United States
Environmental Protection
Agency
Prevention, Pesticides
And Toxic Substances
(7508W)
EPA-738-F-95-003
March 1995
R.E.D. FACTS
Linuron
Pesticide
Reregistration
Use Profile
All pesticides sold or distributed in the United States must be
registered by EPA, based on scientific studies showing that they can be used
without posing unreasonable risks to people or the environment. Because of
advances in scientific knowledge, the law requires that pesticides which
were first registered years ago be reregistered to ensure that they meet
today's more stringent standards.
In evaluating pesticides for reregistration, EPA obtains and reviews a
complete set of studies from pesticide producers, describing the human
health and environmental effects of each pesticide. The Agency imposes
any regulatory controls that are needed to effectively manage each
pesticide's risks. EPA then reregisters pesticides that can be used without
posing unreasonable risks to human health or the environment.
When a pesticide is eligible for reregistration, EPA announces this and
explains why in a Reregistration Eligibility Decision (RED) document. This
fact sheet summarizes the information in the RED document for
reregistration case 0047, 3-(3,4-dichlorophenyl)-l-methoxy-l-methylurea,
commonly known as linuron.
Linuron is a herbicide used to control germinating and newly emerging
grasses and broad-leafed weeds. It is applied to agricultural crops,
ornamental bulbs, and poplar trees for use in shelterbelts in the mid-west.
Most of the linuron applied in the U.S. is to soybean crops. Formulations
include water dispersable granules, wettable powders, flowable concentrates,
and emulsifiable concentrates/liquid suspensions.
Linuron usually is applied after a crop has been planted but before
weeds emerge, using ground or aerial equipment. In some crops, such as
carrots and celery, linuron is applied to newly emerging plants as an over-
top spray. In asparagus, linuron is applied between cuttings of newly
emerging spears for weed control during harvest.
Use practice limitations include prohibitions against applying linuron
directly to water, or to areas where surface water is present, or to intertidal
areas below the mean high water mark; applying linuron aerially (DuPont
only; Griffin allows aerial application to potatoes and soybeans before crop
emerges); and applying linuron through any type of irrigation system.
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Regulatory
History
Human Health
Assessment
Linuron was first registered as a pesticide in the U.S. in 1966. EPA
issued a Registration Standard for Linuron in June 1984 (NTIS #PB85-
149011). From 1984 through 1988, linuron was the subject of a Special
Review because it exceeded oncogenicity risk criteria. However, the weight
of evidence suggested that its cancer-causing potential in humans is weak.
EPA concluded that no regulatory action was warranted, and reduced
linuron's cancer classification from a quantifiable to an unquantifiable Group
C carcinogen (that is, a possible human carcinogen for which there is limited
animal evidence).
EPA issued Data Call-In notices (DCIs) in May 1986, September 1990
and November 1993, requiring additional studies on product chemistry,
chronic toxicity, processing and cooking, ecological effects, phytotoxicity,
and residue chemistry, as well as cropfield trials replacement data for studies
generated by Craven Laboratories. Currently, 23 linuron end-use products
and 5 technical products are registered.
Toxicity
Linuron is of relatively low acute toxicity. It is slightly toxic by the
oral, dermal and inhalation routes, and has been placed in Toxicity Category
III (the second-to-lowest of four categories) for these effects. It causes
slight eye irritation in rabbits (Toxicity Category III), and is not a skin
irritant (Toxicity Category IV) or sensitizer.
A subchronic toxicity study using rats resulted in changes in blood cell
counts, and retarded growth at the high dose level.
In a chronic toxicity and carcinogenicity study using beagle dogs,
linuron caused changes in blood, including red blood cell destruction, and in
liver weight. A study using rats resulted in testicular tumors and blood cell
destruction. Another rat study showed growth retardation and destruction of
red blood cells. A third rat study showed significant changes in blood
pigments. An oncogenicity study using mice caused a statistically
significant increase in liver tumors, as well as decreased body weight and
body weight gain, increased liver weights, and other liver effects. As a
result of the Agency's Special Review, linuron remains classified as an
unquantifiable Group C carcinogen (that is, a possible human carcinogen for
which there is limited animal evidence).
