UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF 

CHEMICAL SAFETY AND

POLLUTION PREVENTION

PC Code No.: 114004

DP Barcode: D 384659

Date: September 7, 2011

MEMORANDUM

SUBJECT: Estimated Drinking Water Concentrations of Parent Amicarbazone and its 

Degradates for New Use on Turf and Conifers.

TO: Kathryn Montague, Risk Manager

Registration Division (7505C)

AND Christina Swartz, RAB2

Health Effects Division

FROM: Andrew Shelby, Physical Scientist.

Environmental Risk Branch VI

Environmental Fate and Effects Division (7507C)

THRU: Mark Corbin, Chief

Environmental Risk Branch VI

Environmental Fate and Effects Division (7507C)

Summary

This memo presents the Estimated Drinking Water Concentrations (EDWCs) for parent 

amicarbazone and its Des-amino and N-methyl Des-amino degradates for use in an FQPA 

human health risk assessment. The two degradates chosen for this assessment are those expected 

to be present in natural/acidic or neutral environments where the parent is proposed to be 

applied. Application of this herbicide is not proposed for soils with pH greater than 7.4. Parent 

amicarbazone and/or its degradates may reach both surface and groundwater under some 

conditions. The registrant is seeking registration for use of this new chemical on turf on golf 

courses, sod farms, residential and commercial turf sites, park and recreation areas, school 

grounds and other turf areas and conifers in nurseries and field plantings (including Christmas 

trees).

The surface water and ground water estimates are calculated using PRZM/EXAMS and SCIGROW, respectively. The estimates are presented in Table 1 for surface water and groundwater

for total toxic residues of amicarbazone to include the des-amino and N-methyl des-amino 

degradates as well as unextracted residues.

Table 1. A list of the surface/ground water EDWC values for amicarbazone.

Chemical Surface water EDWCs (ppb) Ground water 

Acute/Chronic EDWC 

(ppb) Peak 96 hour Peak annual 30 year average
2

average average

Total Toxic 

Residues of 

amicarbazone

33.3 25.8 11.1 136

The above stated values for total toxic residues of amicarbazone represent upper-bound estimates 

that might be found in surface water and groundwater due to the use of amicarbazone on turf and 

conifers using one application at the maximum yearly rate (worst case scenario). EDWCs would 

be reduced if degradates were not assumed equally toxic as amicarbazone or if unextracted 

residues were determined to be bound residues. Exclusion of degradates and bound residue 

results in reduction of EDWCs as much as 70%. Exclusion of bound residue results in reduction 

of EDWCs as much as 20%. 

Environmental fate of amicarbazone

Environmental Persistence

Amicarbazone has a low vapor pressure (9.75 x10-9 mm Hg at 30 oC) and is highly soluble in 

water (solubility 4,600 ppm at 20 oC). Based on submitted environmental fate studies, the

chemical is moderately persistent in aerobic soil (t1/2= 37-87 days determined for five soils, 

shorter half-lives were determined under field conditions: t1/2= 19 to 29 days). It appears to 

slowly degrade into a number of degradation products under different environmental conditions. 

The three major degradates for amicarbazone are Des-amino, N-methyl Des-amino, and 

Decarboxamide. Amicarbazone is stable to direct photolysis (indirect photolysis in natural pond 

water: t1/273 days); hydrolysis (except at pH 9: t1/2= 66 days); and anaerobic aquatic metabolism 

(t1/2= >4 years in the solid phase and 533 days in the water phase). With the exception of natural 

clear water bodies subjected to sunlight, the major route of dissipation of amicarbazone appears 

to be bio-transformation. In clear water bodies subjected to sunlight, indirect photolysis may 

contribute to amicarbazone dissipation. Although photolysis might occur on soil surfaces (t1/2= 

54 days), label recommended incorporation of the pesticide just after application may render this 

process unimportant. Photolysis on soil study suggests that the resultant major degradate is Desamino (Max. of 15% in irradiated samples compared with 6% in the dark) with Decarboxamide 

being a very minor degradate (Max. Of 1% in irradiated samples compared with 3% in the dark).
3

