EPA R2-73-266
June 1973 Environmental Protection Technology Series
Herbicide Contamination of
Surface Runoff Waters
\
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
U. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-R2-73-266
June 1973
HERBICIDE CONTAMINATION OF SURFACE
RUNOFF WATERS
by
John O. Evans
D. R. Duseja
Utah State University
Logan, Utah 84322
Envlror.n.6r:.tal Protection Agency
Llb.r,r;r •. -
Chicago, illli
Project #13030 FDJ
Program Element #1B2039
Project Officer
Dr. James P. Law, Jr.
U. S. Environmental Protection Agency
Robert S. Kerr Environmental Research Laboratory
P. O. Box 1198
Ada, Oklahoma 74820
U.S. Envirorj: .:' •
Roglon 13, .'./.':•. -.
iJoO S.
Qhioago, 1L
Prepared for
OFFICE OF RESEARCH AND MONITORING
U. S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D. C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, B.C. 20402
Price $1.25 domestic postpaid or $1 GPO Bookstore
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EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents necessarily
reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or
recommendation for use.
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ABSTRACT
Field and laboratory studies of the movement of herbicides were con-
ducted to determine their potential as contaminants in irrigation return
flow. Special emphasis was given to the use of herbicides for vege-
tation control along ditches, canals and watersheds where high dosages
are required to control the excessive growth of grasses and broad-
leaved weeds. The following herbicides have been studied: substituted
urea (diuron), triazines (summitol and atrazine), phenoxyacetic acid
(2, 4-D and 2, 4, 5-T) and a substituted pyridine (picloram).
The greatest tendency for transport of herbicides in water coming in
contact with soils occurs during the initial storms following spray app-
lication. If the intensity of the initial precipitation is not sufficient
to cause movement across the soil, the danger of herbicide movement
is essentially eliminated.
The highest concentrations (ppm) of herbicide observed in surface
waters were 1.8, 0. 5, 4. 2, 1.2 and 2. 7 for diuron, summitol, 2, 4-D,
2,4, 5-T and picloram, respectively. These levels were observed
immediately below treated areas receiving the higher recommended
dosages of the herbicides. All herbicide concentrations dropped below
the limit of detection within a few hundred meters below the sprayed
areas. Presumably, soil filtration, adsorption and dilution are
primarily responsible for the loss of herbicides from water.
111
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CONTENTS
Section Page
I Conclusions 1
II Recommendations 3
III Introduction 5
IV Literature Review 9
V Materials and Methods 19
VI Results and Discussion 33
VII Summary 81
VIII Acknowledgments 85
IX References 87
X Publications Resulting from Project 93
XI Appendices 95
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FIGURES
No.
1 A typical Cl breakthrough curve (ETC) used for
calculating dispersion coefficient.
2 Effect of time on adsorption of picloram by four soils
at 1 ppm initial concentration. 44
3 Effect of organic matter content of three soils and
the removal of organic matter on adsorption of
picloram. Adsorption determined at 25° C. 47
4 Picloram adsorption by Chance loam and Providence
silt loam soils as influenced by the pH of soil sus-
pension. 51
5 Effect of concentration of picloram in solution on its
adsorption by two soils. Adsorption determined at
25° C. 60
6 Freundlich plot for adsorption of picloram by Pro-
vidence silt loam, and Chance loam soils at 25° C. 62
7 Relative concentration distribution (C/C ) of pic-
loram in effluent from Millville silt loam soil
column as affected by amount of picloram solution
added on top of the soil column. 68
8 Effect of two rates of picloram application on the
relative concentration distribution (C/C ) of pic-
o
loram in effluent from Millville silt loam soil
column. 69
9 Effect of Ca-saturation on the relative concentra-
tion distribution (C/C ) of picloram in effluent from
o
Millville silt loam soil column. 70
10 Relative concentration distribution of picloram in
Aiken clay soil, (1) as a function of two application
rates (2) as affected by Ca-saturation of the soil. 72
VI
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FIGURES (Continued)
No.
11 Experimental (o) and calculated relative picloram
concentration curve from Millville silt loam soil.
Solid curve was calculated from retardation factor
(K1) from batch studies and dashed curve from
'adjusted factor1 (K") (See Table 22). 74
12 Relative concentration distribution (C/C ) of pic-
o
loram in two columns of Millville silt loam soil of
different length. 76
13 Experimental (o) and calculated relative picloram
concentration distributions from an 8. 9 cm column
of Ca-saturated Millville silt loam soil. Solid
curve was calculated from retardation factor (K1)
from batch studies and dashed curve from 'adjusted
factor' (K'f) (See Table 22). 77
14 Experimental (data points) and theoretical relative
picloram concentration distributions from natural
(o), and Ca-saturated (A) Aiken clay soil. Solid
lines were calculated from retardation factor (K')
from batch studies and dashed curve from 'adjusted
factor' (K") (See Table 22). 79
VII
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TABLES
No.
1 Properties of soils used in the studies.
2 Diuron concentration (ppm) in irrigation canal
water at 10, 100 and 1000 foot distances below
areas receiving a 30 Ib/A dosage to control
ditchbank vegetation. 33
3 Atrazine concentration (ppm) in irrigation canal
water at 10, 100 and 1000 foot distances below
areas receiving a 10 Ib/A dosage to control
ditchbank vegetation. 35
4 A comparison of the quantity of GS-14254 recov-
ered in the runoff water from two treatments at
different distances from the treated area. 36
5 A comparison of the quantity of GS-14254 recov-
ered in the runoff water at the end of the treated
plots from two treatments at different times
during irrigation. 37
6 Average picloram concentration in surface runoff
water at various collection points during 1969. 38
7 Picloram concentrations (ppb) in surface runoff
waters collected at several distances from herbi-
cide treated sites. 40
8 2,4-D concentrations (ppb) in surface runoff waters
collected at several distances from treated areas. 41
9 2,4, 5-T concentrations (ppb) in surface runoff
waters collected at several distances from treated
areas. 41
10 Adsorption of picloram by five soils, in their nat-
ural state and after removal of organic matter. In-
cubations were made at 25° C and picloram concen-
trations of 0. 5 and 1. 0 ppm. 45
Vlll
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TABLES (Continued)
No. Page
11 Effect of soil type and organic matter content on the
release of picloram with 10 ml extractions of deion-
ized water at 25° C. 48
12 Release of picloram from Providence silt loam soil
with four successive 10 ml extractions of deionized
water at 25° C. The soil contained 371 (-igm picloram/
kg soil initially. 49
13 Effect of pH on the adsorption of picloram by Chance
loam and Providence silt loam soils at 25° C (initial
picloram concentration 1 ppm). 50
14 Influence of various salts on the adsorption of pic-
loram by Providence silt loam soil. Initial picloram
concentration was 1. 0 ppm and incubation temperature
was 25° C. 55
15 Cationic composition of the exchange complex of
various soils. 56
16 Effect of temperature on the equilibrium adsorption
of picloram by Providence silt loam, Chance loam,
and Aiken clay soils from 1. 0 ppm concentration. 58
17 Effect of picloram concentration on its adsorption by
Providence, Chance, and Aiken soils at 25 C. 61
18 Effect of increasing dilution with deionized water on
the release of picloram from Providence silt loam
soil at 25° C. 63
19 Effect of soilrsolution ratio on the equilibrium ad-
sorption of picloram by Providence silt loam soil
from aqueous solutions of 1 ppm concentration. 64
20 Correlation coefficients (r) bet-ween soil properties
and adsorption of picloram by five soils. 65
IX
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TABLES (Continued)
No. Page
rl
21 Correlation coefficients (r) of various soil proper-
ties among themselves. 66
22 Physical data for picloram displacement through
Millville silt loam and Aiken clay soils. 73
x
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SECTION I
CONCLUSIONS
1. Many studies have been made to determine the levels of herbicides
in irrigation water and to determine the effects of herbicide residues
in water. The low concentrations that are observed following proper
application of the herbicides would not likely be hazardous to crops
or animals.
2. Herbicides can be detected in ditch and canal water subsequent to
treating the bank to control vegetation. The herbicides are rapidly
diluted and within a short distance are not detectable by using plants
or gas-liquid chromatography.
3. Soil properties play a major role in determining the movement of
herbicides in water. Organic matter content, pH, cation exchange
capacity and sesquioxides are the most important soil properties
influencing the adsorption or release of herbicides. Soil type plays
a minor role in this regard. Five soils were compared for their
tendency to adsorb and release the herbicide, picloram. The ad-
sorption of the herbicide from water containing 1.0 ppm picloram
ranged from 11 to 52% among the five soils.
4. The release of herbicides from soil into surface waters was pri-
marily regulated by organic matter, pH and cation exchange capacities
of soils. Fifty percent of the adsorbed picloram was eluted with four
flushings of water. Continuous flushing with water resulted in the
complete removal of picloram within 24 hours for all soils studied.
5. Concentrations of herbicides in surface water were reduced pro-
bably by infiltration of a portion of the contaminated water into the
soil and by dilution with additional water. Under field conditions, this
reduction occurred within a few hundred meters distance below the
treated areas.
6. The adsorption and release of picloram by soils is influenced by
the salt load of the soil. Calcium saturation of a highly adsorptive
soil further increased its capacity to adsorb the herbicide. The
enhanced picloram adsorption could not be accounted for by the in-
crease in undissociated picloram as a result of the drop in pH caused
by salt additions. Further tests demonstrated that picloram did not
precipitate from solution in the presence of the salts as is commonly
observed among other organic molecules.
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SECTION II
R E C OMME N DAT IONS
The study was quite exhaustive with regard to the movement of pic-
loram in soil and water but other herbicides were limited to one or
two field trials and consequently cannot be considered in detail. The
recommendations will pertain primarily to picloram and its effects
on the quality of irrigation return flow.
Under field conditions, picloram does not present a serious threat to
water quality a short distance downstream from the site of application.
It is evident that precautions given on the herbicide label are adequate
to allow the material to be used safely. To avoid crop or other plant
injury, do not treat or allow picloram to fall directly into water and
do not treat bottoms of irrigation ditches. Broadleaved plants such
as potato, bean, cucumber, alfalfa and others are very sensitive to
picloram and should not be irrigated with water from picloram treated
areas a short distance from the crops.
A very small fraction of the applied herbicide tends to move into
water coming into contact with a treated soil surface. The quantity
that moves with the surface water decreases rapidly as rainfall or
irrigation moves the herbicide into the soil where it is strongly
adsorbed onto the soil colloids and subsequently broken down by
chemical and biological processes. Once adsorbed onto soils, pic-
loram is slowly released with continuous flushing with water. The
flushing tends to reduce its concentration to levels which are nontoxic
to plants. The total quantity of picloram adsorbed on the five soils
studied was recovered with a. 24 hour period of continuous flushing.
Soil particles that are eroded with excessive surface water may carry
significant amounts of the herbicide. Care should be taken to mini-
mize soil erosion in treated areas. Excessive dosages of picloram.
tend to denude the soil and therefore hasten soil erosion. Further
studies are needed to ascertain the desorption characteristics of
herbicides sorbed on soil particles and hence the effect of suspended
soil on the concentrations of herbicides in water.
Picloram might be removed from water by diverting the contaminated
water to holding areas where it will come into contact with soil or
other adsorbant materials. Water contaminated with picloram adsorbed
on suspended material could be decontaminated by this procedure if
the suspended particles will settle out upon standing.
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SECTION III
INTRODUCTION
Since runoff from agricultural and watershed lands and other areas
treated with pesticides may offer a potential hazard to the health of
both animal and plant life, there has been a growing concern over
possible contamination of water systems by runoff from these areas.
The continued use of presently registered herbicides and new candi-
date herbicides may depend on our ability to answer questions as to
their movement in soil and water, effects on other crops, and other
environmental effects.
Considerable information exists concerning many of the common in-
organic constituents in surface waters and streams. Much less is
known about the herbicidal composition of surface runoff waters or
irrigation return flow from treated lands and, further, the existing
data are seldom associated with known properties of a watershed.
The demonstrated presence of herbicides in some streams indicates
their movement from treated sites to nontarget areas where their
effects may constitute a hazard. Each use of water affects its
quality and hence its performance for downstream users. The demand
for high quality water coupled with the ever-increasing use of all
types of agricultural chemicals has completely changed public attitudes
toward the region's water resources. Under multiple use, each
user has an obligation to maintain quality at the highest practicable
level. Little is known of the effects of various pest control practices
on the quality of water and hence on its suitability for municipal,
industrial, recreational, or other uses.
Herbicides can enter surface waters in any of three ways: (a) direct
application to water, (b) via surface runoff, including erosion of
surface soils from treated areas, and (c) via movement through the
soil to ground water that later drains into surface streams. If
movement in surface runoff is demonstrated to be a significant source
of pollution, then control is more difficult and it may have to come
by restricting the use of some chemicals. Few data are available on
the movement of pesticides or their metabolic products in runoff
waters or through the plant root zone.
In the western states, agriculture has long been concerned with the
consequences of water quality for soil conservation and crop produc-
tion. Maintenance of a permanent irrigated agriculture depends upon
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an understanding of the interactions of soil, water and vegetation. An
important part of this success is the judicious use of agricultural
chemicals as fertilizers, amendments and for pest control. The
effects of these chemicals on water quality has, however, received
little attention because this aspect has little apparent relation to crop
production and its importance to nonagricultural users of water was
not appreciated. Since most water entering the public water supply
drains from forest, range or farm land, the downstream user quite
naturally attributes undesirable quality of water to its management
on land within the watershed.
Conflicts of concept and interest are likely to arise between those
concerned with public health, wildlife, or recreation and those con-
cerned with timber and food production unless each group understands
fully the consequences of each use of the available water. For these
reasons agriculture must come to appreciate how its management of
soil and water resources may affect the quality of water for nonagri-
cultural users.
•
A research program concerned with the impact of agriculture on the
quality of water is particularly appropriate for the western region
because irrigation plays a major role in crop production and irrigation
return flows often constitute a major share of the waters that enter
municipal or industrial water supplies or that support fisheries or
recreation. This project is concerned primarily with the movement
of agricultural chemicals from treated areas by surface waters
coming in contact with the soil or movement through the soil profile
by leaching.
Objectives
The purpose of this investigation was an objective study of the inter-
actions between agricultural chemicals, soils, and water that may
result in the degradation or pollution of surface and ground waters.
Specifically the objectives were:
1. To study, under field conditions, the potential movement
of herbicides from treated sites via surface runoff water
and movement through the soil.
2. To determine the physical and chemical properties of
some herbicides and soils that are associated with herb-
icide movement.
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3. To develop analytical techniques for some herbicides to
detect the submicrogram quantities that are involved.
Organization of Research
Field Studies
The major objective was to determine the contamination of water by
surface flow in the field through the use of small watershed or erosion-
runoff study areas where the amount and quality of runoff could be
determined. Closed or well defined drainage areas were used to
better identify the materials added or removed from the system.
Two sites with different soil characteristics were selected where
surface runoff could be measured. Herbicides of known adsorption
characteristics were surface applied; soil and water samples were
taken throughout a two year interval to demonstrate the presence or
absence of the herbicides in the samples. The approach was to select
areas of known drainage characteristics and establish plots that were
treated differentially to determine the role of rate and time of herb-
icide application and quantity and intensity of subsequent precipitation
on the movement of selected herbicides.
Laboratory Studies
Leaching columns of varying lengths were used to follow adsorption,
release and movement of selected herbicides applied to soils of differ-
ing texture, organic matter content, calcium carbonate content, and
exchangeable cation status. An attempt was made to account for all
applied materials by analysis of leachates and column sections.
Radiotracer techniques were used, when applicable, to follow move-
ment of tagged materials. The herbicides were applied at normal
field rates and at multiples thereof. Movement was followed under
conditions of continuous leaching, and also by applying the leaching
solution in increments and allowing sufficient time for equilibration
between applications. Extent of exchange between soil and water was
related to both physical and chemical properties of the herbicides
and soils.
Equilibrium studies were conducted to relate the chemical nature of
picloram (4-amino-3, 5, 6-trichloropicolinic acid), soil texture and
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inorganic salts to adsorption and desorption. The effect of pH, temp-
erature, base saturation and drying on desorption, movement and
degradation was studied. This report is organized according to the
two major areas of investigation; field studies and laboratory investi-
gations.
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SECTION IV
LITERATURE REVIEW
Field Studies
Growing concern has been expressed lately by scientists and others
over the possible contamination of water systems from the runoff
of agricultural and watershed areas (47, 61). Mullison (47) stated
that drainage from watersheds and other herbicide treated areas offer
a potential hazard by possibly causing harmful effects to the health
of domestic animals, wildlife, aquatic invertebrates and vertebrates
as well as man. A publication (5) of the National Academy of Sciences
indicated that herbicides may be carried from their point of applica-
tion to unsprayed areas in surface-water drainage. It also pointed
out that when excess rainfall or irrigation water drains from fields,
herbicide molecules may be carried in solution or in the adsorbed
phase on suspended soil particles and become deposited along the
path of the flowing water. Allan (3) stated that herbicides are not
known to be accumulated by plankton or aquatic fauna and that water
pollution by runoff from treated land is not presently a problem.
