1
November
21,
2003
FIFRA
SCIENTIFIC
ADVISORY
PANEL
(
SAP)
OPEN
MEETING
DECEMBER
3­
5,
2003
FIFRA
SAP
WEB
SITE
http://
www.
epa.
gov/
scipoly/
sap/
OPP
Docket
Telephone:
(
703)
305­
5805
Docket
Number:
OPP­
2003­
0316
SHERATON
CRYSTAL
CITY
HOTEL
1800
JEFFERSON
DAVIS
HIGHWAY
ARLINGTON,
VIRGINIA
22202
703­
486­
1111
Draft
Preliminary
Probabilistic
Exposure
and
Risk
Assessment
For
Children
Who
Contact
CCA­
Treated
Playsets
and
Decks
and
CCA­
Containing
Soil
Around
These
Structures
Questions/
Charge
to
the
Panel
I.
Exposure
Assessment
Background:
revisions
to
the
SHEDS­
Wood
model
and
the
probabilistic
CCA
exposure
assessment
since
the
August
2002
assessment
The
current
SHEDS­
Wood
model
incorporates
a
number
of
code
changes
and
new
analyses
that
address
comments
and
suggestions
received
from
the
2002
SAP
Panel
members,
EPA
reviewers,
public
and
other
external
groups
as
summarized
in
Tables
1
and
2
(
and
in
more
detail
in
Appendix
1)
of
the
exposure
assessment
report.
For
example,
some
of
the
code
changes
and
new
analyses
performed,
include
the
following:

Scenario­
specific
changes
or
analyses
°
comparing
results
for
children
exposed
to
public
playsets
only
to
those
also
exposed
to
residential
CCA­
treated
wood
°
conducting
separate
analyses
for
children
1­
13
years
to
assess
sensitivity
of
results
to
changing
the
age
group
from
1­
6
years
°
conducting
special
analyses,
such
as
changing
dermal
and
GI
absorption
values
°
conducting
a
separate
analysis
for
children
who
exhibit
pica
soil
ingestion
behavior
Changes
to
model
inputs
or
assumptions
2
°
using
revised
body
weight
and
surface
area
equations
based
on
NHANES
III
to
update
the
body
weight
and
hand
size
monthly
rather
than
annually
°
for
residue
dermal
exposure
calculations
replacing
the
transfer
efficiency
and
fraction
of
skin
contacted
per
time
with
user­
specified
distributions
°
determining
the
maximum
dermal
loading
based
on
surface
concentrations
and
transfer
efficiency
°
changing
the
SHEDS­
Wood
approach
for
bathing
events
by
allowing
a
variable
number
of
days
between
baths
Sensitivity
and
uncertainty
analyses
°
conducting
sensitivity
analyses
by
varying
each
variable
up
or
down
by
1
standard
deviation
°
allowing
the
use
of
Beta,
Weibull,
and
Gamma
distributions
for
fitting
distributions
to
model
inputs
°
sampling
parameter
pairs
during
the
uncertainty
analyses
step,
rather
than
independently
sampling
each
parameter
Evaluation
of
SHEDS­
Wood
model
results
°
evaluating
the
comparability
the
SHEDS­
Wood
model
results
to
results
from
other
earlier
(
primarily)
deterministic
CCA
assessments.

Specific
Issues
and
Questions
for
the
FIFRA
SAP
Issue
1:
Documentation,
completeness,
and
clarity
of
the
model
source
code
and
the
exposure
assessment
report
Both
the
SHEDS­
Wood
source
code
and
the
probabilistic
exposure
assessment
report
have
been
significantly
revised
since
the
August
2002
SAP.

Question
A:
The
Source
Code
Directory
on
the
CD
provided
to
the
SAP
includes
annotated
code
for
the
exposure
and
dose
algorithms
used
in
the
SHEDS­
Wood
model.
Are
these
algorithms
consistent
with
the
descriptions
in
the
SHEDS­
Wood
CCA
exposure
assessment
report?
Does
the
revised
SHEDS­
Wood
version
2
code
(
i.
e.,
the
code
submitted
for
the
December
2003
SAP)
accurately
reflect
changes
to
the
version
1
methodology
(
i.
e.,
the
code
and
methodology
presented
to
the
August
2002
SAP)
described
in
the
report?

