UNITED STATES ENVIRONMENTAL PROTECTION 

AGENCY 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM 

PC Code: 109001 

DP Barcode: D420615 

Date: December 5, 2014 

SUBJECT: EFED Registration Review Problem Formulation for Oxadiazon 

FROM: 

TO: 

1: . . 1~/o~jJy Hannah Yingling, Biologist ~ 1S. o.---

!r'Mohammed Ruhman, Ph.D., enior Agroil,~ "'' 11]..,. 

'\ Environmental Risk Branch 5 t'f.;foC 

Environmental Fate and Effects Division (7507P) 

Katherine St. Clair, Risk Manager Reviewer 

Tom Myers, Team Leader 

Risk Management and Implementation Branch 2 

Pesticide Re-Evaluation Division (7508P) 

REVIEWED Justin Housenger, Biologist 

BY: Jose Melendez, Chemist 

Environmental Risk Branch 5 

Environmental Fate and Effects Division (7507P) 

111 /) d /,.1. v t)V-1- THROUG~ah Shamim, Branch Chief ~ "Jo</•r.{ 

Environmental Risk Branch 5 1 

Environmental Fate and Effects Division (7507P) 

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation (attached) for the ecological risk, environmental fate, endangered species, and 

drinking water assessments to be conducted as part of the registration review of oxadiazon. 
2

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION

AGENCY

EFED Registration Review Problem Formulation for Oxadiazon

Oxadiazon: 3-[2, 4-Dichloro-5-(1-methylethoxy) phenyl]-5-(1, 1-dimethyl-ethyl)-1, 3, 4-

oxadiazol-2(3H)-one

CAS No.: 19666-30-9 and PC code: 109001

Hannah Yingling, Biologist

Mohammed Ruhman, Ph.D., Senior Agronomist

Environmental Risk Branch 5

Environmental Fate and Effects Division (7507P)December 4, 2014

Table of Contents

1. Executive summary................................................................................................................. 4

2. Introduction............................................................................................................................. 5

3. Use Characterization............................................................................................................... 5

4. Conclusions from Previous Risk Assessments....................................................................... 6

a. Ecological Risk Assessment ..................................................................................................6

b. Drinking Water Exposure Assessments.................................................................................8

O

N N

O CH3

CH3

Cl

O

Cl

H3C

H3C

CH3
3

c. Clean Water Act Programs ....................................................................................................8

5. Environmental Fate and Transport.......................................................................................... 9

6. Receptors............................................................................................................................... 12

a. Effects to Aquatic Organisms..............................................................................................12

b. Effects to Terrestrial Organisms..........................................................................................13

c. Ecological Incidents.............................................................................................................14

7. Exposure Pathways of Concern ............................................................................................ 15

8. Analysis Plan ........................................................................................................................ 16

a. Stressors of Concern ............................................................................................................16

b. Measures of Exposure..........................................................................................................16

c. Measures of Effect ...............................................................................................................17

9. Endangered Species Assessments......................................................................................... 17

10. Endocrine Disruptor Screening Program............................................................................... 17

11. Preliminary Identification of Data Gaps................................................................................ 18

a. Environmental Fate..............................................................................................................18

b. Effects..................................................................................................................................18

12. References ............................................................................................................................. 23

Appendix A. SIP Output............................................................................................................32

Appendix B. STIR Output .........................................................................................................33
4

1. Executive summary

This problem formulation describes the methods planned to be used during the completion of 

drinking water and ecological risk assessments in support of registration review and provides an 

overview of the environmental fate, ecological effects, and potential risks associated with the use 

of oxadiazon as well as uncertainties unique to the risk assessment of this chemical. This 

document also identifies additional studies that would be beneficial to the conduct before 

executing the future re-registration ecological risk assessment. 

The fate database for oxadiazon is partially complete with the exception of the following studies,

which are requested:

(1) One aerobic soil study (OCSPP 835.4100) for one soil obtained from areas where the 

pesticide is used; 

(2) One terrestrial field dissipation study (OCSPP 835.6100) on turf; and

(3) ECMs and associated ILVs (OCSPP 850.6100) for soil/sediment and water as explained in the 

Preliminary Identification of Data Gaps section, below.

Additionally, the registrant is requested to:

(1) Address the un-extracted residues issue in previously submitted aerobic aquatic metabolism 

study. For this, the registrant is referred to the data evaluation sheet for this newly submitted 

study as well as to EFED un-extracted residue guidance; and

(2) Provide Names, toxicity, structures and CAS no.’s for degradates listed in Section 5, below.

In case data and clarifications are not responded to, EFED will use conservative assumptions such 

as multiplying half-life with a factor of 3 and include the un-extracted residues in calculating halflives. 

The ecological database for oxadiazon is largely complete with a few outstanding data gaps 

from those listed in the 2001 RED that are shown below. Justifications for these data needs 

as well as assumptions that will be made in the absence of these data are provided in Table 

10 and 11.

(1) 850.1400—Early life stage - Freshwater Fish (Submission of the raw data for the rainbow 

trout study MRID 41811601)

(2) 850.4225—Acute toxicity to Terrestrial Vascular Plants: Seedling Emergence

(3) 850.4150— Acute toxicity to Terrestrial Vascular Plants: Vegetative Vigor

(4) 850.4550—Cyanobacteria Toxicity 

There are additionally a number of studies that are being requested in support of registration 

review:

(1) OECD 213—Acute oral toxicity to adult honey bees

(2) OECD 237—Acute oral toxicity to larval honey bees

(3) Non-Guideline—Chronic oral toxicity to adult honey bees
5

(4) Non-Guideline—Chronic toxicity to larval honey bees

(5) Non-Guideline—Pollinator feeding/semi-field/pollen and nectar residue studies – The need 

for these studies is contingent upon the results of lower tier bee studies.

(6) 850.3040—Field testing for pollinators – The need for field testing is contingent upon the 

results of lower tier bee studies.

(7) 850.2100—Avian Acute Oral Toxicity Test with Passerine species

Additionally there are a number of studies that have been submitted and are currently under 

EFED review:

(1) 850.1735 (MRID 46473303)—Whole Sediment Acute Toxicity Freshwater Invertebrates: 

Toxicity to Freshwater Amphipods (Hyalella azteca) during a 10-day Sediment Exposure

(2) 850.1735 (MRID 46487301)—Whole Sediment Acute Toxicity Freshwater Invertebrates: 

Toxicity to Midge (Chironomus riparius) during a 10-day Sediment Exposure

(3) 850.1035 (MRID 46473304)—Mysid Chronic Toxicity Test—Life-cycle toxicity with 

Mysids (Americamysis bahia)

(4) 850.1400 (MRID 48759101)—Oxadiazon Early Life-Stage Toxicity Test (Pimpheales 

promelas) Under High Light Conditions

2. Introduction

Oxadiazon is a light-dependent peroxidizing herbicide (LDPH) in the oxadiazolone chemical 

class. It is used for pre- and post- emergence control of grassy and broadleaf weeds in turf and 

ornamentals. LDPH chemicals target a specific enzyme, protoporphyrinogen oxidase, in the 

heme and chlorophyll biosynthetic pathway. Inhibiting protoporphyrinogen oxidase in plants 

leads to an accumulation of phototoxic heme and chlorophyll precursors that, in the presence of 

light, produce activated oxygen species which rapidly disrupt cell membrane integrity.

EFED evaluated the most recent ecological risk assessments for oxadiazon in association with 

updated toxicity, exposure, and usage information to determine if sufficient data are available and 

if further updates are needed to support Registration Review. Recent ecological risk assessments 

for oxadiazon include the 2001 EFED Risk Assessment for the Reregistration Eligibility Decision 

of Oxadiazon (2001, DP 277968). In addition, EFED considered the latest Agency science 

policies and risk assessment methodologies.

3. Use Characterization

There are 59 registered end-use products for oxadiazon with many formulations including 

granular (density 0.513 to 1.281 g/cm3, most commonly used in turf and mostly formulated with 

fertilizer), soluble concentrate (Liquid/solid), emulsifiable concentrate, flowable concentrate and 

wettable powder (water soluble packaging). The chemical is applied by ground equipment as 

granules (broadcast) or as liquid (foliar spray or weed directed spray depending on the tolerance 

of plant). Application frequency/rate varies by use. Oxadiazon is a weed pre-emergent or early 

post-emergent herbicide used to control grassy weeds (e.g., goosegrass and crabgrass) and 

broadleaf weeds. Oxadiazon is not to be applied on residential turf (by either home owners or 
6

commercial applicators) but could be applied to residential ornamental ground cover and shrub 

beds only by professional applicators. It could also be applied by professional applicators to turf 

in apartment/condominium complexes, parks, athletic fields, playground, and cemeteries) and on 

golf courses (predominant use). In addition, oxadiazon is used on sod farms and on conifer 

plantations/nurseries, nurseries (containerized or non-containerized nursery plants. It can also be 

applied to non-agricultural areas, right-of-way, and landscape ares (i.e., industrial sites, 

ornamental, roadside plantings, woody, ornamental shrubs, vines and trees and herbaceous 

ornamentals). Oxadiazon use sites are classified as non-food sites (i.e., primarily golf course 

fairways), outdoor use, roadsides and nurseries).

Table 1 lists the labeled use patterns categorized by the scenario that will be used in modeling 

exposure EECs. In this table, use sites, maximum single/yearly application rate, minimum 

intervals between applications are included. These parameters represent data obtained at least 

from one of the use sites within the specified scenario category. This means that rates may be 

lower and intervals longer for other uses included in the same scenario category.

