Pesticides
in
Streams:
Summary
Statistics;
Preliminary
Results
from
Cycle
I
of
the
National
Water
Quality
Assessment
Program
(
NAWQA),
1992­
2001
PROVISIONAL
DATA
­­
SUBJECT
TO
REVISION
Jeffrey
D.
Martin,
jdmartin@
usgs.
gov
;
Charles
G.
Crawford,
cgcrawfo@
usgs.
gov
;
and
Steven
J.
Larson,
sjlarson@
usgs.
gov
February
19,
2003
INTRODUCTION
As
part
of
the
National
Water­
Quality
Assessment
Program
(
NAWQA),
76
pesticides
and
7
pesticide
degradation
products
were
analyzed
in
surface­
water
samples
collected
for
one
or
more
years
during
1992
to
2001
at
162
sites
in
49
of
the
nation's
most
important
river
basins
(
NAWQA
study
units).
Previous
studies
have
analyzed
data
collected
early
in
the
period
(
Gilliom
and
others,
1999;
Larson
and
others,
1999;
U.
S.
Geological
Survey,
1999b).
This
report
provides
a
preliminary
analysis
of
the
entire
data
set.
These
data
on
pesticides
in
U.
S.
rivers
and
streams
are
the
most
extensive
ever
collected
for
such
a
wide
range
of
pesticides
and
locations.
The
76
herbicides,
insecticides,
and
fungicides
targeted
in
the
study
account
for
approximately
75
percent
of
the
total
amount
(
by
weight)
of
pesticides
used
for
agriculture
in
the
United
States
and
a
substantial
portion
of
urban
and
suburban
use
(
U.
S.
Geological
Survey,
1999a).
The
purpose
of
this
summary
is
to
estimate
(
1)
the
annual
frequency
of
pesticide
detection
and
(
2)
selected
percentiles
of
the
annual
distribution
of
pesticide
concentrations
in
streams
sampled
for
the
NAWQA
Program
during
1992­
2001.
Estimates
of
the
annual
frequency
of
pesticide
detection
and
percentiles
of
the
annual
distribution
of
pesticide
concentrations
for
NAWQA
surface­
water
sampling
sites
are
summarized
by
land­
use
category
to
provide
estimates
of
pesticide
concentrations
in
streams
draining
agricultural,
urban,
undeveloped,
and
mixed
land
uses.

SUMMARY
OF
METHODS
The
following
sections
provide
a
brief
description
of
the
methods
used
to
select
sites
and
samples
and
to
calculate
summary
statistics.
A
more
detailed
discussion
of
methods
is
available
(
see
Expanded
Methods).
Sample
collection
and
processing:
Surface­
water
sampling
sites
in
each
Study
Unit
were
selected
in
accordance
with
the
NAWQA
national
design
strategy
(
Gilliom
and
others,
1995).
Surface­
water
sites
were
classified
into
four
land­
use
groups
on
the
basis
of
two
national
land­
use
data
sets
and
information
on
point
sources
and
other
influences
on
water
quality
provided
by
Study
Units
(
D.
K.
Mueller,
Nutrient
National
Synthesis,
U.
S.
Geological
Survey,
written
commun.,
October
2,
2002).
Pesticide
samples
generally
were
collected
for
one
year
at
each
site
using
a
combination
of
fixed­
interval
and
extreme­
flow
sampling
(
Gilliom
and
others,
1995,
p.
16).
Two
to
four
samples
generally
were
collected
each
month
during
seasonal
periods
of
high
pesticide
use
and
runoff
and
one
to
two
samples
were
collected
each
month
during
other
periods.
Streamflow­
weighted,
depth­
and
width­
integrated
water
samples
were
collected
using
standard
USGS
methods
(
Shelton,
1994,
p.
14­
17).
All
sample
collection
and
processing
equipment
that
came
in
contact
with
the
pesticide
sample
was
constructed
of
Teflon,
glass,
aluminum,
or
stainless
steel.
Equipment
was
cleaned
with
a
dilute
solution
of
phosphate­
free
detergent
and
rinsed
with
deionized
water
and
pesticide­
grade
methanol.
