APPENDIX B 

HUMAN HEALTH RISK ASSESSMENT 

 HUMAN HEALTH RISK ASSESSMENT

TABLE OF CONTENTS 

Page 

Introduction......................................................................................................................................................................B-1

Human Health Risk Assessment Overview............................................................................................................B-1

Organization of Document......................................................................................................................................B-2

Hazard Identification .......................................................................................................................................................B-2

Chemical Characteristics and Usage ......................................................................................................................B-2

Dicamba..........................................................................................................................................................B-2

Diflufenzopyr..................................................................................................................................................B-2

Diquat..............................................................................................................................................................B-2

Fluridone.........................................................................................................................................................B-2

Imazapic..........................................................................................................................................................B-2

Sulfometuron Methyl......................................................................................................................................B-3

Toxicity Profiles......................................................................................................................................................B-3

General Information .......................................................................................................................................B-3

Dicamba..........................................................................................................................................................B-3

Diflufenzopyr..................................................................................................................................................B-6

Diquat..............................................................................................................................................................B-9

Fluridone.......................................................................................................................................................B-12

Imazapic........................................................................................................................................................B-14

Sulfometuron Methyl....................................................................................................................................B-16

Dose-response Assessment............................................................................................................................................B-17

Types of Dose-response Values............................................................................................................................B-17

Dietary Assessment ......................................................................................................................................B-17

Non-dietary (Occupational or Residential) Assessment..............................................................................B-18

Available Dose-response Values ..........................................................................................................................B-18

Dicamba........................................................................................................................................................B-19

Diflufenzopyr................................................................................................................................................B-20

Diquat............................................................................................................................................................B-23

Fluridone.......................................................................................................................................................B-24

Imazapic........................................................................................................................................................B-25

Sulfometuron Methyl....................................................................................................................................B-26

Inert Ingredients ....................................................................................................................................................B-27

Exposure Assessment ....................................................................................................................................................B-28

Overview of the BLM Vegetation Treatment Program .......................................................................................B-28

Land Programs..............................................................................................................................................B-28

Application Methods ....................................................................................................................................B-30

Herbicide Use Parameters.....................................................................................................................................B-33

Occupational Receptors ........................................................................................................................................B-33

Routine Use Exposure Scenarios .................................................................................................................B-33

Accidental Exposure Scenarios....................................................................................................................B-34

Public Receptors....................................................................................................................................................B-35

Routine Use Exposure Scenarios .................................................................................................................B-35

Accidental Exposure Scenarios....................................................................................................................B-36

Exposure Parameters for Public Receptors..................................................................................................B-37

Calculation of Exposure Point Concentrations.....................................................................................................B-51

Occupational Exposures ...............................................................................................................................B-52

Public Exposures ..........................................................................................................................................B-52

Chemical-specific Parameters...............................................................................................................................B-56

Absorption Factors .......................................................................................................................................B-56

Skin Permeability Constants ........................................................................................................................B-56

Fish Bioconcentration Factors......................................................................................................................B-57

BLM Vegetation Treatments Using Herbicides B-i June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Risk Characterization.....................................................................................................................................................B-57

Approach for Risk Characterization .....................................................................................................................B-57

Food (%PAD) Assessment...........................................................................................................................B-57

Non-food (MOE) Assessment......................................................................................................................B-57

Aggregate Risk Index ...................................................................................................................................B-58

Equations for Quantifying Potential Exposure and Risk .....................................................................................B-58

Estimating Potential Occupational Exposures .............................................................................................B-59

Inhalation of Herbicide.................................................................................................................................B-60

Estimating Potential Exposure for Public Receptors...................................................................................B-61

Dermal Contact with Herbicide....................................................................................................................B-61

Results of Risk Characterization...........................................................................................................................B-67

Occupational Receptors................................................................................................................................B-67

Public Receptors ...........................................................................................................................................B-74

Evaluation of Currently-available Herbicide Active Ingredients.........................................................................B-80

Evaluation of Dose-response Values Used in Previous EISs......................................................................B-81

Evaluation of Receptors and Exposure Pathways Used in the Earlier Human Health Risk Assessments.B-82

Summary of Currently-available Herbicide Active Ingredient Evaluation.................................................B-82

Uncertainty Analysis.............................................................................................................................................B-82

Hazard Identification ....................................................................................................................................B-82

Dose-response Assessment...........................................................................................................................B-83

Exposure Assessment ...................................................................................................................................B-83

Risk Characterization....................................................................................................................................B-84

References......................................................................................................................................................................B-87

List of Tables 

B-1 Acute Toxicity Categories and Definitions .........................................................................................................B-5

B-2 Toxicity Categories for Short-term Tests ............................................................................................................B-5

B-3 Summary of Toxicological Endpoint Data........................................................................................................B-21

B-4 Summary of Herbicide Use - Dicamba..............................................................................................................B-39

B-5 Summary of Herbicide Use - Diflufenzopyr .....................................................................................................B-41

B-6 Summary of Herbicide Use - Diquat .................................................................................................................B-43

B-7 Summary of Herbicide Use - Fluridone.............................................................................................................B-45

B-8 Summary of Herbicide Use - Imazapic..............................................................................................................B-47

B-9 Summary of Herbicide Use - Sulfometuron Methyl .........................................................................................B-49

B-10 Summary of Herbicide Risk Categories by Aggregate Risk Index...................................................................B-71

B-11 Occupational Scenarios with Aggregate Risk Indices Below One ..................................................................B-73

B-12 Routine Exposure Public Scenarios/Receptors with Aggregate Risk Indices Below One...............................B-77

B-13 Accidental Exposure Public Scenarios with Aggregate Risk Indices Below One ...........................................B-78

BLM Vegetation Treatments Using Herbicides B-ii June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

LIST OF ACRONYMS, ABBREVIATIONS, AND SYMBOLS 

AC - Concentration of active ingredient in concentrate 

acute PAD - Acute population adjusted dose 

AGDISP - Agricultural dispersal model 

a.i. - Active ingredient 

ALS - Acetolactate-synthase 

ANS - Accession number system 

AR - Application rate 

ARI - Aggregate risk index 

AT - Acres treated 

ATV - All-terrain vehicle 

BCF - Bioconcentration factor 

BLM - Bureau of Land Management 

BR - Berry residue 

BW - Body weight 

cm/h - Centimeters per hour 

C - Concentration 

CalEPA - California Environmental Protection Agency 

CBI - Confidential business information 

CF - Conversion factor 

chronic PAD - Chronic population adjusted dose 

CREAMS - Chemical runoff erosion assessment management system 

CRP - Conservation Reserve Program 

CSF - Cancer slope factor 

DAF - Dermal absorption factor 

DFR - Dislodgeable foliar residue 

DR - Deposition rate 

EF - Exposure factor 

EIS - Environmental Impact Statement 

EPC - Exposure point concentration 

ERA - Ecological risk assessment 

ET - Exposure time 

F - Fraction 

FQPA - Food Quality Protection Act 

GLEAMS - Groundwater Loading Effects of Agricultural Management Systems 

HDT - Highest dose tested 

HED - Health Effects Division 

HHRA - Human health risk assessment 

HSDB - Hazardous Substances Data Bank 

IAF - Inhalation absorption factor 

IR - Ingestion rate 

IRIS - Integrated Risk Information System 

Kp - Dermal permeability constant 

lb - Pound(s) 

LC50 - Median lethal concentration 

LD50 - Median lethal dose 

LDT - Lowest dose tested 

LOAEL - Lowest observed adverse effect level 

mg/cm2 - Milligrams per cubic centimeter 

mg/kg - Milligrams per kilogram 

mg/kg-day - Milligrams per kilogram of body weight per day 

mg/L - Milligrams per liter 

BLM Vegetation Treatments Using Herbicides B-iii June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

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

ML - Milliliter 

MA DEM/MA 

 DEP - Massachusetts Department of Environmental Management/Massachusetts Department 

of Environmental Protection 

MOE - Margin of exposure 

MRID - Master Record Identification 

NAS - National Academy of Sciences 

NASA - National Aeronautics and Space Administration 

NMF - N-Methyl formamide 

NOAEL - No observed adverse effect level 

NYSDOH - New York State Department of Health 

OEHHA - Office of Environmental Health Hazard Assessment 

OPP - Office of Pesticide Programs 

PAD - Population adjusted dose 

PEIS - Programmatic Environmental Impact Statement 

PHED - Pesticide Handlers Exposure Database 

PPE - Personal protective equipment 

ppm - Parts per million 

RED - Reregistration Eligibility Decision 

RfD - Reference dose 

ROW - Rights-of-way 

S - Spill amount 

SA - Surface area 

SAR - Surface area ratio 

SDTF - Spray Drift Task Force 

SERA - Syracuse Environmental Research Associates, Inc. 

SF - Safety factor 

SOP - Standard operating procedure 

Tc - Transfer coefficient 

UE - Unit of exposure 

UF - Uncertainty factor 

USEPA - United States Environmental Protection Agency 

USDA - United States Department of Agriculture 

USDI - United States Department of the Interior 

USLE - Universal Soil Loss Equation 

BLM Vegetation Treatments Using Herbicides B-iv June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

APPENDIX B 

HUMAN HEALTH RISK ASSESSMENT 

Introduction 

As part of the Programmatic Environmental Impact 

Statement (PEIS), a human health risk assessment 

(HHRA) was conducted to evaluate potential human 

health and environmental risks that may result from 

herbicide exposure both during and after treatment of 

public lands (ENSR 2004). This HHRA appendix 

summarizes the results of that assessment. 

Previous EISs prepared by United States Department of 

the Interior Bureau of Land Management (USDI BLM) 

addressed the use of 20 herbicides, hereafter referred to 

as the “currently-available” herbicides (see Table 2-1 in 

PEIS). Under the current PEIS, this HHRA evaluates 

the following six herbicides, most of which are not 

available for use on public lands, and are hereafter 

called the “new” herbicides: 

• Dicamba (active ingredient [a.i.] along with 

diflufenzopyr in Overdrive®; manufactured by 

BASF); 

• Diflufenzopyr (a.i. along with dicamba in 

Overdrive®; manufactured by BASF); 

• Diquat (a.i. in Reward®; manufactured by 

Syngenta); 

• Fluridone (a.i. in Sonar®A.S.; manufactured by 

SePRO); 

• Imazapic (a.i. in Plateau®; manufactured by 

BASF); and 

• Sulfometuron methyl (a.i. in Oust®; 

manufactured by DuPont). 

Note that in the HHRA, Overdrive® was evaluated as its 

two separate components, dicamba and diflufenzopyr, 

as these two have different toxicological endpoints, 

indicating that their effects on human health are not 

additive. 

Oust® is the only herbicide from the previous EISs that 

is reevaluated in this HHRA. Oust® has been found to 

impact non-target vegetation when carried on soil to 

untreated areas, and these effects were not evaluated in 

the earlier vegetation treatment EISs. Thus, the effects 

of Oust® on target and non-target vegetation are 

analyzed in this HHRA. 

The “currently-available” herbicides are not evaluated 

in this HHRA because the human health effects of these 

herbicides were adequately addressed in the previous 

EISs or HHRAs prepared by the BLM (USDI BLM 

1991) or U.S. Department of Agriculture (USDA; 

USDA Forest Service 2005). A discussion of how the 

“currently available” herbicide risk estimates calculated 

under earlier EISs might change if they were evaluated 

using updated risk assessment methods and toxicity 

values begins on page B-82. 

Human Health Risk Assessment 

Overview 

The risk assessments included in the four previous EISs 

followed HHRA guidelines as developed by the 

National Academy of Sciences (NAS 1983). Since then, 

both the U.S. Environmental Protection Agency 

(USEPA) Superfund program (USEPA 1989) and the 

USEPA Office of Pesticide Programs (OPP; USEPA 

2000a) have developed new guidelines for HHRAs. 

While the original scope of work for development of the 

HHRA stated that the template for the report, exposure 

scenarios, and evaluation would be obtained from the 

previous EISs, the BLM convened an inter-agency work 

group consisting of representatives from the BLM and 

USEPA from May through October of 2002 to review 

these methods and compare them with current risk 

assessment practice. The ultimate goal of these 

discussions was to reach consensus on updated risk 

assessment methods to ensure that the risk assessment 

methodology employed in the current PEIS is 

scientifically defensible, is consistent with currently 

available guidance where appropriate, and meets the 

needs of the BLM vegetation treatment program. 

The HHRA complies with USEPA guidance for 

conducting risk assessments for pesticides including, 

but not limited to, the following documents: 

• The Role of Use-Related Information in 

Pesticide Risk Assessment and Risk 

Management (USEPA 2000a) 

BLM Vegetation Treatments Using Herbicides B-1 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

• Guidance for Performing Aggregate Exposure 

and Risk Assessments (USEPA 1999a) 

• Exposure Factors Handbook (USEPA 1997a) 

Organization of Document 

The HHRA follows the four-step paradigm as identified 

by NAS (1983). The steps are: 

• Hazard identification 

• Dose-response assessment 

• Exposure assessment 

• Risk characterization 

Each of these steps is discussed in the following 

sections. 

Hazard Identification 

The purpose of the hazard identification process is to 

identify and summarize toxicity information for the six 

new herbicides that are quantitatively evaluated in the 

HHRA. 

Chemical Characteristics and Usage 

This section provides simple chemical descriptions and 

usage summaries for the six new herbicides. The BLM 

and the HHRA project team have compiled application 

type and rate information specific to BLM practices for 

each of the six herbicides. 

Dicamba 

Dicamba is the a.i. along with diflufenzopyr in 

Overdrive®. This herbicide is manufactured by BASF. 

According to the manufacturer’s label, dicamba is a 

selective postemergence herbicide for the management 

of annual broadleaf weeds and/or suppression of 

perennial broadleaf weeds. Activity is also noted for 

suppression of annual grassy weeds. As a dry, flowable 

herbicide formulation, a combination of dicamba and 

diflufenzopyr is mixed with water and is presently 

registered for use on corn, rangeland, pasture, and noncropland situations. Dicamba kills broadleaf weeds 

before and after they sprout. Overdrive® is a selective 

systematic herbicide for the control of broadleaf weeds 

pre- or post-emergence. Overdrive® disrupts plant 

hormone balance and protein synthesis. Overdrive® is 

provided as a wettable granular formulation. 

Diflufenzopyr 

Diflufenzopyr is the a.i. along with dicamba in 

Overdrive®. This herbicide is manufactured by BASF. 

According to the manufacturer’s label, diflufenzopyr is 

formulated with dicamba, and the herbicide is a 

selective post-emergence herbicide for the management 

of annual broadleaf weeds and/or the suppression of 

perennial broadleaf weeds. Activity is also noted for 

suppression of annual grassy weeds. Diflufenzopyr acts 

by inhibiting auxin transport. As a dry, flowable 

herbicide formulation, a combination of diflufenzopyr 

and dicamba is mixed with water and is presently 

registered for use on corn, rangeland, pasture, and noncropland situations. 

Diquat 

Diquat is the a.i. in Reward®. This herbicide is 

manufactured by Syngenta (2002). According to the 

manufacturer’s label, Reward Landscape and Aquatic 

Herbicide is a nonvolatile chemical for use as a general 

herbicide to control weeds in non-crop and aquatic 

areas. This herbicide controls weeds by interfering with 

photosynthesis within green plant tissue. In the BLM 

vegetation treatment program, Reward® would only be 

used in aquatic areas. 

Fluridone 

Fluridone is the a.i. in Sonar® A.S. This herbicide is 

manufactured by SePRO. According to the 

manufacturer’s label, Sonar® A.S. herbicide is a 

selective systemic aquatic herbicide for management of 

aquatic vegetation in freshwater ponds, lakes, 

reservoirs, drainage canals, and irrigation canals. Sonar®

A.S. is absorbed from water by plant shoots and from 

hydrosoil by the roots of aquatic vascular plants. It is 

important to maintain the recommended concentration 

of Sonar® A.S. in contact with the target plants for a 

minimum of 45 days. In susceptible plants, Sonar® A.S. 

inhibits the formation of carotene. In the BLM 

vegetation treatment program, Sonar® A.S. would only 

be used in aquatic areas. 

Imazapic 

Imazapic is the a.i. in Plateau®. This herbicide is 

manufactured by BASF. According to the 

manufacturer’s label, Plateau® herbicide is an aqueous 

solution to be mixed with water and applied as a spray 

solution to provide weed control and/or turf height 

suppression on pastures, rangeland, federal 

Conservation Reserve Program (CRP) land and nonBLM Vegetation Treatments Using Herbicides B-2 June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

cropland areas including non-cropland areas that may be 

grazed or cut for hay. For post-emergence applications, 

a surfactant is added to the mixture to increase 

adherence of the herbicide to plant leaves. Plateau®

herbicide is readily absorbed through leaves, stems, and 

roots, and is translocated rapidly throughout the plant, 

with accumulation in the meristematic regions. 

Imazapic is an acetolactate-synthase (ALS) inhibitor, a 

potent herbicide that acts by inhibiting an enzyme 

needed for essential amino acid synthesis. 

Sulfometuron Methyl 

Sulfometuron methyl is the a.i. in Oust®. This herbicide 

is manufactured by DuPont. According to the 

manufacturer’s label, Oust® herbicide is a dispersible 

granule that is mixed in water and applied as a spray. 

Oust® controls many annual and perennial grasses and 

broadleaf weeds in forestry and non-crop sites. Oust®

may be used for general weed control on industrial noncrop sites and for selective weed control in certain types 

of unimproved turf grasses on industrial sites. It can also 

be used for selective weed control in forest site 

preparation and in the release of several types of pines 

and certain hardwoods. Oust® controls weeds by both 

pre-emergence and post-emergence activity. 

Sulfometuron methyl is also an ALS inhibitor. 

Toxicity Profiles 

This section includes toxicity profiles for each of the 

herbicides that summarize the potential toxicity of each 

herbicide and provide information that puts the toxicity 

into context. The toxicity profiles include information 

on acute, subchronic, and chronic toxicity studies, 

reproductive and developmental toxicity studies, cancer 

bioassays, mutagenicity studies, epidemiology studies, 

metabolism, and toxicokinetics. 

General Information 

Much of the toxicity information discussed in this 

section is from USEPA reports, such as the Pesticide 

Fact Sheets or HHRAs conducted by the OPP Health 

Effects Division (HED) to evaluate use of the pesticides 

on specific crops. In addition, a literature search was 

conducted to ensure that relevant available information 

was used in these toxicity profiles. The databases 

searched include the National Library of Medicine’s 

Hazardous Substances Data Bank (HSDB) and Toxline. 

The USEPA receives many unpublished toxicity data 

sets that are referenced in USEPA documents using 

Master Record Identification (MRID) numbers. This is 

the USEPA’s system of recording and tracking studies 

submitted to the USEPA and replaces the earlier 

Accession Number System (ANS). In this HHRA, the 

MRID or Accession numbers are noted where provided 

along with the USEPA document in which they are 

referenced. Due to the confidential business information 

(CBI) status of much of the MRID-referenced 

information, the USEPA reports are generally the 

primary reference for this review. 

Each of the toxicity profiles includes information on 

acute toxicity. As shown in Table B-1, the USEPA has 

developed toxicity categories for pesticides based on 

acute toxicity animal tests conducted in support of 

registration of the pesticides (USEPA 2003e). Acute 

toxicity studies are used to determine a number of 

toxicity endpoints based on a single dose or several 

large doses of a substance. An important endpoint in 

acute testing is the toxicity reference level known as the 

median lethal dose (LD50), which is the dose, usually 

administered orally, that kills 50% of the test animals. 

The lower the LD50, the greater the toxicity of the 

chemical. In addition to the acute oral LD50, the USEPA 

has a battery of laboratory toxicity studies considered as 

acute tests (USEPA 2003e) that include acute dermal, 

acute inhalation (rat), eye irritation (rabbit), dermal 

irritation (rabbit), and dermal sensitization (guinea pig 

tests; Table B-1). For the different toxicity endpoints, 

the USEPA defines four toxicity categories (I through 

IV), with higher toxicity categories representing lower 

herbicide acute toxicity. 

In longer-term toxicity studies (chronic or subchronic) 

the endpoints for evaluation are the No Observed 

Adverse Effect Level (NOAEL) and the lowest dose at 

which an adverse effect has been observed, called a 

Lowest Observed Adverse Effect Level (LOAEL). 

Where both levels can be identified in a single study, for 

a given effect, the LOAEL will always be higher than 

the NOAEL. In some studies, adverse effects are 

observed at all dose levels; in these cases, the lowest 

dose tested (LDT) is identified as the LOAEL. By 

contrast, where no adverse effects are seen at any dose 

level tested, the highest dose tested (HDT; also referred 

to as the limit dose) is identified as the NOAEL. 

Dicamba 

Dicamba is a benzoic acid herbicide active ingredient. It 

can be applied to the leaves or to the soil. Dicamba 

controls annual and perennial broadleaf weeds in grain 

crops and grasslands, and it is used to control brush and 

bracken in pastures. It kills broadleaf weeds before and 

after they sprout. In combination with a 

phenoxyalkanoic acid or other herbicide, dicamba is 

BLM Vegetation Treatments Using Herbicides B-3 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

used in pastures, rangeland, and non-crop areas such as 

fencerows and roadways to control weeds. The USEPA 

has classified this herbicide a.i. as toxicity class III – 

slightly toxic. Products containing dicamba bear the 

Signal Word WARNING (Extension Toxicology 

Network [Extoxnet] 1996c). 

Acute Toxicity 

Table B-2 lists the toxicity categories for dicamba. In 

tests in rats, the acute oral LD50 was 2,740 milligrams 

per kilogram (mg/kg), placing it in Toxicity Category 

III. The acute dermal toxicity study in rats showed an 

LD50 greater than 2,000 mg/kg, placing it in Toxicity 

Category III. The acute inhalation toxicity study in rats 

showed a median lethal concentration (LC50) greater 

than 5.3 milligrams per liter (mg/L), placing it in 

Toxicity Category IV. The primary eye irritation study 

in rabbits places dicamba in Toxicity Category II. The 

primary dermal irritation study categorized dicamba as 

an irritant, placing it in Toxicity Category II. The 

primary dermal sensitization study in guinea pigs did 

not exhibit any sensitization potential (USEPA 2001h). 

Subchronic Toxicity 

In a subchronic neurotoxicity study, Sprague-Dawley 

rats (10/sex/dose) were fed diets containing dicamba at 

0, 3,000, 6,000, or 12,000 parts-per-million (ppm; 0, 

197.1, 401.4, 767.9 milligrams per kilogram of body 

weight per day (mg/kg-day) for males and 0, 253.4, 

472.0, or 1028.9 mg/kg-day for females, respectively) 

for 13 weeks. Neurobehavioral evaluations, consisting 

of locomotor activity, and auditory startle response, 

were conducted at prestudy and during weeks 4, 8, and 

13. No toxicologically significant differences were 

noted in either the mean body weights (BWs) or food 

consumption of the treated animals. Neurobehavioral 

evaluations at the 4-, 8-, and 13-week evaluations 

revealed rigid body tone, slightly impaired righting 

reflex, and impaired gait. At week 13, the incidences of 

these findings were decreased. Rigid body tone was also 

noted during evaluation of the righting reflex and land 

foot splay. The NOAEL was 401 mg/kg-day and the 

LOAEL was 768 mg/kg-day based on rigid body tone, 

slightly impaired righting reflex, and impaired gait 

(MRID No. 43245210; USEPA 2001h). 

Chronic Toxicity/Carcinogenicity 

In a combined chronic toxicity and carcinogenicity 

study in rats, dietary administration of dicamba at 0, 50, 

250 or 2,500 ppm (0, 2.5, 12.5 or 125 mg/kg-day, 

respectively) for 117 weeks resulted in a dose-related 

increase in ventricular dilation of the brain in female 

rats with the incidences at the high dose reaching 

statistical significance. The incidences were 15/49 

(31%), 18/49 (37%), 20/50 (40%) and 30/49 (61%) at 0, 

2.5, 12.5, or 125 mg/kg-day, respectively. There was no 

increased incidence of tumors at any of the doses, 

suggesting that dicamba is not carcinogenic (MRID No. 

000258115; USEPA 2001h). 

Developmental Toxicity 

In a developmental toxicity study, pregnant CD Charles 

River rats (25/dose group) received gavage 

administration of dicamba in corn oil at dose levels of 0, 

64, 160, or 400 mg/kg-day during gestation days 6 

through 19. Maternal toxicity, limited to the high dose 

(400 mg/kg-day), was characterized by mortality in four 

pregnant females that exhibited neurotoxic signs prior to 

death: clinical signs of nervous system toxicity that 

included ataxia, salivation, stiffening of the body when 

held, and decreased motor activity; statistically 

significant decreases in BW gain during the dosing 

period; and decreases in food consumption. For 

maternal toxicity, the NOAEL was 160 mg/kg-day and 

the LOAEL was 400 mg/kg-day based on mortality, 

clinical signs, BW changes, and decreases in food 

consumption. No treatment-related fetal anomalies were 

seen at any dose level. For developmental toxicity, the 

NOAEL was greater than 400 mg/kg-day; a LOAEL 

was not established (MRID No. 00084024; USEPA 

2001h). 

In a development toxicity study, inseminated New 

Zealand White rabbits (19 to 20/dose) were given oral 

capsules containing dicamba at dose levels of 0, 30, 

150, or 300 mg/kg-day from days 6 through 18 of 

gestation. No maternal toxicity was observed at 30 

mg/kg-day. At 150 mg/kg-day, maternal toxicity was 

characterized by abortion (5%) and clinical signs such 

as ataxia, and decreased motor activity. At 300 mg/kgday, maternal toxicity was manifested by abortions, 

clinical signs, decreased BW, and decreased food 

consumption. For maternal toxicity, the NOAEL was 30 

mg/kg-day and the LOAEL was 150 mg/kg-day based 

on abortions and neurotoxic clinical signs. Development 

toxicity at 300 mg/kg-day was manifested by irregular 

ossification of the nasal bones of the skull; no 

developmental toxicity was seen at 30 or 150 mg/kgday. For developmental toxicity, the NOAEL was 150 

mg/kg-day and the LOAEL was 300 mg/kg-day based 

on irregular ossification of internasal bones (MRID No. 

42429401; USEPA 2001h). 

 

BLM Vegetation Treatments Using Herbicides B-4 June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

TABLE B-1 

Acute Toxicity Categories and Definitions 

Toxicity Category I II III IV 

Oral LD50 0 to 50 mg/kg 50 to 500 mg/kg 500 to 5,000 mg/kg > 5,000 mg/kg 

Inhalation LC50

1 0 to 0.2 mg/L 0.2 to 2 mg/L 2 to 20 mg/L > 20 mg/L 

Dermal LD50 0 to 200 mg/kg 200 to 2,000 mg/kg 2,000 to 20,000 mg/kg > 20,000 mg/kg 

Eye effects 

Corrosive, corneal 

opacity not reversible 

within 7 days 

Corneal opacity 

reversible within 7 

days; irritation 

persisting for 7 days 

No corneal opacity; 

irritation reversible 

within 7 days 

No irritation 

Skin effects Corrosive Severe irritation at 

72 hours 

Moderate irritation at 

72 hours 

Mild or slight 

irritation at 72 

hours 1

 LC50 = Median lethal concentration. 

mg/kg = Milligrams of chemical per kilogram of body weight. 

mg/L = Milligrams of chemical per liter of air. 

Source: USEPA (2003e). 

TABLE B-2 

Toxicity Categories for Short-term Tests 

Herbicide Acute 

Oral1

Acute 

Dermal1

Acute 

Inhalation1

Primary 

Eye2

Primary 

Skin2

Dermal 

Sensitizer Reference 

Dicamba III III IV II II No USEPA 2001h 

Diflufenzopyr IV IV IV III IV No USEPA 2001c 

Diquat III II III II IV No USEPA 2001e 

Fluridone IV III III II IV No USEPA 1986a, 

1988 

Imazapic IV III IV III IV No USEPA 2001a 

Sulfometuron methyl NA NA NA NA NA NA (see text) 

NA = Not available from USEPA. 

1

 USEPA labeling guidelines acute, oral, dermal, and inhalation effects: 

I. Severe; oral LD50 0-50 mg/kg, dermal LD50 0-200 mg/kg, and inhalation LC50 0-0.2 mg/L. 

II. Moderate; oral LD50 50-500 mg/kg, dermal LD50 200-2000 mg/kg, and inhalation LC50 0.2-2 mg/L. 

III. Slight; oral LD50 500-5,000 mg/kg, dermal LD50 2,000-20,000 mg/kg, and inhalation LC50 2-20 mg/L. 

IV. Very slight; oral LD50 >5,000 mg/kg, dermal LD50 >20,000 mg/kg, and inhalation LC50 >20 mg/L. 

2 USEPA labeling guidelines for pesticides applied to skin or eyes: 

I. Irreversible corneal opacity at 7 days; corrosive to skin. 

II. Corneal opacity reversible within 7 days; severe skin irritation at 72 hours. 

III. No corneal opacity; moderate skin irritation at 72 hours. 

IV. No irritation to the eyes; mild or slight skin irritation at 72 hours.

BLM Vegetation Treatments Using Herbicides B-5 June 2007 

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Reproductive Toxicity 

In a two-generation reproduction study, SpragueDawley rats (32 or 28/group) received dicamba in the 

diet at dose levels of 0, 500, 1,500, or 5,000 ppm (0, 40, 

122, or 419 mg/kg-day for males and 0, 45, 136, or 450 

mg/kg-day for females, respectively) for two 

generations. Systemic toxicity was observed at 5,000 

ppm, manifested as clinical signs in pregnant females 

from both generations during lactation (stiff body tone 

and slow righting reflex) and significantly increased 

relative liver to BWs in both generations and sexes, 

adults as well as weanlings. For parental systemic 

toxicity, the NOAEL was 122 and 136 mg/kg-day for 

males and females, respectively; and the LOAEL was 

419 and 450 mg/kg-day in males and females based on 

clinical signs of neurotoxicity. Reproductive toxicity at 

1,500 and 5,000 ppm manifested itself as significantly 

decreased pup growth in all generations and matings. In 

addition, delayed sexual maturation was noted in first 

generation males at 5,000 ppm. For offspring toxicity, 

the NOAEL was 45 mg/kg-day and the LOAEL was 

136 mg/kg-day based on significantly decreased pup 

growth (MRID No. 43137101) (USEPA 2001h). 

Neurotoxicity 

In an acute neurotoxicity study, groups of Crl:CD BR 

rats (10/sex/dose) received a single oral administration 

of dicamba in corn oil at doses of 0, 300, 600, or 1,200 

mg/kg. At 300 mg/kg, transiently impaired respiration; 

rigidity upon handling, prodding or dropping; freezing 

of movement when touched; decreased arousal and 

fewer rears/minute compared to controls; and 

impairment of gait and righting reflex were observed in 

both sexes. In addition, males showed decreased 

forelimb grip strength. With the exception of the 

decrease in forelimb grip strength, which persisted until 

day 7, these effects were observed only on the day of 

dosing. In addition, at 600 mg/kg, both sexes showed 

decreases in locomotor activity and males showed 

significant decreases in tail flick reflex and a raised 

posture when placed in an open field. At the highest 

dose level tested (1,200 mg/kg), both males and females 

showed an impaired startle response to an auditory 

stimulus. In addition, males showed decreases in BW, 

BW gain, and food consumption. The LOAEL was 300 

mg/kg based on the several neurologic signs listed 

above; a NOAEL was not established (MRID No. 

42774104; USEPA 2001h). 

Mutagenicity 

Dicamba was negative in tests for mutagenicity 

(Extoxnet 1996c). 

Metabolism 

Dicamba was excreted rapidly by rats, mainly in the 

urine, when administered orally or subcutaneously; 1 to 

4% was excreted in the feces. Mice, rats, rabbits and 

dogs excreted 85% of an oral dose as unmetabolized 

dicamba in the urine within 48 hours of dosing. 

Eventually, between 90% and 99% of the dose was 

excreted unmetabolized in the urine. This indicates that 

dicamba is rapidly absorbed into the bloodstream from 

the gastrointestinal tract. When dicamba was ingested 

daily in the feed, the concentrations in different organs 

reached a steady state within 2 weeks. When daily 

intake stopped, storage in the organs declined rapidly. 

Therefore, dicamba does not bioaccumulate in 

mammalian tissues (Extoxnet 1996c). 

Diflufenzopyr 

Diflufenzopyr is the first a.i. from a chemical class 

called semicarbazones. It is registered for use on field 

corn and grass (USEPA 1999b). In plants, diflufenzopyr 

acts by inhibiting auxin transport, which causes an 

abnormal accumulation of auxins in meristematic shoot 

and root regions, disrupting the delicate auxin balance 

needed for plant growth (BASF 2001). The USEPA has 

completed its review of product chemistry, 

environmental fate, toxicology, ecological effects, and 

residue chemistry data, and their summary statement 

says, “Based on available data, diflufenzopyr has been 

determined to be of low toxicity to humans, birds, 

aquatic organisms, mammals and bees. Acute 

toxicology studies place technical-grade diflufenzopyr 

in Toxicity Category III (Table B-2). It is neither 

teratogenic nor carcinogenic. Additionally, the data 

indicate no significant risk to non-target organisms, and 

diflufenzopyr is not expected to pose a risk of 

groundwater contamination” (USEPA 1999b). 

Acute Toxicity 

Table B-2 lists the toxicity categories for technical 

diflufenzopyr. The term ‘technical’ refers to the 

commercial product that may contain trace impurities, 

as opposed to the pure chemical form. The acute oral 

toxicity study in rats showed an LD50 greater than 5,000 

mg/kg in males and females, placing it in Toxicity 

Category IV. The acute dermal toxicity study in rabbits 

showed an LD50 greater than 5,000 mg/kg in males and 

BLM Vegetation Treatments Using Herbicides B-6 June 2007 

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females, placing it in Toxicity Category IV. The acute 

inhalation toxicity study in rats showed an LC50 greater 

than 2.93 mg/L in males and females, which places it in 

Toxicity Category IV according to USEPA 1999b 

(although according to the table, it would be in Toxicity 

Category III). The primary eye irritation study in rabbits 

showed mild irritation resolved within 48 hours, placing 

it in Toxicity Category III. The primary dermal irritation 

study in rabbits showed no irritation, placing it in 

Toxicity Category IV. The primary dermal sensitization 

study in guinea pigs did not exhibit any sensitization 

potential (USEPA 1999b). 

Subchronic Toxicity 

In a subchronic study in rats, Wistar rats were fed test 

diets containing technical diflufenzopyr at dose levels of 

0, 1,000, 5,000, 10,000 and 20,000 ppm for a period of 

13 weeks. The NOAEL was identified as 5,000 ppm 

(equal to 352 mg/kg-day for males, and 431 mg/kg-day 

for females) based on lower mean BW gain and 

decreased food efficiency in the 10,000 and 20,000 ppm 

groups for both sexes. Additional findings were 

decreased food intake and slight changes in blood 

chemistry (i.e., slight increases in cholesterol and 

alanine aminotransferase and slight decreases in 

chloride levels). Histopathological findings included an 

increased incidence of foamy macrophages in the lungs 

in the 10,000 and 20,000 ppm groups and testicular 

atrophy in the 20,000 ppm group. Following the 4-week 

recovery period, the only treatment-related effects that 

showed partial or no evidence of recovery were foamy 

macrophages in the lungs and testicular atrophy 

(USEPA 1999b). 

In a subchronic study in mice, CD-1 mice were dosed 

with diflufenzopyr at 0, 350, 1,750, 3,500, or 7,000 ppm 

in the diet for 13 weeks. The NOAEL was determined 

to be the HDT of 7,000 ppm (1,225 mg/kg-day in males 

and 1,605 mg/kg-day in females), as no clear toxic 

effects were observed (USEPA 1999b). 

In a subchronic study in dogs, diflufenzopyr was 

administered to beagle dogs in the diet at dose levels of 

0, 1,500, 10,000, or 30,000 ppm for 13 weeks. The 

LOAEL for this study is 10,000 ppm (403 mg/kg-day in 

males and 424 mg/kg-day in females), based on the 

occurrence of erythroid hyperplasia in the bone marrow, 

extramedullary hemopoiesis in the liver, and 

hemosiderin deposits in Kupffer cells. The NOAEL is 

1,500 ppm (58 mg/kg-day in males and 59 mg/kg-day in 

females; USEPA 1999b). 