Table 1. Labeled Use Patterns for Oxadiazon

Scenario Category Labeled Use Pattern

Maximum Single 

Rate (lbs a.i/A)*

Maximum No. of 

Applications*

Maximum Yearly 

Rate (lbs a.i/A)*

Minimum 

Intervals (Months)

Turf

Golf course 4.0 2 8.0 NS

Sod farm and all other turf, except home lawns 4.0-NDC 2 & NS 8.0 & NS 4 & NS

Residential

Shade trees and Ornamentals including: ground 

cover, grasses, lawns and turf, herbaceous plants, 

nonflowering plants, woody shrubs and vines and 

unspecified

4.0-NDC 2 & NS 8.0 & NS 3 & NS

2.0 4 & NS 8.0 & NS 2

1.4 2 2.8 4

Right-of- Way Right-of-way and non-agricultural areas 4.0 2 8.0 ? NS

X-Mass Tree Conifer plantations

4.0 2 & NS 8.0+ & NS 4 & NS

1.4 2 2.8 4

Nursery Established & containerized plants 4.0-NDC NS ? NS 3 & NS

* For some labels the maximum number of applications/year is calculated from the specified single application rate and the maximum 

application per year. For example, if the yearly rate= 8 and the single rate is equal 4, then the maximum number of applications/year= 

8 divided by 4= 2. However, if the single and yearly rate is specified in the label then the maximum number of applications per year is 

calculated; in this example 8 divided by 4= 2 applications. It is also noted that the crop cycle rates stated in some labels are taken to 

mean yearly rates and the registrants are requested to correct the labels accordingly. 

+ For some labels this value is nearly 8.1 lbs a.i/A requested to be corrected as well as other errors specified by the BEAD report.

The registrant is requested to review the information presented above for labeled uses of this 

chemical and inform EFED of any discrepancy. It is noted, that values entered in bold in Table 1

will be considered the maximum exposure scenarios and entries marked “?” need to be given, by 

the registrant, or high conservative values will be used. Registrants are requested to review Table 

1, above and BEAD chemical profile in the docket for accuracy.

4. Conclusions from Previous Risk Assessments

a. Ecological Risk Assessment 

EFED has conducted ecological risk assessments on oxadiazon that serve as the basis for this 
7

problem formulation, including the 2001 EFED chapter for the RED Document, as cited above. 

Risk conclusions are listed below and summarized in Table 2:

 Chronic exposure to freshwater fish and aquatic invertebrates; Chronic LOC was 

exceeded by 132-fold for freshwater fish and 37-fold for aquatic invertebrates. No 

chronic data for estuarine/marine fish was available at time of assessment.

 Chronic exposure to mammals may result in significant reproductive effects. Effects 

seen in maternal toxicity and developmental toxicity included slightly decreased body 

weight change in maternal females, inactive mammary tissue resulting in possible 

starvation of pups, increased fetal reabsorption/post implantation loss, decreased fetal 

weight, and increased incidence of incomplete ossification. 

 Chronic exposure to avian species; maximum three application scenarios resulted in 

LOC exceedances.

 Acute exposure to mammals and avian species does not present significant short term 

toxic risk

 Acute and chronic exposure to aquatic and terrestrial systems may result in a potential 

risk to endangered species that may include mammals, birds, fish and aquatic 

invertebrates. 

 Potential for impact to non-target terrestrial and aquatic plants based on herbicidal 

properties of the compound; limited plant data was available at time of the assessment.

Table 2. Summary of Conclusions from 2001 RED

Birds Mammals Terr 

Plants

Terr 

Inverts Fish BCF Aquatic Inverts

Aquatic 

Plants

Groundwater 

Contamination Persistence Degradates of Concern

Yes1 Yes2 Yes3 No Yes4 Refer to 5 Yes6 Yes No Yes No7

1 Potential for chronic risk to birds; no acute risk

2 Potential for chronic risk to mammals; no acute risk

3 No data was available for risk conclusion; risk was assumed

4 Potential for chronic risk to fish mediated by reproductive effects compounded by potential for photo-toxicity

5 Although the chemical has a high Kow, a study on bioconcentration in fish indicated a moderate bio-concentration potential due to 

rapid depuration.

6 Potential for chronic risk to aquatic invertebrates mediated by reproductive effects compounded by potential for compound to 

bind to sediment and accumulate as well as potential for photo-toxicity

 7Based on current fate data and may change upon review of requested studies and information

The RED recommended that all oxadiazon labels contain the following language:

 For Manufacturing Use Product:

“This pesticide is toxic to fish and aquatic invertebrates. Do not discharge 

effluent containing this product into lakes, streams, ponds, estuaries, oceans, or 

other water unless in accordance with the requirements of a National Pollutant 

Discharge Elimination System (NPDES) permit and the permitting authority has 

been notified in writing prior to discharge. For guidance, contact your State

Water Board or Regional Office of EPA.

 For End-use Product:

“This pesticide is toxic to fish and aquatic invertebrates. Do not apply directly 

to water, or to areas where surface water is present, or to intertidal areas 

below the mean high water mark. Do not contaminate water when disposing 
8

of equipment washwaters or rinsate. Do not apply when weather conditions 

favor drift from treated areas. Runoff and drift from treated areas may be 

hazardous to aquatic organisms in neighboring areas. Do not allow this 

product to drift.”

In addition, the RED proposed risk mitigation measures to reduce risk to non-target 

plants and aquatic organisms. The mitigation measures included the addition of a well 

maintained buffer zone (to decrease the amount of spray drift reaching bodies of water) 

and making a compulsory statement that the turf should be moved prior to application 

and irrigated after application (to assure that most of the chemical reaches the soil 

surface where it is less prone to run-off).

b. Drinking Water Exposure Assessments

The latest drinking water exposure assessment for oxadiazon was conducted in the 

year 2002 and was based on tier II PRZM/ EXAMS modeling1. The stressor of concern

was considered to be parent oxadiazon and modeling was done with FL turf scenario 

with a maximum of three applications at a rate of 8.0 lbs a.i/A/year. This was based on 

the assumption that this use would give the maximum surface water exposure. In 

modeling, the first application of 2.0 lbs a.i/A was assumed to be applied mid-March 

followed by a second application of 2.0 lbs a.i/A and a third application of 4.0 lbs/A at 

30 and 135-day intervals, respectively. 

This problem formulation requests new studies in order to address identified 

deficiencies in the oxadiazon suite of data. In addition, more information/confirmation 

on the labeled use patterns are also requested. Future estimation of the drinking water 

exposure will take into consideration the data obtained from requested studies, a 

possible change in what is considered to be the stressor of concern, and will use 

official models at that time. In this respect, it is noted that current surface water 

exposure models include tier II surface water concentration calculator (SWCC model) 

for surface water exposure and PRZM ground water (PRZM-GW model) for ground 

water. Finally, a report2on the possible effects on oxadiazon in the treatment process 

for drinking water will be considered.

c. Clean Water Act Programs

Oxadiazon is not identified as a cause of impairment for any water bodies listed as impaired under 

section 303(d) of the Clean Water Act at: 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=88

5.

 

1 Tier I1 Estimated Drinking Water Concentrations (EDWCs) for Human Health Risk for oxadiazon on Florida Golf 

Course (DP Barcode: 281176 Dated April 15, 2002

2 Rahman. M. M., Kim T-H, Kwon G-S, Yang J.E, Park M, and Kim J-E. 2009. Removal Efficiency of the Herbicide 

Oxadiazon in Treatment Processes for Drinking Water. J. Korean Soc. Appl. Biol. Chem.; 52(3); 252-257 
9

Furthermore, no Total Maximum Daily Load (TMDL) criteria or Office of Water aquatic life 

criteria have been developed for this chemical. OPP aquatic life benchmarks (fresh water) have 

been established for oxidiazon and can be found at:

http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm.

5. Environmental Fate and Transport

Based on submitted fate studies, Oxadiazon [3-[2, 4-Dichloro-5-(1-methylethoxy) phenyl]-5-(1, 

1-dimethyl-ethyl)-1, 3, 4-oxadiazol-2(3H)-one; CAS No. 19666-30-9; PC code 109001] is 

expected to be mainly affected by abiotic degradation: photolysis in water and hydrolysis in 

alkaline conditions. Therefore, significant degradation of the chemical is expected in alkaline 

conditions and in shallow clear water bodies. In contrast, the chemical appears to be highly 

persistent in most other important environmental compartments/conditions. It is hydrolytically 

stable in acid and neutral condition, degrades very slowly by photolysis on soil and by 

biodegradation in soils and water/ sediment systems under aerobic/anaerobic conditions. 

Volatilization of oxadiazon into the air from dry/wet soils and water is expected to be limited due 

to its relatively low vapor pressure and Henry’s low constant. Possible bio-accumulation in fish 

and aquatic organisms is suggested by the relatively high Kow of 63,096, however, results of the 

bioaccumulation test in bluegill sunfish indicated lower bioconcentration factors and rapid 

depuration.

Oxadiazon is characterized by slight mobility and high persistence in the soil system therefore 

there is potential for the chemical to leach to ground water when applied to coarse-textured soils 

low in organic matter. Oxadiazon physical, chemical, fate and transport data are summarized in 

Table 3.

