**UNITED STA TES ENVIRONMENTA**  **L PROTECTION A GENCY**  **WA SHINGTON, 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: Kathry n Montague, Risk Manager Registration Division (7505C) 

### AND Christina Swartz, RAB2

Health Effects Division 

### FROM: Andrew Shelb y, Phys ical 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 re gistration 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 SCI

GROW, 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**  **. Chem**  **ical** 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). B ased on submitted environmental fate studies, the chemical is moderately persistent in aerobic soil (t 1/2= 37

- 87 days determined for five soils , shorter half

- lives were determined under field conditions: t 1/2= 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: t 1/2 73 days); hydrolysis (except at pH 9: t 1/2= 66 days); and anaerobic aquatic metabolism (t 1/2= >4 ye ars 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 b e bio

-transformation. In clear water bodies subjected to sunlight, indirect photolysis may contribute to amicarbazone dissipation. Although photolysis might occur on soil surfaces (t 1/2= 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 Des

amino (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: Des

amino, N

-methyl Des

- amino and Decarboxamide. D es - 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

f rom hydrolysis in alkaline aqueous systems. M obility s tudies 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 Des

amino and N

-methyl Des

- amino are highly persistent. T able 2 is a summary o f 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
- am ino **None 16%**  **(35 days) 63%** 

**(125 days) None** 

**(Parent is stable)**  **No**

**Accep table**  **Data 26**  **- 27%**  **(59 -**  **61days)** N
- me thyl Des
am ino **None None**  **11% (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). D etermined 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 Lkg- 1 ). Given the moderate persistence/high mobility and solubility

o f 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 D es - 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, surf ace 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 b e highly mobile. P ossible 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 (atm

m3/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 O C, (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 non

sand 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 Des

amino); 48237506 (Des

amino) Aqueous Photolysis Half

- life @ pH 7 (days) Stable 45121803 Aerobic Aquatic Metabolism Half

life (days) 2816 2x Aerobic Soil Metabolism half

- life
Anaerobic Aquatic Metabolism Half

- life (days) Stable
Aerobic Soil Metabolism Half

- life (days) 1408 45121731; 48237507 90 th 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, 2 009. 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 scenario s and application dates are presented below. PRZM/EXAMS output f or 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 MINursery 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, PRZM

GW. 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 S CIGROW 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 19.7 2 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 3 1.57 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 0.0322580 64516129 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 0.80645 1612903226 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
- 8 torr 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 D ate 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)