UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: May 7, 2015 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: Oxadiazon. HED's Response to Public Comments Received on the Preliminary 

Work Plan for Registration Review. 

PC Code: I 0900 I 

Decision No.: 500417 

Petition No.: NA 

Risk Assessment Type: NA 

TXR No.: NA 

MRJD Nos.: NA 

DP Ba rcode: 0425885 

Registration Nos.: NA 

Regula tory Action: Registration Review 

Case No.: 2485 

CAS Nos.: 19666-30-9 

40CFR: NA 

FROM: Linnea Hansen, Ph.D., Biologist ~ ~)\J-_ 

.Cm! 

) - . 

Margarita 

Risk Assessment 

Collantes, 

Branch 

M.S., 

II 

Biologist ~J 

Health Effects Division (7509P) 

THROUGH: Christina Swartz, Branch Chief 

Risk Assessment Branch II 

Health Effects Division (7509P) 

TO: Katherine St. Clair, Chemical Review Manager 

Risk Management and Implementation Branch II 

Pesticide Reevaluation Division (7508P) 

CONCLUSIONS: 

HED has responded to comments received from the registrant, Bayer Environmental Science (a 

division of Bayer CropScience, hereafter referenced as "Bayer"), on the Preliminary Work Plan 

(PWP) for registration review of the herbicide oxadiazon. 

Bayer has addressed issues raised by HED during registration review scoping regarding data 

requirements to support registration review and particulars of the intended use patterns and 

parameters. The issues, Bayer comments and HED responses are briefly summarized in the 

table below. A more detailed response to each comment is provided below under the Discussion 

section of this memorandum. 

Page I of6 
OPP Preliminarv Work Plan Baver Comment HEDComment 

1 Rat 28-day inhalation toxicity For exposure patterns with HED will review the revised 

study is required (OPPTS inhalation MOEs <1000, AHETF is inhalation assessment when it is 

870.3465) unless risk from use developing data that Bayer will use submitted. A determination will be 

patterns with MO Es below I 000 to prepare a revised inhalation made at that time as to the need for 

can be mitigated exposure assessment, where data a 28-day inhalation study, if Bayer 

availability meets registration has not already initiated one. 

review timelines. The revised 

assessment may be used to 

determine if a waiver is supported. 

If not, the 28-day inhalation study 

will be conducted or exposures of 

concern will be addressed 

administratively. 

2 Oislodgeable foliar residue (DFR) A DFR study should not be required A DFR study is required. There is 

and turf transferable residue (TFR) because post-a pp I ication contact potential for post-application foliar 

studies are required (OPPTS with ornamentals plants, vines or contact by nursery workers with 

875.2100) trees is unlikely. treated plants, vines or trees. 

A TTR study should not be required HED concurs that the TTR study is 

because the HED policy of not needed to assess golfers and 

12/ 12/2012 states that the study is golf course maintenance workers 

automatically waived when MOEs using a granular formulation. 

based on default TTRs are ~ I 000. 

Based on current (2012) 

Residential SOPs for turf and lawn, 

the previously submitted TTR 

studies are acceptable and new 

TTR data are not needed. 

However, HED will conduct risk 

assessments for products labelled 

for parks and non-residential 

lawns. HED notes that based on a 

preliminary assessment using these 

studies, there is potential for risks 

of concern for adults and children 

from use of oxadiazon on parks 

and non-residential lawns. 

3 Clarification is requested of the Oxadiazon is not intended to be a Based on this information, HED 

intent to allow or restrict the use of restricted use pesticide and both will conduct handler exposure 

oxadiazon on turf and lawn for professional and residential handler assessments for residential as well 

residential uses. exposure assessments are required. as occupational exposure scenarios 

For homeowner handler exposure, using appropriate application 

granular and liquid spray methods and label directions. 

formulations should be assessed. 

4 Clarification of application Details about application parameters Bayer has submitted adequate 

parameters for some product labels (e.g., application rates, intervals, information regarding application 

is requested for the quantitative frequency, sites, methods and parameters. It will be considered 

risk assessment - otherwise equipment, applications per season, in assessment of handler exposure. 

conservative assumptions will be formulations, and geographic Labels should be revised as 

used. limitations on use) are submitted appropriate to clarify any 

with the comments on the application parameter. 

preliminary work plan. 

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INTRODUCTION: 

EPA requested public comments on the PWP for the Registration Review of Oxadiazon (Docket 

Number EPA-HQ-OPP-2014-0782). Bayer, the registrant, reviewed the document entitled 

"Oxadiazon Preliminary Work Plan: Registration Review: Initial Docket, December 2014" and 

provided comments, as well as relevant information that was requested by the Agency. HED 

was requested to respond to the comments that are pertinent to the human health risk assessment. 

