- Dermal LOAEL of 2 mg/kg/day when adjusted for 7% dermal absorption rate (as shown
in monkeys), results in a equivalent dermal dose is 14 mg/kg/day
(2 mg/kg/day + 0.07 = 14 mg/kg/day).

d. Other Issues

The incident profile for tribufos is as follows: The Minnesota Department of Agriculture
surveyed 32 states about spray drift and found a total of 2,681 complaints from 1993 through 1995.
Tribufos was involved in 27 of these complaints and ranked 10" of 38 of the pesticides reported.
Another survey was conducted by the California Department of Health Services in 1987. A total of
232 exposed residents were interviewed and 175 controls. People with high likelihood of exposure to
tribufos complained of fatigue, eye irritation, rhinitis, throat irritation, difficulty in breathing, wheezing,
nausea, and diarrhea.

The Agency has worked with the California Department of Pesticide Regulation on its review of
tribufos. California regulates on brain cholinesterase inhibition; the Agency regulates on plasma or RBC
cholinesterase inhibition. California considers the 2 mg/kg/day dose in the 21-day rabbit dermal study
to be a NOAEL because cholinesterase inhibition was observed in plasma and red blood cells only, not
brain. The Agency regulates this dose as a LOAEL and applied an additional 3X uncertainty factor to
account for the lack of a NOAEL in this study. .

e. Alternatives and Benefits of Tribufos

Tribufos is applied to cotton prior to harvest. The Agency estimates that approximately 4.5
million pounds of tribufos are applied to approximately 35% of the estimated fourteen million acres of
cotton grown in the U.S. per year. Application rates vary from 0.50 Ibs ai/A (tank-mixed) to 1.875 Ibs
ai/A (tribufos used alone). Tribufos is most typically used in a tank-mix with other defoliants and at a
rate between 0.50 Ibs ai/A to 0.75 Ibs ai/A.

Tribufos is used throughout the cotton belt, which extends from California to Florida and as far
north as Missouri, Tennessee, and Virginia. As stated above, tribufos is applied to more than 35% of
planted cotton acreage, which is an increase from 1991 when less than 1 million acres (<10% of total
acreage) was treated with tribufos.

Alternatives

An alternative analysis was conducted for tribufos. The Agency reviews alternatives to a
pesticide, by considering efficacy against target pests, costs, ease of use, potential resistance
development to the pesticide,impacts on existing integrated pest management (IPM) programs, and
several other characteristics. Although there are other defoliants available, the Agency has concluded

that tribufos exhibits greater efficacy at lower night temperatures than other defoliants. Also, when

37



included in this document, but are available on the Agency's web page (www.epa.gov/pesticides/op)
and in the Public Docket.
I. Chemical Overview

A. Regulatory History

Tribufos was first registered by the United States Environmental Protection Agency in 1961 for
use on cotton as a total defoliant and as a bottom defoliant to reduce or prevent losses from boll rot

organisms. A Registration Standard was not issued for tribufos.

B. Chemical Identification

Tribufos:
oO
i
H,C(CH,),S~/ ~ S(CH,),CH,
S(CH,),CH,
S,S,S-tributyl phosphorotrithioate

e Common Name: Tribufos
e Chemical Name: S,S,S-tributy] phosphorotrithioate
e Chemical Family: Organophosphate

e CAS Registry Number: 78-48-8

e OPP Chemical Code: 074801
e Empirical Formula: Cy2H7OPS3
e Molecular Weight: 314.5 g/mole

e Trade and Other Names: DEF, DEF6, Folex

e Basic Manufacturer: Bayer Corporation





Other PR Notices can be found at http://www.epa.gov/opppmsd1/PR_Notices.

3. Pesticide Product Registration Application Forms (These forms are in PDF format and will
require the Acrobat reader.)

EPA Form No. 8570-1, Application for Pesticide Registration/Amendment
EPA Form No. 8570-4, Confidential Statement of Formula

EPA Form No. 8570-27, Formulator's Exemption Statement

EPA Form No. 8570-34, Certification with Respect to Citations of Data
EPA Form No. 8570-35, Data Matrix

General Pesticide Information (Some of these forms are in PDF format and will require the
Acrobat reader.)

Registration Division Personnel Contact List
Biopesticides and Pollution Prevention Division (BPPD) Contacts
Antimicrobials Division Organizational Structure/Contact List
53 F.R. 15952, Pesticide Registration Procedures; Pesticide Data Requirements
(DF format)
fw CFR Part 156, Labeling Requirements for Pesticides and Devices (PDF
format)

£. 40 CFR Part 158, Data Requirements for Registration (PDF format)

g.. 50 FR. 48833, Disclosure of Reviews of Pesticide Data (November 27, 1985)

Before submitting your application for registration, you may wish to consult some additional
sources of information. These include:

The Office of Pesticide Programs’ Web Site

The booklet "General Information on Applying for Registration of Pesticides in the United
States,” PB92-221811, available through the National Technical Information Service
(NTIS) at the following address:

National Technical Information Service (NTIS)
5285 Port Royal Road
Springfield, VA 22161

The telephone number for NTIS is (703) 605-6000. Please note that EPA is currently in
the process of updating this booklet to reflect the changes in the registration program
resulting from the passage of the FQPA and the reorganization of the Office of Pesticide

97



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Appendix A: Use Patterns Eligible For Reregistration .
NN

Defoliant 98%Technical-BayerCorporation | 1.875 for CA Not for residential use, or

Foliar Spray Reg. No. 3125-96 and AZ other non-occupational
- Groundboom and 1.125 for uses. “Mechanical
the remaining Harvesting Only”; requires|

~Aerial 70.5% End Use Product - Bayer wates use of closed systems.

Reg. No. 3125-282 Do not allow to drift.

70.5% End Use Aventis Crop
Science

Reg No. 264-498

70.5% End Use Product Crystal
Chemical Inter-America

Reg. No. 67801-3

98.1% Technical - Micro Flo
Reg. No. 51036-324

70.5% End Use Product
Micro Flo
Reg. No. 510360-320

57



Glossary of Terms and Abbreviations

AGDCI
ai
aPAD
AR
BCF
CFR
ChE
cPAD
CSF
CSFII
DAT
DCI
DEEM
DFR
DWLOC
EC

NAWQA

Agricultural Data Call-In
Active Ingredient
Acute Population Adjusted Dose
Anticipated Residue
Bioconcentration Factor
Code of Federal Regulations
Cholinesterase
Chronic Population Adjusted Dose
Confidential Statement of Formula
USDA Continuing Surveys for Food Intake by Individuals
Days After treatment
Data Call-In
Dietary Exposure Evaluation Model
Dislodgeable Foliar Residue
Drinking Water Level of Comparison.
Emulsifiable Concentrate Formulation
Estimated Environmental Concentration.
End-Use Product
Environmental Protection Agency
Food and Drug Administration
Federal Insecticide, Fungicide, and Rodenticide Act
Federal Food, Drug, and Cosmetic Act
Food Quality Protection Act
Tier I Surface Water Computer Model
Index Reservoir
Interim Reregistration Eligibility Decision
Median Lethal Concentration. A statistically derived concentration of a substance that can be
expected to cause death in 50% of test animals. It is usually expressed as the weight of substance
per weight or volume of water, air or feed, e.g., mg/I, mg/kg or ppm.
Median Lethal Dose. A statistically derived single dose that can be expected to cause death in
50% of the test animals when administered by the route indicated (oral, dermal, inhalation). It is
expressed as a weight of substance per unit weight of animal, e.g., mg/kg.
Level of Concern
Limit of Detection
Lowest Observed Adverse Effect Level
Micrograms Per Gram
Micrograms Per Liter
Milligram Per Kilogram Per Day
Milligrams Per Liter
Margin of Exposure
Manufacturing-Use Product
Master Record Identification (number). EPA's system of recording and tracking studies submitted.
Not Applicable
USGS National Water Quality Assessment
National Pollutant Discharge Elimination System

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(@WLOC) to ascertain whether the amount estimated in water exceeds this level. If the estimated
water concentration is less than the DWLOC, the Agency is not concerned about tribufos consumption
in drinking water. If model estimates are greater than the DWLOC, the Agency must further evaluate
the potential for drinking water exposure. The Agency uses ground and surface water monitoring data,
when available and of sufficient quantity and reliability, as part of a more in-depth evaluation.

There are no environmental degradates of tribufos that are of toxicological concern. The
drinking water assessment is based on parent tribufos only. Table 4 below summarizes the DWLOCs
and estimated environmental concentrations (EECs) for ground and surface
water (acute and chronic).

a. Surface Water

Tribufos spray drift can potentially contaminate surface water. Substantial amounts of applied
tribufos may remain available for runoff for many months after application due to the aerobic soil
metabolism halflife of 745 days. The relatively high soil/water partitioning of tribufos indicates that
runoff will generally occur primarily via adsorption to eroding soil as opposed to dissolution in runoff
water.

Tribufos is stable to abiotic hydrolysis at pHs 5 and 7, and stable to direct aqueous photolysis.
It has a relatively low volatilization potential, undergoes slow abiotic hydrolysis at pH 9, and appears to

undergo extremely slow biodegradation under aerobic conditions. Consequently, tribufos will probably
be persistent in the water column of most surface waters within which it occurs, except those with short
hydrologic residence times for which flow out of the system may be the major dissipation pathway. The
results of the anaerobic soil and the anaerobic aquatic metabolism studies indicate that tribufos may be
a little less persistent under the anaerobic conditions found in most sediments, but is still relatively
persistent.

Because the Agency does not have any surface water monitoring data fro tribufos, surface
drinking water concentrations were estimated using the PRZM 2/EXAMS II (Tier IL) computer model
with the Index Reservoir and Percent Crop Area. Based on the model scenarios, the estimated peak
(acute) concentration of tribufos in surface water is 5.8 ppb and the annual average concentration of
tribufos in surface water over a 36-year period (chronic) is 1.8 ppb. Table 5 below summarizes the
DWLOCs and EECs for surface water (acute and chronic).

b. Ground Water
According to the EPA Pesticide in Ground water Database: A Compilation of Monitoring
Studies, 1971-1991, A National Summary (EPA 734-12-92-001 September,1992), between 1984

and 1988, 569 wells were tested for tribufos in California and Texas. Tribufos was not detected in any
of these samples. Although an absence of detections of tribufos residues does not necessarily mean

10



Appendix E. Generic Data Call-In

See attached table for a list of generic data requirements. Note that a complete Data Call-In
(CD), with all pertinent instructions, is being sent to registrants under separate cover.



1. A survey by the National Agricultural Aviation Administration (NAAA)
indicates on a good day when weather conditions are extremely favorable,
more than 2000 acres of cotton can be treated.

2. Unlike insecticidal uses, which may be limited to areas of infestation, harvest
aids are typically applied to the entire crop.

3. Fields where cotton is grown may cover very large areas where growers have
only a short window to apply tribufos to an entire crop for defoliation.

i. Dermal Risk

The MOEs listed in Tables 7 and 8 for aerial scenarios are assuming the maximum level of
engineering controls. The resulting MOEs for the proposed rate of 1.125 Ibs ai/A (Table 7) range from
82 (mixing and loading to support aerial application to 1,200 acres per day) to 3,300 (flaggers
supporting aerial application to 1,200 acres per day). For the current maximum label rate of 1.875 Ibs
ai/A (Table 8), MOEs range from 49 (mixing/loading for aerial application to 1,200 acres) to 2,000
(flagging to support aerial application to 1,200 acres per day). Therefore, several of the handler
scenarios are below the dermal target MOE of 300 and are of concern to the Agency.

In the revised human health effects chapter, the MOE for flagger scenarios were calculated with
engineering controls. Because these MOEs (2000 and 3200) were so high at both the 1.125 Ibs ai/A
rate and the 1.875 lbs ai/A rate, the calculations have since been conducted with baseline and
additional PPE. MOEs for dermal exposure ranged from 40 (flaggers with baseline attire at a rate of
1.875 lbs ai/A) to 73 (flaggers with additional PPE at a rate of 1.125 Ibs ai/A). These MOEs are
below the target MOE of 300, therefore, the Agency concludes that engineering controls are necessary
to protect flaggers supporting aerial applications of tribufos at any rate.

The MOEs associated with the use of groundboom equipment, performed at baseline, range
from 760 (mixing and loading at a rate of 1.875 Ibs ai/A) to 780 (applying tribufos at a rate of 1.125 Ibs
ai/A. At baseline, the MOEs for dermal exposure to tribufos are all greater than the target MOE of
300. The Agency, therefore, has no concern for workers who, mix, load, and apply tribufos via
groundboom.

The aerial scenarios for tribufos are based on the maximum level of engineering controls and
the groundboom scenarios are based on baseline assumptions (long sleeved-shirt, long pants, shoes,
and socks). MOEs for dermal exposure are less than the target MOE 300, despite maximum mitigation
measures (engineering controls) for the identified aerial exposure scenarios listed above. One of these

. five scenarios is below 100. In summary, when engineering controls are used, the MOEs for the aerial
mixer, loader, and applicator are below the target MOE of 300 and, therefore, are of concern to the
Agency.

17



associated with aerial as well as other application types where appropriate. In the interim, labels should
be amended to include the following spray drift related language.

For products that are applied outdoors in liquid sprays, regardless of application method, the
following must be added to the labels:

"Do not allow this product to drift"

For outdoor liquid products that are applied aerially, further label language is necessary for
spray drift management. Specific label language is outlined in Table 11, “Summary of Labeling
Changes for Tribufos.”

3. Other Label Modifications

Provided the following risk mitigation measures are incorporated in their entirety into labels for
tribufos-containing products, the Agency finds that all currently registered uses of tribufos would be
eligible for reregistration, pending a cumulative assessment of the organophosphates.

. Increased Restricted Entry Interval to 7 days

. Reduction in maximum label rate to 1.125 Ibs ai/A with the exception of California and Arizona,
which retain the maximum current label rate of 1.875 Ibs ai/A

. Distribute tribufos in a closed loading systems by 2002

. Closed systems for aerial applicators

Vv. What Registrants Need To Do
In order to be eligible for reregistration, registrants need to implement the risk mitigation
measures outlined in Section IV, by submitting label amendments and meeting the data requirements
described in this section.
A. Mannufacturing-Use Products
1. Additional Generic Data Requirements
The generic database supporting the reregistration of tribufos has been reviewed and

determined to be substantially complete. Based on a need to further refine the occupational and
ecological risk assessments, the Agency is requiring the following confirmatory data.

42



are available on the eye irritation potential of tribufos. Dermal irritation is mild to moderate and tribufos
is placed in Toxicity Category IV. Tribufos is not a dermal sensitizer. Inhibition of plasma, erythrocyte
and/or brain ChE activity occurs by all routes (oral, dermal and inhalation) and duration (acute,
subchronic, and chronic) of exposures. In addition to its ChE inhibitory effects, tribufos, at a high dose,
displayed organophosphate-type delayed neuropatholgy in the hen. Tribufos also displayed ocular
toxicity in the rat following either oral or inhalation exposure. Refer to the Human Health Risk
Assessment for Tribufos, dated June 26, 2000, and Table 5 for additional information regarding the
toxicity of tribufos.

Table 5. Acute Toxicity of Tribufos
Guideline
Number

Toxicity

study T:
Study Type MRID Results Category

‘Acute Oral-Rat_ 141954903, ILD, = 195-235 mg/kg I

ILD) =>1000 mg/kg (m)
<2000 mg/kg (f)

JLC., = 4650 mg/nt (m) m
2460 mg/nt (f)

{Acute Dermal - Rabbit 41954902 si

Acute Inhalation - Rat 141782301

{Primary Eye Irritation -Rat None {Data required (irritation likely) NA.

haita to moderate erythema, dry

cracked skin, edema WV

Primary Skin Irritation- Rat [41896203

[Dermal Sensitization 41618812 _ Negative NA

i Dermal Exposure (Short- and Intermediate-Term)

In the preliminary human health risk assessment dated September 14, 1999, (available through
both the EPA public docket and at http:www.epa.gov/opp/op), the Agency determined an MOE of
1000 was required for occupational exposure. This was based on the standard use of 10X for
interspecies variability, 10X for intraspecies variability, and an additional 3X Uncertainty Factor (UF)
which was applied because a NOAEL was not established in the 21-day rabbit dermal study (use of a
LOAEL), and an additional 3X UF due to concern for severe neurotoxic effects seen in the hen study.
Additionally, the ocular lesions seen at 17 mg/kg/day in the chronic study in rats and the retinal toxicity
seen at 22 mg/kg/day in the 90-day inhalation study in rats were also seen at the highest dose tested in
those studies.

The Agency reconsidered this position in June of 2000, and determined that a target MOE of
300 is appropriate (.e., an additional 3X for the use of the LOAEL) and no additional UFs, such as the
additional 3X for severity of effects (as previously determined) are required for the neurotoxic effects
seen in the hen study (“Tribufos - Reassessment of the Toxicity Endpoint Selection - Report of the
Hazard Identification Assessment Review Committee”, June 27, 2000). This determination was made

13



D. Labeling Changes Summary Table

In order to be eligible for reregistration, amend all product labels to incorporate the risk
mitigation measures outlined in section IV. Table 11 describes how language on the labels should be
amended.

45



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The Minnesota Department of Agriculture surveyed 32 states about spray drift and found a
total of 2,681 complaints from 1993 through 1995. Tribufos was involved in 27 of these complaints,
which is only 1% of the total complaints but it ranked 10 out of the 38 pesticides for which incidents
were reported. In a survey by the California Department of Health Services in 1987, a total of 232
exposed residents and 175 controls were interviewed. Those with high likelihood of exposure to
tribufos complained of fatigue, eye irritation, rhinitis, throat irritation, difficulty in breathing, wheezing,
nausea and diarrhea. California no longer allows tribufos to be used within one-half mile of residential
areas for reasons of odor.

Since the Agency’s 1997 review, there have been two drift complaints: one from Georgia in
1996 when a person with flu-like symptoms did not seek medical attention and one from North
Carolina in 1998 where a woman was outdoors when a crop duster flew over. The woman reported
feeling the mist on her skin as well as inhaling it. She also reported nausea, headache, and developed
hypertension. Her physician felt tribufos was likely the cause of her symptoms.

B. Environmental Risk Assessment
1. Environmental Fate

The Agency has determined that ground and surface water contamination are not likely to occur
through runoff. The environmental fate of tribufos has been well characterized in the laboratory;
however, its behavior in the field is not yet clearly understood. Based on the laboratory data, it appears
that tribufos could accumulate in soil with repeated applications. The primary route of dissipation
appears to be degradation in flooded soil under anaerobic conditions, with a half-life of 4-6 months. In
general, tribufos may be described as a persistent and immobile compound. It is also only moderately
soluble, with an aqueous solubility of 2.3 ppm. Tribufos can contaminate surface water at application
by spray drift. Substantial fractions of applied tribufos may remain available for runoff for many months
after application. The relatively high soil/water partitioning of tribufos indicates that runoff will generally
occur primarily via adsorption to eroding soil as oppossed to dissolution in runoff water. In addition,
the concentration of tribufos adsorbed to suspended and bottom sediment will be much greater than its
concentration in sediment pore water or the water column. Based on the tendency to bind to soil,
ground water contamination as a result of tribufos use is not expected.

2. Ecological Assessment

The Agency’s ecological risk assessment compares toxicity endpoints from ecological toxicity
studies to estimated environmental concentrations based on environmental fate characteristics, pesticide
use, and/or monitoring data. To evaluate the potential risk to nontarget organisms from the use of
tribufos products, EPA calculates a Risk Quotient (RQ), which is the ratio of the estimated exposure
concentration to the toxicity endpoint values, such as LDsp (the median lethal dose at which 50% of the
test animals die) or LC. (the median concentration of a substance which causes death to 50% of the

23



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2) The restricted entry interval (RED is to be increased from 24 hours to 7 days;

3) Tribufos products are to be distributed in closed systems starting with the 2002 season.
4) Aerial applicators are to be in enclosed cockpits.

5) A biomonitoring study is to be conducted to confirm the Agency’s risk management
decision that occupational risks associated with the use of tribufos are not of concem. The
biomonitoring study will be submitted to the Agency by September 2003.

The Agency also examines the benefits associated the use of a chemical when worker and
ecological risks are of concern to the Agency. For tribufos, the Agency has received and
reviewed benefits analyses from several stakeholders that ascertain the benefits from the use of
tribufos are numerous, including its efficacy at lower temperatures. The Agency has considered
these submissions and concurs that the benefits from tribufos are numerous and its loss to the
cotton industry would be substantial.

