Document ID: EPA-HQ-RCRA-2006-0097-0084
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2006-05-25T04:00Z

1
Risk
Assessment
for
Use
of
CHAT
in
Transportation
Projects
Review
by
Douglas
Crawford­
Brown
UNC­
Chapel­
Hill
Introduction
I
begin
by
noting
that
the
reasoning
behind
conclusions
in
the
document
is
not
well
laid
out.
This
doesn't
mean
the
conclusions
are
incorrect­
rather
that
the
reader
will
have
a
difficult
time
understanding
precisely
the
contention
of
the
authors.
I
provide
here
my
own
understanding
of
the
reasoning.
My
summary
and
recommendations
are
based
on
this
understanding,
so
if
I
am
incorrect,
please
let
me
know
and
I
will
re­
think
my
conclusions.

I
believe
the
authors
are
arguing
as
follows:

1.
We
want
to
understand
the
human
and
ecological
health
risks
associated
with
the
use
of
CHAT
in
construction,
specifically
in
the
construction
of
roadways.

2.
This
construction
could
potentially
involve
CHAT
in
either
encapsulated
or
unencapsulated
forms,
as
one
or
more
parts
of
the
roadway
cross­
section
in
Figure
1.

3.
Existing
data,
and
resources,
are
insufficient
to
conduct
a
full,
quantitative
risk
assessment
of
these
uses
of
CHAT.
As
a
result,
the
authors
hope
to
draw
at
least
qualitative
conclusions
about
acceptable
uses
of
CHAT.

4.
One
strategy
to
conduct
such
a
qualitative
assessment
is
to
consider
a
series
of
bounding
or
screening
calculations
that
might
place
an
upper
bound
on
the
potential
risk.

5.
These
bounding
calculations
are
of
three
types:
(
i)
the
risks
associated
with
the
piles
of
CHAT
that
exist
at
the
Tar
Creek
site,
where
at
least
effects
on
wildlife
can
be
examined;
(
ii)
the
human
health
risks
associated
with
the
use
of
unencapsulated
CHAT
on
homesites,
where
a
quantitative
risk
assessment
has
been
performed
in
the
past;
and
(
iii)
the
potential
risks
associated
with
leachate
from
both
encapsulated
and
unencapsulated
CHAT,
with
the
assumption
that
people
and/
or
wildlife
might
be
exposed
at
such
concentrations
if
the
leachate
enters
the
groundwater
or
finds
its
way
to
the
surface
undiluted.

6.
Existing
evidence
is
at
least
sufficient
to
suggest
that
the
dominant
risks
are
from
exposures
to
the
metals
lead,
cadmium
and
zinc,
and
so
these
three
pollutants
will
form
the
basis
for
any
of
the
three
risk
characterizations
in
items
5i
through
5iii
above.
The
assumption
appears
to
be
that
if
the
risks
from
these
three
pollutants
are
acceptable,
the
cumulative
risk
from
CHAT
constituents
also
will
be
acceptable.

7.
With
respect
to
item
5i,
evidence
is
presented
to
suggest
that
wildlife
exposed
to
CHAT
on
or
near
contaminated
sites
with
mill
tailings
show
both
elevated
levels
of
these
2
three
pollutants
in
their
tissues
and
an
elevation
of
some
adverse
effects.
From
this,
one
might
conclude
that
the
"
raw"
tailings
pose
a
risk
to
the
health
of
wildife
and
perhaps
humans
(
if
the
humans
were
exposed
at
the
levels
of
the
wildlife,
and
are
approximately
as
sensitive).

8.
With
respect
to
item
5ii,
evidence
is
presented
(
from
a
previously
published
risk
assessment)
that
use
of
unencapsulated
CHAT
in
at
least
home
settings
(
as
fill,
etc),
poses
an
unacceptable
health
risk.
While
the
exposures
through
use
of
CHAT
on
homesites
presumably
is
significantly
higher
than
exposures
associated
with
just
living
near
a
road
constructed
in
part
from
unencapsulated
CHAT,
data
are
insufficient
at
present
to
rule
out
unacceptably
large
health
risks
from
the
latter
uses.