Environmental Metabolites

Laboratory and field studies identified only three major degradates for amicarbazone: Desamino, N-methyl Des-amino and Decarboxamide. Des-amino and N-methyl Des-amino 

degradates were both the result of biodegradation in aerobic soil in the laboratory and in the field 

while Des-amino alone resulted from indirect photolysis in aqueous systems. Decarboxamide 

resulted only from hydrolysis in alkaline aqueous systems. Mobility studies were the only 

reviewed studies for the major three degradates of amicarbazone, however, data from the single 

aerobic soil study on the parent and unreviewed degradate specific studies suggest that both Desamino and N-methyl Des-amino are highly persistent. Table 2 is a summary of available data 

indicating maximum concentrations of degradation products found in submitted fate studies. 

Table 2. Maximum concentrations of various degradation products found in submitted 

fate studies.

Degradate 

Max Degradate Concentration (% of applied) and Time (days) to Max Concentration

Hydrolysis 2

Indirect Aqueous 

Photolysis 1 Aerobic Soil

Anaerobic 

Aquatic

Aerobic

Aquatic TFD 

Des-amino

None

16%

(35 days)

63% 

(125 days)

None

(Parent is 

stable)

No

Accep

table

Data

26-27%

(59-61days)

N-methyl Desamino None None11%

(360 days) None

Decarboxamid

e

29% 

(30 days) 

Only @ pH 9

9% 

(35 days) 

with 2% in 

the dark

None None

1

In natural pond water, pH 8.4, note that parent is stable to direct aqueous photolysis.

Amicarbazone is not to be applied on soils with pH values higher than 7.4. Therefore, the fate of 

the chemical in only neutral and acidic conditions is important to this assessment. In such 

environments, amicarbazone and two of its major degradates (Des-amino, N-methyl Des-amino)

are expected to be important. Only in cases where amicarbazone is transported into alkaline 

ground water, surface water bodies and/or soils, the third degradate (Decarboxamide) is expected 

to become important.

Expected Mobility of Amicarbazone and its Metabolites

Available data suggest that amicarbazone is very highly mobile (Koc range= 16.7 to 37.0 L kg-1, 

from adsorption/desorption and aged leaching studies). Additionally, adsorption/desorption and 

aged leaching studies, suggest that all of the three major degradates of amicarbazone are very

highly mobile (ASTM 1996). Determined Koc values were: Des-amino (Koc range= 26.4 to 42.3 

L kg-1), N-methyl Des-amino (Koc range= 34.3 to 56.4 L kg-1) and Decarboxamide (Koc range= 

9.4 to 16.2 L kg-1). 

Given the moderate persistence/high mobility and solubility of the parent and the apparent high 

persistence/high mobility of its two degradates, parent is expected to dissipate slowly and at the 

same time be vulnerable to leaching/run-off. The resultant Des-amino and N-methyl Des-amino 

degradates are expected to behave similar to their parent and become the major terminal 
4

degradates of this chemical in surface and ground water.

In the case of amicarbazone being transported into alkaline ground water, surface water bodies 

and/or soils, the third degradate (Decarboxamide) is expected to become important contaminant 

to surface and/or groundwater. This is because decarboxamide was the major hydrolysis 

degradate in alkaline conditions and it was determined to be highly mobile. Possible 

contamination of surface and ground water with this degradate is expected to increase if it was 

determined to be highly persistent. 

Estimating Drinking Water Exposure from Surface Water Sources

Surface water EDWCs were estimated using PRZM/EXAMS. Input parameters are presented 

and described in the following table.

Table 3. PRZM/EXAMS input parameter values for ambicarbazone use on turf and 

conifers

PARAMETER (units) VALUE(S) SOURCE COMMENT

Application Rate (kg a.i./ha) Parent: 0.490 Product 

label; 

MRID 

45121731; 

MRID 

48237507

Represents the maximum possible single 

application rate per crop season (year) for 

all new uses. 