Question
B:
The
SHEDS­
Wood
CCA
exposure
assessment
report
presents
the
model
construct,
3
selected
model
inputs,
model
results,
and
comparison
to
other
CCA
model
estimates.
Please
comment
on
the
clarity,
completeness
and
usefulness
of
this
document.

Issue
2.
Modifications
to
SHEDS­
Wood
model
code
and
the
exposure
scenarios
selected
A
number
of
modifications
to
the
model
code
and
scenario­
specific
changes
have
been
made
to
the
SHEDS­
Wood
model
since
the
August
2002
SAP.

Question
A:
Considering
the
limitations
of
available
information
and
state­
of­
the­
art
modeling
methods
required
for
the
assessment
of
children's
exposures
from
contacting
CCA
treated
wood
residues
and
CCA
containing
soil,
are
the
revisions
made
to
the
SHEDS­
Wood
code
or
algorithms
scientifically
sound
and
acceptable
?

Question
B:
The
SHEDS­
Wood
model
has
been
modified
using
feedback
from
the
August
2002
SAP.
In
particular,
the
recent
assessment,
includes:
assessment
of
exposures
of
children
contacting
only
CCA
treated
public
playsets;
sensitivity
of
results
to
changing
the
age
group
of
exposed
children
to
1­
13
years,
and;
a
separate
analysis
for
children
exhibiting
pica
soil
ingestion
behavior.
The
Panel
is
requested
to
comment
on
the
appropriateness
of
the
new
exposure
scenarios
in
the
revised
probabilistic
exposure
and
dose
assessment.

Issue
3.
Key
input
variables
and
specification
of
associated
variability
distributions
Sensitivity
and
uncertainty
analyses
of
the
SHEDS­
Wood
model
results
identified
the
following
as
key
input
variables
influencing
the
model
results:
wood
surface
residue­
to­
skin
transfer
efficiency;
wood
surface
residue
levels;
fraction
of
hand
surface
area
mouthed
per
mouthing
event;
and
GI
absorption
fraction
for
residues.
In
addition
to
the
above
variables,
sensitivity
and
uncertainty
analyses
also
indicated
the
importance
of
following
additional
variables:
average
number
of
days
per
year
a
child
plays
around
CCA­
treated
playsets,
frequency
of
hand
washing,
daily
soil
ingestion
rate,
and
average
fraction
of
non­
residential
time
a
child
plays
on/
around
CCA­
treated
playsets.

Question
A.
Has
the
Agency
used
the
best
available
information
for
developing
input
distributions
for
these
variables?
If
not,
are
there
any
other
data
that
EPA
should
be
aware
of?
Considering
the
limitations
and
uncertainties
with
available
information,
are
the
choices
made
in
developing
distributions
for
each
of
these
key
variables
using
the
available
information
reasonable
and
scientifically
sound?

Question
B.
In
some
of
these
instances
(
see
Table
12,
page
58),
because
of
data
limitations,
the
Agency
has
made
simplifying
assumptions
to
represent
them
as
point
estimates
based
on
professional
judgement.
Are
the
simplifying
assumptions
presented
in
the
draft
exposure
assessment
for
making
these
decisions
adequately
supported
by
relevant
scientific
data?
Are
the
choices
made
to
quantify
these
variables
(
i.
e.,
selected
distributions
or
point
estimates)
reasonable
and
sound?
4
Question
C.
Are
the
methods
used
for
fitting
variability
distributions
that
are
assigned
to
model
input
variables
for
the
CCA
assessment
appropriate?

Question
D.
The
Panel
is
requested
to
comment
on
whether
any
other
model
inputs
are
either
key
drivers
of
results
or
sources
of
large
model
uncertainty.
Do
these
model
input
variables
and
the
distributions
assigned
to
them
appropriately
reflect
available
scientific
data
?
Did
EPA
appropriately
integrate
the
available
data
to
derive
the
distributions
for
these
input
variables?

Issue
4:
Methods
and
results
for
sensitivity
and
uncertainty
analyses
EPA's
draft
CCA
Exposure
Assessment
includes
a
formal
sensitivity
and
uncertainty
analysis
as
well
as
discussion
of
various
sources
of
uncertainty
in
the
model
analyses.

Question
A:
The
Panel
is
requested
to
comment
on
the
utility
and
suitability
of
the
statistical
diagnostic
tools
used
by
SHEDS
for
analyzing
model
results
(
e.
g.,
variability
analyses,
sensitivity
analyses,
uncertainty
analyses).