9.
With
respect
to
item
5iii,
experimental
evidence
is
presented
that
the
leachate
from
unencapsulated
CHAT
contains
one
or
more
of
the
three
pollutants
at
a
concentration
above
levels
of
public
health
concern.
The
assumption
appears
to
be
that,
in
the
worst
case,
this
leachate
reaches
the
groundwater
and
is
undiluted
appreciably,
or
perhaps
that
the
leachate
finds
its
way
to
the
ground
surface
and
exposures
occur
through
exposure
to
this
liquid.
In
either
case,
the
health
risks
would
be
unacceptable.

10.
Further
evidence
suggests
that
the
leachate
from
encapsulated
CHAT
(
especially
from
CHAT
used
in
hot
mix
asphalt)
does
not
contain
the
three
pollutants
at
a
concentration
above
levels
of
health
concern.
Therefore,
even
in
the
worst
case
of
exposure
to
the
leachate,
adverse
effects
are
unlikely.

11.
None
of
the
existing
data
address
the
health
risks
associated
with
construction
processes
for
a
road,
including
manufacturing
of
the
encapsulated
CHAT,
transport
of
the
product,
or
activities
during
construction.
As
a
result,
these
risks
cannot
be
estimatedinstead
only
risks
associated
with
the
final
product
of
a
constructed
road
can
be
considered.
However,
the
claim
is
that
State
and
OSHA
regulations
should
be
sufficient
to
protect
workers
during
the
construction
cycle
(
no
evidence
is
presented
of
this
in
the
present
document),
and
residents
will
be
exposed
only
for
a
short
period
so
the
Average
Daily
Rate
of
Intake
(
ADRI)
will
be
below
levels
of
concern
when
averaged
over
a
lifetime.

12.
Taking
these
arguments
into
account,
it
is
concluded
that
use
of
unencapsulated
CHAT
in
road
construction
probably
is
unwarranted
from
the
perspective
of
public
health
risks,
but
that
encapsulated
CHAT,
particularly
in
the
form
of
hot
mix
asphalt,
may
be
warranted
even
under
the
worst­
case
scenarios
of
exposure
to
leachate
described
in
the
report.

General
Comments
The
reasoning
in
the
Introduction
is
what
I
take
to
be
the
basis
for
conclusions
drawn
by
the
authors.
My
first
recommendation
is
that
this
reasoning,
or
whatever
reasoning
was
used
by
the
authors,
be
outlined
clearly
in
the
report.
The
reader
currently
is
left
to
reconstruct
the
reasoning
based
on
a
variety
of
assertions
made
at
various
points
in
the
3
text.
It
took
me
several
readings
of
the
document
to
begin
to
understand
why,
for
example,
the
authors
were
talking
about
leachate
concentrations.
It
was
not
evident
at
first
reading
that
this
had
anything
to
do
with
risk
(
was
it
being
proposed
that
people
might
drink
the
leachate,
bathe
in
it,
etc?).
I
believe
my
argument
in
the
Introduction
is
what
the
authors
had
in
mind,
but
this
is
not
at
all
clear
in
the
document.
I
am
suggesting
here
that
the
document
presents
information,
but
then
does
not
lead
the
reader
to
understand
the
implications
of
those
data.

The
problem
is
in
part
compounded
by
an
assertion
early
on
that
the
document
will
use
a
weight
of
evidence
format.
I
can
find
nothing
in
the
current
document
to
support
this
claim.
A
weight
of
evidence
determination
requires
several
stages:
(
i)
a
presentation
of
the
available
data
(
which
is
adequate
in
the
current
document);
(
ii)
a
summary
of
the
steps
of
reasoning
that
will
be
needed
(
which
is
not
adequate
in
the
current
document);
(
iii)
an
allocation
of
specific
bodies
of
data
to
specific
steps
in
the
reasoning
(
which
is
present
in
the
current
document);
(
iv)
a
summary
conclusion
from
the
data
with
respect
to
each
specific
step
in
the
reasoning­
a
form
of
at
least
qualitative
meta­
analysis
(
which
is
present
in
the
current
document
in
part
because
there
is
only
one
body
of
data
available
each
for
most
stages
in
the
reasoning);
(
v)
a
clear
statement
of
the
summary
conclusion
for
the
assessment
and
a
characterization
(
qualitative
or
quantitative)
of
the
strength
of
this
conclusion
with
respect
to
the
available
data
(
contained
in
part
in
the
current
document).
I
don't
believe
the
current
document
organizes
the
material
in
a
way
that
makes
this
weight
of
evidence
assessment
evident,
although
I
do
believe
the
authors
have
the
raw
material
in
the
document
to
do
this.
It
is
more
a
matter
of
organization
and
explication
than
of
doing
any
new
analyses.