Table 3. Physical/ Chemical and fate transport properties of Oxadiazon

Parameter Value

Reference MRID(Classification)

And Notes 1

Molecular Mass 345.20 g mole

-1 EFED, 20032

Molecular Formula C15H18Cl2N2O3 EFED, 20032

Aqueous Solubility (mg/L 

@ 20 °C) 1.0 EFED, 20032

; Hardly Soluble

3

Vapor Pressure (20°C) 1.0 x 10

-6

torr

EFED, 20032; Limited volatility 

from dry surfaces

Henry's Law Constant

(20°C; Calculated) 4.5 x 10-7 atm.m3 mole-1

EFED, 20032; Limited volatility 

from water or wet surfaces

Octanol/Water Partition 

Coefficient (Kow) and 

(log Kow) 63,096 (4.8)

EFED, 20032; Indicates possible 

bioaccumulation in aquatic 

organisms such as fish

Hydrolysis t 1⁄2 (25°C) Stable in pH 5 & 7; 38 days in pH 9

418636-03 (A); Data indicate the 

chemical is moderately affected by 

hydrolysis only in alkaline 

conditions
10

Parameter Value

Reference MRID(Classification)

And Notes 1

Aqueous Photolysis t 1⁄2 

(25°C) 3 days

418972-01 (A); Rapid photolysis in

clear/shallow waters

Soil Photolysis t 1⁄2 (25 °C) 165 days

418982-01 (A); Data indicate that the 

degradation pathway is not important

Aerobic Soil Metabolism t 

1⁄2 (24°C) 841 days

427738-01 (A); Only one soil 

indicating that the degradation 

pathway is not important

Anaerobic Aquatic 

Metabolism t 1⁄2 (25°C) 365 days

427738-02 (S); Only one system 

indicating that the degradation 

pathway is not important 

Aerobic Aquatic

Metabolism t 1⁄2 (25°C) 133 & 139 days (un-certain values)

465947-01 (S); Two systems and halflives were calculated considering the 

unidentified un-extracted residues as a 

sink; Need to identify the 

significant un-extracted residues

Soil Water Partition 

Coefficient (Koc) 2,357 L Kg-1

418982-02 (A); Average of 4 soils; 

Slightly mobile 4

Terrestrial Field 

Dissipation t 1⁄2 and

Observed Field Mobility

65 days in CA Sandy loam soil 

planted with junipers and

40 days in NC Loamy sand soil 

planted with azaleas

No dissipation observed during 

winter

417674-01 (A); Relatively slow 

dissipation; Mobility: Residues were 

detected only in the top 30 cm of the 

soils, with occasional small detections 

in the 15-30-cm layers

Fish Bio-concentration

Factors (BCFs) and 

Depuration

BCFs: 368 (edible), 2,239

(non-edible) and 1,111 (whole)

and depuration t1⁄2 ~ 3 days

422267-01 (A); Moderate bioconcentration potential

1 Refer to text below for information about observed degradation products in various fate studies; Classification: A= 

Acceptable; S= Supplemental

2 EFED 2003: EFED Revised Risk Assessment for the Reregistration Eligibility Decision of Oxadiazon (PC Code 109001)

3 When considering that the expected concentration in the top 6” of the soil upon a single application of 4 lb a.i/A gives an 

estimated concentration of nearly 2 ppm.

4 FAO Mobility Classification

With the exception of hydrolysis at pH 9 and aqueous photolysis, the degradation profile for 

oxadiazon shows the presence of many transformation products with minor (i.e <10%) rates of 

formation (Table 4). In all studies, only seven to eight transformation products were identified 

and many were not. For example, in aqueous photolysis 20 degradates were isolated at <8%; in 

hydrolysis other metabolites (number not specified) were present at <10%; in the aerobic soil 

three areas of radioactivity were isolated, but not identified at 1%; and in the anaerobic aquatic 

study, six transformation products were isolated at <2% and one at <6%. Very limited 

mineralization to CO2 was observed in the aerobic soil (3%) and much lower in the 

aerobic/anaerobic aquatic metabolism (1-2% and 0.02%, respectively). Un-extracted [14C] 

residues comprised a maximum of 5% in the aerobic soil and 3% in the anaerobic aquatic study 

(both conducted in 1993). In contrast, un-extracted residues reached 31 to 36% of the applied 

radioactivity in the newly submitted aerobic aquatic study (conducted in 2014).
11

Table 4. Oxadiazon transformation profile: Maximum formed (@T= at termination; D= declined 

after reaching stated maximum, ND= No decline) 

Study 

 TP 1 RP26123

RP 25496

AE 0608021

RP 17272

AE 0618784 RP 26471 RP 26449 RP 36939 RP 37084 RP 36227

Alkaline Hydrolysis 45% @T None None None None None None None

Aqueous Photolysis None None None None None 5% @T 12% @T None

Soil Photolysis None small small None None None None None

Aerobic Soil <1% ND <1% ND <2% ND <1% ND <1% ND None None None

Aerobic Aquatic None <0.5% D None None None None None None

Anaerobic Aquatic <2% <2% None < 2% None None None ≤ 4%

TFD 2 None None <1% D None ~ 6% ND None None None

1 TP= Registrant designations for the transformation products:

RP26123: 1-trimethylacetyl-2-(2,4-dichloro-5-isopropoxyphenyl)hydrazine

RP25496: 2-tertiobutyl-4-(2,4-dichloro-5-hydroxyphenyl)-5-oxo-1,3,4-oxadiazolin

RP17272 (AE 0618784): 3-(2,4-dichloro-5-methoxyphenyl)-5-tertiobutyl-1,3,4-_4-oxadiazolin-2-one

RP26471: 2-(carboxy-2-propyl)-4-(2,4-dichloro-5-hydroxyphenyl)-5-oxo-1,3,4-oxadiazolin

RP26449: 2-(2-carboxy-2-propyl)-4-(2,4-dichloro-5-isopropoxyphenyl)-5-oxo-1,3,4-oxadiazolin 

RP36939 and RP37084: No names reported

RP36227: 2,4-dichloroisopropoxybenzene

2 TFD= Terrestrial Field Dissipation

Not all of the structures for the transformation products were reported by the registrant. However 

examination of the three available metabolite structures indicates the transformation occurring in 

specific moieties as shown in Table 5.

Table 5. Changes in the chemical structure of oxadiazon that produce four of its transformation 

products.

Chemical First Moiety Second Moiety

Parent (CH3)2-C-O C-(CH3)3

RP 17272 (methoxy) CH3-O No change

RP 25496 (phenolic) OH No change

RP 26449 (carboxylic acid) No change C-(CH3)2COOH

Review of the available fate data reveals the following inadequacies: 

(1) Only one aerobic soil metabolism data is available, a minimum of three is required;

However, due to the expected persistence of the chemical a study with one soil will be 

acceptable at this time.

(2) Extraction of oxadiazon residues appears not to be complete in the newly submitted aerobic 

aquatic study. Un-extracted residues reached over 30% of the applied radioactivity with no 

apparent decline. These residues were not identified and apparently no attempt was executed 

to extract these residues. In this respect, it is noted that apparent good extraction procedures 

were employed. In addition, the experiment was terminated much earlier than the expected 

O

N N

O CH3

CH3

Cl

O

Cl

H3C

H3C

CH3
12

half-life of the chemical;

(3) No structures were reported for most of the metabolites; and

(4) No terrestrial field dissipation study was submitted for turf use which is the most important 

usage for this chemical in terms of pounds of active ingredient used annually.

6. Receptors

Table 6 and Table 7 provide a summary of the aquatic and terrestrial taxonomic groups and most 

sensitive surrogate species tested to characterize the acute and chronic ecological effects of 

oxadiazon. As an LDPH compound, there is the potential for oxadiazon to exhibit enhanced 

toxicity through exposure to high levels of solar radiation and increase toxic effects to aquatic 

organisms that inhabit small water bodies. There is currently one study in review conducted 

under enhanced UV lighting. The extent to which UV light enhances the toxicity of oxadiazon to 

other taxa or other life stages is unknown. Anemia and other hematologic consequences have 

been observed in developmental studies with mammals (USEPA, 2002). In wild mammal 

populations, hematologic effects have the potential to magnify since the lack of natural sunlight 

in the laboratory reduces the likelihood of activating the phototoxic effects of oxadiazon. A 

summary of all ecological studies can be found in the 2001 RED document. 

a. Effects to Aquatic Organisms

Oxadiazon is considered to be moderately toxic on an acute basis to freshwater fish, 

estuarine/marine fish, and freshwater invertebrates. On a chronic basis, egg hatchability was the 

most sensitive endpoint upon which the NOAEC was based. The freshwater invertebrate toxicity 

test showed effects in survival, adult mean length, and mean time to brood, and young/adult 

reproduction day. Oxadiazon is considered highly toxic to estuarine/marine invertebrates. There 

is no data available on chronic toxicity of oxadiazon to estuarine/marine fish and estuarine/marine 

invertebrates.

 

Table 6. Most Sensitive Endpoints for Aquatic Species for Oxadiazon

Taxonomic 

Group Study Type Surrogate Species Toxicity Value

Acute 

Toxicity 

Classification

Source

Freshwater 

fish

Acute

Rainbow Trout

Oncorhynchus 

mykiss

LC50=1.2 mg ai/L Moderately 

toxic

42330401

Acceptable

Chronic

Fathead Minnow

Pimephales 

promelas

NOAEC=33 μg 

ai/L

LOAEC=84 μg 

ai/L

(based on egg 

hatchability)

- 41811601

Acceptable1

Freshwater 

Invertebrates Acute

Water flea

Daphnia magna

EC50=2.18 mg ai/L Moderately 

toxic

McCann 

Study 1977

Supplemental2
13

Taxonomic 

Group Study Type Surrogate Species Toxicity Value

Acute 

Toxicity 

Classification

Source

Chronic

Water flea

Daphnia magna

NOAEC=33 μg 

ai/L

LOAEC=55 μg 

ai/L

(based on survival; 

adult mean length; 

mean time to brood 

and young/adult 

reproduction day)

- 41784301

Acceptable

Estuarine/ 

marine fish

Acute

Sheepshead 

Minnow

Cyprinodon 

variegatus

LC50=1.5 mg ai/L Moderately 

toxic

42615801

Core

Chronic No data available

Estuarine/ 

marine 

invertebrates

Acute

Mysid shrimp

Americamysis 

bahia

EC50=0.27 mg ai/L Highly toxic 42615802

Core

Chronic No data available

Aquatic plants 

and algae

Vascular Duckweed

Lemna gibba

EC50=41 μg ai/L

NOAEC=8 μg ai/L

- 41610107

Supplemental3

Nonvascular

Freshwater green 

algae

Selenastrum 

capricornutum

EC50=8 μg ai/L

NOAEC=5.6 μg 

ai/L

- 41610108

Core

Marine Diatom

Skeletonema 

costatum

EC50=5.2 μg ai/L

NOAEC=1.4 μg 

ai/L

- 41610105

Core

Freshwater 

Diatom

Navicula 

pelliculosa

EC50-126 μg ai/L

NOAEC=27 μg 

ai/L

- 41610106

Core

1A study conducted using Rainbow Trout was two orders of magnitude more sensitive than the Fathead minnow 

endpoint with NOAEC = 0.88 ppb and a LOAEC of 1.7 ppb; the study was classified as supplemental because 

individual growth data were not included in the report and thus the statistics could not be verified. This data has 

been requested.

