SOIL
ADSORPTION
TEST
SUBSTANCE
Identity:
Perfluorooctanoic
acid,
ammonium
salt;
may
also
be
referred
to
as
PFOA
ammonium
salt,
Ammonium
perfluorooctanoate,
PFO,
FC­
116,
FC­
126,
FC­
169,
or
FC­
143.
(Octanoic
acid,
pentadecafluoro­,
ammonium
salt,
CAS
#
3825­
26­
l)

Remarks:
The
test
sample
is
FC­
143.
It's
purity
was
not
sufficiently
characterized,
though
current
information
indicates
it
is
a
mixture
of
96.5
100
test
substance
and
0
­
3.5%
Cs,
CT,
and
Cs
perfluoro
analogue
compounds.
The
test
substance
used
was
"C­
labeled.
This
testing
is
being
repeated
per
current
procedures
and
best
available
practices.

Met
hod:
Adsorption­
Desorption
study
using
the
approach
recommended
by
the
U.
S.
EPA
for
pesticide
registration
GLP
(Y/
N):
No
Year
(study
performed):
1978
Statistical
methods:
Statistical
analysis
and
plotting
of
the
data
was
done
with
the
MINITAB
package
of
the
3M
TRAC
computer
service.
Temperature:
16­
l
9°
C
Stock
and
test
solution
preparation:
Test
solutions
were
made
by
diluting
a
stock
solution
of
"C­
labeled
ammonium
perfluorooctanoate.
The
type
of
solvent
used
to
make
the
stock
solution
is
not
noted,
nor
is
the
activity
of
the
"C­
labeled
test
substance.

Remarks
field:
The
Brill
sandy
loam
soil
was
characterized
as
having
57%
sand,
36%
silt,
7%
clay,
2.5%
organic
matter,
1.5%
organic
carbon,
with
pH
6.5
and
cation
exchange
capacity
of
15.3
meq./
lOO
gms.
Standard
solutions
of
the
14C­
labeled
compound
were
prepared
in
D.
I.
water
at
concentrations
of
523
mg/
L,
293
mg/
L,
167
mg/
L,
94
mg/
L,
52
mg/
L,
and
5.2
mg/
L.
Twenty­
five
ml
of
each
solution
was
shaken
with
duplicate
5
gram
samples
of
the
soil
in
a
50
ml
polypropylene
centrifuge
tubes
for
24
hours
on
a
wrist
shaker
at
room
temperature
(16­
l
9OC).

Desorption
extraction
were
performed
with
D.
I.
water
after
the
adsorption
phase
of
the
experiment.
The
samples
from
the
adsorption
and
desorption
experiments
were
centrifuged
individually
at
5000
rpm
for
10
minutes,
after
which,
three
aliquots
of
each
supernatant
solution
were
prepared
for
scintillation
counting.
From
the
raw
counting
data,
compound
concentrations
were
calculated
for
all
of
the
supernatant
solutions.
K:
0.21
(N=
l)
K
,:
14*

*
The
study
report
had
indicated
a
K
of
0.38.
This
is
the
coefficient
of
C
in
the
regression
equation,
not
the
adsorption
coefficient
value,
based
on
best
fit.
Taking
a
mean
value
for
K
based
on
K=(
x/
m)/
C,,
K
=
0.21.
The
Koc
value
based
on
the
initially
reported
organic
carbon
content
of
1.5%
and
the
mean
value
for
K
(K,,
=K
x
100/
I
.5(%
organic
carbon)
becomes
14.

CONCLUSIONS
The
study
substance
is
expected
to
exhibit
high
mobility
in
the
kind
of
soil
tested.

Submitter:
3M
Company,
Environmental
Laboratory,
P.
O.
Box
33331,
St.
Paul,
Minnesota,
55133
DATA
QUALITY
Reliability:
Klimisch
ranking
3.
This
study
lacks
detail
on
the
stock
solution
and
the
purity
of
the
14C­
labeled
test
substance.
There
was
no
analysis
of
the
soil
to
verify
the
amount
remaining
for
mass
balance.
Discrepancies
in
the
organic
carbon
content
are
present.
Use
of
DI
water
instead
of
CaC12.
Additionally,
some
calculations
have
questionable
reliability.
Additional
comments
by
Professor
Stephen
A.
Boyd,
Michigan
State
University,
also
indicate
the
reliability
level
of
this
study.

