of these alternative values.
IMPLEMENTATION
This guidance does not affect or replace statutory or regulatory requirements (e.g.,
CERCLA Section 121 provisions on meeting or waiving ARARs) under CERCLA or
RCRA. For example, the maximum contaminant level (MCL) for dioxin in drinking
water is 30 pg/L, and this should continue to be considered as an ARAR for the cleanup
under CERCLA of ground water that may be used as drinking water (unless a more
stringent state ARAR requires a lower concentration).
These draft recommended interim PRGs are informed by the best available toxicity
values as evaluated using OSWER's toxicity hierarchy (EPA 2003a) and calculated using
current EPA exposure assumptions, which have been updated since the 1998 PRG
guidance (EPA 1998) was issued. Once finalized, regions may consider using these
recommended interim PRGs at both CERCLA and RCRA sites where the Agency is
determining dioxin soil cleanup levels. When EPA's ORD finalizes its dioxin
reassessment, OSWER will evaluate the impact of the dioxin reassessment and will
update these PRGs as appropriate.
These draft recommended interim soil PRGs are national levels protective for cancer and
non-cancer effects from ingestion and dermal contact with surface soils in residential
and commercial/industrial exposure scenarios. Inhalation exposure is not included for
the draft recommended interim PRGs, because at present, there is no available inhalation
unit risk value for dioxin that has been derived in accordance with current guidance for
inhalation risk assessment (EPA 2009d). However, inhalation exposure to dioxin
(particulates and vapor) is expected to be low (< 2.4%) compared to oral exposure in
most cases (see Attachment 1). Therefore, risks due to inhalation of particulates and
vapors are expected to be minimal. Once finalized, the interim guidance will supersede
OSWER's previous PRG guidance for dioxin in soil (EPA 1998). These draft
recommended interim soil PRGs are national levels protective for cancer and non-cancer
effects from human contact (ingestion, dermal contact, and inhalation exposure (this is
minimal for dioxin particulates and vapors)) with surface soils in residential and
commercial/industrial exposure scenarios. Exposure to dioxin by the inhalation route is
not expected to be significant compared to oral exposure (see Attachment 1). Regions
should continue to develop PRGs on a site-specific basis for other media, like sediments,
that involve biotransfer and bioaccumulation up the aquatic food chain to fish consumed
by humans and for ecological assessments where the receptors are terrestrial biota, such
as plants and animals, not humans.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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At CERCLA National Priority List (NPL) sites, including, where appropriate, other
Federal agency-lead and state-lead sites, Regions should consult with the Office of
Superfund Remediation and Technology Innovation (OSRTI) Site Assessment and
Remedy Decisions Branch on all proposed dioxin cleanups that are conducted under
Superfund. Consultation should be initiated at the risk assessment stage, and continue
through the process.
For removal actions, Regions should contact Headquarters for concurrence on non-NPL
removal actions where dioxin is a principal contaminant of concern (EPA 1989). For
non-time critical removal actions involving dioxin, consultation may involve both OEM
and OSRTI. The use of removal authority is determined on a site-specific basis, and
trigger levels for initiating a removal action are sometimes higher than the levels used as
either PRGs (or starting points) or final cleanup levels.
For sites where another Federal agency is the lead agency, OSRTI will notify the Federal
Facilities Restoration Reuse Office of ongoing consultations regarding dioxin soil
cleanup levels. The Office of Site Remediation Enforcement will provide support if
enforcement issues are identified. For consultation procedures, refer to OSWER
Directive 9200.4-19 (EPA 1996) and OSWER Directive 9200.1-18FS (EPA 1997b).
Once finalized, Regions performing five-year-reviews of CERCLA remedial sites where
soils contaminated with dioxin or other dioxin-like compounds have been left in place
should consider this guidance on recommended interim PRGs when evaluating whether
the original remedies in the Records of Decision (ROD) remain protective for the
contaminated areas. Consistent with existing five-year-review guidance (EPA 2001),
OSWER recommends that the five-year-reviews include an evaluation of existing site
data, identification of the need for additional site data, and identification of areas
potentially needing cleanup based on the review of this existing data. This information
can be used to evaluate whether additional data collection and/or site cleanup is
appropriate. Once the final dioxin reassessment has been released, OSWER may issue
additional guidance on implementation of the PRGs.
In the case of EPA-lead RCRA corrective action sites, Regions should provide the
Program Implementation and Information Division within the Office of Resource
Conservation and Recovery (ORCR) with proposed dioxin soil cleanup levels (i.e., prior
to notice and comment) in order to ensure appropriate implementation of the
recommended interim PRGs, once they are finalized. For State-lead RCRA corrective
action sites, we would also encourage States to use the dioxin levels recommended by
this guidance as starting points in developing soil cleanup levels, unless they have
developed their own standards or guidance. Because States are the primary implementers
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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of the RCRA Corrective Action program, this guidance does not recommend specific
procedures for implementation under RCRA. States are encouraged to share their
approaches with the Regions in a manner consistent with established procedures for EPA
support and oversight of state RCRA Corrective Action programs.
