Content uploaded by Matthew Keifer
Author content
All content in this area was uploaded by Matthew Keifer on Jan 12, 2015
Content may be subject to copyright.
Children's
Health
Articles
Biologically
Based
Pesticide
Dose
Estimates
for
Children
in
an
Agricultural
Community
Richard
A.
Fenske,
John
C.
Kissel,
Chensheng
Lu,
David
A.
Kalman,
Nancy
J.
Simcox,
Emily
H.
Allen,
and
Matthew
C.
Keifer
Department
of
Environmental
Health,
School
of
Public
Health
and
Community
Medicine,
University
of
Washington,
Seattle,
Washington,
USA
Current
pesticide
health
risk
assessments
in
the
United
States
require
the
characterization
of
aggregate
exposure
and
cumulative
risk
in
the
setting
of
food
tolerances.
Biologic
monitoring
can
aggregate
exposures
from
all
sources
and
routes,
and
can
integrate
eposures
for
chemicals
with
a
common
mechanism
of
action.
Its
value
was
demonstrated
in
a
recent
study
of
organophosphorus
(OP)
pesticide
exposure
among
109
children
in
an
agricultural
community
in
Washington
State;
91
of
the
children
had
parents
working
in
agriculture.
We
estimated
individual
OP
pesticide
doses
from
urinary
metabolite
concentrations
with
a
eteristic
steady
state
model,
and
com-
pared
them
to
toxicologic
reference
values.
We
evaluated
doses
by
assuming
that
metabolites
were
attributable
entirely
to
either
azinphos-methyl
or
phosmet,
the
two
OP
pesticides
used
most
fre-
quently
in
the
region.
Creatinine-adjusted
average
dose
estimates
during
the
6-
to
8-week
spray-
ing
season
ranged
from
0
to
36
pgkg/day.
For
children
whose
parents
worked
in
agriculture
as
either
orchard
applicators
or
as
fieldworkers,
56%
of
the
doses
estimated
for
the
spray
season
xceeded
the
U.S.
Environmental
Protection
Agency
(EPA)
chronic
dietary
reference
dose,
and
19%
exceeded
the
World
Health
Or
tion
acceptable
daily
intake
values
for
azinphos-methyl
The
corresponding
values
for
children
whose
parents
did
not
work
in
agriculture
were
44
and
22%,
respectively.
The
percentage
of
ciildren
exceeing
the
relevant
reference
values
for
phosmet
was
substantialy
lower
(<
10%).
Single-day
dose
estimates
ranged
from
0
to
72
pg/kg/day,
and
26%
of
these
exceeded
the
EPA
acute
reference
dose
for
azinphos-methyl.
We
also
generated
dose
estimates
by
adjustment
for
total
daily
urine
volume,
and
these
estimates
were
consistently
higher
tha
the
creatnine-adjusted
estimates.
None
of
the
dose
esties
exceeded
the
empiril
derived
no-observable-adverse-effiet
leels
for
these
compounds.
The
study
took
place
in
an
-alll
region
during
a
period
of
active
spraying,
so
the
dose
estimates
for
this
population
should
not
be
considered
representative
of
exposures
in
the
general
population.
The
findings
indicate
that
chil-
dren
living
in
agricultural
regions
represent
an
important
subpopulation
for
public
health
evalua-
tion,
and
that
their
exposures
ial
within
a
range
of
regulatory
concern.
They
also
demonstrate
that
biologically
based
eposure
measures
can
provide
data
for
health
risk
evaluations
in
such
popula-
tions.
Key
words;
biologic
monitoring,
children,
dose,
exposure,
organophosphorus
pesticides,
urinary
metabolites.
Environ
Health
Perspea
108:515-520
(2000).
[Online
21
April
2000]
bttp//ehpnetl1.niehs.nib.gol/docs/2OOO1O8p5)5-520fnskelabs.tract.hgml
The
exposure
of
children
to
environmental
toxicants
has
become
the
focus
of
increased
public
health
concern
over
the
last
decade
(1,.
The
discovery
of
an
association
between
subtle
neurologic
effects
and
low-level
lead
exposure
in
children
(3),
as
well
as
findings
of
developmental
toxicity
from
low-level
intra-
uterine
exposure
to
polychlorinated
biphenyls
(4),
has
led
many
researchers
to
construct
analogous
hypotheses
related
to
pesticides.
Recent
reports
on
the
developmental
neuro-
toxicity
of
the
insecticide
chlorpyrifos
lend
support
to
this
area
of
investigation
(5,6).
The
Food
Quality
Protection
Act
of
1996
(FQPA)
(7)
mandates
that
the
eval-
uation
of
pesticide
health
risks
take
into
account
aggregate
exposure
and
cumulative
risk.
Consequently,
the
U.S.
Environmental
Protection
Agency
(EPA)
must
consider
a)
all
sources
and
routes
of
nonoccupational
expo-
sure
to
a
particular
pesticide
in
setting
accept-
able
residue
levels
in
food
(8),
and
b)
the
health
risks
resulting
from
simultaneous
or
sequential
exposure
to
groups
of
pesticides
that
exhibit
a
common
mechanism
of
action.
The
requirement
to
consider
the
cumulative
risk
of
exposure
to
similarly
acting
pesticides
contrasts
with
the
traditional
method
of
reg-
ulating
on
a
chemical-by-chemical
basis,
as
if
each
chemical
acted
in
isolation
($.
Exposure
models
are
normally
construct-
ed
from
information
on
environmental
con-
centrations
(e.g.,
residues
on
food),
behavior
(e.g.,
the
intake
of
particular
foods),
and
absorption
processes
(e.g.,
models
extrapolat-
ed
from
animal
studies).
Only
dietary
mod-
els
need
be
developed
for
some
compounds;
for
others,
a
full
range
of
models
encompass-
ing
diet,
drinking
water,
and
residential
use
are
required.
Each
of
these
models
contains
uncertainties
regarding
physical
and
biologic
processes.
The
multiplicity
of
models
and
the
accompanying
uncertainties
can
lead
to
the
generation
of
exposure
estimates
that
differ
by
several
orders
of
magnitude.
The
draft
risk
assessment
of
chlorpyrifos
published
by
the
EPA
and
the
accompanying
critique
by
Dow
Agrosciences
(Indianapolis,
IN)
provide
a
current
example
of
how
divergent
risk
esti-
mates
can
be
with
this
approach
(10).