In a developmental toxicity study using rats, the highest dose level
caused maternal toxic effects including decreased body weight gain and food
consumption, as well as increases in postimplantation loss and fetal
resorptions. In a study using rabbits, linuron caused decreases in maternal
body weight, food consumption and liver weight, as well as more abortions,
fewer fetuses per litter, decreased fetal body weight, and an increased
incidence of fetuses with skeletal skull variations.
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In a 2-generation reproductive toxicity study using rats, linuron caused
effects on the parents including decreased body weight gain and
abnormalities in the eyes and testes. Linuron was shown to interfere with
the transmission of male hormones. Rats exposed to linuron could develop
cell tumors in testicular tissue. A 3-generation study using rats showed
reduced body weights and fertility, decreased pup survival, and decreased
weanling body, liver and kidney weights, as well as liver atrophy. Linuron
does not appear to be mutagenic.
Dietary Exposure
People may be exposed to residues of linuron through the diet.
Tolerances or maximum residue limits have been established for linuron in
many vegetables, grain crops, meat, milk, and other agricultural
commodities (please see 40 CFR 180.184(a) and (b)). EPA has reassessed
these tolerances and found that sufficient data are available to support the
established tolerances for carrots; field corn grain; field corn forage and
fodder; celery; cottonseed; parsnips; potatoes; sorghum grain; wheat grain
and straw; meat and milk. Additional residue data are required for
asparagus; sweet corn; sweet corn forage; sorghum forage and fodder;
soybean forage and hay; wheat forage; and field corn grain dust. Several
existing tolerances for barley, oats, and rye, forage, grain, hay, and straw;
and corn, popcorn, forage and fodder will be revoked since there are no
registered uses of linuron on these commodities. New tolerances have been
proposed for lettuce, ginger and taro; several tolerance revisions have been
proposed; and a tolerance for corn fodder needs to be raised.
Food and feed additive tolerance proposals are required for potato
granules, chips, and processing waste. Under the Delaney clause of the
Federal Food, Drug, and Cosmetic Act (FFDCA), however, food and feed
additive tolerances may not be established for pesticides that induce cancer
in man or animals. Although its cancer-causing potential in humans is
weak, EPA still considers linuron to be a chemical that "induces cancer"
within the meaning of the Delaney clause. Therefore, under current policy,
EPA would not issue these food and feed additive tolerances, and would not
continue in effect the tolerance for the associated raw agricultural
commodity, potatoes.
EPA currently is evaluating legal challenges to its policies regarding
pesticide tolerances, registrations and the Delaney clause. Because of these
issues, the Agency is unable to make a reregistration eligibility decision at
this time regarding the use of linuron on potatoes.
Although the basic manufacturer of linuron deleted the cotton use in
1991, cotton still exists on linuron end-use product labels. Registrants of
these end-use products must now either submit a required cottonseed
processing study or delete the cotton use from their labels.
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EPA has assessed the dietary risk posed by linuron. For the overall
U.S. population, chronic exposure from all existing linuron tolerances
represents 2% of the Reference Dose (RfD), or amount believed not to cause
adverse effects if consumed daily over a 70-year lifetime. The two most
highly exposed subgroups are non-nursing infants (less than 1 year old),
whose exposure represents 6% of the RfD, and children age 1 to 6 years
old, with exposures representing 4% of the RfD. Therefore, chronic dietary
risk appears to be minimal.
Acute exposure to the subgroup of greatest concern, women of
childbearing age, results in a Margin of Exposure (MOE) of 1,667 for
developmental toxicity. This is likely to be an overestimate due to the
conservative assumptions used. Thus, acute dietary risk also appears to be
minimal.