Although the Agency’s analyses indicate concern for several ecological species, the Agency is
confident that the above mitigation measures that will be implemented to address human health
risks will also reduce ecological risks. For instance, it is expected that a reduction in the
application rate, largely through tank-mixing, will result in less pesticide availability in the
ecosystem. 7

Next Steps

Numerous opportunities for public comment were offered as this decision was being
developed. The tribufos IRED, therefore, is issued in final (see www.e! W/REDs/ or
www.epa.gov/pesticides/op ), without a formal public comment period. The docket remains
open, however, and any comments submitted in the future will be placed in this public docket.

To implement risk mitigation as quickly as possible, time frames for making the changes
required by the Tribufos IRED are shorter than those in a usual RED. Tribufos labels must be
amended to include the above mitigation and submitted to the Agency within 90 days after
issuance of this IRED.

When the cumulative risk assessment for all organophosphate pesticides is completed, EPA will
issue its final tolerance reassessment decision for tribufos and may result in further risk
mitigation measures. Similarly, the Agency may reconsider any part of this interim decision
based on new information which may come to the Agency’s attention. The Agency will revoke
one tolerance because there are no registered uses and amend one tolerance. For all OPs,
taising and/or establishing tolerances will be considered once a cumulative assessment is
completed.



Table 8. Dermal, Inhalation and Aggregate MOEs at 1.875 Ib ai/A (For CA and AZ)

DermalMOE?* | Inhalation MOE? °
with Eng. Controls | with Eng. Controls
. Acres for aerial - for aerial - and 7
Exposure Scenario Treated Baseline for Baseline for ARI
groundboom groundboom
scenarios scenarios
Mixer/Loader Exposure
Mixing/Loading Liquids for Aerial Application 1200 _ 330 | 0:16-3|
Mixing/Loading Liquids for Groundboom 80 760 5100 24
1Application
Applicator Exposure
Applying Spray via Aerial Application 1200 410
[Groundboom Tractor -- PHED V1.1(3) -at 80 470 570 12
[Baseline
Flagger Exposure .
Flagging Aerial Applications --PHED V1.1(4) | 1200 .] 2000 | : 4000 ~ 4 59

* MOEs greater than 300 for the dermal route are not of concern.
> MOEs greater than 100 for the inhalation route are not of concern.
* ARIs greater or equal to 1 are not of concern.

e. Post-Application Risks

The Agency also assessed post-application risks to workers. Post-application workers who
enter previously treated fields may be exposed because their skin contacts treated surfaces in the area
where they are working. Exposures are directly related to the tasks which are performed. The Agency
examines the amount of pesticide residue found on the workers over time in various studies. The
Agency then evaluates this information to determine the number of days following application that must
elapse before the pesticide residues dissipate to a level where worker MOEs equal or exceed 300
while wearing baseline attire. Baseline attire, consisting of long-sleeved shirt, long pants, shoes and
socks, was used to assess post-application risks to reentry workers. Based on the results of the post-
application worker assessment, the Agency decides if there is a need to establish early entry restrictions
to allow reentry into treated fields for nonroutine hand labor activities using a specified set of PPE,
rather than totally restricting entry for a period of time. For tribufos, restricted entry intervals (REIs)
have been established for post-application activities. These include: raking, picking, tramping, and the
module builder operator.

The Agency also reviewed a chemical-specific post-application worker exposure study. This
chemical-specific study was conducted to determine the dermal and inhalation exposures of workers
engaged in post-application activities. Inhalation exposure is a negligible contributor to the overall risks
associated with the use of tribufos. Table 9 lists the post-application dermal MOEs, based on the

20



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3. Bibliographic Citation (Column 3). If the Agency has acceptable data in its files, this column
list the identify number of each study. This normally is the Master Record Identification
(MIRD) number, but may be a "GS" number if no MRID number has been assigned. Refer to
the Bibliography appendix for a complete citation of the study.

60



United States Prevention, Pesticides EPA 738-R-00-022
Environmental Protection And Toxic Substances September 2000
| Agency (7508C)

SEPA Interim Reregistraion
| Eligibility Decision (IRED)

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Tribufos is an organophosphate defoliant used for cotton crops. It is specifically used to
defoliate cotton in preparation for machine harvesting.

There are about 4,500,000 pounds of active ingredient (ai) applied annually to between 4 and 5
million acres (A) or about 35% of planted cotton acreage in the United States. The typical rate
of application varies from 0.50 Ib ai/A to1.875 lb ai/A. Tribufos is most often applied in a
tank-mix. When it is tank-mixed, the application rate is typically significantly lower than the
maximum label rate.

There are no residential uses of tribufos.

Health Effects

Tribufos can cause cholinesterase inhibition in humans; that is, it can overstimulate the nervous
system causing nausea, dizziness, confusion, and at very high exposures (e.g., accidents or
major spills), respiratory paralysis and death.

Dietary risks from food and drinking water are not of concern to the Agency for all segments of
the population, including children.

The current occupational risk assessment indicates risk concerns for aerial mixers/loaders and
aerial applicators (with closed mixing/loading systems and enclosed cockpits). However, the
Agency believes actual exposures are lower. Risks to workers who mix, load, and apply
tribufos via groundboom are not of concern to the Agency but risks to workers who enter fields
shortly after treatment are of concern.

Ecological risks include acute and chronic concerns for both birds and mammals. The Agency
is also concerned with acute risks to marine fish. Several studies conducted in a variety of
climates where tribufos is used resulted in risks of concern to freshwater and marine
invertebrates.

Risk Mitigation
To mitigate risks to workers, the following measures are necessary:
1) The maximum application rate is to be reduced to 1.5 pints/A (1.125 Ibs ai/A) in all states,

except California and Arizona, which would remain at the higher rate of 2.5 pints/A (1.875 Ib
ai/A). California and Arizona grow hardier varieties of cotton, which require more defoliant.



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conducted using DEEM software and a probabilistic (Monte Carlo) technique. The Monte Carlo
analysis provides a more realistic assessment due to the use of a distribution of residues, rather than.
single residues, to calculate a range of exposures and risks.

This exposure estimate, for both the acute and chronic dietary, has been extensively refined.
No further refinements can be made to these anticipated residues as the USDA Pesticide Data Program
(PDP) and the Food and Drug Administration (FDA) monitoring programs do not analyze for tribufos
at this time.

e. Acute Dietary (Food)

The assessment was based on anticipated residue (AR) values which were calculated using field
trial data, reduction factors from processing studies, and percent of crop treated data (35%). Residues
in meat and milk were estimated using data from livestock metabolism and feeding studies. The
endpoint used to assess acute dietary risk is cholinesterase inhibition in plasma and RBCs, at
Img/kg/day (NOAEL) in the prenatal developmental toxicity study in rats (MRID 40190601). The
Agency applied an uncertainty factor (UF) of 100 to account for both interspecies extrapolation (10X),
an intraspecies variability (10X), and the FQPA Safety Factor (10X). Therefore, the acute Population
Adjusted Dose (aPAD) is calculated to be 0.001 mg/kg. At the 99.9" percentile exposure, the most
highly exposed population subgroup is children (1-6 years) at 9% of the aPAD. The acute dietary risk
(from food) of tribufos does not exceed the Agency’s level of risk concern (i.e., less than 100% of the
aPAD is utilized). The results for the general population and the most sensitive subgroups are
summarized in Table 2.

' Table 2. Acute Dietary (Food) Exposure and Risk Estimates
99.9" Percentile

Population
Exposure (mg/kg/day) %aPAD

U.S. Population 0.000050 5
|Non-nursing Infants (<1 year) 0.000060 6
[Children (1-6 years) 0.000085 9
[Females (13+ years) 0.000026 3

f Chronic Dietary (Food)

The chronic dietary exposure analysis (from food sources) was conducted using anticipated
residues (ARs) from field trial studies and 35% crop treated for cottonseed oil and cottonseed meal.
Residues in meat and milk were estimated using data from livestock metabolism and feeding studies.
The endpoint used in the chronic dietary risk assessment is cholinesterase inhibition in plasma from a
chronic dog study with a NOAEL of 0.1 mg/kg/day (MRID 42007203). As in the acute assessment,
the Agency applied a UF of 100 for both interspecies extrapolation (10X) and intraspecies variability
(10X). The FQPA 10X Safety Factor was retained (10X). Therefore, the chronic Population

8



Appendix C: Technical Support Documents

Additional documentation in support of this Interim RED is maintained in the OPP docket,
located in Room 119, Crystal Mall #2, 1921 Jefferson Davis Highway, Arlington, VA. It is open
Monday through Friday, excluding legal holidays, from 8:30 am to 4 pm.

The docket initially contained the preliminary risk assessments and related documents as of
September 23, 1998. Sixty days later the first public comment period closed. The Agency considered
comments on the revised risk assessments and added the formal “Response to Comments” document
and the revised risk assessment to the docket on September 24, 1999.

All documents, in hard copy form, may be viewed in the OPP docket room or downloaded or
viewed via the Intemet at the following site:

www.epa.gov/pesticides/op

67



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2. Endocrine Disruptor Effects

EPA is required under the FFDCA, as amended by FQPA, to develop a screening program to
determine whether certain substances (including all pesticide active and other ingredients) "may have an
effect in humans that is similar to an effect produced by a naturally occurring estrogen, or other such
endocrine effects as the Administrator may designate." Following the recommendations of its
Endocrine Disruptor Screening and Testing Advisory Committee EDSTAC), EPA determined that
there was scientific basis for including, as part of the program, the androgen and thyroid hormone
systems, in addition to the estrogen hormone system. EPA also adopted EDSTAC’s recommendation
that the Program include evaluations of potential effects in wildlife. For pesticide chemicals, EPA will
use FIFRA and, to the extent that effects in wildlife may help determine whether a substance may have
an effect in humans, FFDCA authority to require the wildlife evaluations. As the science develops and
resources allow, screening of additional hormone systems may be added to the Endocrine Disruptor

Screening Program (EDSP).

When the appropriate screening and/or testing protocols being considered under the Agency’s
EDSP have been developed, tribufos may be subjected to additional screening and/or testing to better
characterize effects related to endocrine disruption.

Cc. Regulatory Rationale
The following is a summary of the rationale for managing risks associated with the use of
tribufos. Where labeling revisions are warranted, specific language is set forth in the summary tables of
Section V of this document.
1. Human Health Risk Mitigation
a. Dietary Risk Mitigation

The Agency has no concern for dietary risks from food and water. Therefore no
mitigation measures for dietary food and water risks are required.

i. Acute Dietary (Food)

Acute dietary exposure is below the Agency's level of concern of all population subgroups.
Infants and children (1-6 years) are exposed to tribufos at a level less than or equal to 9% of the aPAD
(0.005 mg/kg/day) at the 99.9" exposure percentile. Therefore, no mitigation for acute dietary food
tisks is required.

32



BIBLIOGRAPHY

MRID

CITATION

41618813

41618814

41618816

41618817

41689901

41689902

41719401

4178230

Hughes, J. (1990) The Toxicity of DEF Technical to Selanastrum capricornutum (Tier
2 Growth and Reproduction of Aquatic Plants): Lab Project Number: BOS9-02-2:
100230. Unpublished study prepared by Malcolm Pimie, Inc. 36 p.

Schocken, M. ; Philippson, I. (1987) Stability of DEF in Sterile Aqueous Buffer
Solutions: Lab Project Number: 94918. Unpublished study prepared by Mobay
Corp. 23 p.

Jackson, S.; Kesterson, A.; Lawrence, L. (1988) Soil Surface Photolysis of [Carbon
14] DEF in Natural Sunlight: Lab Project Number: 1153: 206: 95673. Unpublished
study prepared by Pharmacology and Toxicology Research Laboratory. 67 p.

Daly, D. (1987) Soil Adsorption/Desorption with [Carbon 14) DEF: Lab Project
Number: 36356: 95600. Unpublished study prepared by: Analytical Bio-Chemistry
Laboratories, Inc. 50 p.

Heimbach, F. (1989) Acute Toxicity of DEF (Technical) to Waterfleas (Daphnia
magna): Lab Project Number: 99630. Unpublished study prepared by Bayer AG. 32
p.

Heimbach, F. (1990) Acute Toxicity of DEF 6 to Waterfleas (Daphnia magna): Lab
Project Number: HBF/DM96: E 320 0403-2: 100208. Unpublished study prepared
by Bayer AG, 33 p.

Carpenter, M. (1990) "Determination of the Aqueous Photolysis Rate of DEF": Lab
Project Number: 38876. Unpublished study prepared by Analytical Bio-Chemistry
Laboratories, Inc. 41 p.

Warren, D. (1990) Acute Four-Hour Inhalation Toxicity Study with Technical Grade
DEF in Rats: Lab Project Number: 90-042-HQ. Unpublished study prepared by
Mobay Corp. 33 p.

74



VI. Related Documents and How to Access Them

This Interim Reregistration Eligibility Document is supported by documents that are presently
maintained in the OPP docket. The OPP docket is located in Room 119, Crystal Mall #2, 1921
Jefferson Davis Highway, Arlington, VA. It is open Monday through Friday, excluding legal holidays,
from 8:30 am to 4 pm.

The docket initially contained preliminary risk assessments and related documents as of
September 10, 1998. Sixty days later the first public comment period closed. The EPA then.
considered comments, revised the risk assessment, and added the formal “Response to Comments”
document and the revised risk assessment to the docket on July 7, 1999.

All documents, in hard copy form, may be viewed in the OPP docket room or downloaded or
viewed via the Intemet at the following site: "http://www.epa.gov/pesticides/op."

53



based on the following factors: 1) in the hen study, Organophosphate Induced Delayed Neuropathy .
(OPIDN) occurred only at the highest dose tested (42 mg/kg/day) and a NOAEL (11 mg/kg/day) was
established for this effect; and 2) application of the 3X factor to the 2 mg/kg/day LOAEL (in the 21-
day rabbit dermal study) yields a dose of 0.7 mg/kg/day, which is 60 times lower than the dose (42
mg/kg/day) that induced the OPIDN in the hens. Therefore, 3X is sufficient to protect against the
OPIDN as observed in the hen study. For short and intermediate-term dermal exposure risk
assessments, the target dermal MOE is 300 and dermal MOEs greater than 300 are not of concern to
the Agency.

ii. Inhalation Exposure (Short- and Intermediate-Term)

The NOAEL of 0.9 mg/kg/day established in the 90-day inhalation study in rats was selected
for short and intermediate-term inhalation exposure assessments. The NOAEL is based on the
inhibition of plasma and erythrocyte cholinesterase activity observed at 4.5 mg/kg/day (LOAEL). The
inhalation target MOE is 100. The toxicological endpoints, and other factors used in the occupational
and residential risk assessments for tribufos are listed in Table 6.

Table 6: Summary of Toxicological Endpoints and Other Factors used in the Human
Occupational Risk Assessment for Tribufos.

Type of Exposure

Endpoi Level
(duration and route) ipoint and Effect Level Study

Endpoint and Effect Level: Plasma, erythrocyte and brain ChE
inhibition; dermal LOAEL of 2 mg/kg/day. This assessment
incorporates the use of a 7X conversion factor to account for the

Short and lifferences in dermal absorption between rabbit and human skin. 21-Day Dermal
Intermediate-Term [Applying the conversion factor results in a dose of 14 mg/kg/day Toxicity study in the
Dermal OAEL), which is then compared to occupational exposure data for Rabbit

alculating MOEs. Refer to the section below for further explanation. (MRID 42007201)
[Target MOE: Due to the use of a LOAEL, an additional 3X is applied
to the risk assessment (in addition to the 10X interspecies and the 10X
Fstraspecies). Therefore, the target MOE is 300

Shortand [Endpoint and Effect Level: Plasma and erythrocyte ChE inhibition;

Intermediate-Term _ inhalation NOAEL of 2.43 mg/L (0.9 mg/kg/day) 90-Day Inhalation
Inhalation [Target MOE: Because a NOAEL was established, an additional 3X Study in the Rat
as not applicable in this assessment. Therefore, the target MOE is (MRID 42399801)

1100 (10X interspecies and the 10X intraspecies differences).

Long-Term Dermal [Long-term dermal or inhalation occupational exposure are not expected
and Inhalation __|to occur for the registered uses of tribufos.

N/A

14



ii. Multiple Applications

The results indicate that for multiple applications of tribufos (0.75 Ibs ai/A applied twice), the
acute LOC for mammals (0.5), the acute restricted use LOC (0.2), and the acute endangered species
LOC (0.1) are exceeded for herbivores and insectivores that feed on short grass or insects. The RQs
ranged from 0.02 for mammals foraging on large insects, to 1.77 for mammals foraging on short grass.
Therefore, acute high risks to herbivores and insectivores are likely and endangered species may be
acutely affected. The Agency is, therefore, concerned with acute risk to mammals when multiple
applications of tribufos are used.

For granivorous mammals, which forage on seeds, multiple applications of tribufos are not of
concer to the Agency. RQs ranged from 0.01 to 0.02 and, therefore, did not exceed the acute high
tisk, restricted use, or endangered species LOC.

In regard to chronic risk, multiple applications (0.75 Ibs ai/A applied twice), resulted in risk
concerms to mammals. As discussed previously, the Agency examined a lower (average) exposure
scenario because, typically, mammals will not be exposed to maximum residues of tribufos throughout
their breeding cycle. RQs for this scenario ranged from 0.53 for mammals feeding on seeds to 8.63 for
mammals feeding on short grass and, therefore, has concern for chronic risks to mammals.

c Risks to Insects

A honeybee study was conducted and results showed that tribufos is practically nontoxic to
bees on an acute contact basis. The Agency, therefore, has no concer with risks to honeybees
associated with the use of tribufos.

d. Risks To Aquatic Species

To assess risks to aquatic species associated with tribufos use, the Agency used estimated
environmental concentrations predicted from the PRZM2/EXAMS II surface water model. However,
the PRZM2/EXAMS II estimates for potential exposure to aquatic organisms do not include the Index
Reservoir (IR) and Percent Crop Area refinements that are part of the human drinking water
assessment. The IR was developed from a real watershed in western Illinois to be used as a standard
watershed to estimate surface drinking water concentrations, and is not appropriate for use to estimate
pesticide concentrations in water bodies available to aquatic organisms. For freshwater fish, acute RQs
ranged from 0.03 to 0.06 at a single application rate of 1.875 Ibs ai/A.. The Agency is not concerned
with acute risk to fish.

In regard to chronic risks to freshwater as well as estuarine fish, data are lacking. The Agency
is requiring further data to better characterize potential risks. Refer to section V for particular studies
required.



Appendix I: List of Related Documents and Electronically Available Forms

Pesticide Registration Forms are available at the following EPA internet site:

http://www.epa.gov/opprd001/forms/.

Pesticide Registration Forms (These forms are in PDF format and require the Acrobat reader)
Instructions

Print out and complete the forms. (Note: Form numbers that are bolded can be filled
out on your computer then printed.)

The completed form(s) should be submitted in hardcopy in accord with the existing
policy.

Mail the forms, along with any additional documents necessary to comply with EPA
regulations covering your request, to the address below for the Document Processing
Desk.

DONOT fax or e-mail any form containing ‘Confidential Business Information’ or
‘Sensitive Information.’

If you have any problems accessing these forms, please contact Nicole Williams at
(703) 308-5551 or by e-mail at williams.nicole@epamail.epa.gov.

The following Agency Pesticide Registration Forms are currently available via the internet:
at the following locations:

8570-1 Application for Pesticide Registration/Amendment hitp://www.epa.gov/opprd001/forms/8570-1 pdf.
8570-4 Confidential Statement of Formula http://www.epa.cov/opprd )01/forms/8570-4.pdf.

8570-5 | Notice of Supplemental Registration of Distribution of a | http://www. /8570-5.pdf.
Registered Pesticide Product

8570-17 Application for an Experimental Use Permit Hi wwew, /8570-17.pdf}

8570-25 Application for/Notification of State Registration of a http://www.epa.gov/ 101 /forms/8570-25.pdft
Pesticide To Meet a Special Local Need



byproducts of cattle, goats, and sheep, and milk to conform to current Agency administrative practice.
Table 10 lists the current tolerances along with proposed changes. Based on FQPA and the results of
an acceptable cottonseed processing study, the established feed additive tolerance for cottonseed hulls
is to be revoked.