REFERENCES
3M
Technical
Report
"Adsorption
of
FC
95
and
FC
143
on
Soil."
S.
K.
Welsh,
Project
9970612633
Fate
of
Fluorochemicals,
Report
No.
1,
Feb.
27,1978
3M
requested
expert
review
by
Professor
Stephen
A.
Boyd,
Michigan
State
University,
May
19,
1993.

OTHER
Last
changed:
5/
25/
00
Attached
are
comments
on
the
3M
Technical
Report
"Adsorption
of
FC
95
and
FC
143
on
Soil.
S.
K.
Welsh,
Project
9970612633
Fate
ofFluorochemicals,
Report
No.
1,
Feb.
27,
1978"
made
by
Professor
Stephen
A.
Boyd,
Michigan
State
University,
dated
May
19,
1993.

.
Review
of
Technical
Report
Summary
Adsorption
of
FC
95
and
FC
143
in
Soil
Material
and
Methods
Should
give
recoveries
of
compoundsin
blank
(no­
soil)
experiments.
States
that
polypropylene
sorbs
less
than
glass
on
polyethylene,
but
doesn't
give
a
numerical
value.

The
large
headspace
(25
ml
in
a
50
tube)
is
undesirable;
any
losses
of
the
14C­
label,
e.
g.,
from
volatilization
or
sticking
to
the
tube,
will
inflate
the
sorption
coefficient
since
the
method
calculates
the
amount
sorbed
by
difference
between
the
initial
and
final
equilibrium
solution
concentrations.
Also
the
24
hour
mixing
period
seems
arbitrary.
Were
experiments
done
for
different
periods
of
time
to
establish
that
equilibrium
was
reached
within
24
hours?

Details
on
the
stock
solution
are
lacking.
What
solvent
was
used
and
what
is
the
specific
activity
and
radiochemical
purity
of
the
14C­
FC
95.

The
idea
of
using
a
cotton
swab
after
the
draining
step
is
unusual.
Hopefully
this
didn't
remove
soil
as
well
as
water.
The
­
20%
or
less
decrease
in
solute
concentration
due
to
sorption
isn't
as
high
as
I'd
like
to
see
it.
A
50%
or
greater
decrease
would
be
better.

This
section
generally
lacks
detail
that
would
normally
be
required
for
publication.

Results
and
Discussion
The
linearity
of
the
isotherm
has
been
shown
over
the
concentration
range
used.
However,
to
demonstrate
that
the
entire
isotherm
is
linear,
the
linearity
must
extend
to
equilibrium
solution
concentrations
that
approach
the
water
solubility
of
the
compound.
Do
you
know
the
solubility
of
FC95
or
FC143:
If
not,
how
were
the
initial
solution
concentrations
selected?

The
sorption
coefficient
(K)
of
FC
95
appears
to
be
about
1
as
indicated.
The
organic
matter
normalized
sorption
coefficient
CK,
=
K/
fa
is
I(,
=
l/
O.
025
=
40,
or
log
K,
=
1.6.
This
is
a
soil
sorption
coefficient
intermediate
between
benzene
and
toluene.
It
would
be
worthwhile
to
examine
some
additional
soils
to
confirm
this
K,
value.
Generally,
the
K,
values
should
converge
within
a
factor
of
2
to
3
for
different
soils.
This
would
increase
my
confidence
in
the
accuracy
of
the
one
measured
value.

I've
spot
checked
the
soil
concentrations
of
FC­
95
for
both
the
sorption
and
desorption
experiments
and
I
get
essentially
the
same
values.
The
calculations
look
good.

The
K
values
for
FC
143
is
lower
than
FC
95
indicating
that
it
probably
has
a
higher
water
solubility.
The
hystersis
in
the
desorption
isotherm
is
surprising,
and
has
been
over­
interpreted.
The
sorption
isotherm
is
linear
indicating
a
single
sorptive
process.
The
conclusion
regarding
"three
different
binding
mechanisms
.
.
.with
stronger
binding
at
higher
concentrations
and
the
converse
at
lower
concentrations"
is
very
speculative
based
on
the
single
experiment.
If
one
examines
column
I
"Amount
Desorbed
as
a
Percent
of
Amount
Adsorbed"
the
values
range
from
26
to
212
percent,
so
it's
pretty
inconclusive.
There
is
a
fairly
good
discussion
of
hysteresis
in
J.
Environ.
Qual.
12:
325­
330
by
Koskinen
and
Cheng
who
observed
this
phenomena
for
the
weak
acid
pesticide
2,4,5­
T.
The
causes
of
hysteresis
are
varied
and
complicated
and
may
include
microbial
degradation
of
the
compound
during
desorption,
and
changes
in
the
physical
and/
or
chemical
properties
of
the
soil­
solution
system.
For
example,
desorption
using
distilled
water
(as
is
the
case
here)
could
result
in
soil
dispersion
so
that
a
clear
supematant
solution
could
not
be
obtained.
This
can
cause
quenching
of
radioactivity
in
solution
and
other
problems
leading
to
error.