Occupational and Residential Exposure
Based on current use patterns, workers may be exposed to linuron
during and after applications to agricultural crops, ornamental bulbs and
poplar trees. The Agency is not aware of any linuron products intended for
home use.
Margins of Exposure (MOEs) were estimated for applicators and
mixer/loaders of linuron. While most MOEs are greater than 100 (the
margin generally considered acceptable), exposure of mixer/loaders during
aerial applications is of concern, as is exposure of handlers using open
mixing/loading methods.
Post-application/reentry worker exposure to linuron is unlikely, except
during asparagus harvesting where linuron is applied between cuttings.
However, a supplemental worker exposure study indicates that all the MOEs
for asparagus harvesters are over 100. A 24-hour reentry interval required
for this use was converted to a 24-hour restricted entry interval (REI) by the
Worker Protection Standard (WPS). EPA is requiring a 24-hour REI for all
linuron uses within the scope of the WPS, based on the asparagus reentry
data.
Personal protective equipment (PPE) requirements for workers should
be based on the acute toxicity of end-use products. However, due to
concerns about worker risks, EPA is establishing minimum handler PPE
requirements for any end-use product containing linuron. Such products
may have more stringent PPE, but in no case may have less stringent PPE
than: coveralls over long-sleeved shirt and long pants, chemical-resistant
gloves, chemical-resistant footwear, and chemical-resistant apron.
Human Risk Assessment
Linuron is of relatively low acute toxicity, but is classified as an
unquantifiable Group C carcinogen (that is, a possible human carcinogen for
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which there is limited animal evidence), and shows some evidence of
developmental and reproductive toxicity.
Although people may be exposed to residues of linuron in a number of
food commodities, acute and chronic dietary risks appear to be minimal.
Handler and post-application worker risks are of concern, but are being
mitigated by requiring a 24-hour REI and minimum PPE for all agricultural
uses of linuron.
Environmental
Assessment
Environmental Fate
Although the environmental fate data base for parent linuron is
essentially complete, two environmental fate data requirements
(leaching/adsorption/desorption and terrestrial field dissipation studies) are
not fulfilled. The environmental fate assessment for linuron is incomplete
and tentative because information on the persistence, mobility and
dissipation pathways of several degradates of linuron is not available.
Parent linuron appears to be moderately persistent and relatively
immobile. Increased mobility may occur under specific environmental
conditions such as in coarse textured soils and soils with low levels of
organic matter. Linuron dissipates principally by biotic processes such as
microbial degradation. In surface soils with adequate organic matter, the
combined processes of adsorption and microbial degradation would limit
linuron's potential to migrate to ground water. Linuron could runoff to
surface water bodies. In that case, it would degrade fairly rapidly to three
primary metabolites. However, information on the persistence and mobility
of these degradates is not currently available.
Linuron exhibits some of the properties and characteristics of
chemicals that have been detected in ground water, and linuron itself has
been detected in ground water in four states (Georgia, Missouri, Virginia
and Wisconsin). Linuron is moderately persistent with an aerobic soil
metabolism half-life ranging from 57 to 100 days. Because linuron is
sufficiently persistent and may be mobile under certain environmental
conditions, it has the potential to impact ground water quality.
Linuron can be applied by ground spray and therefore could
contaminate surface waters through spray drift. It has the potential to be
somewhat persistent in surface waters, particularly those with low
microbiological activity and long hydrological residence times. It may be
less persistent in water and sediment under anaerobic conditions than under
aerobic conditions. Its bioconcentration potential is relatively low.
Linuron is not currently regulated under the Safe Drinking Water Act,
and water supply systems are not required to sample and analyze for it. No
Maximum Contaminant Level (MCL) or drinking water health advisories
have been established for linuron. The primary treatment processes
employed by most water systems may not always be completelyeffective in
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removing linuron. As a result, the Agency does have some moderate
concerns regarding potential risks of linuron to surface water source supply
systems.