Table 10. Tolerance Summary for Tribufos :

Commodi current R Tolerance . Comment/
ommodity ‘com om (Correct Commodity Definition)
Tolerances Listed Under 40 CFR §180.272(a):
Cattle, fat 0.02! 0.15 {Tolerance to be raised (see text above)
Cattle, meat -}0.02" 10.02
Cattle, meat byproducts __}0.02! 10.02
ICottonseed 4 4 (Cotton, undelinted seed)
Cottonseed hulls 6 /Revoke Not warranted based on the results of an
acceptable cottonseed processing study.
Goats, fat 0.02! 0.15 (Goat, fat)
Goats, meat 0.02! 10.02 (Goat, meat)
Goats, meat byproducts _]0.02! 40.02. .{(Goat, meat byproducts)
Milk 0.002! 0.01 {Tolerance to be raised (see text above)
Sheep, fat 0.02! 10.15 [Tolerance to be raised (see text above)
Sheep, meat 0.02! 10.02
Sheep, meat byproducts__|0.02' }0.02
Tolerances to Be Proposed Under 40 CFR §180.272(a):
Cotton Gin byproducts _ {None 40 (Cotton, gin byproducts)
Hog, fat (None 0.15
[Hog, meat [None 0.02
Hog, meat byproducts [None 10.02
Horse, fat [None 0.15
Horse, meat [None 10.02
Horse, meat byproducts __[None. 10.02

‘Negligible residues

* The term “reassessment” here is not meant to imply that the tolerance has been reassessed as required by FQPA,
because this tolerance may be reassessed only upon completion of the cumulative risk assessment of all
organophosphates, as required by this law. Rather, it provides a tolerance level for this single chemical, ifno
cumulative assessment was required, that is supported by all of the submitted residue data.



For estuarine and marine fish, the results indicate that the aquatic acute restricted use, and the
acute endangered species LOCs are very slightly exceeded. RQs ranged from 0.06 to 0.11 at an
application rate of 1.875 Ibs a/A. The Agency is, therefore, concerned with acute risks to estuarine
and marine fish.

In regards to freshwater invertebrates, the results indicate that the aquatic acute restricted use
LOC, the acute endangered species LOC, and the chronic LOC are exceeded for freshwater
invertebrates at the 1.875 lbs ai/A rate. Acute RQs ranged from 0.01 to 0.52 and the chronic RQs
ranged from 0.05 to 3.50. The Agency, therefore, has concems with acute and chronic risk to
freshwater invertebrates.

For estuarine and marine invertebrates, the acute high risk LOC (0.5), the acute endangered
species (0.05), the acute restricted use (0.1), and the chronic LOC (1.0) are exceeded for
estuarine/marine invertebrates at an application rate of 1.875 Ibs ai/A. Acute RQs ranged from 1.60 to
2.80 and, chronic RQs ranged from 10.0 to 23.3. The Agency, therefore, has concerms with acute and
chronic risks to estuarine and marine invertebrates. The Agency is also requiring a chronic
estuarine/marine study to better characterize risks to invertebrates (refer to Section V).

e. Risks To Plants

Terrestrial, aquatic, and semi-aquatic plants may be exposed to tribufos from runoff or spray
drift from adjacent treated sites. Semi-aquatic plants are those that inhabit low-lying wet areas that may
be dry at certain times of the year. Spray drift exposure from ground application is assumed to be 1%
of the application rate. Spray drift from aerial application is assumed to be 5% of the application rate.

. Exposure to non-target vascular aquatic plants is possible through the use of tribufos. Acute
RQs ranged from 0.05 to 0.09. These RQs indicate that the acute LOCs are not exceeded for any use
tate. RQs for exposure to non-vascular plants range from 0.07 to 0.12. The Agency is, therefore, not
concermed with risks to non-target aquatic plants.

The risks to non-target terrestrial plants cannot be assessed because pertinent plant studies are
lacking. The Agency is requiring further data to better characterize potential risks. Refer to section V
for particular studies required.

IV. Interim Reregistration Eligibility and Risk Management Decisions

A. Determination of Interim Reregistration Eligibility

Section 4(g)(2)(A) of FIFRA calls for the Agency to determine, after submissions of relevant
data concerning an active ingredient, whether products containing the active ingredient are eligible for

27







current maximum application rate of 1.875 Ib ai/A, as well as the more typical application rate of 1.125
Ibs ai/A (except CA and AZ which use the 1.875 Ibs ai/A).

The post-application assessment is based on exposures to the pickers, module builders,
takers, and trampers. The exposure assessment is based solely on the data submitted by the registrant.
Based on a recent Agency site visit to Arizona to observe cotton harvesting activities, the assessment is
believed to accurately represent the application and harvesting activities performed.

The Agency used a chemical-specific, passive dosimetry study (MRID 42685901) to
determine the exposure to workers engaged in post-application activities (subsequent REIs were
determined from passive dosimetry data). The study subjects were monitored at the maximum
application rate of 1.875 Ib ai/acre and reduced by a factor of 0.6 to the proposed application rate of
1.125 Ib ai/acre. The Agency also applied a linear extrapolation of the exposure to an 8 hour work day
because the registrant study monitored for a 4.8 hour work day. Moreover, the average exposure of
the 3 or 4 replicates were used, not the highest one monitored.

A transfer coefficient was used to estimate the dermal MOEs.24 hours after application (current
RED) and 7 days after treatment (DAT). Table 9 below provides the results of the dermal MOEs at 24
hours and newly proposed 7 DAT. The resulting MOEs for 24 hours post-treatment at the current
application rate of 1.875 Ibs ai/A ranged from 45 (rakers) tol 10 (module builder operators). The
current label rate at 7 days post-application yielded MOEs ranging from 200 (rakers) to 480 (module

builder operator). At the proposed rate of 1.125 Ibs/ai/A, the MOEs at 24 hours after application
ranged from 74 (rakers) to 180 (module builder operator). MOEs at 7 days post-application ranged
from 340 (rakers) to 840 (module builder operator).

The Agency therefore concludes that there are still risk concerns for three of the four scenarios
(cakers, trampers, and pickers) at the current label rate even after 7 days post-treatment (MOEs below
300); however, it has no risk concerns at the lower proposed application rate with a 7-day REI.



Appendix G: EPA’s Batching of Tribufos Products for Meeting the Acute Toxicity
Data Requirements for Reregistration

In an effort to reduce the time, resources and number of animals needed to fulfill the acute
toxicity data requirements for reregistration of products containing tribufos as the primary active
ingredient, the Agency has batched products which can be considered similar for purposes of acute
toxicity. Factors considered in the sorting process include each product’s active and inert ingredients
(identity, percent composition and biological activity), type of formulation (e.g., emulsifiable
concentrate, aerosol, wettable powder, granular, etc.), and labeling (e.g., signal word, use classification,
precautionary labeling, etc.). Note the Agency is not describing batched products as “substantially
similar” since some products with in a batch may not be considered chemically similar or have identical
use patterns.

Using available information, batching has been accomplished by the process described in the
preceding paragraph. Notwithstanding the batching process, the Agency reserves the right to require,
at any time, acute toxicity data for an individual product should need arise.

Registrants of products within a batch may choose to cooperatively generate, submit or cite a
single battery of six acute toxicological studies to represent all the products within that batch. It is the
registrants’ option to participate in the process with all other registrants, only some of the other
registrants, or only their own products within in a batch, or to generate all the required acute
toxicological studies for each of their own products. If the registrant chooses to generate the data for a
batch, he/she must use one of the products within the batch as the test material. If the registrant
chooses to rely upon previously submitted acute toxicity data, he/she may do so provided that the data
base is complete and valid by to-days standards (see acceptance criteria attached), the formulation
tested is considered by EPA to be similar for acute toxicity, and the formulation has not been
significantly altered since submission and acceptance of the acute toxicity data. Regardless of whether
new data is generated or existing data is referenced, the registrants must clearly identify the test material
by EPA Registration Number. If more than one confidential statement of formula (CSF) exists for a
product, the registrant must indicate the formulation actually tested by identifying the corresponding
CSF.

In deciding how to meet the product specific data requirements, registrants must follow the
directions given in the Data Call-In Notice and its attachments appended to the RED. The DCI Notice
contains two response forms which are to be completed and submitted to the Agency within 90 days of
receipt. The first form, “Data Call-in Response, “ asks whether the registrant will meet the data
requirements for each product. The second form, “Requirements Status and Registrant’s Response,”
lists the product specific data required for each product, including the standard six acute toxicity tests.
A registrant who wishes to participate in a batch must decide whether he/she will provide the data or

91



United States Prevention, Pesticides EPAF-00-020
Environmental Protection and Toxic Substances October 2000
Agency (7508C)

EPA Tribufos Facts

EPA has assessed the risks of tribufos and reached an Interim Reregistration Eligibility Decision
(RED) for this organophosphate (OP) pesticide. Tribufos is eligible for reregistration, pending a full

reassessment of the cumulative risk from all OPs.

Used only on cotton crops, tribufos
residues in food and drinking water do not pose
tisk concerns. Tribufos has no residential uses.
With the implementation of certain risk
mitigation measures, worker and ecological
tisks from tribufos use are believed to be
significantly reduced. Additional data are also
to be submitted to the Agency to confirm this
conclusion.

EPA is reviewing the OP pesticides to
determine whether they meet current health and
safety standards. OPs need decisions about
their eligibility for reregistration under FIFRA.
Additional OPs with residues in food, drinking
water, and other non-occupational exposures
also must be reassessed to make sure they meet
the new Food Quality Protection Act (FQPA)
safety standard.

EPA’s next step under the FQPA is to
complete a cumulative risk assessment and risk
management decision encompassing all the OP

The OP Pilot Public Participation Process

The organophosphates are a group of
related pesticides that affect the functioning of the
nervous system. They are among EPA's highest
priority for review under the Food Quality Protection
Act. .

EPA is encouraging the public to
participate in the review of the OP pesticides.
Through a six-phased pilot public participation
process, the Agency is releasing for review and
comment its preliminary and revised scientific risk .
assessments for individual OPs. (Please contact
the OP Docket, telephone 703-305-5805, or see
EPA's web site, www.epa.gov/pesticides/op .)

EPA is exchanging information with
stakeholders and the public about the OPs, their
uses, and risks through Technical Briefings,
stakeholder meetings, and other fora. USDA is
coordinating input from growers and other OP
pesticide users.

Based on current information from
interested stakeholders and the public, EPA is
making interim risk management decisions for
individual OP pesticides, and will make final
decisions through a cumulative OP assessment.

pesticides, which share a common mechanism of toxicity. The interim decision on tribufos cannot be
considered final until this cumulative assessment is complete. Further risk mitigation may be necessary

at that time.

The tribufos [RED was made through the OP pilot public participation process, which increases
transparency and maximizes stakeholder involvement in EPA’s development of risk assessments and
risk management decisions. EPA worked extensively with affected parties to reach the decisions
presented in this interim decision document, which concludes the OP pilot process for tribufos.



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B. End-Use Products
1. Additional Product-Specific Data Requirements

Section 4(g)(2)(B) of FIFRA calls for the Agency to obtain any needed product-specific data
regarding the pesticide after a determination of eligibility has been made. Registrants must review
previous data submissions to ensure that they meet current EPA acceptance criteria and if not, commit
to conduct new studies. Ifa registrant believes that previously submitted data meet current testing
standards, then study MRID numbers should be cited according to the instructions in the Requirement
Status and Registrants Response Form provided for each product.

A product-specific DCI, outlining specific data requirements, accompanies this IRED.
2. Labeling for End-Use Products

Labeling changes are necessary to implement the mitigation measures outlined in Section IV,
above. Specific language to incorporate these changes is specified in the Table at the end of this
section. Registrants need to submit applications for amended registration. This application should
include the following items: a completed EPA application form 8570-1, five copies of the draft label
with all label amendments outlined in Table 11 of this document incorporated, and a description on the
application, such as, "Responding to Interim Reregistration Eligibility Decision” document. All
amended labels need to be submitted within 8 months of signature of this document. The Product
Reregistration Division (PRB) contact is Bonnie Adler at (703) 308-8523.

Cc. Existing Stocks

Registrants may generally distribute and sell products bearing old labels/labeling for 12 months
from the date of the issuance of this Interim Reregistration Eligibility Decision document. Persons other
than the registrants may generally distribute or sell such products for 24 months from the date of the
issuance of this interim RED. However, existing stocks time frames will be established case-by-case,
depending on the number of products involved, the number of label changes, and other factors. Refer
to “Existing Stocks of Pesticide Products; Statement of Policy”; Federal Register, Volume 56, No.
123, June 26, 1991.

The Agency has determined that registrants may distribute and sell tribufos products bearing old
labels/labeling for 12 months from the date of issuance of this interim RED. Persons other than the
Tegistrants may distribute or sell such products for 24 months from the date of the issuance of this
interim RED. Registrants and persons other than the registrants remain obligated to meet pre-existing
Agency imposed label changes and existing stocks requirements applicable to products they sell or
distribute.



this determination EPA has considered the available information on the special sensitivity of infants and
children, as well as acute and chronic food exposure. An aggregate assessment was conducted for
exposures through food and drinking water. Results of this aggregate assessment indicate that the
human health risks from these combined exposures are considered to be within acceptable levels; that
is, combined risks from all exposures to tribufos “fit” within the individual risk cup.

b. Tolerance Summary

This tolerance discussion is limited to tribufos. The tolerances listed in 40 CFR §180.272 are
expressed in terms of tribufos. The Agency has concluded that tribufos per se is the compound of
toxicological concern. The current tolerance expression is adequate. It should be noted that the
Agency will commence proceedings to revoke one tolerance, cottonseed bulls. Seven tolerances will
remain the same (cattle meat and byproducts, cottonseed, goat meat and byproducts, and sheep meat
and byproducts. The remaining eleven tolerances (seven to be added and four to be raised) will remain
in effect and unchanged until a full reassessment of the cumulative risk from all organophosphates is
completed.

i. Tolerances To Be Proposed Under 40 CFR §180.272

Tolerances for residues of tribufos in the meat and meat byproducts of hogs and horses at 0.02
ppm are to be proposed, as well as tolerances for residues of tribufos in meat fat of hogs and horses at

0.15 ppm. Once adequate data concerning tribufos residues in cotton gin byproducts from cotton
harvested at the established preharvest interval (PHI) are submitted, a tolerance of 40 ppm (as
determined by field trial data) for cotton gin byproducts will be proposed.

ii. Tolerances Listed Under 40 CFR §180.272

Ruminant metabolism and feeding studies indicate that the established tolerances for the meat,
and meat byproducts of cattle, goats, and sheep are adequate. The existing tolerance for residues of
tribufos in milk is 0.002 ppm. Based on maximum theoretical dietary burden using the recommended
cotton gin byproducts tolerance, the existing tolerance for tribufos residues in milk needs to be raised.
Based on the data currently available, milk and fat tolerances have been reassessed at 0.01 and 0.15
ppm, respectively. The registrant may petition to lower the recommended milk tolerance by submitting
analyses of samples from the animal feeding studies using a method with greater sensitivity than 0.01
ppm that quantitatively shows that tribufos residues in milk are less than 0.01 ppm. It should also be
noted, consistent with FQPA, that a milk tolerance can not be set lower than the limit of quantification
(LOQ). Therefore, the existing tolerance of 0.002 is to be increased.

The registrant may petition to lower the tolerance in meat and meat byproducts if they submit an
analytical enforcement method capable of quantifying residues at the proposed lower tolerance levels.
The term "negligible residues" is to be removed from the tolerance expressions for fat, meat, and meat

30



BIBLIOGRAPHY

MRID

CITATION

43325504

43649402

43783701

43821601

43837801

43837802

43978201

44439101

Schmidt, J. (1994) Anaerobic Aquatic Metabolism of (Carbon 14) Tribufos: Lab
Project Number: DE042402: 106767. Unpublished study prepared by ABC Lab.,
Inc. 61 p.

Schroeder, R. (1989) A Two-Generation (Two-Litters) Reproduction Study With AC
92,100 to Rats: Lab Project Numbers: 86-3128: 971-87-132. Unpublished study
prepared by Bio/dynamics, Inc. 1806 p.

Grace, T. (1995) DEF 6EC--Magnitude of Residue in Cotton Processed Products:
Lab Project Number: DE19CTO1: 106988. Unpublished study prepared by Miles
Research Park and Bayer Corp. 405 p.

Mathew, A.; Nguyen, T. (1995) Tribufos-A 28-Day Dairy Cattle Feeding Study: Lab
Project Number: 107104: DE060401: DE130401. Unpublished study prepared by
Bayer Corp. 508 p.

Krolski, M. (1995) DEF 6EC--Magnitude of the Residue on Cotton: Lab Project
Number 106993: DE19CT02: 351-DE001-94D. Unpublished study prepared by
Bayer Corp. 542 p.

Gronberg, R.; Sanders, D. (1995) An Analytical Residue Method for the Determination
of Tribufos Residue in Animal Tissues and Milk: Lab Project Number: 107068:
DE120201. Unpublished study prepared by Bayer Corp. 32 p.

Bowers, L. (1996) Chronic Toxicity of (carbon 14)-DEF to the Waterflea (Daphnia
magna) Under Static Renewal Conditions: Lab Project Number: DE840701: 107327.
Unpublished study prepared by Bayer Corp. 64 p.

Ghillebaert, F. (1997) Toxicology File of Mexel 432 Summary of the Studies.
Unpublished study prepared by Ecotox. 33 p.

79



Tribufos is a colorless to yellow liquid with a mercaptan-like odor and a boiling point of
~150°C. Tribufos is practically insoluble in water (2.3 x 10 + g/100 ml), but is completely miscible in
dichloromethane, n-hexane, 2-propanol, and toluene. Tribufos is relatively stable to heat and under
acidic conditions, but slowly hydrolyzes under alkaline conditions.

Cc. Use Profile

The following information is based on the currently registered use of tribufos.

Type of Pesticide:  Defoliant

Summary of Use:

Sites: Cotton

Food: Cottonseed is processed into cottonseed oil; gin trash is used as
Tuminant feed and meal.

Residential: None

Other Nonfood: None
Formulation Types:

egistered: There are two technical products of tribufos presently registered. One
technical (98.0% ai, liquid) is registered to Bayer Corporation (EPA
Reg. No. 3125-96) and one to Micro Flo Company (98.1% ai with an
EPA Reg. No. 51036-324). There are three liquid end-use products:
one registered to Bayer (EPA Reg. No. 3125-282 - 71.5% ai); one
registered to Aventis Crop Science (EPA Reg. No. 264-498 - 70.5%
ai); and one registered to Micro Flo (EPA Reg. No. 51036-320 -
70.5% ai). There is also one Special Local Need (SLN) product
registered in Texas, (SLN No. TX810045) which Bayer has recently
requested a cancellation on July 24, 2000.

Method and Rates of Application:

Equipment: Aircraft (fixed wing aircraft) and groundboom.





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negligible.

3. Aggregate Risks

An aggregate risk assessment looks at the combined risk from dietary exposure (food and
drinking water routes) and non-occupational exposure sources. Because there are no residential or
other non-occupational uses of tribufos to consider in an acute or chronic aggregate assessment, the
aggregate assessment only includes dietary risks from food and water. The Agency has no concem for
residues of tribufos in ground water and little concern about exposure to tribufos in surface water
sources of drinking water because the drinking water EECs slightly exceed the chronic DWLOCs and
for reasons discussed above. Therefore, the aggregate risk of tribufos is not of concem.

4. Occupational Risk

Occupational workers can be exposed to a pesticide through mixing, loading, and/or applying a
pesticide, or re-entering treated sites. Occupational handlers of tribufos include individual farmers or
growers who mix, load, and/or apply pesticides or professional or custom agricultural applicators. Risk
for all of these potentially exposed populations is measured by a Margin of Exposure (MOE) which
determines how close the occupational or residential exposure comes to a NOAEL.

Inhalation and dermal exposure to tribufos can result from occupational use. The Agency
assessed dermal and inhalation risks for mixers, loaders and applicators during aerial and groundboom
applications, as well as flaggers during aerial application. Tribufos is not expected to be used on a
continuous long-term basis (greater than 6 months a year) that would result in chronic exposure.
Therefore, the occupational risk assessments were conducted for short- (1-7 days) and intermediate-
(one week to several months) term occupational exposure scenarios. The Agency also calculated risks
for reentry workers or others entering a treated site.

The Agency considers the following tasks in assessing exposure (e.g., mixing, loading, and
applying): pesticide formulation (e.g., liquid, granular), application method (e.g., aerial, groundboom),
amount applied or handled, and similar activities. The Agency also reviews any incident data for
occupational handlers if available and applicable.

a. Toxicity

The toxicity of tribufos is integral to assessing the occupational risk. The toxicology database
provides evidence confirming that tribufos, like other organophosphates, has anticholinesterase activity
in all species tested, which include hen, mice, rats, dogs and rabbits. Toxicity Category I is considered
the most toxic, and Toxicity Category IV is considered the least toxic. Technical tribufos is placed in
Toxicity Category II by the oral and dermal routes, and Category III by the inhalation route. No data

12



Appendix H: List of Registrants Sent this Data Call-In



Therefore, the rabbit LOAEL (2 mg/kg/day) was adjusted by the conversion factor (7) to yield
a more realistic toxicity endpoint of 14 mg/kg/day for the risk assessment. This significantly refined the
tisk assessment and groundboom workers are now below the Agency’s level of concern. Reentry of
workers into iribufos treated fields at the 1.125 Ibs ai/A rate are below the Agency’s level of concem
with a 7-day REI.

ec. Information from Bayer

A repeated 21-day dermal study was considered, given that the current study yielded a
LOAEL without establishing a NOAEL. If the study was repeated and a NOAEL was established, the
target MOE would be 100 rather than the current 300. The newly established NOAEL would
essentially need to equal the LOAEL for there to be any improvement to the risk assessment. For
example, if the study were repeated and the determined NOAEL was 2 mg/kg/day, MOEs of concem
for aerial mixers, loaders, and applicators for both the 1.125 Ibs ai/A rate as well as the 1.875 Ibs ai/A.
(for CA and AZ) rate would range from 17 to 50 with a target MOE of 100. These MOEs would still
exceed the Agency’s level of concern.

