UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

PC Code: 128847

DP Barcode: 390040

MEMORANDUM

DATE: June 23, 2011

SUBJECT: The Drinking Water Degradates Identification Memorandum for

Difenoconazole

FROM: Faruque Khan, Ph.D.,Senior Scientist

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

TO: Christine Olinger, Co-chair

Edward Scollon, Co-chair

Residues of Concern Knowledgebase Subcommittee

THRU: Katrina White, Ph.D., EFED ROCKS Representative

William Shaughnessy., Ph.D,, EFED ROCKS Representative

Residues of Concern Knowledgebase Subcommittee

Nancy Andrews, Ph.D., Branch Chief

Sujatha Sankula, Ph.D., Lead Biologist

Environmental Risk Branch I

Environmental Fate and Effects Division

This memorandum identifies the environmental degradates of difenoconazole. These 

data are provided to help determine which environmental degradates are of risk concern 

for conducting a drinking water assessment to support a human health risk assessment. If 

you have questions concerning this memorandum, please contact Faruque Khan at 703-

305-6127.

Difenoconazole is a fungicide in the conazole chemical class. Fungicidal activity of the 

conazole class of compounds is attributed to the inhibition of ergosterol biosynthesis. 

There are several active registrations for formulations of difenoconazole (including 

mixtures) and one for the technical grade product. Based on the field and laboratory

studies, the active ingredient difenoconazole is persistent in soil and slightly mobile. 

Difenoconazole is likely to reach surface water sources of drinking water via spray drift 

and runoff. Detailed description of fate and transport properties of difenoconazole can be 

obtained from previous section 3 assessment (U.S. EPA, 2010; D378927+).
2

Mobility, Volatility, and Propensity to Move into Surface and Ground Water

Based on a low vapor pressure of 2.5 x 10-10 mm Hg and a Henry’s Law constant of 8.9 x 

10-12 atm-m

3

/mol, difenoconazole has a low propensity to volatilize from application site

and surface water. It has a low solubility (15 mg/L) in water. Difenoconazole appears to 

be slightly mobile to hardly mobile in the soil; its Koc values range from 3,471-11,202 

L/kg. Difenoconazole has potential to reach surface water via run-off, erosion, and spray

drift, and is less likely to reach ground water except in soils of high sand and low organic 

matter content.

Degradation

Environmental fate data indicate that difenoconazole is relatively stable to aerobic and 

anaerobic soil metabolisms and aerobic and anaerobic aquatic metabolism. When applied 

at 0.1-0.23 ppm to an aerobic soil, difenoconazole appears to degrade with half-lives 

ranging from 84.5 to 533 days based on laboratory studies conducted on a variety of 

foreign and domestic soils. At concentrations of 10 ppm, difenoconazole degraded with 

the half-lives of 1059-1600 days in aerobic, and 947 days anaerobic loam soil, 

respectively. In aquatic environment under aerobic conditions, difenoconazole 

microbially degraded with half-lives ranging from 315 to 565 days at concentrations up 

to 0.17 mg ai/L, and 860 days in a concentration of 10 mg ai/L. Under anaerobic 

conditions, difenoconazole degraded in 370 days at a concentration of 0.04 mg ai/L, and 

1245 days at concentrations of 10 mg ai/L. The longer half-life values obtained for those 

higher concentration rates may imply that the rate of difenoconazole microbially

mediated degradation may be concentration dependent. In laboratory studies on 

difenoconazole a significant amount of radioactivity was nonextractable (14.4 to 48.9%) 

from soils.

Considering abiotic degradation, difenoconazole is photolyzed in water (half-life of 6 to 

228 days), but stable in soil. The half-life of 228 days was extrapolated from a 15-day

study in which difenoconazole slowly photolyzed from 100% to 91% under artificial light 

conditions (MRID 46950105). Also, the compound is stable to hydrolysis at pH values 

from 4 to 9.

Difenoconazole degraded with half-lives ranging from 139 to 462 days in the terrestrial 

field dissipation studies. The overall stability of the compound in the terrestrial 

environment suggests that difenoconazole may accumulate in soil with successive 

applications from year to year. 