Number of Applications 1 Maximum single application rate equals 

maximum annual application

Molecular weight (g/mol) Parent: 241 Product 

Chemistry

-

Henry’s Law Constant (atmm

3

/mol)

1.5 x 10-12 (Vapor Pressure [torr]/760)/(Solubility 

[mg/L]/Molecular Weight [g/mol])

Vapor Pressure (torr) 2.2 x 10-8-

Solubility in Water @ 20 OC, 

(mg/L or ppm)

4,600 Product 

Chemistry

–

Organic Carbon Partition 

Coefficient (mL/g)

Parent: 16.7 45121719; 

45121732; 

45121801; 

45121733

KOC ranges from 16.7 to 37.0. Lowest nonsand KOC used for modeling. KOC is 

correlated to KD (r2= 0.62).

CAM (Chemical Application 

Method)

1 ground spray; pre-emergence, 

unincorporated

Depth of Incorporation (inches) 0 Product 

label

–
5

Table 3. PRZM/EXAMS input parameter values for ambicarbazone use on turf and 

conifers

PARAMETER (units) VALUE(S) SOURCE COMMENT

Application efficiency (decimal) 0.99

Spray drift fraction (decimal) 0.064

Application date February 15 Multiple application dates surrounding the 

emergence dates for highest agricultural and 

non-agricultural EDWCs were modeled 

also

Hydrolysis Half-life (days) Stable 45121730 

(parent); 

48073601 

(N-methyl 

Desamino); 

48237506 

(Desamino)

Aqueous Photolysis Half-life @ 

pH 7 (days)

Stable 45121803

Aerobic Aquatic Metabolism Halflife (days)2816 2x Aerobic Soil Metabolism half-life

Anaerobic Aquatic Metabolism 

Half-life (days)

Stable

Aerobic Soil Metabolism Half-life 

(days)

1408 45121731; 

48237507

90th percentile average of 5 total toxic 

residue half-life estimates: 533 days, 990 

days, 1155 days, 1155 days and 1733 days. 

These total toxic residue half-lives include 

des-amino and N-methyl des-amino 

degradates along with ambient unextracted 

residues.

Percent Crop Area 1 PCAs for turf and conifers have not been 

developed and/or approved
6

Table 3. PRZM/EXAMS input parameter values for ambicarbazone use on turf and 

conifers

PARAMETER (units) VALUE(S) SOURCE COMMENT

1 “Input Parameter Guidance” refers to Guidance for Selecting Input Parameters in Modeling the Environmental Fate 

and Transport of Pesticides; Version 2.1, October 22, 2009.

For new uses on turf and conifers, nine PRZM scenarios and two application dates were utilized 

with the California Nursery scenario resulting in highest EDWCs. All available scenarios 

representing turf and conifers were used and two early spring application dates were used to 

represent label application recommendations. Results for the all scenarios and application dates

are presented below. PRZM/EXAMS output for the highest modeled concentrations (CA 

Nursery/February 15) is attached as Appendix 1.

Table 4. PRZM/EXAMS EDWCs for amicarbazone use on turf and conifers

Scenario Application 

date

Peak 96 hour 

average (ppb)

Peak annual 

average (ppb)

30-year average 

(ppb)

CA Nursery February 15 33.3 25.8 11.1

March 1 15.2 13.9 6.5

FL Turf February 15 4.3 3.5 2.4

March 1 4.0 3.1 2.4

FL Nursery February 15 12.7 3.3 1.5

March 1 22.3 3.7 1.5

MI Nursery February 15 7.7 2.6 1.5

March 1 9.3 3.2 1.9

NJ Nursery February 15 11.3 3.8 1.5

March 1 12.5 4.6 1.9

OR Christmas 

tree

February 15 5.5 4.6 3.0

March 1 3.8 3.3 2.6

OR Nursery February 15 5.7 3.6 2.0

March 1 5.3 3.3 1.8

PA Turf February 15 4.4 3.7 2.7

March 1 5.3 4.4 3.0

TN Nursery February 15 13.7 4.0 1.8

March 1 14.6 3.1 1.4

Estimating Drinking Water Exposure from Ground Water Sources

Groundwater EDWCs were estimated using SCI-GROW. Input parameters are presented and 

described in the following table. 
7

Table 5. Summary of SCI-GROW input parameters for total toxic residues of 

amicarbazone.