The registrant proposed that the most appropriate toxicological endpoint for dermal risk
assessment is provided by the 90-day inhalation toxicity study in rats. This study provides a systemic
NOAEL of 0.9 mg/kg/day based on inhibition of plasma and erythrocyte ChE activities at the LOAEL
of 4.5 mg/kg/day. The registrant contends that the NOAEL for systemic exposure in an animal study
should be compared with the systemic dose workers may encounter, and therefore, the inhalation study
with the systemic NOAEL is the most appropriate to assess worker dermal risk assessments. The
Agency evaluated this proposal and concluded that the inhalation toxicity study is not appropriate for
use in dermal risk assessments for the following reasons: 1) when a route-specific toxicity study (i.e.,
21-day dermal study) is available for the route of exposure of concer (dermal) for workers the dermal
should be used rather than a study with a different route of exposure (i.¢., inhalation), as proposed by
the Registrant; 2) in the dermal study, systemic absorption was demonstrated as evidenced by ChE
inhibition in males (plasma) and females (RBC) at the lowest dose tested and therefore is a systemic
LOAEL; and 3) the dermal study with the systemic toxicity endpoint (cholinesterase inhibition) of
concern is the most appropriate for regulations.

Additionally, as shown below, the NOAEL in the inhalation study is essentially the same as the
effect level (e., LOAEL) in the dermal study when an adjustment is made for dermal absorption for
both routes (i,e, dermal and inhalation). Therefore, a dose that was shown to be an effect level can not
be used as a no effect effect level.

- Inhalation NOAEL of 0.9 mg/kg/day when adjusted for 7% dermal absorption rate (as
shown in monkeys) results in a equivalent dermal dose of 13 mg/kg/day
(0.9 mg/kg/day + 0.07 = 13 mg/kg/day)



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registrant also submitted a dermal absorption study in the monkey, which the Agency used to obtain a
conversion factor to further refine the risk assessment. Finally, the Agency determined the additional
3X, which was applied in the preliminary Human Health Risk Assessment for severity of effects, should
be removed because the effects were observed at very high doses and that the conventional uncertainty
factors (i.e., 10X for interspecies differences, 10X for intraspecies differences, and the 3X for the use
of a Lowest-Observed-Adverse-Effect-Level (LOAEL) in the 21-day dermal rabbit study) would be
sufficient to adequately characterize the risks associated with the use of tribufos. Further details on the
human health effects of tribufos can be found in the June 26, 2000, Human Health Risk Assessment
(See the EPA public docket for tribufos or http:www.epa.gov/pesticides/op).

1. Dietary Risk From Food
a. Toxicity

The Agency has reviewed all toxicity studies submitted and has determined that the toxicity
database is sufficiently complete to support an interim reregistration eligibility determination for the
currently registered uses of tribufos. A brief overview of the studies used to assess dietary risk are
provided in Table 1.

b. FQPA Safety Factor

The FQPA Safety Factor is intended to provide up to an additional 10-fold safety factor
(10X), to protect for special sensitivity in infants and children to specific pesticide residues in food or to
compensate for an incomplete database. Although no increased sensitivity of fetuses as compared to
maternal animals was observed in developmental toxicity studies in rats and rabbits and no increased
sensitivity of pups was observed in a multi-generation reproduction study in rats, the Agency retained a
10X FQPA Safety Factor for tribufos due to the following toxicity data gaps. The Agency has called
in the following studies:

(a) Acute and subchronic neurotoxicity studies in rats. Data on cholinesterase (ChE)
inhibition, functional observation battery, as well as histopathology of the central and
peripheral nervous systems are not available for evaluation after single or repeated
exposures to tribufos.

A developmental neurotoxicity study is required, based on organophosphate induced
delayed neuropathy (OPIDN). The concern for the developmental neurotoxic potential
of tribufos was elicited by neuropathological lesions in the subchronic study with hens
(MRID 42007202) and in the combined chronic toxicity/carcinogenicity study in rats
(MRID 42335101).



BIBLIOGRAPHY

MRID

CITATION

40228401

40757101

40886301

41171001

41459101

41459102

41459103

41618801

41618802

Mayer, F.; Ellersieck, M. (1986) Manual of Acute Toxicity: Interpretation and Data
Base for 410 Chemicals and 66 Species of Freshwater Animals. US Fish & Wildlife
Service, Resource Publication 160. 579 p.

Beavers, J.; Marselas, G.; Jaber, M. (1988) DEF: A One-generation Reproduction
Study with the Bobwhite (Colinus virginianus): Wildlife International Ltd. Project No.
149-127. Unpublished study prepared by Wildlife International Ltd. 101 p.

Hoberman, A. (1988) A Developmental Toxicity (Embryo-fetal
Toxicity/Teratogenicity) Study with AC 92,100 in Rabbits: Project ID: Argus Research
Laboratories Protocol: 101-008. Unpublished study prepared by Argus Research
Laboratories, Inc. 243 p

Hayes, R. (1989) Oncogenicity Study of Technical Grade Tribufos (DEF) with Mice:
Study No. 86-271-01. Unpublished study prepared by Mobay Corp. 2042 p.

Curren, R.; Gentry, P. (1989) Salmonella/Mammalian-microsome Plate Incorporation
Mutagenicity Assay (Ames Test): Lab Project Number T8299.501. Unpublished
study prepared by Microbiological Assoc. Inc. 49 p.

Curren, R. (1990) Unscheduled DNA Synthesis in Rat Primary Hepatocytes: Lab
Project Number: T8299.380: 1107. Unpublished study prepared by Microbiological
Assoc., Inc. 26 p.

Putman, D.; Morris, M. (1989) Chromosome Aberrations in Chinese Hamster Ovary
(CHO) Cells: Lab Project Number: T8299.337: 98592. Unpublished study prepared
by Microbiological Assoc., Inc. 28 p.

Talbott, T. (1990) Product Chemistry of DEF Technical: Lab Project Number:
VAPO0007: JDM0066: 2172. Unpublished study prepared by Mobay Corp. 65 p.

Talbott, T. (1990) Product Chemistry of DEF Technical: Lab Project Number: 91978:
99857: 99856. Unpublished study prepared by Mobay Corp. 115 p.

72



TABLE OF CONTENTS

Tribufos Team ... 2.0... cece ec ete ee eee ee ee eeee i
Glossary of Terms and Abbreviations ....... 2.2.2.2... 2c cece cece cece eee iti
Executive Summary .......... 0... cece cece cece eee eee e nee eeee scene 1
I. Introduction ... 2.0.66... eee eee ence eee eeeees 1
I. Chemical Overview .......... 2.0.00 cece cece cece cence eee eee eeeees 3
A. Regulatory History ................0 00 2c eee eee e eee
B. Chemical Identification . .
Cc. Use Profile ... 2.0.2... cece een eee eee eees
D. Estimated Usage of Pesticide

A. Human Health Risk Assessment .

1. Dietary Risk From Food . . ++.6
a. Toxicity ©... 2.0... cee eee 6
b. FQPA Safety Factor .... 2.2.0.2... cece eee eee 6
ce Population Adjusted Dose (PAD)
d. Exposure Assumptions
e. Acute Dietary (Food)
fi. Chronic Dietary (Food) wee
g. Cancer Risks 2.0.0... cence teen eee
2. Dietary Risk From Drinking Water...:...........2....000.0000. 9
a. Surface Water ........... -- 10
b. Ground Water ..............0. 0.000 eee ee eee -10
( Drinking Water Levels of Comparison (DWLOC) . ol
3. Aggregate Risks ........... 0.0... cece cee cece eee eee 12
4, Occupational Risk... 2.2.2.0... cece eee eee 12
a. Toxicity

i, Dermal Exposure (Short- and Intermediate-Term) ... . 13

ii. Inhalation Exposure (Short- and Intermediate-Term) . . 14

. Adjustment for Species Differences in Dermal Absorption ... 15
c Occupational Handler Exposure

i Dermal Risk ......... .
ii. Inhalation Risk ................0..000..2000. 0085



Vil. Appendices



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In this IRED, the Agency has determined that tribufos will be eligible for reregistration
provided that all the conditions identified in this document are satisfied, including
implementation of the risk mitigation measures outlined in Section IV of the document. The
Agency believes that current uses of tribufos may pose unreasonable adverse effects to human.
health and the environment, and that such effects can be mitigated with the risk mitigation
measures identified in this IRED. Accordingly, the Agency recommends that registrants
implement these risk mitigation measures immediately. Section IV of this IRED describes
labeling amendments for end-use products and data requirements necessary to implement these

’ mitigation measures. Instructions for registrants on submitting revised labeling and the time
frame established to do so can be found in Section V of this document.

Should a registrant fail to implement any of the risk mitigation measures outlined in this
document, the Agency will continue to have concerns about the risks posed by tribufos . Where
the Agency has identified any unreasonable adverse effect to human health and the environment,
the Agency may at any time initiate appropriate regulatory action to address this concern. At that
time, any affected person(s) may challenge the Agency’s action.

If you have questions on this document or the label changes necessary for reregistration,
please contact the Chemical Review Manager, Anne Overstreet, at (703) 308-8068. For
questions about product reregistration and/or the Product DCI that accompanies this document,
please contact Bonnie Adler at (703) 308-8523.

Ow a. CRL
Lois A. Rossi, Director
Special Review and

Reregistration Division

Attachment



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Appendix B. Table Of Generic Data Requirements And Studies Used To Make The
Interim Reregistration Decision

TO APPE!

Appendix B contains listing of data requirements which support the reregistration for active ingredients
within case #2145 (tribufos) covered by this Interim RED. It contains generic data requirements that apply to
tribufos in all products, including data requirements for which a "typical formulation" is the test substance.

The data table is organized in the following formats:

1 Jata Requirement (Column 1). The data requirements are listed in the order in which they
appear in 40 CFR part 158. the reference numbers accompanying each test refer to the test
protocols set in the Pesticide Assessment Guidance, which are available from the National
technical Information Service, 5285 Port Royal Road, Springfield, VA 22161 (703) 487-
4650.

2. Use Pattern (Column 2). This column indicates the use patterns for which the data
requirements apply. The following letter designations are used for the given use patterns.

Terrestrial food

Terrestrial feed

Terrestrial non-food
Aquatic food

Aquatic non-food outdoor
Aquatic non-food industrial
Aquatic non-food residential
Greenhouse food.
Greenhouse non-food
Forestry

Residential

Indoor food.

Indoor non-food

Indoor medical

Indoor residential

OZER ASTM TOBH OOP

59



Appendix F: Product Specific Data Call-In

See attached table for a list of product-specific data requirements. Note that a complete Data
Call-In (DCI), with all pertinent instructions, is being sent to registrant under separate cover.



identifiable laboratory or testing facility as the author. When no author or laboratory
could be identified, the Agency has shown the first submitter as the author.

Document date. The date of the study is taken directly from the document. When the
date is followed by a question mark, the bibliographer has deduced the date from the
evidence contained in the document. When the date appears as (1999), the Agency
‘was unable to determine or estimate the date of the document.

Title. In some cases, it has been necessary for the Agency bibliographers to create or
enhance a document title. Any such editorial insertions are contained between square
brackets.

Trailing parentheses. For studies submitted to the Agency in the past, the trailing
parentheses include (in addition to any self-explanatory text) the following elements
describing the earliest known submission:

(1) Submission date. The date of the earliest known submission appears
immediately following the word "received."

Administrative number. The next element immediately following the word
"under" is the registration number, experimental use permit number, petition
number, or other administrative number associated with the earliest known
submission.

Submitter. The third element is the submitter. When authorship is defaulted to
the submitter, this element is omitted.

Volume Identification (Accession Numbers). The final element in the trailing
parentheses identifies the EPA accession number of the volume in which the
original submission of the study appears. The six-digit accession number
follows the symbol "CDL," which stands for "Company Data Library." This
accession number is in turn followed by an alphabetic suffix which shows the
relative position of the study within the volume.



tribufos is tank-mixed with other defoliants, a synergistic effect is exhibited which results in better
defoliation with less staining and harvest debris, as opposed to when tribufos or these alternatives are
used alone. These factors are further explained in the benefits discussion below.

Benefits

The Agency has considered numerous submissions from both USDA and the National Cotton
Council and believes that the benefits of tribufos are numerous and its loss to the cotton industry would
be substantial. Below are several factors the Agency considered in its benefits analysis.

1) How defoliants work. Defoliants, used on cotton, cause leaves to abscise, or fall off
the plant. Abscission is controlled in the plant by the amount of ethylene available in the
plant for this process to occur. Ethylene is produced in plants but is usually inhibited in its
action by plant hormones (auxins). There are basically two types of defoliants, herbicidal
and hormonal. Herbicidal defoliants act by causing slight injury to leaves, which causes an
increase in ethylene production within the plant as an injury response. This increase in
ethylene overrides the effects of auxin and causes the abscission process to occur and
therefore defoliation. Tribufos is a herbicidal defoliant. Hormonal defoliants also cause an
increase in ethylene production through a similar enzymatic induction process, which occurs
more slowly than with the herbicidal defoliants. Dimethipin and thidiazuron are hormonal
defoliants. Thidiazuron is also known to inhibit auxin transport, which results in inhibition of
regrowth in defoliated cotton, and, therefore performs well when tank mixed with tribufos.

2) The importance of weather conditions. Cotton defoliant performance is affected by
the condition of the plant at application, weather variables at application time, and ambient
temperature within a week following application. In order to work, the defoliant must
penetrate the leaf surface. Humid weather and high light promote the greatest uptake of the
defoliant. Therefore, best performance is obtained when leaf cuticles (the waxy layer
surrounding the leaf) are thinner and light intensity and humidity are high. High light intensity
and humidity result in more open stomates (tiny openings on the leaves which regulate
moisture exchange between the plant and its environment), which, along with thinner leaf
cuticles, allow maximum uptake through the leaf surface. Thick leaf cuticles, which occur in
drier climates and low humidity, result in lower uptake through leaves. This explains why
higher rates (1.875 Ibs ai/A) of tribufos are required in Califomia and Arizona than in other
cotton growing areas. In regard to the use of the higher rate of 1.875 Ibs ai/A, the Agency
acknowledges that there is a relatively small population of aerial mixers, loaders, and :
applicators who will actually use such a rate in Arizona and California.

Temperature after application is an important factor in performance. Overnight
temperatures below 60°F will limit the effectiveness of defoliants by slowing their activity.
Herbicidal defoliants such as tribufos, are less affected by cool night temperature than

38



The Agency finds that mixers/loaders and applicators involved in aerial applications at typical
1,200 acres per day currently are at risk levels that exceed the Agency’s level of concer. Risk to
post-application workers also exceed the Agency’s level of concem at the higher use rate of 1.875 Ibs
ai/A. To address these concems, the following mitigation measures are necessary:

1) The maximum application rate will be reduced to 1.125 Ibs ai/A in all states except
California and Arizona (which comprise a very small part of the use at the higher rate of
1.875 Ib ai/A). Califomia and Arizona grow hardier varieties of cotton which require
the higher rate for defoliation (also refer to the below discussion regarding the benefits
of tribufos). The total percentage of cotton acres treated with tribufos in California and
Arizona are 13% and 17%, respectively.

2) The restricted entry interval will be increased from 24 hours to 7 days.

3) Tribufos products will be distributed in closed loading systems starting with the 2002
growing season.

4) Enclosed cockpits.

5) A biomonitoring study will be conducted to confirm the Agency’s risk management
decision that the occupational risks will not be of concem. The biomonitoring study will
be submitted to the Agency by September 2003.

The Agency has incorporated the first four mitigation measures in the current risk assessment.
However, concem still remains for workers who mix, load, and apply tribufos by aerial application.

In this IRED occupational risks associated with the use of tribufos were calculated at two rates,
the proposed rate of 1.125 Ibs ai/A, and the current maximum rate of 1.875 Ibs ai/A. In reality, tribufos
is tank-mixed in the majority of applications with other defoliants at a much lower rate (0.50 to 0.75 Ibs
ai/A). The Agency is therefore confident that the occupational and ecological risks associated with the
use of tribufos are generally lower than those discussed in this IRED.

In conclusion, based on the Agency’s experience with other biomonitoring studies, the Agency
is confident that occupational risks associated with tribufos will not be of concem. A determination has
been made that the continued use of tribufos is critical to the cotton industry and therefore should
remain available to growers. The factors leading to this conclusion are discussed below.



slightly exceeded for only the most highly exposed sub-population, children (1-6 years old), and are
below the DWLOCs for all others. The Agency considers the surface drinking water values to be
screening level assessments that may overestimate exposure. Moreover, the Agency has determined
that residues of tribufos are not expected to reach ground water, and therefore, has no concem for
acute or chronic effects from tribufos in ground water sources of drinking water. As a result, aggregate
tisks from tribufos exposure in food and water do not exceed the Agency’s level of concern. There are
no residential uses of tribufos, therefore, aggregate risks were based only on dietary food and water
exposures.

Occupational Risk

The Agency’s human health risk assessment for tribufos indicates that there are risk concerns
for occupational mixers, loaders, applicators for aerial applications, and reentry personnel. For
groundboom applications, the risk concerns are low. The target occupational Margins of Exposure
(MOEs) are 300 for dermal and 100 for inhalation exposure. Restricted entry intervals, as well as the
risks for the mixers, loaders, and applicators were based on a chemical-specific study submitted by the
registrant, Bayer. This chemical-specific study was designed to determine the dermal and inhalation
exposures to workers. :

Inhalation MOEs for all worker scenarios exceed the target MOE of 100. Many of the dermal
tisk estimates for handlers using engineering controls (closed systems for mixers, loaders, and
applicators) fall below the dermal target MOE of 300. Dermal MOEs below the target range from 49
to 150 for aerial mixers, loaders, and applicators. Flagger dermal MOEs supporting aerial application
up to 1,200 acres per day were 2,000 or greater. Dermal MOEs for mixers, loaders, and applicators
using groundboom equipment with baseline attire (long-sleeved shirt, long pants, shoes, and socks) are
all above 300, while engineering controls are necessary for scenarios supporting aerial application.

The occupational aggregate risk assessment combined dermal and inhalation risks for handlers
who were exposed to tribufos by both routes. An Aggregate Risk Index (ARI) method was used
because the dermal and inhalation target MOEs were different. A target ARI of greater than or equal
to 1 is not of concern to the Agency. When assuming engineering controls, the combined ARIs are
below 1 for all aerial mixing, loading and application scenarios. Therefore, occupational risks are of
concern to the Agency and warrant further mitigation measures.

The Agency identified four scenarios for post-application exposure: picker operator, module-
builder operator, raker, and tramper. A chemical-specific study was used to determine the dermal and
inhalation exposures for these scenarios. MOEs at the current restricted entry interval (REI) of 24
hours at the current label rate of 1.875 Ibs ai/A, as well as the lower proposed maximum rate of 1.125
Ibs ai/A, range from 45 to 180. These MOEs are less than the target MOE of 300 and, therefore, are
of concern to the Agency. MOEs at the proposed REI of 7 days at both the current label rate of 1.875
Ib ai/A and the lower rate of 1.125 Ib ai/A range from 210 to 820. At an REI of 7 days, MOEs for the



restricted use LOC (0.2) and endangered species LOC (0.1) are slightly exceeded for some food
items.

