c/EPA
Region 1, New England
RISK UPDATES
iNumber 4
November 1996
R,
JSK UPDATES is a periodic
bulletin prepared by EPA - Region I,
New England risk assessors to provide
information on new regional guidance.
Risk Updates is distributed to contractors
supporting Superfund and RCRA,
regulators, and interested parties. Risk
assessment questions may be directed
to the following EPA scientists (area
code 617):
Regional Risk Assessment Contact
Ann-Marie Burke	223-5528
Superfund
Human Health Risk Assessment
Ann-Marie Burke	223-5528
Sarah Levinson	573-9614
Margaret McDonough 573-5714
Jayne Michaud	223-5583
Ecological Risk Assessment
Susan Svirsky	573-9649
Patti Tyler	860-4342
RCRA Corrective Action

Mary Ballew
573-5718
Stephanie Carr
223-5593
Air Modeling

Brian Hennessey
565-3572
Combustion Risk Issues

Jui-Yu Hsieh
565-3501
Comparative Risk

Katrina Kipp
565-3520
Cost Benefit Analysis

Ronnie Levin
565-9351
Drinking Water

Maureen McClelland
565-3543
Air Risk Issues

Jerri Weiss
565-9448
ORD Technical Liaison
Ruth Bleyler
573-5792
EPA Region I, New England receives
additional ecological technical support
from Ken Finkelstein (223-5537) of the
National Oceanic Atmospheric
Administration (NOAA), and US Fish &
Wildlife (Steve Mierzykowski 207/827-
5938, Ken Munney 603/225-1411, and
Tim Prior 401/364-9124).
Editors
Stephanie Carrand Jayne Michaud
Layout Gloria Hume
Contents
EPA Ecological Guidance
Update	Page 1
Superfund Risk Assessment
Reform Initiatives	Page 2
Risk Characterization
Update	Page 3
Mercury Update	Page 3
EPA Finalizes Soil Screening
Guidance	Page 3
EPA's Proposed Cancer Guidance
and Implementation Plan	Page 4
Ground Water Use and Value
Guidance	Page 5
Lead Risk at CERCLA Sites and
RCRA Correction Action
Facilities	Page 6
Revised Manganese Reference
Dose	Page 8
New Cancer Slope Factors for
PCB's	Page 8
EPA Ecological Risk
Assessment Guidance
Update
The EPA is in the process of
finalizing two major ecological
guidance documents. The first,
Guidelines for Ecological Risk
Assessment, is under
development by the EPA Risk
Assessment Forum (The Forum).
The Forum was established to
promote consensus on risk
assessment issues, as defined in
the 1983 Report of the National
Research Council, and to ensure
that this consensus be
incorporated into Agency risk
assessment guidance. The Forum
consists of risk assessment
experts from throughout the
Agency, including Region I. The
final version of this document will
expand upon the work presented in
the Framework for Ecological Risk
Assessment. The Guidelines will
provide more direction for the
various programs in EPA to follow
when conducting ecological risk
assessment and promise to be a
particularly valuable tool in
understanding the role of ecological
risk assessment in the Superfund
process. The Notice of Availability
and Opportunity to Comment on
Proposed Guidelines was
published in the Monday,
September 9, 1996 Federal
Register (Vol. 61, No.175, page
47552). A copy can be obtained
from the National Technical
Information Service (703/487-4650)
for $47, or from the EPA home
page: http://www.epa.gov/ord/
webpubs/ fedreg.
The second document which is
being developed by the EPA
Environmental Response Team is
entitled Ecological Risk
Assessment Guidance for
Superfund: Process for Designing
and Conducting Ecological Risk
Assessments. This document
provides a "hands-on" approach
for conducting an ecological risk
assessment and gathering the data
to support such an assessment.
This guidance loosely follows the
Risk Assessment Forum approach.
Both of the documents described
above are supplements to existing
ecological guidance and do not
replace existing guidance. EPA
New England will issue regional
guidance explaining how these two
guidance documents should be
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used in the Superfund program.
This is tentatively scheduled for
fall of 1996, depending upon the
progress with the national
guidance.