However, existing and new herbicides must be examined periodically
with the express purpose of preventing environmental contamination.
White _et al. (6l) conducted a study on the losses of atrazine (2-chloro-
4- ethylamino- 6-isopropylamino- s^-triazine) from fallow land caused
by runoff and erosion. In their study, atrazine was applied to the
surface of a fallow field at 3 Ib/A and simulated rainfall was used to
produce runoff. A simulated rainfall of 2. 5 inches in 1 hour applied
96 hours after the herbicide application, caused 7. 3% or 0. 24 Ib/A
of the atrazine to be lost. They mentioned that a storm of this inten-
sity comes only about once in 10 years and that the losses from this
type of storm -would be considerably greater than the normal storm
encountered in the area. They reported that a common size storm
(0. 5 inch) for the area simulated 96 hours after herbicide application
resulted in 0. 06 Ib/A or only 25% as much herbicide loss as the
2. 5 inch simulated rainfall. It was stated that the concentration of
atrazine in the soil fraction of the runoff was higher than in the water
fraction but that most of the atrazine transported was associated with
the water fraction due to the larger amounts of water lost as compared
with soil. Their study also showed that the average concentration of
atrazine in the runoff decreased with increase in storm size.
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Mullison (47) reports: "There is little evidence that herbicides from
agronomic or industrial usage are reaching or accumulating in our
water supplies in amounts to cause a pollution problem. "
The Senate Select Committee on Water Resources has stated that
"water pollution from agricultural chemicals is not as extensive as
some would lead us to believe" (57).
Many studies have been made to determine the effects of herbicidal
residues in water. The low concentrations that are observed following
application of herbicides would not likely be hazardous to crops or
animals.
In spite of the many benefits from agricultural chemical usage, any
biologically active chemical implies a potential hazard that should
be evaluated. In general, herbicides are of a relatively low order
of toxicity and the potential for these being a source of pollution is
minimized.
There is a potential hazard dealing with ditchbank weed control if
herbicide applications are followed by heavy, intense rainfall, where-
by large amounts of herbicide may be washed into the channel.
Recent research has emphasized the dissipation of picloram from im-
pounded water (56) and from runoff water and soils (52). Soil texture,
application rate, season of application, and time interval after treat-
ment were important in the dissipation of picloram from pasture soils
in Nebraska (52). The time interval from application to the first
irrigation affected the amount of picloram removed with surface runoff
or leached into the soil profile of semi-arid rangelands (53). Move-
ment studies indicated that leaching •was an important means of dissi-
pating the herbicide in light textured soils. Surface movement of
picloram from sod-covered and fallow plots occurs with irrigation
sufficient to cause runoff (56). In the studies by Trichell et al. (56),
approximately 5% of the picloram was lost in runoff water when 1. 25
cm of simulated rainfall was applied in 1 hour at 24 hours after herb-
icide treatment. Picloram was readily degraded in clear water by
ultraviolet light. However, degradation from a soil surface by sun-
light was considerably slower than when the herbicide was in aqueous
solution. No definitive information was available as to the occurrence
and persistence of picloram in natural water sources following appli-
cation to the grassland ecosystem.
10
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Laboratory Studies
Laboratory investigations reported in the literature on the adsorption-
desorption and movement of picloram in soils are similar to work done
on the triazines and other herbicides. Also, since picloram is an
anion at the pH range of this study, some literature has been included
on the interactions in soil of inorganic anions like phosphates, borates
and sulfates.
Adsorption-Desorption of Pesticides in General
Factors Affecting Adsorption-Desorption
4-Triazine Herbicides. The structure of atrazine, a common member
of this family, is shown in Appendix A. The pKa (pKa = -log Ka, Ka
is the thermodynamic dissociation constant) of this compound is about
1. 68 and solubility in water is about 70 ppm at 27 C (6). It should,
then, behave as a molecular species at pH above - 3. 68 (pKa + 2).
Harris and Warren (28) reported atrazine to be adsorbed by both anion
and cation exchangers, to be slightly adsorbed by muck soil, and to
be greatly adsorbed by bentonite. Desorption occurred more readily
from bentonite than from muck. Talbert and Fletchall (55) found
montmorillonite to be very adsorptive of atrazine, while no herbicide
was adsorbed on kaolinite. Organic materials were more adsorptive
than clays.
Hilton and Yuen (31) found atrazine to be quite readily adsorbed on
several Hawaiian soils but could not correlate adsorption with any
soil property. Harris (27) found atrazine to be adsorbed in greater
quantities by fine textured soils than by coarse textured soils.
To further understand the behavior of atrazine, a nitrogen containing
ring compound, in soils, the effect of pH and temperature on its
adsorption-desorption was examined by Harris and Warren (28). They
found that atrazine adsorption on muck was temperature independent,
while adsorption on bentonite was temperature dependent. Talbert
and Fletchall (55) reported that increases in temperature decreased
atrazine adsorption on montmorillonite and organic materials.
11
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McGlamery and Slife (40) reported very slight changes in adsorption
of atrazine by a Drummer clay loam soil with temperatures in the
range of 0. 5°C to 40.0°C. Desorption -was increased by increases in
temperature in the same range. However, adsorption of atrazine by
humlc acid was found by these authors to increase with increases in
temperature. Desorption from humic acid was very slight. These
workers proposed van der Waal's forces as the bonding mechanism
in adsorption on clays and ionic bonding in humic acid.
Concerning the effect of pH, Talbert and Fletchall (55) reported that
adsorption of atrazine by montmorillonite and organic materials was
decreased by an increase in pH in the range of 5. 0 to 7. 0. McGlamery
and Slife (40) found similar results in the pH range of 3. 9 to 8. 0, for
atrazine adsorption on Drummer clay loam soil and humic acid. De-
sorption of atrazine from the same soil was increased by increases
in pH. Desorption from humic acid was very slight.
Another compound, of the ^-triazine family, prometone, has a pKa of
4. 30. Prometone exists in molecular form in a neutral aqueous envi-
ronment and associates strongly with hydrogen as the pH is lowered.
Weber, Perry, and Upchurch (59) found that prometone was not ad-
sorbed by kaolinite, but gave s-shaped curves on sodium and/or
aluminum montmorillonite, and the adsorption was inversely related
to pH and temperature.
Phenyl Alkanoic Acid Herbicides. The general molecular structure
of this family of compounds appears in Appendix A.
Weber, Perry and Upchurch (59) found the 2, 4-D (pKa = 2. 80) was
negatively adsorbed by clay minerals. Frissel and Bolt (18) also
obtained similar results. However, Haque et al. (29) found positive
adsorption of 2, 4-D on the clay minerals illite, kaolinite, and mont-
morillonite, although adsorption on kaolinite was minimal. Temper-
ature had little effect on the amount adsorbed.
Bailey, White, and Rothberg (7), studying the effect of pH on 2, 4-D
and 2, 4, 5-T (pKa = 3. 14) adsorption by montmorillonite, found that
the magnitude of adsorption of these compounds was governed by the
surface acidity and not by the pH of suspension.
12
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Effect of Inorganic Salts on
Adsorption-Desorption of Pesticides
The paper of Frissel and Bolt (18) was the earliest report found con-
cerning the effect of inorganic salts on pesticide adsorption. These
authors, working with clay minerals, found that the main variables
in the adsorption of a number of organic acidic and basic herbicides,
were pH and electrolyte concentration of the system. They explained
the salt effect on the basis of "salting out".
Nearpass (49) studied the effects of the predominating cation (Ca, Mg,
K, & Na) on the adsorption of simazine (pK* = 1. 65, pK = 0) and
X i-t
atrazine (pKa = 1. 68) by Bayboro clay soil. He found that adsorption
of these herbicides decreased with increasing degree of saturation
with these cations. The decrease appeared to be a result of the
occupation of adsorption sites by metal cations, rather than a specific
effect of cation species on the adsorption of the herbicide. He also
studied the exchange adsorption of amitrole (3-amino-l, 2, 4-triazole,
pKa = 4. 14) by montmorillonite, including the effect of CaCl and NaCl
CA
on amitrole's adsorption (50). A decrease in amitrole adsorption was
observed with an increase in salt concentration, which he attributed
to occupation of adsorption sites with metal cations. He concluded
that adsorption of amitrole by neutral or alkaline soils may be due to
molecular adsorption by organic matter.
The importance of exchange type reactions in the adsorption-desorption
of charged herbicides is indicated by the work of Weber and Weed (60).
They found that diquat and paraquat (completely ionized) cations were
adsorbed by montmorillonitic and kaolinitic clay minerals to the extent
of their cation exchange capacity. About 80 percent of each of the
herbicides was displaced from kaolinitic clay with Ba ions, whereas
only 5 percent was removed from montmorillonite. The herbicides
were found to exchange for one another. Prometone, a neutral herb-
icide, was adsorbed by montmorillonite but only slightly by kaolinite.
It was released from both minerals more readily with deionized water
+2
than with Ba ions (1M Bad ).
C-t
MacNamara and Toth (38) studied the effect of weak electrolyte solu-
tions on the adsorption of linuron and malathion by soils and clay
minerals and found that, in general, electrolytes suppressed adsorp-
tion under some conditions but had no effect under most conditions
13
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and did not increase the desorption of either linuron or malathion
from soils.
Hance (26) investigated the effect of exchangeable cations on the ad-
sorption of linuron and atrazine by a cation-exchange resin, cellulose
phosphate powder, bentonite, and a peat soil. The cations studied
+2 +2 +2 +3 +4
were Ca , Ni , Cu , Fe , and Ce . The results with linuron
are consistent with the hypothesis that complex formation with exchange-
able cations is a possible mechanism of adsorption. This was not true
with atrazine.
Abernathy and Davidson (1) studied the effect of CaCl , at 0. 01 and
0. 5N concentrations, on the adsorption of prometryne (pKa = 3. 05)
and fluometuron (a neutral species) in soil. In batch equilibrium
studies, fluometuron adsorption was decreased and prometryne
adsorption increased by increasing the CaCl? concentration from
0. 01 to 0. 5_N. The mobility of prometryne decreased in the two
soils by increasing the CaCl? concentration. Fluometuron mobility
was unchanged by the two CaCl concentrations in one soil, but
£4
increased in another soil (Norge loam) at the high CaCl concentration.
Effects of Inorganic Salts on the
Adsorption of Inorganic Anions
Hadas and Hagin (23) studied boron adsorption by soils as influenced
by potassium (K). Potassium-saturated soils adsorbed more boron
than the untreated soils, and Langmuir equations indicated a greater
strength of adsorption by the K-treated soils. They concluded that
potassium influenced the adsorption of boron probably by creating
more favorable conditions for boron adsorption in soil.
+2
Barrow (8) studied the influence of solution concentration of Ca
on the adsorption of phosphate, sulfate, and molybdate by soils.
He showed that adsorption of all three anions increased as the Ca
concentration in soil increased. It was shown that simultaneous
increase in exchangeable Ca also occurred.
14
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Movement in Columns and Application
of Chromatographic Theory
Elrick, Erh, and Krupp (16) devised an apparatus to study miscible
displacement processes in soils. The usefulness of this technique
was illustrated by a brief description of (a) the mixing of Cl in a
glass bead medium; (b) the movement and adsorption of atrazine in
soil; and (c) the movement and microbiological nitrification of NH .-N
to NO -N. Non-conformity of the mathematical model tc the actual
movement of atrazine in soil columns was attributed to intra-aggregate
adsorption and dead-end pores.
Lindstrom jejt aJ_. (37) developed an equation based on chromatographic
theory to predict the theoretical curves for pesticide movement for
two different boundary conditions in saturated soil for various pore
water velocities and diffusion coefficients. They did not test their
model experimentally.
Using miscible displacement techniques to move solutions containing
fluometuron (a neutral species) and diuron (pKa = 1 to 2) through
saturated beds of 250-|J. glass beads and through Norge loam soil
columns at two water flow rates, Davidson and Santelmann (14), found
that (a) more diuron than fluometuron was absorbed by the glass bead
system, (b) the shape of fluometuron distribution curves at two flow
rates were distinctly different, and (c) fluometuron was as mobile
as the chloride ion at both high and low flow rates.
Davidson, Rieck, and Santelmann (13) found that the rate at which
fluometuron and diuron (two substituted urea herbicides) move through
a water saturated glass bead column and uniformly packed soil column
depends upon water flux. Experimental and calculated effluent con-
centration distribution (based on a model similar to the one used in
this study) did not agree when fluometuron was adsorbed by the porous
material (soil).
Davidson and Chang (12) applied the chromatographic theory of pesti-
cide movement to picloram movement in soils. They demonstrated
that average pore water velocity influenced picloram movement more
significantly than variations in bulk density or largest aggregate size
at a given flow rate. The model based on chromatographic theory
failed to predict picloram movement, which they attributed to
15
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complexities of the adsorption process including the influence of pore
size distribution.
King and McCarty (34) employed an equation describing the chroma-
tographic movement of pesticides under noncontinuous flow conditions.
Experimental and theoretical curves agreed fairly well for the
leaching of organic phosphorus insecticides in soil columns.
Adsorption-Desorption of Picloram
Factors Affecting Adsorption-Desorption
Soils. Grover (21) investigated the relationship between the amount
of picloram needed to reduce fresh weight of sunflowers by 50 percent
(ED ) and clay content, organic matter, and cation exchange capacity
of seven Saskatchewan soils maintained under controlled environmental
conditions. There were no significant correlations between ED
values of picloram and soil clay content or cation exchange capacity.
ED values were highly correlated with soil organic matter content,
and increased as the soil pH was lowered or raised from pH 6. 5.
Hamaker, Goring, and Youngson (24) found the greatest adsorption
of picloram, 2, 4-D and 2, 4, 5-T in soils containing a high percentage
of organic matter, in soils rich in Fe and Al components (red soils)
and in acidic soils. Adsorption occurred rapidly by red soils but
slowly by highly organic soils. The data suggest that adsorption of
picloram is primarily caused by organic matter and hydrated metal
oxides, with clays probably playing a minor role. Adsorption of
nonionized picloram and its anion was involved.
Herr, Stroube, and Ray (30) and Keys and Friesen (36) found that
resistance to leaching of picloram in soils was correlated with ad-
sorption. Herr, Stroube, and Ray (30) also observed that picloram
adsorption in soils was inversely related to pH and directly related
to organic matter of the soil.
Exchange Resins, Clay Minerals and Other Adsorptive Materials.
Bailey, White, and Rothberg (7) reported conformity to Freundlich
adsorption equation for picloram, when its aqueous solution was
16
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incubated with samples of 1 to 0. 2 JJL (micron) montmorillonite clays
adjusted to pH values of 3. 35 and 6. 80. They concluded that adsorp-
tion occurred to the greatest extent on the acid H-montmorillonite
compared to the nearly neutral Na-montmorillonite. Negative
adsorption occurred when the adsorbent was Na-montmorillonite.
There appeared to be slightly more of a driving force (molar free
energy) for adsorption of picloram than for phenoxyacetic acid,
although the difference in average free energy (F) values for the
hydrogen system was not great.
Grover (21) studied the adsorption of picloram by various soils,
activated charcoal, anion and cation exchange resin, kaolinite and
montmorillonite, wheat straw, cellulose powder, cellulose tri-
acetate, and peat moss. He concluded that adsorption of the mole-
cular form probably would involve hydrogen bonding -with hydrophobic
surfaces, e.g. those on cellulose triacetate and peat moss. The
absence of adsorption on clay minerals and cellulose powder sug-
gested a total lack of attraction of both forms of picloram for hydro-
philic surfaces.
Field Studies and Movement
in Different Media
Herr, Stroube, and Ray (30) found tha.t the region of highest concen-
tration of picloram in heavy and medium-textured soils, when sampled
9 and 15 months after application, was near the surface.
Merkle, Bovey, and Davis (43) investigated the effect of soil type,
temperature, and moisture on the persistence of picloram. Detect-
able quantities of picloram were present in Houston clay, Axtell
sandy loam, and commercial sand after incubation for one year, at
4, 20, 38° C and moisture levels of both field capacity and 0. 1 field
capacity, from rates as low as 0. 25 u.g per gram soil (0. 5 Ib/A).
Movement studies indicated that leaching was an important means of
dissipating the herbicide in light soils; picloram moved completely
through the surface 2 feet of soil; the greatest herbicide concentrations
generally were found at the deepest sampling depth.
17
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SECTION V
MATERIALS AND METHODS
The herbicides diuron (substituted urea); atrazine and GS-14254
(j$_-triazines); 2,4-D, 2,4, 5-T and picloram (plant hormone types)
have been evaluated for their tendency to move from treated lands
in surface flowing water and a more thorough study was made to
determine whether picloram might also be desorbed from soils to
move in ground water percolating through the soil and ultimately be
discharged into streams nearby.
Field Studies
Several experiments were conducted over a 3-year period to evaluate
the amount of movement of several herbicides when they were employed
as currently recommended for vegetation control along irrigation
canals and watershed areas.
