UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

Drinking Water Assessment for the Proposed New Use of Sedaxane as a Seed 

Treatment on Corn, Sorghum, Dried Shelled Pea and Bean (Subgroup 6C; except 

soybean), Rapeseed (subgroup 20A), and Potato PC Code: 129223; DP 

Barcodes: 405391 and 407956 

Rochelle F. H. Bohaty Ph.D., Chemist /' // !)_ 

James Hetrick Ph.D., Senior Science Adviso~ (A.~~~ 3/t e' /t 3 

Environmental Risk Branch 3 

Environmental Fate and Effects Divi~ion (7507P) 

Dana Spatz, Branch Ch~ Rosanna Louie-Juzwiak, Risk Assessment Proces 

Environmental Risk Branch 3 

Environmental Fate and Effects Division (7507P) 

Heather Garvie, Risk Manager Reviewer 

Cynthia Giles-Parker, Chief 

Fungicide Branch 

Registration Division (7505P) 

EXECUTIVE SUMMARY 

This memorandum provides a drinking water assessment (DW A) for the proposed registration of 

sedaxane as a seed treatment on corn, sorghum, dried shelled pea and bean (Subgroup 6C; except 

soybean), rapeseed (subgroup 20A), and potato to protect against certain soil-borne and seedborne diseases. 

Sedaxane was recently registered for use as a seed treatment for small grain cereals (barley, 

wheat, oats, rye and triticale), soybean and canola. The proposed new uses are on the label for 

Sedaxane 500FS/VibranceTM (Al6148C). 

This DWA takes into account sedaxane (SYN524464), a mixture of two isomers separately 

numbered SYN508210 (trans-isomer of sedaxane) and SYN508211 (cis-isomer of sedaxane), 

and two known environmental transformation products of equal toxicological concern, 

CDCD668094 andCDCD668095. These two chemicals were only observed in aquatic photolysis 

studies; therefore, these residues were only considered as part of the surface water modeling. 

Sedaxane, as well as its transformation products of concern, are referred to collectively as total 

toxic sedaxane residues. This DWA includes estimated drinking water concentrations (EDWCs) 

' 
2

based on Tier I surface water and Tier I groundwater model simulations for all the proposed 

sedaxane uses. 

Seed treatment use of sedaxane on potato is expected to result in the highest exposure scenario 

(Table 1). Peak and post breakthrough PRZM-GW EDWCs in groundwater resulting from the 

proposed sedaxane uses are not expected to be > 22.4 μg/L and 19.3 μg/L, respectively. For the 

proposed potato use, an application made every other year was investigated. The Wisconsin 

Central Sands scenario resulted in a peak PRZM-GW EDWC of 15.1 ppb and a post 

breakthrough average of 13 ppb. The next highest exposure was with the North Carolina Coastal 

scenario, which resulted in a peak PRZM-GW EDWC of 8.09 ppb and a post breakthrough 

average of 6.95 ppb. These EDWCs are higher than those estimated in the new chemical 

drinking water assessment.1

 These groundwater EDWCs are expected to be conservative based 

on the assumption that all the sedaxane applied to a seed is available for leaching. 

Table 1. Results Summary: EDWCs for Total Toxic Sedaxane Residues For the Proposed New Use on Potato 

at 0.1 lbs ai/A. 

Assessment 

Tier/ 

Model 

Crop 

Sedaxane Total Toxic Sedaxane Residues 

Acute 

Peak EDWC 

μg/L (ppb)

Chronic/Cancer 

Yearly Mean μg/L 

(ppb) 

Acute 

Peak EDWC 

μg/L (ppb)

Chronic/Cancer 

Yearly Mean μg/L 

(ppb) 

Tier I/ 

FIRST* Potato 4.1 1.2 

Tier I/ 

SCI-GROW Potato 0.1 0.1 Assumed sedaxane application every 

Tier I/ year. 

PRZM-GW Potato 22.0 19.3** 

Tier I/ 

PRZM-GW Potato 

15.1 13** 

Assumed sedaxane application every 

other year. 

The two highest EDWCs were for 

Wisconsin Central Sands and the NC 

Coastal Plain scenarios, respectively. 

8.09 6.95** 

* Surface water EDWCs have been corrected for a percent cropped area (PCA) of 0.91. 

** Value is not a yearly mean but the mean concentration following breakthrough (time to breakthrough is 1870 

days; other simulations resulted in breakthrough < 1 year after initial application). 

The PRZM-GW estimates are higher than those calculated using SCI-GROW and FIRST. 

Therefore, PRZM-GW EDWCs are the recommended EDWCs for use in the human health risk 

assessment. Depending on the scenario simulated, the EDWCs range from 3.6 μg/L to 22.0 μg/L 

and 3.5 to 19.3 μg/L for peak and post breakthrough concentrations, respectively. Model outputs 

indicate that the time to breakthrough (the time it takes for sedaxane residues to reach the 

underground aquifer) ranges from 3811-10,389 days depending on the scenario. With the 

exception of the potato application made once per year, this analysis is based on 30 years of 

sedaxane use as a seed treatment with two plantings per year. 

 

1 U.S. Environmental Protection Agency, Bohaty. R. Drinking Water Assessment for the Registration of Sedaxane,

Dec. 21, 2011, PC Code: 129223; DP Barcode: 382528, 389464
3

Based on HED’s estimated level of concern, limiting sedaxane use in areas known to be 

vulnerable to groundwater contamination is reasonable given the range of EDWCs calculated 

using the various scenarios in PRZM-GW modeling. Specifically for potatoes, some of the less 

vulnerable of the standard scenarios results in peak and post breakthrough concentrations of 3.6 

μg/L and 3.5 μg/L, respectively. Additional evaluation (Tier II) of the percent organic carbon 

content in the top 20 cm of the soil for four different scenarios indicate that groundwater EDWCs 

will likely be below HED’s level of concern if the organic carbon content of the soil is above 

2%. Another evaluation was conducted to assess the impact of sedaxane applications every other 

year. This analysis indicates that only the Wisconsin Central Plain scenario predicts average 

breakthrough sedaxane concentrations greater than 10 μg/L. 

 

Label Considerations: 

On page one of the proposed VibranceTM label (EPA Reg. No. 100-1374) for potato, a list of use 

sites is presented; however, potato is not included. The sedaxane application rate for potato is to 

treat 0.08 fluid oz product/100 lbs of seed (2.5 grams ai/100 kg seed). These application rates 

are required to control Rhizoctonia solani and Helminthosporium solani. 

On page eight of the proposed VibranceTM label (EPA Reg. No. 100-1374) for corn, sorghum, 

dried shelled pea and bean (Subgroup 6C; except soybean), and rapeseed (subgroup 20A) the use 

rate mg a.i./seed has been changed from the currently registered label. This appears to have been 

done to make the use rates consistent; however, the update should be 0.0041-0.0076 mg a.i./seed 

to correspond with 0.08-0.16 oz product/100 lb seed. 
4

PROBLEM FORMULATION 

Sedaxane (CAS Name: N-[2-[1,1′-bicyclopropyl]-2-ylphenyl]-3-(difluoromethyl)-1-methyl-1Hpyrazole-4-carboxamide CAS No.: 874967-67-6; company code SYN524464; structure shown in 

Figure 1) is a mixture of two diastereoisomers, designated trans- and cis-isomers. These isomers 

are separately numbered; SYN508210 (trans-isomer of sedaxane) and SYN508211 (cis-isomer 

of sedaxane). The proposed specification for sedaxane technical product is 85% by weight 

SYN508210 (trans-isomer) and 13% by weight SYN508211 (cis-isomer). Sedaxane belongs to 

the chemical class of pyrazole-carboxamides in the succinate-dehydrogenase inhibitor (SDHI) 

class of fungicides, which inhibits complex II respiration. 

NH

O

N N

HF2C

CH3

H

H

NH

O

N N

HF2C

CH3

H

H

Trans-isomers 

SYN508210 

NH

O

N N

HF2C

CH3

H

H

NH

O

N N

HF2C

CH3

H

H

Cis-isomers 

SYN508211 

Figure 1. Chemical Structure of Sedaxane 

This DWA uses modeling to estimate groundwater and surface water concentration of sedaxane 

and its environmental transformation products resulting from the uses of sedaxane on sites that 

are vulnerable to pesticide contamination. This analysis provides estimated exposure 

concentrations that may occur in drinking water for the human health dietary risk assessment. 