In a subchronic dermal toxicity study, technical 

diflufenzopyr was administered by dermal application 

to male and female New Zealand White rabbits at dose 

levels of 0, 100, 300, or 1,000 mg/kg per application. 

Duration of application was 6 hours a day, daily for 21 

to 24 consecutive days. The NOAEL for systemic 

toxicity was determined to be 1,000 mg/kg-day, since 

there were no apparent signs of treatment-related 

systemic effects observed in male or female rabbits at 

any dose level tested. A NOAEL for dermal effects 

could not be determined since local dermal irritation 

was observed at all dose levels (there were no 

corresponding findings upon histopathological 

examination, indicating that the dermal effects were all 

local; USEPA 1999b). 

Chronic Toxicity/Carcinogenicity 

In a chronic toxicity study in dogs, diflufenzopyr was 

administered to beagle dogs in the diet at dose levels of 

0, 750, 7,500 or 15,000 ppm for 52 weeks. The LOAEL 

for this study is 7,500 ppm (299 mg/kg-day for males 

and 301 mg/kg-day for females), based on erythroid 

hyperplasia in the bone marrow in bone sections, 

reticulocytosis, and increased hemosiderin deposits in 

the liver, kidneys, and spleen. The NOAEL is 750 ppm 

(26 mg/kg-day for males and 28 mg/kg-day for females; 

USEPA 1999b). 

In a mouse carcinogenicity study, male and female CD1 mice were fed test diets containing technical 

diflufenzopyr at dietary concentrations of 0, 700, 3,500, 

or 7,000 ppm for a period of 78 weeks. The NOAEL for 

systemic toxicity was determined to be 7,000 ppm 

(equal to 1,037 mg/kg-day for males and 1,004 mg/kgday for females). There were no treatment-related 

effects observed at any dose level tested in male rats. 

There was a slight, but statistically significant lower 

mean overall BW gain for females in the 7,000 ppm 

group, primarily due to decreased gain/increased weight 

loss during the second year of the study. In the absence 

of any other treatment-related findings, this result was 

not considered to be an adverse, toxicologically 

significant finding. There was no evidence of oncogenic 

potential of diflufenzopyr for male and female mice at 

any dose level tested (USEPA 1999b). 

In a combined chronic toxicity/carcinogenicity study, 

male and female Wistar rats were fed test diets 

containing technical diflufenzopyr at dietary 

concentrations of 0, 500, 1,500, 5,000, or 10,000 ppm 

for a period of 104 weeks. The NOAEL for systemic 

toxicity was identified as 5,000 ppm (equal to 236 

mg/kg-day for males and 323 mg/kg-day for females). 

BLM Vegetation Treatments Using Herbicides B-7 June 2007 

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Treatment-related effects in the 10,000 ppm group were 

significantly lower BW and BW gains throughout the 

study period and decreased food efficiency. There was 

no evidence of oncogenic potential of diflufenzopyr at 

any dose level tested (USEPA 1999b). 

Developmental Toxicity 

In a developmental toxicity study, technical 

diflufenzopyr was administered by gavage to female 

Sprague Dawley rats at dose levels of 0, 100, 300, or 

1,000 mg/kg-day from days 6 through 15 of gestation. 

The maternal NOAEL is 300 mg/kg-day and the 

maternal LOAEL is 1,000 mg/kg-day based on 

decreases in food consumption and weight gain. 

Developmental effects, characterized as significantly 

lower fetal BWs in males and skeletal variations, 

exhibited as incompletely ossified and unossified sternal 

centra and reduced fetal ossification sites for caudal 

vertebrae, were observed at 1,000 mg/kg-day. The 

developmental LOAEL is 1,000 mg/kg-day, based on 

decreased fetal BWs and skeletal variations. The 

developmental NOAEL is 300 mg/kg-day (USEPA 

1999b). 

In a developmental toxicity study, technical 

diflufenzopyr was administered by gavage to female 

New Zealand White rabbits at dose levels of 0, 30, 100, 

or 300 mg/kg-day from days 6 through 19 of gestation. 

The maternal LOAEL is 100 mg/kg-day, based on 

minimal reductions in BW gain with no reduction in 

food consumption and clinical signs of toxicity 

(abnormal feces). The maternal NOAEL is 30 mg/kgday. Developmental effects, characterized as significant 

increases in the incidence of supernumerary thoracic rib 

pair ossification sites, occurred at the 300 mg/kg-day 

dose. No treatment-related developmental effects were 

noted at the low and mid doses. The developmental 

LOAEL is 300 mg/kg-day based on increased skeletal 

variations (supernumerary rib ossification sites). The 

developmental NOAEL is 100 mg/kg-day (USEPA 

1999b). 

Reproductive Toxicity 

In a 2-generation reproduction study, technical 

diflufenzopyr was administered continuously to Wistar 

rats at dose levels of 0, 500, 2,000, or 8,000 ppm in the 

diet. The systemic LOAEL is 2,000 ppm based on 

reduced BW gain, increased food consumption, and 

increased seminal vesicle weights. The systemic 

NOAEL is 500 ppm. The reproductive LOAEL is 8,000 

ppm based on lower live birth and viability indices, total 

pre-perinatal loss, reduced BWs and BW gain during 

lactation, a higher proportion of runts, and a higher 

percentage of offspring with no milk in the stomach. 

The reproductive NOAEL is 2,000 ppm (113-176 

mg/kg-day; USEPA 1999b). 

Neurotoxicity 

In an acute neurotoxicity study, diflufenzopyr was 

administered by gavage to Crl:CD BR rats at dose levels 

of 0, 125, 500, or 2,000 mg/kg. Diflufenzopyr had no 

definite impact on neurotoxic responses, although a few 

abnormalities were observed in the functional battery on 

the day of dosing. A decrease in immediate righting 

responses that was observed in several males in all 

treatment groups was not concentration-dependent. 

Nasal staining was observed in more rats in the 2,000 

mg/kg treatment groups (six males; three females), but 

was not considered a definite or significant response to 

treatment. Lower mean brain weights in all female 

treatment groups lacked associated macroscopic and 

microscopic histopathological changes, and were only 4 

to 5% lower than the control brain weight. Mean 

locomotor activities for the 2,000 mg/kg female 

treatment groups were decreased on days 7 and 14 after 

dosing, but the pattern of activity for the individual 

animals was similar to the individual controls over time. 

There were no definite treatment-related differences in 

BWs or food consumption in any of the treatment 

groups. There was no evidence of treatment-related 

neuropathology in the 2,000 mg/kg treatment group. A 

LOAEL was not established. The NOAEL for acute 

neurotoxicity is 2,000 mg/kg (the limit dose; USEPA 

1999b). 

In a subchronic neurotoxicity study, diflufenzopyr was 

administered in the diet to Crl:CD BR rats at dose levels 

of 0, 25, 75, or 1,000 mg/kg-day for 13 weeks. No 

treatment-related neurotoxicological effects were 

observed at any treatment level. A LOAEL for 

neurotoxicological effects was not established; the 

NOAEL was 1,000 mg/kg-day for both sexes. 

Treatment-related toxic effects (other than neurotoxic 

effects) were observed at the 1,000 mg/kg-day treatment 

level. The toxicological LOAEL for this study is 1,000 

mg/kg-day, based on decreased BW gains for both 

sexes. The toxicological NOAEL is 75 mg/kg-day 

(USEPA 1999b). 

Mutagenicity 

Diflufenzopyr tested negative for mutagenic potential in 

four assays: a microbial (Salmonella typhimurium) 

mutagenicity assay; an in vitro mammalian cell (mouse 

lymphoma) gene mutation assay; an in vivo mouse bone 

BLM Vegetation Treatments Using Herbicides B-8 June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

marrow micronucleus assay; and an unscheduled DNA 

synthesis assay (USEPA 1999b). 

Metabolism 

In a rat metabolism study, radiolabeled diflufenzopyr 

was administered to Wistar rats as a single intravenous 

dose at 1 mg/kg-day, a single oral dose (gavage) at 10 

or 1,000 mg/kg or a single dose at 10 mg/kg following a 

14-day pretreatment with unlabeled diflufenzopyr at 10 

mg/kg. Following oral administration, diflufenzopyr 

was partially absorbed and rapidly eliminated. By oral 

administration, 20 to 44% of the dose was eliminated in 

urine and 49 to 79% in feces. By contrast, intravenously 

dosed rats excreted 61 to 89% of the dose in urine. 

Biliary elimination accounted for 3 to 19% of the dose 

in all dose groups. Elimination half-life in urine and 

feces was 5.2 to 6.9 hours for all single dose groups and 

7.7 to 10.8 hours for all repeat oral dose groups. Total 

radioactive residues in tissues from rats in all dose 

groups were less than 3% of the administered dose. 

Blood residue levels for all dose groups were less than 

1% of the administered dose at all sampling intervals 

through 72 hours post-dose. Diflufenzopyr was 

eliminated in urine, feces, and bile primarily as 

unchanged parent compound (USEPA 1999b). 

A metabolism study of diflufenzopyr was also 

conducted in laying hens and lactating goats. The data 

showed diflufenzopyr was rapidly eliminated from the 

animals. With a feeding level of 10 ppm in the diet, 

residue levels in edible tissues, milk, and eggs were less 

than 0.12 ppm. The metabolite profile in rat was similar 

in hen and goat (USEPA 1999b). These studies show 

that diflufenzopyr is rapidly eliminated as unchanged 

parent compound. 

Diquat 

Diquat dibromide is a non-selective contact herbicide, 

algicide, desiccant, and defoliant. As an 

herbicide/algicide, it is used to control broadleaf and 

grassy weeds in non-crop and aquatic areas. As a 

desiccant/defoliant, it is used in seed crops and potatoes 

(USEPA 1995). Diquat dibromide is rapidly absorbed 

into the leaves of plants, but usually kills the plant 

tissues necessary for translocation too quickly to allow 

movement to other parts of the plant. It does not kill 

roots, but it does kill the leaves and stems it contacts. It 

produces rapid results by interfering with 

photosynthesis. However, the sudden addition of 

decaying plant biomass to the water column can result 

in decreased oxygen levels (New York State 

Department of Environmental Conservation 1981 cited 

in McLaren/Hart 1995; Extoxnet 1996a). 

Acute Toxicity 

Table B-2 lists the toxicity categories for diquat 

dibromide. Diquat dibromide is not acutely toxic via the 

oral (Toxicity Category III) and inhalation (Toxicity 

Category III) routes of exposure. Diquat dibromide is 

moderately to severely toxic via the dermal route of 

exposure, as evidenced by the acute dermal toxicity 

study (Toxicity Category II). However, diquat 

dibromide was not found to be a dermal irritant 

(Toxicity Category IV) or a dermal sensitizer. Diquat 

dibromide is toxic to the eye, as evidenced by the eye 

irritation study, which showed slight to severe eye 

irritation following acute exposure (Toxicity Category 

II; USEPA 2001e). 

Subchronic Toxicity 

In a subchronic dermal toxicity study (MRID No. 

40308101), Sprague-Dawley rats were exposed to 

technical diquat dibromide by dermal application at 

dose levels of 0, 5, 20, 40, or 80 mg/kg-day (as diquat 

cation). Duration of application was 6 hours a day, for 

21 consecutive days. High mortality was observed in the 

40 mg/kg (67%) and 80 mg/kg (90%) groups. Effects in 

the nonsurvivors included hypothermia, hypoactivity, 

dyspnea, cyanosis, pale extremities, and emaciated 

appearance. The LOAEL for systemic toxicity was 

determined to be 20 mg/kg-day, based on effects 

including sores, severe erythema, fissures, acute 

necrotizing purulent dermatitis, and degeneration of hair 

follicles and sebaceous glands, all at the application site. 

The NOAEL for systemic toxicity was 5 mg/kg-day, 

based on mortality and clinical signs at 20 mg/kg-day 

(LOAEL). Dermal irritation and tissue destruction 

occurred at the application site at all dose levels 

(USEPA 2001e). 

In a subchronic inhalation toxicity study (MRID No. 

40301701), Fischer 344 rats were exposed to respirable 

aerosols of technical diquat at concentrations of 0, 0.49, 

1.1, or 3.8 microgram per liter (μg/L; as diquat cation). 

Exposure duration was 6 hours a day, 5 days per week 

for 21 days. Test animals, which were exposed whole 

body, and control animals were rinsed with tap water 

and blotted dry after each exposure to minimize oral 

exposure from grooming. Treatment-related effects 

observed at the lowest concentration tested included 

significant increases in mean lung weight, mottling and 

reddening of the lungs, and lung lesions. The NOAEL is 

0.1 μg/L (males 0.024 mg/kg-day; females 0.026 

BLM Vegetation Treatments Using Herbicides B-9 June 2007 

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HUMAN HEALTH RISK ASSESSMENT

mg/kg-day), based on increased lung weights and 

microscopic lesions in the lungs at the LOAEL of 0.49 

μg/L (males 0.117 mg/kg-day, females 0.128 mg/kgday (USEPA 2001e). 

Chronic Toxicity/Carcinogenicity 

In a chronic toxicity study in dogs (MRID No. 

41730301), technical diquat dibromide was 

administered to beagle dogs in the diet at dose levels of 

0, 0.5, 2.5, or 12.5 mg/kg-day (as diquat cation) for 52 

weeks. No treatment-related effects were detected at 

any dose level in terms of survival, clinical signs, 

hematology, clinical chemistry, urinalysis, and gross 

pathology (except eye). Decreased BW gains were 

observed only during the first 2 weeks of dosing in both 

sexes at the high-dose level. At necropsy, bilateral lens 

opacity was observed in all high-dose males and threefourths of the high-dose females. The NOAEL is 0.5 

mg/kg-day, based on unilateral cataracts in females and 

decreased weight of the epididymides in males at the 

systemic LOAEL of 2.5 mg/kg-day (USEPA 2001e). 

In a combined chronic toxicity/carcinogenicity study 

(MRID No. 00145855), male and female SpragueDawley rats were fed diets containing diquat cation at 

dietary concentrations of 0, 5, 15, 75, or 375 ppm for 

104 weeks. Treatment-related effects observed in the 75 

ppm group were lens opacity, marked or severe 

cataracts, and extralenticular lesions (adhesions, retinal 

detachment and synechia). Therefore, the systemic 

LOAEL is 75 ppm (equal to 2.91 mg/kg-day for males; 

3.64 mg/kg-day for females) and the NOAEL for 

systemic toxicity was set at 15 ppm (equal to 0.58 

mg/kg-day for males; 0.72 mg/kg-day for females). 

There was no treatment-related increase in tumor 

incidence in either sex (USEPA 2001e). 

In a mouse carcinogenicity study (MRID No. 

42219801), male and female CD-1 mice were fed diets 

containing technical diquat dibromide at dietary 

concentrations of 0, 30, 100, or 300 ppm (as diquat 

cation) for 104 weeks (2 years). Treatment-related 

effects observed in the 100 ppm group included eye 

discharge, decreased weight gain, increased kidney 

weight, tubular dilatation of the kidneys, tubular hyaline 

droplet formation in the kidneys, and lymphoid 

proliferation. Therefore the systemic LOAEL is 100 

ppm (equal to 11.96 mg/kg-day for males; 16.03 mg/kgday for females). The NOAEL for systemic toxicity was 

determined to be 30 ppm (equal to 3.56 mg/kg-day for 

males; 4.78 mg/kg-day for females). Diquat dibromide 

was not carcinogenic in male or female CD-1 mice 

(USEPA 2001e). 

The database for carcinogenicity is considered 

complete. The carcinogenic potential of diquat 

dibromide was classified as Category E (evidence of 

noncarcinogenicity for humans) based on a lack of 

evidence of carcinogenicity in studies with two species, 

rat and mouse (USEPA 2001e). 

Developmental Toxicity 

In a developmental toxicity study (MRID No. 

41198902), diquat dibromide was administered by 

gavage to female Wistar rats at dose levels of 0, 4, 12, 

or 40 mg/kg-day (as diquat cation) on days 7 through 16 

of gestation. The LDT of 4 mg/kg-day was associated 

with decreased maternal weight gain and food 

consumption. The maternal LOAEL is <4 mg/kg-day 

and the NOAEL for maternal toxicity is not established. 

Developmental effects, characterized as significantly 

lower fetal BWs, increased incidence of a hemorrhagic 

kidney, and skeletal variations exhibited as 

incompletely ossified and unossified sternal centra and 

reduced fetal ossification sites for caudal vertebrae, 

were observed at 40 mg/kg-day, the HDT. The 

developmental LOAEL is 40 mg/kg-day, based on 

decreased fetal BWs and skeletal variations. The 

developmental NOAEL is 12 mg/kg-day (USEPA 

2001e). 

In another developmental toxicity study (MRID No. 

41198901), diquat dibromide was administered by 

gavage to female New Zealand White rabbits at dose 

levels of 0, 1, 3, or 10 mg/kg-day (as diquat cation) on 

days 7 through 19 of gestation. The maternal LOAEL is 

3 mg/kg-day, based on decreased maternal weight gain 

and food consumption. The maternal NOAEL is 1 

mg/kg-day. Developmental effects occurred only in the 

high dose group, characterized as increases in the 

incidence of friable livers, mottled livers, partially 

ossified ventral tubercle of cervical vertebrae, and 

partially ossified and unossified sternebra. The 

developmental LOAEL is 10 mg/kg-day (the highest 

dose tested [HDT]), and the developmental NOAEL is 3 

mg/kg-day (USEPA 2001e). 

In a third developmental toxicity study (MRID No. 

00061637), diquat dibromide was administered by 

gavage to female Alderley Park strain SPF albino mice 

at dose levels of 0, 1, 2, and 4 mg/kg-day (as diquat 

cation) on days 6 through 15 of gestation. The maternal 

LOAEL is 2 mg/kg-day, based on effects including a 

decreased maternal weight gain, piloerection, dyspnea, 

respiratory noise, and abnormal posture. The maternal 

NOAEL is 1 mg/kg-day. Developmental effects 

occurred only in the high dose group, characterized as 

BLM Vegetation Treatments Using Herbicides B-10 June 2007 

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 HUMAN HEALTH RISK ASSESSMENT

decreased fetal BW and increases in the incidence of 

skeletal alterations. The developmental LOAEL is 4 

mg/kg-day (the HDT), and the developmental NOAEL 

is 2 mg/kg-day (USEPA 2001e). 

Reproductive Toxicity 

In a 2-generation reproduction study (MRID No. 

41531301), diquat dibromide was administered 

continuously in the diet to Wistar rats at dose levels of 

0, 16, 80, or 400/240 ppm (as diquat cation). Because 

adverse effects were seen in the F1 animals (i.e., the 

first generation animals), the high dose for the F0 

animals (i.e., the parents) was reduced from 400 ppm to 

240 ppm 4 weeks after selection. There were no 

treatment-related deaths. Parental toxicity was observed 

in both generations, mostly at the high-dose level, as 

increased incidences of clinical signs, ophthalmoscopic 

signs, decreased body-weight gains and decrease food 

consumption during the premating period. 

Ophthalmoscopic examination revealed partial/total 

cataracts at the high-dose level in both sexes and both 

generations following the premating dosing periods. At 

the high-dose level in both generations and both sexes, 

the incidence of partial and/or total cataract increased 

with time. 

The systemic LOAEL is 4 mg/kg-day (80 ppm) based 

on decreased BW gain, decreased food consumption, 

and increased incidences of eye opacity, lenticular 

cataracts, and iritis. The systemic NOAEL is 0.8 mg/kgday (16 ppm). The reproductive LOAEL is 400/240 

ppm (20/12 mg/kg-day), based on a decreased number 

of live pups per litter and decreased pup BW gain. The 

reproductive NOAEL is 4 mg/kg-day (80 ppm; USEPA 

2001e). 

Neurotoxicity 

In an acute neurotoxicity study (MRID No. 42666801), 

technical diquat dibromide was administered by gavage 

to Sprague-Dawley rats at dose levels of 0, 25, 75, or 

150 mg/kg (as diquat cation). Diquat dibromide had no 

definite impact on neurotoxic responses in functional 

observational battery and motor activity measurements 

at 6 hours after dosing and on days 8 and 15. Clinical 

evidence of neurotoxicity included increased incidence 

of diarrhea and nasal staining in females in the 75 

mg/kg group. Females in the 150 mg/kg group showed 

additional effects of piloerection, upward curvature of 

the spine, hunched posture, and tip toe gait. The 

systemic NOAEL is 75 mg/kg, based on clinical signs 

and decreased body-weight gain at the systemic 

LOAEL of 150 mg/kg (USEPA 2001e). 

In a subchronic neurotoxicity study (MRID No. 

42616101), technical diquat dibromide was 

administered in the diet to Alpk:APfSD rats at dose 

levels of 0, 20, 100, or 400 ppm for 13 weeks. 

Treatment-related toxic effects observed in the 400 ppm 

group included decreased BWs, decreased BW gain, 

decreased food utilization, incidence of total cataracts, 

and posterior opacities of the lens. There was no 

evidence of neurotoxicity. The NOAEL for 

neurotoxicity is 400 ppm (32.4 mg/kg-day for males, 

38.5 mg/kg-day for females), the HDT. The systemic 

NOAEL is 100 ppm (8.0 mg/kg-day for males, 9.5 

mg/kg-day for females), based on cataracts, decreased 

body-weight gain, and food utilization at the systemic 

LOAEL for this study of 400 ppm (32.4 mg/kg-day for 

males, 38.5 mg/kg-day for females; USEPA 2001e). 

Mutagenicity 

Diquat dibromide was found to be negative for 

mutagenic potential in several assays. These included 

microbial gene mutation assays (Ames assays using five 

strains of Salmonella typhimurium and one strain of 

Escherichia coli; MRID No. 40323103), two structural 

chromosome aberration tests, an in vivo mouse bone 

marrow micronucleus assay (MRID No. 40323104), an 

in vivo dominant lethal assay in mice (MRID No. 

00061636), and assays of other genotoxic effects (e.g., 

unscheduled DNA synthesis in rat hepatocytes in vitro; 

MRID No. 40323107). 

Diquat dibromide was positive in one gene mutation test 

(in vitro mouse lymphoma cell assay; MRID No. 

40323101), in one chromosome aberration test (in vitro

human blood lymphocytes from one male and one 

female donor; MRID No. 40323106; USEPA 1995), 

and in an in vitro genotoxicity assay. However, the 

response was generally weak and was observed at 

cytotoxic levels (levels that are toxic to the cell; USEPA 

2001e). 

Metabolism 

In a rat metabolism study (MRID No. 0055107), [14C]-

labeled diquat dibromide was administered to rats. 

Ninety percent of the orally administered dose was 

eliminated in feces indicating poor gastrointestinal 

absorption. In addition, rats injected subcutaneously 

with [14C]-diquat dibromide excreted nearly all of the 

labeled material in the urine within 2 days (USEPA 

2001e). 

Following a single oral dose of 60 mg/kg (in the form of 

the diquat cation) of [14C]-diquat dibromide, only 5% of 

BLM Vegetation Treatments Using Herbicides B-11 June 2007 

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HUMAN HEALTH RISK ASSESSMENT

the radioactivity was recovered in the urine within 7 

days (MRID No. 00065592). Whole body 

autoradiography indicated that diquat dibromide was 

initially concentrated in the cartilaginous tissues, liver, 

and bladder. After 24 hours, the only radioactivity 

detected was in the bladder and intestines. Feeding 250 

mg/kg (as the diquat cation) of unlabeled diquat 

dibromide to rats for 2, 4, or 8 weeks resulted in no 

accumulation of diquat dibromide in tissues including 

brain, liver, lung, stomach, small and large intestines, 

muscle, and blood. The kidneys retained 0.18 to 1.17 

ppm of diquat dibromide for 2 to 8 weeks (USEPA 

1995). 

Labeled [14C]-diquat dibromide was administered to rats 

by stomach tube or by subcutaneous injection (doses not 

specified) for 4 days (MRID No. 00065593). The rats 

excreted 6.3% of the orally administered diquat 

dibromide in urine and 89.3% in feces within 4 days, 

most during the first 48 hours (5.3% was unmetabolized 

diquat and 1% was diquat monopyridone, diquat 

dipyridone, and unidentified metabolites). Of the 

radioactivity in the sulfuric acid-extractable fraction 

(65.5%), 57.1% was unmetabolized diquat, 4.3% was 

diquat monopyridone, and 4.1% represented 

unidentified metabolites. Following subcutaneous 

administration, 87.1% of the dose was recovered in the 

urine within 4 days (5% within 24 hours), and 78.8% of 

the radioactivity was unmetabolized diquat. The 

amounts of other metabolites were not reported 

(USEPA 1995). 

Fluridone 

Fluridone is a systemic herbicide used to manage 

aquatic vegetation on ponds, lakes, reservoirs, canals, 

and rivers. Fluridone is absorbed from the water by the 

shoots of submerged plants and from the hydrosoil by 

the roots of aquatic vascular plants. It acts by inhibiting 

the synthesis of carotenoid pigments that protect 

chlorophyll from photodegradation. In the absence of 

the colored carotenoid beta-carotene, chlorophyll is 

destroyed and chloroplasts are disrupted in the sunlight, 

causing cellular bleeding. Affected plants become white 

or chlorotic at growing points and slowly die (Bartels 

and Watson 1978 cited in McLaren/Hart 1995, USEPA 

1986a). 

Acute Toxicity 

Table B-2 lists the toxicity categories for fluridone 

(technical). The USEPA (1986a) reported that technical 

grade fluridone is in Toxicity Category IV (very slight) 

for acute oral exposure in the rat. This is supported by 

oral LD50 values of more than 10,000 mg/kg for both 

the rat and the mouse (Elanco 1981 cited in

McLaren/Hart 1995, SePRO 2002). 

A dermal LD50 of greater than 500 mg/kg with no skin 

irritation was originally reported for rabbits exposed to 

technical fluridone (USEPA 1986b), but an LD50 value 

of greater than 2,000 mg/kg was later reported (USEPA 

1988 cited in Massachusetts Department of 

Environmental Management/Massachusetts Department 

of Environmental Protection ((MA DEM/MA DEP) 

2003). SePRO (2002) cites an LD50 of more than 5,000 

mg/kg with no signs of systemic toxicity for the rabbit. 

The more recently reported values place fluridone in 

Category III (slight) for acute dermal effects. 

The USEPA reported that fluridone is moderately toxic 

through acute inhalation exposure, equivalent to 

Toxicity Category II (USEPA 1986a). However, LC50

values for rats exposed to technical fluridone at 

concentrations of 2.13 mg/L (1 hour exposure) and 4.12 

mg/L (4 hour exposure; USEPA 1986b and SePRO 

2002), indicate that fluridone is in Category III (slight) 

for acute inhalation effects. 

Eye irritation has been demonstrated as moderate to 

severe in rabbits with effects including redness, corneal 

dullness, and conjunctivitis, placing fluridone in 

Category II (USEPA 1986a, USEPA 1988 cited in MA 

DEM/MA DEP 2003). However, the manufacturer 

states that ocular irritation was not persistent and 

resulted primarily from the abrasive nature of the 

technical material, therefore fluridone should be in 

Category IV (slight) for eye irritation effects (SePRO 

2002). Fluridone was found to be neither irritating nor a 

sensitizer to rabbit skin at 2,000 mg/kg (USEPA 1988 

cited in MA DEM/MA DEP 2003), thus placing 

fluridone in Category IV for primary skin irritation, and 

designating fluridone as not a skin sensitizer. 

Subchronic Toxicity 

In a subchronic feeding study, rats were fed a test diet 

containing technical fluridone at a range of dose levels 

including 0, 330, and 1,400 ppm for a period of 90 days 

(MRID No. 00135208; USEPA 1986b, USEPA 1988 

cited in MA DEM/MA DEP 2003). Effects observed at 

the 1,400 ppm level included increased liver and kidney 

weights as well as histological identification of liver 

centrilobular hypertrophy (USEPA 1986b). A NOAEL 

of 30 mg/kg-day is reported in USEPA (1988 cited in

MA DEM/MA DEP 2003), based on increased liver 

weights at the 166 mg/kg-day level and no treatmentrelated effects at the 330 ppm level. A NOAEL of 53 

BLM Vegetation Treatments Using Herbicides B-12 June 2007 

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 HUMAN HEALTH RISK ASSESSMENT

mg/kg-day is cited in McLaren/Hart (1995) and 

referenced to the New York State Department of Health 

(NYSDOH 1986), but no information on the derivation 

of the NOAEL is provided. The USEPA (2002a) does 

not cite a NOAEL for this study, but reports a LOAEL 

of 166 mg/kg-day based on increased liver weights at 

the lowest dose tested (LDT). 

In a subchronic feeding study, mice were dosed with 

fluridone at a range of levels including 0, 62, and 560 

ppm in the diet for 90 days (USEPA 1986b, USEPA 

1988 cited in MA DEM/MA DEP 2003). Effects 

observed at the 560 ppm level included histological 

identification of liver centrilobular hypertrophy 

(USEPA 1986b). Morphological changes in the liver 

and an increase in absolute liver weight in males at a 

fluridone concentration of 0.033% are reported in 

USEPA (1988 cited in MA DEM/MA DEP 2003). 

Partial enlargement of livers was observed at the 16.5 

mg/kg-day level and no treatment-related effects at the 

62 ppm level. A NOAEL of 9.3 mg/kg-day is cited in 

McLaren/Hart (1995) and referenced to NYSDOH 

(1986), but no information on the derivation of the 

NOAEL is provided. The USEPA (2002a) does not cite 

this study. 

In a subchronic feeding study in dogs, fluridone was 

administered in the diet at a range of dose levels up to 

200 mg/kg-day for 90 days (MRID No. 0082234). A 

NOAEL of 200 mg/kg-day is based on the observation 

of no treatment-related effects at the HDT (Elanco 

1978a as cited in USEPA 2002a). 

In a subchronic dermal toxicity study, fluridone was 

applied to rabbit skin at doses including 0, 192, 384, and 

768 mg/kg-day for 21 days (MRID No. 00070933). An 

increase in organ weight was noted at 384 mg/kg-day. 

The NOAEL for systemic effects was determined to be 

the HDT of 768 mg/kg-day, since no systemic effects 

were noted at any dose. A NOAEL for dermal effects 

was not determined since dose-dependent skin irritation 

was observed at all doses (USEPA 1988 cited in MA 

DEM/MA DEP 2003; SePRO 2002). 

Chronic Toxicity/Carcinogenicity 

In a combined chronic toxicity/carcinogenicity study in 

rats, male and female Fischer rats were fed test diets 

containing technical fluridone at dietary concentrations 

of 0, 200, 650, or 2,000 ppm (0, 8, 25, or 81 mg/kg-day) 

for a period of 104 weeks (MRID Nos. 00103251, 

00103305). Treatment-related effects observed at 650 

ppm included glomerulonephritis, atrophic testes, eye 

keratitis, and decreased BW and organ weights. The 

NOAEL for systemic toxicity was set at 200 ppm (equal 

to 8 mg/kg-day). There was no evidence of oncogenic 

potential of fluridone at any dose levels tested (USEPA 

2002a). 

In a combined chronic toxicity/carcinogenicity study in 

mice, mice were administered fluridone concentrations 

in the diet including 0, 100, and 330 ppm for 104 weeks 

(MRID Nos. 00103252, 00103305). According to 

USEPA (1988 cited in MA DEM/MA DEP 2003), there 

was a dose-dependent increase in alkaline phosphatase 

in males exposed at the HDT of 330 ppm. No other 

toxic effects or lesions are reported at any other doses. 

The clinical NOAEL is equal to the HDT as evidenced 

by no deaths, no obvious toxic effects, and no 

histopathological lesions. McLaren/Hart (1995) reports 

a NOAEL for systemic toxicity of 11.6 mg/kg-day from 

this study (NYSDOH 1986). A NOAEL of 15 mg/kgday (equal to 100 ppm) is reported by USEPA (2002a). 

There was no evidence of oncogenic potential of 

fluridone at any of the dose levels tested. 

In a 1-year chronic feeding study in which dogs were 

administered fluridone by capsule in food, several 

effects including weight loss, increased liver weight, 

and increased levels of alkaline phosphatase were 

reported at a dose level of 150 mg/kg-day (MRID No. 

00103336); a NOAEL of 75 mg/kg-day was 

extrapolated from this study (USEPA 1988 cited in MA 

DEM/MA DEP 2003, USEPA 2002a). 

Developmental Toxicity 

In an initial developmental toxicity study in which rats 

were exposed to up to 200 mg/kg-day of fluridone, no 

developmental effects were observed at any of the 

levels tested. However, the study was not useful for 

regulatory purposes because no maternal toxicity or 

fetotoxicity was seen at the HDT (200 mg/kg-day); 

therefore, the USEPA requested that a second study be 

conducted (USEPA 1986a). 

In a subsequent rat developmental toxicity study, rats 

(second species) were administered fluridone by oral 

gavage in doses of 0, 100, 300, or 1,000 mg/kg-day 

(MRID No. 00159963). At 300 mg/kg-day there was a 

decrease in maternal BW, and a maternal NOAEL of 

100 mg/kg-day was established. At 1,000 mg/kg-day 

fetal weight loss and delayed ossification were noted; 

therefore the NOAEL for developmental effects was 

established at 300 mg/kg-day. Teratogenic effects 

(skeletal abnormalities in the fetus) were not observed 

in any dose group, so a teratogenic NOAEL of 1,000 

BLM Vegetation Treatments Using Herbicides B-13 June 2007 

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mg/kg-day was established at the HDT (USEPA 1988 

cited in MA DEM/MA DEP 2003, USEPA 2002a). 

In a pilot developmental toxicity study, rabbits were 

exposed to fluridone doses of 0, 250, 500, 750, or 1,000 

mg/kg-day. A maternal NOAEL of 500 mg/kg-day 

(based on effects on the mother) was identified resulting 

from maternal weight loss at the 750 mg/kg-day dose 

level. Fetal resorptions occurred in the 500 mg/kg-day 

dose group, and consequently the developmental 

NOAEL (based on effects on the offspring) in this study 

was set at 250 mg/kg-day (USEPA 1988 cited in MA 

DEM/MA DEP 2003). 

In a separate developmental toxicity study, rabbits were 

exposed to 0, 125, 300, or 750 mg/kg-day of fluridone 

during gestation (MRID No. 00103302 [USEPA 

2002a], MRID No. 00263157 [USEPA 2003a]). Effects 

including maternal weight loss and abortion were noted 

at the 300 mg/kg-day dose level. Therefore, the 

maternal NOAEL for this study was set at 125 mg/kgday. Teratogenic effects were not observed at any dose, 

so the NOAEL for teratogenic effects is the HDT, or 

750 mg/kg-day (USEPA 1988 cited in MA DEM/MA 

DEP 2003; USEPA 2002a). 

Reproductive Toxicity 

In a 3-generation reproduction study, technical fluridone 

was administered continuously in the diet to rats at dose 

levels of 0, 650, and 2,000 ppm (MRID No. 00103304). 

Since no maternal or teratogenic effects were observed 

at the HDT of 2,000 ppm, the maternal and teratogenic 

NOAEL is 2,000 ppm (100 mg/kg-day). The 

developmental NOAEL is 650 ppm (32.5 mg/kg-day), 

based on decreased pup weight reported at the 100 

mg/kg-day level (USEPA 2002a). 

Neurotoxicity 

Studies of fluridone neurotoxicity were not identified. 

No clinical signs of neurotoxicity or neuropathology 

were reported in any of the chronic or reproductive 

toxicity studies conducted. 

Mutagenicity 

Mutagenicity assays submitted for fluridone do not 

indicate potential for genotoxicity, gene mutation, or 

structural chromosomal aberration (USEPA 1986a). 

Fluridone was found to be negative for mutagenic 

potential in four assays: fluridone did not induce 

bacterial mutations in the Ames assay at the highest 

tested concentration of 1,000 ppm; a fluridone 

intraperitoneal dose of 500 mg/kg did not induce sister 

chromatid exchange in Chinese hamster bone marrow 

cells; fluridone did not promote unscheduled DNA 

synthesis in rat hepatocytes when tested at a 

concentration of 300 ppm; and a single oral dose of 

2,000 mg/kg did not cause dominant lethal mutations in 

male rats (USEPA 1988 cited in MA DEM/MA DEP 

2003; SePRO 2002). 