Question
B:
Is
the
bootstrap
approach
that
is
used
for
fitting
uncertainty
distributions,
which
has
been
revised
in
response
to
prior
SAP
comments,
implemented
properly,
or
are
there
alternative
approaches
that
are
recommended?

Question
C:
Are
the
uncertainty
distributions
assigned
to
chemical
and
non­
chemical
specific
model
input
parameters
appropriate?

Question
D:
The
Panel
is
requested
to
comment
on
whether
the
modeling
approach
and
documentation
appropriately
identify
and
address
critical
sources
of
uncertainty
in
the
model
and
the
resulting
exposure
estimates.
Does
EPA's
documentation
adequately
describe
the
uncertainties
inherent
in
the
data
used
for
modeling
and
the
influence
of
these
uncertainties
on
interpretation
of
the
modeling
results?

Question
E.
Does
the
Panel
recommend
performing
any
additional
uncertainty
analyses
to
evaluate
the
impacts
of
using
alternative
input
distributions
on
the
modeling
results
(
e.
g.,
to
address
uncertainties
in
various
factors
determining
the
frequency
of
children's
exposures
to
CCAtreated
wood
in
playsets
and
decks)?

Issue
5:
Special
Model
Simulations
A
number
of
special
simulations
with
the
SHEDS­
Wood
model
were
conducted
in
order
to
examine
the
importance
of
specific
exposure
scenarios
or
the
impact
of
certain
input
assumptions.
For
example,
some
of
these
analyses
included
conducting
separate
simulations
for
children
exposed
to
public
playsets
only,
modeling
exposures
of
the
7­
13
year
old
age
group,
and
studying
exposures
of
children
exhibiting
pica
behavior.
Additional
analyses
were
also
conducted
to
examine
the
impacts
of
using
data
or
assumptions
about
increased
GI
absorption,
decreased
5
dermal
absorption,
lowering
the
transferable
wood
residue
concentrations
by
sealants,
and
hand
washing
after
play
events.
The
results
from
these
special
analyses
were
not
significantly
different
than
the
baseline
model
results,
except
for
the
large
impact
of
assuming
the
use
of
sealants
would
greatly
reduce
wood
residues.

Question
A.
The
Panel
is
requested
to
comment
on
the
appropriateness
of
the
justifications
made
in
characterizing
the
key
factors
or
inputs
for
each
of
these
special
simulations.
Did
the
Agency
provide
adequate
technical
rationale
and
justification
for
its
choices
for
these
alternative
exposure
scenarios
or
input
distributions?
Do
the
results
from
these
special
analyses
reflect
proper
use
of
available
information?

Question
B:
Do
any
of
the
findings
from
these
special
analyses
necessitate
the
Agency
to
consider
revising
certain
scenarios
or
inputs
to
the
baseline
assessment?

Issue
6:
Evaluation
of
the
SHEDS­
Wood
model
results
The
Agency
has
evaluated
the
probabilistic
CCA
exposure
model
results
by
comparing
them
to
results
from
other
earlier
deterministic
CCA
assessments.
In
particular,
the
SHEDS­
Wood
model
results
were
found
to
compare
well
to
a
deterministic
CCA
assessment
performed
by
the
Gradient
Corporation,
and
SHEDS­
Wood
upper
percentiles
compare
well
to
deterministic
Consumer
Product
Safety
Commission
estimates.

Question
A:
Has
EPA
provided
adequate
documentation
of
the
overall
plausibility
of
the
exposure
estimates
generated
by
the
SHEDS­
Wood
model
for
CCA?
Are
the
comparisons
with
the
results
of
other
selected
exposure
assessments
appropriate
and
appropriately
presented?
Are
there
any
other
types
of
benchmarking
approaches
or
data
to
assess
the
reliability
of
the
overall
exposure
model
or
specific
model
elements?

Issue
7:
Overall
completeness
and
acceptability
of
the
SHEDS­
Wood
probabilistic
CCA
exposure
assessment
EPA
has
revised
the
August
2002
SHEDS­
Wood
exposure
assessment
after
carefully
considering
numerous
comments
and
suggestions
that
it
has
received
from
various
parties,
including
those
from
the
August
2002
FIFRA
SAP
members,
EPA/
ORD
and
EPA
Program
Office
peer­
reviewers
of
the
preliminary
draft
September
2003
report,
and
from
the
general
public
and
other
external
groups.