2EFED considered the McCann study as scientifically sound and useful for risk assessment purposes

3Study was classified as supplemental because the exposure concentrations used in the test were too high to establish 

a NOAEC

b. Effects to Terrestrial Organisms

Oxadiazon may be categorized as practically nontoxic to birds on an acute oral and dietary basis. 

The avian reproduction test showed no effect on any reproductive parameter or viability of the 

offspring. However, mortality among females at the highest level was 33% and considered to be
14

treatment. Oxadiazon is characterized as practically nontoxic to mammals on an acute oral basis. 

Chronic toxicity was based on the developmental toxicity test where increased fetal 

reabsorption/post implantation loss, decreased fetal weight and increased incidence of incomplete 

ossification were observed. Oxadiazon is considered practically non-toxic to bees on an acute 

contact basis. Submitted terrestrial plant data were deemed inadequate for determining 

EC25/NOAEC values of the most sensitive species (D166982; 1995 memo to SRRD requesting 

repeat of all ten species due to numerous deficiencies and guideline deviations). Table 7

summarizes the most sensitive endpoints for terrestrial points. No data is available on the acute 

oral toxicity of oxadiazon to passerines.

Table 7. Summary of Most Sensitive Endpoints for Terrestrial Organisms to Oxadiazon

Taxonomic 

Group Study Type Surrogate Species Toxicity Value Acute Toxicity Classification Source

Birds

Acute

Northern 

Bobwhite

Colinus 

virginianus

LD50>2150 mg/kg

(no mortality)

Practically 

nontoxic

416101011

Acceptable

Sub-acute

Northern 

Bobwhite

Colinus 

virginianus

LC50>5000 ppm

(no mortality)

Practically 

nontoxic

41610102

Acceptable

Chronic

Northern 

Bobwhite

Colinus 

virginianus

NOAEC=500 ppm

LOAEC=1000 (based on 

mortality among adult 

females)

- 41993202

Acceptable

Mammals

Acute 

Laboratory rat

Rattus 

norvegicus

LD50>5000 mg/kg Practically 

nontoxic

41866501

Acceptable 

Chronic

SpragueDawley ratNOAEC=12 mg/kg/day

LOAEC=40 mg/kg/day

(maternal and 

developmental toxicity)

- 40470202

Insects Acute 

Contact

Honeybee

Apis mellifera

LD50>25 μg/bee Practically 

nontoxic

42468301

Acceptable

Terrestrial 

Plants

Seedling 

Emergence No data available

Vegetative 

Vigor No data available

1Additional study conducted on the Mallard in 1971 found a more sensitive endpoint of LD50 =1040 mg/kg; the 

study was deemed satisfactory for registration of oxadiazon in the 1970’s but EFED requested a study in 1991 to 

replace the older study (classified under MRID 111806)

c. Ecological Incidents

The Ecological Incident Information System (EIIS) is an OPP database that houses ecological 

incidents that have been reported to the Agency. When available, EIIS includes date and location 

of an incident, type and magnitude of effects observed in various species, uses of pesticides 
15

known or suspected of contributing to the incident and results of any chemical residue analysis or 

other analyses conducted during incident investigation. EIIS incidents are categorized acording 

to the certainty that the incident results from pesticide exposure. The Avian Monitoring System 

(AIMS) is a database maintained by the American Bird Conservancy that contains publicly 

available data on reported avian incidents involving pesticides. Many of the incidents listed here 

are also listed in EIIS.

A preliminary review on September 2, 2014 of EIIS returned two incidents attributed to 

oxadiazon use. 

 Incident I003822-001 occurred in June 1996 at a country club in Orlando, Florida. There had 

been three applications of a product containing oxadiazon, glyphosate, fonofos and 

fenamiphos at the beginning of the month, after which irrigation had been applied in the 

evening. Six days after the first application, a rain event caused the small retention ponds and 

canals to overrun the banks and cover the fairways for several hours before receding. The fish 

kill was found in the shallowest water bodies; most individuals were tilapia and shiners. 

Oxadiazon was classified as “unlikely” the cause of the incident whereas fonofos and 

fenamiphos were listed as the “probable” causes of the incident.

 Incident I012094-001 occurred in August 2001 in Tarrant, Texas. There was a complaint 

issued from a golf course, that Ronstar, containing pendimethalin and oxadiazon, had 

damaged 30 acres of Tifsport Bermuda Fairways. Oxadiazon and pendimethalin were 

classified as the “possible” cause of the incident.

The Aggregate Incident Report for EFED reported 1 minor fish and wildlife incident from 1998 to 

2000, and 8 minor plant incidents occurring from 2000 to 2006. There were no avian incidents 

reported from AIMS. 

7. Exposure Pathways of Concern

The environmental fate and transport properties and use patterns of oxadiazon indicate that runoff 

with eroded soil and spray drift represent the important transport mechanisms of the chemical to 

aquatic and terrestrial organisms. Drinking water and inhalation exposure pathways were 

investigated using the Screening Imbibition Program (SIP) and Screening Tool for Inhalation 

Risk (STIR) screening methods and were found to be exposure pathways of low concern. SIP and 

STIR are described in detail at: 

http://www.epa.gov/pesticides/science/models_pg.htm#terrestrial 

SIP is used to provide an upper bound estimate of exposure of birds and mammals to pesticides 

through drinking water alone. It is used to determine whether or not drinking water exposure 

alone is a potential pathway of concern; it does not aggregate drinking water exposure with other 

exposure routes. The results of SIP conclude that drinking water exposure alone is not a potential 

concern for mammals on an acute basis or chronic basis. For avian species, it concludes that 

exposure through drinking water alone is not a potential concern on an acute or chronic basis. 

STIR indicated that exposure via the inhalation pathway was not likely significant for mammals 

or avian species. Output from models can be found in Appendix A and Appendix B.
16

8. Analysis Plan

a. Stressors of Concern

The stressor of concern for drinking water and aquatic and terrestrial organisms is parent 

Oxadiazon. This decision might change because it is based on currently available data which 

indicate that the chemical is highly persistent. Degradates forming in most important 

environmental compartments, are therefore expected to be at low concentrations. Upon receiving 

requested studies, the degradation profile for the chemical will be established along with expected 

intensity of surface water exposure resulting from the chemical residues of concern. In this future 

exercise, the residues of concern will be revisited based on expected concentrations of varied 

degradates, structural similarity to parent and their toxicity. 

b. Measures of Exposure 

EFED will use standard available models (identified in Table 8) to evaluate potential exposures 

to aquatic and terrestrial organisms as described at 

http://www.epa.gov/pesticides/science/models_db.htm.

Aquatic exposure estimates will be based on estimated environmental concentrations (EECs) 

generated using the Surface Water Concentration Calculator (SWCC) model to simulate a 

waterbody that is considered representative of vulnerable aquatic environmental (e.g., ponds and 

streams in headwater watersheds). Terrestrial exposure will be estimated using a model (T-REX 

version 1.5.2; March 22, 2012. As indicated by the usage data, granular formulations of 

oxadiazon had the highest historical usage. Therefore, the granular characterization module of TREX will be used in terrestrial exposure. Inputs request to run this module include amount of a.i. 

per granule for mesh sizes of the granular formulations. Conservative default values will be used 

in the assessment unless data are provided by the registrants. Exposure to terrestrial plants will be 

estimated using a model (TerrPlant; version 1.2.2; December 26, 2006) that assumes oxadiazon

drifts or moves with runoff to adjacent habitats. For more information on the various models that 

will be used in the risk assessment see the links as outlined in Table 8. 

Two spray drift models, AGDISP and/or AgDRIFT, will be used to assess exposures of aquatic 

and terrestrial organisms to Oxadiazon deposited in terrestrial and aquatic habitats by spray drift. 

AgDRIFT (version 2.1.1; dated 03/07/2012) is the model most commonly used by EFED to 

simulate spray drift into terrestrial and aquatic environments. AGDISP (version 8.26; dated 

03/07/2012) is used when a parameter needs to be modeled that is not available in AgDRIFT. 

Spray drift analysis will be an important part of the analysis in defining the potential area of 

effects for listed species.
17

Table 8. List of various models and the related taxa for which the models will be used

Environment Taxa of Concern Model(s)

Aquatic Fish/Invertebrates/Plants SWCC

Terrestrial

Vertebrate T-REX (dietary item)

AGDISP (Spray drift)

Plants

TerrPlant (run-off)

AgDRIFT

AGDISP (spray drift)

The Agency is aware of monitoring conducted by the registrant (MRID 471993-01 and 465637-

01), federal and state agencies and the literature. This route of exposure will be considered in the 

future risk assessment to the extent that data on oxadiazon are available.

c. Measures of Effect 

Toxicity data presented in Table 6 and Table 7 of this problem formulation will be used to 

calculate risk quotients in future risk assessments. Any additional information submitted by the 

registrant or found in the open literature prior to conduct of the risk assessment will also be 

considered. The open literature studies are identified using EPA’s ECOTOXicology database 

(ECOTOX), which employs a literature search engine for locating chemical toxicity data for 

aquatic life, terrestrial plants, and wildlife. The evaluation of both sources of data can also 

provide insight into the direct and indirect effects of pesticides on biotic communities from loss of 

species that are sensitive to the chemicals and from changes in structure and functional 

characteristics of the affected communities.