Point of Contact
If you have any questions, please contact Marlene Berg by phone at 703-603-8701 or by
e-mail at berg.marlene@epa.gov.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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TABLE 1
RECOMMENDED EQUATION FOR COMPUTING CANCER PRGS FOR
EXPOSURE OF RESIDENTS TO DIOXIN IN SOIL
PRG(pglg) =
TR-AT-365 days/yr
EF • [SF0 • IFsml/ad] + (SF01ABSG1 )-SFS- ABSd • EV] • RBA
Parameter (description)
TR (target cancer risk)
AT (averaging time)
EF (exposure frequency)
SF0 (Oral slope factor)
IFSoii/adj (age-adjusted soil ingestion factor)
ABSGi (gastrointestinal absorption fraction)
SFS (age adjusted dermal factor)
ABSd (dermal absorption fraction)
EV (dermal exposure frequency)
RBA (relative bioavailability)
Units
dimensionless
years
days/yr
(pg-kg-day)"1
g-yr/(kg-d)
pg absorbed/pg ingested
g-yr/kg-event
pg absorbed/pg on skin
events/day
~
Default Value
1E-04 to 1E-06
70
350
1.56E-04(a)
0.114
1.0
0.360
0.03 (b)
1
1
Source: EPA 2002 Equation 3-1
Includes oral and dermal exposure.
(a) Based on EPA (1985)
(b) Based on EPA (2004)
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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TABLE 2
RECOMMENDED EQUATION FOR COMPUTING CANCER PRGS FOR
EXPOSURE OF WORKERS TO DIOXIN IN SOIL
PPG(pglg) =
TR-BW-AT-365days/yr
(EF • ED)[-IR • oSF + (SF01ABSOI )-AF- ABSd • EV • SA] • RBA
Parameter (description)
TR (target cancer risk)
BW (body weight)
AT (averaging time)
EF (exposure frequency)
ED (exposure duration)
SF0 (Oral slope factor)
IR (soil ingestion rate)
ABSGi (gastrointestinal absorption
fraction)
ABSd (dermal absorption fraction)
EV (dermal exposure frequency)
AF (dermal adherence factor)
SA (dermal surface area)
RBA (relative bioavailability)
Units
Dimensionless
Kg
Years
days/yr
Years
(pg-kg-day)"1
g/day
pg absorbed/pg ingested
pg absorbed/pg on skin
events/day
g/cm2
cm2
~
Default Value
Indoor Worker
1E-04 to 1E-06
70
70
250
25
1.56E-04(a)
0.05
1.0
~
~
~
~
1
Outdoor
Worker
1E-04 to 1E-06
70
70
225
25
1.56E-04(a)
0.10
1.0
0.03 (b)
1
2E-04
3300
1
Source: EPA 2002 Equation 4-1
Includes oral and dermal exposure for outside workers. Dermal exposure not quantified for an
indoor worker.
(a) Based on EPA (1985)
(b) Based on EPA (2004)
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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TABLE 3
RECOMMENDED EQUATION FOR COMPUTING NON-CANCER PRGS FOR
EXPOSURE OF RESIDENTS TO DIOXIN IN SOIL
PRG(pglg) =
THQ -BW-AT- 365 days/yr- RSC
EF • ED • [IRsoU I RfDo + (AF • ABSd • EV • SA) I (RfDo • ABSGI)] • RBA
Parameter (description)
THQ (target hazard quotient)
BW (body weight - child)
AT (averaging time)
EF (exposure frequency)
ED (exposure duration)
RfD0 (Oral reference dose)
IRSoii (soil ingestion rate)
ABSGi (gastrointestinal absorption fraction)
AF (dermal adherence factor)
ABSd (dermal absorption fraction)
EV (dermal exposure frequency)
SA (dermal surface area exposed - child)
RBA (relative bioavailability)
RSC (relative source contribution)
Units
dimensionless
kg
years
days/yr
years
pg/kg-day
g/day
pg absorbed/pg ingested
g/cm2
pg absorbed/pg on skin
events/day
cm2
~
~
Default
Value
1
15
6
350
6
1.0 (a)
0.20
1.0
2E-04
0.03 (b)
1
2,800
1
1
Source: EPA 2002 Equation 3-2
Includes oral and dermal exposure.
