									OSWER 9200.3-54

REVIEW OF INTERNATIONAL SOIL LEVELS FOR DIOXIN

Prepared by:

U.S. Environmental Protection Agency

Office of Superfund Remediation and Technology Innovation

Washington, D.C.

with technical assistance from:

SRC, Inc.

Denver, CO

December 28, 2009



EXECUTIVE SUMMARY

A number of foreign nations have evaluated the toxicity of dioxin and
have established concentration values in soil that are intended to
provide protection to humans who may be exposed under residential or
commercial/industrial land uses.  Two types of soil levels have been
established:

Screening Levels are generally interpreted as concentrations below which
health concern is minimal and no further investigations or evaluations
are needed.

Action Levels are generally interpreted as concentrations above which
concern is likely to exist and where some sort of response action is
likely to be needed.

Because dioxin is a carcinogen, the method used to derive screening
levels or action levels depends on the assumed mode of action of dioxin.
 The World Health Organization (WHO) has evaluated the available data
for dioxin, and has determined that cancer effects of dioxin are caused
by a non-linear threshold mode of action.  Consequently, human health
will be protected from both cancer and non-cancer effects if the average
daily ingested dose of dioxin does not exceed the Tolerable Daily Dose
(TDI).

In 1990, the WHO estimated the TDI to be 10 pg/kg-day.  In 1998, the WHO
revised this estimate and identified a range of 1-4 pg/kg-day, with 1
pg/kg-day being the goal.  In 2001, this range was re-evaluated using
several new studies, and a range of 2-2.3 pg/kg-day was identified. 
Nearly all foreign nations have followed the approach recommended by the
WHO for evaluating dioxin toxicity, and have selected TDI levels in the
1-10 pg/kg-day range.  Each of these TDI values or ranges is a suitable
candidate for consideration in EPA’s determination of soil PRG levels,
with preference for the most recent values.

The method for deriving a soil level from a TDI depends upon which soil
exposure pathways are considered (ingestion, inhalation, dermal), and on
the exposure parameters for each pathway.  In some cases, other factors
may also be considered.  Table ES-1 lists soil screening levels and
action levels that were located for foreign nations, indicating the TDI
values that were considered, and the exposure pathways that were
included.  As shown, screening levels range from 1 to 250 ppt, with most
values of about 10 ppt.  Residential action levels range from 10 to
1,500 ppt, with most values in the 100 to 1,000 ppt range. 
Commercial/industrial action levels range from 100 to 18,000 ppt, with
most values in the 1,000 to 10,000 ppt range.  Unfortunately, based on
the information presently located, the detailed basis for the derivation
of these soil levels is not clear except for the Netherlands. 



TABLE OF CONTENTS

  TOC \o "1-3" \h \z \u    HYPERLINK \l "_Toc238874963"  1.0	OVERVIEW	 
PAGEREF _Toc238874963 \h  1  

  HYPERLINK \l "_Toc238874964"  2.0	BASIC STRATEGIES FOR DERIVING SOIL
LEVELS	  PAGEREF _Toc238874964 \h  1  

  HYPERLINK \l "_Toc238874965"  2.1	Linear Non-Threshold Cancer Risk
Model	  PAGEREF _Toc238874965 \h  1  

  HYPERLINK \l "_Toc238874966"  2.2	Non-Linear Threshold Cancer Risk
Model	  PAGEREF _Toc238874966 \h  2  

  HYPERLINK \l "_Toc238874967"  2.3	Exceedence of “Background”	 
PAGEREF _Toc238874967 \h  2  

  HYPERLINK \l "_Toc238874968"  3.0	SEARCH OBJECTIVES AND METHODS	 
PAGEREF _Toc238874968 \h  3  

  HYPERLINK \l "_Toc238874969"  3.1	Search Objectives	  PAGEREF
_Toc238874969 \h  3  

  HYPERLINK \l "_Toc238874970"  3.2	Search Methods	  PAGEREF
_Toc238874970 \h  3  

  HYPERLINK \l "_Toc238874971"  4.0	RESULTS	  PAGEREF _Toc238874971 \h 
4  

  HYPERLINK \l "_Toc238874972"  4.1	Nations that Use the Linear
No-Threshold Risk Model	  PAGEREF _Toc238874972 \h  4  

  HYPERLINK \l "_Toc238874973"  4.2	Nations that Use the Non-Linear
Threshold Risk Model	  PAGEREF _Toc238874973 \h  6  