Question
A:
In
addition
to
the
comments
and
suggestions
already
offered
by
the
Panel
members
under
the
specific
issues
raised
previously,
considering
the
availability
of
data
and
information,
does
6
the
Panel
recognize
any
critical
gaps
in
information
or
methodologies
that
still
need
to
be
addressed
for
the
CCA
exposure
and
dose
assessment?

II.
Risk
Assessment
Issue
8:
In
the
study
by
Nico
et
al.
(
2003),
X­
ray
absorption
spectroscopy
(
XAS)
was
used
to
determine
the
chemical
and
structural
state
of
arsenic
and
chromium
molecules
in
CCA­
treated
wood
residue
samples.
Based
on
the
results
of
their
analysis,
Nico
et
al.
(
2003)
determined
that
arsenic
and
chromium
formed
a
"
chemical
complex
bonded
to
the
wood
structure."
Based
on
this
study,
the
dominant
oxidation
state
of
the
two
elements
is
As(
V)
and
Cr(
III),
and
the
local
chemical
environment
of
the
two
elements
is
best
represented
as
a
stable
Cr/
As
cluster
consisting
of
a
Cr
dimer
bridged
by
an
As(
V)
oxygen
ion.
Nico
et
al.
(
2003)
also
maintained
that
this
chemical
complex
was
quite
resistant
to
leaching.

Question
A:
The
Panel
is
requested
to
comment
on
the
Nico
et.
al.
(
2003)
study
and
particularly
on
the
arsenic
and
chromium
chemical
complex
from
CCA
treated
wood
surface
residue,
and
whether
the
Panel
believes
that
the
chemical
complex
is
formed
during
the
fixation
process.
What
is
the
meaning
of
this
complex
cluster
formation
to
the
current
risk
assessment
Issue
9.
Casteel
et
al.
(
2003),
reported
that
the
relative
bioavailability
(
RBA)
of
dislodgeable
wood
residue
is
27%.
This
value
is
significantly
lower
than
the
default
value
of
100%
that
is
usually
employed
when
reliable
site­
specific
data
are
lacking
and
also
lower
than
the
RBA
value
recommended
by
the
SAP
2001.
The
result
of
this
study
indicates
that
the
arsenic
in
the
dislodgeable
arsenic
material
is
not
as
well
absorbed
as
soluble
arsenic.

Question
A:
Does
the
Panel
agree
that,
in
light
of
the
Casteel
study
and
the
Nico
study
discussed
in
issue
8,
the
Agency
should
use
27%
for
the
RBA
to
estimate
the
bioavailable
dose.

Issue
10:
In
the
2001
SAP
meeting,
the
Panel
cited
the
research
of
Wester
et
al.
(
1993)
as
a
source
of
the
dermal
absorption
rate
of
soluble
arsenic
in
water
and
soil.
The
Panel
recommended
using
a
2­
3
%
dermal
absorption
rate
for
arsenic
residue
on
the
surface
of
wood.
Recently,
a
preliminary
study
by
Wester
et
al.
(
2003)
has
been
submitted
by
the
same
laboratory
compares
the
dermal
absorption
of
arsenic
in
CCA­
treated
wood
surface
residues
with
arsenic
in
water
solution.
Although
the
Agency
has
not
receive
the
complete
results
of
this
study
(
e.
g.,
the
recovery
of
the
arsenic
in
the
urine
of
the
animal
given
IV
dose
of
arsenic),
the
preliminary
results
of
this
study
indicate
that
the
7
dermal
absorption
of
0.01%
from
wood
surface
residue
was
approximately
two
order
of
magnitude
lower
than
the
results
in
water.
The
dermal
absorption
from
this
study
was
based
on
urinary
arsenic
data
following
application
of
arsenic
in
CCA­
treated
wood
residue
that
had
been
weathered
by
the
environment.

Question
A:
Taking
into
consideration
the
Nico
et
al.
study
mentioned
in
issue
8,
the
Panel
is
requested
to
comment
on
whether
this
new
study
conducted
by
Wester
et
al.
provides
a
more
appropriate
estimate
of
dermal
absorption
from
contact
with
CCAtreated
wood
surfaces
than
the
earlier
1993
Wester
et
al.
study.