ANALYSIS 

Use Characterization 

Sedaxane was recently registered in the United States as a seed treatment for small grain cereals 

(barley, wheat, oats, rye and triticale), soybean and canola to protect against certain soil-borne 

and seed-borne diseases. Target fungal pathogens for sedaxane include: Fusarium Spp. Pythium 

spp., Septoria, smut (Ustilago tritici), stink bunt (Tilletia caries), loose smut (Ustilago nuda), 

head smut (Sphacelotheca reiliana) and Rhizoctonia spp. In addition to the technical product, 

three end use products were registered. Two of the proposed end use products contain a 
5

combination of multiple pesticide active ingredients, including difenoconazole, mefenoxam and 

thiamethoxam, as described in Table 2. These uses are considered widespread. 

Table 2. Sedaxane End Use Product Summary for the United States 

Formulation 

Sedaxane 500FS 

A16148C 

VibranceTM

A16874F A17511B 

lb a.i./gal 

product percent lb a.i./gal product percent lb a.i./gal product percent 

Active 

Ingredients 

Sedaxane 4.3 45.45% 0.115 1.22% 0.067 0.72% 

Difenoconazole None 0.552 5.86% 0.308 3.34% 

Mefenoxam None 0.138 1.46% 0.079 3.34% 

Thiamethoxam None None 0.256 2.78% 

Currently Registered Uses 

Canola 

Cereals Cereals Cereals 

Soybean 

Proposed New Uses 

corn 

None None 

dried shelled pea and 

bean (subgroup 6C; 

except soybean) 

potato 

rapeseed (subgroup 20A 

including canola) 

Sedaxane is applied as a water-based slurry to seeds which are then planted according to planting 

practices employed for the respective crops. The current sedaxane application rates for barley, 

canola, oats, rye, soybean, triticale and wheat are provided in Table 3. The number of 

applications of sedaxane that can be applied per season is limited to two. This permits growers to 

reapply sedaxane treated seeds in the event of crop failure. This per season application rate 

restriction does not restrict the number of sedaxane applications that may occur within a calendar 

year. Based on the currently registered uses there are a number of potential crop rotations 

including barley-wheat, soybean-rye and soybean-wheat (list may not be exhaustive). Therefore, 

it is possible; however, unlikely that four applications of sedaxane could be made based on a 

crop rotation both resulting in crop failure once. Due to this concern the registrant has agreed to 

update currently labels to limit sedaxane applications to two per year.2

 This permits initial 

planting of sedaxane treated seeds followed by either replanting of treated seeds in the event of 

crop failure or crop rotation. 

The registrant has proposed the use of sedaxane as a seed treatment on corn, sorghum, dried 

shelled pea and bean (Subgroup 6C; except soybean), rapeseed (subgroup 20A), and potato. 

The proposed new uses are only included on the label for Sedaxane 500FS/VibranceTM

(A16148C)—the single active ingredient formulation. 

The proposed application rates for corn, sorghum, dried shelled pea and bean (subgroup 6C; 

except soybean), rapeseed (subgroup 20A), and potato are provide in Table 4. The per year 

application rate restriction is also two; except for potatoes where a yearly sedaxane application 

rate is restricted to one application. 

 

2 Phone conference with Syngenta on January 16, 2013. 
Table 3. Currently Registered Sedaxane Application Rates 

Crop 

Residential 

Agricultural 

Forestry 

Maximum 

Application 

Rate 

lb a.i. 

/100 lb of 

seed 

Maximum 

Seeding 

Ratea 

lb seed /A 

Maximum Single 

Application Rate 

lb a.i./A 

(kg a.i./ha) 

Maximum Total 

Application Rate 

Maximum Number 

of Applications

PHI (days)c 

Per Year lb a.i./A Per CCb lb a.i./A Per Year lb a.i./A Per CCb lb a.i./A 

barley √ 0.005 98 0.0053 (0.0045) 0.0106 0.0106 2e 2 NS 

canola √ 0.005 5 0.0003 (0.0003) 0.006 0.006 2e 2 NS 

oats √ 0.005 87 0.0047 (0.0042) 0.0094 0.0094 2e 2 NS 

rye √ 0.005 109 0.0059 (0.0053) 0.0118 0.0118 2e 2 NS 

soybean √ 0.005 167 0.0084 (0.0075) 0.0168 0.0168 2e 2 NS 

triticale √ 0.005 109 0.0059 (0.0053) 0.0118 0.0118 2e 2 NS 

wheat √ 0.005 156 0.0084 (0.0075) 0.0168 0.0168 2e 2 NS 

a. The maximum seeding rate was developed based on data provided by BEAD—J. Becker; S. Ratnayake. Acres Planted per Day and Se

the United States, March 24, 2011. 

b. Reported as per crop cycle or per season 

c. PHI – Preharvest interval; REI – reentry interval; MRI – Minimum retreatment interval 

d. The minimum planting depth was taken from the USDA’s National Information System for the Regional IPM Centers crop profiles. Br

crop profile the value was taken from. 

e. The number of applications of sedaxane that can be applied per season is limited to two. The registrant plans to update labels to limit th

applications to two per year. 

NS= not specified 
7

Table 4. Proposed Sedaxane Application Rates 

Crop 

Residential 

Agricultural 

Forestry 

Maximum 

Application 

Rate 

lb a.i. 

/100 lb of 

seed 

Maximum 

Seeding 

Ratea 

lb seed /A 

Maximum Single 

Application Rate 

lb a.i./A 

(kg a.i./ha) 

Maximum Total 

Application Rate 

Maximum Number 

of Applications

PHI (days)c 

Per Year lb a.i./A Per CCb lb a.i./A Per Year lb a.i./A Per CCb lb a.i./A 

corn √ 0.04 33e 0.013 (0.015) 0.026 0.026 2 2 NS N

dried shelled 

pea and bean 

(subgroup 

6C; except 

soybean) 

√ 0.005 42f 0.002 (0.002) 0.004 0.004 2 2 NS N

potato √ 0.003 2875g 0.1 0.1 0.1 1 1 NS N

rapeseed 

(subgroup 

20A 

including 

canola) 

√ 0.005 5 0.0003 (0.0003) 0.006 0.006 2 2 NS N

sorghum √ 0.005 9 0.0046 (0.0052) 0.0092 0.0092 2 2 NS N

a. The maximum seeding rate was developed based on data provided by BEAD—J. Becker; S. Ratnayake. Acres Planted per Day and See

the United States, March 24, 2011. 

b. Reported as per crop cycle or per season on label(s). 

c. PHI – Preharvest interval; REI – reentry interval; MRI – Minimum retreatment interval 

d. The minimum planting depth was taken from the USDA’s National Information System for the Regional IPM Centers crop profiles. Br

crop profile the value was taken from. 

e. Sweet corn [59,739 seeds/A; 1,800 seeds/lb] 

f. Southern pea [139,392 seeds/A; 3,200 seeds/lb] 

g. Based on a maximum of 23,000 seeds planted per acre, weighing 2 ounces per seed (January 28, 2013 letter from National Potato Coun

h. Except canola 

NA = not applicable NS= not specified 
Fate and Transport Characterization

Environmental Fate Assessment 

Environmental transformation of sedaxane follows two pathways (see Figure 2). Laboratory data 

indicate that in the environment sedaxane is persistent. Sedaxane is only susceptible to 

degradation via aerobic soil metabolism. Laboratory half-life values for aerobic soil metabolism 

are 296-400 (soil) days based on single first order (SFO) kinetics; however, aerobic 

biodegradation of sedaxane in soil does not follow single first order kinetics (SFO). In general, 

sedaxane concentrations decrease over the first 100 days (approximate); however, after 100 days, 

sedaxane concentrations remain steady (approximately 50% of the applied radioactivity) through 

study termination (≥365 days). Additional kinetic analysis using Nth-Order Rate Model or 

Indeterminate Order Rate Equation (IORE) and Double First-Order in Parallel (DFOP) models 

resulted in representative half-lives >100 days (often >365 days).3

 A summary of the kinetic 

analysis for the aerobic soil metabolism (MRID 47473448) is provided in APPENDIX A while 

the results are summarized in Table 5. Sedaxane photolysis studies (laboratory half-life of 46 days 

for aqueous photolysis and 253 days for soil photolysis)4 also suggest sedaxane is persistence in 

the environment. Hydrolysis, anaerobic soil and aquatic transformation, and aerobic aquatic 

metabolism are not expected to contribute to the dissipation of sedaxane in the environment. 