The
"material
balance"
as
presented
in
the
report
is
a
little
misleading.
To
obtain
a
material
balance
you
should
measure
the
amount
of
"C­
activity
in
soil
at
the
end
of
the
experiment,
and
add
it
to
the
measured
solution
concentrations.

General
Comments.
The
K,
values
calculated
here
use
an
organic
carbon
content
of
2.2%
whereas
the
value
stated
in
the
Materials
and
Methods
is
1.5%?

The
water
solubilities
are
cited
as
300
mg/
L
for
FC
95
and
>
2Og/
L
for
FC
143.
Surely
the
latter
value
is
wrong.
If
the
solubilities
are
truly
that
different,
then
the
sorptive
properties
should
be
vastly
different,
which
they
are
not.
If
FC143
has
a
solubility
of
>
20,000
mg/
L,
then
I
would
expect
no
sorption.
This
value
must
be
erroneous.

Recommendations:

1.
Obtaining
K,
K,
values
on
additional
soils.
Determine
if
K,
is
relatively
constant.

2.
Obtain
a
true
mass
balance
by
measuring
14C­
activity
in
soil
and
solution
phase.

3.
Interpret
desorption
data
more
cautiously.

4.
Get
correct
value
of
water
solubility
of
FC
143.

003618
.r
J
'
am
.y
'
For=
47
11
A
TEC.
HNICAL
REPORT
SUMMARY
TO:
TECHNICAL
COhlMUNlCATlO~
S
CENTER
­
201.
XN
(tmnportant
­
If
report
is
printed
on
both
sides
of
peper;
send
two
copies
to
TCCJ
Division
0­
t.
Numbr
EE
6
PC
0222
Prolrt
Proloct
Numtmr
Fate
of
Fluorochemicals
9970612633
Report
Title
Report
Numbor
Adsorption
of
FC
95
and
FC
143
on
soil
1
T
o
J?
I*
m
T
a..
on:
s
Authorlr)
SW
Emptoyr
Numborb)

Stephen
K.
Welsh
73583
Notebook
Rofwanca
No.
of
Pager
Including
Covorshoat
140673,
R47704
.
­
14
SECURITY
b
mhat
a
C
l
o
s
e
d
­
3M
CHEMICAL
REGISTRY
b
New
Chemicals
Reporteti
q
Yes
R
No
KEYWORDS:
.
&hct
term8
from
3M
Thesaurus.
Suggest
other
applicable
term8.
l
EE
&
PC
­
Div.

Fluorochemical
Soil
Adsorption
Mobility
Information
Liaison
Ini
tialr:
s#
d
:URRENl
OBJECTIVE:
`.
c
z
To
obtain
an
indication
of
FC
95
and
`FC
143
mobility
in
sandy
loam
soil.

REPORT
ABSTRACT:
(200­
250
words)
This
abstract
information
is
distributed
by
the
TecJtnical
Communications
Center
t,
blat
3M'ers
to
Company
R&
D.

As
a
part
of
the
Fate
of
Fluorochemicals
Project,
an
indication
of
mobility
of
FC
95
and
FC
143
in
sandy
loam
soil
was
Idesired.

Adsorption­
desorption
experiments
(after
David&,
1976,
and
Hamaker;

1975)
along
with
water
solubility
data
can
provide
such.
information.

The
adsorption
coeffi%
nts
for
FC
95
and
FC
143
were
determined
to
be
0.99
and
0.38,
respectively.
For
FC
95
adsorption
and
desorption
'
could
be
described
by
a'single
valued
function
whil'e
for
FC
143,

they
could
not.
Based
on
these
data,
both
compounds
would
be
judged
mobile
in
the
sandy
loam
soil
used
in
this
study.
2
CONCLUSIONS
Adsorption
coefficient
for
FC
95
and
FC
143
were
0.99
and
0.38,

respectively.
For
FC
95,
adsorption
and
desorption
could
be
described
by
a
single
valued
function
while
for
FC
143,
they
could
not,
Considering
adsorption
coefficients,
desorption
characteristics
and
water
solubilities,

both
compounds
would
be
judged
mobile
in
the
sandy
loam
soil
used
in
this
study.