Metabolism 

The residue of concern in drinking water is the parent 

compound fluridone (USEPA 1986a). The primary 

metabolite of fluridone in fish is Metabolite II1

. 

Metabolite II was identified as the major metabolite in 

laboratory hydrosoil studies. N-methyl formamide 

(NMF) was identified as a photolytic breakdown 

product in a laboratory study cited in McLaren/Hart 

(1995). Scientists were concerned with NMF being 

produced by the breakdown of fluridone since NMF has 

been shown to be teratogenic in rabbits at high doses 

and can penetrate human skin; however, NMF has not 

been identified in the natural environment 

(McLaren/Hart 1995). 

Absorption/excretion studies in rats indicate that a 

single oral dose of fluridone is rapidly absorbed, 

extensively metabolized and primarily excreted in the 

feces. The dose was excreted in 72 hours. More than 

80% was excreted in the feces and a trace was excreted 

in the urine (Arnold 1979 cited in McLaren/Hart 1995). 

Imazapic 

Imazapic is a member of the imidazolinone class of 

herbicides that selectively inhibit acetohydroxyacid 

synthetase, an enzyme in certain plant’s biosynthetic 

pathway of three amino acids–valine, leucine, and 

isoleucine. In contrast to plants, mammals do not 

possess the pathway to synthesize these three amino 

acids, and therefore are not susceptible to the primary 

effect pathway of imazapic (USEPA 2001a). 

Acute Toxicity 

Table B-2 lists the toxicity categories for imazapic. 

Imazapic results in low acute toxicity by oral, dermal, 

and inhalation routes of exposure, as well as eye and 

skin irritation (all studies are in Toxicity Category III or 

 

1

1-methyl-3-(4-hydroxyphenyl)-5-[3-(trifluoromethyl)phenyl]-

4(1H)-pyridinone 

BLM Vegetation Treatments Using Herbicides B-14 June 2007 

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 HUMAN HEALTH RISK ASSESSMENT

IV). Imazapic is not a dermal sensitizer (USEPA 

2001a). 

Subchronic Toxicity 

A 21-day dermal toxicity study in rabbits was 

conducted (MRID No. 42711420) where imazapic was 

applied to the clipped backs of New Zealand albino 

rabbits at targeted doses of 0, 250, 500, or 1,000 mg/kgday for 6 hours per day, 5 days per week, for 3 weeks. 

There were no systemic or developmental effects 

observed up to the HDT (1,000 mg/kg-day), therefore a 

toxicity endpoint was not selected from this study 

(USEPA 2001a). 

Chronic Toxicity/Carcinogenicity 

In a 24-month combined chronic feeding and 

carcinogenicity study (MRID No. 43320307), imazapic 

was administered in the diet to groups of 65 male and 

65 female Sprague-Dawley strain rats at doses of 0, 

5,000, 10,000 or 20,000 ppm. At the highest dose level 

tested (20,000 ppm), no treatment-related effects were 

observed. Also, no treatment-related increase in tumors 

of any kind was observed at any dose level. The 

NOAEL in this study for both male and female rats is 

the HDT, 20,000 ppm (1,029 mg/kg-day for males and 

1,237 mg/kg-day for females). A LOAEL was not 

determined. 

In an 18-month chronic feeding/carcinogenicity study 

(MRID No. 43320306), imazapic was administered in 

the diet to groups of 65 male and 65 female CD-1 strain 

mice at dose levels of 0, 1,750, 3,500 or 7,000 ppm. At 

the highest dose level tested (7,000 ppm, the HDT), no 

treatment-related effects were observed in either male or 

female mice. Statistically significant decreases in highand mid-dose male BWs during the first 26 weeks of the 

study were not convincing indicators of toxicity because 

the decreases were small, were noted even before 

initiation of treatment, and were not dose-related. No 

treatment-related increase in tumors of any kind was 

observed in either male or female mice at any dose 

level. The NOAEL in this study for both male and 

female mice is 7,000 ppm (1,134 mg/kg-day for males 

and 1,442 mg/kg-day for females). A LOAEL was not 

determined (USEPA 2001a). 

Developmental Toxicity 

In a developmental toxicity study (MRID No. 

42711422), groups of 25 impregnated Sprague-Dawley 

rats were administered imazapic via gavage at daily 

doses of 0, 250, 500 or 1,000 mg/kg-day on gestational 

days 6 through 15. There were no treatment-related 

effects on mortality, abortions, clinical signs, BW, BW 

gain, food consumption, or Caesarian section 

parameters at any of the doses, including 1,000 mg/kgday. Therefore, the maternal NOAEL is 1,000 mg/kgday, and the maternal LOAEL is greater than 1,000 

mg/kg-day. There were no treatment-related effects on 

resorptions, pre- and post-implantation losses, fetal BW 

and sex ratio, or external, visceral, and skeletal 

malformations and anomalies. Therefore, the 

developmental NOAEL is 1,000 mg/kg-day, and the 

developmental LOAEL is greater than 1,000 mg/kgday. 

In a developmental toxicity study (MRID No. 

42711423), groups of 20 impregnated New Zealand 

White rabbits were administered imazapic via gavage 

during gestation days 7 through 19 at daily doses of 0, 

175, 350, 500, or 700 mg/kg-day. The occurrence of 

only seven litters at 700 mg/kg-day precluded a 

meaningful evaluation of developmental findings at this 

dose, therefore this dose was not considered further in 

the study. The LOAEL for maternal toxicity is 500 

mg/kg-day based on decreased BW gain and food 

consumption during the dosing period. The NOAEL for 

maternal toxicity is 350 mg/kg-day. Although there was 

an increase in fetal incidences of rudimentary ribs, the 

study authors concluded that these effects are not related 

to the treatment. Therefore, the NOAEL for 

developmental toxicity was set at 500 mg/kg-day, and 

the LOAEL for developmental toxicity is greater than 

500 mg/kg-day (USEPA 2001a). 

Reproductive Toxicity 

In a 2-generation rat reproduction study (MRID No. 

43320305), imazapic was administered by diet to two 

groups of 30 per sex Sprague-Dawley rats at levels of 0, 

5,000, 10,000, or 20,000 ppm. There were no 

compound-related effects in any parameter evaluated in 

either male or female parental animals or offspring of 

the first or second generation. Therefore, the parental, 

reproductive, and offspring NOAELs are 20,000 ppm, 

and the LOAELs are greater than 20,000 ppm (USEPA 

2001a). 

Neurotoxicity 

There are no neurotoxicity studies in rats or hens (which 

are a common test species for neurotoxic effects), and 

there were no neurotoxic clinical signs or 

histopathology observed in any of the other toxicity 

studies with imazapic (USEPA 2001a). 

BLM Vegetation Treatments Using Herbicides B-15 June 2007 

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HUMAN HEALTH RISK ASSESSMENT

Mutagenicity 

Imazapic was found to be negative in the following 

mutation assays: a reverse gene mutation assay using 

Salmonella strains (MRID No. 42711424); a 

chromosome aberration assay in Chinese hamster ovary 

cells (MRID No. 42711427); a forward mutation assay 

in Chinese hamster ovary cells (MRID No. 42711425); 

and a rat bone marrow/chromosomal aberration assay 

(MRID No. 42711426; USEPA 2001a). 

Metabolism 

A rat metabolism study demonstrated that only the 

unchanged parent compound was detected in the urine, 

which was the major route of excretion. These results 

indicated that imazapic was not metabolized to other 

compounds. There was no evidence of bioaccumulation 

of imazapic in tissues (USEPA 2001a). 

Sulfometuron Methyl 

Sulfometuron methyl is a non-selective, sulfonyl urea 

herbicide used mainly to control the growth of broadleaf 

weeds and grasses. The mode of action for the sulfonyl 

urea class is the inhibition of the synthesis of essential 

amino acids (Syracuse Environmental Research 

Associates [SERA] 1998). 

Acute Toxicity 

The USEPA has not developed acute toxicity categories 

for sulfometuron methyl (USEPA 2003b). Acute oral 

exposure to sulfometuron methyl results in a low order 

of toxicity. Neither mortality nor overt signs of toxicity 

were observed in rats given single oral doses of up to 

17,000 mg/kg (Trivits 1979 cited in SERA 1998, 

Dashiell and Hall 1980, Dashiell and Hinckle 1980). 

The acute dermal toxicity of the compound is also low. 

The LD50 values for exposure through the skin ranges 

from over 2,000 mg/kg in female rabbits to over 8,000 

mg/kg in male rabbits (USEPA 1990 cited in Extoxnet 

1996b). The technical compound, Oust®, is not a skin 

irritant or skin sensitizer (USEPA 1990 cited in

Extoxnet 1996b), but it has mild eye irritant properties 

in rabbits (Fletcher et al. 1993 cited in Extoxnet 1996b). 

The acute inhalation LC50 is above 5.3 mg/L in rats, 

indicating its slightly toxic nature by this route (Weed 

Science Society of America 1994 cited in Extoxnet 

1996b). 

Subchronic Toxicity 

The most common signs of toxicity from sulfometuron 

methyl involve hemolytic anemia and decreased BW 

gain (SERA 1998). In one subchronic study, 3,400 

mg/kg-day sulfometuron methyl was administered to six 

rats for 14 days (Hinckle 1979 cited in SERA 1998), 

and the investigators observed reduced testicular size in 

one rat and mild testicular lesions in another. No such 

effects were observed in any of the six control rats. 

Chronic Toxicity/Carcinogenicity 

Several toxic effects have been noted with chronic 

exposure to sulfometuron methyl in test animals. At 

doses of 25 mg/kg-day, dogs experienced reduced red 

blood cell counts and increased liver weight (Wood and 

O’Neal 1983 cited in Extoxnet 1996b). In this study, 

dogs were fed the compound in their food for a year. In 

a 2-year feeding study on rats, no effects were noted 

below 7.5 mg/kg-day (USEPA 1990 cited in Extoxnet 

1996b). 

In chronic bioassays conducted in mice (Summers 1990 

cited in SERA 1998) and rats (Mullin 1984 cited in

SERA 1998), toxicity was indicated by hematological 

changes in the high dose groups of both studies. 

Carcinogenicity was not demonstrated in either study. 

Developmental Toxicity 

Two teratogenicity studies were conducted in which 

rabbits were exposed to sulfometuron methyl by 

gavage. The study by Hoberman et al. (1981 cited in

SERA 1998) involved relatively high dose levels (100 

to 1,000 mg/kg BW), while the study by Serota et al. 

(1981 cited in SERA 1998) involved dose levels of 30 

to 300 mg/kg BW. In the Hoberman et al. (1981) study, 

signs of maternal toxicity, including death in some 

female parents, were apparent at all dose levels. 

Possible spontaneous abortions were noted at doses of 

300 mg/kg or greater. In the lower dose study by Serota 

et al. (1981), there were no signs of toxicity in the dams 

or offspring. Nonetheless, the investigators observed an 

increased number of fetuses with anomalies as well as 

an increase in the proportion of fetal anomalies per 

litter, compared with controls (SERA 1998). 

Reproductive Toxicity 

There are three reproduction studies involving dietary 

exposure of rats to sulfometuron methyl (Wood et al. 

1980; Lu 1981; Mullin 1984 cited in SERA 1998). 

Decreases in maternal BW gain associated with 

BLM Vegetation Treatments Using Herbicides B-16 June 2007 

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 HUMAN HEALTH RISK ASSESSMENT

decreased food consumption and hematological changes 

were the most common effects observed in these 

studies. Dietary levels of 5,000 ppm were associated 

with changes in developmental parameters, including 

decreased fetal weight (Lu 1981) and a decreased 

number of pups in the F1 and F2 generations (Mullin 

1984). In addition to these effects, mean absolute brain 

weights decreased significantly in male rats (Mullin 

1984). 

Neurotoxicity 

Specific neurotoxicity studies are not available in the 

database (SERA 1998). 

Mutagenicity 

Sulfometuron methyl did not show mutagenic activity 

in assays of Salmonella typhimurium strains TA 1535, 

TA 1537, TA 98 and TA100 (Taylor 1979 cited in

SERA 1998) and of Chinese hamster ovary cells (Krahn 

and Fitzpatrick 1981 cited in SERA 1998). 

Sulfometuron methyl did not induce chromosomal 

damage in Chinese hamster ovary cells (Galloway 1981 

cited in SERA 1998) or unscheduled DNA synthesis in 

rat hepatocytes (Ford 1982 cited in SERA 1998). 

Metabolism 

In both mammals and bacteria, sulfometuron methyl is 

degraded by cleavage of the sulfonyl urea bridge to 

form sulfonamide and a dimethyl pyrimidine urea or 

pyrimidine amine. Sulfonamide may be further 

degraded by demethylation to the free benzoic acid 

which, in turn, may undergo a condensation reaction to 

form saccharin. At least in bacteria, the pyrimidine 

metabolites may be degraded further to 

hydroxypyrimidine amine and pyrimidine-ol. Although 

data regarding mammalian metabolism of sulfometuron 

methyl are limited, there is an apparent qualitative 

difference between mammalian and microbial 

metabolism that involves changes to sulfometuron 

methyl prior to cleavage of the sulfonyl urea bridge. In 

mammals, the major metabolic route seems to involve 

hydroxylation of a methyl group on the pyrimidine ring 

(Koeppe and Mucha 1991 cited in SERA 1998); in 

bacteria, the major metabolic pathway seems to involve 

demethylation of the methyl ester group on the benzoate 

ring (Monson and Hoffman 1990 cited in SERA 1998). 

Dose-response Assessment 

The purpose of the dose-response assessment is to 

identify the types of adverse health effects a chemical 

may potentially cause and to define the relationship 

between the dose of a chemical and the likelihood or 

magnitude of an adverse effect (response). The doseresponse assessment identifies quantitative or numerical 

dose-response values that are used in risk calculations to 

derive risk estimates. The dose-response values used in 

the HHRA were developed by the USEPA. 

Adverse effects are defined by the USEPA as either 

potentially carcinogenic or noncarcinogenic (i.e., 

potential effects other than cancer). Dose-response 

values for these types of effects are defined by the 

USEPA. None of the six herbicides evaluated in this 

HHRA are designated as potential carcinogens by the 

USEPA; therefore, this toxicity assessment focuses on 

noncarcinogenic effects. 

Types of Dose-response Values 

Under USEPA OPP guidance (USEPA 2000a), 

noncarcinogenic effects are evaluated differently 

depending on whether the assessment is of a dietary or 

non-dietary (occupational or residential) exposure, as 

described below. 

Dietary Assessment 

For noncarcinogenic effects, toxicity is represented by a 

Population Adjusted Dose (PAD) and may be calculated 

for acute effects (i.e., acute PAD) or chronic effects 

(i.e., chronic PAD). A PAD is an acute or chronic 

reference dose (RfD) divided by the Food Quality 

Protection Act (FQPA) Safety Factor (SF). Both the 

RfD and the FQPA are discussed below. 

Under the provisions of the FQPA of 1996, the USEPA 

is directed to consider aggregate exposure, cumulative 

risk, and additional sensitivity of infants and children. 

The FQPA SF is applied to pesticides that exhibit 

threshold effects to “take into account potential pre- and 

post-natal toxicity and completeness of the data with 

respect to exposure and toxicity to infants and children.” 

In applying the factor, the agency takes into account 

information on the toxicity of the pesticide as well as 

the completeness of the toxicity and exposure databases. 

Generally, FQPA SFs range from 1 to 10. 

Reference doses are derived by identifying a NOAEL, 

which is obtained from the acute or chronic toxicity 

studies, and dividing the NOAEL by the appropriate 

uncertainty factors (UFs). The NOAEL is typically 

derived from animal studies where animals are dosed 

with different amounts of the pesticide. Typically for 

pesticides, a 10-fold factor is applied to account for 

BLM Vegetation Treatments Using Herbicides B-17 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

variation within the human population (intraspecies), 

and an additional 10-fold factor is applied to account for 

the differences between humans and animals 

(interspecies). The following equations show the 

definitions of PAD and RfD: 

FQPASafety Factor

RfD PAD =

 where 

FactorsyUncertaint

NOAEL RfD =

In the acute PAD calculation, the acute RfD and the 

NOAEL obtained from an acute toxicity study are used 

in the equation. For the chronic PAD calculation, the 

chronic RfD and the NOAEL obtained from a chronic 

study are used (USEPA 2000a). 

The dietary exposures evaluated in this risk assessment 

are ingestion of drinking water, berries, and fish for the 

public receptors. 

Non-dietary (Occupational or Residential) 

Assessment 

For evaluating noncancer effects for non-dietary 

exposures, toxicity is represented by the NOAEL. The 

NOAEL is divided by the intake rate to calculate a 

Margin of Exposure (MOE). No Observed Adverse 

Effect Levels are identified for a variety of exposure 

durations and exposure routes: 

• Short-term oral NOAEL 

• Intermediate-term oral NOAEL 

• Short-term dermal NOAEL 

• Intermediate-term dermal NOAEL 

• Long-term dermal NOAEL 

• Short-term inhalation NOAEL 

• Intermediate-term inhalation NOAEL 

• Long-term inhalation NOAEL 

In the current USEPA OPP program, short term is 

defined as 1 day to 1 month, intermediate term is 

defined as 1 to 6 months, and long term is defined as 

greater than 6 months (USEPA 2001g). In general, 

NOAELs decrease as exposure time (ET) increases. 

This is because the dose encountered is a factor of 

concentration and duration of exposure. A study 

conducted by the California EPA’s Office of 

Environmental Health Hazard Assessment (OEHHA) 

indicates that both concentration and time of exposure 

contribute to the overall severity of toxic effects. In fact, 

“Haber’s Law” states that the product of the 

concentration and time of exposure required to produce 

a specific physiologic effect is equal to a constant level 

or severity of response (OEHHA 1999). The USEPA 

has not developed long-term oral NOAELs, since longterm oral exposure is similar to dietary exposure, which 

is represented by PADs. The short-term and 

intermediate-term oral NOAELs are used to represent 

incidental ingestion exposures, such as ingesting water 

while swimming. NOAELs represent non-dietary 

exposures and are used to evaluate the occupational 

receptors and the public receptors for the following 

scenarios: dermal contact with spray, dermal contact 

with foliage, dermal contact with water while 

swimming, and incidental ingestion of water while 

swimming. 

For each of the six herbicides evaluated in this HHRA, 

the USEPA has developed NOAELs for a limited set of 

exposure durations and exposure routes. In other words, 

not all of the NOAELs listed above have been 

developed for the six herbicides. 

The NOAEL divided by the intake results in the MOE. 

Unless specified otherwise, the target MOE is 100. The 

target MOE accounts for uncertainties in the NOAEL. 

Margins of Exposure greater than the target MOE 

indicate no significant risk. For each of the herbicides, 

the target MOE is listed along with the dose-response 

values in Table B-3. 

Available Dose-response Values 

For diflufenzopyr, diquat, and imazapic, the USEPA 

provided documents (such as reports from the Hazard 

Identification Assessment Review Committee and 

Health Effects Division) that showed the derivation of 

various PADs and NOAELs for different exposure 

routes and time frames (short, intermediate, and long 

term). At the BLM’s request, the USEPA reviewed the 

available toxicity information for fluridone (USEPA 

2003a) and sulfometuron methyl (USEPA 2003b), and 

developed PADs and NOAELs for oral, dermal, and 

inhalation exposures. For fluridone, the USEPA did not 

develop dietary PADs; therefore, a chronic oral RfD 

listed in USEPA’s Integrated Risk Information System 

(IRIS) database (USEPA 2003c) is used to evaluate 

chronic dietary exposures for fluridone. 

BLM Vegetation Treatments Using Herbicides B-18 June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

Table B-3 shows the USEPA-derived PADs and 

NOAELs for each of the six herbicides. As shown in 

Table B-3 and as previously stated, none of these 

herbicides are considered potential carcinogens. For 

some of the herbicides, USEPA-derived values were not 

available for certain exposure routes and time periods. 

In some cases, these values were not derived because 

the herbicide had not been found to be toxic through 

that particular route of exposure (such as dermal 

NOAELs for diflufenzopyr). In other cases, these values 

were not derived because the USEPA had determined 

that the use of the specific herbicide did not indicate a 

concern for exposure through a specific route (such as a 

long-term inhalation NOAEL for diflufenzopyr). 

However, since this risk assessment evaluated both 

occupational and public exposures through a variety of 

exposure routes, it was important to have toxicity values 

for certain exposures and time frames even if these 

values had not been derived by USEPA. Therefore, if 

information was available, surrogate toxicity values for 

certain exposures and time periods were derived in this 

risk assessment. 

Dicamba 

The USEPA has developed various dose-response 

values specific to different toxicological endpoints. 

Table B-3 summarizes the dose-response values for 

dicamba. As shown here, dicamba and diflufenzopyr are 

evaluated as separate chemicals, even though they are 

present in the same herbicide formulations. This is a 

reasonable approach because dose-response values for 

the two chemicals are based on different toxicological 

endpoints. For example, the acute PAD and chronic 

PAD for dicamba are based on neurological effects and 

developmental effects, respectively. For diflufenzopyr, 

on the other hand, the acute PAD and chronic PAD are 

based on developmental effects and hemolytic effects, 

respectively. The oral, dermal, and inhalation NOAELs 

for dicamba are based on developmental effects, 

whereas the oral and inhalation NOAELs for 

diflufenzopyr are based on hemolytic effects. Therefore, 

for the HHRA, dicamba and diflufenzopyr were 

evaluated separately. 

Dose-response Values for Dietary Exposures 

Acute Dietary PAD. An acute PAD of 1.0 mg/kg-day 

was developed based on an acute neurotoxicity study in 

rats. The LOAEL for this study was 300 mg/kg-day 

based on various neurological effects. No NOAEL was 

identified since this was the LDT. An RfD of 1.0 

mg/kg-day was calculated by dividing the LOAEL by a 

UF of 300. The UF of 300 consists of two factors of 10 

to account for interspecies and intraspecies differences. 

A factor of 3 was included because of the use of a 

LOAEL rather than a NOAEL. It was determined that a 

UF of 3 is adequate based on comparison with a rat 

developmental toxicity study that had similar clinical 

signs with a LOAEL of 400 mg/kg-day that showed no 

progression or worsening of the effects after 10 days of 

treatment (USEPA 2001g). 

The USEPA has not developed an FQPA SF for this 

chemical. However, based on the mild toxicological 

effects at the LOAEL and the adequacy of 

developmental toxicity studies that evaluate risks to the 

offspring, it is assumed that the FQPA SF is 1 and that 

the acute PAD is the same as the acute RfD of 1.0 

mg/kg-day. 

Chronic Dietary PAD. The USEPA has developed a 

chronic dietary PAD of 0.45 mg/kg-day. This value was 

based on a NOAEL of 45 mg/kg-day based on a multigeneration reproduction study in rats. Decreased 

offspring growth was observed at the LOAEL of 136 

mg/kg-day. A chronic RfD was calculated by dividing 

the chronic NOAEL by a UF of 100 (45 mg/kg-day / 

100 = 0.45 mg/kg-day). The FQPA SF is likely to be 1, 

since this study considers effects on young animals. 

Therefore, the chronic PAD is equal to the chronic RfD 

at 0.45 mg/kg-day (USEPA 2001h). 

 Dose-response Values for Non-dietary 

Exposures 

Oral NOAELs. The short-term and intermediate-term 

oral NOAELs are 45 mg/kg-day, based on the multigeneration rat reproduction study on which the chronic 

PAD is based. The USEPA commented that this study is 

of the appropriate route and duration of exposure, 

including short term, since effects were seen on 

lactation day 21 in the second-generation litters and is 

protective of infants and children (USEPA 2001h). 

Dermal NOAELs. The USEPA has identified shortterm, intermediate-term, and long-term dermal 

NOAELs of 45 mg/kg-day based on the multigeneration rat reproduction study on which the chronic 

PAD is based. The USEPA noted that although a 21-day 

dermal study was available, showing no systemic 

toxicity at the HDT of 1,000 mg/kg-day, this dermal 

study did not assess reproductive and offspring effects. 

Offspring toxicity in the rat oral multi-generation 

reproduction study was noted below dosages where 

parental toxicity was evident. In order to be protective 

of these effects, the reproduction study was chosen for 

all time periods of exposure, including short term, since 

BLM Vegetation Treatments Using Herbicides B-19 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

BLM Vegetation Treatments Using Herbicides B-20 June 2007 

Final Programmatic EIS

effects in the offspring were seen on lactation day 21 

(USEPA 2001h). 

The dermal NOAELs should be used with a dermal 

absorption factor (DAF) of 15%. The USEPA 

calculated this DAF by dividing the LOAEL of 150 

mg/kg-day in the rabbit oral developmental study by the 

NOAEL of 1,000 mg/kg-day in the 21-day dermal 

toxicity rabbit study (150 mg/kg-day / 1,000 mg/kg-day 

x 100 = 15%; USEPA 2001h). 

Inhalation NOAELs. The USEPA has identified shortterm, intermediate-term, and long-term inhalation 

NOAELs of 45 mg/kg-day based on the multigeneration rat reproduction study on which the chronic 

PAD is based. The USEPA states that this study is 

protective of effects in the offspring. In order to account 

for effects in the offspring in the absence of any routespecific data, the reproduction study was chosen for all 

time periods of exposure (USEPA 2001h). 

Target Margin of Exposure. The target MOE for 

dicamba for the non-dietary NOAELs is 100 (USEPA 

2001h). 

Cancer Dose-response Value. The USEPA has not 

developed a cancer slope factor (CSF) for dicamba. The 

RfD/Peer Review Committee concluded that dicamba 

should be classified as a Group D carcinogen based on 

the lack of both rat and mouse bioassays being tested at 

high enough levels to induce any significant toxicity in 

the two different species (USEPA 2001h). 

Diflufenzopyr 

The USEPA has developed various dose-response 

values specific to different toxicological endpoints. 

Table B-3 summarizes the dose-response values for 

diflufenzopyr. 

Dose-response Values for Dietary Exposures 

Acute Dietary PAD. An acute PAD of 1.0 mg/kg-day 

was calculated for use in evaluating risks from dietary 

exposures for females 13 to 50 years old. This value 

was based on an acute dietary NOAEL of 100 mg/kgday based on a rabbit developmental study. The 

LOAEL for this study is 300 mg/kg-day based on the 

occurrence of extra ribs and other skeletal variations in 

the rabbit developmental study. These effects can occur 

from a single dose, and females of reproductive age, i.e., 

13 to 50 years of age, are the population subgroup of 

concern. The UF for deriving a human dose-response 

value is 100. Therefore, the acute RfD is 1.0 mg/kg-day 

(100 mg/kg-day / 100). The acute PAD was calculated 

by dividing the RfD by the FQPA SF. The USEPA has 

determined that the FQPA SF for diflufenzopyr is 1, 

indicating that children are unlikely to face higher risks, 

which is appropriate as the results are based on a 

developmental study. Therefore, the acute PAD is the 

same as the acute RfD of 1.0 mg/kg-day (USEPA 

2002b). 

The USEPA has not developed an acute dietary PAD 

for the general population, since appropriate studies 

involving single exposures were not available (USEPA 

2002b). The acute PAD for females 13 to 50 years old 

therefore is used for all receptors. 

Chronic Dietary PAD. The USEPA has developed a 

chronic dietary PAD for all populations of 0.26 mg/kgday. This value was based on a NOAEL of 26 mg/kgday derived from a 52-week dog feeding study. The 

LOAEL of 299 mg/kg-day was based on compensated 

hemolytic anemia in both sexes of dogs. A chronic RfD 

was calculated by dividing the chronic NOAEL by a UF 

of 100 (26 mg/kg-day / 100 = 0.26 mg/kg-day). The 

chronic PAD is also 0.26 mg/kg-day, since the FQPA 

SF is 1 (USEPA 2002b). 

Dose-response Values for Non-dietary 

Exposures

Oral NOAELs. The USEPA has not derived nondietary oral NOAELs for diflufenzopyr (USEPA 

2002b). However, the USEPA established short- and 

intermediate-term inhalation NOAELs of 58 mg/kg-day 

based on a subchronic feeding study in dogs. Inhalation 

exposure assumes 100% absorption. This same 58 

mg/kg-day NOAEL is recommended as the short- and 

intermediate-term oral NOAEL, since this value was 

based on a feeding study. 

Dermal NOAELs. The USEPA has not identified 

dermal toxicological endpoints of concern, citing no 

effects at the limit dose of 1,000 mg/kg-day in a 21-day 

dermal toxicity study in rabbits. Therefore, the USEPA 

has determined that assessment of risk via the dermal 

route is not necessary (USEPA 2002b). 

Inhalation NOAELs. The USEPA has developed a 

short-term and intermediate-term inhalation NOAEL of 

58 mg/kg-day. This value is based on an oral NOAEL 

of 58 mg/kg-day from a subchronic oral dog study. The 

inhalation absorption factor (IAF) was assumed to be 

100%, therefore the inhalation NOAEL is equal to the 

oral NOAEL. The LOAEL in this study was 403
BLM Vegetation Treatment Using Herbicides B-21 June 2007 

Final Programmatic EIS TABLE B-3 Summary of Toxicological Endpoint Data Parameter Dicamba Diflufenzopyr Diquat Fluridone Ima

Acute dietary NOAEL (mg/kg-day) 3001 1002 75 NA NUncertainty factor 300 100 100 NA NFood Quality Protection Act safety factor 1 1 1 NA NAcute population adjusted dose (mg/kg-day) 4 1 1 0.75 NA NChronic dietary NOAEL (mg/kg-day) 45 265 0.5 (0.22) 6 87 13Uncertainty factor 100 100 100 NA 3Food Quality Protection Act safety factor 1 1 1 NA Chronic population adjusted dose (mg/kg-day) (d) 0.45 0.26 0.005 (0.0022) 6 0.089 0Short- and intermediate-term oral NOAEL (mg/kg-day) 45 5810 1 (0.5)11 25 3Short-term dermal NOAEL (mg/kg-day) 4512 NA13 114 25 (125) 15 NAIntermediate-term dermal NOAEL (mg/kg-day) 4512 NA13 0.514 2515 NALong-term dermal NOAEL (mg/kg-day) 4512 NA13 0.514 87 13Short-term inhalation NOAEL (mg/kg-day) 45 5819 0.024 12520 35Intermediate-term inhalation NOAEL (mg/kg-day) 45 5820 0.024 2521 35Long-term inhalation NOAEL (mg/kg-day) 45 2623 0.024 87 13Target margin of exposure for oral, dermal, inhalation 100 10025 100 10025 300/10Cancer slope factor for oral, dermal, inhalation NA NA27 NA28 NA28 NAReferences USEPA 2001h USEPA 2002c USEPA 2001f USEPA 2003a USEPA NA = Not applicable according to USEPA risk assessments. Values in bold indicates where surrogate toxicity data have been used that were not provided in the USEPA documents. Short term is defined as 1 day to 1 month, intermediate term is defined as 1 to 6 months, and long term is defined as over 6 months (USEPA 2001h). 
1 This value is a LOAEL based on an oral neurotoxicity study in rats. 

2 Derived for females of reproductive age (13 to 50 years). Based on a rabbit development study showing a LOAEL of 300 mg/kg-day. 3 An endpoint attributable to a single dose was not identified. 4 The PAD is the NOAEL divided by the uncertainty factor and the FQPA SF. If the FQPA SF is 1, then the PAD equals the Reference Dose (RfD), whi

the uncertainty factor. 5 Derived for all populations. Based on a dog feeding study showing a LOAEL of 299 mg/kg-day. 

6 The numbers in parentheses are RfDs presented on IRIS (USEPA 2003c). 7 The long-term dietary NOAEL of 8 mg/kg-day from the combined chronic rat feeding/carcinogenicity study on which USEPA’s chronic RfD is based 

(http://www.epa.gov/iris/subst/0054.htm ) is used as a chronic dietary NOAEL and as a long-term inhalation NOAEL. 8 Lowest Observed Adverse Effect Level. 

9 Oral RfD value provided in IRIS (USEPA 2003c). 10 Short- and intermediate-term inhalation NOAELs of 58 mg/kg-day were established by the Health Effects Division (USEPA 2002c) based on a subchr

Therefore, assuming 100% absorption via inhalation, the inhalation NOAEL is used to evaluate the oral route of exposure. 

11 The short-term oral NOAEL is 1 mg/kg-day, and the intermediate-term oral NOAEL is 0.5 mg/kg-day. 12 This value is modified using a dermal absorption factor (DAF) of 15% in the exposure calculations. 13 No dermal or systemic toxicity was seen at 1,000 mg/kg-day in a 21-day dermal toxicity study in rabbits. 14 This value is modified using a DAF of 4.1% in the exposure calculations. 15 This value is modified using a DAF of 40% in the exposure calculations. The short-term dermal NOAEL is 25 mg/kg-day for children and 125 mg/kg-16 No systemic toxicity was seen following repeated dermal application at 1,000 mg/kg-day over a 3-week period. Dermal quantification is not required. 17 No systemic or dermal toxicity was seen following repeated dermal applications of up to 2,000 mg/kg-day to rabbits. 18 The chronic dietary LOAEL of 137 mg/kg-day is used. The inhalation absorption factor is assumed to be 100%. 19 Based on a subchronic dog feeding study showing a LOAEL of 403 mg/kg-day and assuming 100% inhalation absorption. 20 The inhalation absorption factor is 100%. 21 The short- and intermediate-term oral NOAEL is used

―the inhalation absorption factor is assumed to be 100%; therefore, no adjustments are necessar

calculations. 

22 A 100% inhalation absorption fraction is used for route-to-route extrapolation from oral to inhalation. 23 Assuming 100% absorption via inhalation, the chronic dietary NOAEL of 26 mg/kg-day was used as the long-term inhalation NOAEL (USEPA 2002c24 The chronic dietary oral LOAEL is 137 mg/kg-day; this value must be modified using a DAF of 50% in the exposure calculations. 25 Not listed, assumed to be 100. 26 Target MOEs are 100 for short- and intermediate-term inhalation and short- and intermediate-term oral, and 300 for long-term inhalation and long-term 

300 is necessary because the long-term dermal and inhalation values are LOAELs rather than NOAELs. 

27 Classified as not likely to be a human carcinogen. 28 Classified as a Group E carcinogen - a chemical for which there is evidence of non-carcinogenicity in humans. 29 Not yet evaluated by the USEPA, but no evidence of carcinogenicity in either mice or rats. 

TABLE B-3 (Cont.) 

Summary of Toxicological Endpoint Data

BLM Vegetation Treatment Using Herbicides B-22 June 2007 

Final Programmatic EIS 
HUMAN HEALTH RISK ASSESSMENT

mg/kg-day based on the occurrence of erythroid 

hyperplasia in the bone marrow, extramedullary 

hemopoiesis in the liver, and hemosiderin deposits in 

Kupffer cells. 

The USEPA has not developed a long-term inhalation 

NOAEL stating that, “the use pattern does not indicate a 

concern for potential exposure via this route. Therefore, 

this risk assessment is not required” (USEPA 2002b). 

However, since long-term use was evaluated in this risk 

assessment, a long-term inhalation NOAEL was derived 

from available information. The USEPA developed a 

chronic dietary NOAEL of 26 mg/kg-day based on a 52 

week dog feeding study. Making the same assumption 

about inhalation absorption as made in developing the 

short- and intermediate-term inhalation NOAELs (i.e., 

100%), a long term inhalation NOAEL of 26 mg/kg-day 

can be derived from the chronic dietary NOAEL. This is 

consistent with the approach taken for developing 

inhalation NOAELs for imazapic and sulfometuron 

methyl. 

Target MOE. The target MOE for diflufenzopyr for the 

non-dietary NOAELs is 100. 

Cancer Dose-response Value. The USEPA has not 

developed a CSF for diflufenzopyr. In accordance with 

the 1996 Proposed Guidelines for Carcinogen Risk 

Assessment (USEPA 1996), diflufenzopyr was 

classified as “Not Likely” to be a human carcinogen. 

This classification is based on the lack of evidence of 

carcinogenicity in mice and rats when tested at doses 

that were judged to be adequate to assess 

carcinogenicity. 

Diquat 

Table B-3 summarizes the dose-response values for 

diquat dibromide. 