I
remain
somewhat
unclear
as
to
how
the
authors
intended
to
use
the
information
on
TCLP
and
SPLP
tests.
I
believe
they
may
have
intended
to
use
it
as
described
in
the
Introduction
above,
but
this
is
never
stated
directly.
I
suppose
the
references
to
groundwater
contamination
are
meant
to
provide
this
clue,
but
I
have
looked
for,
and
not
found,
a
direct
statement
that
a
screening
or
bounding
assumption
might
be
that
this
leachate
reaches
the
groundwater
(
perhaps
a
shallow
aquifer)
undiluted
and
is
then
consumed
at
this
concentration
(
perhaps
a
plume
of
the
leachate
moves
undiluted
to
a
point
of
withdrawal
of
the
groundwater?).
If
this
is
the
assumption
being
made,
it
could
be
addressed
through
the
addition
of
a
few
well­
placed
sentences
to
make
it
evident
to
the
reader.

There
is
a
possibility
of
even
more
dramatic
conclusions
to
be
drawn
from
the
leachate
results.
While
I
am
not
suggesting
that
this
must
be
done,
consider
an
assumption
that
the
relative
leachate
concentrations
between
encapsulated
and
unencapsulated
forms
are
a
sort
of
measure
of
general
mobility
of
the
metals
from
the
CHAT.
If
one
compares,
for
example,
Tables
5
and
14,
it
is
evident
that
leachability
of
the
metals
from
the
encapsulated
form
is
well
below
that
of
the
unencapsulated
form
(
as
expected).
The
risk
assessment
from
Ecology
(
1996)
showed
unacceptably
high
health
risks
associated
with
use
of
unencapsulated
CHAT,
but
the
risks
were
not
dramatically
above
levels
of
concern.
They
are,
for
the
most
part,
within
an
order
of
magnitude
of
acceptable
risk
levels.
The
TCLP
and
SPLP
results
for
encapsulated
CHAT,
however,
are
more
than
an
4
order
of
magnitude
below
those
for
unencapsulated
CHAT.
It
is
possible
to
argue,
therefore,
that
use
of
encapsulated
CHAT
rather
than
unencapsulated
CHAT
at
or
near
the
homes
in
the
Ecology
(
1996)
study
would
have
led
to
at
least
a
proportional
reduction
in
risk,
yielding
risks
that
are
below
levels
of
concern.
This
should
in
turn
suggest
that
the
residents
of
those
homes
would
experience
acceptable
levels
of
risk
if
encapsulated
rather
than
unencapsulated
CHAT
had
been
used.
If
use
of
encapsulated
CHAT
on
homesites
poses
higher
health
risks
than
use
on
a
roadway,
the
risk
in
the
latter
case
also
will
be
acceptable,
even
if
they
lived
adjacent
to
roadways
constructed
with
encapsulated
CHAT.

The
reasoning
in
the
previous
paragraph
is
something
like
the
following:

1.
We
can't
conduct
a
full
multimedia,
aggregate,
risk
assessment
for
residents
of
homes
near
roads
constructed
with
CHAT.

2.
We
have,
however,
a
full
multimedia,
aggregate,
risk
assessment
for
residents
of
homes
where
unencapsulated
CHAT
was
used
in
some
form
during
construction
(
infill,
etc).

3.
This
full
assessment
in
step
2
yielded
a
measure
of
risk
X,
which
has
been
judged
unacceptable.

4.
The
use
of
unencapsulated
CHAT
in
a
roadway
could
produce
risks
in
individuals
living
near
this
roadway
that
are
in
some
sense
bounded
(
on
the
upper
end)
by
a
risk
of
X.

5.
The
ratio
of
leaching
ability
for
encapsulated
over
unencapsulated
CHAT
is
approximately
F.
This
ratio
is
an
approximate
measure
of
the
general
mobility
of
the
three
metals
of
concern
in
the
environment.

6.
As
a
result,
an
approximate
upper
bound
on
the
risks
to
individuals
using
encapsulated
CHAT
in
the
same
aspects
of
home
construction
as
in
2
might
be
approximately
X
*
F.

