APPENDIX C 

ECOLOGICAL RISK ASSESSMENT 

ECOLOGICAL RISK ASSESSMENT

TABLE OF CONTENTS 

Page 

Structure and Methodology of the Ecological Risk Assessment .............................................................................C-1 

Problem Formulation.......................................................................................................................................C-1 

Exposure Characterization...............................................................................................................................C-2 

Effects Characterization...................................................................................................................................C-3 

Literature Review ....................................................................................................................................C-4 

Toxicity Reference Value Development .................................................................................................C-4 

Risk Characterization.......................................................................................................................................C-5 

Rare, Threatened, and Endangered Species.............................................................................................C-6 

Uncertainty Analysis .......................................................................................................................................C-7 

Application Methods and Herbicide Usage .............................................................................................................C-8 

Aerial Application ...........................................................................................................................................C-8 

Ground Application .........................................................................................................................................C-8 

Aquatic Application.........................................................................................................................................C-8 

Non-target Species Exposure Characterization......................................................................................................C-10 

Ecological Receptors .....................................................................................................................................C-10 

Surrogate Species ..................................................................................................................................C-10 

Exposure Pathways........................................................................................................................................C-12 

Direct Spray...........................................................................................................................................C-15 

Off-site Drift..........................................................................................................................................C-16 

Surface Runoff ......................................................................................................................................C-17 

Wind Erosion and Off-site Transport of Terrestrial Herbicide..............................................................C-20 

Accidental Spill .....................................................................................................................................C-22 

Non-target Species Effects Characterization .........................................................................................................C-22 

Terrestrial Species Effects Characterization..................................................................................................C-23 

Bromacil ................................................................................................................................................C-23 

Chlorsulfuron.........................................................................................................................................C-23 

Diflufenzopyr ........................................................................................................................................C-24 

Diquat ....................................................................................................................................................C-24 

Diuron....................................................................................................................................................C-25 

Fluridone ...............................................................................................................................................C-25 

Imazapic ................................................................................................................................................C-26 

Overdrive®.............................................................................................................................................C-27 

Sulfometuron Methyl.............................................................................................................................C-28 

Tebuthiuron ...........................................................................................................................................C-29 

Aquatic Species Effects Characterization......................................................................................................C-29 

Bromacil ................................................................................................................................................C-29 

Chlorsulfuron.........................................................................................................................................C-30 

Diflufenzopyr ........................................................................................................................................C-30 

Diquat ....................................................................................................................................................C-31 

Diuron....................................................................................................................................................C-31 

Fluridone ...............................................................................................................................................C-32 

Imazapic ................................................................................................................................................C-32 

Overdrive®.............................................................................................................................................C-33 

Sulfometuron Methyl.............................................................................................................................C-34 

Tebuthiuron ...........................................................................................................................................C-34 

Rare, Threatened, and Endangered Species Characterization........................................................................C-35 

Non-target Species Risk Characterization .............................................................................................................C-36 

Bromacil ........................................................................................................................................................C-36 

Direct Spray...........................................................................................................................................C-36 

Off-site Drift..........................................................................................................................................C-57 

BLM Vegetation Treatments Using Herbicides C-i June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Surface Runoff ...................................................................................................................................... C-58 

Wind Erosion and Transport Off-site.................................................................................................... C-58 

Accidental Spill to Pond........................................................................................................................ C-58 

Potential Risk to Salmonids from Indirect Effects ................................................................................ C-59 

Chlorsulfuron.................................................................................................................................................C-59 

Direct Spray .......................................................................................................................................... C-59 

Off-Site Drift......................................................................................................................................... C-59 

Surface Runoff ...................................................................................................................................... C-60 

Wind Erosion and Transport Off-site.................................................................................................... C-60 

Accidental Spill to Pond........................................................................................................................ C-60 

Potential Risk to Salmonids from Indirect Effects ................................................................................ C-61 

Diflufenzopyr ................................................................................................................................................C-61 

Direct Spray .......................................................................................................................................... C-61 

Off-site Drift.......................................................................................................................................... C-61 

Surface Runoff ...................................................................................................................................... C-62 

Wind Erosion and Transport Off-site.................................................................................................... C-62 

Accidental Spill to Pond........................................................................................................................ C-62 

Potential Risk to Salmonids from Indirect Effects ................................................................................ C-62 

Diquat ...........................................................................................................................................................C-63 

Direct Spray .......................................................................................................................................... C-63 

Off-site Drift to Terrestrial Plants ......................................................................................................... C-63 

Accidental Spill to Pond........................................................................................................................ C-64 

Potential Risk to Salmonids from Indirect Effects ................................................................................ C-64 

Diuron ...........................................................................................................................................................C-64 

Direct Spray .......................................................................................................................................... C-64 

Off-site Drift.......................................................................................................................................... C-65 

Surface Runoff ...................................................................................................................................... C-65 

Wind Erosion and Transport Off-site.................................................................................................... C-66 

Accidental Spill to Pond........................................................................................................................ C-66 

Potential Risk to Salmonids from Indirect Effects ................................................................................ C-66 

Fluridone .......................................................................................................................................................C-67 

Direct Spray .......................................................................................................................................... C-67 

Off-site Drift to Non-target Terrestrial Plants....................................................................................... C-68 

Accidental Spill to Pond........................................................................................................................ C-68 

Potential Risk to Salmonids from Indirect Effects ................................................................................ C-68 

Imazapic ........................................................................................................................................................C-69 

Direct Spray .......................................................................................................................................... C-69 

Off-site Drift.......................................................................................................................................... C-69 

Surface Runoff ...................................................................................................................................... C-69 

Wind Erosion and Transport Off-site.................................................................................................... C-70 

Accidental Spill to Pond........................................................................................................................ C-70 

Potential Risk to Salmonids from Indirect Effects ................................................................................ C-70 

Overdrive®.....................................................................................................................................................C-71 

Direct Spray .......................................................................................................................................... C-71 

Off-site Drift.......................................................................................................................................... C-71 

Surface Runoff ...................................................................................................................................... C-72 

Wind Erosion and Transport Off-site.................................................................................................... C-72 

Accidental Spill to Pond........................................................................................................................ C-72 

Potential Risk to Salmonids from Indirect Effects ................................................................................ C-73 

Sulfometuron Methyl.....................................................................................................................................C-73 

Direct Spray .......................................................................................................................................... C-73 

Off-site Drift.......................................................................................................................................... C-73 

Surface Runoff ...................................................................................................................................... C-74 

BLM Vegetation Treatments Using Herbicides C-ii June 2007 

Final Programmatic EIS 
ECOLOGICAL RISK ASSESSMENT

Wind Erosion and Transport Off-site ....................................................................................................C-74 

Accidental Spill to Pond........................................................................................................................C-74 

Potential Risk to Salmonids from Indirect Effects ................................................................................C-75 

Tebuthiuron ...................................................................................................................................................C-75 

Direct Spray...........................................................................................................................................C-75 

Off-site Drift..........................................................................................................................................C-76 

Surface Runoff ......................................................................................................................................C-76 

Wind Erosion and Transport Off-site ....................................................................................................C-77 

Accidental Spill to Pond........................................................................................................................C-77 

Potential Risk to Salmonids from Indirect Effects ................................................................................C-77 

Uncertainty Analysis..............................................................................................................................................C-78 

Toxicity Data Availability .............................................................................................................................C-78 

Degradates, Inert Ingredients, Adjuvants, and Tank Mixtures ......................................................................C-78 

Degradates.............................................................................................................................................C-83 

Inerts ......................................................................................................................................................C-83 

Adjuvants and Tank Mixtures ...............................................................................................................C-84 

Concentration Models....................................................................................................................................C-86 

AgDRIFT® ............................................................................................................................................C-86 

GLEAMS...............................................................................................................................................C-86 

CALPUFF .............................................................................................................................................C-87 

Potential Indirect Effects on Salmonids.........................................................................................................C-88 

Herbicide Application Recommendations .............................................................................................................C-88 

References..............................................................................................................................................................C-91 

List of Tables 

C-1 Levels of Concern ......................................................................................................................................C-6 

C-2 Herbicide Application Methods and Usage Statistics ................................................................................C-9 

C-3 Surrogate Species Used in Quantitative ERA Evaluations ......................................................................C-11 

C-4 Vertebrate Surrogate Species Evaluated by Life History.........................................................................C-12 

C-5 Selected Toxicity Reference Values for Bromacil ...................................................................................C-37 

C-6 Selected Toxicity Reference Values for Chlorsulfuron............................................................................C-39 

C-7 Selected Toxicity Reference Values for Diflufenzopyr ...........................................................................C-41 

C-8 Selected Toxicity Reference Values for Diquat .......................................................................................C-43 

C-9 Selected Toxicity Reference Values for Diuron.......................................................................................C-45 

C-10 Selected Toxicity Reference Values for Fluridone ..................................................................................C-47 

C-11 Selected Toxicity Reference Values for Imazapic ...................................................................................C-49 

C-12 Selected Toxicity Reference Values for Overdrive®................................................................................C-51 

C-13 Selected Toxicity Reference Values for Sulfometuron Methyl................................................................C-53 

C-14 Selected Toxicity Reference Values for Tebuthiuron ..............................................................................C-55 

C-15 Risk Levels Used to Describe Typical Herbicide Effects According to Exposure Scenario and 

 Ecological Receptor Group ......................................................................................................................C-79 

C-16 Buffer Distances (feet) to Minimize Risk from Off-site Drift of Herbicides...........................................C-89 

List of Figures 

C-1 Conceptual Model for Terrestrial Herbicides...........................................................................................C-13

C-2 Conceptual Model for Aquatic Herbicides...............................................................................................C-14

BLM Vegetation Treatments Using Herbicides C-iii June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

LIST OF ACRONYMS, ABBREVIATIONS, AND SYMBOLS 

ac - Acres 

a.i. - Active ingredient 

ATV - All terrain vehicle 

BA - Biological Assessment 

BLM - Bureau of Land Management 

BW - Body weight 

CALPUFF - California Puff Model 

CA OEHHA - California Office of Environmental Health Hazard Assessment 

cm - Centimeter 

cms - Cubic meters per second 

CREAMS - Chemical Runoff Erosion Assessment Management System 

Cpond - Concentrations from pond surface water 

EC25 - Concentration causing 25% inhibition of a process (effect concentration) 

EC50 - Concentration causing 50% inhibition of a process (median effective concentration) 

Ed. - Edition 

EEC - Estimated exposure concentration 

EFED - Environmental Fate and Effects Division 

EIS - Environmental Impact Statement 

ERA - Ecological risk assessment 

FCM - Food chain multiplier 

FIFRA - Federal Insecticide, Fungicide, and Rodenticide Act 

ft - Feet 

g - Grams 

gal - Gallon 

GLEAMS - Groundwater Loading Effects of Agricultural Management Systems 

HSDB - Hazardous Substances Data Bank 

in - Inch 

IRIS - Integrated Risk Information System 

kg - Kilogram 

km - Kilometers 

L - Liters 

lbs - Pounds 

LC50 - Concentration causing 50% mortality (median lethal concentration) 

LD50 - Dose causing 50% mortality (median lethal dose) 

LOAEL - Lowest observed adverse effect level 

LOC - Level of concern 

m - Meters 

mg - Milligrams 

mg/kg - Milligrams per kilogram 

mg/L - Milligrams per Liter 

μg - Micrograms 

μm - Micrometers 

MRID - Master Record Identifier Number 

MSDS - Material safety data sheet 

NASA - National Aeronautics and Space Administration 

NASQAN - National Stream Quality Accounting Network 

NCDC - National Climatic Data Center 

NOAEL - No observed adverse effect level 

NMFS - National Marine Fisheries Service 

NWS - National Weather Service 

BLM Vegetation Treatments Using Herbicides C-iv June 2007 

Final Programmatic EIS 
ECOLOGICAL RISK ASSESSMENT

LIST OF ACRONYMS, ABBREVIATIONS, AND SYMBOLS (Cont.) 

OPP - Office of Pesticide Programs 

PEIS - Programmatic Environmental Impact Statement 

PM - Particulate matter 

PM10 - Particulate matter less than 10 micrometers in diameter or less 

PM2.5 - Particulate matter less than 2.5 micrometers in diameter or less 

ROW - Rights-of-way 

RQ - Risk quotient 

RTE - Rare, threatened, and endangered 

RTEC - Registry of Toxic Effects of Chemical Substances 

SAMSON - Solar and Meteorological Surface Observation Network 

SDTF - Spray Drift Task Force 

TRV - Toxicity reference value 

TSP - Total suspended particulates 

US - United States 

USDA - United States Department of Agriculture 

USDI - United States Department of the Interior 

USEPA - United States Environmental Protection Agency 

USFWS - United States Fish and Wildlife Service 

USGS - United States Geological Survey 

USLE - Universal Soil Loss Equation 

> - Greater than 

< - Less than 

= - Equal to 

BLM Vegetation Treatments Using Herbicides C-v June 2007 

Final Programmatic EIS

ECOLOGICAL RISK ASSESSMENT

APPENDIX C 

ECOLOGICAL RISK ASSESSMENT 

The purpose of this appendix is to summarize the 

ecological risks to plants and animals from 10 

herbicides currently used, or proposed for use, by the 

United States Department of the Interior Bureau of 

Land Management (USDI BLM). More detailed 

assessments of these risks are given in Ecological Risk 

Assessments (ERA) prepared for each herbicide (see 

ENSR 2005a-j). These ERAs will be used by the 

BLM, in conjunction with analyses of other treatment 

effects on plants, animals, and other resources, to 

determine which of the proposed treatment alternatives 

evaluated in the Programmatic Environmental Impact 

Statement (PEIS) should be employed by the BLM. 

The BLM field offices will also utilize these ERAs for 

guidance on the proper application of herbicides to 

ensure that impacts to plants and animals are 

minimized to the extent practical when treating 

vegetation and do not pose unacceptable risks to nontarget species, including rare, threatened, and 

endangered (RTE) species. The U.S. Fish and Wildlife 

Service (USFWS) and National Oceanic and 

Atmospheric Administration National Marine 

Fisheries Service (NMFS), will also use the 

information provided by the ERAs to assess the 

potential impact of vegetation treatment actions on fish 

and wildlife and their critical habitats. 

The herbicide active ingredients (a.i.) evaluated in the 

ERAs are bromacil, chlorsulfuron, diflufenzopyr, 

diquat, diuron, fluridone, imazapic, Overdrive® (a mix 

of dicamba and diflufenzopyr), sulfometuron methyl, 

and tebuthiuron. Updated risk assessment methods 

were developed for the ERA process and are described 

in a separate document, Vegetation Treatments 

Programmatic EIS Ecological Risk Assessment 

Methodology (hereafter referred to as the “Methods 

Document” [ENSR 2004]). In addition, eight other 

herbicides are currently being used by the BLM and 

are proposed for continued use. These herbicides have 

been evaluated in a previous BLM EIS (USDI BLM 

1991), as well as more recently in an invasive plant 

EIS prepared by the U.S. Department of Agriculture 

Forest Service (Forest Service; USDA Forest Service 

2005). 

Structure and Methodology 

of the Ecological Risk 

Assessment 

Problem Formulation 

Assessment endpoints represent “explicit expressions 

of the actual environmental value that is to be 

protected, operationally defined by an ecological entity 

and its attributes” (U.S. Environmental Protection 

Agency [USEPA] 1998). In the context of the 

screening-level, programmatic risk assessment, 

ecological entities include terrestrial invertebrates and 

vertebrates, non-target plants, and aquatic organisms 

(including RTE species). The essential biological 

requirements (i.e., survival, growth, and reproduction) 

for each of these groups of organisms are the attributes 

to be protected from herbicide exposure. Assessment 

endpoints, for the most part, reflect direct effects of an 

herbicide on these organisms, but indirect effects were 

also considered (particularly for threatened and 

endangered salmonids). 

Measures of effect are measurable changes in an 

attribute of an assessment endpoint (or its surrogate, as 

discussed below) in response to a stressor to which it is 

exposed (USEPA 1998). For the screening-level ERA, 

the measures of effect associated with the assessment 

endpoints generally consisted of acute and chronic 

toxicity data (from pesticide registration documents 

and from the available scientific literature) for the 

most appropriate surrogate species. Rather than assess 

potential ecological risk to the large number of species 

found on public lands, surrogate species were used to 

represent classes of receptors (e.g., small mammalian 

herbivores, large avian piscivores [fish-eating birds]). 

In general, the surrogate species selected were those 

for which toxicity data were available from tests 

conducted in support of the USEPA pesticide 

registration process. Extrapolating chemical toxicity 

from a surrogate species to a particular species of 

concern can introduce extrapolation uncertainties 

(Fairbrother and Kapustka 1996, SERA 2000), but is 

often necessary in an ERA. 

BLM Vegetation Treatments Using Herbicides C-1 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Assessment endpoints (and associated measures of 

effect) were generated in the problem formulation for 

each herbicide. Selection of specific assessment 

endpoints depends on the type of herbicide and its use 

pattern (e.g., terrestrial vs. aquatic application) and on 

the availability of appropriate toxicity data. 

Assessment endpoints include: 

• Assessment Endpoint 1: Acute mortality to 

mammals, birds, invertebrates, and non-target 

plants. Measures of effect included median 

lethal effect doses (the dose lethal to 50% of 

organisms tested [LD50]) from acute toxicity 

tests with these organisms or suitable 

surrogates. 

• Assessment Endpoint 2: Acute mortality to fish, 

aquatic invertebrates, and aquatic plants. 

Measures of effect included median lethal 

effect concentrations (the concentration lethal 

to 50% of organisms tested [LC50]) from acute 

toxicity tests with these organisms or suitable 

surrogates (e.g., other coldwater fish are used 

to represent threatened and endangered 

salmonids). 

• Assessment Endpoint 3: Adverse direct effects 

on growth, reproduction, or other ecologically 

important sublethal processes. Measures of 

effect included standard chronic toxicity test 

endpoints such as the no observed adverse 

effect level ([NOAEL] the dose or 

concentration tested at which no adverse 

effects on test organisms were noted) for both 

terrestrial and aquatic organisms. Depending 

on data available for a given herbicide, chronic 

endpoints reflect either sublethal individual 

impacts (e.g., survival, growth, physiological 

impairment, behavior), or population-level 

impacts (e.g., reproduction [Barnthouse 1993]). 

For salmonids, careful attention was paid to 

smoltification (i.e., development of tolerance to 

seawater and other changes of parr [freshwater 

stage salmonids] to adulthood), 

thermoregulation (i.e., ability to maintain body 

temperature), migratory behavior, and other 

important life processes, if such data were 

available. With the exception of non-target 

plants, standard acute and chronic toxicity test 

endpoints were used for estimates of direct 

herbicide effects on RTE species. To add 

conservatism to the RTE assessment, levels of 

concern (LOCs) for RTE animals were lower 

than for typical species. Lowest available 

germination NOAELs were used to evaluate 

RTE plants. 

• Assessment Endpoint 4: Adverse indirect 

effects on the survival, growth, or reproduction 

of salmonids. Measures of effect for this 

assessment endpoint depended on the 

availability of appropriate scientific data. 

Unless literature studies were found that 

explicitly evaluated the indirect effects of the 

target herbicides to salmonids and their habitat, 

estimates of indirect effects were qualitative. 

Such qualitative estimates of indirect effects 

include general evaluations of the potential 

risks to food (typically represented by acute 

and/or chronic toxicity to aquatic invertebrates) 

and cover (typically represented by potential 

for destruction of riparian vegetation). The 

USEPA Office of Pesticide Programs (OPP) is 

currently applying approaches similar to these 

qualitative evaluations for RTE species effects 

determinations and consultations. 

Exposure Characterization 

The BLM uses herbicides in a variety of programs 

(e.g., maintenance of rangeland and recreational sites) 

using several different application methods (e.g., 

application by aircraft, vehicle, backpack). In order to 

assess the potential ecological impacts of these 

herbicide uses, a variety of exposure scenarios were 

considered. These scenarios were selected based on 

actual BLM herbicide usage under a variety of 

conditions. There are differences among the individual 

herbicide risk assessment results based on the actual 

uses of a particular herbicide. Differences may include 

those attributable to application methodology (ground 

vs. aerial), area of application (forest vs. non-forest), 

or herbicide type (aquatic vs. terrestrial). 

The exposure scenarios considered in the ERAs were 

organized by potential exposure pathways. In general, 

the exposure scenarios describe how a particular 

receptor group (e.g., terrestrial animals) may be 

exposed to the herbicide as a result of a particular 

exposure pathway. These exposure scenarios were 

designed to address herbicide exposure that may occur 

under a variety of conditions: 

• Direct spray of the receptor or waterbody 

• Indirect contact with dislodgeable foliar residue 

BLM Vegetation Treatments Using Herbicides C-2 June 2007 

Final Programmatic EIS 
ECOLOGICAL RISK ASSESSMENT

• Ingestion of contaminated food items 

• Off-site drift of spray to terrestrial areas and 

waterbodies 

• Surface runoff from the application area to offsite soils or waterbodies 

• Wind erosion resulting in deposition of 

contaminated dust 

• Accidental spills to waterbodies 

These scenarios were developed to address potential 

acute and chronic impacts to receptors under a variety 

of exposure conditions that may occur within public 

lands. These exposure conditions include normal 

application situations and associated off-site transport 

(via drift or wind erosion of dust), as well as accidental 

spills, and long-term overland flow to off-site soils and 

waterbodies (primarily via surface runoff and rootzone groundwater flow). 

Additional details regarding specific receptors (e.g., 

receptor size, diet, RTE species status), application 

rates (e.g., typical vs. maximum applications rates, 

accidental spills), duration of herbicide exposure (e.g., 

one-time event, long-term exposure), and toxicity 

endpoints (e.g., acute, chronic) are discussed below. 

Additional information can be found in the individual 

ERAs and associated risk assessment spreadsheets 

compiled for each herbicide (ENSR 2005a-j). 

Because of the differences in the application methods 

for terrestrial and aquatic herbicides, there were fewer 

exposure scenarios for aquatic herbicides. Off-site 

transport of the aquatic herbicides via surface runoff 

and wind erosion were not considered to be realistic 

scenarios for these applications and were therefore not 

considered for the aquatic herbicides. However, 

accidental direct spray of aquatic herbicides onto 

terrestrial receptors and off-site drift onto terrestrial 

plants were considered. The more conservative direct 

spray scenario was assumed to address any potential 

impacts from the other transport mechanisms. Details 

of the exposure scenarios considered in the risk 

assessments are presented in Section 3.0 of the 

Methods Document (ENSR 2004). 

Herbicide levels resulting in potential risk to surrogate 

species were calculated using conservative 

assumptions. Exposure scenarios were included that 

are unlikely to occur (e.g., direct spray of receptor or 

waterbody, accidental spills to waterbodies). 

Furthermore, animals were assumed to have a home 

range equal to the application area, whereas many 

animals would range outside of application areas, 

reducing exposure. In addition, all applied herbicide 

was assumed to be biologically available, and no 

attempt was made to assess the tendency of herbicide 

degradation or water flow to decrease herbicide 

concentrations and exposure (see Appendix B of the 

ERAs [ENSR 2005a-j] for equations and calculations 

for each of the different exposure scenarios). 

Exposure characterizations depend on the selection of 

appropriate fate and transport models that predict 

herbicide concentrations in various environmental 

media, such as tissues, soils, and water. Some of these 

models are fairly straightforward and only require 

simple algebraic calculations (e.g., water 

concentrations from direct aerial spray), but others 

require more complex computer models (e.g., aerial 

deposition rates, transport from soils). 

The AgDRIFT® computer model (see page C-86) was 

used to estimate off-site herbicide transport due to 

spray drift. The Groundwater Loading Effects of 

Agricultural Management Systems (GLEAMS) 

computer model (see page C-86) was used to estimate 

off-site transport of herbicide in surface runoff and 

root-zone groundwater transport (Knisel and Davis 

2000). The computer model California Puff 

(CALPUFF; see page C-86) was used to predict the 

transport and deposition of herbicides sorbed (i.e., 

reversibly or temporarily attached) to wind-blown 

dust. Each model simulation was approached with the 

intent of predicting the maximum potential herbicide 

concentration that could result from the given 

exposure scenario. 

Effects Characterization 

The ecological effects characterization phase of an 

ERA entails a compilation and analysis of the stressorresponse relationships and any other evidence of 

adverse impacts from exposure to each herbicide. This 

evidence consisted mostly of toxicity studies 

conducted in support of USEPA pesticide registration, 

which generally include the following (additional 

studies may be required depending on herbicide use 

patterns and characteristics: 

• Avian oral LD50

• Avian dietary LC50

• Freshwater fish acute LC50

BLM Vegetation Treatments Using Herbicides C-3 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

• Freshwater invertebrate acute LC50

Additional tests, if required for a particular herbicide, 

may include honeybee acute toxicity, avian 

reproduction, non-target plant toxicity, and chronic 

fish life-cycle tests, among others. As data were not 

available for all receptors or for threatened/endangered 

species, extrapolation of risk based on surrogate 

species data was necessary. Species for which toxicity 

data were available were not necessarily the most 

sensitive species to a particular herbicide (these 

species are used as laboratory test organisms because 

they are generally sensitive to stressors and they can 

be maintained under laboratory conditions). The 

selected toxicity value for a receptor is based on a 

review of the available data for the most appropriate, 

sensitive surrogate species. 

In the majority of cases, toxicological data do not exist 

for the specific ecological receptors of concern. 

Consequently, toxicological data for surrogate species 

were evaluated and used to establish quantitative 

benchmarks for the ecological receptors of concern. 

These benchmark values are referred to as toxicity 

reference values (TRVs). This section of text briefly 

describes the process used to derive TRVs. Once 

developed, TRVs were compared with predicted 

environmental concentrations of the herbicide to 

determine the likelihood of adverse effects to 

ecological receptors. 

Literature Review 

The literature review process for deriving TRVs 

consisted of assembling relevant literature, evaluating 

these information sources, and then establishing 

specific numeric values for each ecological receptor. 

Literature sources included published manuscripts, 

unpublished study reports, and electronic databases. 

Once data from these various sources were compiled, 

the information was reviewed to determine its 

acceptability for deriving ecological TRVs for each of 

the 10 herbicides. In order to be classified as an 

“acceptable” study, the research had to be suitable and 

of adequate quality (see following sections). 

Data Suitability 

For each chemical, the available literature was 

evaluated to determine if the data were suitable for use 

in deriving TRVs. Early in the ERA process, the BLM 

identified receptors that were representative of 

ecological guilds (i.e., general taxonomic groups 

comprised of animals or plants that perform particular 

roles in the ecosystem, including small and large 

mammals, small and large birds, piscivorous birds, 

fish, reptiles, insects, amphibians, terrestrial and 

aquatic plants, and algae) and their primary routes of 

exposure. Evaluation of suitability was based on these 

ecological receptors and routes of exposure. 

Specifically, a study was considered suitable if the 

following criteria were met: 

• The material tested was one of the 10 

herbicides; 

• the test species was in the same guild as an 

ecological receptor; 

• the route of exposure matched the primary 

routes of exposure for species in that guild; and 

• the toxicity assessment endpoint (e.g., 

mortality, reproductive success, growth) was 

considered to be ecologically relevant. 

For the majority of studies, the acute statistical 

measures of effect consisted of LD50, LC50, or EC50

(the concentration resulting in a defined effect in 50% 

of the receptors tested) values. Adverse effect levels in 

chronic studies were most frequently reported as 

lowest observed adverse effect levels (LOAELs). 

Levels at which no effects were noted were generally 

reported in chronic studies as NOAELs. Several 

additional statistical endpoints were evaluated for 

terrestrial plants, including EC25 (the concentration 

resulting in a defined effect in 25% of the receptors 

tested), NOAEL, and highest and lowest NOAEL (for 

germination and emergence endpoints only). 

Data Adequacy 

Once determined to be suitable, a study was then 

evaluated to determine whether the data were 

adequate. For peer-reviewed literature, two senior 

toxicologists independently determined data adequacy. 

Each paper was scored based on several selection 

criteria, including documentation of number of test 

organisms, statistical analysis, and proper use and 

performance of controls. Based on these reviews, the 

study was classified as either “adequate” or “not 

adequate.” 

Toxicity Reference Value Development 

Study findings met both data adequacy and suitability 

criteria were used to develop ecological TRVs. From 

these studies, statistical endpoints were compiled into 

BLM Vegetation Treatments Using Herbicides C-4 June 2007 

Final Programmatic EIS 
ECOLOGICAL RISK ASSESSMENT

a matrix for each chemical and for each receptor. Data Use of the Uncertainty Factor 

were further subdivided into acute adverse effect 

levels, chronic adverse effect levels, and no adverse 

effect levels. 

In some cases, a TRV for a particular assessment 

endpoint had to be extrapolated from available TRVs 

using an uncertainty factor. Based on a review of the 

application of uncertainty factors (Chapman et al. 

1998), an uncertainty factor of 3 was considered to be 

appropriate for ecological TRV derivation in this 

document. For example, a chronic or an acute TRV 

(e.g., 100 mg/kg BW) could be divided by an 

uncertainty factor of 3 to obtain an extrapolated 

NOAEL (e.g., 33 mg/kg BW). Conversely, if a 

NOAEL value was available, but a chronic TRV was 

lacking, the NOAEL TRV could be multiplied by 3 to 

extrapolate the chronic TRV (but not the acute TRV). 

Endpoints for a receptor and routes of exposure were 

converted to the same units (e.g., mg/kg body weight 

[BW]). Endpoints for aquatic organisms and terrestrial 

plants were reported based on exposure concentrations 

(mg/L and lbs/acre [ac], respectively). Dose-based 

endpoints (e.g., LD50) were used for the remaining 

receptors. When possible, dose-based endpoints were 

obtained directly from the literature. When dosages 

were not reported, dietary concentration data (e.g., 

LC50) were converted to dose-based values following 

the methodology recommended in USEPA risk 

assessment guidelines (Sample et al. 1996). See the 

ERA Methods document (ENSR 2004; Table 2-3) for 

a summary of animal body weights and feeding and 

drinking ingestion rates that were used to convert 

concentration endpoints to dose-based endpoints. 

Risk Characterization 

The risk characterization phase of an ERA consists of 

a quantitative estimate of the ecological risks, a 

description of data used in support of these risk 

estimates (including data gaps where appropriate), and 

an overall interpretation of the potential ecological 

impacts of each herbicide (following consideration of 

uncertainties in the analyses). 

Toxicity Reference Value Derivation 

Once the data were expressed in comparable units, the 

numeric values from studies classified as “acceptable” 

were compared to derive TRVs. For each chemical, 

receptor, and route of exposure, the lowest reported 

acute statistical endpoint was selected as the acute 

TRV. Acute TRVs were derived first to provide an 

upper boundary for the remaining TRVs; chronic 

TRVs and NOAELs were always equivalent to, or less 

than, the acute TRV. 

In order to address potential risks to ecological 

receptors, risk quotients (RQs) were calculated by 

dividing the estimated exposure concentration (EEC) 

for each of the previously described scenarios by the 

appropriate toxicity endpoint, an herbicide-specific 

TRV. The TRV may be a surface water or surface soil 

effects concentration, or a species-specific toxicity 

value derived from the literature. 

The toxicity endpoint for most acute studies was 

mortality, immobilization, or failure to germinate, as 

assessed during a short-term exposure. In some cases, 

acute data were not always available. Consequently, 

chronic TRVs, based on longer exposure periods and 

associated endpoints such as growth and reproduction, 

were developed to provide supplementary data to the 

risk assessment. Conversely, when no valid statistical 

endpoints from chronic studies were available, the 

chronic TRV was set equal to the acute TRV. In the 

majority of cases, however, chronic data were 

available. Before the chronic NOAEL TRV was 

determined, a chronic LOAEL was identified, which 

was the lowest herbicide level that was found to cause 

significant adverse effects in a chronic study. Once a 

LOAEL was established, the chronic NOAEL TRV 

was established as the highest NOAEL value that was 

less than both the LOAEL and the acute TRV. 

The RQs were then compared against LOCs 

established by the USEPA OPP to assess potential risk 

to non-target organisms. These LOCs are used by the 

USEPA’s OPP to analyze potential risk to non-target 

organisms and to assess the need to consider 

regulatory action (Table C-1). Distinct® USEPA LOCs 

are currently defined for the following risk 

presumption categories: 

• Acute high risk – the potential for acute risk is 

high. 

• Acute restricted use − the potential for acute 

risk is high, but may be mitigated. 

• Acute RTE species – RTE species may be 

adversely affected. 

BLM Vegetation Treatments Using Herbicides C-5 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

TABLE C-1 

Levels of Concern 

Risk Presumption RQ LOC 

Terrestrial Animals 1

Acute high risk EEC/LC50 0.5 

Acute restricted use EEC/LC50 0.2 

Acute RTE species EEC/LC50 0.1 Birds 

Chronic risk EEC/NOAEL 1 

Acute high risk EEC/LC50 0.5 

Acute restricted use EEC/LC50 0.2 

Acute RTE species EEC/LC50 0.1 Wild mammals 

Chronic risk EEC/NOAEL 1 

Aquatic Animals 2

Acute high risk EEC/LC50 or EC50 0.5 

Acute restricted use EEC/LC50 or EC50 0.1 

Acute RTE species EEC/LC50 or EC50 0.05 

Chronic risk EEC/NOAEL 1 

Fish and aquatic 

invertebrates 

Chronic risk, RTE species EEC/NOAEL 0.5 

Plants 3

Terrestrial/semi-aquatic Acute high risk EEC/EC25 1 

plants Acute RTE species EEC/NOAEL 1 

Acute high risk EEC2/EC50 1 Aquatic plants Acute RTE species EEC/NOAEL 1 1

 Estimated Environmental Concentration is in mg prey wet weight/kg BW for acute scenarios and mg prey wet weight/kg BW/day for chronic 

scenarios. 2

 Estimated Environmental Concentration is in mg/L. 

3

 Estimated Environmental Concentration is in lb/acre. 

• Chronic risk - the potential for chronic risk is 

high. 

A “chronic RTE species” risk presumption category 

for aquatic animals was added for this risk assessment. 

The LOC for this category was set to 0.5 to reflect a 

conservative 2-fold difference in contaminant 

sensitivity between RTE and surrogate test fishes 

(Sappington et al. 2001). 

Risk quotients (RQs) and LOCs were tabulated and 

compared for all appropriate exposure scenarios and 

surrogate species described above. The ecological risk 

implications of various exposure estimates can be 

readily determined by noting which RQs exceed the 

corresponding LOCs. Over 1,000 RQs were generated 

in each ERA. While all RQs are presented in the 

supporting documentation of the risk assessment and 

available to BLM field offices, only selected values 

(e.g., those exceeding LOCs) are discussed within the 

text of each ERA report (ENSR 2005a-j). 

Rare, Threatened, and Endangered Species 

To specifically address potential impacts to RTE 

species, two types of RQ evaluations were conducted. 

For RTE terrestrial plant species, the RQ was 

calculated using different toxicity endpoints but 

keeping the same LOC (1) for all scenarios. The plant 

toxicity endpoints were selected to provide extra 

protection to RTE species. In the direct spray, spray 

drift, and wind erosion scenarios, the selected toxicity 

endpoints were an EC25 for “typical” species and a 

NOAEL for RTE species. In runoff scenarios, high and 

low germination NOAELs were selected to evaluate 

exposure for typical and RTE species, respectively. 

The evaluation of RTE terrestrial animals and aquatic 

species was addressed using a second type of RQ 

evaluation. The same toxicity endpoint was used for 

both typical and RTE species in all scenarios, but the 

acute LOC was lowered for RTE species (see Table C1). 

BLM Vegetation Treatments Using Herbicides C-6 June 2007 

Final Programmatic EIS 
ECOLOGICAL RISK ASSESSMENT

Uncertainty Analysis 

For any ERA, a thorough description of uncertainties 

is a key component that serves to identify possible 

weaknesses in the analysis and to elucidate what 

impact such weaknesses might have on the final risk 

conclusions. In general, an uncertainty analysis lists 

the uncertainties, followed by a logical discussion of 

what bias, if any, the uncertainty may introduce into 

the risk conclusions. This bias would be represented in 

qualitative terms that best describe whether the 

uncertainty might: 1) underestimate risk, 2) 

overestimate risk, 3) be neutral with regard to the risk 

estimates, or 4) be unable to be determined without 

additional study. Key categories of uncertainty for the 

herbicides ERAs include: 

• Limited toxicity data available for a given 

herbicide. For some herbicides, the only 

toxicity data available may be those studies 

conducted as part of the USEPA pesticide 

registration process. In this case, chronic 

toxicity data may be limited or non-existent 

and may not include sublethal studies of 

importance relevant to assessment endpoint 4 

(Adverse indirect effects on the survival, 

growth, or reproduction of salmonids). When 

relevant studies did not exist, the uncertainties 

were discussed as thoroughly as possible. 

• The potential indirect effects of herbicides on 

RTE salmonids. Unless actual field studies 

were identified for a given herbicide, this 

discussion was limited to only qualitative 

estimates of potential indirect impacts on 

salmonid populations and communities. Such 

qualitative estimates were limited to a general 

evaluation of the potential risks to food 

(typically represented by acute and/or chronic 

toxicity to aquatic invertebrates) and cover 

(typically represented by potential for 

destruction of riparian vegetation or aquatic 

vegetation, if appropriate). The USEPA OPP is 

using similar approaches for RTE species 

effects determinations and consultations.1

• Extrapolating from laboratory to field studies. 

It is preferable to base any ecological risk 

analysis on reliable field studies that can 

clearly identify and quantify the amount of 

 

1 http://www.epa.gov/oppfead1/endanger/effects.

potential risk from particular exposure 

concentrations of the chemical of concern as 

field studies provide a more accurate 

representation of environmental conditions. 

When available, incident reports for the 

USEPA’s Environmental Fate and Effects 

Division (EFED) were reviewed in an attempt 

to validate both exposure models and/or 

hazards to ecological receptors. For many of 

the new herbicides, however, such studies were 

not available. Most available incident reports 

present incomplete data, and explicit 

information linking herbicide exposure and 

resulting effects are difficult to interpret. In 

these cases, best professional judgment was 

used to evaluate the potential bias, if any, the 

lack of field studies had on risk conclusions. It 

should be noted, though, that in most cases 

laboratory studies actually overestimate risk 

relative to field studies, supporting the 

conservative nature of the risk assessment 

(Fairbrother and Kapustka 1996). 

• Ecological risks of inert ingredients, adjuvants, 

degradates, and tank mixtures. From an 

ecological point of view, it is desirable to 

estimate risks not just from the a.i. of an 

herbicide, but also from the cumulative 

exposure to other ingredients. However, using 

currently available models (e.g., GLEAMS), 

deterministic risk calculations (i.e., exposure 

modeling, effects assessment, and RQ 

calculations) can only be conducted for a single 

a.i. However, qualitative estimates were made 

of the potential additional risks (if any) posed 

by chemicals added to the a.i. of an herbicide, 

such as inert ingredients (ingredients lacking 

active properties though still potentially toxic), 

adjuvants (chemicals used to enhance the 

pharmacological or toxic agent effect of the 

a.i.), and degradates (chemicals created during 

the natural breakdown or decomposition of 

another chemical). 