Dose-response Values for Dietary Exposures 

Acute Dietary PAD. The USEPA has developed an 

acute PAD of 0.75 mg/kg-day based on an acute 

neurotoxicity study (MRID No. 42666801). Diquat 

dibromide was administered to 10 Alpk:ApfSD rats per 

sex per group via gavage at single dose levels of 0, 25, 

75, or 150 mg/kg. The systemic NOAEL is 75 mg/kg, 

based on clinical signs and decreased body-weight gains 

at the systemic LOAEL of 150 mg/kg. The UF for 

deriving a human dose-response value is 100 (10 to 

account for interspecies differences, and 10 to account 

for intraspecies differences). Therefore, the acute RfD is 

0.75 mg/kg-day (75 mg/kg-day / 100). The acute PAD 

was calculated by dividing the RfD by the FQPA SF. 

The USEPA has determined that the FQPA SF for 

diquat is 1, indicating that children are unlikely to face 

higher risks. Therefore, the acute PAD is the same as 

the acute RfD of 0.75 mg/kg-day (USEPA 2001f). 

Chronic Dietary PAD. The USEPA has developed a 

chronic dietary PAD for all populations of 0.005 mg/kgday. This value was based on a NOAEL of 0.5 mg/kgday derived from a 52-week dog feeding study (MRID 

No. 41730301). The dose levels were 0, 0.5, 2.5, and 

12.5 mg/kg-day. The LOAEL of 2.5 mg/kg-day was 

based on cataracts in females and decreased weights of 

the adrenals and epididymides in males. A chronic PAD 

was calculated by dividing the chronic NOAEL by an 

UF of 100 (0.5 mg/kg-day / 100 = 0.005 mg/kg-day). 

The HED Committee determined that an UF of 100 is 

adequate for the protection of infants and children from 

exposure to diquat dibromide. Therefore, because the 

FQPA SF is 1, the chronic PAD is 0.005 mg/kg-day 

(USEPA 2001f). 

Dose-response Values for Non-dietary 

Exposures 

Oral NOAELs. The USEPA has derived separate 

short- and intermediate-term oral NOAELs for diquat 

dibromide (USEPA 2001f). The short-term oral 

NOAEL of 1 mg/kg-day is based on a developmental 

toxicity study in rabbits (MRID No. 41198901). 

Pregnant New Zealand White rabbits were administered 

technical grade diquat via gavage at dose levels of 0, 1, 

3, and 10 mg/kg-day from gestation days 7 through 19. 

The maternal toxicity NOAEL was 1 mg/kg-day, based 

on maternal body-weight loss and decreased food 

consumption at the LOAEL of 3 mg/kg-day (USEPA 

2001f). 

The intermediate-term oral NOAEL of 0.5 mg/kg-day is 

based on a chronic oral toxicity study in dogs (MRID 

No. 41730301), which is the same study that forms the 

basis for the chronic dietary PAD. The NOAEL of 0.5 

mg/kg-day is based on unilateral cataracts in females 

and decreased adrenal and epididymides weights in 

males at the LOAEL of 2.5 mg/kg-day (USEPA 2001f). 

Dermal NOAELs. The USEPA identified a short-term 

dermal NOAEL of 1 mg/kg-day based on a 

developmental toxicity study in rabbits (MRID No. 

41198901). This is the same study on which the shortterm oral NOAEL is based. In order to use this NOAEL 

to evaluate dermal exposure, the USEPA recommends 

using a dermal absorption factor of 4.1%. This value is 

from a dermal penetration study in rats, based on 

BLM Vegetation Treatments Using Herbicides B-23 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

exposure pattern and duration of exposure (MRID No. 

41238701). Following 24 hours of exposure, dose levels 

of 0.05, 0.5, and 5 mg diquat cation/rat resulted in 2.3%, 

2.1%, and 3.3% absorption, respectively. Based on 

these findings, the dermal absorption of diquat 

dibromide through intact rat skin is considered very low 

(USEPA 2001f). 

The USEPA has identified an intermediate- and longterm dermal NOAEL of 0.5 mg/kg-day based on a 

chronic oral toxicity study in dogs (MRID No. 

41730301). This is the same study on which the 

intermediate-term oral NOAEL is based. The DAF of 

4.1% should be used with this NOAEL, as well 

(USEPA 2001f). 

Inhalation NOAELs. The USEPA has developed an 

inhalation NOAEL of 0.024 mg/kg-day for all exposure 

durations (short, intermediate, and long term). This 

value is based on a subchronic 21-day inhalation study 

in rats (MRID No. 40301701), where male and female 

Fischer 344 rats were exposed via inhalation to 

respirable aerosols of diquat at dose levels of 0, 0.49, 

1.1, and 3.8 ug/L for 3 weeks. A subsequent study 

(MRID No. 40640801), in which male and female 

Fischer 344 rats were exposed via inhalation to 

respirable aerosols of diquat at dose levels of 0 and 0.1 

μg/L for 3 weeks, was performed to determine a 

NOAEL. The NOAEL of 0.024 mg/kg-day (converted 

from 0.1 μg/L) is based on increased lung weights and 

microscopic lesions in the lungs at the LOAEL of 0.117 

mg/kg-day (0.49 μg/L; USEPA 2001f). 

Target MOE. A target MOE of 100 is adequate to 

ensure protection from occupational and residential 

exposures to diquat dibromide by dermal and inhalation 

routes (USEPA 1997b). This is based on the lack of 

increased sensitivity to fetuses as compared to maternal 

animals in developmental and multigenerational 

reproduction toxicity studies. 

Cancer Dose-response Value. The USEPA has not 

developed a CSF for diquat dibromide (USEPA 2001f). 

The carcinogenic potential of diquat dibromide was 

evaluated by the HDT RfD Peer Review Committee on 

March 31, 1994. The Committee classified diquat 

dibromide as a Group E carcinogen (evidence of 

noncarcinogenicity for humans) based on a lack of 

evidence of carcinogenicity in studies with two species, 

rat and mouse. 

Fluridone 

Table B-3 summarizes the dose-response values for 

fluridone. 

Dose-response Values for Dietary Exposures 

Acute Dietary PAD. The USEPA did not provide an 

acute RfD or PAD for fluridone (USEPA 2003a). The 

rationale for this was not provided in the USEPA 

memorandum. 

Chronic Dietary PAD. The USEPA’s Office of 

Pesticides has not developed a chronic dietary RfD or 

PAD for this herbicide (USEPA 2003a). However, the 

USEPA’s IRIS database lists an RfD of 0.08 mg/kg-day 

(USEPA 2003c), which is used in this HHRA to 

evaluate dietary risks. This value was based on a 

NOAEL of 8 mg/kg-day derived from a combined 

chronic feeding/carcinogenicity study (MRID Nos. 

00103251, 00103305) in Fischer rats. In this study, 

fluridone was administered continuously in the diet to 

rats (75/sex/group) at dose levels of 0, 8, 25, or 81 

mg/kg-day for 2 years (60/sex/group) or for 52 weeks 

(15/sex/group). The LOAEL for this study is 25 mg/kgday based on glomerulonephritis, atrophic testes, eye 

keratitis, decreased BW and organ weights. The RfD 

was calculated by dividing the NOAEL by a UF of 100 

(10 for interspecies variation and 10 for intraspecies 

variation). 

Dose-response Values for Non-dietary 

Exposures 

Oral NOAELs. The USEPA has developed a shortterm and intermediate-term oral NOAEL for fluridone 

of 25 mg/kg-day from a 90-day rat feeding study 

(USEPA 2003a). The USEPA does not provide 

additional detail on these NOAELs (USEPA 2003a). 

Dermal NOAELs. The USEPA has developed separate 

short-term dermal NOAELs for children and adults. The 

short-term dermal NOAEL of 25 mg/kg-day for 

children is based on the same 90-day rat feeding study 

as the short-term and intermediate-term oral NOAEL 

for children (USEPA 2003a). However, the short term 

dermal NOAEL of 125 mg/kg-day for workers and 

other adults is based on an oral developmental toxicity 

study in rabbits. In the developmental toxicity study, 

rabbits were exposed to 0, 125, 300, or 750 mg/kg-day 

of fluridone during gestation (MRID No. 00103302 

[USEPA 2002a], MRID No. 00263157 [USEPA 

2003a]). Effects, including maternal weight loss and 

abortion, were noted at the 300 mg/kg-day dose level. 

BLM Vegetation Treatments Using Herbicides B-24 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

The maternal NOAEL is 125 mg/kg-day. The 

developmental NOAEL is 125 mg/kg-day since fetal 

resorptions occurred in the 300 mg/kg-day dose group 

(USEPA 1988 cited in MA DEM/MA DEP 2003, 

USEPA 2002a). 

The intermediate-term dermal NOAEL for all age 

groups of 25 mg/kg-day is based on the same 90-day rat 

feeding study as the short-term and intermediate-term 

oral NOAEL for children. The USEPA has not 

developed a long-term dermal NOAEL (USEPA 

2003a). However, the long-term dietary NOAEL of 8 

mg/kg-day from the combined chronic rat 

feeding/carcinogenicity study on which the USEPA’s 

chronic RfD is based can be used with a DAF to address 

long-term dermal toxicity. 

The dermal NOAELs should be used with a DAF of 

40% since it is based on oral toxicological endpoints. 

An absorption factor of 40% was derived by dividing a 

maternal oral LOAEL of 300 mg/kg-day (rabbit 

developmental study; MRID No. 00103302 [USEPA 

2002a], MRID No. 00263157 [USEPA 2003a]) by the 

dermal NOAEL of 768 mg/kg-day from a 21-day 

dermal toxicity study in rabbits (MRID No. 00070933). 

No systemic effects were noted at any dose, and 768 

mg/kg-day was the HDT. The absorption factor should 

be considered an upper-bound estimate. 

Inhalation NOAELs. The USEPA has developed a 

short-term inhalation NOAEL for all age groups of 125 

mg/kg-day, which is based on the same oral rabbit 

developmental toxicity study as the short-term dermal 

NOAEL for adults discussed above (USEPA 2003a). 

The intermediate-term inhalation NOAEL for all age 

groups of 25 mg/kg-day is based on the same 90-day rat 

feeding study as the short-term and intermediate-term 

oral NOAEL for children. The USEPA has not 

developed a long-term inhalation NOAEL (USEPA 

2003a). However, the long-term dietary NOAEL of 8 

mg/kg-day from the combined chronic rat 

feeding/carcinogenicity study on which the USEPA’s 

chronic RfD is based can be used with an IAF to 

address long-term inhalation toxicity. 

The inhalation NOAELS should assume 100% 

absorption by the inhalation route; therefore, no 

adjustment to the oral NOAELs is required (USEPA 

2003a). 

Target MOE. The target MOE for all NOAELs is 100. 

Cancer Dose-response Value. The USEPA has not 

developed a CSF for fluridone. In accordance with the 

1986 Carcinogen Risk Assessment, fluridone was 

classified as a Group E carcinogen (no evidence of 

carcinogenicity) based on lack of evidence for 

carcinogenicity in two acceptable rodent (mice and rats) 

carcinogenicity studies (USEPA 1997c). 

Imazapic 

Table B-3 summarizes the dose-response values for 

imazapic. 

Dose-response Values for Dietary Exposures 

Acute Dietary PAD. An acute RfD or PAD was not 

established, since an appropriate endpoint attributable to 

a single dose was not available. No developmental 

toxicity was seen in rats or rabbits and maternal toxicity 

in rabbits occurred on days 7 through 19 of gestation 

(USEPA 2001a). 

Chronic Dietary PAD. The USEPA has developed a 

chronic dietary PAD of 0.5 mg/kg-day. This value was 

based on a LOAEL of 137 mg/kg-day derived from a 1-

year dietary toxicity study in dogs (MRID No. 

42711421). In this study, imazapic was administered via 

the diet to groups of six beagle dogs per sex per dose, at 

concentrations of 0, 5,000, 20,000, or 40,000 ppm 

(equivalent to mean achieved dosages of 137, 501, and 

1,141 mg/kg-day in males and 180, 534, and 1,092 

mg/kg-day in females), respectively. The LOAEL in 

this study was 137 mg/kg-day in males and 180 mg/kgday in females based on minimal degeneration and/or 

necrosis of the skeletal muscle of the thigh and/or 

abdomen in both male and, to a lesser extent, female 

dogs. This histological finding was associated with 

minimal lymphocyte and macrophage infiltration. 

Minimal infiltration was also observed in the diaphragm 

of one dog of each sex. Decreased serum creatinine was 

also present in females. A NOAEL was not established 

in this study. 

The chronic RfD was calculated by dividing the 

LOAEL of 137 mg/kg-day by an UF of 300, resulting in 

a value of 0.5 mg/kg-day. The UF of 300 consists of 

factors of 10 for interspecies differences, 10 for 

intraspecies variations, and 3 for the use of a LOAEL 

rather than a NOAEL for this endpoint. The use of a 3-

fold UF, rather than a 10-fold factor, was due to the 

minimal severity of the skeletal muscle degeneration 

and/or necrosis and to the relatively constant severity 

across doses (USEPA 2001a). The USEPA has not 

developed an FQPA SF for this chemical. However, 

BLM Vegetation Treatments Using Herbicides B-25 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

based on the mild toxicological effects at the LOAEL 

and the lack of increased risk to children versus adults, 

it is assumed that the FQPA SF is 1 and that the chronic 

PAD is the same as the chronic RfD of 0.5 mg/kg-day. 

Dose-response Values for Non-dietary 

Exposures 

Oral NOAELs. The USEPA has derived a short-term 

(1 to 7 days) and intermediate-term (7 days to several 

months) oral NOAEL for imazapic of 350 mg/kg-day 

(USEPA 2001a). This value was based on a rabbit 

developmental toxicity study (MRID No. 42711423) in 

which groups of 20 impregnated New Zealand White 

rabbits were administered imazapic during gestation 

days 7 through 19 at daily doses of 0, 175, 350, 500, or 

700 mg/kg-day. The LOAEL for maternal toxicity is 

500 mg/kg-day based on decreased BW gain and food 

consumption during the dosing period. The NOAEL for 

maternal toxicity is 350 mg/kg-day. 

Although there was an increase in fetal incidences of 

rudimentary ribs, it was determined that this effect was 

not related to treatment. The NOAEL for developmental 

toxicity is 500 mg/kg-day, which is higher than the 

NOAEL for maternal toxicity. Therefore, the short-term 

and intermediate-term oral NOAEL was determined to 

be 350 mg/kg-day (USEPA 2001a). 

Dermal NOAELs. The USEPA has not derived shortand intermediate-term dermal NOAELs, since no 

effects were noted in a dermal toxicity study in rabbits. 

The 21-day dermal toxicity study in rabbits was 

conducted (MRID No. 42711420) by applying imazapic 

to the clipped backs of New Zealand albino rabbits at 

targeted doses of 0, 250, 500, or 1,000 mg/kg-day for 6 

hours per day, 5 days per week, for 3 weeks. There were 

no systemic or developmental effects observed up to the 

limit dose (1,000 mg/kg-day), therefore a toxicity 

endpoint was not selected from this study (USEPA 

2001a). 

The USEPA developed a long-term dermal LOAEL of 

137 mg/kg-day that is used with a DAF of 50%. The 

LOAEL of 137 mg/kg-day is based on a 1-year dog 

feeding study (which is also the basis for the chronic 

PAD) and considers an increased incidence of minimal 

degeneration and/or necrosis of the skeletal muscle of 

the thigh and/or abdomen. Since a NOAEL was not 

established in the 1-year dog feeding study, the LOAEL 

of 137 mg/kg-day was selected for the long-term dermal 

exposure scenario. This value should be used with a 

DAF of 50%. The USEPA derived the DAF by dividing 

the oral maternal LOAEL of 500 mg/kg-day (rabbit 

developmental study; MRID No. 42711423) by the 

dermal NOAEL of 1,000 mg/kg-day in the 21-day 

dermal toxicity study in rabbits (MRID No. 42711420). 

The upper bound estimated percent dermal absorption 

was 50%. Additionally, a target MOE of 300 is required 

for this scenario because of the use of a LOAEL rather 

than a NOAEL (USEPA 2001a). 

Inhalation NOAELs. Due to the lack of appropriate 

inhalation studies, the USEPA has selected oral 

NOAELs to be used for inhalation exposure risk 

assessments with appropriate absorption factors. The 

IAF is 100%, therefore no adjustment is needed for the 

oral NOAELs. For evaluating short- and intermediateterm inhalation exposures, the USEPA recommends the 

use of the maternal systemic toxicity NOAEL of 350 

mg/kg-day based on a developmental toxicity study in 

rabbits. A target MOE of 100 is used for this scenario 

(USEPA 2001a). 

For evaluating long-term inhalation exposures, the 

USEPA recommends the use of the systemic oral 

toxicity LOAEL of 137 mg/kg-day based on a 1-year 

oral toxicity study in dogs. A target MOE of 300 is 

required for this exposure scenario because of the use of 

a LOAEL rather than a NOAEL (USEPA 2001a). 

Target MOE. A target MOE of 100 is used for the oral 

NOAELs, and short- and intermediate-term inhalation 

NOAELs. A target MOE of 300 is used for the longterm dermal and long-term inhalation NOAELs because 

these values are based on LOAELs rather than 

NOAELs. 

Cancer Dose-response Value. In accordance with the 

1986 Carcinogen Risk Assessment, imazapic was 

classified as a Group E carcinogen (no evidence of 

carcinogenicity) based on lack of evidence for 

carcinogenicity in two acceptable rodent (mice and rats) 

carcinogenicity studies. 

Sulfometuron Methyl 

The USEPA has developed various dose-response 

values specific for different toxicological endpoints 

(USEPA 2003b). Table B-3 summarizes the doseresponse values for sulfometuron methyl. 

Dose-response Values for Dietary Exposures 

Acute Dietary PAD. An appropriate endpoint 

attributable to a single dose of sulfometuron methyl was 

not available in the toxicology data base. Therefore, an 

acute RfD or PAD was not established (USEPA 2003b). 

BLM Vegetation Treatments Using Herbicides B-26 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Chronic Dietary PAD. The USEPA has developed a 

chronic RfD of 0.05 mg/kg-day. This value was based 

on a NOAEL of 5 mg/kg-day derived from a 1-year 

study in dogs (MRID No. 00129051). The LOAEL for 

this study was 25 mg/kg-day based on mild hemolytic 

anemia. A chronic RfD was calculated by dividing the 

chronic NOAEL of 5 mg/kg-day by a UF of 100 (10 for 

interspecies variation and 10 for intraspecies variation). 

The USEPA has not developed an FQPA SF for this 

chemical. However, based on the mild toxicological 

effects at the LOAEL and because children would not 

be expected to be more prone to this effect than adults, 

it is assumed that the FQPA SF is 1 and that the chronic 

PAD is the same as the chronic RfD of 0.05 mg/kg-day. 

Dose-response Values for Non-dietary 

Exposures 

Oral NOAELs. The USEPA has developed short-term 

and intermediate-term oral NOAELs of 5 mg/kg-day. 

This value was based on a 1-year study in dogs (MRID 

No. 00129051). The LOAEL for this study was 25 

mg/kg-day based on mild hemolytic anemia (USEPA 

2003b). 

Dermal NOAELs. No systemic or dermal toxicity was 

seen following repeated dermal applications of up to 

2,000 mg/kg-day to rabbits. There were no concerns for 

developmental or reproductive toxicity; therefore, 

quantification of dermal risk is not required (USEPA 

2003b). 

Inhalation NOAELs. The USEPA has developed an 

inhalation NOAEL for all exposure durations of 5 

mg/kg-day. This value was based on the same 1-year 

study in dogs (MRID No. 00129051) on which the RfD 

and oral NOAELs were based. The LOAEL for this 

study was 25 mg/kg-day based on mild hemolytic 

anemia (USEPA 2003b). In the absence of chemicalspecific information, the USEPA (2003b) recommends 

using 100% absorption for route-to-route extrapolation. 

Target MOE. The target MOE for all NOAELs is 100. 

Cancer Dose-response Value. The USEPA (2003b) 

states that the carcinogenicity of sulfometuron methyl is 

not yet evaluated. However, no carcinogenic effects 

have been detected in either rats or mice exposed to 

sulfometuron methyl (USEPA 1990 cited in Extoxnet 

1996b). Therefore, it is reasonable to assume that 

sulfometuron methyl would not be classified as a likely 

carcinogen. 

Inert Ingredients 

In addition to the active ingredients, most herbicides 

also contain inert ingredients (i.e., those substances 

included in the formulation that are not the active 

ingredients) that have various functions such as diluents, 

binders, dispersants, carriers, stabilizers, neutralizers, 

antifoamers, and buffers. 

The USEPA categorizes inert ingredients into four lists 

(54 FR 48314): 

• List 1 – Inert ingredients of toxicological 

concern. Any product containing a List 1 

ingredient must include the label statement, 

“this product contains the toxic inert ingredient 

(name of inert).” 

• List 2 – Inerts of unknown toxicity/high 

priority for testing inerts. 

• List 3 – Inerts of unknown toxicity. Inert 

ingredients on this list have not yet been 

determined to be of known potential 

toxicological concern nor have they been 

determined to be of minimal concern. These 

substances will continue to be evaluated to 

determine if they merit reclassification to List 

1, 2, or 4. 

• List 4 – Inerts of minimal concern. List 4 is 

subdivided into List 4A (minimal risk inert 

ingredients) and List 4B (inerts that have 

sufficient data to substantiate they can be used 

safely in pesticide products). 

BLM scientists received clearance from USEPA to 

review Confidential Business Information (CBI) on 

inert compounds identified in products containing the 

six active ingredients evaluated in this risk assessment. 

The information received listed the inert ingredients, 

their chemical abstract number, supplier, USEPA 

registration number, percentage of the formulation and 

purpose in the formulation. Because this information is 

confidential, this information, including the name of the 

ingredients may not be disclosed. 

The USEPA has a listing of regulated inert ingredients 

at http://www.epa.gov/opprd001/inerts/index.html. This 

listing categorizes inert ingredients into the four 

categories listed above. The number of inert ingredients 

present in the formulations containing the six active 

ingredients evaluated in this risk assessment are shown 

below: 

BLM Vegetation Treatments Using Herbicides B-27 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

• List 1 – no inerts found 

• List 2 – no inerts found 

• List 3 – 5 inerts found 

• List 4A –9 inerts found 

• List 4B – 18 inerts found 

Therefore, the majority of the inerts are of minimal risk. 

A few are in the category of unknown toxicity. 

Exposure Assessment 

The purpose of the exposure assessment is to predict the 

magnitude and frequency of potential human exposure 

to the herbicides under consideration in the HHRA. The 

first step in the exposure assessment process is to 

identify potential exposure pathways that are 

appropriate for planned BLM use of the herbicides. This 

step also involves identifying potential receptors (i.e., 

people who may contact the impacted environmental 

media of interest) and the exposure routes by which 

environmental media may be contacted (i.e., ingestion, 

dermal contact, inhalation). Those potential exposure 

pathways that are judged to be complete are evaluated 

quantitatively in the risk assessment. According to the 

USEPA (1989), for an exposure pathway to be 

complete, the following conditions must exist: 

• A source and mechanism of chemical release to 

the environment 

• An environmental transport medium (e.g., air, 

water, soil) 

• A point of potential receptor contact with the 

medium 

• A human exposure route at the contact point 

(e.g., inhalation, ingestion, dermal contact) 

Where one or more of these conditions is not met, an 

exposure pathway is not complete. 

The second step in the exposure assessment process 

involves quantifying exposure for each of the receptors 

and exposure pathways. To estimate the potential risk to 

human health that may be posed by the planned 

herbicide use, it is fist necessary to estimate the 

potential exposure dose of each herbicide for each 

receptor. The exposure dose of each herbicide is 

estimated for each receptor via each exposure 

route/pathway by which the receptor is assumed to be 

exposed. Exposure dose equations combine the 

estimates of herbicide concentration in the 

environmental medium of interest with assumptions 

regarding the type and magnitude of each receptor's 

potential exposure to provide a numerical estimate of 

the exposure dose. The exposure dose is defined as the 

amount of herbicide taken into the receptor and is 

expressed in units of milligrams of herbicide per 

kilogram of BW per day (mg/kg-day). The exposure 

doses are combined with the dose-response values to 

estimate potential risks for each receptor. 

To understand how humans may be exposed to 

herbicides as a result of the BLM vegetation treatment 

program, it is necessary to understand herbicide use 

within the BLM. Within the BLM vegetation treatment 

program, public lands are classified into various land 

programs. Within each program, aerial-, ground- or 

boat-based applications may be used. Various 

application vehicles (airplane, helicopter, all-terrain 

vehicle [ATV], boat, horse, or human) can be used for 

each application type, and for each vehicle, there are 

different application methods, including deposition 

(from an airplane or helicopter), boom/broadcast, and 

spot applications. Similarly, there are different BLM job 

descriptions associated with each application method. It 

is assumed that occupational receptors may be 

incidentally exposed to the herbicide used through 

dermal contact and inhalation exposure pathways. 

These potential exposures are evaluated for each 

herbicide under routine use, and it is assumed that use is 

consistent with label directions. In addition, an 

accidental spill scenario, assuming an herbicide spill to 

worker skin, is evaluated for the occupational receptors. 

Members of the public may also be incidentally exposed 

to herbicides used on public lands. Such receptors may 

include hikers, hunters, berry pickers, swimmers, 

anglers, area residents, and Native Americans using 

natural resources on public lands. Exposures to both 

spray drift and direct spray/accidental spill scenarios are 

evaluated. 

Overview of the BLM Vegetation 

Treatment Program 

This section identifies the land programs, application 

types, application vehicles, and application methods for 

herbicide use in the BLM vegetation treatment program. 

Land Programs 

The BLM vegetation treatment program covers six land 

types or programs: 

BLM Vegetation Treatments Using Herbicides B-28 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

• Rangeland 

• Public Domain Forestland 

• Energy and Mineral Sites 

• Rights-of-way (ROW) 

• Recreation and Cultural Sites 

• Aquatic Sites 

Herbicides are used in rangeland improvement and 

silvicultural practice to improve the potential for 

success of desired vegetation by reducing competition 

for light, moisture, and soil nutrients with less desirable 

plant species. Herbicides are used to manage or restrict 

noxious plant species and to suppress vegetation that 

interferes with manmade structures or transportation 

corridors. 

Weed and vegetation management programs are 

developed to address the occurrence of noxious, 

invasive, and undesirable species which have a negative 

impact on native vegetation, human activities, and 

domestic livestock. Examples of plant species of 

concern include: downy brome, giant salvinia, leafy 

spurge, purple loosestrife, Russian and spotted 

knapweed, tamarisk, and yellow star thistle. The 

noxious weed and poisonous plant control program is 

included as part of the vegetation treatment 

methodology that the BLM uses to maintain the areas 

under its jurisdiction. The BLM uses herbicides, a 

component in an integrated weed management program, 

as one of the options available in its noxious weed 

management program and uses them in varying degrees 

in all land treatment categories. Herbicide use under the 

six land programs is discussed below. 

Rangeland 

Rangeland vegetation treatment operations provide 

forage for domestic livestock and wildlife by removing 

undesirable competing plant species and preparing 

seedbeds for desirable plants. Approximately 89% of 

the herbicide treated acreage in the BLM vegetation 

treatment program falls in the rangeland improvement 

category. 

Of the herbicide active ingredients being evaluated, 

imazapic and diflufenzopyr + dicamba are registered for 

use under rangeland situations. Proposed application 

methods include the following vehicles and methods: 

airplane, helicopter, truck-mounted sprayer 

(boom/broadcast or spot applications), ATV 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). 

Public Domain Forestland 

Public domain forestland vegetation treatment 

operations, designed to ensure the establishment and 

healthy growth of timber crop species, are one of the 

BLM’s least extensive programs for herbicide 

treatment. These operations include site preparation, 

plantation, maintenance, conifer release, precommercial thinning, and non-commercial tree removal. 

Site preparation treatments prepare newly harvested or 

inadequately stocked areas for planting of new tree 

crops. Herbicides used in site preparation reduce 

vegetation that would compete with conifers. In the 

brown-and-burn method of site preparation, herbicides 

are used to dry the vegetation, to be burned several 

months later. Herbicides are used in plantations some 

time after planting to promote the dominance and 

growth of already established conifers (release). Precommercial thinning reduces competition among 

conifers, thereby improving the growth rate of desirable 

crop trees. Non-commercial tree removal is used to 

eliminate dwarf mistletoe infested host trees. These 

latter two silvicultural practices primarily use manual 

applications methods. Herbicide uses in public domain 

forests constitute less than 4% of the vegetation 

treatment operations in the BLM program. 

Imazapic and sulfometuron methyl are proposed for use 

on public domain forestland. Proposed application 

methods include the following vehicles and methods: 

airplane, helicopter, truck (boom/broadcast and spot 

applications), ATV (boom/broadcast or spot 

applications), horseback (spot applications), and 

backpack (spot applications), with the exception that 

sulfometuron methyl would not be applied via airplane. 

Energy and Mineral Sites 

Vegetation treatments in energy and mineral sites 

include the preparation and regular maintenance of 

areas for use as fire control lines or fuel breaks, or the 

reduction of vegetation species that could pose a hazard 

to fire control operations. More than 50% of the 

vegetation treatment programs for energy and minerals 

sites are herbicide applications. 

Of the herbicide active ingredients being evaluated, 

imazapic, diflufenzopyr + dicamba, and sulfometuron 

methyl are proposed for use under the conditions 

described on energy and mineral sites. Proposed 

application methods include the following vehicles and 

BLM Vegetation Treatments Using Herbicides B-29 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

methods: airplane, helicopter, truck (boom/broadcast or 

spot applications), ATV (boom/broadcast or spot 

applications), horseback (spot applications), and 

backpack (spot applications). However, sulfometuron 

methyl would not be applied via airplane, and 

diflufenzopyr + dicamba would not be applied via 

airplane or helicopter. 

Rights-of-way 

Rights-of-way treatments include roadside maintenance 

and maintenance of power transmission lines, 

waterways, and railroad corridors. In roadside 

maintenance, vegetation is removed or reduced from 

ditches and shoulders to prevent brush encroachment 

into driving lanes, to maintain visibility on curves for 

the safety of vehicle operators, to permit drainage 

structures to function as intended, and to facilitate 

maintenance operations. Herbicides have been used in 

nearly 50% of the BLM’s roadside vegetation 

maintenance programs. 

Imazapic, diflufenzopyr + dicamba, and sulfometuron 

methyl are proposed for use on ROW sites. Proposed 

application methods include the following vehicles and 

methods: airplane, helicopter, truck (boom/broadcast or 

spot application), ATV (boom/broadcast or spot 

applications), horseback (spot applications), and 

backpack (spot applications). However, sulfometuron 

methyl would not be applied via airplane, and 

diflufenzopyr would not be applied via airplane or 

helicopter. 

Recreation and Cultural Sites 

Recreation and cultural site maintenance operations 

provide for the safe and efficient use of BLM facilities 

and recreation sites and for permittee/grantee uses of 

public amenities, such as, ski runs, waterways, and 

utility terminals. Vegetation treatments are made for the 

general maintenance and visual appearance of the areas 

and to reduce potential threats to the site’s plants and 

wildlife, as well as, visitor’s health and welfare. The site 

maintenance program includes the noxious weed and 

poisonous plant program. Vegetation treatments in these 

areas are also for fire management. 

The BLM uses herbicides on approximately one-third of 

the total recreation site acreage identified as needing 

regular treatment operations. Imazapic, diflufenzopyr + 

dicamba, and sulfometuron methyl are proposed for use 

on recreation and cultural sites. Proposed application 

methods include the following vehicles and methods: 

airplane, helicopter, truck (boom/broadcast or spot 

application), ATV (boom/broadcast or spot 

applications), horseback (spot applications), and 

backpack (spot applications). However, sulfometuron 

methyl would not be applied via airplane, and 

diflufenzopyr + dicamba would not be applied via 

airplane or helicopter. 

Aquatic Sites 

Aquatic vegetation management involves addressing the 

vegetation in a variety of situations ranging from rivers, 

streams, and canals to ponds, lakes, and water holdings. 

Impacts addressed through the management of aquatic 

vegetation include, but are not limited to, the following: 

altering the flow of water, displacement of 

native/desirable vegetation, and reduction in 

recreational activities. 

Fluridone and diquat are proposed for use on aquatic 

and riparian sites. Proposed application methods include 

the following vehicles and methods: airplane, 

helicopter, boat (boom/broadcast or spot applications), 

truck (boom/broadcast or spot applications), ATV 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). 

However, fluridone would not be applied via spot 

applications using a boat. 

Application Methods 

The BLM conducts pretreatment surveys in accordance 

with BLM Handbook H-9011-1 (Chemical Pest 

Control) before making a decision to use herbicides on 

a specific land area. The herbicides can be applied by a 

number of different methods, and the selected technique 

is dependent upon a number of variables, including the 

following: 

• Treatment objective (removal or reduction) 

• Accessibility, topography, and size of the 

treatment area 

• Characteristics of the target species and the 

desired vegetation 

• Location of sensitive areas in the immediate 

vicinity (potential environmental impacts) 

• Anticipated costs and equipment limitations 

• Meteorological and vegetative conditions of the 

treatment area at the time of treatment 

Herbicide applications are scheduled and designed such 

that there are minimal potential impact on non-target 

BLM Vegetation Treatments Using Herbicides B-30 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

plants and animals, while remaining consistent with the 

objectives of the vegetation treatment program. 

Herbicides are applied either from the air or on the 

ground. The herbicide formulations may be in a liquid 

or granular form, depending upon resources and 

program objectives. Aerial methods employ boommounted nozzles for liquid formulations or rotary 

broadcasters for granular formulations, carried by 

helicopters or airplanes. Ground application methods 

include vehicle- and boat-mounted, backpack, and 

horseback application techniques. Vehicle- and boatmounted application systems use fixed-boom or handheld spray nozzles mounted on trucks or ATVs. 

Backpack systems use a pressurized sprayer to apply an 

herbicide as a broadcast spray directly to one or a group 

of individual plants. Aerial, ground, and aquatic 

application methods are discussed later in this section. 

Aerial Application Methods 

Aerial application methods can be conducted using 

either airplanes (fixed-wing aircraft) or helicopters 

(rotary-wing aircraft). Historically, the BLM has used 

aerial application in more than 50% of its herbicide 

treatment programs. Helicopters have been used more 

than 60% of the time on rangeland projects because the 

many treatment units are far apart and are often small 

and irregularly shaped. 

The size and type of these aircraft may vary, but the 

equipment used to apply the herbicides must meet 

specific guidelines. Contractor-operated helicopters or 

fixed-wing aircraft are equipped with an herbicide tank 

or bin (depending on whether the herbicide is a liquid or 

granular formulation). For aerial spraying, the aircraft is 

equipped with cylindrical jet-producing nozzles no less 

than 1/8-inch diameter. The nozzles are directed with 

the slipstream, at a maximum of 45 degrees downward 

for fixed-wing, or up to 75 degrees downward for 

helicopter application, depending on the flight speed. 

Nozzle size and pressure are designed to produce 

droplets with a diameter of 200 to 400 microns. For 

fixed-wing aircraft, the spray boom is typically 3⁄4 of the 

wingspan, and for helicopters, the spray boom is often 

3⁄4 of the rotor diameter. All spray systems must have a 

positive liquid shut-off device that ensures that no 

herbicide continues to drip from the boom once the pilot 

has completed a swath (i.e., specific spray path). The 

nozzles are spaced to produce a uniform pattern for the 

length of the boom. 

Using helicopters for herbicide application is often more 

expensive than using fixed-wing aircraft, but helicopters 

offer greater versatility. Helicopters are well adapted to 

areas dominated by irregular terrain and long, narrow, 

and irregularly shaped land patterns, a common 

characteristic of public lands. Various helicopter aircraft 

types are used, including Bell, Sikorsky, and Hiller 

models. These helicopters must be capable of 

accommodating the spray equipment and the herbicide 

tank or bin and of maintaining an air speed of 40 to 50 

miles per hour at a height of 30 to 45 feet above the 

vegetation (depending upon the desired application rate 

[AR]), and they must meet BLM safety performance 

standards. 

