Page 1 of 4 **UNITED STATES ENVIRONMENTAL PROTECTION AGENCY**

**WASHINGTON, D.C. 20460** OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION **MEMORANDUM Date:**  March 2 9 , 2012 **Subject :**  Glufosinate Ammonium. Report of the Residues of Concern Knowledgebase

Subcommittee (ROCKS). **PC Code:** 128850 **DP Barcode:** D 397644 **Decision No.:** 424395 **Registration No. :**  NA **Petition No.:** NA **Regulatory Action:** Section 3 Registration **Risk Assessment Type:** Single Chemical Aggregate **Case No.:** NA **T XR No.:**  NA **CAS No.:** 77182 - 82 - 2 **MRID No.:** NA **40 CFR:** 180.437 **From:** Id eliz Negrón - Encarnación , ROCKS Alternate Secretary

Health Effects Division ( 7509P) **Through:** Christine L . Olinger, ROCKS Co - Chair

Edward J. Scollon , ROCKS Co - Chair Health Effects Division ( 7509P ) **To:** Glufosinate Ammonium Risk Assessment Team

Risk Assessment Branch V Health Effects Division ( 7509P) The ROCKS met on January 11, 2012 to discuss the residues of concern for the h erbicide glufosinate ammonium in drinking water . The residue of concern recommendation was subjected to electronic review to consider a subsequent ToxSAC report (02/21/2012). **Team Members Attended:** John Doherty , Chuck Peck, William Donovan, Mike Metzger, and Marietta Echev e rria **ROCKS Members Attended:** Christine Olinger, Edward Scollon , Ray Kent , Richard Loranger , Elizabeth Holman, William Irwin , Leung Chen g , George Kramer , Reuben Baris, Dennis McNeill y and Ideliz Negrón **Material Reviewed:** Briefing Materials: Glufosinate Ammonium ROCKS SubmissionPage 2 of 4

**Background** The residues of concern of the herbicide glufosinate ammonium in plants, rotational crops, livestock and drinking water were previously evaluated (Txt# 0050727, T. Bloem , 05/09/2002). The risk assessment team solicited the ROCKS a re - evaluation of the residues of concern in drinking water. S upplemental toxicity information for water degradates was provided for the ROCKS consideration . Based on input provided by the Tox SAC (02/21/2012) , the recommendation from the ROCKS meeting held on January 11, 2012 was amended. The amended decision memo was circulated electronically t o the ROCKS committee on February 28, 2012 for comments. **Committee Recommendation Summary of Degr**  **adates to be included in the Risk Assessment** Matrix Residues included in Risk Assessment Residues included in Tolerance Expression Drinking Water Glufosinate Ammonium 1 ,2 Not Applicable 1 Glufosinate ammonium is butanoic acid, 2 - amino - 4 - (hydroxymethylphosphinyl) - mo noammonium salt. Although glufosinate ammonium will be dissociated in water, for risk assessment purposes it is described as the salt in order to aggregate the residues in drinking water with those in food where the c oncentration is expressed in terms of the salt. 2 Since MPP is likely less toxic than the parent compound and should not be aggregated with the parent , if MPP EDWCs are not significantly greater than those for glufosinate, the risk assessment for the parent will be protective of any toxicity associated with expo sure to MPP in drinking water and a quantitative risk assessment for MPP will not be required. Summary of Briefing Materials Considered Glufosinate ammonium [ammonium - DL - homoalanin - 4 - yl - (methyl ) - phosphinate ] is a non selective foliar herbicide that acts by inhibiting glutamine sy

nthetase. In addition to the complete toxicity

database for the parent compound, subchronic toxicity and developmental studies are available for the environmental degradates MPP, MPA and NAG (structure s are shown in Appendix 1) . MPA is at least 100 fold less potent than glufosinate ammonium based upon the lack of effects in a 90 - day study in rats. Rabbit developmental studies are also available for GA, NAG, and MPP t o aid in relative potency comparisons. NAG and MPP were 5 - to 10 - fold less potent than the parent ; however, the maternal effects noted were different than those observed than the parent glufosinate ammonium. Glufosinate ammonium is readily miscible in water. Glufosinate will not volatilize significantl y due to a low vapor pressure, and is moderatel y mobile. Glufosinate is considered stable to photoly sis in water but degrades in soil due to photoly sis with a half - life of 17 day s. The metabolism studie s showed that glufosinate degrades in aerobic soil and aqueous environments, with soil half