(a) Based on ATSDR (1998) chronic oral MRL
(b) Based on EPA (2004)
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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TABLE 4
RECOMMENDED EQUATION FOR COMPUTING NON-CANCER PRGS FOR
EXPOSURE OF WORKERS TO DIOXIN IN SOIL
PRG(pglg) =
THQ -BW-AT- 365 days/yr- RSC
EF • ED • [IRsoU I RfDo + (AF • ABSd • EV • SA) I (RfDo • ABSGI)] • RBA
Parameter (description)
THQ (target hazard quotient)
BW (body weight)
AT (averaging time)
EF (exposure frequency)
ED (exposure duration)
RfD0 (oral reference dose)
IR (soil ingestion rate)
ABSGi (gastrointestinal absorption
fraction)
ABSd (dermal absorption fraction)
EV (dermal exposure frequency)
AF (dermal adherence factor)
SA (dermal surface area)
RBA (relative bioavailability)
RSC (relative source contribution)
Units
Dimensionless
Kg
Years
days/yr
Years
pg/kg-day
g/day
pg absorbed/pg ingested
pg absorbed/pg on skin
events/day
g/cm2
cm2
~
~
Default Value
Indoor
Worker
1
70
70
250
25
1.0 (a)
0.05
~
~
~
~
~
1
1
Outdoor
Worker
1
70
70
225
25
1.0 (a)
0.10
1.0
0.03 (b)
1
2E-04
3,300
1
1
Source: EPA 2002 Equation 4-2
Includes oral and dermal exposure for outdoor workers. Dermal exposure not quantified for an
indoor worker.
(a) Based on ATSDR (1998) chronic oral MRL
(b) Based on EPA (2004)
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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ATTACHMENT 1
EVALUATION OF RELATIVE DIOXIN INTAKE
FROM INHALATION AND INGESTION EXPOSURE
Exposure to a contaminant in soil may occur by a number of pathways, including direct
ingestion of soil, dermal contact with soil, inhalation of soil particulates in air, and
inhalation of vapors of the chemical released from soil to air. This Attachment compares
the relative magnitude of human exposure to dioxin in soil by the inhalation route
(including both inhalation of dioxin on airborne particulates and inhalation of dioxin
vapor) compared to intake by the oral route using EPA's default residential and
commercial/industrial land exposure parameters. The dermal pathway is not included in
the comparison because dermal exposure is expressed in terms of absorbed dose, while
the oral and inhalation pathways are expressed in terms of administered dose. However,
based on default exposure assumptions, the dermal pathway is relatively minor compared
to oral. This Attachment does not compare risks associated with oral and inhalation
pathways because there is no available inhalation unit risk value for dioxin that has been
derived in accordance with current guidance for inhalation risk assessment (EPA 2009d).
Relative Contribution from Inhalation of Particulates
The ratio of the amount of dioxin inhaled on respirable soil particles (e.g., PMlOs or
PM2.5s) compared to the amount of dioxin ingested with soil can be calculated as
described below.
Dose Inhaled (mg/day) = Csoii • CPMIO ' BR
Dose Ingested (mg/day) = Cso;i • IR
where:
Csoii = concentration of dioxin in soil
CPMIO = concentration of soil particles less than 10 jim in size in air (mg/m3)
BR = breathing rate (m3/day)
IR = soil ingestion rate (mg/day)
The concentration of PM10 particles in air is given by:
CPMIO (mg/m3) = (1E-06 mg/kg) / PEF
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
Al-1
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DRAFT
where PEF = particulate emission factor (m /kg).
The ratio of the daily intakes of dioxin by these two routes is then:
Ratio(inhal/ingest) = BR / (IR • PEF)
EPA (1991) provides recommended default values for breathing rate and soil ingestion
rate for residents and workers, and EPA (2002) provides a recommended default PEF for
residential and industrial land use. Based on these inputs, the resulting ratio of daily
intakes (inhalation compared to oral) are as follows:
Parameter
BR (m3/day)
IR (kg/day)
PEF (m3/kg)
Ratio (inhalation of dioxin on particulates
vs. oral intake from soil)
Parameter Value
Child
10
2E-04
1.36E+09
0.00004
Adult
20
1E-04
1.36E+09
0.00015
Worker
10
1E-04
1.36E+09
0.00007
As indicated, based on recommended default exposure parameters, the amount of dioxin
inhaled as respirable particulates is likely to be small (« 1%) compared to the amount
ingested with soil.
Relative Contribution from Inhalation of Volatiles
Similarly, the ratio of the daily intake of a chemical due to inhalation of the volatilized
chemical in air to the chemical ingested on soil:
Ratio(inhal/ingest) = BR / (IR • VF)
where VF = volatilization factor (m3/kg).
The value of the VF term may be calculated using Equation 4-8 in EPA (2002).
Recommended default inputs and chemical-specific terms are shown in Table Al-1.