Parameter Value Reference

Application Rate

(lb a.i./acre)

And

(Number of Applications)

0.4375 (1) Maximum label rate for turf and 

conifers

Aerobic Soil Metabolism t1⁄2 

(days)

1155 Median value from 5 studies... 

(451217-31)

Koc (L Kg-1) 24.2 Median of 7 values (451217-

19/32)

* Fate data values are as per Guidance for Selecting Input Parameters in Modeling the Environmental 

Fate and Transport of Pesticides; Version 2.1 October 22, 2009

Refinements to groundwater EDWCs can be made using the provisional Tier II model, PRZMGW. Though mitigation of maximum application rates can be modeled through SCIGROW, 

PRZM-GW can allow for other mitigation options to be explored such as well set-backs and 

geographic restrictions. The groundwater EDWs produced by SCIGROW is 136 ppb for acute 

and chronic endpoints.
8

Appendix 1

stored as CAnursery215.out

Chemical: amicarbazone

PRZM environment: CAnurserySTD.txt modified Tueday, 26 August 2008 at 06:16:36

EXAMS environment: ir298.exv modified Tueday, 26 August 2008 at 06:14:08

Metfile: w23188.dvf modified Tueday, 26 August 2008 at 06:15:38

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 1.279 1.278 1.274 1.266 1.261 1.072

1962 4.07 4.051 3.964 3.924 3.906 3.442

1963 5.155 5.149 5.123 5.098 5.084 4.644

1964 5.391 5.389 5.38 5.363 5.35 5.038

1965 7.55 7.534 7.467 7.089 6.912 5.926

1966 4.056 4.041 3.975 3.889 3.665 3.025

1967 3.598 3.596 3.59 3.57 3.561 3.286

1968 12.23 12.13 11.74 11.32 11.21 9.385

1969 10.49 10.22 9.176 8.997 8.957 8.656

1970 39.93 39.56 39.28 38.83 38.64 32.47

1971 35.55 35.33 34.6 34.24 33.97 32.1

1972 27.5 27.49 27.47 27.41 27.36 26.18

1973 20.34 20.31 20.16 19.75 19.72 19.1

1974 18.04 17.83 16.99 16.16 16.14 15.6

1975 16.28 16.11 15.42 14.42 14.1 13.3

1976 12.97 12.97 12.96 12.34 12.19 11.68

1977 10.45 10.35 10.08 10.06 9.993 8.592

1978 9.111 9.025 8.729 8.203 8.071 7.254

1979 6.108 5.845 4.884 4.257 4.233 4.101

1980 4.654 4.577 4.301 4.012 3.926 3.618

1981 17.87 17.65 16.74 14.83 14.34 11.68

1982 11.18 10.99 10.75 10.44 10.32 9.156

1983 10.19 10.09 9.52 8.392 8.099 7.499

1984 7.997 7.993 7.981 7.952 7.929 7.54

1985 6.423 6.421 6.413 6.397 6.384 5.781

1986 34.54 33.9 31.57 29.46 28.31 22.18

1987 19.03 18.92 18.54 18.43 18.3 17.34

1988 12.29 12.25 12.07 11.75 11.61 9.391

1989 10.09 10.08 10.05 10.01 9.982 9.356

1990 17.31 17.26 17.08 16.96 16.89 15.37

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.032258064516129 39.93 39.56 39.28 38.83 38.64 32.47

