Dermal
Sensitization
Testing
of
Dermal
Sensitization
Testing
of
Chromium
Chromium
Timothy
F.
McMahon,
Ph.
D.

Timothy
F.
McMahon,
Ph.
D.

U.
S.
EPA
U.
S.
EPA
Office
of
Pesticide
Programs
Office
of
Pesticide
Programs
May
2,
2006
May
2,
2006
2
Outline
of
Presentation
Outline
of
Presentation

Allergic
Contact
Dermatitis
(
ACD)

 
Regulatory
framework
 
Science
background

SAP
Review

Nethercott
et
al.
study
3
DERMAL
SENSITIZATION
DERMAL
SENSITIZATION­
CURRENT
CURRENT
APPROACHES
APPROACHES
USEPA,
§
40
CFR
798.4100:


"
Information
derived
from
tests
for
skin
sensitization
serves
to
identify
the
possible
hazard
to
a
population
repeatedly
exposed
to
a
test
substance."
4
DERMAL
SENSITIZATION
DERMAL
SENSITIZATION­
CURRENT
CURRENT
APPROACHES
APPROACHES
Treated
Articles
(
§
40
CFR
152.25)


A
registered
pesticide
is
incorporated
into
an
article
to
protect
the
integrity
of
the
article
or
substance
itself

Treated
articles
such
as
treated
wood
do
not
bear
pesticide
labels
or
other
information
to
inform
the
public
about
potential
hazards,
including
dermal
sensitization
5
Allergic
Contact
Dermatitis
(
ACD)

Allergic
Contact
Dermatitis
(
ACD)


Contact
Hypersensitivity

Contact
Allergy
6
Allergic
Contact
Dermatitis
(
ACD)

Allergic
Contact
Dermatitis
(
ACD)

Delayed
Contact
Hypersensitivity:

  
A
delayed,
immunologically
mediated
inflammatory
skin
disease
consisting
of
various
degrees
of
erythema,

edema,
and
vesiculation. 
(
Marzulli
and
Maibach,
1996)

  
Stimulation
by
chemical
allergen
(
in
an
inherently
susceptible
individual)
of
an
immune
response
of
the
quality
and
vigor
required
to
permit
the
provocation
of
an
elicitation
reaction
upon
subsequent
encounter
with
the
same
chemical. 
(
Kimber,
2004)
7
Allergic
Contact
Dermatitis
(
ACD)

Allergic
Contact
Dermatitis
(
ACD)

Characterized
by
two
phases:


Induction:


Exposure
of
sufficient
magnitude
and/
or
duration
to
activate
specific
immune
mechanisms
resulting
in
the
acquisition
of
sensitization

Elicitation/
challenge
:


Responses
induced
in
sensitized
individuals
upon
exposure
to
the
allergen
by
a
relevant
route
8
Dermal
Irritation
vs.
ACD
Dermal
Irritation
vs.
ACD
ACD
ACD

Edema

Erythema

Reaction
time:
24
 
72
hrs

No
response
on
1st
exposure

Requires
immune
memory
Irritation
Irritation

Erythema

Edema

Reaction
time:

immediate

Response
on
1st
exposure

No
immune
memory
9
INDUCTION
ELICITATION
LOW
MOLECULAR
WT
ALLERGEN
MIGRATION
TO
LOCAL
LYMPH
NODE
IL­
1
 ,
IL­
6,
IL­
12
IL­
1
 ,
TNF­

 ,
GM­
CSF
T­
CELL
LYMPHOCYTE
PROLIFERATION
ICAM­
1
LANGERHANS
CELL
(
LC)
"
PRIMED"
LYMPHOCYTES
SPECIFIC
INFLAMMATORY
RESPONSE
CYTOKINES,

COSTIMULATORY,
ADHESION
MOLECULES
INCREASE
CELLULAR
INFLUX
EDEMA
AND
ERYTHEMA
Contact
Hypersensitivity*

Reprinted
with
permission
from
Sailstad,
2003
10
Background
Summary
Background
Summary
ACD

Generally
recognized
as
a
threshold
phenomenon

Thresholds
largely
determined
by
the
potency
of
the
allergen

Induction/
elicitation
thresholds
vary
among
individuals
(
Kimber
et
al.,
2003)


Dose­
response
relationships
observed
for
both
induction
and
elicitation
(
Scott
et
al.,
2002)
11
Background
Summary
Cont.

Background
Summary
Cont.

ACD

Induction
may
occur
after
a
single
exposure
to
a
sufficiently
large
area
of
skin,
or
as
a
consequence
of
repeated
skin
exposures

Some
data
suggest
sensitizing
potential
may
increase
with
repeated
exposures
(
Griem
et.
al.,
2003)
12
Independent
Science
Reviews
Independent
Science
Reviews
 
May,
2004,
scientific
issues
pertaining
to
Agency s
interest
in
developing
the
foundation
of
a
scientifically
sound
approach
to
quantitative
assessment
of
dermal
sensitization
risks
for
pesticide
chemicals
presented
to
FIFRA
Scientific
Advisory
Panel
(
SAP)

 
Included
chemicals
incorporated
in
other
materials
(
i.
e.,
treated
articles)

 
Included
hexavalent
chromium
as
a
case
study
13
Hexavalent
Hexavalent
Chromium
Chromium

One
of
the
most
common
and
potent
contact
sensitizers

Exposures
occur
in
occupational
and
non­
occupational
settings

Chromium
induced
ACD
evaluated
by
Nethercott
et.
al.
(
1994)
14
Hexavalent
Hexavalent
Chromuim
Chromuim

Both
animal
(
LLNA)
and
human
(
patch
test)

data
are
available
on
dermal
sensitization
of
hexavalent
chromium

SAP
cited
limitations
of
LLNA
for
risk
assessment,
and
deficiencies
in
other
human
studies