9. Endangered Species Assessments

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the 

Agency will evaluate risks to federally listed threatened and/or endangered (listed) species from 

registered uses of pesticides in registration review. The process for evaluating potential risks to 

listed species is further described at 

http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm

10. Endocrine Disruptor Screening Program

Under Federal Food Drug and Cosmetic Act (FFDCA section 408(p), the Agency must screen all 

pesticide chemicals for potential endocrine disruptor activity. Between October 2009 and 

February 2010, EPA issues test orders/data call-ins for the first group of 67 chemicals, which 

compromises 58 pesticide active ingredients and 9 inert ingredients. The herbicide Oxadiazon is 

not among the group of 58 pesticide active ingredients on the initial list to be screened under the 
18

EDSP. For further information on the status of the EDSP, policies and procedures, the list of 67 

chemicals, future lists, the test guidelines and the Tier 1 screening batter, please visit our website 

http://www.epa.gov/endo/

11. Preliminary Identification of Data Gaps 

a. Environmental Fate

Table 9 identify environmental fate studies by MRID that offer data for each guideline 

requirement, as well as study classifications. Requested data needed to support the future risk 

assessment are listed earlier in the executive summary.

Table 9. Submitted environmental fate and transport data for oxadiazon

OCSPP Guideline Data Requirement Submitted Studies (MRID) Study Classifications

835.2120 Hydrolysis 418636-03 Acceptable

835.2240 Aqueous photolysis 418972-01 Acceptable

835.2410 Soil photolysis 418982-01 Acceptable

835.4100 Aerobic soil metabolism 427738-01 Acceptable: One soil

835.4300 Aerobic aquatic metabolism 465947-01

Supplemental: Un-identified/Unextracted Residue

835.4400 Anaerobic aquatic metabolism 427738-02

Acceptable: One system and no 

need for another system because 

the chemical is practically stable

835.1230

835.1240 Adsorption/ desorption & leaching 418982-02 Acceptable

835.6100 Terrestrial field dissipation 417674-01

Acceptable: None on Turf the 

major use pattern

850-1730 Bio-concentration in Fish 422267-01 Acceptable

850.6100

ECM & ILV* for 

soil/sediment and water

An environmental chemistry method with self-validation was included as part of the TFD study 

(MRID 417674-01) to determine oxadiazon and three of its metabolites the methoxy (RP17272) , 

the phenolic (RP25496), and the carboxylic (RP26449) in soil only. The method sensitivity is 

approximately 0.01 ppm (10 ppb). This submittal does not satisfy current requirements for ECMs 

and associated ILVs for soil and water. These studies are requested as per OCSPP Guideline 

number 850.6100. Requested procedures should be more sensitive, state-of-the-art.

*ECMs= Environmental Chemistry Methods & Associated ILVs= Independent Laboratory Validations (ILVs)

b. Ecological Effects

Table 10 and Table 11 identify ecological effects studies by MRID that offer data for each 

guideline requirement, as well as study classifications and whether or not further data are needed 

in order to support risk assessment. Rationale for the additional data requested is presented below 

the tables. 
19

Table 10. Submitted Aquatic Ecological Effects Data for Oxadiazon

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data needed 

to conduct risk 

assessment?

Justification and Assumptions EPA 

will Make in Absence of Data

850.1010 Freshwater 

invertebrate 

acute toxicity

McCann 

1977

Supplemental No --

42331801 Acceptable

850.1025

850.1035

850.1045

850.1055

Saltwater 

invertebrate 

acute toxicity 

42570301 Supplemental No --

42615802 Acceptable

850.1075 Freshwater fish 

acute toxicity 

McCann 

1977

Supplemental No --

42350601 Acceptable

McCann 

1977

Supplemental

42330401 Acceptable

850.1075 Saltwater fish 

acute toxicity 

42615801 Acceptable No --

850.1300 Freshwater 

invertebrate 

life cycle 

41784301 Acceptable No --

850.1350 Saltwater 

invertebrates 

life cycle 

None NA Yes

In review

--

850.1735 Whole 

Sediment Acute 

toxicity 10-day

46487301 NA Yes

In review

-- 

46473303

850.1400 Freshwater fish 

early-life stage

41811601 Supplemental Yes

In review, 

pending 

submission of 

raw data for 

rainbow trout 

(MRID 

41811601)

The Rainbow Trout (MRID 41811601) 

was found to be more sensitive than the 

fathead minnow in the ELS testing. 

The study results of the Rainbow Trout 

could not be verified because 

individual growth data were not 

included in the report.

This information was requested 

(D165510) in 1997 and has not yet been 

submitted thus Guideline 850.1400 is 

unfulfilled.

42921601 Acceptable
20

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data needed 

to conduct risk 

assessment?

Justification and Assumptions EPA 

will Make in Absence of Data

850.1400 Saltwater fish 

early-life stage 

None NA No --

850.1500 Fish life cycle None NA No --

850.4400 Aquatic plant 

Toxicity Test 

using Lemna 

spp.

41610107 Supplemental No --

850.4500 Algal toxicity 41610108 Acceptable Yes

Green algae 

(Anabaena flosaquae)—In 

review

--

41610105 Acceptable

41610106 Acceptable

Table 11. Terrestrial Ecological Effects Data for Oxadiazon

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Justification and Assumptions EPA will Make 

in Absence of Data

850.2100 Avian oral 

toxicity

111807

(112622)

Supplemental Yes Acute oral toxicity data for a passerine species 

are required under 40 CFR Part 158. A study has 

not been submitted for this data requirement. 

A guideline-compliant passerine acute oral 

toxicity test is needed. Acute oral toxicity data 

are only available for one avian species (i.e., 

bobwhite quail). Passerine birds may utilize 

metabolic pathways that are different from larger 

birds and therefore be more sensitive to 

oxadiazon. Furthermore, passerines exhibit 

behavioral responses to pesticide dosing that are 

potential indicators of reduced fitness in the field 

(e.g., regurgitation of contaminated diet) even 

when direct biochemically-mediated lethal 

toxicity is not apparent. 

Though acute toxicity was not detected for the 

mallard or bobwhite, significant effects and 33% 

mortality seen in the avian reproduction study 

raise concern for passerine species. 

In the absence of these data, passerine toxicity 

data for surrogate pesticides may be used to 

characterize the acute toxicity of oxadiazon to 

passerine species.

111806 Supplemental

41610101 Acceptable

850.2200 41610102 Acceptable No --
21

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Justification and Assumptions EPA will Make 

in Absence of Data

Avian dietary 

toxicity 

41610103 Acceptable

850.2300 Avian 

reproduction

41993201 Supplemental No --

41993202 Acceptable

850.3020 Honey bee 

acute contact 

toxicity

42468301 Acceptable No --

OECD 213 Acute oral 

toxicity to 

adult honey 

bees

None NA Yes As part of the Guidance for assessing pesticide 

risks to bees (USEPA, 2014), the following Tier 

I studies are recommended:

 Acute oral toxicity to adult honey bees

 Acute oral toxicity to larval honey bees

 Chronic oral toxicity to adult honey bees

 Chronic oral toxicity to larval honey 

bees

In the absence of these data, honey bee oral 

toxicity data for surrogate pesticides – starting 

with data for closely related pesticides (e.g., 

diphenyl ethers) and proceeding to data for less 

related pesticides – may be used to characterize 

the oral toxicity of oxadiazon to larval and adult 

honey bees. 

Tier II (feeding/semi-field/pollen and nectar 

residue) and Tier III (full field) studies may be 

needed, contingent upon the results of lower tier

studies. 

OECD 237 Acute oral 

toxicity to 

larval 

honeybees

None NA Yes

Non 

Guideline

Chronic oral 

toxicity to 

adult honey 

bees

None NA Yes

Non 

Guideline

Chronic oral 

toxicity to 

larval honey 

bees

None NA Yes

Non 

Guideline

Pollinator 

feeding/semifield/pollen 

and nectar 

residue 

studies –

None NA Need for 

data 

contingent 

upon 

results of 

Tier I bee 

studies

850.3040 Field testing 

for pollinators 

None NA Need for 

data 

contingent 

upon 

results of 

Tier I bee 

studies

850.4100 Seedling 

Emergence

and Seedling 

Growth

None NA Yes Since Oxadiazon is an herbicide, toxic effects to 

plants are anticipated. Lack of adequate data 

represents uncertainty with regards to risk. A 

new study was requested in 1995 (D166982) after

a definitive NOAEC and EC25 were not 

established. 
22

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Justification and Assumptions EPA will Make 

in Absence of Data

850.4150 Vegetative 

Vigor

None NA Yes Since Oxadiazon is an herbicide, there is potential 

for risk to nontarget plants. Lack of adequate 

data represents uncertainty with regards to risk. 

Study repeat was requested in 1995 (D166982) 

after NOAEC and EC25 were not established. 
23

12. References

a. Fate and Transport Studies

 MRID Citation Reference

41863603 Corgier, M.; Robin, J. (1991) [

14C]-Oxadiazon Hydrolysis at 25 

Degrees Centigrade: Lab Project Number: 91-02. Unpublished study 

prepared by Rhone-Poulenc, Secteur Agro. 56 p. 

41897201 Corgier, M.; Plewa, A. (1991) [

14C]-Oxadiazon Photodegradation in 

Aqueous Solution: Lab Project Number: 90-29: AG/CRLD/AN/ 

9115609. Unpublished study prepared by Rhone-Poulenc Secteur 

Agro. 8 p. 

41898201 Das, Y. (1989) Photodegradation of Phenyl(U)[

14C]-Oxadiazon on 

Soil Under Artificial Sunlight: Lab Project Number: 89110. 