Based on these parameters, the value of VF is estimated to be 8.4E+06 mVkg. Based on
this, the ratios of dioxin intake from vapor inhalation compared to soil ingestion are as
follows:
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
Al-2
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Parameter
BR (mVday)
IR (kg/day)
VF (m3/kg)
Ratio (inhalation of vapors vs. oral intake)
Parameter Value
Child
10
2E-04
8.4E+06
0.006
Adult
20
1E-04
8.4E+06
0.024
Worker
10
1E-04
8.4E+06
0.012
As seen, exposure by inhalation of dioxin released to air from soil is likely to be small
(< 2.4%) compared to the amount of dioxin ingested in soil.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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TABLE Al-1
RECOMMENDED DEFAULT INPUTS AND CHEMICAL-SPECIFIC VALUES
USED IN VOLATILIZATION FACTOR CALCULATION
Parameter (description)
Q/Cvol (inverse of the ratio of geometric mean air concentration
to volatilization flux at a center of a square source)
T (exposure interval)
Pb (dry soil bulk density)
0a (air-filled soil porosity)
n (total soil porosity)
0W (water-filled soil porosity)
Ps (soil particle density)
foc (fraction organic carbon in soil)
D; (diffusivity in air)
H' (Henry's law constant)
Dw (diffusivity in water)
Kd (soil-water partition coefficient)
Koc (soil-organic carbon partition coefficient)
Units
g/m2-s per kg/m3
s
g/cm3
Lair/-LSoil
-L^pore'-^soil
-Lair'-Lsoil
g/cm3
g/g
cm2/s
dimensionless
cm2/s
cm3/g
cm3/g
Value
68.18
9.5E+08
1.5
n-0w
l-( Pb/ Ps)
0.15
2.65
0.006
4.7E-02
2.04E-03
8E-06
J^-oc A IDC
3.98E+06
Source
[a]
[a]
[a]
[a]
[a]
[a]
[a]
[a]
[b]
[c,d]
[b]
[a]
[e]
Chemical-specific values are shaded in grey.
[a] EPA (2002)
[b] GSI Chemical Database: http://www.gsi-net.com/en/publications/gsi-chemical-
database/single/240 .html
[c] SRC PHYSPROP Database: http://www.syrres.com/what-we-do/product.aspx?id= 133
[d] Converted to dimensionless using EPA's On-line Tools for Site Assessment Calculation
http://www.epa.gov/athens/learn2model/part-two/onsite/henryslaw.html
[e] SRC CHEMFATE Database: http://www.srcinc.com/what-we-do/databaseforms.aspx?id=381
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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ATTACHMENT 2
DESCRIPTION OF CANDIDATE CANCER AND
NON-CANCER TOXICITY VALUES FOR DIOXIN
A. DERIVATION OF CANCER SLOPE FACTORS
The first step in computing recommended cancer-based Preliminary Remediation Goals
(PRGs) for dioxin is to select the cancer slope factor. A review of the approaches used
by U.S. states, territories (EPA 2009b) and other U.S. health agencies has identified five
potential values, as discussed below.
EPA (1985)
EPA's Office of Health and Environmental Assessment reviewed the toxicity data for
dioxin and prepared a Health Assessment Document (HAD) in September 1985 (EPA
1985). The HAD evaluated the cancer dose-response data from each of two published
studies in animals:
• A two-year oral feeding study in male and female rats (Kociba et al. 1978). The
HAD evaluation considered two alternative pathological analyses of the slides
from the study, including the findings of the original pathologist (Kociba) and
also an independent reviewer (Squire) employed by EPA's Cancer Assessment
Group.
• A two-year oral gavage study in male and female rats and mice performed by the
National Toxicology Program (NTP) of the National Cancer Institute (NTP 1982).
The HAD fit a number of alternative cancer dose response data sets from each of these
studies to the linearized multistage model to derive a series of alternative estimates of an
oral cancer slope factor. These results are summarized in Table A2-1. The HAD found
that the highest slope factor was obtained using the data from Kociba et al. (1978), using
the combined incidence of carcinomas in lung, carcinoma and hyperplastic nodules in
liver, and carcinoma in nasal turbinates and hard palate in female rats. Based on the
histopathological analysis of Kociba, the slope factor was 1.51E-04 (pg/kg-day)"1, while
based on the histological analysis by Squire, the slope factor was 1.61E-04 (pg/kg-day)"1.
The HAD identified the geometric mean of these two values (1.56E-04 (pg/kg-day)"1) as
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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the recommended slope factor. This approach was peer-reviewed by an expert panel
assembled for a peer review workshop in Cincinnati in 1983, and by the Environmental
Effects, Fate and Transport committee of EPA's Science Advisory Board.
EPA (1997)
EPA's Health Effects Assessment Summary Table (HEAST) (EPA 1997a) identifies an
oral cancer slope factor of 1.5E-04 (pg/kg-day)"1. HEAST tables are described in EPA
(1997) as containing "provisional risk assessment information" that "have not had
enough review to be recognized as high quality, Agency-wide consensus information."
The primary source of the oral slope factor value for dioxin is the EPA (1985) HAD, but
the reason that the value listed is 1.5E-04 (pg/kg-day)"1 rather than 1.56E-04 (pg/kg-day)"
1 is not clear. The value was indicated as being provisional, and was qualified as being
under further evaluation. Although the HAD (EPA 1985) is peer-reviewed, specific
information on the peer review status of the value in HEAST has not been found.