Fixed-wing aircraft include the typical, small 

“cropduster” type aircraft. Fixed-wing aircraft are best 

suited for smoother terrain and larger tracts of land 

where abrupt turning is not required. Because the fixedwing aircraft spraying operations are used for treating 

larger land areas, the price per acre is generally lower 

than for helicopter spraying. Aircraft capability 

requirements for fixed-wing aircraft are similar to 

helicopter requirements, except that an air speed of 100 

to 120 miles per hour is necessary, with spraying 

heights of 10 to 40 feet generally used to produce the 

desired ARs. 

Batch trucks are an integral part of any aerial 

application operation. They serve as mixing tanks for 

preparing the correct proportions of herbicide and 

carrier, and they move with the operation when different 

landing areas are required. 

The number of workers involved in a typical aerial 

spray project varies according to the type of activity. A 

small operation may require up to six individuals, while 

a complex operation may require as many as 20 to 35 

workers. An aerial operations crew for range 

management, noxious weed management, and ROW 

maintenance usually consists of five to eight 

individuals. Typically, personnel on a large project 

include a pilot, a mixer/loader, a contracting officer’s 

representative, an observer-inspector, a one-to sixmember flagging crew, one or two law enforcement 

officers, one or two water monitors, and one or two 

laborers. Optional personnel include an air operations 

officer, a radio technician, a weather monitor, and a 

recorder. Workers evaluated in the HHRA for aerial 

applications include a pilot and a mixer/loader, as these 

are the receptors most likely to be exposed to 

herbicides. Other personnel are expected to have less or 

similar herbicide exposure. 

BLM Vegetation Treatments Using Herbicides B-31 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Ground Application Methods 

The BLM does not use ground application extensively. 

In vegetation treatment projects, ground herbicide 

applications normally constitute about 45% of the total 

area that the BLM treats with herbicide. There are two 

types of ground application methods, including human 

application methods (backpack and horseback) and 

vehicle application which includes ATV-based 

application methods (spot-treatment or boom/broadcast 

treatment), and truck-mounted application methods 

(spot-treatment or boom/broadcast treatment). These are 

described in greater detail below. 

Human Application Methods. Humans using either 

backpack or horseback application methods may apply 

herbicides. The backpack method requires the use of a 

backpack spray tank for carrying the herbicide with a 

handgun applicator with a single nozzle for herbicide 

application. These techniques are best adapted for very 

small scale spraying in isolated spots and those areas 

that are not accessible by vehicle. They are primarily 

used for spot treatments around sign posts, spraying 

competing trees in public domain forestland, 

delineators, power poles, scattered noxious weeds, and 

other areas that require selective spraying. 

Backpack treatment is the predominant ground-based 

method for silviculture and range management. The 

principal hand application techniques are injection and 

stump treatment. Injection involves applying an 

herbicide with the hand-held container or injector 

through slits cut into the stems of target plants. 

Individual stem treatment by the injection method is 

also used for thinning crop trees or removing the 

undesirable trees. Stump treatment entails directly 

applying liquid herbicide to the cut stump of the target 

plant to inhibit sprouting. An herbicide can be applied 

by dabbing or painting the exposed cambium of a stump 

or using a squeeze bottle on a freshly cut cambium 

surface. Along with liquid formulations, certain active 

ingredients are formulated in a granular form that 

allows for direct application to the soil surface. 

Pressurized backpack treatment operations typically 

involve a supervisor (who may also function as a 

mixer/loader), an inspector, a monitor, and 2 to 12 

crewmembers. The receptor evaluated in this risk 

assessment is a combined applicator/mixer/loader. 

Vehicle Application Methods. Herbicide treatments 

may use ground-based spray applications using either a 

truck or an ATV. Vehicular application is made using a 

boom with several spray nozzles (boom/broadcast 

treatment) or a handgun with a single nozzle (spot 

treatment). Ground vehicle spray equipment can be 

mounted on ATVs or trucks. Because of its small size 

and agility, the ATV can be adapted to many different 

situations. 

The boom spray equipment used for vehicle operations 

is designed to spray wide strips of land where the 

vegetation does not normally exceed 18 inches in height 

and the terrain is generally smooth and free of deep 

gullies. Ground spraying from vehicles occurs along 

highway ROW, energy and mineral sites, public domain 

forestlands, and rangeland sites. 

Ground spraying operations are also conducted from 

vehicles using spot-gun spraying. The spot-gun 

technique is best adapted for spraying small, scattered 

plots. It may also be used in spraying sign posts and 

delineators within highway ROW and around wooden 

power lines as a means of reducing fire hazards within 

power line ROW. This technique is also used to treat 

scattered noxious weed vegetation, but it is limited to 

those areas that are accessible by vehicles. 

Rights-of-way maintenance projects frequently use 

vehicle-mounted application techniques. A truck with a 

mixing/holding tank uses a front mounted spray boom 

or a hand-held pressurized nozzle to treat roadside 

vegetation on varying slopes. However, using this 

equipment for off-road ROW projects is limited to 

gentle slopes (less than 20%) and open terrain. Workers 

typically include a driver/mixer/loader and an 

applicator. Therefore, receptors evaluated in this HHRA 

include an applicator, a mixer/loader, and a combined 

applicator/mixer/loader. 

Aquatic Application Methods 

Aquatic vegetation, at moderate growth levels, is useful 

because it produces oxygen, food, and cover for fish and 

other aquatic organisms. However, in overabundance, 

aquatic plants can become weedy, crowd out desirable 

plants, adversely affect other aquatic life, and interfere 

with human uses of water. 

Aquatic Application Techniques. 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 feet 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 (SA) should be treated at a time. Applications are 

made to floating or emergent weeds with the spray 

mixture being applied directly to the plants. 

BLM Vegetation Treatments Using Herbicides B-32 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

The whole body of water is treated when working in 

this particular zone. Treatments are usually made to 1/4 

to 1/3 of the total water volume at a time. 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. 

Treating the deepest 1 to 3 feet of water is the principle 

behind making applications in the bottom-layer zone. 

Such treatments 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. 

Aquatic Application Equipment. To treat small areas, 

a compressed-air sprayer with a hand-operated pump 

may be all that is needed. Higher-quality compressedair sprayers with CO2 gas for constant pressure are 

available, but are more expensive. 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. 

Booms with flexible hoses attached to the boom may be 

used to make the application below the water surface. 

Applications of granules and slow-release 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. 

Vegetation Management – Static Water. Static water 

is water in ponds, lakes, or reservoirs that has little or no 

inflow and outflow. Floating and emersed vegetation 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. 

Submersed vegetation and algae can be managed 

through spray or granular applications. Spray 

applications can be made by aircraft, boat, or ground 

application equipment. Applications can be made under 

the water surface by injection through a hose pulled 

behind a boat or by a series of hoses attached to a boom 

that is attached to the boat. Granular herbicides may be 

broadcast by hand or manual spreaders over small areas. 

Special granule spreaders mounted on aircraft or boats 

are used for large-scale applications. 

Vegetation Management – Flowing Water. Aquatic 

vegetation in flowing water is difficult to manage. 

Floating and emersed 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. 

Herbicide Use Parameters 

The ARs are dependent on the target species, the 

presence and condition of non-target vegetation, the soil 

type, the depth to the water table, and the presence of 

other water sources. Tables B-4 to B-9 summarize the 

vegetation treatment program for each of the herbicides. 

Both typical and maximum ARs (in units of pounds of 

a.i. per acre [lb a.i./acre]) are provided for each 

application scenario, vehicle, and method in each land 

program. As can be seen in the tables, and as discussed 

above, not all herbicides are used for all potential 

applications. The ARs for fluridone depend on the type 

of water body (i.e., pond, stream, lake). Therefore, the 

highest typical and maximum ARs for fluridone were 

employed (highest typical is for a pond, and highest 

maximum is for a partial lake/reservoir). 

Occupational Receptors 

A receptor and the exposure pathways by which that 

receptor may come into contact with herbicides used in 

the BLM vegetation treatment program define an 

exposure scenario. Both routine use and accidental 

exposure scenarios are included in the occupational 

evaluation. 

Routine Use Exposure Scenarios 

For aerial applications, occupational receptors that may 

come into contact with herbicides include: 

• Pilot 

• Mixer/loader 

BLM Vegetation Treatments Using Herbicides B-33 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

For ground applications by backpack, as the operation is 

generally very small in scale, the occupational receptor 

is assumed to be an: 

• Applicator/mixer/loader 

For the remaining application methods (horseback; and 

spot and boom/broadcast methods for ATV, truck 

mount and boat applications), the herbicide treatment 

job could be large enough to support a crew, in which 

case the applicator may be a person different from the 

mixer/loader. Alternatively, the job may be small 

enough that the applicator and the mixer/loader are the 

same person. Therefore, for these application methods, 

the following occupational receptors are evaluated: 

• Applicator 

• Mixer/loader 

• Applicator/mixer/loader 

Exposure assumptions for the occupational receptors 

were derived using information from the BLM 

concerning proposed use of the herbicides and unit 

exposure (UE) information from the Pesticide Handlers 

Exposure Database (PHED), which is a generic 

database containing empirical dermal and inhalation 

exposure data for workers mixing, loading, or applying 

pesticides (USEPA 1998a). 

Workers are assumed to weigh 70 kg, which is the 

weight recommended by the USEPA in its Standard 

Default Exposure Assumptions (USEPA 1991). 

Estimates of the number of hours per day a worker may 

be engaged in applying herbicides, the number of days 

per year the worker applies herbicides, and the years of 

potential exposure were provided by the BLM. The 

BLM also provided data regarding the number of acres 

treated (AT) per hour. 

A description of the PHED is provided in a peerreviewed article by Leighton and Nielsen (1995). The 

PHED was developed by the PHED Task Force, which 

consists of representatives from the USEPA, Health 

Canada, the California Department of Pesticide 

Regulation, and member companies of Crop Life 

America. To add consistency to the risk assessment 

process, the USEPA, in conjunction with the PHED 

Task Force, has evaluated all data within the system and 

developed surrogate exposure tables that contain a 

series of standard UE values for various exposure 

scenarios. The majority of the UE values used in this 

risk assessment have been taken from this “surrogate” 

table. In addition to the values presented in this table, 

the USEPA recommended UEs separately for aquatic 

applications of diquat and fluridone. Generally, UEs are 

expressed in units of mg/lb a.i. and equate the 

milligrams of a.i. absorbed by an occupational receptor 

to the pounds of a.i. handled in a given day or exposure 

scenario. 

For the dermal exposure pathway for terrestrial 

herbicides, two sets of UEs are used assuming that 

worker personal protective equipment (PPE) requires 

gloves or does not require gloves. The Oust®

(sulfometuron methyl) label does not require the use of 

gloves, therefore, the UEs for workers not wearing 

gloves were used for this herbicide. Unit exposures 

based on workers wearing gloves were used for the 

remaining terrestrial herbicides, which are Overdrive®

(diflufenzopyr) and Plateau® (imazapic), because the 

labels for these two herbicides state that gloves must be 

worn when applying the herbicides. 

The UEs for aquatic applications were developed for 

this HHRA after consultation with the USEPA (J. Evans 

2003k). For aquatic use of Reward® (diquat), the 

USEPA recommended the use of dermal UE values (in 

units of mg/hr) presented in the Reregistration 

Eligibility Decision (RED) document for diquat 

(USEPA 1995). Specifically, the UEs for hydrilla 

control–applicator and hydrilla control–mixer were 

used. There are no inhalation UEs for this application. 

The USEPA (1995) obtained these UEs from a study 

evaluating worker exposure to paraquat and diquat in 

Florida (Wojeck et al. 1983). For aquatic use of Sonar® 

A.S. (fluridone), the USEPA recommended the use of 

UEs specific for granular application listed in the PHED 

(USEPA 1998a). The Reward® (diquat) label requires 

the use of gloves. The Sonar® A.S. (fluridone) label 

does not discuss the use of PPE, but states that skin 

contact should be avoided. 

Accidental Exposure Scenarios 

Accidental exposures for occupational receptors could 

occur via spills, hose breaks on application equipment, 

or direct spray onto a worker. As a worst case scenario 

for an accidental exposure, a direct spill event on an 

occupational receptor is evaluated. The spill scenario 

evaluated by the BLM in the Final EIS Vegetation 

Treatment on BLM Lands in Thirteen Western States

(1991 13-State EIS; USDI BLM 1991) assumed that 0.5 

L of the formulation is spilled on a worker receptor. It is 

assumed that the 80% of the spill lands on clothing and 

20% lands on bare skin. The penetration rate through 

clothing is assumed to be 30%. 

BLM Vegetation Treatments Using Herbicides B-34 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Public Receptors 

Public lands administered by the BLM are diverse and 

include rangeland, public forestland, energy and 

minerals sites, ROW, and recreational and cultural sites. 

Lakes, ponds, and waterways may also be present on 

these lands. Public land is used by the public for a 

variety of occupational, recreational, and cultural 

activities. Hunters and hikers enjoy these public lands as 

well as anglers and swimmers. Harvesting of natural 

resources by the public occurs on these lands including 

berry picking, harvesting of fish for consumption, and 

the gathering of materials for Native American crafts 

such as basket weaving. 

When herbicides are used as part of a vegetation 

treatment program on public lands, the BLM takes care 

to flag the area to be treated and to post the area with 

warnings about when re-entry can occur safely. 

This HHRA evaluates the potential risk to public 

receptors using public lands treated with herbicides by 

developing exposure scenarios that combine potential 

receptors and exposure pathways to identify potential 

worst-case exposures to the herbicides addressed in this 

PEIS. Two types of public use exposure scenarios are 

addressed: 

• Potential exposure during routine use of public 

lands to herbicides that may have drifted 

outside of the area of application. 

• Accidental scenarios where public receptors 

may prematurely enter a sprayed area, be 

sprayed directly, or may contact water bodies 

that have accidentally been sprayed directly or 

into which an herbicide mixture has 

accidentally been spilled. 

Although all of these public scenarios are expected to 

occur rarely, they are nonetheless used as the basis for 

evaluating potential public health risks associated with 

herbicide use in the BLM vegetation treatment program. 

Based on consideration of potential public uses of BLM 

lands and consistent with the 1991 13-State EIS 

receptors evaluated in this HHRA include the following: 

• Hiker/hunter 

• Berry picker - child and adult 

• Angler 

• Swimmer - child and adult 

• Nearby resident - child and adult 

• Native American – child and adult 

Although there are many different exposure scenarios 

and receptors that could be evaluated, these receptors 

cover a range of potential exposures that could occur 

under worst case conditions on public lands. It is 

assumed that these receptors could be exposed through 

one or more of the following exposure pathways: 

• Dermal contact with spray 

• Dermal contact with foliage 

• Dermal contact with water while swimming 

• Occasional ingestion of drinking water or 

incidental ingestion of water while swimming 

• Ingestion of berries 

• Ingestion of fish 

Although all public receptor exposures to herbicide 

active ingredients used on public lands are considered to 

be accidental, public receptor exposures are evaluated 

under two scenarios. Routine-use exposures are 

assumed to occur when public receptors come into 

contact with environmental media that have been 

impacted by spray drift. As discussed earlier, doseresponse values are available for short, intermediate, 

and long-term exposures. While it is possible that public 

receptors use public lands under intermediate- and longterm time frames, it is unlikely that public receptors 

would be exposed to herbicides under the routine use 

scenario for more than a short-term exposure, which is 

defined as 1 day to 1 month (USEPA 2001h). 

Therefore, short-term dose-response values are used to 

evaluate the public receptors under the routine use 

exposure scenario. To account for the unlikely 

possibility that public receptors could repeatedly enter 

areas that have been recently sprayed, the uncertainty 

analysis includes an evaluation of the public receptors 

under an intermediate and a long-term exposure 

scenario. Accidental exposures are assumed to occur 

when public receptors come into contact with 

environmental media that have been subject to direct 

spray or spills. Tables B-4 through B-9 show for each 

herbicide a.i. the receptors and exposure pathways 

evaluated. Each of these scenarios is discussed below. 

Routine Use Exposure Scenarios 

Signage is used to identify areas that are directly 

sprayed under the BLM vegetation treatment program 

and to warn against reentry. It is assumed that under 

BLM Vegetation Treatments Using Herbicides B-35 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

routine conditions, these warnings are heeded. 

Therefore, public exposures under routine use scenarios 

are assumed to occur “off-site,” where “on-site” is the 

area that has been directly sprayed. 

Although all precautions are taken to limit the amount 

of spray drift from an herbicide application, spray drift 

can result in deposition of herbicide on areas outside of 

the directly sprayed area. Spray drift is associated with 

larger spraying efforts, such as those from aerial or 

boom/broadcast applications. It is assumed that a public 

receptor could walk through vegetated areas upon 

which spray drift had settled. If the spray drift deposits 

in areas where there are wild berries, a public receptor 

could ingest those berries. Spray drift could also settle 

on bodies of water, and those water bodies could be 

contacted by a public receptor either while swimming or 

could be used as a source of water for drinking while 

hiking. Fish could also be ingested from spray driftimpacted bodies of water. Because spray drift could 

potentially affect several environmental media, the 

exposure scenarios developed for each receptor have 

assumed exposure to multiple environmental media. 

The Native American scenario was developed following 

recommendations by the USEPA (2003d). The specific 

receptor is a Native American basket weaver involved 

in gathering plant materials and other activities related 

to weaving baskets. The USEPA suggests evaluating the 

dermal contact with foliage exposure pathway. In its 

memorandum, the USEPA states: 

“It is expected that the oral intake of herbicides 

will be minimal by comparison to the above 

dermal exposure pathway. That is because basket 

weavers tend to “spit-off” plant residues (due to 

after taste) when mouth stripping plant materials” 

(personal communication with M. Dong, 

California Department of Pesticide Regulation). 

For completeness, in addition to the dermal contact 

pathway recommended by the USEPA (2003d), the 

Native American (adult and child) is also assumed to be 

exposed through spray drift, berry ingestion, dermal 

contact while swimming, water for drinking, and fish 

ingestion. 

Accidental Exposure Scenarios 

In addition to exposures due to inadvertent spray drift, 

this HHRA also evaluates potential acute accidental 

exposures by public receptors to the herbicides. 

Accidental exposure could occur through direct spray 

and spills. The same types of receptors introduced 

above are also evaluated for the accidental scenarios. 

However, because direct spray or spills are localized, 

exposures to multiple media are not assumed in these 

scenarios. It is assumed that each of the herbicides could 

be directly sprayed onto humans, foliage, and berries, 

and each of the herbicides could be directly sprayed or 

spilled into a water body. For the aquatic herbicides 

(fluridone and diquat), the direct spray pathway is a 

reentry scenario. 

Direct Spray 

Direct Spray on Receptors. In this scenario it is 

assumed that a receptor is accidentally sprayed with 

herbicide because they have entered a spray area and are 

beneath a spray aircraft or other mode of application. 

Direct spray contact is evaluated for: 

• Adult receptor - hiker/hunter, berry picker, 

angler, nearby resident, and Native American 

• Child receptor - berry picker, nearby resident, 

and Native American 

Contact with Directly Sprayed Vegetation. Re-entry 

is a term used to describe entering an area that has just 

been sprayed (i.e., an “on-site” area, in contrast with the 

scenarios in the previous section where exposure to 

areas of “off-site” spray drift deposition is evaluated). 

Contact with just-sprayed vegetation may result in 

dermal exposure by hikers, berry pickers, and anglers. 

In addition, berry pickers may ingest directly sprayed 

fruit. This scenario is also evaluated for the aquatic 

herbicides, diquat and fluridone, assuming inadvertent 

spraying of terrestrial vegetation. 

Dermal contact with just-sprayed vegetation is 

evaluated for: 

• Adult receptor - hiker/hunter, berry picker, 

angler, nearby resident, and Native American 

• Child receptor - berry picker, nearby resident, 

and Native American 

Ingestion of directly sprayed berries is evaluated for: 

• Adult receptor - berry picker, nearby resident, 

and Native American 

• Child receptor - berry picker, nearby resident, 

and Native American 

Direct Spray onto Water Body. Direct spray onto 

water bodies could occur inadvertently for the three 

herbicides that are used for terrestrial applications 

BLM Vegetation Treatments Using Herbicides B-36 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

(diflufenzopyr, imazapic, and sulfometuron methyl). 

The aquatic herbicides, diquat and fluridone, would be 

used for treatment of the water body. Therefore, 

exposure to a water body treated with diquat and 

fluridone is similar to a re-entry scenario evaluated for 

the terrestrial herbicides. The exposure scenarios for 

both the inadvertently-sprayed and treated water bodies 

are the same. Incidental ingestion and dermal contact 

with water while swimming is evaluated for: 

• Adult receptor - swimmer 

• Child receptor - swimmer 

In addition, the Native American child and adult 

receptors are evaluated for dermal contact while 

swimming and ingestion of drinking water. While 

incidental ingestion of water could occur for this 

receptor while swimming, incidental ingestion was not 

evaluated separately because it results in minimal 

exposure compared to drinking water exposure. 

An angler could fish in and ingest fish from a directly 

sprayed water body. Therefore, fish ingestion is 

evaluated for: 

• Adult receptor – angler and Native American 

• Child receptor - Native American 

In addition, hikers, berry pickers, anglers, and Native 

American receptors could get part of their day's water 

for drinking from a directly sprayed water body. 

Occasional drinking water ingestion is evaluated for: 

• Adult receptor - hiker/hunter, berry picker, 

angler, and Native American 

• Child receptor - berry picker and Native 

American 

Spills 

Members of the public may be exposed to an herbicide 

present in water if a load of herbicide mixture is spilled 

or if a container of herbicide concentrate breaks open 

and spills into a pond. Under this scenario, it is assumed 

that a fully loaded truck or helicopter empties its 

contents into a pond while transporting herbicide to an 

application site. However, it is BLM policy that 

herbicides are mixed at the application site. Therefore, 

this scenario represents a conservative, worst-case 

scenario that is unlikely to occur. 

To evaluate this scenario, it is assumed that a pond is 

subjected to a spill of 140 gallons of herbicide mix from 

a helicopter or 200 gallons of herbicide mix from a 

batch truck. These amounts are approximately the 

largest amounts that can be carried in helicopters or 

trucks, respectively, as used by the BLM. It is assumed 

that the pond size is 1⁄4 acre and 1 meter deep, in 

accordance with the Ecological Risk Assessment (ERA) 

Protocol (ENSR 2004). 

The same receptors and exposure pathways listed above 

for the directly sprayed water body are evaluated for the 

water body that has received a direct spill. 

Exposure Parameters for Public Receptors 

Exposure parameters are the same for routine-use and 

accidental scenarios. Various guidelines and databases, 

such as the USEPA’s Exposure Factors Handbook

(USEPA 1997a) and their draft paper “Framework for 

Assessing Non-Occupational, Non-Dietary (Residential) 

Exposure to Pesticides” (USEPA 1998b), were used to 

develop the exposure parameters. For each exposure 

scenario, the exposure parameters were used to 

calculate an exposure factor (EF), which is then used in 

risk calculations. The use of the EF combines all the 

exposure parameters into one value in order to simplify 

the risk calculations. All adult receptors are assumed to 

weigh 70 kg, and child receptors are assumed to weigh 

15 kg (USEPA 1991). 

Hiker/Hunter 

The hiker/hunter (adult) is assumed to be potentially 

exposed to herbicides via dermal contact with spray, 

dermal contact with sprayed foliage, and ingestion of 

drinking water from a sprayed pond. The hiker/hunter is 

assumed to weigh 70 kg and ingest 2 liters of water 

while hiking (USEPA 1991). It is assumed that the 

hiker/hunter’s lower legs, lower arms, and hands are 

exposed for potential herbicide contact. The 50th

percentile SA of the lower legs, lower arms, and hands 

for men and women is 4,504 cm2

 and was calculated 

based on data in the Exposure Factors Handbook 

(USEPA 1997a). The 50th percentile values were used 

in accordance with USEPA guidance (USEPA 1989). 

The hiker/hunter is assumed to contact foliage for 2 

hours per day. This is the 50th percentile value for time 

spent outdoors away from dwelling or vehicles (USEPA 

1997a). The dermal Transfer Coefficient (Tc) is used to 

estimate the amount of herbicide that may be transferred 

from foliage to skin. A Tc value of 1,000 cm2

/hour was 

selected for the hiker/hunter. The Tc is the central 

tendency value for scouting grapes and sweet corn, and 

was recommended as a surrogate for scouting activity 

BLM Vegetation Treatments Using Herbicides B-37 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

for berries (USEPA 2000b [referenced by USEPA 

2002c]). 

Berry Picker 

The berry pickers (adult and child) are assumed to be 

potentially exposed to herbicides via dermal contact 

with spray, dermal contact with sprayed foliage, 

ingestion of drinking water from a sprayed pond, and 

ingestion of berries containing spray. The adult berry 

picker is assumed ingest 2 liters of water while berry 

picking, and the child berry picker is assumed to ingest 

1 liter of water while berry picking (USEPA 1991). It is 

assumed that the berry picker’s lower legs, lower arms, 

and hands are exposed for potential herbicide contact. 

The 50th percentile SA of the lower legs, lower arms, 

and hands for adult men and women is 4,504 cm2

, and 

was calculated based on data in the Exposure Factors 

Handbook (USEPA 1997a). The 50th percentile SA of 

the lower legs, lower arms, and hands for children is 

1,607 cm2

, and was calculated based on data in the 

Exposure Factors Handbook (USEPA 1997a). The 

adult and child berry pickers are assumed to contact 

foliage for 2 hours per day. A Tc value of 1,500 

cm

2

/hour was selected for the adult berry picker. This 

value is the high end Tc for harvesting blueberries 

(USEPA 2000b). A value of 300 cm2

/hour based on the 

child to adult surface area ratio (SAR; CalEPA 1996) 

was selected for the child berry picker. 

Berry ingestion rates (IRs) for this receptor were 

assumed to be the same as those used for the Native 

American adult and child. Harper et al. (2002) list an IR 

of 320 g/day for an adult for above ground gathered 

terrestrial vegetation for the Native American Spokane 

tribe. Berries are likely to be a small fraction of this 320 

g/day. However, since this rate was not subdivided into 

additional categories, it was conservatively assumed 

that the IR for berries is 320 g/day for an adult Native 

American. The use of this value for the berry picker 

receptor is conservative because the berry IR for the 

berry picker is likely to be lower than that for the Native 

American, who could have a higher rate of subsistence 

activities. For the child berry picker, the IR was scaled 

by BW (i.e., 320 g/day x 15 kg / 70 kg) to 69 g / day. 

The berry IR was converted to units of cm2

/day because 

of the equation used to evaluate this pathway (USEPA 

2002c). 

Angler 

The angler (adult) is assumed to be potentially exposed 

to herbicides via dermal contact with spray, dermal 

contact with sprayed foliage, ingestion of drinking 

water from a sprayed pond, and ingestion of fish from a 

sprayed pond. The angler is assumed ingest 2 liters of 

water while fishing (USEPA 1991). It is assumed that 

the angler’s lower legs, lower arms, and hands are 

exposed for potential herbicide contact. The 50th

percentile SA of the lower legs, lower arms, and hands 

for men and women is 4,504 cm2

, and was calculated 

based on data in the Exposure Factors Handbook

(USEPA 1997a). The angler is assumed to contact 

foliage for 2 hours per day. A Tc value of 1,000 

cm

2

/hour was selected for the angler, similar to the 

value used for the hiker/hunter. The Tc is the central 

tendency value for scouting grapes and sweet corn, and 

was recommended as a surrogate for scouting activity 

for berries (USEPA 2000b [referenced by USEPA 

2002c]). The angler is assumed to ingest 63 grams of 

fish per day, which is the 95th percentile long-term fish 

IR listed in the Exposure Factors Handbook (USEPA 

1997c) for the general population. 

Swimmer 

The swimmers (adult and child) are assumed to be 

potentially exposed to herbicides via dermal contact 

with and incidental ingestion of water from a sprayed 

pond. The USEPA (2001d) recommends an exposed SA 

of 18,000 cm2

 for an adult swimmer and 6,600 cm2 for a 

child swimmer. It is assumed that 50 milliliters (mL; 

0.05 L) of water are ingested from the pond while 

swimming for an hour (USEPA 1989). 

Nearby Resident 

The nearby residents (adult and child) are assumed to be 

potentially exposed to herbicides via dermal contact 

with spray, dermal contact with sprayed foliage, and 

ingestion of berries containing spray. It is assumed that 

the resident could contact foliage in their yard, as well 

as foliage areas outside the house. It is assumed that the 

resident gathers berries from bushes located outside the 

house. 

It is assumed that the resident’s lower legs, lower arms, 

and hands are exposed for potential herbicide a.i. 

contact. The 50th percentile SA of the lower legs, lower 

arms, and hands for adult men and women is 4,504 cm2

, 

and was calculated based on data in the Exposure 

Factors Handbook (USEPA 1997a). The 50th percentile 

SA of the lower legs, lower arms, and hands for 

children is 1,607 cm2 and was calculated based on data 

in the Exposure Factors Handbook. 

BLM Vegetation Treatments Using Herbicides B-38 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-4 

Summary of Herbicide Use - Dicamba 

Application Information Herbicide1

Acres Treated 

Per Hour 

Dicamba Portion of 

Distinct®/Overdrive®

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 Y 0.1875 0.25 Human 

Horseback 0.75 1 Y 0.1875 0.25 

Spot 0.25 0.5 Y 0.1875 0.25 ATV Boom/broadcast 0.8 1.6 Y 0.1875 0.25 

Spot 0.38 1 Y 0.1875 0.25 

Rangeland 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.1875 0.25 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Public 

Domain 

Forest 

Land Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 Y 0.1875 0.25 Human 

Horseback 0.75 1 Y 0.1875 0.25 

Spot 0.25 0.5 Y 0.1875 0.25 ATV 

Boom/broadcast 0.8 1.6 Y 0.1875 0.25 

Spot 0.38 1 Y 0.1875 0.25 

Energy 

and 

Mineral 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.1875 0.25 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 Y 0.1875 0.25 Human 

Horseback 0.75 1 Y 0.1875 0.25 

Spot 0.25 0.5 Y 0.1875 0.25 ATV 

Boom/broadcast 0.8 1.6 Y 0.1875 0.25 

Spot 0.38 1 Y 0.1875 0.25 

Rights-ofway Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.1875 0.25 

BLM Vegetation Treatments Using Herbicides B-39 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-4 (Cont.) 

Summary of Herbicide Use - Dicamba 

Application Information Herbicide1

Acres Treated 

Per Hour 

Dicamba Portion of 

Distinct®/Overdrive®

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 Y 0.1875 0.25 Human 

Horseback 0.75 1 Y 0.1875 0.25 

Spot 0.25 0.5 Y 0.1875 0.25 ATV 

Boom/broadcast 0.8 1.6 Y 0.1875 0.25 

Spot 0.38 1 Y 0.1875 0.25 

Recreation 

and 

Cultural 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.1875 0.25 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Boat Spot 0.63 2 N NA NA 

(diquat) Boom/broadcast 1.3 3 N NA NA 

Boom/broadcast 

(granular) 6.25 5.8 NA NA NA 

Aquatic 

Aquatic 

Boat 

(fluridone) Boom/broadcast 

(liquid) 17.5 16.7 NA NA NA 

1

 All data are based on a single application. 

Typical = Typical application rate; and Max = Maximum application rate. 

NA = Not applicable. 

BLM Vegetation Treatments Using Herbicides B-40 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-5 

Summary of Herbicide Use - Diflufenzopyr 

Application Information Herbicide1

Acres Treated 

Per Hour 

Diflufenzopyr portion of 

Distinct®/Overdrive®

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 Y 0.075 0.1 Human 

Horseback 0.75 1 Y 0.075 0.1 

Spot 0.25 0.5 Y 0.075 0.1 ATV Boom/broadcast 0.8 1.6 Y 0.075 0.1 

Spot 0.38 1 Y 0.075 0.1 

Rangeland 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.075 0.1 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Public 

Domain 

Forest 

Land Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 Y 0.075 0.1 Human 

Horseback 0.75 1 Y 0.075 0.1 

Spot 0.25 0.5 Y 0.075 0.1 ATV 

Boom/broadcast 0.8 1.6 Y 0.075 0.1 

Spot 0.38 1 Y 0.075 0.1 

Energy 

and 

Mineral 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.075 0.1 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 Y 0.075 0.1 Human 

Horseback 0.75 1 Y 0.075 0.1 

Spot 0.25 0.5 Y 0.075 0.1 ATV 

Boom/broadcast 0.8 1.6 Y 0.075 0.1 

Spot 0.38 1 Y 0.075 0.1 

Rights-ofway Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.075 0.1 

BLM Vegetation Treatments Using Herbicides B-41 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-5 (Cont.) 

Summary of Herbicide Use - Diflufenzopyr 

Application Information Herbicide1

Acres Treated 

Per Hour 

Diflufenzopyr portion of 

Distinct®/Overdrive®

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 Y 0.075 0.1 Human 

Horseback 0.75 1 Y 0.075 0.1 

Spot 0.25 0.5 Y 0.075 0.1 ATV 

Boom/broadcast 0.8 1.6 Y 0.075 0.1 

Spot 0.38 1 Y 0.075 0.1 

Recreation 

and 

Cultural 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.075 0.1 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Boat Spot 0.63 2 N NA NA 

(diquat) Boom/broadcast 1.3 3 N NA NA 

Boom/broadcast 

(granular) 6.25 5.8 N NA NA 

Aquatic 

Aquatic 

Boat 

(fluridone) Boom/broadcast 

(liquid) 17.5 16.7 N NA NA 

1

 All data are based on a single application. 

Typical = Typical application rate; and Max = Maximum application rate. 

NA = Not applicable. 

BLM Vegetation Treatments Using Herbicides B-42 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-6 

Summary of Herbicide Use - Diquat 

Application Information Herbicide1

Acres Treated 

Per Hour Diquat (Reward®)

2

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Used 

(Y/N)? Program Scenario Vehicle Method Typical Max 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Rangeland 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Public 

Domain 

Forest 

Land Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Energy 

and 

Mineral 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Rights-ofway Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

BLM Vegetation Treatments Using Herbicides B-43 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-6 (Cont.) 

Summary of Herbicide Use - Diquat 

Application Information Herbicide1

Acres Treated 

Per Hour Diquat (Reward®)

2

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Recreation 

and 

Cultural 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 Y 1 4 Aerial 

Helicopter Rotary 100 200 Y 1 4 

Backpack 0.2 0.4 Y 1 4 Human 

Horseback 0.75 1 Y 1 4 

Spot 0.25 0.5 Y 1 4 ATV 

Boom/broadcast 0.8 1.6 Y 1 4 

Spot 0.38 1 Y 1 4 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 1 4 

Boat Spot 0.63 2 Y 1 4 

(diquat) Boom/broadcast 1.3 3 Y 1 4 

Boom/broadcast 

(granular) 6.25 5.8 N NA NA 

Aquatic 

Aquatic 

Boat 

(fluridone) Boom/broadcast 

(liquid) 17.5 16.7 N NA NA 

1

 All data are based on a single application. 

2

 BLM specified typical and maximum application rates for four different water bodies: Ponds, Whole Lake/Reservoir, Partial 

Lakes/Reservoir, and Canals. The highest typical application rate (Pond) was selected for use as the typical rate and the highest 

maximum application rate (Partial Lake/Reservoir) was selected for use as the maximum application rate. Application rates are 

dependent on water depth, which is assumed to be 1 meter. 

Typical = Typical application rate; and Max = Maximum application rate. 

NA = Not applicable. 

BLM Vegetation Treatments Using Herbicides B-44 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-7 

Summary of Herbicide Use - Fluridone 

Application Information Herbicide1

Acres Treated 

Per Hour Fluridone (Sonar®)

2

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Rangeland 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Public 

Domain 

Forest 

Land Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Energy 

and 

Mineral 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Rights-ofway Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

BLM Vegetation Treatments Using Herbicides B-45 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-7 (Cont.) 