Bioaccumulation

The octanol water partition coefficient, log Kow of 4.4, suggests that defienoconazole has 

a potential to bioaccumulate. Difenoconazole accumulated rapidly in edible and nonedible bluegill sunfish tissues with bioconcentration factors of 170x for edible tissues, 

570x for non-edible tissues, and 330x for whole body. Depuration was also rapid with a 
3

depuration half-life of approximately 1 day and 96-98% clearance after 14 days of 

depuration. From both edible and non-edible tissues, one metabolite was recovered, 

CGA-205375, and accounted for 51-64% of the applied.

Possible Degradates of Toxic and Exposure Concern

Difenoconazole may break down to CGA205375, (1-[2-Chloro-4-(4-chlorophenoxy)-

phenyl]-2-[1,2,4]triazol-1-yl-ethanol), next to triazolyl acetic acid and further to triazole 

methanol and triazole. 1,2,4-triazole and its conjugates (triazole alanine and triazole 

acetic acid) are common metabolites to the class of compounds known as the triazolederivative fungicides (T-D fungicides, conazoles). A separate drinking water assessment 

was conducted on 1,2,4-triazole degradates ((U.S. EPA, 2006; D D320682). The 

majority of the major degradates formed under both abiotic and biotic processes. 

A summary of ecotoxicity data for degradates has been submitted (MRID 453427-01) 

from several submitted studies including data in birds (45284015), earthworms (MRID 

45297201), daphnids (MRID 00133381), fish (MRID 45284017), and algae (MRID 

00133382). The data suggest that 1,2,4-triazole may be less toxic than difenoconazole to 

fish, daphnids, and aquatic plants, but more toxic to earthworms. No toxicity data are 

available on the other major degradates of difenocozole at this time. 

Residues of possible exposure concern for drinking water include the parent and its 

degradates. The submitted environmental fate data for difenconazole and its degradates 

are summarized in Table 1. 
Table 1. Difenconazole and Its Major and Minor Environmental Degradates.

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR (study 

length)

PARENT

Difenconazole

CGA-169374

IUPAC Name: 3-Chloro-4-

[(2RS,4RS;2RS,4SR)-4-

methyl-2-(1H-1,2,4-triazol-1-

ylmethyl)-1,3-dioxolan-2-

yl]phenyl 4-chlorophenyl 

ether.

CAS Name: 1-[2-[2-Chloro-4-

(4-chlorophenoxy)phenyl]-4-

methyl-1,3-dioxolan-2-

ylmethyl]-1H-1,2,4-triazole.

CAS Number: 119446-68-3

Formula: C19H17Cl2N3O3

MW: 406.3 

SMILES: 

O1CC(C)OC1(Cn2ncnc2)c3c(

Cl)cc(Oc4ccc(Cl)cc4)cc3

Hydrolysis pH 5

42245127

---

1

Hydrolysis pH 7 ---

Hydrolysis pH 9 ---

Aqueous Photolysis 42245128 2.50 (30 days)

46950104 1.21±0.5

(30 days)

46950105 94.1 (15 days)

Soil Photolysis 46950106-

46950107

91.4 (30 days)

Aerobic Soil Metabolism 4695109 18.4 ±0.1

(293 days)

46950110 13.6(293 days)

46950111 51.0(228 days)

46950112-

46950113

54.2 ±4.8

(360 days)

46950114

46950115

58.8 ±1.1

(372 days)

Aerobic Aquatic Metabolism 46950116 71.2 (183 days)

46950117-

46950118

81.53±3.22

(112 days)

Anaerobic Aquatic 

Metabolism

46950119-

46950120

42.72  0.88 

(350 days)

Terrestrial Field Dissipation 46950126 44 ppb (531 days)

46950127 14 ppb (535 days)

46950129 302 ppb (422 days)

MAJOR (>10%) TRANSFORMATION PRODUCTS

CGA-179500

[CGA 205375, 

IUPAC Name: 4-[ Not 

reported

CAS Name: alpha-[2-ChloroAqueous Photolysis 42245128 2.9 (5 days) 0.1 (30 days)

46950104 2.04 (14 days) 0.96 (30 days)

46950105 NA NA
5

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR (study 

length)

CGA 211391 and 

M1]

4-(4-chlorophenoxy)phenyl]-

1H-1,2,4-triazole-1-ethanol.