The
difficulty
of
arriving
at
accurate
estimates
is
compounded
when
exposures
or
doses
from
a
group
of
chemicals
are
combined
to
calculate
cumulative
risk.
As
Figure
1
shows,
up
to
39
aggregate
exposure
assessments
need
to
be
developed
to
calculate
cumulative
risk
for
one
dass
of
compounds-the
organophosphorus
(OP)
pesticides.
The
EPA
selected
OP
pesticides
as
among
the
first
dasses
of
compounds
to
be
regulated
under
the
FQPA
(11).
OP
pesticides
were
chosen
because
they
are
widely
used
as
insecti-
cides
in
both
agricultural
and
residential
set-
tings
and
because
they
exhibit
a
common
mechanism
of
action-the
inhibition
of
cholinesterase,
an
essential
nervous
system
enzyme
(12).
These
pesticides
tend
to
be
metabolized
relatively
quickly
and
excreted
primarily
in
the
urine
(13).
Nearly
all
metab-
olize
to
a
dialkylphosphate
moiety
consisting
of
a
phosphate
and
two
ethyl
or
methyl
esters.
We
propose
that
the
measurement
of
dialkylphosphate
metabolites
in
children's
urine
has
utility
for
estimating
dose
ranges
for
the
OP
pesticides
and
thus
can
usefully
inform
a
discussion
of
pesticide
health
risks.
We
examined
exposure
pathways
for
the
pop-
ulation
discussed
here
in
another
paper
(14);
these
pathways
include
an
analysis
of
pesti-
cides
in
housedust,
the
effect
of
residential
proximity
to
agricultural
spraying
on
expo-
sure,
and
the
role
of
parental
transfer
of
pesticides
from
the
workplace
to
the
home.
An
earlier
report
by
Loewenherz
et
al.
(15)
Address
correspondence
to
R.
Fenske,
Department
of
Environmental
Health,
Box
357234,
University
of
Washington,
Seattle,
WA
98195
USA.
Telephone:
(206)
543-0916.
Fax:
(206)
616-2687.
E-mail:
rfenske@u.washington.edu
We
thank
G.
Bellamy,
E.
Doran,
R.
Hahne,
I-C.
Lee,
C.
Loewenherz,
T.
Moate,
J.
Touchstone,
and
K.
Yuknavage.
This
work
was
supported
by
the
U.S.
Environmental
Protection
Agency
(cooperative
agreement
R819186-01),
the
Association
of
Schools
of
Public
Health
(cooperative
agreement
S147-14/16),
and
the
National
Institute
for
Occupational
Safety
and
Health
(Pacific
Northwest
Agricultural
Safety
and
Health
Center,
cooperative
agreement
U07/CCU012926).
Received
20
July
1999;
accepted
2
February
2000.
Environmental
Health
Perspectives
*
VOLUME
108
1
NUMBER
61
June
2000
515
Children's
Health
*
Fenske
et
al.
used
a
biomarker
in
a
subset
of
this
popula-
tion
to
evaluate
exposure
sources,
but
did
not
present
OP
pesticide
dose
estimates.
We
report
here
dose
estimates
based
on
two
of
the
three
dialkylphosphate
metabo-
lites
common
to
the
dimethyl
OP
pesticides
and
compare
the
estimates
to
toxicologic
benchmarks
currently
used
by
the
EPA
as
well
as
those
published
by
the
World
Health
Organization
(WHO).
Materials
and
Methods
The
study
from
which
these
data
were
derived
took
place
in
the
agricultural
region
surrounding
Wenatchee,
Washington,
from
May
to
July
1995.
Our
earlier
report
(15)
induded
detailed
descriptions
of
population
recruitment,
sample
collection,
and
sample
analysis,
all
of
which
are
applicable
to
the
data
set
presented
here.
We
collected
urine
samples
from
109
children
(up
to
6
years
of
age).
Ninety-one
of
the
children
were
from
households
with
at
least
one
adult
engaged
in
field-based
agriculture
(periodic
orchard
pesticide
applications
and/or
field
labor
activ-
ities;
none
were
commercial
pesticide
appli-
cators);
these
were
defined
as
agricultural
children.
The
other
18
children
were
from
households
that
did
not
include
agricultural
workers,
and
were
located
at
least
one-quarter
Figure
1.
Current
regulatory
procedures
require
modeling
of
each
source,
exposure
pathway,
and
expo-
sure
route
to
determine
aggregate
exposure
to
a
single
pesticide.
GI,
gastrointestinal.
Cumulative
risk
assessment
requires
that
all
of
these
aggregate
exposure
assessments
be
combined
to
produce
a
risk
estimate
for
compounds
that
have
a
common
mechanism
of
action.
Approximately
39
OP
pesticides
are
under
review
by
the
U.S.
Environmental
Protection
Agency.
516
VOLUME
108
1
NUMBER
6
of
a
mile
(402
m)
from
treated
farmland;
these
were
defined
as
reference
children.
A
single
child
from
each
household
was
identi-
fied
as
a
focus
child
for
statistical
purposes.
Criteria
for
focus
child
selection
were
com-
pletion
of
two
spot
urine
samples
and
creati-
nine
measurements
for
both
samples.
We
then used
random
selection
for
families
with
more
than
one
child
meeting
the
above
crite-
ria.
There
were
62
agricultural
and
14
refer-
ence
children
designated
as
focus
children.
The
May-July
study
period
coincided
with
pesticide
spraying
for
the
coddling
moth,
the
primary
apple
insect
pest
in
the
region.
Two
OP
pesticides-azinphos
methyl
and
phosmet-were
the
compounds
of
highest
use.
Urine
samples
were
single
voids
collected
at
the
convenience
of
the
child
and
parent.
Two
such
samples
were
collected
from
each
child;
the
second
sample
was
collected
3-7
days
after
the
first.
All
samples
were
collected
from
this
population
within
the 6-
to
8-week
spraying
season.
We
obtained
informed
consent
from
parents
fol-
lowing
the
procedures
established
by
the
University
of
Washington
Human
Subjects
Review
Committee
(Seattle,
WA).