The acute endangered species LOC (0.1), the restricted use LOC (0.2), and the chronic LOC
(1.0) are exceeded for some food items. The RQs for chronic risks range from 0.08 for birds foraging
on seeds, to 1.32 for birds foraging on short grass. In conclusion, the Agency is concemed with
chronic risk to bird species resulting from multiple applications of tribufos, as well as risks to
endangered bird species, which may be acutely affected.

b. Risks To Mammals

For calculating risks to mammals associated with the use of tribufos, two exposure scenarios
were assumed (10 days and 21 days). The LOCs used for comparison to the RQs were 0.5 for acute
high risk, 0.2 for restricted use risk, and 0.1 for concerns to endangered species. The LOC for chronic
tisk is 1.0.

i Single Application

The results indicate that for a single, broadcast application of tribufos, the acute high risk, the
acute restricted use, and the endangered species LOCs are exceeded for all use rates for herbivores
and insectivores that feed on short grass or forage on small insects. Acute RQs for both herbivores and
insectivores ranged from 0.01 to 1.34. The acute endangered species LOC is exceeded when.
mammals feed on large insects at both the 1.875 Ibs ai/A rate and the 1.125 Ibs ai/A rate. Therefore,
the Agency is concemed with acute high risks to herbivores and insectivores.

Acute RQs for single, broadcast applications involving granivores (mammals which feed on
seeds) ranged from 0.01 at an application rate of 0.75 Ibs ai/A, to 0.03 at an application rate of 1.875
Ibs ai/A. The Agency, therefore, has no acute concems for these scenarios at any application rate.

For chronic risks to mammals, the Agency examined a lower (average) exposure scenario
because, typically, mammals will not be exposed to maximum residues of tribufos throughout their
breeding cycle. More likely, such animals would be exposed to initial maximum residues followed by
declining residues. To address this scenario, the Agency used an average of such residues for a time
period of 21 days, a period that would account for the shortest gestation period of a representative
small mammal. RQs for this scenario ranged from 0.34 for seed foraging mammals at an application
rate of 0.75 Ibs ai/A, to 13.94 for mammals feeding on short grass at a maximum application rate of
1.875 Ibs ai/A. The Agency, therefore, has chronic risk concern for these scenarios at all application
rates.



By publishing this interim decision on reregistration eligibility and requesting mitigation measures now for
the individual chemical tribufos , the Agency is not deferring or postponing FQPA requirements; rather,
EPA is taking steps to assure that uses which exceed FIFRA’s unreasonable risk standard do not
remain on the label indefinitely, pending completion of assessment required under the FQPA. This
decision does not preclude the Agency from making further FQPA determinations and tolerance-
related rulemakings that may be required on this pesticide or any other in the future.

If the Agency determines, before finalization of the RED, that any of the determinations
described in this interim RED are no longer appropriate, the Agency will pursue appropriate action,
including but not limited to, reconsideration of any portion of this interim RED.

Sw hase Five Comments and Responses

When making its interim decision, the Agency reviewed all comments received during Phase 5
of the Organophosphate Pilot Process. As stated previously, a mitigation proposal was received from
the Bayer Corporation; details of this proposal are discussed in the next section. Several other
comments were received including those from the National Cotton Council, which described the
benefits of tribufos and impact of loss to the industry in the absence of tribufos. These comments
helped the Agency in understanding the benefits associated with the use of tribufos and the loss that
would be incurred by the cotton industry as a result of removing tribufos from the market. Many of
these comments are addressed below where the Agency’s additional considerations are listed. These
comments and their responses are available in the public docket.

B. Regulatory Position
1. FQPA Assessment
a. “Risk Cup” Determination

As part of the FQPA tolerance reassessment process, EPA assessed the risks associated with
this organophosphate. The assessment was for this individual organophosphate, and does not attempt
to fully reassess these tolerances as required under FQPA. FQPA requires the Agency to evaluate
food tolerances on the basis of cumulative risk from substances sharing a common mechanism of
toxicity, such as the toxicity expressed by the organophosphates through a common biochemical
interaction with the cholinesterase enzyme. The Agency will evaluate the cumulative risk posed by the
entire class of organophosphates once the methodology is developed and the policy concerning
cumulative assessments is resolved.

The Agency has determined that risk from exposure to tribufos is within its own “Sisk cup.”
That is, if tribufos did not share a common mechanism of toxicity with other chemicals, EPA would be
able to conclude today that the tolerances for tribufos meet the FQPA safety standards. In reaching

29





Tribufos Team

Office of Pesticide Programs:

Health Effects Risk Assessment

Jess Rowland
Steve Knizner
Timothy Leighton
Robert Travaglini
Sarah Levy

Environmental Fate and Effects Risk Assessment
Dana Spatz

Nicholas Federoff

Curtis Laird

Use Usage

Kathy Davis

James Saulmon.

Jihad Alsadek
George Keitt

Registration Support
Jim Tompkins

Risk. ement

Anne Overstreet
Michael Goodis



i. Chronic Dietary (Food)

The chronic dietary risk is below the Agency's level of concem and is estimated to be less than
6% of the cPAD for all population subgroups including infants and children (1-6 years). Therefore, no
mitigation for chronic dietary food risks is required.

iii. Acute Drinking Water

The acute DWLOC for the most highly exposed subpopulation, children 1-6 years, is 10 ppb.
The modeled estimate for tribufos is 5.8 ppb in surface sources of drinking water. Based on the
physical/chemical characteristics of tribufos, the Agency determined that residues of tribufos are not
expected to reach ground water and were, therefore, not estimated. The Agency has no concern for
acute effects from tribufos in surface or ground water-sourced drinking water; therefore, no mitigation is
required.

iv. Chronic Drinking Water

The DWLOC for the most highly exposed subpopulation, children 1-6 years, is 1 ppb. Ina
worst case scenario, the modeled annual mean estimate for chronic exposure to tribufos in water is 1-2
ppb. Even though the modeled surface water figures slightly exceed the DWLOCs for only the most
highly exposed sub-population, the Agency believes the modeled drinking water concentrations are
considered high-end estimates and do not represent tribufos levels that people actually consume in
finished dririking water for reasons discussed earlier in the drinking water section of this document.
Based on the physical/chemical characteristics of tribufos, the Agency determined that residues of
tribufos are not expected to reach ground water and were, therefore, not estimated. The Agency has
no concern and is, therefore, not proposing any mitigation for chronic drinking water risks from surface
or ground water sources of drinking water.

b. Occupational Risk Mitigation

Based on the Agency’s revised occupational risk assessment, mixers, loaders, and handlers of
tribufos are exposed dermally at levels that pose risk concerns and require mitigation. With the addition
of engineering controls for aerial scenarios to mitigate dermal occupational risks, estimated MOEs for
inhalation exposure are above the target MOE of 100 for all scenarios. Therefore, inhalation risks are
not a main risk driver or concern for this assessment.

The target MOE for dermal exposure is 300. Dermal MOEs for mixers, loaders, and
applicators supporting groundboom operations range from 780 to 1,300 at baseline (long-sleeved shirt,
long pants, shoes, and socks) at the proposed rate of 1.125 Ibs ai/A and from 470 to 760 at baseline at
the higher application rate of 1.875 Ibs ai/A. These MOEs do not exceed the Agency’s level of
concem and no further mitigation is necessary.





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Rate: Application rates vary from 0.50 lbs ai/A (tank-mixed) to 1.875 Ibs
ai/A (tribufos used alone). Tribufos is most typically used in a tank-mix
with other defoliants at a rate between 0.50 Ibs ai/A to 0.75 Ibs ai/A.

Timing: Pre-harvest application

Trend: In 1999, tribufos was applied to between 4 and 5 million acres or
about 35% of planted cotton acreage. This is an increase from 1990
when less than 15% of total cotton acreage was treated with tribufos.

Use Classification: _ General Use Pesticide
D. Estimated Usage of Pesticide

Based on information available to the Agency and from consultation with the USDA, the
Agency estimates that approximately four and a half million pounds of tribufos are applied to
approximately 35% of the estimated fourteen million acres of cotton grown in the United States each
year. Tribufos is used throughout the cotton belt which extends from California to Florida and as far
north as Missouri, Tennessee, and Virginia.

Tribufos is generally used only once per growing season. It is very often tank-mixed with other
defoliants at a rate ranging from 0.50 Ibs ai/A to 0.75 Ibs ai/A to achieve maximum results. On
occasion, a second application of tribufos may be applied to complete the defoliation process.

Ii. Summary of Risk Assessment

The following discussion summarizes EPA’s revised human health and ecological risk
assessments as fully presented in the documents, “Tribufos Revised HED Chapter for the Reregistration
Eligibility Decision Document,” dated June 26, 2000, “EFED Chapter for Tribufos,” dated November
8, 1996, and an addendum to the EFED chapter “Updated Drinking Water EECs for Tribufos.”
Electronic copies of these supporting documents are available on the Intemet; see
http:www.epa.gov/pesticides/op. Public comment was solicited on the preliminary and revised risk
assessments. In addition, the Agency invited all interested stakeholders to submit risk mitigation
proposals. The risk assessments and risk mitigation measures presented in this IRED considered
stakeholder input.

A. Human Health Risk Assessment

EPA issued its preliminary risk assessment for tribufos in March of 1999. Since that time, the
Agency has refined the preliminary risk assessment using a probablistic (Monte Carlo) analysis. The



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The risks to non-target terrestrial and aquatic plants cannot be fully assessed because pertinent
plant studies are lacking. The Agency is requiring further data to better characterize potential risks.
Refer to section V for particular studies required.

Although the Agency’s analyses indicate concern for several ecological species (RQs ranging
from 0.01 to 23.3), RQs are relatively low. Measures discussed above that will be implemented to
address human health risks will also reduce ecological risks. The Agency has not attempted to quantify
the relative risk reduction resulting from the implementation of these mitigation measures. For instance,
because tribufos is usually tank-mixed at a much lower application rate than was assessed in the IRED,
it is expected that this reduction in the application rate will result in less pesticide availability in the
ecosystem. Therefore, no mitigation measures to address ecological risks are required.

D. Labeling Modifications

In order to remain eligible for reregistration, other use and safety information need to be placed
on the labeling of all end-use products containing tribufos. For the specific labeling statements, refer to
Section V of this document

1. Endangered Species Statement

The Agency has developed a program "The Endangered Species Protection Program" to
identify pesticides whose use may cause adverse impacts on endangered and threatened species and to
implement mitigation measures that will eliminate the adverse impacts. At present, the program
provides information to users to help them protect these species on a voluntary basis. As currently
planned, the final program will call for label modifications referring to limitations on pesticide uses,
typically as depicted in county-specific bulletins or by other site-specific mechanisms as specified by
state partners. A final program will be described in a future Federal Register notice. The Agency is
not imposing label modifications at this time through the IRED. Rather, any requirements for product
use modification will occur in the future under the Endangered Species Protection Program.

2. Spray Drift Management

The Agency has been working with the Spray Drift Task Force, EPA Regional Offices and
State Lead Agencies for pesticide regulation and other parties to develop the best spray drift
management practices. The Agency is now proposing interim mitigation measures for aerial
applications that should be placed on product labels/labeling, as specified in section V of this document.
The Agency has completed its evaluation of the new database submitted by the Spray Drift Task
Force, a membership of U.S. pesticide registrants. The Agency is developing a policy on how to
appropriately apply the data and the AgDRIFT computer model to its risk assessments for pesticides
applied by air, orchard airblast, and ground hydraulic methods. After the policy is in place, the Agency
may impose further refinements in spray drift management practices to reduce off-target drift and risks

41



2) The restricted entry interval (REI) is to be increased from 24 hours to 7 days;
3) Tribufos products are to be distributed in closed systems starting with the 2002 season.
4) The Agency is also requiring closed systems for aerial applicators (enclosed cockpits).

5) A biomonitoring study will be required to confirm the Agency’s risk management decision. The
biomonitoring study will be submitted to the Agency by September 2003.

The Agency has incorporated the first four mitigation measures in the current risk assessment.
However, risk concem still remains for workers who mix, load, and apply tribufos by aerial application.

In this IRED occupational risks associated with the use of tribufos were calculated at two rates,
the proposed rate of 1.125 Ibs ai/A, and the current maximum rate of 1.875 Ibs ai/A. Typically,
tribufos is tank-mixed in the majority of applications with other defoliants at a much lower rate (0.50 to
0.75 Ibs ai/A). The Agency is, therefore, confident that the occupational and ecological risks
associated with the use of tribufos are generally lower than those discussed in this IRED.

In conclusion, based on experience with other biomonitoring studies, the Agency is confident
that occupational risks associated with tribufos will not be of concern. A determination has been made
that the continued use of tribufos is critical to the cotton industry and should remain available to
growers. The factors leading to this conclusion are discussed in further detail in section IV of this
document.

Benefits

Under FIFRA, benefits associated with the use of a chemical are considered when worker and
ecological risks are of concern to the Agency. The Agency has received and reviewed benefits
analyses from both the USDA and the National Cotton Council that ascertain the benefits from the use
of tribufos are numerous, including its efficacy at lower temperatures. The Agency has considered
these submissions and concurs that the benefits from tribufos are numerous and its loss to the cotton
industry would be substantial.

An altemative analysis was also conducted for tribufos. The Agency reviews alternatives to a
pesticide, by considering efficacy against target pests, costs, ease of use, potential resistance
development to the pesticide, impacts on existing integrated pest management (IPM) programs, and
several other characteristics. The Agency determined that tribufos serves a vital role in the cotton
industry and there currently are no suitable replacements under the conditions which tribufos is most
effective. Furthermore, as outlined in Section IV of this document, tribufos exhibits a synergistic effect
when mixed with other defoliants. That is, tribufos alone is less effective than when mixed with other
defoliants. This synergism is of great benefit to the cotton industry and its loss would create a void



b. Adjustment for Species Differences in Dermal Absorption

The previous Human Health Risk Assessment Chapter, dated September 14, 1999, located on
the internet at http:www.epa.gov/pesticides/op) established a LOAEL in the 21-day dermal toxicity
study in rabbits. The revised risk assessment, dated June 26, 2000, considered a new dermal
absorption study in monkeys submitted by the registrant. This study demonstrated that tribufos is
poorly absorbed through the skin of monkeys. After eight hours of dermal exposure, only 7% of the
applied dose had been absorbed through the skin into the systemic circulation. The Agency considered
this new data and revised the risk assessment to reflect the changes discussed below.

With the availability of this new monkey dermal absorption data, the dermal toxicity in rabbits
relative to the poor dermal absorption shown in monkeys was re-evaluated because: 1) in general, the
skin of rabbits is more permeable to chemicals than human skin, and 2) the penetration of a chemical
through the skin of primates (monkeys) can be used as a better surrogate for penetration through human
skin. A dermal absorption study in rats showed absorption is greater in the rat than in the monkey. At
acomparable dose, 48% of the applied dose was absorbed in the rat.

It is presumed that rat and rabbit dermal absorption rates are comparable. However, monkey
dermal absorption is presumed to be a better surrogate for human skin. Therefore, an adjustment can
be made to the dose (LOAEL) used for risk assessment to account for species differences in dermal
absorption. Consequently, using the dermal absorption rates of 48% in rats and 7% in monkeys, a 6.9
conversion factor was obtained to account for species differences in dermal absorption:

Dermal Absorption in Rats (48%) _ =6.9
Dermal Absorption in Monkeys (7%)

The Agency determined that a conversion factor of 7 (rounded up from 6.9) should be applied
to the LOAEL of 2 mg/kg/day selected for short- and intermediate-term dermal exposure assessments.
This resulted in a LOAEL of 14 mg/kg/day to assess occupational dermal risk.

c. Occupational Handler Exposure

Data from the Pesticide Handlers Exposure Database (PHED) as well as a chemical-specific
study were used to estimate occupational exposure risks. PHED is a comprehensive generic/surrogate
exposure database containing a large number of measured values of dermal and inhalation exposures
for pesticide workers (e.g., mixers, loaders, and applicators) involved in handling or applying of
pesticides. The database currently contains data for over 1700 monitored exposure events.

A chemical-specific handler exposure study was also performed for tribufos (MRID
42685901) using passive dosimetry methodologies. It was designed to determine the dermal and
inhalation exposures to the workers. These data were combined with the PHED data to assess the use

15



2. Additional Considerations

The Agency has extensively examined other areas of possible refinement to the risk assessment.
The following is a more detailed description of the Agency’s refinement of the risk assessment and
options for additional refinement considered by the Agency.

a. Chemical-Specific Exposure Data

The registrant has submitted a tribufos-specific passive dosimetry worker exposure study. This
data was used in conjunction with the PHED V1.1 to assess occupational exposure. The chemical-
specific data were combined with PHED to increase the sample size and number of studies in the
database. The Agency determined worker exposures based on the chemical specific study and using
enhanced PHED (i.e., combining the chemical-specific data with PHED).

b. Levels of Dermal Absorption Versus Other Test Species

For occupational exposure risk assessments, a NOAEL or LOAEL (when a NOAEL is not
established) derived by the same route as the human exposure is used to calculate the MOEs. In this
process, unless proven otherwise, it is presumed that human and animal absorption of the chemical is
identical for the same route of exposure.

The toxicity endpoint used to estimate worker risk was derived from a 21-day dermal toxicity
study in rabbits. In this study, a NOAEL was not established. Therefore, the risks were based on a
LOAEL (2 mg/kg/day). The MOEs were calculated using the assumption that dermal penetration of
tribufos through rabbit and human skin is largely equivalent. Since then, Bayer has submitted a dermal
absorption study in monkeys. This study demonstrated that tribufos is poorly absorbed through the skin
of monkeys. After eight hours of dermal exposure, only 7% of the applied dose had been absorbed
through the skin into the systemic circulation.

With the availability of this new monkey dermal absorption data, the dermal toxicity in rabbits
relative to the poor dermal absorption shown in monkeys was re-evaluated because: 1) in general, the
skin of rabbits is more permeable to chemicals than human skin, and 2) the penetration of a chemical
through the skin of primates (monkeys) can be used as a better surrogate for penetration through human.
skin.

The Agency accepted that the dermal absorption data in monkeys can be used as a surrogate
for penetration through human skin. Because it is presumed that rat dermal absorption is comparable to
rabbit dermal absorption, an adjustment can be made to the dose (LOAEL) used for risk assessment to
account for species differences in dermal absorption. Consequently, using the dermal absorption rates
of 48% in rats and 7% in monkeys, a 6.9 conversion factor (rounded to 7) was obtained, to account
for species differences in dermal absorption.

35



Introduction

The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) was amended in 1988 to
accelerate the reregistration of products with active ingredients registered prior to November 1, 1984.
The amended act calls for the development and submission of data to support the reregistration of an
active ingredient, as well as a review of all submitted data by the U.S. Environmental Protection Agency
(referred to as “the Agency”). Reregistration involves a thorough review of the scientific database
underlying a pesticide’s registration. The purpose of the Agency’s review is to reassess the potential
hazards arising from the currently registered uses of the pesticide; to determine the need for additional
data on health and environmental effects; and to determine whether the pesticide meets the “no
unreasonable adverse effects” criteria of FIFRA.

On August 3, 1996, the Food Quality Protection Act of 1996 (FQPA) was signed into law.
This Act amends FIFRA to require tolerance reassessment of all existing tolerances. The Agency has
decided that, for those chemicals that have tolerances and are undergoing reregistration, the tolerance
reassessment will be initiated through this reregistration process. It also requires that by 2006, EPA
must review all tolerances in effect on the day before the date of the enactment of the FQPA, which
was August 3, 1996. FQPA also amends the Federal Food, Drug, and Cosmetic Act (FFDCA), to
require a safety finding in tolerance reassessment based on factors including an assessment of
cumulative effects of chemicals with a common mechanism of toxicity. Tribufos belongs to a group of
pesticides called organophosphates, which share a common mechanism of toxicity - they all affect the
nervous system by inhibiting cholinesterase. Although FQPA significantly affects the Agency’s
reregistration process, it does not amend any of the existing reregistration deadlines. Therefore, the
Agency is continuing its reregistration program while it resolves the remaining issues associated with the
implementation of FQPA.

This document presents the Agency’s revised human health and ecological risk assessments; its
progress toward tolerance reassessment; and the interim decision on the reregistration eligibility of
tribufos. It is intended to be only the first phase in the reregistration process for tribufos. The Agency
will eventually proceed with its assessment of the cumulative risk of the OP pesticides and issue a final
reregistration eligibility decision for tribufos.

The implementation of FQPA has required the Agency to revisit some of its existing policies
relating to the determination and regulation of dietary risk, and has also raised a number of new issues
for which policies need to be established. These issues were developed and refined through
collaboration between the Agency and the Tolerance Reassessment Advisory Committee (TRAC),
which was composed of representatives from industry, environmental groups, and other interested
parties. The TRAC identified the following science policy issues it believed were key to the
implementation of FQPA and tolerance reassessment:





Table 9. Tribufos Dermal Exposures for Picker Operators, Module Builder Operators,
Rakers, and Trampers (Target MOE=300)

Worker Categories *
Pickers Module Rakers | Trampers
Results at 24 hours after treatment °

Average dermal dose @ 1.875 Ib ai/acre 0.30 0.13 031 0.27
(mg/kg/day)”
MOEs at 1.875 Ibs ai/acre? 47 110 45 52

Average dermal dose (mg/kg/day) corrected 0.078
for the lower (1.125 Ib ai A) application rate‘

MOE@ 1.125 Ib ai/acre* 78 180

Results at Seven Days After Treatment (DAT)
Average dermal dose @ 1.875 (mg/kg/day)® 0.066, _ 0.029 0.069
MOEs at 1.875 Ibs ai/acre ¢ 210 480 200

Average dermal dose (mg/kg/day) corrected 0.040 0.017 0.041
for the lower (1.125 Ib ai A) application rate*

MOE @ 1.125 lb ai/acre* 350 — 820 340 -

*Passive dosimetry monitoring data were collected at the California sites (DAT 15 and 17 are from the aerially treated field and
DAT 20 is from the ground-treated field).