Evaluating the potential additional/cumulative risks 

from mixtures of pesticides is substantially more 

difficult, particularly at the level of a PEIS. The 

composition of such mixtures is highly site-specific, 

and thus nearly impossible to address at the 

programmatic level. However, the label information 

from each of the 10 herbicides mentions that most can 

be “tank mixed” with other herbicides and insecticides. 

Therefore, for each herbicide, a qualitative evaluation 

BLM Vegetation Treatments Using Herbicides C-7 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

was made of the potential additional risk that might 

result from applying each as part of a label-approved 

tank mix. It should be emphasized that this evaluation 

was only qualitative, based on risk conclusions from 

existing ERAs conducted for an earlier EIS (USDI 

BLM 1991), for the USDA Forest Service, or by the 

USEPA for registration and/or re-registration. Such an 

analysis can only be qualitative unless reliable 

scientific evidence exists to suggest whether the joint 

action of the herbicides is additive, synergistic, or 

antagonistic. 

• Estimates of herbicide exposure 

concentrations. As in any screening or highertier ERA, a discussion of potential uncertainties 

from fate and exposure modeling is necessary 

to identify potential overestimates or 

underestimates of risk. In particular, the 

uncertainty analysis focused on which 

environmental characteristics (e.g., soil type, 

annual precipitation) exert the most significant 

numeric impact on model outputs. The results 

of the uncertainty analysis have important 

implications about the ability to apply risk 

calculations to different site characteristics 

from a risk management point of view. 

Application Methods and 

Herbicide Usage 

Table C-2 provides herbicide usage statistics, 

including application sites, application methods, and 

application rates. 

Aerial Application 

Aerial application is conducted from fixed-wing planes 

and/or rotary helicopters in the BLM Rangeland, 

Public Domain Forestland, Energy and Mineral Sites, 

Rights-of-way (ROW), Recreation, and Aquatics 

programs. ERA modeling assumed that herbicides 

were applied with buffers of 100, 300, and 900 feet (ft) 

from evaluated receptors, and application heights 

varied depending on whether the application area was 

forested or not. 

Ground Application 

Ground applications take place in the BLM Rangeland, 

Public Domain Forestland, Energy and Mineral Sites, 

ROW, Recreation, and Aquatics programs. 

Applications are conducted on foot or horseback using 

backpack sprayers or from vehicles (truck, all-terrain 

vehicle [ATV], boat) using spot or boom/broadcast 

(low or high boom) methods. For modeling purposes, 

herbicides were applied with buffers of 25, 100, and 

900 ft from evaluated receptors. 

Aquatic Application 

There are four zones in a body of water that may be 

treated for the management of aquatic weeds: water 

surface, total water volume, bottom 1 to 3 ft of water, 

and the bottom soil surface. 

When working in the water surface zone, generally 

only a fourth to a third of the surface area is treated at 

a time. Applications are made to floating or emergent 

weeds with the spray mixture being applied directly to 

the plants. When treating the total water volume, 

applications can be made through the metering or 

injecting of the herbicide into the water from booms 

trailing behind the boat or as a spray over the water 

surface. Applications of this type are made to 

submersed aquatic plants and algae. Treatments to the 

deepest 1 to 3 ft of water are generally made by 

attaching several flexible hoses at specific intervals on 

a rigid boom. Each hose is equipped with a nozzle and 

may be weighted to reach the depth desired. The 

length of hose and the speed of the boat carrying the 

application equipment also affect the depth of 

application. Such applications are beneficial because 

they apply the herbicide in a layer nearer the area 

where the herbicide can be taken up by the weedy 

species. The final zone, bottom soil surface, refers to 

applications made to the bottom soil of a drained pond, 

lake, or channel. 

To treat small areas, a compressed-air sprayer with a 

hand-operated pump may be all that is needed. For 

larger areas, a boat-mounted pump-and-tank rig with 

one line may be used to treat emergent plants on a spot 

treat basis. A boom attached to the boat may be used 

when broadcast applications are made to the surface of 

the water, and booms with flexible hoses attached to 

the boom may be used to make the application below 

the water surface. Applications of granules and slowrelease pellets can be made either using a cyclone 

spreader or by hand. The granules sink to the bottom, 

where the chemical is slowly released in the relatively 

small volume of water where the new shoots are 

beginning to grow. 

Floating and emergent vegetation in static water (i.e., 

water in ponds, lakes, or reservoirs that have little or 

BLM Vegetation Treatments Using Herbicides C-8 June 2007 

Final Programmatic EIS 
ECOLOGICAL RISK ASSESSMENT

TABLE C-2 

Herbicide Application Methods and Usage Statistics 

Application Rate 

Herbicide (lbs. a.i./acre) Programs/Treatment 

Areas Application Method 

Typical Maximum

Bromacil 

Energy and mineral sites 

Rights-of-way 

Recreation 

Backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

4.0 12.0 

Chlorsulfuron 

Rangeland 

Energy and mineral sites 

Rights-of-way 

Recreation 

Plane, helicopter 

backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

0.047 0.062 

Diflufenzopyr 

Rangeland 

Energy and mineral sites 

Rights-of-way 

Recreation 

Backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

0.075 0.1 

Diquat Aquatic 

Plane, helicopter 

backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

1.0 4.0 

Diuron 

Energy and mineral sites 

Rights-of-way 

Recreation 

Backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

6.0 20.0 

Fluridone Aquatic 

Plane, helicopter 

backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

0.15 1.3 

Imazapic 

Rangeland 

Public domain forestland 

Energy and mineral sites 

Rights-of-way 

Recreation 

Plane, helicopter 

backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

0.0313 0.1875 

Overdrive®

Rangeland 

Oil and gas 

Rights-of-way 

Recreation 

Backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

0.2625 0.35 

Sulfometuron methyl 

Public domain forestland 

Energy and mineral sites 

Rights-of-way 

Recreation 

Helicopter 

Backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

0.14 0.38 

Tebuthiuron 

Rangeland 

Energy and mineral sites 

Rights-of-way 

Recreation 

Plane, helicopter 

backpack, horseback, 

ATV, and truck (spot, 

boom/broadcast) 

0.5 4.0 

BLM Vegetation Treatments Using Herbicides C-9 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

no inflow and outflow) is managed by direct foliage 

applications of the spray mixture by aircraft, with 

ground equipment operated from the bank if the pond 

is small or if the weeds occur only around the margins, 

or from a boat using various types of booms or hand 

applicators. 

Aquatic vegetation in flowing water is more difficult 

to manage. Floating and emergent vegetation, when 

treated in flowing water, require the same treatment 

techniques as they do in the static water. Submersed 

vegetation and algae can be controlled effectively in 

flowing water only by continuously applying enough 

herbicide at a given spot to maintain the needed 

concentration and contact time. 

Non-target Species Exposure 

Characterization 

As described earlier, a number of exposure scenarios 

were developed to address potential acute and chronic 

impacts to receptors under a variety of exposure 

conditions that may occur within public lands. These 

exposure conditions include normal application 

situations, accidental spills, and associated off-site 

transport via spray drift, windblown dust, or surface 

runoff and root-zone groundwater. In general, the 

exposure scenarios describe how a particular receptor 

group (e.g., terrestrial animals, terrestrial plants, 

aquatic plants) may be exposed to an herbicide in a 

complete exposure pathway. The selected pathways 

and relevant dose calculations are described in more 

detail in the following sections. 

This section discusses the exposure of terrestrial and 

aquatic receptors to the 10 herbicides proposed for 

new and continued use on public lands in 17 western 

states. The processes of surrogate species selection and 

the calculation of exposure data based on species 

biology and herbicide application rates are presented 

below. 

Ecological Receptors 

Surrogate Species 

Use of surrogate species in a screening ERA is 

necessary to address the broad range of species likely 

to be encountered on public lands as well as to 

accommodate the fact that toxicity data may be 

restricted to a limited number of species. In this ERA, 

surrogates were selected to account for variation in the 

nature of potential herbicide exposure (e.g., direct 

contact, food chain) as well as to ensure that different 

taxa and their behaviors were considered. Generally, 

the surrogate species that were used in the ERAs are 

species commonly used as representative species in 

ecological risk assessments. Many of these species are 

common laboratory species, or are described in the 

USEPA (1993a, b) Wildlife Exposure Factors 

Handbook. Other species were included in the 

California Wildlife Biology, Exposure Factor, and 

Toxicity Database (California Office of Environmental 

Health Hazard Assessment [CA OEHHA] 2003), or 

are those recommended by USEPA OPP for tests to 

support pesticide registration. 

Toxicity data from surrogate species were used in the 

development of TRVs. The surrogate species used for 

development of TRVs in each herbicide ERA are 

presented in Table C-3. For vertebrate terrestrial 

animals, in addition to these surrogate species, specific 

species were selected to represent populations of 

similar species (Table C-4). Interspecies extrapolation 

of toxicity data often produces unknown bias in risk 

calculations; therefore, higher trophic-level species 

were grouped according to shared life-history traits 

(e.g., herbivore vs. carnivore). Whenever possible, the 

species selected are found throughout the range of land 

included in the PEIS; all species selected are found in 

at least a portion of the range. The surrogate species 

are common species whose life histories are well 

documented (USEPA 1993a, b; CA OEHHA 2003). 

Because species-specific data, including body weight 

and food ingestion rates, can vary for a single species 

throughout its range, data from studies conducted in 

western states or with western populations were 

selected preferentially. This life-history procedure was 

not done for plants, invertebrates, and fish, as most 

exposure of these species to herbicides is via direct 

contact (e.g., foliar deposition, dermal deposition, 

dermal/gill uptake) rather than ingestion of 

contaminated prey items. Therefore, altering the life 

history of these species would not result in more or 

less exposure. In addition, potential impacts to nontarget terrestrial plants were considered by evaluating 

two non-target plant receptors: the “typical” (i.e., nonRTE) species and the RTE species. 

Very few laboratory studies have been conducted 

using reptiles or amphibians. Therefore, data specific 

to the adverse effects of a chemical on species of these 

taxa are often unavailable. These animals, being coldblooded, have very different rates of metabolism than 

mammals or birds (i.e., they require lower rates of 

BLM Vegetation Treatments Using Herbicides C-10 June 2007 

Final Programmatic EIS 
ECOLOGICAL RISK ASSESSMENT

TABLE C-3 

Surrogate Species Used in Quantitative ERA Evaluations 

Surrogate Species Scientific Name Receptor Herbicide 

Honeybee Apis mellifera Pollinating insects 

Bromacil, chlorsulfuron, diflufenzopyr, 

diquat, diuron, fluridone, imazapic, 

sulfometuron methyl, and tebuthiuron 

Mouse Mus musculus Mammals Bromacil, diquat, fluridone, sulfometuron 

methyl, and tebuthiuron 

Rat Rattus norvegicus spp. Mammals 

Bromacil, chlorsulfuron, diflufenzopyr, 

diquat, diuron, fluridone, imazapic, 

sulfometuron methyl, and tebuthiuron 

Dog Canis familiaris Mammals 

Bromacil, chlorsulfuron, diflufenzopyr, 

diquat, diuron, fluridone, imazapic, 

sulfometuron methyl, and tebuthiuron 

Rabbit Leporidae sp. Mammals 

Bromacil, chlorsulfuron, diflufenzopyr, 

diquat, diuron, fluridone, imazapic, 

sulfometuron methyl, and tebuthiuron 

Guinea pig Cavia sp. Mammals Chlorsulfuron 

Mallard Anas platyrhynchos Birds 

Bromacil, chlorsulfuron, diflufenzopyr, 

diquat, diuron, fluridone, imazapic, and 

sulfometuron methyl 

Bobwhite quail Colinus virginianus Birds Bromacil, diflufenzopyr, diquat, diuron, 

sulfometuron methyl, and tebuthiuron 

Ring-necked 

pheasant Phasianus colchicus Birds Diquat, fluridone, and imazapic 

Japanese quail Coturnix coturnix Birds Diquat 

Chicken Gallus gallus Birds Tebuthiuron 

Rape Orobanche sp. Non-target terrestrial plants Bromacil 

Soybean Glycine max Non-target terrestrial plants Bromacil, diuron, and imazapic 

Canola Brassica napus Non-target terrestrial plants Chlorsulfuron 

Dyer's woad 

(weed) Isatis tinctoria Non-target terrestrial plants Chlorsulfuron 

Turnip Brassica rapa Non-target terrestrial plants Diflufenzopyr 

Tomato Lycopersicon esculentum Non-target terrestrial plants Diflufenzopyr and diuron 

Corn Zea mays Non-target terrestrial plants Diquat and imazapic 

Garden pea Pisum sativum Non-target terrestrial plants Diuron 

Vegetative crop 9 species, monocotyledons and 

dicotyledons Non-target terrestrial plants Imazapic 

Onion Allium cepa Non-target terrestrial plants Imazapic 

White mustard Sinapis alba Non-target terrestrial plants Sulfometuron methyl 

Leafy spurge Euphorbia esula Non-target terrestrial plants Sulfometuron methyl 

Sorghum Sorghum bicolor Non-target terrestrial plants Sulfometuron methyl 

Sugarbeet Beta vulgaris Non-target terrestrial plants Sulfometuron methyl 

Cabbage Brassica sp. Non-target terrestrial plants Tebuthiuron 

Daphnid Daphnia magna Aquatic invertebrates Bromacil, chlorsulfuron, diflufenzopyr, 

diquat, imazapic, and sulfometuron methyl 

Daphnid Ceriodaphnia dubia Aquatic invertebrates Sulfometuron methyl and tebuthiuron 

Scud Gammarus fasciatus Aquatic invertebrates Diuron 

Amphipod Hyalella azteca Aquatic invertebrates Diquat 

Midge Chironomus tentans Aquatic invertebrates Fluridone 

Snail Helisoma and Physa spp. Aquatic invertebrates Tebuthiuron 

BLM Vegetation Treatments Using Herbicides C-11 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

TABLE C-3 (Cont.) 

Surrogate Species Used in Quantitative ERA Evaluations 

Surrogate Species Scientific Name Receptor Herbicide 

Fathead minnow Pimephales promelas Fish Bromacil, diuron, sulfometuron methyl, and 

tebuthiuron 

Channel catfish Ictalurus punctatus Fish Chlorsulfuron 

Bluegill sunfish Lepomis macrochirus Fish Diflufenzopyr and tebuthiuron 

Walleye Stizostedion vitreum Fish Diquat 

Brown trout Salmo trutta Fish/salmonids Chlorsulfuron 

Rainbow trout Oncorhynchus mykiss Fish/salmonids Bromacil, diflufenzopyr, diquat, fluridone, 

imazapic, and sulfometuron methyl 

Cutthroat trout Oncorhynchus clarki Fish/salmonids Diuron 

Sago pondweed Potamogeton pectinatus Non-target aquatic plants Chlorsulfuron 

American 

pondweed Potamogeton nodosus Non-target aquatic plants Fluridone 

Green algae Selanastrum capricornutum Non-target aquatic plants Bromacil, diflufenzopyr, diuron, and 

tebuthiuron 

Algae Chlorella pyrenoidosa Non-target aquatic plants Diuron 

Duckweed Lemna sp. Non-target aquatic plants Diquat and imazapic 

Macrophyte Myriophyllum sibiricum Non-target aquatic plants Sulfometuron methyl 

 

TABLE C-4 

Vertebrate Surrogate Species Evaluated by Life History 

Species Scientific Name Trophic Level/Guild Pathway 

Evaluated 

American robin Turdus migratorius Avian invertivore/vermivore/insectivore Ingestion 

Canada goose Branta canadensis Avian granivore/herbivore Ingestion 

Deer mouse Peromyscus maniculatus Mammalian frugivore/herbivore Direct contact and 

ingestion 

Mule deer Odocoileus hemionus Mammalian herbivore/gramivore Ingestion 

Bald eagle 

(northern) Haliaeetus leucocephalus alascanus Avian carnivore/piscivore Ingestion 

Coyote Canis latrans Mammalian carnivore Ingestion 

food consumption). Nonetheless, mammals and birds 

were used as the surrogate species for reptiles and 

adult amphibians because of the lack of data for these 

taxa (fish were used as surrogates for juvenile 

amphibians). 

Aquatic exposure pathways were evaluated using fish, 

aquatic invertebrates, and non-target aquatic plants for 

two types of generic aquatic habitat: 1) a small pond 

1⁄4-acre in area, 1 meter (m) in depth, and 1,011,715 

liters (L) in volume, and 2) a small stream 

representative of Pacific Northwest low-order streams 

that provide habitat for critical life-stages of 

anadromous salmonids (the stream is defined as 2 mwide and 0.2-m deep, with a mean water velocity of 

approximately 0.3 m per second, resulting in a base 

flow discharge of 0.12 cubic meters per second [cms]). 

Exposure Pathways 

The following is a brief description of the scenarios 

used to address potential impacts to non-target 

organisms both within the area where the herbicide is 

being applied and outside the application area 

(accidental exposures not typical of BLM practices). 

Conceptual models were developed that provide 

working hypotheses about how terrestrial (Figure C-1) 

and aquatic (Figure C-2) herbicides might pose risk to 

the ecosystem and ecological receptors. The 

conceptual models indicate the possible exposure 

BLM Vegetation Treatments Using Herbicides C-12 June 2007 

Final Programmatic EIS 
BLM Vegetation Treatment Using Herbicides C-13 June 2007 

Final Programmatic EIS 

FIGURE C-1. Conceptual Model for Terrestrial Herbicides. 

IMPACTED SOIL

Infiltration

Percolation

Aquatic

Plants

 [direct contact]

Off-site Drift

Surface Runoff

Non-Target

Terrestrial Plants

[direct seed

contact with soil]

IMPACTED ROOT ZONE GROUNDWATER

Non-Target

Terrestrial

Plants [direct

contact]

Direct Spray

IMPACTED 

POND OR STREAM

Inv

[dir

Pisciv

Bird [ing

contamin

Wind

Erosion

Terrestrial Wildlife

[direct contact;

indirect contact;

ingestion]

Application of terrestrial herbicides may occur by aerial (i.e., plane, helicopter) or ground (I.e., truck, backpack) methods.See Figure 4-2 for simplified food web & evaluated receptors.
FIGURE C-2. Conceptual Model for Aquatic Herbicides. 

Aquatic

Plants

 [direct contact]

Accidental Direct Spray

IMPACTED

POND OR STREAM

Fish and

Aquatic

Invertebrates

[direct contact]

Terrestrial Wildlife

[direct contact;

indirect contact;

ingestion] Non-Target

Terrestrial

Plants [direct

contact]

Application of aquatic herbicides may occur from a boat or from the shoreline.

Normal Direct Spray 

Accidental Direct Spra

BLM Vegetation Treatment Using Herbicides C-14 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

BLM Vegetation Treatments Using Herbicides C-15 June 2007 

Final Programmatic EIS

pathways for the herbicides, as well as the receptors 

evaluated for each exposure pathway. 

Direct Spray 

Plant and wildlife species may be unintentionally 

impacted during application of either a terrestrial or 

aquatic herbicide as a result of direct spray of the 

receptor or the waterbody inhabited by the receptor, 

indirect contact with dislodgeable foliar residue after 

herbicide application, or consumption of prey items 

sprayed during application. These exposures may 

occur within the application area (e.g., consumption of 

prey items) or outside of the application area (e.g., 

terrestrial plants accidentally sprayed during 

application of aquatic herbicide). Generally, impacts 

outside of the intended application area are accidental 

exposures that are not typical of BLM application 

practices. 

Direct Spray of Terrestrial or Aquatic 

Herbicide on Terrestrial Wildlife 

Scenarios involving direct spray of an herbicide 

consider acute exposures of vertebrate and invertebrate 

species considered most sensitive to herbicide 

exposure under laboratory conditions. It was assumed 

that small mammals are the most sensitive terrestrial 

vertebrate species, and that mobile pollinating 

invertebrates that spend time foraging among different 

plant species (e.g., honeybees) are the most sensitive 

terrestrial invertebrate receptor. If available literature 

data for a particular herbicide suggested that other 

terrestrial vertebrates (e.g., birds) or invertebrates (e.g., 

earthworms) were more sensitive, the more sensitive 

receptor was used for this scenario. 

The extent of exposure from direct spray of a receptor 

is based on three variables: the herbicide application 

rate, the surface area of the receptor species, and the 

rate of dermal absorption. Both typical and maximum 

herbicide application rates were evaluated for each 

herbicide for representative sensitive species. For each 

receptor it was assumed that exposure occurred over 

one-half the body surface. The surface area calculation 

was obtained from the Wildlife Exposure Factors 

Handbook (USEPA 1993a). 

Two scenarios were evaluated for the honeybee and 

small mammal to address the potential differences in 

absorption. The first case considered 100% absorption 

(intake through the skin) over 24 hours (i.e., all of the 

herbicide falling on the receptor was assumed to 

penetrate the skin). The second scenario considered the 

absorbed dose over 24 hours assuming first order 

dermal absorption (i.e., taking into consideration the 

potential for some herbicide to not be absorbed). 

Indirect Contact with Foliage after Direct 

Spray of Terrestrial or Aquatic Herbicide 

Scenarios involving direct spray of an herbicide 

consider only acute exposures. Foliage that has been 

sprayed with herbicide may transfer this herbicide to 

terrestrial animals through dermal contact with 

dislodgeable foliar residue. However, there is little 

information available on the potential magnitude of 

this transfer from plant to animal. Therefore, it was 

assumed that the amount of herbicide transferred to the 

animal was 1

/10 the amount the animal received during 

direct spray scenarios. This assumption was based on 

the work of Harris and Solomon (1992). It was also 

assumed that all herbicide transferred to the outside of 

the animal was completely adsorbed within 24 hours. 

Ingestion of Food Items Contaminated by 

Direct Spray of Terrestrial or Aquatic 

Herbicide 

Scenarios involving ingestion of food items consider 

both acute and chronic exposures. The terrestrial 

receptors considered for these scenarios included small 

and large mammals and small and large birds. 

Ingestion rates for the species consuming 

contaminated food items were obtained from field 

studies based on allometric equations presented in the 

Wildlife Exposure Factors Handbook (USEPA 1993a). 

It was conservatively assumed that the exposed 

receptors obtain 100% of their diet from the herbicide 

contaminated prey items and that 100% of the applied 

herbicide drifts onto the prey item. Concentrations of 

the herbicide on vegetation and insects were predicted 

using individual herbicide application rates and 

generic residue relationships for different types of 

vegetation derived by Hoerger and Kenaga (1972). 

The residue rate for forage crops was used as a 

surrogate for contaminated insects. Residue rates were 

not available for small mammals. 

Two exposure scenarios were considered for the 

ingestion of contaminated prey items. The first 

scenario assumes that the prey item is consumed on 

the same day it is contaminated with herbicide (no 

degradation period). Ingested doses for this scenario 

were compared to acute toxicity endpoints. The second 

scenario assumes the prey is consumed up through 90 

days after the application of the herbicide. Assuming 

first-order decay rates, the herbicide dose is predicted 
ECOLOGICAL RISK ASSESSMENT

as a time-weighted average of the herbicide mass on 

the foliage over the 90-day period. This dose is 

compared to chronic toxicity endpoints. 

Direct Spray of Terrestrial or Aquatic 

Herbicide on Non-target Terrestrial Plants 

In the direct spray scenario, a non-target plant is 

sprayed during normal application of the terrestrial 

herbicide. Unintended direct spray of a non-target 

receptor is considered an accidental exposure scenario 

that is not typical of BLM application practices. The 

typical and maximum application rates were used to 

represent the amount accidentally sprayed on the nontarget species. These application rates were directly 

compared to appropriate toxicity endpoints to 

determine potential impacts to non-target typical and 

RTE plants. 

Direct Spray of Terrestrial or Aquatic 

Herbicide onto Pond 

The normal application of aquatic herbicides to a pond 

was considered to evaluate potential impacts to aquatic 

receptors other than the target plant species. For this 

scenario, the typical and maximum application rates of 

the herbicides were applied directly to the pond, and 

the associated water concentration was calculated 

based on the pond area and volume. Neither 

degradation nor sorption of the herbicide to sediments, 

aquatic vegetation, or suspended solids were 

considered, resulting in a conservative estimate of the 

herbicide concentration in pond water. The pond water 

concentrations were compared against appropriate 

acute and chronic toxicity endpoints to evaluate 

potential impacts to fish, aquatic invertebrates, and 

non-target aquatic plants. 

Accidental Direct Spray of Terrestrial or 

Aquatic Herbicide onto Stream 

Aquatic and terrestrial herbicides may be accidentally 

directly sprayed onto the surface of a stream (stream 

plants are not targeted with herbicide applications). 

The typical and maximum application rates of the 

herbicides were applied directly to the stream, and the 

associated water concentrations were calculated. 

Degradation and sorption of the herbicide and 

transport from flow of the stream were not considered, 

and therefore, this represents a conservative 

calculation of the stream water concentration 

(essentially an instantaneous concentration). The 

stream concentrations were compared against 

appropriate acute and chronic toxicity endpoints to 

evaluate potential impacts to fish, aquatic 

invertebrates, and non-target aquatic plants. 

Off-site Drift 

During normal application of herbicides, it is possible 

for a portion of the herbicide to drift outside of the 

treatment area and deposit onto non-target receptors. 

Off-site spray drift and resulting terrestrial deposition 

rates and waterbody (pond and stream) concentrations 

were predicted using the computer model AgDRIFT® 

Version 2.0.05. AgDRIFT® is a product of the 

Cooperative Research and Development Agreement 

between the USEPA’s Office of Research and 

Development and the Spray Drift Task Force (SDTF; a 

coalition of pesticide registrants). It is based on, and 

represents an enhancement of, the computer program 

for agricultural dispersion (AGDISP). AGDISP was 

developed by the National Aeronautics and Space 

Administration (NASA), the USDA Forest Service, 

and the U.S. Army. AgDRIFT® was developed for use 

in regulatory assessments of off-site drift associated 

with agricultural use of pesticides through aerial, 

ground, or orchard/airblast applications. AgDRIFT® is 

based upon the idea that pesticide or herbicide drift is 

primarily a function of application technique (e.g., 

droplet size and release height), environmental 

conditions, and physical properties of the spray 

solution, and is not a function of the chemical 

properties of the a.i. itself. The computational 

approach employed by AgDRIFT® is based on a 

method that has evolved over a period of more than 20 

years, and yields high correlation with field 

measurement data sets. The model was selected for use 

in this risk assessment because of its existing use in 

regulatory assessments of off-target drift and its 

suitability to this particular application. 

AgDRIFT® enables the user to take a tiered approach 

to the modeling of drift by allowing the user to choose 

between three tiers (Tiers I, II, and III) of increasingly 

complex evaluations of off-target drift and deposition. 

The basic difference between the three tiers is the 

number of model input variables the users can change. 

Further, Tier I supports the evaluation of aerial and 

ground application scenarios, whereas Tiers II and III 

only support the evaluation of aerial application 

scenarios (agricultural and forestry applications). Tier 

I is based on a set of standard “Good Application 

Practices,” requires little knowledge of the actual 

application conditions or herbicide properties, and 

allows the user to modify a small number of model 

variables. Tiers II and III are based on the same set of 

“Good Application Practices;” however Tiers II and III 

BLM Vegetation Treatments Using Herbicides C-16 June 2007 

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ECOLOGICAL RISK ASSESSMENT

allow the user to modify variables to make the 

scenario evaluated representative of the conditions 

under which herbicides will be applied. Tier I was 

used in the ERAs to evaluate off-site drift associated 

with ground application scenarios, and Tier II was 

used to evaluate off-site drift associated with 

agriculture-like (e.g., rangeland) and forestry 

application scenarios. The implementation of the Tier I 

ground and Tier II aerial application model and the 

model input variables (including the variables specific 

to the application method and environmental setting 

and specific to the herbicide being evaluated) are 

discussed and presented in Appendix A of the Methods 

document (ENSR 2004). 

In accordance with actual BLM herbicide practices, 

ground application scenarios were modeled using a 

low- or high-placed boom. Aerial application scenarios 

were modeled from either a helicopter or a plane at 

two different heights representing forested or nonforested land types. Drift depositions were estimated at 

25, 100, and 900 ft from the application area for 

ground applications and at 100, 300, and 900 ft for 

aerial applications. The AgDRIFT® model determined 

the fraction of the application rate that would be 

deposited on the off-site location without considering 

herbicide degradation. 

Off-site Drift of Terrestrial Herbicide onto 

Plants 

Surface soil concentrations calculated by AgDRIFT® 

were directly compared against appropriate toxicity 

endpoints to determine potential impacts to non-target 

typical and RTE plants. 

Off-site Drift of Terrestrial Herbicide onto 

Pond or Stream 

During normal application, is possible for a portion of 

the terrestrial herbicide to drift outside of the treatment 

area. This off-site drift may eventually reach a pond or 

stream and contaminate the waterbody. AgDRIFT® 

was used to calculate pond and stream water 

concentrations of the herbicide in the various 

application scenarios. The waterbody concentrations 

calculated by AgDRIFT® do not consider herbicide 

degradation, sorption, or dissipation, and likely 

overestimate actual concentrations. AgDRIFT® does 

consider the dilution of the herbicide in the volume of 

the pond, but the rate of deposition estimated by 

AgDRIFT® was diluted into the stream based on the 

assumed flow rate. 

The predicted surface water concentrations in the pond 

and stream as a result of the various application 

scenarios were compared to the appropriate acute and 

chronic toxicity endpoint for each of the three aquatic 

receptors. 

Consumption of Fish from Pond Contaminated 

by Off-site Drift of Terrestrial Herbicide 

Off-site drift of herbicide may eventually reach off-site 

ponds and contaminate the resident fish population, 

which may be consumed by piscivorous bird species. 

In this scenario, impacted pond water is modeled using 

AgDRIFT® input variables described above. Exposure 

for the piscivorous bird was evaluated by modeling 

fish tissue concentrations from pond surface water 

(Cpond) employing bioconcentration factors and food 

chain multipliers (FCMs) for different trophic levels. 

Food chain multipliers assumed a trophic level 3 for 

fish and a trophic level 2 for the prey of fish (e.g., 

aquatic invertebrates). FCMs were obtained from 

USEPA (1995a). 

The calculated dose to the piscivorous bird is a 

function of the concentration in the fish tissue, the 

food ingestion rate in wet weight, the proportion of the 

diet that is contaminated (assumed to be 100%), and 

the body weight of the bird. The dose estimate to the 

piscivorous bird was compared to appropriate chronic 

toxicity values. 

Surface Runoff 

Precipitation may result in the transport of herbicide 

applied to soils from the application area via surface 

runoff and root-zone groundwater flow. GLEAMS was 

used in this risk assessment to calculate soil 

concentrations at the site of application, transport of 

herbicides to adjacent soils, and the amount of 

herbicide that might runoff into aquatic habitats (e.g., 

ponds, streams). One benefit of GLEAMS is the ability 

to estimate a wide range of potential herbicide 

exposure concentrations as a function of site-specific 

parameters, such as soil characteristics and annual 

precipitation. 

GLEAMS Overview 

GLEAMS is a modified version of the CREAMS 

(Chemical Runoff Erosion Assessment Management 

System) model that was originally developed to 

evaluate non-point source pollution from field-size 

areas. Specifically, the hydrology, plant nutrient, and 

pesticide components of the CREAMS model were 

BLM Vegetation Treatments Using Herbicides C-17 June 2007 

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ECOLOGICAL RISK ASSESSMENT

modified to consider movement of water and 

chemicals within and through the root zone. These 

modifications allow the GLEAMS model to simulate 

edge-of-field and bottom-of-root-zone loadings of 

water, sediment, pesticides, and plant nutrients from 

the complex climate-soil-management interactions. 

Agricultural pesticides are simulated by GLEAMS 

using three major components: 

• Hydrology – considers the effects of 

precipitation, surface runoff, and percolation 

through the unsaturated zone of the soil and 

simulates the effects of vegetation on surface 

water runoff, infiltration, and 

evapotranspiration. 

• Erosion – considers the movement of sediment 

over the land surface using the Universal Soil 

Loss Equation (USLE) and pesticide loss 

associated with particle erosion. 

• Pesticide – considers chemical-specific 

characteristics (e.g., soil adsorption, decay) and 

application methods to determine the amount 

of herbicide that is available for extraction into 

surface runoff and/or movement into the soil 

profile and groundwater. 

The GLEAMS model has evolved through several 

versions from its inception in 1984 to the present, and it 

has been evaluated in numerous climatic and soil 

regions around the world. The model was selected for 

use in this investigation because of its widespread 

acceptance, its suitability to this particular application, 

and the previous use of the model to support similar risk 

assessments for the USDA Forest Service (e.g., SERA 

2003). 

Data Requirements. The information required for a 

GLEAMS simulation includes a wide variety of sitespecific data to describe the climate, topography, 

subsurface soils, vegetation type and growing 

potential, and herbicide-specific properties. The 

following briefly describes a subset of the data 

required to successfully simulate the effects of an 

herbicide on an agricultural site using GLEAMS: 

• Precipitation – Daily rainfall records for the 

entire simulation period are required to provide 

input to the hydrologic simulation. The volume 

of precipitation strongly influences the amount 

of runoff and percolation of associated 

herbicides. 

• Climate – Daily averages of standard 

meteorological data are necessary to define 

precipitation as either rain or snow and to 

calculate variations in monthly 

evapotranspiration. Because evapotranspiration 

is a large component of the hydrologic cycle, 

the climate (e.g., temperature, humidity) can 

affect the volume of water moving through the 

application area. 

• Soil characteristics – Soil characteristics (as 

identified by soil type) are applied to the 

GLEAMS model to facilitate the calculation of 

runoff and percolation from the application 

area. 

• Vegetation/ground cover – Plant growth 

controls the partitioning of pesticide to either 

the soil or foliar surfaces and controls the rate 

of evapotranspiration. 

• Herbicide properties – The varying distribution 

of pesticide concentrations predicted by 

GLEAMS in an agricultural system is largely 

dependent on the chemical-specific properties 

used in the model, such as sorption coefficients 

and decay rates. As these values are herbicidespecific and can vary significantly, 

concentrations predicted by GLEAMS can be 

quite different among herbicides. 

GLEAMS Model Scenarios 

The GLEAMS model was run using a variety of model 

inputs designed to simulate a broad range of 

representative environmental conditions. The effect of 

changing environmental conditions on the export of 

herbicide from an application area was assessed in two 

distinct phases: 

• Variable soil type and annual precipitation – 

The effects of soil type and cumulative annual 

precipitation were investigated by developing a 

single realistic GLEAMS scenario (base case) 

and then varying these two components. Soil 

type and precipitation were selected for the first 

phase of the modeling application because they 

are the factors most likely to affect the outcome 

of a simulation. The model was used to 

calculate herbicide export in environments with 

the three soil types (sand, loam, and clay) 

assuming annual precipitation rates of 5, 10, 

25, 50, 100, 150, 200, and 250 inches (in). In 

BLM Vegetation Treatments Using Herbicides C-18 June 2007 

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ECOLOGICAL RISK ASSESSMENT

total, there were 24 simulation combinations in 

this first phase of the modeling application. 

• Variable physical characteristics – The effect 

of varying six physical parameters (soil type, 

soil erodibility factor, size of application area, 

hydraulic slope, surface roughness, and 

vegetation type) was investigated by changing 

each parameter individually. There were 3 

variations for each of the 6 parameters, 

resulting in 18 simulations in this second phase 

of the modeling application. 

The combination of scenarios included in each of the 

two phases of GLEAMS modeling produced results 

for 42 simulations. These simulations provide an 

indication of the effects of a variety of environmental 

conditions on the export of herbicide to off-site 

receptors. These scenarios were used to predict 

herbicide concentrations in soil and in the surface 

water of a stream and a pond. 

The GLEAMS model predicts daily herbicide export 

rates. Because conservative assumptions were used in 

the model, it is likely that the export rates predicted by 

GLEAMS are high. This is substantiated by the 

comparison of the GLEAMS export rates modeled 

here to measured data presented by Lerch and 

Blanchard (2003), where GLEAMS export rates were 

higher than measured rates. Details of this comparison 

are presented in Appendix B of the ERA Methods 

document (ENSR 2004). 

The daily export rates were used to calculate both 

surface soil and ambient water concentrations. The 

predicted runoff and percolation rates, and the mass of 

herbicide associated with each of these exports, were 

used to determine the amount of herbicide deposited at 

the edge of the application area. 

The soil concentrations were calculated as 52, 7-day 

average concentrations from the final year of the 

GLEAMS run (when the model reaches a quasi-steady 

state). Ambient water concentrations were calculated 

using GLEAMS model daily predictions of herbicide 

export rates for acute and chronic exposure scenarios 

in a river and a pond immediately adjacent to the 

application area. Acute exposure scenario 

concentrations were calculated from the maximum 3-

day average herbicide export rate from the last year of 

the simulation. Chronic exposure scenario 

concentrations were calculated from the daily average 

herbicide export rate from the last year of the 

simulation. 

The following subsections present a general overview 

of the calculation of media concentrations in a variety 

of different terrestrial exposure scenarios (the surface 

runoff scenarios are not considered relevant for the 

aquatic herbicides). A more detailed discussion 

(including assumptions and equations) is presented in 

Appendix B of the ERA Methods document (ENSR 

2004). Each herbicide risk assessment (ENSR 2005a-j) 

contains an herbicide-specific description of the model 

outputs. 

Surface Runoff of Terrestrial Herbicide to Offsite Soils 

The maximum of the 7-day average loadings 

calculated by GLEAMS was assumed to affect a soil 

area immediately downslope of the application area. 

The loading was expressed as a proportion of the total 

herbicide loading to the application area. For example, 

if 30% of the applied herbicide was found to run off, 

the soil concentration off-site was predicted to be 30% 

of that in the application area. These off-site soil 

concentrations were compared against appropriate 

toxicity endpoints to determine potential impacts to 

non-target typical and RTE plants. This particular 

exposure pathway may impact seed germination; 

therefore, toxicity data relevant to seed germination, a 

sensitive endpoint, were used for evaluation. 

Overland Flow of Terrestrial Herbicide to Offsite Pond and Stream 

As described previously, precipitation may result in 

the transport of terrestrial herbicides via surface runoff 

and root-zone groundwater flow. This overland flow of 

herbicide applied to soil (via runoff and groundwater) 

may eventually reach an off-site pond or stream 

resulting in the contamination of the waterbody. The 

daily predictions of herbicide export rates from the 

GLEAMS model were used to calculate ambient water 

concentrations of herbicide in the various watershed 

scenarios. GLEAMS considers the subsequent runoff 

and the natural decay processes that reduce the 

ambient pond water concentrations over time. Pond 

concentrations were calculated by assuming a fixed 

pond volume and a daily inflow of mass and water to 

the pond depending on recent precipitation, runoff, and 

percolation characteristics. The GLEAMS exports 

were used to calculate two pond and two stream water 

concentrations for comparison against acute and 

chronic toxicity endpoints for each of the three aquatic 

receptor groups. 

