SUBSTITUTE CHEMICAL
i] i
ill?
INITIAL SCIENTIFIC
i
MINIECONOMIC REVIEW
i
MONURON
NOVEMBER 1975
• lECTION AGENCY
OFFICE OF PESTICIDE PROGRAMS
CRITERIA AND EVALUATION DIVISION
WASHINGTON, D.C. 20460
f EPA-540/1-75-028
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This report has been compiled by the
Criteria and Evaluation Division,
Office of Pesticide Programs, EPA, in
conjunction with other sources listed
in the Preface. Mention of trade
names or commercial products does not
constitute endorsement or recommendation
for use.
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PREFACE
The Alternative (Substitute) Chemicals Program was initiated under Public
Law 93-135 of October 24, 1973, to "provide research and testing of substitute
chemicals." The legislative intent is to prevent using substitutes, which in
essence are more deleterious to man and his environment, than a "problem"
pesticide suspected of causing "unreasonable adverse effects to man or his
environment." The major objective of the program is to determine the suitabil-
ity of potential substitute chemicals which now or in the future may act as
replacements for those uses (major and minor) of pesticides that have been
cancelled, suspended, or are in litigation or under internal review for poten-
tial unreasonable adverse effects on man and his environment.
The substitute chemical is reviewed for suitability considering all appli-
cable scientific factors such as: chemistry, toxicology, pharmacology and
environmental fate and movement; and socio-economic factors such as: use
patterns and costs and benefits. EPA recognizes the fact that even though a
compound is registered, it still may not be a practical substitute for a par-
ticular use or uses of a problem pesticide. The utilitarian value of the
"substitute" must be evaluated by reviewing its biological and economic data.
The reviews of substitute chemicals are carried out in two phases. Phase I
conducts these reviews based on data bases readily accessible at the present
time. An Initial Scientific Review and Minieconomic Review are conducted simul-
taneously to determine if there is enough data to make a judgment with respect
to the "safety and efficacy" of the substitute chemical. Phase II is only
performed if the Phase I reviews identify certain questions of safety or lack
of benefits. The Phase II reviews conduct in-depth studies of these questions
of safety and cost/benefits and consider both present and projected future
uses of the substitute chemicals.
The report summarizes rather than interprets scientific data reviewed
during the course of the studies. Data is not correlated from different
sources. Opinions are not given on contradictory findings. Where applicable,
the review also identifies areas where technical data may be lacking so that
appropriate studies may be initiated to develop desirable information.
This report contains the Phase I Initial Scientific and Minieconomic
Review of Monuron. Monuron was identified as a registered substitute
chemical for certain cancelled and suspended uses of 2,4,5-T.
The review covers all uses of monuron and is intended to be adaptable
to future needs. Should monuron be identified as a substitute for a
problem pesticide other than 2,4,5-T, the review can be updated and made
readily available for use. The data contained in this report was not intended
to be complete in all areas. Data-searches ended in April, 1975. The review
was coordinated by a team of EPA scientists in the Criteria and Evaluation
iii
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FIGURES
No. Page
1 Proposed Photodecomposition Reaction Sequence of Monuron
in Aqueous Solution under Aerobic Conditions .,..,,,,.,, 26
2 Photolysis of Monuron in Methanol under Anaerobic Conditions .... 28
3 Photolysis of Fenuron in Methanol under Anaerobic Conditions .... 29
vi
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TABLES
No. Page
1 Photodecomposition Products of Mbnuron 25
2 Acute Toxicity of Monuron to Goats by Single Drench 40
3 Induction of Heptatic Microsomal Enzyme Activity of Rats 42
4 Summary of the Action of Mbnuron on Experimental Animals 44
5 Results of the Action of Mbnuron on Experimental Animals 45
6 Observations on the Tumorigenicity of Monuron to Rats and Dogs . . 46
7 Acute Toxicity of Monuron to Fish 53
8 Effect of Formulation on the Acute Toxicity of Monuron to Fish . . 54
9 Effects of Monuron on Quail, Pheasant and Mallard Ducks 60
10 Effect of Mbnuron on Bobwhite Quail and Pheasant 60
11 Monuron Noncrop Uses 93
12 Monuron 80% Wettable Powder Specimen Label 94
13 Estimated Uses of Monuron in the U.S. by Use Categories, 1973 . . 101
14 Monuron Uses in California by Major Crops and Other Uses,
1970 to 1973 102
15 Use of Monuron (including Monuron-TCA) in California in 1972
by Crops and Other Uses, Applications, Quantities, and Acres
Treated 104
16 Use of Monuron (including Monuron-TCA) in California in 1973
by Crops and Other Uses, Applications, Quantities, and Acres
Treated 105
17 Economic Benefits of Chemical and Alternative Control 112
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PART I. SUMMARY
CONTENTS
Page
Production and Use 2
Toxicity and Physiological Effects 3
Food Tolerances and Acceptable Intake 5
Environmental Effects
Efficacy and Cost Effectiveness
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This section contains a summary of the "Initial Scientific and Mini-
economic Review" conducted on monuron. The section summarizes rather than
interprets scientific data reviewed.
Production and Use
Monuron [(3-p_-chlorophenyl)-l, 1-dimethylurea] is a broad-spectrum
herbicide used for the control of many grasses and herbaceous weeds on
noncropland areas, such as rights-of-way, industrial sites, and drainage
ditchbanks.
The chemical, the first of a series of urea herbicides, was discovered
by researchers of the E. I. du Pont de Nemours and Company, Inc. (du Pont)
in 1951. The specific properties of water solubility and resistance to
microbial decomposition were designed through manipulation of molecular
substitutions. Varying degrees of soil stability and water solubility were
achieved through the amount of chlorination and the choice of alkyl groups.
The compound was first registered for use in 1955. The only domestic
producer is du Pont.
Eight methods have been reported for the synthesis of monuron. One is:
H
-NH2
COC12
> Cl(O)-N-C-Cl + HC1 (1)
ja-Chloroanilihe Phosgene
£-Chlorophenylcarbamyl
Chloride
Cl (O) -N-C-C1
Cl(O)-N-C»0 + HC1 (2)
p_-Chlorophenyl
Isocyanate
CH3
-N-C-0 + HN(CH3>2
(3)
Dimethylamine
Monuron
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Du Pont also holds a patent for an alternate method of producing p_-
chlorophenylcarbamyl chloride from phenyl isocyanate which may be used instead
of the reaction, as cited in Equation 1.
Monuron is a white, odorless, crystalline solid with very low solubility
in hydrocarbon solvents or water. Monuron has a low vapor pressure, and is
noncorrosive and nonflammable. It can be decomposed either by ultraviolet
radiation or certain microorganisms. It is fairly stable to oxidation and
hydrolysis under normal conditions.
The most widely used formulation of monuron is an 80% wettable powder.
Monuron is also available in several granular formulations, both as the only
active ingredient, and in combination with sodium metaborate, sodium
tetraborate, trichloroacetic acid, and sodium chlorate.
The domestic supply of monuron in 1973 is estimated to have ranged from
550,000 to 950,000 Ib, including approximately 150,000 Ib of Imports. About
one-sixth of the domestic supply was used for agricultural purposes, and one-
sixth by government agencies, with essentially the remainder being used by the
industrial/commercial sector.
Toxicity and Physiological Effects
Data was found on the toxicity of monuron to laboratory and domestic
animals. An acute oral LD^Q for monuron in the range of 3.4 to 3.6 g/kg
body weight was reported for male albino rats. The reported value for a
monuron formulation, NH-174 (8% monuron, 86% sodium tetraborate) for groups
of mixed male and female rats was 5.6 (+0.25) g/kg body weight. In one study,
the approximate lethal oral dose was 7.5 g/kg. The only acute oral LD5Q
value reported in available studies was 1.48 (+0.21) g/kg body weight for
male albino rats.
Only approximate lethal oral doses have been reported for other labora-
tory animals; the respective values for guinea pigs and rabbits were 670 and
1,500 mg/kg body weight.
General signs of toxicity to rats are those of methemoglobinemia, such
as cyanosis, enlarged dark spleen, and compensatory, red blood cell (RBC)
formation in the spleen and bone marrow. Dead animals generally show pulmonary
edema, congestion, and hemorrhaging accompanied by anemia of liver, kidneys,
and spleen.
Administration of 5 subacute doses per week (500 mg/kg by stomach tube)
for 2 weeks to rats resulted in cyanosis and continued weight losses, but no
deaths. Continuous (6 weeks) administration in ground laboratory chow at
levels of 0.005%, 0.05% and 0.5% resulted in clinical signs of intoxication
only at the highest dose. At necropsy, animals fed 0.5% monuron showed signs
of methemoglobinemia and possible blood cell degeneration.
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Monuron fed to rats at levels up to 2,500 ppm (in the feed) caused no
deaths over a 2-yr period, although decreased weight (compared to controls)
was seen at the highest dose level. The weight differential was more pro-
nounced in males than in females. Histological examination revealed no tissue
abnormalities other than slightly increased liver and spleen weights at the
2,500 ppm level. The no-effect level was 250 ppm.
One-year chronic feeding studies of beagles caused no deaths, no abnormal
animal health effects, and no abnormalities in histological profiles at the
highest daily dose fed (25.0 mg/kg body weight). The no-effect level was
1,000 ppm.
Studies with domestic animals indicated an acute oral toxicity for goats
in the range of 600 to 1,600 mg/kg.
Sheep survived 10 daily doses of monuron at 50 mg/kg by drench. Four
doses at 100 mg/kg resulted in signs of toxicity and weight loss, with death
occurring after 9 doses.
Cattle survived multiple daily doses of 25 to 250 mg/kg of monuron, 80%
wettable powder (WP) by drench. Diarrhea developed, without weight loss, at
doses of 50 to 250 mg/kg. At a single dose of 500 mg/kg, a yearling exhibited
signs of poisoning with an 11% weight loss, but survived.
In chickens, 25 and 50 mg/kg dosages resulted in 14 and 27% reduction in
weight gain, respectively. A 20% mortality resulted from administration of
100 mg/kg, while 250 mg/kg resulted in 100% mortality after 6 to 9 doses.
A dose of 2,250 mg/kg applied to the unabraded skin of a rabbit caused no
irritation or clinical signs of toxicity. Aqueous pastes (4, 8, 16, and 23
g/kg) applied over 10% of the body surface of rabbits for a 24-hr period
resulted in no apparent toxicity.
Tests with guinea pigs indicated no skin irritation and no skin sensiti-
zation.
Application of saturated solution to the eyes of rabbits indicated no
irritation 'of ocular tissue.
Rats exposed to fine dusts (5 to 35 ym) at a concentration equal to
245.5 g/m^ of monuron for 4 hr exhibited no clinical signs of toxicity over a
14-day postobservation period.
Definitive studies on the absorption, distribution, and residual potential
of monuron have not been conducted with mammalian systems. Studies have been
made on the metabolic fate in rats by urinalysis of rats fed 4.8 g of monuron
over an 8-day period. The major metabilites retained the urea structure and
the chief pathway of degradation appeared to be a stepwise demethylation with
a minor step leading to hydroxylation of the benzene nucleus. About 15% of
the administered compound was excreted as N-(4-chlorophenyl) -urea, 7% as
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N-(2-hydrozy-4-chlorophenyl) urea, and about 2.5% as N-(3-hydroxy-4~chlorophenyl)
urea. The transformations of monuron In plants and animals, and by soil bacteria
appear to be similar.
The enzyme systems for monuron degradation in mammalian liver appear to
be inducible rather than constitutive.
A 3-generation reproductive study with dosages up to 2,500 ppm monuron in
the feed of rats indicated no deviation from normal reproduction, no effect on
lactation, and no clinical signs of toxicity. At the 2,500 ppm dosage, a
slight reduction in average number of pups in each of 6 litters was noted.
In teratogenic tests, monuron caused no significant increase in anomalies
in 3 strains of mice at 215 mg/kg.
Results of experiments on the oncogenicity of monuron are variable. In a
preliminary screening study with mice and rats, a significantly higher tumor
rate was reported after an 18-month feeding period for rats (450 mg/kg in
ration), and after a 15-week feeding period (6 mg/week as single dose) for
mice. The results of a more detailed evaluation in mice were indecisive, with
the treated mice having a slightly higher, but not statistically significant,
tumor incidence.
Still other chronic feeding studies with dogs and rats indicated no signi-
ficant increase in tumors that could be attributed to monuron over feeding
periods of 1 and 2 yr, respectively.
Monuron did not induce point mutations when evaluated with histidine de-
pendent mutants of Salmonella typhimurium.
Food Tolerances and Acceptable Intake
In the past, monuron was registered for selective control of weeds on
several crops. Tolerances for monuron residues were established at 7 ppm for
asparagus, and 1 ppm on avocados, cottonseed, grapes, dry bulb onions, pine-
apples, spinach, sugarcane, and several citrus fruits. However, due to
inadequate data to support the safety of tolerances, all tolerances for monuron
in food and feeds tuffs were revoked, effective July 26, 1973. Monuron is no
longer registered for use on any agricultural crop.
An acceptable daily intake CADI) has not been determined for monuron.
Environmental Effects
The acute toxicity data for fish from laboratory investigation is
summarized as follows:
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Species
Striped mullet (Mugil cephalus)
White mullet (Mugil curema)
Coho salmon (Qncorhynchus kisutch)
Rainbow trout (Salmo gairdneri)
Carp (Cyprinus carpio)
Largemouth bass (Micropterus
salmoides)
Exposure
time
(hr)
48
24
48
24
48
24
48
48
Toxicity
calcu-
lation
LC50
TLm
TLm
LC50
LC50
TLm
48 10% Mortality
ToxLcity
measure
Cppm)
16.3
20.0
16.3
115
110
180
100
230
Goldfish (Carassius auratus) have been reported to survive a 5-day
exposure to 59.5 ppm monuron, and a 35-day exposure to 14.9 ppm monuron.
Twenty ppm did not cause death of small bluegills (Lepomia macrochirus)
during a 12-day exposure period, nor did exposure to 10 ppm monuron for 8
days cause any loss of fry of bluegill or lake chubsucker (Erimyzon sucetta).
However, green sunfish (Lepomis cyanellus) fry survived no longer than 5 days,
and smallmouth bass (Micropterus dolomieu) fry survived for only 4 days when
exposed to 10 ppm monuron.
A Russian formulation of 10% monuron and 10% TCA (TCA alone is more toxic
to fish than monuron alone) applied at a rate of 40 kg/ha Al (20 mg/1 Al) to
artificial ponds caused decreased hemoglobin, erythrocyte and hematocrit
counts in Leuciscus idus and Rutilus rutilus for up to 75 days after treatment.
There was also a 46% loss of fish over the test period.
Exposure of adult white shrimp (Penaeus setiferas) to 1.0 mg/1 concentra-
tions of monuron for 24 hr had no effect; exposure of the Eastern oyster
(Crassostrea virginica) to 2.0 mg/1 for 96 hr caused a 12% decrease in shell
growth. The 50% immobilization concentration (1650) of monuron to Daphnia
magna was found to be 106 ppm. Monuron at 1 to 2 ppm reduced the number and
weight of bottom-dwelling, fish-food organisms (primarily weed-clinging
species of Gastropoda, Odonata and Trichoptera) by 38 and 18%, respectively.
The growth of pure cultures of marine plankton (Protococcus species,
Chlorella species, and Dunaliella euchlora) was completely inhibited at 0.02
ppm monuron; 0.25 and 0.28 ppm completely inhibited growth of unicellular
algae (Chlorococcum species, Dunaliella tertiolecta. and Phaeodactylum
tricornutum at 0.28 ppm, and Isochrysis galbana at 0.28 ppm). Monuron has
also been shown to be effective in controlling a number of other algae at
0.5 to 2.0 mg/1. It has also been demonstrated that monuron is toxic to algae
in the light, but not in the dark, regardless of presence of an energy source.
The oral LC5Q of monuron for bobwhite quail (Colinus virginianus),
Japanese quail (Coturnix coturnix japonica), and the mallard duck (Anas
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platyrhynchoa) is greater than 5,000 ppn In the feed; the LCso for the
ring-necked pheasant (Phasianus colchicus) is 4,682 ppm.
The LDso of monuron to honeybees CApis mellifera) is 110 yg/bee when
applied as dust. Probit analysis of test data indicates that high increases
in dosage rate would be required to increase toxicity to bees.
The interactions of monuron with lower terrestrial organisms have been
fairly extensively investigated. The major results from studies of various
microflora and microfauna are summarized as follows:
Species
Test rate
or conditions
Microflora
Aspergillus niger 1,000 ppm
Fungus of the genus Fusarium Agar
Rhizopus japonicus
Bacillus sphaericus
Pseudomonas fluroescens
Aerobic
conditions at
30° C
Soil
5 to 40 mg/1
Yeast mitochondria -
Soil microorganisms (including 250 ppm in agar
Pseudomonas, Bacillus, Peni-
cillium and Aspergillus)
Soil organisms 0.9 to 2.7
Ib/acre
Soil organisms
Soil organisms
Soil organisms
Microfauna
Soil Invertebrates
1.3 Ib/acre
7.1 Ib/acre
Normal field
rates
10 Ib/acre
Result
Complete inhibition
Apparent utilization of monuron
as carbon source
Demethylation of monuron
Decomposition of monuron
Stimulation of dehydrogenase
in absence of other energy
source
Inhibition of respiration
No adverse effect on population
No effect on nitrogen or
water-soluble organic
content of soil
Decreased number of Azotobacter
and ammonia-fixing bacteria
Decrease in total quantity
microorganisms; Increase in
actinomycetes, and nitrogen-
fixing organisms
No effect on oxygen uptake
Significantly fewer wireworms
(Elateridae), millipedes
CDiplopoda), earthworms
(Lumbricidae), spring tails
(Collembola), and mites
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Test rate
Species or conditions Result
(Acarinal) (virtual elimina-
tion of grasses, increased wild
carrot and sheep sorrel)
Soil invertebrates 17.8 Ib/acre Decreased number of millipedes
and spring tails
Earthworms Emersion in 10% mortality at 1 ppm; 100%
solution for mortality at 100 ppm
2 hr
Reports on the effect of monuron on soil nitrification are in conflict.
Applications of monuron at 1 to 5 Ib/acre were reported to inhibit soil
nitrification. However, application rates of 7.1 to 8.9 Ib/acre and 50 ppm
were reported to have no noticeable effect on soil nitrification rate and
nitrifying microorganisms, respectively. From still another investigation
(involving growth and metabolism studies of Azotobacter and Clostridium
species), it was concluded the phenylurea herbicides are without effect on
free-living, nitrogen-fixing organisms except at concentrations far in excess
of normal agricultural field rates.
The persistence of monuron in the soil has been extensively investigated
both in the United States and abroad. These studies have, in general, shown
that when monuron is applied at the lower, selective rates (which are no
longer registered in the United States) phytotoxic concentrations disappear
within 1 yr. For example, one study involving several selective application
rates and soil types had an overall rate of monuron disappearance of 83%
after 12 months. In a recent review of herbicides, it was concluded that 80%
of the monuron applied at selective rates would disappear within 1 yr of
application for most climatic and edaphic conditions. When monuron is
applied at nonselective rates for total vegetation control (current registered
uses), phytotoxic activity can persist for several seasons. Massive rates of
monuron (20 to 200 Ib/acre) have required up to 3 yr to dissipate.
The mobility of monuron (and several other herbicides) in soil have been
evaluated by measuring its Rf value on a thin-layer (400 ym) soil chromatogram
for 4 agricultural soils. In each of these soils, monuron was intermediate in
its mobility compared to other similarly tested herbicides. The mobility of
monuron is apparently not affected by pH over the range of 5.4 to 8.9
although mobility is apparently reduced with increased content of organic
matter in the soil.
Greenhouse leaching studies (72 in of simulated rainfall over a 90-day
test) showed that 4 to 62% of the original monuron remained in the soil, 0 to
56% was found in the leachate, with unaccounted losses of 38 to 85%. The
investigators concluded that leaching can occur under conditions of extremely
high rainfall on porous soils. Russian investigators have also shown that
monuron was rapidly backed down into "red-earth soil" -under intensive rainfall.
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Data on the monuron content of water is limited. One investigation of the
persistence of monuron in river water has been reported. Acetone solutions of
monuron were injected into water samples which were maintained at room tempera-
ture and exposed to natural and artificial light. The percent of monuron
remaining in the test samples was as follows:
Quantity remaining (%) Time (weeks)
40 1
30 2
20 4
None detected 8
Fhotodecomposition of aqueous monuron solutions has been investigated.
Fourteen days exposure to summer sunlight in California yielded decomposition
of less than 6%. Photodecomposition is enhanced, however, in the presence of
naturally-occurring photosensitizers such as riboflavin-5-phosphate.
Data is not available on the origin, presence, or persistence of monuron
in the air. The low vapor pressure of monuron and its use pattern indicates
that little monuron will be present in the air.
In bioaccumulation and biomagnification studies, a Russian formulation of
10% monuron and 10% trichloroacetic acid (TCA) was applied to artificial ponds
stocked with fish at a rate of 40 kg/ha (20 kg/ha of monuron). Over the 60-day
test period the concentration of monuron in the water ranged from 0.1 to 0.3 mg/1.
After 5 days monuron concentrations of 15 ppm were found in Rutilus rutilus heart
tissue and 5.3 ppm in Leuciscus cephalus brain tissue. In Leuciscus idus
muscle tissue, monuron concentrations decreased from 0.95 ppm after 10 days to
trace amounts after 60 days.
Efficacy and Cost Effectiveness
Monuron is a preemergent herbicide used for control of annual weeds and
grasses along canal banks, railroads, highways and utility lines. Until 1973,
it had been registered for use in controlling numerous grasses and weeds in
selected commercial crops.
Monuron is used at rates varying from 20 to 100 Ib/acre for control of a
wide variety of annual weeds and grasses along highways, railroads, levees,
irrigation ditches and other specific locations. Several tests have shown
that rates of 40 to 100 Ib/acre provide 80 to 100% seasonal control of a broad
variety of weeds and grasses. A test to determine the long-term effect of
monuron has shown that massive doses of 224 Ib/acre have resulted in 80 to
100% control of most weeds and grasses in 1 yr, but by the end of the second
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yr, 47% of the area was again covered with vegetation. Coverage increased to
80% at the end of the third yr and 100% at the end of 15 yr.
Tests on specific grasses have shown that monuron at 80 Ib/acre will kill
80 to 90% of nutgrass tubers. Monuron at 40 Ib/acre controlled bindweed for
2-1/2 months; at 1.0 Ib/acre it controlled 81% of clubmoss.
Comparisons of the costs of soil-applied herbicides to those of alternative
methods (such as mechanical or hand-labor control of non crop weeds and grasses)
for control of weed and brush along California irrigation ditches showed economic
effects ranging from an increased cost of $34.70/acre for chemical control, as
compared to mechanical methods, and a $118.10 cost reduction for chemical con-
trol when compared to hand weeding.
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PART II. INITIAL SCIENTIFIC REVIEW
SUBFART A. CHEMISTRY
CONTENTS
Page
Synthesis and Production Technology 12
Physical Properties 17
Analytical Methods 19
Multi-Residue Methods 19
Residue Analysis 19
Formulation Analysis 21
Composition and Formulation • • 21
Chemical Properties, Degradation and
Decomposition Processes 21
Photodecomposition. ........ 23
Other Properties and Reactions 27
Occurrence of Residues in Food and Feed
Commodities 30
Acceptable Daily Intake 30
Tolerances 30
References 31
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Synthesis and Production Technology
Monuron EC3-<£-chlorophenyl}-l, 1-dimethylurea], the first of a series of
phenyl urea herbicides, was discovered by du Pont researchers in 1951. It
was the first of a group selected by du Pont in which the specific properties
of water solubility and resistance to microbial decomposition were designed
through manipulation of molecular substitutions. Varying degrees of soil
stability and water solubility were achieved through the amount of chlorina-
tion and the choice of alkyl groups (Martin, 1964). Monuron was first regis-
tered for use in 1955. It is presently produced domestically at a du Pont
plant in La Porte, Texas (Stanford Research Institute, 1974).
Eight methods for synthesizing monuron have been reported. They are
summarized below.
Method I - Sittig (1967) describes the probable method in the manufacture of
monuron using j>-chloroaniline, phosgene, and dimethylamine as raw materials.
The reaction sequence is shown below:
H 0
+ COC12 > Cl /O / -N-C-C1 + HC1 (1)
£-Chloroaniline Phosgene £-Chlorophenylcarbamic*
Chloride
-> Cl(O)-N=C=0 + HC1 (2)
£-Chlorophenyl
Isocyanate
-N=C=0 + HN (CH3) 2 > Cl /-N-C-N (3)
Dimethylamine
*also called carbamyl or carbamoyl.
12
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A partial description of the conditions for Reaction (3) is found in a
patent owned by du Pont (Todd, 1953).
The amine-isocyanate reaction is most readily carried out in
the presence of an inert solvent, such as toluene, anisole, benzene,
chlorobenzene, or dioxane. No catalyst is needed, and since the
reaction is exothermic it is ordinarily unnecessary to supply heat.
Thus, the reaction is conveniently carried out by first mixing the
isocyanate with the inert solvent at room temperature and then
gradually adding the secondary amine reactant while permitting the
temperature to increase through the range of, say, 25 to 75°C. The
trisubstituted urea products are generally quite insoluble in the
solvent used and, therefore, precipitate out as formed and are
readily separated from the reaction mass. The halophenyl dialkyl
ureas produced are white crystalline solids. They are insoluble
or only slightly soluble in water and cold benzene and, in general,
appreciably soluble in dioxane, acetone, ethyl acetate, ethanol and
hot benzene.
The Todd patent also describes a laboratory preparation of monuron:
Anhydrous hydrogen chloride was passed into a solution of 191.2
parts by weight of j>-chloroaniline in 1,550 parts by weight of
dioxane until in excess. The reaction temperature was permitted to
rise to 70 - 75°C during the addition, and after the solution was
saturated, phosgene was passed into the slurry at the same temperature
until a clear solution of jg-chlorophenyl isocyanate was obtained
(about 4 hr). The excess phosgene and hydrogen chloride were removed
by distillation of approximately 300 parts by weight of the dioxane.
After cooling to 25°C, dimethylamine was passed into the reaction
mixture at 25-40° until present in excess. The slurry was cooled to
10° and 3-(p_-chlorophenyl)-2, 2-dimethylurea (261.5 parts by weight;
88% yield) removed by filtration.