0.0645161290322581 35.55 35.33 34.6 34.24 33.97 32.1

0.0967741935483871 34.54 33.9 31.57 29.46 28.31 26.18

0.129032258064516 27.5 27.49 27.47 27.41 27.36 22.18
9

0.161290322580645 20.34 20.31 20.16 19.75 19.72 19.1

0.193548387096774 19.03 18.92 18.54 18.43 18.3 17.34

0.225806451612903 18.04 17.83 17.08 16.96 16.89 15.6

0.258064516129032 17.87 17.65 16.99 16.16 16.14 15.37

0.290322580645161 17.31 17.26 16.74 14.83 14.34 13.3

0.32258064516129 16.28 16.11 15.42 14.42 14.1 11.68

0.354838709677419 12.97 12.97 12.96 12.34 12.19 11.68

0.387096774193548 12.29 12.25 12.07 11.75 11.61 9.391

0.419354838709677 12.23 12.13 11.74 11.32 11.21 9.385

0.451612903225806 11.18 10.99 10.75 10.44 10.32 9.356

0.483870967741936 10.49 10.35 10.08 10.06 9.993 9.156

0.516129032258065 10.45 10.22 10.05 10.01 9.982 8.656

0.548387096774194 10.19 10.09 9.52 8.997 8.957 8.592

0.580645161290323 10.09 10.08 9.176 8.392 8.099 7.54

0.612903225806452 9.111 9.025 8.729 8.203 8.071 7.499

0.645161290322581 7.997 7.993 7.981 7.952 7.929 7.254

0.67741935483871 7.55 7.534 7.467 7.089 6.912 5.926

0.709677419354839 6.423 6.421 6.413 6.397 6.384 5.781

0.741935483870968 6.108 5.845 5.38 5.363 5.35 5.038

0.774193548387097 5.391 5.389 5.123 5.098 5.084 4.644

0.806451612903226 5.155 5.149 4.884 4.257 4.233 4.101

0.838709677419355 4.654 4.577 4.301 4.012 3.926 3.618

0.870967741935484 4.07 4.051 3.975 3.924 3.906 3.442

0.903225806451613 4.056 4.041 3.964 3.889 3.665 3.286

0.935483870967742 3.598 3.596 3.59 3.57 3.561 3.025

0.967741935483871 1.279 1.278 1.274 1.266 1.261 1.072

0.1 33.836 33.259 31.16 29.255 28.215 25.78

Average of yearly averages: 11.1254

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: CAnursery215

Metfile: w23188.dvf

PRZM scenario: CAnurserySTD.txt

EXAMS environment file: ir298.exv

Chemical Name: amicarbazone

Description Variable Name Value Units Comments

Molecular weight mwt 241 g/mol

Henry's Law Const. henry 1.5E-12 atm-m^3/mol

Vapor Pressure vapr 2.2E-8torr

Solubility sol 4600 mg/L

Kd Kd mg/L

Koc Koc 16.7 mg/L

Photolysis half-life kdp 0 days Half-life

Aerobic Aquatic Metabolism kbacw 2816 days Halfife

Anaerobic Aquatic Metabolism kbacs 0 days Halfife
10

Aerobic Soil Metabolism asm 1408 days Halfife

Hydrolysis: pH 7 0 days Half-life

Method: CAM 1 integer See PRZM manual

Incorporation Depth: DEPI 0 cm

Application Rate: TAPP 0.49 kg/ha

Application Efficiency: APPEFF 0.99 fraction

Spray Drift DRFT 0.064 fraction of application rate applied to pond

Application Date Date 15-02 dd/mm or dd/mmm or dd-mm or dd-mmm

Record 17: FILTRA

IPSCND 1

UPTKF

Record 18: PLVKRT

PLDKRT

FEXTRC 0.5

Flag for Index Res. Run IR Reservoir

Flag for runoff calc. RUNOFF none, monthly or total(average of entire run)