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U. S. ENVIRONMENTAL PROTECTION AGENCY

Washington, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

PC Code: 112602

Parent DP Barcode: 377936

Sub DP Barcode: 395601

MEMORANDUM October 28, 2011

SUBJECT: Tier II Drinking Water Assessment for Trinexapac-Ethyl use on Turf

TO: Bethany Benbow, Risk Manager Reviewer, RAB2

Kathryn Montague, Risk Manager, RAB2

Registration Division (7505P)

Felicia Fort, Branch Chief, Risk Assessment Branch 6

Sheila Piper, Chemist

Health Effects Division (7509P)

FROM: Christopher M. Koper, Chemist

Environmental Fate and Effects Division (7507P)

THROUGH: Nancy Andrews, Branch Chief

Sujatha Sankula, Lead Biologist

Environmental Fate and Effects Division (7507P)
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EXECUTIVE SUMMARY

This drinking water assessment is an addendum to the previous assessment performed on cereals 

and sugarcane dated 09 August 2011 (D377936). This assessment includes trinexapac-ethyl’s 

use on turf which was previously registered but a drinking water assessment was not performed 

since the action was a non-agricultural use. Modeled application rates represent the maximum 

application rates from the label (Primo® WSB; EPA Reg. No. 100-752). The maximum 

application rate is 2.7 lbs. a.i./acre (8 applications at 0.34 lbs. a.i./acre). 

The recommended estimated drinking water concentrations (EDWCs) for the human health riskassessment are based on highest predicted value for surface water and groundwater (Table 1). 

The recommended EDWCs in surface water and ground water are based on 8 applications of 

0.34 lbs. a.i./acre/year on Pennsylvania turf. Input parameters for the PRZM/EXAMS and SCIGROW models are listed in Table 2 and Table 3. Representative PRZM/EXAMS and SCIGROW model outputs with input parameter data are attached in Appendix I.

For surface water, a foliar ground application to Pennsylvania turf yielded the highest EDWCs. 

The 1-in-10 yr annual peak (acute) concentration was 12.61 μg/L, the 1-in-10 yr annual mean 

(chronic) concentration was 1.56 μg/L and the 30-year annual mean (cancer chronic) 

concentration was 1.04 μg/L. For groundwater, based on the proposed highest annual use rate 

for turf, the SCI-GROW model estimated the trinexapac ethyl concentration at 0.009 μg/L. 

These values supersede the previous EDWCs reported for Louisiana sugarcane (D377936). To 

summarize, Table 1 compares the recommended EDWCs in bold font to the previously reported 

values in italicized font. If additional refinements are necessary, please contact Chris Koper at 

703.347.8065 or koper.christopher@epa.gov.

Table 1. Trinexapac-Ethyl Estimated Drinking Water Concentrations (EDWCs)1for 

Surface Water and Ground Water based on selected Crop Scenarios

Proposed

Label Use

PRZM/EXAMS

Scenario1

(first app date)

Method2

Maximum 

Application Rate

(interval between 

applications)

1-in-10 

year 

acute 

(μg/L)

1-in-10 

year 

chronic 

(μg/L)

30- year 

average 

(μg/L)

Primo® WSB

Surface Water

Turf 

FL Turf

(Feb 15 – foliar)

G 8 app @ 0.34 lb a.i./acre 10.16 1.22 0.84

PA Turf

(April 15 – foliar) G 8 app @ 0.34 lb a.i./acre 12.61(10.92)

1.56

(0.98)

1.04

(0.59)

Ground Water

SCIGROW Turf -- 8 app @ 0.34 lb a.i./acre 0.009

(0.001)

0.009

(0.001)

0.009

(0.001)

1 For surface water (PRZM/EXAMS), EDWC values adjusted with a Percent Cropped Area (PCA) factor of 1.0. For 

ground water (SCI-GROW), no PCA adjustment was utilized. 

