Page
1
of
2
Memorandum
From:
Lynn
Zipf
USEPA/
OW/
OST
ph:
(
202)
566
1429
zipf.
lynn@
epa.
gov
To:
304(
m)
Record
(
EPA
Docket
Number
OW­
2003­
0074)

Date:
August
18,
2004
Re:
Slope
Factors
for
Dioxin
Congeners
EAD
continues
to
use
the
1985
slope
factor
for
2,3,7,8
tetrachlorodibenzo­
p­
dioxin
(
TCDD)
in
calculating
Toxic
Weighting
Factors
(
TWFs).
The
1985
slope
factor
of
TCDD
is
160,000
(
mg/
kg/
d)­
1.
(
U.
S.
EPA,.
1985)

The
slope
factors
of
the
other
congeners
are
estimated
by
multiplying
the
slope
factor
of
TCDD
by
the
respective
Toxic
Equivalency
Factor
(
TEF).
In
accordance
with
the
ongoing
reassessment
of
dioxin
(
U.
S.
EPA,
2000),
EAD
used
the
1998
WHO
TEFs
(
Van
den
Berg
et
al.,
1998)
to
adjust
the
1985
slope
factors,
and
then
calculated
the
updated
human
health
values
and
the
corresponding
TWFs.
EAD
revised
the
TWFs
for
the
17
Dioxin
and
Furan
congeners
that
have
WHO
TEFs
(
Zipf
and
Matuszko,
2004).
Table
1
gives
the
CAS
numbers,
names
and
TEF
for
the
17
congeners.

Table
1.
Dioxins
and
their
Toxic
Equivalency
Factors
CAS
Number
Chemical
Name
Abbreviated
Name
Toxic
Equivalency
Factor
CDDs
1746­
01­
6
2,3,7,8­
tetrachlorodibenzo­
p­
dioxin
2,3,7,8­
TCDD
1
40321­
76­
4
1,2,3,7,8­
pentachlorodibenzo­
p­
dioxin
1,2,3,7,8­
PeCDD
1
39227­
28­
6
1,2,3,4,7,8­
hexachlorodibenzo­
p­
dioxin
1,2,3,4,7,8­
HxCDD
0.1
57653­
85­
7
1,2,3,6,7,8­
hexachlorodibenzo­
p­
dioxin
1,2,3,6,7,8­
HxCDD
0.1
19408­
74­
3
1,2,3,7,8,9­
hexachlorodibenzo­
p­
dioxin
1,2,3,7,8,9­
HxCDD
0.1
35822­
46­
9
1,2,3,4,6,7,8­
heptachlorodibenzo­
p­
dioxin
1,2,3,4,6,7,8­
HpCDD
0.01
3268­
87­
9
1,2,3,4,6,7,8,9­
octachlorodibenzo­
p­
dioxin
1,2,3,4,6,7,8,9­
OCDD
0.0001
CDFs
51207­
31­
9
2,3,7,8­
tetrachlorodibenzofuran
2,3,7,8­
TCDF
0.1
57117­
41­
6
1,2,3,7,8­
pentachlorodibenzofuran
1,2,3,7,8­
PeCDF
0.05
57117­
31­
4
2,3,4,7,8­
pentachlorodibenzofuran
2,3,4,7,8­
PeCDF
0.5
CAS
Number
Chemical
Name
Abbreviated
Name
Toxic
Equivalency
Factor
Page
2
of
2
70648­
26­
9
1,2,3,4,7,8­
hexachlorodibenzofuran
1,2,3,4,7,8­
HxCDF
0.1
57117­
44­
9
1,2,3,6,7,8­
hexachlorodibenzofuran
1,2,3,6,7,8­
HxCDF
0.1
72918­
21­
9
1,2,3,7,8,9­
hexachlorodibenzofuran
1,2,3,7,8,9­
HxCDF
0.1
60851­
34­
5
2,3,4,6,7,8­
hexachlorodibenzofuran
2,3,4,6,7,8­
HxCDF
0.1
67562­
39­
4
1,2,3,4,6,7,8­
heptachlorodibenzofuran
1,2,3,4,6,7,8­
HpCDF
0.01
55673­
89­
7
1,2,3,4,7,8,9­
heptachlorodibenzofuran
1,2,3,4,7,8,9­
HpCDF
0.01
39001­
02­
0
1,2,3,4,6,7,8,9­
octachlorodibenzofuran
1,2,3,4,6,7,8,9­
OCDF
0.0001
For
the
congeners
of
2,3,7,8
TCDD,
EAD
used
a
toxic
equivalency
value
in
place
of
the
slope
factor
in
calculating
the
TWF.
The
toxic
equivalency
value
is
calculated
as
follows:

=
160,000
(
slope
factor)
x
TEF
For
example,
for
hexachlorodibenzo­
p­
dioxin1,2,3,7,8,9,
the
toxic
equivalency
value
is
calculated
as
follows:

=
160,000
(
slope
factor)
x
0.1
(
TEF)
=
16,000
To
understand
how
this
value
is
used
in
the
TWF
calculation,
please
see
Memorandum:
Revisions
to
TWFs
for
Dioxin
and
its
Congeners
and
Recalculated
TWPEs
for
OCPSF
and
Petroleum
Refining,
dated
August,
10,
2004
(
Zipf
and
Matuszko,
2004).

References:

U.
S.
EPA.
1985.
Health
assessment
document
for
polychlorinated
dibenzo­
p­
dioxins.
Office
of
Health
and
Environmental
Assessment,
EPA/
600/
8­
84/
814F
U.
S.
EPA
2000.
Exposure
and
Human
Health
Reassessment
of
2,3,7,8­
Tetrachlorodibenzo­
p­
Dioxin
(
TCDD)
and
Related
Compounds,
Draft.
June
2000.

Van
den
Berg,
et
al.,
1998.
Toxic
Equivalency
Factors
(
TEFs)
for
PCBs,
PCDDs,
PCDFs
for
Humans
and
Wildlife.
Environ.
Health
Perspect.
106:
775­
792.

Zipf,
Lynn
and
Jan
Matuszko.
2004.
Memorandum:
Revisions
to
TWFs
for
Dioxin
and
its
Congeners
and
Recalculated
TWPEs
for
OCPSF
and
Petroleum
Refining.
August
10,
2004.
EPA
Docket
Number
OW­
2003­
0074.