Unpublished study prepared by Innovative Scientific Services, Inc. 

119 p. 

42773801 Waring, A. (1993) Aerobic Soil Metabolism: [

14C]-Oxadiazon: 

Final Report: Lab Project Number: 68/111: 7218. Unpublished 

study prepared by Hazleton UK. 79 p. 

42773802 Waring, A. (1993) Aerobic Aquatic Metabolism: (carbon 14)-

Oxadiazon: Final Report: Lab Project Number: 68/112: 7214. 

Unpublished study prepared by Hazleton UK. 95 p. 

46594701 Roohl, A. 2003. [14C]-Oxadiazon: Degradation and retention in 

two water/sediment systems. Unpublished study performed by 

Battelle AgriFood Ltd., Ongar, Essex, United Kingdom, sponsored 

by Bayer CropScience SA, Lyon, France, and submitted by Bayer 

CropScience, Stilwell, Kansas. Battelle Study No. CX/02/075. PSI 

Activity Code: MEOAX007. Experiment started August 21, 2002, 

and completed March 16, 2003 (p. 7). Final report issued May 19, 

2003.

41898202 Dykes, J. (1990) Soil Adsorption/Desorption with carbon 14|-

Oxadiazon: Final Report: Lab Project Number: 37723. Unpublished 

study prepared by Analytical Bio-chemistry Laboratories, Inc. 57 p. 

42226701 Norris, F. (1991) A Terrestrial Field Soil Dissipation Study with 

Oxadiazon: Lab Project Number: 900102: 40642: EC/P-89-0014. 

Un- published study prepared by Rhone-Poulenc Ag Co., in 

cooperation with A & L Eastern Agric., Labs. Inc. and others. 221 

p. 
24

42226701 Armstrong, K.; Cameron, B.; Chapleo, S.; (1991) Oxadiazon: 

Bioaccumulation Test in Bluegill Sunfish: Lab Project Number: 

8385: 381195. Unpublished study prepared by Inveresk Research 

International. 94 p. 

47199301 Nendihalli, U.B. and D.L. Woodard. 2007. Surface Water 

Monitoring for Residues of Oxadiazon in High Use Areas in the 

United States. An unpublished study performed by Bayer 

CropScience (Residue Analyses), Stillwell, KS, and sponsored by 

Bayer CropScience, Research Triangle Park, NC. Study Number 

04RAOAY001. 

46563701 Nendihalli, U.B. and D.L. Woodard. 2005. Interim Report 1. 

Surface Water Monitoring for Residues of Oxadiazon in High Use 

Areas in the United States. An unpublished study performed by 

Bayer CropScience (Residue Analyses), Stillwell, KS, and 

sponsored by Bayer CropScience, Research Triangle Park, NC. 

Study No 04RAOAY001, Doc. No B004944, Lynx/PSI Code 

RAOAY001.

b. Ecological Effects Studies

71-1 Avian Single Dose Oral Toxicity

MRID Citation Reference

111806 Posner, S.; McGee, G.; Freeman, L. (1971) Acute Toxicity (LD50) in 

Mallard Ducks: ?RP-17623 Technical Assay 99.1|: Experimental 

Reference No. A-408. (Unpublished study received Aug 23, 1972 under 

359-658; prepared by Biometric Testing, Inc., submitted by RhonePoulenc, Inc., Monmouth Junction, NJ; CDL:003179-B) 

111807 Posner, S.; McGee, G.; Freeman, L. (1971) Acute Toxicity (LD50) in 

Bobwhite Quail: ?RP-17623 Technical Assay 99.1|: Experimental 

Reference No. A-408. (Unpublished study received Aug 23, 1972 under 

359-658; prepared by Biometric Testing, Inc., submitted by RhonePoulenc, Inc., Monmouth Junction, NJ; CDL:003179-C) 

112622 Posner, S.; McGee, G.; Freeman, L. (1971) Acute Toxicity (LD50) in 

Bobwhite Quail: Experimental Reference No. A-408. (Unpublished study 

received Oct 14, 1972 under 2F1269; prepared by Biometric Testing, Inc., 

submitted by Rhodia, Inc., New Brunswick, NJ; CDL:091824-D) 

41610101 Pedersen, C. (1990) Oxadiazon Technical: 21-Day Acute Oral LD50 Study 

in Bobwhite Quail: Lab Project Number: BLAL/NO/89 QD 139. 

Unpublished study prepared by Bio-Life Associates, Ltd. 35 p. 
25

71-2 Avian Dietary Toxicity

MRID Citation Reference

41610102 Pedersen, C. (1990) Oxadiazon Technical: 8-Day Acute Dietary LC50 

Study in Bobwhite Quail: Lab Project Number: BLAL/NO/89 QC 141. 

Unpublished study prepared by Bio-Life Associates, Ltd. 82 p. 

41610103 Pedersen, C. (1990) Oxadiazon Technical: 8-Day Acute Dietary LC50 

Study in Mallard Ducklings: Lab Project Number: BLAL/NO/89 DC 137. 

Unpublished study prepared by Bio-Life Associates, Ltd. 80 p. 

ACC 091824 1974. 8-Day Acute Dietary LC50 Study in Bobwhite Quail: Biometric 

testing- supplemental

71-4 Avian Reproduction

MRID Citation Reference

41993201 Fletcher, D.; Pedersen, C. (1991) Oxadiazon Technical: Toxicity and 

Reproduction Study in Mallard Ducks: Lab Project Number: 89 DR 35. 

Unpublished study prepared by Bio-Life Associates, Ltd. 138 p. 

41993202 Fletcher, D.; Pedersen, C. (1991) Oxadiazon Technical: Toxicity and 

Reproduction Study in Bobwhite Quail: Lab Project Number: 89 QR 39. 

Unpublished study prepared by Bio-Life Associates, Ltd. 145 p. 

72-1 Acute Toxicity to Freshwater Fish

MRID Citation Reference

68524 Roberts, S. (1977) Report: Static 96-hour Toxicity Study of Rhodia 

Oxadiazon in Bluegill Sunfish and Rainbow Trout: Laboratory No. 7E5605. (Unpublished study received Mar 31, 1977 under 359-679; prepared 

by Cannon Laboratories, Inc., submitted by Rhone-Poulenc Chemical Co., 

Monmouth Junction, N.J.; CDL: 229201-A) 

68525 Roberts, S. (1977) Report: Static 96-hour Toxicity Study of Rhodia 

Ronstar EC in Bluegill Sunfish and Rainbow Trout: Laboratory No. 7E5604. (Unpublished study received Mar 31, 1977 under 359-679; prepared 

by Cannon Laboratories, Inc., submitted by Rhone-Poulenc Chemical Co., 

Monmouth Junction, N.J.; CDL: 229201-B) 

111808 Posner, S.; Jolly, E.; Grim, J. (1971) Acute LC50 96-hour (Static) of RP 

17623 to Rainbow Trout (Salmo Gairdneri); Crayfish (Oronectes) and 

Brown Bullheads (Ameiurus Nebulous): Experi- mental Reference No. 
26

49-269A. (Unpublished study received Aug 23, 1972 under 359-658; 

prepared by Biometric Testing, Inc., submitted by Rhone-Poulenc, Inc., 

Monmouth Junction, NJ; CDL: 003179-D) 

112623 Posner, S.; Jolly, E.; Grim, J. (1971) Acute LC50 96-hour (Static) of RP 

17623 to Rainbow Trout (Salmo gairdneri); Crayfish (Oro- nectes) and 

Brown Bullheads (Ameiurus nebulosus): Experimental Reference No. 49-

269A. (Unpublished study received Oct 14, 1972 under 2F1269; prepared 

by Biometric Testing, Inc., submitted by Rhodia, Inc., New Brunswick, 

NJ; CDL:091824-E) 

42330401 Sword, M.; Northup, R. (1992) Acute Flow-Through Toxicity of 

Oxadiazon to Rainbow Trout (Oncorhynchus mykiss): Lab Project 

Number: 39729. Unpublished study prepared by ABC Laboratories, Inc. 

211 p. 

42350601 Sword, M.; Northup, R. (1992) Acute Flow-through Toxicity of 

Oxadiazon to Bluegill (Lepomis macrochirus): Final Report: Lab Project 

Number: 39728. Unpublished study prepared by ABC Labs., Inc. 194 p. 

TN 1075 McCann, J.A. 1977. Beltsville Animal Biology Lab Acute Rainbow trout 

test with 2% formulation

TN 1077 McCann, J.A. 1977. Beltsville Animal Biology Lab Acute Rainbow trout 

test with technical

TN 1082 McCann, J.A. 1977. Beltsville Animal Biology Lab Acute Rainbow trout 

test with 25%EC Formulation

TN 1086 McCann, J.A. 1977. Beltsville Animal Biology Lab Acute Bluegill test 

with technical

92135003 Gregg, B. (1990) Rhone-Poulenc Ag Company Phase 3 Summary of 

MRID 00068524 and Related MRIDs 00068525. Oxadiazon - Static 96-hr 

Toxicity Study of Rhodia Oxadiazon (Technical) in Bluegill Sunfish and 

Rainbow Trout: Project 7E-5605 and Project 7E-5604. Prepared by 

Cannon Laboratories, Inc. 26 p. 

72-2 Acute Toxicity to Freshwater Invertebrates

MRID Citation Reference

61810 Rhone-Poulenc Chemical Company (19??) Herbicides--

Toxicity of Oxa- diazon to Daphnia (~Daphnia pulex~): 

Addendum to Report R.P./ R.D./C.N.G. No. 18939. 