Summary of Herbicide Use - Fluridone

Application Information Herbicide1

Acres Treated 

Per Hour Fluridone (Sonar®)

2

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Recreation 

and 

Cultural 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 Y 0.41 1.3 Aerial 

Helicopter Rotary 100 200 Y 0.41 1.3 

Backpack 0.2 0.4 Y 0.41 1.3 Human 

Horseback 0.75 1 Y 0.41 1.3 

Spot 0.25 0.5 Y 0.41 1.3 ATV 

Boom/broadcast 0.8 1.6 Y 0.41 1.3 

Spot 0.38 1 Y 0.41 1.3 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.41 1.3 

Boat Spot 0.63 2 N NA NA 

(diquat) Boom/broadcast 1.3 3 N NA NA 

Boom/broadcast 

(granular) 6.25 5.8 Y 0.41 1.3 

Aquatic 

Aquatic 

Boat 

(fluridone) Boom/broadcast 

(liquid) 17.5 16.7 Y 0.41 1.3 

1

 All data are based on a single application. 

2

 BLM specified typical and maximum application rates for four different water bodies: Ponds, Whole Lake/Reservoir, Partial 

Lakes/Reservoir, and Canals. The highest typical application rate (Pond) was selected for use as the typical rate and the highest 

maximum application rate (Partial Lake/Reservoir) was selected for use as the maximum application rate. Application rates are 

dependent on water depth, which is assumed to be 1 meter. 

Typical = Typical application rate; and Max = Maximum application rate. 

NA = Not applicable. 

BLM Vegetation Treatments Using Herbicides B-46 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-8 

Summary of Herbicide Use - Imazapic 

Application Information Herbicide1

Acres Treated 

Per Hour Imazapic (Plateau®) 

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 Y 0.031 0.19 Aerial 

Helicopter Rotary 100 200 Y 0.031 0.19 

Backpack 0.2 0.4 Y 0.031 0.19 Human 

Horseback 0.75 1 Y 0.031 0.19 

Spot 0.25 0.5 Y 0.031 0.19 ATV Boom/broadcast 0.8 1.6 Y 0.031 0.19 

Spot 0.38 1 Y 0.031 0.19 

Rangeland 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.031 0.19 

Plane Fixed wing 250 500 Y 0.031 0.19 Aerial 

Helicopter Rotary 100 200 Y 0.031 0.19 

Backpack 0.2 0.4 Y 0.031 0.19 Human 

Horseback 0.75 1 Y 0.031 0.19 

Spot 0.25 0.5 Y 0.031 0.19 ATV 

Boom/broadcast 0.8 1.6 Y 0.031 0.19 

Spot 0.38 1 Y 0.031 0.19 

Public 

Domain 

Forest 

Land Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.031 0.19 

Plane Fixed wing 250 500 Y 0.031 0.19 Aerial 

Helicopter Rotary 100 200 Y 0.031 0.19 

Backpack 0.2 0.4 Y 0.031 0.19 Human 

Horseback 0.75 1 Y 0.031 0.19 

Spot 0.25 0.5 Y 0.031 0.19 ATV 

Boom/broadcast 0.8 1.6 Y 0.031 0.19 

Spot 0.38 1 Y 0.031 0.19 

Energy 

and 

Mineral 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.031 0.19 

Plane Fixed wing 250 500 Y 0.031 0.19 Aerial 

Helicopter Rotary 100 200 Y 0.031 0.19 

Backpack 0.2 0.4 Y 0.031 0.19 Human 

Horseback 0.75 1 Y 0.031 0.19 

Spot 0.25 0.5 Y 0.031 0.19 ATV Boom/broadcast 0.8 1.6 Y 0.031 0.19 

Spot 0.38 1 Y 0.031 0.19 

Rights-ofway Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.031 0.19 

BLM Vegetation Treatments Using Herbicides B-47 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-8 (Cont.) 

Summary of Herbicide Use - Imazapic 

Application Information Herbicide1

Acres Treated 

Per Hour Imazapic (Plateau®) 

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 Y 0.031 0.19 Aerial 

Helicopter Rotary 100 200 Y 0.031 0.19 

Backpack 0.2 0.4 Y 0.031 0.19 Human 

Horseback 0.75 1 Y 0.031 0.19 

Spot 0.25 0.5 Y 0.031 0.19 ATV 

Boom/broadcast 0.8 1.6 Y 0.031 0.19 

Spot 0.38 1 Y 0.031 0.19 

Recreation 

and 

Cultural 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.031 0.19 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Boat Spot 0.63 2 N NA NA 

(diquat) Boom/broadcast 1.3 3 N NA NA 

Boom/broadcast 

(granular) 6.25 5.8 N NA NA 

Aquatic 

Aquatic 

Boat 

(fluridone) Boom/broadcast 

(liquid) 17.5 16.7 N NA NA 

1

 All data are based on a single application. 

Typical = Typical application rate; and Max = Maximum application rate. 

NA = Not applicable. 

BLM Vegetation Treatments Using Herbicides B-48 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-9 

Summary of Herbicide Use - Sulfometuron Methyl 

Application Information Herbicide1

Acres Treated 

Per Hour Sulfometuron Methyl (Oust®) 

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Rangeland 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 Y 0.14 0.38 

Backpack 0.2 0.4 Y 0.14 0.38 Human 

Horseback 0.75 1 Y 0.14 0.38 

Spot 0.25 0.5 Y 0.14 0.38 ATV 

Boom/broadcast 0.8 1.6 Y 0.14 0.38 

Spot 0.38 1 Y 0.14 0.38 

Public 

Domain 

Forest 

Land Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.14 0.38 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 Y 0.14 0.38 

Backpack 0.2 0.4 Y 0.14 0.38 Human 

Horseback 0.75 1 Y 0.14 0.38 

Spot 0.25 0.5 Y 0.14 0.38 ATV 

Boom/broadcast 0.8 1.6 Y 0.14 0.38 

Spot 0.38 1 Y 0.14 0.38 

Energy 

and 

Mineral 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.14 0.38 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 Y 0.14 0.38 

Backpack 0.2 0.4 Y 0.14 0.38 Human 

Horseback 0.75 1 Y 0.14 0.38 

Spot 0.25 0.5 Y 0.14 0.38 ATV Boom/broadcast 0.8 1.6 Y 0.14 0.38 

Spot 0.38 1 Y 0.14 0.38 

Rights-ofway Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.14 0.38 

BLM Vegetation Treatments Using Herbicides B-49 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

TABLE B-9 (Cont.) 

Summary of Herbicide Use - Sulfometuron Methyl

Application Information Herbicide1

Acres Treated 

Per Hour Sulfometuron Methyl (Oust®) 

Program Scenario Vehicle Method Typical Max Used 

(Y/N)? 

Typical 

Rate (lb 

a.i./acre) 

Max 

Rate (lb 

a.i./acre) 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 Y 0.14 0.38 Human 

Horseback 0.75 1 Y 0.14 0.38 

Spot 0.25 0.5 Y 0.14 0.38 ATV 

Boom/broadcast 0.8 1.6 Y 0.14 0.38 

Spot 0.38 1 Y 0.14 0.38 

Recreation 

and 

Cultural 

Sites Ground 

Truck 

mount Boom/broadcast 1.5 2.25 Y 0.14 0.38 

Plane Fixed wing 250 500 N NA NA Aerial 

Helicopter Rotary 100 200 N NA NA 

Backpack 0.2 0.4 N NA NA Human 

Horseback 0.75 1 N NA NA 

Spot 0.25 0.5 N NA NA ATV 

Boom/broadcast 0.8 1.6 N NA NA 

Spot 0.38 1 N NA NA 

Ground 

Truck 

mount Boom/broadcast 1.5 2.25 N NA NA 

Boat Spot 0.63 2 N NA NA 

(diquat) Boom/broadcast 1.3 3 N NA NA 

Boom/broadcast 

(granular) 6.25 5.8 N NA NA 

Aquatic 

Aquatic 

Boat 

(fluridone) Boom/broadcast 

(liquid) 17.5 16.7 N NA NA 

1

 All data are based on a single application. 

Typical = Typical application rate; and Max = Maximum application rate. 

NA = Not applicable. 

BLM Vegetation Treatments Using Herbicides B-50 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

The adult and child resident are assumed to contact 

foliage for 2 hours per day. A Tc value of 14,500 

cm

2

/hour was selected for the adult resident, and 5,200 

cm

2

/hour was selected for the child resident (USEPA 

2001i). These Tc values are higher than those used for 

the other receptors, and assumes that contact with 

herbicide active ingredients in foliage could occur in the 

residents’ yards (i.e., playing in the grass is an activity 

that could result in greater transfer than walking through 

the brush or woods). 

Berry IRs for this receptor were assumed to be the same 

as those used for the Native American adult and child. 

The rates are 320 g/day for an adult and a scaled IR of 

69 g/day for a child, and are based on rates of above 

ground gathered terrestrial vegetation for the Native 

American Spokane tribe (Harper et al. 2002). The berry 

IR was converted to units of cm2

/day because of the 

requirements of the equation used to evaluate this 

pathway (USEPA 2002c). 

Native American 

The Native American receptors (adult and child) are 

assumed to be potentially exposed to herbicides via 

dermal contact with spray, dermal contact with sprayed 

foliage, ingestion of drinking water from a sprayed 

pond, ingestion of berries containing spray, dermal 

contact with water in a sprayed pond, and ingestion of 

fish from a sprayed pond. The adult Native American is 

assumed ingest 1 liter of water per day (Harper et al. 

2002) from the sprayed pond. According to Harper et 

al., a representative Spokane Tribe subsistence exposure 

scenario assumes that an adult consumes 4 liters of 

water per day out of which 2 liters/day are consumed 

from the home drinking water well, 1 liter/day is 

consumed at the work site, and 1 liter/day is consumed 

in a sweat lodge (where water is poured over hot rocks 

to create a steam bath). It is assumed that the 1 liter/day 

from the work site could come from a sprayed pond. 

The child Native American is assumed to consume half 

the adult rate resulting in 0.5 liter/day from a sprayed 

pond. 

Harris and Harper (1997) and Harper et al. (2002) do 

not provide specific data regarding Native American 

body SA or BW. It is assumed that the Native 

American’s lower legs, lower arms, and hands are 

exposed for potential herbicide contact. The 50th

percentile SA of the lower legs, lower arms, and hands 

for adult men and women is 4,504 cm2

, and was 

calculated based on data in the Exposure Factors 

Handbook (USEPA 1997c). The 50th percentile SA of 

the lower legs, lower arms, and hands for children is 

1,607 cm2

, and was calculated based on data in the 

Exposure Factors Handbook (USEPA 1997a). The 

Native American receptors are assumed to contact 

foliage for 3 hours per day of subsistence activities 

(Harper et al. 2002). A Tc value of 1,500 cm2

/hour was 

selected for the adult. This value is the high end Tc for 

harvesting blueberries (USEPA 2000b). A value of 300 

cm

2

/hour, based on the child to adult SAR (CalEPA 

1996), was selected for the child. 

The USEPA (2001d) recommends an exposed SA of 

18,000 cm2

 for an adult swimmer and 6,600 cm2 for a 

child swimmer. Because no specific data are available 

regarding SA, these estimates have been used to 

evaluate the Native American child and adult in this 

HHRA. The ET for swimming is assumed to be 2.6 

hours/day in accordance with Harris and Harper (1997) 

which gives a swimming exposure frequency of 2.6 

hours/day for 70 days/year. Incidental ingestion during 

swimming is not evaluated for the Native American 

since it is assumed that the pond is also used as a source 

of drinking water, and any incidental ingestion during 

swimming is therefore included in the drinking water 

scenario. 

The berry IR was developed from information provided 

in Harper et al. (2002), which lists an IR of 320 g/day 

for an adult for above ground gathered terrestrial 

vegetation for the Native American Spokane tribe. 

Berries are likely to be a small fraction of this 320 

g/day. However, since this rate was not subdivided into 

additional categories, it was conservatively assumed 

that the IR for berries is 320 g/day for an adult Native 

American. For the child Native American, the IR was 

scaled by BW (i.e., 320 g/day x 15 kg / 70 kg) to 69 g 

/day (CalEPA 1996). 

The adult fish IR was assumed to be 885 g/day based on 

a high fish diet scenario Harper et al. (2002). The high 

fish diet consists primarily of fish, supplemented by big 

game, amphibians, crustaceans, mollusks, small 

mammals, and upland game birds. This value is much 

higher than the 95th percentile fish IR of 170 g/day 

recommended in USEPA (1997a) for a Native 

American subsistence population. For the child Native 

American, the IR was scaled by BW (i.e., 885 g/day x 

15 kg / 70 kg) to 190 g /day; CalEPA 1996). 

Calculation of Exposure Point 

Concentrations 

Exposure points are located where potential receptors 

may contact herbicides. The herbicide concentration in 

BLM Vegetation Treatments Using Herbicides B-51 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

the environmental medium that receptors may contact 

must be estimated in order to determine the magnitude 

of potential exposure. The concentration at the point of 

contact is referred to as the exposure point concentration 

(EPC). 

Occupational Exposures 

It is assumed that workers could be exposed via dermal 

contact and inhalation through routine-use of herbicides 

and via an accidental spill to worker skin. 

Routine Exposures 

For the routine exposures, the exposure dose is 

calculated using the herbicide AR (lbs a.i./day) and the 

AT per day. This information is provided in Tables B-4

to B-9. 

Accidental Exposures 

To calculate exposures from an accidental spill to 

worker skin, the concentration of a.i. in the formulation 

(in lbs of a.i. per gallon of formulation) must be derived. 

These concentrations are provided or can be calculated 

from the information provided on the herbicide labels. 

Three of the herbicides evaluated in the risk assessment 

(diquat, fluridone, and imazapic) may be present in a 

concentrated liquid formulation. Fluridone and imazapic 

are also present in a dry formulation; however, for this 

evaluation it is assumed that the worker is exposed to 

the concentrated liquid formulation. For the worker spill 

scenario, it is assumed that the worker is exposed to the 

concentrated liquid; therefore, the pounds of a.i. per 

gallon listed on the labels are used for the calculation. 

For diquat, fluridone, and imazapic, the concentrated 

liquid concentrations are 2 pounds a.i./gallon, 4 pounds 

a.i./gallon, and 2 pounds a.i./gallon, respectively. 

Diflufenzopyr and sulfometuron methyl are in a dry 

form, and need to be mixed with water before 

application. The concentration of a.i. present in the 

application-ready formulation is calculated using 

maximum ARs (lb of a.i./acre, Tables B-4 to B-9) and 

the minimum spray rate (in gallons per acre, 

information provided by the BLM). The combination of 

maximum AR and minimum spray rate results in the 

most concentrated solution. The concentration is 

calculated using the following equation: 

Concentration (lb a.i./gallon) = Application rate (pounds 

a.i./acre)/Spray rate (gallons/acre) 

The helicopter spray rate of 5 gallons/acre results in the 

most concentrated solution, therefore the helicopter 

spray rate is used in the calculation. The maximum ARs 

for diflufenzopyr and sulfometuron methyl of 0.1 

pounds a.i./acre and 0.38 pounds a.i./acre, respectively, 

is divided by the spray rate (5 gallons/acre) resulting in 

concentrations of 0.02 pounds a.i./gallon and 0.076 

pounds a.i./gallon, respectively. 

The accidental spill scenario for diquat and fluridone 

resulted in unacceptable risks to occupational receptors. 

Because of the unlikely nature of the scenario (i.e., a 

spill of concentrated liquid directly to worker skin), 

EPCs were also calculated assuming a spill to worker 

skin after the herbicide is mixed at the maximum or 

typical AR using the equation listed above. 

Public Exposures 

It is assumed that the public could have routine 

exposures to herbicides present in spray drift that have 

deposited onto the receptor, foliage, ponds, and berries. 

It is also assumed that there could be accidental direct 

spray onto the receptor, foliage, pond, and berries, as 

well as a direct spill into the pond. 

Routine Exposure Point Concentrations 

Off-target spray drift refers to the amount of sprayed 

pesticide that does not come into contact with the target 

area, but rather drifts in the air and settles on an offtarget area. The magnitude of potential human exposure 

to herbicides as a result of off-target spray drift and 

surface runoff of herbicides from the target application 

area was estimated from modeled terrestrial deposition 

rates (DRs) and water body concentrations. A 

hypothetical quarter acre, 1-meter deep pond was 

assumed for these calculations. Off-target spray drift 

and resulting terrestrial DRs and waterbody 

concentrations were predicted using the computer 

model AgDRIFT® (Spray Drift Task Force [SDTF] 

2002). Surface runoff of herbicides from the target 

application area and resulting waterbody (hypothetical 

pond) concentrations were predicted using the computer 

model GLEAMS (Groundwater Loading Effects of 

Agricultural Management Systems). 

AgDRIFT®. AgDRIFT® Version 2.0.05 (SDTF 2002) 

is a computer model that is a product of the Cooperative 

Research and Development Agreement between the 

USEPA’s Office of Research and Development and the 

SDTF (a coalition of pesticide registrants). It is based 

on, and represents an enhancement of, its preceding 

computer program, AGDISP (Agricultural Dispersal 

BLM Vegetation Treatments Using Herbicides B-52 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Model), which was developed by the National 

Aeronautics and Space Administration (NASA), the 

U.S. Department of Agriculture Forest Service (USDA 

Forest Service), and the U.S. Army. AgDRIFT®

 was 

developed for use in regulatory assessments of offtarget drift associated with agricultural use of pesticides 

through aerial, ground, or orchard/airblast applications. 

AgDRIFT® is based upon the simple 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 not of the a.i. itself. To implement 

this idea, the computational approach employed by 

AgDRIFT® is based on a simple method that has 

evolved over a period of more than 20 years and yields 

high correlation with field measurement datasets. 

AgDRIFT® was selected for use in this risk assessment 

because it allows for the simulation of a broad range of 

aerial and ground application practices and associated 

off-target spray drift. Further, the cooperative 

development of AgDRIFT® by the USEPA and the 

SDTF and the associated use of AgDRIFT® in 

regulatory assessments of off-target pesticide drift 

reinforces 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 of increasingly complex evaluations 

of off-target drift and deposition. The basic difference 

between the three tiers (Tiers I, II, and III) is the amount 

of control users have in selecting model input variables. 

Also, Tier I supports the evaluation of aerial and ground 

application scenarios, whereas Tiers II and III support 

the evaluation of only aerial application scenarios (for 

agricultural and forestry applications). Tier I is based on 

a set of standard “Good Application Practices” and 

requires little knowledge of the actual application 

conditions or herbicide properties. Tier I 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” as Tier I. However, to implement either Tier 

II or III the user must have a progressively greater 

knowledge of the specific conditions under which 

herbicides will be applied. Tiers II and III allow the user 

to modify a progressively larger set of variables to make 

the scenario evaluated representative of the conditions 

under which herbicides will be applied. 

Tier I was used in this EIS to evaluate off-target drift 

associated with ground application scenarios. Tier II 

was used to evaluate off-target drift associated with 

aerial application of herbicides to agricultural and 

forestry land types. The agricultural land type represents 

land having a relatively short vegetative canopy (e.g., 

non-forested land such as rangeland). The forestry land 

type represents land having a higher vegetative canopy 

(e.g., forested land). The Tier I ground application 

model does not allow the user to select between land 

types. It simply models drift from ground application in 

an agriculture-like setting. Both Tier I and Tier II of the 

AgDRIFT® model were utilized to evaluate off-target 

spray drift to a terrestrial area or waterbody (e.g., a 

hypothetical pond) located perpendicular to, and 

downwind of, the herbicide application area. The 

terrestrial area simply represents a point on the ground 

at a fixed distance downwind of the application area. 

AgDRIFT® calculates the DR in milligrams per square 

centimeter (mg/cm2

) for the terrestrial location of 

interest. The hypothetical pond is intended to represent 

a non-flowing waterbody approximately 1⁄4 acre in size 

and 1 meter deep. The concentration of the herbicide 

being modeled in pond water is generated in the 

AgDRIFT® model based on the assumption of 

instantaneous mixing throughout the waterbody. 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 the HHRA protocol document (ENSR 2005). 

GLEAMS. 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 

agricultural field-size areas. One of the benefits of the 

GLEAMS model is the ability to estimate a wide range 

of potential herbicide exposure concentrations as a 

function of important site-specific parameters such as 

soil characteristics, annual precipitation, etc. The model 

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

loadings of water, sediment, pesticides (or herbicides), 

and plant nutrients from the complex climate-soilmanagement interactions. The GLEAMS model has 

evolved through several versions from its inception in 

1984 to the present, and 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 (SERA 2001). 

In this application, the GLEAMS model was used to 

simulate the fate and transport of the three terrestrial 

herbicides considered in this HHRA from an area 

BLM Vegetation Treatments Using Herbicides B-53 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

representing a typical BLM application area. The fate 

and transport of the three herbicides was simulated by 

GLEAMS using a precipitation record and three other 

model components intended to represent hydrology, 

erosion, and pesticide movement: 

• Precipitation Record – Rainfall distribution 

was described in the GLEAMS model using a 

daily hyetograph from Medford, Oregon from 

1990 when a total of approximately 13.5 inches 

of precipitation was recorded. The GLEAMS 

model used the hyetograph from 1990 to 

describe the annual distribution of precipitation 

during the model simulations and eight 

different precipitation totals including 5, 10, 

25, 50, 100, 150, 200, and 250 inches/year. By 

scaling the eight different hypothetical 

precipitation totals by the precipitation record 

measured during 1990, the daily rainfall totals 

were increased in the model, while the annual 

distribution of precipitation was retained. 

• Hydrology – The hydrology component of the 

GLEAMS model simulates the movement of 

water through an agricultural system by 

considering the effects of precipitation on 

surface runoff and percolation through the 

unsaturated zone. Three soil types were 

simulated in this application including silt, 

sand, and clay. The simulated application area 

was a 10-acre square with a 5% slope, and the 

climate applied to the simulation was the 

measured annual average at Medford, Oregon. 

• Erosion – The erosion component of GLEAMS 

simulates the movement of sediment over the 

land surface using the Universal Soil Loss 

Equation (USLE). Typical values were used to 

represent the soil erodibility factor and a 

Manning Roughness coefficient. 

• Pesticide – The pesticide component of the 

GLEAMS model was used to simulate the 

movement of the herbicides diflufenzopyr, 

imazapic, and sulfometuron methyl (the three 

herbicides designated for terrestrial deposition) 

through the ecosystem by associating the 

herbicides with both water and sediment. 

Literature values describing water solubility, 

foliar half-life, partitioning, washoff, and soil 

half-life were used to facilitate the GLEAMS 

model calculations. 

The GLEAMS model was used to simulate the fate and 

transport and eventual waterbody (e.g., pond) loading of 

each of the three terrestrial herbicides assuming they 

were each applied to a single application area within the 

vicinity of a hypothetical pond and using combinations 

of each of the eight precipitation rates and each of the 

three soil types. 

Ambient water concentrations were calculated for a 

pond immediately adjacent to the application field using 

model predicted runoff and percolation rates, and the 

mass of herbicide a.i. associated with each of these 

exports. Statistical values of concentrations were 

calculated using an entire year of predicted results 

extracted once the model had reached a quasi-steady 

state. The GLEAMS model provides daily predictions 

of herbicide a.i. export rates, which were used to 

calculate ambient water concentrations in a pond, and 

the daily values were used to determine short-term (7 

day), intermediate-term (30 day), and long-term 

(annual) surface water concentrations. These exposure 

durations correspond to the exposure durations used to 

evaluate the toxicology endpoint data (Table B-3). 

Long-term concentrations were calculated as the annual 

daily average from the last year of the 10-year 

simulation. Intermediate-term concentrations were 

calculated as the maximum 30-day average from the last 

year of the 10-year simulation. Short-term 

concentrations were calculated as the maximum 7-day 

average from the last year of the 10-year simulation. 

While it is possible that public receptors use public 

lands under intermediate and long term time frames, it 

is unlikely that public receptors would be exposed to 

herbicides under the routine use scenario for more than 

a short-term exposure, which is defined as 1 day to 1 

month (USEPA 2001g). Therefore, short-term 

concentrations are used to evaluate the public receptors 

under the routine use exposure scenario. An evaluation 

of the public receptors under an intermediate and a 

long-term exposure scenario is included in the 

Uncertainty Analysis. 

Pond concentrations for 42 scenarios were calculated 

for each time frame (18 from varying soil type and 

precipitation totals and 24 from a sensitivity analysis 

where soil type and 5 other parameters were varied). 

The highest calculated pond concentrations were 

selected from all of the scenarios for each time frame in 

order to provide the most conservative pond 

concentrations as an input to the HHRA. The 

timeframes were selected to correlate with USEPA’s 

short-term, intermediate-term, and long-term NOAELs. 

A detailed discussion of the GLEAMS modeling 

BLM Vegetation Treatments Using Herbicides B-54 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

approach is presented in the HHRA protocol document 

(ENSR 2005). The individual ERA reports developed 

for each herbicide contain a description of herbicidespecific GLEAMS model inputs and present a summary 

of GLEAMS model results for each herbicide. 

Terrestrial Deposition Rates and Exposure Point 

Concentrations. The initial terrestrial DRs predicted 

using the AgDRIFT® Tier I ground application and Tier 

II aerial application models were used to evaluate the 

following potential human exposure pathways:

• Dermal contact with herbicide in spray drift 

• Dermal contact with herbicide on foliage 

• Ingestion of herbicides that have deposited on 

berries 

Spray drift DRs were estimated for two application 

scenarios, aerial and ground. For the aerial scenario, 

AgDRIFT® evaluates two land types (agricultural and 

forestry) for estimation of DRs. As the agricultural land 

type represents land having a relatively short vegetative 

canopy, it was used to estimate spray drift DRs resulting 

from aerial applications over non-forested areas, while 

the forestry land type (representing land having a higher 

vegetative canopy) was used to estimate spray drift DRs 

resulting from aerial applications over forested areas. To 

encompass all possibilities, both sets of DRs were used 

to evaluate public receptor exposures. Deposition rates 

were also calculated separately for plane and helicopter 

applications; therefore, there are four sets of aerial DRs 

calculated using Tier II of the model: 

• Agricultural land type, airplane application 

• Agricultural land type, helicopter application 

• Forestry land type, airplane application 

• Forestry land type, helicopter application 

Off-target spray drift and the resulting terrestrial 

impacts from the aerial application scenarios were 

predicted at distances of 100, 300, and 900 feet 

downwind of the herbicide application area. The closest 

distance to the receptor (e.g., 100 feet downwind), was 

used as the basis for the HHRA. 

For ground applications using Tier I of the model, 

estimation of spray drift DR is not dependent on land 

type. Ground applications may be conducted using 

either a high boom or a low boom, and DRs vary by the 

height of the boom. Therefore, there are two sets of 

ground DRs calculated for each herbicide: 

• Ground application, low boom 

• Ground application, high boom 

Off-target spray drift and the resulting terrestrial 

impacts from the ground application scenarios were 

predicted at distances of 25, 100, and 900 feet 

downwind of the herbicide application area. The closest 

distance to the receptor (e.g., 25 feet downwind) was 

used as the basis for the HHRA. 

Pond Deposition Rates and Exposure Point 

Concentrations. The surface water (pond) herbicide 

concentrations predicted using AgDRIFT® represent 

short-lived concentrations due to off-target spray drift. It 

is likely that these predicted herbicide levels are flushed 

out of the hypothetical pond within a few days. For the 

aquatic herbicides, it is assumed that these herbicides 

are sprayed onto a target pond and the spray drift settles 

onto an adjacent pond that was not targeted for 

spraying. 

The pond herbicide concentrations predicted using the 

GLEAMS model represent the potential impact of 

surface runoff of herbicides and assume a constant 

loading to the pond. Therefore, the GLEAMS 

concentrations represent potential longer-term 

concentrations in the pond. The processes of spray drift 

onto and surface runoff into a surface water body are 

not directly additive, since they may not occur over the 

same time frame. However, as a conservative approach, 

the hypothetical herbicide concentrations due to spray 

drift predicted using AgDRIFT® were used in 

calculating the short-, intermediate-, and long-term 

surface water EPCs for all six herbicides. The short-, 

intermediate-, and long-term concentrations of 

terrestrial herbicides calculated using the GLEAMS 

model were added to the AgDRIFT® predictions for 

those herbicides. Using AgDRIFT® output for short-, 

intermediate-, and long-term time frames is a 

conservative approach since AgDRIFT® mainly 

represents short-lived concentrations. These combined 

concentrations are used to evaluate: 

• Dermal contact with herbicide in water while 

swimming 

• Ingestion of herbicide in water used as drinking 

water or while swimming 

• Ingestion of herbicide that may bioconcentrate 

in the edible tissue of recreationally caught fish 

BLM Vegetation Treatments Using Herbicides B-55 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

As for the terrestrial DRs, pond concentrations were 

calculated for several land types and application 

scenarios: 

• Agricultural land type, airplane application 

• Agricultural land type, helicopter application 

• Forestry land type, airplane application 

• Forestry land type, helicopter application 

• Ground application, low boom 

• Ground application, high boom 

Off-target spray drift and the resulting aquatic impacts 

were predicted at distances 100, 300, and 900 feet 

downwind of the aerial application areas and 25, 100, 

and 900 feet downwind of the ground application areas. 

Again, for the HHRA, the nearest distances to the 

receptor were used (e.g., 100 feet and 25 feet downwind 

for the aerial and ground applications, respectively). 

Accidental Exposure Point Concentrations.

Accidental exposures involving direct spray are 

estimated using the herbicide ARs (in pounds of a.i. per 

acre) shown in Tables B-4 to B-9. It is assumed that the 

herbicide is sprayed at the maximum AR directly onto 

the receptor, foliage, berries, or pond. The equation used 

to calculate the pond concentration is as follows: 

Pond concentration (mg/L) = (Application rate [lb 

a.i./acre] * 453,600 * 35.31 ft3

/m3 x 0.001 m3/L) / 

(43,530 ft2

/acre * pond depth [feet]). 

Spill. It is assumed that a pond receives a spill of 140 

gallons of herbicide mix from a helicopter or 200 

gallons of spray mix from a batch truck. These amounts 

are approximately the largest amounts that can be 

carried in helicopters or trucks, respectively, as used by 

the BLM. Similar to the worker spill scenario, the 

concentration of a.i. in the formulation must be derived. 

It is assumed that the herbicides are present in 

application-ready concentrations as they are being 

transported. Therefore, for the herbicides that may be 

present in concentrated liquid form (diquat, fluridone, 

and imazapic), a diluted concentration is calculated. 

Diflufenzopyr and sulfometuron methyl are in solid 

form, and the concentration of a.i. in the applicationready formulation is calculated. 

Similar to the worker spill scenario, the following 

equation is used to calculate the concentration of a.i. 

present in the application-ready formulation: 

Concentration (pounds a.i./gallon) = (Application rate 

[pounds a.i./acre]) / (Spray rate [gallons/acre]) 

Two spray rates are used in the equation to represent 

spraying from helicopters and trucks. Based on 

information provided by the BLM, the lowest spray rate 

from a helicopter is 5 gallons/acre and from a truck is 

25 gallons/acre. While a range of spray rates is possible, 

these spray rates represent the lower end of the range, 

and thus result in higher concentrations. Maximum ARs 

(shown in Tables B-4 to B-9) were used for each of the 

six herbicides. The equation used to calculate the pond 

concentration is as follows: 

Pond concentration (mg/L) = (Gallons spilled * lb 

a.i./gallon * 453,600 mg/lb * 35.31 ft3

/m3 * 0.001 m3/L) 

/ (43,530 ft2

/acre * pond size [acre] * pond depth [ft]) 

Both the accidental truck and helicopter spill scenarios 

for diquat resulted in unacceptable risks to public 

receptors. To provide a more realistic estimate of risk, 

EPCs were also calculated assuming spills at the typical 

AR using the equation listed above. 

Chemical-specific Parameters 

Several chemical-specific parameters are used in the 

calculation of exposure doses described in the next 

section. These include absorption factors, skin 

permeability factors, and bioconcentration factors 

(BCFs). Each parameter is described below. 

Absorption Factors 

Absorption factors are used in this HHRA when the 

endpoint used to select the NOAEL and the exposure in 

the environmental medium of interest differ. For 

example, absorption factors are used with the dermal 

NOAELs for diquat, fluridone, and imazapic because 

oral studies were used to determine the dermal 

NOAELs. The derivation of these absorption factors 

were discussed earlier for diquat, fluridone, and 

imazapic. 

Skin Permeability Constants 

The estimation of exposure doses resulting from 

incidental dermal contact with surface water requires 

the use of a dermal permeability constant (Kp) in units 

of centimeters per hour (cm/hr). This method assumes 

that the behavior of constituents dissolved in water is 

described by Fick’s Law. In Fick’s Law, the steadystate flux of the solute across the skin (mg/cm2

/hr) 

equals the permeability constant (Kp, cm/hr) multiplied 

BLM Vegetation Treatments Using Herbicides B-56 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

by the concentration difference of the solute across the 

membrane (mg/cm3

). This approach is discussed by the 

USEPA (USEPA 1989, 1992, 2001d). For the six 

herbicides evaluated in the risk assessment, Kps were 

calculated using an equation presented in the USEPA’s 

Supplemental Guidance for Dermal Risk Assessment

(USEPA 2001d). 

Fish Bioconcentration Factors 

To estimate concentrations of herbicides in fish tissue, a 

BCF is used to approximate the amount of herbicide 

that bioconcentrates from the water into the fish tissue. 

 Risk Characterization 

The purpose of the risk characterization is to provide 

estimates of the potential risk to human health from 

exposure to herbicides. The results of the exposure 

assessment are combined with the results of the doseresponse assessment to derive quantitative estimates of 

risk, or the probability of adverse health effects 

following assumed potential exposure to herbicides. 

Since none of the six herbicides evaluated in this HHRA 

are considered to be potential carcinogens by the 

USEPA, the potential noncancer risk associated with the 

herbicide use scenarios is estimated. 

The USEPA risk assessment guidance for pesticides 

(USEPA 2000a) provides different noncancer methods 

for evaluating food and non-food exposures. For food 

exposure, a percent PAD (%PAD) method is used, and 

for non-food exposure, an MOE method is used. In 

order to estimate total exposure and risk from all 

exposure pathways, the USEPA has also developed an 

aggregate risk approach, which combines potential risks 

from various pathways expressed as MOEs and %PADs 

(USEPA 1999a, USEPA 2001b). 

The following sections discuss the overall approach for 

risk characterization, present equations for quantifying 

exposure and risk, present the results of the risk 

characterization, and discuss uncertainties inherent in 

the risk assessment process. 

Approach for Risk Characterization 

The food (%PAD) and non-food (MOE) methods are 

summarized below, followed by the aggregate risk 

approach for combining these risk estimates. 

Food (%PAD) Assessment 

This assessment method evaluates exposures to 

herbicide residues in food and water. Toxicity is 

represented by a PAD and may be calculated for acute 

effects (acute PAD) or chronic effects (chronic PAD). A 

PAD is defined as an acute or chronic RfD divided by 

the FQPA SF (a value between 1 and 10), where 

appropriate. 

The noncancer risk estimate is the ratio of the exposure 

level (expressed as intake of the herbicide in mg/kgday) to the PAD and is calculated using the following 

equation: 

100

PAD(mg/kg day)

Food Intake(mg/ day)kg %PAD × −− =

Exposures that are less than 100% of the PAD do not 

exceed the USEPA’s level of concern. 

As shown in Table B-3, only diflufenzopyr has an acute 

PAD developed by the USEPA. Chronic PADs are 

available for diflufenzopyr, diquat, imazapic, and 

sulfometuron methyl. The FQPA SF for each of these 

herbicides is 1; therefore, the PAD is equal to the RfD. 

For fluridone, the USEPA did not provide a PAD; 

therefore, the oral RfD provided in the USEPA’s IRIS 

database (USEPA 2003c) was used to evaluate chronic 

oral exposure. 

Non-food (MOE) Assessment 

This assessment method evaluates exposures via all 

non-food pathways (e.g., incidental ingestion, dermal, 

inhalation). The toxicity of the chemical is represented 

by a NOAEL identified from the scientific literature. 

The noncancer risk estimate is the ratio of the toxicity 

value to the exposure level and is calculated using the 

following general equation: 

Exposure(m day)g/kg

NOAEL(mg/k day)g Noncancer, MOE −

− =

Target MOEs are derived to account for the 

uncertainties associated with the NOAEL. Target MOEs 

are generally set at 100 to account for a factor of 10 for 

interspecies extrapolation and factor of 10 for 

intraspecies variability. Additional factors are applied 

when a LOAEL is used rather than a NOAEL. 