Movement of Herbicides Following Heavy Dosage
Applications to Irrigation Canal Banks
An irrigation canal in Trenton, Utah with a 60-70 cfs maximum dis-
charge was selected as a test site since it was infested with several
troublesome plant species and represented many similar canals in
the state. During the 1968 irrigation season, four plots along the
canal were selected and staked; the treatments were made with a
6-foot boom sprayer on November 4 after the water was removed
from the canal. Two plots were treated with diuron at 30 Ib/A and
the remaining two plots down the canal were treated with 10 Ib/A
atrazine. Each plot was 500 feet long and extended from 5 feet above
the water line on the bank to the bottom of the canal; both banks were
treated making the plots approximately 20 feet wide. The four plots
were spaced approximately one-half mile apart along the canal.
Water samples were taken in May, 1969 as the canal received the
first water. One liter samples were taken of the first flush of water
and a second collection was made when the canal reached approximately
90 percent of its capacity 4 hours later. Duplicate samples were taken
10, 100 and 1000 feet downstream from each plot.
19
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A similar test was conducted on the North Logan-Smlthfield canal
near Logan, Utah. Two 20 by 500 foot plots were treated with
30 Ib/A diuron on December 2, 1968 and two plots received 10 Ib/A
atrazine the same day. Plots were approximately one-half mile
apart to facilitate sampling at 10, 100 and 1000 foot distances below
the plots. Duplicate one-liter samples were taken when the first
flush of irrigation water reached the treated areas and again the
same day when the canal was approximately 60 percent of its 80 cfs
maximum discharge. The water samples were taken to the laboratory
and prepared for analysis within three hours after collection.
Diuron Analysis
The water samples were analyzed chromatographically for herbicide
residues using the experimental procedure of McKone and Hance (42).
One hundred ml of water was measured into a 250 ml separatory
funnel and extracted for 1 minute each with two 25 ml portions of
dichloromethane. The organic layers were collected in a separate
250 ml separatory funnel. The solution was concentrated to about
. 5 ml under reduced pressure on a water bath at 35° C. The remaining
solvent was removed with a stream of air. Five ml of saturated
sodium chloride solution was added and the flask was shaken for 15
seconds. Fifteen ml of 2, 2, 4-trimethylpentane was added and the
flask shaken for 1 minute. Aliquots of the upper 2, 2, 4-trimethylpen-
tane layer were taken and diluted for gas chromatography.
A Hewlett Packard 5750 gas chromatograph was used with a 1. 8 m by
3 mm i. d. glass column packed with 3. 5% DC 200 on 80-100 mesh
Gas Chrom. The injector temperature was 200 C, the detector
225° C, and the column 150° C.
A standard solution of diuron containing 1 mg/ml was prepared in
redistilled methanol. Ten p.1 of the solution were transferred to a
25 ml volumetric flask and diluted with 2, 2, 4-trimethylpentane to
10 ml, making a 1 ppm solution containing 1 ng in 1 (0.1 which was the
injection volume. This solution was diluted to give a . 5 ppm solution
containing . 5 ng in 1 jj.1.
A fortified solution of 1 ppm was obtained by diluting 1 ml of the 1 mg/ml
diuron in methanol solution to 1 liter with distilled water. This
solution was extracted to determine percent recovery.
20
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Atrazine Analysis
The analytical method used •was a modification of the one by White
jst _al_. (61). Water samples (100 ml) were mixed with 5 grams of
MgCO - Ca(OH) (10 to 4) to flocculate the particulate material.
3 £
Samples were vacuum filtered through Whatman No. 42 filter paper
in a BUchner funnel. The filtrate was extracted with three successive
75 ml portions of chloroform. The chloroform extracts were combined
and evaporated to approximately 20 ml with a gentle air stream and
transferred to a basic aluminum oxide column (pyrex columns con-
taining 10 grams of grade IV aluminum oxide) and eluted with 50 ml
of chloroform-ether (95:5). The column effluent was evaporated to
20 ml and transferred to a 100 ml separatory funnel. Two ml of 50%
H SO were added, and the samples shaken gently for two hours.
<-t ~t
Twenty ml of water were added and thoroughly mixed by shaking for
10 minutes. The aqueous layer was collected and 1 ml aliquots were
removed and read on a Beckman DU spectrophotometer at 225, 240
and 255 m|i; atrazine concentrations •were determined using a base-
line technique of Knusli, Burchfield and Storrs (35). Reagent blanks
and samples from untreated plots were used in making background
corrections. Standard curves were made using known amounts of
atrazine. The limit of atrazine detection in the water samples was
0. 02 ppm.
Effec*" of Surface Irrigation on the Lateral
Movement of GS-14254 from Treated Cropland
A well established, uniform stand of furrow irrigated alfalfa was
selected on the Utah State University South Farm for this study.
The crop was established with irrigation furrows in alternating rows
to allow for irrigation as is commonly practiced in the area. The
soil type was a Nibley clay loam with 3. 2% organic matter and a
pH of 7. 6. The percentages of clay, silt and sand were 35. 5, 6l. 8
and 2. 7, respectively. The cation exchange capacity was 23. 7 meq/100
gm oven-dry soil.
The treatments consisted of two rates of herbicide and a control. The
treatments were arranged in a randomized block design with three
replications. After the first cutting of alfalfa was removed, the
field was furrowed to prevent any crossover of irrigation water be-
tween rows. Each plot was 8 x 50 ft. GS-14254 (2-methoxy-4-s-
21
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butylamino-6-ethylamino-^-triazine) was applied to the plots on
July 2, 1971, at 1. 5 and 3. 0 Ib/A with a bicycle sprayer having 8003
nozzle tips. It was applied at 35 psi pressure and equivalent to 1 9
gallons of water per acre. The plot was sprinkled with approximately
0. 25 inch of water over a 2. 5 hour period to both fix and leach the
chemical into the soil.
The field was irrigated four days later with 1. 25 inch irrigation tubes
regulated to permit the water to run down the furrows at about 300
feet per hour. Water samples "were collected in 110 ml sampling
bottles from the first water reaching the sampling points at 0, 10, 50,
and 120 feet below the end of the plots. A second sample was collected
at the end of the plots after 10 minutes. Prior to the collection of
samples, the sample bottles were washed with soap and rinsed four
times with water. To prevent microbial degradation of the chemical,
collected samples were stored in a cooler at 4° C until they were
analyzed.
The chemical extraction procedure used was a modification of a. Geigy
Agricultural Chemical extraction procedure (19) for extracting chloro-
triazines from water. A 50 to 100 ml sample of water was extracted
three times with 13 ml portions of chloroform in a separatory funnel.
The chemical was then converted from methoxytriazine to hydro-
xytriazine following the procedure outlined by Geigy Agricultural
Chemical Corporation for the hydrolysis of methlthiotriazine residues
with several modifications. Following extraction, the chloroform was
evaporated to dryness in 18 by 150 mm test tubes in a Buchler Rotary
Evapo-Mix. Five ml of 1 N H^SO was added to each test tube and
K — 24
placed in a boiling water bath for three hours. After the tubes had
cooled to room temperature, the acid solution was transferred to a
250 ml separatory funnel and washed with 10 ml of 20% diethyl ether
in chloroform. The organic layer was drained off and the aqueous
layer was washed by shaking with 10 ml of diethyl ether. All extrac-
tions and washings followed a one minute vigorous shaking and separ-
ation period. The aqueous layer was then transferred to a three ml
silica cell and the adsorbancy was measured and recorded on a Beck-
man DB-G grating spectrophotometer at 225, 240, and 255 m)a.. The
net absorbance (E) was then determined at 240 m)J. by using a baseline
technique according to the following equation:
E=A24°- (A225 ,
22
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where A , A , and A are the absorbancies at 225, 240, and 255
mfx, respectively,
A standard curve was made by running known amounts of GS-14254
through the same hydrolysis procedure as the field samples. This
standard curve was used for determining the ppm of GS-14254 in the
water. Reagent blanks were run simultaneously with the standards
and samples. The minimum level of detection of GS-14254 in water
was 0. 04 ppm.
Movement of Hormone-Type Herbicides in Surface
Waters Following Field Application
In the spring of 1969 two experimental sites were selected and treated
with a 1 Ib/A dosage of picloram and monitored for a period of sixteen
months thereafter.
One site was located in Wasatch County approximately three miles
southeast of Heber City, Utah. The site consisted of a small drain-
age area (approximately 4 acres) that was isolated in a small draw
and free from surface flowing water in the surrounding area. A
small wash led from the drainage and emptied into Center Creek
approximately two miles away. The treatments were made on May 7,
using a truck-mounted boom sprayer and 8003 nozzle tips. The
area varied in slope from approximately 3 percent to 1 0 percent or
more near the upper side. The potassium salt of picloram was
applied broadcast in 16 gpa water; an attempt was made to spray the
complete watershed with the 1 Ib/A rate of picloram. The collection
points were established 10, 100 and 1000 meters below the treated
area and the watershed was situated in such a way that nearly all of
the runoff would pass the 10 meter collection point. A very small
amount of runoff from adjacent areas may have entered the wash at
the 100 and 1000 meter distance. One liter samples were taken from
a small metal container placed in the bottom of the wash to collect the
water. Duplicate samples were taken and collections were made by
the landowner during periods of natural precipitation. Water samples
were taken in opaque jars and refrigerated until they were processed.
All analysis were performed within 48 hours after collection.
An eight-acre watershed was treated with the potassium salt of pic-
loram at a dosage of 1 Ib/A near Trenton, Utah. The site consisted
of a single isolated slope covered with a mixed stand of grasses and
perennial weeds. Approximately 80 percent of the area was treated
23
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using a truck-mounted boom sprayer delivering a volume of 1 6 gallons
of water per acre. The drainage tapered toward a small drainage ditch
at the lower side and was free of any outside surface flowing water.
The drain ditch emptied into the Trenton irrigation canal approximately
three-fourths of a mile below the watershed. Water samples were
taken in duplicate in 1 liter opaque jars and coincided with periods of
natural precipitation of sufficient intensity to cause runoff. Collections
were made four times during the 1969 summer season.
In 1971 a series of experimental trials were established to test the
movement of picloram, 2, 4- D and 2, 4, 5-T. The experimental area
was located approximately eight miles northwest of Evanston, Wyoming.
The general area is characterized by many miles of undulating foot-
hills rising 50 to 100 feet above the broad valley floors with numerous
creeks fed year-around by the Wasatch range. The foothills selected
for these studies had a well deliniated north drainage slope and a
south drainage slope. The south facing slope was selected for its
numerous small, well defined drainageways that emptied into Duck
Creek approximately 1.2 miles to the south. The four experimental
sites were similar in size, slope and vegetation and were about one-
half mile apart. The predominate soil type was a loam with slightly
less than 1 percent organic matter content. All the drainages tapered
sufficiently to allow a collection site such that essentially all the runoff
water would pass through. Additional collections were made in the
washes which extended to Duck Creek.
Site I consisted of two small adjacent drainages; one drainage was
(~ 2. 0 acres) treated with 1 Ib/A picloram using the truck-mounted
sprayers. Site II was established as a replicate of Site I; one drainage
(~ 2. 0 acres) received a dosage of 1 Ib/A picloram and the second
drainage (~ 2. 5 acres) was treated with picloram at a 2 Ib/A rate.
Sites III and IV were used to test the movement of 2, 4-D and 2, 4, 5-T.
Site III consisted of one drainage (~ 5. 5 acres) treated with a tank-mix
of 2, 4-D at 2 Ib/A plus 2, 4, 5-T at 1 Ib/A and a second drainage
(~ 2. 5 acres) treated with 4 Ib/A 2, 4-D plus 2 Ib/A of 2, 4, 5-T. The
treatments made on Site III were repeated on Site IV with one water-
shed (~ 1.5 acres) receiving the 2 Ib/A rate of 2, 4-D plus 1 Ib/A
2, 4, 5-T and a second watershed (~ 1. 25 acres) treated with the com-
bination of 2, 4-D and 2, 4, 5-T at the highest rates.
The picloram, 2, 4-D and 2,4, 5-T treatments were applied June 29
and a rainstorm occurred one week later that deposited 1. 56 inches
of rain in a three-day period. Duplicate 3 liter samples were collected
24
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from each of the collection points during the runoff period of the storm.
The samples were immediately cooled on blocks of CO and transferred
to the laboratory where they were refrigerated and processed within
seven days. Quantitative determinations were made in triplicate on
each sample,
Picloram Analysis
The picloram content of the water samples was determined chromato-
graphically using a Varian Aerograph Model 1800 chromatograph
equipped with a tritium electron capture detector and a five foot
stainless steel column with an inside diameter of 1. 8 mm packed
with SE-30 oil on 80/100 mesh Chromosorb Q. Purified nitrogen at
a flow rate of 60 ml per minute was used as the carrier gas. The
injector, column and detector temperatures were 225, 195 and 21 5° C,
respectively.
The method of Merkle, Bovey and Hall (44) with minor modifications
was used to determine the picloram concentration in 500 ml samples
of water. The samples were made basic with KOH and reduced to
about 250 ml on a hotplate. The concentrated sample was acidified to
pH 2. 0 with HC1 and extracted twice with 100 ml portions of diethyl
ether. The ether extracts were combined and evaporated to -1.0
ml on an evaporator. The methyl ester of picloram was made by
reactiug it with 8 milliliters of boron trifluride in methanol. Ten ml
of water was added and the solution was transferred to a separatory
funnel and washed with an equal volume of hexane. The two phases
were thoroughly mixed and allowed to separate. The organic phase
was collected and used to inject into the chromatograph. As determined
in our laboratory, the lower limit of detection by this method was 3
to 4 ppb picloram. Plant bioassays were used for qualitative measure-
ments of picloram in the runoff waters. The technique verified the
quantitative determinations of other methods but was noticeably
inferior to GLC at the lower concentration levels. Safflower plants
were grown in greenhouse pots in 500 gm of silt loam soil. When the
plants reached a height of 4 inches the runoff water taken from the
field was used in the normal watering routine; approximately 25 ml
was added to the soil every third day. Water of known picloram
concentrations was used to develop rate-response curves for com-
parison.
25
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Picloram concentrations were verified in most field samples by an
abbreviated analytical procedure developed by the authors and described
in Appendix B.
Phenoxy Herbicide Analysis
Water samples containing 2, 4-D and 2, 4, 5-T were brought to pH 10. 0
with NaOH according to the method of Frank and Comes (17) and ex-
tracted with chloroform after acidification to pH 2. 0 with HC1. The
2, 4-D was removed from the chloroform with 0. 1 _N sodium bicar-
bonate and, after acidification to pH 2. 0, was again extracted with
chloroform. The chloroform was evaporated to dryness and the
methyl ester was made by reacting the residue with diazomethane
in ethyl ether and taken up in isooctane. The two compounds were
separated by gas chromatography on a 5 foot column packed with
60/80 mesh Chromosorb W coated with 10% QF-1 over 0. 5% Carborwax
20-M. Two procedures were followed to check the identity of the two
herbicides in the water samples. A 5 foot column prepared with 5%
SE 30 on Gas Chrom Q was used as a second method to resolve the
compounds. The 2, 4-D and 2, 4, 5-T contents were determined by
comparing the peak height produced to that produced by known quan-
tities of the individual herbicides. The recoveries from water were
96 and 90 percent for 2,4-D and 2,4, 5-T, respectively. The lower
limit of detection was approximately 50 ppb for each herbicide.
Laboratory Studies
14
Stock solutions containing 0. '<_,--• to 10 pprn of C-labeled picloram
14
(carboxyl - C, specific acti. ity 4. 1 3 |ac /mg) were prepared in
deionized water. Calibration curves were made by counting aliquots
of the stock solutions on a Packard TriCarb liquid scintillation counter
according to the method of Yaron, Swoboda, and Thomas (62). One ml
aqueous sample was added to 1 9. 0 ml of liquid scintillator, dissolved
by slight shaking and counted for at least three 10-minute periods.
Radioactivity was usually high and the counting efficiency was approx-
imately 65 percent or better. The counting error was -3 percent.
A preliminary experiment was performed to check any picloram ad-
sorption on glass containers, polypropylene centrifuge tube walls,
rubber corks, or degradation by sunlight. Twenty-five ml of each of
26
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the stock solutions were exposed to the containers for a 30-day period.
As a precautionary measure, all subsequent experiments were con-
ducted in a dark room, because the actual handling of samples sub-
jected them to different light conditions from one experiment to
another.
To check for degradation of picloram during the course of an experi-
ment, a thin layer chromatography (TLC) technique was used. A
100 A sample (column effluent in case of column studies) was applied
to the TLC plate in quadruplicate. The TLC plate had a coating,
250 u thick, of Silicic AR TLC - 7GF, a neutral sorbent produced by
Mallinckrodt, which contained approximately 84 percent silicic acid,
10 percent CaSO , and 6 percent Phosphor.
The developing solvent was benzene-.acetic acid (152:48). TLC plates
were viewed under UV light. Portions of adsorbent containing the
spot were scraped with a clean spatula into a scintillation vial,
scintillation fluid added, and counted, along with samples of known
radioactivity. Portions of TLC plates, with their R values corres-
ponding to known degradation products of picloram, were also counted.
Samples were applied to TLC plates immediately after elution from the
column, along with samples of known radioactivity.
Factors Affecting Soil Adsorption-
Desorption of Picloram (Batch Studies)
A series of experiments •were conducted to determine the influence of
incubation time, soil type, organic matter, herbicide concentration,
pH, and inorganic salts on the soil adsorption and release of picloram.