Terrestrial field dissipation data (DT50 value 114-132 days) suggest sedaxane will persist in the 

environment consistent with laboratory metabolism and photolysis data. 

Trans- and cis- isomers of sedaxane show comparable degradation rates in soil; however, only a 

few submitted studies distinguish the two isomers. There is one aerobic soil metabolism study 

that contains both data for sedaxane degradation after direct soil application, as well as soil 

dissipation and transformation data following soil incorporation of sedaxane treated seeds. In 

addition, the registrant submitted several additional aerobic soil dissipation studies that explored 

the dissipation of sedaxane after planting of treated seeds. While seed treatment studies represent 

the intended use pattern and permit the identification of potential environmental transformation 

products, these studies do not permit the calculation of an aerobic soil metabolism rate (or 

corresponding half-life values), as other dissipation mechanisms may occur [i.e., plant uptake in 

roots or shoots (shoots were analyzed in the submitted studies; however, the roots were analyzed 

as part of the soil matrix), or chemical sorption to seed coat] which cannot be parsed out due to 

the study design. In addition, a large amount of unextracted residues further complicates the 

interpretation of the seed studies. The amount of unextracted residues increases throughout the 

study. Despite these complications, these aerobic dissipation/degradation studies suggest that 

metabolism of sedaxane in soil is faster [laboratory half-life values of 88-181 days (seed)] in the 

presence of germinating seed. This is supported by known literature that describes the influence 

of plant roots and germinating seeds on microbial activity in the rhizosphere. 

 

3 “Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media” Health Canada, U.S. 

Environmental Protection Agency, December 2011 

4 The photolysis half-lives were calculated based on the assumption that the average daily solar radiation is 

approximately 75% of the maximum intensity over a 12 hour period. This was taken into account in the comparison 

of the artificial light source and that of natural summer sunlight, conducted by the study authors. Because solar 

intensity of natural summer sunlight is likely not 100% during a 12 hour period, and because the sedaxane is 

proposed as a seed treatment and likely incorporated in the soil, the reviewers did not adjust the half-life values to 

represent 100% soil radiation over the 12 hour period. 
NH

O

N N

HF2C

CH3

NH

O

N N

HF2C

CH3

OH

NH2

O

N N

HF2C

CH3

NH

O

N N

HF2C

CH3

HO

O

NH

O

N N

H

HF2C

NH

O

N N

H

HF2C

OH

OH

O

N N

HF2C

CH3

OH

O

N N

H

HF2C

AM

AM AM

AM

AM

AM and P

AM

AM

AM and P

AM

CO2

AM AM and P

NH

O

N N

HF2C

CH3

HO

HO

P

O

N N

HF2C

C

Sedaxane

668094

210616

798670

667584 

728931

465008

Figure 2. Proposed Environmental Transformation Pathways for Sedaxane; Aerobic Metabolism (AM); Pcompany chemical codes have been shortened (letters have been removed) for brevity 

Major (>10%) transformation product Minor (<10%) transformation product 
Table 5. Chemical Properties and Environmental Fate Parameters of Sedaxane

Parameter Value Source/Classification (Comments)

Selected Physical/Chemical Parameters 

Molecular formula C18H19F2N3O Calculated 

using ChemDraw 

Molecular weight 331.37 g/mol Calculated 

using ChemDraw 

Vapor pressure 

20C 6.5 x 10-8 Pa 

1.3 x 10-9 atm 

25C 1.7 x 10-7 Pa 

1.3 x 10-9 mm Hg 

4.9 x 10-10 atm 

MRID 47473326 

Aqueous solubility at 25 C pH 

6.5 14 mg/L MRID 47473326 

Henry’s Law Constant 

calculated based on 14 g/m3

 

and 1.7 x 10-7 Pa at 25 C pH 

6.5 

4.0 x 10-6 Pa m3

/mol 

3.95 x 10-11 atm-m3

/mol 

MRID 47473326 

Calculated 

Log octanol-to-water partition 

coefficient (log KOW) 

at 25°C pH 6.67 

3.3 (KOW=2100) MRID 47473326 

Dissociation constant (pKa) None (pH 1-12) MRID 47473326 

Transformation Mechanisms1,2

Hydrolysis half-life 

at 20C and 50C 

No substantial degradation 

(pH 4, 7, and 9) 

MRID 47473318/ 

Acceptable 

Aqueous photolysis half-life at 

25C 46 days (identified parent only)

MRID 47473319/ 

Upgradable 

(up to 20% of the extracted residues 

were not identified) 

Soil photolysis half-life at 

20C 

253 days (average value)

213 days (pyrazole-label)

292 days (phenyl-label) 

MRID 47473446/ 

Supplemental 

MRID 47473447/ 

Supplemental 

Aerobic soil metabolism halflife at 20°C 

71days (SFO DT50) 

IORE DT50= 63 d; DT90= 400 d; 

tR IORE = 120 d (Gatrenacker loam) 

extracted parent from seed studies

*observed: DT50= 62-84 days DT 90=not observed 

MRID 47473444/ 

Supplemental 

(high application rate; seed treatment)

71 days (SFO DT50)3

IORE DT50= 44 d; DT90= 883 d; 

tR IORE = 266 d (Marsillargues silty clay) 

extracted parent from seed studies

*observed: DT50= 27-49 days DT 90=not observed 

MRID 47473445/ 

Supplemental 

(high application rate; seed treatment)
11

Parameter Value Source/Classification (Comments)

54 days (SFO DT50)3

SFO DT50= 64 d; DT90= 212 d; 

SFO tR = 64 d (Gartenacker loam)

extracted parent from seed studies

*observed: DT50= 27-81 days DT 90=123-365 

78 days (SFO DT50) 

SFO DT50= 78 d; DT90= 258 d; 

SFO tR = 78 d (Paperlacker loamy sand) 

extracted parent from seed studies

*observed: DT50= 27-81 days DT 90=not observed 

95 (SFO DT50) 

IORE DT50= 83 d; DT90= 8504 d; 

tR IORE = 2560 d (18 acres sandy clay) 

extracted parent from seed studies

*observed: DT50= 81-123 days DT 90=not observed 

87 days (SFO DT50) 

SFO DT50= 87 d; DT90= 288 d; 

SFO tR = 78 d Gartenacker loam) 

extracted parent from seed studies

*observed: DT50= 31-50 days DT 90=237-365 

MRID 47473448/ 

Supplemental 

[high application rate; high levels of 

unextracted residues; some studies 

were conducted on treated seeds; halflife values are calculated well beyond 

the study termination (up to 365 days)]

78 days (SFO DT50) 

IORE DT50= 34 d; DT90= 3763 d; 

tR IORE = 1130 d (California sand) 

extracted parent from seed studies

*observed: DT50= 31-81 days DT 90=not observed 

133 days [average of 105 (SFO DT50; phenyl) and 160 

(SFO DT50; pyrazole) days] 

DFOP DT50= 49 d; DT90= 894 d; 

DFOP Slow t1/2 = 373 d (North Dakota clay loam, 

pyrazole) 

extracted parent from seed studies

*observed: DT50= 80-122 days DT 90=not observed 

DFOP DT50= 42.4 d; DT90= 1094 d; 

DFOP Slow t1/2 = 544 d (North Dakota clay loam, phenyl)

extracted parent from seed studies

*observed: DT50= 31-50 days DT 90=not observed 

tR DFOP Slow t1/2 = 459 d (average of both labels) 

296 days (SFO DT50) 

DFOP DT50= 222 d; DT90= 3005 d; 

DFOP Slow t1/2 = 1200 d (Gartenacker loam) 

extracted parent from soil studies

*observed: DT50= 241-367 days DT 90=not observed 
12

Parameter Value Source/Classification (Comments)

373 days (SFO DT50)3

DFOP DT50= 423 d; DT90= 3376 d; 

DFOP Slow t1/2 = 1270 d (California sand) 

extracted parent from soil studies

*observed: DT50= 241->367 days DT 90=not observed 

400 days [average of 422 (SFO DT50;phenyl) and 377 

(SFO DT50;pyrazole) days] 

DFOP DT50= 98 d; DT90= >>365 d; 

DFOP Slow t1/2 = 1280 d (North Dakota clay loam, 

pyrazole) 

extracted parent from soil studies

*observed: DT50= 80-122 days DT 90=not observed 

DFOP DT50= 437 d; DT90= 2306 d; 