Two new Eco Updates were
recently released by the EPA
Office of Emergency and
Remedial Response and can be
found on the EPA home page.
Ecotox Thresholds (EPA
540/f-95/038)
Ecological Significance
and Selection of
Candidate Assessment
End points (EPA 540/f-
95/037).
The Ecotox Thresholds bulletin
provides an overview of the
development and use of ecotox
benchmark values in Superfund
ecological risk assessments. The
"Endpoints" bulletin provides
guidance to risk assessors and
managers in the selection of
appropriate assessment
endpoints for ecological study.
Currently under development are
Eco Update bulletins describing
the screening process and how
to use ecotox benchmarks
correctly, and bioaccumulation of
contaminants.
written by Susan Svirsky
Superfund
Risk Assessment
Reform Initiatives
Specific areas of the Superfund
risk assessment process were
identified by the Superfund
Administrative Reforms Initiative
announced in 1995. Two EPA
workgroups are currently
addressing the risk assessment
reform requirement to ensure
reasonable and consistent risk
assessments. The respective
goals of these workgroups are:
To establish national criteria
to plan, report, and review
risk assessments; and
To revise Risk Assessment
Guidance for Superfund
(RAGS).
The first work group is tasked
with establishing national criteria
for the review, approval, and
reporting of Superfund risk
assessments. The products of
this work group will also address
the four core values of EPA
Administrator Carol Browner's
Risk Characterization Policy and
Guidance Memorandum of
transparency, clarity,
consistency, and reasonableness
(refer to Risk Characterization
Update on the next page). To
date, the work group has drafted
a standard statement of work for
risk assessments, standard risk
assessment reporting tables, and
a risk assessment data quality
assurance checklist. The EPA
workgroup has also solicited and
received stakeholder input on
these draft documents.
The RAGS Reform Work Group
has developed a list of key
technical focus areas where the
Superfund program would most
benefit with respect to improving
risk assessment and its application
to Superfund, and also responds to
critics of the program. The focus
areas are toxicity assessment,
exposure assessment, and risk
communication. Two stakeholder
dialogue meetings have been
planned for late October and early
November with representatives of
the community, public, and private
sector stakeholder groups. The
goal of these meetings is to receive
stakeholder input on which issues
EPA should focus resources when
revising and updating RAGS.
In Region I, preliminary stake-
holder advisory opinions were
obtained earlier this year at an EPA
Federal Facilities Risk Assessment
meeting at which the Air Force,
Army, Navy, contractors, and
States were present. The following
technical issues were ranked
highest among the participants:
background determination, use of
the reasonable maximum exposure
method in decision making,
uncertainty/probabilistic analysis,
and land and groundwater use.
The upcoming stakeholder
dialogue meetings will provide
formal input into the RAGS Reform
Initiative.
For more information on the
Superfund Administrative Reforms
Initiatives, please contact Ann-
Marie Burke or Jayne Michaud.
written by Jayne Michaud
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Risk
Characterization
Update
In response to criticism that the
EPA's risk assessments are
often difficult to understand and
communicate, EPA Administrator
Carol Browner issued a
memorandum on Risk
Characterization on March 21,
1995. This memorandum
presents policies and guidance to
serve as "building blocks" for
development of program specific
and region specific policies and
procedures for improving risk
characterizations. This policy will
provide a basis for greater clarity,
transparency, reasonableness
and consistency in risk
assessments across Agency
programs. To achieve clarity,
risk assessments must clearly
identify the purpose and scope of
the assessment, and present its
uncertainties, strengths and
weaknesses, and assumptions.
To achieve transparency, the
decision-making process must
clearly separate scientific or
technically-based conclusions
from those based on policy. To
achieve reasonableness, the
components of the risk
assessment must be based on
sound scientific information and
reasonable judgement and be
integrated into an overall
conclusion. The implementation
of this policy will improve overall
consistency of risk
assessments.
Region I has developed a plan
for implementing this policy in the
Risk Characterization
Implementation Plan for Region I.