Dimethyl
phosphate
(DMP),
dimethyl
thiophosphate
(DMTP),
and
dimethyl
dithiophosphate
(DMDTP)
are
the
three
common
metabolites
of
dimethyl
OP
pesti-
cides.
We
measured
metabolite
concentra-
tions
by
gas
chromatography
at
the
University
of
Washington
Environmental
Health
Labo-
ratory
in
Seattle.
DMP
measurements
were
inconsistent
across
batches,
and
recovery
efficiencies
were
low
(<
50%)
and
variable.
The
DMP
values
were
ultimately
deemed
unreliable
by
the
laboratory,
so
we
did
not
indude
them
in
this
analysis.
We
used
the
fol-
lowing
reporting
conventions
for
DMTP
and
DMDTP:
samples
with
no
analytical
response
were
considered
nondetectable
and
were
assigned
a
value
of
zero;
samples
with
peak
response
less
than
the
limit
of
quantitation
(LOQ)
(0.015-0.030
pg/mL)
were
assigned
one-half
the
batch
LOQ;
and
samples
with
peak
response
equivalent
to
or
greater
than
the
LOQ
were
reported
as
numerical
values
in
micrograms
per
milliliter.
Dose
estimation
procedures.
We
selected
a
deterministic
approach
to
dose
estimation
because
deterministic
calculations
are
rela-
tively
simple
and
are
consistent
with
current
regulatory
procedures
for
pesticides
(10.
A
deterministic
model
also
allows
direct
back-
calculation
of
doses
from
metabolite
concen-
trations,
whereas
a
probablistic
approach
applied
to
these
data
would
require
deconvo-
lution.
For
our
purposes-approximation
of
a
range
of
doses
in
children
for
comparison
with
regulatory
benchmarks-the
determin-
istic
approach
appeared
to
be
the
most
straightforward.
5I
June
2000
*
Environmental
Health
Perspectives
Children's
Health
*
Pesticide
dose
estimates
for
children
We
converted
metabolite
concentrations
to
OP
pesticide
doses
in
two
ways.
Estimates
derived
by
averaging
each
child's
two
samples
were
designated
"spray
season
doses"
and
were
considered
a
best
estimate
of
daily
expo-
sure
for
the
6-
to
8-week
spraying
season
dur-
ing
which
the
samples
were
collected.
In
a
few
cases
only
a
single
urine
sample
was
avail-
able,
and
it
was
used
as
the
best
estimate
of
spray
season
exposure.
Estimates
derived
from
a
single
urine
sample
were
designated
"single-day
doses"
and
were
considered
to
represent
a
child's
dose
for
1
day.
We
used
four
steps
for
dose
calculation.
First,
we
adjusted
metabolite
concentrations
for
incomplete
extraction
efficiency
(80
and
62%
for
DMTP
and
DMDTP,
respectively).
Second,
we
converted
metabolite
concentra-
tions
to
their
molar
equivalents
and
summed
them
to
produce
a
single
dialkylphosphate
concentration
for
each
sample.
Third,
we
converted
dialkyl-phosphate
molar
concen-
trations
to
OP
pesticide
concentrations
by
the
use
of
an
OP
pesticide
molecular
weight
of
317
g/mol
(the
molecular
weight
of
both
azinphos-methyl
and
phosmet).
Fourth,
we
converted
OP
pesticide
concentrations
to
doses
either
with
age-specific
daily
creatinine
excretion
values
(16)
or
with
age-specific
esti-
mates
of
daily
urinary
excretion
volume
(17).
Each
of
these
measures
was
then
divided
by
body
weight
(18)
to
produce
the
final
dose
estimates.
We
considered
the
values
derived
from
these
dose
calculations
to
be
equivalent
to
what
is
commonly
referred
to
as
absorbed
dose
(19).
The
dose
calculations
included
several
assumptions.
One
assumption
(step
3)
was
that
the
DMTP
and
DMDTP
metabolites
were
due
primarily
to
either
azinphos-methyl
or
phosmet,
although
it
was
recognized
that
other
dimethyl
OP
pesticides
could
have
contributed
to
the
measured
levels.
A
second
assumption
(step
4)
was
that
metabolite
con-
centrations
in
the
spot
samples
were
repre-
sentative
of
steady
state
conditions.
A
final
assumption
(step
4)
was
that
100%
of
the
absorbed
dose
was
expressed
in
urine
as
the
dimethyl
OP
pesticide
metabolites
DMTP
and
DMDTP.
Toxicologic
benchmarks.
We
compared
dose
estimates
to
toxicologic
benchmarks
for
azinphos-methyl
and
phosmet,
the
primary
dimethyl
OP
pesticides
used
in
the
region
during
the
study
period.
There
are
measur-
able
amounts
of
both
of
these
compounds
in
the
housedust
of
nearly
all
residences
sam-
pled
in
the
region
to
date
(14,20).
We
selected
the
reference
dose
(RfD),
developed
by
the
EPA
(21),
and
the
accept-
able
daily
intake
(ADI),
promulgated
by
the
WHO
(22),
as
the
toxicologic
benchmarks.
Such
benchmarks
have
been
developed
for
chronic
ingestion
of
pesticides
and
are
normally
based
on
a
no-observable-adverse-
effect
level
(NOAEL)
derived
from
laborato-
ry
studies
and
the
addition
of
one
or
more
uncertainty
factors.
The
EPA
current
RfDs
for
the
OP
pesticides
range
from
0.05
to
20
pglkg/day.
Phosmet
is
among
the
least
haz-
ardous
OP
pesticides
according
to
this
scale,
with
an
RfD
of
11
pg/kg/day
(23),
whereas
azinphos-methyl
falls
into
the
middle
range,
with
an
RfD
of
1.5
pg/kg/day
(24).
The
cur-
rent
WHO
ADIs
for
azinphos-methyl
and
phosmet
are
5
and
20
pg/kg/day,
respective-
ly
(22).
The
differences
between
the
WHO
and
EPA
benchmarks
for
the
OP
pesticides
can
be
attributed
in
most
cases
to
the
EPA
selection
of
plasma
rather
than
red
blood
cell
cholinesterase
inhibition
as
an
adverse
end
point,
and
to
the
greater
reliance
of
the
EPA
on
animal
data
rather
than
human
data
for
critical
effects
studies
(21).
EPA
investigators
have
also
developed
an
acute
RfD
to
evaluate
very
short-term
exposures
(e.g.,
single-day
exposures)
(25).