INTRODUCTION
As
a
part
of
the
Fate
of
Fluorochemicals
Project,
an
indication
of.
c
mobility
of
FC
95
and
FC
143
in
sandy
loam
soil
was
de3iired.

Adsorptiondesorption
experiments
(after
Davidson,
1976,
and
Hamaker,
1975)
along
with
water
solubility
data
can
provide
this
indication
of
mobility.
This
approach
is
used
by
the
0.
S.
EPA
in
pesticide
registration
requirements.

MATERIALS
AND
METHODS
Duplicate
S­
g
samples
of
air­
dried
Brill
sandy
loam
soil
(57%
sand,

36%
silt,
7%
clay,
2.5%
organic
matter,
1.5%
organic
carbon,
with
pH
6.5
and
C.
E.
C.
of
15.3
meq./
lOOg)
were
shaken
with
25
ml
of
solution
in
SO
ml..

poly
propylene
centrifuge
tubes
for
24
hours
on
a
wrist
action
shaker
at
room
temp.

(16­
19°
c).
Polypropylene
tubes
were
used
because
they
were
found
in
separate
experiments
(3M
Tech
Notebook
#470673,
`C.
H.
Schrandt)
to
absorb
less
FC
95
and
FC
143
than
glass
or
polyethylene
tubes.

Solutions
were
made
by
diluting
a
stock
solution
of
each
chemical.

Concentrations
o
f
14C­
labeled
FC
95
were
282
mg/
l.,
158
mg/
l.,
90
mg/
l.,

51
mg/.
l.,
2
8
mg/
l.,
(lOO%,
56%,
32%,
18%,
lo%,
1%
of
stock).
Concentrations
o
f
14C.­
labeled
F
C
1
4
3
w
e
r
e
mg/
l.,
2
9
3
523
mg/
l.,
167
mg/
l.,
94
mg/
l.,
52
mg/
l.,

and
5.2
mg/
l.
After
shaking
the
initial
solutions
as
well
as
the
three
desorption
extractions
with
deionized
water,
the
samples
Were
centrifuged
at
5000
rpm
for
10
min.,
and
three
aliquots
of
each
supernatant
solution
were
taken
for
scintillation
counting.

After
the
adsorption
step,
22.5
ml
of
solution
were
recovered.

Therefore,
it
was
assumed
that
2.5
ml
of
liquid
remained
with
the
soil
in
each
step
and
this
amount
was
accounted
for
in
the
desorption'calculations
(see
Results
and
Discussion
section).

In
the
FC
95
experiment,
the
supernatant
liquid
was
simply
drained
`r
off
at
each
step
and
the
next
25
ml
of
liquid
were
`&
t
into
the
tubes.

In
the
FC
143
experiment,
the
supernatant
liquid
remaining
after
the
draining
step
was
absorbed
with
a
cotton
swab
before
putting
the
iext
25
ml
of
liquid
into
the
tubes.

The
procedures
for
the
FC
95
and
FC
143
experiments
were
recorded
in
3M
Technical
Notebook
#40673,
p.
49
and
p.
51,
respectively.

From
the
raw
counting
data,
disintegrations
per
minute
(DPM)
and
.
FC
95
and
FC
143
concentrations
were
calculated
for
all
of
the
supernatant
solutions.

Statistical
analysis
and
plotting
of
the
data
was
done
with
the
MINITAB
package
of
the
3M
TRAC
computer
service.

RESULTS
AND
DISCUSSION
FC
95
Adsorption
data
for
FC
95
are
presented
in
TABLE
I
and
FIGURE
1.

Comparing
the
regression
equation
of
the
adsorption
isotherm
(FIGURE
1)

x/
m
=
­0.29
+
0.99C
with
the
Freundlich
equation
x/
m
=
KC
l/
N
,
it
could
be
seen
that
the
adsorption
coefficient,
K,
equaled
0.99
and
the
exponent,
N,
GO362:
equaled
one.
The
linear
shape
of
the
adsorption
isotherms
(N=
l)
indicated
4
4
that
FC
95
adsorption
on
sqil
would
be
independent
of
concentration.
The
low
adsorption
coefficient
(K=
O.
99)
indicated
that
FC
95
would
be
niohile,

i
.e
.,
it
would
move
readily
with
the
ground
water
through
this
sandy
loam
soil.