  HYPERLINK \l "_Toc238874974"  4.2.1	TDI Values	  PAGEREF _Toc238874974
\h  6  

  HYPERLINK \l "_Toc238874975"  4.2.2	Derivation of Soil Levels	 
PAGEREF _Toc238874975 \h  8  

  HYPERLINK \l "_Toc238874976"  4.3	Nations that Use the Exceedence of
Background Approach	  PAGEREF _Toc238874976 \h  10  

  HYPERLINK \l "_Toc238874977"  5.0	EVALUATION	  PAGEREF _Toc238874977
\h  10  

  HYPERLINK \l "_Toc238874978"  6.0	REFERENCES	  PAGEREF _Toc238874978
\h  11  

 



LIST OF ABBREVIATIONS AND ACRONYMS

BMD	Benchmark Dose

COT	Committee on the Toxicity of Chemicals in Food

EC	European Commission

ECEH	European Centre for Environmental Health Safety

IPCS 	International Programme on Chemical

JECFA 	Joint FAO/WHO Expert Committee on Food Additives

LOAEL	Lowest Observed Adverse Effect Level

oSF	Oral Slope Factor

OSWER	Office of Solid Waste and Emergency Response

PBPK	Physiologically-based pharmacokinetic

PCDD	Polychlorinated dibenzodioxins

PCDF	Polychlorinated dibenzofurans

RfD	Reference Dose

SCF	Scientific Committee on Food

TCDD	2,3,7,8-tetrachloro-p-dibenzodioxin

TDI	Tolerable daily intake

TEQ	TCDD Equivalents

USEPA	United States Environmental Protection Agency

WHO	World Health Organization



REVIEW OF INTERNATIONAL SOIL LEVELS FOR DIOXIN

OVERVIEW

Regulatory agencies in many nations have sought to identify a default
concentration of dioxin (2,3,7,8-TCDD) and related polychorinated
dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) in soil that does not
pose an unacceptable health risk to humans.  These values are generally
expressed in terms of TCDD-equivalent (TEQ) concentrations, which
include the contributions from all of the relevant PCDD and PCDF
congeners.

In general, one or both of two types of soil level have been
established:

Screening Levels are generally interpreted as concentrations below which
health concern is minimal and no further investigations or evaluations
are needed.

Action Levels are generally interpreted as concentrations above which
concern is likely to exist and where some sort of response action is
likely to be needed.

The purpose of this report is to review the methods that have been used
by other countries to derive screening levels and/or action levels for
dioxin in soil, and to characterize the values that have been
established.

BASIC STRATEGIES FOR DERIVING SOIL LEVELS

Review of the approaches used by various nations for deriving soil
levels for dioxin have identified three basic strategies.  These are
discussed below.

Linear Non-Threshold Cancer Risk Model

Dioxin is a carcinogen.  If the risk of cancer from dioxin is assumed to
be linear in the low-dose range and to have no threshold, then the basic
equation for calculating the soil level that corresponds to some
specified acceptable "target cancer risk" is as follows:

 

As seen, the soil level for cancer depends on the slope factor, the
intake rate of soil, and the target cancer risk.  The slope factor is
usually derived by fitting the linearized multistage model to an
appropriate set of cancer exposure-response data (animal data), while
intake rate is based on default assumptions about residential or worker
exposure to soil.  Target cancer risk is a risk management choice, and
is typically in the 1E-04 to 1E-06 range.

Because dioxin also causes non-cancer as well as cancer effects, it is
also appropriate to calculate a soil level that will protect against
non-cancer effects, as follows:

 

As seen, the soil level for non-cancer effects depends only on the ratio
of the threshold dose (an intake level that does not cause any adverse
effects) to the soil intake rate.

Given the cancer and non-cancer soil levels, the lower of the two is
generally selected to ensure protection against both types of effect.

Non-Linear Threshold Cancer Risk Model

If the cancer effects of dioxin are assumed to occur via a non-linear
threshold mode of action, then exposures that are below the threshold
for non-cancer effects are assumed to be safe for both cancer and
non-cancer effects.  In this case, the soil level is calculated using
the non-cancer equation described above:

 

The threshold dose is usually referred to as a Reference Dose (RfD) in
the United States, and as a Tolerable Daily Intake (TDI) in Europe and
Asia.  These two terms are conceptually equivalent and both describe the
total amount of dioxin/TEQ that may be ingested per day that will not
result in an adverse health effect.