DFOP Slow t1/2 = 805 d (North Dakota clay loam, phenyl)

extracted parent from soil studies

*observed: DT50= 241-367 days DT 90=not observed 

tR DFOP Slow t1/2 = 1043 d (average of both labels) 

Aerobic aquatic metabolism 

half-life (20C) 

849 (river; SFO DT50) and 920 (pond; SFO DT50) days 

(whole system) 

MRID 47473468/ 

Supplemental 

[high application rate; >10% applied 

radioactivity present as unextracted 

residues; half-life values are calculated 

well beyond the study termination (360 

days)] 

Anaerobic soil metabolism 

half-life (20C) 

375 days 

**dissipation half-life of extracted parent from seed 

studies** 

MRID 47473443/ 

Supplemental 

[high application rate; >10% applied 

radioactivity present as unextracted 

residues; study was conducted on 

treated seeds; half-life values are 

calculated well beyond the study 

termination (123 days)] 

Anaerobic aquatic metabolism 

half-life (20C) 

4693 (river; SFO DT50) and 1970 (pond; SFO DT50) 

days (whole system) 

MRID 47473468/ 

Supplemental 

[high application rate; >10% applied 

radioactivity present as unextracted 

residues; half-life values are calculated 

well beyond the study termination (360 

days)] 

Mobility

Range of Freundlich soil-water 

partition coefficients (KF); 

1/n value; and 

Freundlich organic carbonnormalized coefficients (KFOC) 

6.7, 2.8, 16.3, 3.1, 2.0, and 12.9 L/kg-soil; 

0.81, 0.85, 0.90, 0.92, 0.87, and 0.83; and 

256.6, 268.5, 587.5, 584.9, 662.5, and 528.9 mL/gOC 

MRID 47473461/ 

Acceptable 
13

Parameter Value Source/Classification (Comments)

Field Dissipation 

Terrestrial field dissipation 

half-life 

Washington loamy sand: 31 days 

North Dakota sandy loam: 95 days 

California sandy loam: 31 days 

(seed studies) MRID 47473453/ 

Supplemental Washington loamy sand (in furrow 1.5 g/ha): 119 days 

Washington loamy sand (in furrow 91 g/ha): 132 days 

(soil studies) 

France silt loam: 119 days 

Italy silty clay loam: 131 days 

(seed studies) 

MRID 47473454/ 

Supplemental 

1. Reported half-life values used in this assessment were calculated using the draft NAFTA degradation kinetics3; Single 

First Order (SFO), Nth-Order Rate Model or Indeterminate Order Rate Equation Model (IORE), and Double First-Order 

in Parallel (DFOP); Representative half-life to be used to calculate model input value for IORE (tR IORE). Values reported 

in the new chemical assessment are shown in italic. At the time of the new chemical assessment half-life values provided 

were based on single first order (SFO) rates that may not have represented the “best” fit or representative kinetic model 

for degradation. Selected representative half-life values are shown in bold. 

2. Reported half-life values are for total extracted sedaxane residues [(SYN524464) or SYN508210 (trans-isomer of 

sedaxane) and SYN508211 (cis-isomer of sedaxane) combined]. 

3. Value was incorrectly reported in new chemical assessment. 

As mentioned above, a large amount of unextracted residues were observed in the soil studies 

(up to 42% of the applied radioactivity). At least twice as much unextracted radioactivity was 

observed in some of the seed treatment studies. It is unclear if these residues are non-extracted 

residues or bound residues, or in the case of the seed studies, residues sorbed to the seed coat or 

taken up by the roots (only shoots were examined separately from the soil). The extraction 

method employed in these studies was not verified for soil aged sedaxane residues or the 

transformation products. Furthermore, the uses of different extraction systems (different 

solvents) were not explored in the submitted studies. Therefore, it cannot be determined if 

another solvent system may have been better suited for these studies. 

The application rates used in all the submitted aerobic metabolism (seed and soil) studies are 

much higher (>15X) than the maximum seed treatment application rates for barley, canola, oat, 

rye, soybean, triticale, and wheat. For some chemicals, the application rate has been shown to 

alter the degradation rate. For example, high application rates may adversely impact the 

microbial activity within a soil decreasing metabolism and limiting the potential identification of 

transformation products. The microbial activity of the treated soils was also not reported in the 

submitted studies; therefore, it cannot be determined if the soil remained active throughout the 

study. 

Sedaxane is moderately mobile (mean KF of and mean 7.3 L/kg-soil; 1/n ranged from 0.81-0.92; 

mean KFOC of 481 L/kgOC; n=6). The leaching potential of sedaxane through soil is correlated 

with the organic carbon fraction of the soil. Based on the KOW (log KOW = 3.3) for sedaxane, it is 

not expected to bioaccumulate in aquatic and terrestrial organisms. A fish bioconcentration study 

confirms that accumulation does not occur. Sedaxane is nonvolatile and volatilization is not 

expected to be a route of dissipation for sedaxane in the environment.
14

Under conditions conductive to degradation (aerobic soil metabolism and photolysis), sedaxane 

has been shown to form five major transformation products, including carbon dioxide. The 

anticipated transformation pathway along with the chemical structures of each of the 

transformation products are presented in Figure 2. Two of the major transformation products, 

CDCD668094 and CDCD668095, retain both the pyrazole and the phenyl ring moieties. Both of 

these transformation products were observed in aquatic photolysis experiments conducted with 

natural water. Two other products, CSCD465008 and CSAA798670, are pyrazole ring amide 

cleavage products with and without the N-methyl group, respectively. Both of these 

transformation products were observed under aerobic soil conditions, while only CSAA798670 

was observed in photodegradation studies. Table 6 provides the maximum observed 

concentrations of each of the sedaxane transformation products identified in the submitted 

environmental fate studies. Several other minor degradation products were observed in the 

degradation studies including: CSCC210616, CSCD728931 and CSCD667584. A number of 

other minor transformation products were not identified in the submitted studies. 

Table 6. Maximum Observed Concentrations of Each of the Sedaxane Transformation Products 

Code Name/ 

Synonym Study Type MRID/ 

Classification 

Maximum Percent 

of Applied 

(interval) 

Major 

CSCD465008 

R958945 

Aerobic Soil 

Metabolism 

835.4100 

47473448/ 

Supplemental 

32.76 

(237 days; North Dakota seed) 

CSAA798670 

SYN449410 

NOA449410 

Aerobic Soil

Metabolism 

835.4100

47473448 

Supplemental 

15.37 

(367 days; California soil) 

Aqueous 

Photolysis 

835.2240 

47473319/ 

Upgradable 

25.69 

(28 days; natural water) 

CSCD668094 

Aqueous 

Photolysis 

835.2240 

47473319/ 

Upgradable 

16.66 

(28 days; natural water) 

CSCD668095 

Aqueous 

Photolysis 

835.2240 

47473319/ 

Upgradable 

18.09 

(28 days; natural water) 

Minor 

CSCD667584 

Aerobic Soil 

Metabolism 

835.4100 

47473445 

Supplemental 

4.9 

(81 days; Gartenacker seed) 

CSCC210616 

SYN508272 

Aerobic Soil 

Metabolism 

835.4100 

47473448/ 

Supplemental 

2.98 

(367 days; California soil)

Aqueous 

Photolysis 

835.2240

47473319/ 

Upgradable

5.42 

(28 days; natural water) 
15

Code Name/ 

Synonym Study Type MRID/ 

Classification 

Maximum Percent 

of Applied 

(interval) 

Major 

CSCD728931 

Aerobic Soil 

Metabolism 

835.4100 

47473448/ 

Supplemental 

7.91 

(241 days; California soil)

Aerobic soil metabolism data were provided for the sedaxane environmental transformation 

product CSCD465008, as well as adsorption/desorption data. These data indicate that 

CSCD465008 may be persistent to aerobic soil metabolism (half-life values range from 40 to 157 

days) in the environment. Mobility data suggest that CSCD465008 is highly mobile in soil (mean 

KFOC of 0.04 L/kg; 1/n ranged from 0.73-1.0; and mean KOC 2 mL/g; n=3). These data are 

summarized in Table 7. The registrant recently submitted two studies environmental fate studies 

(MRIDs 48836611 and 48836612). These studies are currently under review; however, the 

results of this review are not expected to have any impact on this assessment as the test materials 

used in these two studies are not considered as residues of concern by the Health Effects 

Division. 