CalEPA (1986, 2002)
California (CalEPA 1986, 2002) also reviewed the cancer data from the study of Kociba
et al. (1978) (including the histological analyses by both Kociba and Squire) and by NTP
(1982). A number of different data sets were fit to the linearized multistage model to
derive inhalation unit risk values. These unit risk values, and the equivalent oral cancer
slope factors, are summarized in Table A2-2. In this analysis, the highest slope factor
was found to occur using data from the NTP (1982) study on the incidence of carcinomas
and adenomas in male mouse liver. This slope factor was 1.3E-04 (pg/kg-day)"1 (CalEPA
1986). This slope factor was peer-reviewed in August 1986 by an independent nine-
member Scientific Review Panel.
Michigan (MDEQ 1998)
Michigan uses a slope factor of 7.5E-05 (pg/kg-day)"1, which is based on a re-analysis of
the histological slides of livers from female rats from the Kociba et al. (1978) study using
the liver tumor classification scheme proposed by NTP in 1986 (Maronpot et al. 1986).
In this revised histological classification, lesions that were previously classified as
"neoplastic nodules" and were counted as liver tumors are divided into "hepatocellular
hyperplasia" and "hepatocellular adenoma." The term "hyperplasia" is reserved for
proliferative lesions that are secondary responses to degenerative changes in the liver,
and these are not considered to be liver tumors. Foci of cellular alteration, including
hepatocellular adenoma and hepatocellular carcinoma, are considered to represent a
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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DRAFT
spectrum of changes that comprise the natural history of liver neoplasia, and these are
counted as liver tumors (Maronpot et al. 1986).
The pathology slides from Kociba et al. (1978) were originally reclassified by Squire (an
independent pathologist serving as a consultant to EPA's Carcinogen Assessment
Group), who reported that preliminary results from the re-reading indicated substantially
lower liver tumor incidence (EPA 1990). Based on a request from the Maine Science
Advisory Panel, the slides were subsequently re-evaluated under the new system by
seven independent pathologists referred to as the Pathology Working Group (PWG)
(Sauer 1990, Goodman and Sauer 1992). Table A2-3 summarizes the results for liver
lesions derived using the original and the revised classification schemes. As shown, the
incidence of liver tumors is substantially lower based on the new classification scheme
than the original scheme. Based on total significant tumors (liver, lung, nasal turbinates
and hard palate), the cancer slope factor based on the revised classification scheme is
7.5E-05 (pg/kg-day)"1, as opposed to a value of 1.51E-04 using the original analysis (EPA
1990).
A three page document is publicly available on the Michigan Department of
Environmental Quality website that summarizes the reevaluation of the Kociba data by
the PWG; however, a description of the derivation of the cancer slope factor is not
included nor is information about external peer review of that derivation. The findings of
the PWG, however, were published in the peer reviewed literature. In short,
documentation of the slope factor of 75,000 (mg/kg-day)"1, including its derivation, peer
review and supporting information, is very brief, and the information that is publicly
available is limited or not completely transparent.
Minnesota (MNDOH 2003)
Minnesota uses a value of 1.4E-03 (pg/kg-day)"1, which is based on the re-evaluation of
the exposure-response data for liver cancer in female rats reported in the EPA 2003 draft
dioxin reassessment (EPA 2003b). In this approach, the tumor incidence data reported by
Goodman and Sauer (1992) were used, which are based on the revised liver pathology
scheme developed by NTP in 1986 (Maronpot et al. 1986). However, the dose metric
was changed from administered dose (ug/kg-day) to body burden (ug/g). This approach
helps account for the large difference in half-life of TCDD in humans and rats (EPA
2003b). The dose corresponding to a specified body burden was estimated using the
following equation:
Intake (pg/kg-d) = Tissue Burden (pg/kg) • ln(2) / [ti/2 • f]
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
A2-3
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where:
ti/2 = half-life of dioxin in the body (days). A value of 2593 days was assumed
for humans and 25 days in rats.
f = fraction of an ingested dose that is absorbed (assumed to be 0.8)
Using the linearized multistage model and adjusting the dose metric as described, EPA
(2003b) derived a cancer slope factor of 1.4E-03 (pg/kg-day)"1. This value is 8.7 times
higher than the cancer slope factor derived by EPA (1985), and reflects the combined
effect of using body burden rather than ingested dose (31 times higher) and the effect of
using the revised histopathology incidence data (3.6 times lower).
This approach and the resultant slope factor have not undergone final Agency approval or
final peer review.
B. DERIVATION OF NON-CANCER TOXICITY VALUES
The first step in computing recommended non-cancer-based PRO concentrations for
dioxin is to select a non-cancer toxicity value (RfD). 2 EPA currently does not have an
Agency RfD for dioxin. Therefore, EPA reviewed non-cancer values used by states,
foreign nations or other health agencies.