DISCUSSION: 

The following comments from Bayer on the Oxadiazon PWP for Registration Review were 

received and are addressed by HED: 

(1) Anticipated Data Needs, GDLN 870.3465, Rat 28-Day Inhalation Toxicity 

Study 

Preliminary Work Plan: A 28-day inhalation toxicity study in the rat was required by the 

Agency, based on concerns for the potential for portal-of-entry toxicity to the respiratory tract 

and inhalation margins of exposure (MOEs) for certain use patterns that were below the level of 

concern (LOC) of 1000. If additional mitigation measures are added by the registrant for the 

scenarios with MO Es of concern, the Agency may waive the inhalation study requirement. This 

data requirement was reviewed by the HED Hazard and Science Policy Committee (HASPOC, 

HED TXR No. 0057091). 

Bayer Comment: Bayer's response is as follows: 

"Bayer has calculated inhalation exposure and MOEs based on the unit exposures 

provided in the March 2013 handlers surrogate guide. Inhalation MOEs less than 1000 

have been confirmed for certain use patterns such as mixing/loading with the WP 

formulation and some of the hand held spray applications. The scenarios in which the 

MO Es are less than the 1000 required for a waiver of the 28-day inhalation study are 

scenarios which the Agricultural Handlers Exposure Task Force (AHETF) has recently 

completed data development or has initiated the data development phase. Bayer intends 

to incorporate the revised inhalation unit exposures into a revised assessment for 

scenarios where the data are available consistent with the registration re-evaluation 

timeline and determine if a waiver is supported. If use scenarios remain that have MO Es 

less than 1000, Bayer will either commit to conduct the 28-day inhalation toxicity study 

or administratively address the use patterns with MO Es less than 1000." 

EPA Response: The Agency will await submission of the revised inhalation exposure 

assessment from Bayer that will be based on data now being developed for use patterns 

with inhalation risk that currently exceed the level of concern (LOC) of 1000. The need 

for a 28-day inhalation toxicity study will be determined at that time. 

(2) Anticipated Data Needs, GDLN 870.2100, Dislodgeable Foliar Residue and 

Transferable Residues 

Page3of6 
Preliminary Work Plan: Dislodgeable foliar residue (DFR) and turf transferable residue (TTR) 

studies are required for oxadiazon, In general, TTR data are required for al I occupational (e.g .. 

sod fanns, golf courses, parks, and recreational areas) or residential turf uses that could result in 

post-application exposure to turf. In the absence of chemical-specific TTR data, EPA uses 

default values. Two TTR studies were submitted in support of the oxadiazon RED; however, 

they were found to be unacceptable due to transfer efficiencies less than 1 %. 

Bayer Comment: Bayer's response is as follows: 

"Based on the use patterns of oxadiazon, there is not an anticipation of post application 

foliar contact with ornamental plants, vines, or trees. Therefore, Bayer does not believe 

that a dislodgeable foliar residue study is required. Post application turf exposure can 

occur to golfers and to golf course maintenance workers. Exposure can occur to either the 

granular formulation or the liquid sprays. The Health Effects Division issued a policy 

notice on 12 December 2012 that provides for an automatic waiver of the turf 

transferrable residue (TTR) study if the margins of exposure (MO Es) based on the default 

TTRs are 1000 or greater. 

For the granular formulations, Bayer has estimated the post application exposure to both 

golfers and golf course maintenance personnel assuming that the highest TTRs are 0.2% 

of the 4 lb a.i./acre application rate or 0.089 μg/cm2. Default transfer coefficients and 

durations of exposure as provided in the 2012 Residential SOPs were used to calculate 

the daily exposure to golfers. The golf course maintenance worker transfer coefficient of 

3700 cm2/hr and an 8-hour work day were used to estimate the golf course occupational 

post application exposure. Based on a dermal NOAEL of 12 mg/kg/day and a dermal 

absorption of 9%, the MO Es for golfers aged 6 years or older were 4900 and the MOE 

for maintenance workers was 3500. Therefore, a granular TTR study is not required. 

Bayer previously conducted a TTR study for the liquid spray application of oxadiazon 

using the 50 WP formulation in North Carolina. The TTRs expressed as a percentage of 

the application rate were 3. 7% for non-irrigated turf and 2.0% for irrigated turf based on 

the highest TTRs sampled. The results from a study (MRID 44995502) conducted in GA 

with the wettable soluble powder (WSP) formulation are provided in Table D-17 of the 

Residential SOPs and were 2.6% of the application rate. Based on the existing liquid 

spray application TTR data, additional TTR data should not be required as a part of the 

re-evaluation process." 