Ecological Effects
Linuron is practically nontoxic to mammals on an acute basis, and
practically nontoxic to honey bees. Linuron is slightly toxic to birds on an
acute basis. Though studies are not available, US Fish and Wildlife Service
extrapolation suggests that linuron would be slightly toxic to practically
nontoxic to birds on a subacute dietary basis. However, linuron causes
reproductive effects in birds.
In acute oral toxicity studies, linuron is moderately toxic to both cold
and warm water fish. Acute testing using a formulated product indicates
that linuron is slightly toxic to moderately toxic to fish. In a fish early life
stage chronic study, linuron caused effects on fish length even at the lowest
dose level, so additional testing is required.
Linuron is highly toxic to aquatic invertebrates, while the formulated
product is moderately toxic to freshwater aquatic invertebrates. A life cycle
chronic test produced inconsistent results so additional testing is required.
In estuarine/marine acute toxicity studies, linuron is highly toxic to the
sheepshead minnow and moderately toxic to the eastern oyster and mysid
shrimp.
A number of additional studies are required.
Ecological Effects Risk Assessment
Linuron poses minimal risk to honeybees. However, chronic risk to
birds is posed at all use sites. Restricted use levels of concern are exceeded
for birds on short grass, and endangered species levels of concern are
exceeded for all uses evaluated.
Regarding mammals, the smaller the animal, the greater the level of
concern for acute effects from exposure to linuron. For example, levels of
concern are exceeded for the least shrew but not for the rat. Chronic effects
in wild mammals are likely.
Regarding aquatic risks, restricted use and endangered species levels
of concern are exceeded for fish from exposure to linuron in rights of way
(ROW), and for aquatic invertebrates at all use sites evaluated. Chronic
effects cannot be fully assessed without further testing.
Although further data on the toxicity of linuron to nontarget plants is
needed, a preliminary aquatic plant risk assessment indicates that high risk
and endangered plant levels of concern are exceeded for aquatic plants. The
risk to terrestrial plants cannot be assessed without further data.
Endangered species levels of concern are exceeded in some
circumstances for acute and chronic effects to birds, wild mammals and
aquatic organisms, and for acute effects to nontarget plants. When the
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Endangered Species Protection Program goes into effect, limitations on the
use of linuron will be required to protect endangered and threatened species.
Risk Mitigation Since the current uses of linuron exceed ecological effects levels of
concern in many circumstances, EPA is requiring the following risk
mitigation measures proposed by the technical registrant, DuPont:
• Reduce application rates for use of linuron on soybeans, field corn,
potatoes and asparagus.
• Limit the maximum number of applications to 1 per year (pre-
emergent use only) for soybeans, field corn, and potatoes, and to 3 per
year for asparagus.
• Prohibit aerial applications.
• Prohibit use on sand or loamy sand, and on soils of less than 1%
organic matter.
• Voluntarily cancel the high application rate uses including hybrid
poplar and non-cropland (rights-of-way) uses.
• Add a ground water advisory to all product labels.
• Add a surface water advisory to all product labels.
Since it meets the proposed triggers, EPA will consider linuron as a
candidate for classification as a restricted use pesticide due to ground water
concerns, once the ground water restricted use rule is finalized. Also, the
potential for spray drift exists when linuron is applied by ground spray.
Once pertinent data are submitted and reviewed, EPA will decide whether
spray drift labeling statements are required for linuron.
Additional Data EPA is requiring the following generic studies for linuron to confirm
RGCjUJrGd its regulatory assessments and conclusions:
Starting Materials and Manufacturing Process;
Foliar Dislodgeable Residues (Carrots/Celery);
Soil Dislodgeable Residues (Carrots/Celery);
Dermal Exposure (Carrots/Celery);
Inhalation Exposure (Carrots/Celery);
Cropfield Trials - Asparagus, Corn Aspirated Fractions (Grain Dust),
Sorghum Forage and Fodder and Wheat;
Cropfield Trials - Soybean Forage and Hay;
Acute Avian Dietary Toxicity with TGAI - Quail and Duck;
Acute Aquatic Invertebrate Toxicity;
Fish Early Life Stage - Both Rainbow Trout and Sheepshead Minnow;
Aquatic Invertebrate Life Cycle - Mysid Shrimp;
Leaching/Adsorption/Desorption;
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Product Labeling
Changes Required
Terrestrial Field Dissipation;
Cottonseed Processing Study - To support use on cotton;
Cropfield Trials - Sweet corn - To support use on sweet corn;
Acute Marine/Estuarine (TEP) - Sheepshead Minnow using DF
formulation for rights-of-way.