EPA Office of Drinking Water (1987)
In 1987, EPA's Office of Drinking Water (ODW) developed an oral RfD of 1 pg/kg-day
for use in deriving a Lifetime Health Advisory value (EPA 1987). This RfD was based
on a 3-generation reproductive study in rats (Murray et al. 1979). In this study, animals
were exposed to TCDD in the diet at concentrations that produced average doses of 0,
0.001, 0.01, or 0.1 ug/kg-day. Significant decreases in fertility and neonatal survival of
offspring were observed in animals exposed to the 0.1 ug/kg-day dose level. At the dose
of 0.01 ug/kg-day, signs of toxicity included decreases in gestational survival, decreased
pup size at birth, and decreased neonatal survival and growth. For the 0.001 ug/kg-day
dose group, no effect on fertility, litter size, or postnatal body weight was observed in any
generation, and effects on neonatal survival were inconsistent. However, a re-evaluation
of these data by Nisbet and Paxton (1982), using different statistical methods indicated
2 An RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral
exposure to the human population (including sensitive subgroups) that is likely to be without an
appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL,
LOAEL, or benchmark dose, with uncertainty factors generally applied to reflect limitations of
the data used..
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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that there was a reduction in the gestational index, decreased fetal weight, increased liver
to body weight ratio, and increased incidence of dilated renal pelvis at the 0.001 ug/kg
dose. From these results, EPA (1987) determined that a dose of 0.001 ug/kg-day was the
lowest-observed-adverse-effect-level (LOAEL), and calculated an RfD by dividing the
LOAEL by an uncertainty factor of 1,000, yielding a result of 1E-06 ug/kg-day (1 pg/kg-
day). The uncertainty factor of 1,000 was chosen in accordance with National Academy
of Sciences (NAS) and EPA ODW guidelines for use with a LOAEL from an animal
study. This uncertainty factor accounts for uncertainty in extrapolation from animals to
humans (10x), variation in sensitivity between humans (10x), and use of a LOAEL rather
than a NOAEL (lOx). ODW states that this value has been peer-reviewed, but
documentation of the peer review was not located.
ATSDR(1998)
ATSDR has derived a chronic oral Minimal Risk Level (MRL)3 of 1 pg/kg-day (ATSDR
1998). This value is based on a study by Schantz et al. (1992) in which female monkeys
were exposed to dioxin in the diet for 16 months at 0, 5 or 25 ppt TCDD. After 7 months
of exposure, the females were bred with unexposed males. Exposure of the females
continued through mating, gestation and lactation. Only one monkey in the high dose
group delivered a viable offspring, so this group was not studied further. When offspring
from the control group and the 5 ppt group were 8.6 months of age, they were placed in
peer groups of 4 monkeys (2 exposed, 2 control) and allowed to play without
interference. Behavioral patterns (social interactions, vocalizations, locomotion, self-
directed behavior, environment exploration) were monitored 4 days/week for 9 weeks.
No overt signs of toxicity were observed in the mothers or the offspring, and birth
weights were not adversely affected. However, significant alterations were observed in
play behavior, displacement and self-directed behavior, with a tendency for offspring
from exposed mothers to initiate more rough/-tumble play bouts, to retreat from play less
often, and to engage in more self-directed behavior. Based on this, a dietary exposure
level of 5 ppt was identified as a LOAEL. The estimated dose from this diet was 1.2E-04
ug/kg-day. This dose was adjusted by dividing by an overall uncertainty factor of 100 to
account for use of a minimal LOAEL, inter-species extrapolation, and inter-individual
variability. This yielded an MRL of 1E-06 ug/kg-day (1 pg/kg-day). All ATSDR
Toxicity Profiles are peer reviewed and publicly available.
3 An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be
without appreciable risk of adverse noncancer health effects over a specified duration of
exposure. These substance-specific estimates, which are intended to serve as screening levels, are
used by ATSDR health assessors and other responders to identify contaminants and potential
health effects that may be of concern at hazardous waste sites.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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WHO (1991, 1998); JECFA (2002)
The World Health Organization (WHO) has been organizing expert consultations and
workgroups for a number of years to derive toxicity values for the evaluation of dioxin
toxicity. The results of their first consultation was issued in 1990. At that time, WHO
(1991, 1992) concluded that TCDD was carcinogenic in animals, acting as a non-
genotoxic promoter-carcinogen. Therefore, the consultation decided to establish a
Tolerable Daily Intake (TDI)4 based on general toxicological effects. Based on liver,
immunological and reproductive effects in animals, the no-effect dose was estimated to
be about 1,000 pg/kg-day. This value was adjusted to an equivalent human dose of 100
pg/kg-day using toxicokinetic data. After applying an uncertainty factor of 10 to account
for insufficient data on reproductive effects in humans, a TDI of 10 pg/kg-day was
recommended.