Table 7. Chemical Properties and Environmental Fate Parameters of CSCD465008 an Environmental 

Transformation Product of Sedaxane 

Parameter Value Source/ Classification

Selected Physical/Chemical Parameters 

Molecular formula C5H4F2N2O2

Calculated 

using ChemDraw 

Molecular weight 162.10 g/mol Calculated 

using ChemDraw 

Vapor pressure 2.0 x 10-4 mmHg EpiWeb 4 (modified Grain 

method) 

Aqueous solubility at 25 C 20 g/L EpiWeb 4 (Wat Sol (v1.01 

est) 

Henry’s Law Constant 25 C 3.3 x 10-5 Pa m3

/mol 

2.0 x 10-10 atm-m3

/mol

Log octanol-to-water partition coefficient 

(log KOW) 0.30 EpiWeb 4 (KOWWIN v1.67 

estimate) 

Transformation Mechanisms1

Aerobic soil metabolism half-life at 20°C 

Marsillargues silty clay: 324 days 

Gartenacker loam: 266 days 

18 acres sandy clay: 168 

47473451/ 

Supplemental 

(high application rate) 
16

Parameter Value Source/ Classification

Marsillargues silty clay: 157 days 

Gartenacker loam: 99 days 

18 acres sandy clay: 40 

(extracted 5008 from soil studies) 

47473452/ 

Supplemental 

(high application rate) 

Mobility

Range of Freundlich soil-water partition 

coefficients (KF); 1/n value; Freundlich 

organic carbon-normalized coefficients 

(KFOC) 

0.013, 0.02, and 0.10 L/kg-soil; 

0.73, 0.96, and 1.0; 

0.55, 1.89, and 3.59 mL/gOC 

47473463/ 

Supplemental 

1. The half-life values provided are based on single first order (SFO) rates and may not represent the “best” 

fit kinetic model for degradation. The aerobic soil metabolism of sedaxane does not follow single first 

order kinetics in the submitted studies. IORE and DFOP half-life values were also calculated following 

the draft NAFTA guidance: Guidance for Evaluating and Calculating Degradation Kinetics in 

Environmental Media (see Appendix A). 

Conceptual Model 

Possible routes of dissipation of pesticides including sedaxane and its environmental 

transformation products are illustrated in Figure 3. While sedaxane is a seed treatment with 

relatively low application rates (maximum single application rate currently registered 0.008 lb 

a.i./a; maximum single application rate proposed 0.1 lb a.i./A), it is persistent. Data suggest 

sedaxane is susceptible to degradation via aerobic soil and photolysis. Sedaxane may leach to 

groundwater or may move to surface water bodies via runoff of dissolved or soil sorbed residues. 

Figure 3. Probable Routes of Pesticide Dissipation in the Environment 

Drinking Water Exposure Modeling

Since the new chemical assessment was completed, the Health Effects Division’s (HED) 

Residues of Concern Knowledgebase Subcommittee (ROCKS) reevaluated the residues of 

concern considered in the human health assessment. ROCKS determined that CSCD465008 and 

CSAA798670 are no longer considered residues of concern based on recently submitted toxicity 
17

data.5 Therefore, the residues of concern for the human health assessment are sedaxane 

(SYN524464), a mixture of two isomers separately numbered SYN508210 (trans-isomer of 

sedaxane) and SYN508211 (cis-isomer of sedaxane) and two known environmental 

transformation products of equal toxicological concern, CDCD668094 and CDCD668095. These 

compounds are referred to collectively as total toxic sedaxane residues (TTSR). Both 

CSCD465008 and CSAA798670 were only observed to form in the aquatic photolysis studies; 

therefore, since aquatic photolysis is not considered as part of the groundwater modeling 

approach, TTSR are only considered in surface water modeling. 

This DWA includes estimated drinking water concentrations (EDWCs) based on Tier I surface 

water and Tier I groundwater model simulations for all the proposed sedaxane uses. 

Models 

As part of PRZM-Groundwater (PRZM-GW version 1.0, December 11, 2012) the 

implementation phase, Tier I groundwater EDWCs are derived using both SCI-GROW 

(Screening Concentration in Groundwater, version 2.3, August 8, 2003) and PRZM-GW using 

the GW-GUI (Graphical User Interface, version 1.0, December 11, 2012). 

SCI-GROW is an empirical model based on a linear best fit of 13 prospective 

groundwater studies (one year of application). SCI-GROW was designed solely for use as 

a Tier I screening tool and does not have the capability to consider mitigating 

circumstances such as variability in leaching potential of different soils, weather 

(including rainfall), depth to aquifer, nor does it consider multiple years of application. 

PRZM-GW is a one-dimensional, finite-difference model that estimates the 

concentrations of pesticides in groundwater. It accounts for pesticide fate in the crop root 

zone by simulating pesticide transport and degradation through the soil profile after a 

pesticide is applied to an agricultural field. PRZM-GW permits the assessment of 

multiple years of pesticide application (up to 100 years) on a single site. Six standard 

scenarios, each representing a different region known to be vulnerable to groundwater 

contaminations, are available for use with PRZM-GW for risk assessment purposes. In 

PRZM-GW simulations, each of these standard scenarios was used. PRZM-GW output 

values represent pesticide concentrations in a vulnerable groundwater supply that is 

located directly beneath a rural agricultural field. 

The PRZM scenarios used in groundwater simulations are representative of vulnerable sites—

shallow unconfined aquifers under an agricultural field with leaching prone soil—and output 

values represent pesticide concentrations that may be observed in drinking water resulting from 

the use of groundwater vulnerable to pesticide contamination as source water. The results are 

expected to represent the upper bound values on the concentrations of sedaxane that may be 

found in drinking water supplied by groundwater. The PRZM-GW conceptual model has been 

reviewed by two different Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) 

 

5 U.S. Environmental Protection Agency, Holman, E. Sedaxane Seed treatment Drinking Water Revisit. Report of 

the Residues of Concern Knowledgebase Subcommittee Dec. 19, 2012, PC Code: 129223; DP 406945 
18

Scientific Advisory Panels (SAP) and recommended for implementation as a risk assessment tool 

in OPP.6,7 

Tier I surface water EDWCs resulting from the proposed uses of sedaxane were calculated using 

FQPA Index Reservoir Screening Tool (FIRST) model. The default percent cropped area (PCA) 

value of 91% for non-turf uses is used in this assessment to account for the sedaxane use on 

multiple crops. The PRZM scenario used for FIRST development was among the most 

vulnerable, and thus resulting surface water concentrations that represent the upper bound values 

on the concentrations that might be found in drinking water from the use of sedaxane. 

FIRST is a metamodel of PRZM (Pesticide Root Zone Model, version 3.12.3, June 2006) 

and EXAMS (EXposure Analysis Modeling System, version 2.98.04.06, April 2005) 

models. PRZM is used to simulate pesticide transport as a result of runoff and erosion 

from an agricultural field. EXAMS estimates environmental fate and transport of 

pesticides in surface water for an index reservoir. FIRST was developed by making 

multiple runs of PRZM using varying sorption coefficients and determining the 

concentration in the EXAMS index reservoir scenario after a two-inch single storm event. 

The single runoff event moves a maximum of 8% of the applied pesticide into the 

reservoir. This amount can be reduced by degradation or effects of binding to soil in the 

field. Additionally, FIRST can account for spray drift and adjusts for the area within a 

watershed that is planted with the modeled crop. 

Modeling Approach and Input Parameters 

No data are available on the amount of sedaxane that may come off a treated seed once it is 

planted; therefore, in all model runs 100% of sedaxane applied to the treated seed is assumed to 

be available for runoff and leaching in the form of sedaxane or total toxic sedaxane residues. 

Uncertainties exist in choosing input parameters. For this reason, this assessment incorporates all 

scientifically available data to conservatively and reasonably estimate sedaxane residue levels 

resulting from the proposed uses. The input parameters used in this DWA are selected from the 

environmental fate data submitted by the registrant in accordance with US EPA-OPP EFED 

water model parameter guidance.8

The half-life values used in aquatic modeling for sedaxane have been updated and are consistent 

with the NAFTA guidance: Guidance for Evaluating and Calculating Degradation Kinetics in 

Environmental Media. As mentioned in the fate and transport section of this document, aerobic 

biodegradation of sedaxane in soil does not follow single first order kinetics. In general, 

sedaxane concentrations decrease over the first 100 days (approximate); however, after 100 days, 

 

6U.S. Environmental Protection Agency. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific 

Advisory Panel: N-Methyl Carbamate Pesticide Cumulative Risk Assessment: Pilot Cumulative Analysis, February 

15-18, 2005, 2005-01, Docket Number: OPP-2004-0405. 