TABLE
I
A
A
B
Initial
FC
95
Equil.
Cont.,
Cont.,
mg/
l
C,
mg/
l.

2
8
2
.2
2
8
2
.2
2
3
3
.9
2
3
3
.9
1
5
8
.0
1
5
8
.0
1
3
4
.2
1
3
4
.2
9
0
.0
9
0
.0
7
6
.9
7
6
.9
51.0
4
2
.0
4
2
.0
2
8
.0
2
8
.0
2
2
.1
2
2
.1
2
.8
2
.8
2
.0
2
.0
D
D
Total
FC
95
Total
FC
95
in
In
Initial
Sol'n
Sol'n
at
Equil;,
mg
(A
x
0.025
liters]
(B
x
0.025
liters)

7.0500
5.847.50
5.847.50
3
.9
5
0
0
3
.9
5
0
0
3.35soo
3.35soo
2.2soo
2.2soo
1
.9
2
2
5
0
1
.9
2
2
5
0
1
.2
7
5
0
1
.2
7
5
0
1.05000
0
.7
0
0
0
0
.7
0
0
0
0.
sszso
0
.0
7
0
0
0
.0
7
0
0
0.05000
FC
95
ADSORPTION
DATA
E
C
%
Removed
A,
BBy
Soil
.(
T
x
100
>
.

(1
7
.1
(1
7
.1
15.1
1
4
.6
1
4
.6
1
7
.8
1
7
.8
2
1
.1
2
1
.1
2
7
.0
2
7
.0
f'..
f'..
,,\
3
,,\
3
!
!

F
I'.`.

F
C
95
Adsorbed
o
n
S
o
i
l
,
x
m
,
Vg/
g
((
D­
E)
x
10
5
@/
mg
I
S
g
Soil
2
4
0
.8
2
4
0
.8
119.0
6
5
.7
6
5
.7
4
5
.3
4
5
.3
2
9
.5
2
9
.5
3
.8
3
.8
Desorption
data
for
FC
95
are
shown
in
TABLE
II
and
FIGURE
2.
For
comparison,

desorption
isotherms
for
the
pesticide
fluometuron
are
given
in
FIGURE
3.

For
clarity
FC
95
desorption
isotherms
are
not
drawn
in
FIGURE
2.

However,
all
of
the
data
points
lie
very
close
to
the
adsorption
isotherms
indicating
that
adsorption
and
desorption
could
be
described
by
a
single­
valued
function
with
desorption
coefficients,
K*
,equaling
the
adsorption
coefficient,

K
.
K
.
4I?
x?
36;
22
4I?
x?
36;
22
5
240
A
A
c
0
Regression
Eqn.:
Y
=
­0.29
+
Regression
Eqn.:
Y
=
­0.29
+
0.99
X
0.99
x
R­
Squared
=
0.985
R­
Squared
=
0.985
Actual
Data
Points'
Actual
Data
Points'
Predicted
Y
Values
Predicted
Y
Values
60
120
180
240
300
Equil.
Cont.,
C,
mg/
l
FIGURE
1
FC
95
Adsorption
Isotherm
This,
along
with
the
observation
that
approximately
all
of
the
adsorbed
FC
95
was
subsequently
desorbed
(TABLE
II,
Column
H)
indicated
that
binding
forces
were
weak
and
would
be
another
indication
of
high
mobility
of
FC
95.

Material
balance
data
for
FC.
95
are
presented
in
TABLE
III
and
these
data
indicate
that
all
of
the
chemical
was
accounted
for
throughout
the
experiment.
.
6
TABLE
II
FC
95
DESORPTION
ISOTHERM
DATA*

A
Equil.
Cont.
in
Solution,
C,
mg/
l.

233.900
134.200
76.900
42.000
22.100
2.000
E
Amount
Adsorbed
on
Soil,
x/
m
ug/
g
(Column
F,
TABLE
I)

240.800
67.6000
12.0000
­9.1500
119.000
19.4500
­14.9000
­25.8000
65.700
3.3000
­16.7000
­23.9500
45.300
13.2000
2.0500
­2.0000
29.500
11.4000
4.7000
2.2500
3.800
1.7000
0.9000
0.4500
B
Equil.
Cont.
in
First
Desorption
mg/
I.

52.7000
30.3000
18.3000
9.6000
5.3000
0.6000
C
Equil.
Cont.
in
Second
Desorption
w/
l.