The plan describes risk
assessments conducted by or for
Region I and outlines the criteria
that should be used to determine
whether the four fundamental
values presented above have
been addressed. The Risk
Characterization Implementation
Plan for Region I was signed by
John DeVillars, Regional
Administrator, on October 24,
1996. Copies of the
Administrator's March 21, 1995
memorandum and Region I's
Implementation Plan are
available from Jerri Weiss or
Margaret McDonough.
written by Margaret McDonough
Mercury-
Update
Combustion facilities or
incinerators are potentially a
large source of environmental
mercury contamination. To
reduce emiss-ions of mercury
and other hazardous air
pollutants, the revised MACT
standards proposed for
hazardous waste combustion
facilities were signed by EPA
Administrator Carol Browner on
March 20, 1996 under the joint
authority of the Clean Air Act
(CAA) and the Resource
Conservation and Recovery Act
(RCRA). The rules were
proposed on April 19, 1996 (61
FR 17358) and are scheduled to
be finalized by March, 1998.
The proposed MACT standards
for mercury are 50 ug/dscm
(micrograms per dry weight
standard cubic meter) for
hazardous waste incinerators
and hazardous waste-burning
cement
kilns, and 72 ug/dscm for
hazardous waste-burning light
weight aggregate kilns. Under this
proposal, continuous emission
monitors (CEMs) would be required
for particulate matter and mercury.
The CAA 112(n)(1)(B) requires
EPA to submit a study on the
atmospheric mercury emissions to
Congress (the Mercury Report).
The release of this report to
Congress has been delayed. EPA
released the report to the Science
Advisory Board (SAB) in the
beginning of July. The SAB was
asked to review the issues related
to effects of methyl mercury on
child development and to develop a
process for evaluating new data
that is forthcoming from two large
epidemiological studies. This
report will also address mercury
speciation, atmospheric deposition,
bioconcentration factors, and
toxicity data which are important
for meaningful quantitative risk
assessments.
The EPA has made the Mercury
Study SAB Review Draft Report to
Congress (document number EPA-
452/R-96-001) available through
the National Technical Information
Service (703/487-4650).
written by Jui-Yu Hsieh
EPA
Finalizes Soil
Screening
Guidance
EPA finalized the Soil Screening
Guidance in April, 1996. This
guidance provides methods for
calculating site-specific soil
screening levels (SSLs) which can
be used to identify areas of a
hazardous waste site which do not
warrant further federal attention.
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The SSL guidance is expected to
help standardize and accelerate
the evaluation and cleanup of
contaminated soils at sites with a
future residential land use.
SSLs are not national standards
and alone do not trigger the need
for response actions nor do they
define "unacceptable" levels of
contaminants in soils. The SSL
Guidance contains 110 general
soil values as well as a
methodology for derivation of
site-specific concentrations. If
soil screening levels are
exceeded, further assessment
but not necessarily cleanup is
generally warranted. The generic
soil values and methodology are
designed to protect against
exposures resulting from soil
ingestion, inhalation of
particulates and ingestion of
contaminated groundwater
resulting from soil leachate.
Soil screening levels are limited
in their application by the fact
that 1) they do not address
ecological threats and 2) they are
only developed for a residential
exposure scenario. EPA has
issued the guidance in two parts:
1. Soil Screening Guidance:
User's Guide
(OSWER Directive 9355.4-
23, PB96-963505). The
User's Guide is designed for
the EPA site manager or
Regional Manager seeking to
understand the basic
concepts, approaches, and
assumptions in the soil
screening decision
framework.
2. Soil Screening Guidance:
Technical Background
Document (TBD)
(OSWER Directive 9355.4-
17A, PB96-963502). The
Technical Background
Document provides a
comprehensive analysis of
the technical and policy
issues and choices.