In 1998, the WHO European Centre for Environmental Health (WHO-ECEH) and
International Programme on Chemical Safety (IPCS) performed a re-assessment of the
available information on the toxicity of dioxin (WHO 1998), and reached the following
key conclusions:
• The cancer effects of dioxin are mediated by a non-genotoxic mode of action that
is mediated via a receptor binding mechanism. Consequently, cancer risk has a
threshold, and exposures that do not cause non-cancer effects will not increase
cancer risk.
• The most sensitive non-cancer effects caused by dioxin include developmental
and reproductive effects in rats and monkeys.
• The most reliable metric of exposure for use in risk evaluation is tissue burden
rather than ingested dose.
Based on these key conclusions, WHO (1998) estimated the TDI (pg/kg-day) for lifetime
exposure in a series of 3 steps, as follows:
Step 1: Identify the tissue burden effect level for the most sensitive (and relevant)
adverse responses. Based on studies in rats and monkeys, the WHO estimated that the
LOAEL tissue burdens ranged from 28-73 ng/kg (28,000-73,000 pg/kg).
4
A TDI is an estimate of the amount of a substance in air, food or drinking water that can be taken in daily
over a lifetime without appreciable health risk. TDIs are calculated on the basis of laboratory toxicity data
to which uncertainty factors are applied.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
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Step 2: Given the tissue burden range, calculate the TDI that would yield this
tissue burden range. The WHO computed the TDI using a simple steady-state
pharmacokinetic model of the following form:
TDI (pg/kg-d) = Tissue Burden (pg/kg) • [l-exp(-ln(2)/ti/2)] / f
where:
ti/2 = half-life of dioxin in the body (days)
f = fraction of an ingested dose that is absorbed
WHO utilized a half-life of 7.5 years (2,738 days), and an assumed fractional absorption
of 0.5 (50%). Based on this, the TDI was estimated to range from 14-37 pg/kg-day.
Step 3: Adjust the TDI to account for uncertainties. A factor of 10 was applied to
address the following uncertainties: a) the use of a range of LOAELs instead of a no-
effect level, b) the possible differences in susceptibility between humans and
experimental animals, c) the potential differences in susceptibilities within the human
population, and d) differences in half-lives of elimination for the compounds of a
complex TEQ mixture. After application of the uncertainty factor, the TDI (rounded)
was estimated to range from 1-4 pg/kg-day. The WHO (1998) consultation stressed that
the upper range of the TDI of 4 pg/kg-day should be considered a maximal tolerable
intake on a provisional basis and that the ultimate goal is to reduce human intake levels to
below 1 pg/kg-day.
More recently, the Joint FAO/WHO Expert Committee on Food Additives (JECFA 2002)
re-evaluated dioxin toxicity based on two new reproductive studies (Ohsako et al. 2001
and Faqi et al. 1998) published since the previous assessment.
Faqi et al. (1998) exposed female rats subcutaneously with TCDD at 0, 25, 60 or 300
ng/kg, followed by weekly maintenance doses of 0, 5, 12 or 60 ng/kg, beginning 2 weeks
before the beginning of mating and continually through mating, gestation and lactation.
Male offspring were assessed for sexual development and were bred to untreated females.
Adverse effects on sperm were detected at all doses on postnatal day 170.
Ohsako et al. (2001) administered a single oral dose of 0, 12.5, 50, 200 or 800 ng/kg of
TCDD to pregnant rats, and male offspring were assessed for reproductive development.
Adverse effects that were noted on postnatal day 49 and/or day 120 included reduced
anogenital distance (50, 200 or 800 ng/kg), reduced ventral prostate weight (200 or 800
ng/kg), reduced androgen receptor messenger ribonucleic acid (mRNA) production in
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
A2-7
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DRAFT
ventral prostate (all doses) increased 5-alpha-reductase type 2 mRNA in ventral prostate
(all doses), and decrease androgen receptor mRNA in the ventral prostate (all doses).
JECFA (2002) used two alternative models (linear model and power model) to estimate
the relationship between fetal and maternal body burden and to calculate a Provisional
Tolerable Monthly Intake (PTMI) for each of these two new studies. The resulting
values are summarized in Table A2-4.
Based on these calculations, JECFA (2002) concluded that the range of PTMI values was
40-100 pg/kg-month, and chose the mid-point of this range (70 pg/kg-month) as the final
PTMI. Assuming 30 days/month, this is equivalent to a TDI of 2.3 pg/kg-day.
Because all of the evaluations described above were performed by panels of expert
scientists, all of the TDI values derived are considered to be adequately peer-reviewed.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW
AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY FINAL AGENCY
DETERMINATION OR POLICY.
