United States
Environmental Protection
Agency
Prevention, Pesticides
And Toxic Substances
(7508C)
EPA-738-F99-009
September 1999
R.E.D. FACTS
Pesticide
Reregistration
Pebulate
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 before
November 1, 1984, 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 that describe the human health and
environmental effects of each pesticide. To implement provisions of the Food
Quality Protection Act of 1996, EPA considers the special sensitivity of infants and
children to pesticides, as well as aggregate exposure of the public to pesticide
residues from all sources, and the cumulative effects of pesticides and other
compounds with common mechanisms of toxicity. The Agency develops mitigation
measures or regulatory controls needed to effectively reduce each pesticide's risks.
EPA then reregisters pesticides that meet the safety standard of the FQPA and can
be used without posing unreasonable risks to human health or the environment.
When a pesticide is eligible for reregistration, EPA explains the basis for its
decision in a Reregistration Eligibility Decision (RED) document. This fact sheet
summarizes the information in the RED document for reregistration of Pebulate,
case 2500.
Use Profile
Regulatory
History
Pebulate is an herbicide used for control of grassy and broadleaf weeds in
sugar beets, tobacco, and tomatoes. Pebulate is predominantly applied before
planting and is immediately soil incorporated to prevent volatilization. There is also
a layby application (an application of pesticide which occurs in conjunction with
mechanical weeding), which is used in the western states (defined as California,
Arizona, and Nevada) only. There are no residential uses for this herbicide.
Pebulate was first registered as a pesticide in the United States in 1961.
There were three products registered that contained the active ingredient Pebulate.
These products were Tillam Technical, Tillam 6E, and Tillam 10G. In 1987, these
products were transferred from Stauffer Basic Chemical Holdings, Inc., to Zeneca
Ag Products.
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Human Health
Assessment
In 1996, Tillam 10G was canceled at the request of the registrant following
an Agency request for residue data for the 10G formulation. As of 1999, the
registrant is supporting continued registration of the technical grade product, EPA
Reg. No. 10182-213, and one end-use product, the 6 Ib. active ingredient per
gallon emulsifiable concentrate (EC), EPA Reg. No. 10182-158.
Toxicity
Pebulate is in the class of thiocarbamates and is a reversible cholinesterase
inhibitor. As with other chemicals in this class, neurotoxicity is the major toxic
effect for pebulate. Pebulate had low acute oral, dermal, and inhalation toxicity. It
was a slight to mild irritant to the eye or skin and was not a skin sensitizer. Toxicity
categories, which are classified as 1 (most toxic) through 4 (least toxic), were
either 3 or 4 for Pebulate. There was no evidence of increased tumor incidence in
the carcinogenicity studies in rats and mice, and the mutagenic test battery also
indicated that pebulate was not mutagenic. Therefore, pebulate was classified as
"not likely" to be a human carcinogen.
Dietary Exposure
All doses for risk assessment purposes were assessed using the conventional
safely factors of lOx for interspecies extrapolation and lOx for intraspecies
variability. In addition, the FQPA safety factor of lOx was retained for pebulate
because of (i) the severe neuropathology exhibited in studies with adult animals, (ii)
the structural similarities to other thiocarbamates for which increased susceptibility
of developing fetuses has been demonstrated, and (iii) the outstanding requirement
for a developmental neurotoxicity study. In the current analysis, the 1 Ox safety
factor was applied to the various populations of infants and children as well as to
females (13-50 years, i.e., females of childbearing age), because the Agency is
concerned about potential developmental (in utero exposure) effects of pebulate.
The lOx FQPA factor is not applied to males or to the general population. Acute
and chronic dietary risk estimates are calculated as <1% of the acute and chronic
population adjusted doses (aPAD and cPAD, respectively) for adults, infants, and
children, which are significantly below the Agency's level of concern.
For the aggregate risk to a population subgroup, the Agency adds the
calculated risk from exposures to food, drinking water, and residential exposure;
for Pebulate there are no expected residential exposures. The Agency concludes
that the aggregate risk estimate is not of concern for infants, children, and woman
(13-50 years of age).
Cumulative Risk Assessment
At this time, the Agency does not believe it has enough reliable information
concerning common mechanism issues to determine whether pebulate, a
thiocarbamate, shares a common mechanism of toxicity with other cholinesterase-
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inhibiting chemicals. Therefore, for the purposes of this RED, the Agency has
assumed that pebulate does not share a common mechanism of toxicity with
cholinesterase-inhibiting chemicals.
Occupational and Residential Exposure
With the use of personal protective equipment (PPE), risks for occupational
handlers were below the Agency's level of concern, which is a margin of exposure
(MOE) greater than 100, for most scenarios involving pebulate mixers and loaders.
In addition to the PPE which is currently on the label (long-sleeved shirts, long
pants, shoes, socks, protective eyewear, and chemical-resistant gloves), organic
vapor respirators are required when preparing solutions for chemigation and
application at the highest use rates in the western states (defined as California,
Arizona, and Nevada). For commercial operators, closed systems are required for
mixing and loading of pebulate impregnated on dry bulk fertilizer and in liquid
formulation in combination with fluid fertilizer. The MOEs for the pebulate
applicator exposures are acceptable with the PPE that is currently on the label, with
one exception. Applying dry bulk fertilizer to tobacco in the western states will also
require the use of an organic vapor respirator or an enclosed cab with an organic
vapor air filtration system. In the absence of dermal exposure data, the Agency is
also requiring that chemical-resistant gloves be worn during transplanting of crop
seedlings and is calling in data on this practice.
Environmental
Assessment
Based on laboratory studies, pebulate residues appear to be mobile, through
volatility, leaching, and runoff to surface water and may persist in soil under both
aerobic and anaerobic conditions. However, the mobility and persistence of
pebulate and its degradates in the field is less clear because of inadequate data.