Calculated MOEs above the target MOE do not exceed 

the USEPA’s level of concern. Calculated MOE values 

less than the target MOE indicate a potential concern for 

BLM Vegetation Treatments Using Herbicides B-57 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

human health. As shown in Table B-3, target MOEs are 

defined for each of the herbicides. Target MOEs are 100 

for all herbicides, except for imazapic. The imazapic 

target MOE for long-term dermal and long-term 

inhalation exposures is 300, to account for the fact that 

the toxicity values is based on a LOAEL rather than a 

NOAEL. For all other exposure routes and time frames, 

the target MOE is 100. 

Aggregate Risk Index 

The %PAD method presents the risk result as the 

exposure estimate divided by the allowable exposure 

level (the PAD) and is expressed as a percentage of the 

total allowable exposure. Results less than or equal to 

100% of the PAD are considered acceptable. However, 

for the MOE method, the identified NOAEL is divided 

by the estimated exposure, and is, therefore, the reverse 

of the %PAD method. For the MOE method, when the 

ratio is greater than the target MOE, the risk is 

considered to be negligible. Risk results using these 

different methods cannot be directly combined to 

account for cumulative risk from various exposure 

pathways. An aggregate approach, described below, is 

therefore used. 

The USEPA’s OPP (USEPA 1999a, USEPA 2001b) 

has developed the Aggregate Risk Index (ARI) 

approach, which combines potential risks from various 

pathways expressed as MOEs and %PADs. In this 

approach, it is important that only exposure pathways 

encompassing similar exposure durations be combined 

(i.e., acute exposures cannot be combined with chronic 

exposures). The ARI is an extension of the MOE 

concept. The ARI is compared against a target value of 

one. Values greater than 1 do not exceed the USEPA’s 

level of concern; values below 1 indicate a potential 

concern for human health. 

The ARI method allows for direct comparisons between 

routes and between chemicals. The ARI method 

considers each route’s potency when route-specific 

NOAELs that may have different target MOEs are used. 

(Note that USEPA [1999a] designates target MOEs as 

UFs. This report uses the term target MOEs for 

consistency with an earlier section, Dose-Response 

Assessment.) The %PAD calculated for oral exposures 

can also be incorporated into the ARI approach, using 

the following equation: 

I

I

D

D

MOE

TM

MOE

TM PAD%

1 ARI

O ++

= 

where: 

ARI = Aggregate Risk Index 

%PADO = %PAD for oral exposure, expressed as a 

ratio (i.e., 80% = 0.8) 

TMD = Target MOE for dermal exposure 

MOED = Site-specific MOE estimated for dermal 

exposure 

TMI = Target MOE for inhalation exposure 

MOEI = Site-specific MOE estimated for inhalation 

exposure 

Not all herbicides include all of these toxicity endpoints. 

For example, some herbicides may not be toxic through 

the dermal route; therefore, the dermal MOE would not 

be included. The USEPA (1999a) provides the 

following example for an herbicide and receptor that 

has a dermal MOE of 100, dermal target MOE of 100, 

inhalation MOE of 1,000, inhalation target MOE of 

300, and an oral %PAD of 80% (expressed as a ratio, 

0.8): 

I

I

D

D o

1000

300

100

100 8.0

1 ARI

++

= = 0.48 

In this example, the ARI (0.48) suggests a risk of 

concern because it is less than 1. It should be noted that, 

when listed separately, the oral PAD would be listed as 

percent oral PAD (in this case, 80%). However, when 

included in this equation, the actual fraction (not the 

percentage) is listed. 

Therefore, for this HHRA, the %PAD approach has 

been used to evaluate potential exposures to herbicides 

in food and water, the MOE approach to evaluate 

potential exposures to herbicides via non-food and 

incidental ingestion pathways, and the ARI approach to 

evaluate combined exposures. 

Equations for Quantifying Potential 

Exposure and Risk 

To estimate the potential risk to receptors from 

exposure to herbicides, it is first necessary to estimate 

the potential exposure dose of each herbicide. The 

exposure dose is estimated for each herbicide via each 

exposure pathway by which the receptor is assumed to 

be exposed. Exposure dose equations combine the 

BLM Vegetation Treatments Using Herbicides B-58 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

estimates of herbicide concentration in the 

environmental medium of interest with assumptions 

regarding the type and magnitude of each receptor’s 

potential exposure to provide a numerical estimate of 

the exposure dose. The exposure dose is defined as the 

amount of herbicide taken into the receptor and is 

expressed in units of milligrams of herbicide a.i. per 

kilogram of BW per day. Exposure doses are calculated 

separately for different time frames, such as short-term, 

intermediate-term, and long-term exposures. 

The standardized equations for estimating a receptor’s 

average daily dose are presented below. The following 

sections also show whether the dose is used with a 

NOAEL or PAD to estimate risks. NOAELs are used 

for non-dietary and incidental ingestion (such as 

ingestion of water while swimming) pathways to 

calculate MOEs. Potential risks from dietary exposure 

(such as drinking water, berry ingestion, and fish 

ingestion) are estimated using PADs. 

Estimating Potential Occupational Exposures 

Occupational exposures via dermal contact and 

inhalation are evaluated using the PHED UE values. For 

the worker accidental exposure, it is assumed that the 

worker receives a direct spill and is exposed through 

dermal contact. The equations used are as follows 

(additional information is provided for parameters in the 

equations that have not already been defined). 

Dermal Contact with Herbicide 

Equations (1) and (2) are used to evaluate occupational 

exposure through dermal contact. 

(1) (kg)BW

*a.i.)a.i./lb(mg DAF(unitless) derm *AT/acre)a.i.(lbAR UE*)(acres/day

(mg/kg day) routine Dose =−

and 

(2) )kg(BW

)unitless(DAF*)unitless(SAR*) gallon/.i.alb

L/.i.amg (CF*)gallon/.i.alb(AC*)day/L(S

)daykg/mg( accident Dose =− 

where: 

Parameter Units Definition 

AR lb a.i./acre Herbicide application rate 

AT acres/day Acres treated per day 

UEderm mg a.i./lb a.i. Dermal unit exposure factor 

DAF unitless Dermal absorption factor 

S L/day Spill amount = 0.5 L of concentrate 

AC lb a.i./gallon Concentration of active ingredient in concentrate 

CF 1.2E+05 mg a.i./L

 lb a.i./gallon 

Conversion factor used to convert units of lb a.i. per gallon to units of 

mg a.i. per liter 

SAR unitless 

Surface area ratio = Ratio of surface area exposed to total surface area, 

expressed as a percent (80% spilled to clothing, with a 30% penetration 

rate, and 20% spilled to bare skin; [(0.8*0.3)+0.2 = 0.44]) 

BW Kg Body weight 

While most UEs are expressed in units of mg a.i./lb a.i., 

for aquatic application of diquat, the available UEs are 

in units of mg a.i./hr. The UEs to be used in the risk 

assessment are those for hydrilla control-applicator and 

hydrilla control-mixer listed in the RED for diquat 

(USEPA 1995), which are expressed in terms of mg a.i. 

per hour. Daily exposure doses for diquat are calculated 

using equation (3). 

BLM Vegetation Treatments Using Herbicides B-59 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Table B-3 lists the short-term, intermediate-term and 

long-term dermal NOAELs for the six herbicides. There 

are no dermal NOAELs for diflufenzopyr and 

sulfometuron methyl because neither has been shown to 

result in toxicity in response to dermal exposure. 

Dermal NOAELs are available for the remaining 

herbicides. Therefore, potential risks were not 

calculated for the herbicides and specific time frames 

that lacked dermal NOAELs. 

Inhalation of Herbicide 

Equation (4) is used to evaluate occupational exposure 

through inhalation. 

(3) (kg)BW

*a.i./hr)(mgUE ET(hr/day) DAF(unitless) Dose (mg/kg day) derm

routine

∗ =−

where: 

Parameter Units Definition 

ET hours/day Exposure time 

MOEs are calculated as follows: 

Dose NOAEL Type MOE Equation 

Dermal – short-term (ds) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

ds

−

−

Dermal – intermediate-term (di) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

di

−

− Routine - Dermal 

Dermal – long-term (dl) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

dl

−

−

Accident Dermal – short-term (ds) )daykg/mg(Dose

)daykg/mg(NOAEL

accident

ds

−

−

(4) )kg(BW

)unitless(IAF*.)i.alb/.i.amg(UE*)day/acres(AT*)acre/.i.alb(AR )daykg/mg(Dose inh

routine =−

where: 

Parameter Units Definition 

AR lb a.i./acre Herbicide application rate 

AT acres/day Acres treated 

UEinh mg a.i./lb a.i. Inhalation unit exposure from PHED database 

IAF unitless Inhalation absorption factor 

BW kg Body weight 

MOEs are calculated as follows: 

BLM Vegetation Treatments Using Herbicides B-60 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Dose NOAEL Type MOE Equation 

Inhalation – short-term (is) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

is

−

−

Inhalation – intermediate-term (ii) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

ii

−

− Routine 

Inhalation – long-term (il) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

il

−

−

Table B-3 lists the short-term, intermediate-term, and 

long-term inhalation NOAELs for the six herbicide 

active ingredients. Inhalation NOAELs are available for 

all of the herbicides and time frames, which are 

reflected in the risk calculations. 

Estimating Potential Exposure for Public Receptors 

Exposure assumptions for public receptors are presented 

in Table B-4 to B-9. The equations used to calculate 

exposure doses are shown below. Additional 

information is provided for parameters in the equations 

that have not already been defined. As discussed earlier, 

dose-response values are available for short, 

intermediate, and long-term exposures. While it is 

possible that public receptors use public lands under 

intermediate- and long-term time frames, it is unlikely

that public receptors would be exposed to herbicides 

under the routine use scenario for more than a shortterm exposure, which is defined as 1 day to 1 month 

(USEPA 2001h). Therefore, short-term dose-response 

values are used to evaluate the public receptors under 

the routine use exposure scenario. To account for the 

unlikely possibility that public receptors could 

repeatedly enter areas that have been recently sprayed, 

the Uncertainty Analysis includes an evaluation of the 

public receptors under an intermediate and a long-term 

exposure scenario. 

Dermal Contact with Herbicide 

Equations (5) and (6) are used to evaluate dermal 

contact with herbicides for public receptors through 

spray drift and accidental direct spray. 

Spray Drift 

(5) )unitless(DAF*)cm/.i.amg(DR*)daykg/cm(EF)daykg/mg(Dose 2 2

routine =− dp −

Direct Spray 

(6) 

)unitless(DAF*)cm/acre(CF*)lb/mg(CF*)acre/.i.alb(AR*)daykg/cm(EF)daykg/mg(Dose 2

1 2

2

accident =− dp −

where: 

)kg(BW

)day/cm(SA )daykg/cm(EF

2

2

dp =−

and where: 

BLM Vegetation Treatments Using Herbicides B-61 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Parameter Units Definition 

EFdp cm

2

/kg-day Exposure factor for dermal pathway 

AR lb a.i./acre Herbicide application rate, direct spray, accidental scenarios 

DR mg a.i./cm2 Herbicide deposition rate due to spray drift 

CF1 4.54x105 mg/lb Conversion factor used to convert pounds to mg 

CF2 2.47x10-8 acre/cm2 Conversion factor used to convert acres to cm2

DAF Unitless Dermal absorption factor 

SA cm

2

/day Surface area of skin exposed 

BW kg Body weight 

MOEs are calculated as follows: 

Dose NOAEL Type MOE Equation 

Routine Dermal – short-term (ds) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

ds

−

−

Accident Dermal – short-term (ds) Dose )daykg/mg(

)daykg/mg(NOAEL

accident

ds

−

−

The short-term dermal NOAELs are presented in Table 

B-3. Note that two of the herbicides, diflufenzopyr and 

sulfometuron methyl, have been identified as not 

inducing dermal toxicity; therefore, dermal MOEs are 

not calculated for these herbicides. For certain 

herbicides, the dose is calculated by including a DAF in 

the numerator of the equation to account for dermal 

absorption when the endpoint is selected from an oral 

study. The calculation of dermal doses for diquat, 

fluridone, and imazapic include DAFs of 4.1%, 40%, 

and 50%, since the dermal NOAELs are based on oral 

studies. For the other herbicides, the USEPA has 

determined that dermal absorption is insignificant or 

that the dermal NOAELs are based on dermal studies 

and a DAF is not required. 

Dermal Contact with Foliage 

It is assumed that recreational and residential receptors 

could be exposed through dermal contact with 

herbicides present on foliage while hiking or berry 

picking. The equations for this pathway are based on 

information provided in two documents: 

• Draft Standard Operating Procedures (SOPs) 

for Residential Exposure Assessments (USEPA 

1997d) 

• Occupational and Residential Exposure and 

Risk for the Proposed Use of Metsulfuronmethyl on Sorghum (USEPA 2002c) 

Equation (7) is used to quantify this potential exposure 

is as follows: 

(7) DAF*)cm/mg(DFR*)daykg/cm(EF)daykg/mg(Dose 2 2 =− df −

where: 

(kg)BW

(hr/day)ET*/hr)(cmT day)/kg(cmEF

2

2 c

df =−

DFR (unitless)F *)a.i./cm(mgRD)(mg/cm2 2

routine =

DFR CF*(mg/lb)CF*a.i./acre)(lbAR*(unitless)F)(mg/cm )(acre/cm2

1 2

2

accident =

and where: 

BLM Vegetation Treatments Using Herbicides B-62 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Parameter Units Definition 

EFdf cm

2

/kg-day Exposure factor for dermal foliage pathway 

DFR mg/cm2 Dislodgeable foliar residue (calculated) 

Tc cm

2

/hr Transfer coefficient (described below) 

ET hr/day Exposure time 

BW kg Body weight 

DR mg a.i./cm2 Herbicide deposition rate due to spray drift 

F unitless Fraction active ingredient retained on foliage (described below) 

AR lb a.i./acre Herbicide application rate direct spray, accidental scenario 

CF1 4.54x105 mg/lb Conversion factor used to convert pounds to mg 

CF2 2.47x10-8 acre/cm2 Conversion factor used to convert acres to cm2

MOEs are calculated as follows: 

Dose NOAEL Type MOE Equation 

Routine Dermal – short-term (ds) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

ds

−

−

Accident Dermal – short-term (ds) )daykg/mg(Dose

)daykg/mg(NOAEL

accident

ds

−

−

The short-term dermal NOAELs are presented in Table 

B-3. Note that two of the herbicides, diflufenzopyr and 

sulfometuron methyl, have been identified as not 

inducing dermal toxicity, therefore, dermal MOEs are 

not calculated for these herbicides. For certain 

herbicides, the dose is calculated by including a DAF in 

the numerator of the equation to account for dermal 

absorption when the endpoint is selected from an oral 

study. The calculation of dermal doses for diquat, 

fluridone, and imazapic include DAFs of 4.1%, 40%, 

and 50%, since the dermal NOAELs are based on oral 

studies. For the other herbicides, the USEPA has either 

determined that dermal absorption is insignificant, or 

the dermal NOAELs are based on dermal studies and a 

DAF factor is not required. 

The dermal Tc is used to estimate the amount of 

herbicide that may be transferred from foliage to skin. 

Transfer coefficients for each receptor were selected as 

follows: 

• Hiker/hunter and angler - 1,000 cm2/hour the 

central tendency Tc value for scouting grapes 

and also for scouting sweet corn, and 

recommended as a surrogate for scouting 

activity for berries) from USEPA 2000b 

(referenced by USEPA 2002c) 

• Adult berry picker - 1,500 cm2/hour (the high 

end blueberry value) from USEPA 2000b 

(referenced by USEPA 2002c) 

• Child berry picker - 300 cm2/hour, based on the 

child to adult SAR (CalEPA 1996) 

• Residential adult – 14,500 cm2/hour (USEPA 

2001k) 

• Residential child – 5,200 cm2/hour (USEPA 

2001k) 

• Native American adult – 1,500 cm2/hour (the 

high end blueberry value) from USEPA 2000b 

(referenced by USEPA 2002c) 

• Native American child – 300 cm2/hour based 

on the child to adult SAR (CalEPA 1996) 

The fraction of a.i. retained on foliage is assumed to be 

20%. This is the fraction assumed to be present on 

foliage on the day of application (USEPA 1997d). This 

value is based on the professional judgment and 

experience of USEPA staff, and is assumed to represent 

an upper-percentile value. 

Dermal Contact with Water While Swimming 

Equation (8) used to estimate a receptor’s potential 

exposure via dermal contact with surface water is as 

follows: 

BLM Vegetation Treatments Using Herbicides B-63 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

(8) Dose (mg/kg (cmEFday) )(L/cmCF*a.i./L)(mgC*(cm/hr)Kp *day)hr/kg 3

w 3

2 =− dw −−

where: 

)kg(BW

)day/hr(ET*)cm(SA )daykg/hrcm(EF

2

2

dw =−−

and where: 

Parameter Units Definition 

EFdw cm

2

-hr/kg-day Exposure factor for dermal water pathway 

Kp cm/hr Permeability constant for skin 

Cw mg a.i./L Concentration in water 

CF3 L/1,000 cm3 Conversion factor used to convert liters to cm3

SA cm

2 Surface area of skin exposed 

BW kg Body weight 

MOEs are calculated as follows: 

Dose NOAEL Type (a) MOE Equation 

Routine Oral – short/intermediate-term (o) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

o

−

−

Accident Oral – short/intermediate-term (o) Dose )daykg/mg(

)daykg/mg(NOAEL

accident

o

−

−

The short-term water concentration is used with the 

short- and intermediate-term NOAEL to derive an MOE 

for short-term exposure. Water concentrations for the 

accidental scenarios are used with the short- and 

intermediate-term NOAELs to derive MOEs for the 

accidental scenarios. As discussed previously, the 

intermediate- and long-term exposure scenario is 

evaluated in the Uncertainty Analysis. 

The accidental spill scenario assumes that 140 gallons 

of herbicide mix from a helicopter or 200 gallons of 

herbicide mix from a batch truck are spilled. These 

amounts are approximately the largest amounts used by 

the BLM that can be carried in helicopters or trucks, 

respectively. The pond is assumed to be 1⁄4 acre in size 

and 1 meter in depth. 

Oral NOAELs are used to evaluate the dermal contact 

with water pathway because the dermal dose in the 

equation assumes that the herbicide is absorbed into the 

body. Dermal NOAELs assume that the dose is applied 

to the skin and that the skin acts as a barrier. Therefore, 

use of dermal NOAELs with an absorbed dose may 

result in an underestimation of the amount of herbicide 

absorbed. Although oral NOAELs have not necessarily 

been adjusted to reflect an absorbed dose, absorption of 

these herbicides is assumed to be much higher via the 

oral exposure route than the dermal exposure route. 

Therefore, it is more appropriate to use oral NOAELs 

for the dermal contact with water pathway. Table B-3

lists the short- and intermediate-term oral NOAELs for 

each of the herbicides. 

Ingestion of Drinking Water or Swimming 

Water 

The equation used to estimate a receptor’s potential 

exposure via ingestion of drinking water or swimming 

water is as follows: 

)L/mg(C*)daykg/L(EF)daykg/mg(Dose =− iw − w

where: 

)kg(BW

)day/L(IR )daykg/L(EF w

iw =−

BLM Vegetation Treatments Using Herbicides B-64 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

and where: 

Parameter Units Definition 

EFiw L/kg-day Exposure factor for ingestion of water pathway 

Cw mg/L Concentration in water 

IRw L/day Ingestion Rate for water 

BW kg Body weight 

For incidental ingestion pathways (swimmer), the risk 

assessment uses the oral NOAELs to calculate MOEs. 

Oral NOAELs are used rather than PADs because this 

ingestion is considered incidental rather than dietary. 

MOEs are calculated as follows: 

Dose NOAEL Type MOE Equation (Incidental Ingestion) 

Routine Oral – short/intermediate-term (o) )daykg/mg(Dose

)daykg/mg(NOAEL

routine

o

−

−

Accident Oral – short/intermediate-term (o) Dose )daykg/mg(

)daykg/mg(NOAEL

accident

o

−

−

Table B-3 lists the short- and intermediate-term oral 

NOAELs for each of the herbicides. For drinking water 

pathways (hiker/hunter, berry picker, angler, and Native 

American), it is more relevant to compare the dose with 

 a PAD and calculate a %PAD. The drinking water 

pathway represents dietary exposure. The PADs are 

calculated as follows: 

Dose PAD Type %PAD Equation (Drinking Water) 

Routine Acute PAD %100*

)daykg/mg(PAD

)daykg/mg(Dose

chronic

routine

−

−

Accident Acute PAD %100*

)daykg/mg(PAD

Dose )daykg/mg(

acute

accident

−

−

Table B-3 lists acute and chronic PADs for the six 

herbicides. The acute PAD was used for the accidental 

and short-term routine exposure scenarios. The USEPA 

has developed an acute PAD only for diflufenzopyr and 

diquat. Chronic PADs are available for all six 

herbicides. 

Concentrations in water due to spray drift and runoff are 

calculated for short-, intermediate-, and long-term 

exposure. As discussed previously, the intermediateand long-term exposure scenarios are evaluated in the 

uncertainty analysis. The short-term water concentration 

is used with the short- and intermediate-term NOAEL to 

derive an MOE for short-term swimming exposure and 

with the acute PAD to derive a %PAD for the shortterm drinking water pathway. Water concentrations are 

used with the short/intermediate-term NOAELs to 

derive MOEs for the accidental swimming scenarios 

and with the acute PADs to derive %PADs for the 

accidental drinking water scenarios. 

Ingestion of Fish 

A recreational angler may ingest fish that have 

bioaccumulated herbicides present in surface water. The 

equation used to estimate a receptor’s potential 

exposure via fish ingestion is as follows: 

BLM Vegetation Treatments Using Herbicides B-65 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Dose (mg/kg (mg/kgEFday) CF*(L/kg)BCF*(mg/L)C*day) (kg/mg) =− fi − w 4

where: 

)kg(BW

)day/mg(IR )daykg/mg(EF f

fi =−

and where: 

Parameter Units Definition 

EFfi mg/kg-day Exposure factor for fish ingestion pathway 

Cw mg/L Concentration in water 

BCF L/kg Bioconcentration factor 

CF4 10-6 kg/mg Conversion factor used to convert mg to kg 

IRf mg/day Ingestion rate for fish 

BW kg Body weight 

PADs are calculated as follows: 

Dose PAD Type %PAD Equation 

Routine Acute PAD %100*

)daykg/mg(PAD

)daykg/mg(Dose

chronic

routine

−

−

Accident Acute PAD %100*

)daykg/mg(PAD

Dose )daykg/mg(

acute

accident

−

−

The BCF is defined as the ratio of chemical 

concentration in the organism to that in surrounding 

water. Bioconcentration occurs through uptake and 

retention of a substance from water only, and through 

gill membranes or other external body surfaces. The 

BCFs for each of the herbicides have been estimated 

using information from the literature. 

Concentrations in water are calculated for short-, 

intermediate-, and long-term exposures due to spray 

drift and runoff. As discussed previously, the 

intermediate and long-term exposure scenarios are 

evaluated in the Uncertainty Analysis. The short-term 

water concentration is used with the acute PAD to

derive a %PAD for short-term exposure. Water 

concentrations are used with the acute PADs to derive 

%PADs for the accidental scenarios. 

Ingestion of Berries 

It is assumed that several receptors (berry picker, nearby 

resident, and Native American) could be exposed to 

herbicides through berry ingestion. None of the USEPA 

pesticide documents specifically list an equation for 

evaluating berry or other food ingestion. However, 

USEPA (2002c) provides an equation for a pathway 

involving toddler ingestion of pesticide-treated grass. 

This equation was used to evaluate ingestion of berries: 

)daykg/cm(EF*)cm/mg(BR)daykg/mg(Dose 2

bi

2 =− −

where: 

)kg(BW

)day/cm(IR )daykg/cm(EF

2

2 b

bi =−

F*)cm/mg(DR)cm/mg(BR 2 2

routine =

BLM Vegetation Treatments Using Herbicides B-66 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

)cm/acre(CF*)lb/mg(CF*F*)acre/.i.alb(AR)cm/mg(BR 2

1 2

2

accident =

and where: 

Parameter Units Definition 

EFbi cm

2

/kg-day Exposure factor for berry ingestion pathway 

IRb cm

2

/day Ingestion rate for berries 

BW kg Body weight 

BR mg/cm2 Berry residue (calculated) 

DR mg/cm2 Herbicide deposition rate due to spray drift 

F unitless Fraction of a.i. available on berry (discussed below) 

AR lb a.i./acre Herbicide application rate, direct spray accidental scenarios 

CF1 4.54x105 mg/lb Conversion factor to convert pounds to mg 

CF2 2.47x10-8 acre/cm2 Conversion factor to convert acres to cm2

PADs are calculated as follows: 

Dose PAD Type %PAD Equation 

Routine Acute PAD %100*

)daykg/mg(PAD

)daykg/mg(Dose

chronic

routine

−

−

Accident Acute PAD %100*

)daykg/mg(PAD

Dose )daykg/mg(

acute

accident

−

−

The equation presented in USEPA (2002c) for toddler 

grass ingestion uses an IR of 25 cm2

/day assuming that 

a child eats a handful of grass (2 inch x 2 inch). 

Therefore, it was necessary to convert the berry IR in 

units of mg/day to a berry IR in units of cm2

/day. The 

conversion required SA (cm2

) to weight (mg) of berry 

ratio. Cheung and Yen (1996) calculated a SA to weight 

ratio of 2 cm2

/g for Thompson Seedless grapes. This 

value was used to estimate the berry IR in units of 

cm

2

/day. It was assumed that herbicides deposit only on 

the top half of a berry. Therefore, half of the SA was 

used in the equation. The following equation was used 

to convert the berry IR from units of mg/day to units of 

cm

2

/day: 

Ingestion Ingestion[)day/cm(rate 5.0*]g/cm2[*]mg1000/g1[*)]day/mg(rate 2 2 =

The fraction a.i. retained on the berry (F) is assumed to 

be 20%, similar to the assumption for foliage. This is 

the fraction assumed to be present on foliage on the day 

of application (USEPA 1997d). As stated in USEPA 

(1997d), this value is based on the professional 

judgment and experience of USEPA staff, and is 

assumed to represent an upper-percentile value. 

Results of Risk Characterization 

Using the equations provided above, %PADs and 

MOEs were calculated for each of the herbicide active 

ingredients for individual receptors. Some of the 

herbicides lacked specific PADs and NOAELs; 

therefore, it was not possible to conduct risk 

calculations for all exposure pathways and herbicides. 

For the accidental scenarios, it was assumed that a 

receptor is exposed to one accidental exposure pathway; 

therefore, the accidental risks from different scenarios 

were not added together. For the routine-use scenarios, 

it was assumed that a receptor could be exposed to a 

specific herbicide through several exposure pathways. 

Therefore, ARIs were calculated for routine-use 

scenarios. The risk characterization results for the 

occupational and public receptors are discussed 

separately. Table B-10 shows the generalized risk level 

(low, medium, high) that each application scenario for 

each chemical presents to each receptor. 

Occupational Receptors 

For the occupational receptors, separate calculations 

were conducted for routine-use typical AR scenarios, 

BLM Vegetation Treatments Using Herbicides B-67 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

routine-use maximum AR scenarios, and accidental 

scenarios. For the routine-use scenarios, exposure 

through dermal and inhalation exposures was evaluated 

(if appropriate information was available for the specific 

herbicide). In the current USEPA OPP program, shortterm is defined as 1 day to 1 month, intermediate-term 

is defined as 1 to 6 months, and long-term is defined as 

greater than 6 months (USEPA 2001h). The accidental 

scenario evaluated exposure through dermal absorption. 

The results for each herbicide are summarized below. 

Dicamba 

oader, and a combined 

applicator/mixer/loader. 

dance of the USEPA’s level of concern (Table 

B-11). 

e ARIs are also below 1, indicating a level 

of concern. 

nario evaluated, but 

not under the routine use scenario. 

Diflufenzopyr 

oader, and a combined 

applicator/mixer/loader. 

ting no exceedance of 

the USEPA’s level of concern. 

ted, an accidental scenario ARI was not 

calculated. 

e 

occupational receptors under the scenarios evaluated. 

Diquat 

er/loaders, and combined 

applicator/mixer/loaders. 

Dicamba is proposed for use on rangeland, energy and 

mineral sites, ROW, and recreation and cultural sites. 

Dicamba may be applied using the following methods: 

truck (boom/broadcast or spot applications), ATV 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). 

Therefore, potential occupational receptors include an 

applicator, a mixer/l

Routine use ARIs were calculated for inhalation and 

dermal exposures under both typical and maximum AR 

scenarios. Routine use ARIs are greater than 1 under 

both the typical and maximum AR scenarios, indicating 

no excee

Under the accidental scenario, it is assumed that 

dicamba is spilled directly onto an occupational 

receptor. Because dicamba is provided by the 

manufacturer in granular form, it cannot be spilled as a 

concentrated liquid. Therefore, under the accidental 

scenario, it is assumed that dicamba is spilled on the 

skin after it has been mixed at the maximum AR 

concentration. The ARIs for the accidental scenario 

(maximum AR) for all occupational receptors are less 

than 1, indicating a level of concern. Because of the 

conservative nature of the scenario, ARIs were also 

calculated assuming a spill to worker skin at the typical 

AR, and thes

These results show that dicamba risks exceed the 

USEPA’s level of concern for all of the occupational 

receptors under the accidental sce

Diflufenzopyr is proposed for use on energy and 

mineral sites, ROW, and recreation and cultural sites. 

Diflufenzopyr may be applied using the following 

methods: truck (boom/broadcast or spot applications), 

ATV (boom/broadcast or spot applications), and 

backpack (spot applications). Diflufenzopyr may also be 

applied via horseback in recreation and cultural sites. 

Therefore, potential occupational receptors include an 

applicator, a mixer/l

Routine use ARIs were calculated for inhalation 

exposures under both typical and maximum AR 

scenarios. No dermal toxicity values are available for 

diflufenzopyr, which, based on laboratory data, is not 

expected to be toxic through the dermal route. Routine 

use ARIs are greater than 1 under both the typical and 

maximum AR scenarios, indica

Under the accidental scenario, it is assumed that 

diflufenzopyr is spilled directly onto an occupational 

receptor. Because diflufenzopyr is provided by the 

manufacturer in granular form, it cannot be spilled as a 

concentrated liquid. Therefore, under the accidental 

scenario, it is assumed that diflufenzopyr is spilled on 

the skin after it has been mixed at the maximum AR 

concentration. However, based on laboratory data, 

diflufenzopyr is not expected to be toxic through the 

dermal route and therefore does not have a short-term 

dermal NOAEL. Therefore, while spill concentrations 

were calcula

These results show that diflufenzopyr risks do not 

exceed the USEPA’s level of concern for any of th

Diquat is proposed for use on aquatic sites. Diquat may 

be applied using the following methods: airplane, 

helicopter, truck (boom/broadcast or spot applications), 

ATV (boom/broadcast or spot applications), boat 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). 

Therefore, potential occupational receptors include 

pilots, applicators, mix

Routine use ARIs were calculated for dermal and 

inhalation exposures under both typical and maximum 

AR scenarios. Inhalation UEs are not applicable to the 

boat scenario. Therefore, long-term ARIs were not 

calculated for the boat scenario. Under the typical AR 

BLM Vegetation Treatments Using Herbicides B-68 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

scen o

scenario el of concern: 

re) 

rm exposure) 

Under the maximum AR scenario, ARIs are less than 1 

for e 

concern: 

re) 

rm exposure) 

g-term exposure) 

osure) 

• boom/broadcast 

 spill of diquat solution 

ern for the occupational 

receptors und the majority of terrestrial scenarios 

evaluated, as listed above. 

), boat 

upational receptors include 

ari , ARIs are less than 1 for the following 

s, indicating a lev

• Airplane pilot (short-, intermediate-, and longterm exposure) 

• Airplane mixer/loader (short-, intermediate-, 

and long-term exposu

• Helicopter pilot (short-, intermediate-, and 

long-term exposure) 

• Helicopter mixer/loader (short-, intermediate-, 

and long-term exposure) 

• Backpack applicator/mixer/loader (short-, 

intermediate-, and long-te

• Horseback applicator (short-, intermediate-, 

and long-term exposure) 

• Horseback applicator/mixer/loader (short-, 

intermediate-, and long-term exposure) 

th following scenarios, indicating a level of 

• Airplane pilot (short-, intermediate-, and longterm exposure) 

• Airplane mixer/loader (short-, intermediate-, 

and long-term exposu

• Helicopter pilot (short-, intermediate-, and 

long-term exposure) 

• Helicopter mixer/loader (short-, intermediate-, 

and long-term exposure) 

• Backpack applicator/mixer/loader (short-, 

intermediate-, and long-te

• Horseback applicator (short-, intermediate-, 

and long-term exposure) 

• Horseback mixer/loader (short-, intermediate-, 

and long-term exposure) 

• Horseback applicator/mixer/loader (short-, 

intermediate-, and lon

• ATV spot applicator (short-, intermediate-, and 

long-term exposure) 

• ATV spot applicator/mixer/loader (short-, 

intermediate-, and long-term exposure) 

• ATV boom/broadcast applicator (short-, 

intermediate-, and long-term exposure) 

• ATV boom/broadcast mixer/loader (short-, 

intermediate-, and long-term exposure) 

• ATV boom/broadcast applicator/mixer/loader 

(short-, intermediate-, and long-term exp

• Truck mount spot applicator (short-, 

intermediate-, and long-term exposure) 

• Truck mount spot mixer/loader (short-, 

intermediate-, and long-term exposure) 

• Truck mount spot applicator/mixer/loader 

(short-, intermediate-, and long-term exposure) 

• Truck mount boom/broadcast applicator 

(short-, intermediate-, and long-term exposure) 

• Truck mount boom/broadcast mixer/loader 

(short-, intermediate-, and long-term exposure) 

Truck mount 

applicator/mixer/loader (short-, intermediate-, 

and long-term exposure) 

All application scenarios for diquat require the use of 

gloves. Diquat is provided by the manufacturer in liquid 

form. Therefore, accidental scenario ARIs were 

calculated assuming the concentrated herbicide is 

spilled directly onto an occupational receptor. The ARIs 

for the accidental scenario (concentrated liquid) for all 

occupational receptors are less than 1, indicating a level 

of concern. Because of the conservative nature of the 

scenario (i.e., a spill of concentrated liquid directly to 

worker skin), ARIs were also calculated assuming a 

spill to worker skin after at the maximum and typical 

ARs. The ARIs, assuming a

under both the typical and maximum ARs, are below 1, 

indicating a level of concern. 

These results show that diquat risks exceed the 

USEPA’s level of conc

er

Fluridone 

Fluridone is proposed for use on aquatic sites. Fluridone 

may be applied using the following methods: airplane, 

helicopter, truck (boom/broadcast or spot applications), 

ATV (boom/broadcast or spot applications

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). 

Therefore, potential occ

pilots, applicators, mixer/loaders, and combined 

applicator/mixer/loaders. 

BLM Vegetation Treatments Using Herbicides B-69 June 2007 

Final Programmatic EIS
HUMAN HEALTH RISK ASSESSMENT

Routine use ARIs were calculated for dermal and 

inhalation exposures under both typical and maximum 

AR scenarios. Routine use ARIs are greater than 1 for 

the typical AR scenarios, indicating no exceedance of 

the USEPA’s level of concern. Under the maximum AR 

scenario, ARIs are less than 1 for the following 

scen o

-

luridone solution under both the typical and 

maximum ARs, are below 1, indicating a level of 

, and 

for the helicopter mixer/loader under the routine use 

(max scenario for long-term exposures. 

upational receptors include 

pilots, applicators, mixer/loaders, and combined 

ARIs are greater than 1 under both the typical and 

ied. Therefore, while spill concentrations 

were calculated, an accidental scenario ARI was not 

d 

to exceed the USEPA’s level of concern for any of the 

occupational receptors under the scenarios evaluated. 

occupational receptors include pilots, applicators, 

RIs are greater than 1 

under both the typical and maximum AR scenarios, 

ntified. Therefore, while spill 

concentrations were calculated, an accidental scenario 

ARI was not calculated. 

ari s, indicating a level of concern: 

• Airplane mixer/loader (intermediate- and long

term exposure) 

• Helicopter mixer/loader (long-term exposure) 

Fluridone is provided by the manufacturer in liquid 

form. Therefore, accidental scenario ARIs were 

calculated assuming the concentrated herbicide is 

spilled directly onto an occupational receptor. The ARIs 

for the accidental scenario for all occupational receptors 

are less than 1, indicating a level of concern. Because of 

the conservative nature of the scenario (i.e., a spill of 

concentrated liquid directly to worker skin), ARIs were 

also calculated assuming a spill to worker skin after at 

the maximum and typical ARs. The ARIs, assuming a 

spill of f

concern. 