BLM Vegetation Treatments Using Herbicides C-19 June 2007 

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ECOLOGICAL RISK ASSESSMENT

Consumption of Fish from Pond Contaminated 

by Surface Runoff of Terrestrial Herbicide 

Surface runoff containing herbicide bound to soil may 

eventually reach an off-site pond, and resident fish 

may uptake herbicide. The fish, in turn, may be 

consumed by piscivorous bird species. In this scenario, 

impacted pond water was modeled using the 

GLEAMS model described above. Since 

bioaccumulation is a long-term process, the chronic 

exposure concentration (i.e., the overall average 

concentration from the final year of the GLEAMS run) 

was used to predict fish tissue concentrations. A 

bioconcentration factor and food chain multipliers for 

different trophic levels were included in the estimate. 

Food chain multipliers assumed a trophic level 3 for 

fish and a trophic level 2 for the prey of fish (e.g., 

aquatic invertebrates). Food chain multipliers were 

obtained from USEPA (1995a). The calculated dose to 

the piscivorous bird is a function of the concentration 

in the fish tissue, the food ingestion rate in wet weight, 

the proportion of the diet that is contaminated 

(assumed to be 100%), and the body weight of the 

bird. 

Wind Erosion and Off-site Transport of Terrestrial 

Herbicide 

Dry conditions and wind may also allow transport of 

herbicide from the application area as wind-blown soil 

(fugitive dust) onto non-target plants some distance 

away. This transport due to wind erosion of the surface 

soil was modeled using the USEPA’s guideline air 

quality CALPUFF air pollutant dispersion model 

(referenced in Appendix W of 40 CFR Part 51; see the 

Air Quality Modeling for BLM Vegetation Treatment 

Methods report [“Air Quality Modeling report;” ENSR 

2005k] for CALPUFF details and assumptions). 

CALPUFF “lite” version 5.7 was selected because of 

its ability to screen potential air quality impacts within 

and beyond 50 kilometers (km) and its ability to 

simulate plume trajectory over several hours of 

transport based on limited meteorological data. Three 

distinct watersheds were modeled using CALPUFF to 

determine herbicide concentrations in particulate 

matter assumed to deposit on plants (i.e., total 

suspended particulates [TSPs] ranging between 0.1 

and 50 micrometers [μm] in diameter, particulate 

matter [PM] 2.5 μm in diameter and smaller [PM2.5], 

and PM10 μm in diameter and smaller). The 

concentrations were modeled after a wind event, with 

dust deposition estimates calculated at distances 

ranging from 1.5 to 100 km from the application area. 

At each radius considered, the maximum predicted rate 

of herbicide deposition in a given wind event was 

calculated. The dust estimates calculated within the 

model were then compared against the appropriate 

non-target plant toxicity values. 

The dust exposure scenario was not considered for 

aquatic herbicides. 

Source Characterization 

A high wind event may cause the surface soil (with the 

applied herbicide) to migrate from the application area. 

In this modeled event, CALPUFF determines the rate 

of herbicide deposition as a function of the rate of dust 

deposition at the downstream receptor location. It was 

assumed that all of the applied herbicide was adsorbed 

by the top 1 mm of soil. The depth of 1 mm is believed 

to be conservative (thinner affected soil depths result 

in elevated herbicide emissions during fugitive dust 

events), and is less than that assumed by others (e.g., 

SERA [2003] assumed 1 cm). The modeling assumed 

a square, flat area of 1,000 acres was treated with 

herbicide applied from the air using a fixed-wing 

aircraft. For suspended particulate matter, modeled 

impacts were directly proportional to the modeled 

emission rate. Therefore, the modeling assumed a unit 

rate of chemical application/deposition (i.e., 1.0 gram 

per square meter). The model results can be scaled 

directly to accommodate varying application rates to 

bare, undisturbed soil. The modeling results were 

expressed as the fractional downwind deposition based 

on this initial application. 

Determination of Wind Erosion Event 

The CALPUFF model was used to estimate acute 

exposures. The maximum 1-hour and 24-hour, and 

annual average, deposition rates from a conservative 

impact migration event (i.e., an event modeled using 

very conservative properties such that the potential for 

dust migration is high) were computed for the distance 

ranges being modeled (1.5 to 100 km). Although a 

given area would be sprayed with herbicide only once 

per year, a full year was modeled to consider a large 

range of meteorological conditions that could 

influence the herbicide migration potential for a single 

event. The highest impact was considered to represent 

a “reasonable, but conservative” impact under the 

range of the meteorological conditions tested. For this 

modeling, there was no initial restriction on the timing 

of the herbicide application except as noted below. 

The herbicide was assumed to adhere to undisturbed 

surface soil, which can be picked up and transported 

BLM Vegetation Treatments Using Herbicides C-20 June 2007 

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ECOLOGICAL RISK ASSESSMENT

by sufficiently high winds. The threshold wind speed 

for such an event is linked to the “friction velocity,” 

which is a measure of the mechanical turbulence at the 

soil-atmosphere interface, and thus is a good gauge of 

the ability of the wind to pick up surface particles. 

Friction velocity increases with increasing wind speed 

and increasing surface roughness. Threshold friction 

velocities for undisturbed soils were determined from 

Gillette (1988), as described in the Air Quality

Modeling for BLM Vegetation Treatment Methods

report (ENSR 2005k). The BLM (Ypsilantis 2003) 

identified appropriate soil types for each of the 

“example” modeling analysis locations, as discussed in 

more detail in the air quality modeling report. 

The CALPUFF modeling procedures assumed that, for 

each modeled hour of the entire year, the friction 

velocity exceeded the threshold friction velocity for 

undisturbed soil. A portion of the herbicide spray mass 

from the 1,000-acre area therefore became airborne, 

subject to additional conditions listed below. This 

assumption is conservative because it also assumes 

that all of the chemical herbicide would be present in 

the soil at the commencement of a windy event, and 

that no reduction due to vegetation interception/uptake, leaching, solar or chemical half-life would have 

occurred since the time of aerial application. However, 

the use of a full year of meteorology provides a robust 

procedure to assess the maximum meteorological 

condition (i.e., the weather most likely to cause dust 

migration) for short-term impacts. 

In addition to the threshold friction velocity 

requirement for hourly fugitive emissions of 

windblown soil, other triggering conditions were 

considered: 

• Wet soil adjustment - assumed no hourly 

particulate matter emissions when there was 

measurable hourly precipitation (at least 0.01 

in). 

• Frozen soil adjustment - assumed no hourly 

particulate matter emissions when the hourly 

ambient temperature was at/below 28 degrees 

Fahrenheit. 

• Snow cover adjustment - assumed no hourly 

particulate matter emissions when the hourly 

snow depth was at least 1 inch. 

• Operational adjustment - assumed only one 

application of chemical herbicide per given 

1,000 ac location in the same year. 

For these conditions, the surface soil is resistant to 

movement because it is wet, frozen, and/or covered 

with an insulating layer of snow. It was assumed that 

there would be no spraying on a snow-covered surface, 

although a layer of snow could appear after a spraying 

event. 

Determination of Herbicide Emission Rates 

The initial incorporation depth of herbicide (1 mm) 

determines the concentration of herbicide on eroded 

dust and defines the depth of erosion at which the mass 

of herbicide would be exhausted. This mixed depth is 

based on fast-acting physical processes and does not 

include leaching of herbicide into the soil due to 

precipitation. 

The mixed layer depth is estimated to account for three 

processes: 

• Physical infiltration of the herbicide into the 

soil. This is likely a minor factor as little 

herbicide volume is available to drive 

infiltration. 

• Settling of the herbicide at different depths 

relative to a given elevation due to uneven soil 

surface. 

• Preferential erosion of fine-grained soils by the 

wind resulting in segregation of soil particles 

and mixing of the surface layer. 

It was also assumed that there is an even distribution 

of the herbicide across the soils and that the mass of 

the herbicide is negligible compared to the mass of the 

soil. Given a typical soil density of 1 g/cm3

, the mass 

of a 1-mm depth of soil occupying a square meter is 

1,000 grams (g). This represents the total mass of soil 

per square meter that has to be removed by the wind 

before all of the herbicide is re-suspended. Using the 

meteorological data for each site, the mass of soil 

removed by the wind was calculated for every hour 

that herbicide re-suspension is possible. The fraction 

of the herbicide applied to the area that could be 

released was determined by dividing the mass of soil 

removed per square meter by 1,000 g (per square 

meter) for each hour. This percentage was applied at 

each herbicide’s maximum application rate. The 

resulting value represented the amount of herbicide 

potentially released each hour, which was assigned to 

each of the three particle sizes (PM2.5, PM10, and TSP) 

to estimate potential herbicide deposition. 

BLM Vegetation Treatments Using Herbicides C-21 June 2007 

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ECOLOGICAL RISK ASSESSMENT

Calculation of Herbicide Deposition 

The deposition algorithm in CALPUFF simulated the 

effective mass distribution of the adsorbed herbicide, 

based on particulate matter size (small particles have a 

larger surface area relative to their mass and, therefore, 

will carry the majority of the herbicide mass). 

Dispersion modeling estimated the maximum 1-day 

and 30-day deposition values at each receptor distance. 

The results were scaled for typical and maximum 

application rates. 

Watersheds Evaluated 

Three watersheds were used in the simulation: 

• Glasgow International Airport, Glasgow, 

Montana 

• Medford/Jackson County Airport, Medford, 

Oregon 

• Lander/Hunt Field, Lander, Wyoming 

These locations were selected as representative of 

various regions of the western states addressed by the 

PEIS. For each location, 1 year of surface 

meteorological data from the Solar and Meteorological 

Surface Observation Network (SAMSON) data set that 

has been produced by National Climatic Data Center 

(NCDC) was used. After a review of available data 

capture, the most recent SAMSON year with complete 

surface and mixing height data was selected for each 

station. The SAMSON data set is particularly 

applicable for CALPUFF modeling because it contains 

hourly values of relative humidity and solar radiation, 

which are needed for chemical transformation 

calculations. Mixing height data for these sites were 

obtained from the USEPA’s Technology Transfer 

Network Support Center for Regulatory Air Models.2

The highest impact was considered to represent a 

reasonable, but conservative impact under the range of 

meteorological conditions tested. 

Further details about the CALPUFF model inputs and 

assumptions can be found in the air quality modeling 

report (ENSR 2005k). 

 

2 http://www.epa.gov/ttn/scram/

Accidental Spill 

Two spill scenarios were modeled to represent worstcase potential impacts to the pond. The scenarios 

included a truck or a helicopter spilling entire loads 

(200 gallon [gal] spill and 140 gal spill, respectively) 

of herbicide mixed for the maximum application rate 

into the 1⁄4 acre, 1-meter-deep pond. To represent an 

acute exposure event for the three types of aquatic 

receptors, the pond concentration was compared 

against the appropriate toxicity endpoint for the fish, 

aquatic invertebrates, and non-target aquatic plants. 

The concentration of herbicide in the pond water is 

based on the concentration in the spilled solution, the 

volume spilled, and the volume of the pond, assuming 

instantaneous mixing. 

Non-target Species Effects 

Characterization 

This section summarizes the toxicity of the 10 

herbicides to terrestrial and aquatic species found on 

public lands. There are eight terrestrial herbicide 

a.i./formulations (bromacil, chlorsulfuron, 

diflufenzopyr, diuron, imazapic, Overdrive®, 

sulfometuron methyl, and tebuthiuron) and two aquatic 

herbicide a.i. (diquat and fluridone). The effects these 

herbicide active ingredients have on non-target species 

were evaluated for different categories of plants and 

animals (via surrogate species). The categories of 

terrestrial species evaluated include terrestrial plants, 

mammals, birds, reptiles, amphibians, and insects; the 

categories of aquatic species evaluated include aquatic 

plants, fish, aquatic invertebrates, and amphibians (in 

aquatic life stages). 

This effects characterization section identifies the 

TRVs selected from detailed laboratory and field 

toxicity studies evaluating the acute and chronic 

impacts of proposed herbicide usage on non-target 

plants and animals. TRVs were chosen as the lowest 

reported value for a given type of herbicide exposure 

(e.g., acute dermal exposure). For a given surrogate 

species, if an herbicide toxicity level exceeds the 

chosen TRV, that species and those it represents are at 

risk of experiencing adverse effects as a result of 

herbicide application. 

BLM Vegetation Treatments Using Herbicides C-22 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Terrestrial Species Effects 

Characterization 

The TRVs representing the effects of each of the 10 

herbicides on terrestrial species are presented below 

and are summarized by receptor type in Tables C-5 to 

C-15. 

Bromacil 

Bromacil poses a low toxicity hazard to terrestrial 

animals (mammals, birds, and honeybees [USEPA 

1996]). However, terrestrial plants are sensitive to 

bromacil, with concentrations as low as 0.0023 pounds 

(lbs) a.i./ac affecting the growth of non-target plants 

(about 0.06% of the typical application rate). 

Mammals 

Based on USEPA re-registration documents (USEPA 

1996), bromacil is considered to pose a low to 

moderate acute oral and dermal toxicity hazard to 

mammals. The oral LD50 (641 milligram [mg] 

a.i./kilogram [kg] BW) and chronic dietary NOAEL 

(13.3 mg a.i./kg BW-day) were selected as the dietary 

small mammal TRVs. The dermal small mammal TRV 

was established at >5,000 mg a.i./kg BW. Because no 

large mammal LD50s were identified in the available 

literature, the small mammal LD50 was used as a 

surrogate value. The large mammal dietary NOAEL 

TRV was established at 4.65 mg a.i./kg BW-day. 

Birds 

Data from the available literature indicate that 

bromacil has low toxicity to birds. The bobwhite quail 

dietary LD50 (>30,195 mg/kg BW) and chronic 

NOAEL (936 mg/kg BW-day) were selected as the 

small bird dietary TRVs. The mallard dietary LD50

(>5,000 mg/kg BW) and NOAEL (155 mg/kg BWday) were selected as the large bird dietary TRVs. 

Terrestrial Invertebrates 

Bromacil poses practically no toxicity risk to 

invertebrates. The honeybee dermal LD50 TRV was set 

at 193 microgram (μg)/bee. Based on a honeybee 

weight of 0.093 g, this TRV was expressed as 2,075 

mg/kg BW. 

Terrestrial Plants 

Terrestrial plants are at high risk from exposure to 

bromacil. The lowest and highest germination-based 

NOAELs were selected to evaluate risk to terrestrial 

plants in surface runoff scenarios. Emergence 

endpoints were used when germination data were 

unavailable. These TRVs were 0.0117 and 0.188 lb 

a.i./ac. Two additional endpoints were used to evaluate 

other plant scenarios. These included an EC25 of 

0.0023 lb a.i./ac and a NOAEL of 0.008 lb a.i./ac 

(extrapolated from the EC25 by dividing by an 

uncertainty factor of 3). 

Chlorsulfuron 

Chlorsulfuron poses little to no acute toxicity hazard to 

mammals via dermal and oral exposure. Adverse 

effects to small mammals have been documented from 

long-term dietary exposure to chlorsulfuron. 

Chlorsulfuron also has low toxicity to birds and slight 

toxicity to honeybees. 

Adverse effects to non-target terrestrial plants occurred 

at concentrations as low as 0.047 lb a.i./ac. 

Mammals 

Based on USEPA re-registration documents (USEPA 

2002), chlorsulfuron is characterized as not acutely 

toxic to mammals via dermal and oral exposure routes. 

The oral LD50 (1,363 mg a.i./kg BW) and chronic 

dietary NOAEL (5 mg a.i./kg BW-day) were selected 

as the dietary small mammal TRVs. The dermal small 

mammal TRV was established at >3,400 mg a.i./kg 

BW. Because no large mammal LD50s were identified 

in the available literature, the small mammal LD50 was 

used as a surrogate value. The large mammal dietary 

NOAEL TRV was established at 65.6 mg a.i./kg BWday. 

Birds 

Data from the available literature indicate that 

chlorsulfuron has low toxicity to birds. The bobwhite 

quail dietary LD50 (>16,970 mg/kg BW) and chronic 

NOAEL (100 mg/kg BW-day) were selected as the 

small bird dietary TRVs. The mallard dietary LD50

(>1,500 mg/kg BW) and NOAEL (99 mg/kg BW-day) 

were selected as the large bird dietary TRVs. 

Terrestrial Invertebrates 

Chlorsulfuron poses a slight toxicity risk to 

invertebrates. The honeybee dermal LD50 TRV was set 

at >25 μg/bee. Based on a honeybee weight of 0.093 g, 

this TRV was expressed as 269 mg/kg BW. 

BLM Vegetation Treatments Using Herbicides C-23 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Terrestrial Plants 

Chlorsulfuron is very highly toxic to plants. The 

lowest and highest germination-based NOAELs were 

selected to evaluate risk in surface runoff scenarios. 

These TRVs were 0.0157 and 0.0052 lb a.i./ac, based 

on the unverified dyer’s woad germination study 

(EC100 divided by uncertainty factors of 3 and 9, 

respectively). Two additional endpoints were used to 

evaluate other plant scenarios. These included a lifecycle NOAEL of 0.000021 lb a.i./ac and an EC25 of 

0.000063 lb a.i./ac (extrapolated from the NOAEL by 

multiplying by an uncertainty factor of 3). 

Diflufenzopyr 

As defined by the USEPA, diflufenzopyr alone poses 

little to no acute toxicity hazard to mammals via 

dermal and oral exposure. Adverse effects to small 

mammals have been documented from long-term 

dietary exposure to technical grade diflufenzopyr. 

Diflufenzopyr is practically non-toxic to birds and 

causes slight toxicity to honeybees. However, adverse 

effects to non-target terrestrial plant species have 

occurred at concentrations as low as 0.0008 lbs. a.i./ac, 

which is approximately 1/100 of the typical 

application rate. 

Mammals 

Based on USEPA conditional registration documents 

(USEPA 1999), diflufenzopyr is characterized as 

having low toxicity to small mammals. The oral LD50

(3,300 mg/kg BW) and chronic dietary NOAEL (42.2 

mg/kg BW-day) were selected as the dietary small 

mammal TRVs. The dermal small mammal TRV was 

established at >5,000 mg/kg BW. Since no large 

mammal LD50s were identified in the available 

literature, the small mammal LD50 was used as a 

surrogate value. The large mammal dietary NOAEL 

TRV was established at 59 mg/kg BW-day.

Birds 

Data from the available literature indicate that 

diflufenzopyr has low toxicity to birds. The small bird 

chronic dietary NOAEL was set at 634 mg/kg BWday. Since an acute adverse effect level was not 

established in the literature, the NOAEL was 

multiplied by an uncertainty factor of 3, resulting in a 

small bird dietary LD50 of 16,970 mg/kg BW. 

Similarly, the large bird dietary NOAEL TRV was set 

at 105 mg/kg BW-day, and using an uncertainty factor 

of 3, the LD50 was estimated to be >2,810 mg/kg BW. 

Terrestrial Invertebrates 

A honeybee dermal toxicity test suggests that 

diflufenzopyr has low toxicity to terrestrial 

invertebrates. Because a suitable LD50 could not be 

determined from the literature, the NOAEL was 

multiplied by an uncertainty factor of 3. The resulting 

honeybee dermal LD50 TRV was calculated to be 75 

μg/bee. Based on a honeybee weight of 0.093 g, this 

TRV was expressed as 806 mg/kg BW. 

Terrestrial Plants 

Terrestrial plants appear to be at high risk of toxic 

effects from application of diflufenzopyr. The lowest 

and highest germination-based NOAELs were selected 

to evaluate risk in surface runoff scenarios of the risk 

assessment (TRVs = 0.028 and 0.0001 lb a.i./ac). 

Emergence endpoints were used when germination 

data were unavailable. Two additional endpoints were 

used to evaluate other plant scenarios: an EC25 of 

0.0008 lb a.i./ac and a NOAEL of 0.0003 lb a.i./ac 

(extrapolated from the EC25 by dividing by an 

uncertainty factor of 3). 

Diquat 

Diquat is moderately toxic to mammals, particularly 

via dermal exposure. Diquat is also moderately toxic 

to birds and honeybees. In addition, adverse effects to 

non-target terrestrial plant species occurred with 

exposure to low concentrations of diquat (0.0046 lbs 

a.i./acre; 0.5% of the typical application rate). 

Mammals 

According to USEPA re-registration eligibility 

documents (USEPA 1995b), diquat is considered to be 

moderately toxic to mammals. Based on these 

findings, the oral LD50 (121 mg/kg BW) and chronic 

dietary NOAEL (0.8 mg a.i./kg BW-day) were 

selected as the dietary small mammal TRVs. The 

dermal small mammal TRV was established at 262 mg 

a.i./kg BW. Since no large mammal LD50s were 

identified in the available literature, the small mammal 

LD50 was used as a surrogate value. The large mammal 

dietary NOAEL TRV was established at 0.5 mg a.i./kg 

BW-day. 

Birds 

Data from the literature indicate that diquat has 

moderate toxicity to birds. The bobwhite quail dietary 

LD50 (150 mg a.i./kg BW) and chronic NOAEL (12 

BLM Vegetation Treatments Using Herbicides C-24 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

mg a.i./kg BW-day) were selected as the small bird 

dietary TRVs. The pheasant dietary LD50 (215 mg 

a.i./kg BW) and the mallard dietary chronic NOAEL 

(0.6 mg a.i./kg BW-day) were selected as the large 

bird dietary TRVs. 

Terrestrial Invertebrates 

A dermal toxicity study in honeybees suggests that 

diquat has low toxicity to terrestrial invertebrates. The 

honeybee dermal TRV was set at 47 μg/bee, the 5-day 

LD50 value. Based on a honeybee weight of 0.093 g, 

this TRV was expressed as 505 mg/kg BW. 

Terrestrial Plants 

Terrestrial plants appear to be at high risk of toxic 

effects from exposure to diquat. Two endpoints were 

used to evaluate terrestrial plant scenarios for aquatic 

herbicides. These included an EC25 and a NOAEL. 

Since the lowest EC25 identified in the database (0.047 

lb a.i./ac) was lower than the lowest reported NOAEL, 

the terrestrial plant NOAEL TRV (0.0016 lb a.i./ac) 

was calculated by dividing the EC25 value by an 

uncertainty factor of 3. 

Diuron 

Diuron is not considered to be highly toxic to most 

terrestrial species. In mammals, diuron is considered to 

have low acute oral and dermal toxicity. However, 

adverse effects have been demonstrated in mammals 

from long-term exposure to diuron in the diet. Diuron 

is slightly toxic to birds but essentially non-toxic to 

honeybees. Significant adverse effects were noted in 

non-target terrestrial plant species after 14 days 

exposure to concentrations as low as 0.08 lb a.i./ac. 

Mammals 

Because fairly large single doses of diuron are required 

before adverse effects are noted, diuron is considered 

to have low acute toxicity to mammals, but diuron 

does have moderate chronic toxicity to mammals. The 

oral LD50 (1,017 mg a.i./kg BW) and chronic dietary 

NOAEL (2.5 mg a.i./kg BW-day) were selected as the 

dietary small mammal TRVs. The dermal small 

mammal TRV was established at >2,500 mg a.i./kg 

BW. Since no large mammal LD50s were identified in 

the available literature, the small mammal acute LD50

(1,017 mg a.i./kg BW-day) was used as a surrogate 

value. The large mammal dietary chronic NOAEL 

TRV was established at 0.6 mg a.i./kg BW-day. 

Birds 

Data from available literature indicate that diuron has 

low toxicity to birds (toxicity is higher for large birds 

than small birds). The bobwhite quail dietary LD50

(5,225 mg/kg BW-day) and the mallard dietary LD50

(865 mg/kg BW-day) were selected as the small and 

large bird dietary TRVs. Since NOAEL values for 

small and large birds were unavailable, the LD50s were 

divided by an uncertainty factor of 3 to derive NOAEL 

TRVs of 348 and 58 mg/kg BW-day for small and 

large birds, respectively. 

Terrestrial Invertebrates 

A dermal toxicity study in honeybees suggests that 

diuron has low toxicity to terrestrial invertebrates. The 

honeybee dermal LD50 TRV was set at 145.03 μg/bee. 

Based on a honeybee weight of 0.093 g, this TRV was 

expressed as 1,560 mg/kg BW. 

Terrestrial Plants 

Terrestrial plants appear to be at high risk of toxic 

effects from diuron application. The lowest and 

highest germination-based NOAELs were selected to 

evaluate risk in surface runoff scenarios. However, 

because germination data were not available for 

diuron, the emergence TRVs of 0.047 and 12 lb a.i./ac 

were selected instead. Two additional endpoints were 

used to evaluate other plant scenarios. These included 

a seed emergence EC25 of 0.08 lb a.i./ac and a 

vegetative vigor NOAEL of 0.001 lb a.i./ac. 

Fluridone 

Fluridone has low toxicity to most terrestrial animals. 

Studies conducted with mammals found that acute 

exposure to fluridone usually does not cause adverse 

effects, even to mammals that were exposed to 

fluridone for longer periods of time or during 

pregnancy. Similarly, short-term exposure to fluridone 

did not result in adverse effects in birds, even at high 

exposure levels. Long-term exposure to fluridone did 

result in reduced growth in large and small birds. 

Fluridone was practically non-toxic to honeybees. 

While no quantitative data were found to evaluate 

fluridone’s effects on terrestrial plants, the 

manufacturer’s user guide (Eli Lilly and Company 

2003) provided qualitative results indicating that the 

sensitivity of terrestrial plants is variable. Some 

species (e.g., grasses and sedges) were more sensitive 

than other plant species (e.g., willow). 

BLM Vegetation Treatments Using Herbicides C-25 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Mammals 

Fluridone poses little acute risk to small mammals. 

The oral LD50 (>10,000 mg a.i./kg BW) and chronic 

dietary NOAEL (8 mg a.i./kg BW-day) were selected 

as the dietary small mammal TRVs. The dermal small 

mammal TRV was established at >5,000 mg a.i./kg 

BW. Since no large mammal LD50s were identified in 

the available literature, the small mammal LD50

(>10,000 mg a.i./kg BW) was used as a surrogate 

value. The large mammal dietary NOAEL TRV was 

established at 75 mg a.i./kg BW-day. Overall, acute 

exposure to fluridone causes few adverse effects to 

mammals, but adverse effects can occur if mammals 

are chronically exposed to fluridone. Small mammals 

may be slightly more susceptible to fluridone than 

large mammals. 

Birds 

Information related to avian exposure to fluridone 

suggests that acute oral exposure to fluridone is 

practically non-toxic to birds. The bobwhite quail 

dietary LD50 (>13,135 mg/kg BW) and chronic 

NOAEL (604 mg a.i./kg BW-day) were selected as the 

small bird dietary TRVs. The mallard dietary LD50

(>2,270 mg/kg BW) and NOAEL (100 mg a.i./kg BWday) were selected as the large bird dietary TRVs. 

Terrestrial Invertebrates 

Honeybee dermal toxicity studies indicate that 

fluridone has low toxicity to terrestrial invertebrates. 

Because an LD50 was not established in the literature, 

the NOAEL was multiplied by an uncertainty factor of 

3, resulting in an LD50 of 1,088 μg/bee. Based on a 

honeybee weight of 0.093 g, this TRV was expressed 

as 11,699 mg a.i./kg BW. 

Terrestrial Plants 

No quantitative toxicity studies were found in the 

reviewed literature that addressed toxicity of fluridone 

to terrestrial plants. In the manufacturer’s user’s guide 

(Eli Lilly and Company 2003), grasses and some 

sedges are considered to be “sensitive” or 

“intermediate” in their tolerance to the Sonar 

herbicide, while rushes tend to be “intermediate” to 

“tolerant.” Shoreline plants, such as willow and 

cypress, were considered “tolerant,” while the 

tolerance of members of the evening primrose and 

acanthus families was classified as “intermediate.” 

Imazapic 

The information identified during the literature review 

indicates that imazapic is not highly toxic to most 

terrestrial animal species, although it is fairly toxic to 

non-target terrestrial plant species. Since the herbicide 

is rapidly metabolized and excreted in urine and feces, 

imazapic does not bioaccumulate in animals. In 

mammals, pesticide registration studies found that 

exposure to imazapic does not frequently cause 

adverse effects, even at relatively high dose levels. 

Nevertheless, mammals may be more susceptible 

during pregnancy, and large mammals may be slightly 

more sensitive to imazapic than small mammals. 

During short-term acute exposures, imazapic did not 

cause adverse effects in birds; however, long-term 

exposure to imazapic did result in reduced growth in 

large and small birds. For terrestrial plants, significant 

adverse effects were noted in non-target plant species 

after 14 days exposure to concentrations as low as 0.01 

lb a.i./ac (approximately 1/3 of the typical application 

rate). 

Mammals 

Included in the registration reports were acute oral 

toxicity studies conducted in rats that demonstrated 

that exposure to imazapic typically does not cause 

adverse effects, even at relatively high dose levels 

(e.g., >5,000 mg a.i./kg BW; SERA 2001). Based on 

these findings, the oral LD50 (>5,000 mg a.i./kg BW) 

and chronic dietary NOAEL (1,728 mg/kg BW-day) 

were selected as the dietary small mammal TRVs. The 

dermal small mammal TRV (LD50) was established at 

>2,000 mg/kg BW. Because a NOAEL was not 

identified in the available literature, it was calculated 

by dividing the LOAEL (137 mg/kg BW-day) by an 

uncertainty factor of 3, resulting in a large mammal 

dietary NOAEL TRV of 46 mg/kg BW-day. Overall, 

exposure to imazapic causes few adverse effects to 

mammals under most circumstances, even at high 

concentrations. However, large mammals may be more 

susceptible to imazapic than small mammals, and 

mammals may be more susceptible to imazapic during 

pregnancy. 

Birds 

Based on available data, imazapic appears to have low 

toxicity to birds. No adverse effects were observed in 

bobwhite quail administered imazapic at dose levels as 

high as 2,150 mg/kg BW for 21 days (USEPA 2003). 

The bobwhite quail dietary LD50 (>15,095 mg/kg BW) 

and chronic NOAEL (113 mg/kg BW-day) were 

BLM Vegetation Treatments Using Herbicides C-26 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

selected as the small bird dietary TRVs. The mallard 

dietary LD50 (>2,500 mg/kg BW) and NOAEL (65 

mg/kg BW-day) were selected as the large bird dietary 

TRVs. 

Terrestrial Invertebrates 

A dermal toxicity study in honeybees suggested that 

imazapic poses low toxicity hazard to terrestrial 

invertebrates. The honeybee dermal LD50 TRV was set 

at >100 μg/bee. Based on a honeybee weight of 0.093 

g, this TRV was expressed as 1,075 mg/kg BW. 

Terrestrial Plants 

Imazapic appears to be highly toxic to terrestrial 

plants. The lowest and highest germination-based 

NOAELs were selected to evaluate risk in surface 

runoff scenarios. These TRVs were 0.064 and 0.032 lb 

a.i./acre. Two additional endpoints were used to 

evaluate other plant scenarios. These included an EC25

of 0.01 lb a.i./acre and an NOAEL of 0.008 lb a.i./acre. 

Overdrive® 

Overdrive® is a formulation containing dicamba and 

diflufenzopyr. Because Overdrive® is a recently 

approved herbicide, no Overdrive® toxicity data were 

identified. However, the herbicide Distinct® contains 

the same ratio of dicamba and diflufenzopyr, and 

several Distinct® studies were identified in the 

literature review. Therefore, Distinct®, dicamba, and 

diflufenzopyr toxicity data were examined to evaluate 

the toxicity of Overdrive® to receptor species. 

Diflufenzopyr poses little to no acute toxicity hazard to 

mammals via dermal and oral exposure, Distinct® 

herbicide poses a slight toxicity hazard to mammals, 

and dicamba is considered to be slightly toxic to 

mammals via dermal and oral exposures. Adverse 

effects to small mammals have been documented from 

long-term dietary exposure to technical grade 

diflufenzopyr. Long term exposures to dicamba did not 

show significant mortality, reproductive, or teratogenic 

effects at the tested levels (up to 25 mg/kg/day). 

Diflufenzopyr and dicamba are considered practically 

non-toxic to birds. Diflufenzopyr causes slight toxicity 

to honeybees, but dicamba is considered non-toxic to 

honeybees. For terrestrial plants, adverse effects to 

non-target species occurred at diflufenzopyr 

concentrations as low as 0.0008 lbs. a.i./acre, at 

dicamba concentrations as low as 0.00027 lb a.i./ac, 

and at Distinct® concentrations as low as 0.0043 lb 

a.i./ac. 

Diflufenzopyr is moderately toxic to fish and aquatic 

invertebrates, while dicamba has low toxicity to 

aquatic organisms. Diflufenzopyr was toxic to aquatic 

macrophytes, specifically duckweed, with Distinct®

being more toxic and dicamba being less toxic. 

Mammals 

Diflufenzopyr poses little to no acute toxicity hazard to 

mammals via dermal and oral exposure, but may pose 

chronic risk. Distinct® and dicamba pose slight toxicity 

hazards to mammals via dermal and oral exposures. 

The dermal small mammal TRVs were established at 

>5,000 mg/kg BW for diflufenzopyr and Distinct®, 

and >5,050 mg/kg BW for dicamba. The dietary small 

mammal diflufenzopyr TRV based on the oral LD50

was 3,300 mg/kg BW for diflufenzopyr. The dietary 

small mammal TRV based on the oral LD50 was 566 

mg/kg BW for dicamba. The dietary small mammal 

TRV based on the oral LD50 was 1,600 mg/kg BW for 

Distinct®. 

Based on the NOAEL, the chronic dietary small 

mammal TRV was established at 42.2 mg/kg BW-day 

for diflufenzopyr and at 3 mg/kg BW-day for dicamba. 

No small mammal chronic studies were reported for 

Distinct® or Overdrive®, and therefore, no TRV could 

be developed. 

Because no large mammal LD50s for diflufenzopyr, 

dicamba, or Distinct® were identified in the available 

literature, the small mammal LD50 was used as 

surrogate values. In addition, no large mammal 

chronic toxicity data were identified for Distinct® 

or 

Overdrive®, and consequently no TRV could be 

developed. Based on the available data, the large 

mammal dietary NOAEL TRV for diflufenzopyr was 

established at 59 mg/kg BW-day, and the chronic large 

mammal dietary TRV was established at 0.15 mg/kg 

BW-day for dicamba. 

Birds 

Data from the available literature indicate that 

diflufenzopyr has low toxicity to birds. The 

diflufenzopyr acute small bird dietary LD50 TRV was 

set at >16,970 mg/kg BW based on the bobwhite quail, 

and the acute large bird dietary LD50 TRV was set at 

>2,810 mg/kg BW. The diflufenzopyr chronic small 

bird dietary NOAEL was set at 634 mg/kg BW-day, 

based on the bobwhite quail, and the large bird 

BLM Vegetation Treatments Using Herbicides C-27 June 2007 

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ECOLOGICAL RISK ASSESSMENT

NOAEL was set at 105 mg/kg BW-day, based on the 

mallard. 

Dicamba is classified as practically non-toxic to birds. 

The dicamba acute small bird dietary LD50 was set at 

>30,190 mg/kg BW, based on the bobwhite quail, and 

the large bird LD50 was set at >5,000 mg/kg BW, 

based on the mallard. The dicamba chronic small bird 

dietary NOAEL was set at 170 mg/kg BW-day, based 

on the bobwhite quail, and the large bird NOAEL was 

set at 92 mg/kg BW-day, based on the mallard. 

Only one acute study was identified for Distinct®. The 

Distinct® acute small bird dietary LD50 was set at 

>18,360 mg/kg BW, based on the bobwhite quail. 

Because no chronic data were available, the 8-day 

NOAEL, 3,672 mg/kg BW-day, was used as the small 

bird NOAEL TRV. Due to a lack of additional data, no 

large bird TRVs were derived. 

Terrestrial Invertebrates 

Diflufenzopyr and dicamba appear to be practically 

non-toxic to terrestrial invertebrates, as represented by 

the honeybee. The honeybee dermal LD50 for 

diflufenzopyr was calculated to be 806 mg/kg BW. For 

dicamba, the LD50 value was calculated as 974 mg/kg 

BW. No honeybee data were identified for Distinct®. 

Terrestrial Plants 

Because germination data were unavailable, the lowest 

and highest emergence-based NOAELs were selected 

to evaluate risk in surface runoff scenarios of the risk 

assessment. The diflufenzopyr TRVs were 0.0001 and 

0.028 lb a.i./acre. Two additional endpoints were used 

to evaluate other plant scenarios. These included an 

EC25 of 0.0008 lb a.i./acre and a NOAEL of 0.0003 lb 

a.i./acre. 

The dicamba TRVs were <0.0022 and 0.53 lb a.i./ac. 

To evaluate other plant scenarios, two additional 

endpoints were used. These included the lowest 

dicamba EC25 of 0.00027 lb a.i./ac and the highest 

NOAEL that was still below the selected EC2.5. The 

only NOAEL that met this criteria was the <0.0022 lb 

a.i./ac germination value. 

The Distinct® TRVs were 0.0016 and 0.046 lb a.i./ac. 

To evaluate other plant scenarios, two additional 

endpoints were used. These included the lowest 

Distinct® EC25 of 0.0043 lb a.i./ac and the highest 

NOAEL that was still below the selected EC25 of 0.004 

lb a.i./ac for vegetative vigor in tomatoes (USEPA 

2003; Master Record Identifier (MRID) number 

45047301). 

Sulfometuron Methyl 

Sulfometuron methyl has low toxicity to most 

terrestrial species. In mammals, sulfometuron methyl 

is considered to have low acute oral and dermal 

toxicity. However, adverse effects were demonstrated 

in mammals from long-term exposure to sulfometuron 

methyl in the diet or via oral gavage during pregnancy. 

Sulfometuron methyl is essentially non-toxic to birds 

and honeybees. There appears to be little difference in 

the high sensitivities of weeds and non-target plants to 

sulfometuron methyl. Pine species are less sensitive 

than broadleaves or grasses. Rare, threatened, and 

endangered species do appear to be particularly 

sensitive to sulfometuron methyl. 

Mammals 

Sulfometuron methyl is considered to have low acute 

toxicity to mammals, but moderate chronic toxicity. 

The oral LD50 (>5,000 mg a.i./kg BW) and the chronic 

dietary NOAEL (18 mg a.i./kg BW-day) were selected 

as the dietary small mammal TRVs. The dermal small 

mammal TRV was established at >8,000 mg a.i./kg 

BW. Because no large mammal LD50s were identified 

in the available literature, the small mammal LD50 was 

used as a surrogate value, and the large mammal 

chronic dietary NOAEL TRV was established at 28 

mg a.i./kg BW-day. 

Birds 

In the studies evaluated, no adverse effects have been 

demonstrated in birds exposed to sulfometuron methyl. 

The bobwhite quail dietary LD50 (>16,970 mg a.i./kg 

BW-day) and extrapolated NOAEL (1,131 mg a.i./kg 

BW-day) were selected as the small bird dietary 

TRVs. The mallard dietary LD50 (>2,300 mg a.i./kg 

BW-day) and extrapolated NOAEL (153 mg a.i./kg 

BW-day) were selected as the large bird dietary TRVs.