Water
samples
were
filtered
using
pre­
combusted
glass­
fiber
filters
with
a
nominal
0.7­

µ
m
pore
diameter
to
remove
suspended
particulate
matter.
Collection
and
processing
methods
are
described
by
Shelton
(
1994).
Analytical
methods:
Water
samples
were
analyzed
for
pesticides
at
the
National
Water
Quality
Laboratory
(
NWQL)
of
the
USGS
in
Colorado.
Data
from
two
analytical
methods
are
described
in
this
summary
and
both
use
solid­
phase
extraction
to
remove
pesticides
from
water
samples.
Additional
information
on
analytical
performance,
pesticide
use,
and
water­
quality
criteria
for
these
pesticides
is
provided
in
U.
S.
Geological
Survey
(
1999a).
The
GC/
MS
method
was
the
primary
analytical
method
used
by
all
Study
Units.
The
GC/
MS
method
provides
analyses
of
47
pesticides
or
degradation
products
by
gas
chromatography/
mass
spectrometry
and
selected­
ion
monitoring
(
Zaugg
and
others,
1995).
The
pesticide
acetochlor
was
added
to
the
GC/
MS
method
in
June
1994
(
Lindley
and
others,
1996).
The
HPLC
method
was
used
extensively
by
Study
Units
that
began
investigations
in
1991
and
1994.
The
HPLC
method
provides
analyses
of
36
additional
pesticides
or
degradation
products
by
high­
performance
liquid
chromatography
and
photodiode­
array
detection
(
Werner
and
others,
1996).
A
third
analytical
method,
developed
to
replace
the
HPLC
method,
was
used
extensively
by
Study
Units
that
began
investigations
in
1997.
Unfortunately,
many
of
the
water
samples
analyzed
by
this
method
exceeded
the
holding
times
for
the
method
and
none
of
the
data
from
this
analytical
method
are
used
in
this
national
summary.
Reporting
levels
for
the
analytical
methods
have
changed
through
time.
A
reporting
level
is
the
"
less
than"
concentration
used
to
indicate
a
nondetection
of
a
pesticide
(
for
example:
<
0.005
µ
g/
L).
For
this
summary,
the
maximum
reporting
levels
routinely
used
by
NWQL
for
water
years
1992
to
2001
are
given
in
Tables
1­
4.
Low­
level
detections
of
pesticides
by
these
methods
are
not
censored
at
the
reporting
limit.
All
detections
(
pesticides
conclusively
identified
by
retention
time
and
spectral
characteristics)
are
quantified.
Data
analysis:
A
one­
year
period
of
pesticide
data
was
selected
for
each
site
to
describe
an
annual
distribution
of
pesticide
concentrations.
Sites
with
few
samples
or
significant
gaps
between
samples
were
excluded
from
the
national
summary.
The
size
of
the
drainage
area,
the
length
of
the
pesticide
use
and
runoff
season,
and
the
seasonal
frequency
of
sample
collection
were
important
variables
in
the
selection
of
sites
and
samples.
The
maximum
gap
allowed
between
samples
was
longer
for
large
streams
than
for
small
streams
and
was
longer
during
periods
when
pesticide
concentrations
were
expected
to
be
lower
and
less
variable.
In
general,
the
selected
one­
year
period
was
the
year
with
the
most
samples
and
did
not
coincide
with
the
start
of
a
water
year
or
calendar
year,
but
with
the
initiation
of
sampling
(
often
in
spring).
Annual
detection
frequencies
and
annual
percentiles
of
concentration
for
land­
use
categories
were
computed
from
the
one­
year
time
series
of
concentrations
for
all
sites
in
the
land­
use
category.
These
statistics
were
calculated
by
weighting,
by
site,
each
concentration
in
the
time
series
by
the
amount
of
time
it
was
used
to
represent
the
pesticide
concentration
in
that
stream.
Sample
weights
for
sites
in
the
land­
use
category
were
pooled
and
normalized
by
the
number
of
sites
in
the
pooled
data
set.