Dilution of the filtrate with water gave an additional 19.1
parts by weight of 3-(p_-chlorophenyl)-l, 1-dimethylurea, increasing
the total yield of crude product (M.P. 164.5 - 168°) to 280.6 parts
by weight or 94.5% of theory. Recrystallation of a portion of the
crude product from 95% aqueous methanol resulted in 76% recovery of
shiny white scales which melted at 170.5 - 171.2°.
In another report, Sittlg (1971) lists the following conditions for
Reaction (3):
1- Temperature; The temperature for reaction of p_-ehlorophenyl
isocyanate with dimethylamine is 25 to 40°C.
2» Pressure; This reaction is carried out at atmospheric pressure.
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3. Reaction time; After passage of dimethylamine into the isocyanate
solution until it is present in excess, the mixture may be heated
an additional half hour. <.
4. Reaction medium; This reaction is conducted in the liquid phase.
5. Catalyst; No catalyst is employed in the condensation of dimethyl-
amine with j>-chlorophenyl isocyanate.
6. Reactor design; A stirred, jacketed reactor of conventional design
may be used for this reaction.
7. Product recovery; The 3-(p_-chlorophenyl)-l, 2-dimethylurea product
precipitates from the cooled reaction mixture and is removed by fil-
tration in a vacuum oven at 50° for over 30 min (U.S. 2,655,444).
Searle and Todd (1953) in a du Pont patent concerned with this process,
explained that a molal excess of 10 to 20% of amine over isocyanate is
preferred, with a reaction time of approximately 2 hr after mixing.
Method II - The sequence of Method I may be altered by treating dimethylamine
with phosgene to yield dimethylcarbamyl chloride, (CH3)2NCOC1, which is then
treated with jj-chloroaniline (Sittig, 1967).
Method III - Du Pont also owns a patent (Julian and Siefen, 1961) for the
synthesis of 2rchl°r°Pkenylcarbamic chloride by chlorination of phenyl
isocyanate.
HO
N-c'-Cl >C1(O)-N=C=0 + HCl(g) (4)
(Catalyst) \—A
Purge
This reaction can be used as the first step of Method I.
According to this patent, the chlorination of phenyl isocyanate is
carried out in two steps. In the first step, only 80 to 98% of the chlorina-
tion takes place at -15° to 15°C and at 5 atmospheric pressure. One-third or
more of the feed of the first step is unchlorinated phenyl isocyanate. In the
second step the remaining 2 to 20% of chlorine is added under unspecified
conditions. This 2-step process avoids undesirable by-products caused by
overchlorination or orthochlorination.
Method IV - A method of producing monuron that avoids the by-product hydrogen
chloride is described in a patent owned by Imperial Chemical Industries
(Jones, 1956). The 2 Jones method reactions are:
14
-------
0 H
/—. || 100 - 200°C /—. I
C1/Q\-NH2 + H2NCNH2 '" ^ Cl/Q\ -N-C-NH2 4- NH3 (5)
\ / Alcohol or \—/
p_-Chloroaniline Urea Phenol solvent
C1(O~N~C~NH2
(6)
Dimethylamine Monuron
The reaction mixture is refluxed until ammonia evolution ceases, then the
dime thy lamine is added to the hot product until all the solvent is removed
by distillation.
Method V - An alternate method of production is described in another patent
issued to du Font (Thompson 1954). The claimed advantage of the patent is
that the water may be used as a solvent. The reactions for this method are:
CO(NH2)2 -^ Cl(O>NHCONH2 + NHAC1 (7)
pj-Chloroanlline Urea _p_-Chlorophenylurea
hydrochloride
+ NH3 (8)
Dimethylamine Monuron
The first reaction (urea reaction) is carried out at 70° - 105°
(preferably 90° - 105°) under pressure, if desired, for about 6 hr. Urea Is
added in 2- to 4-fold excess. The second reaction (dimethylamine reaction) is
conducted under reflex at 135° - 225° for about 3.5 hr. Pressure Is de-
termined by the choice of solvent, DMF, O^dichlorobenzene, anisole, ethyl
acetate, toluene or other aromatics. Excess dimethyamine is added stifficent
to maintain at least .01 percent free dimethylamine in reaction mixture.
V
15
-------
Method VI - Melnikov (1971) notes 2 methods of producing monuron in addition
to methods I and II. The first additional method is:
H 0 H
/-A Ml I ^
C1(O)-N-C-N- Cl + (CH3)2NH >
V-/ ^ A (9)
N,N' -bis (|p_-Chloropheny 1) - Dimethy lamine
urea
n
Cl -N-C-N + H2N cl
N
CH3
Monuron £-Chloroaniline
Method VII - The other method reported by Melnikov (1971) is direct chlorina-
tion:
O-NHCON(CH3)2+ C12 - > ClO1™001^01^ + HC1 (10)
Method VIII - Another method is described in a German patent owned by Quimco
G.m.b.H. (Hearsey and Mehta, 1973). The first step is the preparation of an
intermediate:
(CH3)2NH + CO + S >[(CH3)2H2N] + [(CH3)2NCOS] (11)
Dimethylammonium
dimethylthiolcarbamate
The solvent for this reaction may be benzene, toluene, xylene, 0-dichloro-
benzene, or chlorobenzene, and the reaction is carried out at 50 to 60 atmos-
pheres and 100°C for 20 to 30 min. This intermediate is then azeotropically
vacuum-distilled with the solvent and treated with jg-chloroaniline to produce
monuron at 95% of theoretical yield. This second reaction takes place in a
16
-------
chlorophenol solvent, with the £-chloroaniline present in less than stoichio
metric quantity. The reactants are refluxed at 80°C or reacted at greater
than 100°C under nitrogen pressure for 1 to 15 hr.
Physical Properties
Chemical names: 3-(p_-chlorophenyl)-l, 1 dimethylurea
N'-(4-chlorophenyl)-N, N-dimethylurea
Common names; Monuron, CMU
Trade names; Telvar®
Pesticide class; Herbicide, substituted urea
Empirical formula: CgHnCl^O
Structural formula; H
CH3
Molecular weight; 198.65
Analysis; C 54.41%; H 5.58%; Cl 17.85%; N 14.10%; 0 8.05%.
Physical state; White, odorless, crystalline solid (Martin, 1971).
Crystallization from methanol gives thin rectangular
prisms. Slight odor. (Merck, 1968).
Specific gravity; 1.27 (20/20°C)
Melting point; 176 to 177°C (commercial) (Merck, 1968)
170.5 to 171. 5°C (crystallized from methanol)
(Merck, 1968)
174 to 175°C (Martin, 1971)
Boiling point; Decomposes at 185 to 200°C
Solubility; Zhuravlev (1969) reports the following solubilities and heats
of solution of monuron in water:
17
-------
Temperature Weight % Differential heat of solution
(°C) monuron (kcal/g mole)
10 0.0195 3.41
15 0.0210 3.53
20 0.0240 3.66
25 0.0260 3.78
30 0.0290 3.91
35 0.0330 4.04
40 0.0365 4.17
45 0.0400 4.31
50 0.0440 4.44
At 25°C and pH of 5.7, the solubility is 262 ppm in water (Hurle and
Freed, 1972).
Monuron is sparingly soluble in petroleum oils and polar organic solvents
such as acetone (Martin, 1971). Monuron is moderately soluble in methanol,
ethanol, and acetone. It is practically insoluble in hydrocarbon solvents
(Merck, 1968).
The Herbicide Handbook (1970) lists the following solubilities:
Solvent Temperature (°C) Weight (ppm)
Acetone 27 52,000
Benzene 27 2,900
Butyl stearate 27 1,500
Cottonseed oil (refined) 27 1,100
No. 3 diesel oil 25 230
Water 25 230
Heat of solution; 3.0 kcaI/mole (Hurle and Freed, 1972)
Heat of sublimation: 27.4 kcal/mole (Wiedemann, 1972)
Vapor pressure; 5 x 10~7 mm Hg at 25°C
3.4 x 1(T6 mm Hg at 50°C (Hill, 1971)
Wiedemann (1972) lists the following vapor pressures for
monuron, determined experimentally by thermogravimetry.
Temperature Vapor Pressure
C°O (torr)
30.3 4.00 x 10-7
42.8 1.83 x ID'6
56.6 1.40 x 10-5
57.4 1.55 x 10-5
57.9 1.66 x 10-5
65.6 5.29 x 10-5
68.2 7.09 x 10-5
18
-------
Temperature Vapor Pressure
C°C) (torr)
72.5 7.91 x 10-5
76.3 1.53 x 10-4
83.8 3.97 x 10-4
85.5 4.02 x 10-4
77.0 4.21 x 10-4
105.9 2.99 x 10-3
If plotted graphically, the above values of Wiedmann (1972)
follow the equation: log p - 13.3052 - A/T, where A = 5988.39
+ 275.51 (p = pressure in torr, T - temperature in °K).
Corroslvlty: Noncorrosive
Flammability: Nonflammable
Formation of Clathrates and Inclusion Complexes: In general clathrates and
inclusion complexes are readily formed by ureas upon crystalli-
zation (Finar, 1971). The practical consequence is the diffi-
culty in removing impurities by recrystallizing.
.j^r-jtvi.
Analytical Methods
This subsection reviews analytical methods for monuron. The review
describes multi-residue methods, residue analyses, and formulation analyses.
Available information concerning sensitivity and selectivity is also presented.
Multi-Residue Methods - Monuron has not been reported as a significant residue
in any class of food nor is it routinely searched for in the Food and Drug
Administration (FDA) multi-residue analytical system which is used to monitor
pesticide residues in food. The apparent reason for the absence of monuron
residue data is that the herbicide is not used on food and feed items. However,
individual compound methods exist for measuring monuron residues. The Pesticide
Analytical Manual (PAM, Vol. I, 1971) contains data on the recovery of monuron
following extraction and cleanup. PAM also lists relative retention times and
responses.
Residue Analysis - PAM (Vol. II, 1971) lists 3 methods of residue analysis.
The first is the method of Dalton and Pease (1962), and is applicable to
residues of monuron and related urea herbicides. This method Involves
quantitative alkaline hydrolysis of the substituted ureas to the aromatic
amines, with simultaneous partitioning into an organic solvent. The amines
are then extracted into dilute acid and determined colorimetrically after
diazotization and a coupling reaction. The extracts are separated on a
cellulose column and can then be analyzed for mixtures of the 4 herbicides, or
for a single herbicide. Test recoveries for monuron ranged from 89 to 100% on
asparagus, sugarcane and several types of fruit, with residues in the range of
0.04 ppm to 3.2 ppm.
19
-------
The second method Is from Major (1962). it is a qualitative and semi-
quantitative method designed to be used as a screening procedure for monuron
and related urea herbicides. This method does not involve conversion to
another product. After extraction and cleanup of the residue, a paper
chromatographic procedure is employed in which the size and position of spots
of the unknown are compared with those of standards. The authors reported 90
to 100% recoveries with detection as low as 0.5 ppm.
The third method is from Katz (1966) who describes both a quantitative
and a qualitative method. Both methods are for residues of monuron and
related urea herbicides in surface waters. In the quantitative method the
herbicide is extracted from water with chloroform and hydrolyzed under reflux
conditions with 6N HC1. The resulting aniline is diazotized and condensed
with N-(l-naphthyl)-ethylenediamine to form a magenta dye, which is extracted
with n-butanol and measured colorimetrically at 555 run. Levels as low as 0.03
ppm monuron were detected. Qualitative determination is made by TLC. The
herbicide is extracted from water with chloroform, and the volume is reduced.
After development, the chromatograms are sprayed with ninhydrin and visualized.
Lowen et al. (1964) noted that monuron and other urea herbicides are
determined by hydrolysis to the corresponding aromatic amine (p_-chloroaniline)
and then isolated from the substrate by distillation. Determination of the
amine can then be made by 4 methods described by Lowen et al. (1964). The
first amine method is the colorimetric method of Bleidner et al. (1954).
This is the predecessor of the previously described method of Dalton and
Pease (1962), but it is for monuron only. For example, it does not involve
the separation technique of Dalton and Pease. The second method from
Bleidner (1954) may be used for soil and plant tissue residues. This
colorimetric procedure employs a simple technique for removing an interfering
azo dye. The interfering dye is formed from o-aminoacetophenone, a compound
resulting from the hydrolysis of naturally occurring material (tryptophan).
The removal of the interfering dye is accomplished by a separation procedure
using a cellules column. The other 2 methods for amine determination de-
scribed by Lowen et al. (1964) are for multi-substituted urea residues. The
programmed-temperature gas chromatography method of Kirkland (1962) can
determine monuron and another urea herbicide simultaneously and has been
employed for analyses of residues on fruits, vegetables, and soil in the 0.1
to 1.5 ppm range. The colorimetric method of Pease (1962) allows for simulta-
neous detection of monuron and another urea herbicide residues by a column
chromatographic procedure which separates the corresponding azo dyes by an
extension of the Bleidner method. Recoveries were greater than 90% in the
0.06 to 3.0 ppm range on asparagus, sugarcane and various fruits.
Zweig and Sherma (1972) described the method of Gutenmann and List (1964),
which involves extraction of the residue with acetone and partitioning into
hexane. Bromination is then done simultaneously with the hydrolysis step.
The brominated aniline is then determined by electron-affinity gas chromatog-
raphy. Bromo compounds have a much greater electron affinity than chloro
compounds. Monuron was tested in grapes, for which the recoveries ranged from
79 to 107%. Sensitivity of the method is about 0.02 ppm.
20
-------
Formulation Analysis - Lowen et al. (1964) described 2 methods of formulation
analysis. One method is from Lowen and Baker (1952). This method involves
hydrolysis of the monuron to dlmethylamine. Lowen and Baker note that acid
of alkaline hydrolysis may be employed, but Lowen et al. (1964) recommends
the acid hydrolysis, as shown in the following equation:
H 0
L
CI/Q)-»-C-N
-------
Most of the available Information concerning the degradation and
decomposition reactions of monuron is contained in articles on losses that
occur when the product is used as a herbicide. Monuron must reach and enter
the roots of a plant in order to destroy it. There are many ways that monuron
may be lost before entering the roots. The primary methods of loss are:
chemical decomposition, (by oxidation or hydrolysis, for example) photodecom-
position, evaporation (volatilization), leaching through the soil by water,
and decomposition by soil microorganisms.
The available information concerning chemical decomposition, photodecom-
position, and evaporation is summarized in this section; leaching and decom-
position by soil microorganisms are discussed in the Fate and Significance in
the Environment section, p. 71.
There is some disagreement as to which method of loss is the more impor-
tant. Hill et al. (1955) studied the rate of disappearance of several
substituted urea herbicides (primarily monuron) on several types of soil under
field conditions. They concluded that volatilization, leaching and chemical
decomposition are very minor causes of disappearance. Photodecomposition may
be an important factor where there is little rainfall. However, according to
these investigators, the primary cause of disappearance is microbiological
decomposition.
Lowen et al. (1964) reported that monuron is stable toward oxidation and
hydrolysis under normal conditions, but at elevated temperatures they can be
hydrolyzed quantitatively. Martin (1971) adds that the hydrolysis rate in-
creases in acid or alkaline conditions. The equation for alkaline hydrolysis
is as follows:
N(CH3)2 + H20 + OH" —^ 01/0^2 + (CH3)2NH + HC03" (12)
The equation for acid hydrolysis Number 13 is shown in the Analytical Methods
subsection.
Hance (1965) reported that a herbicide with a molecular weight of about
180 and a vapor pressure of about 10~^ mm Hg could be lost from the soil
surface by evaporation at an approximate rate of 24 Ib/acre/month. On this
basis, material such as monuron, which has a vapor pressure of 5 x 10~? mm Hg
at 25°C, would be 200 times less volatile, and the loss of monuron in this way
would not be significant. Hance further noted that under field conditions "it
is difficult to distinguish between accelerated evaporation and photochemical
decomposition."
With regard to chemical decomposition, Hance stated:
Many herbicides contain groups which are susceptible to hydrolysis.
At normal soil pH values, such processes will be slow, but at the
surface of soil colloids, particularly the organic colloids, the local
22
-------
pH may be appreciably lower than the bulk pH of the soil and hydrolysis
could then occur with significant speed. Little is known of the extent
to which herbicides undergo oxidation or reduction in the sojl.
However, it is reasonable to suppose that the molecular distortion
imposed when a molecule is absorbed may lead to increased suscepti-
bility to oxidation by atmospheric oxygen.
Hance (1965) agreed with other sources on the proposition that microbio-
logical breakdown is one of the most important decomposition processes. Hance
also noted that leaching may move the herbicide into the desired root area, or
move it out of that area.
According to Hill (1971), soil is not always the same, but its ability to
degrade organic compounds depends upon such factors as temperature, pH, moisture
content, amount of rainfall, and the soil fertility, texture, structure and
content of organic matter. Though he provided new information on biological
degradation, his conclusions were the same as noted earlier in Hill et al.
(1955).
Geissbuhler (1969) contended: "Although no systematic studies have been
carried out, urea herbicides appear to be sufficiently stable under normal
temperature and soil conditions to resist hydrolytic breakdown or oxidation by
purely chemical means."
Photodecomposition - Hill et al. (1955) reported that an 83% loss of monuron
occurred when a solution containing 88.3 ppm monuron in glass-distilled water
was exposed in sealed quartz tubes to sunlight for 48 days. Decomposition
products were not reported.
Weldon and Timmons (1961) described an experiment in which monuron and
another urea herbicide were exposed to an 85-W mercury-vapor lamp. They pre-
pared 10 ppm solutions of the recrystallized herbicides in 95% ethyl alcohol.
These solutions were scanned from 215 to 360 nm using a spectrophotometer.
After evaporating the alcohol from the samples in petri dishes, the residues
were exposed to the lamp for periods of 0, 2, 8, and 28 hrs. Those exposed to
the ultraviolet radiation for short periods of time were left exposed to air
at room temperature up to the 28-hr period. The radiant energy levels emitted
at various wavelengths by the lamp were as follows:
Wavelength Radiant Energy
(nm) (W)
Far ultraviolet 220-280 0.73
Middle ultraviolet 280-320 3.70
Near ultraviolet 320-400 5.07
Visible 400-760 8.93
23
-------
After exposure, the residues were redissolved in ethyl alcohol and again
scanned with the spectrophotometer.
For monuron, the largest changes in percent transmittance occurred at 245
and 220 nm. The other urea herbicide underwent more extensive photochemical
change than monuron. No explanations were proposed concerning the chemical
changes which were caused by the ultraviolet radiation.
In a variation of the above experiment, Weldon and Timmons (1961)
measured the effects on oat growth of 28-hr irradiated and nonirradiated
monuron. These samples were prepared as in the experiment previously de-
scribed. Their data indicated a 75% reduction in biological activity of
irradiated, as compared to nonirradiated, herbicide. Weldon and Timmons (1961)
did not identify any chemical products from the effects of irradiation.
In another photochemical study, Jordan et al. (1965) investigated the
effect of ultraviolet (UV) radiation on herbicides. They subjected samples
of monuron and several other herbicides to various sources of UV radiation.
Three sources of UV radiation were used: far UV (wavelength range, 240 to 260
nm, peak at 253.7 nm); middle UV (275 to 375 nm, peak at 311 nm) and near UV
(320 to 450 nm, peak at 360 nm). The lamps emitted approximately 15 W at the
peak wavelength. The samples were prepared by allowing solutions (1 x 10~3
molar) to evaporate on 1 in diameter aluminum planchets. The samples were
placed 1 ft from the UV sources.
Examination of the UV absorption spectra showed that the most extensive
decomposition of monuron was caused by far-UV radiation. The greatest
decreases in absorbance for monuron occurred at 240 to 260 and 205 to 215 nm.
However, a thin layer of decomposed product apparently protected the lower
layers, indicating that very little protection is required to prevent photo-
decomposition in this instance. The author noted that far-UV radiation does
not remain in natural sunlight reaching the earth's surface. However, there
is significant UV radiation in sunlight above 290 nm and the photodecomposition
mechanism is probably the same at all UV wavelengths. Similar results obtained
by Wright (1967) indicated that far-UV radiation produces more rapid decom-
position of monuron than middle- or near-UV radiation.
The products of monuron photodecomposition have also been investigated.
One of the most extensive studies was that of Crosby and Tang (1969). Their
irradiation experiments were done using a 200 ppm solution of monuron in de-
ionized water. Some samples were held under aerobic conditions and some under
anaerobic conditions. Some samples were exposed to sunlight for 14 days
(during which 6% of the monuron decomposed), and others were exposed to a 40-W
G.E. F40BL blacklight-fluorescent lamp for 7 days. Blacklight-fluorescent
lamps emit ultraviolet radiation in the middle-UV range in a. broad band around
366 nm. They emit practically no radiation in the far-UV range. The results
indicated a close similarity between decomposition by sunlight and ultraviolet
lamp radiation. Several extracts of the irradiated solutions were analyzed by
thin layer chromatography (TLC). Photoproducts were identified by comparison
of their spectral or chromatographic properties with those of authentic
24
-------
standards. Table 1 lists the photodecompsoition products of monuron. Figure
1 shows the reaction scheme proposed by Crosby and Tang (1969) to account for
some of these products.
Table 1. PHQTODECOMPOSITION PRODUCTS OF MDNURON
Compound Structure
Monuron A
3- (p_- chloropheny1) -1-
formyl-1-methylurea B
1- (p_-chlorophenyl)-3-
methylurea C
1- (p_-chlouophenyl) -3-
formylurea§/ ' D
p_-chlorophenylurea£/ E
3- (p_-chloro-o-hydroxy-
pheny1)-1,1-dimethylurea F
4,4'-dichlorocarbanilide G
p_-chloroformanilidea/ H
p_-chlor oanilinej*/ I
£-hydroxyphenyl urea J (one month)
a/ Chromatographic and chromogenic identification only.
Compound C was the principal product. The conversion of Products B and
D into C and E, respectively, did not occur when the compounds were ir-
radiated on a dry chromatoplate. Thus, these reactions appear to require the
presence of water. These reactions are also very slow in the absence of light.
Crosby and Tang (1969) noted that the oxidation of p_-chloroaniline forms
a red compound, but the mass spectrum of their red pigment was not conclu-
sively shown to be the same as that from the oxidation of p_-chloroaniline.
The brown polymers observed by Crosby and Tang (1969) were reported to be
similar to humic acid.
Further biological decomposition of p_-chloroaniline apparently occurs in
the soil. The microbial degradation of monuron, as well as further reaction
of some of its initial degradation products (e.g., oxidation of p_-chloroani-
line), are discussed in the Fate and Significance in the Environment section
of this report (p. 71).
Crosby and Tang (1969) concluded that replacement of the aromatic
chlorine of monuron represented a minor reaction, if it occurred at all. These
investigators found no evidence of a hydroxy compound among the decomposition
products, and they noted that the pH did not change (approximately pH 8), in-
dicating that no hydrogen chloride was formed.
25
-------
Cl
Ill
6
A
Cl
£-Chlorophenyl
isocyanate*
A
S-L
Principal
product
C
Red pigments **
brown polymers
***
NH,
CH3
Figure 1. Proposed photodecomposition reaction sequence of monuron
in aqueous solution under aerobic conditions.
* Possible intermediate.
** Characterized by indoanilineamine.
*** Characterized by homic acid.
Source: Adapted from Crosby and Tang (1969); Rosen (1969); and Sweetser (1963),
26
-------
Under anaerobic conditions, the rate of photodecomposition was greatly
reduced. The investigators therefore concluded that photooxidation represents
by far the most important route of monuron photodecomposition.
Rosen et al. (1969) investigated the photolysis of phenylurea herbicides,
including monuron. They exposed aqueous samples containing 55 ppm herbicide
to sunlight for 17 days. Because they knew of the work of Crosby and Tang
(1969), they did not attempt to identify most of the monuron decomposition
products. They did find one new product that co-chromatographed with, and had
the same infrared spectrum as, 3-(p_-hydroxyphenyl)-l,l-dimethylurea. As noted
above, Crosby and Tang (1969) were unable to find any hydroxy compound.
Hill (1971) recognized the photodecomposition work of previous investiga-
tors, but noted that all of the work involved laboratory tests. He commented
that, under field conditions, photodecomposition was not found to be a major
factor in the disappearance of monuron from the soil.
Mazzocchi and Rao (1972) then investigated the photodecomposition products
of fenuron by irradiating it (in methanol solution) for 13 days. Figure 3 shows
the degradation products of fenuron. Since fenuron is a photodegradation prod-
uct of monuron, the products illustrated are actually ultimate degradation
products of monuron. However, the authors note that the rate of photodegrada-
tion of monuron is about 4 times the rate of photodegradation of fenuron. This
difference in rate explains the fact that, in the photodecomposition of monuron,
there is a buildup of fenuron.
Figure 2 shows the degradation products and the proposed mechanisms of
Mazzocchi and Rao. Note that HC1 was formed. Fenuron was the major degrada-
tion product of monuron. These photodecomposition products are entirely
different from those reported by Crosby and Tang (1969) who employed aqueous
solutions. (See Table 1 and Figure 1.)
Mazzocchi and Rao (1972) then investigated the photodecomposition
products of fresh fenuron by irradiating it (in methanol solution) for 13 days.
Figure 3 shows the degradation products of fenuron. Since fenuron is a photo-
degradation product of monuron, the products illustrated are actually ultimate
degradation products of monuron. However, the authors note that the rate of
photodegradation of monuron is about 4 times the rate of photodegradation of
fenuron. This difference in rate explains the fact that, in the photodecom-
position of monuron, there is a buildup of fenuron.
In their discussion of results, Mazzocchi and Rao (1972) noted that their
results did not agree with the results of other investigators. Since their
tests were carried out under artificial laboratory conditions (anaerobically
in methanol), their results have little relevance to photodegradation in the
natural environment.
Other Properties and Reactions - Cluett (1962) titrated certain substituted
phenylureas, including monuron, as acids in n-butylamine, with a titrant
27
-------
Cl
Monuron
Cl
N=C=0
j>-Chlorophenyl
isocyanate
CH30H
\hv
Cl
• + /^
•NH(
CH-3
'CH,
0
Methyl £-chlorophenyl-
carbamate (minor product)
r»u
CH3
Fenuron
(major product)
Figure 2. Photolysis of monuron in methanol under anaerobic conditions,
Source: Adapted from Mazzocchi and Rao (1972).
28
-------
R/CH3
NHCN
Penuron
hv.
Aniline
CH3GH3
Figure 3. Photolysis of fenuron in methanol under
anaerobic conditions.
Source: Adapted from Mazzocchi and Rao (1972).