Terrestrial Invertebrates 

A honeybee dermal toxicity study suggests that 

sulfometuron methyl is of low toxicity to terrestrial 

invertebrates. The honeybee dermal LD50 TRV was set 

at 300 μg/bee (extrapolated from the NOAEL). Based 

on a honeybee weight of 0.093 g, this TRV was 

expressed as 3,226 mg/kg BW. 

BLM Vegetation Treatments Using Herbicides C-28 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Terrestrial Plants 

Sulfometuron methyl appears to be highly toxic to 

terrestrial plants. The lowest and highest germinationbased NOAELs were selected to evaluate risk in 

surface runoff scenarios of the risk assessment. These 

terrestrial plant TRVs were established as 0.000028 

and 1.12 lb a.i./ac, based on emergence data. Two 

additional endpoints were used to evaluate other plant 

scenarios; these included an EC25 of 0.22 lb a.i./ac BW 

and a NOAEL of 0.000028 lb a.i./ac. 

Tebuthiuron 

Tebuthiuron has moderate toxicity to most terrestrial 

species. In mammals, tebuthiuron is considered to 

have low acute dermal toxicity, but adverse effects can 

occur when organisms are exposed for greater periods 

of time (e.g., via diet or oral gavage). Tebuthiuron is 

essentially non-toxic to birds and slightly toxic to 

honeybees. Tests conducted on crop plant species 

found adverse effects at concentrations as low as 0.03 

lbs a.i./ac (6% of the typical application rate). 

Mammals 

Tebuthiuron is considered to have moderate toxicity to 

mammals. The oral LD50 (58 mg a.i./kg BW) and 

chronic dietary NOAEL (7 mg a.i./kg BW-day) were 

selected as the dietary small mammal TRVs. The 

dermal small mammal TRV was established at >5,000 

mg a.i./kg BW. The large mammal dietary LD50 was 

established at >500 mg a.i./kg BW-day, and the 

NOAEL TRV was established at 12.5 mg a.i./kg BWday. 

Birds 

In the studies evaluated, no adverse effects were 

reported in birds exposed to tebuthiuron. The small 

bird dietary LD50 was established at >15,440 mg 

a.i./kg BW, based on the bobwhite quail study. A 

small bird dietary NOAEL value was calculated by 

dividing the daily dose by an uncertainty factor of 3. 

The resulting NOAEL was 1,029 mg a.i./kg BW-day. 

The large bird dietary LD50 was established at >2,545 

mg a.i./kg BW-day, based on the mallard duck. The 

large bird NOAEL was established at 1,000 mg a.i./kg 

BW-day, based on hens. 

Terrestrial Invertebrates 

Based on a honeybee dermal toxicity study, 

tebuthiuron appears to have low toxicity to terrestrial 

invertebrates. The honeybee dermal LD50 TRV was set 

at 30 μg a.i./bee. Based on a honeybee weight of 0.093 

g, this TRV was expressed as 323 mg a.i./kg BW. 

Terrestrial Plants 

Available data suggest that tebuthiuron has high 

toxicity to terrestrial plants. The NOAEL TRVs were 

established at >6 and 0.01 lb a.i./ac (extrapolated from 

the EC25 of 0.03 lb a.i./ac), based on germination and 

emergence data, respectively. Two additional 

endpoints were used to evaluate other plant scenarios. 

Aquatic Species Effects 

Characterization 

This aquatic effects characterization section 

summarizes the acute and chronic toxicity study 

results demonstrating the impacts of proposed 

herbicide usage on non-target aquatic plants, aquatic 

invertebrates, fish, and aquatic life stages of 

amphibians. 

The acute toxicity levels of the herbicides are 

classified according to the observed LC50 values: 

• less than 0.1 mg/L – very highly toxic 

• 0.1 to 1 mg /L – highly toxic 

• 1 to 10 mg/L – moderately toxic 

• 10 to 100 mg/L – slightly toxic 

• greater than 100 mg/L – practically non-toxic 

Bromacil 

Bromacil is slightly toxic to effectively non-toxic to 

most aquatic animals. For fish, acute toxic effects of 

bromacil occurred at concentrations of 36 mg/L, and 

coldwater fish species appear to be slightly more 

sensitive to bromacil than warmwater species. Also, 

bromacil does not tend to bioconcentrate appreciably 

in fish tissue. Compared to fish, aquatic invertebrates 

are less sensitive to acute bromacil exposures, with 

acute adverse effect concentrations occurring at 65 mg 

a.i./L. In contrast, growth of the green algae, 

Selenastrum capricornutum, was adversely impacted 

by bromacil concentrations as low as 0.0068 mg/L. No 

acceptable toxicity studies were found for amphibians. 

BLM Vegetation Treatments Using Herbicides C-29 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Fish 

Bromacil is slightly toxic to fish. The coldwater 96-

hour LC50 of 36 mg/L was selected as the acute TRV 

(the lower of the cold- and warmwater fish endpoints 

were selected as the TRVs for fish), and the 

warmwater fish NOAEL of 0.33 mg /L was used as the 

TRV for chronic effects. 

Amphibians 

Bromacil is slightly toxic to amphibians. The LC50

(230 mg/L) was selected as an amphibian acute TRV. 

The NOAEL was extrapolated from the LC50 using an 

uncertainty factor of 3. The resulting NOAEL TRV 

was 77 mg/L. 

Aquatic Invertebrates 

Bromacil is also slightly toxic to aquatic invertebrates. 

The LC50 (65 mg a.i./L) was selected as the 

invertebrate acute TRV. Since no NOAEL value in the 

reviewed literature was lower than the LC50, the LC50

was divided by an uncertainty factor of 3 to estimate a 

NOAEL TRV of 22 mg a.i./L. It may be noted that the 

use of this NOAEL TRV to evaluate chronic scenarios 

is conservative, as it is based on a short-term study, but 

not a chronic study. 

Aquatic Plants 

Bromacil is very highly toxic to aquatic plants. The 

EC50 (0.0068 mg/L) was selected as the aquatic plant 

acute TRV. Because no NOAEL values in the 

reviewed literature were lower than the EC50, the EC50

was divided by an uncertainty factor of 3 to estimate a 

NOAEL TRV of 0.0023 mg /L. It may be noted that 

the use of this NOAEL TRV to evaluate chronic 

scenarios is conservative, as it is based on a short-term 

study, but not a chronic study. 

Chlorsulfuron 

Chlorsulfuron is slightly toxic to fish and aquatic 

invertebrates. No toxicity studies conducted on 

amphibian species were found in the literature 

reviewed. Chlorsulfuron is very highly toxic to aquatic 

macrophytes. Aquatic macrophytes are adversely 

affected by concentrations as low as 0.00007 mg/L. 

Fish 

Chlorsulfuron is slightly toxic to fish. The coldwater 

96-hour LC50 of 40 mg/L was selected as the acute 

TRV (the lower of the coldwater and warmwater fish 

endpoints). The warmwater fish NOAEL (17 mg /L; 

extrapolated from the LC50) was used as the TRV for 

chronic effects (coldwater and warmwater fish species 

may have comparable sensitivity to chlorsulfuron). 

Chlorsulfuron is not likely to bioconcentrate in fish 

tissue. It may be noted that the use of this NOAEL 

TRV to evaluate chronic scenarios is conservative, as 

it is based on a short-term study, but not a chronic 

study. 

Aquatic Invertebrates 

Chlorsulfuron is practically non-toxic to aquatic 

invertebrates. The LC50 (368.9 mg/L) was selected as 

the invertebrate acute TRV and the 21-day NOAEL 

(20 mg/L) was selected as the chronic TRV. 

Aquatic Plants 

Chlorsulfuron is very highly toxic to aquatic plants. 

The EC50 (0.00007 mg a.i./L) was selected as the 

aquatic plant acute TRV. The highest NOAEL below 

the acute TRV was the NOAEL from the same study 

(0.004 mg a.i./L).

Diflufenzopyr 

Diflufenzopyr is moderately toxic to fish and aquatic 

invertebrates. No toxicity studies conducted on 

amphibian species were found in the literature 

reviewed. Diflufenzopyr is also toxic to aquatic 

macrophytes, which are adversely affected by 

diflufenzopyr and its various formulations at 

concentrations as low as 0.0078 mg/L. There do not 

appear to be appreciable differences in sensitivities 

among aquatic macrophytes, diatoms, and algae. 

Fish 

Results from coldwater and warmwater fish species 

suggest that diflufenzopyr has relatively low toxicity 

to fish species. The lower of the coldwater and 

warmwater fish endpoints were selected as the TRVs 

for fish. Therefore, the coldwater 96-hour LC50 of 106 

mg/L was selected as the acute TRV, and the 

warmwater fish NOAEL of 16 mg/L was used as the 

TRV for chronic effects. 

Aquatic Invertebrates 

Based on toxicity studies in daphnids, diflufenzopyr 

appears to be slightly to moderately toxic to aquatic 

invertebrates. The EC50 (15 mg/L) and NOAEL (9.7 

mg/L) were selected as the invertebrate TRVs. 

BLM Vegetation Treatments Using Herbicides C-30 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Aquatic Plants 

In studies with duckweed, diflufenzopyr has high 

toxicity to aquatic plants. In 14-day toxicity tests, 50% 

of the duckweed plants were adversely affected by 

concentrations as low as 0.11 mg a.i./L (the EC50) of 

Distinct® herbicide (USEPA 2003). The green algae 

EC50 (0.1 mg/L) and NOAEL (0.0078 mg/L) were 

selected as the aquatic plant TRVs. 

Diquat 

Diquat has relatively high toxicity to fish and aquatic 

invertebrates. Diquat does not appear to appreciably 

bioconcentrate in fish tissue. No acute toxicity studies 

conducted on amphibian species were found in the 

literature. Aquatic macrophytes were adversely 

affected by diquat concentrations as low as 0.00075 

mg/L. There did not appear to be appreciable 

differences in sensitivities among aquatic 

macrophytes, diatoms, and algae. 

Fish 

Results from coldwater and warmwater fish species 

suggest that diquat has high toxicity to fish species. 

The lower of the coldwater and warmwater fish 

endpoints were selected as the TRVs for fish; 

therefore, the warmwater 96-hour LC50 of 0.75 mg 

a.i./L was selected as the acute TRV. Because the 

NOAEL in a chronic study on rainbow trout was 

determined to be <0.5 mg a.i./L, the coldwater fish 

NOAEL was calculated by dividing this value by an 

uncertainty factor of 3. The resulting NOAEL TRV for 

coldwater fish species was 0.17 mg a.i./L; this was 

selected as the chronic fish TRV. In addition, the 

bioconcentration potential for diquat is low. 

Amphibians 

In a chronic toxicity study on northern leopard frogs, 

diquat was found to have moderate toxicity to 

amphibians. In a 16-day exposure, frogs were 

adversely affected by diquat concentrations as low as 5 

mg/L, while no adverse effects were observed at 2 

mg/L. The NOAEL (2 mg/L) was selected as an 

amphibian chronic TRV. 

Aquatic Invertebrates 

Toxicity studies on daphnids and amphipods suggest 

that diquat is highly toxic to aquatic invertebrates. The 

LC50 (0.14 mg/L) was selected as the invertebrate 

acute TRV, and the NOAEL of 0.044 mg/L was 

selected as the chronic TRV. 

Aquatic Plants 

Duckweed toxicity studies suggest that diquat is very 

highly toxic to aquatic plants. In 14-day studies, 50% 

of the duckweed plants were adversely affected by 

concentrations as low as 0.00075 mg/L of diquat (i.e., 

the EC50; USEPA 2003; MRID 41883002). The EC50

(0.00075 mg/L) was selected as the aquatic plant acute 

TRV. Because no NOAEL values in the reviewed 

literature were lower than the EC50, the EC50 was 

divided by an uncertainty factor of 3 to estimate a 

NOAEL TRV of 0.0003 mg/L. 

Diuron 

Diuron is moderately toxic to fish and highly toxic to 

aquatic plants and aquatic invertebrates. Toxicity tests 

indicate that diuron is toxic to fish species at 

concentrations as low as 0.71 mg/L. Diuron has a low 

to moderate potential to bioconcentrate in fish tissue. 

Amphibians were less sensitive to diuron than any 

other aquatic taxa. Aquatic invertebrates were affected 

by diuron concentrations of 0.16 mg a.i./L. Aquatic 

plants were affected at concentrations as low as 0.0013 

mg a.i./L (about 0.02% of the typical application rate). 

Fish 

Diuron is considered moderately to highly toxic to 

fish. The lower of the coldwater and warmwater fish 

endpoints were selected as the TRVs for fish. 

Therefore the coldwater 96-hour LC50 of 0.71 mg/L 

was selected as the acute TRV, and the warmwater fish 

NOAEL of 0.033 mg a.i./L was used as the TRV for 

chronic effects. 

Amphibians 

Toxicity tests suggest that diuron is slightly toxic to 

amphibians. Acute toxicity was observed in 

amphibians exposed to diuron concentrations of 12.7 

mg/L. In chronic toxicity tests, adverse effects on 

growth were observed at concentrations of 14.5 mg/L, 

with no effects observed at 7.6 mg a.i./L. The LC50

(12.7 mg/L) was selected as an amphibian acute TRV, 

and the NOAEL (7.6 mg/L) was selected as the 

chronic TRV. 

BLM Vegetation Treatments Using Herbicides C-31 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Aquatic Invertebrates 

Diuron is considered to have relatively high toxicity to 

aquatic invertebrates. The LC50 (0.16 mg/L) was 

selected as the invertebrate acute TRV. Since none of 

the observed chronic NOAEL values were below the 

selected acute TRV, the chronic LOAEL from a 28-

day daphnid assay was divided by an uncertainty 

factor of 3 to estimate a chronic NOAEL TRV of 

0.067 mg a.i./L. 

Aquatic Plants 

Toxicity tests on green algae (the most sensitive of 

aquatic plants tested) suggest that diuron is very highly 

toxic to aquatic plants. The EC50 (0.0013 mg/L) was 

selected as the aquatic plant acute TRV, and the 

NOAEL (0.00044mg/L) was selected as the chronic 

TRV. 

Fluridone 

In the available literature, aquatic plants were affected 

by concentrations less than 1 mg/L. Acute and chronic 

toxicity tests indicate that fluridone is toxic to fish 

species at concentrations less than 10 mg/L, and some 

adverse effect concentrations approach 1 mg/L. No 

data were found to evaluate the toxicity of fluridone to 

amphibians. Acute toxicity concentrations for aquatic 

invertebrates were as low as 1.3 mg/L, which is equal 

to the maximum application rate. 

Fish 

Fluridone is considered to be moderately toxic to fish 

species. The lower of the coldwater and warmwater 

fish endpoints were selected as the TRVs for fish. 

Therefore, the coldwater 96-hour LC50 of 4.2 mg a.i./L 

was selected as the acute TRV, and the warmwater fish 

NOAEL of 0.48 mg a.i./L was used as the TRV for 

chronic effects. 

Amphibians 

No toxicity studies for amphibians were found in the 

literature reviewed for fluridone. 

Aquatic Invertebrates 

Fluridone appears to be moderately toxic to aquatic 

invertebrates. Acute toxicity was observed in aquatic 

invertebrates exposure to fluridone concentrations as 

low as 1.3 mg/L. NOAELs for several species were 

derived from chronic or short-term chronic studies. 

The NOAEL for D. magna is 0.2 mg/L and the 

NOAELs for Gammarus pseudolimnaeus and 

Chironomus plumosus are 0.6 mg/L. The LC50 (1.3 

mg/L) was selected as the invertebrate acute TRV, and 

the NOAEL of 0.6 mg/L was selected as the chronic 

TRV. 

Aquatic Plants 

Toxicity studies on American pondweed suggest that 

fluridone is moderately toxic to aquatic plants. No 

adverse effects to aquatic macrophytes were detected 

with fluridone concentrations of 1 mg/L, and the 

NOAEL was set at 1 mg/L. Because no EC50 values 

were identified in the literature, the NOAEL was 

multiplied by an uncertainty factor of 3 to estimate an 

EC50 of 3 mg/L. 

Imazapic 

Imazapic is relatively toxic to aquatic plants, but is 

much less toxic to aquatic animal species. Aquatic 

plants were affected at concentrations as low as 0.0042 

mg/L. Toxicity tests indicate that imazapic has low 

toxicity to fish species and does not appreciably 

bioconcentrate in fish tissue. No data were found to 

evaluate the toxicity of imazapic to amphibians. Most 

studies reported that aquatic invertebrates were 

unaffected by imazapic concentrations of 100 mg/L; 

however, one unverifiable report suggested that 

chronic toxicity to aquatic invertebrates may occur at 

concentrations as low as 0.18 mg/L. 

Fish 

Imazapic is considered to have low toxicity to fish 

species. The coldwater 96-hour LC50 of >100 mg/L 

(the lower of the coldwater and warmwater fish 

endpoints) was selected as the acute TRV. The LC50

was divided by an uncertainty factor of 3, to produce a 

coldwater fish NOAEL of 33 mg/L used as the TRV 

for chronic effects. It may be noted that the selected 

chronic TRV, extrapolated from an LC50 indicating 

essentially no risk, is 3 times lower than the true 

chronic NOAEL observed for warmwater fish. This 

may overestimate chronic risk to fish. 

Amphibians 

No toxicity studies for amphibians were found in the 

published literature or in USEPA registration 

documents. 

BLM Vegetation Treatments Using Herbicides C-32 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Aquatic Invertebrates 

Imazapic is generally considered to have low toxicity 

to aquatic invertebrates. The LC50 (>100 mg/L) was 

selected as the invertebrate acute TRV. The 21-day 

NOAEL (96 mg a.i./L) was selected as the invertebrate 

chronic TRV. 

Aquatic Plants 

Toxicity studies on duckweed suggest that imazapic is 

very highly toxic to aquatic plants. In these studies, 

25% of the duckweed plants were adversely affected 

by concentrations of 0.0042 mg/L after 14 days 

exposure. The no effect concentration in this study was 

0.0026 mg/L. Compared to duckweed, freshwater 

algae and diatoms were at least 10 times more tolerant 

of imazapic. In 5-day acute toxicity tests, LC50 values 

for algae and diatoms were greater than the highest 

concentration tested (at least 0.04 mg/L). The aquatic 

plant TRVs were set at 0.0042 mg/L (EC25) and 

0.0026 mg/L (NOAEL). 

Overdrive® 

Based on toxicity data from dicamba, diflufenzopyr, 

and Distinct®, and using the conservative assumption 

that Overdrive® is slightly more toxic than dicamba 

and diflufenzopyr, Overdrive® may be considered 

slightly toxic to fish, moderately toxic to aquatic 

invertebrates (Distinct® was much less toxic to aquatic 

invertebrates than dicamba), and highly toxic to 

aquatic plants. Dicamba is practically non-toxic to 

amphibians, but no data were available for the other 

chemicals. 

Fish 

Toxicity tests suggest that diflufenzopyr is practically 

non-toxic to fish, and dicamba is slightly toxic to fish. 

No fish toxicity tests were identified for Distinct®. The 

selected fish TRVs for diflufenzopyr were established 

at 106 mg/L (warmwater LC50) and 16 mg/L 

(coldwater NOAEL). The selected fish TRVs for 

dicamba were established at 28 mg/L (coldwater LC50) 

and 9.3 mg/L (estimated coldwater NOAEL). No 

chronic toxicity studies on freshwater fish were found 

in the available literature, and therefore all TRVs are 

based on acute duration endpoints. 

The bioconcentration factor for diflufenzopyr is 3.16, 

indicating that diflufenzopyr would not appreciably 

bioconcentrate in fish tissue (National Library of 

Medicine 2002). In contrast, the bioconcentration 

factor for dicamba range from 8 to 28, indicating that 

dicamba may bioconcentrate in fish tissue (HSDB 

2002). 

Amphibians 

A single amphibian toxicity study was found during 

the literature review, and it suggested that dicamba is 

practically non-toxic to amphibians. The 96-hour 

toxicity test with dicamba (as the a.i. in Banvel) using 

tadpoles of two frog species resulted in LC50s of 106 

and 185 mg a.i./L (Johnson 1976). A NOAEL of 35.3 

mg a.i./L was estimated by applying an uncertainty 

factor of 3 to the lowest LC50. 

Aquatic Invertebrates 

Toxicity tests indicate that diflufenzopyr is slightly 

toxic, dicamba is moderately toxic, and Distinct® is 

practically non-toxic to aquatic invertebrates. One 

diflufenzopyr acute toxicity test using water fleas (e.g., 

Daphnia magna) was found in the literature. The 

selected invertebrate TRVs for diflufenzopyr were 

established at 15 mg/L (EC50) and 9.7 mg/L (NOAEL), 

indicating that diflufenzopyr is slightly toxic to aquatic 

invertebrates. 

Several dicamba aquatic invertebrate tests were 

identified, resulting in LC50s ranging from 3.8 mg/L 

for the scud (Hurlbert 1975) to >1,000 mg/L for the 

water flea (Forbis et al. 1985). The selected dicamba 

LC50 (3.8 mg /L) was divided by an uncertainty factor 

of 3, to result in a dicamba NOAEL of 1.27 mg/L. 

One 48-hour acute Distinct® water flea test was 

identified. No effects were observed at the highest 

tested concentration, 130 mg a.i./L (USEPA 2003; 

MRID 45310903). The NOAEL (130 mg/L) was 

multiplied by an uncertainty factor of 3, to result in a 

Distinct® EC50 of 390 mg/L. 

No chronic toxicity studies on freshwater aquatic 

invertebrates were found in the available literature, and 

therefore, all TRVs are based on acute duration 

endpoints. 

Aquatic Plants 

Standard toxicity tests conducted on aquatic plants, 

including aquatic macrophytes, freshwater diatoms, 

and algae, suggest that diflufenzopyr, dicamba, and 

Distinct® are highly toxic to aquatic plants. The green 

algae EC50 (0.1 mg/L) and NOAEL (0.0078 mg/L) 

were selected as the aquatic plant TRVs for 

BLM Vegetation Treatments Using Herbicides C-33 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

diflufenzopyr. The selected dicamba EC50 (0.1 mg 

a.i./L) was divided by an uncertainty factor of 3, to 

result in a dicamba NOAEL of 0.033 mg a.i./L. Based 

on the data above, the selected aquatic plant TRVs for 

Distinct® were established at 0.11 mg/L (EC50) and 

0.0023 mg/L (NOAEL). 

Sulfometuron Methyl 

Sulfometuron methyl is toxic to aquatic plants. Tests 

indicate that sulfometuron methyl has low acute 

toxicity to fish and aquatic invertebrates, though 

chronic toxicity can occur from long-term exposure. 

Sulfometuron methyl has a low potential to 

bioconcentrate in fish tissue. Overall, amphibians were 

more sensitive to sulfometuron methyl than most other 

aquatic biota. 

Fish 

Sulfometuron methyl is considered moderately toxic to 

fish. The coldwater 96-hour LC50 of >148 mg/L (the 

lower of the coldwater and warmwater fish endpoints) 

was selected as the acute TRV, and the warmwater fish 

NOAEL of 0.71 mg/L was used as the TRV for 

chronic effects. 

Amphibians 

Toxicity tests on frogs suggest that sulfometuron 

methyl is moderately toxic to amphibians. After 96-

hours of exposure, 50% of the frogs exposed to 

sulfometuron methyl concentrations as low as 4.2 

mg/L exhibited malformations. In chronic toxicity 

tests with this same species, malformations were 

observed in frogs exposed to concentrations as low as 

1 mg/L, with no effects observed at 0.1 mg/L. The 

EC50 (4.2 mg/L) was selected as the amphibian acute 

TRV and the NOAEL (0.1 mg a.i./L) was selected as 

the chronic TRV. 

Aquatic Invertebrates 

Sulfometuron methyl is considered to have slight acute 

toxicity to aquatic invertebrates (chronic toxicity is 

higher). The LC50 (802 mg/L) was selected as the 

invertebrate acute TRV and the 21-day NOAEL (6.1 

mg/L) was selected as the chronic TRV. However, one 

unverifiable report suggested that chronic toxicity to 

aquatic invertebrates may occur at concentrations as 

low as 0.18 mg/L. 

Aquatic Plants 

Sulfometuron methyl was most toxic to water milfoil, 

an aquatic macrophyte; tests on this plant suggest that 

this herbicide is very highly toxic to aquatic plants. 

Adverse effects to 50% of the milfoil plants (the EC50) 

were observed in concentrations containing 0.00012 

mg a.i./L, and the EC25 was 0.00006 mg a.i./L 

(Roshon et al. 1999). The EC50 (0.00012 mg a.i./L) 

was selected as the aquatic plant acute TRV. Because a 

NOAEL was not reported, it was extrapolated by 

dividing the EC50 by an uncertainty factor of 3; the 

resulting NOAEL was 0.00004 mg a.i./L. 

Tebuthiuron 

Tebuthiuron has low toxicity to coldwater and 

warmwater fish and amphibians and slight toxicity to 

aquatic invertebrates. Amphibians were more tolerant 

of tebuthiuron than fish. While tebuthiuron was not 

highly toxic to aquatic plants under acute exposure 

conditions, chronic exposure resulted in toxicity at 

relatively low concentrations. Tebuthiuron is not 

expected to bioconcentrate in aquatic organisms. 

Fish 

Tebuthiuron is considered to have low acute toxicity to 

fish (chronic toxicity is higher). The warmwater 96-

hour LC50 of 112 mg/L (the lower of the coldwater and 

warmwater fish endpoints) was selected as the acute 

TRV and the warmwater fish NOAEL of 9.3 mg/L was 

used as the TRV for chronic effects. 

Amphibians 

Toxicity tests on bullfrogs suggest that tebuthiuron is 

practically non-toxic to amphibians. After 96-hours of 

exposure, the LC50 concentration was determined to be 

less than 398 mg/L, but greater than 306 mg/L. The 

LC50 (398 mg/L) was selected as an amphibian acute 

TRV. Because there was no suitable NOAEL reported 

in the literature, the NOAEL was extrapolated from 

the LC50 using an uncertainty factor of 3; the resulting 

NOAEL TRV was 133 mg/L. 

Aquatic Invertebrates 

Tebuthiuron has low acute toxicity to aquatic 

invertebrates (chronic toxicity is higher). In 48-hour 

aquatic toxicity tests, acute toxicity was observed in 

aquatic invertebrates exposed to concentrations of 297 

mg/L of tebuthiuron. In chronic tests with 

chironomids, adverse effects were observed in the 

BLM Vegetation Treatments Using Herbicides C-34 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

lowest concentration tested, 0.2 mg/L. No adverse 

effects were observed in snails exposed to 0.1 mg/L. 

The LC50 (297 mg/L) was selected as the invertebrate 

acute TRV. The snail NOAEL (0.1 mg/L) was selected 

as the invertebrate chronic TRV. 

Aquatic Plants 

Tebuthiuron appears to be highly toxic to aquatic 

plants. In acute toxicity tests, the EC50 was reported to 

be as low as 0.05 mg/L. NOAELs ranged from 0.013 

mg/L for green algae to 0.18 for various algal species. 

The EC50 (0.05 mg/L) was selected as the aquatic plant 

acute TRV, and the NOAEL (0.013 mg/L) was 

selected as the aquatic plant chronic TRV. 

Rare, Threatened, and Endangered 

Species Characterization 

Rare, threatened, and endangered species have the 

potential to be impacted by herbicides applied for 

vegetation control. Rare, threatened, and endangered 

species are of potential increased concern to screening 

level ERAs, which utilize surrogate species and 

generic assessment endpoints to evaluate potential 

risk, rather than examining site- and species-specific 

effects to individual RTE species. Several factors 

complicate the evaluation of the effects of herbicide 

applications on RTE species: 

• Toxicological data specific to the species (and 

sometimes even class) of organism are often 

absent from the literature. 

• The other assumptions involved in the ERA 

(e.g., rate of food consumption, surface-tovolume ratio) may differ for RTE species 

relative to selected surrogates and/or data for 

RTE species may be unavailable. 

• The high level of protection afforded RTE 

species by regulation and policy suggests that 

secondary effects (e.g., potential loss of prey 

or cover), as well as site-specific 

circumstances that might result in higher rates 

of exposure, should receive more attention. 

A common response to these issues is to design 

screening level ERAs to be highly conservative. This 

includes assumptions such as 100% exposure to an 

herbicide by simulating scenarios where the organism 

lives year-round (not likely for larger and migratory 

animals) in the most affected area (i.e., area of highest 

concentration), or that the organism consumes only 

food items that have been impacted by the herbicide. 

The screening level ERA incorporates additional 

conservatism in the assumptions used in the herbicide 

concentration models such as GLEAMS. Even with 

highly conservative assumptions in the ERA, however, 

concern may still exist over the potential risk to 

specific RTE species. 

Potential direct impacts to receptors, including RTE 

species, are the measures of effect typically used in 

screening level ERAs. Direct impacts, such as those 

resulting from direct or indirect contact or ingestion 

were assessed in the ERAs by comparing calculated 

RQs to receptor-specific LOCs. An RQ greater than 

the LOC indicates the potential for risk to that receptor 

group via that exposure pathway. As described below, 

the selection of TRVs and the use of LOCs were 

pursued in a conservative fashion in order to provide a 

greater level of protection for RTE species. 

The LOCs used in the ERA (Table C-1) were 

developed by the USEPA for the assessment of 

pesticides (LOC information obtained from Michael 

Davy, USEPA OPP on June 13, 2002). In essence, the 

LOCs act as uncertainty factors often applied to TRVs. 

For example, using an LOC of 1.0 provides the same 

result as dividing the TRV by 10. The LOC for avian 

and mammalian RTE species is 0.1 for acute and 

chronic exposures. For RTE fish and aquatic 

invertebrates, acute and chronic LOCs were 0.05 and 

0.5, respectively. Therefore, up to a 20-fold 

uncertainty factor has been included in the TRVs for 

animal species. As noted below, such uncertainty 

factors provide a greater level of protection to the RTE 

to account for the factors listed in the beginning of this 

section. 

For RTE plants, the exposure concentration, TRVs, 

and LOCs provided a direct assessment of potential 

impacts. For all exposure scenarios, the maximum 

modeled concentrations were used as the exposure 

concentrations. The TRVs used for RTE plants were 

selected based on highly sensitive endpoints, such as 

germination, rather than direct mortality of seedlings 

or larger plants. Conservatism has been built into the 

TRVs during their development; the lowest suitable 

endpoint concentration available was used as the TRV 

for RTE plant species. Therefore, the RQ calculated 

for RTE plant exposure is intrinsically conservative. 

Given the conservative nature of the RQ, and to be 

consistent with USEPA policy, no additional levels of 

protection were required for the LOC (i.e., all plant 

LOCs are 1). 

BLM Vegetation Treatments Using Herbicides C-35 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

BLM Vegetation Treatments Using Herbicides C-36 June 2007 

Final Programmatic EIS

Protection levels for different species and individuals 

vary. Some organisms are protected on a community 

level; that is, slight risk to individual species may be 

acceptable if the community of organisms (e.g., 

wildflowers, terrestrial insects) is protected. Generally, 

community level organisms include plants and 

invertebrates. Other organisms are protected on a 

population level; that is, slight risk to individuals of a 

species may be acceptable if the population, as a 

whole, is not endangered. However, RTE species are 

protected as individuals; that is, risk to any single 

organism is considered unacceptable. This higher level 

of protection motivates much of the conservative 

approach taken in this ERA. Surrogate species were 

grouped by general life strategy: sessile (i.e., plants), 

water dwelling (i.e., fish), and mobile terrestrial 

vertebrates (i.e., birds, mammals, and reptiles). The 

approach to account for RTE species was divided 

along the same lines. Plants, fish, insects, and aquatic 

invertebrates were assessed using TRVs developed 

from surrogate species. All species from these taxa 

(identified in Appendix C of each ERA [ENSR 2005aj]) were represented by the surrogate species presented 

in Tables C-3 and C-4. 

Non-target Species Risk 

Characterization 

The risk analysis evaluates the effects of the 10 

herbicides on non-target terrestrial and aquatic flora 

and fauna. The risk that non-target flora and fauna face 

from herbicide applications depends on the toxicity of 

herbicides to individual species and the exposure of 

organisms to herbicides as a result of BLM 

applications. In order to address potential risks to 

ecological receptors, RQs were calculated by dividing 

the EEC for each of the previously described exposure 

pathways by the appropriate herbicide-specific TRV. 

Over 1,000 RQs were generated in each ERA. These 

RQs were then compared to LOC established by the 

USEPA OPP for all appropriate exposure scenarios 

and surrogate species. Ecological risk is implied when 

RQs exceeded the corresponding LOCs. LOCs are 

defined for the following risk presumption categories 

(see Table C-1): 

• Acute high risk – the potential for acute risk is 

high. 

• Acute restricted use – the potential for acute 

risk is high, but may be mitigated. 

• Acute RTE species – RTE species may be 

adversely affected. 

• Chronic risk – the potential for chronic risk is 

high. 

Specific risks to applicable terrestrial and aquatic 

receptor groups from each individual herbicide are 

presented below according to the particular exposure 

pathway. See the tables and figures in Section 4 of the 

ERAs for each herbicide for risk information on 

ecological receptor groups according to herbicide 

application method. Indirect risks to salmonids are 

presented at the end of each herbicide section. In 

addition to direct effects of herbicides on salmonids 

and other fish species in stream habitats (i.e., mortality 

due to herbicide concentrations in water), reduction in 

vegetative cover or food supply may indirectly impact 

individuals or populations. No literature studies were 

identified that explicitly evaluated the direct or indirect 

effects of the herbicides on salmonids and their 

habitat; therefore, only qualitative estimates of indirect 

effects were possible. These estimates were 

accomplished by evaluating predicted impacts to prey 

items and vegetative cover in the stream scenarios of 

accidental direct spray, off-site drift, and surface 

runoff. An evaluation of impacts to non-target 

terrestrial plants was also included as part of the 

discussion of vegetative cover within the riparian zone. 

Food items for salmonids and other potential RTE 

species may include other fish species, aquatic 

invertebrates, and aquatic plants. It should be noted 

that the selected chronic fish TRV was based on a 

NOAEL for the fathead minnow (Pimephales 

promelas), which is much lower than any chronic 

values identified for salmonids. This indicates that 

chronic impacts to salmonids may be overestimated in 

this assessment. 

Bromacil 

Direct Spray 

Terrestrial Wildlife 

In general, acute RQs for terrestrial wildlife were 

below the most conservative LOC (0.1; acute risk RTE 

species at the typical application rate). However, direct 

spray of the pollinating insect resulted in elevated RQs 

at both the typical and maximum application rates. 

This is a conservative scenario that assumes the insect 

absorbs 100% of the herbicide with no degradation or 

limitations to uptake. Acute RQs above the most 

conservative LOC were also predicted at the maximum 
TABLE C-5 

Selected Toxicity Reference Values for Bromacil 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee 193 ug/bee NR LD50 TechnicaLarge bird > 5,000 mg/kg bw 8 d LD50 Mallard Dietary; Large bird 155 mg/kg bw-day 22 w NOAEL Mallard 98.1% a.Piscivorous bird 155 mg/kg bw-day 22 w NOAEL Mallard 98.1% a.Small bird > 30,195 mg/kg bw 8 d LD50 Bobwhite quail 80% a.i. Small bird 936 mg/kg bw-day 21 w NOAEL Bobwhite quail 98.1% a.Small mammal 13.3 mg a.i./kg bw-day 2 y NOAEL Rat Small mammal - dermal > 5,000 mg a.i./kg bw NR LD50 Rabbit Small mammal - ingestion 641 mg a.i./kg bw NR LD50 Rat Water exLarge mammal 641 mg a.i./kg bw > 14 d LD50 Rat Small maLarge mammal 4.65 mg a.i./kg bw-day 2 y NOAEL Dog Terrestrial Plants Typical species - direct spray, drift, dust 0.0023 lb a.i./acre NR EC25 Rape Vigor RTE species - direct spray, drift, dust 0.0008 lb a.i./acre NR NOAEL Rape ExtrapolTypical species - runoff 0.188 lb a.i./acre 14 d NOAEL Soybean EmergenRTE species - runoff 0.0117 lb a.i./acre NR NOAEL Rape EmergenAquatic Species Aquatic invertebrates 65 mg a.i./L 48 h EC50 Water flea Fish 36 mg/L 96 h LC50 Rainbow trout 96.6% a.Aquatic plants and algae 0.0068 mg/L 5 d EC50 Green algae 96.5% a.Aquatic invertebrates 22 mg a.i./L 48 h NOAEL Water flea ExtrapolFish 0.33 mg a.i./L 64 d NOAEL Fathead minnow ExtrapolAquatic plants and algae 0.0023 mg/L 5 d NOAEL Green algae Extrapol

BLM Vegetation Treatment Using Herbicides C-37 June 2007 

Final Programmatic EIS
BLM Vegetation Treatment Using Herbicides 

C-38 June 2007 

Final Programmatic EIS

TABLE C-5 (Cont.) 

Selected Toxicity Reference Values for Bromacil 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints

Amphibian 230 mg a.i./L 48 h LC50 Tadpole “Unaccep

% a.i. pro

Amphibian 77 mg a.i./L 48 h NOAEL Tadpole 

Extrapol“unaccep% a.i. pro

Warmwater fish 71 mg/L 48 h LC50 Bluegill No % a.iWarmwater fish 0.33 mg a.i./L 64 d NOAEL Fathead minnow ExtrapolColdwater fish 36 mg/L 96 h LC50 Rainbow trout 96.6% a.Coldwater fish 16.9 mg/L 96 h NOAEL Rainbow trout 96.6% a.

1 Piscivorous bird TRV = Large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 

2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo
TABLE C-6 

Selected Toxicity Reference Values for Chlorsulfuron 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee > 25 μg/bee 48 h LD50 98.2% aLarge bird > 1,500 mg/kg bw 8 d LD50 Mallard TechnicLarge bird 99 mg/kg bw-day 1 generation NOAEL Mallard 98.2% aPiscivorous bird 99 mg/kg bw-day 1 generation NOAEL Mallard 98.2% aSmall bird > 16,970 mg/kg bw 8 d LD50 Bobwhite quail TechnicSmall bird 100 mg/kg bw-day 27 w NOAEL Bobwhite quail 98.2% aSmall mammal 1,363 mg a.i./kg bw NR LD50 Guinea pig Small mSmall mammal – dermal 66 mg a.i./kg bw-day 1 y NOAEL Dog Small mammal – ingestion 5 mg a.i./kg bw-day 90 d NOAEL Rat Large mammal > 3,400 mg a.i./kg bw 24 h LD50 Rabbit Large mammal 1,363 mg a.i./kg bw NR LD50 Guinea pig Water eTerrestrial Plants Typical species - direct spray, drift, dust 0.000063 lb a.i./acre life cycle EC25 Canola ExtrapoRTE species - direct spray, drift, dust 0.000021 lb a.i./acre life cycle NOAEL Canola Typical species - runoff 0.0157 lb a.i./acre NR NOAEL Dyer's woad (weed) Extrapo

EC100

RTE species - runoff 0.0052 lb a.i./acre NR NOAEL Dyer's woad (weed) Extrapo

NOAEL 

Aquatic Species Aquatic invertebrates 368.9 mg a.i./L 48 h LC50 Water flea (D. magna) 91% a.iFish 40 mg/L 96 h LC50 Brown trout No % aAquatic plants and algae 0.0007 mg a.i./L 96 h EC50 Duckweed TechnicAquatic invertebrates 20 mg a.i./L 21 d NOAEL Water flea (C. dubia) 95.4% aFish 17 mg/L 96 h NOAEL Channel catfish 91% a.i

from LC

Aquatic plants and algae 0.0004 mg a.i./L 96 h NOAEL Duckweed Technic

BLM Vegetation Treatment Using Herbicides C-39 June 2007 

Final Programmatic EIS
BLM Vegetation Treatment Using Herbicides 

C-40 June 2007 

Final Programmatic EIS

TABLE C-6 (Cont.) 