Given the volatile nature of the compound, it is likely that significant volatilization of
pebulate occurs under field conditions, even with soil incorporation. Uncertainties
in the environmental fate of pebulate residues are associated with the lack of
environmental fate data for pebulate sulfoxide. Environmental fate data are needed
for pebulate sulfoxide to clarify the fate of pebulate residues in the environment.
Pebulate is not likely to pose an acute risk to birds or most mammals. Some
acute and chronic risk to strictly insectivorous mammals may exist before
incorporation, although exposure may be mitigated by volatility and incorporation of
pebulate into soils.
Pebulate does not appear to pose a significant risk to aquatic organisms.
Risk quotients for freshwater fish, invertebrates, and aquatic plants were below the
Agency's levels of concern for acute effects. Chronic toxicity endpoints are not
expected to be substantially lower than predicted estimated environmental
concentrations, although no direct conclusions are possible due to the lack of actual
chronic toxicity data. Chronic aquatic data may be requested if pebulate uses are
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increased. Although pebulate use on tobacco could result in estuarine exposure,
the potential risk to estuarine species is difficult to predict because there are no
acceptable estuarine toxicity data.
Little hazard to nontarget terrestrial plants is expected from incorporated
applications of pebulate. However, risk quotients based on default spray drift
assumptions from irrigation systems and possible runoff exposure suggest potential
adverse effects on growth in nontarget terrestrial plants exposed to pebulate. There
is uncertainty for this conclusion because (1) there are no data from which to
directly estimate drift exposure and (2) pebulate is volatile, which is likely to reduce
exposure. There is also some uncertainty associated with the potential for exposure
from volatilized residues depositing on nontarget plants. Risk to honeybees or other
beneficial insects is expected to be minimal because pebulate is soil-incorporated.
Risk Mitigation
To lessen the risks posed by pebulate, the Agency is requiring the following
mitigation measures for products containing pebulate. The specific language for the
label is specified in Section V of the RED document.
To reduce the amount of residue in food crops, the Agency is requiring a
plantback harvest interval of 30 days for tomatoes, and establishing a 4 month
plantback interval (FBI) for all rotated food crops. To protect workers, the
Agency is requiring the use of additional PPE (including coveralls, chemical-
resistant gloves, and organic vapor respirators) for all chemigation mixers/loaders
and for mixers/loaders when preparing solutions for an application in the western
states at the highest use rate (>6 Ib ai/Acre). In addition, closed loading systems
are required for commercial operations that impregnate dry bulk fertilizer with
pebulate and that combine pebulate (fluid formulation) with liquid fertilizer. An
organic vapor respirator or an enclosed cab with a filtration system equal to that of
an organic vapor respirator is required for commercial applicators when applying
dry bulk fertilizer impregnated with pebulate to tobacco. Chemical-resistant gloves
are required for workers involved with mechanical transplanting or mechanically
assisted transplanting of tomatoes and tobacco.
Additionally, the label must specify that pebulate is prohibited for greenhouse
uses and must contain language that requires the use of best management practices
to protect nontarget terrestrial and semiaquatic plants (mainly grass related species)
from runoff and drift.
Additional Data
R6Q U i red
EPA is requiring the following additional generic studies for Pebulate to
its regulatory assessments and conclusions: stability to metals, estuarine
toxicity, developmental neurotoxicity, dermal and inhalation studies,
leaching/adsorption/desorption, field volatility, and terrestrial field dissipation.
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Product Labeling
Changes Required
All pebulate end-use products must comply with EPA's current pesticide
product labeling requirements and with the following. For a comprehensive list of
labeling requirements, please see the pebulate RED document.
The label must specify that chemical-resistant gloves must be worn while
transplanting tomato and tobacco seedlings. In addition, an organic vapor
respirator must be worn by most mixers/loaders. Commercial mixer/loaders and
some commercial applicators must use closed systems, because of the high volume
of chemical to which they will be exposed. Also, the label must specify that use of
pebulate in a greenhouse is prohibited.
Reg UI atO ry The use of currently registered products containing pebulate in accordance
Concl USJOn with approved labeling will not pose unreasonable risks or adverse effects to
humans or the environment. Therefore, all uses of these products are eligible for
reregi station.
For More
Information
EPA is requesting public comments on the Reregistation Eligibility Decision
(RED) document for pebulate during a 60-day time period, as announced in a
Notice of Availability published in the Federal Register. To obtain a copy of the
RED document or to submit written comments, please contact the Pesticide
Docket, Public Information and Records Integrity Branch, Information Resources
and Services Division (7502C), Office of Pesticide Programs (OPP), US EPA,
Washington, DC 20460, telephone
703-305-5805. Electronic copies of the RED and this fact sheet are available on
the Internet (http://www.epa.gov/REDs).
Printed copies of the RED and fact sheet can be obtained from EPA's
National Service Center for Environmental Publications (EPA/NSCEP), PO Box
42419, Cincinnati, OH 45242-2419, telephone
1-800-490-9198; fax 513-489-8695.
Following the comment period, the pebulate RED document also will be
available from the National Technical Information Service (NTIS), 5285 Port Royal
Road, Springfield, VA 22161, telephone 1-800-553-6847 and 703-605-6000.
For more information about EPA's pesticide reregi station program, the
pebulate RED, or reregi station of individual products containing pebulate, please
contact the Special Review and Reregistation Division (7508C), 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, contact the National
Pesticide Telecommunications Network (NPTN). Call toll-free 1-800-858-7378,
from 6:30amto4:30 pm Pacific Time, or 9:30 am to 7:30 pm Eastern Standard
Time, seven days a week (ace.orst.edu/info/nptn).
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