The value of the TDI or RfD can be derived in several ways, including:

Direct observation of no-effect dose levels in reliable studies

Benchmark dose (BMD) modeling of reliable non-cancer dose-response data

Calculations from a tissue-based no-effect level, using an appropriate
physiologically based pharmacokinetic (PBPK) model

Exceedence of “Background”

If it is assumed that any excess exposure to dioxin is undesirable
because of its high potency for both non-cancer and cancer effects, then
the soil level may be set equal to the “background” level of dioxin
in soil.  This approach does not require any data on toxicity or
exposure, but does require robust data on the distribution of
concentration values in soils that are considered to be
“background”.  Because dioxin can be released from a variety of
sources (ATSDR 1998), soil “background” levels may vary as a
function of location and setting (rural, industrial, urban, pristine,
etc.). 

SEARCH OBJECTIVES AND METHODS 

3.1	Search Objectives

The goal of this search effort was to identify soil action levels for
dioxin that have been adopted by various nations.  In addition, the
primary objective was to document the underlying basis of these soil
levels (e.g., toxicity value, derivation approach, exposure parameters)
with regard to the following criteria.  The resulting objective was to
identify international soil levels based on the most recent, sound
science and evaluate the levels based on the following criteria:

Nature of peer review

Transparency/reproducibility & public availability

Scientific basis

These criteria are consistent with those recommended for Tier 3 human
health toxicity value sources indicated in USEPA Office of Solid Waste
and Emergency Response (OSWER) Directive 9285.7-53, Human Health
Toxicity Values in Superfund Risk Assessments (USEPA 2003).

3.2	Search Methods

Searches for information on international soil levels for dioxin were
primarily performed using web-based search engines.  These searches were
initially quite broad in scope in an attempt to locate any
publicly-available information on dioxin (or TEQ) toxicity assessments
and/or soil levels.  These initial searches did not target specific soil
level types (e.g., residential/commercial, screening/action level), and
did not attempt to target specific nations or regions.  Information on
dioxin soil levels for European nations was initially located in two key
summary reports:

Carlon, C. (ed.).  2007.  Derivation Methods of Soil Screening Values in
Europe.  A Review and Evaluation of National Procedures Towards
Harmonization.  European Commission, Joint Research Centre, Ispra, EUR
22805-EN, 306 pp.    HYPERLINK
"http://www.nicole.org/news/downloads/EUR22805-EN%20(3)_27_AUG.pdf" 
http://www.nicole.org/news/downloads/EUR22805-EN%20(3)_27_AUG.pdf  

AEA Technology.  1999.  Summary Report: Compilation of EU Dioxin
Exposure and Health Data.  Task 1 - Member State Legislation and
Programmes.  Produced for European Commission DG Environment, UK
Department of the Environment Transport and the Regions.  October.   
HYPERLINK "http://ec.europa.eu/environment/dioxin/download.htm" 
http://ec.europa.eu/environment/dioxin/download.htm  

When potentially relevant dioxin information was located for a
particular nation, a more focused search of specific agency websites and
peer-reviewed literature was performed to identify and gather the
underlying documents providing the detailed information on the basis and
derivation of the specified soil levels.

4.0	RESULTS

4.1	Nations that Use the Linear No-Threshold Risk Model

Only one foreign nation (Germany) evaluated the cancer effects of dioxin
assuming a linear no-threshold mode of action.  Based on information
reported in Carlon (2007), both oral exposure and inhalation exposure
are considered, and both cancer and non-cancer effects are evaluated. 
Two types of values are identified:

“Trigger levels” are concentrations in soil that warrant further
investigation to determine if the concentration of the contaminant in
soil is hazardous.

“Action levels” are concentrations in soil that, as a rule, indicate
that a hazard is present that must be addressed.  Further investigation
is usually not necessary.