Selected Toxicity Reference Values for Chlorsulfuron 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints

Amphibian no data Amphibian no data Warmwater fish 50 mg a.i./L 96 h LC50 Channel catfish 91% a.i. Warmwater fish 17 mg a.i./L 96 h NOAEL Channel catfish 91% a.i. 

from LC

Coldwater fish 40 mg a.i./L 96 h LC50 Brown trout No % a.iColdwater fish 31 mg a.i./L 77 d NOAEL Rainbow trout 97.9% a.

1 Piscivorous bird TRV = Large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 

2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo
TABLE C-7 

Selected Toxicity Reference Values for Diflufenzopyr 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee 75 

μg/bee 48 h LD50 Extrapolate

a.i. product 

Large bird > 2,810 mg/kg bw 8 d LD50 Mallard 94.7% a.i. pLarge bird 105 mg/kg bw-day 21 w NOAEL Mallard 94.3% a.i. pPiscivorous bird 105 mg/kg bw-day 21 w NOAEL Mallard 94.3% a.i. pSmall bird > 16,970 mg/kg bw 8 d LD50 Bobwhite quail 94.7% a.i. pSmall bird 634 mg/kg bw-day 20 w NOAEL Bobwhite quail 94.3% a.i. pSmall mammal 42.2 mg/kg bw-day 2 generation NOAEL Rat 93% a.i. prSmall mammal - dermal > 5,000 mg/kg bw NR LD50 Rabbit 96.4% a.i. pSmall mammal - ingestion 3,300 mg/kg bw NR LD50 Rat Water expo

98.1% a.i. p

Large mammal 3,300 mg/kg bw NR LD50 Rat Small mamLarge mammal 59 mg/kg bw-day 1 y NOAEL Dog No % a.i. liTerrestrial Plants Typical species - direct spray, drift, dust 0.0008 lb a.i./acre 14 d EC25 Turnip Based on eRTE species - direct spray, drift, dust 0.0003 lb a.i./acre 14 d NOAEL Turnip ExtrapolateTypical species – runoff 0.028 lb a.i./acre 14 d NOAEL Tomato No germina

emergence 

RTE species - runoff 0.0001 lb a.i./acre NR NOAEL Turnip No germina

emergence 

Aquatic Species Aquatic invertebrates 15 mg/L 48 h EC50 Water flea 94.7% a.i. pFish 106 mg/L 96 h LC50 Rainbow trout 97.4% a.i. pAquatic plants and algae 0.1 mg/L 5 d EC50 Green algae 99.5% a.i. pAquatic invertebrates 9.7 mg/L 48 h NOAEL Water flea 94.7% a.i. pFish 16 mg/L 96 h NOAEL Bluegill sunfish 97.4% a.i. pAquatic plants and algae 0.0078 mg/L 5 d NOAEL Green algae 99.5% a.i. p

BLM Vegetation Treatment Using Herbicides C-41 June 2007 

Final Programmatic EIS
BLM Vegetation Treatment Using Herbicides 

C-42 June 2007 

Final Programmatic EIS

TABLE C-7 (Cont.) 

Selected Toxicity Reference Values for Diflufenzopyr 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints

Amphibian no data Amphibian no data Warmwater fish > 135 mg/L 96 h LC50 Bluegill sunfish 97.4% aWarmwater fish 16 mg/L 96 h NOAEL Bluegill sunfish 97.4% aColdwater fish 106 mg/L 96 h LC50 Rainbow trout 97.4% aColdwater fish 80 mg/L 96 h NOAEL Rainbow trout 97.4% a

1 Piscivorous bird TRV = Large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 

2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo
TABLE C-8 

Selected Toxicity Reference Values for Diquat 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee 47 μg/bee 5 d LD50 Extrapolate

a.i. listed 

Large bird 215 mg a.i./kg bw NR LD50 Ring neck pheasant Large bird 0.6 mg a.i./kg bw-day 1 generation NOAEL Mallard Piscivorous bird 0.6 mg a.i./kg bw-day 1 generation NOAEL Mallard Small bird 150 mg a.i./kg bw NR LD50 Japanese quail Small bird > 12 mg a.i./kg bw-day NR NOAEL Bobwhite quailSmall mammal 0.8 mg a.i./kg bw-day 104 w NOAEL Rat Small mammal - dermal 262 mg a.i./kg bw NR LD50 Rabbit Small mammal - ingestion 121 mgkg bw > 14 d LD50 Rat Water expo

% a.i. listed 

Large mammal 121 mg/kg bw > 14 d LD50 Rat Small mamLarge mammal 0.5 mg a.i./kg bw-day 1 y NOAEL Dog Terrestrial Plants Typical Species - direct spray, drift 0.0047 lb a.i./acre NR EC25 Cotton Vigor RTE Species - direct spray, drift 0.0016 lb a.i./acre NR NOAEL Cotton Vigor; extrAquatic Species Aquatic invertebrates 0.14 mg/L 48 h EC50 Amphipod No % a.i. lFish 0.75 mg a.i./L 96 h LC50 Walleye Aquatic plants and algae 0.00075 mg a.i./L 14 d EC50 Giant duckweed 35.3% a.i. pAquatic invertebrates 0.044 mg a.i./L life cycle NOAEL Water flea 41.4% a.i. pFish 0.17 mg a.i./L NR NOAEL Rainbow trout Extrapolate

swimming 

Aquatic plants and algae 0.0003 mg a.i./L 14 d NOAEL Giant duckweed Extrapolate

BLM Vegetation Treatment Using Herbicides C-43 June 2007 

Final Programmatic EIS
BLM Vegetation Treatment Using Herbicides 

C-44 June 2007 

Final Programmatic EIS

TABLE C-8 (Cont.) 

Selected Toxicity Reference Values for Diquat 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints

Amphibian no data Amphibian 2 mg/L 16 d NOAEL Northern leopard frog No % a.iWarmwater fish 0.75 mg a.i./L 96 h LC50 Walleye Warmwater fish 0.58 mg a.i./L 34 d NOAEL Fathead minnow 41% a.i. Coldwater fish 14.83 mg/L 96 h LC50 Rainbow trout 19.8% a.Coldwater fish 0.17 mg a.i./L NR NOAEL Rainbow trout Extrapol

LOAEL/

1 Piscivorous bird TRV = Large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 

2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo
TABLE C-9 

Selected Toxicity Reference Values for Diuron 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee 145.03 

μg/bee 48 h LD50 Technic

Large bird 865 mg/kg bw 8 d LD50 Mallard No % aLarge bird 58 mg/kg bw-day 8 d NOAEL Mallard No % a

from LD

Piscivorous bird 1,017 mg a.i./kg bw NR LD50 Rat Small mSmall bird 0.6 mg a.i./kg bw-day 2 y NOAEL Dog Small bird 58 mg/kg bw-day 8 d NOAEL Mallard No % a

from LD

Small mammal 5,225 mg/kg bw 8 d LD50 Bobwhite quail No % aSmall mammal – dermal 348 mg/kg bw-day 8 d NOAEL Bobwhite quail No % a

from LD

Small mammal – ingestion 2.5 mg a.i./kg bw-day 3 m NOAEL Rat Large mammal > 2,500 mg a.i./kg bw > 14 d LD50 Unknown Large mammal 1017 mg a.i./kg bw NR LD50 Rat Water eTerrestrial Plants Typical species - direct spray, drift, dust 0.08 lb a.i./acre NR EC25 Tomato Based oRTE species - direct spray, drift, dust 0.001 lb a.i./acre 21 d NOAEL Vigor Typical species - runoff 12 lb a.i./acre 14 d NOAEL Garden pea; soybean Based oRTE species - runoff 0.047 lb a.i./acre NR NOAEL Tomato Based oAquatic Species Aquatic invertebrates 0.16 mg/L 96 h EC50 Scud (Gammarus) 95% a.iFish 0.71 mg/L 96 h LC50 Cutthroat trout 95% a.iAquatic plants and algae 0.0013 mg/L NR EC50 Chlorella pyrenoidosa (algae) No % aAquatic invertebrates 0.067 mg/L 28 d NOAEL Daphnid 98% a.i

from ch

Fish 0.033 mg/L chronic NOAEL Fathead minnow 98.6% aAquatic plants and algae 0.00044 mg/L 96 h NOAEL Selenastrum (algae) 98.6% a

BLM Vegetation Treatment Using Herbicides C-45 June 2007 

Final Programmatic EIS
BLM Vegetation Treatment Using Herbicides 

C-46 June 2007 

Final Programmatic EIS

TABLE C-9 (Cont.) 

Selected Toxicity Reference Values for Diuron 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints

Amphibian 12.7 mg/L 21 d LC50 Bullfrog 99.8% a.Amphibian 7.6 mg/L 21 d NOAEL Bullfrog 99.8% a.Warmwater fish 2.8 mg/L 96 h LC50 Bluegill sunfish 95% a.i. Warmwater fish 0.03 mg/L chronic NOAEL Fathead minnow 98.6% a.Coldwater fish 0.71 mg/L 96 h LC50 Cutthroat trout 95% a.i. Coldwater fish 0.24 mg/L 96 h NOAEL Cutthroat trout 95% a.i. 

from LC

1 Piscivorous bird TRV = Large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 

2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo
BLM Vegetation Treatment Using Herbicides C-47 June 2007 

Final Programmatic EIS

TABLE C-10 

Selected Toxicity Reference Values for Fluridone 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee 1,088 μg/bee 48 h LD50 Extrapolate

a.i. product 

Large bird > 2,270 mg/kg bw 8 d LD50 Mallard Technical g

a.i. 

Large bird 100 mg a.i./kg bw-day 1 generation NOAEL Mallard ReproductiPiscivorous bird 100 mg a.i./kg bw-day 1 generation NOAEL Mallard Small bird > 13,135 mg/kg bw 8 d LD50 Bobwhite quail Technical g

a.i. 

Small bird 604 mg a.i./kg bw-day 1 generation NOAEL Bobwhite quail ReproductiSmall mammal 8 mg a.i./kg bw-day 2 y NOAEL Rat Small mammal - dermal > 5,000 mg a.i./kg bw 8 d LD50 Rabbit Small mammal - ingestion > 10,000 mg a.i./kg bw NR LD50 Mouse and rat Water expoLarge mammal > 10,000 mg a.i./kg bw NR LD50 Mouse and rat Small mamLarge mammal 75 mg a.i./kg bw-day 1 y NOAEL Beagle Terrestrial Plants Terrestrial plants - typical species no data Terrestrial plants- RTE species no data Aquatic Species Aquatic invertebrates 0.14 mg/L 48 h EC50 Amphipod No % a.i. lFish 0.75 mg a.i./L 96 h LC50 Walleye Aquatic plants and algae 0.00075 mg a.i./L 14 d EC50 Giant duckweed 35.3% a.i. pAquatic invertebrates 0.044 mg a.i./L life cycle NOAEL Water flea 41.4% a.i. pFish 0.17 mg a.i./L NR NOAEL Rainbow trout Extrapolate

swimming 

Aquatic plants and algae 0.0003 mg a.i./L 14 d NOAEL Giant duckweed Extrapolate
BLM Vegetation Treatment Using Herbicides 

C-48 June 2007 

Final Programmatic EIS

TABLE C-10 (Cont.) 

Selected Toxicity Reference Values for Fluridone 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints

Amphibian no data Amphibian no data Warmwater fish 8.2 mg/L 96 h LC50 Channel catfish 98 – 99% Warmwater fish 0.5 mg/L life cycle NOAEL Fathead minnow 98 – 99% Coldwater fish 4.2 mg/L 96 h LC50 Rainbow trout 98 – 99% Coldwater fish 1.4 mg/L 96 h NOAEL Rainbow trout Extrapol

1 Piscivorous bird TRV = Large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 

2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo
TABLE C-11 

Selected Toxicity Reference Values for Imazapic 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee > 100 

μg/bee 48 h LD50 93.7% a

Large bird > 2,500 mg a.i./kg bw 8 d LD50 Mallard 93.7% aLarge bird 65 mg a.i./kg bw-day 22 w NOAEL Mallard 96.9% aPiscivorous bird 65 mg a.i./kg bw-day 22 w NOAEL Mallard 96.9% aSmall bird > 15,095 mg a.i./kg bw 8 d LD50 Bobwhite quail 93.7% aSmall bird 113 mg a.i./kg bw-day 24 w NOAEL Bobwhite quail 96.9% aSmall mammal 1,728 mg/kg bw-day 3 m NOAEL Rat Technic

extrapo

Small mammal - dermal > 2,000 mg/kg bw NR LD50 Rabbit No % aSmall mammal - ingestion > 5,000 mg a.i./kg bw NR LD50 Rat Water eLarge mammal > 5,000 mg a.i./kg bw NR LD50 Rat Same as 

water ex

Large mammal 46 mg/kg bw-day 1 y NOAEL Dog Technic

extrapo

Terrestrial Plants Typical species - direct spray, drift, dust 0.01 lb a.i./acre 14 d EC25 Corn Based oRTE species - direct spray, drift, dust 0.008 lb a.i./acre 21 d NOAEL Soybean Based oTypical species – runoff 0.064 lb a.i./acre 6 d NOAEL Vegetable crops Based oRTE species - runoff 0.032 lb a.i./acre 6 d NOAEL Onion Based oAquatic Species Aquatic invertebrates > 100 mg/L 48 h LD50 Water flea 93.7% aFish > 100 mg/L 96 h LD50 Rainbow trout 93.7% aAquatic plants and algae 0.0042 mg/L 14 d EC25 Duckweed 96.9% aAquatic invertebrates 96 mg/L 21 d NOAEL, ELEL Water flea 97% a.iFish 33 mg/L 96 h NOAEL Rainbow trout 93.7% a

from 96 

Aquatic plants and algae 0.0026 mg/L 14 d NOAEL Duckweed 96.9% a

BLM Vegetation Treatment Using Herbicides C-49 June 2007 

Final Programmatic EIS
BLM Vegetation Treatment Using Herbicides 

C-50 June 2007 

Final Programmatic EIS

TABLE C-11 (Cont.) 

Selected Toxicity Reference Values for Imazapic 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints

Amphibian no data Amphibian no data Warmwater fish > 100 mg/L 96 h LD50 Bluegill 93.7% a.Warmwater fish 96 mg/L 32 d NOAEL Fathead minnow 97% a.i. Coldwater fish > 100 mg/L 96 h LD50 Rainbow trout 93.7% a.Coldwater fish 33 mg/L 96 h NOAEL Rainbow trout 93.7% a.

from 96 

1 Piscivorous bird TRV = Large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 

2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo
TABLE C-12 

BLM Vegetation Treatment Using Herbicides C-51 June 2007 

Final Programmatic EIS

Selected Toxicity Reference Values for Overdrive

®

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee 75 ug/bee 48 h LD50 Extrapo

a.i. prod

Large bird > 2,810 mg/kg bw 8 d LD50 Mallard 94.7% aLarge bird 105 mg/kg bw-day 21 w NOAEL Mallard 94.3% aPiscivorous bird 3,300 mg/kg bw LD50 Rat Small mSmall bird 59 mg/kg bw-day 1 y NOAEL Dog No % aSmall bird 105 mg/kg bw-day 8 d NOAEL Mallard 94.7% aSmall mammal > 16,970 mg/kg bw 8 d LD50 Bobwhite quail 94.7% aSmall mammal - dermal 634 mg/kg bw-day 20 w NOAEL Bobwhite quail 94.3% aSmall mammal - ingestion 42.2 mg/kg bw-day 2 generation NOAEL Rat 93% a.iLarge mammal > 5,000 mg/kg bw LD50 Rabbit 96.4% aLarge mammal 3,300 mg/kg bw LD50 Rat Water e

availabl

Terrestrial Plants Typical species - direct spray, drift, dust 0.0008 lb a.i./acre 14 d EC25 Turnip Based oRTE species - direct spray, drift, dust 0.0003 lb a.i./acre 14 d NOAEL Turnip ExtrapoTypical species - runoff 0.028 lb a.i./acre 14 d NOAEL Tomato No germ

emergen

RTE species - runoff 0.0001 lb a.i./acre NR NOAEL Turnip No germ

emergen

Aquatic Species Aquatic invertebrates 15 mg/L 48 h EC50 D. magna 94.7% aFish 106 mg/L 96 h LC50 Rainbow trout 97.4% aAquatic plants and algae 0.1 mg/L 5 d EC50 Green algae 99.5% aAquatic invertebrates 9.7 mg/L 48 h NOAEL D. magna 94.7% aFish 16 mg/L 96 h NOAEL Bluegill sunfish 97.4% aAquatic plants and algae 0.0078 mg/L 5 d NOAEL Green algae 99.5% a
BLM Vegetation Treatment Using Herbicides 

C-52 June 2007 

Final Programmatic EIS

TABLE C-12 (Cont.) 

Selected Toxicity Reference Values for Overdrive®

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints

Amphibian no data Amphibian no data Warmwater fish > 100 mg/L 96 h LD50 Bluegill 93.7% a.Warmwater fish 96 mg/L 32 d NOAEL Fathead minnow 97% a.i. Coldwater fish > 100 mg/L 96 h LD50 Rainbow trout 93.7% a.Coldwater fish 33 mg/L 96 h NOAEL Rainbow trout 93.7% a.

from 96 

1 Piscivorous bird TRV = Large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 

2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo
TABLE C-13 

Selected Toxicity Reference Values for Sulfometuron Methyl 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee 300 μg/bee 48 h LD50 Extrapo

99.8% a

Large bird > 2,300 mg a.i./kg bw 8 d LD50 Mallard Large bird 153 mg a.i./kg bw-day 8 d NOAEL Mallard ExtrapoPiscivorous bird 153 mg a.i./kg bw-day 8 d NOAEL Mallard Small bird > 16970 mg a.i./kg bw 8 d LD50 Bobwhite quail 95.2% aSmall bird 1,131 mg a.i./kg bw-day 8 d NOAEL Bobwhite quail 

Extrapoa.i. prod

Small mammal 18 mg a.i./kg bw-day 18 m NOAEL Mouse Small mammal - dermal > 8,000 mg a.i./kg bw LD50 Rabbit Small mammal - ingestion > 5,000 mg a.i./kg bw LD50 Rat Water eLarge mammal > 5,000 mg a.i./kg bw LD50 Rat Small mLarge mammal 28 mg a.i./kg bw-day 1 y NOAEL Dog Terrestrial Plants Typical species-direct spray, drift, dust 0.22 lb a.i./acre EC25 White mustard Growth RTE species-direct spray, drift, dust 0.000028 lb a.i./acre 14 d NOAEL Sorghum Based oTypical species – runoff 1.12 lb a.i./acre NOAEL Leafy spurge Based oRTE species – runoff 0.000028 lb a.i./acre NOAEL Sorghum, sugar beet Based oAquatic Species Aquatic invertebrates 802 mg/L LC50 Cladoceran 93% a.iFish > 148 mg/L 96 h LC50 Rainbow trout 99.6% aAquatic plants and algae 0.00012 mg a.i./L EC50 Water milfoil Based oAquatic invertebrates 6.1 mg/L 21 d NOAEL Water flea (D. magna) Extrapo

a.i. prod

Fish 0.71 mg/L chronic NOAEL Fathead minnow 95% a.iAquatic plants and algae 0.00004 mg a.i./L NOAEL Water milfoil Extrapo

BLM Vegetation Treatment Using Herbicides C-53 June 2007 

Final Programmatic EIS
BLM Vegetation Treatment Using Herbicides 

C-54 June 2007 

Final Programmatic EIS

TABLE C-13 (Cont.) 

Selected Toxicity Reference Values for Sulfometuron Methyl 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints

Amphibian 4.2 mg/L EC50 African clawed frog 85% a.i. Amphibian 0.1 mg/L chronic NOAEL African clawed frog 85% a.i. Warmwater fish > 150 mg/L LC50 Bluegill sunfish 99.6% a.Warmwater fish 0.71 mg/L chronic NOAEL Fathead minnow 95% a.i. Coldwater fish > 148 mg/L 96 h LC50 Rainbow trout 99.6% a.Coldwater fish 49 mg/L 96 h NOAEL Rainbow trout Extrapol

product 

1 Piscivorous bird TRV = Large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 

2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo
TABLE C-14 

Selected Toxicity Reference Values for Tebuthiuron 

Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Receptors Included in the Food Web Model 

Terrestrial Animals Honeybee 30 μg/bee NR LD50Large bird > 2,545 mg a.i./kg bw 8 d LD50 Mallard Large bird 1,000 mg a.i./kg bw-day 30 d NOAEL Chicken Piscivorous bird 1,000 mg a.i./kg bw-day 30 d NOAEL Chicken Small bird > 15,440 mg a.i./kg bw 8 d LD50 Bobwhite quail Small bird 1,029 mg a.i./kg bw-day 8 d NOAEL Bobwhite quail ExtrapoSmall mammal 7 mg a.i./kg bw-day 2 generations NOAEL Rat Small mammal - dermal > 5,000 mg a.i./kg bw NR LD50 Rabbit Small mammal - ingestion 58 mg a.i./kg bw acute LD50 Mouse Water eLarge mammal > 500 mg a.i./kg bw acute LD50 Dog Large mammal 12.5 mg a.i./kg bw-day 90 d NOAEL Dog Water eTerrestrial Plants Typical species - direct spray, drift, dust 0.03 lb a.i./acre NR EC25 Cabbage Based oRTE species-direct spray, drift, dust 0.01 lb a.i./acre NR NOAEL Cabbage Extrapo

seed em

Typical species – runoff > 6 lb a.i./acre 5 d NOAEL 10 species Based oRTE species – runoff 0.01 lb a.i./acre 5d NOAEL Cabbage Extrapo

seed em

Aquatic Species Aquatic invertebrates 802 mg/L LC50 Cladoceran 93% a.iFish > 148 mg/L 96 h LC50 Rainbow trout 99.6% aAquatic plants and algae 0.00012 mg a.i./L EC50 Water milfoil Based oAquatic invertebrates 6.1 mg/L 21 d NOAEL Water flea (D. magna) Extrapo

a.i. prod

Fish 0.71 mg/L chronic NOAEL Fathead minnow 95% a.iAquatic plants and algae 0.00004 mg a.i./L NOAEL Water milfoil Extrapo

BLM Vegetation Treatment Using Herbicides C-55 June 2007 

Final Programmatic EIS
TABLE C-14 (Cont.) Selected Toxicity Reference Values for Tebuthiuron Receptor Selected TRV1 Units Duration2 Endpoint3 Species 

Additional Endpoints Amphibian < 398 mg/L 96 h LC50 Bullfrog > 97% a.

Amphibian 133 mg/L 96 h NOAEL Bullfrog ExtrapolWarmwater fish 112 mg/L 96 h LC50 Bluegill sunfish ~ 100% Warmwater fish > 9.3 mg a.i./L 33 d NOAEL Fathead minnow Growth Coldwater fish 115 mg/L 96 h LC50 Rainbow trout > 97% a.Coldwater fish 26 mg/L 45 d NOAEL Rainbow trout Growth; 

1 Piscivorous bird TRV = large bird chronic TRV; and fish TRV = Lower of coldwater and warmwater fish TRVs. 2 Duration: h = hours; d = days; w = weeks; m = months; y = years; and NR = not reported. 3 Toxicity endpoints for terrestrial animals: LD50 to address acute exposure, and NOAEL to address chronic exposure. Toxicity endpoints for terres

direct spray, drift, and dust impacts on typical species; NOAEL to address direct spray, drift, and dust impacts on RTE species; highest germ

surface runoff impacts on typical species; and lowest germination NOAEL to address surface runoff impacts on RTE species. Toxicity endpoints 

or EC50 to address acute exposure (appropriate toxicity endpoint for non-target aquatic plants will be an EC50) and NOAEL to address chronic expo

BLM Vegetation Treatment Using Herbicides C-56 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

application rate for ingestion of contaminated prey by 

the small mammalian herbivore, the large mammalian 

herbivore, the large avian herbivore, and the large 

carnivorous mammal, with the exception of the large 

mammalian herbivore with an RQ of 1.3, these RQs 

were below LOC for acute risk. 

Risk quotients for chronic ingestion scenarios were 

below the associated LOC of 1, except the ingestion of 

contaminated prey by the small avian insectivore and 

the large mammalian carnivore. Chronic RQs for the 

small mammalian herbivore and the large avian 

herbivore were just above the LOC at the maximum 

application rate. The large mammalian herbivore 

scenario resulted in elevated chronic RQs at both the 

typical and maximum application rates. 

Therefore, direct spray impacts may pose a risk to 

insects and large herbivores, primarily when the 

maximum application rate is used. 

Non-target Plants – Terrestrial and Aquatic 

As expected, because of the mode of action of 

herbicides, RQs for non-target terrestrial and aquatic 

plants impacted by direct spray were above the plant 

LOC of 1 for all modeled scenarios. RQs for direct 

spray of non-target terrestrial plants ranged from 1,740 

to 15,000. RQs for non-target aquatic plants impacted 

by accidental direct spray of the pond or stream ranged 

from 66 to 2,924. Therefore, direct spray impacts are 

likely to pose a risk to plants in both aquatic and 

terrestrial environments. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for aquatic invertebrates in the 

pond were below the most conservative LOC of 0.05 

(acute RTE species), indicating that direct spray 

impacts are not likely to pose a risk to these aquatic 

species. The predicted acute toxicity RQs for fish and 

aquatic invertebrates in the stream were above the 

most conservative LOC of 0.05 (acute risk RTE 

species). These results indicate the potential for acute 

risk to aquatic species, especially RTE species, in a 

stream accidentally sprayed with bromacil. 

The chronic RQs for the accidental direct spray over 

the pond and stream scenarios were below the most 

conservative chronic LOC (0.5; chronic risk RTE 

species) for all aquatic invertebrate scenarios. These 

results indicate that impacts from direct spray are 

generally not likely to pose chronic risk to these 

aquatic species. However, chronic RQs for fish in the 

pond and stream impacted by accidental direct spray 

were above the chronic LOCs for RTE species and 

general chronic risk in most scenarios. This indicates 

the potential for chronic risk to fish due to accidental 

direct spray. 

Off-site Drift 

Non-target Plants – Terrestrial and Aquatic 

All of the RQs for non-target terrestrial plants affected 

by off-site drift were above the plant LOC of 1. The 

RQs ranged from 1.17 (predicted 900 ft from 

application with a low boom at the typical application 

rate) to 312 (predicted 25 ft from application with a 

high boom at the maximum application rate). These 

results indicate that impacts from off-site drift pose a 

risk to non-target terrestrial plant species within 900 ft 

of the application area. 

The majority of the RQs for non-target aquatic plants 

affected by off-site drift at the typical application rate 

were below the plant LOC of 1. However, RQs above 

the LOC were predicted for six chronic waterbody 

scenarios (25 ft from low boom applications, 25 and 

100 ft from high boom applications in both the pond 

and the stream) and one acute stream scenario (25 ft 

from high boom application). 

At the maximum application rate, off-site drift to the 

stream and pond resulted in elevated acute RQs 25 ft 

from low-boom applications and 25 and 100 ft from 

high-boom applications. Elevated chronic RQs were 

predicted in both waterbodies for these three scenarios 

as well as for the scenario of 100 ft from low boom 

applications. These results indicate that impacts from 

off-site drift may pose a risk to aquatic plants within 

100 ft of the application area. In addition, slightly 

more elevated risks were predicted in the stream than 

in the pond. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

(acute RTE species). All chronic RQs were well below 

the LOC for chronic risk to RTE species (0.5). These 

results indicate that impacts from off-site drift are not 

likely to pose acute or chronic risk to these aquatic 

species. 

BLM Vegetation Treatments Using Herbicides C-57 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Piscivorous Birds 

Risk quotients for piscivorous birds were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that this scenario is not likely to pose 

a risk to piscivorous birds. 

Surface Runoff 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for typical non-target terrestrial plant 

species affected by surface runoff were all below the 

plant LOC of 1, indicating that transport due to surface 

runoff is not likely to pose a risk to these receptors. 

Most RQs for RTE non-target terrestrial plant species 

were also below the plant LOC of 1; however, four 

scenarios did result in elevated RQs. These scenarios 

were for the base watershed with clay soils and greater 

than 100 in of rain per year at the maximum 

application rate (between 150 and 250 in of rain per at 

the typical application rate). Therefore, there is 

potential for risk to RTE plant species in this 

watershed type with high amounts of precipitation. 

This scenario is unlikely on most public lands because 

of arid and semi-arid conditions. 

Risk quotients for non-target aquatic plants impacted 

by surface runoff exceeded the plant LOC for nearly 

all pond scenarios. Acute RQs for non-target aquatic 

plants in the stream were also above the plant LOC of 

1 in 33 of the 42 scenarios at the typical application 

rate. At the maximum application rate, elevated RQs 

occurred in 36 of the 42 scenarios. These results 

indicate the likelihood for acute impacts to aquatic 

plants in the stream. 

Chronic RQs in the stream were generally below the 

plant LOC at the typical application rate, except in the 

base watershed with sandy soils and precipitation of 

more than 50 in per year and in the larger application 

areas (100 and 1,000 ac). Most chronic stream RQs 

were above the plant LOC when the maximum 

application rate was considered. The only scenarios 

below this LOC were the base watershed with sand, 

clay, or loam soils and less than 25 in of rain per year, 

the base watershed with clay-loam soil and 50 in of 

rain per year, and the 1 acre application area. These 

results indicate the likelihood for chronic impacts to 

aquatic plants in the stream under most conditions. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were below the most conservative LOC of 0.05 for all 

stream scenarios and nearly all pond scenarios. Three 

acute toxicity RQs for fish in the pond were just over 

the most conservative LOC, but below the remaining 

two acute LOCs, with values of 0.052, 0.056, and 

0.051. These results indicate that impacts from surface 

runoff are not likely to pose a risk to most aquatic 

species, but may pose a slight risk to RTE fish. 

Chronic risk RQs for aquatic invertebrates in the pond 

and stream and fish in the stream were well below the 

LOC for chronic risk to RTE species (0.5), indicating 

that these scenarios are not likely to result in long-term 

risk to these receptors. However, chronic risk RQs for 

fish in the pond were above the LOC for chronic risk 

to RTE species in several scenarios. At the typical 

application rate, elevated RQs ranged from 0.51 in the 

base watershed with sandy soil and 50 in of 

precipitation per year to 1.69 in the same watershed 

with 25 in of precipitation per year. Only two of these 

RQs were elevated above the chronic risk LOC of 1. 

At the maximum application rate, RQs over the LOC 

for chronic risk to RTE species (0.5) occurred in 35 of 

42 modeled scenarios. These results indicate the 

potential for negative chronic impacts to fish in 

downgradient ponds due to surface runoff, especially 

at the maximum application rate. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that this scenario is not likely to pose 

a risk to piscivorous birds. 

Wind Erosion and Transport Off-site 

Risk quotients for typical and RTE terrestrial plants in 

this scenario were all well below the plant LOC (1), 

indicating that wind erosion is not likely to pose a risk 

to non-target terrestrial plants. 

Accidental Spill to Pond 

Risk quotients for the spill scenario were 1.2 for fish, 

0.66 for aquatic invertebrates, and 6,330 for non-target 

aquatic plants. Potential risk to fish, aquatic 

invertebrates, and non-target aquatic plants were 

indicated for the truck spills mixed for the maximum 

application rate. 

BLM Vegetation Treatments Using Herbicides C-58 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

Risk quotients in excess of the acute LOCs for aquatic 

invertebrates were only observed for the accidental 

direct spray scenario. All other acute and chronic RQs 

from accidental spray, off-site drift, and surface runoff 

scenarios were below the associated LOCs. Because 

aquatic invertebrates are not predicted to be directly 

impacted by herbicide concentrations in the stream as 

a result of normal applications, salmonids are not 

likely to be indirectly affected by a reduction in prey. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

Aquatic plant RQs for accidental direct spray scenarios 

were above the plant LOC at both the typical and 

maximum application rates. Elevated acute and 

chronic aquatic plant RQs (ranging from 1.01 to 10.7) 

were also observed as a result of off-site drift within 

100 ft of the application area. Acute risk was observed 

for nearly all surface runoff scenarios. Chronic risk 

due to surface runoff was also predicted in most 

scenarios at the maximum application rate. At the 

typical application rate, minimal chronic risk was 

observed in the base watershed with sandy soils, and 

more significant risk was predicted when the 

application area was increased from 10 acres to 100 

and 1,000 acres. These results indicate the potential for 

a reduction in cover and indirect impacts to salmonids 

as a consequence of multiple exposure pathways. 

Risk quotients for terrestrial plants were elevated 

above the LOC for accidental direct spray scenarios at 

both the typical and maximum application rates, 

indicating the potential for a reduction in this plant 

community. Risk quotients above the plant LOC for 

typical terrestrial plants were also observed for all offsite drift scenarios modeled for bromacil. However, 

non-target terrestrial plant RQs in excess of the LOC, 

as a result of surface runoff, were only observed for 

the base watershed with clay soil and at least 100 in of 

rain per year. All other runoff scenarios predicted RQs 

less than 1. Therefore, in addition to the potential loss 

of aquatic vegetative cover, under most scenarios a 

reduction in riparian vegetation and loss of terrestrial 

vegetative cover to salmonids are likely results of 

accidental direct spray and off-site drift of bromacil. 

Chlorsulfuron 

Direct Spray 

Terrestrial Wildlife 

Risk quotients for terrestrial wildlife were all below 

the most conservative LOC of 0.1 (acute RTE species), 

indicating that direct spray impacts are not likely to 

pose a risk to terrestrial animals. 

Non-target Plants – Terrestrial and Aquatic 

As expected, because of the mode of action of 

herbicides, RQs for non-target terrestrial plants ranged 

from 746 to 6,667, and RQs for non-target aquatic 

plants ranged from 7.5 to 196. The lowest RQs were 

calculated for typical species at the typical application 

rate, and the highest RQs were calculated for RTE 

species at the maximum application rate. All of the 

RQs were above the plant LOC of 1, indicating that 

direct spray impacts pose a risk to plants in both 

aquatic and terrestrial environments. 

Fish and Aquatic Invertebrates 

RQs for fish and aquatic invertebrates were all below 

the most conservative LOC of 0.05 (acute RTE 

species), indicating that direct spray impacts are not 

likely to pose a risk to these aquatic receptors. 

Off-site Drift 

Non-target Plants – Terrestrial and Aquatic 

The majority of the RQs for non-target terrestrial 

plants affected by off-site drift to soil were above the 

plant LOC of 1. Only RQs based on off-site drift 900 ft 

from ground application with a low or a high boom 

were below the plant LOC. These results indicate the 

potential for risk to off-site non-target terrestrial plants 

due to drift. 

The majority of the RQs for non-target aquatic plants 

affected by off-site drift were below the plant LOC of 

1. However, chronic toxicity RQs above the LOC 

occurred with some aerial applications. Chronic 

toxicity RQs in the stream were elevated for off-site 

drift 100 ft from applications by plane and helicopter 

at the maximum application rate. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

BLM Vegetation Treatments Using Herbicides C-59 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

(acute RTE species). All chronic RQs were well below 

the LOC for chronic risk to RTE species (0.5). These 

results indicate that off-site drift of chlorsulfuron is not 

likely to pose acute or chronic risk to these aquatic 

species. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that this scenario is not likely to pose 

a risk to piscivorous birds. 

Surface Runoff 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for non-target terrestrial plants affected 

by surface runoff to off-site soil were all below the 

plant LOC of 1, indicating that transport due to surface 

runoff is not likely to pose a risk to typical or RTE 

terrestrial plant species. 

Acute RQs for non-target aquatic plants in streams 

impacted by surface runoff of herbicide were generally 

below the plant LOC of 1. However, there were some 

scenarios where values exceeded the plant LOC at the 

typical or maximum application rate. At both the 

typical and maximum application rates, elevated RQs 

were predicted in sandy watersheds with annual 

precipitation above 100 in. In addition, at the 

maximum application rate, elevated acute RQs were 

predicted in the clay watershed with at least 100 in of 

annual precipitation. These scenarios are unlikely to 

occur on public lands because of arid and semi-arid 

conditions. Chronic RQs for non-target aquatic plants 

in the stream impacted by runoff or overland flow of 

herbicide were all below the plant LOC of 1. 

Therefore, it is possible that in some locations aquatic 

plants in the stream would be at acute risk from 

surface runoff of chlorsulfuron, but this transport 

mechanism is not likely to pose a chronic risk to 

aquatic plant species in the stream. 

Risk quotients exceeded the LOC for several pond 

scenarios at both typical and maximum application 

rates. Elevated acute RQs based on the typical 

application rate ranged from 1.11 to 11.8 in the 

following scenarios: surface runoff through sandy soil 

in the base watershed with annual precipitation above 

50 inches; through clay watersheds with annual 

precipitation above 25 inches; through loam 

watersheds with annual precipitation above 200 

inches; and through three variations of the base 

watershed with 50 in of rain per year (silt loam, silt, 

and clay loam soils). Elevated acute RQs ranging from 

1.54 to 35.3 were predicted at the maximum 

application rate resulting from surface runoff through 

the same scenarios that generated elevated RQs at the 

typical application rate, as well as sandy watersheds 

with at least 25 inches of precipitation per year and 

loam watersheds with at least 100 inches of 

precipitation per year. Of the 42 scenarios modeled for 

the pond, acute RQs were elevated above the LOC for 

16 scenarios at the typical application rate and 19 

scenarios at the maximum application rate. Chronic 

RQs ranging from 1.1 to 4.4 were predicted due to 

surface runoff to the pond at the typical application 

rate, and chronic RQs ranging from 1.2 to 13.1 were 

predicted due to surface runoff at the maximum 

application rate. Of the 42 scenarios modeled, chronic 

RQs were elevated above the LOC for 4 scenarios with 

the typical application rate and 12 scenarios with the 

maximum application rate. This suggests that aquatic 

plants in the pond are at acute and chronic risk from 

surface runoff of chlorsulfuron resulting from most 

application scenarios. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

(acute RTE species) for all pond and stream scenarios, 

and chronic toxicity RQs were well below the LOC for 

chronic risk to RTE species (0.5), indicating that these 

scenarios are not likely to result in long-term risk to 

aquatic animals in streams or ponds. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that this scenario is not likely to pose 

a risk to piscivorous birds. 