- lives ranging from 8.5 to 23 day s , and aquatic half - lives ranging from 11 to 87 day s. Glufosinate in the anaerobic soil environment degraded with a measured half - l ife of 37 day s in one study , but the chemical was persistent in the anaerobic aquatic environment, with a measured half

- life of 415 day s in another study .Page 3 of 4

MPP was a major degradate in the soil photoly sis study , reaching a maximum of 60.4% (Day 30 ) . MPP was also a major degradate in all metabolism studies with the exception of the anaerobic aquatic study. In aerobic systems, maximum MPP values ranged from 26 to 55% in soil and 17 to 80% in aquatic environments. In anaerobic soil, MPP reached a maximum of 42% at the end of the study (Day 60). MPA was a major or minor degradate in all of metabolism studies with the exception to the anerobic aquatic metabolism . In aerobic systems, maximum MPA values ranged from 3 to 28% in soil and 7 to 20% in aquatic environments. When MPA was a major degradate, it tended to form at the end of the study , supporting the supposition that it forms as a result of MPP degradation. In anaerobic soil and soil photolysis, MPA was a minor degradate. NAG was major degradate of photolysis in soil, reaching maximum of 17.7% (Day 4 ). It was a minor degradate in one of two aerobic aquatic studies and not detected in the other . In addition, it was not detected in the anaerobic aquatic study, and aerobic and anaerobic soil studie s . Rationale MPA: A 90 - day

rat feeding study

showed no effects at the highest dose tested which is about 100 - fold higher than the NOAEL of the parent; therefore, MPA is considered less toxic than the parent. Even though it is a major degradate in some studies, considering its much lower toxicity th an the parent, ROCKS recommends its exclusion as a residue of concern in drinking water. NAG: Based on the rabbit developmental studies NAG can be considered slightly less toxic than the parent. It was onl y observed as a major degradate during photolysis in soil; therefore, its exposure is significantl y lower to that of the parent in drinking water . The ROCKS recommends its exclusion as a residue of concern in drinking water. MPP: The ROCKS noted that MPP may have different toxicity

than the parent and is likel y to have a lower toxicity

but not so low that it could be definitel y excluded from consideration. After the ROCKS m eeting , the team consulted with Health Effects Division To xSAC regarding the toxicity

of MPP (J. Kidwell, 02/21/2012). The consensus of the ToxSAC was that glufosinate ammonium, the parent , and MPP, the degradate , show different toxicities, such that they should not be aggregated. Moreover, the Environmental Fate and Effects Division have indicated that the acute concentrations of MPP are not likely to be significantly

greater than that of glufosinate in drinking water. However, given the minimal fate data available for MPP that indicates MPP does not degrade in aerobic aquatic environments, it is unclear if this will be true for chronic concentrations of MPP and glufosinate. Since MPP is likely less toxic than the parent compound and should not be aggregated with the parent , if MPP EDWCs are not significantly greater than those for glufosinate, the risk assessment for the parent will be protective of any toxicity associated with exposure to MPP in drinking water. Therefore, a quantitative risk assessment for MPP in drinking water will not be required.Page 4 of 4

**A ppendix**  **1 .**  **Glufosinate Ammonium and it**  **m ajor**  **d egradates**  **in water .**  **Comm on**  **Name C**  **hemical Name**  **Structure Glufosinate**  **amm onium (parent)**  ( HOE 039866 ) IUPAC name: ammonium - DL - homoalanin 4 - yl - (methyl) -phosphinate CAS name: butanoic acid, (±) - 2 - amino - 4 - (hydroxymethylphosphinyl) - , mo noammonium salt P N H 2 O O H O C H 3 - O N H 4 + **MP P**  **(**HOE 061517 ) CAS Name: 3 - methylphosphinico -propionic

acid P H O C H 3 O O H

O **MPA (** HOE 064619 ) CAS Name: 2 - methylphosphinico - acetic acid P H O C H 3 O O

O H **NAG (** HOE 085355/HOE 099730 ) CAS Name: 2 - acetamido - 4 -

methylphosphinico -butanoic acid

P H O C H 3 O O

O H N H C H 3 O