29
-------
of 0.1 N tetra-n-butylammonium hydroxide and methoxide in 9:1 benzene-methanol
solution. These titrations were performed potentiometrically and followed
photometrically and conductimetrically. From this data, a table of relative
acidity as measured by half-neutralization potentials in millivolts was prepared
(the lower the potential, the stronger the acid). Cluett presented data for
many substituted phenylureas, some of which are shown below together with data
for 2 common acids for comparison:
Half-neutralization
Compound potential (mv)
Phenylurea 870
Monuron 745
Benzoic acid 500
HC1 420
Lee and Fang (1971) determined that, when monuron is extracted from
spinach by Soxhlet extraction with ethanol, the monuron was converted to ethyl
p-chlorophenylcarbamate.
Occurrence of Residues in Food and Feed Commodities
The Food and Drug Administration (FDA), Department of Health, Education,
and Welfare, monitors pesticide residues in the nation's food supply. There
are two programs; one is commonly known as the "total diet program," the other
is called a "market basket" study.
Monuron has not been reported as a significant residue in any food class,
nor is it routinely searched for in the FDA multi-residue analytical system
which is used to monitor pesticide residues in food. The pesticide is no longer
used on food items.
Acceptable Daily Intake
The acceptable daily intake (ADI) is defined as the daily intake which,
during an entire lifetime, appears to be without appreciable risk on the basis
of all known facts at the time of evaluation (Lu, 1973). It is expressed in
milligrams of the chemical per kilogram of body weight (mg/kg).
The ADI is established by the Food and Agricultural Organization/World
Health Organization (FAO/WHO). An ADI has not yet been determined for monuron.
Tolerances
Due to inadequate toxicity data to support the safety of tolerances, EPA
revoked all previous tolerances for monuron, effective July 26, 1973 (Federal
Register, 1973). Residue tolerances in effect at the time of the revocation
were 7 ppm for asparagus, and 1 ppm on the following crops: avocados, cotton-
seed, grapes, dry bulb onions, pineapples, spinach, sugarcane, and citrus
fruits including oranges, lemons, limes, grapefruit, kumquats, tangerines, and
citron (Federal Register 1955, 1956, 1957).
30
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References
Bleidner, W. E., "Application of Chromatography in Determination of Micro
Quantities of 3-(^-Chlorophenyl)-!,1-dimethylurea," J. Agr. Food Chem.t
(13):682-684 (1954).
Bleidner, W. E., H. M. Baker, M. Levitsky, and W. K. Lowen, "Determination of
3-(p_-Chlorophenyl)-l,l-dimethylurea in Soils and Plant Tissue," J. Agr. Food
Chem., 2(9):476-479 (1954).
Cluett, M. L., "Study of the Titration of Selected Substituted Fhenylureas, as
Acids in n-Butylamine." Anal. Chem.. 34(11):1491-1495 (October, 1962).
Crosby, D. G., and C. S. Tang, "Photodecomposition of 3-(p_-Chlorophenyl)-l,l-
demethylurea (Monuron)," J. Agr. Food Chem.» 17(5):1041-1044 (September-
October, 1969).
Dalton, R. L., and H. L. Pease, "Determination of Residues of Diuron, Monuron,
Fenuron, and Neburon," J. Ass. Offie. Agr. Chem.. 45(2):377-381 (1962).
Finar, J. L., Organic Chemistry, Vol. I., Longmane, London (1971).
Geissbuhler, H., "The Substituted Ureas," Degradation of Herbicides,
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34
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PART II. INITIAL SCIENTIFIC REVIEW
SUBPART B. PHARMACOLOGY AND TOXICOLOGY
CONTENTS
Page
Acute, Subacute and Chronic Toxicity 36
Toxicity to Laboratory Animals 36
Acute Oral Toxicity - Rats 36
Approximate Lethal Dose - Rats 36
Approximate Lethal Dose - Guinea Pigs 37
Approximate Lethal Dose - Rabbits 37
Subacute Oral Toxicity - Rats 37
Chronic Oral Toxicity - Rats 38
Chronic Oral Toxicity - Dogs 38
Acute Dermal Toxicity - Rabbits 39
Primary Irritation and Skin Sensitization -
Guinea Pigs 39
Symptomology and Pathology Associated
with Mammals 39
Toxicity to Domestic Animals 39
Acute Toxicity - Goats 39
Subacute Toxicity - Sheep 40
Subacute Toxicity - Cattle 40
Subacute Toxicity - Chickens 40
Metabolism 41
Effect on Reproduction 43
Teratogenic Effects 43
Oncogenesis 43
Mutagenic Effects 47
Effects on Humans 47
References 48
35
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This section reviews pharmacological and toxicological data on monuron.
The acute, subacute and chronic toxicity data for a number of species by
various routes of administration is discussed. Data is presented on metabo-
lism, effects on reproduction, and teratogenic, oncogenic and mutagenic effects.
Human exposure to monuron is also considered. The section summarizes rather
than interprets data reviewed.
Acute, Subacute, and Chronic Toxicity
Toxicity to Laboratory Animals -
Acute Oral Toxicity - Rats - The acute oral LDso toxicity of monuron to
male albino rats (10 per test group) was determined to be 3,600 mg/kg body
weight with confidence limits of 2,800 to 4,400 mg/kg (Zapp 1955). All of the
rats which died suffered from pulmonary edema and congestion which was fre-
quently accompanied by anemia of liver, kidneys, and spleen. Rats which
survived showed signs of methemoglobinemia, such as cyanosis, enlarged dark
spleen, and compensatory red blood cell (RBC) formation in the spleen and bone
marrow. Some of the survivors also showed kidney pathology, possibly due to
the test dose of monuron.
Another LDso value for acute oral toxicity of monuron to rats was reported
to be 3.4 g/kg (Hodge et al., 1957).
The results of a study by Boyd and Dobos (1969) indicated that the U>50
of monuron (94%) to male albino rats was 1.48 + 0.21 g/kg when fed a standard
laboratory feed. In the same study, it was shown that the lethal action of
monuron varied with the amount and the nature of protein in the diet. The
test animals were fed various diets from weaning to the test age of 2 months.
The rats fed diets containing 3.5% casein were 3 times as susceptible to the
toxic effect of monuron as rats fed a normal (26%) casein diet (LDso of 0.95
g/kg versus 2.88 g/kg).
The clinical toxicity signs for doses of monuron in the range of the oral
LDso were essentially similar, regardless of the type of diet which had been
fed.
The LDso was higher in rats fed from weaning on a purified diet containing
normal amounts of protein such as casein than in rats fed normal amounts of
protein such as laboratory feed.
Approximate Lethal Dose - Rats - The approximate lethal dose (ALD) of
monuron for male albino rats was found to be 7,500 mg/kg body weight when
administered by stomach tube as a 10 or 30% suspension of monuron in peanut
oil containing 20% acetone (Zapp, 1955).
Rats receiving sublethal doses became weak, pale, cyanotic, and were
frequently paralyzed in the hind legs. Higher doses resulted in labored
respiration, marked weakness, and unconsciousness. Rats which survived were
36
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sacrificed 10 weeks after treatment and were found to have enlarged, dark, and
congested spleens containing foci of blood formation. Blood destruction and
increased erythropoiesis were indicated.
Approximate Lethal Dose - Guinea Pigs - The ALD of monuron for guinea pigs
was determined to be 670 mg/kg body weight. Monuron was administered by stomach
tube as a 30% suspension. Sublethal doses resulted in marked weakness and loss
of weight. Lethal dose signs were weakness and paralysis with slow respiration
and lacrimation. Surviving animals, sacrificed 10 to 12 days posttreatment,
showed no significant signs of toxicity, although one guinea pig showed evidence
of a healed kidney injury (Zapp, 1955).
Approximate Lethal Dose - Rabbits - The ALD for rabbits was determined to
be 1,500 mg/kg body weight. Animals "administered oral doses of 200 and 450
mg/kg, as a 20% suspension in peanut oil, showed no clinical signs and no ab-
normal pathology when sacrificed at 12 days posttreatment. Weakness and a loss
of appetite were observed in rabbits receiving oral doses of 670 and 1,000
mg/kg. Posttreatment sacrifice of survivors after 10 days indicated no signifi-
cant pathological changes. Animals receiving lethal doses became unconscious
shortly after treatment and died within 20 hr (Zapp, 1955).
Subacute Oral Toxicity - Rats - Doses of 1,500 mg/kg (1/5 ALD) were admin-
istered by stomach tube to 6 male albino rats, 5 times a week. By the eighth
treatment, all 6 animals had died. During treatment the animals showed dis-
comfort, weakness, and continuous weight loss. Autopsy revealed pulmonary edema
and congestion as well as damage to liver, kidneys, and spleen (Zapp, 1955).
Because of the severe cumulative toxicity at 1,500 mg/kg, the subacute dose
was reduced to 500 mg/kg, 5 times per week for 2 weeks. Animals showed dis-
comfort after treatment, lost weight continuously, and became cyanotic. During
the posttreatment observation period, weight was regained to almost the original
level. At 10 days posttreatment, all animals were sacrificed. Spleens were
large, dark, and congested with small foci of blood formation in all cases.
Deposition of brown granules of blood pigment (hemosiderin) in spleens was
indicative of blood destruction.
In another subacute oral study, Zapp used 3 test groups of rats (5 males
and 5 females per group). Monuron was incorporated into ground laboratory
feed and fed at test levels of 0.005, 0.05, and 0.5%. Food consumption in the
test group was measured and compared to a control group fed the same ration but
without monuron. Blood counts were performed after 1 month's feeding, and the
experiment was terminated at 6 weeks.
In the group that received the 0.005% level of monuron, food consumption
and weight gain were comparable to the control group; blood counts were normal,
and no clinical signs were observed. After sacrifice, 2 of 5 males showed
evidence of methemoglobinemia and/or compensatory RBC formation. No females
showed significant pathology.
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In the 0.05% group, feed consumption and weight gain for the test group
was comparable to the controls. No clinical signs were observed and blood
counts were within normal ranges. At sacrifice, signs of methemoglobinemia
were apparent, and compensatory RBC formation was found in the spleen.
The 0.5% group consumed much less food, and consequently gained much less
weight than the other test groups or controls. The animals were pale and
cyanotic with lowered blood counts. The blood was dark brown and contained
many degenerate RBC's. At necropsy methemoglobinemia was apparent as well as
possible blood destruction. Compensatory RBC formation was found in the spleen
and bone marrow of all animals. No mortality occurred, even at the highest
level fed (0.5%).
Chronic Oral Toxicity - Rats - Four groups of 60 Rochester strain rats
(30 male and 30 female rats per group) were fed for 2 yr on diets containing
monuron at concentrations of 0 (controls), 25, 250, and 2,500 ppm (Hodge et al.,
1958). Throughout the feeding period, diets and tap water were supplied ad
libitum.
Both male and female rats fed 25 and 250 ppm monuron showed no differences
in weight gain over the 2 yr period as compared to the control group. Hale
rats fed 2,500 ppm monuron showed a growth retardation of 20 g after the first
month and maintained a moderate weight differential throughout the experimental
period. Female rats fed 2,500 ppm monuron showed a similar but less marked
differential throughout the feeding trial.
Although 70 to 90% of the colony was lost by the end of the second year
due to epidemics of upper respiratory infection, the lifespan of the surviving
rats was unaffected by the feeding of monuron at all dose levels. The protein
and sugar concentrations in pooled urine samples, taken throughout the 2 yr
period, were found to be normal.
At the termination of the experiment, all survivors were sacrificed for
pathological examination. Other than a slight Increase In weights of livers
and spleens from female rats fed 2,500 ppm monuron, no significant differences
were noted in size and weights of individual organs from control and treated
animals. Histological examination revealed no abnormalities in kidney, heart,
brain, lung, spleen, liver, adrenal, bladder, gonad, stomach, intestines, and
bone marrow tissues.
In addition to 30 deaths due to spontaneous tumors throughout the 2-yr pe-
riod, 24 tumors of various kinds were found during necropsy of survivors. The
incidence of tumors was found to be no higher in the experimental than in the
control groups. The oral no-effect level for rats was determined to be 250 ppm.
Chronic Oral Toxicity - Dogs - Pairs of young beagles, consisting of 1
male and 1 female, were fed monuron for 1 yr at daily levels of 0 (controls),
2.5, 12.5, and 25.0 mg/kg body weight (Hodge et al. 1958). During the feeding
period, no deaths occurred, and no adverse effect on animal health was noted.
Analyses of blood and urine samples taken throughout the study indicated normal
profiles.
38
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At the time of sacrifice, organ size and weights were normal for livers,
kidneys, brains, hearts, lungs, and spleens. Normal histological profiles
were found for tissues of all organs examined after necropsy.
On the basis of the 1-yr chronic study on dogs, a no-effect level of mon-
uron for dogs was determined to be 25 mg/kg body weight for long-term exposure.
The no-effect level for monuron as ingested in food by dogs is 1,000 ppm.
Acute Dermal Toxicity - Rabbits - A 20% suspension of monuron in dimethyl
phthalate was applied to shaved skin between the shoulders of a male rabbit.
A maximum feasible dose of 2,250 mg/kg was administered over an 8-hr period by
rubbing it into the skin with a glass rod. Five hours after treatment, the
material was caked on the rabbit's back. The material disappeared within 2
days, and the rabbit showed no clinical signs of intoxication. No significant
clinical pathology was found at sacrifice, 11 days after treatment (Zapp, 1955).
Primary Irritation and Skin Sensitization - Guinea Pigs - A 33% water
paste of monuron was applied to both intact and abraded skin of male albino
guinea pigs. The compound was practically nonirrltating and did not cause
allergic skin sensitization. No further details were given on such parameters
as numbers used or period of experimentation.
The author concluded that a moderate amount of skin contact with CMU
(monuron) would not be harmful because it is not an irritant or a sensitizer,
nor is it significantly absorbed through the skin (Zapp, 1955).
Svmptomology and Pathology Associated with Mammals - It appears that the
signs of toxicity which will be observed in most animals will be similar and
will consist of one or more of the following, depending on the size of the
dose: loss of appetite, weakness, weight loss, diarrhea, labored respiration,
lacrimation, cyanosis, ptosis, paralysis (especially handquarter), and
unconsciousness. Pathological examination could show some of the following
conditions: lowered blood count, methemoglobinemla, acute gastritis with
inflammation and hemorrhaging, pulmonary edema, congestion of liver and kidney,
and enlargement of spleen with foci of blood formation. (Zapp, 1955; Kay, 1957;
Palmer and Radeleff, 1969).
Toxicity to Domestic Animals -
Acute Toxicity - Goats - Goats were given a single oral drench using a
50% aqueous slurry of 80% CMU (monuron). The results, shown in Table 2, in-
dicate that the LDso for goats falls in the range of 600 to 1,600 mg/kg body
weight (E. 1. du Pont de Nemours and Company 1952).
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Table 2. ACUTE TOXICITY OF MONURON TO GOATS BY SINGLE DRENCH
Dose (mg/kg) Symptoms Mortality
3,200 Intoxicated in 2-1/2 hr 1/1 after 12 hr
1,600 Intoxicated in 2-1/2 hr 1/1 after 12 hr
600 Intoxicated in 6 hr (normal in 48 hr) 0/1
300 Intoxicated in 20 hr (normal in 48 hr) 0/1
150 No symptoms 0/1
Subacute Toxicity - Sheep - One sheep survived 10 daily doses of monuron
at 50 mg/kg (by drench) with no ill effects. Of 2 sheep dosed at 100 mg/kg
(by drench) one exhibited signs of poisoning after 4 doses, but survived; the
other animal died after 9 doses, with a 20% weight loss. A fourth animal
given 100 mg/kg by capsule for 10 doses exhibited signs of poisoning, but
survived (Palmer and Radeleff, 1969).
Subacute Toxicity - Cattle - Cattle were administered monuron (80%
wettable powder) in multiple daily doses from 25 mg/kg to 250 mg/kg by drench.
The animals developed diarrhea after 1 to 5 doses at 50, 100, and 250
mg/kg although no other ill effects were noted. The diarrhea was not severe
enough to result in any significant weight loss.
After a single dose at a 500-mg/kg level, one yearling exhibited signs of
poisoning and exhibited an 11% weight loss, but survived.
One yearling was dosed at 50 mg/kg daily by capsule for 10 days without
exhibiting any diarrhea or other ill effects (Palmer and Radeleff, 1969).
Subacute Toxicity - Chickens - Chickens were administered monuron (80%
wettable powder) in capsules in doses from 10 mg/kg to 250 mg/kg for up to 10
days.
When treated chickens were compared to controls the 10-mg/kg dose was
found to have had no effect on weight gain. At 25 mg/kg, the chickens ex-
hibited a weight gain 14% lower than that attained by controls. At a dosage
of 50 mg/kg, treated chickens had a weight gain 27% below the gain of un-
treated controls.
When the dosage was 1QO mg/kg one of 5 treated chickens died after 8
doses. The survivors all exhibited a weight loss.
At 250 mg/kg all 5 treated chickens died after doses 6 to 9 (Palmer and
Radeleff, 1969).
40
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Metabolism
In a study on the metabolic fate of urea herbicides, rats were each fed
4.8 g of monuron in 8 days; the urine was then collected and analyzed. The
analyses determined that the majority of the metabolites retained the urea
structure and that the chief pathway was a step-by-step demethylation, with a
minor step leading to hydroxylation of the benzene nucleus. Monuron and its
corresponding dlchlorinated analog were the only urea herbicides of those
studied in which a total demethylation occurred without simultaneous hydroxy-
lation (Ernst, 1969). The metabolic pathways proposed for monuron were as
follows:
NH-CO-NH2
OH
NH-CO-NH-
Source: Adapted from Ernst (1969).
Determinations of quantitative proportions indicated that the metabolites
were distributed so that about 15% excretion was in the form of (II) N-(4-
chlorophenyl) urea, about 7% excretion as (III) N-(2-hydroxy~4-chlorophenyl)-
urea, and about 2.5% as (IV) N-(3-hydroxy-4-chlorophenyl)-urea.
The enzyme systems responsible for the stepwise demethylation of monuron
in rats have not been identified. However, Geissbuhler and Voss (1971) re-
ported that the plant enzyme system involved in N-demethylation is a mixed-
function oxidase that is located in the microsomal fraction of plant extracts
and which requires molecular oxygen and either NADPH or NADH as cofactors.
The authors also concluded that the pathways of transformations of urea
herbicides in plants, animals, and soils are so similar as to make a separate
discussion of each process unnecessary.
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From the results of their studies, Geissbuhler and Voss (1971) concluded
that, in animals and in plants, degradation of urea herbicides to the corres-
ponding anilines does not represent a major pathway of transformation for the
urea herbicides. From their survey of the literature, they also concluded
that the formation of azobenzenes from metabolically-formed anilines does not
represent significant terminal residues of urea herbicides.
Excretion - Geissbuhler and Voss (1971) suggested that hydroxylated
animal metabolites of urea herbicides could be eliminated mainly in the urine
as glucuronides or ester sulfates. Formation of these conjugates lead to very
water-soluble compounds. It must be emphasized, however, that the chemical
structure of these conjugates has not been verified. The authors believed that
the conjugates were B^-D-glucoside compounds.
Enzyme Induction - Monuron and other urea herbicides have been found to be
inducers of hepatic microsomal enzyme syntheses (Kinoshita and DuBoise, 1970).
Weanling and adult female rats were fed monuron for 1 week at 1,000 ppm,
and then the changes in enzymatic activities of 0-demethylase, N-demethylase
and the hepatic detoxification system were determined. The results of these
analyses are shown in Table 3. 0-demethylase appeared to be induced to high
activity from the feeding of monuron although activity of the hepatic detox-
ification system and N-demethylase were not increased significantly.
Table 3. INDUCTION OF HEPATIC MICROSOMAL ENZYME ACTIVITY OF RATS
Test Days fed at Hepatic 0-Demethylasea/ N-Demethylasek/
group 1,000 ppm detoxification
system**/
Controls: 7 3.5 + 0.14 6.6 + 0.19 3.2 + 0.23
weanling
adult 7 2.8+0.07 5.8+0.22 3.1+0.16
Monuron: 7 3.9 + 0.32 8.7 + 0.34£/ 3.0 + 0.26
weanling
adult 7 2.8 + 0.10 6.7 + 0.49 3.1 + 0.35
a/ yg £-Nitrophenol per 50 mg liver per hr.
b/ yg 4-Aminoantipyrlne per 100 mg liver per 1/2 hr.
£/ Significantly different from controls (p £ 0.05).
Source: Adapted from Kinoshita and DuBois (1970).
42
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Monuron was also studied in relation to its effect on enzymes that
regulate glycolysis in the liver (Rubenchik, 1970). Enzymatic activity was
depressed in liver homogenates from rats fed monuron for 10 weeks when compared
to that of rats fed regular diets. However, after 18 weeks of feeding, the
activity of the glycolytic systems of monuron-treated animals was increased to
levels higher (18.8 versus 10.7 mg lactic acid/g protein) than that of the
controls.
Phosphofructokinase (PFK) activity in the livers of rats fed monuron (450
mg/kg) for 10 days was also depressed below control values. As with total
glycolysis at 18 weeks, the activity of PFK was higher in monuron-treated rats
than it was in controls. Hexokinase activity did not appear to change because
of monuron treatment. Known carcinogens and monuron were shown to have
produced similar changes in the profile of glycolysis activity in the liver,
although tumors were found in the livers of the carcinogen-treated animals,
but not in the livers of monuron-treated ones.
Effect on Reproduction
A 3-generation reproductive study was carried out with male and female
Rochester strain rats (Sherman and Culic 1971). The animals were fed 0, 125,
and 2,500 ppm AI in the diet for 3 generations. Two litters of offspring were
produced per generation. At the lower feeding level, no clinical signs of
toxicity or deviations from normal reproduction and lactation were observed.
At the 2,500 ppm feeding level, the average size of 6 litters was slightly
lower than the control group and the 125-ppm group.
Ten male and 10 female weanling rats from each group of FSj, generation
were sacrificed. The following tissues were evaluated histologically: lung,
trachea, liver, kidney, spleen, thymus, testes, ovary, epididymis, uterus,
skeletal muscle, stomach, duodenum, colon, heart, brain, adrenals, eye, and
bone marrow. No pathological changes were observed which could be attributable
to the test material.
Teratogenic Effects
In a teratogenic screening study, monuron caused no significant increases
of anomalies in 3 strains of mice at 215 mg/kg (U.S. Department of Health, Ed-
ucation, and Welfare, 1969).
Oncogenesis
Experiments were conducted on 100 random-bred male white rats, 50 random-
bred white mice, and 45 mixed sex, C57BL black mice (low cancer incidence).
The rats were fed for 18 months on a diet containing 450 mg/kg monuron (0.12
LDso). Mice received monuron orally in milk at the rate of 6 mg/week, as a
single dose, for a period of 15 weeks. The observation period was 27 months
for rats and 13 months for mice. All animals which died during the experiment
were subjected to necropsy, and tissues from each were evaluated histologi-
cally. Animals surviving the experimental period were likewise sacrificed and
subjected to necropsy and hlstological examination (Rubenchik et al., 1970).
43
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The incidence of occurrence and time of appearance of tumors is shown in
Table 4. The types of tumors found and time of detection are given in Table 5.
Of the rats fed monuron, 18 were sacrificed early in the experiment when the
tumor incidence was low. Of the 32 remaining animals, tumors occurred in 15
(46.5%). No tumors were found in the 30 control rats sacrificed at comparable
time periods.
Table 4. SUMMARY OF THE ACTION OF MONURON ON EXPERIMENTAL ANIMALS
Time of de- Animals alive Animals with tumors
tection of up to detec- of different locali-
first tumor tion of first Animals with zation occurring at
Animal species (weeks) tumor tumors the same time
I Rats 18 32 15 8
II Mice,
random-bred 16 23 13 4
III Mice,
C57BL strain 4 26 7 1
Source: Adapted from Rubenchiktet al. (1970).
Malignant and benign tumors were found in 56.5% of the random-bred mice
and in 26.9% of the C57BL strain. In the controls only 1 tumor occurred (3.9%)
in the C57BL strain mouse.
In a study of herbicide metabolism, monuron was fed to rats for 18 weeks
at 450 mg/kg without producing tumors in the liver. During the same period,
known carcinogens produced liver tumors in all rats tested (Rubenchik 1970).
Monuron was one of 130 compounds evaluated for tumorigenicity by Innes
et al. (1969). Male and female mice of 2 hybrid strains (C57BL/6 x C3H/
Anf and C57BL/6 x AKR) were given maximal tolerated doses (215 mg/kg) daily
by stomach intubation starting at 7 days and continuing until weaning at 4
weeks of age. Following weaning, the same daily dose was administered in the
diet until necropsy at 18 months of age. A total of 72 animals were fed
throughout the experimental period (18 of each sex for both strains). At
necropsy the mice fed monuron had elevated tumor incidence. The range, how-
ever, was uncertain and not significant enough to definitely place the com-
pound in the tumorigenic category. It was recommended that the compound be
further evaluated.
44
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Table 5. RESULTS OF THE ACTION OF MONURON ON EXPERIMENTAL ANIMALS
In
Animal
Species
Rats
Number of
tumors
Time in
weeks
Random-Bred
Mice
Number of
tumors
Time in
weeks
Mice, C57BL
Number of
tumors
Time in
weeks
Stomach Intestine Liver Lung Testis Kidney
Adenoma Hepato- Cancer Cancer
Malig- Lym- Cyto- Hepatoma cellular Alveole- Micro- Semi-
nant Scirrhus phoma blastema Benign Cancer cellular cellular noma Cancer
1 lb_/ - 1 1 2 242-
84 83 - 94 72 108, 118 84, 104 18, 100, 68, 72
102, 118
1--- 4 4 2--2
17 12, 17, a/ 17,b/ 69 16, 30 - - 17, 104
28
--1- 2 2 1--1
64 4, 14 8, 20 90 69
a/ aeveraj. Luuiura ueLecueu ac uue »
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Table 6. OBSERVATIONS ON THE TUMORIGENICITY OF MONURON TO RATS AND DO*GS
Animal
2 dogs
2 dogs
2 dogs
60 rats
60 rats
60 rats
60 rats
Strain or
type
Beagle
Beagle
Beagle
Rochester
Rochester
Rochester
Rochester
Sex - — Dose
1 M, 1 F 2.5 mg/kg body weight
in food for 1 year
1 M, 1 F 12.5 mg/kg body weight
in food for 1 year
1 M, 1 F 25 mg/kg body weight
in food for 1 year
30 M, 30 F 0.0025% in basal and
meat diet for 2 years
30 M, 30 F 0.025% in basal and
meat diet for 2 years
30 M, 30 F 0.25% in basal and
meat diet for 2 years
30 M, 30 F Control
Treated
Animals
with tumors
significantly
higher than
controls
0
0
0
0
0
0
Survival
Killed at termination
experiment
Killed at termination
experiment
Killed at termination
experiment
70 to 90% died by end
second year
70 to 90% died by end
second year
70 to 90% died by end
second year
70 to 90% died by end
second year
of
of
of
of
of
of
of
Source: Adapted from Hodge et al. (1958).