SAP
identified
Nethercott
et
al.
study
as
the
critical
study
15
Human
Testing
of
Chromium
for
Dermal
Sensitization:

Nethercott
et.
al.
16
Nethercott
Nethercott
Human
Testing
Human
Testing

113
possible
volunteers
selected
from
examination
of
6000
patient
files

Ultimately,
102
took
part
in
the
study
(
78
men,
24
women)


All
study
participants
believed
to
be
chromium
+
6
sensitive
based
on
previous
patch
tests
performed
by
their
physicians
17
Nethercott
Nethercott
Human
Testing
Human
Testing

Persons
taking
immunosuppresive
or
steroidal
medications
excluded

Written
consent
provided
to
participate
in
study

Medical/
occupational
history
questionnaire
filled
out

Information
on
allergic
and
atopic
dermatitis
available
for
all
102
subjects
18
Nethercott
Nethercott
et.
al
et.
al.


Concentrations
selected
based
on
best
estimate
of
a
range
from
review
of
open
literature
where:


Highest
dose
provided
100%
response

Lowest
dose
elicited
<
10%
response

Concentrations
from
0.018­
4.4
µ
g/
cm
2
chosen
19
Nethercott
Nethercott
et.
al
et.
al.
Cont.

.
Cont.


Three
rounds
of
testing
using
TRUE­
test
patches

In
all
rounds,
patches
applied
to
the
upper
sides
of
the
back
7
cm
apart

Patches
remained
in
place
48
hours
20
Nethercott
Nethercott
et.
al
et.
al.
cont.

.
cont.

Round
one:


Patch
test
with
4.4
ug
of
Cr+
6/
cm2

102
subjects
to
verify
sensitization

Those
responding
positively
moved
on
to
round
two
­
54
subjects
(
39
men,
15
women)
21
Nethercott
Nethercott
et.
al.
Cont.

et.
al.
Cont.

Round
Two:


Patch
test
with
0.018
and
0.088
µ
g
Cr+
6/
cm2

Those
showing
positive
responses
to
either
0.018
or
both
0.018
and
0.088
Cr+
6/
cm2
were
not
tested
in
round
three
Round
Three:


49
nonresponding
subjects
(
breakdown
by
sex
not
reported)


Tested
with
Cr+
6
concentrations
of
0.18
and
0.88
µ
g/
cm2
22
Nethercott
Nethercott
et.
al.
cont.

et.
al.
cont.


Round
one
response:
54
positive
responses
to
4.4
µ
g
Cr
+
6
/
cm
2

Round
two
response:
4/
54
positive
at
0.088
but
not
0.018
µ
g
Cr
+
6
/
cm
2
.
1/
54
positive
at
both
0.088
and
0.018
µ
g
Cr
+
6
/
cm
2
.
49
nonresponders

Round
three
response:
1
positive
at
both
0.88
and
0.18
µ
g
Cr
+
6
/
cm
2
.
22
positive
at
0.88
but
not
0.18
µ
g
Cr
+
6
/
cm
2
.
Remainder
negative
at
both
concentrations
23
Nethercott
Nethercott
et.
al.
cont.

et.
al.
cont.


Cumulative
response
showed
a
2%

response
at
the
lowest
concentration
of
0.018
µ
g
Cr
+
6
/
cm
2

The
10%
MET
was
calculated
as
0.089
µ
g
Cr
+
6
/
cm
2
24
Nethercott
Nethercott
et
al.
Cumulative
Response
et
al.
Cumulative
Response
25
Nethercott
Nethercott
et.
al.
Cont.

et.
al.
Cont.


SAP
identified
Nethercott
et
al.
as
best
available,
based
on
animal
and
human
data

Panel
identified
the
critical
dose
as
0.089
µ
g/
cm
2

This
was
considered
a
conservative
level
26
Strengths/
Weaknesses
of
Strengths/
Weaknesses
of
Nethercott
Nethercott

Strengths:


Both
males
and
females
represented
in
study

Large
pop.
of
sensitized
individuals

Good
experimental
design
w/
several
rounds
of
testing
to
establish
dose­
response
relationship
for
elicitation

TRUE
test
patches
used;
sensitive
for
metals
testing
27

Weaknesses:


MET
value
may
be
conservative
based
on
possibility
of
misreading
irritant
vs.
allergic
reactions
Strengths/
Weaknesses
of
Strengths/
Weaknesses
of
Nethercott
Nethercott
28
Nethercott
Nethercott
et.
al.
cont.

et.
al.
cont.


Agency
used
SAP
recommendation
for
selection
of
10%
MET
but
did
not
use
UF
<
1
in
deriving
the
total
UF

The
Agency
has
concluded
that
the
Nethercott
study
contains
information
sufficient
for
assessing
human
risk
from
potential
dermal
exposure
to
chromium
29
Scientific
Considerations
Scientific
Considerations

EPA
has
identified
a
study
performed
with
subjects
who
had
documented
sensitivity
to
chromium
(
Nethercott,
et
al.,
1994)


The
study
was
conducted
to
identify
a
level
of
exposure
to
chromium
below
which
dermal
exposure
did
not
appear
to
elicit
an
ACD
response
30
Scientific
Considerations
Scientific
Considerations

The
Agency
has
concluded
that
the
Nethercott
study
contains
information
sufficient
for
assessing
human
risk
resulting
from
potential
dermal
exposure
to
hexavalent
chromium

Please
comment
on
whether
the
Nethercott
study
is
sufficiently
sound,
from
a
scientific
perspective,
to
be
used
to
estimate
a
safe
level
of
dermal
exposure
to
hexavalent
chromium