Wind Erosion and Transport Off-site 

Risk quotients for typical and RTE terrestrial plants 

were all well below the plant LOC (1), indicating that 

wind erosion is not likely to pose a risk to non-target 

terrestrial plants. 

Accidental Spill to Pond 

Risk quotients for the spill scenarios resulted in 

elevated RQs only for non-target aquatic plants, with 

fish and aquatic invertebrates generating values below 

the identified LOC. Potential risk to non-target aquatic 

BLM Vegetation Treatments Using Herbicides C-60 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

plants was indicated for both the truck and helicopter 

spills mixed for the maximum application rate. 

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

No RQs in excess of the appropriate acute or chronic 

LOCs were observed for aquatic invertebrates in any 

of the stream scenarios. Because aquatic invertebrates 

are not predicted to be directly impacted by herbicide 

concentrations in the stream, salmonids are not likely 

to be indirectly affected by a reduction in prey. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

Aquatic plant RQs for accidental direct spray scenarios 

were above the plant LOC at both the typical and 

maximum application rates, indicating the potential for 

a reduction in the aquatic plant community. In the 

unlikely event that a stream was accidentally sprayed, 

there would be the potential for indirect impacts to 

salmonids caused by a reduction in available cover. 

Minimal elevated aquatic plant chronic RQs (RQs of 

1.07 and 1.23) were also observed as a result of offsite drift from selected aerial applications of 

chlorsulfuron, indicating the potential for a reduction 

in cover overtime. No elevated aquatic plant acute 

RQs were predicted due to drift. No RQs in excess of 

the LOC were observed for aquatic plant species in the 

stream for any of the surface runoff scenarios. 

Risk quotients for terrestrial plants were elevated 

above the LOC for accidental direct spray scenarios at 

both the typical and maximum application rates, 

indicating the potential for a reduction in this plant 

community. In addition, RQs for typical terrestrial 

plants were observed above the plant LOC (ranging 

from 1.52 to 21.4) for nearly all scenarios as a result of 

off-site drift. No RQs in excess of the LOC were 

observed for terrestrial plant species for any of the 

surface runoff scenarios. These results indicate the 

potential for a reduction in riparian cover under 

selected conditions.

Diflufenzopyr 

Direct Spray 

Terrestrial Wildlife 

Risk quotients for terrestrial wildlife were all below 

the most conservative LOC of 0.1 (acute RTE species), 

indicating that direct spray impacts are not likely to 

pose a risk to terrestrial animals. 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for non-target terrestrial plants ranged 

from 93.8 to 333, and RQs for non-target aquatic 

plants ranged from 0.084 to 7.19. As expected because 

of the mode of action of herbicides, all of the 

terrestrial plant RQs were above the plant LOC of 1, 

indicating that direct spray impacts may pose a risk to 

these receptors. Aquatic plant RQs were below the 

plant LOC in all acute scenarios and above the plant 

LOC in all chronic scenarios, indicating the potential 

for long-term harm to these receptors. 

Fish and Aquatic Invertebrates 

All acute and chronic toxicity RQs for fish and aquatic 

invertebrates were below the most conservative LOC 

(0.05 for acute risk RTE species; 0.5 for chronic risk 

RTE species). These results indicate that impacts from 

direct spray are generally not likely to pose acute or 

chronic risk to these aquatic species. 

Off-site Drift 

Non-target Plants – Terrestrial and Aquatic 

The majority of the RQs for non-target terrestrial 

plants affected by off-site drift to soils were below the 

plant LOC of 1. However, RQs did exceed the LOC 

(ranging from 1.13 to 7.0) for several application 

scenarios. Off-site drift 25 ft from ground application 

with a low or high boom at the typical and maximum 

application rates resulted in RQs above the LOC for 

both typical and RTE species. Additional risk was also 

predicted for RTE species within 100 ft of a low-boom 

application at the typical application rate, and within 

100 ft of a high-boom application at the typical and 

maximum application rates. Therefore, there is 

potential risk to typical terrestrial plant species from 

off-site drift of diflufenzopyr within 25 ft of the 

application, and there is risk to RTE terrestrial plant 

species from herbicide drift within 100 ft of the 

application area. 

BLM Vegetation Treatments Using Herbicides C-61 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

All RQs for non-target aquatic plants affected by offsite drift were below the plant LOC of 1, indicating 

this transport mechanism is not likely to impact these 

receptors. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

(acute RTE species), and all chronic RQs were well 

below the LOC for chronic risk to RTE species (0.5). 

These results indicate that impacts from off-site drift 

are not likely to pose acute or chronic risk to these 

aquatic species. 

Piscivorous Birds 

Risk quotients for piscivorous birds were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that this scenario is not likely to pose 

a risk to these species. 

Surface Runoff 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for typical non-target terrestrial plant 

species affected by surface runoff to off-site soil were 

all below the plant LOC of 1, indicating that transport 

due to surface runoff is not likely to pose a risk to 

these receptors. Most RQs for RTE non-target 

terrestrial plant species were also below the plant LOC 

of 1; however, a couple scenarios did result in elevated 

RQs at the typical or maximum application rate. These 

scenarios were surface runoff in the base watershed 

with clay soils and more than 25 inches of 

precipitation per year and runoff in the base watershed 

with silt-loam, silt, or clay-loam soils and 50 inches of 

precipitation per year. This indicates the potential for 

risk to RTE plant species in selected watersheds at the 

typical and maximum application rates with greater 

than 25 inches of precipitation per year. 

Acute and chronic RQs for non-target aquatic plants in 

the pond and streams impacted by overland flow of 

diflufenzopyr were all below the plant LOC of 1. In 

addition, acute RQs for non-target aquatic plants in the 

pond were also below the plant LOC. These results 

indicate that this transport mechanism is not likely to 

pose a risk to aquatic plant species under these 

conditions. 

Fish and Aquatic Invertebrates 

Acute and chronic toxicity RQs for fish and aquatic 

invertebrates in ponds and streams were all below the 

most conservative LOCs (0.05 and 0.5, respectively), 

indicating that impacts from surface runoff are not 

likely to pose a risk to these aquatic species. 

Piscivorous Birds 

Risk quotients for piscivorous birds were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that this scenario is not likely to pose 

a risk to piscivorous birds. 

Wind Erosion and Transport Off-site 

Risk quotients for typical and RTE terrestrial plants 

were all well below the plant LOC (1), indicating that 

wind erosion is not likely to pose a risk to non-target 

terrestrial plants. 

Accidental Spill to Pond 

Risk quotients for the spill scenario ranged from 

0.00338 for fish and 0.0239 for aquatic invertebrates to 

3.59 for non-target aquatic plants. Potential risk to 

non-target aquatic plants was indicated for the truck 

spill with diflufenzopyr mixed for the maximum 

application rate. 

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

No RQs in excess of the appropriate acute or chronic 

LOCs were observed for aquatic invertebrates in any 

of the stream scenarios. Because aquatic invertebrates 

are not predicted to be directly impacted by herbicide 

concentrations in the stream, salmonids are not likely 

to be indirectly affected by a reduction in prey. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

Chronic aquatic plant RQs for accidental direct spray 

scenarios were above the plant LOC at both the typical 

and maximum application rates, indicating the 

potential for a reduction in the aquatic plant 

community over time. Therefore, in the unlikely event 

that a stream is accidentally sprayed, there would be 

the potential for indirect impacts to salmonids caused 

by a reduction in available cover. 

BLM Vegetation Treatments Using Herbicides C-62 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

No RQs in excess of the LOC were observed for 

stream aquatic plant species for any of the off-site drift 

or surface runoff scenarios. 

Risk quotients for terrestrial plants were elevated 

above the LOC for accidental direct spray scenarios at 

both the typical and maximum application rates, 

indicating the potential for a reduction in this plant 

community. 

Risk quotients for typical terrestrial plants were also 

observed above the plant LOC (ranging from 1.13 to 

7.00) as a result of off-site drift. Off-site drift 25 ft 

from ground application with a low or high boom 

resulted in RQs above the LOC at the typical and 

maximum application rates for both typical and RTE 

species. Additional risk was also predicted for RTE 

species within 100 ft of a low-boom application at the 

typical application rate and within 100 ft of a highboom application at the typical and maximum 

application rates. These results indicate the potential 

for a reduction in riparian cover under selected 

conditions. 

No RQs in excess of the LOC were observed for 

terrestrial plant species for any of the surface runoff 

scenarios.

Diquat 

Direct Spray 

Terrestrial Wildlife 

Acute RQs for terrestrial wildlife were above the most 

conservative LOC of 0.1 (acute RTE species) for 

several scenarios. Accidental direct spray of the 

pollinating insect resulted in elevated RQs at both the 

typical and maximum application rates. Risk was also 

predicted for the pollinating insect as a result of 

indirect contact with foliage accidentally sprayed at 

the maximum application rate. No risks to the small 

mammal were predicted due to direct spray or indirect 

contact with foliage. 

Acute exposure RQs were elevated above the 

associated LOC (0.1; acute risk RTE species) for two 

scenarios using the typical application rate (large 

mammalian herbivore and small avian insectivore) and 

for five scenarios at the maximum application rate 

(large and small mammalian herbivores, large avian 

herbivore, large mammalian carnivore, and small avian 

insectivore). 

Chronic exposure RQs were elevated above the 

associated LOC (1.0) for three scenarios using the 

typical application rate (large and small mammalian 

herbivore and large avian herbivore) and for four 

scenarios at the maximum application rate (large 

mammalian and avian herbivores, small mammalian 

herbivore, and small avian insectivore). 

This evaluation indicates that accidental direct spray 

impacts may pose a risk to insects, birds, and wildlife, 

primarily when the maximum application rate is used. 

Non-target Plants – Terrestrial and Aquatic 

As expected, because of the mode of action of 

herbicides, RQs for non-target terrestrial and aquatic 

plants impacted by direct spray were above the plant 

LOC of 1 for all modeled scenarios. Risk quotients for 

direct spray of non-target terrestrial plants ranged from 

213 to 2,500. Risk quotients for non-target aquatic 

plants impacted by routine application to the pond or 

accidental direct spray of the stream ranged from 149 

to 7,472. Therefore, direct spray impacts pose a risk to 

plants in both aquatic and terrestrial environments. 

Fish and Aquatic Invertebrates 

Acute and chronic toxicity RQs for fish and aquatic 

invertebrates in the pond and stream were all above the 

most conservative associated LOCs (0.05 for acute risk 

RTE species; 0.5 for chronic risk RTE species). 

These results indicate there is potential risk to aquatic 

species, especially RTE species, in a pond or stream 

sprayed with diquat. 

Piscivorous Birds 

Risk quotients for piscivorous birds were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that diquat application is not likely to 

pose a risk to piscivorous birds. 

Off-site Drift to Terrestrial Plants 

Risk quotients for both typical and RTE terrestrial 

plant species were elevated over the plant LOC of 1 

for several scenarios. At the typical application rate, 

RQs were elevated for typical and RTE plant species 

within 900 ft of the aerial application of the herbicide 

(helicopter and fixed-wing plane) and within 100 ft of 

ground applications (high boom). At the maximum 

application rate, RQs for typical plant species were 

elevated for all aerial applications and within 100 ft of 

BLM Vegetation Treatments Using Herbicides C-63 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

ground applications (low and high booms). Risk 

quotients for RTE plant species were elevated for all 

evaluated herbicide applications using the maximum 

rate, and for all but two scenarios at the typical 

application rate (low- and high-boom ground 

applications with 900 foot buffers). These results 

indicate that potential risk to non-target terrestrial 

plants exists due to off-site drift during application of 

this aquatic herbicide. 

Accidental Spill to Pond 

Potential risks to fish, aquatic invertebrates, and nontarget aquatic plants were indicated for the truck and 

helicopter spills mixed for the maximum application 

rate. Risk quotients for the truck spill scenario were 

19.1 for fish, 102 for aquatic invertebrates, and 19,129 

for non-target aquatic plants. Risk quotients for the 

helicopter spill scenario were higher at 67 for fish, 359 

for aquatic invertebrates, and 66,952 for non-target 

aquatic plants. 

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

Risk quotients in excess of the acute LOCs for aquatic 

invertebrates were observed for the accidental direct 

spray scenario at both the typical and maximum 

application rates. This conservative evaluation predicts 

that fish and aquatic invertebrates would be directly 

impacted by herbicide concentrations in the stream. 

Accordingly, their availability as prey item 

populations may be impacted, and this may result in an 

indirect effect on salmonids. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

Aquatic plant RQs for accidental direct spray scenarios 

were above the plant LOC at both the typical and 

maximum application rates. Therefore, there is the 

potential for indirect impacts to salmonids due to a 

reduction in available cover in the unlikely event that a 

stream is accidentally sprayed. 

In addition, RQs for terrestrial plants were elevated 

above the LOC for accidental direct spray scenarios at 

both the typical and maximum application rates, 

indicating the potential for a reduction in this plant 

community and potential indirect impacts to salmonids 

due to a loss of riparian cover. 

Diuron 

Direct Spray 

Terrestrial Wildlife 

In general, most acute RQs for terrestrial wildlife were 

below the most conservative LOC of 0.1 (acute RTE 

species). However, direct spray of the pollinating 

insect resulted in elevated RQs at both the typical and 

maximum application rates. In addition, at the 

maximum application rate, risk was also predicted for 

the pollinating insect from indirect contact with foliage 

impacted by direct spray. 

Risk quotients for acute ingestion scenarios were 

below the most conservative LOC (0.1; acute risk RTE 

species) when herbicide is applied at the typical rate, 

but above the LOC in all cases at the maximum 

application rate. 

Risk quotients for chronic ingestion scenarios were 

above the associated LOC of 1.0 for three receptors 

(the small and large mammalian herbivores and the 

large mammalian carnivore) when herbicide is applied 

at the typical or maximum application rate. At the 

maximum application rate, elevated RQs were also 

predicted for the small mammalian herbivore and the 

large avian herbivore. 

This evaluation indicates that direct spray impacts may 

pose a risk to insects, birds, and mammals, primarily 

when the maximum application rate is used. 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for non-target terrestrial plants ranged 

from 75 to 20,000, and RQs for non-target aquatic 

plants ranged from 517 to 25,474. All of the RQs were 

above the plant LOC of 1.0, indicating that, as 

expected, direct spray impacts pose a risk to plants in 

both aquatic and terrestrial environments. 

Fish and Aquatic Invertebrates 

Acute and chronic toxicity RQs for fish and aquatic 

invertebrates in the pond and stream were above the 

most conservative LOCs (0.05 for acute risk RTE 

species; 1.0 for chronic risk), indicating that direct 

spray impacts may pose a risk to these aquatic species. 

BLM Vegetation Treatments Using Herbicides C-64 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Off-site Drift 

Non-target Plants – Terrestrial and Aquatic 

Many of the RQs for non-target terrestrial plants 

affected by off-site drift to off-site soils were above 

the plant LOC of 1.0. For typical terrestrial plant 

species, elevated RQs were predicted at the typical 

application rate 25 ft from application with a high 

boom and at the maximum application rate within 100 

ft from application with a low or high boom. Elevated 

RQs were predicted for RTE terrestrial plant species 

under all off-site drift scenarios. These results indicate 

that terrestrial plants, particularly RTE species, located 

near applications areas may be impacted by herbicide 

drift. 

The majority of the RQs for non-target aquatic plants 

affected by off-site drift were above the plant LOC of 

1.0. The only scenario that did not consistently predict 

elevated RQs was off-site drift 900 ft from the 

application area. More elevated RQs were predicted 

with application using the high boom. These results 

indicate that off-site drift may impact aquatic plants in 

waterbodies adjacent to application areas. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish were below the most 

conservative LOC of 0.05 (acute RTE species) for all 

scenarios except one (off-site drift to the stream 25 ft 

from the maximum application with a high boom). 

Acute toxicity RQs for aquatic invertebrates were 

generally also below the most conservative LOC of 

0.05 (acute RTE species). However, off-site drift to the 

pond and stream within 25 ft of a low-boom 

application or within 100 ft of a high-boom application 

at the maximum application rate predicted elevated 

RQs for aquatic invertebrates. Off-site drift within 25 

ft of a high-boom application at the typical application 

rate also predicted a slightly elevated RQ (0.077) in 

the stream. These results indicate the potential for 

acute risk to fish and invertebrates due to off-site drift 

under selected application conditions. 

Most chronic RQs were well below the LOC for 

chronic risk to RTE species (0.5). However, 

application at the maximum application rate resulted in 

elevated RQs for one aquatic invertebrate scenario (in 

the stream 25 ft from the high-boom application) and 

three fish scenarios (in the pond 25 ft from the highboom application and in the stream 25 ft from the lowand high-boom applications). For fish, the only the 

scenario with an RQ above the chronic LOC of 1.0 

was for the stream 25 ft from application at the 

maximum rate with a high boom. These results 

indicate minimal potential for chronic risk, except 

within 25 ft of the application area at the maximum 

application rate. 

Piscivorous Birds 

Risk quotients for piscivorous birds were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that this scenario is not likely to pose 

a risk to piscivorous birds. 

Surface Runoff 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for typical non-target terrestrial plant 

species affected by surface runoff to off-site soil were 

all below the plant LOC of 1.0, indicating that 

transport due to surface runoff is not likely to pose a 

risk to these receptors. Most RQs for RTE non-target 

terrestrial plant species were also below the plant LOC 

of 1.0; however, several scenarios did result in 

elevated RQs. At the typical application rate, RQs for 

the base watershed with clay soils and between 100 

and 250 inches of rain per year (250 inches per year 

was the maximum rainfall modeled) ranged from 1.0 

to 2.85. At the maximum application rate, RQs were 

elevated above 1.0 for the base watershed with clay 

soils and at least 50 inches of rain per year, for the 

base watershed with loam soils and at least 200 inches 

of rain per year, and for the base watershed with clayloam soil and 50 inches of rain per year (no other 

rainfall amounts were modeled for this scenario). This 

indicates the potential for risk to RTE plant species in 

certain watersheds (with precipitation greater than 50 

inches) at the typical or maximum application rates 

(these scenarios are unlikely on many public lands 

because of arid and semi-arid conditions). 

Acute and chronic RQs for non-target aquatic plants 

impacted by herbicide runoff exceeded the plant LOC 

for nearly all pond scenarios modeled at both the 

typical and maximum application rates. 

Acute RQs for non-target aquatic plants in the stream 

were also generally above the plant LOC of 1.0. At the 

typical application rate, elevated RQs occurred in 35 

of the 42 scenarios. At the maximum application rate, 

elevated RQs occurred in 37 of the 42 scenarios. These 

results indicate the high potential for acute impacts to 

aquatic plants in the stream. 

BLM Vegetation Treatments Using Herbicides C-65 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Chronic RQs in the stream at the typical application 

rate were above the plant LOC for several scenarios 

(base watershed with sandy soils and precipitation of 

more than 25 inches per year; base watershed with 

clay or loam soils and precipitation of more than 100 

inches per year; and 100 and 1,000 ac application 

areas). 

Most chronic stream RQs were above the plant LOC 

when the maximum application rate was considered. 

The only scenarios below this LOC were the base 

application watershed with sandy soils and less than 10 

inches of rain per year; the base application watershed 

with clay or loam soil and less than 25 inches of rain 

per year; the 1 acre application area; and the base 

watershed with silt soil and 50 inches of rain per year. 

These results indicate the potential for chronic impacts 

to aquatic plants in the stream under most conditions at 

the maximum application rate. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were above the most conservative LOC of 0.05 (acute 

RTE species) for nearly all pond scenarios. At the 

typical application rate, RQs were elevated above 0.05 

for fish in 35 of 42 scenarios, and for aquatic 

invertebrates in 36 of 42 scenarios. At the maximum 

application rate, this increased to 36 and 38 of 42 

scenarios for fish and aquatic invertebrates, 

respectively. Acute RQs for aquatic invertebrates in 

the stream were greater than the LOC of 0.05 for most 

scenarios at the maximum application rate (35 of 42 

scenarios) and for high precipitation scenarios at the 

typical application rate (18 of 42 scenarios). Acute 

RQs for fish in the stream were greater than the LOC 

for high precipitation scenarios at the maximum 

application rate (16 of 42 scenarios) and for high 

precipitation scenarios in clay soils at the typical 

application rate (3 of 42 scenarios). This suggests that 

diuron poses substantial acute risks to aquatic animals 

in ponds and limited acute risks to aquatic stream 

animals (i.e., at the maximum application rate and in 

wet watersheds). 

Chronic toxicity RQs in the stream were well below 

the LOC for chronic risk to RTE species (0.5), 

indicating that these scenarios are not likely to result in 

long-term risk to fish or aquatic invertebrates. 

However, chronic RQs for fish and aquatic 

invertebrates were elevated above this LOC in several 

pond scenarios. At the maximum application rate, RQs 

were elevated above 0.5 for fish in 36 of 42 scenarios, 

and for aquatic invertebrates in 33 of 42 scenarios. At 

the typical application rate, RQs were elevated above 

0.5 for fish in 30 of 42 scenarios, and for aquatic 

invertebrates in 10 of 42 scenarios. At the typical 

application rate, only 10 of the fish RQs and 3 of the 

aquatic invertebrate RQs were above the chronic LOC 

of 1 for typical species, indicating significantly less 

risk to non-RTE species. These results indicate the 

potential for risk to fish and aquatic invertebrates in 

the pond, especially RTE species, as a result of surface 

runoff. 

Piscivorous Birds 

Risk quotients for the piscivorous bird exposed to 

surface runoff of diuron were all well below the most 

conservative terrestrial animal LOC (0.1), indicating 

that this scenario is not likely to pose a risk to 

piscivorous birds. 

Wind Erosion and Transport Off-site 

Risk quotients for typical and RTE terrestrial plants 

were all well below the plant LOC (1), indicating that 

wind erosion is not likely to pose a risk to non-target 

terrestrial plants. 

Accidental Spill to Pond 

Risk quotients for the spill scenario were 101 for fish, 

448 for aquatic invertebrates, and 55,180 for nontarget aquatic plants. Therefore, there is the potential 

for risk to fish, aquatic invertebrates, and non-target 

aquatic plants under the scenario of a truck spill with 

diuron mixed for the maximum application rate. 

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

Risk quotients in excess of the acute and chronic 

LOCs for aquatic invertebrates were observed for the 

accidental direct spray scenario. 

The off-site drift scenarios predicted elevated RQs for 

aquatic invertebrates (mostly RTE species) under 

selected conditions, primarily within 100 ft of the 

application area at the maximum application rate (two 

scenarios predicted acute risk to aquatic invertebrates 

in the stream at the typical application rate and for a 

buffer of more than 100 and less than 900 ft). All 

chronic RQs for aquatic invertebrates in the stream 

impacted by surface runoff were below the associated 

LOCs. Acute RQs for these surface runoff scenarios 

were elevated above the most conservative LOC for 

BLM Vegetation Treatments Using Herbicides C-66 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

several scenarios; most significantly for aquatic 

invertebrates at the maximum application rate. 

Because fish may be directly impacted by herbicide 

concentrations in the stream as a result of normal 

applications, their availability as prey item populations 

may be impacted, and there may be an indirect effect 

on salmonids. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

Aquatic plant RQs for accidental direct spray scenarios 

were above the plant LOC at both the typical and 

maximum application rates, indicating the potential for 

a reduction in the aquatic plant community. Therefore 

there is the potential for indirect impacts to salmonids 

due to a reduction in available cover in the unlikely 

event that a stream is accidentally sprayed. 

Elevated aquatic plant RQs were also observed in the 

stream scenario as a result of off-site drift of the 

ground application of the herbicide more than 100 and 

less than 900 ft from the stream, indicating the 

potential for a reduction in cover, most significantly at 

the maximum application rate (chronic risk to aquatic 

plants are also predicted with greater than a 900-foot 

buffer at the maximum application rate). Elevated RQs 

were also predicted for many of the surface runoff 

scenarios. These results indicate there is the potential 

for indirect impacts to salmonids due to reduction in 

available cover due to off-site drift and surface runoff 

of the applied herbicide. 

Risk quotients for typical and RTE terrestrial plants 

were elevated above the LOC for accidental direct 

spray scenarios at both the typical and maximum 

application rates, indicating the potential for a 

reduction in this plant community. However, as 

discussed above, this scenario is unlikely to occur as a 

result of BLM practices and represents a worst-case 

scenario. 

Risk quotients for typical terrestrial plants were also 

observed above the plant LOC (ranging from 1.1 to 

5.19) as a result of off-site drift from the ground 

application of the herbicide. At the typical application 

rate, risk was predicted at least 25 ft and less than 100 

ft from the application area, and at the maximum 

application rate, risk was predicted at least 100 ft and 

less than 900 ft from the application area. Elevated 

RQs for RTE species were also observed for all 

modeled application scenarios. These results indicate 

the potential for a reduction in riparian cover and 

indirect effects to salmonids due to off-site drift under 

selected conditions. 

No RQs in excess of the LOC were observed for 

typical terrestrial plant species for any of the surface 

runoff scenarios. Elevated RQs were predicted for 

RTE terrestrial plant species under selected surface 

runoff conditions, primarily in clay or loam soils at 

high precipitation levels. These results indicate the 

limited potential for a reduction in riparian cover due 

to surface runoff, primarily when RTE plant species 

are present.

Fluridone 

Direct Spray 

Terrestrial Wildlife 

Acute RQs for terrestrial animals were below the most 

conservative LOC of 0.1 (acute RTE species) for all 

scenarios. At the maximum application rate, the small 

mammalian herbivore had an RQ of 2.22, all other 

RQs were well below the LOC of 1. These results 

indicate that accidental direct spray impacts are not 

likely to pose a risk to insects, birds, or mammals. 

Non-target Plants – Terrestrial and Aquatic 

No toxicity data were identified for non-target 

terrestrial plant species; therefore, a quantitative 

evaluation is not possible. However, the ecological 

incident report described earlier suggests that impacts 

to terrestrial plants are possible due to unintended 

contact with fluridone. In the manufacturer’s user’s 

guide for the Sonar® aquatic herbicide (Eli Lilly and 

Company 2003), grasses and some sedges are 

considered to be “sensitive” or “intermediate” in their 

tolerance to the herbicide, while rushes tend to be 

“intermediate” to “tolerant.” Shoreline plants, such as 

willow and cypress, were considered “tolerant,” while 

the tolerance of members of the evening primrose and 

acanthus families was classified as “intermediate.” No 

concentrations were associated with these qualitative 

statements. It is the more tolerant shoreline plants that 

are more likely to come in contact with fluridone 

during normal pond applications. 

For aquatic plants, all of the RQs were below the plant 

LOC of 1, indicating that direct spray impacts are not 

predicted to pose a risk to aquatic plants in the stream 

or the pond. 

BLM Vegetation Treatments Using Herbicides C-67 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Fish and Aquatic Invertebrates 

Normal application of fluridone within a pond resulted 

in one RQ elevated over the associated LOC. The 

acute RQ for aquatic invertebrates in the pond 

impacted by the maximum application rate of 

fluridone was 0.11, just above the LOC for acute risk 

to RTE species (0.05). 

Accidental direct spray of fluridone over the stream 

resulted in elevated acute and chronic RQs. Elevated 

acute RQs were 0.17 for fish at the maximum 

application rate, and 0.065 and 0.56 for invertebrates 

at the typical and maximum application rates, 

respectively. These RQs were all above the acute risk 

to RTE species LOC, but below or nearly consistent 

with the acute high risk LOC. Elevated chronic RQs 

were 1.5 for fish and 1.8 for invertebrates at the 

maximum application rate. These RQs were above the 

LOC for chronic risk to RTE species (0.5) and the 

LOC for chronic risk (1). 

These results indicate there is potential for risk to 

aquatic species, especially RTE species, in a stream 

sprayed with fluridone. However, this scenario is not 

likely to occur as fluridone is reserved for use in 

ponds. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that the direct spray scenario is not 

likely to pose a risk to piscivorous birds. 

Off-site Drift to Non-target Terrestrial Plants 

As described previously, no toxicity data were 

identified for non-target terrestrial plant species; 

therefore, a quantitative evaluation of this scenario is 

not possible. However, impacts to terrestrial plants are 

possible due to unintended contact with fluridone. 

It may be noted that the concentrations of fluridone 

predicted due to off-site drift are significantly lower 

than those modeled for accidental direct spray of 

fluridone on near-shore terrestrial plants. This 

comparison indicates that the maximum deposition 

(100 ft from aerial applications) was only 23.8% of the 

typical application rate and only 0.87% of the 

maximum application rate. On average, off-site drift 

modeled using the typical application rate was less 

than 10% of the typical application rate used in the 

direct spray scenario. Off-site drift modeled using the 

maximum application rate was less than 1% of the 

maximum application rate used in the direct spray 

scenario. This indicates the reduction in deposition and 

associated risks that occur with off-site drift relative to 

direct accidental spray. 

Accidental Spill to Pond 

Risk quotients for the truck spill scenario were 1.10 for 

fish, 3.58 for aquatic invertebrates, and 1.56 for nontarget aquatic plants. Risk quotients for the helicopter 

spill scenario were slightly higher at 3.83, 12.6, and 

5.44 for fish, aquatic invertebrates, and non-target 

aquatic plants, respectively. Therefore, potential risks 

to fish, aquatic invertebrates, and non-target aquatic 

plants are indicated for the unlikely events of truck and 

helicopter spills mixed for the maximum application 

rate. 

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

Risk quotients in excess of the acute LOCs for aquatic 

invertebrates were observed for the accidental direct 

spray scenario. This conservative evaluation predicts 

that aquatic invertebrates may be directly impacted by 

herbicide concentrations in the stream. Accordingly, 

their availability as prey item populations may be 

impacted, and there may be an indirect effect on 

salmonids. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

Aquatic plant RQs for accidental direct spray scenarios 

were below the plant LOC at both the typical and 

maximum application rates, indicating that impacts to 

the aquatic plant community are not predicted. This 

evaluation indicates that indirect impacts to salmonids 

due to a reduction in available cover are unlikely. 

It is uncertain whether or not a reduction in riparian 

cover is likely, but a review of incident reports and the 

manufacturer’s user’s guide indicate that shoreline 

plant species are generally tolerant of fluridone 

exposures. 

BLM Vegetation Treatments Using Herbicides C-68 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Imazapic 

Direct Spray 

Terrestrial Wildlife 

Risk quotients for terrestrial wildlife were all below 

the most conservative LOC of 0.1 (acute RTE species), 

indicating that direct spray impacts are not likely to 

pose a risk to terrestrial animals. 

Non-target Plants – Terrestrial and Aquatic 

As expected, because of the mode of action of 

herbicides, RQs for non-target terrestrial plants ranged 

from 3.1 to 23.8, and RQs for non-target aquatic plants 

ranged from 0.82 to 41.0. The lowest RQs were 

calculated for typical species at the typical application 

rate, and the highest RQs were calculated for RTE 

species impacted at the maximum application rate. All 

of the RQs were above the plant LOC of 1, indicating 

that direct spray impacts pose a risk to plants in both 

aquatic and terrestrial environments. The only possible 

exception is the accidental direct spray of the pond at 

the typical application rate. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were below the most conservative LOC of 0.05 (acute 

RTE species), indicating that direct spray impacts are 

not likely to pose a risk to these aquatic species. All 

chronic RQs were well below the LOC for chronic risk 

to RTE species (0.5). These results indicate that 

impacts from direct spray are not likely to pose acute 

or chronic risk to fish and aquatic invertebrates. 

Off-site Drift 

Non-target Plants – Terrestrial and Aquatic 

The majority of the RQs for non-target terrestrial 

plants affected by off-site drift to soil were below the 

plant LOC of 1. However, RQs for several aerial 

application scenarios did exceed the LOC, with RQs 

between 1.06 and 6.98. Off-site drift 100 ft from aerial 

application by plane or helicopter over forested or nonforested lands consistently resulted in an RQ above the 

LOC at the maximum application rate. In addition, offsite drift 300 ft from the aerial application by a plane 

over forested land also predicted an elevated RQ at the 

maximum application rate. Risk at the typical 

application rate was only predicted for RTE species as 

a result of drift 100 ft from the aerial application by a 

plane over forested lands. The predicted RQ of 1.06 

was only slightly over the LOC, indicating that use of 

the typical application rate is not likely to result in risk 

to most non-target terrestrial species. 

The majority of the RQs for non-target aquatic plants 

affected by off-site drift were below the plant LOC of 

1. However, as with impacts to terrestrial plants, RQs 

above the LOC occurred with some aerial applications 

resulting in RQs between 1.07 and 2.36. Off-site drift 

100 ft from the aerial application by a plane over 

forested lands consistently resulted in acute and 

chronic RQs above the LOC at the maximum 

application rate in the pond and the stream. Off-site 

drift 100 ft from the aerial application by a helicopter 

over forested land also predicted an elevated chronic 

RQ in the stream when applied at the maximum 

application rate. No elevated RQs were predicted at 

the typical application rate. Slightly more elevated 

risks were predicted in the stream than the pond. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

(acute RTE species). All chronic RQs were well below 

the LOC for chronic risk to RTE species (0.5). These 

results indicate that impacts from off-site drift are not 

likely to pose acute or chronic risk to these aquatic 

species. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that off-site drift is not likely to pose a 

risk to piscivorous birds. 

Surface Runoff 

Minimal acute risk to non-target aquatic plants in the 

pond may occur when herbicides are applied at the 

maximum rate in watersheds with sandy soils and 

precipitation between 50 and 150 inches per year (RQs 

were just above 1); chronic risks to non-target aquatic 

plants in the pond may occur in watersheds with sandy 

soil and annual precipitation of 25 inches or greater. 

No risks were predicted for non-target terrestrial 

plants, non-target aquatic plants in the stream, fish, 

aquatic invertebrates, or piscivorous birds. 

BLM Vegetation Treatments Using Herbicides C-69 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for non-target terrestrial plants affected 

by surface runoff to off-site soil were all below the 

plant LOC of 1, indicating that transport due to surface 

runoff is not likely to pose a risk to typical or RTE 

terrestrial plant species. 

Most RQs for non-target aquatic plants in streams 

impacted by surface runoff of herbicide were below 

the plant LOC of 1. The one exception was an acute 

RQ of 1.03 (just above the LOC), when imazapic is 

applied at the maximum rate in a watershed with clay 

soils and at least 250 inches of precipitation per year. 

However, this is a minimal exceedance; transport due 

to surface runoff is not likely to pose a risk to aquatic 

plants species in streams. 

Risk quotients exceeded the LOC for several pond 

scenarios at the maximum application rate. Acute RQs 

greater than the LOC were predicted at the maximum 

application rate in the base watershed with sandy soils 

and at least 25 inches of precipitation per year (RQs 

ranged up to 4.34), in clay and clay/loam watersheds 

with at least 50 inches of precipitation per year (RQs 

ranged up to 7.51), and in loam watersheds with at 

least 100 inches of precipitation per year (RQs ranged 

up to 1.97). Acute RQs greater than the LOC were 

predicted at the typical application rate in watersheds 

with clay soils and at least 150 inches of precipitation 

per year (RQs ranged up to 1.72). Chronic RQs were 

predicted in the base watershed with sandy soil and 

annual precipitation greater than 25 inches. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

(acute RTE species) for all pond and stream scenarios, 

indicating that impacts from surface runoff are not 

likely to pose a risk to these aquatic species. 

Chronic toxicity RQs were well below the LOC for 

chronic risk to RTE species (0.5), indicating that these 

scenarios are not likely to result in long-term risk to 

aquatic animals in streams or ponds. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that surface runoff is not likely to 

pose a risk to piscivorous birds. 

Wind Erosion and Transport Off-site 

Risk quotients for typical and RTE terrestrial plants 

were all well below the plant LOC (1), indicating that 

wind erosion is not likely to pose a risk to non-target 

terrestrial plants. 

Accidental Spill to Pond 

Risk quotients for the spill scenarios ranged from 

0.00681 for fish and aquatic invertebrates to 564 for 

non-target aquatic plants. Potential risk to non-target 

aquatic plants was indicated for both the truck and 

helicopter spills mixed for the maximum application 

rate. 

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

No RQs in excess of the appropriate acute or chronic 

LOCs were observed for aquatic invertebrates in any 

of the stream scenarios. Because aquatic invertebrates 

are not predicted to be directly impacted by herbicide 

concentrations in the stream, salmonids are not likely 

to be indirectly affected by a reduction in prey. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

Aquatic plant RQs for accidental direct spray scenarios 

were above the plant LOC at both the typical and 

maximum application rates, indicating the potential for 

a reduction in the aquatic plant community. Therefore, 

in the unlikely event that a stream is accidentally 

sprayed, there would be the potential for indirect 

impacts to salmonids caused by a reduction in 

available cover. 

Slightly elevated aquatic plant RQs (ranging from 1.45 

to 2.6) were also observed as a result of off-site drift 

100 ft from the aerial application of imazapic, 

indicating the potential for a reduction in cover. One 

slightly elevated acute RQ (1.03) was predicted for 

aquatic plant species in streams impacted from surface 

runoff in the base watershed with clay soil and annual 

precipitation of 250 inches. No other elevated acute or 

chronic RQs were observed for any other surface 

runoff scenarios. 

Risk quotients for terrestrial plants were elevated 

above the LOC for accidental direct spray scenarios at 

both the typical and maximum application rates, 

BLM Vegetation Treatments Using Herbicides C-70 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

indicating the potential for a reduction in this plant 

community. 

Risk quotients for typical terrestrial plants were also 

observed above the plant LOC (ranging from 1.29 to 

5.58) as a result of off-site drift from aerial application 

at the maximum rate. Off-site drift 100 ft from the 

application area resulted in risk when imazapic was 

applied from a helicopter or plane over forested and 

non-forested lands. Potential risk was also indicated 

300 ft from the application area when applied by a 

plane over a forest. Elevated RQs for RTE species 

were also observed for the same application scenarios. 

These results also indicate the potential for a reduction 

in riparian cover under selected conditions. 

Overdrive® 

Direct Spray 

Terrestrial Wildlife 

Risk quotients for terrestrial wildlife were all below 

the most conservative LOC of 0.1 (acute RTE species), 

indicating that direct spray impacts are not likely to 

pose a risk to terrestrial animals. Risk quotients for 

chronic ingestion scenarios were below the associated 

LOC of 1 for all scenarios, except the ingestion of 

contaminated food items by the large mammalian 

herbivore. The scenario predicted elevated RQs of 1.4 

and 12.8 at the typical and maximum application rates, 

respectively. This evaluation indicates that direct spray 

impacts may pose a risk to large herbivorous 

mammals, primarily when the maximum application 

rate is used. 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for non-target terrestrial plants ranged 

from 61.0 to 273, and RQs for non-target aquatic 

plants ranged from 0.267 to 107. All of the terrestrial 

plant RQs were above the plant LOC of 1, indicating 

that direct spray impacts may pose a risk to these 

receptors. Aquatic plant RQs were below the plant 

LOC in the acute pond scenarios and above the plant 

LOC in all other pond and stream scenarios, indicating 

the potential for acute risk in the stream and long-term 

risk of harm in the pond and stream. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were below the most conservative LOC of 0.05 (acute 

RTE species), indicating that direct spray impacts are 

not likely to pose a risk to these aquatic species. In 

addition, all chronic toxicity RQs for fish and aquatic 

invertebrates were well below the LOC for chronic 

risk to RTE species (0.5). These results indicate that 

impacts from direct spray are generally not likely to 

pose acute or chronic risk to these aquatic species. 