The
respective
RfD
values
for
azinphos-
methyl
and
phosmet
are
3
and
11
pglkg/day
(23,24).
Results
Summary
statistics
of
the
dose
estimates
for
focus
children
are
presented
in
Tables
1
and
2.
Both
creatinine-adjusted
and
urinary
vol-
ume-adjusted
dose
estimates
are
provided.
Spray
season
average
dose
estimates
(Table
1)
were
consistently
higher
when
based
on
urinary
volume
adjustment
as
compared
to
creatinine
adjustment.
Median
values
of
orchard
applicator
children
were
4-9
times
higher
than
those
of
reference
children,
and
estimates
for
all
agricultural
children
were
3-6
times
higher
than
those
of
reference
children,
the
latter
with
marginal
statistical
significance.
Summary
statistics
for
single-
day
dose
estimates
(Table
2)
were
derived
from
143
individual
urine
samples.
The
same
general
patterns
were
observed,
with
median
agricultural
children
values
2-3
times
those
of
the
reference
children.
Figure
2A
and
B
indicates
the
distribu-
tion
of
creatinine-adjusted
doses
for
the
entire
population
(focus
children
and
their
siblings)
sampled
in
the
study:
91
agricultur-
al
and
18
reference
children.
Inclusion
of
the
Table
1.
Spray
season
dose
estimatesa
(pg/kg/day).
Children
(group)
Creatinine-adjusted
Volume-adjusted
Appl
FW
Agricb
Ref
AppI
FW
Agricb
Ref
(n
=
49)
(n=
13)
(n=
62)
(n
=
14)
(n
=
49)
(n
=
13)
(n
=
62)
(n=
14)
Median
2.8*,**
1.2*
2.0#
0.3**
3.2*,**
2.8*
3.0# 0.8**,#
25th
percentile
0.8
0.6
0.7
0.1
1.2
0.7
1.0
0.4
75th
percentile
4.4
4.1
4.3
3.2
7.8
4.5
7.0
7.3
Mean
±
SD
3.8
±
4.6
2.4
±
2.5
3.5
±
4.2
2.0
±
3.1
5.4
±
6.2
3.8
±
4.4
5.1
±5.9
3.5
±
5.0
Range
0-19.5
0-7.5
0-19.5
0-10.3
0-15.3
0-15.3
0-29.0
0-15.6
Abbreviations:
agric,
agricultural;
appl,
applicator;
FW,
farmworker;
ref,
reference.
*Spray
season
dose
estimates
were
based
on
the
mean
of
two
samples
for
each
focus
child.
All
samples
were
collected
during
the
May-July
spraying
season.
In
cases
with
missing
samples,
a
single
sample
was
used
to
estimate
average
dose.
Dose
estimates
were
adjusted
either
by
daily
creatinine
or
daily
urine
volume
output
for
children
0-6
years
of
age
in
an
agricultural
community,
based
on
urinary
concentrations
of
two
of
the
three
dialkylphosphate
metabolites
(DMTP
and
DMDTP)
common
to
the
dimethyl
OP
pesticides.
bAgric
children
are
a
combination
of
appl
and
FW
children.
*AppI
and
FW
children
dose
estimates
were
not
statistically
different
(Mann-Whitney
U-test).
**AppI
and
ref
children
dose
estimates
were
statistically
different
using
creatinine-adjusted
dose
estimates
(p
=
0.05,
Mann-Whitney
U-test),
and
mar-
ginally
different
for
volume-adjusted
dose
estimates
(p
=
0.09,
Mann-Whitney
U-test).
'Agric
and
ref
children
dose
esti-
mates
were
marginally
different
(p
=
0.06
for
creatinine-adjusted
dose
estimates,
p
=
0.10
for
volume-adjusted
dose
esti-
mates;
Mann-Whitney
U-test).
Table
2.
Single-day
dose
estimatesa
(pg/kg/day).
Children
(group)
Creatinine-adjusted
Volume-adjusted
AppI
FW
Agricb
Ref
AppI
FW
Agricb
Ref
(n=
92)
(n=
25)
(n=
117)
(n=
26)
(n=
92)
(n=
25)
(n
=
117)
(n=
26)
Median
1.7*,**
1.2*
1.5'
0.5**'$
2.2*,**
1.9*
2.1'
1.0**
#
25th
percentile
0000
0
0
0
0
75th
percentile
5.2
3.6
4.9
2.6
7.1
5.1
6.2
3.6
Mean
±
SD
4.0
±
6.5
2.5
±
3.3
3.7
±
5.9
2.1
±
4.1
5.5
±
8.6
4.0
±
5.4
5.1
±
8.0
3.3
±
6.3
Range
0-33.6
0-11.4
0-33.6
0-17.7
0-58
0-20
0-58
0-27.4
Abbreviations:
agric,
agricultural;
appl,
applicator;
FW,
farmworker;
ref,
reference.
"Single-day
dose
estimates
were
based
on
individual
urine
samples
collected
from
all
focus
children.
Dose
estimates
were
adjusted
either
by
daily
creatinine
or
daily
urine
volume
output
for
children
0-6
years
of
age
in
an
agricultural
com-
munity,
based
on
urinary
concentrations
of
two
of
the
three
dialkylphosphate
metabolites
(DMTP
and
DMDTP)
common
to
the
dimethyl
OP
pesticides.
bAgric
children
are
a
combination
of
appl
and
FW
children.
*AppI
and
FW
children
dose
estimates
were
not
statistically
different
(Mann-Whitney
U-test).
**Appi
and
ref
children
dose
estimates
were
marginally
different
(p
=
0.06
for
creatinine-adjusted
dose
estimates,
p
=
0.09
for
volume-adjusted
dose
estimates;
Mann-Whitney
U-
test).
'Agric
and
ref
children
dose
estimates
were
marginally
different
(p
=
0.07
for
creatinine-adjusted
dose
estimates,
p
=
0.09
for
volume-adjusted
dose
estimates;
Mann-Whitney
U-test).
Environmental
Health
Perspectives
*
VOLUME
108
1
NUMBER
6
1
June
2000
517
Children's
Health
*
Fenske
et
al.
siblings
introduced
several
high
values
to
the
distributions:
spray
season
doses
ranged
up
to
36
pg/kg/day
in
the
full
population,
and
two
single-day
doses-50
and
72
pg/kg/day-
were
beyond
the
scale
of
the
graph.