14.9000
9.0000
5.3000
2.9000
1.7000
0.2000
F
Amount
on
Soil
After
First
Desorption,
pg/
g
G
'9
Amount
'on'%
Soil
After
Second
Desorption,
pg/
g
D
Equil.
Cont.
in
Third
Desorption
mg/
l.

5.20000
2.80000
1.80000
1.00000
0.60000
0.10000
H
Amount
on
Soil
After
Third
Desorption,
ug/
g
*Columns
F,
G,
and
H
were
calculated
in
the
same
way
as
Column
F,:
TABLE
I
with
correction
for
the
amount
of
FC
95
in
the
2.5
ml
of­
solution
remaining
from
the
previous
step
in
each
case
(See
Materials
and
Methods
Section.)

FIGURE
2
FIGURE
3
FC
95
DESORPTION
DATA
POINTS
AND
ADSORPTION
ISOTHERM
ADSORPTION
AND
DESORPTION
ISOTHERMS
FOR
FLlJOMEI'URON
ON
COBB
SAND.
SOLID
AND
BROKEN
LINES
ARE
BEST
FIT
FOR
ADSORPTION
AND
DESORPTION
_
RESPECTIVELY­
fFrom
Davidson.
­­
­.­
7
TABLE
III
FC
95
Material
Balance*

A
Total
Initial'
FC
95
in
Solution,
mg.
fColumn
D;
TABLE
1)
'.

7;
05000
5.84750
1.20250
3.95000
3.35500
0.59500
2.25000
1.99250
0.32750
1.27500
1.0500
0.2250
'
0.7000
0.55250
0.14750
0.07oofl
0.05000
0.02000
D
E
.­
F
Amount
Removed
by
Amount
Removed
by
Amount
Removed
by
First
Desorption,
mg.
Second
Desorption,
mg.
Third
Desorption,
mg.

0.864500
0.278000
0.105750
0.497750
0.171750
0.054500
0.311000
0.100000
0.036250
0.159000
0.055750
0.020250
0.090500
0.033500
0.012250
0.011500
0.004000
0.002250
G
Total
Amount
Desorbed
by
Three
Desorptions,
mg
(D+
E+
F)

1.2483
­0.45750
103.805
0.7240
­0.12900
121.681
0.4473
­0.11975
136.565
0.2350
­0.01000
104.444
0.1363
0.11250
92.373
0.0178
0.002250
88.750
*Columns
D,
E,
and
F
were
obtained
by
first
calculating
the
amount
(mg)
B
FC
95
in
Solution
at
Equil.,
mg.
'(
Column
E,
TABLE
I>

H
Amount
Remaining
on
Soil
After
3
Desorptions
mg.
CC
­
G)
C
FC
95
on
soil
at
Equil.,
mg.
(A
­
Bl
I
Amount
Desorbed
as
Percent
of
Amount
Adsorbed
(G/
C
x
100).

of
FC­
95
in
27.5
ml
(25
ml
added
plus
2.5
ml
remaining
from
previous
step)
of
solution
in
each
respective
step
and
then
subtracting
the
amount
(mg)
in
the
2.5
ml
of
solution
remaining
from
the
previous
step.
8
FC
143
Data
for
FC
143
are
presented
in
TABLE
IV
and
TABLE
V
and
in
FIGURE
4.

The
adsorption
isotherm
indicated
FC
143
mobility
similar
to
that
of
FC
95
with
K=
0.38
and
N=
l.
Regression
analyses
were
not
performed
on
the
desorption
isotherms,
however,
the
graphed
data
(FIGURE
4)
indicated
that
adsorption
and
desorption
could
not
be
described
by
a
single­
valued
function.
That
is,
the
K'
and
N'
values
for
desorption
would
not
be
the
same
as
K
and
N
for
adsorption.
Subjective
evaluation
would
indicate
that
the
desorption
coefficient
I
K
,
would
be
much
smaller
than
the
adsorption
Coefficient,
K,
at
solution
concentrations
greater
than
about
25
mg/
l,
since
the
slope
of
the
adsorption
`1
isotherm
was
much
greater
than
the
slopes
of
the
!&
sorption
isotherms
in
i
this
range.
At
solution
concentrations
less
than
25
mg/
l.,
the
desorption
coefficients
would
appear
to
be
much
greater
than
the
adsorption
coefficient.