Equations for calculating “Trigger Levels” utilized by Germany are
as follows:

Effect	Pathway	Equation

Cancer	Oral	TL = Dtb ∙ frc ∙ 8.75 / IR

	Inhalation	TL = Dtb ∙ frc ∙ 8.75 / (IR ∙ AF)

Non-Cancer	Oral	TL = Dtb ∙ (frc - 0.8) / IR

	Inhalation	TL = Dtb ∙ frc  / (IR ∙ AF)



where:

	TL = Trigger Level in soil (pg/g)

	Dtb = Tolerable body dose (pk/kg-day)

	frc = risk connecting factor

	8.75 = ratio of averaging time to assumed exposure duration for cancer
(70 yrs/8 yrs)

	0.8 = fraction of total daily dioxin intake that is derived from the
diet

	IR = average daily soil intake (g/kg-day)

	AF = accumulation factor of dioxin in dust

Default values employed by Germany in the computation of Trigger Levels
for dioxin for residential land use are as follows (Carlon 2007):

Parameter	Cancer	Non-cancer

	Oral	Inhal	Oral	Inhal

Dtc (pg/kg-day)	6.7E-02	6.0E-02	1.0	--

frc	5	5	3.2	--

IR (g/kg-day)	1.65E-02	4.1E-05	1.65E-02	--

AF	--	10	--	--



Note that the soil ingestion rate (16.5 mg/kg-day) used by Germany is
substantially higher than the default value used by the United States
Environmental Protection Agency (USEPA) (3.81 mg/kg-day).  Likewise, the
soil inhalation rate used by Germany (4.1E-02 mg/kg-day) is also higher
than the USEPA default (2.3E-04 mg/kg-day), although the air pathway
remains minor in both cases.  Also note that the exposure duration for
cancer effects (8 years) is much shorter than assumed by USEPA (30
years), and that for non-cancer effects, only 20% of the allowable daily
intake is allocated to soil.

For cancer effects, the oral slope factor (oSF) utilized by Germany may
be calculated as follows:

	oSF = Target Risk / Dtc = 1E-05 / 6.7E-02 = 1.5E-04 (pg/kg-day)-1

This is the same value utilized by the United States.

Based on the inputs provided above, the derived soil Trigger Levels for
dioxin are as shown below:

Effect	Toxicity

Value	Target Risk	Trigger Level (pg/g)



	Oral	Inhal.	Combined

Cancer	1.5E-04 (pg/kg-day)-1	1E-05	178	6400	173

Non-cancer	1.0 pg/kg-day	HQ = 1	145	--	145



As seen, the Trigger Level for cancer effects (1E-05) is 173 ppt, and
the Trigger Level for non-cancer effects is 145 ppt.  Presuming that the
lower of the two values is selected as the final value, the final soil
Trigger Level for dioxin would be 145 ppt.  However, no information was
located on the selected Trigger Level for dioxin in the literature.  

As noted above, Germany utilizes an approach in which both a Trigger
Level and an Action Level are identified.  The residential Action Level
for dioxin selected by Germany is 1,000 ppt.  No information was located
on the process used by Germany to derive the selected soil Action Level.

4.2	Nations that Use the Non-Linear Threshold Risk Model

4.2.1	TDI Values

Most foreign nations for which information was located follow the
approach in which the cancer effects of dioxin are believed to be
mediated by a non-linear threshold mode of action.  This approach has
been developed mainly by the World Health Organization (WHO) and several
other international health groups.  Table 1 provides a summary of TDI
values that have been derived by WHO and others.  These are discussed in
greater detail below.

WHO 1990

In 1990, the World Health Organization (WHO) Regional Office for Europe
organized several expert consultations and working groups to perform a
toxicological evaluation for TCDD (WHO 1991, 1992).  It was concluded
that TCDD was carcinogenic in animals, acting as a non-genotoxic
promoter-carcinogen.  Therefore, the consultation decided to establish a
TDI based on general toxicological effects.  The no-effect dose was
estimated to be about 1,000 pg/kg-day in various laboratory animals,
which 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.

WHO 1998

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 included
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 lowest observed adverse effect level (LOAEL)
tissue burdens ranged from 28-73 ng/kg (28,000-73,000 pg/kg).

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) · [1-exp(-ln(2)/t1/2)] / f

where:

		t1/2 = half-time of dioxin in the body (days)

		f = fraction of an ingested dose that is absorbed

WHO utilized a half-time 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 bw-day.

EC-SCF and JECFA 2001

In 2001, the European Commission Scientific Committee on Food (EC-SCF)
and the Joint FAO/WHO Expert Committee on Food Additives (JECFA)
incorporated several new studies published since the 1998 WHO
re-assessment and estimated the TDI to be 2.0-2.3 pg/kg-day,
respectively, using an approach similar to the one described above.

Table 1a summarizes the TDI values recommended by these various
international organizations.