-------
Table 6 depicts data for chronic feeding studies performed on dogs and
rats (Hodge, et al. 1958). Dogs were given daily oral doses of 2.5, 12,5,
and 25 mg/kg body weight monuron in food for 1 yr. Rats were fed 0,0025, 0.025,
and 0.25% monuron in the diet for a 2-yr period. The incidence of tumors was
observed to be no higher in the experimental groups than in the control groups.
Monuron is currently undergoing chronic testing under the auspices of the
National Cancer Institute (at Frederick Cancer Research Center), Both male
and female rats and mice are being fed diets containing monuron at the maximum
tolerated dose and one-half the maximum tolerated dose.
Mutagenic Effects
Monuron (no precise concentrations given) did not induce point mutations
when evaluated with histidine dependent mutants of Salmonella typhimurium
(Anderson et al., 1972). The assays were conducted without exposure to meta-
bolic activation agents.
Morphological and somatic chromosomal aberrations induced by pesticides
in barley (Hordeum vulgare) were studied. Barley seeds were exposed to monuron
and to a number of other pesticides at a concentration of 1,000 ppm for 12 hr.
The mutation rate obtained by these treatments was compared to untreated con-
trols, and to the effects of x-ray radiation at 5,500 roentgens. "Relative
efficiency" ratings were assigned to each treatment on a scale from 1 (control)
to 32 (mutation rate produced by the x-ray treatment). On this scale monuron
evidenced a "relative efficiency" of 10 (U.S. Department of Health, Education,
and Welfare, 1969).
Effects on Humans
Data from the EPA Pesticide Episode Review System (PERS) shows a total of
5 episodes involving monuron and formulations containing monuron. The system
evaluates'episodes involving humans, animals, plants exposure and area contam-
ination. Cause-effect relationships were not established for those incidences
involving monuron and combinations with monuron. Two incidences which involved
human exposure reported contact dermatitis and itching.
47
-------
References
Anderson, K. J., E. G. Leighty, and M. T. Takabashi, "Evaluation of Herbicides
for Possible Mutagenic Properties." J. Agr. Food Chem.. 20(3):649-656
(1972).
Boyd, E. M., and I. Dobos, "Acute Oral Toxicity of Monuron in Albino Rats Fed
from Weaning on Different Diets," J. Agr. Food Chem.. 17:1213-1216 (1969).
E. I. Du Pont de Nemours and Company, Report on Monuron, EPA Pesticide Peti-
tion No. 17 (1952).
Ernst, W., "Metabolism of Substituted Dinitrophenols and Ureas in Mammals and
Methods for the Isolation and Identification of Metabolites," J. S. African
Chem. Inst.. 22:579-588 (1969).
Geissbuhler, H., and G. Voss, "Metabolism of Substituted Urea Herbicides,"
contained in A. S. Tahori (ed.), Pesticide Terminal Residues; Invited
Papers from the International Symposium on Pesticide Terminal Residues,
, Held at Tel Aviv, Israel, February 17-19, 1971, Butterworth and Company,
London (1971).
Hodge, H. C., E. A. Maynard, W. L. Downs, and R. D. Coye, "Chronic Toxicity
of 3-(p_-Chlorophenyl)-l,-l-Dimethyl Urea (Monuron)," A.M.A. Arch. Ind.
Health. 17:45-47 (1958).
Hodge, H. C., E. A. Maynard, W. L. Downs, and R. D. Coye, Report on Monuron,
EPA Pesticide Petition No. 17, Vol. I (1957).
Innes, J. R. M., B. M. Ulland, M. G. Valerio, L. Petrucelli, L. Fishbein,
E. R. Hart, A. J. Pallotta, R. R. Bates, H. L. Falk, J. J. Gart, M. Klein,
I. Mitchell, and J. Peters, "Bioassay of Pesticides and Industrial Chemicals
for Tumorigenicity in Mice: A Preliminary Note," J. Nat. Cancer Inst., 42:
1101-1114 (1969).
JCay, J. H., Report on Monuron, EPA Pesticide Petition No. 17, Industrial Bio-
Test Laboratories report for National Aluminate Corporation (-1957) .
Kinoshita, F. K. and K. P. DuBois, "Induction of Hepatic Microsomal Enzymes
by Herban, Diuron, and Other Substituted Urea Herbicides," Toxicol. Appl.
Pharmacol.. 17:406-417 (1970).
Palmer, J. S., and R. D. Radeleff, "The Toxicity of Some Organic Herbicides
to Cattle, Sheep, and Chickens," U.S. Department of Agriculture Research
Report No. 106 (1969).
Rubenchik, B. L., "Effect of Administration of Hepatocarcinogens and the
Herbicide Monuron on Intensity of Glycolysis and Activity of Its Regulating
Enzymes in Rat Liver Hyalplasm," Byull. Eksp. Biol. Med.. 69:61-63 (1970).
48
-------
Rubenchik, B. L., N. E. Botsman, and G. P. Gorban, "The Carcinogenic Action of
the Herbicide Monuron," Voprosy Onkologii, 16(10)51-53 (1970).
Sherman, H., and R. Culik, Report on Monuron, Haskell Laboratory Report No.
300-17, EPA Pesticide Petition No. 17, Vol. I (1971).
U.S. Department of Health, Education, and Welfare, Report of the Secretary's
Commission on Pesticides and Their Relationship to Environmental Health
(1969).
Zapp, J. A., Jr., Report on Monuron, EPA Pesticide Petition No. 17, Vol. II
(1955).
49
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PART II. INITIAL SCIENTIFIC REVIEW
SUBPART C. FATE AND SIGNIFICANCE IN THE ENVIRONMENT
CONTENTS
Page
Effects on Aquatic Species 52
Fish 52
Laboratory Studies 52
Special Laboratory Studies 52
Field Studies 52
Lower Aquatic Organisms 55
Laboratory Studies on Animals 55
Field Studies 59
Effects on Wildlife 60
Laboratory Studies 60
Effects on Beneficial Insects 61
Synergism of Insecticides with Monuron 61
Interactions with Lower Terrestrial Organisms 61
Microflora 61
Microfauna 66
Residues in Soil 67
Laboratory Studies 67
Field and Greenhouse Studies 71
Residues in Water 77
Residues in Air 79
Residues in Nontarget Plants %.,.•,. 79
Bioaccumulation, Biomagnification and Environmental
Transport Mechanisms , . , . 80
References , 82
51
-------
This section contains data on the environmental effects of monuron,
including effects on aquatic species, wildlife and beneficial insects,
interactions with lower terrestrial organisms and effects on residues in
soil, water and air. The section summarizes rather than interprets data
reviewed.
Effects on Aquatic Species
Fish -
Laboratory Studies - Available data on the acute toxicity of monuron to
fish is summarized in Table 7. The effect of various formulations for several
fish species is shown in Table 8. The data indicates that a combination of
monuron and trichloroacetic acid (TCA), is more toxic to fish than monuron
alone (Walker, 1965).
Goldfish (Carassius auratus) have been reported to survive a 5-day
exposure to 59.5 ppm monuron, and a 35-day exposure to 14.9 ppm (Lawrence,
1962).
The 3-hr approximate safe upper limit for initial concentration of
monuron applied to fish-bearing waters is reported to be 20 ppm (Edson,
1958).
Special Laboratory Studies - Romarovsky and Popovich (1971) have reported
the chronic effects of monuron to Leuciscus idus (golden orfe) and Rutilus
rutilus. "Monurox" (10% monuron, 10% TCA, [TCA alone is more toxic to fish
than monuron alone] 80% inert ingredients) applied at the rate of 40 kg/ha
active ingredient (Al) (20 mg/1 Al) to artificial ponds caused decreased hemo-
globin, erythrocyte and hematocrit counts in fish for up to 75 days after
treatment when compared to fish in control ponds. There was also a 46% loss
of fish over the test period.
Field Studies - Springer (1957) studied the toxicity of monuron to small
golden shiners (Notemigonus crysoleucas) in ponds. He reports that "some
mortality" (not quantified) occurred at a dosage of 20 ppm of monuron.
Bond et al. (1959) reported that the treatment of ponds with monuron at
5 and 10 ppm caused no mortality either to Coho salmon (Oncorhynchus kisutch),
frogs or tadpoles.
52
-------
Table 7. ACUTE TOXICITY OF MONURON TO FISH
in
u»
.,
Species
Striped mullet
(Mugil cephalus)
White mullet
(Mugil curema)
Rainbow trout
(Salmo gairdneri)
Largemouth bass
(Micropterus salmoides)
Coho salmon
(Oncorhynchus kisutch)
Carp
(Cyprinus carpio)
Purity Exposure
(%) time (hr)
48
24
48
80 24
48
4+ 48
-H- 24
48
48
•s.
Temperature Toxicity
(°C) calculation
LC
28 TL +
TLm
28 LC,n
LC
20 10%
mortality
20 TL
20 TLm
m
TL
Toxicity
value
(ppm)
16.3*
20.0
16.3
180
100
230
115
110
>10
References
a/
b/
'£/
c*/
d/
e/
* Standing water test.
+ Median tolerance limit.
•H- Concentrations are given in terms of active ingredient.
&/ Butler (1965).
b/ U.S. Fish and Wildlife Service (1963).
cj Alabaster (1969).
d/ Bond (1959).
e/ Nishiuchi (1974).
-------
Table 8. EFFECT OF FORMULATION ON THE ACUTE TOXICITY OF MONURON TO FISH
Formulation
Monuron 80% WP
Monuron 80% WP
Monuron 25% pellet
Monuron 25% pellet
Monuron-borate
4% granular
Monuron-TCA
3 Ib/gal
Monuron-TCA
3 Ib/gal
Monuron-TCA
3 Ib/gal
Monuron-TCA
11% granular
Monuron-TCA
22% granular
Monuron-TCA
technical
Monuron-TCA
technical
Monuron-TCA
technical
Monuron-TCA
technical
Monuron-TCA
technical
Fish species
Bluegill
(Lepomis macrochirus)
Brown bullhead
(Ictalurus nebulosis)
Bluegill
(Lepomis macrochirus)
Red ear sunfish
(Lepomis microlophus)
Bluegill
(Lepomis macrochirus)
Bluegill
(Lepomis macrochirus)
Bluegill
(Lepomis macrochirus)
Largemouth bass
(Micropterus salmoides)
Bluegill
(Lepomis macrochirus)
Bluegill
(Lepomis macrochirus)
Pumpkinseed
(Lepomis gibbosus)
Bluegill
(Lepomis macrochirus)
Bluegill
(Lepomis macrochirus)
Redear sunfish
(Lepomis microlophus)
Largemouth bass
(Micropterus salmoides
Size
(inc.)
4-5
3-4
4-5
4-5
4-5
2-3
4-5
4
2-3
4-5
2-3
2-3
4-5
4-5
4
Concentration (ppm)
EC10a/
20.0
40.0
27.0
31.5
17.5
0.7
1.0
1.1
2.0
2.3
1.7
2.0
2.4
3.1
3.0
EC50a/
33.0
57.0
40.0
47.0
26.0
1.5
1.8
2.7
3.8
4.8
3.3
4.5
5.0
5.4
4.8
K90*/
55.0
80.0
60.0
60.0
40.0
3.0
3.1
6.0
7.0
10.0
6.0
9.6
10.0
9.0
8.0
'10'
'50'
'90
£/ ECin, EC,.n, ECQn = Effective concentration in parts per million which
produced 10%, 50%, and 90% mortality, respectively,
in a 96-hr exposure period.
Source: Adapted from Walker (1965).
54
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When 2 ppm monuron (as 80% AI commercial wettable powder) was sprayed on
a pond for algae control, smallmouth bass appeared to be agitated but no dead
fish were found (Maloney, 1958) . The fish returned to normal the following
day. It was concluded by the investigator that the agitation was due to
reduction of dissolved oxygen by the dead or dying algae and not due to
agitation by monuron per se.
Hiltibran (1967) undertook studies to determine the toxicity of several
herbicides, including monuron to fish embryos and fry. In a preliminary
experiment in which monuron was not included, it was determined that the
exposure of fertilized eggs of the stoneroller (Campos toma anomalum) to
concentrations of different herbicides ranging from 5 to 50 ppm did not
prevent the development of fry. Because of the difficulties involved in
using fertilized fish eggs in toxicity experiments, only fry were used in
subsequent tests in which monuron was included. Fish fry appeared to be more
susceptible to the toxic action of the herbicides than fertilized fish eggs.
Monuron was used in the form of a granular monuron-TCA formulation (concentra-
tion not specified) at 22 to 25° C. Twenty ppm was the highest concentration
of monuron which did not cause death of small bluegills (Lepomis macrochirus)
during a 12-day exposure period. At 10 ppm, monuron did not cause any loss of
fry of bluegill or lake chubsucker (Erimyzon sucetta) , exposed for 8 days . At
the same rate, green sunfish (Lepomis cyanellus) fry survived no longer than
5 days, and smallmouth bass (Micropterus dolomieu) fry survived for only
4 days.
Lower Aquatic Organisms -
Laboratory Studies on Animals - The toxicity of monuron to estuarine ani-
mals was studied by Butler (1963) . Adult white shrimp (Penaeus setiferus)
were exposed to monuron for 24 and 48 hr at an average temperature of 24°C,
and 30 parts per thousand salinity. At the highest rate tested, 1.0 mg/1,
monuron had no effect (death, paralysis, or loss of equilibrium) on the test
animals . The Eastern Oyster (Crassostrea virginica) was exposed to monuron
at an average temperature of 22°C, and a salinity of 25%. At a concentration
of 2.0 mg/1, there was a 12% decrease in oyster shell growth after an
exposure of 96 hr. In these tests, monuron was considerably less toxic to
the test organisms than most other pesticides tested under similar experi-
mental conditions.
Davis and Hidu (1969) studied the acute and subacute toxic effects of
pesticides and solvents on the American (or Eastern) oyster and the hard clam
(Mercenaria mercenaria) . The temperature was 24°C and the pesticide medium
was removed and renewed every second day. Monuron in water solution had
48 hr. and 12 day TL 's of > 5.00 ppm both for the oyster and hard clam.
The authors reported that the TLm values listed are of significance fpr rough
comparisons of toxicity only because some compounds drastically reduce the
rate of larvae growth at concentrations too low to cause appreciable mortal-
ity. Some concentrations may kill embryos at lower levels than are required
to affect growth or survival of larvae. Davis and Hidu also listed effects on
development of eggs and survival and growth of clam larvae (expressed as per-
centages of control) at 4 concentrations for monuron:
55
-------
Concentration
(ppm) Eggs developing (%) Larval survival (%) Larval growth (%)
0.25 93 120 114
0.50 99 122 109
1.00 91 128 86
5.00 92 111 93
Springer (1957) reported that at a dosage of 20 ppm applied to water,
monuron did not cause mortality in amphipods or isopods.
Crosby and Tucker (1966) determined the toxicity (median immobilization
concentration) of a number of herbicides, including monuron, to Daphnia magna.
The tests were performed aJL 21.1°C in boiled deepwell tap water to which a
nonionic surfactant (Tween 20) was added at a concentration of 1 ppm. Monuron
caused immobilization of 50% of the test animals (ICso) at a concentration of
106 ppm. Monuron was 1 of 5 herbicides whose ICso concentrations were above
100 ppm.
Nishiuchi (1974) reported the TL value (3 hr) for Daphnia pulex as >
.- m —
0.5 ppm.
Walker (1965) conducted extensive studies on monuron and several other
substituted phenyl-urea herbicides to determine their usefulness as aquatic
herbicides. Field tests followed laboratory bioassay tests for fish toxicity
(reviewed in the preceding subsection) which showed that monuron was less
toxic to fish than other herbicides of this type. At a dosage rate of 1 to 2
ppm, monuron reduced the total numbers and the total weight in grams of
bottom-dwelling fish-food organisms 3 months after treatment. Primarily,
weed-clinging species of Gastropoda, Odonata and Trichoptera were eliminated,
along with Ephemeroptera (mayfly nymphs) which are quite sensitive to pol-
lution. The total number of bottom-dwelling fish-food organisms per square
foot was reduced from 153 in an untreated area to 95 in the monuron-treated
area, and the total .weight of such organisms was reduced from 1.87 g
(untreated) to 1.53 g in the monuron-treated areas. These counts were taken
3 months after monuron application. Walker concludes that monuron showed
potential for the control of aquatic plants at rates of 1 to 5 ppm, or 20
to 50 Ib/acre. According to the author, monuron and the related substituted
urea herbicides tested "did not appear to seriously reduce fish-fbod
organisms, and no fish mortalities were observed under field conditions at
concentrations up to 10 ppm of monuron."
Shcherban (1971) studied the effects of monuron on the productivity of
several species of planktonic Cladocera. At the rate of 2 mg/1 monuron
significantly increased the number of days between births in Daphnia magna,
Moina rectirostris and Scapholeberis macronata, and also significantly in-
creased the time necessary for offspring to -reach fertility in M. rectirostris
and S.. macronata. Monuron significantly decreased the average lifespan of
Ceriodaphnia quadrangula, the total number of births in a lifespan in all 4
species, the number of young produced per birth in M. rectirostris, £. quad-
rangula and in £. macronata. and the potential productivity of ID. magna,
M. rectirostris, and jS. macronata.
56
-------
Fidgaiko (1971) investigated the effect of monuron and 2 related urea
herbicides on the rate of reproduction of zooplankton species by exposing
them to the pesticides in aquarium water and determining the offspring which
developed between 20 to 75 days after treatment. Monuron and the related
herbicides greatly suppressed the rate of reproduction, especially of
Scapholeberis macronata.
Imam and Ghabbour (1966) studied the effects of 5 herbicides on the aqua-
tie oligochaete Branchiura sbwerbyi (Tubificidae), an indirect pest in rice
nursery beds. Ii. sbwerbyi survived for 2 weeks in monuron (pond) at a concen-
tration of 100 ppm. They survived for only 4 days at 500 ppm and one-half day
at 1000 ppm.
Laboratory Studies on Plants - Ukeles (1962) studied the toxicity of
monuron and several related phenylurea herbicides to pure cultures of marine
plankton, including Protococcus sp., Chlorella sp., Dunaliella euchlora,
Phaeodactylum tricornutum, and Monochrysis lutheri. Monuron completely
inhibited the growth of these organisms at 0.02 ppm. Only one pesticide
tested in this series was more toxic than monuron to most of the marine
phytoplankton species tested. Fifteen other pesticides studied under the
same conditions were considerably less toxic to these organisms than monuron.
Butler (1965) investigated the effects of a large number of pesticides on
estuarine phytoplankton. The organisms (described only as "phytoplankton,"
not individually identified) were exposed to the pesticides at a standard con-
centration of 1.0 ppm for 4 hr. Under these conditions, monuron reduced
carbon fixation by 94%; it was the most toxic among 26 herbicides tested.
Five other herbicides reduced carbon fixation by more than 75%, while 9 herbi-
cides caused no decrease in carbon fixation.
Walsh (1972a) studied the effects of a number of different herbicides and
herbicidal formulations on photosynthesis and growth of 4 species of marine
unicellular algae, including the chlorophytes Chlorococcum species, Dunaliella
tertiolecta, the chrysophytes Isochrysis galbana, and Phaeodactylum tricor-
nutum. The organisms were grown and tested in a medium of artificial seawater
at 20°C supplemented with trace elements and vitamins. The salinity of the
medium was 30 parts per thousand, and the pH ranged from 7.9 to 8.1. Monuron
was tested only in the form of the technical acid. The concentrations of
monuron that decreased oxygen evolution of the study organisms by 50% (EC--)
and 100% (EC-00), and the concentrations that decreased growth by 50 and 100%,
respectively, were as follows:
Chlorococcum Dunaliella Isochrysis Phaeodactylum
Oxygen evolution
EC,-n, ppm 0.10 0.09 0.10 0.09
EC100' ppm 0.20 0.16 0.17 0.17
Growth reduction
EC—, ppm 0.10 0.15 0.13 0.10
ppm 0.25 0.25 0.28 0.25
57
-------
In general, triazine herbicides investigated under the same conditions
were more toxic or as toxic as substituted urea herbicides.
Walsh and Grow (1971) investigated the effects of different salinities
on the inhibition of the growth of 6 genera of marine unicellular algae by
4 urea herbicides, including monuron. Test organisms included the same 4
species studied by Walsh (1972b), and 2 additional chlorophytee, including
Dicrateria inornata and Nannochloris species. When Chlorococcum species were
exposed to monuron at concentrations of 10, 50, and 100 ppb at salinities of
5, 10, 20, and 30 parts per thousand, it was found that salinity had no ef-
fect on the inhibition of growth by the herbicide. The growth of Chloro-
coccum was inhibited by 10 to 12% at 10 ppb of monuron; 22 to 25% at 50 ppb;
and 52 to 62% at 100 ppb. Growth inhibition data for all other species of
algae were similar. Again, monuron was less toxic to the test organisms than
some other herbicides of this type. The herbicides did not affect total
protein, total chlorophyll, or carotenoid contents of the algae at any
salinity. They did, however, produce changes in the carbohydrate content in
relation to salinity; increasing salinity produced increasing depression of
carbohydrate content. Chlorococcum, the most susceptible species, lost 65.6%
of its total carbohydrate when treated with monuron at 100 ppb at 30 parts
per thousand salinity or with concentrations of other urea herbicides that
inhibited growth by 50 to 75%.
Braginskii et al. (1969) investigated more than 400 chemicals for
their suitability to control 4 species of algae, including Microcystis
aeruglnosa. M. pulveraea, Anabaena hassalii, and A. variabllis. While
most of the substances were inactive, monuron and several other herbicides
were active at 0.5 to 2.0 mg/1. None of the chemicals tested were 100%
effective, and most of the herbicides did not act upon blue-green algae.
Hoffman (1971) and Sweetser and Todd (1961) demonstrated that monuron is
toxic to algae (including Chlorella sp. and Euglena sp.) in the light, but not
in the dark, regardless of whether or not the growth medium contains energy
sources.
Sweetser (1963) in further studies on the mechanism of action, found
that the addition of monuron (no rate given) to a culture of Chlorella in
light resulted in the immediate inhibition of photosynthesis as determined
by the C0« fixation rate. When FMN (riboflavin-51-phosphate) was added to
the culture (rate not given), photosynthesis returned to the pre-inhibltion
level within a few minutes. When FMN was incubated with monuron (rates not
given) in flat-sided flasks exposed to white light (from a 150 W reflector
spot lamp for 5 hr, while heat from the lamp was filtered out), the reaction
mixture no longer inhibited CO- fixation by Chlorella. The author concluded
from these observations that FnN photochemically inactivated monuron both in
the presence and absence of algae. A high molecular weight compound which
was no longer antiphotosynthetic was isolated from the monuron-FMN reaction
mixtures. The isolated reaction product had a meling point of around 300°C
(with decomposition), and a molecular weight of 1,250 to 1,300. Nuclear Magnetic
58
-------
Resonance analysis showed only phenyl and CH» protons with no indication of
hydroxy protons. The ratio of phenyl protons to methyl protons was 200:318.
Analysis of the reaction product for p_-chloroaniline indicated a content of
only 3 to 5%, while a monuron control gave the theoretical 64%. On the basis
of this analytical data, it was not possible to assign a structure to the
monuron-FMN reaction product. The author speculates that several monuron
molecules condense to form a major portion of this molecule. The discovery
of this photochemical inactivation of monuron by FMN points to the possibility
that monuron may inhibit photosynthesis by interacting with FMN or a flavo-
protein in the photosynthesis pathway.
Vandermeulen et al. (1972) utilized the properties of monuron and a
closely related herbicide as selective photosynthesis inhibitors in a study on
algae-invertebrate symbiotic associations. Monuron at 99.35 ppm completely
inhibited photosynthesis both in intact branches and in suspensions of iso-
lated zooxanthellae from the reef-building coral Pocillopora damicomis, as
well as in 8 other marine coelenterates symbiotic with zooxanthellae, and in 1
marine gastropod symbiotic with functional chloroplasts. The inhibitory ef-
fect was totally reversible within 1 to 3 hr after removal of the inhibitor.
Monuron did not appear to affect the behavior of the various hosts. Monuron
also reyersibly inhibited light-enhanced calcification in P_. damicomis at
5 x 10~* M.
Field Studies - A search of the literature and of other data sources
failed to produce any reports in English-language primary publications on the
effects of monuron on lower aquatic organisms under field conditions. How-
ever, one report by Russian authors was found.
Pidgaiko and Shcherban (1970) studied the development of zooplankton and
zoobenthos in reservoirs treated with monuron for the control of algae, es-
pecially Microcystis aeruginosa and M. pulverea. Monuron was used in the form
of a granular formulation (rate of application not specified). During a 2-yr
period, the biomass of zooplankton and zoobenthos decreased by 75% as a '
result of oxygen depletion and direct toxic effects of monuron. The popula-
tions of Cladocera and Oligochaeta were suppressed to a greater degree than
those of Copepoda and Chironomidae.
The Federal Water Pollution Control Administration (1968) classifies
substituted urea compounds in "Pesticide Group B" as to their hazard to
marine and estuarine organisms. Pesticides in this category are charac-
terized as "generally not acutely toxic at levels of 1.0 mg/liter or less."
It is recommended that an application factor of 1/100 be used and, in the
absence of acute toxicity data, that environmental levels of not more than
10 Ug/1 be permitted. An acute toxicity factor must be established for each
chemical in the group to ascertain if it is not more toxic than related compounds.
In this system, pesticides are grouped according to their relative toxicity to
shrimp, "one of the most sensitive groups of marine organisms."
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Effects on Wildlife
Laboratory Studies - Heath et al. (1972) have calculated dietary LC--
values for monuron for 4 species of birds. The values were determined by
administering monuron in feed to bobwhite quail (Colinus virginianus),
Japanese quail (Coturnix coturnix japonica), ring-necked pheasants
(Phasianus colchicus), and mallard ducks (Anas platyrhnchos). Birds, 2- to 3-
weeks old, were fed the treated diets for 5 days followed by a 3-day observa-
tion period to detect chemical mortality induced beyond the treatment period.