1-[2-Chloro-4-(4-

chlorophenoxy)phenyl]-2-

[1,2,4]-triazol-1-yl-ethanol.

CAS Number: 117018-19-6

Aerobic Soil metabolism 46950109 5.1± 1.4

(84days)

3.7± 0.1

(293 days)

46950110 4.6± 0.1

(56days)

2.7± 0.5

(293 days)

46950111 9.4± 05

(120days)

9.0(228 days)

46950112-

46950113

14.8±1.8 

(360days)

14.8± 1.8

(360 days)

4695114-

4695115

9.4± 0.1

(372 day)

9.4± 0.1

(372 day)

Aerobic Aquatic Metabolism 46950116 11.4 (183 days) 11.4 (183 days)

Anaerobic Aquatic 

Metabolism

46950119-

46950120

12.60± 0.42

(175days)

6.2 ± 0.76

(350 days)

Terrestrial Field Dissipation 46950126 11 ppb (358 

days)

6.2ppb (531days)

46950127 12 ppb (123 

days)

5.6 ppb (531days)

46950129 18ppb (364 

days)

12.0 2ppb 

(535days)

N

N

N

O Cl

Cl

OH
Code Name/ 

Synonym Chemical Name Chemical Structure

CGA-71019 IUPAC Name: 4-[ Not 

reported

CAS Name: 1H-1,2,4-Triazole 

CAS Number: 288-88-0

CGA-142856 IUPAC Name: 4-[ Not 

reported

CAS Name: 1H-1,2,4-

Triazole-1-acetic acid

CAS Number: 28711-29-7

CGA-107069 IUPAC Name: 4-[ Not 

reported

CAS Name: 1H-1,2,4-

Triazole-1-methanol

CAS Number: 74205-82-6

Carbon

Dioxide

CAS Number: 124-38-9

Formula: CO2

MW: 44.1 g/mol

HO

6

Chemical Structure Study Type MRID

Aqueous Photolysis 42245128

46950104

46950105

Aerobic Soil Metabolism 4695110

4695111

4695114-

4695115

Anaerobic Aquatic 

Metabolism

46950119-

46950120

Terrestrial Field Dissipation 46950129

Aqueous Photolysis 46950104

Terrestrial Field Dissipation 46950126

Aqueous Photolysis 46950104

Aqueous Photolysis 46950104

46950105

HO

O

N

N

N

C

H2

N

N

N O

O C O

Maximum 

%AR (day)

Final %AR (study 

length)

13.4 (9 days) 10.9 (30 days)

12.27 ± 0.7 

(30days)

12.27 ± 0.7 

(30 days)

NA2 NA

20.6

(190 day)

17.8± 2.8

(293 day)

1.6±0.4

(120 day)

0.9

(228day)

7.8± 0.1

(372 day)

7.8± 0.1

(372 day)

25.62± 0.35

(350 day)

25.62± 0.35

(350 day)

3.5 ppb (36 

days)

< LOQ (535days)

41.83 ±0.9 

(30days)

41.83±0.9 

(30 days)

<LOQ311 ppb 

(358 days)

Reported as combined residue with 

CGA 71019

2.01 (30 day) 2.01± 2.5(30 days)

0.01 (3days) <0.1 (15 days)
7

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR (study 

length)

Soil Photolysis 46950106

46950107

0.02 (30days) 0.2 (30 days)

Aerobic Soil Metabolism 46950109 23.4 ± 1.9

 (293 days)

23.4 ± 1.9

 (293 days)

46950110 4.5 ± 2.4

 (293 days)

4.5 ± 2.4

 (293 days)

46950111 19.2

 (228 days)

19.2

 (228 days)

46950112

46950113

15.0 ± 1.3

 (360 days)

15.0 ± 1.3

 (360 days)

46950114

46950115

4.2 ± 0.1

 (372 days)

4.2 ± 0.1

 (372 days)

Aerobic Aquatic Metabolism 46950116 3.9(183 days) 3.9 (183 days)

46950117

46950118

0.59 ± 0.28

 (98 days)

0.29 ± 0.03

 (112 days)