From
this
it
would
appear
that
two
or
three
different
binding
mechanisms
were
involved
with
stronger
binding
occuring
at
the
higher
concentrations
and
the
converse
at
lower
concentrations.
While
this
may
indicate
a
tendency
for
FC
143
to
be
immobile
at
high
concentrations,
it
would
be
quite
mobile
in
any
situations
involving
low
concentrations.
m
Material
balance
data
for
FC
143
are
presented
in
TABLE
VI.
While
the
two
concentrations
resulting
in
212%
and
201%
desorption
(last
column
in
TABLE
VI)
were
erratic,
in
general,
the
data
indicated
that
all
of
the
FC
143
was
accounted
for
throughout
the
experiment;
'
.

.
9
.
.

TABLE
IV
FC
143
Adsorption
Data
A
B
c
Initial
FC
143
Cont.,
mg/
l.
.

,
Equil.
cont.,
c,
q/
l.

522.5
522.5
4
8
5
.8
4
8
5
.8
292.6
292.6
279.1
167.2
167.2
160.3
160.3
9
4
.1
9
4
.1
9
2
.2
9
2
.2
52.3
52.3
4
9
.9
4
9
.9
5
.2
5
.2
5
.1
5
.1
D
Total
FC
143
in
Initial
Sol'n,

(?
'x
0.025
liters)

13.0625
13.0625
7.3150
7.3150
4.1800
4.1800
2.3525
2.3525
1.3075
0.1300
0.1300
X
Removed
By
Soil
(*
T
x
100)

7
.0
7
.0
.
.
5
5
'
i
4
.6
'
i
4
.6
4.1
4.1
2.0
2.0
4.5
4.5
1.9
E
F
Total
FC
143
in
FC
143
Adsorbed
Sol'n
at
Equll.,
(B"
px
0.025
liters)
on
Soul,
x&
m,
vg/
g
(CD­
Ej
(CD­
Ej
X
X
10
5
pg/+
nsQ$
­_

12.1450
12.1450
183.5
183.5
6.9775
6.9775
6
7
.5
6
7
.5
4.0075
4.0075
34.5
34.5
2.3050
2.3050
9
.5
9
.5
1.2475
1.2475
12.0
12.0
0.1275
0.1275
0.5
0.5
10
TABLE
v
FC
143
Desorption
Isotherm
Data*

A
B
Equil.
Cont.
in
Equil.
Cont.
Solution,
C,
in
first
Desorpmp
l
tion
Solution,
mn/
l.

(Column
B,
Table
ry)

485.800
47.6000
279.100
28.8000
160.300
17.2000
92.200
10.7000
49.900
6.1000
5.100
0.6000
E
F
Amount
Adsorbed
Amount
on
Soil
on
Soil,
x/
m,
wf3
After
First
DesorpW
R
tion
(Column
F,
TABLE
IV)

183.500
164.600
67.500
50.850
34.500
20.050
9.500
­3.250
12.000
3.400
0.500
­0.250
C
Equil.
Cont.
Equil.
Cont.
in
Second
Desorp­
in
Third
Desorption
tion
Solution,
mg/
l.
solution,
mg/
l.

6
.8
0
0
0
0
4.80000
3.40000
2.00000
0.80000
0.100G0
.;
L
t
G
Amount
on
Soil
Amount
on
Soil
After
Second
Desorpw
f!!
tion
After
Third
Desorpw
g
t
i
o
n
151.000
38.650
9.950
­8.900
135.150
25.100
0.650
­10.650
2.050
­
1.350
D
3.50000
2.90000
2.00000
0.50000
0.20000
0.01000
H
­0.500
­0'.
505
*Columns
F,
G,
and
H
were
calculated
in
the
same
way
as
Column
F,
TABLE
IV
with
correction
for
the
amount
of
FC
143
in
the
2.5
ml
of
solution
remaining
from
the
previous
step
in
each
case
(See
Materials
and
Methods
Section).
.
11
200
150
100
50
0
­50
BP
B
­B
­
.­

­


Y=
­16.3
+
0.38.
X
R­
SQUARED
=
0.936
0
100
200
300
400
500
Equil.
Cont.,
C,
mg/
l
FIGURE
4
FC
143
ADSORPTION
AND
DESORF'TION
ISOTMERMS
Solid
line
is
best
fit
adsorption
isotherm.
Dotted
lines
are
esti­
mated
desorption
isotherms.
A's
are
adsorption
isotherm
data
points.
B,
C,
D,
E,
and
F
are
desorption
data
points
for
the
respective
concentrations.