Data from the study is summarized as follows:
Table 9. EFFECTS OF MONURON ON QUAIL, PHEASANT AND MALLARD DUCKS
No. of concen-
Species
Bobwhite quail
Japanese quail
Ring-necked
pheasant
Mallard Ducks
Birds per
LC
50,
trations tested concentration (ppm in feed)
3
3
5
3
6
14
9
10
> 5,000
> 5,000 (21% mortality at
5,000)
4,682 (95% conf. limit
3,902 - 5,746)
> 5,000 (10% mortality at
5,000)
Longer-term studies have been conducted on bobwhite quail and an unspeci-
fied species of pheasant (DeWitt et al. 1963):
Table 10. EFFECT OF MONURON ON BOBWHITE QUAIL AND PHEASANT
Percentage mortality Time
Monuron Number Length of at end of; to 50%
in diet of test period Test mortality
(ppm) birds (days) 10 days 30 .days period ..(days)
Species
Bobwhite quail
(1 to 2 days
of age at
start of
test)
Ring-necked
pheasant
(adult)
5,000
2,500
21
21
5,000 10
14
14
87
86
57
100
100
4
5
50
80
24
60
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Effects on Beneficial Insects
Atkins et al. (1973) summarized the results of toxicity tests of a large
number of pesticides and other agricultural chemicals to honeybees (Aplis mel-
lifera) in a laboratory procedure which primarily measures a pesticide's
contact effect. Pesticides are applied in dust form to groups of 25 bees per
test level, 3 replicates for each of 3 colonies, for a total of 9 replicates
per test level. The procedure permits determination of an LD value for each
pesticide in micrograms of chemical per bee.
Honeybees were exposed to monuron for 48 hr at 80°F (26.7°C) and 65%
relative humidity. Under these test conditions, the UJ50 of monuron was
110 yg/bee, which according to Atkins et al. would equal a rate of 110 Ib/acre
and places it in Group II, "moderately toxic to honeybees."
In their test procedure, Atkins et al. (1973) also determined the slopes
of the dosage-mortality curves and recorded a "slope value" in terms of probit
units for each pesticide tested. Pesticides with a slope value of 4 probits
or'higher can often be made safer to honeybees by lowering the dosage only
slightly. Conversely, by increasing the dosage only slightly, such pesticides
can become highly hazardous to bees. Monuron rated a very low "slope value"
of 0.78, indicating that very large changes in dosage rate would be required
to change its bee toxicity. This data indicates that monuron would be
moderately toxic to honeybees if rates exceeded recommended application rates.
Synergism of Insecticides with Monuron
Lichtenstein et al. (1973) have studied the synergistic effect of 4 herbi-
cides, including monuron, on the toxicity of 12 insecticides. Monuron was
tested against only 2 insecticides,"- an organophosphate and a chlorinated
hydrocarbon. Monuron had a statistically significant synergistic effect on
the toxicity of the-organophosphate to the fruit fly, Drosophila melanogaster,
and to the mosquito, Ades aegypti. In tests using the housefly, Musca domes-
tlca, monuron had a significant synergistic effect on the toxicity of the 2
insecticides.
Interactions wibn^Lower Terrestrial Organisms
Microflora -
Fungi and Actinomycetes - Murray et al. (1969) studied the degradation of
monuron and 4 other substituted urea herbicides by Aspergillus niger, A.
sydowi. and A. tamarii and the effects of urea nitrogen levels of 0, 45, 450
and 900 ppm on this process. The toxicity of monuron to the 3 Aspergillus
species was intermediate between 2 other herbicides of this type. Monuron
completely inhibited the growth of A. niger at 1,000 ppm, while A. sydowi and
A. tamarii made some growth at this concentration. At 10 and 100 ppm of mon-
uron, there was relatively little inhibition of the growth of A. niger as
61
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compared to monuron-free cultures. A. sydowi and A^. tamacii were less toler-
ant to these lower levels of monuron than A. niger. The higher nitrogen
levels resulted in delayed spore formation and changed the appearance of the
mycelial pad.
The degradation of monuron and the other substituted urea herbicides was
determined by growing isolates of the 3 fungi on both media containing the
herbicides at levels of 0, 5, 10, and 20 ppm. After incubation for 5 days,
the dry mycelial pads and the residual media were mixed thoroughly into
Eufaula sand (pH 5.7; 90% sand, 7% silt, 3% clay, 0.5% organic matter; ex-
change capacity 2.7 meq with low levels of available phosphorus and potassium).
Three successive plantings of cucumber were grown in 4-in square plastic pots
of this treated soil.' The same Eufaula sand was also used to determine the
phytotoxicity of monuron and the other herbicides as affected by soil organic
matter composition. In these tests, 1% by weight of 3 different combinations
of organic material were added to the Eufaula sand, representing high carbon-
low nitrogen, medium carbon and nitrogen, and low carbon-high nitrogen mix-
tures .
•
Monuron was more resistant to decomposition by the 3 Aspergillus species
than other herbicides of this type, especially at the 20 ppm level. The cu-
cumber plant yields increased significantly with increased soil organic
nitrogen levels without herbicide additions. All rates of monuron depressed
the cucumber plant yields. In this test series, monuron again was more resist-
ant to decomposition than the other substituted urea herbicides studied.
Lopez and Kirkwood (1972, 1974) studied the growth patterns of a fungus of
the genus Fusarium as affected by different concentrations of monuron and a
related herbicide. The fungus and 2 unidentified bacteria were isolated by
plating out small samples of a fine sandy loam which had been profused with
monuron at a concentration of 500 yg/ml for 2 weeks on Czapek's solution agar.
The 3 isolates were tested for their ability to use different concentrations
of the herbicides as sources of carbon. In the presence of 1 g/1 of
yeast extract, the fungus attained optimal growth at 10 and 20 ppm of monuron.
Without yeast extract, best growth was observed at 2 ppm of monuron. In the
latter test series, the fungus grew better in media containing 2 ppm of monuron
than in those containing none, as determined by colony diameter and CO- evolu-
tion. The authors suggest that the Fusarium species as well as the 2 unidenti-
fied isolated bacteria may be able to use monuron as a carbon source.
Lanzilotta and Pramer (1970) isolated an enzyme, identified as acylami-
dase, from Fusarium solani. The substrate range and affinity of the enzyme,
which was found capable of hydrolyzing an acetanilide pesticide, was investi-
gated. It was determined that the acylamidase had a high affinity for
acetanilides but was unable to hydrolyze monuron and several other herbicides.
Wallnofer et al. (1973) investigated the interactions between Rhizopus
japonicus and 4 phenylurea herbicides, including monuron. The fungus was
grown in a synthetic glucose medium on a gyratory shaker under aerobic condi-
tions at a temperature of 30°C, at pH ranging from 6.0 to 7.5. Under these
62
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conditions, li. japonicus demethylated monuron into the metabolite 3-(p_-chloro-
phenyl)-l-methylurea. Three related phenylurea herbicides were also dealkyl-
ated. The metabolites were identified by nuclear magnetic resonance and mass
spectrometric analysis. They were present after incubation for 1 week.
Hachimori et al. (1968) found that monuron and several other related
phenylurea herbicides inhibited the respiration of yeast mitochondria, while
2 uracil and 2 triazine herbicides were ineffective.
Based on an extensive review of the literature on interactions between
herbicides (and other pesticides) and the microflora, Audus (1970) concluded
that most herbicides, including the phenylureas, are without effect on fungal
populations at normal field rates. Actinomycetes are, in general, very
tolerant to phenylureas and other herbicides.
Audus further reported that the root rot of barley, a seedling disease
caused by Helminthosporlum satlvum, was alleviated by soil applications of
monuron (and several other herbicides). The mechanism of this effect was not
reported; however, it is believed that the herbicides may have altered the
pathogen's infectivity.
The fate of 4-chloroaniline, which is produced from monuron by photodecom-
position and through the metabolic process of certain plants (Smith and Sheets,
1967; Swanson and Swanson, 1968), has been studied by Kaufman et al. (1973).
The experiment was performed using a laboratory flask, not actual soil; only
one microbial species, the fungus Fusarium oxysporum, was used.
Kaufman et al. (1973) determined that the major pathway of Fusarium oxy-
sporum degradation of 4-chloroaniline was oxidation of the aromatic amine
group. A secondary pathway was acylation of the aromatic amine group. The
degradation scheme proposed by Kaufman et al. (1973) is shown in Figure 4.
Another compound, tentatively identified, but not shown in Figure 4, is
2-chloro-4-nitrophenol. The formation of this compound Implies migration of
the chlorine substituent. The production of the chloride ion was also detected
during the metabolism; Kaufman et al. (1973) note that as much as 98% of the
organically bound chloride was liberated after incubation periods of 10 to 12
days. All of the metabolites identified by these authors contained chlorine;
however, they detected two phenolic metabolites which were not characterized.
Bacteria - Hill et al. (1955) and Hill and McGahen (1955) demonstrated
that soil microorganisms play an important role in the decomposition of
monuron and other phenylurea herbicides in soils. By use of the dilution
plate technique, they found that monuron applied to agar medium at a concen-
tration of 250 ppm had no adverse effect on soil microbe populations. The
authors isolated bacteria species of Pseudomonas. Xanthomonas, Sarcina. and
Bacillus, and two fungi, Penicillium and Aspergillus, which utilized monuron
as the sole source of carbon. Other soil microorganisms were found which
were capable of oxidizing monuron if accessory growth factors found in organic
63
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materials, such as yeast extract, are present. Since such growth factors are
normally present in the soil organic or mineral matter, the authors conclude
that probably both types of organisms are active in the decomposition of
monuron under field conditions. The microorganisms studied are commonly found
in all agricultural soils.
Wallnofer (1969) studied the decompositon of monuron and several other
phenylurea herbicides by Bacillus sphaericus isolated from soil previously
treated with a methoxy phenylurea herbicide in a basal medium fortified with
3.7 mg of a vitamin mixture per 1,000 ml. Three methoxy phenylurea herbicides
were degraded by 1J. sphaericus within 1 week, whereas monuron and several
other N-alkyl (as opposed to N-alkoxy)-substituted phenylureas appeared to be
resistant to decomposition by B. sphaericus. In a series of additional studies,
Wallnofer and Bader (1970), and Engelhardt et al. (1971) studied the degrada-
tion of urea herbicides by several different strains of B^. sphaericus, and by
cell-free extracts of this organism. An enzyme preparation obtained from a
cell-free extract was found to be responsible for the hydrolysis of N1-methoxy
phenylurea herbicides. However, as in the studies with whole cells, the N1,
N'dimethyl phenylurea herbicides, such as monuron, were relatively resistant to
decomposition by the cell-free extracts.
Audus (1970) reports that monuron at normal field rates inhibited nitrifi-
cation (ammonia oxidation) in soil perfusion tests for at least 2 weeks. This
inhibition was accompanied by an accumulation of nitrite, suggesting that
Nitrobacter was more sensitive to monuron than Nitrosomonas. These findings
agree with earlier reports, including that by Quastel and Scholefield (1953)
who described monuron as a powerful inhibitor of soil nitrification. Likewise,
Otten et al. (1957) reported that monuron at normal application rates (1 to 5
Ib Al/acre) inhibited soil nitrification. However, Hale et al. (1957) reported
that at a concentration of 50 ppm, monuron had no noticeable effect upon nitri-
fying microorganisms.
Audus (1970) reports further that the phenylurea herbicides are without
effect except at very high concentrations far in excess of normal field rates,
on free-living nitrogen-fixing organisms, based on extensive studies on the
growth and metabolism of Azotobacter species and a few studies on Clostridlum.
Likewise, phenylurea herbicides did not have any adverse effects at normal
field rates on Rhizobia, on cellulolytic soil organisms, or on gross bacterial
numbers.
Goguadze (1968) studied the effects of herbicides on the development of
Azotobacter in the western Georgia region of the Soviet Union. Monuron applied
as a spray to an alluvial soil at the rate of 7.1 to 8.9 Ib/acre (8 to 10 kg/
ha) did not affect the development of Azotobacter above pH 5, but suppressed it
at pH 5. Chuderova and Zubets (1970) likewise reported that the application of
monuron (and of more than 20 other herbicides) to sod-podzolic soils during the
growing season had no significant effect on the nitrification rate of the
soils, nor on the number of nitrifying bacteria. All herbicides were applied
64
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at normal field rates recommended by the manufacturers. On the other hand,
Babak (1968) reported on laboratory studies which indicated that Azotobacter
chroococcum and A. galophilum isolated from various soils were sensitive to
monuron and to 11 other herbicides studied.
Shchetinskaya and Bagnyuk (1972) found that monuron at the rate of 5 to
40 mg stimulated the dehydrogenase activity of Pseudomonas fluorescens in the
absence of other energy sources, but not when glucose or peptone were present.
Algae - Pantera (1970) studied the effects of monuron and several other
urea and triazine herbicides on algae in the soil. Monuron and the other
herbicides were applied once a year during a 4-yr period at rates used in
field practice, and, in a parallel test series, at rates several times higher.
Among the herbicides studied, monuron was most toxic, while ethoxy phenylurea
herbicide and the 3 triazine herbicides had only negligible effects on the
algae at the high dosage rates.
Pillay and Tchan (1972) developed an algal bioassay method using
Chlorella and Chlamydomonas species to study the soil factors affecting the
toxiclty of herbicides. They found that organic matter adsorbed 18 times the
amount of herbicides adsorbed by clay. Among the herbicides studied, phenyl-
ureas were more toxic to algae than triazines. Within the phenylurea group,
monuron was less toxic to algae than 2 other herbicides.
Unidentified or Mixed Soil Microorganisms - Danuta (1967) studied the
effects of monuron and other herbicides on the oxygen uptake of unidentified
soil microorganisms, using the Warburg method. The herbicides were used at
normal field rates, and the treated soils were incubated in Warburg vessels
for 14 or 19 days. Neither monuron nor any of the other herbicides tested
had any effects on the oxygen uptake by the soil, or on the number of soil
microorganisms as determined by a routine plate method.
McClure (1970) investigated the effects of microbial substrates on the
degradation of monuron and other herbicides in soil. Small flats of composted
Norfolk dry. loam were treated with monuron at the rate of 1.5 Ib/acre. Double
strength Czapek-Dox broth and Difco nutrient broth (200 ml) were added to some
of the flats which were then incubated at 30°C for 7 or 21 days before plant-
ing with 5 different test plant species. In a second test series, flats were
incubated for longer periods of time, with additional broth treatments given
at biweekly intervals. The broth treatments accelerated the degradation of
phytotoxic residues of all herbicides studied, including monuron.
Polyvyannyi (1970) applied several herbicides, including monuron at 0.89
and 2.7 Ib/acre (1 and 3 kg/ha), to several different soils and studied the
effect of these treatments on the concentrations of nitrate, ammonium nitro-
gen, and the water-soluble organic matter. Observations on untreated con-
trols, freshly treated soil samples, and samples after 3 hr of autoclaving
showed that the herbicide treatments and autoclaving produced a similar effect
on concentration of nitrogen and water-soluble organic matter. The killing
65
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of soil microorganisms liberated their cell constituents into the soil solu-
tion. The herbicide treatments had no effects on the concentrations of nitro-
gen and water-soluble organic matter in previously sterilized soil samples.
Tulabaev (1971) studied the effects of monuron and several other herbi-
cides on the microflora of meadow soil. Monuron applied at the rate of 1.3 lb/
acre (1.5 kg/ha) decreased the number of Azotobacter and ammonia-fixing bac-
teria in the soil. Fungi and cellulose-assimilating bacteria were less af-
fected. In the monuron plots as well as in those treated with the other herbi-
cides, the number of weeds and the consequent loss of nitrogen and phosphorus
from the soil were decreased, and the yields of corn and cotton were improved.
. Akopyan and Agaronyan (1968) studied the effects of monuron and several
other herbicides on the soil microflora in a vineyard in Armenia. Monuron and
the other herbicides were applied by soil incorporation at the rate of 7.1 lb/
acre (8 kg/ha) prior to weed emergence. Counts of microorganisms in the 0 to
11.8 in (0 to 30 cm) soil layer showed that monuron had only a slight effect
on the soil microflora. There were no significant effects on the nitrifying
capacity of the soil.
Goguadze (1969) studied the change in the composition of the soil micro-
flora due to the use of herbicides in various stages of grapevine development
in alluvial soils. Monuron was applied at the rate of 7.1 Ib/acre (8 kg/ha)
to the soil, pH 6.0 to 6.5. In the early part of the season, the total quan-
tity of microorganisms in the treated area decreased, but fungi, actinomycetes,
and nitrogen-fixing organisms increased. Later in the growing season, several
bacterial species increased.
Pantera (1972) investigated the effect of high doses of monuron and
several other herbicides on selected groups of soil microorganisms. Among 4
herbicides studied in a 5-yr field experiment, monuron inhibited microbial
growth most strongly.
Microfauna - Fox (1964) studied the effects of monuron and 4 other herbicides
on the numbers of soil invertegrates in grassland soil. Monuron was applied
at the rate of 10 Ib/acre. Fourteen months after this application, the
following significant reductions were reported: wireworms (Elateridae) 87.5%,
millipedes (Diplopoda), 57%, earthworms (Lumbricidae), 43%, springtails (Col-
lembola), 64%, and mites (Acarina), 76% in the monuron-treated plots. Monuron
and several other herbicides almost eliminated grasses, but increased stands
of wild carrot (Daucus carota) and sheep sorrel (Rumex acetosella). The author
suggested that the major effects of the herbicides on the soil microfauna may
be indirect and attributable to changes in the floristic composition of the
treated grassland, although a combination of these indirect effects and direct
actions on the soil invertebrates cannot be excluded.
Edwards (1970) reviewed the effects of herbicides on the soil. He re-
ported that at the rate of 17.8 Ib/acre (20 kg/ha) monuron decreased the number
of millipedes and springtails in the soil. On the basis of the findings by
Fox (1964), Wojewodin (1958), and observations of his own, Edwards concluded
66
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that monuron and several other herbicides may affect the numbers of soil in-
vertebrates but, he pointed out, the direct effects of these herbicides on the
soil microfauna were never severe with monuron, and occurring only after very
large doses were applied to the soil.
Martin and Wiggans (1959) studied the toxicity of monuron to earthworms.
Test animals were emersed in monuron solutions for 2 hr. There was 10% mortal-
ity of earthworms at a monuron concentration of 1 ppm, 100% mortality at 100
ppm.
Van der Drift (1970) reviewed the effects of pesticides on the soil fauna.
He concluded: "Herbicides and fungicides, which are designed to control weeds
and fungal parasites, generally affect the soil fauna only to a limited de-
gree."
Residues in Soil
Laboratory Studies - Harris (1966) studied the adsorption, movement, and
phytotoxicity of monuron and several triazine herbicides in 4 different Mary-
land soils (Lakeland sandy loam, Wehadkee silt loam, Chillum silt loam, and
Hagerstown silty clay loam). All herbicides studied were least adsorbed on the
Lakeland sandy loam, and most highly adsorbed on either the Chillum silt
loam, or the Hagerstown silty clay loam. The rates of adsorption of monuron
on Chillum silt loam was at the low end of the range, while on the other 3
soils, it ranged intermediate between the 5 triazine herbicides included in
the tests. The movement of herbicides in the 4 soils was studied in 3-in
diameter columns that were filled to a depth of 1.75 in with soil treated with
the herbicides at the rate of 2 Ib Al/acre, topped by untreated soil to a total
depth of 7 in. Upward movement of water through these columns from a free
water supply was used to effect herbicide movement. After 5 days, the columns
were sliced into 1-in segments for bioassay, using oat seeds as a sensitive
indicator plant. Reduced growth of oats as compared with oats growing in seg-
ments from untreated columns indicated the presence of a herbicide. The rate
of movement of monuron was very similar to that of the triazine herbicides,
with the exception of one which remained predominantly in the lower 2 segments
in all soils.
The initial phytotoxicity of the herbicides in the 4 soils was studied by
applying a seizes of 6 concentrations of each herbicide to each soil to deter-
mine the concentration, in parts per million by weight, necessary to reduce
the fresh weight of oats by 50% (ED50). The EDeQ values of monuron were
intermediate between those of the trlazines. For all herbicides, the ED 's
were lowest in the Lakeland sandy loam and highest in the Hagerstown silty
clay loam. Harris concluded that phytotoxicity and movement of monuron (and
of the triazine herbicides studied) were inversely related to the extent of
soil adsorption. The adsorption of monuron was less affected by pH than
that of the other herbicides.
In further studies, Harris (1967) found that monuron ranged intermediate
between pesticides having the highest and lowest mobility.
67
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Bayer (1967) studied the effects of surfactants on the leaching of mon-
uron and several other substituted urea herbicides in a Yolo sandy loam. The
herbicides were applied at a rate equivalent to 10 Ib/acre to the top of soil
columns with a 2 in diameter and 20 in tall. Several surfactants at rates of
1.0 and 10.0% weight/volume were applied together with the herbicides. Simu-
lated rainfall equivalent to 5 and 10 in of water was applied at the rate of
5 in/hr as the leaching agent. At the end of 24 and 48 hr, the columns were
allowed to drain for 48 hr, then they were sectioned into 2-in segments and
bioassayed with oat seeds. Most of Bayer's tests were conducted with a pesti-
cide closely related to monuron; but in one comparative set of tests, it was
found that the leaching behavior of monuron was similar to that of the related
herbicide tested. Several surfactants nearly eliminated any downward movement
of the substituted urea herbicides. The author suggested that a sorption com-
plex of the substituted urea herbicide, the surfactant, and the soil may be
formed. Cationic surfactants containing the dilauryl moiety were most effec-
tive in reducing the downward movement of the herbicides, while related sur-
factants containg lauryl, dioctyl, and dlstearyl substitutions had little or
no effect on leaching.
Rhodes et al. (1970) studied the movement of monuron and several other
herbicides in soils by measuring their R_ (ratio of distance moved by a solute
to distance moved by the solvent front) values on thin layer (400 ym) soil
chromatograms. Four agricultural soils from different locations were selected,
i.e., muck from Florida; Muscatine brown silt loam from Macomb, Illinois; Key-
port silt loam from Newark, Delaware; and Cecil loamy sand from Raleigh, North
Carolina. The Freundlich isotherm constants (K-values) were determined in
soil-water systems. In terms of the mobility classes suggested by Helling and
Turner (1968), monuron may be assigned to mobility class 3 (R~ values ranging
from 0.35 to 0.64).
The effect of soil pH on the mobility of monuron and the other 4 herbi-
cides was studied in Keyport silt loam by Rhodes et al. (1970). Over a pH
range from 5.4 to 8.9, the mobility of monuron was not affected significantly.
An estimate of the lateral diffusion of the herbicides was made by dividing
the width of appropriate spots on TLC plates by the width of the applied spot.
The nonvolatile compounds with the highest mobility showed slightly greater
lateral diffusion than those with lower mobility.
y " '. r!
Helling (1971a) also used the soil TLC technique in studies of the
mobility of 40 pesticides, including monuron, in Hagerstown silty clay loam.
In this soil, the Rf value of monuron was 0.48, also placing,it into
mobility class 3 in the system of Helling and Turner (1968).
In a companion study (Helling, 1971b), the mobility of monuron and 11
other pesticides was determined in 14 different soils selected to include a
broad range in clay content (11 to 51%), organic matter content (0.1,to 8.0%),
and pH (4.3 to 7.7). For monuron, as well as for the other pesticides studied,
there was a general trend toward reduced mobility with increased soil organic
68
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matter content. The Rf values of monuron as determined by soil thin-layer
chromatography ranged from 0.38 in Berkley silty clay (8.2% organic matter) to
0.84 in Norfolk sandy loam (0.14% in organic matter). The average Rf of mon-
uron was 0.54.
Moyer (1972) and Mover et al. (1972) studied the adsorption and desorption
of monuron and a number of other herbicides with soil colloids, including mont-
morillonite, kaolinite, silt, and peat. The adsorption of monuron to mont-
morillonite was found to be reversible after a 24-hr adsorption period, as well
as after drying. With a peat preparation, monuron was adsorbed reversibly if
desorption was carried out immediately after adsorption. However, after dry-
ing, the monuron was Irreversibly adsorbed to the peat at 62 to 85% relative
humidity. The authors do not believe that degradation of monuron (or of the
other herbicides studied) could account for the irreversible adsorption._
Hurle and Freed (1972) investigated the effects of electrolytes on the
solubility and soil adsorption of monuron, 2 other substituted ureas, and 3
triazine herbicides. Their objective was not primarily to study adsorption
mechanisms per se, but to show the influence of electrolyte concentration on
the solubility and adsorption of these herbicides. The solubilities of monuron
and the other herbicides were determined in water and in solutions of ammonium,
potassium, and calcium chloride at ionic strengths of 0.3 and 0.6. All 3 salts
decreased the solubility of monuron (and of the other herbicides); increasing
the ionic strength resulted in further lowering of the solubility. By intro-
ducing monuron into the electrolyte solutions, the pH was lowered by about 1 pH
unit. The decrease in solubility of monuron (and of the other herbicides) in
the salt solutions, according to the authors, is simply a "salting out" ef-
fect. The salt ions attract around themselves the polarizable water molecules,
making the solution more polar and reducing the amount of water molecules
available.
The increased adsorption of these herbicides on soil in the presence of
rather high electrolyte concentrations is probably due mainly to the decrease
of the herbicide solubility. Adsorption studies on 2 monuron-related herbi-
cides suggested that under conditions of high salt concentrations in soil solu-
tion (such as those following fertilizer application or soil-drying), more
herbicide, expectedly, would be absorbed and more tightly bound. This could
result in a longer residual life of the herbicide in the soil and restricted
availability for weed control. However, under normal farm conditions, the
electrolyte cbncentration of the soil solution decreases due to uptake by
plants and/or dilution by precipitation. The findings and tentative conclusion
by Hurle and Freed (1972) may explain certain observations made in other labo-
ratory studies, such as those by Moyer (1972) and Moyer et al. (1972).