7 U.S. Environmental Protection Agency. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific 

Advisory Panel: Preliminary N-Methyl Carbamate Cumulative Risk Assessment, August 23-26, 2005, 2005-04, 

Docket Number: OPP-2005-0172. 

8 Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides, Version 2.1, October 22, 2009. 
19

sedaxane concentrations remain steady (approximately 50% of the applied radioactivity) through 

study termination (≥365 days). 

The input parameters used in the groundwater and surface water analysis are provided in the 

subsections below. 

Groundwater 

Input values used in the model runs for SCI-GROW are summarized in Table 8. Rationale for 

choosing each input parameter is discussed in the subsection below the table. Application 

scenarios model used SCI-GROW are summarized in Table 9. 

Table 8. Input Parameters Used in SCI-GROW Modeling to Estimate Sedaxane Concentrations Resulting 

From the Proposed Uses on Corn, Sorghum, Dried Shelled Pea and Bean (Subgroup 6C; Except Soybean), 

Rapeseed (Subgroup 20A), and Potato

Input Parameter 

(Symbol; Unit) 

Value for Sedaxane 

(parent only) Reference Comment 

Aerobic Soil (t1/2; 

days)] 1298 days 47473448/ Supplemental

Input value used in previous assessment 

was based on SFO kinetics (415 days). 

This value was derived from soil studies 

only. 

Representative half-life values used to 

derive the model input value used in this 

assessment were developed following the 

NAFTA kinetics guidance.

Average Soil 

Partition Coefficient 

Kfoc = 557 mL/g 

Koc = 623 mL/g 

47473461/ 

acceptable 

Table 9. SCI-GROW Representative Application Scenarios 

Use 

Number of 

Applications/ 

Application Rate 

(lb a.i./A) 

corn 2/0.02 

sorghum 2/0.005 

dried shelled pea and 

bean 2/0.002 

rapeseed 2/0.0003 

potato 1/0.1 

corn-wheat rotation 1/0.01 and 1/0.008 
20

Aerobic Soil Metabolism Half-life 

The registrant provided aerobic soil metabolism data for sedaxane in three different soils 

(MRID 47473448). 

The rate constant for disappearance of extractable sedaxane residues was calculated for 

four different experiments at 20 °C. The difference in the two studies was the position of 

the radiolabel; therefore, a representative half-life for the North Dakota soil was 

calculated by averaging the two half-life values. The representative half-lives calculated 

ranged from 459-1270 days. The observed DT50 values ranged from 222-423; however, 

DT90 values ranged from 2306-3005 days. This indicates a substantial decrease in 

transformation over time. Two of the four reported half-live values were derived from 

the same soil (North Dakota sandy clay loam). The upper 90th percentile confidence 

bound on the mean half-life value for sedaxane from the three soils was determined to be 

1298 days [1171 (average of 1043, 1200, and 1270) + (1.886 x 116)/√3]. 

Note: As stated earlier there is a large amount of unextracted residues in both of the 

aerobic soil metabolism studies. Additional data should be provided by the registrant to 

confirm that the unextracted residue is not sedaxane or a degradate of toxicological 

concern. 

Soil Partition Coefficient 

The registrant provided adsorption/desorption data necessary to determine parameters, Kd

and Kf for adsorption of sedaxane (MRID 47473461) to soil. 

Analysis of sedaxane adsorption data showed that the Freundlich 1/n value ranged from 

0.81-0.90 indicating that sorption is slightly nonlinear. Soil adsorption of sedaxane was 

shown to correlate with the organic carbon content (i.e. the coefficient of variation for 

Koc and Kfoc values are less than that for Kd and Kf values) of the soil. Kfoc values for 

sedaxane ranged from 257-662 mL/g with a median value of 557 mL/g (mean value of 

481 mL/g). Koc values for sedaxane ranged from 290-728 mL/g with a median value of 

623 mL/g (mean value of 537 mL/g). 

Groundwater analysis was completed using PRZM-GW. Input values used in the model runs for 

PRZM-GW are summarized in Table 10. Standard scenarios, application interval, and data of the 

first application are provided in Table 11. Rationale for choosing each input parameter is 

provided in the subsections below. 

Table 10. Input Parameters Used in PRZM-GW Modeling to Estimate Sedaxane Concentrations Resulting 

From the Proposed Uses on Corn, Sorghum, Dried Shelled Pea and Bean (Subgroup 6C; Except Soybean), 

Rapeseed (Subgroup 20A), and Potato 

Input Parameter 

(Symbol; Unit) 

Value for Sedaxane 

(parent only) Reference Comment 

Hydrolysis (t1/2; 

days)] 0 47473318/ Acceptable 
21

Aerobic Soil (t1/2; 

days)] 1298 days 47473448/ Supplemental

Previous input value used based on SFO 

kinetics is 415 days. Value derived from 

soil studies only. Representative half-life 

values used to derive the model input 

value were developed following the 

NAFTA kinetics guidance. 

Average Soil 

Partition Coefficient 

Kfoc = 481 mL/g 

Koc = 537mL/g 

47473461/ 

acceptable 

 
22

Table 11. PRZM-GW Representative Model Scenarios 

Use 

Number of 

Applications/ 

Application Rate 

(kg a.i./ha) 

Interval Between 

Applications (days) Application Date(s) 

Scenario/ 

Weather 

corna 2/0.02 30 or 138 

4/30 

and 5/30 or 

9/15 

NC Eastern 

Coastal Plain/ 

W13722 

WI Central Sands/ 

W14920 

Delmarva/ 

W13781 

GA Coastal Plain/ 

W93805 

FL Central Ridge/ 

W12842 

FL Jacksonville/ 

W13889

sorghum 2/0.005 138 4/30 

9/15 

dried shelled pea and 

bean 2/0.002 138 4/30 9/15 

rapeseed 2/0.0003 138 4/30 

9/15 

potato 1/0.09 NA 4/30 

corn-wheat rotation 1/0.02 and 1/0.008 138 4/30 

9/15 

a. Since the highest single application is for corn and it can be reapplied after crop failure it is the only scenario 

modeled. 

na = not applicable 

Hydrolysis 

The registrant provided the hydrolysis data for sedaxane (MRID 47473318). These data 

suggest that sedaxane is stable to hydrolysis over a range of pHs as well as elevated 

temperatures. 

Aerobic Soil Metabolism Half-life 

See model input value selection for SCI-GROW. 

Soil Partition Coefficient 

A discussion of the experimental results is provided in the model input values for SCIGROW. The mean Kfoc value was used according to input parameter guidance for 

sedaxane. 

Surface Water 

Input values used in FIRST (PRZM-EXAMS) model runs are summarized in Table 12. 

Rationale for choosing each input parameter is provided in the subsections below. The input 
23

values used in groundwater simulations are the same as those used in surface water simulations 

for hydrolysis, aerobic soil metabolism, and sorption; therefore, rationale for these input 

parameters are not reported in this section. The input value used for aquatic photolysis was 

recalculated for total toxic sedaxane based on the recent ROCKS decision5. No spray drift was 

considered in the model runs (assumed granular application) since sedaxane is expected to be 

dried to the surface of the seed coat when the seed is planted. In addition, since the incorporation 

depth of each plated seed varies between crops, a quick screen that assumed no soil incorporation 

was completed. 

Table 12. Input Parameters Used in FIRST (PRZM-EXAMS) Modeling to Estimate Sedaxane and Total 

Toxic Sedaxane Residue Concentrations Resulting From the Proposed Uses on Corn, Sorghum, Dried Shelled 

Pea and Bean (Subgroup 6C; Except Soybean), Rapeseed (Subgroup 20A), and Potato

Input Parameter 

(Symbol; Unit) 

Value for 

Sedaxane Comment 

Reference/ 

Classification 

Molecular Weight 331.37 g/mol Parent value Calculated 

using ChemDraw 

Henry’s constant (25 oC) 3.95 x 10-11

atm-m3/mol Parent value MRID 47473326 Calculated 

Vapor Pressure (torr) 1.3 x 10-9 25 °C 

4.9 x 10-9 20 °C 

Parent value; only 

empirical data available 

for sedaxane 

47473326 

Solubility in Water (g/L 

at 20 o

C) 14 mg/L Parent value 47473326 

Hydrolysis Half-life (t1/2

at pH 7) 0, stable Parent value 47473318/ Acceptable 

Aquatic Photolysis Halflife (days; t1/2 at pH 7) 541 Value for TTR 47473319/ 

Upgradable 

Aerobic Soil Metabolism 

[upper 90th percentile 

confidence bound on the 

mean half-life value (t1/2; 

days)] 

1298 

Parent value 

Unidentified/unextracted 

material made up 

>>10% of the applied 

radio activity at any 

point during the 

experiment. 