In addition, an overview is
provided in the Soil Screening
Guidance: Fact Sheet (OSWER
Directive 9533.1-14FSA, PB96-
963501). An overview of the
EPA's response to comments
received during the public
comment period is also available
in the Soil Screening
Guidance: Response to
Comments (OSWER Directive
9355.4-22, PB96-963506). These
can be purchased from the
National Technical Information
Service (703/ 487-4650).
written by Stephanie Carr
EPA's Proposed
Cancer Guidance
and
Implementation
Plan
EPA released the Proposed
Guidelines for Carcinogen Risk
Assessment in April, 1996 for a
120-day public review and
comment period. The proposed
revisions to the guidelines are a
result of extensive EPA and other
federal and independent
scientific reviews, as well as
recommendations from the
National Academy of Sciences
1994 report, Science and
Judgement in Risk Assessment.
The Proposed Guidelines are a
revision of EPA's 1986
Guidelines for Carcinogen Risk
Assessment (51FR 33992), and
when final will replace the 1986
guidelines.
The Proposed Guidelines will allow
scientists to provide more relevant
and up-to-date information in
cancer evaluations on dose-
response, route of exposure, and
chemical structure of regulated
chemicals. The major changes in
the Proposed Guidelines are
summarized below:
Mode of Action: Perhaps the
most important aspect of the
proposal is the emphasis on
mode of action, which
considers how a substance
causes cancer. More emphasis
on the mode of action is
expected to reduce the
uncertainty in describing
likelihood of harm and in
determining dose-response
approaches.
Three descriptors for
classifying human
carcinogenic potential:
1) "known/likely", 2) cannot be
determined, and 3) not likely
replace the six alphanumeric
categories (A, B1, B2, C, D, E)
in the 1986 guidelines. In
addition, a weight of evidence
narrative, targeted at the risk
manager, is added. This
narrative summarizes the key
evidence for the classification
and presents significant
strengths, weaknesses and
uncertainties of the contributing
evidence.
Biologically-based
extrapolation model is the
preferred approach for
quantifying risk.
Three default approaches -
Linear, Nonlinear, or Both
are provided. Curve fitting in
the observed range would be
used to determine the effective
dose corresponding to the
lower 95% limit on a dose
associated with a 10%
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response (LED10). The LED10
would then be used as a
point of departure for
extrapolation to the origin as
the linear default or for a
margin of exposure
discussion as the
nonlinear default.
Hazard characterization is
added to integrate the Data
Analysis of all relevant
studies into one weight of
evidence conclusion of
hazard.
Risk characterization is
more fully developed by
providing direction on how
the overall conclusion and
confidence of risk is
presented to the risk
manager. Descriptions of
major default assumptions
and criteria for departing from
them are described.
Until the guidelines are final, EPA
will continue to rely on existing
assessments. Once they are
final, EPA will assess existing
cancer values considering new
risk assessment methods,
principles and data.
Reevaluating all existing cancer
values on EPA's Integrated Risk
Information System (IRIS)
database would be time and
resource prohibitive; therefore,
EPA has developed a
prioritization process to ensure
that agents which warrant
reevaluation are given the
highest priority.
A five-step process will be used
for determining which chemicals
should be reevaluated. 1. EPA
publishes an annual Federal
Register notice requesting
candidates for reevaluation. 2.
Candidates are submitted. 3.
EPA reviews and prioritizes
candidates. 4. Candidates that
EPA selects are published in a
Federal Register notice. 5.
Reassessment takes place in the
following fiscal year during which
time chemicals are peer reviewed
and placed on IRIS.
It should be noted that pending
finalization of the Proposed
Guidelines, the principles and
approaches of the Proposed
Guidelines may be applied in part
or in whole, on a case-by-case
basis. The proposed process for
using the new guidelines can be
found in the Federal Register (61
FR 32799).
The Proposed Guidelines are
available in the Federal Register
(61 FR 17960). An electronic
version is also available through
EPA's Office of Research and
Development home page on the
Internet at http://www.epa.gov
/ORD. To obtain a 3.5" disc in
WordPerfect 5.1 format, contact:
ORD Publications Technology
Transfer and Support Division,
National Risk Management
Laboratory, USEPA, 26 W.
Martin Luther King Drive,
Cincinnati, OH 43268
Telephone: 513/560-7562; Fax:
513/569-7566.