All
dose
estimates
fell
within
the
range
of
0-100
pg/kg/day,
and
none
reached
the
empirically
derived
NOAELs
for
these
compounds:
149
and
1,100
pg/kg/day
for
azinphos-methyl
and
phosmet,
respectively
(EPA
chronic
dietary
NOAELs)
(23,24).
Table
3
indicates
the
fraction
of
spray
sea-
son
doses
that
exceeded
the
RfD
values
for
azinphos-methyl
and
phosmet
in
the
full
pop-
ulation.
For
creatinine-adjusted
values,
56%
of
the
agricultural
children's
doses
and
44%
of
the
reference
children's
doses
exceeded
the
azinphos-methyl
RfD;
9%
of
the
agricultural
children's
doses
and
none
of
the
reference
children's
doses
exceeded
the
phosmet
RfD.
The
percentage
of
children
exceeding
the
azinphos-methyl
ADI
was
19%
for
agricultur-
al
children
and
22%
for
reference
children;
3%
of
the
agricultural
children
and
none
of
the
reference
children
exceeded
the
phosmet
ADI.
Thirty-five
percent
of
the
agricultural
children's
single-day
doses
and
27%
of
the
reference
children's
doses
exceeded
the
EPA
acute
RfD
for
azinphos-methyl,
whereas
7
and
3%
of
the
doses
in
these
respective
groups
exceeded
the
acute
RfD
for
phosmet.
The
use
of
urinary
volume-adjusted
data
pro-
duced
percentages
that
were
consistently
higher
than
those
based
on
the
creatinine-
adjusted
data
(Table
3).
For
example,
the
per-
centage
of
doses
for
agricultural
children
that
exceeded
the
chronic
RfD
for
azinphos-
methyl
was
69%
as
compared
to
the
55%
cal-
culated
from
creatinine-adjusted
estimates.
Discussion
These
findings
provide
a
population-based
assessment
of
children's
OP
pesticide
doses
15
c
b._
10
_-
10
S
S
.5
a
2
5
derived
from
biologic
monitoring.
The
study
population
resided
in
an
agricultural
region,
so
the
dose
estimates
should
not
be
consid-
ered
representative
of
exposures
in
the
general
population.
Further,
because
sample
collec-
tion
occurred
during
a
period
of
OP
pesticide
application,
the
dose
estimates
may
represent
peak
levels
for
the
study
population
itself.
Nonetheless,
the
spray
season
dose
estimates
reported
here
probably
reflect
levels
that
occur
for
at
least
40-50
days/year
for
these
children.
A
majority
of
the
children
dassified
as
refer-
ence
for
this
study
(no
parental
involvement
in
agriculture
and
homes
distant
from
treated
farmland)
had
measurable
dialkylphosphates
in
their
urine,
and
a
substantial
fraction
had
doses
that
exceeded
the
reference
values
for
azinphos-methyl.
Our
current
studies
include
sampling
children
in
this
community
across
an
entire
year
to
address
the
issue
of
temporal
exposure
variability.
The
calculation
of
absorbed
dose
from
biologic
measures
such
as
urinary
metabolites
has
gained
acceptance
in
the
assessment
of
occupational
pesticide
exposure
(26-28),
and
is
implicit
in
such
guidance
documents
as
the
Biological
Exposure
Indices
published
by
the
American
Conference
of
Governmental
Industrial
Hygienists
(29).
Underlying
the
estimation
of
doses
from
urinary
metabolite
concentrations
in
this
study
were
the
assump-
tions
that
spot
urine
samples
are
representa-
tive
of
total
daily
excretion
(steady-state
assumption),
and
that
dialklyphosphate
con-
centrations
are
equivalent
to
OP
pesticide
absorbed
doses
on
a
molar
basis.
Urine
sam-
ples
were
collected
at
various
times
through-
out
the
day,
at
the
convenience
of
the
parents,
and
the
effect
of
the
variability
thus
intro-
duced
is
not
known,
but
it
is
likely
that
both
over-
and
underestimates
of
actual
daily
doses
were
generated.
Creatinine
adjustment
is
a
common
interpretive
step
in
biologic
...
,,,
.ultural
children
rnechildren
5
*40
30
E
20
;
10
1
0
0
monitoring
studies,
but
its
merits
are
debated
in
the
scientific
community
(30).
No
systematic
evaluation
of
the
validity
of
creati-
nine
adjustment
has
been
conducted
for
chil-
dren.
In
this
study,
creatinine-adjusted
doses
were
lower
than
those
calculated
with
daily
urine
volume.
The
human
pharmacokinetics
of
most
OP
pesticides
are
not
well
character-
ized,
but
many
compounds
in
this
dass
have
metabolic
half-lives
in
the
range
of
12-48
hr
(31).
Virtually
no
data
are
available
regarding
the
absorption,
metabolism,
and
excretion
of
OP
pesticides
in
children.
The
use
of
urinary
dialkylphosphate
metabolites
as
a
gauge
of
absorbed
dose
probably
underestimates
the
true
dose.
In
the
case
of
azinphos-methyl,
for
example,
intravenous
dosing
of
human
volunteers
with
a
radiolabeled
compound
demonstrated
that
only
approximately
70%
of
azinphos-
methyl
is
excreted
in
urine
(31),
in
contrast
to
the
100%
value
used
in
our
analysis.
The
use
of
an
adjustment
factor
based
on
this
percentage
would
increase
the
dose
estimates
by
approximately
43%.
Also,
the
dose
esti-
mates
reported
here
are
necessarily
incom-
plete,
in
that
they did
not
include
the
three
metabolites
of
the
diethyl
OP
pesticides
or
one
of
the
three
metabolites
of
the
dimethyl
OP
pesticides
(DMP).
In
our
current
stud-
ies,
we
are
measuring
all
six
dialkylphosphate
compounds
(32).
Preliminary
results
indi-
cate
that
DMP
represents
approximately
one-third
of
total
dimethyl
metabolite
excre-
tion,
and
that
dimethyl
alkylphosphate
con-
centrations
were
significantly
higher
than
the
diethyl
alkylphosphates.