The following studies also are required, though they are not part of the
target data base:
Seed Germination/Seedling Emergence - 10 Species;
Vegetative Vigor - 10 Species;
Aquatic Plant Growth - 4 Additional Species.
The Agency also is requiring product-specific data including product
chemistry and acute toxicity studies, revised Confidential Statements of
Formula (CSFs) and revised labeling for reregistration.
All linuron end-use products must comply with EPA's current
pesticide product labeling requirements, and with the following:
Worker Protection Standard
Entry Restrictions
WPS Uses - A 24-hour restricted entry interval (REI) is required for
all uses within the scope of the Worker Protection Standard (WPS). The
personal protective equipment (PPE) required for early entry must be the
PPE required for handlers of linuron (see below). Labels of multiple active
ingredient products that contain linuron must bear the more protective of
either these entry restrictions or those on current labeling.
Non-WPS Uses - Labels of products with uses outside the scope of the
WPS must bear the following statement:
For liquid applications: "Do not enter or allow others to enter the
treated area until sprays have dried."
Personal Protective Equipment Requirements
Products containing linuron may contain more stringent PPE, but in
no case may require less stringent PPE than the following requirements.
Producers must compare the PPE requirements in this section with those on
current labeling and retain the more protective.
Handler PPE for Occupational Use Products - For all uses of linuron,
both within and outside the scope of the WPS, the minimum or baseline
PPE requirements for pesticide handlers (mixers and loaders) are:
0 coveralls over long-sleeved shirt and long pants,
° chemical-resistant footwear,
° chemical-resistant gloves, and
° chemical-resistant apron.
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Early Entry PPE - Since linuron is in Toxicity Category III for eye
and skin irritation potential and acute dermal toxicity, the PPE required for
early entry is coveralls, chemical-resistant gloves, shoes and socks.
Other Labeling Requirements
Environmental Hazard Section - The labels of all linuron end-use products
must be revised to bear the following statements under this section:
Ground Water Advisory
"This chemical is known to leach through soil into ground water under
certain conditions as a result of agricultural use. Use of this chemical
in areas where soils are permeable, particularly where the water table
is shallow, may result in ground-water contamination."
Surface Water Advisory
"Linuron may contaminate surface water through spray drift or, under
certain conditions, from surface runoff into adjacent surface water
bodies (ponds, lakes, streams, etc.). For several weeks post-
application, linuron has a high potential to runoff when applied to
fields with any of the following conditions: sloping land draining into
nearby surface waters; very poorly to somewhat poorly drained soils;
areas with extremely shallow ground water; frequently flooded areas;
fields with surface water canals or ditches; and highly credible land
cultivated with poor management practices."
For Terrestrial Uses Except Rights-of-Way
"This pesticide is toxic to fish and aquatic invertebrates. Do not apply
to water or to areas where surface water is present, or to intertidal
areas below the mean high water mark. Do not apply when weather
conditions favor drift from treated areas. Do not contaminate water
when disposing of equipment wash water or rinsate."
For Rights-of-Way - If a registrant chooses to support the rights-of-
way use, he must submit the data required in this RED document and his
labels must bear the following statement:
"This pesticide is toxic to fish and aquatic invertebrates. Do not
contaminate water when disposing of equipment washwaters or
rinsate."
If a registrant does not support the rights-of-way use, he must amend his
labels to delete this use.