A2-8
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TABLE A2-1 CANCER SLOPE FACTORS DEVELOPED BY EPA (1985)
Study
Kociba et al. 1978
Kocibaetal. 1978
Kociba et al. 1978
Kocibaetal. 1978
NTP 1982
NTP 1982
NTP 1982
Pathologist
Kociba
Squire
Kociba
Squire
NTP
NTP
NTP
Species
Rat
Rat
Rat
Rat
Rat
Mouse
Mouse
Gender
Male
Male
Female
Female
Female
Male
Female
Tissue(s)
Nasal turbinates/hard palate
Nasal turbinates/hard
palate/tongue
Lung
Nasal turbinate/hard palate
Liver
Lung
Nasal turbinate/hard palate
Liver
Liver
Liver
Subcutaneous tissue
Blood
Liver
Tumor Type(s)
Carcinoma
Carcinoma
Carcinoma
Carcinoma
Hyperplastic nodules or carcinoma
Carcinoma
Carcinoma
Hyperplastic nodules or carcinoma
Carcinoma and neoplastic nodules
Carcinoma
Fibrosarcoma
Lymphoma or leukemia
Carcinoma or adenoma
CSF
(pg/kg-day)"1
1.5E-05
1.7E-05
1.51E-04
1.61E-04
3.3E-05
7.5E-05
4.6E-05
Shaded cells indicate the slope factors recommended by EPA (1985) for use.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY
FINAL AGENCY DETERMINATION OR POLICY.
A2-9
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DRAFT
TABLE A2-2 CANCER SLOPE FACTORS DEVELOPED BY CALEPA (1986)
Study
Kociba et al.
1978
Kociba et al.
1978
Kociba et al.
1978
Kociba et al.
1978
NTP 1982
NTP 1982
NTP 1982
Pathologist
Kociba
Squire
Kociba
Squire
NTP
NTP
NTP
Species
Rat
Rat
Rat
Rat
Rat
Mouse
Mouse
Gender
Male
Male
Female
Female
Female
Male
Female
Tissue(s)
Nasal turbinates/hard palate
Nasal turbinates/hard
palate/tongue
Liver
Liver
Liver
Liver
Subcutaneous tissue
Tumor Type(s)
Carcinoma
Carcinoma
Carcinoma and
neoplastic nodules
Carcinoma and
neoplastic nodules
Carcinoma and
neoplastic nodules
Carcinoma and
adenomas
Fibrosarcoma
iUR
(ng/m3)"1 x 103
4.2
4.9
27
25
9.4
38
2.4
CSF
(pg/kg-day)-l
1.5E-05
1.7E-05
9.5E-05
8.8E-05
3.3E-05
1.3E-04
8.4E-06
Shaded cell indicates the slope factor recommended by CalEPA (1986) for use.
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW AND SHOULD NOT BE CONSTRUED TO
REPRESENT ANY FINAL AGENCY DETERMINATION OR POLICY.
A2-10
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TABLE A2-3
RECOMMENDED EQUATIONS FOR COMPUTING CANCER PRGS FOR
EXPOSURE OF RESIDENTS TO DIOIXN IN
SOIL LIVER TUMOR OCCURRENCE IN FEMALE RATS (KOCIBA ET AL. 1978) BASED ON
TWO ALTERNATIVE HISTOPATHOLOGICAL CLASSIFICATION METHODS
Dose
(ug/kg-day)
0
0.001
0.010
0.100
Original Analysis (EPA 1985)
Hyperplastic
nodules
8/86
3/50
18/50
23/49
Hepatocellular
carcinomas
1/86
0/50
2/50
11/49
Total Animals
with Liver
Tumors
9/86
3/50
18/50
34/48
Reanalysis (EPA 1990)
Adenoma
2/86
1/50
9/50
14/45
Hepatocellular
Carcinoma
0/86
0/50
0/50
4/45
Total Animals
with Liver
Tumors
2/86
1/50
9/50
18/45
Source: EPA (1990, 2003b)
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY
FINAL AGENCY DETERMINATION OR POLICY.
A2-11
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TABLE A2-4. RECOMMENDED EQUATION FOR COMPUTING CANCER PRGS FOR
EXPOSURE OF WORKERS TO DIOXIN IN SOIL
TDI CALCULATIONS FROM JECFA (2002)
Parameter
LOEL Maternal body burden (ng/kg)
Equivalent body burden with repeated dosing (ng/kg)
Body burden from feed (ng/kg)
Total body burden (ng/kg)
EHMIa (pg/kg per month)
Safety factor
PTMI (pg/kg per month)
TDIb (pg/kg-day)
Faqietal. (1998)
Linear
Model
25
25
3
28
423
9.6
44
1.5
Power
Model
25
39
3
42
630
9.6
66
2.2
Ohsakoetal. (2001)
Linear
Model
7.6
13
3
16
237
3.2
74
2.5
Power
Model
7.6
19
3
22
330
3.2
103
3.4
Equivalent human monthly intake
Calculated based on 30 days per month
THE FINDINGS AND CONCLUSIONS IN THIS DOCUMENT ARE FOR PUBLIC REVIEW AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY
FINAL AGENCY DETERMINATION OR POLICY.
A2-12
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