A slurry technique (25) was used throughout the series and quantitative
determinations of the herbicide were made primarily by using radio-
labelled picloram. The folio-wing procedures were common to all
experiments unless otherwise noted.
Ten grams of air-dried (5 grams for Chance and Aiken soils) 60-mesh
soil were weighed into a polypropylene tube and 10 ml of herbicide
solution added. The tubes were stoppered and placed on a mechanical
shaker in a constant temperature bath until equilibrium was reached
or for the indicated time. After shaking, the slurry was centrifuged
at 1500 RPM for 10 minutes. A 1 ml aliquot of the supernatant was
taken at various intervals and counted. The herbicide adsorbed was
determined by subtracting the concentration found in the supernatant
27
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from the initial concentration. The temperature fluctuation in the watei
bath was — 0. 3°C. All determinations were made in duplicate. Five
soils were used for these experiments. Important characteristics
of these soils are described in Table 1.
Effect of time on adsorption-desorption of picloram -was investigated
by the above mentioned slurry technique by taking aliquots after each
6-hour interval, except in Aiken soil where samples were taken at
1/2-hour intervals. When no change in the picloram concentration
of the supernatant was observed, it was assumed that equilibrium
had been reached. Similar procedures were followed for desorption,
except the time interval for sampling was generally four hours.
One experiment was designed to determine the influence of soil type
and organic matter on soil adsorption of picloram. Organic matter
was removed from the soil by heating to 350° C for 24 hours in an
electric furnace. Adsorption of picloram by the five soils was deter-
mined after removing the organic material by using the slurry technique.
Desorption of picloram was studied utilizing the following technique.
Adsorption equilibrium was allowed to take place and 1 ml sample
of the supernatant was taken after centrifuging the sample. Ten ml
water was added and the system was allowed to re-equilibrate; the
tubes were centrifuged and a 1 ml aliquot was again taken from the
supernatant for analysis. To study the effect of dilution on desorption
of picloram, the soil-solution was diluted with additional water after
adsorption equilibrium. They were allowed to re-equilibrate for 24
hours and 1 ml samples were withdrawn from the supernatant for
counting.
The influence of herbicide concentrations on adsorption of picloram
was studied using picloram concentrations ranging from .05 to 10
ppm and following the procedure outlined above.
Four different temperatures (17. 7° C, 25° C, 28. 2° C, 34. 7° C) were
used with Providence and Chance soils and three temperatures (17. 7° C,
25° C, and 34. 7° C) were used with Aiken soil to study the effect of
temperature on adsorption and desorption of picloram.
Another experiment was designed to determine the effect of pH on
adsorption of picloram by Providence and Chance soils. The pH
change was induced by adding either KOH or HC1. Twenty-four hours
were allowed for equilibration. The pH effects above pH 9. 2 in Pro-
vidence soil and above pH 8. 5 in Chance loam could not be studied
28
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CO
03
n~t
3
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d
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because of solubilization of organic matter by the high alkalinity and
consequent interference during scintillation counting.
The influence of several salts on adsorption of picloram onto the
Providence soil was investigated. Dilute solutions (1 to 5 meq/1) of
KC1, K SO, CaSO , and CaCl were used, and their influence on
£ ^r ~r £
picloram adsorption was studied using the slurry technique. A
preliminary test using concentrations of 66 meq/1 and 660 meq/1
Bad was performed. The effect of CaCl concentrations on the ad-
*-< C*
sorption of picloram by the other four soils was examined at 0, 5, 10,
25, 50, and 5000 meq/1.
Mechanical analyses (particle size distribution) and organic matter
analyses were performed by the Utah State University Soil Testing
Laboratory. The former was based on a method adapted from Kilmer
and Alexander (33). The latter was adapted from the Walkley-Black
wet digestion method of Allison (4).
Cation exchange capacity (CEC) was determined by the method of
Chapman (11) by the Utah State University Soil Testing Laboratory.
Factors Affecting Soil Adsorption-
Desorption of Picloram (Column Studies)
Columns used in this study were made of pyrex glass, 2 cm diameter,
with fitted glass bottoms. There was a narrow outlet at the center of
the bottom of each column. Soil was packed into the column to depth of
14. 5 cm. Soil in the column was saturated with deionized water to
eliminate air in the column by gradually immersing the column into
water in a graduated cylinder and leaving it until free water appeared
on the top of the soil column. Deioniz,ed water was then passed through
the soil from the top for 24 hours before the herbicide was added. The
soil column contained glass beads to a depth of about 0. 5 cm at the top
of the soil to prevent the soil from puddling.
After the soil had been washed free of herbicide at the end of the ex-
periment, the same column was used to determine the dispersion
coefficient (D ). A solution of 0. IN CaCl_ was used to obtain the
o — c
Cl breakthrough curve (BTC). The dispersion coefficient was cal-
culated from the Cl BTC according to the following equation:
30
-------
D
_ _
at = - *o sz o Sz2
where C is the concentration of herbicide in solution, t is time, Z is
the distance along the column, v is the interstitial flow velocity, and
D is the dispersion coefficient.
o
The chloride concentration was determined by the potentiometric ti-
tration with 0. 01 N_ AgNO . A Corning Model 12 pH meter with an
expanded scale was used; the electrodes were a double junction
reference electrode and a silver billet indicator electrode.
A Heath Recording Electrometer Model Eu-20-11 was used to monitor
flow rates from the column. The average interstitial flow velocity
(v ) was obtained by averaging the pore-water velocities for different
column effluent fractions (3 ml each). There was a slight decrease in
flow rate over the period of a particular experiment; a typical break-
through curve for Millville silt loam soil is shown in Figure 1.
31
-------
o
o
~^
o
0 9-
0.8-
0 .7-
0.6-
0 .5-
0.4-
0.3-
0.2-
0. I -
Millville silt loam
DQ = 0.7544
0-0
4 8 12 16 20 24
Effluerr! Number (3 ml fractions)
Figure 1. A typical Cl breakthrough curve (ETC) used for
calculating dispersion coefficient.
32
-------
SECTION VI
RESULTS AND DISCUSSION
Field Experiments
Movement of Herbicides Following Heavy
Applications to Canal Banks
Water samples were taken as the initial flush of water crossed the
treated plots and reached the collection points. The highest average
concentration of diuron in the water taken from the Trenton canal
was 1. 78 ppm (Table 2). This concentration was the average of four
determinations ranging from a high of 1. 89 ppm to a low of 1. 47 ppm
and taken at a distance of 1 0 feet below the treated plots. The con-
centration of diuron in the runoff water was greatest at the collection
point nearest the treated area and dropped rapidly when the samples
were taken further down the canal. The limit of detection using the
method of McKone and Hance (41) was . 02 ppm when the untreated
canal water was used to prepare the calibration standards.
Table 2. Diuron concentration (ppm) in irrigation canal water at 10,
100 and 1000 foot distances below areas receiving a 30 Ib/A
dosage to control ditchbank vegetation.
Canal
Trenton
North Logan
Distance below
treated site (ft)
10
100
1000
10
100
1000
Diuron concentration (ppm)*
(First flush)
1. 78
0. 93
<0. 02
0. 72
<0. 02
<0. 02
(Part capacity)**
<0. 02
<0. 02
<0.02
<0. 02
<0. 02
<0.02
* Average of four determinations
^Approximately 90 percent in the Trenton canal and 60 percent in
the North Logan canal
33
-------
A similar pattern of diuron movement was observed in the North* Logan
canal. The highest concentration of diuron was observed in samples
taken 10 feet below the treated plots but was not detectable in the
samples taken 100 or 1000 feet from the treated area. The average
diuron concentration in the North Logan canal water samples taken 10
feet below the plots was 0. 72 ppm compared to 1. 78 in Trenton. The
two canals differed in vegetative cover at the time of treatment -which
may influence the quantity of herbicides moving in the surface water.
Most of the samples analyzed contained less than 0. 02 ppm diuron.
Chancellor (10) found that diuron concentrations up to 180 ppm are
nonpoisonous to man and livestock; it also has a low toxicity to fish.
Even at 1. 89 ppm, the highest concentration of diuron in water in this
study, there is very little chance that injury to fish, livestock, or
plants would result from treating the canal banks for the control of
undesirable plant species.
Atrazine demonstrated a very small tendency to move in irrigation canal
waters when used as a ditchbank spot treatment at the end of a cropping
season. It appears reasonable to assume that its potential to move with
the water would be greatly increased if it were used immediately prior
to filling the channel with water.
Atrazine movement appeared greatest in the Trenton canal as compared
to the North Logan canal probably due to the difference in vegetative
cover. The average atrazine concentration in water taken 10 feet below
the plots was 0. 86 ppm at Trenton and 0.44 ppm in the North Logan
canal (Table 3). The samples collected 100 feet below the plots
averaged 0. 72 ppm atrazine in the Trenton canal while no detectable
level was observed in the 100-foot samples collected in North Logan.
Atrazine was not found in the initial water flush samples collected
1000 feet below the treated areas in either canal. Samples collected
on the same day but after the canals had received most of their capa-
city of water did not reveal any measurable quantity of herbicide.
Atrazine movement in these studies was considerably lower than that
reported by White et ed. (61). In their study, however, application was
made 1 hour and 96 hours prior to wash-off. The samples were not
taken in the present study for a period of approximately six months
after the application. The smaller quantity of atrazine moving is pro-
bly due to several interacting processes. Adsorption and leaching into
the soil profile during the time between treatment and sample collection
would cause the herbicide to be less available for movement in the sur-
face -water and would also allow for degradation of the herbicide.
34
-------
Table 3. Atrazine concentration (ppm) in irrigation canal water at 10,
100 and 1000 foot distances below areas receiving a 10 Ib/A
dosage to control ditchbank vegetation.
Canal
Trenton
North Logan
Distance below
treated site (ft)
10
100
1000
10
100
1000
Atrazine concentration (ppm)*
(First flush)
0. 86
0.72
<0. 72
0. 44
<0. 02
<0. 02
(Part capacity)**
<0. 02
<0. 02
<0. 02
<0. 02
<0. 02
<0. 02
* Average of four determinations
^^Approximately 90 percent in the Trenton canal and 60 percent in the
North Logan canal
Atrazine and diuron concentrations in surface water shown in Tables
2 and 3 are probably of the magnitude encountered normally since the
recommended procedure is to allow a 4 to 6-month interval to im-
mobilize the herbicides in the soil prior to using the canal for irri-
gation. Previous studies (61) have also shown that the major portion
of atrazine in wash-off is contained in the water fraction as opposed
to that adsorbed onto the soil particles in the wash-off material;
consequently, the herbicide concentrations shown in Tables 2 and 3
would not change significantly if the quantity of atrazine in the sedi-
ment was added to each determination.
Effect of Surface Irrigation on the Lateral
Movement of GS-14254 from Treated Cropland
The average levels of GS-14254 in irrigation water declined rapidly
with increased distance from the treated plots (Table 4). The irriga-
tion return flow from the plots treated with 2. 0 Ib/A GS-14254 con-
sistently had higher residue levels than that from the plots treated with
1. 5 Ib/A (Table 4). The differences in residue levels between treat-
ments at equal distances from treated plots were significant at the
10% probability level. The average GS-14254 concentration in the
irrigation water for the 1. 5 Ib/A treatment ranged from . 272 ppm at
35
-------
the end of the treated plots to . 005 ppm at 120 feet from the treated
plots. For the 3.0 Ib/A treatment, GS-14254 concentrations ranged
from . 487 ppm at the end of the plots to . 035 ppm at 120 feet from
the plots (Table 4).
Table 4. A comparison of the quantity of GS-14254 recovered in the
runoff water from two treatments at different distances
from the treated area.
Distance
(feet)
0
10
50
120
Rate of
GS-14254 applied
(Ib/A)
1. 5
3. 0
1. 5
3.0
1.5
3.0
1. 5
3.0
Concentration
in runoff
(ppm)
.272 a
.487 b
. 122 c
. 147 c
. 013 d
. 053 d
. 005 d
. 035 d
Values followed by the same letter are not significantly different at
the 5% level as determined by the L. S. D. test. Each value is the
mean of three replications.
Residue levels in the runoff water dropped off rapidly with time.
Table 5 shows that the concentration of GS-14254 in the first flush
of water was . 272 ppm for the 1. 5 Ib/A rate and that it dropped off
to .010 ppm in the water passing the same point 10 minutes later.
It also shows that the concentration in the first flush of water was
. 487 ppm for the 3. 0 Ib/A rate and that it dropped off to . 043 ppm
after 10 minutes.
These data agree with the runoff studies conducted by White _et al.
(61) on the loss of atrazine from fallow land. They found that losses
were highest during the early stages of runoff followed by a gradual
tapering off.
36
-------
Table 5. A comparison of the quantity of GS-14254 recovered in the
runoff water at the end of the treated plots from two treat-
ments at different times during irrigation.
Time
(min)
Rate of
GS-14254 applied
Concentration
in runoff
/ \a
(ppm)
0
1. 5
3.0
. 272 a
.487 b
10
1.5
3. 0
. 010 c
. 043 c
Values followed by the same letter are not significantly different at
the 5% level as determined by the L. S. D. test. Each value is the
mean of three replications.
Losses of GS-14254 due to erosion 'were not included in this study.
It was estimated that the 110 ml water sample contained 1 to 2 gm of
soil. White ^et al_. (61) stated that the concentrations of atrazine in
the soil fraction were much higher than in the water fraction (the
ratio of concentration of atrazine in the soil to atrazine in the water
was about 10 to 1). However, due to the greater amounts of water
that were lost as compared to soil, there were about 10 times as
much atrazine lost in the water as in the soil fraction. Although
no measurement of the level of GS-14254 was made in the soil fraction
of the water sample, a similar 1 to 10 ratio might be expected since
the two herbicides have similar solubilities and soil adsorption char-
acteristics.
GS-14254, like atrazine, will move in irrigation or precipitation run-
off. The concentration of GS-14254, however, drops off rapidly with
increased distance from the treated areas (Table 4). In areas where
_s_-triazine sensitive crops are grown, phytotoxicity symptoms might
occur on sensitive plants from runoff from treated areas.
37
-------
Movement of Hormone-Type Herbicides
in Surface Waters Following Field Application
Table 6 shows the concentration of picloram in surface waters from
an area treated with picloram at 1 Ib/A following four periods of
natural precipitation. At the time of the first collection there had
been 0. 25 inch of rain on the Wasatch experiment. It was sufficient
rain to move water across the site and allow collection of water at
various intervals below the treated site. Picloram was detected in
surface waters at 10 and 100 meter distances below the treated area;
the concentrations of picloram were 28 and 21 ppb, respectively.
Collections made at distances greater than 100 meters did not contain
detectable amounts of the herbicide.
Table 6. Average picloram. concentration in surface runoff water at
various collection points during 1969.
Site
Wasatch County
Cache County
Collection
date
May 16
June 26
July 20
Aug. 17
May 15
June 16
June 27
July 8
Precipitation
after
treatment,
inches
(cumulative)
0.25
2. 32
2. 80
4. 08
0. 20
1. 10
3.55
4. 04
Concentration (ppb)*
Location
(meters
10
28
3
0
0
10
0
0
0
from
100
21
10
T*
0
8
0
0
0
treated area)
1000
0
0
* 0
0
T#*
0
0
0
* Each value is the mean of six determinations
**T = Trace
A second period of storms occurred on June 26, 1969, and produced
runoff from the treated area. Only the waters collected at 1 0 and 100
meter distances contained measurable amounts of picloram. A concen-
tration of 3 ppb was observed in the water 10 meters below the site
and 10 ppb was measured in moving water 100 meters below the
38
-------
experiment. This small increase in concentration from 10 to 100
meters was primarily due to one of the triplicate samples taken at
100 meters being quite high. Subsequent samples taken in July and
August in 1969 and throughout the 1970 season failed to produce
measurable quantities of the herbicide in runoff waters.
A similar experiment was conducted in Cache County, Utah to eval-
uate the influence of soil type and vegetation on picloram movement.
Samples of runoff water from the first major rainstorm demonstrated
some picloram movement. Ten ppb picloram was observed in the
samples taken 10 meters below the treated area and 8 ppb picloram
was observed in water taken 100 meters below the plot (Table 6). It
was not possible to detect measurable quantities of the herbicide at
distances greater than 100 meters from the treated area during the
first collection period, nor was it possible to detect picloram in any
samples taken during succeeding rainstorms during the 1969 season.
The experiment was monitored for picloram movement during the 1970
season and no picloram was detected in the surface waters.
Bioassay with safflower plants confirmed quantitatively the results
obtained with chromatographic analysis of water samples. The bio-
assay technique also demonstrated the presence of a significant
amount of picloram in the soil within the boundaries of the treated
site throughout the course of the experiment.
Four experimental sites were selected in 1971 and treated as shown in
Tables 7, 8, and 9. The four sites were located in Rich County, Utah.
The sites consisted of four similar well-defined small watersheds with
a medium stand of rabbitbrush (Chrysothanmus nauseosus) and grass
species. Total precipitation during the initial storm was 1. 56 inches;
precipitation during the remainder of the summer months was not
adequate to allow collection of runoff samples.