Incorporation
of
these
factors
in
our
calculations
would
increase
the
dose
estimates,
but
by
no
more
than
about
a
factor
of
two.
Furthermore,
the
significance
of
these
doses
might
also
be
understated
if
an
OP
pesticide
more
toxic
than
azinphos-methyl
were
a
significant
Spray
season
dose
(g/kg/day)
U
15
DU
D
Single-day
dose
(g/kg/day)
Figure
2.
Distributions
of
OP
pesticide
dose
estimates
for
children
in
an
agricultural
community,
derived
from
urinary
metabolite
measurements
and
adjusted
for
creatinine
concentration.
All
children
(focus
children
and
their
siblings)
are
included
in
the
graphs.
(A)
Spray
season
dose
estimates
for
109
children:
91
agricul-
tural
children
and
18
reference
children.
(B)
Single-day
dose
estimates
from
200
individual
urine
samples
collected
from
109
children:
166
samples
from
agricul-
tural
children
and
34
samples
from
reference
children.
Two
high
dose
estimates
were
not
displayed
in
B
to
maintain
consistency
in
scales:
50
and
72
pg/kg/day
for
an
applicator
child
and
a
farmworker
child,
respectively.
VOLUME
1081
NUMBER
6
1
June
2000
*
Environmental
Health
Perspectives
518
Children's
Health
*
Pesticide
dose
estimates
for
children
contributor
to
the
dialkylphosphate
metabolite
concentrations
measured
in
these
children.
Finally,
it is
possible
that
metabolites
found
in
urine
represent
exposure
to
the
breakdown
products
themselves
rather
than
to
the
parent
compounds.
If
this
were
true-
and
at
present
there
is
no
evidence
to
indi-
cate
that
it
is,
at
least
in
the
case
of
dialkyl-
phosphates-pesticide
doses
would
tend
to
be
overestimated.
Source
attribution.
Biologic
monitoring
data
are
not
normally
evaluated
by
agencies
such
as
the
EPA
Office
of
Pesticide
Programs.
The
integration
of
exposure
through
all
routes
and
pathways,
which
is
the
great
strength
of
biomonitoring,
is
also
its
chief
drawback
from
a
regulatory
perspective.
Chemical-by-chemi-
cal
evaluation
requires
that
exposure
be
restricted
to
a
single
compound
from
a
known
source
and
that
the
relative
importance
of
the
dermal,
oral,
and
respiratory
routes
be
known.
These
constraints
have
led
to
an
almost
exclusive
reliance
on
models
that
incorporate
source-specific
environmental
concentration
data,
behavioral
factors,
and
route-specific
absorption
factors.
Default
assumptions
tend
to
be
used
for
many
of
these
model
parame-
ters
in
the
absence
of
reliable
data.
For
exam-
ple,
EPA
investigators
have
proposed
a
set
of
standard
operating
procedures
for
residential
exposures
that
include
numerous
default
modeling
values
(33).
Biologic
monitoring
provides
a
point
of
comparison
for
estimates
obtained
through
such
modeling.
Biologic
monitoring
that
uses
the
com-
mon
dialkylphosphate
metabolites
to
assess
OP
pesticide
exposure
is
clearly
problematic
for
current
risk
management
procedures.
At
present,
it
is
not
possible
to
attribute
doses
to
specific
compounds
without
detailed
knowl-
edge
of
sources
and
exposure
pathways.
For
the
findings
reported
here,
it
is
likely
that
doses
were
the
result
not
only
of
direct
expo-
sure
to
agricultural
OP
pesticides,
but
also
to
pesticide
residues
in
food.
Determining
appropriate
toxicologic
benchmarks
for
such
multipathway
and
multichemical
exposures
will
require
use
of
a
toxicity
equivalence
factor
similar
to
that
recommended
by
the
National
Research
Council
(2).
Our
use
of
azinphos-
methyl
and
phosmet
as
representative
OP
pesticides
in
this
analysis
sidesteps
this
issue
for
the
moment,
but
an
RfD
value
could
be
constructed
for
these
data
through
an
expo-
sure
pathway
analysis.
Additional
safety
factors
for
children.
The
requirement
within
the
FQPA
that
an
additional
safety
factor
be
incorporated
into
pesticide
risk
assessments
under
certain
cir-
cumstances
is
perhaps
the
most
controversial
provision
of
the
new
law
(7).
Such
factors
have
sometimes
been
incorporated
into
WHO
ADIs
on
a
case-by-case
basis
(34).
The
addition
of
a
10-fold
safety
factor
to
the
ADIs
was
recently
proposed
for
evaluating
acceptable
pesticide
residue
levels
in
infant
foods,
with
case-by-case
adjustments
where
adequate
toxicologic
data
are
available
(35).
If
a
10-fold
safety
factor
were
applied
to
the
current
EPA
RfDs,
virtually
all
children
with
detectable
metabolites
in
our
study
would
exceed
this
level.
A
recent
analysis
of
1,000
U.S.
adults
found
measurable
urinary
metabolites
of
the
OP
pesticide
chlorpyrifos
in
82%
of
the
samples,
indicating
that
OP
pesticide
exposures
are
widespread
(36).
It
seems
plausible
to
speculate
that
biomonitor-
ing
surveys
of
young
children
in
the
United
States
which
assayed
the
common
metabo-
lites
of
the
OP
pesticides
would
find
measur-
able
levels
in
a
large
fraction
of
samples.
Conclusions
The
data
presented
here
demonstrate
that
OP
pesticide
exposures
among
children
in
agricultural
communities
fall
into
a
range
of
regulatory
concern
and
require
further
inves-
tigation.
Biologically
based
exposure
moni-
toring
can
usefully
inform
the
evaluation
of
aggregate
exposure
and
cumulative
risk,
and
Table
3.