Issue
11:
In
the
2001
SAP
meeting,
the
Panel
recommended
that
a
biomonitoring
study
be
performed
on
children
who
are
normally
exposed
to
CCA­
treated
playground
equipment
and
decks.
The
Panel
recommended
that
the
study
should
be
designed
according
to
well­
accepted
epidemiological
principles,
including
adequate
sample
size,
to
resolve
the
issue
of
whether
there
are
substantial
exposures
to
children
from
arsenic
residues
after
playing
on
decks
and
playsets.
The
Panel
indicated
data
from
such
a
biomonitoring
study
could
be
directly
used
in
the
risk
assessment
and
could
be
used
to
validate
the
exposure
assessment
model.
Recently,
a
proposed
protocol
for
a
pilot
study
was
submitted
to
OPP
for
peer
review;
this
proposed
protocol
is
an
attempt
to
determine
if
changes
in
exposure
to
arsenic
can
be
assessed
by
examining
changes
in
the
urinary
excretion
of
arsenic.
EPA
has
provided
the
Panel
with
a
copy
of
the
proposed
protocol
for
the
pilot
study.
In
summary,
the
proposed
pilot
study
will
determine
whether
a
significant
difference
in
urinary
arsenic
can
be
discerned
when
a
population
of
children
are
switched
from
arsenic­
containing
tap
water
to
an
essentially
arsenic­
free
source
of
drinking
water.

Question
A.
The
Panel
is
requested
to
comment
on
the
strengths
and
limitations
of
the
approach
to
be
employed
in
the
proposed
pilot
study
to
help
resolve
the
issue
of
whether
there
are
substantial
exposures
to
children
from
arsenic
residues
after
playing
on
decks
and
playsets.
In
particular,
please
comment
on
the
feasibility,
the
potential
confounding
background
sources
from
the
statistical
analysis,
the
sensitivity
and
accuracy
of
analytical
method
for
quantitation
of
arsenic
in
urine
to
detect
changes,
the
determination
of
intraindividual
variation
and
interindividual
variation
based
on
the
current
knowledge
of
exposure;
and
any
other
aspects
of
the
proposed
pilot
study
that
might
affect
its
utility.

Question
B.
The
Panel
is
asked
to
describe
approaches
for
gathering
additional
data
 
e.
g.,
data
on
the
efficiency
of
transfer
of
surface
residues
to
the
skin
surface
(
which
has
been
identified
as
one
of
most
critical
model
inputs
based
on
the
uncertainty
analysis)
 
to
improve
the
estimates
of
exposure
and
/
or
the
level
of
confidence
in
such
estimates,
and
with
respect
to
these
approaches,
as
well
as
the
proposed
pilot
study,
to
comment
on
the
cost
of
data
generation,
the
amount
of
time
to
generate
the
data,
8
and
the
degree
to
which
the
data
will
reduce
uncertainty
about
the
accuracy
of
the
model
estimates.

Issue
12.
Prior
to
the
availability
of
probabilistic
models,
such
as
SHEDS,
OPP
estimated
the
lifetime
average
daily
dose
(
LADD)
and
corresponding
cancer
risk
to
pesticides
via
a
deterministic
approach
using
central
tendency
input
parameters
(
median
or
mean
values).
Probabilistic
models
now
allow
OPP
to
express
input
parameters
as
distributions
and
subsequently
generate
a
distribution
of
LADDs
and
corresponding
pesticide
cancer
risks.
In
other
words,
the
deterministic
approach
results
in
a
single
cancer
risk
value
and
the
probabilistic
approach
results
in
a
distribution
of
cancer
risk
values.

Question
A.
The
Panel
is
requested
to
comment
on
whether
in
this
probabilistic
approach
of
using
the
upper
bound
arsenic
cancer
slope
factor
combined
with
using
high­
end
LADDs
would
result
in
a
significant
overestimation
of
the
risk
for
the
more
highly
exposed
percentiles
of
the
population
?
If
this
is
an
overestimate,
what
other
values
would
the
panel
recommended
using
as
replacements,
or
in
addition
to
the
values
that
were
used
that
would
minimize
the
overestimation
of
risk
without
substantially
underestimating
the
risk
for
such
percentiles.

In
this
assessment,
the
estimated
risks
are
considered
approximations
because
inaccuracies
may
occur
when
exposures
are
summed
across
routes
at
the
quartile
level
especially
in
the
upper
percentile.
This
is
due
to
the
way
the
Monte
Carlo
simulations
were
conducted
and
the
outputs
summarized.

Question
B.
The
Panel
is
requested
to
comment
on
the
range
of
percentiles,
if
any,
at
which
there
is
a
significant
decrease
in
the
reliability
of
the
estimates
of
risk.
