UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

PC Code: 128850 

DP Barcode: 401123 

Date: 28 January 2013 

Subject: Preliminary Ecological Risk Assessment for the Registration Review of the 

Herbicide, Glufosinate-ammonium 

To: Katie Weyrauch, Chemical Review Manager 

Margarita Collantes, Acting Team Leader 

Risk Management and Implementation Branch III 

Pesticide Re-evaluation Division (Mail Code 7508P) I I "'? 

. I 1 <j I .} 

From:$_<--( Catherine Aubee, Biologist rvJ..~,., ~ . Chuck Peck, Environmental Engineer <.__j.)~ .?-e J .A iJ ~L -3 

Environmental Risk Branch IV 

Thru: 

Environmental Fate and Effects Division (Mail Code 7507P) 

Jim Carleton, Ph.D., Senior Scientist //· ~ ~ L/ l/2"r/.Jotl 1 

Thomas Steeger, Ph.D., Senior Scienc~~~ 1 /~s I I 3 

Marietta Echeverria, Branch Chief 1\1\ A :Hz_ ,c. . • I c { ., 

Environmental Risk Branch IV . 'Vt~ ~ r 2 1 1..) 

Environmental Fate and Effects Division (Mail Code 7507P) 

The Environmental Fate and Effects Division (EFED) has completed the preliminary 

environmental fate and ecological risk assessment (attached) for the Registration Review of the 

herbicide, glufosinate-arnmonium (PC Code 128850), hereafter referred to as glufosinate. 

The preliminary problem formulation (2008) identified uncertainties regarding the potential 

toxicity of glufosinate degradates. Recently reviewed aquatic ecotoxicity data are summarized in 

the risk assessment. These data demonstrate that glufosinate degradates (MPA, MPP, NAG) are 

generally equally or less toxic than glufosinate technical grade active ingredient (TGAI) but may 

cause adverse effects through acidification of the aquatic environment through the formation of 

these degradates. With this in mind, the preliminary risk assessment only evaluates exposure and 

risk to the parent compound, glufosinate, as exposure to the parent below the levels of concern 

should be protective of any exposure to the degradates. 

The preliminary assessment identifies potential chronic risk to mammals from most registered 

uses of glufosinate and risk to terrestrial and wetland plants from multiple agricultural and nonagricultural uses; these risks are substantiated by multiple lines of evidence including RQ values 

that exceed the Agency's Levels of Concern (LOCs). Certain uses of glufosinate may also result" 

in acute risk to mammals and chronic risks to birds, reptiles, and terrestrial-phase amphibians 
Transmittal Memo for the Registration Review PRA – Glufosinate-ammonium 

2 

exposed to glufosinate in the diet. The potential for acute risk to birds, reptiles, and terrestrialphase amphibians is based on sublethal effects (lethargy and diarrhea) through oral exposure 

estimates and is uncertain given the relatively high dietary exposure levels that would need to 

occur for animals foraging on a treated field to approach the equivalent oral dose. No mortalities 

or sublethal effects were observed in subacute dietary toxicity tests with birds at the limit dose 

(5,000 mg/kg diet). Acute risk to mammals and risks to birds are likely to be below the 

Agency’s LOCs when glufosinate is applied at “typical” application rates (and intervals). 

Off-site transport of glufosinate to surface water presents risk that exceeds the LOC for federally 

listed threatened and endangered species (hereafter referred to as “listed”) of aquatic nonvascular 

plants (e.g., algae). While there are currently no listed species of aquatic nonvascular plants, the 

degree to which direct effects on the aquatic plant community may result in indirect effects on 

other organisms is uncertain. Risks to aquatic nonvascular plants may be reduced below the 

listed species LOC by reducing the number of applications for certain uses. Risks to aquatic 

animals are not expected except as associated with the direct application of glufosinate to rice 

paddies. Uses on rice present risk to estuarine/marine invertebrates that exceeds the acute risk to 

listed species LOC, although the potential co-location of estuarine/marine invertebrates with 

treated rice paddies and receiving waters immediately downstream is uncertain. Overall, 

formulated glufosinate is generally more toxic to aquatic and terrestrial animals than the TGAI. 

