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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND

 POLLUTION PREVENTION

MEMORANDUM

Date: February 16, 2012

SUBJECT: Trinexapac-ethyl: Response to Syngenta’s Comments on Rotational Crop 

Plantback Interval.

PC Code: 112602 DP Barcode: 397932

Decision No.: 432768 and 433096 Registration Nos.: 100-727, 100-949 and 100-

1241

Petition Nos.: 0F7719 and 0F7720 Regulatory Action: Section 3 First Food Use 

Registrations

Risk Assessment Type: NA Case No.: NA

TXR No.: NA CAS No.: 95266-40-3

MRID No.: 48043709 40 CFR: NA

FROM: Sheila Piper, Chemist

Risk Assessment Branch VI

Health Effects Division (7509P)

THROUGH: Felecia Fort, Branch Chief

Risk Assessment Branch VI

Health Effects Division (7509P)

TO: Bethany Benbow, Risk Manager Reviewer

Kathryn Montague, Risk Manager

Herbicide Branch

Registration Division (7505P)

This memorandum is the Health Effects Division’s response to a proposal received from 

Syngenta Crop Protection following receipt of the human health risk assessment (D377921, S. 

Piper, 11/23/11) and summary of analytical chemistry and residue data (D3378491, S. Piper, 

11/23/11) memoranda for trinexapac-ethyl use on cereal grains, sugarcane, and grasses grown 

for seed.
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Syngenta proposes a 30-day plantback interval (PBI) for all crops other than those listed on the 

label and a 0-day plantback interval for crops with proposed tolerances listed on the label. The 

registrant stated that results of the confined accumulation in rotational crop study (MRID 

48043709) support this position based on current EPA guidance. 

Background

Previously, HED concluded that the trinexapac-ethyl label must be modified to specify a 30-day 

plantback restriction for cereal grains and leafy vegetables, and prohibit the planting of all other 

crops not listed on the label. This was based on the results from the confined rotational crop 

study (MRID 48043709) which showed that TRR values were >0.01 ppm in lettuce (0.017 

ppm), wheat forage (0.010 ppm), and wheat hay (0.011 ppm) samples at the 30-day PBI. 

In the study, only the leafy vegetable (lettuce) and cereal raw agricultural commodities (wheat 

forage and hay) at the 30-day PBI had total radioactive residues (TRR) slightly greater than 0.01 

mg/kg. At subsequent PBIs (120, 270 and 309 days), TRRs for all crops were <0.01 ppm. Under 

EPA guidance, these ppm levels would allow the next interval (120 days) as a PBI. Furthermore, 

additional guidance states that if the TRR is greater than 0.01 mg/kg yet if the residue of concern 

is less than 0.01 mg/kg a PBI can be set at that interval. Table 1 below summarizes the findings 

(compiled from report tables) and demonstrates no individual extractable 14C-residue (free + 

conjugated) was found to be ≥ 0.01 mg/kg for any raw agricultural commodity (RAC) at any 

PBI. 
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Table 1: Summary of Trinexapac-ethyl Results

Rotational 

Crops 

Plantback 

(DAT)

Crop RAC or 

stage

Initial 

Combustion

Sum of 

Fraction

ppm of Levels of Major Extractable 

14C-Residues

PES ppm Levels

30 Total 

ppm

Total 

ppm

ACN/

Water

Parent CGA

179500

CGA

312753

0.1M 

KOH

24% 

KOH

Final PES

Lettuce immature 0.010 0.011 0.004 ND ND ND 0.001 0.005 0.001

mature 0.018 0.017 0.007 ND ND ND 0.001 0.006 0.003

Radish foliage 0.005 NA

roots 0.002 NA

Wheat forage 0.010 0.010 0.005 ND 0.002 ND NA NA 0.005

hay 0.009 0.011 0.004 ND 0.001 0.002 NA NA 0.007

straw 0.003 NA

grain 0.005 NA

120 Lettuce immature 0.004 NA

mature 0.004 NA

Radish foliage 0.007 NA

roots 0.002 NA

Wheat forage 0.004 0.004 0.002 ND ND ND NA NA 0.002

hay 0.009 0.009 0.003 ND ND 0.001 0.001 0.004 0.001

straw 0.004 NA

grain 0.008 0.007 0.001 NA NA NA NA NA 0.006

270 Lettuce immature 0.007

NA

mature 0.001

Radish

(309 

DAT)

foliage 0.001

roots 0.001

Wheat forage 0.002

hay 0.008

straw 0.004

Grain 0.003

ppm=mg/kg; DAT=days after treatment; ND=not detectable; NA=not applicable; PES=post-extracted solids

Agency’s Recommendations:

No individual extractable 14C-residue (free + conjugated) was found to be ≥ 0.01 mg/kg for any 

raw agricultural commodity (RAC) at any PBI. The Agency concurs with Syngenta’s proposal 

for 0 day PBI on grasses grown for seed, cereal grains, and sugarcane. All other crops can be 

planted 30 days after the last application.
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References

DP#: 378491

Subject: Trinexapac-ethyl: Application for the Section 3 Registration Action on Cereal 

Grains and Sugarcane (PP#0F7720), and Grasses Grown for Seed (PP#0F7719). 

Summary of Analytical Chemistry and Residue Data.

From: S.Piper

To: B. Benbow

Date: 11/23/11

MRIDs: 48043701-09, 47101606, 47101603, 48043601-04, 45898901-09, 46809305-06

DP#: 377921

Subject: Trinexapac-ethyl: Human Health Risk Assessment for the Section 3 Registration 

Action on Cereal Grains, Sugarcane, and Grasses Grown for Seed.

From: S.Piper

To: B. Benbow

Date: 11/23/11

MRIDs: NA