TDI Values Selected by Various Nations

Table 2 provides a summary of the information that was located for
nations that follow the TDI approach for evaluating dioxin toxicity.  As
indicated, a majority of nations have chosen to adopt TDI values
recommended by WHO.  This includes:

WHO (1990)

TDI = 10 pg/kg-day	WHO (1998)

TDI = 1-4 pg/kg-day	JECFA (2001)

TDI = 2.3 pg/kg-day

Austria

Italy	France

Germany

Netherlands

New Zealand	Australia

Canada



However, several nations (see Table 1b) have performed their own
re-assessment of the available toxicity data for dioxin to derive a TDI,
rather than adopting TDI values derived by others.  Japan derived a TDI
of 4 pg/kg-day, which is equivalent to the maximum TDI established by
WHO (1998).  For the United Kingdom, the Government’s independent
advisory Committee on the Toxicity of Chemicals in Food (COT)
recommended a TDI of 2 pg/kg-day, which is equivalent to the TDI
identified by EC-SCF (2001).  In August 2000, several countries
(Denmark, Finland, Sweden) considered revising the Nordic Council TDI
value of  5 pg/kg-day to a value of 4 pg/kg-day in accord with WHO
(1998), but it was determined that no change was appropriate (Johansson
and Hanberg 2000).

4.2.2	Derivation of Soil Levels

As noted above, given a TDI, the soil level is computed as follows:

 

The soil intake rate may be computed in a number of different ways,
depending on which exposure pathways are considered (ingestion, dermal
contact, inhalation of particulates, and/or ingestion of crops or
livestock that have been impacted by soil).  The general form of the
equation is:

 

where:

	TDI = Tolerable daily intake

	ki = Ratio of dioxin concentration in medium “i” to concentration
in soil

	IRi = Intake rate of medium “i”

For example, if only the soil ingestion pathway is considered, the basic
equation is:

 

where:

TDI = Tolerable daily intake (pg/kg-day)

IRs = 	Average soil intake rate (g/kg-day)

If dermal contact, inhalation exposure and intake of foods (e.g., garden
vegetables) grown in contaminated soil are considered, the equation is:

 

where:

	IRd = Intake rate of soil from dermal exposure (g/kg-day)

	kair = Concentration in air (pg/m3) divided by concentration in soil
(pg/g)

	IRPM10 = Intake rate of air (m3/kg-day)

	kveg = Concentration in vegetable (pg/g) divided by concentration in
soil (pg/g)

	IRgv = Intake rate of garden vegetables (g/kg-day)

Note that inhalation exposure from PM10 particles usually contributes
only a small dose compared to oral exposure (typically <1%). 
Consequently, whether the inhalation pathway is included or not
generally has little influence on the result.

Soil Levels Identified by Various Nations

Not all nations that utilize the TDI approach have derived soil levels. 
Table 2 provides the detailed information for all soil levels located
for various nations.  This table includes a variety of different soil
levels and nomenclature in describing these levels.  As described above,
the various soil levels reported by the nations were stratified into two
broad categories – screening levels and action levels.  Screening
levels are soil values below which no further investigation is likely to
be needed.  Usually these screening values are not land use specific,
but are applied to all land use types.  Action levels are soil values
above which cleanup actions are warranted.  These values are often
effects-based (i.e., derived from a TDI) and land use specific.  The
most common land use types are residential and commercial/industrial,
although some nations also derive action levels for agricultural and
recreational land uses.

Table 3 summarizes the screening levels and action levels for
residential and commercial/ industrial soils that have been derived. 
Figure 1 presents these soil levels in a graphical format.  As shown,
screening levels (Panel A) range from 1 to 250 ppt, with most values of
about 10 ppt.  Residential action levels (Panel B) range from 10 to
1,500 ppt, with most values in the 100 to 1,000 ppt range. 
Commercial/industrial action levels (Panel C) range from 100 to 18,000
ppt, with most values in the 1,000 to 10,000 ppt range.

Figure 2 presents the soil action levels for residential (Panel A) and
commercial/industrial (Panel B) grouped by the selected TDI.  As shown,
there is a wide range of soil levels within each TDI value (e.g.,
residential action levels range from 100 to 1,000 ppt for a TDI of 1
pg/kg-day).  This suggests that the primary reason for the differences
in the derived soil levels is due to differences in the exposure
parameters utilized. 

