Glyphosate Human-Health Risk Assessment D381826

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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

MEMORANDUM

Date: 24-March-2011

Subject: Glyphosate. Section 3 Registration for Application of the Potassium Salt of Glyphosate 

to Roundup Ready®Field Corn. Human-Health Risk Assessment. 

PC Codes: 103613 and 417300 DP Barcode: D381826

Decision No.: 437140 Registration Nos.: 524-537; 524-549

Petition No.: 0F7741 Regulatory Action: Section 3

Risk Assessment Type: aggregate Case No.: 178

TXR No.: not applicable CAS No.: 70901-20-1

MRID No.: not applicable 40 CFR: 180.364 

From: Tom Bloem, Chemist

Risk Assessment Branch 1; Health Effects Division (RAB1/HED; 7509P)\

Through: Dana M. Vogel, Branch Chief

George F. Kramer, Ph.D., Senior Chemist

RABI/HED (7509P)

To: James Tompkins/Hope Johnson RM 25

Registration Division (RD; 7505P)

Glyphosate (N-(phosphonomethyl) glycine) is a nonselective Group 9 herbicide that is currently 

registered for pre- and post-emergence application to a variety of fruit, vegetable, and field crops. 

Tolerances are currently established for residues of glyphosate in/on various plant commodities at 0.2-

400 ppm (40 CFR §180.364(a)) and for the combined residues of glyphosate and N-acetyl-glyphosate 

(expressed as glyphosate) in/on field corn, soybean, aspirated grain fractions, and livestock 

commodities at 0.1-310 ppm. The Glyphosate Reregistration Eligibility Decision document was 

issued September 1993. 

Monsanto indicated that they have developed a new variety of genetically-altered field corn (MON 

87427 and MON87441) which enables properly timed glyphosate applications to provide tassel 

control. Monsanto indicated that tassel control is desired as this will allow the generation of specific 

cross pollinations without the use of traditional methods to control self pollination. This new variety

of field corn is to be used only in seed corn production (Monsanto termed the process Round 

Hybridization SystemTM (RHSTM)) and involves slightly later glyphosate application than that 

currently registered for field corn (same seasonal application rate; see Attachment 1 for proposed 

application scenario). 
Glyphosate Human-Health Risk Assessment D381826

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The petitioner has submitted adequate magnitude of the residue data which indicates that the 

currently established field corn forage and grain tolerances, as well as the currently established 

livestock tolerances, are adequate to cover the proposed new use. However, the field corn 

forage tolerance, for the combined residues of glyphosate and N-acetyl-glyphosate (expressed 

as glyphosate), should be increased to 13 ppm (D383931, T. Bloem, 16-Mar-2011). 

HED recently completed a human-health risk assessment associated with the application of 

glyphosate to glyphosate-tolerant sweet corn (D372052, T. Bloem et al., 31-Aug-2010). This 

assessment yielded an aggregate exposure to glyphosate which did not exceed HED's level of 

concern. HED concludes that a revised human-health risk assessment is unnecessary to 

support the current-proposed uses for the following reasons:

●No new toxicological data were submitted since the previous risk assessment (see D372052 (T. 

Bloem et al., 31-Aug-2010) for a summary of the toxicological data).

●The previous dietary exposure analysis assumed tolerance-level residues and 100% crop treated and 

the current action result in an increase in only the field corn forage tolerance (livestock feed item). 

●Since no new toxicological data were submitted and a revised dietary exposure analysis is 

unnecessary, the previous conclusions concerning the Food Quality Protection Act (FQPA) Safety 

Factor remain valid. 

●The proposed new field corn application scenario does not necessitate a revised occupational 

exposure assessment (assessment conducted as part of the currently registered field corn application 

scenario remains valid). 

Recommendation: Provided the petitioner submits revised Sections B and F (see below), HED 

concludes that the toxicological, residue chemistry, and occupational/residential exposure 

databases support a conditional registration for the proposed application of glyphosate to field 

corn. An unconditional registration may be established upon submission of data which adequately 

addresses the toxicological deficiencies specified below.

Summary of Deficiencies:

Acute and subchronic neurotoxicity studies.

Immunotoxicity study.

●Section B: HED requests that the supplemental labels be altered to indicate the following: (1) the 

minimum spray volume for ground and aerial application is >2 gallons per acre (GPA); (2) 

postemergent directions should indicate that they apply to field corn up to the V8 crop stage and that a 

maximum of 2.3 lb ae/acre/season may be applied; and (3) preharvest interval (PHI) of 30 days for 

forage and 7 days for grain and stover.

●Section F: HED requests that a revised Section F be submitted proposing a 13-ppm field corn 

forage tolerance for the combined residues of glyphosate and N-acetyl-glyphosate (expressed as 

glyphosate). 

Attachment 1: Proposed Application Scenarios and Requested Changes to the Proposed Labels

T. Bloem:S10945:Potomac Yard 1:703-605-0217:7509P:RAB1
Glyphosate Human-Health Risk Assessment D381826

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Attachment 1: Proposed Application Scenarios and Requested Changes to the Proposed Labels.

The petitioner submitted proposed supplemental labels for Roundup WeatherMAX®(EPA Reg. No. 

524-537) and Roundup Power MAX®(Reg. No. 524-549); both of these products are solubleconcentrate (SC) formulations consisting of glyphosate as the potassium salt at 4.51 lb ae/gallon. 

The submitted supplemental labels indicate that the application scenarios are for use in research field 

trials and for seed production of corn hybrids using the RHSTM system. Table 1 is a summary of the 

proposed application scenarios. The proposed use directions are similar to that currently registered 

with the exception of the tassel control instructions (V8-V13); maximum seasonal application rate is 

the same. HED requests that the supplemental labels be altered to indicate the following (a revised 

Section B is requested): (1) the minimum spray volume for ground and aerial application is >2 

GPA; (2) postemergent directions should indicate that they apply to field corn up to the V8 crop 

stage and that a maximum of 2.3 lb ae/acre/season may be applied; and (3) PHI of 30 days for forage 

and 7 days for grain and stover.

Table 1: Summary of Proposed Roundup Ready® Field Corn Application Scenario.

Formulation

(EPA Reg. No.) App. Timing App. Rate(lb ae/acre)

Max. App. Rate 

(lb ae/acre) Use Directions and Limitations

Roundup WeatherMAX®

(EPA Reg. No. 524-537; 

SC; 4.51 lb ae/gal)

Roundup Power MAX®

(EPA Reg. No. 524-549; 

SC; 4.51 lb ae/gal)

preplant, at planting, preemergence not specified 3.72

-For use in research field trails 

and for seed production of corn

hybrids using RHSTM. 

-Allow a minimum of 10 days 

between postemergent 

applications.

postemergence 0.56-0.78 not specified

tassel control (V8-V13 or 100 growing 

degree units; before flowering) 0.39-1.13 2.26

preharvest 0.78 not specified

postharvest not specified not specified

maximum seasonal application rate -- 5.98