Children's
OP
pesticide
doses
relative
to
the
EPA
acute
dietary
and
RfDs
and
the
WHO
ADIs
for
azinphos-methyl
and
phosmet.a
Doses
exceeding
reference
value
(%)
Creatinine-adjusted
Urine
volume-adjusted
Agricultural
Reference
Agricultural
Reference
Regulatory
reference
value
children
children
children
children
EPA
chronic
reference
dose
(21)
Azinphos-methyl
(1.5
pg/kg/day)
(24)
56b
44b
69b
50b
Phosmet
(11
pg/kg/day)
(23
8.9b
ob
1
b
b
WHO
acceptable
daily
intake
(22)
Azinphos-methyl
(5
pg/kg/day)
1
b
22b
33b
28b
Phosmet
(20
pg/kg/day)
3.3b
ob
3.3b
ob
EPA
acute
reference
dose
Azinphos-methyl
(3
pg/kg/day)
(24)
35c
26c
42C
32C
Phosmet
(1
1
pg/kg/day)
(23)
6.6c
2.9c
14c
1
5c
aincludes
all
children
(focus
children
and
siblings);
assumes
doses
are
attributable
entirely
to
either
azinphos-methyl
or
phosmet.
bSpray
season
doses
based
on
90
(creatinine-adjusted)
or
91
(urine
volume-adjusted)
spray
season
dose
esti-
mates
for
agricultural
children
and
18
spray
season
dose
estimates
for
reference
children.
cSingle-day
doses
based
on
166
(creatinine-adjusted)
or
173
(urine
volume-adjusted)
single-day
dose
estimates
for
agricultural
children
and
34
sin-
gle-day
dose
estimates
for
reference
children.
may
be
helpful
as
a
point
of
comparison
for
conventional
models.
A
more
accurate
interpretation
of
such
biologic
data
will
require
detailed
analysis
of
exposure
pathways
relevant
to
children.
Source
identification
and
apportionment
studies
for
identifiable
subpopulations
are
needed
to
better
prioritize
risk
management
decisions.
The
interpretation
of
such
exposure
measurements
will
also
be
facilitated
by
har-
monization
of
toxicologic
benchmarks
by
agencies
such
as
the
EPA
and
the
WHO.
By
working
from
a
common
toxicologic
data-
base,
these
agencies
should
be
able
to
reach
a
consensus
on
the
potential
health
risks
of
these
compounds
for
adults
and
children.
Laws
such
as
the
FQPA
(7)
represent
important
public
health
interventions.
An
essential
but
often
neglected
aspect
of
such
interventions
is
an
evaluation
of
their
effec-
tiveness
(34).
In
the
case
of
OP
pesticides,
urinary
metabolite
monitoring
offers
an
opportunity
to
measure
progress
in
reducing
children's
exposures,
as
has
been
done
for
organochlorine
pesticide
exposure
in
the
gen-
eral
U.S.
population
(38).
Biomonitoring
sur-
veys
of
selected
child
populations
at
an
early
stage
of
FQPA
implementation
could
provide
important
baseline
data
for
intervention
effec-
tiveness
evaluation.
REFERENCES
AND
NOTES
1.
International
Life
Sciences
Institute.
Similarities
and
Differences
between
Children
and
Adults:
Implications
for
Risk
Assessment.
Washington,
DC:ILSI
Press,
1992.
2.
National
Research
Council.
Pesticides
in
the
Diets
of
Infants
and
Children.
Washington,
DC:National
Academy
Press,
1993.
3.
National
Research
Council.
Measuring
Lead
Exposure
in
Infants,
Children,
and
Other
Sensitive
Populations.
Washington,
DC:National
Academy
Press,
1993.
4.
Jacobson
JL,
Jacobson
SW.
Intellectual
impairment
in
children
exposed
to
polychlorinated
biphenyls
in
utero.
N
EngI
J
Med
335:783-789
(1996).
5.
Whitney
KD,
Seidler
FJ,
Slotkin
TA.
Developmental
neu-
rotoxicity
of
chlorpyrifos:
cellular
mechanisms.
Toxicol
AppI
Pharmacol
134:53-62
(1995).
6.
Chanda
SM,
Pope
CN.
Neurochemical
and
neurobehav-
ioral
effects
of
repeated
gestational
exposure
to
chlor-
pyrifos
in
maternal
and
developing
rats.
Pharmacol
Biochem
Behav
53:771-776
(1996).
7.
Food
Quality
Protection
Act
of
1996.
Public
Law
104-170,
1996.
8.
International
Life
Sciences
Institute.
Workshop
on
Aggregate
Exposure
Assessment.
Washington,
DC:ILSI
Press,
1998.
9.
International
Life
Sciences
Institute.
A
Framework
for
Cumulative
Risk
Assessment.
Washington,
DC:ILSI
Press,
1999.
10.
U.S.
Environmental
Protection
Agency
Office
of
Pesticide
Programs.
Organophosphate
Pesticides:
Documents
for
Chlorpyrifos.
Available:
http://
www.epa.gov/pesticides/op/chlorpyrifos.htm
[cited
10
January
2000].
11.
U.S.
EPA.
1996
Food
Quality
Protection
Act
Implementation
Plan.
Washington,
DC:U.S.
Environmental
Protection
Agency
Office
of
Prevention,
Pesticides,
and
Toxic
Substances,
1997.
12.
Mileson
BE,
Chambers
JE,
Chen
WL,
Dettbarn
W,
Ehrich
M,
Eldefrawi
AT,
Gaylor
DW,
Hamernik
K,
Hodgson
E,
Karczmar
AG,
et
al.
Common
mechanisms
of
toxicity:
a
case
study
of
organophosphorus
pesticides.
Toxicol
Sci
41:8-20
11998).
Environmental
Health
Perspectives
*
VOLUME
108
1
NUMBER
6
1
June
2000
519
Children's
Health
*
Fenske
et
al.
13.
Gallo
MA,
Lawryk
NJ.
Organic
Phosphorus
Pesticides.
In:
Handbook
of
Pesticide
Toxicology.
New
York:Academic
Press,
1991;917-1123.
14.
Fenske
RA,
Lu
C,
Simcox
NJ,
Loewenherz
C,
Touchstone
J,
Moate
TF,
Allen
EH,
Kissel
JC.
Strategies
for
assessing
children's
organophosporus
pesticide
exposures
in
agri-
cultural
communities.
J
Exp
Anal
Environ
Epidemiol
(in
press).
15.
Loewenherz
C,
Fenske
RA,
Simcox
NJ,
Bellamy
G,
Kalman
D.
Biological
monitoring
of
organophosphorus
pesticide
exposure
among
children
of
agricultural
work-
ers.
Environ
Health
Perspect
105:1344-1353
(1997).
16.
International
Commission
on
Radiological
Protection.