Unfortunately, the basis of these soil levels is not always clear. 
Carlon (2007) sought to determine the methods that had been used by each
nation to establish the soil levels, and concluded that, in most cases,
the basis of the soil levels was not well documented.  Even in cases
where documentation is available, derived soil values are not always
reproducible.  Therefore, it is suspected that most soil values reflect
risk management decisions that are not based solely on risk-based
exposure-response models.

4.3	Nations that Use the Exceedence of Background Approach

Two nations (Canada and Czech Republic) were identified in which the
soil screening level is stated to be based on background levels of
dioxin.  For Canada, the soil screening level identified as the average
background level is 4 ppt, and this value is intended to apply to all
land use types (i.e., agricultural, residential, commercial,
industrial).  For the Czech Republic, there are two soil screening
levels identified:  1 ppt, which was identified as the 95th percentile
of background, and 100 ppt, which is a value selected between background
and the “limit of pollution”.  Most nations, including the United
States (USEPA 2007), report background concentrations within range of
1-10 ppt.

5.0	EVALUATION

In order for the USEPA to consider a human health toxicity value (TDI,
slope factor) for use in risk calculations or in the derivation of a
soil level, it must meet the criteria of a Tier 3 value established by
USEPA OSWER Directive 9285.7-53 (USEPA 2003).  As noted above, these
criteria are as follows:

Nature of peer review – in accord with USEPA (2003), “draft
assessments are not appropriate for use until they have been through
peer review, the peer review comments have been addressed in a revised
draft, and the revised draft is publicly available”.

Transparency/reproducibility and public availability – in accord with
USEPA (2003), values should be “available to the public,
and…transparent about the methods and processes used to develop the
values”.  In addition to being transparent, values should be
reproducible (i.e., able to be derived based on the provided
information).

Scientific basis – in accord with USEPA (2003), values should be
“based on similar methods and procedures” as USEPA guidance (e.g.,
cancer risk assessment guidelines, soil screening guidance).

Table 4 presents a matrix of the evaluation criteria for the TDI values
(top panel) and soil action levels (bottom panel) currently utilized by
various nations.  In general, most of the TDI values derived by the WHO
and other international health groups have been peer reviewed, are
transparent/reproducible and publically available, and are based on
science that is consistent with current USEPA guidance procedures
(assuming that a threshold mode of action is accepted).  Thus, all of
these TDI values would rank as appropriate for use as Tier 3 human
health toxicity values.  TDI values developed by various nations (e.g.,
Japan), do not meet all of the specified criteria in full.

For the soil action levels (Table 4, lower panel), with the exception
the Netherlands, no nations provided sufficient detail to document the
underlying basis of the adopted soil values and no information was
located on the peer review process associated with the adopted values. 
For the Netherlands, soil levels were derived using an exposure model
called CSOIL.  Detailed information on this model and the underlying
exposure parameters and assumptions are documented in the Technical
Evaluation of the Intervention Values for Soil/Sediment and Groundwater
(RIVM 2001).  The derived soil values are subject to review by the
Netherland Technical Soil Protection Committee and Health Council.

6.0	REFERENCES

ATSDR (Agency for Toxic Substances and Disease Registry).  1998. 
Toxicological Profile

for Chlorinated Dibenzo-p-dioxins (CDDs).  Agency for Toxic Substances
and Disease Registry.  December 1998.

Carlon, C. (Ed.) (2007). Derivation methods of soil screening values in
Europe. A review and evaluation of national procedures towards
harmonization. European Commission, Joint Research Centre, Ispra, EUR
22805-EN, 306 pp.  

  HYPERLINK
"http://eusoils.jrc.ec.europa.eu/esdb_archive/eusoils_docs/other/EUR2280
5.pdf" 
http://eusoils.jrc.ec.europa.eu/esdb_archive/eusoils_docs/other/EUR22805
.pdf 

Johansson, N. and A Hanberg. 2000. Report from a Nordic meeting on the
1998 WHO consultation on assessment of the health risks of dioxins;
re-evaluation of the tolerable daily intake (TDI). Organohalogen
Compounds. 48:252-255.

Kimbrough RD, Falk H, Stehr P.  1984.  Health Implications of
2,3,7,8-tetrachloro-dibenzodioxin (TCDD) Contamination of Residential
Soil.  J. Toxicol. Environ. Health 14:47-93. 