Please provide your name,
mailing address, document title
and the following EPA number
(EPA/600/P-921003(a)).
written by Ann-Marie Burke
Ground Water
Use and Value
Guidance
EPA-Region I recently finalized a
new guidance document entitled
the Ground Water Use and Value
Determination Guidance. This
guidance combines the goals of
two major regional initiatives, the
Superfund Beneficial Reuse
Initiative and the Comprehensive
Ground Water Protection
Strategy. As part of the Superfund
Beneficial Reuse Initiative, this
guidance is intended to result in
more informed and focused
decision-making and more
common-sense, cost-effective
ground water cleanups which will
facilitate the beneficial reuse of
contaminated parcels. To
accomplish these objectives, this
guidance incorporates the
resource-based considerations
used in EPA's Comprehensive
Ground Water Protection Strategy.
Specifically, this guidance
document establishes an approach
for determining the relative "use"
and "value" of site ground water
resources and explains how this
determination affects EPA-Region
I ground water remedial decision
making process.
The guidance is a good example of
how EPA intends to provide more
flexibility to the states. The six New
England States have provided
comments on this guidance and
support the process and concepts
it contains.
Overview
The new Approach to Superfund
ground water decision making will
be as follows:
The Approach will be
implemented in States with
EPA-endorsed Comprehensive
State Ground Water Protection
Programs or CSGWPPs, but
only where such States have
entered into a Memorandum of
Agreement (MOA) with EPA-
Region I concerning the
implementation of the
Approach;
In states that have entered into
an MOA for the implementation
of this guidance, EPA-New
England will no longer rely on
the 1986 Draft EPA Guidelines
for Ground Water Classification
in setting goals for ground
water remediation and in
making decisions on the level
of cleanup necessary;
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Instead, a site specific
determination will be made
on the relative "use" and
"value" of the ground water.
States will play a pivotal
role in determining the
relative "use" and "value" of
site ground water and will
seek input from local
officials and the public, as
appropriate;
EPA-New England will
utilize the Use and Value
Determinations performed
by the States, in
establishing remedial
action objectives and
making ground water
remedial action decisions.
Application of This Guidance
The Approach provided in this
guidance will be considered at
current and future sites in the
pre-remedial or RI/FS stages, to
the extent possible. This
guidance is for use by EPA-
Region I and State Remedial
Project Managers in scoping
Remedial Investigations,
conducting Risk Assessments,
developing Remedial Action
Objectives and identifying
Remedial Alternatives. EPA-
Region I does not intend to re-
open remedy selection decisions
based on this guidance. This
guidance is for internal Agency
use and contains no right,
substantive or procedural, for any
party.
Relationship To Risk
Assessment
In performing the Human
Health Risk Assessment for
the site, exposure scenarios
will generally be based on the
generally allowed uses under
the state ground water
classification system. Risk
assessors should not vary their
existing risk assessment
procedures as a result of this
policy, other than to consider
exposures based on the state
classification rather than the
1986 draft federal guidelines.
The Use and Value
Determination prepared by the
States may be discussed as
part of the exposure
assessment section of the
Risk Assessment. In other
words, the Use and Value
Determination may be used to
place the exposure scenarios
in perspective.
If you have any questions on
how this guidance should be
applied or would like to receive
a copy of the guidance
document, please contact any
one of the following staff:
Lynne Jennings, (617) 573-
9634; Margery Adams, (617)
565-3746; Audrey Zucker,
(617) 565-3444.
written by Lynne Jennings
Lead Risk at
CERCLA Sites
and RCRA
Correction Action
Facilities
EPA takes a multimedia
approach to estimating the risk
from exposure to inorganic
lead at a hazardous waste
sites. Risks to children
exposed to lead are estimated
by predicting blood lead levels
using a pharmacokinetic
model. Risks to adults are
estimated through use of a
slope-factor approach. These
methods for estimating risks
are described below.
Lead Risks for Children in a
Residential Setting
For sites with a current or future
potential residential land use, the
sensitive receptor should be a
child. EPA's Integrated
Exposure Uptake and Biokinetic
(IEUBK) model estimates the
risk to a child resident. It is not
appropriate to use this model for
the adult resident, an older child
(i.e., ages 9-18), or the adult
worker. For future residential
exposure scenarios, only a
child's exposure to lead need be
evaluated since this is the most
sensitive receptor.