Table 7 shows the picloram concentrations in the surface runoff
collected at various distances from the two sites treated with pic-
loram. Picloram was found in surface runoff waters adjacent to
areas treated when rainfall was sufficient to result in runoff from
the treated areas within a 7-day period after application of the chem-
icals. Higher concentrations were observed below Site I than were
observed below Site II (Table 7) probably due to increased vegetation
on Site II and slight differences in soil characteristics. Concentra-
tions observed below Site I ranged from 1082 to 1 7 ppb at 10 and 1000
meter distances below the plot treated with 1 Ib/A dosage of picloram.
Runoff water collected at the various distances below the 2 Ib/A
39
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treatment of Site I had a greater quantity of herbicide than those col-
lected below the area treated at a 1 Ib/A rate of picloram as shown
in Table 7. Nearly equal amounts of picloram were recorded in the
surface waters collected at various distances below Site II from the
1 Ib/A and 2 Ib/A treatments. On this site, application rate did not
influence the quantity of herbicide moved; the additional vegetation on
the site may have limited the quantity of herbicide available for move-
ment. After 12 weeks, the picloram concentration had decreased to
1 ppb or less at all sampling points. Within 1 year the concentrations
of picloram in runoff water remained below the limit of detection of
the analytical methods used.
The movement of 2,4-D in surface waters was determined after treat-
ing two watersheds with a tank mix of ester formulations of 2,4-D
and 2,4, 5-T. Treatments were made on June 29, 1971, using the
same procedure as was used on the picloram sites. Only one rain-
storm produced runoff sufficient for analysis during the summer
season and consequently only one sampling of 2,4-D concentration
is reported in Table 8. Each value is the mean of the two samples
collected at each of the collection points during the initial runoff
period.
Where 2,4-D was applied at 2 Ib/A on Sites III and IV the herbicide
observed in surface runoff waters ranged from 210 ppb at 1000 meters
below the plot to 3240 ppb at a 5 meter distance below the plots. No
detectable amount of 2,4-D entered the native stream slightly more
than 1.6 Km from the experimental sites. Likewise, no detectable
levels of 2,4-D -were observed in surface -water in the fall of 1971 nor
during the growing season of 1972. The dosage of 2,4-D influenced
the amount of herbicide loss; however, this differential was more
pronounced on Site III than on Site IV. Table 8 shows that the loss of
2,4-D from Site III nearly doubled as the rate of application was
doubled. Only a slight increase in 2,4-D movement was observed
when the dosage of 2, 4-D was doubled on Site IV. Thus the rate of
application must be considered in relation to soil texture and vege-
tative cover in predicting the surface movement of herbicides. As
vegetative cover decreases, more herbicide is deposited on the soil
surface and consequently more readily moved in the surface waters,
this would probably be more likely in the sandy soils as opposed to
heavier soils.
Similar movement patterns were observed with 2,4, 5-T as were found
for 2,4-D. The lower quantities observed were probably a result of
the lower dosag&s applied in the case of 2,4, 5-T. The concentration
42
-------
of 2,4,5-T in runoff waters ranged from approximately 100 ppb adja-
cent to the plots as shown in Table 9. There were only minor differ-
ences in the 2, 4, 5-T levels observed in water samples taken below
the 1 Ib/A dosage treatment plots when compared with the 2 Ib/A
treatment plots. The level of 2,4, 5-T in surface waters was below
the detection limit 12 weeks after application and after over-wintering.
One year after applying the herbicides, no detectable amounts of
2, 4, 5-T were observed in surface waters generated as spring runoff.
Laboratory Studies
Degradation of Picloram
Various aqueous solutions of picloram (0. 05 to 1. 0 ppm) were exposed
to normal amounts of sunlight in the laboratory for a 12 day period.
No degradation was noted as determined by TLC and liquid scintillation
counting. Adsorption onto walls of the reaction containers was shown
to be extremely small and no adjustments were deemed necessary.
Factors Affecting Soil Adsorption-
Desorption of Picloram (Batch Studies)
As shown in Figure 2, adsorption equilibrium for picloram was attained
after about 50 hours by Millville and Nibley soils, and was nearly com-
plete for the Providence soil within 120 hours. Aiken soil attained
equilibrium within 4 hours (not shown in Figure 2). Chance loam soil
was still adsorbing after 120 hours at 34. 7° C. The adsorption kinetics
of soils in Figure 2 shows soils with higher organic matter took longer
to reach equilibrium. Although the soils differed in many properties,
organic matter appeared to account for a major portion of adsorption
on these soils.
The effect of soil type and organic matter content of the five soils on
the adsorption of picloram at two concentrations, 0. 5 and 1. 0 ppm,
is given in Table 10. The adsorption ranged from 10. 8 to 58. 2%.
Adsorption on Millville, Nibley, and Providence soils, all with simi-
lar pH values, increased with an increase in organic matter content.
For each 1% increase in organic matter there appears to be about
150 |agm/kg increase in picloram adsorption. When the soil organic
matter was altered or removed from the five soils by heating to 350° C,
43
-------
1000
900-
800-
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Chance (34.7°C)
A
Providence (25° C)
Millville (25°C)
a
-n 1 1 1 r—
20 40 60 80 100
Time (hours)
120
Figure 2. Effect of time on adsorption of picloram by four soils
at 1 ppm initial concentration.
44
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a reduction of up to 91% of the total adsorption occurred as shown in
Figure 3. Although Hance (?6) has noted that all of the organic matter
is probably not removed by the heating procedure and that some dis-
ruption of clay minerals may occur, this experiment demonstrates the
importance of organic matter in the adsorption of picloram.
The release (desorption) of picloram already in equilibrium with the
soil is shown in Table 11. Desorption was accomplished by two succes-
sive washings with 10 ml portions of deionized water. The percent of
picloram desorbed (of that initially adsorbed) generally decreased
inversely with the amount of organic matter. This demonstrates the
importance of organic matter in soils in the retention of picloram. The
total picloram eluted by two water extractions was 41% to 72% of that
initially adsorbed. Four extractions were performed on the Providence
soil and demonstrated that after the second water extraction picloram
is removed with considerably more difficulty, only 5.6% and 2. 8% of
adsorbed picloram was desorbed in the third and fourth extractions,
respectively (Table 12).
The relationship between the adsorption of picloram and the pH of the
soil suspension is given in Table 13 and Figure 4 for Providence silt
loam and Chance loam soils; pH was adjusted by adding 0. 1 N KOH
or 0. 1_N HC1 to the soils. There was a sharp increase in adsorption
as pH decreased. In Table 13, the percentage of dissolved free acid,
calculated using a pKa of 4. 1 for the carboxylic group is shown. Ad-
sorption appears to increase as the undissociated acid form increases
with decreasing pH. Hamaker, Goring, and Youngson (24) have re-
cently shown a sharp increase in adsorption of picloram as the soil
slurry pH is lowered from 6. 5 to 4. 0.
The adsorption of picloram was influenced by the pH of the soil sus-
pension. The following regression equations show this relationship
for Chance loam and Providence silt loam, respectively (Figure 4):
l°g-
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o
o»
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v^
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400 -
300 -
£ 200 -
100 -
Adsorption on the natural soils
•
'777A Adsorption on the soils after
removal of organic matter
C.M. 1.9%
0 M. 3.6%
Providence
Figure 3. Effect of organic matter content of three soils and the
removal of organic matter on adsorption of picloram.
Adsorption determined at 25 C.
47
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Table 13. Effect of pH on the adsorption of picloram by Chance loam
and Providence silt loam soils at 25° C (initial picloram
concentration 1 ppm).
PH
3. 40
4. 35
5. 15
b, 75
6. 20
6. 55
6. 90
7. 05
7. 25
7. 55
8. 00
8. 50
3. 60
4. 50
5. 30
5. 95
7. 10
7. 45
8. 00
8. 60
9. 20
Picloram adsorbed
fjLgm/kg soil
Chance loam soil
1832
1584
1278
1132
962
850
868
780
764
730
612
522
Providence silt loam soil
916
806
697
594
251
297
303
251
200
Picloram
undissociated
%
83.4
36. 0
8. 2
2. 19
. 79
. 35
.16
. 11
. 07
. 04
. 01
. 004
76. 0
28. 5
5. 9
1.4
. 1
. 05
.01
. 003
. 0008
50
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8 1000
a. 800
^ 600
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300-
200-
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TD
O
£
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-------
soil is governed, to a large extent, by the hydrogen ion activity rela-
tionships which occur between the solution and solid phase of soil.
Although adsorption of picloram is affected by solution pH, it is evi-
dent that ionization of picloram is not the only factor. Even above
pH's at which picloram was essentially ionized (Table 13), there was
a continued decrease in adsorption with increases in pH.
Bailey, White, and Rothberg (7) have suggested hydrogen bonding to
clay minerals as a possible mechanism for picloram adsorption. It
appears that the proton involved in hydrogen bonding at lower pH
values came from the carboxylic group of picloram. A sharp increase
in adsorption with decreased pH parallels the sharp increase in undis-
sociated species of picloram (Table 13). Whether or not protons
associated with soil constituents play any part is unclear. However,
at pH values where the adsorbate is completely ionized or completely
undissociated, adsorption changes with pH. Picloram is completely
undissociated below pH 2. 1; and completely ionized above pH 6. 1.
Measurements were not made below pH 3. 4 in either of the soils. At
lower pH values, other complications occur because of solubilization
of clay lattice Fe and Al. However, adsorption of picloram above pH
6. 1, when the picloram is 100 percent in ionic form, can be considered.
A number of adsorption mechanisms were discussed by Bailey, White,
and Rothberg (7) for the bonding of picloram at pH values higher than
6. 1 (pKa + 2). The hydrogen bonding through the amino group, through
the carboxylic acid group, or bridging through metal cations (by co-
ordination with water), are likely to be influenced by addition of OH~.
They also concluded that surface acidity of montmorillonite is 3 to 4
pH units lower than the pH of the bulk solution. It is conceivable, then,
that with the addition of more hydroxyls, protons from weak hydroxyls
on clay mineral edges will continue to react. Consequently, any
bonding of picloram anions through these protons will be reduced at
pH values that seem to be above the pH range affecting picloram ion-
ization. The replaced protons are incapable of reacting with the car-
boxylic group of picloram in solution due to its acidity (pKa = 4. 1).
The same explanation applies to replacement of protons from - NH
L*
and -OH groups of organic matter and -OH groups of hydroxy oxides
in the soil.
The above seems to be the most feasible explanation for the reduced
adsorption at pH values above - 6. 1. However, the increased ad-
sorption below pH 6 can have an explanation other than the result of
52
-------
In preliminary studies on the adsorption of picloram by soils, small
amounts of inorganic salts increased picloram adsorption consider-
ably. Due to differences in the water quality used for irrigation,
differences in salt content of soils and water, and variations in salt
concentrations as the moisture is depleted from soils, the effect of
these inorganic salts on picloram adsorption is of interest. No liter-
ature, in this respect, has appeared concerning picloram.
Picloram adsorption from 1. 0 ppm initial picloram concentration by
Providence silt loam soil is given in Table 14. The salts investigated
were Bad , KC1, K SO , CaCl , and MgCl . Concentration of each
^ C* ~C W t.4
electrolyte was 5 meq/1 of solution, except BaCl and KC1 also had
o
concentrations up to 666. 0 meq/1 and 130.43 meq/1, respectively.
There was, generally, a drop in soil suspension pH with the addition
of salts. However, the enhanced picloram adsorption could not be
accounted for by the theoretical increase in molecular picloram as a
result of drop in pH. Miller (46) has observed significant adsorption
changes as a direct effect of pH change occurring within — 3 pH units
of the pKa value of the various phenols or 2, 4-D sorbed to an organo-
clay. The pH changes below pH 7 would be within this range since the
pKa of picloram is about 4. 1. Perhaps the apparent salt effect is
largely a pH effect.
The drop in pH was expected on the basis of replacement of exchange-
able H from the exchange complex of soil by the metallic cations.
However, at higher BaCl_ and KC1 concentrations, replacement of pro-
C*
tons from the weak hydroxyls of exposed layers of clay minerals, hy-
droxy oxides, and organic matter -NH and -OH groups is also a
Ci
possibility. An unexplainable slight increase in pH was obtained with
the addition of small amounts of BaCl_. Increased salt concentrations
c*
induced some increases in picloram adsorption independent of changes
in pH; therefore, the pH effect is not likely to be the sole cause of
increased adsorption.
The disappearance of picloram from solution with the addition of inor-
ganic electrolytes may have been a result of herbicide precipitation
rather than soil adsorption. Such precipitation commonly occurs where
salts are added to an aqueous solution containing neutral organic mole-
cules (1). Picloram precipitation was investigated by centrifuging
solutions of picloram-BaCl^, and picloram-CaCl7 concentrations from
L* £1
54
-------
increased hydrogen bonding through carboxylhydrogen. At pH values
below - 5. 0, there exists a possibility of releasing lattice Fe and
+3 +
Al due to hydronium (HO ) ions acting on the clay lattice. The
released Fe and Al ions are capable of complex formation with
picloram. Increased adsorption can occur as a result of this complex
formation.
In summary, the adsorption of picloram by Providence and Chance
soils is negatively but strongly correlated with pH of the soil suspen-
sion. The mechanism of adsorption at pH values lower than about 6
(pH < pKa + 2) is probably by hydrogen bonding. The hydrogen atom
on the carboxylic group would be the most likely part of picloram to
be involved in such a bond. Another possibility at much lower pH
values (pH < - 5) is the complexation with Fe and Al , which
would be released as a result of hydronium ion attack on the clay
lattice. The adsorption mechanism at higher pH values (pH > pKa + 2)
appears to be hydrogen bonding through carbonyl group of picloram to
the weakly acidic protons on the various functional groups on the organ-
ic matter and clays of the soil. Bailey, White, and Rothberg (7) referred
to physical adsorption as another possible mechanism at pH > pKa + 2 .
The above investigators also indicated the possibility of metal-cation-
picloram complex directly, or through coordination with water, at
pH > pKa + 2.
Adsorption of picloram by Providence silt loam soil (3. 52% organic
matter) and Chance loam soil (18. 7% organic matter) was highly and
negatively dependent on pH changes induced by KOH and KC1. This
was true even at pH values at which picloram molecules would theo-
retically be 100% dissociated. Adsorption of picloram by these two
soils, and by the additional three soils of diverse properties, was
greatly increased by increasing concentrations of BaCl , KC1, K SO ,
CaCl and MgCl from 0 to 500 meq/1. A complex formation between
Cj £*
picloram and metal cations is suggested as a possible mechanism for
the increased adsorption.
Hamaker _et _aL (24) have demonstrated that only one dissociation con-
stant is obtained corresponding to the dissociation of one proton from
the carboxylic group of picloram. Accordingly, based on a pKa of 4. 1
reported by these authors for the above dissociation, the proportion
of the two species obtainable at the pH's of concern in these studies is
given in Table 13. It is seen from this table that more than 97% of
picloram existed as the anion in these studies.
53
-------
Table 14. Influence of various salts on the adsorption of picloram by
Providence silt loam soil. Initial picloram concentration
was 1. 0 ppm and incubation temperature was 25° C.
Salt Salt concentration
meq/1
BaCl 0
1. 16
2. 84
5. 53
62. 10
666. 00
KC1 0
5.0
74. 10
130. 43
K2S04 0
5.0
CaCl2 0
5.0
MgCl2 0
5.0
Equilibrium pH
7. 10
7.40
7. 30
7. 15
6.41
5. 90
7.05
6. 95
6. 66
6.45
7.05
6. 94
7. 05
6. 79
7. 05
6.81
Adsorption
|agm/kg soil
356
356
402
442
643
752
352
388
531
555
352
344
352
411
352
387
LSD (.05) = 13.6
5. 0 to 500 meq/1. Picloram concentrations before and after centri-
fuging were not significantly different, indicating that precipitation did
not occur.
Comparison of picloram adsorption (Table 14) at 5.0 meq/1 of KC1,
CaCl , and MgCl_ revealed that divalent cations, generally, were
<-> C*
more effective in increasing adsorption on Providence soil than are
monovalent cations. Although the replaced protons did not react with
55
-------
picloram anion in solution to produce the molecular form at the pH's
obtained at 5. 0 meq/1 concentrations, the divalent ions generally pro-
duced a lower pH than did monovalent ions. The increase in picloram
adsorption at higher salt concentrations could not be accounted for by
theoretical increases in molecular picloram, but the metal cations may
serve as a bond between the exchange site and the herbicide. This was
suggested by Mortland (48) for organic molecules and clay minerals,
and by Hance (26) for linuron adsorbed to several adsorbents saturated
with metal cations. Hance (26) concluded that atrazine did not complex
this way.
The carboxyl of picloram is the most likely group to be involved in com-
plex formation with the metal cations. However, Providence soil is 74
percent base-saturated in the natural state, and about 85 percent of these
bases are the divalent cations, Ca and Mg (Table 15). Therefore, the
continued increase in picloram adsorption with increasing BaCl and
KC1 concentrations cannot be the result of picloram complexing with
+2 +
additional Ba (or K ) ions adsorbed on the soil. The picloram ad-
sorption occurring at 130.43 meq/1 KC1 and 666.0 meq/1 Bad con-
LJ
centrations (Table 14) was much higher than expected on this basis.