47473448/ 

Supplemental 

Aerobic Aquatic 

Metabolism Half-life 

[water column; upper 

90th percentile confidence 

bound on the mean halflife value (t1/2; days)] 

994 

Parent value 

Unidentified material 

made up <10% of the 

applied radio activity at 

any point during the 

experiment. 

47473468/ 

Supplemental 

Anaerobic Aquatic 

Metabolism Half-life 

[benthic; upper 90th

percentile confidence 

bound on the mean halflife value (t1/2; days)] 

7522 

Parent value 

Unidentified material 

made up <10% of the 

applied radio activity at 

any point during the 

experiment. 

47473468/ 

Supplemental 

Average Soil Partition 

Coefficient (Koc; mL/g) 

Kfoc = 481 

mL/g 

Koc = 723 mL/g 

47473461/ 

Acceptable 
24

Gray shading indicates data is not considered in FIRST; however, PRZM-EXAMS modeling 

incorporates such data so it is provided for completeness. 

1. Dark control-adjusted (rate of irradiated – rate of non-irradiated) as well as adjusted to a 12-

hour/day photoperiod at 40 °N latitude. The artificial light source used in this experiment 

was determined to be equivalent to 0.9 days at 40 °N latitude. 

 
25

Aquatic Photolysis Half-life 

The registrant provided aquatic photolysis data for sedaxane in buffered solution as well 

as in natural water (MRID 47473319). Only the results for the buffered solution were 

used for modeling purposes. The rate constant for disappearance of extractable total toxic 

sedaxane residues was calculated using pyrazole-labeled sedaxane data, as the two 

additional residues of concern both retain the pyrazole moiety. 

Up to 20% of the extracted residues were not identified in the submitted aqueous 

photolysis study. Confirmation that these unidentified residues are not sedaxane, a 

transformation of toxicological concern, or a transformation product that reaches a 

concentration greater than 10% of the applied material during the course of the study 

should be provided. 

Aerobic Aquatic Metabolism Half-life 

The registrant provided data on the aerobic aquatic degradation of sedaxane. The 

formation of several unknown transformation products (accounting for <10% of the 

radioactivity) was observed; however, none of these products were identified. The 90th

percentile confidence bound on the mean total toxic sedaxane half-life value is 994 days= 

(average of 849 and 920) + [(3.078 x 50.2)/√2)]. These studies did not report the 

formation of the two sedaxane transformation products of toxicological concern. 

Aerobic Aquatic Metabolism Half-life 

The registrant provided data on the anaerobic aquatic degradation of sedaxane. The 

formation of several unknown transformation products (accounting for <10% of the 

radioactivity) was observed; however, none of these products were identified. The 90th

percentile confidence bound on the mean total toxic sedaxane half-life value is 994 days= 

(average of 4693 and 1970) + [(3.078 x 50.2)/√2)]. These studies did not report the 

formation of the two sedaxane transformation products of toxicological concern. 

Groundwater

PRZM-GW Tier I groundwater EDWCs for sedaxane resulting from the proposed sedaxane uses 

on corn, sorghum, dried shelled pea and bean (Subgroup 6C; except soybean), rapeseed 

(subgroup 20A), and potato are highlighted in Table 13. The PRZM-GW estimates are higher 

than those calculated using SCI-GROW (Table 166); therefore, PRZM-GW EDWCs are the Tier 

I groundwater estimates recommended for use in the human health risk assessment. Peak and 

post breakthrough average EDWCs in groundwater resulting from the proposed sedaxane uses 

are not expected to be > 22.4 μg/L and 19.3 μg/L, respectively. These estimates were derived 

based on the proposed potato use. Depending on the scenario simulated, the EDWCs range from 

3.6 μg/L to 22.4 μg/L and 3.5 to 19.3 μg/L for peak and post breakthrough concentrations, 

respectively. Model outputs indicate that the time to breakthrough (the time it takes for sedaxane 

residues to reach the underground aquifer) ranges from 3811-10,389 days depending on the 

scenario. With the exception of potato, this analysis is based on 30 years of sedaxane use as a 
26

seed treatment with two plantings per year. Some of the model output files are provided in 

APPENDIX D. 

Table 13. Tier I PRZM-GW EDWCs for Sedaxane From the Proposed Uses Proposed Uses on Corn, 

Sorghum, Dried Shelled Pea and Bean (Subgroup 6C; Except Soybean), Rapeseed (Subgroup 20A), and 

Potato 

Crop 

Sedaxane 

Peak Scenario 

(μg/L) 

Post-Breakthrough 

Average (μg/L) 

Days to 

Breakthrough 

corn 

9.9 8.4 9547 WI Central Sands 

2.5 2.1 8328 GA Coastal Plain 

7.2 6.3 4973 NC Eastern 

Coastal Plain 

5.8 5.3 3811 Delmarva 

6.1 5.5 4164 FL Central Ridge 

1.6 1.6 10,389 FL Jacksonville 

sorghum 

2.5 2.1 9547 WI Central Sands 

0.6 0.5 8328 GA Coastal Plain 

1.8 1.6 4973 NC Eastern 

Coastal Plain 

1.5 1.4 3811 Delmarva 

1.6 1.4 4164 FL Central Ridge 

0.4 0.4 10,389 FL Jacksonville 

dried shelled pea and bean 

(subgroup 6C; Except Soybean)

1.0 0.8 9547 WI Central Sands 

0.3 0.2 8328 GA Coastal Plain 

0.7 0.6 4973 NC Eastern 

Coastal Plain 

0.6 0.5 3811 Delmarva 

0.6 0.5 4164 FL Central Ridge 

0.2 0.2 10,389 FL Jacksonville 

rapeseed 

(subgroup 20A)

0.1 0.1 9547 WI Central Sands 

0.04 0.03 8328 GA Coastal Plain 

0.1 0.09 4973 NC Eastern 

Coastal Plain 

0.09 0.08 3811 Delmarva 

0.09 0.08 4164 FL Central Ridge 

0.02 0.02 10,389 FL Jacksonville 
27

potato1

22.4 19.3 9547 WI Central Sands 

5.8 4.9 8328 GA Coastal Plain 

16.0 13.9 4973 NC Eastern 

Coastal Plain 

12.9 11.7 3811 Delmarva 

13.7 12.4 4164 FL Central Ridge 

3.6 3.5 10,389 FL Jacksonville 

corn-wheat rotation 

6.9 6.0 9547 WI Central Sands 

1.8 1.5 8328 GA Coastal Plain 

5.0 4.4 4973 NC Eastern 

Coastal Plain 

4.0 3.7 3811 Delmarva 

4.3 3.8 4164 FL Central Ridge 

1.1 1.1 10,389 FL Jacksonville 

Bold font indicates highest value 

1- One application of sedaxane every year @ 0,1 kg/ha 

As part of a Tier II analysis, PRZM-GW was used to examine the impact of the organic carbon 

content of the top layer of soil (20 cm) on the potato EDWCs. These analyses were completed 

for the Wisconsin Central Sands scenarios since it provides the most conservative Tier I EDWCs 

as well as for Delmarva and North Carolina Eastern Coastal Plain scenarios as these scenarios 

are thought to reasonably represent potato growing regions with groundwater supplies vulnerable 

to contamination via pesticide leaching. The results of these analyses are provided in Table 14. 