Directions for Use Section - The labels of all linuron end-use products must
be revised to bear the following statements under this section:
Application Restrictions:
"Do not apply this product in a way that will contact workers or other
persons, either directly or through spray drift. Only protected
handlers may be in the area during application."
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Regulatory
Conclusion
"Aerial application is prohibited."
"Use on sand or loamy sand is prohibited."
"Use on soils of <1% organic matter is prohibited."
Crop Uses Section - The labels of all linuron end-use products must be
revised to bear the following application rates for the respective crops, under
this section:
Application Rates:
For use on soybeans: A maximum application rate of 1.0 Ib ai/A,
with use limited to single application (pre-emergent use only) per year.
For use on corn, field: A maximum application rate of 0.75 Ib ai/A,
with use limited to single application (pre-emergent use only) per year.
For use on potatoes: A maximum application rate of 1.5 Ibs ai/A,
with use limited to single application (pre-emergent use only) per year.
For use on asparagus: A maximum application rate of 2.0 Ibs ai/A
per year, with use limited to 3 applications per year.
Do not exceed 2.0 Ibs total per acre per year.
Although levels of concern are exceeded for ecological effects and
ground water quality, most uses of currently registered products containing
linuron, amended to reflect the risk mitigation measures imposed in this
RED, will not pose unreasonable risks or adverse effects to humans or the
environment. Therefore, products containing linuron for all registered uses
except use on cotton, non-cropland (rights-of-way), sweet corn, and
potatoes are eligible for reregistration.
EPA is unable to make a reregistration eligibility decision for use of
linuron on cotton, non-cropland (rights-of-way) and sweet corn because the
Agency does not have key generic data to support these uses. The basic
manufacturer, DuPont, has voluntarily cancelled or plans to cancel these
uses, so end-use product registrants must either delete the uses from their
labels or submit the required data.
EPA also is unable to make a reregistration eligibility decision
regarding the use of linuron on potatoes because, under current policy, the
food additive tolerances needed to support this use appear to be barred by
the Delaney clause in the FFDCA.
Linuron products with eligible uses will be reregistered once the
required product-specific data, revised Confidential Statements of Formula,
and revised labeling are received and accepted by EPA.
POT MOTG EPA is requesting public comments on the Reregistration Eligibility
Information Decision (RED) document for linuron during a 60-day time period, as
announced in a Notice of Availability published in the Federal Register. To
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obtain a copy of the RED document or to submit written comments, please
contact the Pesticide Docket, Public Response and Program Resources
Branch, Field Operations Division (7506C), Office of Pesticide Programs
(OPP), US EPA, Washington, DC 20460, telephone 703-305-5805.
Electronic copies of the RED and this fact sheet can be downloaded
from the Pesticide Special Review and Reregistration Information System at
703-308-7224. They also are available on the Internet on EPA's gopher
server, GOPHER.EPA.GOV, or using ftp on FTP.EPA.GOV, or using
WWW (World Wide Web) on WWW.EPA.GOV.
Printed copies of the RED and fact sheet can be obtained from EPA's
National Center for Environmental Publications and Information
(EPA/NCEPI), PO Box 42419, Cincinnati, OH 45242-0419, telephone
513-489-8190, fax 513-489-8695.
Following the comment period, the linuron RED document also will
be available from the National Technical Information Service (NTIS), 5285
Port Royal Road, Springfield, VA 22161, telephone 703-487-4650.
For more information about EPA's pesticide reregistration program,
the linuron RED, or reregistration of individual products containing linuron,
please contact the Special Review and Reregistration Division (7508W),
OPP, US EPA, Washington, DC 20460, telephone 703-308-8000.
For information about the health effects of pesticides, or for assistance
in recognizing and managing pesticide poisoning symptoms, please contact
the National Pesticides Telecommunications Network (NPTN). Call toll-
free 1-800-858-7378, between 8:00 am and 6:00 pm Central Time, Monday
through Friday.
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