7.
This
value
of
X
*
F
might
then
be
an
upper
bound
on
the
risk
to
individuals
living
near
a
roadway
built
with
encapsulated
CHAT,
by
analogy
with
step
4
above.

8.
The
ratio
of
X
over
a
level
of
unacceptable
risk
is
significantly
smaller
than
the
inverse
of
F,
and
so
the
product
of
X
*
F
will
be
acceptable.
This
establishes
as
a
first
approximation
that
the
risks
from
encapsulated
CHAT
in
roadways
will
be
acceoptable.

Again,
I
am
not
suggesting
that
such
reasoning
must
be
presented
in
the
document,
but
it
does
seem
to
me
a
possibility
for
further
articulating
your
position.

Some
Specific
Comments
1.
On
page
3­
6,
it
is
mentioned
that
"
Other
encapsulated
uses 
are
typically
covered
by
a
layer
of
asphalt ".
This
presumably
is
to
give
assurance
that
these
"
other
uses"
will
not
5
be
subject
to
exposure
to
air
and/
or
erosion,
leaving
only
the
groundwater
pathway.
This
assumes,
however,
that
the
upper
layer
remains
intact,
which
becomes
problematic
if
there
are
significant
potholes.
I
assume
such
potholes
would
represent
only
a
small
fraction
of
the
overall
surface
of
the
road,
so
this
may
be
a
good
assumption.
But
the
issue
should
at
least
be
raised
and
then
put
to
rest
in
some
way.

2.
Figure
3
is
not
clear
to
me.
There
are
several
boxes
(
Dispersion,
Deposition
and
Indoor
dust)
that
are
unconnected
to
any
other
boxes.
It
is
not
clear
what
they
are
intended
to
represent.

3.
On
page
4­
1,
there
is
the
statement
that
"
almost
90%
of
the
raw
chat
matrix
was
considered
non­
hazardous
when
incorporated ".
I
am
not
sure
what
this
means.
Does
it
mean
90%
of
the
elements
or
compounds
were
each
non­
hazardous
when
incorporated,
or
that
their
toxicity
was
in
some
way
reduced
by
90%
for
each
element
or
compound?

4.
Section
4.0
summarizes
the
various
studies
examined.
However,
the
results
of
those
studies
are
not
presented
in
this
section,
being
presented
instead
later.
As
a
reader,
I
found
this
odd.
I
kept
marking
in
the
margins
phrases
such
as "
So,
what
were
the
actual
numerical
results?".
The
relevant
results
do
appear
later
in
the
document,
so
this
early
section
of
Section
4.0
can
be
viewed
as
simply
a
qualitative
statement
that
data
do
in
fact
exist
(
and
will
be
described
later).
But
as
a
reader,
my
attention
was
not
directed
to
this
fact,
and
so
I
ended
that
Section
thinking
it
was
woefully
inadequate
in
providing
the
data
themselves.
This
could
be
dealt
with
either
by
including
the
actual
data
in
this
Section
under
each
review
of
a
citation,
or
starting
the
Section
with
a
note
to
the
reader
to
explain
the
organization
you
have
chosen
(
i.
e.
a
qualitative
description
of
the
kinds
of
data
in
each
paper,
followed
later
by
discussion
of
the
actual
data
in
the
context
of
specific
calculations
or
conclusions).

5.
The
discussion
of
the
"
baseline
risk
assessment"
(
and
I
don't
know
what
"
baseline"
means
in
this
case,
since
it
usually
refers
to
a
risk
in
the
absence
of
any
policy)
starting
on
page
4­
19
seems
to
me
inadequate,
especially
given
some
of
the
potential
reasoning
I
provided
previously
(
particularly
the
argument
that
X
*
F
might
be
acceptably
small).
I
have
reviewed
the
Ecology
(
1996)
paper
and
it
seems
to
me
that
providing
the
numerical
results
from
that
study
would
bolster
your
case
here,
given
that
X
*
F
appears
to
me
to
lead
to
acceptable
risk
levels.
But
the
reader
can't
draw
this
conclusion
from
the
qualitative
details
provided
in
the
current
document.