2 G = ground application.

Bold numbers denote maximum EDWC values. Italicized numbers denote maximum EDWC values from previous 

drinking water assessment (D377936).
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Table 2. PRZM/EXAMS Input Parameters for Trinexapac-Ethyl 

Input Parameter: Value: Comment: Source:

Scenario(s): FL Turf

PA Turf

representative scenarios for turf 

use

NA

Maximum Single 

Application Rate

lbs a.i./acre (kg a.i./ha)

0.338 (0.380)

maximum single application 

rate for residential and 

commercial uses1

Primo® WSB label

EPA Reg. No. 100-752

Applications per Year 8

derived by dividing the 

maximum yearly application 

rate by the maximum single 

application rate

Primo® WSB label

EPA Reg. No. 100-752

Application Interval (days) 7

Interval was arbitrarily selected 

to represent actively growing 

turf as written on the label

Primo® WSB label

EPA Reg. No. 100-752

Date of Initial Application

(scenario: day-month)

FL Turf: 15-02

PA Turf: 15-04

Date of initial application was 

based on the maturation date 

from crop scenarios

Crop Scenarios

Application Method Foliar: ground (boom sprayer) label directions Primo® WSB label

EPA Reg. No. 100-752

CAM Input 2 linear foliar based on crop 

canopy

US EPA, 2005

IPSCND Input 2 remaining pesticide on foliage 

is completely removed after 

harvest

US EPA, 2005

Spray Drift Fraction 0.064 (ground) drift fraction for ground boom Input parameter guidance 

(USEPA, 2009) 

Application Efficiency 0.99 (ground) -- Input parameter guidance 

(USEPA, 2009)

Molecular Mass (g/mol) 252.3 -- MRID 41604201

Vapor Pressure at 25°C 

(torr)

1.62 x 10-5-- MRID 41604203

Henry’s Law Constant

(atm-m

3

/mol)

5.27 x 10-10-- Calculated from water 

solubility, vapor pressure 

and molecular weight

Solubility in Water (mg/L) 10200 at pH 5.5 MRID 41604203

Organic Carbon Partition 

Coefficient (KOC) (L/kgOC)

416 2represents the average KOC

from 4 values for the acid 

(CGA-163935)

MRID 41663937

Aerobic Soil Metabolism 

Half-life (days)

5.2 3represents the 90th percentile 

confidence bound on the mean 

half-life of 3 values

MRID 46809303

Appendix II B

Aerobic Aquatic 

Metabolism Half-life 

(days)

17.4 4represents the 90th percentile 

confidence bound on the mean 

half-life of 2 values

MRID 46809304

Appendix II C

Anaerobic Aquatic 

Metabolism Half-life 

(days)

533 5represents the 90th percentile 

confidence bound on the mean 

half-life of 2 values

MRID 48043712

Appendix II D

Hydrolysis Half-lives 

(days)

0 (stable) pH 7 MRID 41563930

MRID 46809301
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Table 2. PRZM/EXAMS Input Parameters for Trinexapac-Ethyl 

Input Parameter: Value: Comment: Source:

Aqueous Photolysis

Half-life (days)

22.8 6recalculated environmental 

phototransformation half-life

MRID 46809302

Appendix II A

NA = Not Applicable

1

= The maximum single application rate for residential and commercial uses. The edging/banding rate was higher but not utilized because this 

application is more specialized and does not truly represent turf as the residential and commercial uses.

2

= The average Koc obtained from four values (144, 328, 581 and 609) for the acid (CGA-163935). This value was modeled because of conversion of 

the ester to the acid in the environment. 

3

= Following the Total Toxic Residue (TTR) approach, this value represents the 90th percentile confidence bound on the mean half-life of 3 values 

(3.0, 3.6 and 5.2). See Appendix II B

4

= Following the Total Toxic Residue (TTR) approach, this value represents the 90th percentile confidence bound on the mean half-life of 2 values 

(12.3 and 14.8). See Appendix II C

5

= Following the Total Toxic Residue (TTR) approach, this value represents the 90th percentile confidence bound on the mean half-life of 2 values 

(290 and 56). See Appendix II D

6

= Following the Total Toxic Residue (TTR) approach, this value represents the recalculated environmental phototransformation half-life. See 

Appendix II A

Table 3. SCI-GROW Input Parameters for Trinexapac Ethyl.