The
use
of
"
time­
weighted"
values
reduces
the
bias
in
estimates
of
annual
detection
frequencies
and
percentiles
of
concentration
that
is
introduced
by
an
increased
sampling
frequency
during
the
high­
use
pesticide
season.

RESULTS
Statistical
summaries
of
pesticide
detections
and
concentrations
by
land
use
are
provided
in
Tables
1­
4.
Summaries
for
agricultural
land
use
are
provided
in
Table
1,
for
mixed
land
use
in
Table
2,
for
undeveloped
land
use
in
Table
3,
and
for
urban
land
use
in
Table
4.
Table
5
identifies
the
sites
used
for
the
statistical
summaries
of
pesticide
detections
and
concentrations.
NOTES
FOR
USING
TABLES:
1.
Frequency
of
detection:
Detection
frequencies
indicate
how
often
a
compound
was
detected
in
samples.
Four
detection
frequencies
are
provided
in
Tables
1­
4:
"
All"
detections,
detections
at
concentrations
>
0.01
µ
g/
L,
detections
at
concentrations
>
0.1
µ
g/
L,
and
detections
at
concentrations
>
1
µ
g/
L.
(
The
symbol
">"
means
"
greater
than
or
equal
to.")
The
values
for
"
All"
detections
provide
the
percentage
of
detections
for
a
given
compound,
but
should
not
be
directly
compared
among
compounds
because
reporting
levels
(
detection
capabilities)
varied
among
compounds.
Because
reporting
levels
varied,
detection
frequencies
were
calculated
using
three
common
detection
thresholds
(
0.01,
0.1,
and
1
µ
g/
L).
The
use
of
these
detection
thresholds
facilitates
comparisons
among
compounds
by
censoring
detections
to
a
common
reference
concentration.
Adjustments
of
this
type
are
essential
in
order
to
answer
questions
like
"
is
compound
x
detected
more
often
than
compound
y?"
For
most
pesticides
analyzed
by
GC/
MS,
the
lowest
appropriate
detection
threshold
for
comparisons
among
compounds
is
0.01
µ
g/
L.
Several
compounds
(
azinphos­
methyl
for
example)
have
maximum
reporting
levels
that
exceed
the
0.01
µ
g/
L
threshold.
In
these
cases,
the
detection
frequency
is
preceded
by
a
">"
symbol
to
indicate
that
the
true
percentage
of
samples
with
concentrations
greater
than
the
threshold
probably
is
greater
than
or
equal
to
that
reported
in
the
table.
For
most
pesticides
analyzed
by
HPLC,
the
lowest
appropriate
detection
threshold
for
comparisons
among
compounds
is
0.1
µ
g/
L.
Nonetheless,
several
compounds
have
maximum
reporting
levels
that
exceeded
the
threshold.
In
these
cases,
the
detection
frequencies
may
underestimate
the
true
percentage
of
samples
with
concentrations
greater
than
the
threshold
and
detection
frequencies
are
preceded
with
a
">"
symbol.
Nearly
all
of
the
pesticides
can
be
compared
at
the
1
µ
g/
L
threshold.
Use
of
this
threshold
censors
the
majority
of
the
pesticide
detections,
but
allows
comparisons
among
pesticides
measured
at
high
concentrations.
Detections
in
water
samples
were
time
weighted
and
the
pooled
detection
frequency
was
calculated
across
all
sites
in
a
land
use.
As
a
consequence,
the
frequency
of
detection
may
be
interpreted
as
an
estimate
of
the
percentage
of
time
that
pesticides
are
detected
at
NAWQA
sites
in
that
particular
land
use.
For
example,
52
surface­
water
sites
in
areas
of
agricultural
land
use
had
sufficient
monitoring
data
to
estimate
an
annual
distribution
of
concentrations
of
acetochlor
(
Table
1).
Acetochlor
was
detected
31.44
percent
of
the
year
at
NAWQA
sites
draining
agricultural
land
use
and
was
detected
23.41
percent
of
the
year
at
concentrations
greater
than
or
equal
to
0.01
µ
g/
L.
2.