(Unpublished study received Apr 27, 1977 under 359-679; 

CDL:229610-A) 
27

66074 Roberts, S.; Parke, G.S.E.; Charles, S.J., III (1977) Report: 

Static 96-hour Toxicity Study of Oxadiazon Technical 97.2% in 

Daphnids: Laboratory No. 7E-6485. (Unpublished study 

received Jul 18, 1977 under 359-679; prepared by Cannon 

Laboratories, Inc., submitted by Rhone-Poulenc Chemical Co., 

Monmouth Junction, N.J.; CDL:230862-A) 

111808 or 

112623

Posner, S.; Jolly, E.; Grim, J. (1971) Acute LC50 96-hour 

(Static) of RP 17623 to Rainbow Trout (Salmo Gairdneri); 

Crayfish (Oronectes) and Brown Bullheads (Ameiurus 

Nebulous): Experi- mental Reference No. 49-269A. 

(Unpublished study received Aug 23, 1972 under 359-658; 

prepared by Biometric Testing, Inc., submitted by RhonePoulenc, Inc., Monmouth Junction, NJ; CDL: 003179-D) 

CDL:091824-E)

111809 Jolly, E.; Grim, J. (1971) RP17623 (Ronstar): Subacute 

Toxicity and Residues in Crayfish (Oronectes): Biological 

Phase (Static): Experimental Reference No. F-269. 

(Unpublished study received Aug 23, 1972 under 359-658; 

prepared by Biometric Testing, Inc., submitted by RhonePoulenc, Inc., Monmouth Junction, NJ; CDL: 003179-E) 

111842 Roberts, S.; Parke, G. (1977) Static 48-hour LC50 of Ronstar in 

Daphnids: Laboratory No. 7E-7354. (Unpublished study 

received Apr 24, 1978 under 359-675; prepared by Cannon 

Laboratories, Inc., submitted by Rhodia, Inc., Monmouth 

Junction, NJ; CDL: 097047-B) 

42331801 Blasberg, J.; Bowman, J. (1992) Acute Toxicity of Oxadiazon 

to Daphnia magna under Flow-through Conditions: Amended

Final Report: Lab Project Number: 39730. Unpublished study 

prepared by ABC Labs, Inc. 254 p. 

92135004 Gregg, B. (1990) Rhone-Poulenc Ag Company Phase 3 

Summary of MRID 00066074. Oxadiazon--Static 96-hr 

Toxicity Study--Daphnids: Project 7E-6485. Prepared by 

Cannon Laboratories, Inc. 25 p. 

36620 or 

113944 

Rhodia, Incorporated (1971) Report of the Analysis of the 

Crayfish and Water for RP 17623 Samples Obtained in the 

Study Titled: RP 17623 (Ronstar) Subacute Toxicity and 

Residues in Crayfish (Oronectes) Biological Phase (Static). 

(Unpublished study re- ceived Oct 14, 1972 under 2F1269; 

CDL:092170-I) CDL:091824-G)

113943 Jolly, E.; Grim, J. (1971) RP17623 (Ronstar): Subacute 

Toxicity and Residues in Crayfish (Oronectes) Biological Phase 

(Static): Experimental Reference No. F-269. (Unpublished 

study received Oct 14, 1972 under 2F1269; prepared by 
28

Biometric Testing, Inc., submitted by Rhodia, Inc., New 

Brunswick, NJ; CDL:091824-F) 

48561 Ambrosi, D.; Desmoras, J.; Savary, ? (1976) Herbicides: 

Toxicity of Oxadiazon to Daphnia (~Daphnia pulex~): 

R.P./R.D./ C.N.G. No. 18 939. (Translation; unpublished study 

received Jan 28, 1977 under 359-659; prepared by RhonePoulenc Industries, France, submitted by Rhone-Poulenc 

Chemical Co., Monmouth Junc- tion, N.J.; CDL:227657-C) 

TN 1087 McCann, J.A. 1977. Beltsville Animal Biology Lab Acute 

daphnia test with technical

72-3 Acute Toxicity to Estuarine/Marine Organisms

MRID Citation Reference

42570301 Dionne, E. (1992) Oxadiazon Technical--Acute Toxicity to Eastern 

Oyster (Crassostrea virginica) under Flow-through Conditions: Final 

Report: Lab Project Number: 92-7-4329: 10566. 0392.6238.504. 

Unpublished study prepared by Springborn Labs, Inc. 63 p. 

42615801 Machado, M. (1992) Oxadiazon Technical--Acute Toxicity to Sheepshead 

Minnow (Cyprinodon variegatus) under Flow-through Conditions: Final 

Report: Lab Project Number: 92-8-4383 10566.0392.6237.505. 

Unpublished study prepared by Springborn Labs, Inc. 66 p. 

42615802 Machado, M. (1992) Oxadiazon Technical--Acute Toxicity to Mysid 

Shrimp (Mysidopsis bahia) under Flow-through Conditions: Final Report: 

Lab Project Number: 92-7-4348: 10566.0392.6236.515. Unpublished 

study prepared by Springborn Labs, Inc. 65 p. 

72-4 Fish Early Life Stage/Aquatic Invertebrate Life Cycle Study

MRID Citation Reference

41784301 Blakemore, G.; Burgess, D. (1991) Chronic Toxicity of Oxadiazon 

Technical to Daphnia magna under Flow-thru Conditions: Final Report: 

Lab Project Number: 38369. Unpublished study prepared by Analytical 

Bio-Chemistry Labs., Inc. 349 p. 

41811601 Rhodes, J.; McAllister, W.; Leak, T. (1991) Early Life-stage Toxi- city of 

?carbon 14|-Oxadiazon Technical to the Rainbow Trout (Oncorhynchus 

mykiss) Under Flow-through Conditions: Final Report: Lab Project 

Number: 38370. Unpublished study prepared by ABC Laboratories, Inc. 

129 p. 
29

42921601 Rhodes, J. (1993) Early Life-Stage Toxicity of Oxadiazon Technical to 

the Fathead Minnow (Pimephales promelas) Under Flow-Through 

Conditions: Lab Project Number: 40024. Unpublished study prepared by 

ABC Labs. Inc., Environmental Toxicology. 432 p. 

46473304 Lima, W. (2004) Oxadiazon Technical - Life-Cycle Toxicity Test with 

Mysids (Americamysis bahia). Project Number: EBOAX014, 

13798/6146, 040103/FIFRA/MYSID/LC. Unpublished study prepared by 

Springborn Smithers Laboratories. 86 p.

46473301 Chalmers, A. (2005) Rationale for Waiver Requests for Three Aquatic 

Studies with Oxadiazon: 850.1400 Fish Early Life-Stage Toxicity Test, 

Aquatic Phototoxicity Study, Aquatic Sediment Testing (Chronic). 

Unpublished study prepared by Bayer CropScience LP. 8 p.

122-1 Seed Germination/Seedline Emergence and Vegetable Vigor

MRID Citation Reference

46676501 Christ, M.; Lam, C. (2005) Tier I Seedling Emergence and Vegetative 

Vigor Nontarget Toxicity Study. Project Number: 2011154, Y0455001, 

Y0455002. Unpublished study prepared by Bayer Environmental Science. 

47 p.

122-2 Aquatic plant growth

MRID Citation Reference

42659001 Mihaich, E. (1993) Response to EPA Review of Oxadiazon Anabaena 

flos-aquae Study (MRID 41610104) and Selenastrum caprocornutum (sic) 

Study (MRID 41610108): Lab Project No. NS/EMM-93-03. Unpublished 

study prepared by Rhone-Poulenc Ag Co. and Springborn Labs., Inc. 10 

p.

123-1 Seed germination/seedling emergence and vegetative vigor

MRID Citation Reference

41898001 Hoberg, J. (1991) Oxadiazon Technical--Determination of Effects on 

Seed Germination, Seedling Emergence and Vegetative Vigor of Ten 

Plant Species: Final Report: Lab Project Number: 90-11-3547: 10566-

0790-6165-610. Unpublished study prepared by Springborn 

Laboratories, Inc. 164 p. 
30

46676502 Christ, M.; Lam, C. (2005) Tier II Seedling Emergence: Nontarget 

Phytotoxicity Study Using Ronstar WP50. Project Number: 201246, 

EBOAX011. Unpublished study prepared by Bayer CropScience LP. 57 

p.

46676503 Christ, M.; Nuessle, C. (2005) Tier II Vegetative Vigor: Nontarget 

Phytotoxicity Study Using Ronstar WP50. Project Number: 201247, 

EBOAX013. Unpublished study prepared by Bayer CropScience LP. 69 

p.

123-2 Aquatic plant growth

MRID Citation Reference

41610105 Giddings, J. (1990) Oxadiazon Technical-Toxicity to the Marine Dia- tom 

Skeletonema costatum: Lab Project Number: 90-7-3384: 10566- 1089-

6137-450. Unpublished study prepared by Springborn Labora- tories, Inc. 

55 p. 

41610106 Giddings, J. (1990) Oxadiazinon Technical-Toxicity to the Fresh- water 

Diatom Navicula pelliculosa: Lab Project Number: 90-8-3423; 10566-

1089-6137-440. Unpublished study prepared by Springborn Laboratories, 

Inc. 52 p. 

41610107 Giddings, J. (1990) Oxadiazon Technical-Toxicity to the Duckweed 

Lemma gibba G3: Final Report: Lab Project Number: 90-7-3389; 

10566.1089.6137.410. Unpublished study prepared by Springborn 

Laboratories, Inc. 48 p. 

41610108 Giddings, J. (1990) Oxadiazon Technical-Toxicity to the Freshwater Green 

Alga Selenastrum capricornutum: Amended Report: Lab Pro- ject Number: 

90-8-3422; 10566.1089.6137.437. Unpublished study prepared by 

Springborn Laboratories, Inc. 52 p. 

141-1 Honey bee acute contact

MRID Citation Reference

42468301 Beevers, M. (1992) Acute Contact Toxicity of Oxadiazon Technical to 

Honey Bees (Apis mellifera L.): Lab Project Number: CAR 160-92. 