*The dermal exposure represents workers wearing cotton/polyester coveralls over the whole body dosimeters. The average
dermal dose is calculated from the data reported in MRID 427016-01 at an application rate of 1.875 Ib ai/acre. The dermal
exposure data were collected on 15, 17, and 20 DAT and corresponding cotton boll residues were also collected. Based on the:
data, transfer coefficients were calculated to extrapolate the dose from 15, 17, and 20 DAT down to 24 hours and 7 DAT.
‘Corrected Average dermal exposure (mg/kg/day) = Avg dermal exposure@1.875 Ib ai/A (mg/kg/day) x 0.6correction factor for
new application rate (i.e., 1.125 Ib ai/A/1.875 Ib ai/A). Where the Avg. Daily Dermal Dose (mg/kg/day) = (Avg. Dermal
exposure(ug/hr) x 8 hrs/day x 0.001 mg/ug unit conversion)/70 kg BW.

¢MOE = 14 mg/kg/day (LOAEL of 2 mg/kg/day x a conversion factor of 7)/Dermal Dose mg/kg/day. Target MOE is 300.

fi. Human Incident Reports

The Office of Pesticide Programs (OPP) Incident Data System (IDS), Poison Control Centers
database, California Department of Food and Agriculture database, and the National Pesticide
Telecommunications Network (NPTN) have been consulted for poisoning incident data on tribufos.
From the review of the IDS and reports from California, it appears that a significant number of spray
drift cases result from the use of tribufos. It is not clear from the information collected how many of
these cases are due to anticholinergic effects versus the odor of the pesticide. Some cases reportedly
resulted in flu-like symptoms as a result of spraying tribufos near residential areas. There were too few
incidents involving mixer/loader workers that applied tribufos for the Agency to make any conclusions.



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defoliant rate is “1 + 1 to 10". This term refers to 1 gallon of DEF 6 + 1 pound of Dropp
to 10 acres of cotton.

6) Loss to the cotton industry. The Agency has had a tremendous amount of input in
regards to the incurrence of cost and loss to the cotton industry if tribufos were unavailable.
It is well understood that tribufos is critical to achieving good defoliation in adverse weather
conditions, as well as its improved efficacy in tank mixes. The docket contains more
detailed information submitted by both the National Cotton Council and USDA, including a
comprehensive analysis of cost replacement and losses to yield and fiber quality. Ina
typical year of cotton production, it is estimated that the total loss to the cotton industry as a
result of losing tribfuos would exceed $156 million per year. This cost estimate takes into
account the impact of losing tribufos as a defoliant as well as the impact to quality and
quantity of cotton yields.

3. Environmental Risk Mitigation

In addition to the human health risks, the Agency is also concemed with ecological risks
potentially caused by the use of tribufos. Overall, ecological risk concerns for some species exist but
the exceedences are relatively low. The Agency is concemed with acute and chronic risks to birds and
mammals when both single and multiple applications of tribufos are used (RQs ranged from 0.01 to
13.94). The Agency assessed both acute and chronic risks to birds using a Bobwhite Quail study.
Therefore, the Agency is requiring a mallard duck study to more comprehensively assess risks to birds
(refer to Section V for data requirements).

The Agency is not concerned with acute risk to freshwater fish associated with the use of
tribufos (RQs ranged from 0.03 to 0.06). However, acute risks to estuarine/marine fish are of concern
to the Agency with RQs ranging from 0.06 to 0.11. Data to assess chronic risks to both freshwater
and estuarine/marine fish are lacking and therefore will be required in Section V of this document.

With regards to freshwater and estuarine/marine invertebrates, the Agency has concerns for
both acute and chronic risks associated with the use of tribufos (RQs ranged from 1.6 to 23.3). The
Agency is also requiring a chronic estuarine/marine study to better characterize risks to invertebrates
(refer to Section V).

Exposure to non-target vascular aquatic plants is possible through the use of tribufos. Acute
RQs ranged from 0.05 to 0.09. These RQs indicate that the acute LOCs are not exceeded for any use
rate. RQs for exposure to non-vascular plants range from 0.07 to 0.12. The Agency is, therefore, not
concerned with risks to non-target aquatic plants.



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Adjusted Dose (cPAD) is calculated to be 0.0001 mg/kg. The most highly exposed population
subgroup is children (1 - 6 years), at 6% of the cPAD. The chronic dietary risk (from food) of tribufos
does not exceed the Agency’s level of risk concern (i.e., less than 100% of the cPAD is utilized). The
results for the general population and the various subgroups are summarized in Table 3.

Table 3. Chronic Dietary (Food) Exposure and Risk Estimates

99.9% Percentile
Population
Exposure (mg/kg/day) % cPAD
U.S. Population 0.000003 3
lon-nursing infants <1 yr 0.000001 1
[Children (ages 1-6 years) 0.000006 6
[Females (13-19) 0.000003 3

g. Cancer Risks

Tribufos is classified as an unlikely human carcinogen at low doses but is a likely carcinogen at
high doses. However, the cancer risk from dietary exposure is not of concern to the Agency for the
following reasons: .

@M although the chronic NOAEL was 0.1 mg/kg/day for plasma ChE inhibition (in the
chronic dog study), tumors were seen in mice only at the highest dose tested (48
mg/kg/day), which is a wide span in dosing between the NOAEL and the tumors;

(2) the dose of 0.1 mg/kg/day used for deriving the chronic R£D is approximately 500-fold
lower than the dose that caused tumors (i.e., 48 mg/kg/day);

QB) the primary concern is the non-cancer risk, which manifests as ChE inhibition at a very
low dose; and .

(4) the application of the 10X FQPA Safety Factor to the chronic RfD yields a cPAD that
provides even more protection than for non-cancer dietary risk (e., the CPAD of
0.0001mg/kg/day is 500,000 times lower than the dose at which tumors were seen).

For these reasons, the Agency has determined that a quantitative dietary cancer risk assessment
‘was not necessary for tribufos.

2. Dietary Risk From Drinking Water

Drinking water exposure to pesticides can occur through ground and surface water
contamination. EPA considers both acute (one day) and chronic (lifetime) drinking water risks and
uses either modeling or actual monitoring data, when available, to estimate those risks. To determine
the maximum contribution from water allowed in the diet, EPA first looks at how much of the overall
allowable risk is contributed by food and then determines a drinking water level of comparison



Interim Reregistration Eligibility
Decision

for
Tribufos



test animals). The RQ is a means of integrating the results of ecological exposure and ecological
toxicity. These RQ values are compared to levels of concern (LOCs), which provide an indication of
the relative risk the particular pesticide and/or use may pose for nontarget organisms. If the RQ does
not exceed the LOC, it is unlikely that the pesticide will pose a significant risk. Similarly, when RQs are
equal to or greater than the LOC, additional refinements or mitigation may be necessary. Use, toxicity,
fate, and exposure are considered to characterize the risk as well as the level of certainty and
uncertainty in the assessment. Refer to the Ecological Effects and Fate Chapter for the Tribufos IRED
for additional information located on the internet at http:www.epa.gov/pesticides/op.

a. Risks To Birds

For calculating risks to birds associated with the use of tribufos, an exposure scenario of 10
days was assumed. The LOCs used for comparison to the RQs were 0.5 for acute high risk, 0.2 for
restricted use risk, and 0.1 for concerns to endangered species. The LOC for chronic risk is 1.0. The
Agency assessed both acute and chronic risks to birds using a Bobwhite Quail study. Therefore, the
Agency is requiring a mallard duck study to more comprehensively assess risks to birds (refer to
Section V for data requirements).

i. Single Application

The results indicate that for a single, broadcast application of tribufos, the acute high risk LOC
is not exceeded for any use rate. RQs ranged from 0.01 for birds foraging on seeds at an application
rate of .75 Ibs ai/A, to an RQ of 0.18 for birds'foraging on short grass at an application rate of 1.125
Ibs ai/A. The acute endangered species LOC is exceeded at 1.875 Ibs ai/A, and the 1.125 labs ai/A
rate for birds foraging on short grass.

Furthermore, the results indicate that for a single, broadcast application of tribufos, the chronic
risk to birds (LOC=1.0), is exceeded for different food items at all use rates. RQs ranged from 0.07
for birds foraging on seeds at an application rate of 0.75 Ibs ai/A, to 3.04 for birds foraging on short
grass at an application rate of 1.875 Ibs ai/A.

The Agency, therefore, has no concer for acute high risk to bird species, but chronic risks are
possible to bird species that feed on particular food items. Endangered species may be affected both
acutely and chronically.

ii. Multiple Applications

The results indicate that for multiple broadcast applications of tribufos (0.75 Ibs ai/A applied
twice), the avian acute high risk (0.5) is not exceeded for any use rate or food item. RQs ranged from
0.01 for birds foraging on seeds to 0.24 for birds foraging on short grass. However, the acute





ii. Inhalation Risk

Tables 7 and 8 summarize inhalation risks from tribufos use. The inhalation MOEs are as
follows: at the current label rate of 1.875 Ibs ai/A, MOEs range from 330 (mixing and loading to
support aerial application to 1,200 acres per day) to 5,100 at baseline (mixing and loading liquids for
groundboom application); at the proposed label rate of 1.125 Ibs ai per acre, MOEs range from 560
(mixing and loading for aerial application to 1,200 acres per day) to 8,400 at baseline (mixing and
loading liquids for groundboom application). With engineering controls for aerial scenarios and baseline
for groundboom equipment, the inhalation MOEs are significantly above the target MOE of 100 (refer
to Tables 7 and 8).

d. Combined Dermal and Inhalation Risks

The Agency also performed an occupational risk assessment combining both the dermal and
inhalation risk for workers who are exposed to tribufos by both routes. An Aggregate Risk Index
(ARI) method was used because the dermal target MOE is 300 and the inhalation target MOE is 100.
An ARI of greater than 1 is not of concern to the Agency, whereas, an ARI less than 1 is of concern to
the Agency. The combined dermal and inhalation risks which reflect the current maximum label rate of
1.875 Ibs ai/A range from 0.16 (mixing and loading to support application 1,200 acres per day) to 5
(flaggers supporting aerial application to 1,200 acres per day).

The combined dermal and inhalation ARIs reflecting the proposed amended label rate of 1.125
Ibs ai/A range from 0.26 (mixing and loading to support aerial application to 1,200 acres per day) to
9.5 (flaggers supporting aerial application to 1,200 acres per day). These scenarios are accurate with
the exception of California and Arizona, which use the higher rate of 1.875 Ibs ai/A for defoliation for
reasons discussed in chapter IV of this document. Two of the five combined inhalation and dermal
scenarios yield ARIs below 1, and therefore, are of concern even when engineering controls are used.
Tables 7 and 8 list the scenarios applicable to tribufos as well as MOEs and ARIs.



Programs. We anticipate that this publication will become available during the Fall of
1998.

3. The National Pesticide Information Retrieval System (NPIRS) of Purdue University's
Center for Environmental and Regulatory Information Systems. This service does charge a
fee for subscriptions and custom searches. You can contact NPIRS by telephone at (765)
494-6614 or through their Web site.

4. The National Pesticide Telecommunications Network (NPTN) can provide information on
, active ingredients, uses, toxicology, and chemistry of pesticides. You can contact NPIN _
by telephone at (800) 858-7378 or through their Web site: ace.orst.edw/info/nptn.

The Agency will return a notice of receipt of an application for registration or amended
registration, experimental use permit, or amendment to a petition if the applicant or
petitioner encloses with his submission a stamped, self-addressed postcard. The postcard
must contain the following entries to be completed by OPP:

Date of receipt
EPA identifying number
Product Manager assignment

Other identifying information may be included by the applicant to link the acknowledgment
of receipt to the specific application submitted. EPA will stamp the date of receipt and
provide the EPA identifying File Symbol or petition number for the new submission. The
identifying number should be used whenever you contact the Agency concerning an
application for registration, experimental use permit, or tolerance petition.

-To assist us in ensuring that all data you have submitted for the chemical are properly
coded and assigned to your company, please include a list of all synonyms, common and
trade names, company experimental codes, and other names which identify the chemical
Gncluding "blind" codes used when a sample was submitted for testing by commercial or
academic facilities). Please provide a CAS number if one has been assigned.

Documents Associated with this RED

The following documents are part of the Administrative Record for this RED document and may
included in the EPA's Office of Pesticide Programs Public Docket. Copies of these documents are not
available electronically, but may be obtained by contacting the person listed on the respective Chemical
Status Sheet. :

a. Health and Environmental Effects Science Chapters.
b. Detailed Label Usage Information System (LUIS) Report.

98



pickers, rakers, and trampers at the current label rate (1.875 Ib ai/A) are less than 300 and, therefore,
are of concern to the Agency, but are above 300 for all workers at the rate of 1.125 Ibs ai/A.

Ecological Risks

In addition to the human health effects, the Agency also assessed ecological risks potentially
caused by the use of tribufos under all use scenarios. Overall, ecological risk concems for some
species exist but the exceedences are relatively low. The Agency is concemed with acute and chronic
tisks to birds.and mammals when both single and multiple applications of tribufos are used. Risk
Quotients (RQs) ranged from 0.01 to 13.94. The Agency is requiring an additional avian study to more
comprehensively assess risks to birds (refer to Section V for data requirements).

The Agency is not concemed with acute risk to freshwater fish associated with the use of
tribufos (RQs ranged from 0.03 to 0.06). However, acute risks to estuarine/marine fish are of concen
to the Agency with RQs ranging from 0.06 to 0.11. Data to assess chronic risks to both freshwater
and estuarine/marine fish are lacking and therefore will be required (refer to Section V of this
document).

With regards to freshwater and estuarine/marine invertebrates, the Agency has concems for
both acute and chronic risks associated with the use of tribufos (RQs ranged from 1.6 to 23.3). The
Agency is also requiring a chronic estuarine/marine study to better characterize risks to invertebrates
(refer to Section V).

Exposure to non-target vascular aquatic plants is possible through the use of tribufos. Acute
RQs ranged from 0.05 to 0.09. These RQs indicate that the acute LOCs are not exceeded for any use
rate. RQs for exposure to non-vascular plants range from 0.07 to 0.12. The Agency is, therefore, not
concemed with risks to non-target aquatic plants.

The risks to non-target terrestrial and aquatic plants cannot be fully assessed because pertinent
plant studies are lacking. The Agency is requiring confirmatory data to better characterize potential
risks. Refer to section V for particular studies required.

Risk Mitigation
The Agency has adopted several measures to help mitigate occupational risks to aerial mixers,

loaders, and applicators, as well as ecological risks. These mitigation options have been included in the
tisk calculations for this IRED and are as follows:

1) The maximum application rate is to be reduced to 1.5 pints/A (1.125 Ibs ai/A) in all states, except
California and Arizona, which would remain at the higher rate of 2.5 pints/A/year (1.875 Ib ai/A).
California and Arizona grow hardier varieties of cotton, which require more defoliant.





UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460

OFFICE OF
PREVENTION, PESTICIDES
AND TOXIC SUBSTANCES,

OCT 2 4 2008

CERTIFIED MAIL
Dear Registrant:

This is to inform you that the Environmental Protection Agency (hereafter referred to as
EPA or the Agency) has completed its review of the available data and public comments received
related to the preliminary and revised risk assessments for the organophosphate pesticide
tribufos. The public comment period on the revised risk assessment phase of the reregistration
process is closed. Based on comments received during the public comment period and additional
data received from the registrant, the Agency revised the human health and environmental effects
tisk assessments and made them available to the public on September 24, 1999. During Phase 5,
all interested parties were invited to participate and provide comments and suggestions on ways
the Agency might mitigate the estimated risks presented in the revised risk assessments. This
public participation and comment period commenced on September 24, 1999, and closed on
November 24, 1999.

Based on its review, EPA has identified risk mitigation measures that the Agency
believes are necessary to address the human health and environmental risks associated with the
current use of tribufos. The EPA is now publishing its interim decision on the reregistration
eligibility of and risk management decision for the current uses of tribufos and its associated
human health and environmental risks. The reregistration eligibility and tolerance reassessment
decisions for tribufos will be finalized once the cumulative assessment for all of the
organophosphate pesticides is complete. The Agency’s decision on the individual chemical
tribufos can be found in the attached document entitled, "Interim Reregistration Eligibility
Decision" which was approved on September 28, 2000, contains the Agency’s decision on the
individual chemical tribufos .

A Notice of Availability for this Interim Reregistration Eligibility Decision for tribufos is
being published in the Federal Register. To obtain a copy of the interim RED (IRED) document,
please contact the OPP Public Regulatory Docket (7502C), US EPA, Ariel Rios Building, 1200
Pennsylvania Avenue NW, Washington, DC 20460, telephone (703) 305-5805. Electronic
copies of the interim RED and all supporting documents are available on the Internet. See
http:www.epa.gov/pesticides/op.



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Applying the FQPA 10-Fold Safety Factor :

Whether and How to Use "Monte Carlo" Analyses in Dietary Exposure Assessments
How to Interpret "No Detectable Residues" in Dietary Exposure Assessments
Refining Dietary (Food) Exposure Estimates

Refining Dietary (Drinking Water) Exposure Estimates

Assessing Residential Exposure

Aggregating Exposure from all Non-Occupational Sources

How to Conduct a Cumulative Risk Assessment for Organophosphate or Other
Pesticides with a Common Mechanism of Toxicity

Selection of Appropriate Toxicity Endpoints for Risk Assessments of
Organophosphates

Whether and How to Use Data Derived from Human Studies

The process developed by the TRAC calls for EPA to provide one or more documents for
public comment on each of the policy issues described above. Each of these issues is evolving and ina
different stage of refinement. Most issue papers have already been published for comment in the
Federal Register and others will be published shortly.

In addition to the policy issues that resulted from the TRAC process, the Agency published in
the Federal Register on August 12, 1999, a draft Pesticide Registration (PR) Notice that presents
EPA’s proposed approach for managing risks from organophosphate pesticides to occupational users.
This notice describes the Agency’s baseline approach to managing risks to handlers and workers of
organophosphate pesticides. Generally, basic protective measures such as closed mixing and loading
systems, enclosed cab equipment, or protective clothing, as well as increased restricted entry intervals
will be necessary for most uses where current risk assessments indicate a risk and such protective
measures are feasible. The draft guidance policy also states that the Agency will assess each pesticide
individually, and based upon the risk assessment, determine the need for specific measures tailored to
the potential risks of the chemical. The measures included in this IRED are consistent with that draft
Pesticide Registration Notice.