Percentiles
of
concentration:
Annual
time­
weighted
concentrations
measured
for
each
pesticide
are
summarized
using
percentiles.
The
25th,
50th,
75th,
90th,
and
95th
percentiles
of
concentration
by
land­
use
category
are
provided
in
Tables
1­
4.
Percentiles
provide
information
about
the
magnitude
and
duration
of
concentrations
at
selected
points
in
the
cumulative
frequency
distribution
of
the
ranked,
time­
weighted
concentrations.
For
example,
concentrations
of
acetochlor
at
NAWQA
sites
draining
agricultural
land
use
were
less
than
0.005
µ
g/
L
for
25
percent
of
the
year,
less
than
0.005
µ
g/
L
for
50
percent
of
the
year,
less
than
or
equal
to
0.009
µ
g/
L
for
75
percent
of
the
year,
less
than
or
equal
to
0.052
µ
g/
L
for
90
percent
of
the
year,
and
less
than
or
equal
to
0.165
µ
g/
L
for
95
percent
of
the
year
(
Table
1).
If
percentiles
are
not
censored
(
reported
as
less
than
a
specified
concentration­­
for
example,
<
0.005
µ
g/
L),
the
percentiles
also
may
be
interpreted
as
the
percentage
of
the
year
where
concentrations
were
greater
than
a
given
concentration.
For
example,
concentrations
of
acetochlor
at
NAWQA
sites
draining
agricultural
land
use
were
greater
than
or
equal
to
0.009
µ
g/
L
for
25
percent
of
the
year,
greater
than
or
equal
to
0.052
µ
g/
L
for
10
percent
of
the
year,
and
greater
than
or
equal
to
0.165
µ
g/
L
for
5
percent
of
the
year
(
Table
1).
Tables
1­
4
include
a
column
for
"
Maximum."
The
concentrations
in
this
column
are
the
maximum
measured
concentrations
in
the
pooled
annual
data
sets
for
each
land­
use
category.
Concentrations
greater
than
the
value
reported
as
maximum
may
have
been
measured
at
sites
but
are
not
reported
because
they
were
not
measured
during
the
oneyear
periods
selected
to
describe
the
annual
distribution
of
concentrations.
In
addition,
the
probability
is
low
that
a
water
sample
was
collected
at
the
time
of
the
annual
maximum
concentration
for
any
pesticide.
Consequently,
the
maximum
concentrations
reported
in
Tables
1­
4
should
be
interpreted
as
a
lower
bound
for
the
true
maximum
concentrations.
3.
Estimated
concentrations:
All
pesticides
denoted
with
"(
E)"
have
more
biased
and/
or
variable
analytical
performance
than
the
other
pesticides
in
the
method.
Information
on
analytical
performance
is
provided
in
the
method
reports
(
Zaugg
and
others,
1995;
Werner
and
others,
1996)
and
is
summarized
for
the
period
1992­
96
in
Martin
(
1999).
Individual
concentrations
that
exceed
the
calibration
curve
of
the
analytical
method
are
marked
with
an
"
E"
to
indicate
that
the
uncertainty
in
these
concentrations
is
greater
than
for
concentrations
within
the
calibration
range.
TABLES
OF
SUMMARY
STATISTICS
FOR
PESTICIDES
IN
STREAMS:
Table
1.
For
agricultural
stream
sites.
Table
2.
For
mixed
land
use.
Table
3.
For
undeveloped
land
use.
Table
4.
For
urban
land
use.
Table
5.
List
of
stream
sites
used
for
statistics
in
Tables
1­
4.

REFERENCES
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R.
J.,
Alley,
W.
M.,
and
Gurtz,
M.
E.,
1995,
Design
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the
National
Water­
Quality
Assessment
Program:
Occurrence
and
distribution
of
water­
quality
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U.
S.
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http://
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usgs.
gov/
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circ/
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99/
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79,
no.
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966.
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J.
D.,
1999,
Quality
of
pesticide
data
for
environmental
water
samples
collected
for
the
National
Water­
Quality
Assessment
Program,
1992­
96,
and
examples
of
the
use
of
quality­
control
information
in
water­
quality
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S.
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accessed
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