Report
of
the
Task
Group
on
Reference
Man:
A
Report
Prepared
by
a
Task
Group
of
Committee
2
of
the
International
Commission
on
Radiological
Protection.
Oxford,
NY:Pergamon
Press,
1975.
17.
Meites
S,
ed.
Pediatric
Clinical
Chemistry:
A
Survey
of
Reference
(Normal)
Values,
Methods,
and
Instrumentation,
With
Commentary.
3rd
ed.
Washington,
DC:The
American
Association
for
Clinical
Chemistry,
1988.
18.
U.S.
Environmental
Protection
Agency.
Exposure
Factors
Handbook,
Vol.
1.
Washington,
DC:National
Center
for
Environmental
Assessment,
1997.
19.
U.S.
EPA.
Guidelines
for
exposure
assessment.
Fed
Reg
57:22888-22938
(1992).
20.
Simcox
NJ,
Fenske
RA,
Wolz
SA,
Lee
I-C,
Kalman
D.
Pesticides
in
housedust
and
soil:
exposure
pathways
for
children
of
agricultural
families.
Environ
Health
Perspect
103:1126-1134
(1995).
21.
Office
of
Pesticide
Programs.
Reference
Dose
Tracking
Report.
Washington,
DC:U.S.
Environmental
Protection
Agency,
1997.
22.
Lu
F.
A
review
of
acceptable
daily
intakes
of
pesticides
assessed
by
WHO.
Regul
Toxicol
Pharmacol
21:352-364
(1995).
23.
U.S.
Environmental
Protection
Agency
Office
of
Pesticide
Programs.
Organophosphate
Pesticides:
Documents
for
Phosmet.
Available:
http://www.epa.gov/pesticides/
op/phosmet.htm
[cited
10
January
20001.
24.
U.S.
Environmental
Protection
Agency
Office
of
Pesticide
Programs.
Organophosphate
Pesticides:
Documents
for
Azinphos-Methyl.
Available:
http://www.epa.gov/pesti-
cides/op/azm.htm
[cited
10
January
20001.
25.
U.S.
EPA
Office
of
Pesticide
Programs.
Hazard
Assessment
of
the
Organophosphates.
Report
of
the
Hazard
Identification
Assessment
Review
Committee.
Washington,
DC:U.S.
Environmental
Protection
Agency,
1998.
26.
Franklin
CA,
Muir
NI,
Moody
RP.
The
use
of
biological
monitoring
in
the
estimation
of
exposure
during
the
application
of
pesticides.
Toxicol
Lett
33:127-136
(1986).
27.
Chester
G,
Hart
TB.
Biological
monitoring
of
a
herbicide
applied
through
backpack
and
vehicle
sprayers.
Toxicol
Lett
33:137-149
(1986).
28.
Curry
PB,
lyengar
S,
Maloney
PA,
Maroni
M,
eds.
Methods
of
Pesticide
Exposure
Assessment.
New
York:Plenum
Press,
1995.
29.
ACGIH.
1999
TLVs
and
BEls:
Threshold
Limit
Values
for
Chemical
Substances
and
Physical
Agents:
Biological
Exposure
Indices.
Cincinnati,
OH:American
Conference
of
Governmental
Industrial
Hygienists,
1999.
30.
Sata
F,
Araki
S,
Yokoyama
K,
Murata
K.
Adjustment
of
creatinine-adjusted
values
in
urine
to
urinary
flow
rate:
a
study
of
eleven
heavy
metals
and
organic
substances.
Int
Arch
Occup
Environ
Health
68:64-68
(1995).
31.
Feldmann
RJ,
Maibach
Hi.
Percutaneous
absorption
of
some
pesticides
and
herbicides
in
man.
Toxicol
AppI
Pharmacol
28:126-132
(1974).
32.
Moate
T,
Lu
C,
Fenske
RA,
Hahne
R,
Kalman
DA.
Improved
cleanup
and
determination
of
dialkyl
phos-
phates
in
the
urine
of
children
exposed
to
organophos-
phorus
insecticides.
J
Anal
Toxicol
23:230-236
(1999).
33.
U.S.
EPA
Office
of
Pesticide
Programs.
Standard
Operating
Procedures
(SOPs)
for
Residential
Exposure
Assessments.
Washington,
DC:U.S.
Environmental
Protection
Agency,
1997.
34.
WHO.
Environmental
Health
Criteria
170:
Assessing
Human
Health
Risks
of
Chemicals:
Derivation
of
Guidance
Values
for
Health-Based
Exposure
Limits.
Geneva:World
Health
Organization,
1994.
35.
Schilter
B,
Renwick
AG,
Huggett.
Limits
for
pesticide
residues
in
infant
foods:
a
safety-based
proposal.
Regul
Toxicol
Pharmacol
24:126-140
(1996).
36.
Hill
RH,
Head
Sl,
Baker
S,
Gregg
M,
Shealy
DB,
Bailey
SL,
Williams
CC,
Sampson
EJ,
Needham
LL.
Pesticide
residues
in
urine
of
adults
living
in
the
United
States:
reference
range
concentrations.
Environ
Res
71:99-108
(1995).
37.
Teutsch
SM.
A
framework
for
assessing
the
effective-
ness
of
disease
and
injury
prevention.
Morb
Mortal
Wkly
Rep
41(RR-3):1-12
(1992).
38.
National
Research
Council.
Monitoring
Human
Tissues
for
Toxic
Substances.
Washington,
DC:National
Academy
Press,
1991.
For
as
little
as
$
3.09*
per
year
per
user,
your
students
can
have
full
Internet
access
to
the
Environmental
Health
Information
Service
(EHIS)!
The
EHIS
offers
online,
searchable
access
to:
Environmental
Health
Perspectives
*
Environmental
Health
Perspectives
Supplements
:.
_
_*
National
Toxicology
Program
Technical
and
Toxicity
Reports
*
Report
on
Carcinogens
*
Chemical
Health
and
Safety
Database
*
Rodent
Historical
Control
Database
For
more
information
on
ordering
call
1-800-315-3010.
*Price
is
baseel
on
Multiple
lJscr
Internet
Access.
I
ducation
Accounts
including
full
Internet
access
for
250
users
and
print
copies
of
1.!',.
EllI'
Supplements,
and
N'l'P
reports.
520
VOLUME
108
NUMBER
6
June
2000
-
Environmental
Health
Perspectives