Unpublished study prepared by California Agricultural Research, Inc. 14 p. 

850.1735 Whole sediment: acute freshwater invertebrates
31

MRID Citation Reference

46473303 Putt, A. (2004) Oxadiazon - Toxicity to Freshwater Amphipods (Hyalella 

azteca) During a 10-Day Sediment Exposure. Project Number: 

EBOAY002, 13798/6152, 102803/10/DAY/HYALELLA. Unpublished 

study prepared by Springborn Smithers Laboratories. 64 p.

46487301 Putt, A. (2004) Oxadiazon - Toxicity to Midge (Chironomus tentans) 

During a 10-Day Sediment Exposure. Project Number: EBOAY/003, 

13798/6151. Unpublished study prepared by Springborn Smithers 

Laboratories. 69 p.

c. Other References

Rahman. M. M., Kim T-H, Kwon G-S, Yang J.E, Park M, and Kim J-E. 2009. Removal Efficiency 

of the Herbicide Oxadiazon in Treatment Processes for Drinking Water. J. Korean Soc. 

Appl. Biol. Chem.; 52(3); 252-257

USEPA. 2001. EFED Risk Assessment for the Reregistration Eligibility Decision of Oxadiazon. 

DP Barcode D277968.

USEPA. 1995. Data Reviews for Oxadiazon. D166982.
32

Appendix X. SIP output

Table 1. Inputs

Parameter Value

Chemical name Oxadiazon

Solubility (in water at 25oC; mg/L) 1

Mammalian LD50 (mg/kg-bw) 5000

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian 

species

Mammalian NOAEL (mg/kg-bw) 12

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian 

species

Avian LD50 (mg/kg-bw) 2150

Avian test species northern bobwhite quail

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 1000

Bobwhite quail NOAEC (mg/kg-diet) 500

NOAEC (mg/kg-diet) for other bird species 0

Body weight (g) of other avian species

NOAEC (mg/kg-diet) for 2nd other bird 

species 0

Body weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 0.1720 0.1720

Adjusted toxicity value (mg/kg-bw) 3845.8028 9.2299

Ratio of exposure to toxicity 0.0000 0.0186

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Table 3. Avian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 0.8100 0.8100

Adjusted toxicity value (mg/kg-bw) 1548.9235 49.6126

Ratio of exposure to acute toxicity 0.0005 0.0163

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for birds

Drinking water exposure 

alone is NOT a potential 

concern for birds

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. 

Therefore, when aggregated with other routes (i.e., diet, inhalation, dermal), pesticide exposure through 

drinking water may contribute to a total exposure that has potential for effects to non-target animals.
33

Appendix X. STIR Output for 

Oxadiazon Welcome to the 

EFED 

Screening Tool for Inhalation Risk

This tool is designed to provide the risk assessor with a rapid method for determining the potential

significance of the inhalation exposure route to birds and mammals in a risk assessment.

Input

Application and Chemical Information

Enter Chemical Name Oxadiazon

Enter Chemical Use Turf

Is the Application a Spray? (enter y or n) y

If Spray What Type (enter ground or air) ground

Enter Chemical Molecular Weight (g/mole) 345.2

Enter Chemical Vapor Pressure (mmHg) 1.00E-06

Enter Application Rate (lb a.i./acre) 4

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 2150

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 0.178

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 5000

Enter Lowest Rat Inhalation LC50 (mg/L) 1.94

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 1.86E-02

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.34E-03

Adjusted Inhalation LD50 4.65E+00

Ratio of Vapor Dose to Adjusted Inhalation LD50 5.02E-04 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 4.23E-01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 9.09E-02 Exposure not Likely Significant

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 1.86E-02
34

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.94E-03

Adjusted Inhalation LD50 1.15E+02

Ratio of Vapor Dose to Adjusted Inhalation LD50 2.54E-05 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 5.31E-01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 4.60E-03 Exposure not Likely Significant
35

APPENDIX C. Study Justification Tables

Oxadiazon is not to be applied on residential turf (by either home owners or commercial 

applicators) but could be applied to residential ornamental ground cover and shrub beds only by 

professional applicators. It could also be applied by professional applicators to turf in 

apartment/condominium complexes, parks, athletic fields, playground, and cemeteries and on golf 

courses (predominant use). In addition, oxadiazon is used on sod farms and on conifer 

plantations/nurseries, and other nurseries (containerized or non-containerized nursery plants). It 

can also be applied to non-agricultural areas, right-of-way, and landscape areas (i.e., industrial 

sites, ornamental, roadside plantings, woody, ornamental shrubs, vines and trees and herbaceous 

ornamentals). Oxadiazon use sites are classified as non-food sites (i.e., primarily golf course 

fairways, outdoor use, roadsides and nurseries).

Guideline Number: Special Study

Study Title: Adult Honey Bee Chronic Oral Toxicity

Rationale for Requiring the Data

This study is needed for the assessment to evaluate risks to honey bees if the registered uses of 

oxadiazon will result in adverse effects to honey bees or other insect pollinators. Registered use 

sites of oxadiazon include: ornamental ground cover, turf in parks, field, playground, cemeteries 

and golf courses, sod farms, conifer nurseries, and landscapes. Therefore, oxadiazon residues 

may result in exposure to foraging bees. Residues can in turn be brought back to bee colonies 

where in-hive bees including young adult and developing brood (i.e., eggs, larvae and pupae) 

may be exposed. Therefore, exposure at all bee life stages would be expected and may extend for 

chronic exposures.

EPA now requires this study for all use sites where potential exposure to pollinators may occur

(2014). Registrants may request a waiver of the study if use practices significantly restrict 

exposure of the pesticide to bees.

Although EPA has not developed a guideline for this study and OECD has yet to finalize test 

guidance for chronic studies, efforts are currently underway to develop standardized guidelines 

for assessing effects from chronic (10-day) exposures to adult bees in the laboratory. At this 

time, EFED is asking that a protocol for the study be submitted beforehand to increase the 

likelihood of an acceptable study submission.

Practical Utility of the Data

How will the data be used and how could the data impact the Agency’s future decisionmaking? 

The 10-day toxicity study with young adult bees provides no-observed adverse effect level 

(NOAEL) and lowest-observed adverse effect level (LOAEL) for assessing potential chronic 

effects. Data obtained from this study will be used in estimating chronic risk to individual adult 

bees. Risk estimates based on these data will be considered along with other lines of evidence to 

determine whether higher-tier studies are needed at the whole colony level.
36

Guideline Number: Special Study

Study Title: Adult Honey Bee Chronic Oral Toxicity

Rationale for Requiring the Data

These data are needed for the registration review risk assessment and for future endangered species 

assessments. The data would allow the Agency better characterize the potential for risk to insects 

(including beneficial pollinators) from the use of oxadiazon. These data will help the Agency 

determine whether any mitigations are needed. If the registration review and any future 

endangered species risk assessments are performed without these data, the Agency would have to 

assume that oxadiazon "may affect" insects, including bees and beneficial pollinators, directly (and 

endangered species from other taxa indirectly), and uses of oxadiazon might need to be restricted 

in areas where pollinators could be exposed. 

Guideline Number: Non-Guideline

Study Title: Larval Honey Bee Acute and Chronic Oral Toxicity

Rationale for Requiring the Data

This study is needed for the assessment to evaluate risks to honey bees if the registered uses of 

oxadiazon will result in adverse effects to honey bees or other insect pollinators. Registered use 

sites of oxadiazon include: ornamental ground cover, turf in parks, field, playground, cemeteries 

and golf courses, sod farms, conifer nurseries, and landscapes. Therefore, oxadiazon residues 

may result in exposure to foraging bees. Residues can in turn be brought back to bee colonies 

where in-hive bees including young adult and developing brood (i.e., eggs, larvae and pupae) 

may be exposed. Therefore, exposure at all bee life stages would be expected and may extend for 

chronic exposures.

EPA now requires this study for all use sites where potential exposure to pollinators may 

occur. Registrants may request a waiver of the study if use practices significantly restrict 

exposure of the pesticide to bees.

Although EPA has not developed a guideline for this study, the 21-day larval toxicity study 

currently under development by OECD provides both acute and chronic oral toxicity data on 

developing bee brood and (when this guidance is finalized) may be used to satisfy the 

requirement for both acute and chronic oral toxicity to honey bee larvae. Registrant may submit 

a separate acute (single dose) larval toxicity study following OECD TG237 as well as the 21-day 

repeat dose chronic toxicity study.

Practical Utility of the Data

How will the data be used and how could the data impact the Agency’s future decisionmaking? 

The 21-day larval toxicity study under development by OECD provides both acute and chronic 

toxicity data on developing bee brood and will yield a median lethal dose (LD50) for assessing 

acute toxicity during the early part of the study as well as a 21-day no-observed adverse effect level 

(NOAEL) and lowest-observed adverse effect level (LOAEL) for assessing chronic 

effects. Effects on survival and development (adult bee emergence) from repeat exposures to the 

active ingredient will be used in estimating chronic risk to individual brood. Risk estimates based 
37

Guideline Number: Non-Guideline

Study Title: Larval Honey Bee Acute and Chronic Oral Toxicity

Rationale for Requiring the Data

on these data will be considered along with other lines of evidence to determine whether highertier studies are needed at the whole colony level.

These data are needed for the registration review risk assessment and for future endangered species 

assessments. The data would allow the Agency better characterize the potential for risk to insects 

(including beneficial pollinators) from the use of oxadiazon. These data will help the Agency 

determine whether any mitigations are needed. If the registration review and any future 

endangered species risk assessments are performed without these data, the Agency would have to 

assume that oxadiazon "may affect" insects, including bees and beneficial pollinators, directly (and 

endangered species from other taxa indirectly), and uses of oxadiazon might need to be restricted 

in areas where pollinators could be exposed.