Van Bladel and Moreale (1974) investigated the adsorption of monuron and
another urea herbicide by 2 montomorillonite clays. They were a Volclay ben-
tonite from Wyoming with a lattice charge originiating from tetrahedral and
octahedral layers, and a typical montmorillonite from Camp Berteau, Morocco,
with a lattice charge only from octahedral layers. The authors determined the
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solubility of monuron at 3.5 and 26.5°C in plain water, and at different elec-
trolyte levels ranging from 0.005 to 3 Normal (N). The effect of salt concen-
tration on the solubility of both substituted ureas was almost negligible at
0.1 N, but pronounced at 1 N, and even more so at 3 N. Salt concentration had
little or no influence on the adsorption of monuron by the clay minerals up to
an ionic strength of approximately 0.5 to 0.1 N; above that range, the adsorp-
tion increased and became very dependent on the ionic strength. The adsorption
of both herbicides was greater on hydrogen-saturated montmorillonite than on
sodium-, calcium-, or magnesium-saturated montmorillonite. In general, monuron
adsorption was greater than that of the other herbicide tested. Adsorption of
both chemicals was lower on the Camp Berteau clay which had only octahedral
substitution.
Briggs (1969) investigated the relationships between the molecular struc-
ture of herbicides and their sorption by soils. Sorption isotherms were deter-
mined for 22 substituted phenylurea herbicides, including monuron, by a wet
slurry technique on 4 neutral Rothamsted soils, containing 1 to 4% organic
matter. The substituted phenylureas yielded a linear relationship between the
log of the partition coefficient and Hammett's sigma constant for meta- and
para-substituents in the phenyl ring. Even better fit was obtained by using
a combination of the sigma constant and the Taft constant for substituents of
the side-chain nitrogen. The author concludes that for phenylureas with short
alkyl side chains, ring deactivation by ring substituents, or by replacement of
a methyl group on the side-chain nitrogen by hydrogen or methoxy, appears to be
the factor controlling sorption, possibly through charge-transfer bonding to
activated sites on organic matter.
Kazarina (1965) investigated the translocation of monuron in soil. Air-
dried samples of several different soils were studied in laboratory soil column
experiments. Column surfaces were treated with monuron at a rate equivalent to
4.0 Ib/acre (4.5 kg/ha), and the soil moisture was kept at 40 and 70% of water
capacity for 1 month. Oat bioassays of soils from different column layers
indicated that at 40% soil moisture, monuron remained within the upper 1.0 in
(2.5 cm) of the soil surface in both soils, while at 70% of water capacity,
monuron penetrate;! to about 3.0 in (7.5 cm) in the loamy sand, and to about
2.0 in (5.0 cm) in the medium sandy loam. However, in both soils the majority
of the monuron applied remained in the surface soil layer. When simulated
rainfall was applied to the same soil columns, almost all of the monuron re-
mained in the,0 to 1.0 in (0 to 2.5 cm) layer following irrigation with 50 ml
of water. Following irrigation with 200 ml of water, the major portion of the
monuron applied still remained in the surface soil layer, but traces were found
in deeper soil layers.
Spirldonov and Kamenskii (1971) investigated the stability of monuron in
5 different soils in relation to soil temperature, humidity, and oxygen supply.
The phytotoxicity of monuron (applied to soil samples at the rate of 3 mg/kg)
to oats declined more rapidly when the treated soils were incubated at 40 to
60°C with high humidity under anaerobic conditions, than when incubation oc-
curred at 0 to 30°C under aerobic conditions. The different soil types studied
had little effect on the loss of phytotoxicity of monuron.
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Sheets (1964) reviewed known facts concerning the disappearance of
monuron and other substituted urea herbicides from soil. Bis presentation in-
cludes information available from approximately 1965, although there is lit-
tle specific information on monuron. However, many studies on monuron's dis-
appearance from soil have been carried out since that time.
Field and Greenhouse Studies - Hill et al. (1955) studied the persistence of
monuron and a related'urea herbicide under field conditions over a 2-yr period
in plots established on silt loam soils in Delaware and Louisiana, on a loamy
sand in North Carolina, and on a sandy soil in Florida. When monuron was ap-
plied once at the rate of 1 Ib/acre, 84 to 85% of the applied rate disappeared
within 12 months from sand, loamy sand, and silt loam soils. Following one
application of 2 Ib/acre of monuron, 89 to 98% of the applied rate disappeared
from the same soils within 12 months. When a second application of monuron at
1 Ib/acre was made after 12 months to the plots treated the preceding year at
1 Ib/acre, 69% of the total quantity applied disappeared within 8 months after
the second application in the silt loam (Louisiana) plots; 73 and 19% of the
combined rate disappeared within 12 months after the second application in the
sandy (Florida) and sandy loam (North Carolina) plots, respectively. When a
second application of monuron at 2 Ib/acre was applied to plots that had re-
ceived 2 Ib/acre of monuron the preceding season, 76% of the combined rate
disappeared within 8 months after the second application of the silt loam
plots, and 71% within 12 months after the second application in the sandy
loam plots. The overall rate of disappearance of monuron in all plots and
at all application rates was 83% during a 12-month period. In all tests,
phytotoxic concentrations from 1 and 2 Ib/acre applications disappeared
from the treated soils within 4 to 8 months after application. A 4 Ib/acre
application was reduced to nonphytotoxic levels in cultivated soils 12 to 16
months after the initial application.
In a lysimeter leaching study carried out in the greenhouse, monuron was
applied to the surface of 8 in diameter columns 36 in tall, at the rate of 10
Ib/acre; the columns were leached with the equivalent of 72 in of simulated
rainfall, applied at the rate of 1 in/day for 5 days. After 2 rain-free days,
1 in of rainfall per day was again applied for 5 days, and the same procedure
repeated until the total amount of 72 in had been applied over a period of ap-
proximately 90 days. Leachate samples were collected, and upon completion of
the leaching phase, soils were removed from the lysimeters in separate 4 in
layers and analyzed. Parallel tests were carried out in 11 different soil
types from 7 locations throughout the United States. At the conclusion of the
test, the amounts of monuron remaining in the soils varied from 4 to 62%; those
found in the leachate varied from 0 to 56%; those unaccounted for varied from
38 to 85%. The authors concluded that leaching can occur under conditions of
extremely high rainfall on a porous soil. However, under field conditions and
at application rates of 1 to 2 Ib/acre, removal of monuron from the soil by
percolating water is not regarded as a major cause of disappearance because
essentially all of the monuron recovered upon sampling is found in the upper
0 to 4 In layer of soil.
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Based on these findings, combined with the results of studies on the
biological degradation of monuron reviewed in the preceding subsection, Hill
et al. (1955) concluded that the microorganisms are a primary factor in the
disappearance of monuron residues from soil. Preliminary observations from
chemical studies indicate that hydrolysis or oxidation of monuron proceed slowly
at ambient temperatures. Photodecomposition can occur and may be a significant
factor in the disappearance of monuron residues from soil when little rainfall
occurs after application and the chemical remains on the soil surface.
Rahn and Baynard (1958) investigated the persistence and penetration of
monuron in asparagus beds in Delaware on a loamy sand soil using the oat bio-
assay technique for detection of monuron residue. In a 3-yr study, monuron
did not persist from one year to the next when applied twice annually at the
rate of 1.6 Ib/acre. When twice this rate was used, an estimated 0.3 to 0.4
Ib/acre of monuron persisted from one year to the next, but there was no ac-
cumulation. Monuron disappeared more rapidly following the second application,
applied in mid-summer, than following the spring application. Following the
mid-summer application, 36% of the quantity applied (1.6 Ib/acre) disappeared
during the first month, while only 14% of the same quantity applied in the
spring disappeared during the first month. Small quantities of monuron (maxi-
mum 0.2 Ib/acre) penetrated to the 4- to 8-in soil horizon at all rates used.
Monuron residues had completely disappeared from this soil layer by 1 November.
Cultivation accelerated disappearance of monuron from the treated soil. The
herbicide disappeared more rapidly from soils with higher organic matter con-
tent. In periods of below-normal rainfall, irrigation slightly accelerated
the disappearance of monuron from the top 4 in of soil, while it did not in-
crease movement to the 4- to 8-in soil layer. When rainfall was near normal,
irrigation had no effect on persistence or penetration of monuron.
Welker and Brogdon (1972) investigated the effects of continued use of
monuron and 8 other herbicides. This test was conducted in a Freehold sandy
loam with an organic matter content of 1.6%. Monuron was applied at the rate
of 2.2 kg/ha (about 2.0 Ib/acre) either once or twice each year for 7 consec-
utive years. Monuron and several other herbicides gave excellent weed control;
1 application of monuron was as effective for weed control during the cutting
season as 2 applications, but weed control in the fall was improved by making
a second monuron application. There was no indication that the continuous use
of monuron (or of any of the other herbicides studied) resulted in a build-up
of residues in the soil or in plants, or in any deleterious effect on the crop
yield.
Shadbolt and Whiting (1961) compared the persistence of monuron and a
related herbicide in Romona sandy loam under field conditions. Monuron was
applied at the rates of 2, 4, and 8 Ib/acre. Fifty percent of the quantities
applied disappeared from the treated soils in 4 to 5 months, whereas 8 to 9
months were required for the other herbicide tested to decline to 50% of the
rate applied.
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Arle et al. (1965) and Hamilton and Arle (1968) reported on extensive
investigations on the disappearance of monuron and several other herbicides
from irrigated soils in the southwestern United States. Permanent field plots
were established at 2 locations in Arizona, and one in California. In tests
in a silt loam soil at Tolleson, Arizona, monuron and a related herbicide were
applied to cotton as layby treatments each year from 1954 to 1962. The herbi-
cides were applied as a broadcast, directed spray at rates of 0.8 and 1.6 lb/
acre. The plots were flood-irrigated 8 times during each growing season.
Annual irrigation totaled 40 in/yr, and 4 of the irrigations, totaling 16 in
of water,-occurred after application of the herbicides. Injury to cotton in
the form of chlorosis of the foliage was noticed each year after the annual
application of monuron, persisting for 4 to 5 weeks after treatment. In 1958
and each year thereafter, characteristic symptoms usually associated with
monuron injury were noticed on the foliage of a few cotton seedlings in plots
treated the previous 4 seasons at the higher rate of monuron. After a period
of retarded development, these plants resumed normal growth. Monuron did not
affect the yield of cotton in the first 7 yr of this test. In the eighth and
ninth yr, the yield from plots treated annually with monuron at 1.6 Ib/acre
were lower than those from untreated plots.
Arle et al. (1965) conducted a similar experiment on sandy loam in Ari-
zona for 5 successive seasons (1957 to 1961). Monuron was applied at the rate
of 1 Ib/acre each year before the fourth irrigation. There was no evidence of
injury to cotton seedlings from carry-over of monuron from the previous season,
and there were no adverse effects on cotton yield from the annual monuron
treatments compared to untreated controls. A third set of field tests were run
on sandy loam in California. Monuron was applied at rates of 1.0 to 1.5 lb/
acre as a broadcast, directed spray to furrow-irrigated cotton at layby.
Herbicide applications were made annually during July or early August from
1956 through 1961. After harvest of cotton each year, the experimental area
was seeded to barley. During the study period, there were no apparent effects
on emergence or development of cotton seedlings due to carry-over of monuron
residues from the previous year's application, and cotton yields were not ad-
versely affected by either rate of monuron. Stands of barley sown in the
winter after cotton harvest were reduced by both rates of monuron in all ex-
cept one year. Monuron caused more injury to winter-sown barley than a
related herbicide tested in parallel plots.
Dawson et al. (1968) studied the residues of 3 urea herbicides, including
monuron, remaining in a furrow-irrigated vineyard on Warden silt loam soil.
Monuron (from a wettable-powder formulation) was applied at the rate of 2.5
lb Al/acre annually for 6 yr (1958 through 1963). The herbicides were sprayed
under the trellises of Concord grapes each year in late February or early
March. For the first 4 yr, monuron was also applied (to different plots) at
the rate of 7.2 lb Al/acre, but this treatment was discontinued after 1961
because of severe injury to grape vines. Shortly after application, the
study herbicides were incorporated into the upper 2 in of soil by hand tools
or a small, power-driven rotary tiller. After the last of the 6 annual
applications, residues remaining at different depths were determined by the
oat bioassay technique. Monuron residues found were as follows:
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Total
Residues - ppm weight Ib/acre
Lb/acre Soil depth - inches upper
Yearly Total 0-2 2-4 4-8 8-12 12 in
2.4* 14.4 1.49 0.75 0.09 0.00 1.6
7.2** 28.8* 0.54 0.22 0.13 0.06 0.8
* There was a 1 yr period between the last application of monuron at this
rate and the collection of samples for residue analysis.
** Monuron at 7.2 Ib/acre was not applied at the last 2 of the 6 scheduled
annual application dates. There was a 3 yr period between the last
application of monuron and the collection of samples for residue
analysis.
This data shows that most of the residual herbicide was located close to
the soil surface. The total quantity of monuron remaining 1 yr after the
last annual application at the rate of 2.4 Ib/acre amounted to two-thirds of
one annual application. Three years after the last of 4 annual applications
of monuron at 7.2 Ib/acre, the residue remaining had been reduced to 11% of
one annual application. These findings indicate that persistence of phyto-
toxic residues for at least 1 yr after application can be expected under the
conditions of this experiment. Injury to sensitive plant species may occur
following annual applications of monuron. Therefore, the authors recommended
that monuron should not be used on a tolerant crop the season before rotating
to a sensitive crop, especially in fields under furrow irrigation.
Hill (1971) reported on a long-term study on the rate of disappearance of
monuron initiated at Newark, Delaware, in the spring of 1952. The test area
was on a Keyport silt loam with restricted Internal drainage, with average an-
nual rainfall of 40+ in. Experimental plots were treated with monuron at the
rate of 2.0 Ib/acre each spring for 18 consecutive years, for a total applica-
tion of 36 Ib. Each year, the soil was disced to a depth of 4 in and rolled
for seedbed preparation. Prior to retreatment each year, soil samples were
taken at 0 to 4, 4 to 8, and 8 to 12 in depths and bioassayed with oats in the
greenhouse. The results indicated that no phytotoxic residues were present in
the soil as determined by normal growth of the oats. Hill concludes that
there was no accumulation of phytotoxic levels of monuron under these condi-
tions. Less than 1 Ib/acre of monuron was present in the soil after 18 annual
treatments of monuron at the rate of 2 Ib/acre/year.
Upchurch et al. (1968) studied the soil sterilization properties of
monuron and 3 other herbicides on a Norfolk sandy loam soil under field
conditions in North Carolina. The purpose of these tests was to identify
herbicides and application parameters that would result in reasonable soil
sterility without excessive lateral herbicide movement. Monuron and the
other herbicides were applied initially to test plots at 40 Ib/acre. This
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application was followed by one of the following retreatment schedules: no
retreatment, retreatment at 20 Ib/acre annually for 3 yr, or retreatment in
the second or third year only. Initial treatments were made in April 1960,
and retreatment each spring thereafter as required by the retreatment schedule.
Of all the herbicides studied, monuron acted most rapidly. A single reapplica-
tion of 20 Ib/acre of any of the 3 herbicides was adequate to restore a reason-
able level of vegetation control, regardless of whether the retreatment oc-
curred 1, 2, or 3 yr after the initial 40 Ib/acre treatment. Annual retreat-
ment was necessary to maintain a continuously high level of sterility. All 3
herbicides caused injury to vegetation downslope from the treatment area.
Lateral movement of monuron was less severe than with other pesticides tested.
Isensee et al. (1973) initiated an investigation in 1954 at Beltsville,
Maryland, in order to determine the initial and long-term results of applica-
tion of massive quantities of monuron and several other herbicides. Field
plots 4m in size, surrounded by concrete borders 0.2 m wide by 0.9 m deep,
were established, with concrete borders projecting about 20 cm above the plot
surface to prevent lateral movement of herbicides or revegetation from adja-
cent plots by rootstock propagation. The soil in the area was a Matapeake
silt loam (pH 5.3, organic matter 1.5%, sand 38.4%, silt 49.4%, and clay
12.2%). Monuron was applied in May of 1954 at rates of 56, 112, and 224 kg/ha
(about 50, 100, and 200 Ib/acre), rates exceeding recommended agricultural
rates by 10 to 100 times. Vegetative responses were determined 1, 2, 3, and
15 yr after treatment.
After 3 yr, vegetation covered 80 to 89% of the soil surface in the
monuron-treated plots. The authors concluded that under the conditions of this
test, massive rates of monuron (as well as of most of the other herbicides
studied) dissipated in 1 to 3 yr. Bioassays in 1968, 14 years after the treat-
ment, Indicated no residual phytotoxicity in the monuron-treated plots. Among
the phenylurea herbicides included in this study, monuron was the second most
rapidly dissipated.
The authors suggest that several processes, including microbial metabolism,
adsorption to mineral and organic colloids, volatility, and leaching may ac-
count for this dissipation. Based on adsorption characteristics, monuron is
one of the most available herbicides tested for microbial degradation and was
consequently degraded more rapidly than 2 other related herbicides. The
authors further observed that the water solubilities of monuron and the 3
other phenylurea compounds appeared to be positively correlated with their
residual phytotoxicity.
Pimentel (1971) reported that monuron applied at the rate of 1 to 3 lb/
acre persisted for 3 to 6 months in a moist loam soil with little or no
leaching under summertime conditions in a temperate climate. Holly and Roberts
(1963) found that monuron applied at 0.5 Ib/acre persisted in the soil for 28
weeks. Birk (1955) reported that, following application at the rate of 20 lb/
acre, monuron residues persisted in the soil for 3 yr.
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Several additional greenhouse and field soil-persistence tests with mon-
uron, conducted mostly in the 1950's, were reviewed by Sheets (1964). The
results of these tests are generally in agreement with the field observations.
Among the phenylurea herbicides, the rate of degradation of monuron was usually
intermediate.
Mullison (1970), in a review of the significance of herbicides to non-
target organisms, concluded that 80% of the quantities of monuron and related
herbicides applied at field rates were found to have disappeared during the
year following application in most climatic and edaphic conditions. Repeat
treatment disappeared at about the same rate as the original treatments. The
use of monuron in citrus orchards or asparagus plantings did not result in
residue buildup in the soil, but if the land use were to be changed, and if
it were to be planted immediately with a sensitive crop, there probably would
have been a risk of damage. The residual phytotoxicity of monuron in the
field, as summarized in this review, lasted 5 to 6 months following applica-
tions at 2 to 4 Ib/acre, and 12 months following application at 4 to 6 Ib/acre.
In the greenhouse, residual phytotoxicity persisted for 1 to 3 months following
applications at 2 to 5 Ib/acre.
Several Russian investigators also studied the soil persistence of monuron
under different conditions. Kuznetsov and Mikhailov (1969) reported on the
residual action of monuron and several other herbicides in the second and third
year after the planting of an apple tree nursery in a peat soil. Monuron was
applied (rate not specified) before planting of the apple seedlings. Some
residual herbicidal efficacy was retained in the third year, but monuron was
less persistent than another herbicide tested.
Khubutiya and Gigineishvili (1971) studied the residual effectiveness of
monuron applied in the early spring at the rate of 8.9, 12.0, and 14.2 Ib/acre
(10, 13.5 and 16 kg/ha) in citrus plantations. Monuron (and several other
herbicides studied) penetrated 15.7 in (40 cm) into the soil during the first
2 months after application. Small residues were detected in citrus leaves
following the 2 higher application rates. Monuron did not accumulate when ap-
plied at the rate of 8.9 Ib/acre for several years in succession.
Spiridonov, Kamenskii and Yakolev (1970) and Spiridonov et al. (1970,
1972) studied the effectiveness and persistence of monuron and several other
herbicides under humid, subtropical conditions in different soils. They found
that monuron was rapidly leached down into the 31- to 39-ln (80 to 100 cm)
soil layer in "red-earth soil" under intensive rainfall; only 0.7 to 1.4 lb/
acre (0.8 to 1.6 kg/ha) remained in the upper 0- to 4-in (0 to 10 cm) soil
level 110 days after application (initial rate of application not given).
Within an additional 40 days, residues of monuron disappeared from the soil
due to the action of soil microorganisms. Monuron showed no significant toxic
effects on soil bacteria, fungi, or cellulolytic microorganisms. 'However,
within 40 to 70 days of application, both herbicides temporarily reduced the
activity of the soil microflora and that of several soil enzymes. Increased
soil concentrations of available potassium, nitrogen and phosphorus were ob-
served in the soil during this period, except under weed-free sections of the
soil where there were no effects on the mobility of these nutrients.
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In meadow-bog soil, monuron applications of 7.1 Ib/acre (8 kg/ha) were
completely inactivated in 110 days. When applied at 10.6 and 14.2 Ib/acre
(12 and 16 kg/ha), the herbicides were inactivated in 150 days by the combined
action of microorganisms and chemical hydrolysis. The herbicide treatments
did not affect the total numbers of bacteria or oligonitrophils in the soil
but, during the period 40 to 70 days after treatment, the total number of soil
fungi decreased, while the activity of cellulose-metabolizing microorganisms
increased.
Spiridonov, Kamenskii and Yakolev (1970) investigated the reasons for the
rapid loss of herbicidal activity of monuron and a related herbicide in water-
logged meadow and red subtropical soils. The leaching rate of both herbicides
was 2 to 3 times greater in the subtropical red soil than in soils in temperate
climate. Following applications at 8.9 and 17.8 Ib/acre (10 and 20 kg/ha) ,
both herbicides penetrated to a depth of 15.7 in (40 cm) in the water- logged
meadow soil, and to 19.7 to 27.6 in (50 to 70 cm) in the red soil in 1.5 to 2.5
months. The authors contended that high moisture saturation and temperature
during the 5 to 6 months of the growing season promoted intensive microbial
degradation of monuron.
Residues in Water
According to Hurle and Freed (1972) , the solubilities of monuron and 2
other herbicides (in parts per million) at 25°C in water and in solutions of
3 different electrolytes at 2 different ionic strengths of each are as follows:
H20 (pH 5.7) KC1 (pH 4.7) NH4C1 (pH 4.5) CaClg (pH 4.5)
Ionic Strength Ionic Strength Ionic Strength
.03 _ .06 .03 _ .06 .03 _ .06
Monuron
solubilities: 262 220 195 228 217 226 215
It is noteworthy that the various electrolytes decrease the water solu-
bility of monuron as well as of the 2 related herbicides, as already pointed
out above in regard to the influence of this effect on the adsorption of these
herbicides in the soil.
E. I. du Pont de Nemours and Company (1972) reported that the water solu-
bility of monuron is approximately 230 ppm at 25°C in distilled water.
Frank (1966) studied the persistence and distribution of monuron and a
related herbicide in an aquatic environment. Objectives were to determine the
distribution of the herbicides between soil and water, and their persistence in
water and submersed soil. The soil used in the study was an amorphous deposit
from a local irrigation canal consisting of 17% clay, 47% silt, 36% sand, and
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2.31% organic matter. Air-dry soil was placed in metal tubs 17 in high with a
diameter of 22 in and covered with 6 in of water. After allowing the tubs to
stabilize for 1 month, wettable powder suspensions of the herbicides were
sprayed over the water surface at a rate equivalent to 40 Ib/acre. Samples of
water and soil were taken from each tub at intervals of 1, 2, 4, 8, 16, 32, 64,
and 128 weeks after treatment and analyzed chemically for herbicide residues.
Appreciable loss of monuron did not occur until 16 weeks after treatment, and
the disappearance rate was greatest between the sixteenth and thirty-second
week during which 40% of the monuron was lost. When about 50% of either herbi-
cide was lost, their disappearance continued at a reduced rate until the end of
the experiment. Approximately 15% of the monuron, and 39% of the other herbi-
cide applied, remained after 128 weeks. More monuron was found in the water
than in the soil during the first 42 weeks. After that time, most of the
monuron was found in the soil, primarily in the top 4 in. Monuron moved down
in the soil more readily than the other herbicide tested. Both herbicides
permeated the soil very rapidly, within the first week after treatment. The
author points out that many submersed soils, including the soil used in his
study, seem to have much of their pore space filled with gases. Evaporation
from the soil solution, followed by diffusion through the gas-filled pore space,
may have accounted, at least in part, for the rapid transport of the herbicides
to a depth of 8 in. According to Frank, "the total quantities of monuron
recovered from water exceeded those recovered from soil throughout the first 16
weeks of sampling."
Eichelberger and Lichtenberg (1971) investigated the persistence of mon-
uron and a number of other common pesticides in raw river waters over an 8-
week period. Aliquots of 10 yg/1 of monuron from a freshly prepared 0.1%
solution in acetone were injected into samples of raw river water from the
Little Miami River, a relatively small stream receiving domestic and indus-
trial wastes and farm runoff. The dosed raw river water was kept in the
laboratory in closed glass containers at room temperature and exposed to
natural and artificial light. Under these conditions, 80% of the original
concentration of monuron was recovered at 0 time, 40% remained after 1 week,
30% after 2 weeks, and 20% after 4 weeks; no monuron was detected after 8
weeks. The only other phenylurea herbicide included in these tests disap-
peared more rapidly than monuron; 20% of the applied rate was still present
after 2 weeks, and 0 after 4 weeks.
Mikhailov (1967) studied the physical and chemical properties of monuron
and a related urea herbicide to establish an experimental basis for permissible
concentrations of these herbicides in reservoir waters. Monuron could be
detected by smell at 5 mg/1, and by taste at 6.6 mg/1. The smell was very
stable. Monuron increased the biological oxygen demand (BOD). Monuron began
to inhibit ammonification and nitrification processes at 25 to 50 mg/1. Based
on these properties, and on the acute and chronic toxicity of monuron to
laboratory rodents, the permissible concentration was established at 5 mg/1
for monuron.
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Bersonova (1967) studied the effects of monuron applied in irrigation
water on the yield of cotton being irrigated with the treated water in an
experiment simulating field conditions. Cotton plants grown in large pots
were watered with aqueous solutions of monuron at 1.04, 0.44, and 0.22 mg/1.
Plants watered with herbicide-free water served as controls. The higher con-
centrations of monuron caused some growth retardation. The cotton yield was
decreased only by the highest concentration of monuron; it was not significantly
different from the controls in all other treatments. The author concluded that
the growth and development of cotton plants would not be affected by concentra-
tions of monuron that would be used in field practice.' Therefore, irrigation
water could be used for irrigation of cotton plants while the irrigation system
is being treated with herbicides.
Some researchers feel that in order to determine what photo conversions
are possible in the environment, photosensitization should not be ignored, and
that chemicals in the environment obviously do not exist in isolation. Trans-
location through plants or dispersion in aqueous media that contain micro-
organisms enhance the possibilities of contact with photosensitizers such as
flavins and chlorophylls.
As reported in the subsection on lower aquatic organisms, Sweetser (1963)
found that FUN caused photochemical inactivation of monuron (and of other
substituted phenylureas).