In
addition,
the
Ecology
(
1996)
study
shows
that,
at
least
for
lead,
the
inhalation/
dust
pathway
dominates.
This
is
good
for
the
extrapolation
to
encapsulated
CHAT,
since
it
is
likely
that
leaching
will
dominate
in
that
case.
Let's
assume
that
about
82%
of
the
risk
in
the
Ecology
(
1996)
study
was
from
inhalation
(
the
value
cited
for
lead
in
the
current
document,
and
lead
is
probably
the
metal
of
most
concern).
It
can
be
assumed
that
this
route
will
be
largely
removed
from
the
use
of
encapsulated
CHAT,
leaving
the
leaching
part
as
the
dominant
pathway.
That
in
turn
would
suggest
that
the
value
of
X
*
F
given
previously
as
an
upper
bound
might
even
further
overstate
the
risks.
If
the
remaining
18%
of
risk
from
the
Ecology
(
1996)
study
were
all
from
leachate,
the
risk
from
use
of
6
encapsulated
CHAT
might
be
between
0.18
*
X
*
F
(
if
the
inhalation
pathway
was
completely
removed
by
encapsulation)
and
X
*
F
(
if
the
inhalation
pathway
remained
and
the
leachability
measure
were
taken
as
a
measure
of
more
general
mobility
into
the
environment
by
all
pathways).
In
any
event,
more
quantitative
detail
on
the
full
risk
assessment
is
in
order
here.

Charge
Questions
To
address
these,
I
reviewed
the
document
and
each
of
the
citations,
and
did
an
enhanced
literature
search
through
the
internet,
through
various
literature
search
engines,
and
through
journals
likely
to
contain
such
publications.

1.
I
could
find
no
additional
studies
that
are
relevant
to
these
calculations.
The
new
NAAQS
Criteria
Document
for
lead
(
which
I
am
reviewing
for
the
Agency)
does
provide
some
insights
into
transport
by
air,
but
these
are
generic
and
do
not
provide
insights
specific
to
the
use
of
CHAT
in
roadways,
even
during
transportation.
There
are
sufficient
models
available
to
perform
at
least
some
bounding
calculations
of
the
risk
associated
with
this
pathway
(
these
would
be
the
same
ones
used
for
the
National­
Scale
Air
Toxics
Assessment
or
NATA),
but
the
current
assessment
is
predicated
on
the
claim
that
such
modeling
efforts
are
not
warranted
or
feasible
at
present,
in
part
because
one
needs
the
source
term
to
use
the
air
dispersion
models,
and
this
source
term
is
not
available
at
present.

2.
The
report
does
present
the
data
in
an
unbiased
manner,
but
as
I
described
earlier,
the
assumptions
underlying
any
reasoning
performed
by
the
authors
is
not
at
all
clear.
This
part
of
the
assessment
can
be
improved
greatly.
In
general,
I
would
say
that
(
i)
the
presentation
of
the
data
is
good,
(
ii)
the
evaluation
of
the
data
is
good,
(
iii)
the
explanation
of
the
relevance
of
the
data
to
steps
of
reasoning
is
inadequate,
and
(
iv)
the
assembly
of
the
data
to
show
how
they
support
the
final
conclusion
is
inadequate.
The
document
does
not
represent
an
adequate
weight
of
evidence
discussion.

3.
I
think
the
data
marginally
support
the
conclusions.
The
problem
lies
not
in
the
quality
of
the
data
themselves
(
the
methods
generally
are
acceptable),
but
in
the
assumptions
that
must
be
introduced
on
the
relevance
of
leaching
results
in
drawing
conclusions
on
risk.
The
authors
may
need
to
better
establish
that
leaching
into
groundwater
is
the
dominant
pathway,
or
at
least
state
clearly
at
the
beginning
that
this
will
be
the
assumption
for
encapsulated
CHAT.
I
also
suspect
that
results
for
leaching
may
be
highly
variable,
and
the
sampling
to
date
has
not
been
extensive.
The
use
of
milling
of
encapsulated
CHAT
to
reflect
weathering
worries
me
a
bit,
because
I
am
not
convinced
this
reflects
all
forms
of
weathering
(
especially
if
there
is
differential
weathering
of
the
CHAT
and
of
the
matrix,
which
I
suspect
is
the
case).
However,
the
value
of
F
mentioned
previously
is
sufficiently
small
that
I
doubt
additional
samples
would
produce
a
new
value
that
is
significantly
larger.
I
suspect
a
larger
value
of
F
might
be
associated
with
road
materials
that
pass
through
large
freeze­
thaw
cycles
during
a
year,
but
the
areas
of
the
country
using
the
CHAT
for
roadways
probably
don't
have
this
issue.
7
An
area
where
I
am
less
comfortable
with
conclusions
is
in
the
assumption
of
effects
on
wildlife
near
contaminated
lands.
Those
data
seem
to
me
too
poor
to
justify
a
claim
of
adverse
effects
associated
with
unencapsulated
CHAT.
The
measurements
of
effect
are
not
convincing.
This
result,
however,
does
not
play
a
central
role
in
the
overall
conclusions.