The IEUBK is a software
package designed to combine
exposures from lead in air,
water, soil, dust, diet, paint, and
other sources with a
pharmacokinetic model. The
output is a predicted distribution
of blood lead levels in a child or
a population of children from 6
months to 7 years of age. From
this distribution, the model
calculates the probability that
blood lead concentration of a
child or population of children will
exceed a selected level of
concern (the default value is a
blood lead level of 10
micrograms lead per deciliter of
blood). The user can then
explore an array of possible
changes in exposure media that
would reduce the probability of
unacceptable risk to those
populations.
The model allows the user to
input site-specific values other
than the concentration of lead in
soil; i.e., the concentration of
lead in household dust, air, or
drinking water, or the
bioavailability of lead. The model
can also be used to develop
cleanup goals for lead at a
hazardous waste site. In cases
where site-specific data are not
available, the standard default
exposure assumptions built into
the model should be used. This
will result in a cleanup goal of
400 mg/kg (ppm) for residential
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soils. The model's default
values are the basis for the
risk screening value of 400
mg/kg recommended in the
"Revised Interim Soil Lead
Guidance for CERCLA Sites
and RCRA Corrective Action
Facilities" (OSWER Directive
#9355.4-12) and the EPA Soil
Screening Guidance
(Publication number 9355.4-
23).
When presenting the IEUBK
model results to EPA, the user
should include: 1) the age of
the child targeted; 2) site-
specific parameter values; 3)
standard defaults; and, 4) the
percentage of children
predicted to have blood leads
above the EPA cutoff of 10
micrograms/deciliter. In the
IEUBK computer model, the
user should choose the graph
for the probability density
function and enter the
appropriate parameters.
Both the IEUBK computer
model (Pub. No. 9285.7-15-2;
PB93-963511) and the
guidance manual (Pub. No.
9285.7-15-1; PB93-963510)
are available to the public
through the National Technical
Information Service (703/487-
4650) or the EPA Region I
Library (617/565-3300).
Lead Risks for Commercial
or Industrial Workers and
Youth Trespassers
The EPA Technical Review
Workgroup for Lead (TRW) is
conducting additional research
on a biokinetic mode for adult
exposures. The TRW consists
of risk assessors, scientists,
policy analysts, statisticians,
and project managers
including Region I
representatives Margaret
McDonough and Mary Ballew.
As an interim approach, the
TRW has recommended a
simplified slope factor
approach. The slope factor
approach is conceptually
similar to that proposed by
Bowers et al. (1994) which
was adapted for use at the
California Gulch NPL site in
Region 8 (Weston, 1995).
On October 26, 1995, the
TRW published a report,
Review of a Methodology for
Establishing Risk-Based Soil
Remediation Goals for
Commercial Areas of the
California Gulch Site. The
TRW has endorsed the slope
factor approach presented in
this report, as an interim
method for evaluating the risks
to adults exposed to lead.
This fall, the TRW expects to
release a more generic
guidance document that will
contain a clear method for
calculating a preliminary
remediation goal for an
industrial or commercial
exposure scenario and the
rationale for each parameter
used in this new approach.
The TRW has emphasized
the importance of collecting
data to support site-specific
parameter estimates, however,
default parameter guidance
will also be provided.
Preliminary calculations by the
TRW suggest that the slope
factor approach could be
adapted for use in a
trespasser scenario.
Parameters should be
adjusted to account for any
age-related differences. It is
appropriate to use the slope
factor approach when
trespassing frequency is equal
to or greater than once per
week over the course of a
minimum duration of ninety
days.
The 1995 California Gulch
review report is available from
the Region I library. The TRW
report Methodology for
Assessing Risks Associated
with Adult Exposures to Lead
in Soil will be available by the
end of 1996. A copy will be
available at the Region I library
617/565-3300 or Toll Free at
800-EPA-LIBR.
written by Mary Ballew and
Margaret McDonough
References
Bowers et al. 1994: Bowers, TS,
Beck BD, Karam HS.1994.