Residues in Air
Vengerskaia and Rur (1969) developed a method for the determination of
small quantities of monuron in air, based on the property of urea derivatives
to hydrolyze quantitatively at elevated temperature with the formation of
aromatic amines. Standard solutions of monuron (10 to 100 yg/ml) are placed
in colorimetric test tubes to which alcohol and alkali are added. Upon com-
pletion of hydrolysis, diazotization is effected in an acetate buffer solution
with a mixture of potassium nitrite and bromide. After combining the reaction
products in an alkaline medium with alphanaphthol, the monuron content is
determined photometrically. According to the authors, the method is simple,
sufficiently sensitive, and applicable to studying working conditions when
monuron is being applied to the soil. However, no examples of practical ap-
plication of the method were included.
Hill (1971) reported that the vapor pressure of monuron is extremely low,
for example, 3.4 x 10~ mm Hg at 50°C. He pointed out that water is 30 million
times more volatile than monuron. 'Thus, Hill concluded that loss of monuron
from the soil into the atmosphere by volatilization is negligible.
Residues in Nontarget Plants
Brandes and Heltefuss (1971) reported that winter and spring wheat showed
an increased incidence of mildew (Erysiphe graminis) after application of
-------
monuron, another urea herbicide, and triazine herbicides. When this obser-
vation was followed up in greenhouse experiments, it was found that treatment
of infected wheat with these herbicides resulted in a reduction of IS. graminis
and of another fungal pathogen of wheat, Cercosporella herpotrichoides. The
incidence of mildew on herbicide-treated wheat in the greenhouse approached
that of untreated control plants during the early stages of development of the
plants, but was higher in the herbicide-treated plants during the blooming
stage. The weight and mildew incidence of herbicide-treated wheat during
the early stage was increased by supplementing the plants with glucose, or by
exposing them to higher 'light intensities. Further herbicide treatment de-
creased the mildew incidence under all conditions. The authors contended that
the difference in disease incidence was related to changes in the physiologi-
cal conditions of the host plant induced by the herbicides.
Bourke et al. (1964) studied-the effect of monuron on the metabolism of
glucose in pea roots by means of C-labeled glucose. Monuron was found to
slightly inhibit both the pentose cycle and glycolysis. Of the two pathways,
the pentose cycle was more strongly inhibited. Monuron appeared to have no
effect on anabolic reactions and an insignificant effect on catabolic pro-
cesses.
Frear and Swanson (1972) isolated 2 polar 0-glucoside metabolites of
monuron-14C from cotton leaves. The metabolites identified as 3-D glucoside
of 3-(-4 Chlorophenyl)-l-hydroxymethyl-l-methylurea and 3-(4-Chlorophenyl)-
1-hydroxymethylurea provide direct evidence for the formation of N-hydroxy-
methyl intermediates in the oxidative N-demethylation of substituted phenyl-
urea herbicides in higher plants. In the same paper the authors reported
that in vivo and in vitro tests failed to demonstrate any significant aniline
metabolites. This agrees with the work of Geissbuhler (1969). The authors
concluded that results from previous studies, notably, Smith and Sheets (1967)
and Swanson and Swanson (1968) that demonstrated the degradation of substituted
phenylurea herbicides in higher plants may have reflected impurities in the
sample or photochemical or microbial degradation before absorption by plant
tissues.
Bioaccumulation, Biomagnification, and Environmental Transport Mechanisms
Only one paper on the uptake of monuron has been found. Komarovsky (1972)
applied "Monurox" (10% monuron, 10% TCA) to artificial ponds containing
Leuciscus idus, Rutilus rutilus,. and Leuciscus cephalus at a rate of 40 kg/ha
AI (20 kg/ha of monuron) equivalent to approximately 17.88 Ib/acre of monuron.
The concentration of monuron in the water ranged from 0.1 to 0.3 mg/1. After
5 days, R. rutilus had monuron concentrations of 15 ppm in the heart and 0.42
ppm in the gills; after 60 days, 0.13 ppm monuron was found in muscle. L. idus
muscle contained concentrations of monuron of 0.95 ppm after 10 days, 0.30 ppm
after 15 days, 0.59 ppm after 18 days and only trace amounts after 60 days;
after 15 days 1.2 ppm monuron was found in the skin. In L. cephalus, brain
tissue contained 5.3 ppm monuron after 5 days, and muscle contained 1.5 ppm
after 15 days.
80
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Compared to other pesticides, monuron appears to be relatively resistant
to photodecomposition by itself. However, one report indicates that it is
readily photodegraded in the presence of FMN, a photodesensitizer. In another
study, £-chloroaniline was tentatively identified as one of several minor
photodegradation products of monuron. Other tests showed that the FMN-sensiti-
zed photolysis of _p_-chloroaniline yielded 4,4'-dichloroazobenzene and 4-chloro-
4'-(4-chloroanilino)azobenzene, but this photolysis did not take place in the
absence of FMN. No reports were found on the possible occurrence, rate or sig-
nificance of these transformations under field conditions.
81
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90
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PART II. INITIAL SCIENTIFIC REVIEW
SUBPART D. PRODUCTION AND USE
CONTENTS
Registered uses of Monuron 92
Federally Registered Uses 92
State Regulations 93
Production and Domestic Supply 98
Volumfe of Production 98
Imports 98
Exports 98
Domestic Supply 99
Formulations 99
Use Patterns of Monuron in the United States 100
General 100
Agricultural Uses of Monuron 100
Nonagricultural Uses of Monuron 100
Monuron Uses in California 101
Monuron Usage in Arizona 103
References 106
91
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This section contains information on the registration and on the produc-
tion and uses of monuron. The section summarizes rather than interprets data
reviewed.
Registered Uses of Monuron
Federally Registered Uses - Monuron is a broad-spectrum general herbicide used
in the control of many annual and perennial grasses and herbaceous weeds on
noncropland areas where bare ground is desired. The degree of control and
duration of effect vary with the amount of monuron applied, the soil type,
rainfall, and other conditions. Most annual weeds are controlled at lower
rates than perennial weeds.
Monuron is registered (U.S. Environmental Protection Agency,1974) in the
United States for nonselective weed control on noncropland areas including
utility, highway, pipeline, railroad, and other rights-of-way; petroleum tank
farms; lumberyards; storage areas; industrial plant sites; and on irrigation
and drainage ditchbanks; 4.0 to 16.0 Ib Al/acre are used for the control of
most annual and perennial weeds. Additional treatment may be required where
a longer period of control is desired, or where deep-rooted, hard-to-kill
perennial weeds such as Johnson grass are present. In low rainfall areas,
monuron may not satisfactorily control deep-rooted perennial weeds.
For vegetation control on irrigation ditchbanks, monuron should be ap-
plied during the noncrop season, when the ditch is not in use, and before
expected seasonal rainfall. Following treatment, at least 4 in of rainfall
are required to fix monuron in the soil sufficiently so as to avoid injury to
crops from irrigation water supplied by monuron-treated ditches. If the
rainfall following monuron treatment does not total at least 4 in, it is
recommended that the ditch be filled with water allowed to stand for 72 hr.
The water must not be used for irrigation, but should be drained off before
the ditch is used for irrigation purposes. Monuron should not be used for
the treatment of any ditches into which roots of trees or other desirable
plants may extend because injury may result.
In the past, monuron was also registered and recommended for selective
control of weeds (including barnyard grass (water grass), crabgrass,
Colorado grass, foxtail, Johnson grass, pigweed, purslane, Spanish needles,
ragweed, chickweed, wild mustard, annual morning glory, and lamb's quarters)
and on several crops including asparagus, cotton, sugarcane, pineapple, avocados,
and citrus fruits. Tolerances for residues of monuron were established at 7 ppm
for asparagus, and 1 ppm for the following crops: avocados; cottonseed; grapes;
dry bulb onion; pineapples; spinach; sugarcane; and citrus fruits, including
oranges, lemons, limes, grapefruit, kumquats, tangerines, and citron. All of these
tolerances were revoked effective July 26, 1973, and monuron is no longer registered
or recommended for use on any of these crops.
92
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Monuron is also registered in combination with TCA (trichloroacetic acid),
with sodium meta and tetra berates, or with sodium chlorate and metaborate.
These products are registered and used for the same weed control purposes as
formulations containing only monuron.
In addition, monuron is registered in combination with several other
herbicides for the control of weeds in dichondra lawns. Typical products of
this kind contain approximately one part of monuron active Ingredient per 10
parts active Ingredient of the other herbicide component, such as monuron (0.35%)
combined with bensulide (4.42%), or monuron (0.383%) combined with diphenamld
(3.44%). In a number of dichondra lawn products, these herbicide combinations
have been combined with fertilizers, minor elements, and/or Insecticides.
For more details on the registered uses of monuron, including general and
specific use directions, precautions, limitations of use, and other details,
see Table 10, which presents a commercial label of the most frequently used
monuron formulation (80% wettable powder). The label contains selective crop
uses cancelled in 1973, with a notation of cancellation. In the past, uses on
crops contributed significantly to the total quantities of monuron used. Table
11 presents a representative use of monuron.
State Regulations - In a number of states, the sale and use of pesticides
are subject to State pesticide laws and regulations, in addition to Federal
statutes. For Instance, In California, 42 specific pesticides have been desig-
nated as "injurious or restricted materials." The use of pesticides in this
category is subject to special restrictions under regulations administered by
the California State Department of Agriculture. Monuron has not been
designated as an "Injurious or restricted" pesticide in California.
Table 11. MONURON NONCROP USAGE
Use
Tolerance
(ppm)
Dosage
Ib AI*/acre
Limitations
Irrigation and
drainage ditches
extended
80
Apply during noncrop
season when ditch is
not In use. Waste
first water after
treatment before irri-
gatlng crops.
*AI « active ingredient
Source: U.S. Environmental Protection Agency, EPA Compendium of Registered
Pesticides. Vol. I (1974).
93
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Table 12. MONURON 80% WETTABLE POWDER SPECIMEN IABEL
vO
WETTABLE
ACTIVE INGREDIENT:
Monuron [3-(p-chlorophenyl)-l,l-diniethylurea]........... 80%
INERT INGREDIENTS .& 20%
EPA K«g. No. 352-Mi-AA
Keep out of reach of children.
MAY IRRITATE EYES. NOSE,
THROAT. AND SKIN.
Avoid breathing dust or spray mist.
Avoid contact with skin, eyes, and clothing.
GENERAL INFORMATION-Du Pont "Telvar" Monuron Weed Killer is a wettable
powder to be mixed in water and applied as a spray to the surface of the ground
for control of weeds. Effects are slow to appear and will not become apparent until
the chemical has been carried into the root zone of the weeds by moisture. It is non-
corrosive to equipment, non-volatile, and non-flammable.
CAUTION 1
POWDER
IMPORTANT: Injury to or loss of desirable trees or other plants may result from
failure to observe the following: Do not apply (except as recommended for crop
use), or drain or flush equipment on or near desirable trees or other plants, or on
areas where their roots may extend, or in locations where the chemical may be
washed or moved into contact with their roots. Do not use on lawns, walks, drive-
ways, tennis courts, or similar areas. Prevent drift of dry powder or spray to desir-
able plants. Do not contaminate domestic waters. Keep from contact with fertilizers.
insecticides, fungicides, and seeds. Thoroughly clean all traces of "Telvar" from
application equipment Immediately after use. Flush tank, pump, hoses, and boom
with several changes of water after removing nozzle tips and screens (clean these
parts separately).
Do not re-use container. Crush and bury when empty.
IMHJ I.R
NET 5O LBS.
R \T«P \ . ? i
COMF>ANY?YINC.)
te^i&^t^**-^-^*-*'*; •• £..
NGTON, DELAWARE
-------
Table 12. (continued)
DIRECTIONS
Use a fixed-boom power sprayer properly calibrated to a constant speed and rate ot delivery. For details on
spray equipment and calibration, see Du Pont booklet "Instructions lor Applying Du Pont Weed Killers for
Selective Weed Control in Crops". Use sufficient water (min. 40 gals, per acre for non-cropland: 25 to 40 gals.
per acre for crops) to provide thorough and uniform coverage of the ground. Spray booms must be shut off
while starting, turning, slowing or stopping, or injury to the crop may result. Continuous agitation in the spray
tank is required to keep the material in suspension.
When a range of dosage rates is listed, use the lower ratts on lighter soils (sandy loams, loams, and soils low
in organic matter) and the higher rates on heavier soils (clay loams, clays, and soils high in organic matter).
NON-CROP WEED CONTROL
"Telvar" is an effective general herbicide for the control of many annual and perennial grasses and herba-
ceous weeds on non-cropland areas where bare ground is desired. The degree of control and duration of effect
will vary with the amount of chemical applied, soil type, rainfall, and other conditions.
"Telvar" may be used at any time for non-cropland weed control, except when ground is frozen, provided ade-
quate moisture is supplied by rainfall or artificial means to activate the chemical. Best results are obtained
if applied shortly before weed growth begins. If dense growth is present, remove tops and spray the ground.
GENERAL WEED CONTROL: To control most weeds for an extended period of time on non-cropland such
as UTILITY, HIGHWAY, PIPELINE and RAILROAD RIGHT OF WAYS. PETROLEUM TANK FARMS. LUMBER-
YARDS. STORAGE AREAS. INDUSTRIAL PLANT SITES, and AROUND FARM BUILDINGS-Apply 5 to 20 Ibs. of
"Telvar" per acre to control most annual weeds. Use 20 to 60 Ibs. per acre for perennial weeds; additional
treatment may be required where a longer period of control is desired or when hard-to-kill, deep-rooted peren-
nial weeds such as Johnsongrass are present. In low rainfall areas, "Telvar" may not provide satisfactory con-
trol of deep-rooted perennial weeds.
IRRIGATION AND DRAINAGE DITCHES: Apply 5 to 20 Ibs. per .acre to control most annual weeds; use
20 to 60 Ibs. per acre to control both annual and perennial weeds. For irrigation ditches, apply during the non-
crop season, and when ditch is not in use. To minimize movement of "Telvar" with irrigation water (to avoid
possible crop injury), it is essential that the herbicide be fixed in the soil by moisture. Apply before expected
seasonal rainfall (if possible when soil in the ditch is still moist). Following treatment, if rainfall has not totaled
at least 4 inches, fill ditch with water and allow tq stand for 72 hours; drain off and waste remaining water
before using ditch. Do not treat any ditch into which roots of trees or other desirable plants may extend as
injury may result.
FOR SMALL AREAS: One-half cupful of "Telvar" per 100 sq. ft. is approximately 50 Ibs. per acre. A hand
sprayer or sprinkling can may be used for application; shake or stir frequently.
SELECTIVE USE IN CROPS
"Telvar" should be used only in accordance with recommendations on this label,
or in separate published Du Pont recommendations available through local dealers.
"Telvar" selectively controls weed seedlings such as barnyardgrass (watergrass), crabgrass, Coloradograss, fox-
tail, Johnsongrass. pigweed, purslane. Spanishneedles. ragweed, chickweed. wild mustard, annual morningglory,
and lambsquarters. Results vary with soil types (the lower rates are effective on the lighter soils and the higher
rates on heavier soils) and environmental conditions. Moisture is necessary to activate the chemical; best results
are obtained if moisture is supplied by rainfall or irrigation within two weeks after application. Soil should be
well prepared and as free as possible from trash and clods; any well established weeds should-be eliminated
by mechanical or other means. Unless otherwise directed, surface of the soil should not be cultivated or dis-
turbed after application of "Telvar" as efficiency may be reduced.
IMPORTANT—Unless otherwise directed, do not replant treated areas to any crop within two years after
last application as injury to subsequent crops may result.
ASPARAGUS: Do not apply to newly seeded asparagus nor to young plants during the first growing season
after setting nor on plants with exposed roots as severe injury may result. Apply as a band or broadcast treat-
ment. On light, sandy soils and other soils low in clay or organic matter, apply 1 to 2 Ibs. per acre (for band
application, use proportionately less). On soils high in clay or organic matter, use 2 to 4 Ibs. per acre. Two
applications may be used: the first application should be made before weeds become established but no earlier
than 4 weeks before spear emergence and no later than the early cutting period (if weeds are controlled into
the cutting period by cultural practices, application may be delayed until immediately after the last cultivation);
a second application may be made immediately following completion of harvest provided rainfall is expected.
When two applications are used in one season, do not exceed 3 Ibs. per acre per application. In Washington
(irrigated crop), apply only a single treatment of 4 Ibs. per acre in late November or December.
ORANGES, LEMONS, AND AVOCADOS—California (except Imperial and Coachalla Valley*): Use
only under trees established in the grove for at least one year. Apply as a directed spray avoiding contact of
foliage and fruit with spray or drift. Do not apply under citrus trees that have been subjected to freezing within
6 months; do not apply in home plantings of citrus or in areas where the roots of other valuable plants or
trees may extend: do not use on light (sand, loamy sand or gravelly) soils nor where organic matter is less
than 1% as injury may result.
Make a single application of 3 tq 4 Ibs. per acre as a broadcast spray shortly after grove has been laid-up in
final form (non-tillage program) in late fall or early winter. As an alternative, apply 2 Ibs. per acre in October
or November, and repeat at the same rate in March or April. Subsequent annual applications of 2 to 3 Ibs.
will usually give adequate weed control.
COTTON—Prewnergence (except Arizona and California): Make a single application as a broadcast or
band spray after planting but before cotton emerges. Use at the following rates:
95
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Table 12. (continued)
Broadcast Treatment tbs. "Telvar" Per Acre Lbs. Monuron
Soil Type* (in 25 to 40 Gals. Water) Applied/Acre
"Clay-Jpw organic matter 1,25 1?'°
"Clay—moderate organic matter ~ TB ~ 1.3
"Clay—high organic matter
2.0 ' T.6
•Use only on heavy (clay) soils. For other soil types, use "Karmex" Diuron Weed Killer.
Band Treatment: Use proportionately less; for example, for 14" band on 42" row, use Vi of the broadcast rate.
Apply immediately after cotton is planted; wherever possible, planting and spraying should be combined in one
operation. For best results, soil should be well prepared and as free as possible from trash and clods. Shallow
incorporation (no deeper than '/«") with a rotary hoe or similar equipment following planting usually improves
results particularly during dry weather. A wide press wheel following planting should be used to provide a level
seed bed for subsequent early season postemergence treatments.
Treatment usually provides weed control for a period of 3 to 8 weeks. Sufficient moisture (usually 1" to 2")
in the form of rainfall or irrigation is necessary after treatment to carry the chemical into the root zone of
germinating weeds; best results are obtained when this occurs within 2 weeks after application. If moisture is
insufficient to activate "Telvar" or if soil becomes crusted before crop emerges, a shallow rotary hoeing (no
deeper than Vi") should be made before weeds become well established.
If initial seeding fails to produce a stand, cotton may be replanted in soil treated with "Telvar". Wherever
possible, avoid disturbing original bed. If necessary to rework soil before replanting, use shallow cultivation
such as discing: do not re-list nor move soil into the original drill area; plant seed at least 1 inch deep; do not
retreat field with a second preemergence application of "Telvar" during the same crop year as injury to the
crop may result.
Note: Use of "Telvar" in conjunction with systemic phosphate insecticides (applied as seed treatment or as
soil treatment at planting) is NOT recommended as injury to cotton may result.
Late Season (Lay-By)—Arizona and California; other area* on heavy soils only: Use 1 to l'/4 Ibs. per
acre. Do not use on light (sand, loamy sand) soils nor where organic matter is less than 1% as injury to cotton
may result. Direct spray to cover the soil beneath cotton plants and between rows, keeping contact with crop
plants at a minimum. DO NOT SPRAY OVER TOP OF COTTON. Apply immediately after the last cultivation,
but not before the cotton has reached a height of at least 20 inches. In irrigated cotton, best weed control is
obtained if the field is irrigated within 3 to 4 days after application; thoroughly wet the surface of the ground
over the row to carry the chemical into the root zone of germinating weeds.
Subsequent Crops:
"Telvar"-Type of Application Crops That May Follow Treated Cotton.
Band preemergence Any crop 4 months after application.
Broadcast preemergence Cotton, soybeans, corn or grain sorghums (not sorgos or forage sor-
ghums nor grass sorghums) the next spring. Do not replant treated
areas to any other crop within one year after last application as injury
to subsequent crops may result.
Lay-by only Cotton, corn, grain sorghums (not sorgos or forage sorghums nor grass
•or- sorghums) the next spring. Do not replant treated areas to any other
Preemergence plus lay-by crop within one year after last application as injury to subsequent crops
may result.
Note: During a single crop season, do not exceed 2.2 Ibs. monuron per acre as injury to subsequent crops
may result.
PINEAPPLE—Hawaii: Apply 4 to 8 Ibs. per acre as a broadcast spray immediately after planting and prior
to weed emergence. Use 4 Ibs. after harvesting plant crop (for ratoon crop). For plant crop only, a second and
third broadcast or interspace application may be made prior to differentiation at the rate of 2 Ibs. per acre
at intervals of not less than 2 months. Additional applications to plant crop may be made as needed to inter-
space only, using 2 Ibs. per acre. Do not apply more than 3 broadcast sprays (maximum 12 Ibs. per acre) prior
to differentiation nor more than 16 Ibs. total per acre per plant crop. Treated areas may be planted to pine-
apple or sugar cane one year, after last application.
SUGAR CANE: To prevent possible crop injury on new cane varieties, tolerance to "Telvar" should be deter-
mined prior to adoption as field practice. Do not treat sugar cane growing on thinly covered sub-soils or rocky
areas; do not use on light (sand, loamy sand or gravelly) soils nor where organic matter is less than 1% as
injury to cane may result. Temporary chlorosis of the crop may result from application over emerged cane; to
minimize chlorosis, use directed postemergence sprays. The following rates are for broadcast treatment; for
band application, use V> of broadcast rate when treating V4 of the area.
Florida: For high organic soils, apply 2 to 4 Ibs. per acre prior to v/eed emergence after planting or after har-
vesting plant crop (for ratoon crop). A second and third application of 2 Ibs. per acre may be made as needed
by directed spray inter-row. Do not apply more than 3 treatments nor more than 6 Ibs. total per acre between
planting (or ratooning) and harvest.
Hawaii and Puerto Rico: Apply 4 to 6 Ibs. per acre prior to weed emergence after planting or after harvest-
ing plant crop (for ratoon crop). A second and third application of 2 to 3 Ibs. per acre may be made as a
broadcast spray over emerged cane or by directed spray inter-row. Do not apply more than 3 treatments nor
more than 10 Ibs. total per acre between planting (or ratooning) and harvest. Treated areas may be planted
to sugar cane or pineapple one year after last application.
Louisiana: Use on plant cane seeded on fallowed ground. Apply 3 to 3% Ibs. per acre either in the fall (August
through October) or spring (January through April) before weeds or cane emerge.
NOTICE TO BUYER-Seller warrants that this product conforms to the chemical description on the label
thereof and is reasonably fit for purposes stated on such label only when used in accordance with directions
under normal use conditions. This warranty does not extend to use of this product contrary to label use direc-
tions, or under abnormal use conditions, or under conditions not reasonably foreseeable to seller; buyer
assumes all risk of any such use. Seller makes no other warranties, express or implied.
96
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Table 12. (continued)
TELVAR* MONURON WEED KILLER
EPA REG. NO. 3S2-246
CROPS: "Telvar" is no longer registered for use in crops;
use only for non-crop weed control.
NON-CROP WEED CONTROL: Use in accordance with
directions on product label.
B-21W4 2-73
97
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Production and Domestic Supply
Volume of Production - Reports issued by the U.S. Tariff Commission (1970,
1971, 1972, 1973), list only one basic producer of monuron in the United
States in the 1970 to 1973 period, E. I. du Pont de Nemours and Company.
The Farm Chemicals Handbook (1974) reports that monuron is produced abroad
by Makhteshim-Agan Chemical Manufacturers Limited, Ashdod, Israel.
Monuron-TCA combination products are produced by Allied Chemical
Corporation.
The TC reports do not individually report the production and sales
volumes of monuron. Monuron is included in the category "Pesticides and
Related Products, Cyclic," in a classification entitled "All Other Cyclic
Herbicides and Plant Hormones. The total production volume (as active
Ingredient) for this classification was: 231,021,000 Ib in 1970, 358,433,000
Ib in 1971, 344,789,000 Ib in 1972, and 357,310,000 Ib in 1973.
Compared to the major herbicides in this classification, the production
and sales volumes of monuron are too small for TC data to be of value in
making quantitative estimates on monuron.
The U.S. Department of Agriculture (1968, 1970, 1974) conducted surveys
on the quantities of pesticides used by U.S. farmers in 1964, 1966, and 1971.
In these reports, monuron is shown individually only in the 1964 survey.
According to this source, a total of 231,000 Ib of monuron AI were used on
farm crops in 1964 in the United States. In the 1966 and 1971 USDA surveys,
monuron was included in a category entitled "Other Phenyl Urea Herbicides."
Since the USDA reports cover only agricultural uses of pesticides, production
and use volumes of monuron (since the 1973 revocation of uses on crops) are
not obtainable from this source.
According to RvR Consultants estimates, the volume of production of
monuron in the United States in 1973 was less than 1 million Ib AI, probably
ranging between 500,000 to 900,000 Ib. Somewhat larger quantities of monuron
are believed to have been produced in past years when monuron was registered
for crop uses and had less competition from more recently developed phenyl
urea and other organic herbicides.
Imports - TC reports on benzenoid chemicals for 1972 and 1973 list the fol-
lowing figures for imports of monuron active ingredient into the United
States: 35,000 Ib, 1971; 111,800 Ib, 1972; 142,138 Ib, 1973.
Exports - Monuron is not listed separately in Bureau of Census commodity de-
scriptions on herbicide exports. Total exports in 1972 for technical herbi-
cidal preparations were placed at 38,967,237 Ib. Based on other sources,
Midwest Research Institute (MRI) estimates that the export volume of monuron
in 1972 and 1973 amounted to about 100,000 Ib Al/yr.
98
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Domestic Supply - MRI estimates of the 1973 domestic supply of monuron are:
U.S. production, 500,000 to 900,000 Ib; imports, 150,000 Ib; exports,
100,000 Ib; domestic supply, 550,000 to 950,000 Ib.
Indications are that domestic production volume and quantities of monuron
used are on the decline. This is partially attributed to the fact that all
uses of monuron on agricultural crops have been discontinued and the residue
tolerances covering these uses have been revoked. In addition, a number of
more recently developed phenyl urea and other herbicides are replacing
monuron*s noncrop uses.