4.
I
have
already
suggested
changes
to
the
methodology,
or
at
least
to
the
reasoning
used
to
draw
conclusions.
I
don't
believe
you
can
do
a
quantitative
uncertainty
analysis
here.
Rather,
you
must
focus
on
bounding
calculations
and
show
the
"
margin
or
safety",
"
margin
of
error",
"
margin
of
exposure"
or
other
related
concept
associated
with
these
calculations.
Again,
I
believe
you
can
use
X
*
F
as
a
kind
of
bounding
calculation,
and
then
show
how
close
this
is
to
levels
of
health
concern.
If
this
is
done,
I
believe
you
will
find
that
the
plausible
upper
bound
of
risk
for
use
of
encapsulated
CHAT
remains
below
the
level
of
concern.

5.
I
think
the
current
assessment
can
be
used
to
state
only
one
thing:
that
the
use
of
CHAT
in
encapsulated
form,
and
specifically
for
hot
mixed
asphalt,
will
produce
acceptable
levels
of
risk
to
individuals
living
near
these
constructed
roadways.
I
don't
think
you
can
state
what
those
levels
of
risk
ARE,
only
that
they
are
likely
to
be
below
levels
of
concern.
I
don't
think
the
data
support
use
of
CHAT
in
unencapsulated
form.
They
show
the
risks
will
be
unacceptable
under
some
uses
such
as
in
home
construction.
Further,
the
data
are
insufficient
to
allow
extrapolation
from
this
home
use
to
road
use,
other
than
in
the
form
of
a
bounding
calculation
of
the
plausible
upper
bound
on
the
risk
from
use
of
unencapsulated
CHAT
in
roadways­
an
upper
bound
risk
that
appears
unacceptable.

The
data
also
are
insufficient
to
establish
the
risks
from
use
of
encapsulated
CHAT
in
forms
other
than
HMA.
All
we
can
really
say
is
that
these
uses
should
be
between
the
risk
from
HMA
(
which
is
acceptable)
and
the
risk
from
unencapsulated
CHAT
in
home
construction
(
which
is
unacceptable).
It
is
likely
that
the
risk
from
"
other"
encapsulated
forms
will
be
closer
to
HMA
than
to
unencapsulated
forms,
but
it
is
not
possible
to
state
how
close
it
will
be
to
the
HMA
risks.

I
worry
a
bit
about
the
argument
presented
for
lack
of
concern
over
risks
during
road
construction.
The
argument
appears
to
be
(
and
correct
me
if
I
am
misstating
that
argument)
that
there
may
be
elevated
exposures
during
construction,
but
these
will
be
short
in
duration
and,
when
averaged
over
the
Averaging
Time
of
any
calculation
of
Average
Daily
Rate
of
Intake,
will
produce
ADRI
values
that
are
acceptable.
The
one
point
that
worries
me
here
is
the
possibility
of
short­
term
exposures
of
the
fetus
and
neonates
during
critical
and
sensitive
periods
of
growth,
where
even
relatively
short­
term
exposures
can
be
problematic.
I
see
nothing
in
the
present
document
(
or
even
anything
in
the
existing
literature)
to
either
characterize
or
alleviate
this
concern.
If
it
remains
a
concern,
I
see
no
way
to
address
it
other
than
a
full
modeling
study.

I
close
with
a
comment
on
health
risk
from
lead.
The
human
health
risks
cited
in
the
document
reviewed
here
were
developed
when
the
level
of
concern
for
lead
in
the
blood
8
was
10
µ
g/
dL.
The
OAQPS
is
considering
revising
this
target
downwards
significantly,
perhaps
even
as
low
as
2
to
3
µ
g/
dL.
If
this
occurs,
much
of
the
"
margin
of
safety"
I
mentioned
above
for
encapsulated
CHAT
may
be
eroded.
The
only
advice
I
can
offer
is
to
keep
in
touch
with
OAQPS
on
this
issue.