Assessing the relationship
between environmental lead
concentrations and adult blood
lead levels. Risk Analysis
14:183-89.
Weston 1995: Roy F. Weston,
Inc. 1995. Baseline human
health risk assessment for the
California Gulch Superfund site.
February. Prepared for USEPA
Region 8, Denver CO.
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Revised
Manganese
Reference Dose
The manganese reference
dose (RfD) in the IRIS data
base was revised in
November, 1995. This
revision results in a lower risk
(and thus, higher cleanup
level) for drinking water
compared to the previous RfD.
The IRIS RfD of 1.4E-1
mg/kg/day is for the total oral
intake of manganese. As
stated in the IRIS file, it is
recommended that a modifying
factor of 3 be applied to the
RfD for non-dietary exposures.
Background
Prior to November, 1995 the
IRIS data base provided two
references doses for
manganese, one for food and
one for water. The food RfD
was based on dietary intake of
manganese. The water RfD
was based on a study of
humans who had ingested
drinking water containing
elevated levels of manganese
as well as on assumptions
regarding differences in
absorption of manganese in
food as opposed to water.
The drinking water RfD was
withdrawn from IRIS in
November, 1995 because of
concerns about the validity of
the human exposure study and
because new information
indicated that the disparity
between absorption of
manganese from food as
opposed to water was
overestimated.
New Approach
The revised RfD for
manganese is for the total oral
intake of manganese. This
value is 0.14 mg/kg/day and is
derived as follows:
• 10 mg/day of manganese
may be consumed without
adverse effects (the
"critical dose"). This value
comes from several dietary
studies.
average adult body
weight = 70 kg
Therefore, the RfD =
10 ma/dav =0.14 mg/kg/day
70 kg
A modifying factor of 3 is
recommended in IRIS when
assessing exposure from
drinking water.
Drinking Water Exposures
The average dietary
manganese content of the
U.S. population, 5 mg/day, is
subtracted from the "critical
dose" of 10 mg/day:
10 mg/day - 5mg/day =
5 mg/day
Apply modifying factor of 3 per
IRIS recommendation:
5 ma/dav = 1.67 mg/day
3
Compute RfD:
1.67 ma/dav = .024 mg/kg day
70 kg
The Hazard Index (HI) for
drinking water is calculated as
follows (using a simplified
equation):
Concentration(ma/L) * 2liters/dav
0.024 mg/kg/day *70 kg
A HI of 1 corresponds to a
concentration of 840 ug/L.
Soil Exposure
A modifying factor of 3 may be
appropriate for assessing risks
via exposure to soils if neonates
(a child 12 months or younger)
are a potentially exposed
population. For most RCRA and
Superfund risk assessments
neonates are unlikely to be
exposed to significant amounts
of soils. Therefore, a modifying
factor of 1 is appropriate.
Assuming exposure to a young
child under a residential
scenario, a hazard index of 1 for
manganese in soil would
correspond to a soil
concentration of 5,500 mg/kg.
written by Margaret McDonough
New
Cancer Slope
Factors
for PCBs
EPA recently reassessed the
scientific evidence for the
carcinogenicity	of
polychlorinated biphenyls
(PCBs). A range of new cancer
slope factors for PCB mixtures
were posted on the IRIS
chemical information data base
on October 1, 1996. The new
slope factors reflect the current
knowledge of EPA scientists and
national experts concerning:
•	the influence on toxicity of
PCBs by chemical
transformation in the
environment;
•	the tendency of PCBs to
partition into various media;
and
•	the potential for PCBs to
biomagnify through the food
chain.
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To fully understand the
scientific basis for the slope
factors and to correctly apply
them in a risk assessment,
carefully read EPA's
supporting technical
document, PCBs: Cancer
Dose-response Assessment
and Application to
Environmental Mixtures, which
explains in greater detail the
basis for the PCB
reassessment.
The PCB reassessment
results in different cancer
slope factors for PCB mixtures
based on a consideration of
several different factors. First,
the reassessment recognizes
that environmental processes
may significantly change the
toxicity of Aroclor mixtures
released into the environment.