Table 15. Cationic composition of the exchange complex of various
soils.
Cation exchange Base
Soil _ _ca_pac_ity saturation _ __ _C_a_ + M_g_
meq/100 gm
soil
% of
exchangeable bases'
Nibley silty
clay loam
Millville
silt loam
Chance loam
Aiken clay
Providence
silt loam
25. 7
15. 6
37. 0
16. 3
30. 5
- 100
100
95. 7
49.9
74. 0
91. 2
83. 7
87. 6
87. 1
84. 8
bases denote Na + K + Ca + Mg
56
-------
It is conceivable that the picloram anion in solution will undergo the
following reactions with added metal cations in solution:
P"
M+ + P~ ^ [MP]+ * [MP ]°
1
M+ + P" - [MP]° [1]
III
[MP ]° + M+2 + P" - [MP]+ + [MP ]°
I
II
where P is picloram anion, M is a metal cation, and I, II, and III
refer to molecular or ionic species. The most likely constituent of
picloram to be involved in the formation of species I and II would be
the carboxyl group (7).
The species [MP] may be involved in cation exchange with inorganic
cations on the exchange complex of the soil. This possibility was
suggested by Dekking (15) for the adsorption of polystyrene by kaoli-
nite and montmorillonite. A quantitative estimate of the extent of
[MP] as a function of M concentration in solution is not available,
+2
although it would increase with increasing M ions.
A number of other possibilities exist for the increased picloram ad-
sorption with enhanced salt concentrations. Salts would change the
thickness of the double layer of ions, which could result in increased
metal ion-picloram complexation. Hemi-salt formation, which occurs
•when the amount of adsorbed base on a surface exceeds the number of
protons available for cation formation, is also possible. According to
Mortland (48), in hemi-salt formation, the already protonated molecule
at the surface of clay retains its proton against attraction by the non-
protonated molecule, and a cation of [B - H] type results. It is
LJ
possible that additional salts contribute to [B - H] formation by
L^i
making more base (picloram anions) available for bonding. The exact
mechanism by which this occurs is not clear.
The increase in picloram adsorption with increasing monovalent cations
(K , for example, in Table 14) is unexplained. However, from
57
-------
Equation [l], the species [MP] , the result of monovalent cation and
picloram anion interaction, is neutral. It is conceivable that a neutral
species will have a greater tendency to adsorb by physical forces (7)
than an anionic species, which will be repelled by the negative charges
on the soil. McCall et al_. (39) found that picloram was adsorbed by
cationic resin (H-form), non-ionic resin and anionic resin, respectively.
They concluded that picloram was adsorbed mainly in the anionic form
by Coulombic forces (electrostatic) and to a lesser degree by weak
physical bonding (van der Waal's forces).
The effect of temperature (17. 7, 25.0, 28.2, and 34. 7° C) on the ad-
sorption of picloram by the Chance loam, Providence silt loam, and
Aiken clay soils is given in Table 16. An increase in temperature from
17. 7 to 25. 0 C resulted in an increase in adsorption. A decrease in
adsorption occurred as the temperature increased to 28. 2° C and 34. 7°C.
This suggested that two mechanisms are operative in adsorption.
Table 16. Effect of temperature on the equilibrium adsorption of
picloram by Providence silt loam, Chance loam, and Aiken
clay soils from 1.0 ppm concentration.
Soil Temperature Adsorption
C |J.gm/kg soil
Providence
s ilt loam
Chance loam
Aiken clay
17. 7
25. 0
28. 2
• 4. 7
17.7
25. 0
28. 2
34. 7
17. 7
25. 0
34. 7
339
371
412
313
968
1042
1020
1006
268
-
254
58
-------
Haque _et jil_. (29) found little effect of temperature on adsorption of
2,4-D on clays at 25 and 40° C, whereas Talbert and Fletchall (51)
found a decrease in adsorption with increased temperatures for
14 14
simazine- C and atrazine- C by Marshall silty clay loam.
Apparently, the two mechanisms of adsorption of picloram, which have
opposite temperature coefficients, increase or decrease adsorption
depending on temperatures. In earlier studies, Hamaker, Goring,
and Youngson (24) reported that diffusion of picloram was a dominant
factor in adsorption. Diffusion is an endothermic process, and is
enhanced by increases in temperature. An apparent decrease, after
an initial increase in adsorption suggests physical adsorption, or a
weak bonding, at the pH levels of these soils.
The amount of picloram adsorbed at various herbicide concentrations
by Providence silt loam and Chance loam soils is shown in Figure 5
and Table 17. Table 17 shows adsorption values of Aiken soils at two
herbicide concentrations. As picloram concentrations in solution were
increased from 0. 05 to 10 ppm, the amount adsorbed increased
(Table 17).
As shown in Figure 6, the adsorption data follow the Freundlich e-
quation (correlation coefficient 0. 999). The values of b and n are the
y intercept and slope. They were found to be 538. 3 |agm/kg and 0. 972
for Providence silt loam and 2009 (agm/kg and 0. 837 for the Chance
loam soil. The value of b can be interpreted to be equal to the concen-
tration of picloram adsorbed by the adsorbent in equilibrium with a
unit concentration of the herbicide (in this case 1 ppm).
To study the release of picloram with additional elutions of water, 1
ppm solutions of picloram were allowed to equilibrate •with soil at 25° C;
the soil:solution ratio was 1:1. The bulk solution, which was in equi-
librium with the adsorbed picloram, was diluted •with deionized water
to create different concentration gradients. The system was then
allowed to reach equilibrium. The results are presented in Table 18
for the Providence silt loam soil. Dilutions of equilibrated bulk sol-
ution from 1. 5 times to 3. 22 times the original quantity of water was
used.
The data show the amount of picloram remaining after the first wash,
the equilibrium concentration of the bulk solution and the theoretical
amount of picloram expected to be adsorbed at the three equilibrium
concentrations as extrapolated from the adsorption isotherm (Figure 5).
59
-------
9000
Providence silt loom
0
Herbicide concentration (ppm)
Figure 5. Effect of concentration of picloram in solution on its
adsorption by two soils. Adsorption determined at
25°C.
60
-------
Table 17. Effect of picloram concentration on its adsorption by
Providence, Chance, and Aiken soils at 25° C.
Initial
Soil concentration
ppm
Providence
silt loam
.
1.
2.
4.
8.
10.
Chance loam 0.
I.
2.
4.
8.
10.
Aiken clay 0.
1.
05
10
50
00
015
033
0
0
5
0
016
033
0
0
5
0
Equilibrium
concentration
ppm
. 032
. 064
. 325
. 652
1. 168
2. 524
5. 184
6. 436
.209
. 479
1.0502
2. 13
4. 435
5. 6134
0.433
0. 867
Amount adsorbed
[Jigm/kg soil
18.
36.
175.
347.
863.
1515.
2790.
3611.
582
1042
1930
3806
7130
8773
135
268
6
3
0
7
0
0
0
0
61
-------
iOOOO
0)
c>
o
CO
o»
-X
v.
E
o>
1000
O
to
T3
O
E
o
a
CL
100-
20-
0 Providence bilt loam
A Chance loam
.0!
O.I
T-
3
T~
6
Equilibrium concentration ppm (log scale)
Figure 6. Freundlich plot for adsorption of picloram by Providence
silt loam and Chance loam soils at 25° C.
62
-------
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ni
63
-------
The reversibility of adsorption at lower dilution (1.5) is evident. How-
ever, at higher dilutions, the adsorption is not completely reversible.
The effect of the soil: solution ratio was studied by an experiment
(Table 19) in which soil:solution ratios ranging from 1:5 to 1:0. 5
were used. It was found that soil.-solution ratios between 1:5 and
1:2. 5 did not have any measurable influence on adsorption per unit
weight of soil.
Table 19. Effect of soilrsolution ratio on the equilibrium adsorption
of picloram by Providence silt loam soil from aqueous
solutions of 1 ppm concentration.
Soil: solution ratio Amount of picloram adsorbed
|agm/kg soil
1:5. 0
1:2. 5
1:1. 66
1:1. 25
1:1. 00
1:0. 66
1:0. 50
345
338
316
350
342
307
268
In an attempt to relate the soil characteristics affecting adsorption of
picloram, correlation coefficients were determined (Table 20). Ad-
sorption of picloram was most closely related to organic matter con-
tent, pH and sesquioxides (Fe and Al oxides).
Correlation between adsorption and cation exchange capacity was sig-
nificant at the 0. 05 level. Correlation was very poor with clay and
silt content. Cation exchange capacity and organic matter are closely
associated with each other (Table 21). The pH was negatively cor-
related with adsorption.
The positive correlation of organic matter with sorption is consistent
with the results of Sheets, Crafts, and Drever (54) who reported that
organic matter was the best single predictor of herbicide sorption
among the four factors of organic matter, clay content, soil pH, and
cation exchange capacity.
64
-------
Table 20. Correlation coefficients (r) between soil properties and
adsorption of picloram by five soils.
Soil property Correlation coefficient
Si
Organic matter 0. 99
Cation exchange capacity 0. 84
Sand 0.64
Silt -0.10
Clay -0.25
Sesquioxides +Q> %
-0. 98
Reduction in organic matter 0. 98
Chance and Aiken soils excluded
A correlation coefficient of 0. 80 at 5 percent level and 0. 90 at
1 percent level is required for significance
The role of hydrated Fe and Al oxides as sorption agents was illustra-
ted by the work of Hamaker, Goring, and Youngson (24), who found
that organic matter and hydrated metal oxides are principally re-
sponsible for the adsorption of picloram on the 10 soils they studied.
14
They found the percentage of sorption of C-labelled picloram to be
21 percent and 34 percent in one hour from 1 ppm solution of Fe O
£* J
(amorphous) and Fe O (partially crystalline), respectively.
C* D
65
-------
Table 21. Correlation coefficients (r) of various soil properties
among themselves.
Soil property CEC Sand Silt Clay R,O pH
O. M. .18
C. E. C.
Sand
Silt
Clay
Sesquioxides
.52 .1 -.36
.45 .15 -.34
-.49 -.38
-. 59
-.40
-. 54
. 12
-. 90
. 74
-.48
-. 32
-. 74
. 83
-. 30
-. 56
A correlation coefficient of 0. 81 at . 05 level and 0. 92 at . 01 level
is required for significance
Sesquioxides
Factors Affecting Soil Adsorption-
Desorption of Picloram (Column Studies)
Columns simulate the field conditions more closely than batch studies,
and allow better control of variables. The influence of herbicide do-
sage level and Ca-saturation of the soil were studied in the two soils,
Millville silt loam and Aiken clay. The columns were also used to
test the predictability of a mathematical model based on the chromato-
graphic theory of herbicide movement, a theory often used to predict
behavior of herbicides in the soil.
Millville Silt Loam. Soil
Characteristic properties of this soil are given in Table 1. Since
small amounts (5 ml and 3. 52 ml) of herbicide solution were used,
it was considered necessary to evaluate the possibility of the diffusion
of the "penetrated" part of the herbicide into the water on the surface
of the soil (back diffusion). A 1. 0 ppm solution of picloram was eluted
through an 8. 9 cm column of Millville soil. The volume of solution
66
-------
varied from 3. 52 ml in one case to 5. 0 ml in another. It is seen in
Figure 7 that back diffusion effects, expected to be exhibited as hold
back (displacing or spreading the distribution curve) are essentially
absent. The left side (adsorption phase) of 5. 0 ml sample curve is
shifted to the left of that of 3. 52 ml sample probably because of
slightly higher pore water flow velocity of the 5. 0 ml sample.
Effect of Application Rate of Picloram. The distribution of picloram
eluted from an 8. 9 cm column of Millville silt loam soil at two con-
centrations of picloram is shown in Figure 8. The two curves are
essentially identical, except for a slightly higher peak and slightly
higher C/C points on the desorption side of the elation curve, for the
1. 0 Ib/A (10. 0 ppm). The slightly lower flow velocity (v ) for the
1. 0 Ib/A dosage resulted in a greater peak height than expected com-
pared to the lower dosage. However, these differences are assumed
to have occurred because of errors of detection, sampling, etc.
Figure 8, therefore, shows that adsorption isotherm of picloram on
Millville silt loam soil is essentially linear at room temperature from
1. 0 ppm (0. 1 Ib/A.) to 10. 0 ppm (1. 0 Ib/A) picloram concentrations.
The appearance of picloram in the effluent (at 0. 5 pore volume) much
before one pore volume of liquid at both concentrations of picloram
indicates molecular diffusion is significant during picloram movement
in this soil. One limitation to mathematical prediction of solute move-
ment in porous media, is the inability to adequately characterize dif-
fusion. Nielsen and Biggar (51) have reported that h\drodynamic
dispersion increases as v decreases; therefore, the diffusion effects
o
noted in this experiment may be related to the v 's used in these
studies.
Effect of Calcium Saturation of the Soil. In Figure 9, the movement of
a 0. 1 Ib/A dosage picloram as related to calcium saturation of Mill-
ville silt loam is given. Calcium saturation of the 8. 9 cm column of
soil did not appreciably affect the amount of adsorption as shown by
the peak heights of the curves. The slightly lower peak for the Ca-
saturated soil is consistent with a lower flow velocity of water (0. 5882
_ i
cm hr ) for this soil. This is consistent with results from batch
studies showing that Ca-saturation did not appreciably affect picloram
adsorption by this soil.
67
-------
0.4_
0.3_
O
O 0.2.
0.1 -
0 3.52 ml of 1.0 ppm picloram, «0 = 4.0967 cm hr"'
A 5.00 ml of 1.0 ppm picloram, v>0 = 4.4923 cm hr~'
I
2
I
3
I
4
V/V
Figure 7. Relative concentration distribution (C/C ) of picloram
in effluent from Millville silt loam soil column as
affected by amount of picloram solution added on top
of the soil column.
68
-------
0. 3 -
O 0.2 -
O
0. I -
0
0
0 0 10 Ib/acre picloram, \>0=20I83 cm hr
.00 Ib/acre picloram, \>Q - i.2708 cm hr"
[
2
I
3
V/V
I
4
Figure 8. Effect of two rates of picloram application on the relative
concentration distribution (C/C ) of picloram in effluent
o
from Millville silt loam soil column.
69
-------
0.4 -
0.3 -
o
o
0.2 J
0. I -
0 Co-saturated Millville soil u0= 0.5882 cm hr"
A Natural Millville soil u0 = 2.0183 cm hr"
0
I
4
V/Vr
Figure 9. Effect of Ca-saturation on the relative concentration
distribution (C/C ) of picloram in effluent from Mill-
o
ville silt loam soil column.
70
-------
The flatter desorption leg of Ca-saturated soil (compared to natural
soil) indicates slower desorption rate. However, it seems that the
effect of pore-water velocity (0. 588 vs. 2. 02 cm/hr) is superimposed
on the effect of Ca in these data. The relative shape and position
of the curves could be rationalized on velocity difference alone.
Aiken Clay Soil
Some properties of the Aiken clay soil are listed in Table 1. Move-
ment of picloram in a soil column (12. 3 cm long) was studied as
related to herbicide concentration and calcium saturation of the soil.
Effect of Application Rate of Picloram. The distribution curve for
1. 0 Ib/A dosage is shifted slightly to the right of 0. 10 Ib/A curve
(Figure 10), indicating greater soil adsorption at the higher concen-
tration. The tendency of greater adsorption of the higher dosages is
also evident from the later appearance of picloram in the effluent.
Both dosages of picloram started to appear in the effluent of the Aiken
soil after about one pore volume of liquid had passed through the column,
and all picloram was eluted after 2. 25 to 2. 5 pore volumes had passed.
Effect of Calcium Saturation of the Soil. Calcium saturation of the Aiken
soil increased the herbicide adsorption capacity almost two-fold. The
picloram did not appear in the effluent until about 2. 25 pore volumes
had passed through the salt saturated soil even when the flow velocities
were nearly equal. About four pore volumes of displacing liquid were
required to elute all of the herbicide. This is consistent •with obser-
vations from batch adsorption studies with Ca-saturated Aiken soil.
Test of Mathematical Model for Picloram
Movement in Natural and Ca-saturated
Millville and Aiken Soils
The model of Davidson, Rieck, and Santelmann (13) was used to pre-
dict picloram movement in the Millville and Aiken soils. The choice
of soils was arbitrary, dictated by their availability. They did,
however, represent soils of diverse properties in organic matter,
71
-------
0.4
i
0.3 -
0.2 -
O.I _J
0 0.10 Ib/acre o0 = 2.9601 cm hr~
D I.OOIb/acre v>0 = 2.5382 cm hr"
Ca-saturation
A (O.iO Ib/acre) \>0 = 2.6595 cm hr"
0
V/Vr
Figure 10. Relative concentration distribution of picloram in Aiken
clay soil, (1) as a function of two application rates (2) as
affected by Ca-saturation of the soil.
72
-------
clay and sesquioxides contents; properties found in batch studies to be
important in picloram adsorption (See Table 1).