Kociba RJ, Keyes DG, Beyer JE, et al . 1978.  Results of a Two-Year
Chronic Toxicity and oncogenicity Study of
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in rats.  Toxicol. Appl.
Pharmacpol. 46:279-303.

NTP (National Toxicology Program).  1982.  Carcinogenesis Bioassay of
2,3,7,8-tetrachlorodibenzo-p-dioxin (CAS No. 1746-01-6) in
Osborne-Mendel rats and B6C3F1 Mice (Gavage Study).  National Toxicology
Program Technical  Report Series, Issue 209:195.

RIVM.  2001.  Technical Evaluation of the Intervention Values for
Soil/Sediment and Groundwater: Human and ecotoxicological risk
assessment and derivation of risk limits for soil, aquatic sediment and
groundwater.  National Institute of Public Health and the Environment
(RIVM).  RIVM report 711701 023.  February 2001.

  HYPERLINK
"http://rivm.openrepository.com/rivm/bitstream/10029/9660/1/711701023.pd
f" 
http://rivm.openrepository.com/rivm/bitstream/10029/9660/1/711701023.pdf
 

USEPA (U.S. Environmental Protection Agency).  1985.  Health Assessment
Document for Polychlorinated Dibenzo-p-Dioxins.  U.S. Environmental
Protection Agency, Office of Health and Environmental Assessment,
Environmental Criteria and Assessment Office.  Cincinnati, OH.  EPA
600/8-84-014F.

USEPA.  1997.  Health Effects Assessment Summary Tables (HEAST).  U.S.
Environmental Protection Agency, Office of Solid Waste and Emergency
Response.  EPA-540-R-97-036.  July 1997.

USEPA.  1998.  Approach for Addressing Dioxin in Soil at CERCLA and RCRA
Sites.  Memo from Timothy Fields, USEPA Acting Administrator, to
Regional Directors.  OSWER Directive 9200.4-26.  April 13, 1998.

USEPA.  2003.  Human Health Toxicity Values in Superfund Risk
Assessments. OSWER

Directive 9285.7-53.  U.S. Environmental Protection Agency, Office of
Solid Waste and Emergency Response, Washington, DC.  December 5, 2003.

  HYPERLINK "http://www.epa.gov/oswer/riskassessment/pdf/hhmemo.pdf" 
http://www.epa.gov/oswer/riskassessment/pdf/hhmemo.pdf  

USEPA.  2005.  Guidelines for Carcinogen Risk Assessment.  U.S.
Environmental Protection Agency, Risk Assessment Forum. Washington, DC. 
EPA/630/P-03/001B.  March 2005.

USEPA.  2007.  Pilot Survey of Levels of Polychlorinated
Dibenzo-P-Dioxins (PCDDs), Polychlorinated Dibenzofurans (PCDFs),
Polychlorinated Biphenyls (PCB) and Mercury in Rural Soils of the U.S.
U.S.   Environmental Protection Agency, Washington, DC. 
EPA/600/R-05/043F.    HYPERLINK
"http://cfpub.epa.gov/ncea/CFM/recordisplay.cfm?deid=150944" 
http://cfpub.epa.gov/ncea/CFM/recordisplay.cfm?deid=150944  

WHO (World Health Organization).  1991.  Summary Report – Consultation
on Tolerable Daily Intake from Food of PCDDs and PCDFs.  Bilthoven, the
Netherlands, December 1990, EUR/ICP/PCS 030(S) 0369n, World Health
Organization, Regional Office for Europe, Copenhagen.

WHO.  1992.  Tolerable daily intake of PCDDs and PCDFs.  Toxic
Substances Journal 12:101-128.

WHO.  1998.  Assessment of the Health Risk of Dioxins: A Re-evaluation
of the Tolerable Daily Intake (TDI), Consultation, May 1998, World
Health Organization, Geneva.  Available on-line at:   HYPERLINK
"http://www.who.int/pcs/docs/dioxin-exec-sum/exe-sum-final.html" 
http://www.who.int/pcs/docs/dioxin-exec-sum/exe-sum-final.html  

 EC-SCF recommended a tolerable weekly intake (TWI) of 14 pg/kg, while
JECFA recommended a tolerable monthly intake (TMI) of 70 pg/kg.  These
values correspond to TDI values of 2.0 to 2.3 pg/kg-day.

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7 New Zealand has recently adopted the WHO 1998 TDI values; however, the
soil action levels identified utilize WHO 1990 TDI values.

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