Typical end-use product (TEP) data indicate that the use of formulated glufosinate on rice 

triggers additional risks for fish and amphibians that exceed the acute risk to listed species LOC. 

Finally, a spatial co-occurrence analysis that compares the best available data regarding 

glufosinate potential and documented use areas and listed species occurrence is needed to more 

explicitly address potential risk to listed species of concern. 

Additional Considerations for Listed Species 

At this stage of the Registration Review process, it is premature to make effects determinations 

for listed species until further refinements are conducted. In order to make effects 

determinations for individual species, useful refinements may include analyses of 1) more 

detailed, species-specific ecological and biological data; 2) more detailed and accurate 

information on glufosinate use patterns; and 3) sub-county level spatial proximity data for the cooccurrence of potential effects areas and listed species and any designated critical habitat. 

Examples of such refinements are described below. 

EFED is currently developing tools that are expected to further refine the assessment and are 

designed to support effects determinations for individual listed species and their designated 

critical habitats (where applicable). Scientific information obtained from the U.S. Fish & 

Wildlife Service (USFWS), the National Marine Fisheries Service (NMFS), and other reliable 

sources is being collated by EFED to address all currently listed species. The information will be 

stored in an Office of Pesticide Programs Pesticide Registration Information SysteM (PRISM) 

knowledgebase. The listed species knowledgebase will consist of an information repository that 

houses biological and behavioral information relevant to individual species (e.g., habitat, diet, 

and life history, including specific temporal and spatial associations) and a document repository 

that contains supporting documents (e.g., USFWS recovery plans) and electronic information 

(e.g., GIS data files). For terrestrial taxa, the biological information relevant to risk quotient 

(RQ) calculations (e.g., diet and body weight) will be used to parameterize exposure estimates to 
Transmittal Memo for the Registration Review PRA – Glufosinate-ammonium 

3 

derive species-specific RQs using a method consistent with currently used methods in the TREX and T-HERPS models. 

Refinements may also include more detailed analyses of the registered uses and their use patterns 

that result in LOC exceedances for federally listed species in the screening-level assessment. 

The analyses may include more information on where, when, and how glufosinate is used for 

agricultural and non-agricultural applications. Actual usage data (when available) and national 

land-cover datasets that indicate potential use sites [e.g., national land cover dataset (NLCD), 

crop data layer (CDL)] may be used to support a more refined analysis of where glufosinate is 

reasonably expected to be used. Similarly, refinements for the timing of applications and how 

glufosinate is used may be based on the analysis of additional usage data, beyond what were 

available at the time of the screening-level assessment, and a more in-depth exploration of 

agronomic practices. 

In addition, a committee of the National Research Council (NRC) has been tasked with 

providing advice on ecological risk assessment tools and scientific approaches under ESA and 

FIFRA (Project Identification Number DELS-BEST-11-01). The committee has been asked to 

review the use of “best available data”; methods for evaluating sublethal, indirect, and 

cumulative effects; the state of the science regarding assessment of mixtures and pesticide inert 

ingredients; the development, application, and interpretation of results from predictive models; 

uncertainty factors; and what constitutes authoritative geospatial and temporal information for 

the assessment of individual species and habitat effects. The Agency anticipates that this NRC 

report, tentatively expected in Spring 2013, will provide recommendations to ensure the 

scientific soundness and maximize the utility of risk assessment refinements for listed species. 

The refinements based on individual species data; additional, detailed usage information, when 

available; and further recommendations from the NRC report are expected to help to more 

accurately identify potential areas of effect and to better inform effects and habitat 

determinations for listed species and any designated critical habitats. For example, if glufosinate 

is used when a particular species of concern is not present (e.g., it is migratory) or is not colocated in space, then risk of potential direct effects to the species may often be precluded. If 

LOCs are still exceeded for taxa after conducting the refined analyses, further analyses of the 

potential spatial and temporal co-occurrence of listed species of concern (and any designated 

critical habitat) may be conducted. The extent of possible refinement in the analyses of 

spatial/temporal co-occurrence will largely depend on the scale and quality of the available subcounty level use site (e.g., NLCD, CDL) and species location data.