Millville Silt Loam Soil. The relative concentration distribution
(C/C ) as a function of pore volume (V/V ), i. e. , the number of pore
o o
volumes passed through the column, is presented in Figure 11. The
theoretical distribution curve (solid line) for the same pore water
velocity (v ) and distribution coefficient (K) calculated from batch
studies (Table 22), is also given. The experimental curve is the same
as the one given in Figure 9, with picloram applied at 0. 10 Ib/A and
with a v of 2. 0183 cm/hr.
o
Table 22. Physical data for picloram displacement through Millville
silt loam and Aiken clay soils.
Soil
Average pore
water velocity
cm hr
K
Retardation
factor
K
Adjusted
retardation factor
Millville
silt loam
Ca- saturated
Millville
silt loam
Aiken clay
Ca-saturated
Aiken clay
2.0183
0. 5882
2.9601
2. 6595
1. 2289
1.2365
1.6395
3. 4649
0. 971
0. 696
0. 926
The model (solid line) predicts quite well the concentration of picloram
in the effluent at the start of the leaching, near the end of leaching and
estimates peak height reasonably well. However, the model over-
estimates adsorption over most of the leaching process as evidenced
by the shift of the theoretical curve to the right. The occurrence of
peak height of the theoretical curve at a pore volume greater than
73
-------
0.3 -
o
o
v.
O
0.2 J
0. I J
0
Oo 0
0
4
Figure 11. Experimental (o) and calculated relative picloram con-
centration curve from Millville silt loam soil. Solid
curve was calculated from retardation factor (K!) from
batch studies and dashed curve from 'adjusted factor'
(K") (See Table 22).
74
-------
was shown experimentally is also indicative of overestimation of ad-
sorption by the model.
Some investigators (9, 12) have encountered similar problems in pre-
dicting picloram movement in soils, and have calculated a retardation
factor to compensate for the apparent increase in pore volume due to
linear retention processes. This factor supposedly helps to correct
the overestimation of adsorption. The dashed line in Figure 11 is the
theoretical curve based on this lower retardation factor (Table 22),
The model adequately describes the left hand (adsorption) side of the
elution curve, as well as the position of the peak.
If a lack of equilibrium between the soil and flowing system was re-
sponsible for the failure of calculated curves (Figure 11) to describe
the movement of the herbicide, then the left hand portion of each dis-
tribution curve obtained for different herbicide concentration and
column lengths would not be the same (9). The concentration distri-
bution curves for 8. 9 and 14. 5 cm columns of Millville silt loam soil,
at nearly equal v 's, are shown in Figure 12. The picloram concen-
tration in the effluent for each of the column lengths are similar in the
left hand portions of the curve. The lower quantity of picloram re-
covered from the larger column probably resulted from adsorption of
picloram onto the additional soil; the amount of picloram added to
each column was the same. The data in Figure 12 show that an equi-
librium does exist between the liquid phase and the soil. The amount
of picloram adsorbed by Millville silt loam soil in a transient system
was less than that determined with the adsorption isotherm procedure
(Figure 5).
Ca-saturated Millville Silt Loam Soil. The dotted line in Figure 13
shows the influence of calcium saturation on the movement of picloram
through a Millville silt loam soil column. The solid line curve in
Figure 13 represents the theoretical curve. The results obtained
with the Ca-saturation are similar to those obtained with natural
Millville soil (Figure 11). Again, the model overestimated adsorption
as indicated by the shift of the theoretical curve to the right of the
experimental curve. A lower peak height and slightly more tailing
of the theoretical curve on the desorption side was evident. The model
was tested using the lower retardation factor and described the data
quite well (Figure 13). In order to obtain a fit to tne experimental
data, the retardation factor used for Ca-saturated Millville soil was
0. 696 compared to the value of 0. 971 used for natural Millville soil
75
-------
0.4 -
0.3 -
o
-V.
O
0.2 -
0. I -
0
0
0 8.9 cm column u0 = 4.0967 cm hr
A 14.5cm column u0 = 4 5765 cm hr
1
2
1
3
Figure 12. Relative concentration distribution (C/C ) of picloram
in two columns of Millville silt loam soil of different
length.
76
-------
0.3 -
0,2 -
o
O
\
O
o.i -
0
0
2 3
V/V0
Figure 13. Experimental (o) and calculated relative picloram
concentration distributions from an 8. 9 cm column
of Ca-saturated Millville silt loam soil. Solid curve
was calculated from retardation factor (K1) from batch
studies and dashed curve from 'adjusted factor' (K")
(See Table 22).
77
-------
(Table 22). Experimental data (Table 22) suggests that the retardation
factor for picloram for the Ca-saturated Millville soil should not be
very different from natural Millville soil.
Aiken Clay Soil. Figure 14 gives the relative concentration distribution
(C/C ) of picloram in the effluent as a function of pore volumes (V/V )
of solution passing through columns of Aiken clay and Ca-saturated
Aiken clay soil. The solid line (No. 1) in Figure 14 is the theoretical
curve for Aiken clay soil based on the retardation factor of picloram
obtained from batch adsorption studies (Table 22). Inadequacy of the
model to describe the experimental data is evident. The model over-
estimated adsorption on this soil as shown by the predicted later
arrival of picloram in the effluent and the reduced peak height. By
selecting a lower retardation factor (dashed curve) for this soil the
model described the left hand portion of the curve but was inadequate
in some respects.
Ca-saturated Aiken Clay Soil. In Figure 14, the theoretical curve
(No. 2) for Ca-saturated Aiken soil is based on the retardation factor
of picloram movement in this soil. In this case, however, the model
actually underestimated adsorption, as evidenced by shift of the
theoretical curve to the left of the experimental points, rather than to
the right of the experimental points as obtained in the earlier cases
(Figures 11, 12 and 13).
From the discussion above, it appears that part of the failure of the
model to describe the movement of picloram in soil columns is re-
lated to overestimation of the picloram retardation factor based on
the distribution coefficient calculated from batch studies. Although
it was established, for the Millville soil (Figure 13), that picloram
in liquid flowing through a column was in equilibrium with that in
the soil, it seems that the distribution coefficient for picloram changes
as the solution moves through the column. When the herbicide first
enters the soil column at a concentration C , some of it is retained;
o
the solution containing the remaining herbicide moves forward at a
lower concentration to be retained and so on, until it travels the
complete length of the soil column. This allows a large quantity of
herbicide to be retained at the start, but a smaller amount at the
effluent end. It offers a possible explanation for the early arrival of
picloram observed compared to that calculated using the retention
78
-------
0.3-
o
O
\
O
0.2
!
o o
O.I -
1
1
2
3
i
4
V/Vn
Figure 14. Experimental (data points) and theoretical relative
picloram concentration distributions from natural (o),
and Ca-saturated (A) Aiken clay soil. Solid lines were
calculated from retardation factor (K') from batch
studies and dashed curve from 'adjusted factor1 (K")
(See Table 22).
79
-------
isotherm. A knowledge of the distribution of adsorbed phase with soil
depth would assist in solving this problem.
Few reports were encountered which attempted to determine distri-
butions of adsorbed herbicides at various depths in soil columns under-
going leaching with herbicides. Lai (36) did this type of study with
Ca^-Mg, Na -*• Ca, and Na->-Mg exchange in soil columns undergoing
miscible displacement with considerable success. Such an approach
may be fruitful in the study of herbicides.
A lower retardation factor helped to predict picloram movement for the
left hand portion of the distribution curve only. Further studies may
benefit from an approach similar to the one used by Lai (36) in which
he utilized a gradation of retardation factors as a function of soil depth.
Davidson, Rieck, and Santelmann (13) and Cargill and Davidson (9)
studied fluometuron (a urea derivative herbicide) movement and
Davidson and Chang (12) studied picloram movement in soil columns
and used the model to predict herbicide movement. They reported
that the model failed to adequately predict herbicide movement in
soil columns and that the prediction was improved by assuming a
lower retardation factor. They suggested that mixing processes in
the column, a consequence of different size pores, could be a compli-
cating factor in prediction. The distribution of the solute as a function
of soil depth may account for differences that result from differential
adsorption when a solution moves through varying size pores in the
soil at different velocities (mixing).
80
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SECTION VII
SUMMARY
The results of field studies of the lateral movement of herbicides in-
dicate that small but significant amounts of herbicides are transported
in irrigation runoff or surface runoff following periods of natural
precipitation. The concentration of herbicides in canal water fol-
lowing heavy dosage applications to control ditchbank weeds was
detectable in the initial flush of water as the canal was filled with
water. The concentration of herbicide in the initial flush of water is
quickly diluted to levels below that necessary to cause injury to crops
or animals subsequently using the irrigation water. Fall applications
of the higher dosages to control persistent ditchbank weeds appeared
to be a safe practice if the natural precipitation moved the herbicide
into the soil prior to filling the canal with water. Diuron and atrazine
were observed to behave similarly when used as ditchbank herbicides;
the low concentrations that were observed in the water samples would
not likely be hazardous to crops or animals with either herbicide.
Small but significant amounts of GS- 14254 are transported in irrigation
runoff from a stand of alfalfa established in a clay loam soil. The
concentration of GS-14254 in the water decreased rapidly with in-
creased distance from the treated plots and with time.
The movement of picloram, 2,4-D and 2,4, 5-T in natural precipitation
runoff from range sites was observed when runoff occurred immediately
after spraying. The concentration of the herbicides diminished as a
function of distance below the treated area and time after herbicide
application. Picloram was consistently observed in runoff water col-
lected 100 meters below the treated plots but only one sample collected
more than 100 meters below the plots contained detectable amounts of
picloram. The tendency for 2,4-D to move in surface water was
slightly greater than for picloram or 2, 4, 5-T but 2, 4-D was not ob-
served in measurable amounts when the samples were taken more than
1000 meters from the sprayed areas.
Equilibrium studies on five soils, Chance loam, Providence silt loam,
Nibley silty clay loam, Millville silt loam, and Aiken clay, with varying
organic matter contents, were conducted to study the influence of
various soil variables on the adsorption and desorption of picloram
(4-amino-3, 5, 6-trichloropicolinic acid). Comparison of the adsorption
of these soils before and after removal of organic matter (at 350° C)
81
-------
revealed that up to 91 percent of the adsorption could be accounted for
by organic matter.
The five soils adsorbed from 10. 8 to 58. 2 percent of the added pic-
loram in the picloram concentration range of 0. 05 to 10 ppm. At the
0. 01 level, adsorption was significantly correlated with organic matter
(r = 0. 991), pH (r = - 0. 98) and sesquioxides content (r = 0. 96) of the
soils and was significantly correlated with CEC (r = 0. 84) at the 0. 05
level. However, CEC and organic matter were also correlated with
each other. Correlation between adsorption and clay content of the
soils was poor.
Kinetic studies on the five soils revealed that soils with higher amounts
of organic matter take longer to reach equilibrium, (up to 120 hours).
Studies of the effect of temperatures from 17. 7° C to 28. 2° C on pic-
loram adsorption by three of the five soils revealed that the picloram
adsorption within this temperature range is endothermic. A further
increase in temperature to 34. 7° C decreased picloram adsorption.
Adsorption by two of the soils, Chance loam and Providence silt loam,
was linear at 25° C from 0. 05 to 10 ppm initial picloram concentrations.
In studies of the effect of induced pH on picloram adsorption by Chance
loam and Providence silt loam soils, it was found that adsorption was
inversely related to pH of soil suspension from pH 3. 6 to pH 9. 2.
The regression equations relating the adsorption with pH were:
Chance loam soil:
log (ugms adsorbed/kgm soil) = 3.654 - 0.107 pH
r = 0. 993
Providence silt loam soil:
log (jj-gms adsorbed/kgm soil) = 3.460 - 0.125 pH
r = 0. 985
In studies on desorption from the three soils, Providence silt loam,
Nibley clay loam, and Millville silt loam, with two successive water
extractions, it was shown that 41. 0 to 71. 8 percent of the initially
adsorbed picloram could be desorbed at 25° C with the first two
extractions. The desorption thereafter was very slow.
82
-------
Contrary to reports in the literature concerning precipitation of herb-
icides with the addition of inorganic electrolytes, no evidence was
found of this occurring in picloram solutions without soil. Inorganic
electrolytic salts did not appear to significantly alter the adsorption
or desorption of picloram on the soils tested; the inorganic salts used
were Bad KC1, K SO CaSO CaCl and MgCl . The divalent
Ct £* *T ~r L* £i
cations appeared to be more effective than monovalent cations in in-
creasing picloram adsorption. The results, in this respect, however,
were not conclusive. The magnitude of picloram adsorption by Nibley,
Millville, and Chance soils was generally the same whether natural
soils or Ca-saturated soils were used. These observations suggested
an exchange type reaction of picloram with soil, picloram acting as a
cation.
Work with Aiken soil, high in hydroxy oxides of Fe and Al and low in
bases, provided further evidence that another mechanism for picloram
adsorption is through hydrogen bonding. Ca-saturation of this soil
resulted in increased picloram adsorption by two-fold, suggesting that
cation-complex formation with the soil surface is also a mechanism of
picloram adsorption.
Column studies of picloram with Millville and Aiken soils corroborated
the observation that picloram adsorption is essentially linear between
1. 00 ppm and 10. 00 ppm concentration. Ca-saturation of these soils
did not appreciably affect picloram movement in Millville soil, but
considerably reduced it in Aiken soil. This is in agreement with data
obtained in batch studies and showed that batch work is reliable in
estimating picloram movement in soils.
Applicability of a mathematical model to picloram movement in soils
columns was tested. After adjusting the retardation factor, prediction
of picloram concentration in the column effluent improved. However,
the prediction was not good after the peak concentration was attained.
This was probably due to changing distribution coefficients of picloram
with soil depth.
83
-------
SECTION VIII
ACKNOWLEDGMENTS
Many individuals assisted, encouraged, or supported various phases
of work leading to this report. The authors would particularly like
to acknowledge the help of Dr. H. B. Peterson, USU, who directed
the research grant in its first year, and Dr. L. G. King, USU, who
directed the research grant from October, 1969, until completion of
this work.
An advisory committee offered valuable help from time-to-time. This
committee consisted of USU faculty members N. B. Jones, Dr. R. L.
Smith, Dr. H. B. Peterson, Dr. E. J. Middlebrooks, and EPA per-
sonnel M. B. Rainey, Richard Sotiros, Jim Vincent, Russel Freeman,
and Dr. J. P. Law, Jr.
The research work was begun on July 1, 1968, under grant #WP-
01492-01 (N)l. The work continued from October 1, 1969, until
March 31, 1972, under grant #13030 ED J. Mr. Richard Sotiros,
EPA, Denver, served as Project Officer from the beginning of the
research until June 30, 1971. From July 1, 1971, Dr. James P. Law,
Jr. , EPA, Ada was Project Officer.
85
-------
SECTION IX
REFERENCES
1. Abernathy, J. R. , and J. M, Davidson. 1971. Effect of calcium
chloride on prometryne and fluometuron adsorption in soil.
Weed Science 19:517-20.
2. Adamson, A. W. 1967. Physical Chemistry of Surfaces. Second
edition. Inter Science Publishers, New York. 401 p.
3. Allan, J. R. 1970. Water pollution with herbicides. Min. and
Rep. Can. Weed Comm. (West. Sect. ) p. 44-49.
4. Allison, L. E. 1965. Organic carbon. In Method of Soil Analysis
Amer. Soc. of Agron. Series No. 9 Madison, Wisconsin.
5. Anonymous. 1968. Weed control. National Academy of Sciences,
Washington, B.C. Publ. No. 1597. 471 p.
6. Bailey, G. W. , and J. L. White. 1970. Factors influencing the
adsorption, desorption, and movement of pesticides in soil. Res.
Rev. 32:29-92.
7. Bailey, G. W. , J. L. White, and T. Rothberg. 1968. Adsorption
of organic herbicides by montmorillonite: Role of pH and chem-
ical character of adsorbate. Soil Sci. Soc. Amer. Proc. 32:
222-234.
8. Barrow, N. J. 1972. Influence of solution concentration of cal-
cium on the adsorption of phosphate, sulfate, and molybdate by
soils. Soil Sci. 113:175-180.
9. Cargill, R. L. , and J. M. Davidson. 1969. Movement and ad-
sorption of fluometuron in Norge loam. Proc. , 22 annual
meeting, S. Weed Sci. Soc., pp. 361-366.
10. Chancellor, A. A. 1958. The control of aquatic weeds and algae.
Ministry of Agriculture, Fisheries and Food, Her Majesty's
Stationery Offices, London, England.
87
-------
11. Chapman, H. D. 1965. Cation exchange capacity. In Methods of
Soil Analysis. Amer. Soc. of Agron. Series No. 9. Madison,
Wis consin.
12. Davidson, J. M. , and R. K. Chang. 1972. Transport of picloram
in relation to soil physical conditions and pore water velocity.
Soil Sci. Soc. Amer. Proc. 36:257-261.
13. Davidson, J. M. , C. E. Rieck, and P. W. Santelmann. 1968.
Influence of water flux and porous material on the movement of
selected herbicides. Soil Sci. Soc. Amer. Proc. 32:629-633.
14. Davidson, J. M. , and P. W. Santelmann. 1968. Displacement of
fluometuron and diuron through saturated glass beads and soil.