EPA Response: 

DFR study requirement for ornamentals: 

There are several Bayer product labels (Reg Nos. 432-893, 432-887, and 432-886) which specify 

use of oxadiazon in commercial ornamental and conifer nurseries. There is potential for post 

application foliar contact with ornamental plants, vines, or trees by nursery workers as a result of 

direct spray to soils and over-the-top applications to ornamentals and conifers. Therefore, the 

Agency continues to conclude that a dislodgeable foliar residue study is required for oxadiazon. 

Page 4 of6 
TTR study requirements for turf/lawns/parks: 

The EPA concurs that a TTR study is not needed for assessing golfers and golf course 

maintenance workers using a "granular" formulation. Furthermore, based on the refinements 

made to the revised transfer coefficients in the 2012 Residential SOPs for turf and lawn, the 

Agency also concurs that the previously submitted TTR studies (MRID# 449955-0land 449955-

02) are acceptable. Since the oxadiazon RED, the supporting science and guidance for 

developing transfer coefficients (Tc) and their respective TTR transfer efficiencies has 

significantly evolved. The previously submitted studies incorporated the use of the modified 

California roller method which resulted in TTR transfer efficiencies of - 1-5% (transfer 

efficiency = % of the application rate) which correspond to the current transfer coefficients used 

in the 2012 Residential Turf SOPs. 

In addition, there are currently several Bayer product labels (Reg. Nos 432- 983, 432-887 and 

432-886) formulated as liquids and granules which are registered for use on "parks" and "nonresidential lawns". The Agency continues to support the decision to perform a dermal postapplication exposure assessment for these uses. Based on a preliminary assessment using the 

above mentioned studies, there is potential for risks of concern for adults and children resulting 

from use of oxadiazon on parks and non-residential lawns. 

(3) Clarification requested by EPA regarding intention for product use on 

residential or home lawns/turf 

Preliminarv Work Plan: EPA requested that the registrant clarify whether oxadiazon turf and 

lawn uses would be restricted use or allowed for residential use by residential handlers. 

Bayer Comment: Bayer's response is as follows: 

"Handler exposure assessments will be necessary for professional application by vehicle 

drawn groundboom sprayers, broadcast spreaders, and by professional hand-held spray 

gun application. In addition, homeowner application of the granular formu lation or the 

liquid spray formulations will be assessed as the oxadiazon formulations are general use 

pesticides and are not restricted use pesticides. Bayer anticipates that the handler 

exposure data developed by the Agricultural Handlers Exposure Task Force, the Outdoor 

Residential Exposure Task Force, or the data in the Pesticide Handlers Exposure 

Database will address all handler exposure scenarios and will be based on the version of 

the surrogate handler unit exposure guide available at the time that the assessment is 

conducted. Bayer is a member of both task forces." 

EPA Response: Based on the registrant's intent to include homeowner application of granular 

and liquid spray formulations, a residential handler exposure assessment will be performed for 

oxadiazon. 

( 4) Clarification requested by EPA regarding application parameters as provided 

on current product labels 

Page 5 of6 
Preliminary Work Plan: The EPA stated that certain labels for oxadiazon products were unclear 

on some parameters of application, including: sites of application, formulations, application 

methods and equipment, maximum application rates, frequency of application, application 

intervals and maximum number of applications per season, and geographic limitations on use. 

Bayer Comment: Bayer provided the following information: 

Region 

"Typically oxadiazon is applied in the late winter/early spring for pre-emergent control of 

weeds. Applications are either made as a single spray application at 3 - 4 lb ai/A or as a 

granular with 2 applications at the 2 lb ai/A rate. Granular applications to landscape or 

nursery plants are made in the Spring or Fall. Most applications are in the Southeast 

United States. 73% of all applications were made in seven states: FL, NC, GA, SC, TX, 

TN, and AL. Timing of the first application depends on weed seed germination in 

different geographies of the US (shown below). Intervals between applications are made 

30 - 60 days for the split application in the spring (2 lb ai/A). 

First Aoolication Timinq 

South Florida January 

Southeast US February 

VA. OK March 

Northern US March - snow melt 

Further information on the applications for Bayer Labels is provided in the attached pdf 

(Oxadiazon EFED Table 1 Use Patterns Bayer Pre-lim Comment)." [note: see Docket for 

this information]. 

EPA Response: Bayer has provided information on application parameters as requested in the 

PWP. The Agency will use these parameters in conducting handler exposure assessments. In 

addition, label directions for these products should be updated as appropriate. 

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