This document consists of six sections. Section I contains the regulatory framework for
reregistration/tolerance reassessment as well as descriptions of the process developed by TRAC for
public comment on science policy issues for the organophosphate pesticides and the worker risk
management PR notice. Section II provides a profile of the use and usage of the chemical. Section III
gives an overview of the revised human health and environmental effects risk assessments resulting from
public comments and other information. Section IV presents the Agency's interim decision on
reregistration eligibility and risk management decisions. Section V summarizes label changes necessary
to implement the risk mitigation measures outlined in Section IV. Section VI provides information on
how to access related documents. Finally, the Appendices list uses that are eligible for interim
reregistration, guideline, and other data used to conduct the assessments outlined in this document as
well as Data Call-In (DCI) information. The revised risk assessments and related addenda are not



Iv.

e. Post-Application Risks
£ Human Incident Reports
B. Environmental Risk Assessment
1, Environmental Fate
2. Ecological Assessment
a. Risks To Birds
i. Single Application ...
ii. Multiple Applications . .
Risks To Mammals
i. Single Application
ii. Multiple Applications
ce Risks to Insects
da. Risks To Aquatic Species
e. Risks To Plants

Interim Reregistration Eligibility and Risk Management Decisions

A. Determination of Interim Reregistration Eligibility
B. Regulatory Position
1. FQPA Assessment
a. “Risk Cup” Determination
b. Tolerance Summary
i. Tolerances To Be Proposed Under 40 CFR §180.272

ii. Tolerances Listed Under 40 CFR §180.272
2. Endocrine Disruptor Effects
Regulatory Rationale
1. Human Health Risk Mitigation .
a. Dietary Risk Mitigation
i. Acute Dietary (Food) ....
ii. Chronic Dietary (Food) .
iii. Acute Drinking Water
iv. Chronic Drinking Water
b. Occupational Risk Mitigation ...
Additional Considerations
a. Chemical-Specific Exposure Data .
b. Levels of Dermal Absorption Versus Other Test Species ... .
Cc. Information from Bayer .
d. Other Issues
e. Alternatives and Benefits of Tribufos
3. Environmental Risk Mitigation
Labeling Modifications
1. Endangered Species Statement



A Data Call-In (DCI) requiring the above studies was sent to registrants of OP pesticides
currently registered under FIFRA on August 6, 1999. The DCI requirements included acute,
subchronic, and developmental neurotoxicity studies. The due date for these studies is September
2001.

c Population Adjusted Dose PAD)

The Population Adjusted Dose (PAD), is a relatively new term that reflects the Reference Dose
(RfD), either acute or chronic, that has been adjusted to account for the FQPA Safety Factor. For the
acute dietary risk assessment, risk is calculated by comparing what is eaten in one day (consumption)
with maximum, high-end residue values in food. For chronic exposures, dietary risk is calculated using
the average consumption value for food over a 70-year lifetime and average residues found in food.
When the FQPA Safety Factor is applied to the risk assessment, the R£D is divided by the FQPA
Safety Factor, which results in a potentially different figure, the PAD. The PAD is now referred to in
regulatory decisions rather than the R£D. In the case of tribufos, the FOPA Safety Factor is 10, which
results in a PAD that is 10 times more protective than the acute or chronic RD. A risk estimate that is
less than 100% of the acute or chronic PAD does not exceed the Agency’s risk concern. A brief
overview of the studies used to assess dietary risk is outlined in Table 1.

Table 1: Summary of Toxicological Endpoints and Other Factors Used in the Human Health
Risk Assessment of Tribufos

Type of Exposure
{duration and route)

Endpoint and Effect Level [study

Plasma and red blood cell (RBC) ChE inhibition; No-Observed-
Adverse-Effect-Level (NOAEL) of 1 mg/kg/day
Acute RED: 0.01 mg/kg/day Prenatal Developmental
|Acute Dietary [Toxicity study in rats

Uncertainty Nactor (UF): FOQPA Safety Factor: 10 {(MIRID 40190601)

Acute PAD: 0.001 mg/kg/day

Plasma ChE inhibition; NOAEL of 0.1 mg/kg/day
Chronic Rf£D: 0.001 mg/kg/day

{Chronic Dietary Uncertainty Factor (UF)
UF: 100

Chronic PAD: 0.0001 mg/kg/day

‘hronic study in the dog
_ FQPA Safety Factor: 10 42007203)

d. Exposure Assumptions

. The Agency's dietary risk assessment for tribufos uses the Dietary Exposure Evaluation Model
(DEEMTM), which incorporates consumption data generated from the USDA’s Continuing Surveys of
Food Intakes by Individuals (CSFII), 1989-1992. The acute and chronic exposure analysis was



BIBLIOGRAPHY

MRID

CITATION

42007205

42034501

42034502

42034503

42040101

42184701

42335101

42350003

Stevenson, T.; Leimkuehler, W. (1990) The Metabolism of Tribufos in Soil Under
Anaerobic Conditions: Lab Project Number: 100333. Unpublished study prepared by
Mobay Corp., R & D Dept. 31 p.

Kao, M.; Middien, R.; Bosnak, L.; et al. (1991) Disposition and Metabolism of
[Carbon 14]-Tribufos in Rats: Lab Project Number: 101331: DEO41801.
Unpublished study prepared by Mobay Corp. 145 p.

Hall, L. (1991) The Metabolism of [Carbon 14] and [S 35]-Tribufos in Hens: Lab
Project Number: DE040501: 101329. Unpublished Study prepared by Mobay Corp.
123 p.

Sahali, Y. (1991) Metabolism of [Carbon 14]-Tribufos in Lactating Goats: Lab
Project Number: DE041001: 101330. Unpublished study prepared by Mobay Corp.
83 p.

Selman, F. (1991) Responses to the EPA Review of Ciba-Geigy Protocol No. 17-91
for Small-Scale Prospective Ground-Water Monitering Study for Primisulfuron-Methyl
(Beacon): Lab Project Number: ABR-91068. Unpublished study prepared by
Ciba-Geigy. 80 p.

Leimkuehler, W.; Moore, K. (1991) Carbon 14 Tribufos Residues in Confined
Rotational Crops: Lab Project Number: DE051601. Unpublished study prepared by
Mobay Corp. 37 p.

Christenson, W. (1992) Technical Grade Tribufos (DEF): A Chronic
Toxicity/Oncogenicity/ Neurotoxicity Feeding Study in the Fisher 344 Rat: Lab Project
Number: 88-271-AA. Unpublished study prepared by Miles Inc. 3672 p.

Schroeder, R. (1992) Dermal Absorption of Tribufos by Rats from a DEF 6
Emulsifiable Formulation using [carbon 14] Tribufos: Lab Project Number: 91-
722-KW. Unpublished study prepared by Miles, Inc. 54 p.



Appendix D. Citations Considered To Be Part Of The Database Supporting the
Interim Reregistration Eligibility Decision (Bibliography)

GUIDE TO APPENDIX D

1. CONTENTS OF BIBLIOGRAPHY. This bibliography contains citations of all studies
considered relevant by EPA in arriving at the positions and conclusions stated elsewhere in the
Reregistration Eligibility Document. Primary sources for studies in this bibliography have been
the body of data submitted to EPA and its predecessor agencies in support of past regulatory
decisions. Selections from other sources including the published literature, in those instances
where they have been considered, are included.

2. UNITS OF ENTRY. The unit of entry in this bibliography is called a "study." In the case of
published materials, this corresponds closely to an article. In the case of unpublished materials
submitted to the Agency, the Agency has sought to identify documents at a level parallel to the
published article from within the typically larger volumes in which they were submitted. The
resulting "studies" generally have a distinct title (or at least a single subject), can stand alone for
purposes of review and can be described with a conventional bibliographic citation. The
Agency has also attempted to unite basic documents and commentaries upon them, treating
them as a single study.

3. IDENTIFICATION OF ENTRIES. The entries in this bibliography are sorted numerically by
Master Record Identifier, or "MRID” number. This number is unique to the citation, and should
be used whenever a specific reference is required. It is not related to the six-digit "Accession
Number" which has been used to identify volumes of submitted studies (see paragraph 4(d)(4)
below for further explanation). In a few cases, entries added to the bibliography late in the
review may be preceded by a nine character temporary identifier. These entries are listed after
all MRID entries. This temporary identifying number is also to be used whenever specific
reference is needed.

4. FORM OF ENTRY. In addition to the Master Record Identifier (MRID), each entry consists
of a citation containing standard elements followed, in the case of material submitted to EPA, by
a description of the earliest known submission. Bibliographic conventions used reflect the
standard of the American National Standards Institute (ANSI), expanded to provide for certain
special needs.

a Author. Whenever the author could confidently be identified, the Agency has chosen to
show a personal author. When no individual was identified, the Agency has shown an.

69



2. Spray Drift Management ...
3. Other Label Modifications

Vv. What Registrants Need To Do

A. Manufacturing-Use Products
1. Additional Generic Data Requirements .. . .
2. Labeling for Manufacturing-Use Products
End-Use Products
1. Additional Product-Specific Data Requirements
72. Labeling for End-Use Products
Existing Stocks
Labeling Changes Summary Table

VI. Related Documents and How to Access Them
VII. . Appendices

A: Use Patterns Eligible For Reregistration

B. Table Of Generic Data Requirements And Studies Used To Make
The Interim Reregistration Decision

': Technical Support Documents

Citations Considered To Be Part Of The Database Supporting the
Interim Reregistration Eligibility Decision (Bibliography)
Generic Data Call-In
Product Specific Data Call-In
EPA’s Batching of Tribufos Products for Meeting the Acute Toxicity
Data Requirements for Reregistration
List of Registrants Sent this Data Call-In
List of Related Documents and Electronically Available Forms



BIBLIOGRAPHY

MRID

CITATION

41896301

41896302

41954902

41954903

42007201

42007202

42007203

42007204

Ward, G. (1991) DEF: Acute Toxicity to The Mysid, Mysidopsis bahia, Under
Flow-ThroughTest Conditions: Lab Project Number: J900802-4B: 101245.
Unpublished study prepared by Mobay Corp. 45 p.

Gagliano, G. (1991) Acute Toxicity of DEF Technical to the Sheep-head Minnow
(Cyprinodon variegatus) Under Flow-Through Conditions: Lab Project Number:
DE831201: 101240. Unpublished study Prepared by Mobay Corp. 31 p.

Sheets, L.; Phillips, S. (1991) Acute Dermal Toxicity Study with Technical Grade
Tribufos (DEF) in Rabbits: Lab Project Number: 90-025-FE: 100698. Unpublished
study prepared by Mobay Corp. 20 p.

Sheets, L. (1991) Acute Oral Toxicity Study with Technical Grade Tribufos (DEF) in
Rats: Lab Project Number: 90-012-ES: 100697. Unpublished study prepared by
Mobay Corp. 20 p.

Sheets, L.; Phillips, S. (1991) 21-Day Dermal Toxicity Study with Technical Grade
Tribufos (DEF) in Rabbits: Lab Project Number: 90-125-FP. Unpublished study
prepared by Mobay Corp., Toxicology Dept. 445 p.

heets, L. (1991) Subchronic Delayed Neurotoxicity Study with Technical Grade
Tribufos (DEF) in Hens: Lab Project No: 89-428-CS. Unpublished study prepared by
Mobay Corp., Toxicology Dept. 189 p.

Christenson, W. (1991) Chronic Feeding Toxicity Study of Technical Grade Tribufos
(EF) with Dogs: Lab Project Number: 88-274-AB. Unpublished study prepared by
Mobay Corp., Toxicology Dept. 585 p.

Stevenson, T.; Leimkuehler, W.; Mathew, A. (1991) The Metabolism of Tribufos in
Soil Under Aerobic Conditions: Lab Project Number DE042101: 100338.
Unpublished study prepared by Mobay Corp., R & D Dept. 33 p.

75



BIBLIOGRAPHY

MRID CITATION

44439201 Krolski, M. (1997) DEF 6 EC-Magnitude of the Residue on Cotton: Lab Project
Number: DE19CT03: 107903: 105026. Unpublished study prepared by Bayer Corp.
270 p.

45019901 Willis, M. (2000) A Dermal/Intravenous crossover study to determine the dermal
absorption of 14C-DEF 6(S, S, S-tributylphosphorotrothioate) in male rhesus
monkeys. Sierra biomedical Lab. Study Number: 0834-90. Bayer study Number:
99C-B29-FR. .



8570-27 | Formulator's Exemption Statement http://www.epa. gov/opprd00 1/forms/8570-27.pdf}
8570-28 Certification of Compliance with Data Gap Procedures http://www.epa.gov/opprd00 1/forms/8570-28.pdf|
8570-30 | Pesticide Registration Maintenance Fee Filing http://www.epa.gov/opprd00 1/forms/8570-30.pdf|
8570-32 Certification of Attempt to Enter into an Agreement with //www.epa.gov/ 3/8 570-32.pdfi
other Registrants for Development of Data
8570-34 | Certification with Respect to Citations of Data (in PR ttp://www.epa.gov/ (PR_Notices/pr98b5.
Notice 98-5) pdf,
8570-35 | Data Matrix (in PR Notice 98-5) http://www.epa.gov/opppmsd 1/PR_Notices/pr98-5
-pdf.
8570-36 | Summary of the Physical/Chemical Properties (in PR Notij y w.epa.gov/ Notices/pr98h1
98-1) apdf.
8570-37 Self-Certification Statement for the Physical/Chemical http://www.epa.gov/opppmsd1/PR_Notices/pr981
Properties (in PR Notice 98-1) pdf.
Pesticide Registration Kit www.epa.gov/pesticides/registrationkit/.
Dear Registrant:

For your convenience, we have assembled an online registration kit which contains the following
pertinent forms and information needed to register a pesticide product with the U.S. Environmental
Protection Agency's Office of Pesticide Programs (OPP):

1,

The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the Federal Food,
Dmg and Cosmetic Act (FFDCA) as Amended by the Food Quality Protection Act

(FQPA) of 1996.

Pesticide Registration (PR) Notices

a. 83-3 Label Improvement Program--Storage and Disposal Statements

db. 84-1 Clarification of Label Improvement Program

c. 86-5 Standard Format for Data Submitted under FIFRA

d. 87-1 Label Improvement Program for Pesticides Applied through Irrigation
Systems (Chemigation)

e 87-6 Inert Ingredients in Pesticide Products Policy Statement

£ 90-1 Inert Ingredients in Pesticide Products; Revised Policy Statement

g 95-2 Notifications, Non-notifications, and Minor Formulation Amendments

h 98-1 Self Certification of Product Chemistry Data with Attachments (This

document is in PDF format and requires the Acrobat reader.)

96



. Eye Irritation - (§ 870.2400)

° Magnitude of Residues - Crop Field Trials for ULV Applications (§ 860.1500)

. Residue in Analytical Method - ILV of milk (§ 860.1340)

. Avian Reproduction - mallard duck (§ 850.2300)

. Freshwater Fish Early Life Stage Study - rainbow trout (§ 850.1400)

. Estuarine /Marine Fish Early Life Stage Study - (sheepshead minnow) (§ 850.1400)

° An Estuarine/Marine Invertebrate Life Cycle Study (mysid species preferred)
(§850.1350)

. Nontarget Terrestrial Plant Studies (§850.4250)

: Nontarget Aquatic Plant Studies (§850.4400)

. Field Dissipation (§835.6100)

Also, a DCI was sent to registrants of OP pesticides currently registered under FIFRA [August
6, 1999 (64FR42945-42947), and August 18 (64FR44922-44923)]. DCI requirements included
acute, subchronic, and developmental neurotoxicity studies; due dates are 9/2001.

2. Labeling for Manufacturing-Use Products

To remain in compliance with FIFRA, manufacturing use product (MUP) labeling should be
revised to comply with all current EPA regulations, PR Notices, and applicable policies.

All registrants need to submit applications for amended registration. This application should
include the following items: completed EPA application form 8570-1, five copies of the draft label with
all label amendments outlined in Table 11 of this document incorporated, and a description on the
application, such as "Responding to Interim Reregistration Eligibility Decision” document. All amended
labels need to be submitted within 8 months of signature of this document. The Product Reregistration
Division (PRB) contact is Bonnie Adler at (703) 308-8523.



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Glossary of Terms and Abbreviations

NR
NOAEL
OP
OPP
OPPTS
PCA
PAD
PDP
PHED
PHI
ppb
PPE

ppm

RBC
RED
REL
RD
RQ
RUP

SAP
SF

SLC
SLN

TRR

Not Required

No Observed Adverse Effect Level
Organophosphate

EPA Office of Pesticide Programs
EPA Office of Prevention, Pesticides and Toxic Substances
Percent Crop Area

Population Adjusted Dose

USDA Pesticide Data Program
Pesticide Handler's Exposure Data
Preharvest Interval

Parts Per Billion

Personal Protective Equipment

Parts Per Million

Tier II Surface Water Computer Model
Raw Agriculture Commodity

Red Blood Cell

Reregistration Eligibility Decision
Restricted Entry Interval

Reference Dose

Risk Quotient

Restricted Use Pesticide

Tier I Ground Water Computer Model
Science Advisory Panel

Safety Factor |

Single Layer Clothing

Special Local Need (Registrations Under Section 24(c) of FIFRA)
Technical Grade Active Ingredient
Total Radioactive Residue

United States Department of Agriculture
United States Geological Survey
Uncertainty Factor

Worker Protection Standard



BIBLIOGRAPHY

MRID

CITATION

42350004

42350005

42350009

42350010

42350011

42382701

42399801

42553601

Schocken, M.; Parker, G. (1987) Leaching of Aged Soil Residues of DEF in California
Sandy Loam: Lab Project Number: 95016. Unpublished study prepared by Mobay
Corp. 23 p.

Grace, T.; Cain, K. (1990) Dissipation of Tribufos in California Soils: Lab Project
Number: ML022101: 89. 022: 892010. 1-5K. Unpublished study prepared by Plant
Sciences, Inc.; Siemer and Associates, Inc. and PTRL West. 668 p.

Chopade, H. (1992) Metabolism of [n-Butylthio-1-carbon 14] Tribufos in Cotton: Lab
Project Number: DE41601: 102639. Unpublished study prepared by Miles, Inc. 87
p.

Hall, L. (1992) The Metabolism of [carbon 14] and {sulfur 35] Tribufos in Laying
Hens: Lab Project Number: DE040501: 101329-1. Unpublished study prepared by
Miles, Inc. 158 p.

Sahali, Y.; Jett, C. (1992) Metabolism of [1-carbon 14] Tribufos in Lactating Goats:
Lab Project Number: DE041001: 101330-1. Unpublished study prepared by Miles,
Inc. 114 p.

Fontaine, L. (1992) Supplement to MRID 41618803: Product Chemistry of DEF
Technical: Lab Project Number: BR 1804. Unpublished study prepared by Miles Inc.
6p.

Pauluhn, J. (1992) DEF (Common Name: Tribufos): Study of the Subchronic Inhalation
Toxicity to Rats in Accordance with OECD Guideline No. 413: Lab Project Number:
102697. Unpublished study prepared by Bayer Ag, Wuppertal, Germany. 1050 p.

Christenson, W. (1992) Technical Grade Tribufos (DEF): A Chronic Toxicity/
Oncogenicity/Neurotoxicity Feeding Study in the Fischer 344 Rat: A Supplement: Lab
Project Number: 88-271-AA: 102675-1. Unpublished study prepared by Miles, Inc.
183 p.



which other chemicals could not fill. In summary, the Agency has determined that the continued use of
tribufos is critical to the cotton industry and, therefore, should remain available to growers.

The Agency is issuing this IRED for tribufos, as announced in a Notice of Availability published
in the Federal Register. This IRED document includes guidance and time frames for complying with
any label changes for products containing tribufos. As part of the process discussed by the Tolerance
Reassessment Advisory Committee (TRAC), which sought to open up the process to interested parties,
the Agency’s risk assessments for tribufos have already been subject to public comment periods. The
Phase 6 of the pilot process did not include a public comment period. With regard to complying with
the risk mitigation options outlined in this document, the Agency has shortened this time period so that .
the risks identified herein are mitigated as quickly as possible. Neither the tolerance reassessment nor
the reregistration eligibility decision for tribufos can be considered final, however, until the cumulative
tisk assessment for all organophosphate pesticides is complete. The cumulative assessment may result
in further risk mitigation measures for tribufos.

For the uses of tribufos, the Agency has determined that, with the adoption of all of the label
amendments noted in this document, these uses may continue until the outcome of the cumulative
assessment of all of the organophosphates has been decided.



reregistration. The Agency has previously identified and required the submission of the generic (Le., an
active ingredient specific) data required to support reregistration of products containing tribufos.

The Agency has completed its assessment of the occupational and ecological risks associated
with the use of pesticides containing the active ingredient tribufos , as well as a tribufos -specific dietary
tisk assessment that has not considered the cumulative effects of organophosphates as a class. Based
on a review of these data and public comments on the Agency’s assessments for the active ingredient
tribufos, EPA has sufficient information on the human health and ecological effects of tribufos to make
interim decisions as part of the tolerance reassessment process under FFDCA and reregistration under
FIFRA, as amended by FQPA. The Agency has determined that tribufos is eligible for reregistration
provided that: (i) current data gaps and additional data needs are addressed; (ii) the risk mitigation
measures outlined in this document are adopted, and label amendments are made to reflect these
measures; and (iii) the cumulative risk assessment for the organophosphates support a final
reregistration eligibility decision. Label changes are described in Section IV. Appendix B identifies the
generic data requirements that the Agency reviewed as part of its interim determination of reregistration
eligibility of tribufos, and lists the submitted studies that the Agency found acceptable.

Although the Agency has not yet completed its cumulative risk assessment for the
organophosphates, the Agency is issuing this interim assessment now in order to identify risk reduction
measures that are necessary to support the continued use of tribufos. Based on its current evaluation of
tribufos alone, the Agency has determined that tribufos products, unless labeled and used as specified in
this document, would present risks inconsistent with FIFRA. Accordingly, should a registrant fail to
implement any of the risk mitigation measures identified in this document, the Agency may take
regulatory action to address the risk concems from use of tribufos.