Off-site Drift 

Non-target Plants – Terrestrial and Aquatic 

Most of the RQs for typical species of non-target 

terrestrial plants affected by off-site drift to off-site 

soils were below the plant LOC of 1. RQs for typical 

non-target terrestrial plants were elevated (ranging 

from 1.30 to 2.14) when located 25 ft from ground 

application with a low boom at the maximum 

application rate, and with a high boom at the typical or 

maximum application rate. RQs for several application 

scenarios with RTE plant species did exceed the LOC, 

with RQs between 1.09 and 5.74. At the typical 

application rate, elevated RQs for RTE species were 

predicted 25 ft from ground application with a low 

boom and 100 ft from ground application with a high 

boom. At the maximum application rate, elevated RQs 

for RTE species were predicted 100 ft from ground 

application with a low or high boom. These results 

indicate the potential for risk to typical and RTE 

species located at least 25 to 100 ft from the 

application area, depending on the boom height and 

application rate. 

The majority of the RQs typical species of non-target 

terrestrial plants affected by off-site drift to off-site 

soils were below the plant LOC of 1. RQs for typical 

non-target terrestrial plants were elevated (ranging 

from 1.30 to 2.14, depending on the testing scenario) 

when located 25 feet from ground application with a 

low boom at the maximum application rate and with a 

high boom at the typical or maximum application rate. 

RQs for several application scenarios with RTE plant 

species did exceed the LOC, with RQs between 1.09 

and 5.74. At the typical application rate, elevated RQs 

for RTE species were predicted 25 feet from ground 

application with a low boom and 100 feet from ground 

application with a high boom. At the maximum 

application rate, elevated RQs for RTE species were 

predicted 100 ft from ground application with a low or 

high boom. These results indicate the potential for risk 

to typical and RTE species located at least 25 to 100 

feet from the application area, depending on the boom 

height and application rate. 

BLM Vegetation Treatments Using Herbicides C-71 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

All RQs for non-target aquatic plants affected by offsite drift were below the plant LOC of 1, indicating 

this transport mechanism is not likely to impact these 

receptors. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

(acute RTE species). All chronic RQs were well below 

the LOC for chronic risk to RTE species (0.5). These 

results indicate that off-site drift is not likely to pose 

acute or chronic risk to these aquatic species. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that this scenario is not likely to pose 

a risk to piscivorous birds. 

Surface Runoff 

Non-target Plants – Terrestrial and Aquatic 

RQs for typical non-target terrestrial plant species 

affected by surface runoff to off-site soil were all 

below the plant LOC of 1, indicating that transport due 

to surface runoff is not likely to pose a risk to these 

receptors. Most RQs for RTE non-target terrestrial 

plant species were also below the plant LOC of 1. 

However, several scenarios did result in elevated RQs 

at the typical and maximum application rates. These 

scenarios included the base watershed with clay soils 

and more than 25 inches of precipitation per year and 

three variations on the base watershed with 50 inches 

of precipitation per year (silt loam, silt, and clay-loam 

soil). This indicates the potential for risk to RTE plant 

species in selected watersheds dominated by clay soils 

at the typical and maximum application rates with 

greater than 25 inches annual precipitation, with 

additional risk associated with soils dominated by silt 

and clay under situations exceeding 50 inches annual 

precipitation. 

Acute and chronic RQs for non-target aquatic plants in 

the stream impacted by overland flow of herbicide 

were all below the plant LOC of 1. Acute RQs for nontarget aquatic plants in the pond were also below the 

plant LOC, with one exception. An RQ of 1.04 was 

predicted at the maximum application rate in the base 

watershed with sandy soil and 150 inches of 

precipitation per year. However, this LOC exceedance 

was minimal and in general these results indicate that 

this transport mechanism is not likely to pose a risk to 

aquatic plant species under these conditions. 

Chronic RQs exceeded the LOC for several pond 

scenarios. Elevated RQs ranged from 1.02 to 3.74 at 

the typical application rate and from 1.15 to 4.06 at the 

maximum application rate. Risk quotients above the 

plant LOC of 1 were predicted in 14 scenarios at the 

typical application rate and 16 scenarios at the 

maximum application rate. The maximum RQ was 

predicted in the base watershed with clay soils and 50 

inches of precipitation per year. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

(acute RTE species) for all pond and stream scenarios, 

indicating that impacts from surface runoff are not 

likely to pose a risk to these aquatic species. 

Chronic risk RQs were well below the LOC for 

chronic risk to RTE species (0.5), indicating that these 

scenarios are not likely to result in long-term risk to 

aquatic animals in the stream or pond. 

Piscivorous Birds 

RQs for the piscivorous bird were all well below the 

most conservative terrestrial animal LOC (0.1), 

indicating that this scenario is not likely to pose a risk 

to piscivorous birds. 

Wind Erosion and Transport Off-site 

RQs for typical and RTE terrestrial plants were all 

well below the plant LOC (1), indicating that wind 

erosion is not likely to pose a risk to non-target 

terrestrial plants. 

Accidental Spill to Pond 

Risk quotients for the spill scenario were 0.0040 for 

aquatic invertebrates, 0.043 for fish and 14.3 for nontarget aquatic plants. These scenarios are highly 

conservative and represent unlikely and worst case 

conditions (limited waterbody volume, tank mixed for 

maximum application). Spills of this magnitude are 

possible, but are not likely to occur. However, 

potential risk to non-target aquatic plants was 

indicated for the truck spill mixed for the maximum 

application rate. 

BLM Vegetation Treatments Using Herbicides C-72 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

No RQs in excess of the appropriate acute or chronic 

LOCs were observed for fish or aquatic invertebrates 

in any of the stream scenarios. Because fish and 

aquatic invertebrates are not predicted to be directly 

impacted by herbicide concentrations in the stream, 

their availability as prey item populations is not likely 

to be impacted, and there is not likely to be an indirect 

effect on salmonids due to a lack of prey. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

No RQs in excess of the LOC were observed for 

aquatic plant species in the stream for any of the offsite drift or surface runoff scenarios. RQs for terrestrial 

plants were elevated above the LOC for accidental 

direct spray scenarios at both the typical and maximum 

application rates, indicating the potential for a 

reduction in this plant community. RQs for non-target 

typical and RTE terrestrial plants were also observed 

above the plant LOC as a result of off-site drift. At the 

typical application rate, elevated RQs were predicted 

25 ft from ground application with a low boom and 

100 ft from ground application with a high boom. At 

the maximum application rate, elevated RQs were 

predicted 100 ft from ground application with a low or 

high boom. Risk quotients in excess of the LOC were 

also predicted for RTE terrestrial plants due to surface 

runoff in clay watersheds with at least 25 inches of 

precipitation per year and in clay-loam, silt-loam, and 

silt watersheds with at least 50 inches of precipitation 

per year. These results indicate the potential for a 

reduction in riparian cover under selected conditions 

as a result of off-site drift and/or surface runoff.

Sulfometuron Methyl 

Direct Spray 

Terrestrial Wildlife 

Risk quotients for terrestrial wildlife were all below 

the most conservative LOC of 0.1 (acute RTE species), 

indicating that direct spray impacts are not likely to 

pose a risk to terrestrial animals. 

Non-target Plants – Terrestrial and Aquatic 

The majority of RQs for terrestrial and aquatic plants 

were above the LOC of 1.0. Risk quotients for nontarget terrestrial plants ranged from 0.636 to 13,571. 

Risk quotients for non-target aquatic plants under the 

accidental direct spray over pond scenario ranged from 

131 to 1,060, and the RQs for the accidental direct 

spray over stream scenario ranged from 650 to 5,320. 

Therefore, direct spray impacts pose a risk to plants in 

both aquatic and terrestrial environments. The only 

exception was the accidental direct spray of the nontarget terrestrial plants at the typical application rate. 

Fish and Aquatic Invertebrates 

Acute and chronic toxicity RQs for fish and aquatic 

invertebrates were below the most conservative LOCs 

(0.05 for acute risk RTE species; 0.5 for chronic risk 

RTE species). These results indicate that direct spray 

impacts are not likely to pose a risk to fish and aquatic 

invertebrates. 

Off-site Drift 

Non-target Plants – Terrestrial and Aquatic 

The RQs for typical non-target terrestrial plants 

affected by off-site drift to soils were all below the 

plant LOC of 1. However, RQs for all of the RTE nontarget terrestrial plants did exceed the LOC, with RQs 

between 3.43 and 2,536. Risks were more significant 

for helicopter forested applications than for any other 

scenario. These results indicate that off-site drift is not 

likely to result in significant risk to typical non-target 

terrestrial species, but risks to RTE species may occur. 

The majority of the RQs for non-target aquatic plants 

affected by off-site drift were above the plant LOC of 

1, indicating the potential for negative impacts as a 

result of off-site drift to waterbodies. Acute and 

chronic RQs in the pond and stream were elevated 

above the LOC for all aerial application scenarios, 

suggesting that sulfometuron methyl should not be 

sprayed aerially or that a buffer zone of more than 900 

ft (maximum modeled distance) is needed. Elevated 

RQs were also predicted 100 ft from ground 

application areas. These results indicate that off-site 

drift has the potential to negatively impact aquatic 

plants, but that impact may be reduced through the use 

of wider buffer zones or the use of ground rather than 

aerial applications. 

Fish and Aquatic Invertebrates 

Acute and chronic toxicity RQs for fish and aquatic 

invertebrates were all below the most conservative 

LOCs. These results indicate that impacts from off-site 

BLM Vegetation Treatments Using Herbicides C-73 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

drift are not likely to pose acute or chronic risk to 

these aquatic species. 

Piscivorous Birds 

Risk quotients for piscivorous birds were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that this scenario is not likely to pose 

a risk to piscivorous birds. 

Surface Runoff 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for typical non-target terrestrial plant 

species affected by surface runoff to off-site soil were 

all below the plant LOC of 1, indicating that transport 

due to surface runoff is not likely to pose a risk to 

these species. Risk quotients for RTE species were 

elevated over the plant LOC for several scenarios. At 

the typical application rate, elevated RQs for RTE 

species were predicted in the base watershed with clay 

soils and more than 10 inches of precipitation per year, 

in the base watershed with loam soil and 150 inches of 

precipitation per year, and in the base watershed with 

two soil variations (silt-loam and clay-loam) at 50 

inches of precipitation per year. Chronic RQs were 

elevated in these same scenarios as well as in the base 

watershed with loam soil and more than 100 inches of 

precipitation per year and in the base watershed with 

silt soil and 50 inches of precipitation per year. 

Acute and chronic RQs for non-target aquatic plants in 

the pond impacted by herbicide runoff were above the 

plant LOC of 1 for most scenarios. Only watersheds 

with relatively minimal annual precipitation (5 to 25 

inches, depending on soil type) did not predict 

elevated RQs. 

Acute toxicity RQs for aquatic plants in the stream 

were elevated above the plant LOC in 13 scenarios at 

the typical application rate and 17 scenarios at the 

maximum application rate. At the typical rate the 

following scenarios predicted potential risk: base 

watershed with sandy soil and greater than 25 inches 

of annual precipitation, base watershed with clay soil 

and greater than 100 inches of annual precipitation, 

and base watershed with loam soil and greater than 

150 inches of annual precipitation. The four additional 

scenarios predicting risk at the maximum application 

rate were: base watershed with clay soil and greater 

than 50 inches of annual precipitation; base watershed 

with loam soil and greater than 100 inches of annual 

precipitation; base watershed with clay-loam soil and 

greater than 5 inches of annual precipitation; and base 

watershed with loam soil, greater than 5 inches of 

annual precipitation, and a 1,000 acre application area. 

Minimal chronic risk to aquatic plants was predicted in 

the stream, with RQs of 1.02 predicted in two scenarios: 

base watershed with sand soil, and 200 or 250 inches of 

annual precipitation. At the maximum application rate, 

elevated RQs were also predicted in the base watershed 

with sand soil and greater than 50 inches of annual 

precipitation. 

These results indicate the potential for risk to 

terrestrial and aquatic plants due to surface runoff 

under most conditions. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

(acute RTE species) for all pond and stream scenarios, 

indicating that impacts from surface runoff are not 

likely to pose a risk to these aquatic species. In 

addition, chronic risk RQs were well below the LOC 

for chronic risk to RTE species (0.5); therefore, 

surface runoff scenarios are not likely to result in longterm risk to aquatic animals in the stream or pond. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that surface runoff is not likely to 

pose a risk to piscivorous birds. 

Wind Erosion and Transport Off-site 

Risk quotients for typical and RTE terrestrial plants 

were all well below the plant LOC (1), indicating that 

wind erosion is not likely to pose a risk to non-target 

terrestrial plants. 

Accidental Spill to Pond 

Risk quotients for the spill scenarios were below the 

associated acute LOC for fish and aquatic 

invertebrates. However, potential risk to non-target 

aquatic plants was indicated for both the truck and 

helicopter spills mixed for the maximum application 

rate. 

BLM Vegetation Treatments Using Herbicides C-74 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

No RQs in excess of the appropriate acute or chronic 

LOCs were observed for aquatic invertebrates in any 

of the stream scenarios; therefore, salmonids are not 

likely to be indirectly affected by a reduction in prey. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

Aquatic plant RQs for accidental direct spray scenarios 

were above the plant LOC at both the typical and 

maximum application rates, indicating the potential for 

a reduction in the aquatic plant community. Therefore, 

in the unlikely case that a stream is accidentally 

sprayed, there would be the potential for indirect 

impacts to salmonids caused by a reduction in 

available cover. 

Elevated aquatic plant RQs were also observed as a 

result of off-site drift more than 900 ft from aerial 

application and within 100 ft of the ground application 

of the herbicide, indicating the potential for a 

reduction in cover. Elevated RQs were also predicted 

for several surface runoff scenarios: primarily in sand 

watersheds with more than 25 inches of annual 

precipitation; clay watersheds with more than 50 

inches of annual precipitation; and loam watersheds 

with more than 100 inches of annual precipitation. 

Risk quotients for terrestrial plants were elevated 

above the LOC for accidental direct spray scenarios at 

both the typical and maximum application rates, 

indicating the potential for a reduction in riparian 

cover. 

Risk quotients for RTE terrestrial plants were observed 

above the plant LOC under all of the modeled 

conditions. No risks were predicted for typical plant 

species. A similar pattern was also predicted for risks 

due to surface runoff. These results further indicate the 

potential for a reduction in riparian cover and possible 

indirect impacts to salmonids.

Tebuthiuron 

Direct Spray 

Terrestrial Wildlife 

Risk quotients for the pollinating insect were above the 

most conservative LOC of 0.1 (acute RTE species) for 

impacts from direct spray of the insect (typical and 

maximum application rates) and indirect contact with 

foliage after direct spray (maximum application rate). 

These results suggest there may be potential for risk to 

pollinating insects due to direct spray and indirect 

contact with foliage. 

Acute and chronic RQs for terrestrial wildlife 

impacted by the typical application rate were all below 

the most conservative LOC of 0.1 (acute RTE species). 

At the maximum application rate, three acute exposure 

scenarios (ingestion of contaminated food by small 

and large mammalian herbivores and the large avian 

herbivore) predicted RQs above the most conservative 

LOC (0.1; acute RTE species). The small mammalian 

herbivore acute RQ of 1.86 was also above the “acute 

high risk” LOC of 0.5. Two chronic exposure 

scenarios (ingestion of contaminated food by the 

smaller large mammalian herbivores) were above the 

chronic LOC of 1, with an RQ of 3.58 and 3.79, 

respectively at the maximum application rate. These 

results indicate that direct spray impacts are not likely 

to pose a risk to terrestrial animals at the typical 

application rate. Acute and chronic risk to avian and 

mammalian herbivores is predicted at the maximum 

application rate. 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for non-target terrestrial plants ranged 

from 16.7 to 400. Risk quotients for non-target aquatic 

plants in the pond ranged from 1.12 to 39.5, and RQs 

for non-target aquatic plants in the stream ranged from 

5.6 to 172. Therefore, direct spray impacts pose a risk 

to plants in both aquatic and terrestrial environments. 

Fish and Aquatic Invertebrates 

Acute and chronic toxicity RQs for fish, and acute 

toxicity RQs for aquatic invertebrates were below the 

most conservative LOC of 0.05 (acute RTE species), 

indicating that direct spray impacts are not likely to 

pose acute or chronic risk to fish or acute risk to 

aquatic invertebrates in the pond or stream. 

The chronic RQs for the aquatic invertebrates for the 

accidental direct spray ranged from 0.56 to 4.48 for the 

pond scenario and from 2.8 to 22.4 for the stream 

scenario. These values were greater than the LOC for 

chronic risk to RTE species (0.5), indicating the 

potential for risk to these receptors. These results 

suggest that impacts from direct spray may pose a 

chronic risk to RTE aquatic invertebrates in the pond 

or stream. 

BLM Vegetation Treatments Using Herbicides C-75 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

Off-site Drift 

Non-target Plants – Terrestrial and Aquatic 

The majority of the RQs for non-target terrestrial 

plants affected by off-site drift to soil were below the 

plant LOC of 1. However, RQs for 6 of the 24 

application scenarios did exceed the LOC, with RQs 

between 1.04 and 6.59. Elevated RQs were predicted 

for RTE species impacted by off-site drift in the 

following situations: 25 ft from the ground application 

using a high boom at the typical application rate, 25 ft 

from the ground application using a low or a high 

boom at the maximum application rate, and 100 ft 

from the ground application using a high boom at the 

maximum application rate. 

All of the acute and chronic toxicity RQs for nontarget aquatic plants affected by off-site drift in the 

pond and stream were below the plant LOC of 1. 

These results indicate that impacts from off-site drift 

are not likely to pose acute or chronic risk to aquatic 

plants. 

Fish and Aquatic Invertebrates 

Acute and chronic toxicity RQs for fish and aquatic 

invertebrates were all below the most conservative 

LOCs. These results indicate that impacts from off-site 

drift are not likely to pose acute or chronic risk to 

these aquatic species. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that off-site drift of tebuthiuron is not 

likely to pose a risk to piscivorous birds. 

Surface Runoff 

Non-target Plants – Terrestrial and Aquatic 

Risk quotients for typical, non-target terrestrial plant 

species affected by surface runoff to off-site soil were 

all below the plant LOC of 1, indicating that transport 

due to surface runoff is not likely to pose a risk to 

these species. Risk quotients for RTE species were 

elevated for four scenarios at the typical application 

rate: runoff from the base watershed with clay soil and 

annual precipitation of 100, 150, 200, and 250 inches 

(RQs ranged from 1.24 to 1.43). Risk quotients for 

RTE species were elevated for eight scenarios at the 

maximum application rate: runoff from the base 

watershed with clay soil and annual precipitation of 

50, 100, 150, 200, and 250 inches and runoff from the 

base watershed with annual precipitation of 50 inches 

and three different soil types—silt-loam, silt, and clayloam (RQs ranged from 1.34 to 11.5). These risk 

scenarios involve high levels of precipitation (50 

inches and greater), and therefore, are not likely on 

most public lands, which experience arid and semi-arid 

conditions. 

Acute RQs for non-target aquatic plants in the pond 

impacted by runoff of herbicide were generally below 

the plant LOC of 1 at the typical application rate. 

However, elevated acute RQs were predicted at the 

typical application rate in the base watershed with 

sandy soil and precipitation greater than 10 inches per 

year, in the base watershed with clay soil and 

precipitation of 50 to 100 inches per year, and in the 

clay loam variation of the base watershed with 50 

inches of precipitation per year (no other precipitation 

levels modeled for this watershed). At the maximum 

application rate, elevated RQs were predicted in all but 

five modeled scenarios. These results indicate there is 

potential for acute impacts to aquatic plants in the 

pond under selected conditions at the typical 

application rate and under most conditions at the 

maximum application rate. 

Chronic RQs for non-target aquatic plants in the pond 

were elevated above the plant LOC in several 

scenarios. At the typical application rate, 10 of the 42 

RQs were above the plant LOC (ranging from 1.29 to 

10.2). The majority of these exceedances occurred in 

sandy watersheds. At the maximum application rate, 

37 of the 42 RQs were above the plant LOC. These 

results suggest the potential for chronic impacts to 

aquatic plants in the pond under selected conditions at 

the typical application rate and under most conditions 

at the maximum application rate. 

Acute RQs for non-target aquatic plants in the stream 

impacted by surface runoff of herbicide were all below 

the plant LOC of 1 at the typical application rate. At 

the maximum application rate, elevated acute RQs 

were predicted in the base watershed with sandy soil 

and more than 50 inches of precipitation per year, in 

the base watershed with clay soil and more than 100 

inches of precipitation per year, and in the loam 

watershed at 50 inches of precipitation per year when 

the application area was increased to 100 and 1,000 

acres. Chronic RQs for non-target aquatic plants in the 

stream were below the LOC in all scenarios. These 

results indicate the potential for acute, but not chronic, 

BLM Vegetation Treatments Using Herbicides C-76 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

impacts to aquatic plants in the stream under selected 

conditions at the maximum application rate. 

Fish and Aquatic Invertebrates 

Acute toxicity RQs for fish and aquatic invertebrates 

were all below the most conservative LOC of 0.05 

(acute RTE species) for all pond and stream scenarios, 

indicating that surface runoff of tebuthiuron is not 

likely to pose acute risks to these aquatic species. 

Chronic risk RQs for fish were well below the LOC 

for chronic risk to RTE species (0.5) in both pond and 

stream scenarios. At the typical application rate, 

chronic risk RQs for aquatic invertebrates were below 

the LOC for chronic risk to RTE species (0.5) in all 

but one modeled scenario (RQ of 1.28 for base 

watershed with sand soil and 10 inches of precipitation 

per year). At the maximum application rate in the pond 

scenario, chronic RQs for aquatic invertebrates were 

elevated above the LOC for chronic risk to RTE 

species (0.5) in 31 of 42 scenarios. In addition, 11 of 

the 42 pond RQs were above the chronic risk LOC (1). 

The majority of these elevated RQs occurred in 

watersheds with sandy soil. No RQs for aquatic 

invertebrates in the stream scenario were above their 

LOCs. 

These results indicate that these scenarios are not 

likely to result in long-term risk to fish in the stream or 

pond or to aquatic invertebrates in the stream at the 

typical application rate. Long-term impacts to aquatic 

invertebrates in the pond, especially RTE species, may 

occur at the maximum application rate. 

Piscivorous Birds 

Risk quotients for the piscivorous bird were all well 

below the most conservative terrestrial animal LOC 

(0.1), indicating that surface runoff is not likely to 

pose a risk to piscivorous birds. 

Wind Erosion and Transport Off-site 

Risk quotients for typical and RTE terrestrial plants 

were all well below the plant LOC (1), indicating that 

wind erosion is not likely to pose a risk to non-target 

terrestrial plants. 

Accidental Spill to Pond 

Risk quotients for the truck spill scenario ranged from 

0.048 for aquatic invertebrates to 287 for non-target 

aquatic plants. Risk quotients for the helicopter spill 

scenario were higher, ranging from 0.196 for aquatic 

invertebrates to 1,170 for non-target aquatic plants. 

Potential risk to fish and non-target aquatic plants was 

indicated for the truck spill, and risk to fish, aquatic 

invertebrates, and non-target aquatic plants was 

indicated for the helicopter spill. 

Potential Risk to Salmonids from Indirect Effects 

Qualitative Evaluation of Impacts to Prey 

No RQs in excess of the appropriate acute or chronic 

LOCs were observed for aquatic invertebrates in any 

of the stream scenarios associated with off-site drift or 

surface runoff. However, chronic RQs for 

invertebrates were greater than the associated chronic 

LOC for the accidental direct spray scenario. Because 

aquatic invertebrates are not predicted to be directly 

impacted by herbicide concentrations in the stream 

during normal application of tebuthiuron, salmonids 

are not likely to be indirectly affected by a reduction in 

prey. 

Qualitative Evaluation of Impacts to Vegetative 

Cover 

Aquatic plant RQs for accidental direct spray scenarios 

were above the plant LOC at both the typical and 

maximum application rates. Therefore, there is the 

potential for indirect impacts to salmonids due to a 

reduction in available cover in the unlikely event that a 

stream is accidentally sprayed. 

No elevated aquatic plant RQs were observed resulting 

from off-site drift to the stream. Acute RQs in excess 

of the LOC were observed for aquatic plant species in 

the stream for selected surface runoff scenarios at the 

maximum application rate, most strongly within sandy 

watersheds. No chronic RQs were elevated in the 

surface runoff scenarios. These results indicate the 

potential for a reduction in cover in some locations as 

a result of surface runoff when the herbicide is applied 

at the maximum rate. 

Risk quotients for terrestrial plants were elevated 

above the LOC for accidental direct spray scenarios at 

both the typical and maximum application rates, 

indicating the potential for a reduction in this plant 

community in response to this unlikely event. 

Risk quotients for typical terrestrial plants were also 

observed above the plant LOC as a result of off-site 

drift 25 ft from the ground application of the herbicide 

at the maximum rate. In addition, elevated RQs at the 

BLM Vegetation Treatments Using Herbicides C-77 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

BLM Vegetation Treatments Using Herbicides C-78 June 2007 

Final Programmatic EIS

typical application rate were observed for RTE species 

at 25 ft from the ground application using a high 

boom. Elevated RQs at the maximum application rate 

were observed for RTE species at 25 ft from the 

ground application and 100 ft from the ground 

application using a high boom. These results indicate 

the potential for a reduction in riparian cover under 

selected conditions as a result of off-site drift from a 

nearby tebuthiuron application. 

No RQs in excess of the LOC were observed for 

typical terrestrial plant species for any of the surface 

runoff scenarios. Elevated RQs as a result of surface 

runoff were observed for RTE terrestrial plant species 

in 4 of 42 scenarios at the typical application rate and 

8 of 42 scenarios at the maximum application rate. 

Therefore, a reduction in plant cover is likely as a 

result of accidental direct spray and under selected 

scenarios as a result of off-site drift and surface runoff. 

In these circumstances, salmonids could be indirectly 

affected by the reduction in cover. 

Uncertainty Analysis 

For any ERA, a thorough description of uncertainties 

is a key component that serves to identify possible 

weaknesses in the analysis and to elucidate what 

impact such weaknesses might have on the final risk 

conclusions. The uncertainties of this risk assessment 

are discussed below (also see Table 7-1 in the 

herbicide ERAs [ENSR 2005a-j]). 

Toxicity Data Availability 

The majority of the available toxicity data was 

obtained from studies conducted as part of the USEPA 

pesticide registration process. There are a number of 

uncertainties related to the use of this limited data set 

in the risk assessment. In general, it would be 

preferable to base any ecological risk analysis on 

reliable field studies that clearly identify and quantify 

the amount of potential risk from particular exposure 

concentrations of the chemical of concern. However, 

in most risk assessments it is more common to 

extrapolate the results obtained in the laboratory to the 

receptors found in the field. It should be noted, 

however, that laboratory studies often overestimate 

risk relative to field studies (Fairbrother and Kapustka 

1996). 

Species for which toxicity data are available may not 

necessarily be the most sensitive species to a particular 

herbicide. These species have been selected as 

laboratory test organisms because they are generally 

sensitive to stressors and can also be maintained under 

laboratory conditions. Toxicity values for the most 

appropriate sensitive surrogate species for each 

receptor were selected by qualified toxicologists based 

on a thorough review of the available toxicity data; 

however, there is a possibility that some non-tested 

receptors in a given receptor group would be more 

sensitive. 

Furthermore, the surrogate species used in the 

registration testing are not an exact match to the 

wildlife receptors included in the ERA. For example, 

avian data are only available for two primarily 

herbivorous birds: the mallard duck and the bobwhite 

quail. However, TRVs based on these receptors were 

also used to evaluate risk to insectivorous and 

piscivorous birds. Species with alternative feeding 

habits may be more or less sensitive to the herbicide 

than those species tested in the laboratory (see Tables

C-3 and C-4 for a list of surrogate species and their 

receptor groups). 

In general, the most sensitive available endpoint for 

the appropriate surrogate test species was used to 

derive TRVs. This approach is conservative as there 

may be a wide range of data and effects for different 

species. For example, the EC50s available for aquatic 

invertebrates exposed to bromacil ranged from 65 mg 

a.i./L to >1,000 mg a.i./L. Accordingly, 65 mg a.i./L 

was selected as the aquatic invertebrate TRV, even 

though the majority of results were well above this 

value. In general, this selection criterion for TRVs has 

the potential to overestimate risk within the ERA. 

In addition, several of the toxicity tests conducted 

during the registration process did not use herbicide 

formulations with 100% a.i. The assumption has been 

made that any toxicity observed in the tests is due to 

the herbicide a.i.; however, it is possible that the 

additional ingredients in the different formulations also 

had an effect. For purposes of TRV derivation and the 

ERA, it was assumed that all toxicity data applies to 

the a.i. itself and not the particular product formulation 

tested. This may result in an overestimate of risk to 

certain receptors and species guilds. 

Degradates, Inert Ingredients, 

Adjuvants, and Tank Mixtures 

In a detailed herbicide risk assessment, it is preferable 

to estimate risks not just from the a.i. of an herbicide, 

but also from the cumulative risks of degradates, inert 
TABLE C-15 

Risk Levels Used to Describe Typical Herbicide Effects According to Exposure Scenario and Ecological Rece

BROMACIL CHLOR DIFLU DIQUAT DIURON FLURIDONE IMAZAPIC OVERDRIVE 

Typ Max Typ Max Typ Max Typ Max Typ Max Typ Max Typ Max Typ Max 

Direct Spray 

0 0 0 0 0 0 0 M 0 0 0 0 0 0 0 0 

Terrestrial animals 

[14:16] [8:16] [16:16] [16:16] [16:16] [16:16] [10:16] [7:16] [12:16] [6:16] [16:16] [15:16] [16:16] [16:16] [15:16] [15:16] [

H H H H M H H H M H NE NE L M M H 

Terrestrial plants [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] RTE terrestrial H H H H H H H H H H NE NE L M H H plants [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] [1:1] 

L L 0 0 0 0 L M M H 0 0 0 0 0 0 

Fish pond [1:2] [1:2] [2:2] [2:2] [2:2] [2:2] [2:2] [1:2] [2:2] [1:2] [2:2] [2:2] [2:2] [2:2] [2:2] [2:2] 

M M 0 0 0 0 M M H H 0 L 0 0 0 0 

Fish stream 

[1:2] [1:2] [2:2] [2:2] [2:2] [2:2] [1:2] [2:2] [1:1] [1:1] [2:2] [2:2] [2:2] [2:2] [2:2] [2:2] 

Aquatic 0 0 0 0 0 0 M H M H 0 L 0 0 0 0 invertebrates pond [2:2] [2:2] [2:2] [2:2] [2:2] [2:2] [2:2] [1:2] [2:2] [1:2] [2:2] [1:2] [2:2] [2:2] [2:2] [2:2] Aquatic 0 L 0 0 0 0 H H H H L M 0 L 0 0 invertebrates stream [2:2] [1:2] [2:2] [2:2] [2:2] [2:2] [1:2] [2:2] [1:1] [1:1] [1:2] [1:2] [2:2] [1:2] [2:2] [2:2] 

H H M H L L H H H H 0 0 L L M M 

Aquatic plants pond [1:2] [2:2] [1:2] [2:2] [1:2] [1:2] [2:2] [2:2] [2:2] [2:2] [2:2] [2:2] [1:2] [2:2] [1:2] [1:2] Aquatic plants H H M H L L H H H H 0 0 L M M H stream [2:2] [2:2] [2:2] [2:2] [1:2] [1:2] [2:2] [2:2] [1:1] [1:1] [2:2] [2:2] [2:2] [2:2] [1:2] [1:2] 

NA NA NA NA NA NA NA NA NA NA 0 0 NA NA NA NA 

Piscivorous bird 

[1:1] [1:1] 

Accidental Spill 

NE M NE 0 NE 0 NE H NE H NE M NE 0 NE 0 

Fish pond [1:1] [2:2] [1:1] [2:2] [1:1] [2:2] [2:2] [1:1] Aquatic NE L NE 0 NE 0 NE H NE H NE H NE 0 NE 0 invertebrates pond [1:1] [2:2] [1:1] [2:2] [1:1] [1:2] [2:2] [1:1] 

NE H NE H NE H NE H NE H NE L NE H NE M 

Aquatic plants pond [1:1] [2:2] [1:1] [2:2] [1:1] [2:2] [2:2] [1:1] 

BLM Vegetation Treatment Using Herbicides C-79 June 2007 

Final Programmatic EIS
TABLE C-15 (Cont.)

Risk Levels Used to Describe Typical Herbicide Effects According to Exposure Scenario and Ecological Rece

BROMACIL CHLOR DIFLU DIQUAT DIURON FLURIDONE IMAZAPIC OVERDRIVE 

Typ Max Typ Max Typ Max Typ Max Typ Max Typ Max Typ Max Typ Max 

Off-Site Drift 

NA NA NA NA NA NA NA NA NA NA NE NE NA NA NA NA 

Terrestrial animals 

M M M M 0 0 L M 0 L NE NE 0 0 0 0 

Terrestrial plants [3:6] [3:6] [5:12] [8:12] [4:6] [4:6] [7:12] [7:12] [5:6] [4:6] [18:18] [13:18] [5:6] [4:6] 

M H M M L L M M M H NE NE 0 0 L L 

RTE terrestrial plants [3:6] [3:6] [7:12] [7:12] [4:6] [4:6] [7:12] [7:12] [3:6] [3:6] [17:18] [13:18] [3:6] [4:6] 

0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 

Fish pond [12:12] [12:12] [24:24] [24:24] [12:12] [12:12] [12:12] [11:12] [36:36] [36:36] [12:12] [12:12] 

0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 

Fish stream 

[12:12] [12:12] [24:24] [24:24] [12:12] [12:12] [12:12] [9:12] [36:36] [36:36] [12:12] [12:12] 

Aquatic invertebrates 0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 pond [12:12] [12:12] [24:24] [24:24] [12:12] [12:12] [12:12] [9:12] [36:36] [36:36] [12:12] [12:12] Aquatic invertebrates 0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 stream [12:12] [12:12] [24:24] [24:24] [12:12] [12:12] [11:12] [8:12] [36:36] [36:36] [12:12] [12:12] 

0 L 0 0 0 0 NA NA L M NA NA 0 0 0 0 

Aquatic plants pond [9:12] [7:12] [24:24] [24:24] [9:12] [8:12] [8:12] [6:12] [36:36] [34:36] [9:12] [8:12] 

0 L 0 0 0 L NA NA L M NA NA 0 0 0 L 

Aquatic plants stream [8:12] [6:12] [24:24] [22:24] [8:12] [6:12] [6:12] [6:12] [36:36] [33:36] [8:12] [6:12] 

0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 

Piscivorous bird 

[6:6] [6:6] [12:12] [12:12] [6:6] [6:6] [6:6] [6:6] [18:18] [18:18] [6:6] [6:6] 

Surface Runoff 

NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 

Terrestrial animals 

0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 

Terrestrial plants [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] 

0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 

RTE terrestrial plants [39:42] [38:42] [42:42] [42:42] [34:42] [33:42] [38:42] [34:42] [42:42] [42:42] [34:42] [33:42] 

0 0 0 0 0 0 NA NA L L NA NA 0 0 0 0 

Fish pond [65:84] [46:84] [84:84] [84:84] [84:84] [84:84] [60:84] [48:84] [84:84] [84:84] [84:84] [47:84] 

0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 

Fish stream 

[84:84] [84:84] [84:84] [84:84] [84:84] [84:84] [81:84] [68:84] [84:84] [84:84] [84:84] [83:84] 

BLM Vegetation Treatment Using Herbicides C-80 June 2007 

Final Programmatic EIS
TABLE C-15 (Cont.)

Risk Levels Used to Describe Typical Herbicide Effects According to Exposure Scenario and Ecological Rece

BROMACIL CHLOR DIFLU DIQUAT DIURON FLURIDONE IMAZAPIC OVERDRIVE 

Typ Max Typ Max Typ Max Typ Max Typ Max Typ Max Typ Max Typ Max 

Surface Runoff (Cont.) Aquatic invertebrates 0 0 0 0 0 0 NA NA 0 L NA NA 0 0 0 0 pond [84:84] [84:84] [84:84] [84:84] [84:84] [84:84] [38:84] [34:84] [84:84] [84:84] [84:84] [84:84] Aquatic invertebrates 0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 stream [84:84] [84:84] [84:84] [84:84] [84:84] [84:84] [66:84] [49:84] [84:84] [84:84] [84:84] [84:84] Aquatic plants pond M H 0 0 0 0 NA NA M H NA NA 0 0 0 0 

[70:84] [45:84] [64:84] [53:84] [84:84] [84:84] [50:84] [64:84] [80:84] [62:84] [70:84] [67:84] 

0 L 0 0 0 0 NA NA L L NA NA 0 0 0 0 

Aquatic plants stream [45:84] [55:84] [80:84] [77:84] [84:84] [84:84] [35:84] [39:84] [84:84] [83:84] [84:84] [84:84] 

0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 

Piscivorous bird 

[42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] [42:42] 

Wind Erosion 

NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 

Terrestrial animals 

0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 

Terrestrial plants [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] 

0 0 0 0 0 0 NA NA 0 0 NA NA 0 0 0 0 

RTE terrestrial plants [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] [9:9] 

NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 

Fish pond 

NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 

Fish stream Aquatic invertebrates NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA pond Aquatic invertebrates NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA stream 

NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 

Aquatic plants pond 

NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 

Aquatic plants stream Piscivorous bird NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 

BLM Vegetation Treatment Using Herbicides C-81 June 2007 

Final Programmatic EIS
TABLE C-15 (Cont.) Risk Levels Used to Describe Typical Herbicide Effects According to Exposure Scenario and Ecological Rece

Notes: The reported risk level is based on the risk level of the majority of the RQs for each exposure scenario within each of the above receptor groups and ex

spray/spill, off-site drift, surface runoff, and wind erosion). As a result, risk may be higher than the reported risk category for some scenarios withshould consult the risk tables in Section 4 of the ERAs to determine the specific scenarios that result in the displayed level of risk for a given receptor 

Abbreviations Risk Categories CHLOR = Chlorsulfuron 0 = No Risk (RQ<LOC) DIFLU = Diflufenzopyr L = Low Risk (RQ 1-10x LOC) SULFM = Sulfometuron methyl M = Moderate Risk (RQ 10-100x LOC) TEBU = Tebuthiuron H = High Risk (RQ >100 LOC) NA = Not Applicable NE = Not Evaluated Typ = Typical application rate Max = Maximum application rate Number in brackets represents Number of RQs in the Indicated Risk Level: Number of Scenarios Evaluated 

BLM Vegetation Treatment Using Herbicides C-82 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

ingredients (inerts), and adjuvants. Other pesticides 

may also factor into the risk estimates, as herbicides 

can be tank mixed to expand the level of control and to 

accomplish multiple identified tasks (the BLM usually 

only tank mixes herbicides with other herbicides). 