Anaerobic Aquatic 

Metabolism

46950119-

46950120

0.55± 0.33

(245days)

0.25 ± 0.02

(350 days)

Non-extractable 

Residues

Soil Photolysis 46950106/

46950107

0.55± 0.33

(245days)

0.25 ± 0.02

(350 days)

Aerobic Soil Metabolism 4695109 38.0 ±1.3

(293days)

38.0 ±1.3

(293days)

46950110 48.9 ±0.6

(293 days)

48.9 ±0.6

(293 days)

46950111 22.9

(228 days)

22.9

(228 days)

46950112

46950113

14.4 ±1.0

(360 days)

14.4 ±1.0

(360 days)

46950114

46950115

18.4 ±1.0

(372 days)

18.4 ±1.0

(372 days)

Aerobic Aquatic Metabolism 46950116 8.7 (183 days) 8.7 (183 days)

46950117

46950118

8.87 ± 3.04

 (112 days)

8.87 ± 3.04

 (112 days)
8

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR (study 

length)

Anaerobic Aquatic 

Metabolism

46950119-

46950120

8.06± 1.24

(302days)

7.11 ± 0.32

(350 days)

Unidentified 

Unknowns4

Aqueous Photolysis 42245128 20.0 (15days) 6.5 (30 days)

46950104 29.02 ± 2.9 

(30days)

29.02 ± 2.9

(30days)

46950105 16.7(15 days) 11.1 (15 days)

Aerobic Soil Metabolism 4695111 0.4

(228 days)

0.4

(228 days)

Aerobic Aquatic Metabolism 46950116 5.5

(127days)

5.7

(183day)

46950117-

46950118

5.56± 0.03

(98days)

4.26± 1.34

(112days)

46950119-

46950120

0.77± 0.23

(245 day)

<LOQ (350 days)

Anaerobic Aquatic 

Metabolism

46950119-

46950120

5.69± 0.57

(302 day)

5.21± 0.98

(350 day)

MINOR (<10%) TRANSFORMATION PRODUCTS

CGA-205374 

[CGA176459]

IUPAC Name: 2-(4-

Cyclopropyl-2,4-dioxo-butyl)-

succinic acid

CAS Name: 1-[2-Chloro-4-

(4-chlorophenoxy)phenyl]-2-

(1H-1,2,4-triazol-1-yl)-

ethanone.

CAS Number: 136815-80-0

Aqueous Photolysis 42245128 1.5 (0 day) < LOQ (30 days)

46950104 1.11± 0.11

(14 days)

0.13 ± 0.1

(30 days)

46950105 NA NA

Aerobic Soil Metabolism 46950114-

46950115

2.1 ± 0.4

(272days)

1.4 ± 0.1

(293 days)

Anaerobic Aquatic 

Metabolism

46950119-

46950120

0.77± 0.23

(245 day)

<LOQ (350 days)

M2 Aerobic Soil Metabolism 46950109 1.5

(28days)

1.4 ± 0.1

(293 days)

O

N

N

N

O Cl

Cl
9

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR (study 

length)

46950110 2.1± 1.81

(293days)

2.1± 1.81

(293days)

46950111 1.5

(228days)

1.5

(228days)

Anaerobic Aquatic 

Metabolism

46950119-

46950120

5.79± 1.42

(245 days)

< LOQ (350 days)

M4 Aerobic Soil Metabolism 46950109 1.2

(190days)

1.0 ± 0.4

(293 days)

1

= Stable

2

= Not Analyzed

3

= Limit of Quantitation

4 Unidentified unknowns may consists of M4, M5, M6, M7 and several other unidentified components with no zone exceeding 5.68% of applied radioactivity.

References:

US EPA, 2011. Ecological Risk Assessment for the Proposed New Uses of Difenoconazole as a Foliar Spray for Carrot, 

Chickpea, Soybean, Stone Fruit (Group 12), and Strawberry and as a Seed Treatment for Oat and Rye

. February 22, 2011. (378927+)

US EPA, 2006. 1,2,4-Triazole, Triazole Alanine, Triazole Acetic Acid: Drinking Water Assessment in Support of 

Reregistration and Registration Actions for Triazole-derivative Fungicide Compounds. February 28, 2006. (D320682)