Input Parameter Value Comment Source

Maximum Single Application Rate per 

growing season (lbs a.i./A)

0.34 maximum single application rate from 

proposed label

Primo® WSB label

EPA Reg. No. 100-752

Applications per Year 8 label directions

Organic Carbon Partition Coefficient (KOC) 

(L/kgOC)

144 lowest KOC value of the acid data set because 

there was greater than a three-fold variation 

among four values

MRID 41663937

Aerobic Soil Metabolism

Half-life (days)

3.9 1 mean half life because there is less than 4 

values as directed by SCI-GROW guidance 

(US EPA, 2009)

MRID 46809303

1

= Following the Total Toxic Residue (TTR) approach, this value represents the mean half-life of 3 values (3.0, 3.6 and 5.2). 

Appendix I:

Model Outputs: PRZM/EXAMS and SCI-GROW
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Representative PRZM/EXAM Output: Pennsylvania Turf – Ground Application

stored as PATurfG.out

Chemical: Trinexapac

PRZM environment: PAturfSTD.txt modified Thuday, 23 February 2006 at 18:55:08

EXAMS environment: ir298.exv modified Tueday, 26 August 2008 at 06:14:07

Metfile: w14751.dvf modified Tueday, 26 August 2008 at 06:14:59 Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 4.27 4.00 3.67 2.98 2.46 0.77