Thus, new slope factors are
determined by the
environmental pathway of
exposure rather than by
reference to a toxicity study for
the particular Aroclor. Second,
toxicity studies which formed
the basis of the previous slope
factor for PCBs were
reanalyzed using new criteria
and nomenclature for rat liver
tumors, which resulted in a
reduced number of tumors
reported for Aroclor mixtures.
Third, new PCB toxicity
studies, sponsored by the
General Electric Company,
were considered in the
derivation of the new cancer
slope factors. Fourth, a
revised cross-species scaling
factor as recommended in
EPA's Proposed Guidelines for
Carcinogen Risk Assessment,
61FR 17960, was incorporated
into the derivation of the new
slope factors. Lastly, a new
method for extrapolating risk to
low doses from experimental
data as recommended in
EPA's New Cancer Guidelines
was utilized in deriving the new
slope factors.
The reassessment
recommends a tiered
approach for determining
central tendency and high end
cancer slope factors for use in
risk assessment. When
congener information is
limited, the exposure pathway
is used to indicate whether
environmental processes have
increased or decreased a PCB
mixture's potency. When
congener information is
available, further refinement of
the potency estimate can
occur. Three categories of
slope factors are developed
based on the exposure
pathway or, if more information
is available, the PCB congener
makeup of the mixture. A
"high-risk" category is used for
exposure pathways associated
with environmental processes
that tend to increase risk: a
"low-risk" category for those
that tend to decrease risk; and
a "lowest risk" category for
cases where congener or
isomer analyses verifies the
absence of congeners with
more than 4 chlorines
(establishing sufficient
similarity of an environmental
mixture to the least potent
PCB Aroclor tested).
Additional highlights of the
reassessment include the
following:
• Changes in the types of
environmental	data
collected for PCBs are
recommended. At present,
data are collected for the
commercially available
mixtures of PCBs
(Aroclors) and the total
amount of PCBs. The
reassessment
recommends collecting
data on either the total
amount of PCBs or on
congeners (which
represent up to 209
different arrangements of
the chlorine atoms on the
PCB molecule).
• Analysis of dioxin-like PCBs
is recommended, if thev are
thought to be present. For
samples containing dioxin-
like PCBs, the risk of the
dioxin-like PCBs is added to
the risks calculated using the
cancer slope factors for
nondioxin-like PCBs
presented in this
reassessment. Only a
congener-specific analysis
can determine whether
dioxin-like PCBs are present.
The risks from dioxin-like
PCBs are evaluated using a
toxicity equivalence factor
(TEF) approach, (See the
PCB reassessment and
March 1989 Interim
Procedures For Estimating
Risks Associated With
Exposures to Mixtures of
Chlorinated Dibenzo-p-
dioxins and -Dibenzofurans
(CDDs and CDFs) and 1989
Update (EPA/625/3-89/016)
for more details.)
• New highly exposed and
highly sensitive populations
who merit specific evaluation
are identified. "Highly
exposed populations include
some nursing infants and
consumers of game fish and
game animals contaminated
through the food chain.
Highly sensitive populations
include people with
decreased liver function and
infants."
The reassessment may produce
changes in the way we
investigate hazardous waste
sites and estimate risks for
PCBs. Lower estimates of risk
from PCBs could result for
several exposure pathways.
When assessing the risks from
PCB mixtures, please contact a
Region I risk assessor.
The PCB reassessment is
available on the Office of
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Research and Development
home page on the Internet at
http://www.epa.gov/ORD. A
copy is also available at the
Region I EPA library and it
may be copied onto a disk if
you bring your own. The
library has a new toll free
number for calls within New
England: 888-EPA-LIBR.
written by Mary Ballew
& Ann-Marie Burke
To be included on future mailing list,
please send your address including
Internet address to: Jayne Michaud
or Stephanie Carr at:
michaud.jayne@epamail.epa.gov
carr.stephanie@epamail.epa.gov
USEPA - New England
JFK Federal Building, HBT
Boston, MA 02203
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