 
28

Table 14. Organic Carbon Soil Content Analysis 

Organic Carbon 

Content of the Top 

Layer of Soil a 

Sedaxane 

Peak Scenario

(μg/L) 

Post-Breakthrough 

Average (μg/L) 

Days to 

Breakthrough 

0.5% 

22.1 19.1 8630 WI Central Sands

16.6 14.4 4521 NC Eastern 

Coastal Plain 

12.9 11.8 4160 Delmarva 

1% 

18.3 15.9 9448 WI Central Sands

14.2 12 6443 NC Eastern 

Coastal Plain 

11.6 10.5 4515 Delmarva 

1.5% 

14.8 13.7 10340 WI Central Sands

12.2 10.3 8404 NC Eastern 

Coastal Plain 

10.4 9.4 4869 Delmarva 

2% 

19.4 b 17.7 b 11258 b

WI Central Sands 17.8 6.8 11258 c

10.4 9.2 10340 NC Eastern 

Coastal Plain 

9.4 8.4 5201 Delmarva 

3% 

14.8 b 13.9 b 13013 b WI Central Sands

8.2 b 7.5 b 14350 b NC Eastern 

Coastal Plain 

7.6 7.0 5867 Delmarva 

a. 20 cm

b. extended weather file used; 100 year simulation with 100 years of repeated applications 

c. extended weather file used; 100 year simulation with 30 years of repeated applications 

Essentially, this analysis shows that increasing the amount of organic carbon content in the top 

layer of the soil (increased hold up) allows for increased degradation of sedaxane and reduces the 

EDWCs. Examination of the potential impact of well setbacks and increased depth to aquifer 

were not pursued, as increasing the pesticide transport time in the layers of the soil where 

minimal degradation is expected will only delay the time to breakthrough and have little impact 

on the EDWCs based on the model half-life value. 

Another assessment was conducted to evaluate the impact of a sedaxane application (0.1 kg/ha) 

every other year in the potato growing regions (Table 15). All scenarios except the Wisconsin 

Central Sands scenarios have post breakthrough average sedaxane concentrations less than 10 

μg/L. The average time breakthrough time for sedaxane occurrence in ground water ranged from 

4164 to 10,346 days. 
29

Table 155. PRXM GW EDWCs for a Single Sedaxane Application Every Other Year on Potato 

Scenario Peak 

(μg/L) 

Post-Breakthrough 

Average 

(μg/L)

Breakthrough 

Time 

(days)

Wisconsin Central Sands 15.1 13 8593a

Florida Citrus 6.85 6.24 4164 

Florida Potato 2.06 1.92 10346a

Delmarva 6.59 6.00 4186 

NC Coastal Plain 8.09 6.95 4957 

GA Coastal Plain 3.77 3.4 8800a

 a-Model simulation was conducted using a 100 year weather file. 

 

Table 166. Tier I SCI-GROW Groundwater EDWCs for Sedaxane From the Proposed Uses on Corn, 

Sorghum, Dried Shelled Pea and Bean (Subgroup 6C; Except Soybean), Rapeseed (Subgroup 20A), and 

Potato

Crop 

Sedaxane Peak

(μg/L) 

corn 0.05 

sorghum 0.01 

dried shelled pea and bean 0.05 

rapeseed 0.0008 

potato 0.1 

corn-wheat rotation 0.02 

Bold font indicates highest value

These groundwater EDWCs generated using PRZM-GW are expected to be conservative based 

on the assumption that all the sedaxane applied to a seed is available for leaching. 

Based on HED’s estimated level of concern, limiting sedaxane use in areas known to be 

vulnerable to groundwater contamination is reasonable, given the range of EDWCs calculated 

using the various scenarios in modeling. Specifically, for potatoes some of the less vulnerable of 

the vulnerable scenarios result in peak and post breakthrough concentrations of 3.6 μg/L and 3.5 

μg/L, respectively. 

Surface Water

Tier I surface water EDWCs for sedaxane resulting from the proposed uses on barley, corn, 

sorghum, dried shelled pea and bean (Subgroup 6C; except soybean), rapeseed (subgroup 20A), 

and potato are listed in Table 17. The model output files are provided in APPENDIX C. 

Sedaxane EDWCs resulting from sedaxane use as a seed treatment on potato once a year provide 

the most conservative Tier I surface water EDWCs; however, these values are less than those 
30

estimated for groundwater using PRZM-GW. Therefore, PRZM-GW groundwater EDWCs are 

recommended for use in the Human Health Risk Assessment. 

Table 17. Tier I Surface Water PCA Corrected EDWCs for Sedaxane from the Proposed Uses on Corn, 

Sorghum, Dried Shelled Pea and Bean (Subgroup 6C; Except Soybean), Rapeseed (Subgroup 20A), and 

Potato 

Crop 

Total Toxic Sedaxane Residues 

Peak EDWC 

μg/L (ppb) 

Yearly Mean 

μg/L (ppb) 

corn 2.0 0.6 

sorghum 0.5 0.1 

dried shelled pea 

and bean 

(subgroup 6C; 

Except Soybean) 

0.2 0.06 

rapeseed 

(subgroup 20A) 0.03 0.009 

Potato 4.1 1.2 

Bold font indicates highest value

Monitoring Data 

No monitoring data are available at this time, as sedaxane was only recently registered in the 

United States. 

Assumptions and Limitations 

In all model runs, all the sedaxane applied to treated seeds was assumed to be available for 

runoff and leaching. In reality, not all the applied sedaxane will leach from the seed coat to the 

surrounding soil. Some of the sedaxane may be taken up by the spouting seed while some of the 

sedaxane may remain sorbed to the seed coat. This assumption likely results in EDWCs that are 

conservative. 

In the aquatic photolysis study some of the samples have up to 20% extracted residues that are 

not identified. These residues could be sedaxane or a transformation product that is of 

toxicological concern. The unidentified residues were not considered when calculating the halflife values or corresponding modeling input values for sedaxane. Additional data are needed to 

confirm that these unidentified residues are not sedaxane, a transformation product of 

toxicological concern or a transformation product that reaches concentrations greater than 10% 

of the applied radioactivity. Since the EDWCs for groundwater are higher than those for surface 

water where aquatic photolysis half-life is a model input value, the inclusion of the up to 20% 

unidentified residues in the model input calculations is not likely to substantially change the 

reported EDWCs. The conclusions or representation of the reported EDWCs in this assessment 

may change if the unidentified residues are of potential toxicological concern (previously 

identified or not). 

In addition, in several of the studies including aerobic soil metabolism [and aerobic soil 

dissipation (seed treatment studies)], there is an increasingly large amount of unextracted 

residues. Additional data is needed to confirm that the solvent used in the studies provides an 
31

exhaustive extraction method. This includes confirmation that the solvent system is sufficient to 

extract soil aged sedaxane residues as well as its transformation products. This data is needed for 

confirmation; however, it is not expected to have a substantial impact on the results reported in 

this assessment. The only impact this is likely to have on this assessment is that additional 

transformation products may have been considered of potential toxicological concern. Inclusion 

of the unextracted residues in the total toxic residues would increase the model input value for 

the aerobic soil metabolism; however, a longer half-life value would only result in a minimal 

increase in the EDWCs. This is because the sensitivity of the models used in this assessment to 

aerobic soil metabolism half-life values >100 days is small. 

Spray drift was not considered in the model runs (assumed granular like application) since 

sedaxane is expected to be dried to the surface of the seed coat when planted. Spray drift is not 

expected to be a route of sedaxane dissipation for the proposed seed treatment uses. 

Incorporation of treated seeds was not considered. For surface water the EDWCs could be lower 

as a result of incorporation; however, since EDWCs for surface water are less than those 

estimated for groundwater. Consideration of incorporation will not have an effect on the 

groundwater EDWCs; therefore, no impact on this DWA is expected. 

 
32

APPENDIX A 

SEDAXANE KINETIC ANALYSIS 

Aerobic Soil Metabolism of Sedaxane (MRID 47473448) 
33
34
35

APPENDIX B 

GROUNDWATER ANALYSIS 

PRZM-GW Output 

Potato “sedaxane only” 
36

APPENDIX D 

SURFACE WATER ANALYSIS 

Potato “Total Toxic Sedaxane Residues” 

RUN No. 5 FOR Sedaxane ON Potato * INPUT VALUES * 

 -------------------------------------------------------------------- 

 RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP 

 ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN) 

 -------------------------------------------------------------------- 

 0.080( 0.080) 1 1 481.0 14.0 GRANUL( 0.0) 91.0 0.0 

 FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

 -------------------------------------------------------------------- 

 METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC 

COMBINED 

 (FIELD) RAIN/RUNOFF (RESERVOIR) (RES.-EFF) (RESER.) (RESER.) 

 -------------------------------------------------------------------- 

 1298.00 2 N/A 54.00- 6696.00 944.00 827.36 

 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.1 MAR 26, 2008 

 -------------------------------------------------------------------- 

 PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) 

 CONCENTRATION CONCENTRATION 

 -------------------------------------------------------------------- 

 4.095 1.203