1962 3.99 3.72 3.42 2.84 2.34 0.75

1963 4.12 3.84 3.53 2.87 2.34 0.75

1964 4.25 3.97 3.59 3.06 2.53 0.80

1965 3.88 3.62 3.33 2.76 2.26 0.71

1966 4.11 3.80 3.53 2.85 2.30 0.82

1967 4.66 4.34 4.06 3.25 2.73 0.93

1968 12.79 12.22 9.95 6.30 5.05 1.57

1969 4.05 3.77 3.48 2.86 2.35 0.89

1970 3.97 3.71 3.40 2.84 2.36 0.76

1971 4.32 4.01 3.73 3.01 2.44 0.77

1972 15.89 14.92 11.38 6.73 5.56 1.87

1973 8.61 8.24 6.79 4.62 3.76 1.26

1974 4.67 4.39 4.16 3.35 2.73 0.88

1975 4.60 4.36 4.00 3.45 2.88 0.91

1976 5.11 4.74 4.35 3.37 2.74 0.88

1977 4.00 3.75 3.43 2.85 2.36 0.76

1978 5.28 5.02 4.81 3.73 3.10 0.98

1979 4.60 4.32 3.98 3.18 2.68 0.88

1980 5.26 4.98 4.69 3.58 2.92 0.91

1981 4.11 3.84 3.53 2.88 2.36 0.76

1982 16.89 16.39 14.39 9.47 7.32 2.32

1983 7.14 6.83 6.35 5.41 4.56 1.49

1984 8.82 8.41 7.11 4.92 4.04 1.31

1985 5.74 5.46 5.23 4.29 3.51 1.16

1986 4.34 4.05 3.80 3.23 2.70 0.88

1987 4.27 3.98 3.49 3.15 2.72 0.89

1988 4.15 3.87 3.57 2.92 2.39 0.79

1989 6.61 6.30 6.03 5.05 4.04 1.26

1990 11.01 10.48 8.53 5.62 4.52 1.45

Sorted results

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

0.03 16.89 16.39 14.39 9.47 7.32 2.32

0.06 15.89 14.92 11.38 6.73 5.56 1.87

0.10 12.79 12.22 9.95 6.30 5.05 1.57

0.13 11.01 10.48 8.53 5.62 4.56 1.49

0.16 8.82 8.41 7.11 5.41 4.52 1.45

0.19 8.61 8.24 6.79 5.05 4.04 1.31

0.23 7.14 6.83 6.35 4.92 4.04 1.26

0.26 6.61 6.30 6.03 4.62 3.76 1.26

0.29 5.74 5.46 5.23 4.29 3.51 1.16

0.32 5.28 5.02 4.81 3.73 3.10 0.98

0.35 5.26 4.98 4.69 3.58 2.92 0.93

0.39 5.11 4.74 4.35 3.45 2.88 0.91

0.42 4.67 4.39 4.16 3.37 2.74 0.91

0.45 4.66 4.36 4.06 3.35 2.73 0.89

0.48 4.60 4.34 4.00 3.25 2.73 0.89

0.52 4.60 4.32 3.98 3.23 2.72 0.88

0.55 4.34 4.05 3.80 3.18 2.70 0.88

0.58 4.32 4.01 3.73 3.15 2.68 0.88

0.61 4.27 4.00 3.67 3.06 2.53 0.88

0.65 4.27 3.98 3.59 3.01 2.46 0.82

0.68 4.25 3.97 3.57 2.98 2.44 0.80

0.71 4.15 3.87 3.53 2.92 2.39 0.79

0.74 4.12 3.84 3.53 2.88 2.36 0.77

0.77 4.11 3.84 3.53 2.87 2.36 0.77

0.81 4.11 3.80 3.49 2.86 2.36 0.76

0.84 4.05 3.77 3.48 2.85 2.35 0.76

0.87 4.00 3.75 3.43 2.85 2.34 0.76

0.90 3.99 3.72 3.42 2.84 2.34 0.75

0.94 3.97 3.71 3.40 2.84 2.30 0.75

0.97 3.88 3.62 3.33 2.76 2.26 0.71

0.10 12.61 12.05 9.81 6.23 5.00 1.56

Average of yearly averages: 1.04

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: PATurfG

Metfile: w14751.dvf

PRZM scenario: PAturfSTD.txt

EXAMS environment file: ir298.exv

Chemical Name: Trinexapac

Description Variable NameValue Units Comments

Molecular weight mwt 252.3 g/mol

Henry's Law Const. henry 5.27E-10 atm-m^3/mol

Vapor Pressure vapr 1.62E-05 torr

Solubility sol 10200 mg/L

Kd Kd mg/L

Koc Koc 416 mg/L

Photolysis half-life kdp 22.8 days Half-life

Aerobic Aquatic Metabolism kbacw 17.4 days Halfife

Anaerobic Aquatic Metabolism kbacs 533 days Halfife

Aerobic Soil Metabolism asm 5.2 days Halfife

Hydrolysis: pH 7 0 days Half-life

Method: CAM 2 integer See PRZM manual

Incorporation Depth: DEPI cm

Application Rate: TAPP 0.38 kg/ha

Application Efficiency: APPEFF 0.99 fraction

Spray Drift DRFT 0.064 fraction of application rate applied to pond

Application Date Date 15-04 dd/mm or dd/mmm or dd-mm or dd-mmm

Interval 1 interval 7 days Set to 0 or delete line for single app.

app. rate 1 apprate 0.38 kg/ha

Interval 2 interval 7 days Set to 0 or delete line for single app.

app. rate 2 apprate 0.38 kg/ha

Interval 3 interval 7 days Set to 0 or delete line for single app.

app. rate 3 apprate 0.38 kg/ha

Interval 4 interval 7 days Set to 0 or delete line for single app.

app. rate 4 apprate 0.38 kg/ha

Interval 5 interval 7 days Set to 0 or delete line for single app.

app. rate 5 apprate 0.38 kg/ha

Interval 6 interval 7 days Set to 0 or delete line for single app.

app. rate 6 apprate 0.38 kg/ha

Interval 7 interval 7 days Set to 0 or delete line for single app.

app. rate 7 apprate 0.38 kg/ha

Record 17: FILTRA

IPSCND 2

UPTKF

Record 18: PLVKRT

PLDKRT

FEXTRC 0.5

Flag for Index Res. Run IR Reservoir

Flag for runoff calc. RUNOFF total none, monthly or total(average of entire run)
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SCI-GROW Output: Turf

SCIGROW

VERSION 2.3

ENVIRONMENTAL FATE AND EFFECTS DIVISION

OFFICE OF PESTICIDE PROGRAMS

U.S. ENVIRONMENTAL PROTECTION AGENCY

SCREENING MODEL

FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3

chemical:Trinexapac Ethyl

time is 10/27/2011 15:46:12

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

 Application Number of Total Use Koc Soil Aerobic

 rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

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

 0.340 8.0 2.720 1.44E+02 3.9

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

groundwater screening cond (ppb) = 8.82E-03 or 0.009