However, using currently available models (e.g., 

GLEAMS), it is only practical to make deterministic 

risk calculations (i.e., exposure modeling, effects 

assessment, and RQ derivations) for a single a.i. 

In addition, information on inerts, adjuvants, and 

degradates is often limited by the availability of, and 

access to, reliable toxicity data for these constituents. 

The sections below present a qualitative evaluation of 

the potential risks from degradates, inert ingredients, 

adjuvants, and tank mixtures. 

Degradates 

The potential toxicity of degradates should be 

considered when selecting an herbicide. However, it is 

beyond the scope of this risk assessment to evaluate all 

of the possible degradates of the various herbicide 

formulations of the 10 herbicides. Degradates may be 

more or less mobile and more or less toxic in the 

environment than their source herbicides (Battaglin et 

al. 2003). Differences in environmental behavior (e.g., 

mobility) and toxicity between parent herbicides and 

degradates makes prediction of potential impacts 

challenging. For example, a less toxic, but more 

mobile bioaccumulative, or persistent degradate may 

have a greater adverse impact due to residual 

concentrations in the environment. A recent study 

indicated that 70% of degradates had either similar or 

reduced toxicity to fish, daphnids, and algae than the 

parent pesticide. However, 4.2% of the degradates 

were more than an order of magnitude more toxic than 

the parent pesticide, with a few instances of acute 

toxicity values below 1 mg/L (Sinclair and Boxall 

2003). No evaluations of impacts to terrestrial species 

were conducted in the study. The lack of data on the 

toxicity of degradates of the specific herbicides 

represents a source of uncertainty in the risk 

assessment. 

Inerts 

Pesticide products contain both active and inert 

ingredients. The terms “active ingredient” (a.i.) and 

“inert ingredient” have been defined by federal law—

the Federal Insecticide, Fungicide, and Rodenticide 

Act (FIFRA)—since 1947. An a.i. is one that prevents, 

destroys, repels, or mitigates the effects of a pest, or is 

a plant regulator, defoliant, desiccant, or nitrogen 

stabilizer. By law, the a.i. must be identified by name 

on the label, together with its percentage by weight. 

An inert ingredient is simply any ingredient in the 

product that is not intended to affect a target pest. For 

example, isopropyl alcohol may be an a.i. and 

antimicrobial pesticide in some products; however, in 

other products, it is used as a solvent and may be 

considered an inert ingredient. The law does not 

require inert ingredients to be identified by name and 

percentage on the label, but the total percentage of 

such ingredients must be declared. Because neither the 

federal law nor the regulations define the term “inert” 

on the basis of toxicity, hazard or risk to humans, nontarget species, or the environment, it should not be 

assumed that all inert ingredients are non-toxic. 

The USEPA has a listing of regulated inert ingredients 

at http://www.epa.gov/opprd001/inerts/index.html. 

This listing divides inert ingredients into four lists. The 

number of inert ingredients found in the nine 

herbicides evaluated in the ERAs for each category is 

shown below (nine inerts were not found on the 

USEPA lists): 

List 1 - Inert Ingredients of Toxicological 

Concern: None. 

List 2 - Potentially Toxic Inert Ingredients: None. 

List 3 - Inerts of Unknown Toxicity: 12. 

List 4 - Inerts of Minimal Toxicity. List 4 is 

subdivided into List 4A (minimal risk inert 

ingredients) and List 4B (inerts that have 

sufficient data to substantiate that they can be used 

safely in pesticide products): Over 50. 

Toxicity information was also searched in the 

following sources: 

• TOMES (a proprietary toxicological database 

including USEPA’s IRIS, the Hazardous 

Substance Data Bank, and the Registry of 

Toxic Effects of Chemical Substances 

(RTEC). 

• USEPA’s ECOTOX database which includes 

AQUIRE (a database containing scientific 

papers published on the toxic effects of 

chemicals to aquatic organisms). 

• TOXLINE (a literature searching tool). 

BLM Vegetation Treatments Using Herbicides C-83 June 2007 

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• Material Safety Data Sheets from suppliers. 

• Other sources, such as the Farm Chemicals 

Handbook. 

• Other cited literature sources. 

Relatively little toxicity information was found. A few 

acute studies on aquatic or terrestrial species were 

reported. No chronic data, no cumulative effects data, 

and almost no indirect effects data (food chain species) 

were found for the inerts in the 10 herbicides. 

A number of the List 4 compounds (Inerts of Minimal 

Toxicity) are naturally-occurring earthen materials 

(e.g., clay materials or simple salts) that would 

produce no toxicity at applied concentrations. 

However, some of the inerts, particularly the List 3 

compounds and unlisted compounds, may have 

moderate to high potential toxicity to aquatic species 

based on information in Material Safety Data Sheets or 

on published data. 

As a tool to evaluate List 3 and unlisted inerts in the 

ecological risk assessment, the exposure concentration 

of the inert compound was calculated and compared to 

toxicity information. As described in more detail in 

Appendix D of the ERAs, the GLEAMS model was set 

up to simulate the effects of a generalized inert 

compound in the base-case watershed (annual 

precipitation rate of 50 inches per year, application 

area of 10 acres, slope of 0.05, surface roughness of 

0.015, erodibility of 0.401 tons per acre, and 

vegetation type of weeds) with a sand soil type. The 

chemical characteristics of the generalized inert 

compound were set at either extremely high or low 

values to describe it as either a very mobile or stable 

compound. The application rate of the inert/adjuvant 

compound was fixed at 1 lb a.i./acre. Under these 

conditions, the maximum predicted ratio of inert 

concentration to herbicide application rate was 0.69 

mg/L per lb a.i./acre (3 day maximum in the pond), 

and in every case (acute and chronic, pond and stream 

scenarios) the inert concentrations exceeded herbicide 

a.i. concentrations. 

In general, higher application rates resulted in higher 

exposure concentrations of surfactant inerts, exceeding 

1 mg/L for the maximum pond scenario. This suggests 

that inerts associated with the application of herbicides 

may contribute to acute toxicity to aquatic organisms if 

they reach the aquatic environment. However, due to 

the lack of specific inert toxicity data, this may be an 

overestimate of the potential toxicity. It is assumed 

that toxic inerts would not represent a substantial 

percentage of the herbicide and that minimal impacts 

to the environment would result from these inert 

ingredients. 

Adjuvants and Tank Mixtures 

Evaluating the potential additional/cumulative risks 

from mixtures and adjuvants of pesticides is 

substantially more difficult than evaluating the inerts 

in the herbicide composition. While many herbicides 

are present in the natural environment along with other 

pesticides and toxic chemicals, it is extremely difficult 

to estimate the potential cumulative risks of such 

mixtures. The composition of such mixtures is highly 

site-specific, and thus nearly impossible to address at 

the programmatic level of the EIS. 

Herbicide label information indicates whether a 

particular herbicide can be tank mixed with other 

pesticides. Adjuvants (e.g., surfactants, crop oil 

concentrates, fertilizers) may also be added to the 

spray mixture to improve the herbicide efficacy when 

mixed and applied to according to the label. Without 

product specific toxicity data, it is impossible to 

quantify the potential impacts of these mixtures. In 

addition, a quantitative analysis could only be 

conducted if reliable scientific evidence allowed a 

determination of whether the joint action of the 

mixture was additive, synergistic, or antagonistic. 

Such evidence is not likely to exist unless the mode of 

action is common among the chemicals and receptors. 

Adjuvants 

Adjuvants generally function to enhance or prolong 

the activity of an a.i. For terrestrial herbicides, 

adjuvants aid in proper wetting of foliage and 

absorption of the a.i. into plant tissue. Adjuvant is a 

broad term that includes surfactants, selected oils, antifoaming agents, buffering compounds, drift control 

agents, compatibility agents, stickers, and spreaders. 

Adjuvants are not under the same registration 

guidelines as pesticides; the USEPA does not register 

or approve the labeling of spray adjuvants. Individual 

herbicide labels contain lists with “label-approved” 

adjuvants for use with a particular herbicide under 

specific conditions. 

Following the same procedure used to address inerts in 

Appendix D of the ERAs, the GLEAMS model was 

used to estimate the potential portion of an adjuvant 

that might reach an adjacent waterbody via surface 

runoff. In addition, sources (Muller 1980; Lewis 1991; 

BLM Vegetation Treatments Using Herbicides C-84 June 2007 

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Dorn et al. 1997; Wong et al. 1997) generally suggest 

that the acute toxicity of surfactants and anti-foam 

agents to aquatic life ranges from 1 to 10 mg/L, and 

that chronic toxicity ranges as low as 0.1 mg/L. This 

evaluation indicates that, for herbicides with high 

application rates, adjuvants have the potential to cause 

acute, and potentially chronic, risk to aquatic species. 

However, more specific modeling and toxicity data 

would be necessary to define the level of uncertainty. 

Selection of adjuvants is under the control of BLM 

land managers, and it is recommended that land 

managers follow all label instructions and abide by any 

warnings. In general, adjuvants compose a relatively 

small portion of the volume of herbicide applied; 

however, selection of adjuvants with limited toxicity 

and low volumes is recommended to reduce the 

potential for the adjuvant to influence the toxicity of 

the herbicide. 

Tank Mixtures 

The use of tank mixtures of labeled herbicides, along 

with the addition of an adjuvant (when stated on the 

label), may be an efficient use of equipment and 

personnel; however, knowledge of both products and 

their interactions is necessary to avoid unintended 

negative effects. In general, herbicide interactions can 

be classified as additive, synergistic, or antagonistic: 

• Additive effects occur when mixing two 

herbicides produces the same response as the 

combined effects of each herbicide applied 

alone. The products neither hurt nor enhance 

each other. 

• Synergistic responses occur when two 

herbicides provide a greater response than the 

added effects of each herbicide applied 

separately. 

• Antagonistic responses occur when two 

herbicides applied together produce less control 

than if you applied each herbicide separately. 

While a quantitative evaluation of all of these mixtures 

is beyond the scope of this ERA, a qualitative 

evaluation may be made if the assumption is made that 

the products in the tank mix will act in an additive 

manner. The predicted RQs for two active ingredients 

can be summed for each individual exposure scenario 

to see if the combined impacts result in additional RQs 

elevated above the corresponding LOCs. 

The RQs for any two herbicides in a tank mix were 

combined to simulate a tank mix in Appendix E of 

each ERA (diquat, fluridone, and tebuthiuron are not 

generally tank mixed by the BLM and were not 

included in this analysis). The application rates within 

the tank mix are not necessarily the same as each 

individual a.i. applied alone. See Table 7-2 in each 

ERA (ENSR 2005a-j) for a comparison of the percent 

of RQs exceeding LOCs for each of the 10 herbicide 

active ingredients applied alone and in a tank mix. 

These comparisons indicate that tank mixes for 

bromacil (with sulfometuron methyl) and imazapic 

with diflufenzopyr do not result in more RQs above 

the associated LOCs for birds, mammals, fish, and 

invertebrates (and aquatic plants for imazapic), than 

were predicted for bromacil, imazapic, or 

diflufenzopyr alone. Additional elevated RQs are 

predicted for both aquatic and RTE terrestrial plants 

when tank mixes of bromacil with sulfometuron 

methyl, and imazapic with diflufenzopyr, are applied 

(aquatic plant risk is not elevated versus imazapic 

applied alone). This suggests that in some cases plant 

species may be particularly sensitive to the tank mix. 

However, when chlorsulfuron and diuron are tank 

mixed, all receptors are at higher risk than with 

application of chlorsulfuron alone (risks are not higher 

than with the application of diuron alone), and most 

receptors are also at higher risk when sulfometuron 

methyl is applied with bromacil versus sulfometuron 

methyl alone. 

The comparison of the RQs from herbicide a.i. and 

tank mixes of these herbicides indicate that results are 

specific to each tank mix. Aquatic plants and RTE 

terrestrial plants may be at greater risk from the tank 

mixed application than from the a.i. alone. However, 

in some cases all receptors are at greater risk and 

precautions (e.g., increased buffer zones, decreased 

application rates) should be taken to reduce risk. There 

is some uncertainty in this evaluation because 

herbicides in tank mixes may not interact in an 

additive manner; this may overestimate risk if the 

interaction is antagonistic, or it may underestimate risk 

if the interaction is synergistic. In addition, other 

products may also be included in tank mixes and may 

contribute to the potential risk. 

Selection of tank mixes, like adjuvants, is under the 

control of BLM land managers. To reduce 

uncertainties and potential negative impacts, it is 

required that land managers follow all label 

instructions and abide by any warnings. Labels for 

both tank mixed products should be thoroughly 

BLM Vegetation Treatments Using Herbicides C-85 June 2007 

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ECOLOGICAL RISK ASSESSMENT

reviewed and mixtures with the least potential for 

negative effects should be selected. This is especially 

relevant when a mixture is applied in a manner that 

may have increased potential for risk. Use of a tank 

mix under these conditions increases the level of 

uncertainty in risk to the environment. 

Concentration Models 

The ecological risk assessment relies on different 

models (i.e., AgDRIFT, GLEAMS, CALPUFF) to 

predict the off-site impacts of herbicide use. These 

models have been developed and applied in order to 

produce a conservative estimate of herbicide loss from 

the application area to off-site locations (via off-site 

drift, surface runoff, and wind erosion). The 

uncertainty analysis focused on which environmental 

characteristics (e.g., soil type, annual precipitation) 

exert the biggest numeric impact on model outputs. 

The results of this uncertainty analysis also have 

important implications for the ability to apply risk 

calculations to different site characteristics from a risk 

management perspective. 

AgDRIFT®

Off-site spray drift and resulting terrestrial deposition 

rates and waterbody concentrations (hypothetical pond 

or stream) were predicted using the computer model, 

AgDRIFT® Version 2.0.05 (SDTF 2002). As with any 

complex ecological risk assessment model, a number 

of simplifying assumptions were made to ensure that 

the risk assessment results would be protective of most 

environmental settings encountered in the public land 

management program. 

Predicted off-site spray drift and downwind deposition 

can be substantially altered by a number of variables 

intended to simulate the herbicide application process 

(e.g., nozzle type used in the spray application of an 

herbicide mixture, ambient wind speed, release height 

[application boom height], and evaporation). 

Hypothetically, any variable in the model that is 

intended to represent some part of the physical process 

of spray drift and deposition can substantially alter 

predicted downwind drift and deposition patterns. 

Recognizing the incomplete knowledge of all the 

scenarios likely to be encountered in BLM programs, 

these assumptions were developed to be conservative 

and likely result in overestimation of actual off-site 

spray drift and resulting environmental impacts. 

GLEAMS 

The GLEAMS model was used to predict the loading 

of herbicide to nearby soils, ponds, and streams from 

overland runoff, erosion, and root-zone groundwater 

runoff. 

Herbicide Loss Rates 

The trends in herbicide loss rates (herbicide loss 

computed as a percent of the herbicide applied within 

the watershed) and water concentrations predicted by 

the GLEAMS model echo trends that have been 

documented in a wide range of streams located in the 

Midwestern U.S. A recently published study (Lerch 

and Blanchard 2003) recognized three primary factors 

affecting herbicide transport to streams, and they can 

be organized into four general categories: 

• Intrinsic factors – soil and hydrologic 

properties and geomorphologic characteristics 

of the watershed; 

• Anthropogenic factors – land use and 

herbicide management; 

• Climate factors – precipitation and 

temperature; and 

• Herbicide factors – chemical and physical 

properties and formulation of herbicide 

product. 

These findings were based on the conclusions of 

several prior investigations, data collected as part of 

the U.S. Geological Survey’s (USGS) National Stream 

Quality Accounting Network (NASQAN) program, 

and the results of runoff and baseflow water samples 

collected in 20 streams in northern Missouri and 

southern Iowa. The investigation concluded that the 

median runoff loss rates for atrazine, cyanazine, 

acetochlor, alachlor, metolachlor, and metribuzin 

ranged from 0.33 to 3.9% of the mass applied—loss 

rates that were considerably higher than other areas of 

the U.S. The study indicated that the runoff potential 

was a critical factor affecting herbicide transport. The 

median total loss rates range from 0.27 to 36%, and the 

median runoff loss rates range from 0.02 to 0.27%. 

The results of the GLEAMS simulations indicate 

trends similar to those identified in the Lerch and 

Blanchard (2003) study. First, the GLEAMS 

simulations demonstrated that the most dominant 

factors controlling herbicide loss rates are soil type and 

BLM Vegetation Treatments Using Herbicides C-86 June 2007 

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ECOLOGICAL RISK ASSESSMENT

precipitation (increased precipitation and less porous 

soil types result in increased herbicide runoff). This 

was demonstrated in each of the GLEAMS simulations 

that considered the effect of highly variable annual 

precipitation rates and soil type on herbicide transport. 

In all cases, the GLEAMS model predicted that runoff 

loss rate was positively correlated with both 

precipitation rate and soil type. Second, estimating the 

groundwater discharge concentrations by using the 

predicted root-zone concentrations as a surrogate is 

extremely conservative. For example, while the 

median runoff loss rates predicted using GLEAMS 

range from 0.02 to 0.27%, the median total loss rates 

are substantially higher. This discrepancy may be due 

to the differences between the watershed 

characteristics in the field investigation and those used 

to describe the GLEAMS simulations, as well as to the 

conservative nature of the baseflow predictions. 

Based on the results and conclusions of prior 

investigations, the runoff loss rates predicted by the 

GLEAMS model are approximately equivalent to loss 

rates determined within the Mississippi River 

watershed and elsewhere in the U.S., but the 

percolation loss rates are probably conservatively high. 

This confirms that the GLEAMS modeling approach 

used in the ERAs either approximates or overestimates 

the rate of loadings observed in the field. 

CALPUFF 

The USEPA’s CALPUFF air pollutant dispersion 

model was used to predict impacts of the potential 

migration of herbicide between 1.5 and 100 km from 

the application area by windblown soil (fugitive dust). 

Several assumptions were made that could 

overestimate or underestimate the deposition rates 

obtained from this model. 

The modeling conservatively assumed that all of the 

herbicide would be present in the soil at the 

commencement of a windy event, and that no 

reduction due to vegetation interception/up-take, 

leaching, or solar or chemical half-life would occur 

following aerial application. Thus, the model likely 

overestimates the deposition rates unless the herbicide 

is taken by the wind as soon as it is applied. It is more 

likely that a portion of the applied herbicide would be 

sorbed to plants or degraded over time. 

The model assumes a 1-mm penetration depth, which 

is less than the depth used in previous herbicide risk 

assessments (SERA 2003) and the depth assumed in 

the GLEAMS model (1 cm surface soil). This 

penetration depth is conservative and likely 

overestimates impacts. 

The use of flat terrain could underestimate deposition 

for mountainous areas. In these areas, hills and 

mountains would likely focus wind and deposition into 

certain areas, resulting in pockets of increased risk. 

The use of bare, undisturbed soil results in less uptake 

and transport than disturbed (e.g., tilled) soil. 

However, the BLM does not apply herbicides to 

agricultural areas so this assumption may be 

appropriate for public lands. 

The surface roughness in the vicinity of the application 

site directly affects the deposition rates predicted by 

CALPUFF. The surface roughness length used in the 

CALPUFF model is a measure of the height of 

obstacles to the wind flow and varies by land-use 

types. Forested areas and urban areas have the highest 

surface roughness lengths (0.5 m to 1.3 m) while 

grasslands have the lowest (0.001 m to 0.10 m). 

Predicted deposition rates are likely to be higher near 

the application area and lower at greater distances if 

the surface roughness in the area is relatively high 

(above 1 meter, such as in forested areas). Therefore, 

overestimation of the surface roughness could 

overpredict deposition within about 50 km of the 

application area and underpredict deposition beyond 

50 km. Overestimation of the surface roughness could 

occur if, for example, prescribed burning was used to 

treat a typically forested area prior to planned 

herbicide treatment. 

The surface roughness also affects the calculated 

“friction velocity” used to determine deposition 

velocities, which in turn are used by CALPUFF to 

calculate the deposition rate. Friction velocity 

increases with increasing wind speed and increasing 

surface roughness. Higher friction velocities result in 

higher deposition velocities and higher deposition 

rates, particularly within about 50 km of the emission 

source. 

The CALPUFF modeling assumes that the data from 

the selected National Weather Service stations are 

representative of meteorological conditions in the 

vicinity of the application sites. Site-specific 

meteorological data (e.g., from an on-site 

meteorological tower) could provide slightly different 

wind patterns, possibly due to local terrain, which 

could impact the deposition rates as well as locations 

of maximum deposition. 

BLM Vegetation Treatments Using Herbicides C-87 June 2007 

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Overall, conservative assumptions employed in 

exposure characterization will tend to overestimate 

risk, and therefore, may provide a buffer for the effects 

of uncertainties. 

• Review, understand, and conform to the 

“Environmental Hazards” section on the 

herbicide label. This section warns of known 

pesticide risks to wildlife receptors or to the 

environment and provides practical ways to 

Potential Indirect Effects on avoid harm to organisms or to the environment. 

Salmonids • Avoid accidental direct spray and spill 

conditions to reduce the largest potential 

impacts. Use the typical application rate, rather 

than the maximum application rate, to reduce 

risk to most species for most herbicides. 

No actual field studies or ecological incident reports 

on the effects of the 10 herbicides on salmonids were 

identified during the ERA. Therefore, any discussion 

of direct or indirect impacts on salmonids was limited 

to qualitative estimates of potential impacts on 

salmonid populations and communities. In some 

herbicide evaluations TRVs are based on warmwater 

species because these have the highest risk, and this 

may result in an overestimate of risks to salmonids, 

which are coldwater species. These evaluations 

indicated that for most herbicides (except diuron, 

diquat, and fluridone), salmonids are not likely to be 

indirectly impacted by a reduction in food supply (i.e., 

fish and aquatic invertebrates). However, they could 

be affected by a reduction in vegetative cover, which 

may occur under some conditions. 

• Limit the use of terrestrial herbicides 

(especially bromacil, diuron, and sulfometuron 

methyl) in watersheds with downgradient 

ponds and streams if potential impacts to 

aquatic plants are of concern. 

• Establish appropriate (herbicide specific) 

buffer zones to downstream waterbodies, 

habitats, or species/populations of interest (see 

Table C-16). 

• Consider the proximity of application areas to 

salmonid habitat and the possible effects of 

herbicides on riparian and aquatic vegetation. 

Maintain appropriate buffer zones around 

salmonid-bearing streams (see Table C-16 and 

recommendations in individual ERAs). 

It is anticipated that these qualitative evaluations 

overestimate the potential risk to salmonids because of 

the conservative selection of TRVs for salmonid prey 

and vegetative cover, the application of additional 

LOCs (with uncertainty/safety factors applied) to 

assess risk to RTE species, and the use of conservative 

stream characteristics in the exposure scenarios (i.e., 

low order stream, relatively small instantaneous 

volume, limited consideration of herbicide degradation 

or absorption in models). 

• The results from these ERAs contribute to the 

evaluation of proposed alternatives in the 

PEIS and to the development of the Biological 

Assessment (BA), specifically addressing the 

potential impacts of vegetation treatments to 

proposed and listed RTE species on public 

lands. Furthermore, the ERAs will assist BLM 

field offices on the proper application of 

herbicides to ensure that impacts to plants and 

animals and their habitats are minimized to 

the extent practical. 

Herbicide Application 

Recommendations 

The following general recommendations are designed 

to reduce potential unintended impacts to the 

environment from the application of herbicides in the 

BLM vegetation management program (see the 

individual ERAs for recommendations specific to each 

herbicide): 

• Select herbicide products carefully to minimize 

additional impacts from degradates, adjuvants, 

inert ingredients, and tank mixtures. This is 

especially important for application scenarios 

that already predict potential risk from the a.i. 

itself. 

BLM Vegetation Treatments Using Herbicides C-88 June 2007 

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ECOLOGICAL RISK ASSESSMENT

TABLE C-16 

Buffer Distances (feet) to Minimize Risk from Off-site Drift of Herbicides 

Application 

Scenario BROM CHLR DIFLU DIQT DIUR FLUR IMAZ OVER SULF TEBU 

Buffer Distance from Non-target Aquatic Plants 

Typical Application Rate 

Aerial NA 0 NA NE NA NE 0 NA 1,300 NE 

Low Boom 100 0 100 NE 900 NE 0 100 900 0 

High Boom 900 0 900 NE 1,000 NE 0 900 900 0 

Maximum Application Rate 

Aerial NA 300 NA NE NA NE 300 NA 1,500 NE 

Low Boom 900 0 900 NE 1,000 NE 0 900 900 0 

High Boom 900 0 900 NE 1,000 NE 0 900 900 0 

Buffer Distance from Non-target Terrestrial Plants 

Typical Application Rate 

Aerial NA 1,350 NA 1,200 NA NE 0 NA 0 NE 

Low Boom 950 900 100 100 0 NE 0 0 0 0 

High Boom 950 900 100 900 100 NE 0 100 0 0 

Maximum Application Rate 

Aerial NA 1,350 NA 1,200 NA NE 900 NA 0 NE 

Low Boom 1,000 1,000 100 900 200 NE 0 100 0 50 

High Boom 1,000 1,000 100 900 500 NE 0 100 0 50 

Buffer Distance from Rare, Threatened, and Endangered Terrestrial Plants 

Typical Application Rate 

Aerial NA 1,400 NA 1,200 NA NE 300 NA 1,500 NE 

Low Boom 1,200 1,000 100 900 1,000 NE 0 100 1,100 0 

High Boom 1,200 1,000 900 900 1,000 NE 0 900 1,100 50 

Maximum Application Rate 

Aerial NA 1,400 NA 1,200 NA NE 900 NA 1,500 NE 

Low Boom 1,200 1,050 900 1,000 1,000 NE 0 900 1,100 100 

High Boom 1,200 1,000 900 1,000 1,000 NE 0 900 1,100 500 

Buffer distances are the smallest modeled distance at which no risk was predicted. In some cases, buffer distances were 

extrapolated (if the largest distance modeled still resulted in risk) or interpolated (if greater precision was required). 

NA = Not applicable; NE = Not evaluated; BROM = Bromacil; CHRL = Chlorsulfuron; DIFLU = Diflufenzopyr; DIQT = Diquat; 

DIUR = Diuron; FLUR = Fluridone; IMAZ = Imazapic; OVER = Overdrive®; SULF = Sulfometuron methyl; and TEBU = 

Tebuthiuron. 

BLM Vegetation Treatments Using Herbicides C-89 June 2007 

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References 

Barnthouse, L. 1993. Population-level Effects. Pages 

247-274 in G. W. Suter, II (ed.). Ecological Risk 

Assessment. Lewis Publishers, Boca Raton, 

Florida. 

Battaglin, A.W., E.M. Thurman, S.J. Kalkhoff, and 

S.D. Porter. 2003. Herbicides and 

Transformation Products in Surface Waters of the 

Midwestern United States. Journal of the 

American Water Resources Association. 

California Office of Environmental Health Hazard 

Assessment (CA OEHHA). 2003. California 

Wildlife Biology, Exposure Factor, and Toxicity 

Database (Cal/Ecotox). State of California Office 

of Environmental Health Hazard Assessment and 

University of California at Davis. Available at: 

http://www.oehha.ca.gov/cal_ecotox/default.htm. 

Chapman, P.M., A. Fairbrother, and D. Brown. 

1998. A Critical Evaluation of Safety 

(Uncertainty) Factors for Ecological Risk 

Assessment. Environmental Toxicology and 

Chemistry 17:99-108. 

Dorn, P. B., J. H. Rodgers, Jr., W.B. Gillespie, Jr., 

R. E. Lizotte, Jr., and A. W. Dunn. 1997. The 

Effects of C12-13 Linear Alcohol Ethoxylate 

Surfactant on Periphyton, Macrophytes, 

Invertebrates and Fish in Stream Mesocosms. 

Environmental Toxicology and Chemistry, 

16(8):1634-1645. 

Eli Lilly and Company. 2003. Sonar Guide to 

Aquatic Habitat Management: User’s Guide. 

ENSR. 2004. Vegetation Treatments Programmatic 

EIS Ecological Risk Assessment Protocol. Final 

Report. Prepared for the Bureau of Land 

Management. Westford, Massachusetts. 

________. 2005a. Vegetation Treatments 

Programmatic EIS – Bromacil Ecological Risk 

Assessment Final Report. Prepared for the 

Bureau of Land Management. Westford, 

Massachusetts. 

________. 2005b. Vegetation Treatments 

Programmatic EIS – Chlorsulfuron Ecological 

Risk Assessment Final Report. Prepared for the 

Bureau of Land Management. Westford, 

Massachusetts. 

________. 2005c. Vegetation Treatments 

Programmatic EIS – Diflufenzopyr Ecological 

Risk Assessment Final Report. Prepared for the 

Bureau of Land Management. Westford, 

Massachusetts. 

________. 2005d. Vegetation Treatments 

Programmatic EIS – Diquat Ecological Risk 

Assessment Final Report. Prepared for the 

Bureau of Land Management. Westford, 

Massachusetts. 

________. 2005e. Vegetation Treatments 

Programmatic EIS – Diuron Ecological Risk 

Assessment Final Report. Prepared for the 

Bureau of Land Management. Westford, 

Massachusetts. 

________. 2005f. Vegetation Treatments 

Programmatic EIS – Fluridone Ecological Risk 

Assessment Final Report. Prepared for the 

Bureau of Land Management. Westford, 

Massachusetts. 

________. 2005g. Vegetation Treatments 

Programmatic EIS – Imazapic Ecological Risk 

Assessment Final Report. Prepared for the 

Bureau of Land Management. Westford, 

Massachusetts. 

________. 2005h. Vegetation Treatments 

Programmatic EIS – Overdrive® Ecological Risk 

Assessment Final Report. Prepared for the 

Bureau of Land Management l. Westford, 

Massachusetts.

________. 2005i. Vegetation Treatments 

Programmatic EIS – Sulfometuron methyl 

Ecological Risk Assessment Final Report. 

Prepared for the Bureau of Land Management. 

Westford, Massachusetts. 

________. 2005j. Vegetation Treatments 

Programmatic EIS – Tebuthiuron Ecological Risk 

Assessment Final Report. Prepared for the 

Bureau of Land Management. Westford, 

Massachusetts. 

________. 2005k. Air Quality Modeling for BLM 

Vegetation Treatments Methods. Final Report. 

Prepared for the Bureau of Land Management. 

Westford, Massachusetts. 

BLM Vegetation Treatments Using Herbicides C-91 June 2007 

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ECOLOGICAL RISK ASSESSMENT

Fairbrother, A., and L.A. Kapustka. 1996. Toxicity 

Extrapolations in Terrestrial Systems. Ecological 

Planning and Toxicology, Inc. 

Forbis, A., D. Burgess, and L. Georgie. 1985. Acute 

Toxicity of CN 10-6471 (Banvel Herbicide) to 

Daphnia magna: Report No. 33173. Unpublished 

Study Prepared by Analytical Bio-chemistry 

Laboratories, Inc. [(Banvel Herbicide)] MRID 

00153152. 

Gillette, D.A. 1988. Threshold Friction Velocities for 

Dust Production for Agricultural Soils. Journal of 

Geophysical Research 93(D10):12,645-12,662. 

Harris, S.A., and K.R. Solomon. 1992. Human 

Exposure to 2,4-D Following Controlled 

Activities on Recently Sprayed Turf. Journal of 

Environmental Science and Health B27:9-22. 

Hoerger, F., and E.E. Kenaga. 1972. Pesticide 

Residues on Plants: Correlation of Representative 

Data as a Basis for Estimation of Their 

Magnitude in the Environment. In Environmental 

Quality and Safety, Volume I: Global Aspects of 

Toxicology and Technology as Applied to the 

Environment. F. Coulston and F. Kerte (eds.). 

Academic Press. New York, New York. 

Hurlbert, S.H. 1975. Secondary Effects of Pesticides 

on Aquatic Ecosystems. Residue Review 57:81-

148. 

Johnson, C.R. 1976. Herbicide Toxicities in Some 

Australian Anurans and the Effect of Subacute 

Dosages on Temperature Tolerance. Zoological 

Journal Linnaean Society 59(1):79-83. 

Knisel, W.G., and F.M. Davis. 2000. GLEAMS: 

Groundwater Loading Effects of Agricultural 

Management Systems. Version 3.0. SEWRKWGK/FMD-050199, Revised 081500, U.S. 

Department of Agriculture. Tifton, Georgia. 

Lerch, R.N., and P.E. Blanchard. 2003. Watershed 

Vulnerability to Herbicide Transport in Northern 

Missouri and Southern Iowa Streams. 

Environmental Science and Technology 

37(24):5518-5527. 

Lewis, M.A. 1991. Chronic and Sublethal Toxicities 

of Surfactants to Aquatic Animals: a Review and 

Risk Assessment. Water Research 25(1):101-113. 

Muller, R. 1980. Fish Toxicity and Surface Tension of 

Non-ionic Surfactants: Investigations of Antifoam Agents. Journal of Fish Biology 16:585-

589. 

National Library of Medicine. 2002. Hazardous 

Substance Data Bank. National Institutes of 

Health, Department of Health and Human 

Services. Accessed on April 21, 2005. Available 

at: http://toxnet.nlm.nih.gov. 

Roshon, R.D., J.H. McCann, D.G. Thompson, and 

G.R. Stephenson. 1999. Effects of Seven 

Forestry Management Herbicides on 

Myriophyllum sibiricum, as Compared with other 

Nontarget Aquatic Organisms. Canadian Journal 

of Forest Research 29:1158-1169. 

Sample, B.E., D.M. Opresko, and G.W. Suter. 1996.

Toxicological Benchmarks for Wildlife: 1996 

Revision. Risk Assessment Program. Document 

ES/ER/TM-86/R-3. Oak Ridge National 

Laboratory. Oak Ridge, Tennessee. Available at: 

http://www.hsrd.ornl.gov/ecorisk/reports.html. 

Sappington, L.C., F.L. Mayer, F.J. Dwyer, D.R. 

Buckler, J.R. Jones, and M.R. Ellersieck. 2001.

Contaminant Sensitivity of Threatened and 

Endangered Fishes Compared to Standard 

Surrogate Species. Environmental Toxicology 

and Chemistry 20:2869-2876. 

Sinclair, C.J., and A.B.A. Boxall. 2003. Assessing 

the Ecotoxicity of Pesticide Transformation 

Products. Environmental Science and Technology 

37:4617-4625. 

Spray Drift Task Force (SDTF). 2002. A User's 

Guide for AgDRIFT 2.0.05: a Tiered Approach 

for the Assessment of Spray Drift of Pesticides. 

Regulatory Version. 

Syracuse Environmental Research Associates, Inc 

(SERA). 2000. Preparation of Environmental 

Documentation and Risk Assessments. Prepared 

for the United States Department of Agriculture 

(USDA) Forest Service, Forest Health Protection. 

SERA MD 2000-10-01b. Fayetteville, New York. 

________. 2001. Imazapic [Plateau and Plateau DG]-

Human Health and Ecological Risk Assessment 

Final Report. Prepared for USDA Forest Service, 

Forest Health Protection. SERA TR 00-21-28-

01e. Fayetteville, New York. 

BLM Vegetation Treatments Using Herbicides C-92 June 2007 

Final Programmatic EIS
ECOLOGICAL RISK ASSESSMENT

________. 2003. Imazapic – Human Health and 

Ecological Risk Assessment – Peer Review Draft. 

Prepared for USDA Forest Service, Forest Health 

Protection. SERA TR 02-43-17-04a. Fayetteville, 

New York. 

U.S. Department of Agriculture Forest Service. 

2005. Preventing and Managing Invasive Plants, 

Final Environmental Impact Statement. U.S. 

Department of Agriculture Forest Service Pacific 

Northwest Region. Available at: 

http://www.fs.fed.us/r6/invasiveplant-eis/.

U.S. Department of the Interior Bureau of Land 

Management (USDI BLM). 1991. Final 

Environmental Impact Statement, Vegetation 

Treatment on BLM Lands in Thirteen Western 

States. Casper, Wyoming. 

United States Environmental Protection Agency 

(USEPA). 1993a. Wildlife Exposure Factors 

Handbook. Vol. I. Office of Research and 

Development, EPA/600-R/R-93/187a, 187b. 

Washington, D.C. 

________. 1993b. Review Plant Data Submission. 

Douglas Urban of the Ecological Effects Branch, 

February 11, 1993. MRID 424911-01. 

Washington, D.C. 

________. 1995a. Great Lakes Water Quality 

Initiative Technical Support Document for the 

Procedure to Determine Bioaccumulation 

Factors. EPA-820-B-95-005. Office of Water. 

Washington, D.C. 

________. 1995b. Reregistration Eligibility Decision 

(RED) Diquat Dibromide. Prevention, Pesticides 

and Toxic Substances. EPA 738-R-95-016. 

Washington, D.C. 

________. 1996. Pesticide Tolerance for Cadre. Final 

Rule Published in the Federal Register. 40 CFR 

Part 180.490. Docket Number: PP 

4F4390/R2215. 

________ 1998. Guidelines for Ecological Risk 

Assessment. EPA/630/R-95/002F. Washington, 

D.C. 

________. 1999. Pesticide Fact Sheet: Diflufenzopyr. 

Office of Prevention, Pesticides and Toxic 

Substances. Washington, D.C. 

________. 2002. Toxicology Disciplinary Chapter for 

the Registration Eligibility Decision (RED) 

Document. Health Effects Division, Pesticides 

Programs, Office of Prevention, Pesticides, and 

Toxic Substances. Prepared by L.L. Taylor, 

Reregistration Branch I. PC Code: 118601. 

________. 2003. USEPA Pesticide Ecotoxicity 

Database. Provided by Brian Montague, Office of 

Pesticide Programs. Washington, D.C. 

Wong, D., P.B. Dorn, and E.Y. Chai. 1997. Acute 

Toxicity and Structure-activity Relationships of 

Nine Alcohol Ethoxylate Surfactants to Fathead 

Minnow and Daphnia magna. Environmental 

Toxicology and Chemistry 16(9):1970-1976. 

Ypsilantis, B. 2003. Personal Communication to Scott 

F. Archer, BLM Senior Air Resource Specialist, 

Including Manuscript Titled Typical Soil 

Properties; Fugitive Dust Dispersion Modeling 

Scenarios; Vegetation Treatment EIS Risk 

Assessment, Prepared by B. Ypsilantis, BLM 

National Science and Technology Center Soil 

Scientist. Denver, Colorado. 

BLM Vegetation Treatments Using Herbicides C-93 June 2007 

Final Programmatic EIS