GENERAL
COMMENTS
The
FC
95
and
FC
143
adsorption
coefficients
from
these
experiments
may
be
converted
to
the
analogous
constants
based
on
soil
organic
carbon
content
Koc,
with
the
equation
Koc
=
100
K/(%
organic
carbon)
giving'

a
Koc
of
45
for
FC
95
and
17
for
FC
143
(2.2%
organic
carbon
for
this
soil).
Comparing
these
values
to
those
in
TABLE
VII,
it
can
be
seen
that
FC
95
and
FC
143
are
at
the
low
end
of
the
spectrum,
again
indicating
high
mobility
of
these
compounds.
­­.

'
.

A
Total
FC
143
Initially
in
Solution
(Co?&
D,
Table
IV}

13.0625
12.1450
7.3150
6.9775
4.1800
4.007s
2.3525
2.3050
1.307s
1.2475
.
0.1300
0.1275
D
Amount
Removed
by
First
Desorption,
mg.
Amount
Removed
by
Second
Desorption,
mg.
Amount
Removed
by
Third
Desorption,
mg.

0.09450
0.06800
0.079250
0.08325
0.06100
0.066750
0.07225
0.05050
0.046500
0.06375
0.02825
0.008750
0.04300
0.00675
0.003500
0.0037s
0.0012s
0.00002s
G
H
Total
Amount
Desorbed
by
Three
Desorptions,
mg
(D+
E+
F)
Amount
Remaining
on
Soil
After
3
Desorptions
mg.
cc
­
G­)
I
w
Amount
Desorbed
as
percent
of
Amount
Adsorbed
(G/
C
x
100)

0.2418
0.676750
26.349
0.2120
0.125500
62.815
0.1693
0.003250
98.116
0.1008
­0.053250
212.10s
O.
'OS35
0.006750
88.750
0.0050
­0.002525
201.000
12
TABLE
VI
FC.
143
MATERIAL
BALANCE*

B
FC
143
in
Solution
FC
143
on
Soil
at
Equil.,
mg.
at
Equil.,
mg.
(Column
E,
TABLE
IV)
(A
­
91
E
C
0.917s
.
0.337s
0.1725
0.047s
0.0600
0.0025
'..
t
+
F
*Columns
D,
E,
and
F
were
obtained
by
first
calculating
the
amount
(mg)
of
FC
343
in
27.5
ml
(25
ml
added
plus
2.5
ml
remaining
from
previous
step)
of
solution
in
each
respective
step
and
then
subtracting
the
amount
(mg)
in
the
2.5
ml
of
solution
remaining
from
the
previous
step.

003630
c
.
.
­<
13
TABLE
VII
Comparison
of
Adsorption
Coefficients
for
a
Selected
Group
of
Pesticides
I
(Hamakcr
and
Thompson,
1972)

Chemical
K
oc
(mobile]
Chloramben
12.8
(FC
143
­
­
­
­
­
­
­
­
­
17)
2
,4
­D
32
(FC
95
­
­
­
­
­
­
­
­
­
­45)
Propham
51
Bromacil
71
Monuron
8
3
Simazine
135
Propazine
152
Dichlobenil
164
Atrazine
172
Chloropropham
245
Prometone
300
Ametryn
380
Diuron
485
Prometryne
513
.
.::
t
Chloroxuron
Paraqua
t
4,986
F,,
2c!
zz
20,000
(immobile)
DDT
243,000
The
small
amounts
adsorbed
and
ease
of
desorption
is
consistent
with
the
relatively
high
water
solubility
of
FC
95
(300
mg/
l)
and
IC
143
(>
20
g/
l.)

and
with
the
chemical
nature
of
the
molecules
­
organic
salts
which
ionize
in
aqueous
solution:

C8FljS03­
K+
C7FlSC02
NH4+

FC
95
FC
143
.
t

14
Terms
DPM
­
Disintegrations
per
minute
C
­
Concentration
of
chemical
in
solution
at
equilibrium
x/
m
­
Concentration
of
chemical
adsorbed
on
soil
at
equilibrium
R2
­
Coefficient
of
determination
K
­
Adsorption
coefficient
K'
­
Desorption
coefficient
N
­
Exponential
term
in
Freundlich
Equation
.
:z
1.
t
N'
­
Exponential
term
for
desorption
equation
QC
­
Adsorption
coefficient
based
on
soil
organic
carbon
content
References
Davidson
J.
M.,
et.
al.,
1975,
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