At the time that a cumulative assessment is conducted, the Agency will address any outstanding
tisk concems. For tribufos, if all changes outlined in this document are incorporated into the labels,
then all current risks will be mitigated to an acceptable level. But, because this is an interim RED, the
Agency may take further actions, if warranted, to finalize the reregistration eligibility decision for tribufos
after assessing the cumulative risk of the organophosphate class. Such an incremental approach to the
reregistration process is consistent with the Agency’s goal of improving the transparency of the
reregistration and tolerance reassessment processes. By evaluating each organophosphate in tum and
identifying appropriate risk reduction measures, the Agency is addressing the risks from the.
organophosphates in as timely a manner as possible.

Because the Agency has not yet completed the cumulative risk assessment for the
organophosphates, this reregistration eligibility decision does not fully satisfy the reassessment of the
existing tribufos food residue tolerances as called for by the Food Quality Protection Act (FQPA).
When the Agency has completed the cumulative assessment, tribufos tolerances will be reassessed in
that light. At that time, the Agency will reassess tribufos along with the other organophosphate
pesticides to complete the FQPA requirements and make a final reregistration eligibility determination.

28



BIBLIOGRAPHY

MRID

CITATION

41618803

41618804

41618805

41618806

41618807

41618808

41618811

41618812

Talbott, T. (1990) Product Chemistry of DEF Technical: Lab Project Number: 90606:
94500: 94682. Unpublished study prepared by Mobay Corp. 29 p.

Grau, R. (1990) DEF Technical Grade: 5-day Dietary LC50 to Bobwhite Quail: Lab
Project Number: BV-007: E2950351-5: 100223. Unpublished study prepared by
Bayer Ag. 36 p.

Grau, R. (1990) DEF Technical Grade: 5-day Dietary LC50 to Mallard Duck: Lab
Project Number: VE-002: E2970426-0: 100224. Unpublished study prepared by
Bayer Ag. 43 p.

Grau, R. (1990) DEF Technical Grade: Acute Toxicity to Bluegill Sunfish in a
Flow-through Test: Lab Project Number: FB-003: E2860137: 100222. Unpublished
study prepared by Bayer Ag. 36 p.

Grau, R. (1990) DEF 6: Acute Toxicity to Bluegill Sunfish in a Flow-through Test:
Lab Project Number: FB-006: E02860355-9: 100219. Unpublished study prepared
by Bayer Ag. 40 p.

Grau, R. (1990) DEF Technical Grade: Acute Toxicity to Rainbow Trout in a
Flow-through Test: Lab Project Number: FF-286:2810136-1: 100221. Unpublished
study prepared by Bayer Ag 36 p.

Cohle, P. (1990) Uptake, Depuration and Bioconcentration of (Carbon 14)-DEF by
Bluegill (Lepomis macrochirus): Lab Project Number: 38466: 100236. Unpublished
study prepared by Analytical Bio-Chemistry Laboratories, Inc. 48 p.

Sheets, L. (1990) Dermal Sensitization Study with Technical Grade Tribufos (DEF) in
Guinea Pigs: Lab Project Number: 90-324-GK: 100268. Unpublished study prepared
by Mobay Corp. 24 p.



there is no exposure potential, data indicate that tribufos should not be a concern in ground water,
because environmental fate testing indicates that tribufos binds to the soil and appears to be immobile.
Based on the physical/chemical characteristics of tribufos, the Agency determined that residues of
tribufos are not expected to reach ground water and were, therefore, not estimated. The Agency has
no concern for acute or chronic effects from tribufos in ground water-sourced drinking water.

c. Drinking Water Levels of Comparison (DWLOC)
To determine the maximum allowable contribution of tribufos from water in the diet, the
Agency first looks at how much of the overall allowable risk is contributed by food and then determines
a DWLOC to ascertain whether expected concentrations exceed this level.

Table 4. DWLOC and EEC Comparisons

DWLOCS (ppb) EECs (ppb)
Population Subgroup Surface Water (PRZM2/EXAMS I)
Acute |Chronic | Ground Water
Acute Chronic
Males 33 3
7 Residues Not -
Children (1-6 years) 10 1 Expected 58 18

Females (13+ nursing) 29 3

* Due to the environmental fate characteristics, residues of tribufos are not expected, therefore, a ground water
assessment is not necessary

The chronic modeled surface drinking water concentrations (1.8 ppb) of tribufos slightly
exceeded the DWLOCs for the most highly exposed sub-population, children 1-6 years old (1 ppb),
and are below the DWLOCs for all others. The Agency considers the estimates to be conservative for
the following reasons:

1) The estimates are based on a scenario (i.e., high rainfall, spray drift, and soils
with maximum runoff potential) that is upper bound for site
characteristics.

2) Drinking water treatment effects are not included. It is possible that with a
compound like tribufos, the primary treatment effects such as flocculation,
sedimentation, and filtering could remove tribufos.

3) The maximum application rate was used (1.875 Ibs ai/A). The Agency
acknowledges that this rate is very seldom used. The tank-mix rates of 0.50
Ibs ai/A to 0.75 Ibs ai/A are more commonly used.

4) The modeled chronic surface water estimated concentration only exceeds the
DWLOC by 0.8 ppb. Because the sensitivity of this model (PRZM2/EXAMS

et



Executive Summary

Tribufos is an organophosphate defoliant used for cotton crops. It is specifically used to
defoliate cotton in preparation for machine harvesting. It was first registered in the United States in
1961. There are about 4,500,000 pounds of active ingredient (ai) applied annually to between 4 and 5
million acres (A) or about 35% of planted cotton acreage in the United States. The typical rate of
application varies from 0.50-Ib ai/A to1.875 lb ai/A. Tribufos is most often applied in a tank-mix.
When it is tank-mixed, the application rate is typically significantly lower than the maximum label rate.
Even though the maximum registered rate for tribufos is 1.875 lbs ai/A, the Agency acknowledges that
there is a relatively small population of aerial mixers, loaders, and applicators who need to apply this
rate in California and Arizona. The total percentage of cotton acres treated with tribufos in California
and Arizona is 13% and 17%, respectively.

EPA has completed its review of public comments on the revised risk assessments and is
issuing its risk management decisions for tribufos. The decisions outlined in this document do not
include the final tolerance reassessment decision for tribufos; however, a single tolerance on cottonseed
hulls will be revoked now, because it is not warranted based on the results of an acceptable cottonseed
processing study. The final tolerance reassessment decision for this chemical will be issued once the
cumulative assessment for all of the organophosphates is complete. The Agency may need to pursue
further risk management measures for tribufos once the cumulative assessment is finalized.

The revised risk assessments are based on review of the required target data base supporting
the use patterns of currently registered products and new information received. The Agency invited
stakeholders to provide proposals, ideas or suggestions on appropriate mitigation measures before the
Agency issued its risk mitigation decision on tribufos. After considering the revised risks, mitigation
proposed by Bayer, the technical registrant of tribufos, comments, and suggestions from other
interested parties, the Agency developed its risk management decision for uses of tribufos that pose
risks of concern. This decision is discussed fully in this document.

Dietary Risk

The Agency’s human health risk assessment for tribufos indicates that there are no concerns
for dietary risks from residues of tribufos in food. Acute dietary risk (food only) for the most highly
exposed sub-population, children (1-6 years old), is 9% of the Population Adjusted Dose (PAD) at the
99.9th percentile. Chronic dietary risk for the most highly exposed population, (children 1-6 years), is
3% of the Population Adjusted Dose (PAD) at the 99.9th percentile. Risk less than 100% of the PAD
is not of concern to the Agency.

The Agency also evaluates dietary risks from residues in drinking water. For tribufos, the
acute and chronic modeled surface drinking water concentrations of tribufos are below the Drinking
Water Levels of Comparison (DWLOCs) for all sub-populations, and the chronic concentrations are



hormonal defoliants, and therefore, are able to achieve faster defoliation. Generally,
hormonal defoliants work at night temperatures of 65°F or above and herbicidal defoliants
are effective to temperatures as low as 50°F.

3) The importance of tank mixing. Most cotton producers today use tank-mix
combinations of defoliants to get best results. Many times, other materials are also used at
defoliation time, including boll openers and regrowth inhibitors, which increase the yield and
quality of cotton. Ethephon is a boll opening accelerant which causes bolls to open more
rapidly when used in combination with defoliants. Ethephon, however, is not a very
effective defoliant on it own. It is often used in combination with tribufos and thidiazuron.
One of the most widely used combinations of materials used in defoliation is ethephon +
tribufos + thidiazuron. This combination promotes more rapid boll opening, provides the
most consistent defoliation, and provides for regrowth suppression. Suppressing regrowth
is important in limiting the amount of green stain that will be introduced into the cotton
during harvest. In addition to promoting boll opening, ethephon synergizes or enhances
defoliation of both tribufos and thidiazuron. Tribufos provides consistency in defoliation,
especially at lower night temperatures, and thidiazuron contributes to defoliation under
warmer condition, as well as providing regrowth suppression. This combination has proven
very effective and necessary for maintaining both the yield and quality of cotton, thus
providing growers with a suite of tank mixes to chose from based on environmental
conditions present at time of harvest.

~ 4) Timing of harvest. The choice of a defoliant is influenced by several factors, one of
which is how quickly a grower anticipates picking can be accomplished. Larger acreage
growers usually have their own harvesting equipment and, barring weather interference, can
usually plan fairly accurately when they will pick their cotton. They typically would apply
ethephon + tribufos or tribufos alone, depending on the need for a boll opener, and pick
their cotton about 12 to 14 days later. Growers would not be very concerned about
regrowth suppression, because regrowth normally does not become a problem until 21 or
so days after defoliation. Smaller acreage growers, or those who depend on contracted
harvesting, would more typically use tribufos + thidiazuron with or without ethephon. The
growers cannot predict as accurately when the crop will be harvested and are more
concemed with regrowth problems.

5) The rate necessary to maintain efficacy. As mentioned above, the efficacy of
defoliants and desiccants is dependent upon a number of factors. Tribufos is the only
defoliant currently available which can achieve maximum defoliation in a variety of
conditions. Tribufos is most often tank mixed to achieve the most efficacious results. Most
growers who use combination defoliants use 0.75 pints of DEF 6 (0.56 lb ai tribufos) and
0.1 Ib of Dropp (thidiazuron) per acre. A common term cotton growers use in referring to

39



depend on someone else to do so. If the registrant supplies the data to support a batch of ‘products,
he/she must select the one of the following options: Developing data (Option 1), Submitting an existing
Study (Option 4), Upgrading an existing Study (Option 5), or Citing an Existing Study (Option ). Ifa
registrant depends on another’s data, he/she must choose among: Cost sharing (Option 2), Offers to
Cost Share (Option 3) or Citing an Existing Study (Option 6). Ifa registrant does not want to
participate in a batch, the choices are Options 1, 4, 5 or 6. However, a registrant should know that
choosing not to participate in a batch does not preclude other registrants in the batch from citing his/her
studies and offering to cost share (Option 3) those studies.

Five products were found which contain tribufos as the active ingredient. These products have
been placed into two batches in accordance with the active and inert ingredients and type of
formulation.

Batch 1 EPA Reg. No.
3125-96 98.0 Liquid
51036-324 98.0 4+ Liquid

Batch 2
264-498 15S Liquid
3125-282 70.5 Liquid
51036-320 70.5 Liquid
67801-3 70.5 Liquid



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The IRED is based on the updated technical information found in the tribufos public
docket. The docket not only includes background information and comments on the Agency’s
preliminary risk assessments, it also now includes the Agency’s revised risk assessments for
tribufos (revised as of June 26, 2000), and a document summarizing the Agency’s Response to
Comments. The Response to Comments document addresses corrections to the preliminary risk
assessments submitted by chemical registrants, as well as responds to comments submitted by
the general public and stakeholders during the comment period on the risk assessment. The
docket will also include comments on the revised risk assessment, and any risk mitigation
proposals submitted during Phase 5. For tribufos, a proposal was submitted by Bayer, the
technical registrant. Comments on mitigation or mitigation suggestions were submitted by the
National Cotton Council and the USDA.

This document and the process used to develop it are the result of a pilot process to
facilitate greater public involvement and participation in the reregistration and/or tolerance
reassessment decisions for these pesticides. As part of the Agency’s effort to involve the public
in the implementation of the Food Quality Protection Act of 1996 (FQPA), the Agency is
undertaking a special effort to maintain open public dockets on the organophosphate pesticides
and to engage the public in the reregistration and tolerance reassessment processes for these
chemicals. This open process follows the guidance developed by the Tolerance Reassessment
Advisory Committee (TRAC), a large multi-stakeholder advisory body that advised the Agency
on implementing the new provisions of the FQPA. The reregistration and tolerance reassessment
reviews for the organophosphate pesticides are following this new process.

Please note that the tribufos risk assessment and the attached IRED concern only this
particular organophosphate. This IRED presents the Agency’s conclusions on the dietary risks
posed by exposure to tribufos alone. The Agency has also concluded its assessment of the
ecological and worker risks associated with the use of tribufos. Because the FQPA directs the
Agency to consider available information on the basis of cumulative risk from substances sharing
a common mechanism of toxicity, such as the toxicity expressed by the organophosphates
through a common biochemical interaction with cholinesterase enzyme, the Agency will evaluate
the cumulative risk posed by the entire organophosphate class of chemicals after completing the
risk assessments for the individual organophosphates. The Agency is working towards
completion of a methodology to assess cumulative risk and the individual risk assessments for
each organophosphate are likely to be necessary elements of any cumulative assessment. The
Agency has decided to move forward with individual assessments and to identify mitigation
measures necessary to address those human health and environmental risks associated with the
current uses of tribufos. The Agency will issue the final tolerance reassessment decision for
tribufos and finalize decisions on reregistration eligibility once the cumulative assessment for all
of the organophophates is complete.

This document contains a generic and/or a product-specific Data Call-In(s) (DCI) that
outline(s) further data requirements for this chemical. Note that registrants of tribufos must
respond to DCIs issued by the Agency within 90 days of receipt of this letter.



BIBLIOGRAPHY

MRID

CITATION

00001999

00019258

00049258

00147533

00160000

40094602

40098001

40190601

Atkins, L., Jr; Anderson, L.D. (1967) Toxicity of Pesticides and Other Agricultural
Chemicals to Honey Bees: Laboratory Studies. (Unpublished study received Jan 30,
1969 under 9G0802; prepared by the Univ. of California-Riverside, Dept. of
Entomology, submitted by Hercules, Inc., Agricultural Chemicals, Wilmington, Del.;
CDL:093111-D)

Buchanan, G.A. (1969) Preemergence Weed Control in Soybeans: Research Report
CF-4621. (Unpublished study received Nov 13, 1969 under 8192-5; prepared by
Auburn Univ., submitted by Ciba Agro-chemical Co., Summit, N.J.; CDL:018027-B)

Lamb, D.W.,; Jones, R.E. (1972) Acute Oral Toxicity of (R}= DEF Technical to
Bobwhite Quail and Mallard Ducks: Report No. 35016. (Unpublished study received
Mar 22, 1976 under 3125-71; submitted by Mobay Chemical Corp., Kansas City,
Mo.; CDL:224114-P)

Rodwell, D. (1985) A Teratology Study with AC 92, 100 in Rats: Project No.
‘WIL-35014: Final Report. Unpublished study prepared by WIL Research
Laboratories, Inc. 212 p.

Hudson, R.; Tucker, R.; Haegele, M. (1984) Handbook of toxicity of pesticides to
Wildlife: Second edition. US Fish and Wildlife Service: Resource Publication 153. 91

p.

Johnson, W.; Finley, M. (1980) Handbook of Acute Toxicity of Chemicals to Fish and
Aquatic Invertebrates: Resource Publication 137. US Fish and Wildlife Service,
Washington, D.C.106 p.

Mayer, F.; Ellersieck, M. (1986) Manual of Acute Toxicity: Interpretation and Data
Base for 410 Chemicals and 66 Species of Freshwater Animals. US Fish & Wildlife
Service, Resource Publication 160. 579 p.

Kowalski, R. (1986) A Teratology Study with DEF Technical in the Rat: Report No.
87320. Unpublished study prepared by Miles Laboratories, Inc. 213 p.

7



on cotton with a more robust database. By combining the chemical-specific data with PHED, the
Agency was able to increase the sample size and number of studies. This allows the Agency to better
characterize the variety of equipment used throughout the country and accounts for the large variability
of exposures among handlers.

Occupational handler exposure assessments are conducted by the Agency using different levels
of personal protection. The Agency typically evaluates all exposures with minimal protection and then
adds additional protective measures using a tiered approach to obtain an appropriate MOE (i.e., going
from minimal to maximum levels of protection). The lowest level of PPE is baseline. MOEs are less
than the target MOE (target dermal MOE is 300 and target inhalation MOE is 100), increasing levels of
tisk mitigation (personal protective equipment (PPE) are applied. If MOEs are still less than the target
MOE, engineering controls (EC) are applied. In some cases, EPA will conduct an assessment using
PPE or ECs taken from a current label. The levels of protection that formed the basis for calculations
of exposure from tribufos activities include:

° Baseline: Long-sleeved shirt and long pants, shoes and socks.

° Minimum PPE: Baseline + chemical resistant gloves and a respirator.

. Maximum PPE: Coveralls over long-sleeved shirt and long pants, chemical
resistant gloves, chemical footwear plus socks, chemical
resistant headgear for overhead exposures, and a respirator if
tisk is driven by inhalation.

Engineering controls: Engineering controls such as a closed cab tractor for
application scenarios, or a closed mixing/loading system, such.
as a closed mechanical transfer system for liquids or a
packaged based system (e.g., Lock N Load for granulars or
water soluble packaging for wettable powders). Some
engineering controls are not applicable for certain scenarios
(e.g., for handheld application methods there are no known
devices that can be used to routinely lower the exposures).

In reviewing the use patterns of tribufos, the Agency identified four major application exposure
scenarios: (1) mixing/loading liquid formulations for aerial and groundboom equipment; (2) aerial
application (3) groundboom application; and (4) flagging during aerial spray applications. The Agency
assessed the aerial and ground scenarios using surrogate data from PHED version 1.1 as well as
incorporating a tribufos-specific handler study as discussed above. The Agency also assumed that an
applicator applies tribufos to 1,200 acres per day aerially, and 80 acres per day by groundboom at the
maximum label rate of 1.875 lb ai (pounds of active ingredient) per acre and at 1.125 Ibs ai per acre.
Mixing/loading, and application are assumed to be performed by different individuals. The Agency
normally uses 350 acres as a typical value for the number of acres treated aerially in a single day.
However, the Agency has determined that 1,200 acres is more representative for the following reasons:



BIBLIOGRAPHY

MRID

CITATION

42685901

42701601

42799001

42848001

42848002

42848003

43080401

43325501

Eberhart, D. (1993) Evaluation of Worker Exposures to Tribufos During Aerial and
Ground Applications of DEF 6 to Cotton: Lab Project Number: DE202301: 103889.
Unpublished study prepared by MILES, Inc. 334 p.

Eberhart, D.; Ellisor, G. (1993) Evaluation of Worker Exposure to Tribufos During
Harvesting of Cotton Treated with DEF 6: Lab Project Number: DE202302: 105103.
Unpublished study 6 prepared by Miles Inc. 307 p.

Bajzik, M. (1992) The Independent Laboratory Method Validation for the Analysis of
Tribufos in Cottonseed and Soapstock: Lab Project Number: DE111601: 105003.
Unpublished study prepared by Huntingdon Analytical Services. 90 p.

Gronberg, R.; Sanders, D. (1993) An Improved Analytical Residue Method for the
Dermination of Tribufos in Cottonseed and Cottonseed Processed Products: Lab
Project Number: A012.004: DE111603: 105026. Unpublished study prepared by
Huntingdon Analytical Services and Miles Inc. 126 p.

Gronberg, R.; Sanders, D. (1993) A Registered Product Interference Study for the
Analytical Residue Method for Tribufos in Cottonseed and Cottonseed Processed
Products: Lab Project Number: DE141601: 105178. Unpublished study prepared by
Miles Inc. 131 p.

Gronberg, R.; Sanders, D. (1993) Extraction Efficiency of the Analytical Residue
Method for Tribufos in Cottonseed: Lab Project Number: DE111602: 105179.
Unpublished study prepared by Miles Inc. 21 p.

Leimkuehler, W.; Moor, K. (1993) Identification and Characterization of Radioactive
Residues of (carbon 14) Tribufos in Bluegill Sunfish (Lepomis Macrochirus): Lab
Project Number: DE040301. Unpublished study prepared by Miles Inc. 84 p.

Valadez, S.; Dehart, B.; Cain, K. (1993) Field Dissipation of Tribufos on Georgia Soil:
Lab Project Number: DE022101: 105163: 52373. Unpublished study prepared by
Miles Research Farm; Miles Research Park; and Harris Environmental Technologies,
Inc. 81 p.

B



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