Weed Science 16:544-48.
15. Dekking, H. G. G. 1964. Preparation and properties of some
polymer-clay compounds. Clays Clay Miner. 12:603-616.
16. Elrick, D. E. , K. T. Erh, and H. K. Krupp. 1966. Applications
of miscible displacement techniques to soils. Water Resource
Res. 2(4):717-727.
17. Frank, P. A. , and R. D. Comes. 1967. Herbicide residues in
pond water and hydrosoil. Weeds 15:210-213.
18. Frissel, M. J. , and G. H. Bolt. 1962. Interaction between certain
ionizable organic compounds (herbicides) and clay minerals.
Soil Sci. 94:284-291.
19. Geigy Chemical Corp. 1965. Anal. Bull. No. 10: The deter-
mination of thiomethyltriazine residues in plant material, ani-
mal tissues, milk and water using an ultraviolet method.
Agricultural Analytical Chemistry, Analytical Department,
Geigy Chemical Corp. , Ardsley, New York.
20. Greenland, D. J. 1965. Interaction between clays and organic
compounds in soils. I. Mechanisms of interaction between clays
and defined organic compounds. Soil Fertilizer 28:415-417.
21. Grover, R. 1968. Influence of soil properties on phytotoxicity
of 4-amino-3, 5, 6-trichloropicolinic acid (picloram). Weed Res.
8:226-232.
88
-------
22. Haas, R. H. , J. C. Scifres, R. R. Hahn, G. O. Hoffman, and M. G.
Merkle. 1971. Occurrence and persistence of picloram in range-
land water. Weed Res. 11:54-72.
23. Hadas, A., and J. Hagin. 1972. Boron adsorption by soils as
influenced by potassium. Soil Sci. 113:189-193.
24. Hamaker, J. W. , C.A.I. Goring, and C.R. Youngson. 1966.
Sorption and leaching of 4-amino-3, 5, 6-trichloropicolinic acid
in soils, p. 23-36. In Organic Pesticides in the Environment:
Advances in Chemistry Series 60. Amer. Chem. Soc. , Wash-
ington, D. C.
25. Hance, R. J. 1965. The adsorption of urea and some of its
derivatives by a variety of soils. Weed Res. 5:98-107.
26. Hance, R. J. 1971. Complex formation as an adsorption mech-
anism for linuron and atrazine. Weed Res. 11:106-110.
27. Harris, C.I. 1966. Adsorption, movement, and phytotoxicity
of monuron and ^-triazine herbicides in soils. Weeds 14:6-10.
28. Harris, C. I. , and G. F. Warren. 1964. Adsorption and desorp-
tion of herbicides by soils. Weeds 12:120-126.
29. Haque, R. , F. T. Lindstrom, V. H. Freed, and R. Sexton. 1968.
Kinetic study of the sorption of 2,4-D on some clays. J. Envir.
Sci. Tech. 2:207-211.
30. Herr, D. E. , E. W. Stroube, and D. A. Ray. 1966. The move-
ment and persistence of picloram in soil. Weeds 14:248-250.
31. Hilton, H. W. , and Q. H. Yuen. 1963. Adsorption of several
pre-emergence herbicides by Hawaiian sugar-cane soils. J.
Agr., Food Chem. 11:230-234.
32. Keys, C. H. , and H. A. Friesen. 1968. Persistence of piclorarr
activity in soils. Weeds 16:341.
33. Kilmer, V. J. , and L. T. Alexander. 1949. Methods of making
mechanical analysis of soils. Soil Sci. 68:15-24.
89
-------
King, H. , and P. L. McCarty. 1968. A chromatographic model
for predicting pesticide migration in soils. Soil Set. 106:248-
261.
Knu'sli, E. , H. P. Burchfield, and E. E. Storrs. 1964. Simazine,
In G. Zweig (Ed. ). Analytical methods for pesticides, plant
growth regulators, and food additives. Vol. IV. New York,
Academic Press.
Lai, S. 1970. Cation exchange and transport in soil columns
undergoing miscible displacement. Unpublished PhD Dissertation.
Utah State University Library, Logan, Utah.
Lindstrom, F. T. , R. Haque, V. H. Freed, and L. Boersma.
1967. Theory on the movement of some herbicides in soils:
Linear diffusion and convection of chemicals in soils. J. Env,
Sci. Tech. 7:561-565.
MacNamara, G. , and S. J. Toth. 1970. Adsorption on linuron and
malathion by soils and clay minerals. Soil Sci. 109:234-238.
McCall, H. G. , R. W. Bovey, M. G. McCully, and M. G. Merkle,
1972. Adsorption and desorption of picloram, trifluralin, and
paraquat by ionic and nonionic exchange resins. Weed Science
20:250-255.
McGlamery, M. D. , and F. W. Slife. 1966. The adsorption and
desorption of atrazine as affected by pH, temperature, and con-
centration. Weeds 14:237-239.
McKone, C. E. , and R. J. Hance. 1968. The gas chromatography
of some substituted ur*. .> herbicides. J. Chrornatography. 36:
234-237.
McKone, C. E. , and R. J. Hance. 1969. A method for estirnatiaL'
diuron (N1-(3, 4-dichlorophenyl)-N, N-dimethyi urea) in surface
water by electron capture gas chromatography. Bull, Envir.
Contam. Toxicol. 4:31-38.
Merkle, M. G. , R. W. Bovey, and F. S. Davis. 1967. Factors
affecting the persistence of picloram in soil. Agron. J. 59:
413-415.
90
-------
44. Merkle, M. G. , R. W. Bovey, and R. Hall. 1966. The rU-tor-
ation of picloram residues in soil using gas chromatograr.r j\
Weeds 14:l6l-l64.
45. Merkle, M. G. , and F. S. Davis. 1966. The use of gas chro-,v
graphy in determining translocation of picloram and 2, 4, "• •"•'.
Proc. SWC 19:557-561.
46. Miller, R. W. 1972. Personal communication, Professor c'
soils, Utah State University, Logan, Utah.
47. Mullison, W. R. 1970. Effects of herbicides on water and \', .
inhabitants. Weed Science 18:738-750.
48. Mortland, M. M. 1970. Clay-Organic Complexes and Inter-
actions. Advances in Agronomy Series No. 22. Academic Pi-
New York. 80 p.
49. Nearpass, D. C. 1967. Effect of predominating cation on the a
sorption of simazine and atrazine by Bayboro clay soil. Soil
Sci. 103:177-182.
50. Nearpass, D. C. 1970. Exchange of 3-amino- 1, 2, 4-triazoK i.
montmorillonite. Soil Sci. 109:77-84.
51. Nielsen, D. R. , and J. W. Biggar. 1963. Miscible displacement
IV. Mixing in glass beads. Soil Sci. Soc. Amer. Proc. 27;
10-13.
52. Scifres, D. J. , O. C. Burnside, and M. K. McCarty. 196').
Movement and persistence of picloram in pasture soils 01
Nebraska. Weed Science 1 7:486-488.
53. Scifres, C. J. , R.R. Hahn, J. Diaz-Colon, and M. G. MerU-
1971. Picloram persistence in semi-arid rangeland soils a'ni
water. Weed Science 19:381-384.
54. Sheets, T. J. , A. A. Crafts, and H. R. Drever. 1962. Influenc
of soil properties on the phytotoxicities of the s-triazine herb
icides. J. Agr. Food Chem. 10:458-462.
55. Talbert, R. E. , and O. H. Fletchall. 1965. The adsorption •'><"
some s-triazines in soils. Weeds 13:46-52.
91
-------
56. Trichell, D. W. , H. L. Morton, and M. G. Merkle. 1968. The loss
of herbicides in runoff waters. Weed Science 16:447-449.
57. Wadleigh, C. G. 1967. Agricultural pollution of water resources.
Soil Conservation 33:27-30.
58. Weber, J. B. 1970. Mechanisms of adsorption of ^-triazines by
clay colloids and factors affecting plant availability. Res. Rev.
32:93-130.
59. Weber, J. B. , P. W. Perry, and R. P. Upchurch. 1965. The
influence of temperature and time on the adsorption of paraquat,
diquat, 2,4-D, and prometone by clays, charcoal, and on anion-
exchange resin. Soil Sci. Soc. Amer. Proc. 29:678-688.
60. Weber, J. B. , and S. B. Weed. 1968. Adsorption and desorption
of diquat, paraquat, and prometone by montmorillonitic and kao-
linitic clay minerals. Soil Sci. Soc. Amer. Proc. 32:485-487.
61. White, A. W. , A. P. Barnett, E.G. Wright, and J. H. Holladay.
1967. Atrazine losses from fallow land caused by runoff and
erosion. Envir. Sci. Tech. 1:740-744.
62. Yaron, B. , A. R. Swoboda, and G. W. Thomas. 1967. Aldrin
adsorption by soils and clays. J. Agr. Food Chem. 15:671-675.
92
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SECTION X
PUBLICATIONS RESULTING FROM PROJECT
Wocknitz, R. W. , and J. O. Evans. 1971. The potential contamina-
tion of surface waters by herbicides. Proc. New Mexico Water Conf.
16:122-123.
Evans, J. O. Soil-applied herbicides and the role of mechanical soil-
incorporation on their phytotoxicity. Idaho Vegetable Growers Seminar.
Boise, Idaho. January, 1971.
Evans, J, O. Decarboxylation of picloram as a rapid, sensitive method
for quantitative determination in water. (Submitted for review for J.
Water Qual. Research).
Evans, J. O. , and R. W. Wocknitz. The isolation and characterization
of a major photochemical and thermochemical product from picloram
in water. (Being prepared for Weed Science).
Duseja, D. R. , J. O. Evans, and R. W. Miller. 1972. Effects of
soil type, herbicide concentration and temperature on the equilibrium
adsorption and desorption of picloram in soils. (Being prepared for
Weed Science).
Duseja, D. R. , R. W. Miller, and J. O. Evans. 1972 a. Miscible
displacement of picloram in soils (Being prepared for Weed Science).
Duseja, D. R. , J. O. Evans, and R. W. Miller. 1972. The effect of
soil pH and inorganic electrolytes on adsorption of picloram by soils.
(Being prepared for Soil Science).
Duseja, D. R. , R. W. Miller, and J. O. Evans. 1972. The application
of chromatographic theory to picloram movement in soils. (Being
prepared for Soil Science).
93
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Theses and Dissertations
Duseja, D. R. 1972. Adsorption-desorption and movement of picloram
in soils. PhD Dissertation. Utah State University.
Chase, Richard L. 1972. Effects of selected herbicides on perennial
grasses and water pollution under tropical, high rainfall conditions.
MS Thesis. Utah State University.
Nelson, Zeldon A. 1972. The surface movement of a new _s_-triazine
herbicide from treated cropland and its environmental effects.
MS Thesis. Utah State University.
Oral Presentations
Evans, J. O. 1972. Field studies concerning the persistence and
movement of picloram and the phenoxy herbicides. Paper presented
at N. W. Reg. Section Amer. Chem Society Mtgs. Corvallis, Oregon,
June 15-16. Abstract No. 86.
Duseja, D. R. , J. O. Evans, and R. W. Miller. 1972. Effect of soil
type, pH, temperature, and concentration on picloram absorption-
desorption in soils. Paper presented at N. W. Reg. Section Amer.
Chem. Soc. Mtgs. Corvallis, Oregon, June 15-16. Abstract No. 87.
Duseja, D. R. , J. O, Evans, and R. W. Miller. 1972. Adsorption-
Desorption of Picloram in Soils. Utah State University, Logan.
West. Soc. Soil Science. Eugene, Oregon, June 13.
94
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SECTION XI
APPENDICES
A Structure of Some _s_-Triazine and Phenyl Alkanoic Acid Herbicides
Referred to in the Manuscript
B Cleanup and Extraction Procedure for Picloram in Water Samples
95
-------
APPENDIX A
Structu re of Some -i - T riazine and Phenyl Alkanoic Acid
Herbicides Referred to in the Manuscript
5-Tnazines
General structure.-
R,
N'
N -C.
Common Name
Atrazine
1 *2
H -CH^
>./-* ij
Specific Groups
O C3
R3 R4
H -C2H5
R5
Cl
Prometone
Simazine
H -CH
H
H
H
-OCH
Cl
Phenyl Alkonoic Acids
Genera! structure:
OR
6^ ^^,2
OCH2COOH
Cl
Cl
2,4-dichlorophenoxyacetic acid
OCH2COOH
2,4,5-trichlorophenoxyacetic acid
96
-------
APPENDIX B
Cleanup and Extraction Procedure for
Picloram in Water Samples
A procedure for the extraction of picloram from water samples suit-
able for gas chromatograph has been developed. The water samples
from appropriate places along the waterways are collected in dark-
colored bottles. The sample-containing bottles are kept in the dark
in cold storage. Picloram extraction and determinations are made
as soon as possible after the collection of samples.
Extraction
A 500 ml water sample is acidified with HC1 immediately after taking
it out of the cold storage. The pH of the sample is brought to 2 by
adding HC1. The acidified sample is transferred to a separatory funnel
and washed with 100 ml of purified diethyl ether. The separatory
funnel is shaken for 3-4 minutes so as to thoroughly mix the ether and
water. The two layers are allowed to separate for 10-15 minutes. The
ether portion is separated from the water with the help of a separatory
funnel. Following the first washing, a second 100 ml portion of the
diethyl ether is added to the water sample in the separatory funnel.
The second portion of the diethyl ether is shaken and after separating
from the aqueous layer, is drawn from the separatory funnel. The
two ether fractions are combined and the water layer discarded.
Evaporation
The diethyl ether containing picloram is evaporated at 40° C under
vacuum in the flash evaporator.
Pyrolysis
After the ether has been completely removed, the picloram is subjected
to pyrolysis (Figure 1). The picloram is pyrolyzed between 190 to
200° C, under vacuum to decarboxylated picloram (Figure 2). The
decarboxylated picloram is thoroughly washed from the collection
flask with double distilled acetone. The sample is then ready for
gas chromatographic analysis.
97
-------
standards are prepared in the laboratory by the addition of known
•ut rations of picloram in water. The standard and check samples
extracted in the same manner as field samples. The concentration
:: loram in waterways is determined by comparing with the stan-
!' * "V'ocedure
,. Chromatograph: Varian Aeorgraph Model N. 1800 with electron
O / o
jture (H or Ni ) detector was used.
/••foot glass column containing 5% SE 30 on Gas Chrom SOW. Oper-
..ig conditions: column 1 95° C, injection port 205° C, detector 205° C,
rogen carrier gas 30 ml/min through a nitrogen filter.
•,'litiori column overnight at required temperature. When the column
' onditioned, inject 5 A of each sample into gas chromatograph. If
, .jOfjsa is too great, dilute solutions.
98
-------
c\
outlet
Calcium
chloride
Flask containing picloram
Heating mantle
Vacuum
pump
Figure 1. Typical apparatus for pyrolysis of picloram after remo.-a1.
extraction solvents.
NH,
C!
Cl
NH,
Cl
200° C
Vacuum
CO,
Figure 2, Probable reaction sequence of picloram subjected to ther-
pyrolysis.
99
fiUS GOVERNMENT PRINTING OFHCt ill
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
W
HERBICIDE CONTAMINATION OF SURFACE RUNOFF WATERS,
Evans. J.O. and Duseja, D.R.
Utah State University, Logan,
Department of Plant Science
EPA 13030 FDJ
EPA 13030 FDJ
Environmental Protection Agency Report No. EPA-R2-73-266, June 1973
Field and laboratory studies of the movement of herbicides were conducted to deter-
mine their potential as contaminants in irrigation return flow. Special emphasis was
given to the use of herbicides for vegetation control along ditches, canals and water-
sheds where high dosages are required to control the excessive growth of grasses and
broadleaved weeds. The following herbicides have been studied: substituted urea (diu-
ron), triazines (summitol and atrazine), phenoxyacetic acid (2,4-D and 2,4,5-T) and a
substituted pyridine (picloram).
The greatest tendency for transport of herbicides in water coming in contact with
soils occurs during the initial storms following spray application. If the intensity of
the initial precipitation is not sufficient to cause movement across the soil, the danger
of herbicide movement is essentially eliminated.
The highest concentrations (ppm) of herbicide observed in surface waters were 1.8,
0.5, 4.2, 1.2 and 2.7 for diuron, summitol, 2,4-D, 2,4,5-T and picloram, respectively.
These levels were observed immediately below treated areas receiving the higher recom-
mended dosages of the herbicides. All herbicide concentrations dropped below the limit
of detection within a few hundred meters below the sprayed areas. Presumably, soil fil-
tration, adsorption and dilution are primarily responsible for the loss of herbicides
from water. (Evans-Utah State)
Herbicides, Weed control, Water pollution, Persistence, Urea pesticide, Triazine pesti-
cide, 2,4-D, 2,4,5-T, Return flow
*Herbicide runoff, *Picloram adsorption, Picloram leaching, Herbicide residues,
Herbicide adsorption, Canal bank weed control, Diuron, Picloram
05A, 05G
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON, D.C. 2024O
John 0. Evans
Utah State University
-------
rrntc.3tion Agenoy
1 Ilc-rth \, "...I. _-;e
Chicago, Illj-i^U 60606
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