Formulations - Monuron is available to users in the United States in several
different concentrations and formulations, offered by about a dozen different
suppliers.
The most widely used monuron formulation is an 80% wettable powder.
Suppliers of monuron in this form include du Pont, Aceto Chemical Company,
and Allied Chemical Corporation.
Several monuron granular formulations are available, including one con-
taining 8% active ingredient, offered by Horne-Boatright Chemical Company
(Minneapolis, Minnesota) and one containing 3.2% active ingredient, offered
by Ralston Purina Company (St. Louis, Missouri).
Several formulators offer granular formulations in which low concentra-
tions of monuron (generally 2.4 to 4.0%) are combined with sodium metaborate,
sodium tetraborate and/or sodium chlorate. Suppliers of such formulations
include Crown Chemicals (St. Louis, Missouri) and Chipman Chemical, Limited
(London, Ontario).
Several formulations containing monuron-TCA (trichloroacetic acid) as
active ingredient are available, including granulars containing 5.5, 11, and
22% of combined active ingredient, and a liquid-oil concentrate containing
32.4% of active ingredient. The principal supplier of these monuron-TCA
products which are offered under the trade name "Urox" is Allied Chemical
Corporation, Union Texas Petroleum Division, Agricultural Department, Houston,
Texas.
Suppliers of dichondra lawn herbicides containing monuron include the
Kelly Western Seed Division of the Pax Company, and the Pax Company, both at
Salt Lake City, Utah,and the Occidental Chemical Company, Lathrop, California.
Monuron technical (probably primarily from overseas production) is of-
fered by at least 2 suppliers, Aceto Chemical Company, Inc. (Flushing, New
York) and Chempar Chemical Company, Inc. (New York City).
In the past, a liquid suspension formulation of monuron containing 28%
active ingredient (2.8 Ib Al/gal) was available under the trade name "Telvar
ML" from du Pont. The formulation is no longer produced.
There are no dusts or pressurized formulations of monuron available.
99
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Use Patterns of Monuron in theUnited States
General - Monuron is a broad spectrum, soil-applied herbicide. It controls
susceptible weed seedlings and is absorbed through the roots and translocated
upwards in the transpiration system. Uptake through stems or leaves is also
possible, but occurs to a much lesser extent. Like all substituted phenyl
urea herbicides, monuron is a strong inhibitor of the Hill reaction (the
evolution of oxygen in the presence of chloroplasts) and thus of photosynthe-
sis. The herbicidal action of monuron and of other substituted phenyl urea
herbicides is believed to be due in part to the buildup of a substance which
is toxic to the oxygen-liberating pathway in photosynthesis (Ashton and
Crafts, 1973).
In the 1950's and 1960's, monuron was used as a selective herbicide on a
few crops, including cotton, sugarcane, asparagus, dry bulb onions, pineapple,
and as a directed spray in citrus and avocado groves. All crop uses were dis-
continued in 1973.
As a nonselective herbicide, monuron has been, and continues to be used
for total vegetation control on noncropland areas such as utility, highway,
pipeline, railroad, and other rights-of-way, petroleum tank farms, lumber-
yards, and other industrial storage areas and plant sites, around farm
buildings, and on irrigation and draining ditchbanks while the ditches are
not in use.
Agricultural Uses of Monuron - In a survey by the U.S. Department of Agri-
culture (1968) on the quantities of pesticides used by farmers in 1964,
monuron uses were cited. At the time monuron outranked all other farm crop
herbicides. Out of a total of 329,000 Ib AI of phenyl herbicide use reported
for 1964, 231,000 Ib AI was for monuron, including 80,000 Ib for cotton and
147,000 for fruit and vegetable crops. In 1966 and 1971 surveys, monuron was
not listed separately, but included in the category "Other Phenyl Urea Herbi-
cides." The total reported use for these herbicides was 644,000 Ib AI in 1966
declining to 259,000 Ib AI in 1971. Based on other sources, MRI estimates
that 180,000 Ib of monuron was used on farm crops in 1966 and about 125,000 Ib
in 1971. Use of monuron is expected to decline further as a result of the
1973 revocation of monuron tolerances and registrations for use on all agri-
cultural crops.
Nonagricultural Uses of Monuron - For nonselective, general vegetation control,
monuron is registered for use on noncropland such as rights-of-way, industrial
plant sites and storage areas. Monuron users in these non agricultural areas
include Federal, state, county, city, and other governmental agencies; irri-
gation, flood control, vector control, and water resource districts; and
industrial and commercial organizations. There may be some uses of monuron on
or around private residential properties, although the total quantities appear
to be negligible. Small quantities of monuron are used in combination with
other herbicides (typically at the ratio of one part of monuron to 10 parts of
the other herbicide component), and with fertilizers, minor elements and/or
insecticides for dichondra lawns.
100
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Table 13 summarizes the estimated uses of monuron in the United States by
major use categories in 1973, assuming 2 different levels of use, 600,000 Ib
(Case A) and 800,000 Ib (Case B).
Table 13. ESTIMATED USES OF MONURON IN THE U.S. BY USE CATEGORIES, 1973
Category Case A^' Case B—'
Founds of active ingredient
Agriculture 100,000 125,000
Industrial/commercial 400,000 550,000
Government agencies 100,000 125,000
Home and garden Small Small
Totals 600,000 800,000
af Case A: Assuming total U.S. use = 600,000 Ib.
b/ Case B: Assuming total U.S. use = 800,000 Ib.
Source: RvR Consultants, Shawnee Mission, Kansas, estimates.
As pointed out, the total U.S. supply of monuron in 1973 ranged between
550,000 and 950,000 Ib AI. Use volumes assumed in Case A and Case B, respec-
tively, appear to be realistic.
According to Table 13, industrial and commercial uses accounted for 60 to
70% of the total domestic use of monuron in 1973. The quantities of monuron
used by governmental agencies (including all levels of government) in 1973 are
about equal to the quantities used on crops, and these 2 use categories com-
bined account for the remaining 30 to 40% of the total estimated domestic
consumption of monuron.
Monuron Uses in California - California keeps detailed records of pesticide
uses by crops and commodities. The reports are published quarterly and sum-
marized annually. Table 14 summarizes the uses of monuron in California, by
major crops and other uses for the 1970 to 1973 period.
101
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Table 14. MONURON^' USES IN CALIFORNIA BY MAJOR CROPS
AND OTHER USES, 1970 TO 1973
Year
Crop /Use
Asparagus
Cotton
Citrus
Avocado
Other crops—
c/
All other uses-
Total, all uses
1973
4,420
1,492
2,969
123
56
12,494
21,554
1972
Pounds of active
8,502
965
7,968
1,681
-
14,767
33,883
1971
ingredient
4,578
456
1,168
278
-
7,703
14,183
1970
5,680
215
3,276
28
319
12,244
21,762
a/ Include small quantities of monuron-TCA.
b_/ Include alfalfa, oats, several minor uses on other crops, and use
on fallow (open) ground.
cj Include Federal, state, county, city, and other agencies; irrigation,
flood control, vector control districts; the University of California;
and uses on or around industrial, residential, turf, water, and other
nonagricultural areas.
Source: California Department of Agriculture, Pesticide use reports for
1970, 1971, 1972, and 1973.
In California, monuron is not subject to the special restrictions and
reporting requirements imposed upon the sale and use of pesticides designated
as "injurious or restricted materials." For this reason, the percentage of
all monuron uses reported to the California State Department of Agriculture
and included in its statistics is probably not as high as in the case of
restricted use pesticides.
According to the reports, the quantities of monuron (including small
quantities of monuron-TCA) used in California for all purposes ranged from
14,183 Ib AI in 1971 to 33,883 Ib AI in 1972. Quantities used in 1970
(21,762 Ib AI) and in 1973 (21,554 Ib AI) were intermediate.
102
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More monuron was used in California on asparagus than on any other
single crop. Citrus fruits were next in line, followed by cotton and avocado.
In each of the 4 yr covered in Table 14, 'larger quantities of monuron were
used for nonagricultural purposes in California as compared to farm uses.
Nonfarm uses of monuron varied from 7,703 Ib AI in 1971 to 14,767 Ib AI in
1972, with monuron volumes used in this category in 1970 (12,244 Ib AI) and
1973 (12,494 Ib AI) ranging in between.
The data summarized in Table 14 does not indicate any clear trend in
total use, nor in any of the major crop and other use categories shown
individually.
It appears that the California statistics include only a fraction, of the
'total quantity of monuron actually used in the state since pesticides whose
use is not restricted are often applied by private interests to their own
land, or used for nonagricultural purposes.
Tables 15 and 16 present the uses of monuron in California in detail,
by crops and other uses, number of applications, pounds of active ingredient,
and number of acres treated for 1972 and 1973, the two most recent years for
which such data are available. These tables expand and provide further
insight into the monuron uses in California in 1972 and 1973 included in
summary form in Table 14.
Monuron Usage in Arizona
Total agricultural volume data from Arizona on crop and noncrop usage
was reported by Ware et al. (1974). In the late 1960's, monuron usage
ranged from 12,500 to 17,800 Ib. A downward trend in volume appeared in
the early 1970's; 15,800 Ib in 1971 and 3,000 Ib in 1973.
103
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Table 15. USE OF MONURON (INCLUDING MONURON-TCA) IN CALIFORNIA IN 1972
BY CROPS AND OTHER USES, APPLICATIONS, QUANTITIES, AND ACRES TREATED*
Chemical/Commodity
Applications
Pounds
Acres
Monuron TCA, Urox
City agency
Irrigation district
Nonagricultural areas
Other agencies
School district
Water resources
TOTAL
Monuron
Asparagus
Avocado
Citrus
City agency
Cotton
County Agricultural Commissioner
County or city parks
County roads
Federal agency
Flood control
Grape
Irrigation district
Lemon
Lettuce/head
Nonagricultural areas
Orange
Other agencies
Residential control
School district
State highway
Structural control
Turf
University of California
Vector control
Water areas
TOTAL
1
1
67
21
15
18
2
85
2
9
53
6
1
279
0.51
1.53
371.52
40.40
119.27
4.59
537.82
8,502.35
1,681.17
470.22
13.28
964.98
8.10
145.33
700.40
3,170.84
928.00
0.06
6,530.56
106.02
966.94
1,901.77
445.15
269.18
62.40
28.80
6,348.89
52.28
48.00
0.15
33,344.87
9.00
9.00
3,597.50
575.50
230.50
1,113.00
23.50
2,839.00
29.00
9.75
958.00
517.00
5.00
9,897.75
^Disparities in usage in relation to recommended rates may result from data
from incomplete reports for number of applications, poundage, or acreage.
Source: California Department of Agriculture, Pesticide Use Report 1972 (1972)
104
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Table 16. USE OP MONURON (INCLUDING MDNURON-TCA) IN CALIFORNIA IN 1973
BY CROPS AND OTHER USES, APPLICATIONS, QUANTITIES, AND ACRES TREATED*
Chemical/Commodity
Applications
Pounds
Acres
Monuron TCA, Urox
City agency
Other agencies
Residential control
School district
Water resources
TOTAL
Monuron
Alfalfa 7
Asparagus 42
Avocado 7
City agency
Cotton 22
County Agricultural Commissioner
County or city parks
County road
Pederal agency
Fallow (open ground) 1
Flood control
Grapefruit 1
Irrigation district
Lemon 35
Nonagricultural areas 3
Oats 1
Orange 24
Other agencies
Residential control
School district
State highway
Structural control
Turf 8
University of California
Vector control
TOTAL 151
23.04
12.28
20.28
49.05
2.23
106.88
7.99
4,420.00
122.74
19.74
1,491.58
21.19
171.23
206.90
7,760.56
48.00
583.20
3.20
4.80
2,577.71
46.40
0.23
387.81
944.77
815.94
171.59
9.60
32.00
1,498.40
81.60
20.00
21,446.91
558.00
2,394.00
66.25
1,062.00
3.00
40.00
1,057.50
5.00
58.00
294.00
609.00
6,146.75
^Disparities in usage in relation to recommended use rates may result from
data from incomplete reports for number of applications, poundage, or acreage.
Source: California Department of Agriculture, Pesticide Use Report 1973 (1973)
105
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References
Ashton, F. M., and A. S. Crafts, Mode of Action of Herbicides, John Wiley
and Sons, New York (1973).
California Department of Agriculture, Pesticide Use Reports for 1970, 1971,
1972, and 1973.
Farm Chemicals Handbook. Meister Publishing Company, Willoughby, Ohio (1974).
U.S. Bureau of the Census, U.S. Exports, Schedule B. Commodity by Country.
FT 410 (1972).
U.S. Department of Agriculture, Quantities of Pesticides Used by Farmers in
1964, Agricultural Economic Report No. 131, Economic Research Service
(1968).
U.S. Department of Agriculture, Quantities of Pesticides Used by Farmers in
1966, Agricultural Economic Report No. 179, Economic Research Service
(1970).
U.S. Department of Agriculture, Farmer's Use of Pesticides in 1971 . . .
Quantities, Agricultural Economic Report No. 252, Economic Research
Service (1974).
U.S. Environmental Protection Agency, EPA Compendium of Registered Pesti-
cides. Vol. I (1974).
U.S. Tariff Commission, Imports of Benzenoid Chemicals and Products, 1972,
TC Publication 601 (1973).
U.S. Tariff Commission, Imports of Benzenoid Chemicals and Products, 1974,
TC Publication 688 (1974).
U.S. Tariff Commission, Synthetic Organic Chemicals. U.S. Production and
Sales (1970, 1971, 1972, 1973).
Ware, 6. W., C. H. Kreader, and L. Moore, "Agricultural Use of Pesticides in
Arizona," Progressive Agriculture in Arizona, 26 (4):12-16, College of
Agriculture, University of Arizona, Tucson (1974).
106
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PART III. MINIECONOMIC REVIEW
CONTENTS
Page
Introduction 108
Efficacy of Noncrop Control 109
Effect on Nonselective Weeds 109
Effect on Specific Grasses Ill
Effect on Woody Plants Ill
Economic Benefits of Weed and Grass Control Ill
References 113
107
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This section contains a general assessment of the efficacy and cost
effectiveness of monuron. Data on the production of monuron in the United
States, as well as an analysis of its use patterns at the regional level
and by major application, were developed as part of the Scientific Review
(Part II) of this report. The section summarizes rather than interprets
data reviewed.
Introduction
The efficacy and cost effectiveness of a specific pesticide should be
measurable in terms of the increased yield or improved quality of a treated
crop which would result in a greater income or lower cost than would be
achieved if the pesticide had not been used. Thus, one should be able to pick
an isolated test plot of a selected crop, treat it with a pesticide, and com-
pare its yield with that of a nearby untreated test plot. The difference in
yield should be the increase due to the use of the pesticide. The increased
income (for example, the yield increase multiplied by the selling price of
the commodity) less the additional cost (i.e., the pesticide, its application,
and the harvesting of the increased yield) is the economic benefit due to the
use of the pesticide.
Unfortunately, this method has many limitations. The data derived is
incomplete and should be examined with caution. Midwest Research Institute's
review of the literature and EPA registration files revealed that experimental
tests comparing crops treated with specific pesticides to the same crop with-
out treatment are conducted by many of the state agricultural experimental
stations. Only a few of these, however, have attempted to measure increased
yield and most of this effort has been directed toward just a few crops such
as cotton, potatoes, and sorghum. Most other crop tests measure the amount
of reduction in pest levels which cannot be directly related to yield.
Even the test plot yield data are marginally reliable since these tests
are conducted under actual field conditions that may never be duplicated
again and are often not representative of actual field use. Thus, yield is
affected by rainfall, fertilizer use, severe weather conditions, soil type,
region of the country, pesticide infestation levels, and the rate, frequency,
and method of pesticide application.
Because of these factors, yield tests at different locations and in dif-
ferent years will show a wide variance ranging from a yield decline to signi-
ficant increases.
The use of market price to estimate the value received by the producer
also has its limitations. If the use of the pesticide increases the yield of
a crop and the national production is increased, then the market price should
decline. According to J. C. Headley and J. N. Lewis (1967), a 1% increase in
quantity marketed has at times resulted in a greater than 1% decrease in
price. Thus, the marginal revenue from the increased yield would be a better
measure of the value received.
108
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A third limitation to the quantification of the economic costs and bene
fits is the limited availability of data on the quantities of the pesticide
used by crop, or pest, the acres treated, and the number of applications.
In most cases the amount of monuron used on each crop application is not
available.
As a result of these limitations, an overall economic benefit by crop
or pest cannot be determined. Where applicable a range of the potential
economic benefits derived from the use of the pesticide for control of a
specific pest on a specific crop is developed. This economic benefit or loss
is measured in dollars per acre for the highest and lowest yield developed
from experimental tests conducted by the pesticide producers and the state
agricultural experimental stations. The high and low yield increases are
multiplied by the price of the crop and reduced by the cost of the pesticide
and its application to generate the economic benefit range in dollars per acre.
Economic benefits from noncrop applications (for example, grass and
brush control along highways, utility lines, and railroads) are best measured
by an alternative costing method. Alternative methods to chemical control
include mechanical control such as mowing, discing, bulldozing, and the use
of brush-cutting machines. Hand labor is often required for mowing around
trees, poles, and other objects, and for weeding or cutting brush. In some
cases, burning for control of grasses along canal banks is an alternative.
The true economic benefits cannot be measured because much of the non-
crop weed control is for aesthetic reasons such as beautification of highways.
It is also a form of preventive maintenance to keep fires from causing damage
when grasses are dry. Therefore, the cost of the chemical control should be
subtracted from the alternative control cost, such as hand labor or mechanical
control, to determine the economic benefit from the use of monuron.
Efficacy of Noncrop Control
Effect on Nonselective Weeds - Monuron is currently registered for non-
selective control (semi-soil sterilization) of weeds and grasses along
highway rights-of-way, canal banks, railroads, utility lines, and localized
weed and grass problems.
In studies on control of weeds under guardrails along highways, Rogerson
et al. (1966) conducted experiments in 1963 and 1964 to evaluate the effec-
tiveness of several herbicides. Monuron (as the 80% wettable powder) at a
rate of 20 Ib/acre controlled mixed broadleaved weeds at 3 separate locations.
Control ranged from 73 to 99% 4 months after treatment.
Aldred (1968) reported on tests conducted by the Tennessee Valley Author-
ity to determine the effectiveness of several soil sterilants on grass and
woody plants. Monuron was applied at 54 Ib/acre in 1966 and resulted in a
75% rate of kill. Species remaining in 1967 included maypop, plantain, black-
berry, broomsedge, cudweed, box elder, and panicum.
109
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Sigler (1961) evaluated raonuron for control of weeds along railroads and
for industrial applications. Tests, comparing several soil sterilants, ware
conducted In 1957 by the Tennessee Agriculture Experiment Station at Knoxville,
Tennessee. The dominant vegetation Included: broomsedge, crownbeard, Bermuda
grass, common blackberry, Kentucky bluegrass, goldenrod, and tall red tops.
Within 10 days after treatment with a 50 Ib/acre dosage monuron apparently
killed the vegetation. Monuron did not kill as rapidly as other sterilants,
but Its delayed action was effective against all the tested weeds except
Bermuda grass.
Lewis (1968) compared several herbicides for soil sterilization and
general weed control in Florida soils. Monuron was applied to soil containing
annual grasses, such as Bahia, spurge, pokeweed, Bermuda, vasey grass, nut
sedge, crabgrasa, and smut grass. The results of the tests, using a weed
control rating of 0 to 10 (0 - no control and 10 • complete control), showed
that monuron, 2 months later, applied at 40 Ib/acre had a rating of 8,
declining to 7, 11 months later.
Dunn (1967) evaluated several sterilants for control of weeds and brush
in riprap along levees in Louisiana. Weeds Included square stem, coffee bean,
pack, goat, yankee, and ragweed; brush Included false willow trees and tallow;
and grasses present were Bermuda and vasey. Monuron was applied at rates of
20, 40 and 60 Ib/acre. At 40 and 60 Ib/acre, false willow was completely
controlled, and 80% control of Bermuda and vasey grass occurred. At 20 lb/
acre the control was much less and the grasses reappeared.
Upchurch et al. (1969) also compared the soil sterilization properties of
several herbicides in North Carolina soils. Dominant grasses were tall fescue,
Bermuda grass, horse nettle, broomsedge, Johnson grass, and trumpet creeper.
Monuron at 40 Ib/acre, applied in early spring, gave good vegetation control
for 1 yr after which retreatment was required to maintain reasonable control.
Weldon and Tlmmons (1959) evaluated several herbicides for control of
miscellaneous weeds in a farm irrigation ditch in Wyoming. Within 2 months,
monuron at rates of .10, 20, and 40 Ib/acre gave 98 to 99% control. However,
control after 19 months dropped to zero. When a second application at 10 lb/
acre was made 1 yr after an initial 10 Ib/acre rate, 40% control was evidenced
after 19 months.
The possibility of converting southern desertland into more productive
grassland prompted Schmutz (1967) to evaluate several herbicides for control
of the creosotebush, whitethorn, and tarbush in the Chlhuahuan Desert near
Tombstone, Arizona. Monuron was applied at rates of 2, 4, and 8 Ib/acre.
At the 2-lb/acre rate, very little effect was observed on the grasses. At
the 8-lb rate, almost complete death of the grasses was observed; near
sterilization of the soil was observed for 3 yr.
110
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Long-term studies of the effect of massive application of monuron to the
soil were conducted by Isenee et al. (1973). Rates of monuron varying from
56 to 224 Ib/acre were applied to soil near Beltsville, Maryland, in 1954.
This resulted in 99 to 100% reduction of broadleaf weeds after the first yr.
However, even at the heaviest dose, 47% of the area was covered with vegeta-
tion at the end of the second yr. This increased to 80% at the end of the
third yr and 100% at the end of 15 yr.
Effect on Specific Grasses - Monuron has been shown to be effective against
nut grass. Loustalot et al. (1954) found that 80 to 90% reduction in the num-
ber of tubers was achieved in plots that were plowed under and treated with
80 Ib/acre of monuron. The rate of control depended upon the depth of the
tubers In the soil since monuron did not move more than 2 in below the soil.
Szabo and Gould (1959) evaluated various rates of monuron for control of
field bindweeds. The degree of control after 2-1/2 months was 99.45% with 40
Ib/acre of monuron and 97.45% with 90 Ib/acre.
Clubmoss Is a serious competitor of grasses on Western rangeland. Stroud
and Baker (1966) evaluated several herbicides for control of clubmoss in the
late fall of 1964 and early spring of 1965. Monuron applied at a rate of 1.0
Ib/acre in the fall of 1964 provided 81% control. Clubmoss control in the
spring of 1965 was only 31%, and the yield of total vegetation compared to an
untreated check plot was 122%. When 2 Ib/acre of monuron were applied in
1965, control of clubmoss was 98%; the yield of total vegetation was 109% of
the total vegetation on the untreated check plot.
Effect on Woody Plants - Hoffman (1964) evaluated several herbicides for con-
trol of woody species in Texas. He found that 4 g of active monuron were re-
quired for effective control of 4-in meaquite. A mixture of 10 lb/100 gal of
water was applied in a narrow band around the base of the tree to achieve
this control.
Selfres et al. (1974) found that monuron did not cause significant foliar
damage to redberry juniper at rates up to 2 g/ft canopy diameter during tests
conducted in north Texas.
Economic Benefits of Weed and Grass Control
Hand labor and mechanical control with various devices, such as mowers,
discs and bulldozers were considered as alternative costing methods to chemical
crop control.
McHenry and Parsons (1967) compared various methods of controlling canal
bank weeds in California. In a survey of Irrigation districts, they found that
chemical costs for soil-applied herbicides averaged $46.78/acre, mechanical
weed control averaged $12.10/acre, burning of weeds averaged $13.85/acre, and
hand weeding averaged $164.91/acre.
Ill
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The results of these various field evaluations show that the economic
benefits of chemical control over other methods varied from a loss of $34.68/
acre when compared to mechanical weed control on California canal banks to a
gain of $118.13/acre when compared to hand weeding along the same area.
The results of these tests are summarized in Table 17:
Table 17: ECONOMIC BENEFITS OF CHEMICAL AND ALTERNATIVE CONTROL
Alternative
Type
Mechanical
Burning
Hand weeding
Control
Cost
($/acre)
12.10
13.85
164.91
Chemical
Control
Cost
($/acre)
46.78
46.78
46.78
Economic
Benefit
($/acre)
(34.6S)-7
(32.93)
118.18
Source
a/
a/ McHenry and Parsons (1967).
b/ Data in parentheses represent negative values.
112
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References
Aldred, J. R., "Soil Sterilants on Silt Loams of the Tennessee Valley
Region." South. Weed Sci. Soc. Proceedings. 21:265-272 (1968).
Boat, W. M., Director, Cooperative Extension Service, Mississippi State,
Mississippi, personal letter to D. F. Hahlen (1974).
Dunn, C. R., "Riprap Test Work on Lake Pontchartrain Levees," South. Weed
Sci. Soc. Proc.. 20:207-211 (1967).
Headley, J. C., and J. N. Lewis, The Pesticide Problem; An Economic
Approach to Public Policy. Resources for the Future, Inc., Washington, D.C.
(1967).
Hoffman, G. 0., "Brush Control with Substituted Urea Herbicides," South. Weed
Conf. Proc.. 17:391-393 (1964).
Isenee, A. R., W. C. Shaw, W. A. Centner, C. R. Swanson, B. C. Turner, and
E. A. Woolson, "Revegetation Following Massive Application of Selected
Herbicides." Weed Sci.. 21(5):409-412 (1973).
Lewis, W. F., "Tests of Soil Sterilants in West Florida on Sand Soil,"
South. Weed Sci. Soc. Proc., pp. 273-274 (1968).
Loustalot, A. S., H. J. Cruzado, and J. S. Muzik, "Effect of CMU on
Nutgrass (Cyperus rotundus L.)," Weeds, 2:196-201 (1954)-
McHenry, W. B., and P. S. Parsons, "Cost of Controlling Canal Bank Weeds
by Water Agencies," California Weed Conf. Proc.. 19:38-41 (1967).
McKesson Chemical, Kansas City, Missouri, personal communication to D. F.
Hahlen (1974).
McRae, G. N., H. F. Arle, and K. C. Hamilton, "A Study of the Effects on
Seedling Cotton of Urea Herbicides Applied by Different Methods," Research
Progress Report Western Weed Control Conference (1959).
eU.S. GOVERNMENT PRINTING OFFICE: 1975-210-810:47
113
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