These results show that fluridone risks could exceed 

USEPA’s level of concern for all occupational receptors 

under the accidental scenario, for the airplane 

mixer/loader under the routine use (maximum AR) 

scenario for intermediate- and long-term exposures

imum AR)

Imazapic 

Imazapic is proposed for use on rangeland, publicdomain forestland, energy and mineral sites, ROW, and 

recreation and cultural sites. Imazapic may be applied 

using the following methods: airplane, helicopter, truck 

(boom/broadcast or spot applications), ATV 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). 

Therefore, potential occ

applicator/mixer/loaders. 

Routine use ARIs were calculated for dermal and 

inhalation exposures under both typical and maximum 

AR scenarios. No short- or intermediate-term dermal 

NOAELs are available for imazapic as dermal toxicity 

tests were negative even at high doses. Therefore, the 

short- and intermediate-term ARIs are based on the 

inhalation pathway, and the long-term ARI is based on 

both the dermal and inhalation pathways. Routine use 

maximum AR scenarios, indicating no level of concern. 

Imazapic is provided by the manufacturer in liquid 

form. Therefore, under the accidental scenario, it was 

assumed that the concentrated herbicide is spilled 

directly onto an occupational receptor. However, 

imazapic has not been shown to be toxic via short-term 

exposures via the dermal route, and no NOAELs have 

been identif

calculated. 

These results show that imazapic risks are not expecte

Sulfometuron Methyl 

Sulfometuron methyl is proposed for use on publicdomain forestland, energy and mineral sites, ROW, and 

recreation and cultural sites. Sulfometuron methyl may 

be applied using the following methods: helicopter, 

truck (boom/broadcast or spot applications), ATV 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications); 

however, helicopter applications would not occur on 

recreation and cultural sites. Therefore, potential

mixer/loaders, and combined applicator/mixer/loaders. 

Routine use ARIs were calculated for dermal and 

inhalation exposures under both typical and maximum 

AR scenarios. Routine use A

indicating no level of concern. 

Under the accidental scenario, it is assumed that 

sulfometuron methyl is spilled directly onto an 

occupational receptor. Because sulfometuron methyl is 

provided by the manufacturer in granular form, it cannot 

be spilled as a concentrated liquid. Therefore, under the 

accidental scenario, it is assumed that sulfometuron 

methyl is spilled on the skin after it has been mixed at 

the maximum AR concentration. However, 

sulfometuron methyl has not been shown to be toxic via 

short-term exposures via the dermal route and no 

NOAELs have been ide

BLM Vegetation Treatments Using Herbicides B-70 June 2007 

Final Programmatic EIS
TABLE B-10 

Summary of Herbicide Risk Categories by Aggregate Risk Index 

Dicamba Diflufenzopyr Diquat Fluridone Imazapic 

Typ1 Max Accid Typ Max Accid Typ Max Accid Typ Max Accid2 Typ Max 

Occupational Receptor 

Plane – pilot NE3 NE NE NE NE NE L M H 0 0 L-H 0 0 Plane - mixer/loader NE NE NE NE NE NE M H H 0 L [2:3] L-H 0 0 Helicopter – pilot NE NE NE NE NE NE L M H 0 0 L-H 0 0 Helicopter - mixer/loader NE NE NE NE NE NE M H H 0 L [1:3] L-H 0 0 Human/backpack -applicator/mixer/loader 0 0 L 0 0 NE L M H 0 0 L-H 0 0 Human/horseback –applicator 0 0 L 0 0 NE L L H 0 0 L-H 0 0 Human/horseback - mixer/loader 0 0 L 0 0 NE 0 L H 0 0 L-H 0 0 Human/horseback - applicator/mixer/loader 0 0 L 0 0 NE L M H 0 0 L-H 0 0 ATV – applicator4 0 0 L 0 0 NE 0 L H 0 0 L-H 0 0 ATV - mixer/loader 0 0 L 0 0 NE 0 L H 0 0 L-H 0 0 ATV - applicator/mixer/loader 0 0 L 0 0 NE 0 L H 0 0 L-H 0 0 Truck – applicator 0 0 L 0 0 NE 0 M H 0 0 L-H 0 0 Truck - mixer/loader 0 0 L 0 0 NE 0 L H 0 0 L-H 0 0 Truck - applicator/mixer/loader 0 0 L 0 0 NE 0 M H 0 0 L-H 0 0 Boat – applicator NE NE NE NE NE NE 0 0 H 0 0 L-H NE NE Boat - mixer/loader NE NE NE NE NE NE 0 0 H 0 0 L-H NE NE Boat - applicator/mixer/loader NE NE NE NE NE NE 0 0 H 0 0 L-H NE NE 

BLM Vegetation Treatment Using Herbicides B-71 June 2007 

Final Programmatic EIS 
TABLE B-10 (Cont.) 

Summary of Herbicide Risk Categories by Aggregate Risk Index 

Dicamba Diflufenzopyr Diquat Fluridone Imazapic 

Typ Max Accid Typ Max Accid Typ Max Accid Typ Max Accid1 Typ Max A

Public Receptor 

Hiker/hunter (adult) 0 0 0 0 0 0 0 L [2:4] L [2:5] M [1:5] 0 0 0 NE NE Berry picker (child) 0 0 0 0 0 0 0 L [2:4] L [3:6] M [1:6] 0 0 L [1:2] NE NE Berry picker (adult) 0 0 0 0 0 0 0 L [2:4] L [2:6] M [1:6] 0 0 0 NE NE Angler (adult) 0 0 0 0 0 0 0 L [2:4] L [2:8] M[1:8] 0 0 0 NE NE Residential (child) 0 0 0 0 0 0 L [2:4] L [2:4] M [2:3] 0 0 L NE NE Residential (adult) 0 0 0 0 0 0 0 L [2:4] M [2:3] 0 0 0 0 0 Native American (child) 0 0 0 0 0 0 0 L [2:4] L [2:12] M[1:12] 0 0 L [1:5] 0 0 Native American (adult) 0 0 0 0 0 0 0 L [2:4] L [1:12] M[1:12] 0 0 0 0 0 Swimmer (child) 0 0 0 0 0 0 0 0 L [1:3] M [1:3] 0 0 0 0 0 Swimmer (adult) 0 0 0 0 0 0 0 0 L [2:3] 0 0 0 0 0 1 Typ = Typical application rate; Max = Maximum application rate; and Accid = Accidental application rate. 2 For all occupational receptors accidentally exposed to fluridone, there is low risk from exposure to solutions mixed with water to the typical application rate, moderate 

mixed with water to the maximum application rate, and high risk from exposure to concentrated solutions (prior to mixing with water). 

3 Risk categories: 0 = No Risk (ARI>1); L = Low Risk (1>ARI>0.1); M = Moderate Risk (0.1>ARI>0.01); H = High Risk (ARI<0.01); and NE = Not evaluated. Typic

categories for occupational scenarios include short-, intermediate-, and long-term exposures. For public receptors, only short-term exposures were evaluated. Accid

accidents with herbicide mixed at both typical and maximum application rates and with concentrated herbicide. Numbers in brackets represent the number of times the Ag

fell within the indicated Risk Category compared to the number of scenarios evaluated for that receptor. If there are no brackets, the Risk Category was consistent fo

receptor. 

4 ATV and Truck categories include spot and boom/broadcast application scenarios. 

BLM Vegetation Treatment Using Herbicides B-72 June 2007 

Final Programmatic EIS 
TABLE B-11 

Occupational Exposure Scenarios with Aggregate Risk Indices Below One1

Typical Application Rate Scenario ARIs Maximum Application Rate Scenario ARIs 

Application 

Type 

Application 

Vehicle 

Application 

Method Receptor Short-term Intermediate- term Long-term Short-term Intermediate- term Long- term 

Aerial Plane Fixed wing Pilot Diquat Diquat Diquat Diquat Diquat Diquat Aerial Plane Fixed wing Mixer/loader Diquat Diquat Diquat Diquat Diquat, fluridone Diquat, fluridone Aerial Helicopter Rotary Pilot Diquat Diquat Diquat Diquat Diquat Diquat Aerial Helicopter Rotary Mixer/loader Diquat Diquat Diquat Diquat Diquat Diquat, fluridone Ground Human Backpack Applicator/ Mixer/loader Diquat Diquat Diquat Diquat Diquat Diquat Ground Human Horseback Applicator Diquat Diquat Diquat Diquat Diquat Diquat Ground Human Horseback Mixer/loader No ARI<1 No ARI<1 No ARI<1 Diquat Diquat Diquat Ground Human Horseback Applicator/ mixer/loader Diquat Diquat Diquat Diquat Diquat Diquat Ground ATV Spot Applicator No ARI<1 Diquat Diquat Diquat Diquat Diquat Ground ATV Spot Mixer/loader No ARI<1 No ARI<1 No ARI<1 Diquat Diquat Diquat Ground ATV Spot Applicator/ mixer/loader Diquat Diquat Diquat Diquat Diquat Diquat Ground ATV Boom/broadcast Applicator No ARI<1 No ARI<1 No ARI<1 Diquat Diquat Diquat Ground ATV Boom/broadcast Mixer/loader No ARI<1 No ARI<1 No ARI<1 Diquat Diquat Diquat Ground ATV Boom/broadcast Applicator/ mixer/loader No ARI<1 No ARI<1 No ARI<1 Diquat Diquat Diquat Ground Truck mount Spot Applicator Diquat Diquat Diquat Diquat Diquat Diquat Ground Truck mount Spot Mixer/loader No ARI<1 No ARI<1 No ARI<1 Diquat Diquat Diquat Ground Truck mount Spot Applicator/ mixer/loader Diquat Diquat Diquat Diquat Diquat Diquat Ground Truck mount Boom/broadcast Applicator No ARI<1 No ARI<1 No ARI<1 Diquat Diquat Diquat Ground Truck mount Boom/broadcast Mixer/loader No ARI<1 No ARI<1 No ARI<1 Diquat Diquat Diquat Ground Truck mount Boom/broadcast Applicator/ mixer/loader Diquat Diquat Diquat Diquat Diquat Diquat Aquatic Boat Spot Applicator No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 Aquatic Boat Spot Mixer/loader No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 Aquatic Boat Spot Applicator/ mixer/loader No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 Aquatic Boat Boom/broadcast Applicator No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 Aquatic Boat Boom/broadcast Mixer/loader No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 Aquatic Boat Boom/broadcast Applicator/ mixer/loader No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 1 ARI values less than 1 indicate a level of concern.2 Concentrated solution and mixed solutions (maximum application rate and typical application rate). 3 Boom/broadcast includes both granular and liquid forms of fluridone. 

BLM Vegetation Treatment Using Herbicides B-73 June 2007 

Final Programmatic EIS 
HUMAN HEALTH RISK ASSESSMENT

 

These results show that sulfometuron methyl risks are 

not expected to exceed the USEPA’s level of concern 

for any of the occupational receptors under the scenarios 

evaluated. 

Public Receptors 

The following public receptors were evaluated for 

potential exposure to herbicides under both routine 

(typical and maximum AR) and accidental exposure 

scenarios: 

• Angler 

• Berry picker - adult 

• Berry picker - child 

• Hiker/hunter 

• Native American - adult 

• Native American - child 

• Nearby resident - adult 

• Nearby resident - child 

• Swimmer - adult 

• Swimmer - child 

The assumption under the routine-use scenarios is that 

public receptors are potentially exposed to media 

impacted by spray drift, while the assumption under the 

accidental scenarios is that receptors are potentially 

exposed to media directly sprayed by herbicide 

applications. While it is possible that public receptors 

use public lands under intermediate- and long-term time 

frames, it is unlikely that public receptors would be 

exposed to herbicides under the routine use scenario for 

more than a short-term exposure, which is defined as 1 

day to 1 month (USEPA 2001g). Therefore, short-term 

exposures are evaluated below. An evaluation of the 

public receptors under an intermediate- and a long-term 

exposure scenario is included in the Uncertainty 

Analysis. Therefore, public receptors may be impacted 

by spray drift under routine use scenarios for the 

following applications: 

• Aerial – plane 

• Aerial – helicopter 

• Boom/broadcast (truck or ATV), both low and 

high boom scenarios were evaluated 

Because spot applications are small and focused, and 

very little if any spray drift is generated, public 

receptors are not assumed to be impacted by herbicide 

spray through routine use from the following 

applications: 

• Backpack 

• Horseback 

• ATV - spot 

• Truck - spot 

Public receptors may be impacted by direct spray under 

the accidental scenarios for all the application methods. 

However, the evaluation of the spot scenarios may 

result in an overestimate of exposure as the spot 

application method is very focused, and may not 

encompass an area of vegetation large enough to 

support some of the exposure scenarios (e.g., a spot 

application may not encompass enough berries to 

support the assumed IR or may not encompass enough 

foliage to support the assumed dermal contact). 

Dicamba 

Dicamba is proposed for use on rangeland, energy and 

mineral sites, ROW, and recreation and cultural sites. 

Dicamba may be applied using the following methods: 

truck (boom/broadcast or spot applications), ATV 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). All 

public receptors are assumed to be potentially exposed 

to dicamba spray drift resulting from boom/broadcast 

(both low-boom and high-boom) application methods 

from trucks or ATVs. As noted above, spot applications 

are small and focused, and very little, if any, spray drift 

is generated; therefore, public receptors are not assumed 

to be impacted by herbicide a.i. spray from spot 

applications. 

Under the routine use scenario, it is assumed that public 

receptors are exposed to spray drift via dermal contact, 

incidental ingestion, and dietary exposure pathways 

under both typical and maximum AR scenarios. The 

ARIs combine all the exposure estimates to derive a 

cumulative effect ARI. Routine use scenario ARIs are 

greater than 1 under both the typical and maximum AR 

scenarios for all public receptors, indicating no level of 

concern (Table B-12). 

Under the accidental scenario, it is assumed that public 

receptors are exposed directly to maximum herbicide 

a.i. ARs (as shown in Table B-4) via dermal contact 

(direct spray of receptor, contact with directly sprayed 

vegetation, and contact with directly sprayed water), 

BLM Vegetation Treatments Using Herbicides B-74 June 2007 

Final Programmatic EIS 
HUMAN HEALTH RISK ASSESSMENT 

incidental ingestion of water while swimming, or 

dietary exposure pathways (drinking water, berry 

ingestion, and fish ingestion). The same maximum AR 

applies to all dicamba treatment application methods, as 

shown in Table B-4. The accidental scenario for a pond 

assumes that receptors swim in or obtain drinking water 

from a pond that has been directly sprayed with 

herbicide a.i. or that has received a spill from a truck. 

Cumulative accidental ARIs were not calculated, as it is 

assumed that each receptor would be accidentally 

exposed via one potential exposure pathway. All 

accidental scenario ARIs are greater than 1, indicating 

no level of concern (Table B-13). 

These results indicate that dicamba risks are not 

expected to exceed the USEPA’s level of concern for 

public receptors under the scenarios evaluated. 

Diflufenzopyr 

Diflufenzopyr is proposed for use on energy and 

mineral sites, ROW, and recreation and cultural sites. 

Diflufenzopyr may be applied using the following 

vehicles and methods: truck (boom/broadcast or spot 

applications), ATV (boom/broadcast or spot 

applications), and backpack (spot applications). All 

public receptors are assumed to be potentially exposed 

to diflufenzopyr spray drift resulting from 

boom/broadcast (both low-boom and high-boom) 

application methods from trucks or ATVs. As noted 

above, spot applications are small and focused, and very 

little if any spray drift is generated; therefore, public 

receptors are not assumed to be impacted by herbicide 

spray from spot applications. 

Under the routine use scenario, it is assumed that public 

receptors are exposed to spray drift via dermal contact, 

incidental ingestion, and dietary exposure pathways 

under both typical and maximum AR scenarios (ARs 

are shown in Table B-5). The ARIs combine all the 

exposure estimates to derive a cumulative effect ARI. 

Because laboratory studies have demonstrated that 

diflufenzopyr is not toxic by the dermal exposure route, 

dermal NOAELs were not identified, and the dermal 

pathway is not evaluated for diflufenzopyr in this 

HHRA. Routine use scenario ARIs are greater than 1 

under both the typical and maximum AR scenarios for 

all public receptors, indicating no level of concern. 

Under the accidental scenario, it is assumed that public 

receptors are exposed directly to maximum herbicide 

ARs (as shown in Table B-5) via dermal contact (direct 

spray of receptor, contact with directly sprayed 

vegetation, and contact with directly sprayed water), 

incidental ingestion of water while swimming, or 

dietary exposure pathways (drinking water, berry 

ingestion, and fish ingestion). The same maximum AR 

applies to all diflufenzopyr treatment application 

methods, as shown in Table B-5. The accidental 

scenario for a pond assumes that receptors swim in or 

obtain drinking water from a pond that has been directly 

sprayed with herbicide or that has received a spill from 

a truck. Cumulative accidental ARIs were not 

calculated, as it was assumed that each receptor would 

be accidentally exposed via one potential exposure 

pathway. The ARIs for dermal contact pathways were 

not calculated because diflufenzopyr has not been 

shown to be toxic via the dermal exposure pathway. All 

accidental scenario ARIs are greater than 1, indicating 

no level of concern. 

Diquat 

Diquat is proposed for use on aquatic sites. Diquat may 

be applied using the following methods: airplane, 

helicopter, truck (boom/broadcast or spot applications), 

ATV (boom/broadcast or spot applications), boat 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). All 

public receptors are assumed to be potentially exposed 

to diquat spray drift resulting from aerial applications 

from airplanes or helicopters and boom/broadcast (both 

low-boom and high-boom) application methods from 

trucks, ATVs, or boats. As noted above, spot 

applications are small and focused, and very little if any 

spray drift is generated; therefore, public receptors are 

not assumed to be impacted by herbicide spray from 

spot applications. 

Under the routine use scenario, it is assumed that public 

receptors are exposed to spray drift via dermal contact, 

incidental ingestion, and dietary exposure pathways 

under both typical and maximum AR scenarios (ARs 

shown in Table B-6). The ARIs combine all the 

exposure estimates to derive a cumulative effect ARI. 

The ARIs are below 1 for the following scenarios under 

the typical AR scenario, indicating a level of concern: 

• Residential (child) – airplane and helicopter 

applications 

Aggregate Risk Indices for diquat are below 1 for the 

following scenarios under the maximum AR scenario, 

indicating a level of concern: 

• Hiker/hunter (adult) – airplane and helicopter 

applications 

BLM Vegetation Treatments Using Herbicides B-75 June 2007 

Final Programmatic EIS 
HUMAN HEALTH RISK ASSESSMENT

 

• Berry picker (child) – airplane and helicopter 

applications, and high-boom applications 

• Berry picker (adult) – airplane and helicopter 

applications 

• Angler (adult) – airplane and helicopter 

applications 

• Residential (child) – airplane and helicopter 

applications, low-boom applications, and highboom applications 

• Residential (adult) – airplane and helicopter 

applications, low-boom applications, and highboom applications 

• Native American (child) – airplane and 

helicopter applications, and high-boom 

applications 

• Native American (adult) – airplane and 

helicopter applications 

Under the accidental scenario, it is assumed that public 

receptors are exposed directly to maximum herbicide 

ARs (as shown in Table B-6) via dermal contact (direct 

spray of receptor, contact with directly sprayed 

vegetation, and contact with directly sprayed water), 

incidental ingestion of water while swimming, or 

dietary exposure pathways (drinking water, berry 

ingestion, and fish ingestion). The same maximum AR 

applies to all diquat treatment application methods, as 

shown in Table B-6. The accidental scenario for a pond 

assumes that receptors swim in, or obtain drinking water 

from, a pond that has been directly sprayed with 

herbicide or that has received a spill (from a truck or 

helicopter). Cumulative accidental ARIs were not 

calculated, as it is assumed that each receptor would be 

accidentally exposed via one potential exposure 

pathway. The ARIs for diquat are less than 1 for the 

following receptors and pathways, indicating a level of 

concern. 

• Angler (adult) – direct spray, contact with 

directly sprayed foliage, and drinking water 

from a pond receiving a helicopter spill 

• Berry picker (adult) – direct spray, contact 

with directly sprayed foliage, and drinking 

water from a pond receiving a helicopter spill 

• Berry picker (child) – direct spray, contact with 

directly sprayed foliage, and drinking water 

from a pond receiving a truck or helicopter 

spill 

• Hiker/hunter (adult) – direct spray, contact with 

directly sprayed foliage, and drinking water 

from a pond receiving a helicopter spill 

• Native American (adult) – direct spray and 

contact with directly sprayed foliage 

• Native American (child) – direct spray, contact 

with directly sprayed foliage, and drinking 

water from a pond receiving a helicopter spill 

• Nearby resident (adult) – direct spray and 

contact with directly sprayed foliage 

• Nearby resident (child) – direct spray and 

contact with directly sprayed foliage 

• Swimmer (adult) – swimming in a pond 

receiving a truck or helicopter spill 

• Swimmer (child) – swimming in a pond 

receiving a truck or helicopter spill 

A second set of calculations was performed for the 

scenarios listed above with ARIs below 1 under the 

maximum AR assuming that herbicide is sprayed or 

spilled at the typical rather than the maximum AR (see 

Table B-6). Aggregate Risk Indices for diquat for the 

following receptors and scenarios are below 1, 

indicating a level of concern: 

• Angler (adult) – direct spray 

• Berry picker (adult) – direct spray 

• Berry picker (child) – direct spray and drinking 

water from a pond receiving a helicopter spill 

• Hiker/hunter (adult) – direct spray 

• Native American (adult) – direct spray 

• Native American (child) – direct spray 

• Nearby Resident (adult) – direct spray and 

contact with directly sprayed foliage 

• Swimmer (child) – swimming in a pond 

receiving a truck or helicopter spill 

These results show that diquat risks could exceed the 

USEPA’s level of concern for public receptors under 

certain scenarios. No risks were indicated for low-boom 

or high-boom application methods under typical ARs 

for short-, intermediate-, or long-term exposure 

scenarios for diquat. 

BLM Vegetation Treatments Using Herbicides B-76 June 2007 

Final Programmatic EIS 
TABLE B-12 

Routine Exposure Public Scenarios/Receptors with Aggregate Risk Indices Below One1

Routine Exposure Scenarios 

Typical Application Rate Scenario ARIs Maximum Application Rate S

AgDrift® Scenario: Aerial Aerial Ground Ground Aerial Aerial GLand Type2 Agricultural Agricultural Agricultural Agricultural Agricultural Agricultural AgrEquipment3 Plane Helicopter Low Boom High Boom Plane 

Helicopter Low 

Hiker/hunter (adult) No ARI<1 No ARI<1 No ARI<1 No ARI<1 Diquat Diquat No Berry picker (child) No ARI<1 No ARI<1 No ARI<1 No ARI<1 Diquat Diquat No Berry picker (adult) No ARI<1 No ARI<1 No ARI<1 No ARI<1 Diquat Diquat No Angler (adult) No ARI<1 No ARI<1 No ARI<1 No ARI<1 Diquat Diquat No Residential (child) Diquat Diquat No ARI<1 No ARI<1 Diquat Diquat DResidential (adult) No ARI<1 No ARI<1 No ARI<1 No ARI<1 Diquat Diquat DNative American (child) No ARI<1 No ARI<1 No ARI<1 No ARI<1 Diquat Diquat No Native American (adult) No ARI<1 No ARI<1 No ARI<1 No ARI<1 Diquat Diquat No Swimmer (adult) No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No Swimmer (child) No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No ARI<1 No 1 ARI values less than 1 indicate a level of concern. Only short-term exposures were considered. 2 Agricultural land type is used as a proxy for a pond for aerial scenarios. Ground scenarios are not differentiated in AgDRIFT® by land type. 3 Low and High boom applies to a truck mount or a boat mount boom. 

BLM Vegetation Treatment Using Herbicides B-77 June 2007 

Final Programmatic EIS 
 TABLE B-13 

Accidental Exposure Public Scenarios with Aggregate Risk Indices Below One1

Accidental Exposure Scenarios 

Swimming Drinkin

Receptor

Direct Spray of 

Receptor 

Dermal Contact 

with Foliage Helicopter Spill Truck Spill Helicopter Sp

Hiker/hunter (adult) Diquat (M,T)1 Diquat (M) NE NE Diquat (M) Berry picker (child) Diquat (M,T) fluridone (M) Diquat (M) NE NE Diquat (M,TBerry picker (adult) Diquat (M,T) Diquat (M) NE NE Diquat (M) Angler (adult) Diquat (M,T) Diquat (M) NE NE Diquat (M) Residential (child) Diquat (M,T) fluridone (M) Diquat (M,T) fluridone (M,T) NE NE NA Residential (adult) Diquat (M,T) Diquat (M,T) fluridone (M) NE NE NA Native American (child) 

Diquat (M,T) 

fluridone (M) Diquat (M) NE

NE Diquat (M) 

Native American (adult) Diquat (M,T) Diquat (M) NE NE No ARI<1 Swimmer (child) NE NE Diquat (M,T) Diquat (M,T) NE Swimmer (adult) NE NE Diquat (M) Diquat (M) NE 1 ARI values less than 1 indicate a level of concern. These results indicate that diflufenzopyr risks are not expected to exceed the USEPA’s level of conc

the scenarios evaluated. 

2 M = Maximum application rate scenario; T = Typical application rate scenario; NE = Not evaluated; and NA = Receptor not exposed via this pathway.

BLM Vegetation Treatment Using Herbicides B-78 June 2007 

Final Programmatic EIS 
 HUMAN HEALTH RISK ASSESSMENT

Fluridone 

Fluridone is proposed for use on aquatic sites. Fluridone 

may be applied using the following methods: airplane, 

helicopter, truck (boom/broadcast or spot applications), 

ATV (boom/broadcast or spot applications), boat 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). All 

public receptors are assumed to be potentially exposed 

to fluridone spray drift resulting from aerial applications 

from airplanes or helicopters and boom/broadcast (both 

low-boom and high-boom) application methods from 

trucks, ATVs, or boats. As noted above, spot 

applications are small and focused, and very little if any 

spray drift is generated; public receptors are not 

assumed to be impacted by herbicide spray from spot 

applications. 

Under the routine use scenario, it is assumed that public 

receptors are exposed to spray drift via dermal contact, 

incidental ingestion, and dietary exposure pathways 

under both typical and maximum AR scenarios (shown 

in Table B-7). The ARIs combine all the exposure 

estimates to derive a cumulative effect ARI. Toxicity 

values are not available for acute dietary exposure for 

fluridone. Therefore, short-term ARIs are based on 

dermal and incidental oral exposure. 

Routine use scenario ARIs are greater than 1 under the 

typical and maximum AR scenarios for all public 

receptors, indicating no exceedance of the USEPA’s 

level of concern. 

Under the accidental scenario, it is assumed that public 

receptors are exposed directly to maximum herbicide 

ARs (shown in Table B-7) via dermal contact (direct 

spray of receptor, contact with directly sprayed 

vegetation, and contact with directly sprayed water), 

incidental ingestion of water while swimming, or 

dietary exposure pathways (drinking water, berry 

ingestion, and fish ingestion). The accidental scenario 

for a pond assumes that receptors swim in or obtain 

drinking water from a pond that has been directly 

sprayed with herbicide or that has received a spill (from 

a truck or helicopter). Cumulative accidental ARIs were 

not calculated, as it is assumed that each receptor would 

be accidentally exposed via one potential exposure 

pathway. Accidental scenario ARIs were calculated for 

dermal exposure and incidental oral pathways only, 

because acute dietary toxicity values are not available. 

Aggregate Risk Indices for fluridone are less than 1 for 

the following receptors and pathways, indicating a level 

of concern: 

• Berry picker (child) – direct spray 

• Native American (child) – direct spray 

• Residential (child) – direct spray and contact 

with directly sprayed foliage 

A second set of calculations was performed for the 

scenarios listed above with ARIs below 1 under the 

maximum AR assuming that herbicide is sprayed or 

spilled at the typical AR rather than the maximum AR 

(see Table B-7). The ARI are equal to or above 1, 

indicating no exceedance of USEPA’s level of concern. 

These results show that fluridone risks do not exceed 

the USEPA’s level of concern under the routine-use 

typical AR scenario, but could exceed the USEPA’s 

level of concern for the nearby resident (adult and child) 

under the routine-use maximum AR scenario and the 

nearby resident (adult and child), the berry picker 

(child), and the Native American (child) under the 

accidental scenarios. 

Imazapic 

Imazapic is proposed for use on rangeland, publicdomain forest land, energy and mineral sites, ROW, and 

recreational and cultural sites. Imazapic may be applied 

using the following methods: airplane, helicopter, truck 

(boom/broadcast or spot applications), ATV 

(boom/broadcast or spot applications), horseback (spot 

applications), and backpack (spot applications). All 

public receptors are assumed to be potentially exposed 

to imazapic spray drift resulting from aerial applications 

from airplanes or helicopters and boom/broadcast (both 

low-boom and high-boom) application methods from 

trucks or ATVs. As noted above, spot applications are 

small and focused, and very little if any spray drift is 

generated; therefore, public receptors are not assumed to 

be impacted by herbicide spray from spot applications. 

Under the routine use scenario, it is assumed that public 

receptors are exposed to spray drift via dermal contact, 

incidental ingestion, and dietary exposure pathways 

under both typical and maximum AR scenarios (ARs 

are shown in Table B-8). The ARIs combine all the 

exposure estimates to derive a cumulative effect ARI. 

Toxicity values are not available for acute dietary 

exposure, short-term dermal exposure, and 

intermediate-term dermal exposure. Therefore, shortterm ARIs are based on incidental oral exposure (and 

therefore are calculated only for swimming pathways). 

Routine use scenario ARIs for imazapic are greater than 

1 under both the typical and maximum AR scenarios for 

all public receptors, indicating no exceedance of the 

BLM Vegetation Treatments Using Herbicides B-79 June 2007 

Final Programmatic EIS 
HUMAN HEALTH RISK ASSESSMENT

USEPA’s level of concern under the scenarios 

evaluated. 

Under the accidental scenario, it is assumed that public 

receptors are exposed directly to maximum herbicide 

ARs (as shown on Table B-8) via dermal contact (direct 

spray of receptor, contact with directly sprayed 

vegetation, and contact with directly sprayed water), 

incidental ingestion of water while swimming, or 

dietary exposure pathways (drinking water, berry 

ingestion, and fish ingestion). The accidental scenario 

for a pond assumes that receptors swim in or obtain 

drinking water from a pond that has been directly 

sprayed with herbicide or that has received a spill (from 

a truck or helicopter). Cumulative accidental ARIs were 

not calculated, as it is assumed that each receptor would 

be accidentally exposed via only one potential exposure 

pathway. Accidental scenario ARIs for imazapic were 

calculated for incidental oral pathways only, because 

acute dietary and short-term dermal toxicity values are 

not available. Therefore, ARIs were calculated only for 

the swimming pathways. The ARIs for the swimming 

pathways are greater than 1, indicating exceedance of 

the USEPA’s level of concern under the scenarios 

evaluated. 

These results show that imazapic risks are not expected 

to exceed the USEPA’s level of concern for any of the 

public receptors under the scenarios evaluated. 

Sulfometuron Methyl 

Sulfometuron methyl is proposed for use on publicdomain forest land, energy and mineral sites, ROW, and 

recreational and cultural sites. Sulfometuron methyl 

may be applied using the following vehicles and 

methods: helicopter, truck (boom/broadcast or spot 

applications), ATV (boom/broadcast or spot 

applications), horseback (spot applications), and 

backpack (spot applications). All public receptors are 

assumed to be potentially exposed to sulfometuron 

methyl spray drift resulting from aerial applications 

from helicopters and boom/broadcast (both low-boom 

and high-boom) application methods from trucks or 

ATVs. As noted above, spot applications are small and 

focused, and very little if any spray drift is generated; 

therefore, public receptors are not assumed to be 

impacted by herbicide spray from spot applications. 

Under the routine use scenario, it is assumed that public 

receptors are exposed to spray drift via dermal contact, 

incidental ingestion, and dietary exposure pathways 

under both typical and maximum AR scenarios (ARs 

are shown in Table B-9). The ARIs combine all the 

exposure estimates to derive a cumulative effect ARI. 

Toxicity values are not available for acute dietary 

exposure or dermal exposure. Therefore, short-term 

ARIs are based on incidental oral exposure (and 

therefore are calculated only for swimming pathways). 

Routine use scenario ARIs for sulfometuron methyl are 

greater than 1 under both the typical and maximum AR 

scenarios for all public receptors, indicating no 

exceedance of the USEPA’s level of concern under the 

scenarios evaluated. 

Under the accidental scenario, it is assumed that public 

receptors are exposed directly to maximum herbicide 

ARs via dermal contact (direct spray of receptor, 

contact with directly sprayed vegetation, and contact 

with directly sprayed water), incidental ingestion of 

water while swimming, or dietary exposure pathways 

(drinking water, berry ingestion, and fish ingestion). 

The accidental scenario for a pond assumes that 

receptors swim in or obtain drinking water from a pond 

that has been directly sprayed with herbicide or that has 

received a spill (from a truck or helicopter). Cumulative 

accidental ARIs were not calculated, as it is assumed 

that each receptor would be accidentally exposed via 

only one potential exposure pathway. Accidental 

scenario ARIs were calculated for incidental oral 

pathways only because acute dietary and short-term 

dermal toxicity values are not available. Therefore, 

ARIs were calculated only for the swimming pathways. 

The ARIs for the swimming pathways are greater than 

1, indicating no exceedance of the USEPA’s level of 

concern under the scenarios evaluated. 

These results show that sulfometuron methyl risks are 

not expected to exceed the USEPA’s level of concern 

for any of the public receptors under the scenarios 

evaluated. 

Evaluation of Currently-available 

Herbicide Active Ingredients 

This section evaluates the toxicity values used for 

various herbicide active ingredients that are currently 

available for use by the BLM and have been evaluated 

in previous reports, namely the Final Environmental 

Impact Statement, Vegetation Treatment on BLM 

Lands in Thirteen Western States (1991 13-State EIS; 

USDI BLM 1991) and the Final Environmental 

Impact Statement, California Vegetation Management

(1988 California EIS; USDI BLM 1988). This section 

also compares the receptors and exposure pathways 

used in these HHRAs with those used in this HHRA. 

The purpose of this comparison is to determine 

BLM Vegetation Treatments Using Herbicides B-80 June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

whether the earlier BLM HHRAs are appropriate for 

current use. 

Evaluation of Dose-response Values Used in 

Previous EISs 

This section compares the dose-response values used for 

herbicide active ingredients that are in current use and 

were evaluated in previous EISs with values developed 

under current USEPA OPP policy. Most of the 

herbicide active ingredients were evaluated in the 1991 

13-State EIS HHRA. Three of the herbicides (asulam, 

2,4-DP, and fosamine) were evaluated in the 1988 

California EIS HHRA. The 1988 California EIS and 

1991 13-State EIS HHRAs used two NOAELs for each 

herbicide active ingredient—a systemic NOAEL and a 

reproductive/teratogenic NOAEL. In contrast, the 

current approach from the USEPA OPP uses a variety 

of NOAELs based on exposure duration rather than 

specific health outcome, as well as acute and chronic 

dietary PADs. The PAD is the NOAEL divided by an 

uncertainty factor, typically 100. Therefore, multiplying 

the PAD by 100 allows one to compare the value to a 

NOAEL. The NOAELs used in the current risk 

assessment are based on the most sensitive effect (i.e., 

they were not identified separately by endpoints, such as 

systemic effects or reproductive/teratogenic effects); 

therefore, they are conservative values. Lower NOAELs 

indicate higher potential toxicity. The Cancer Slope 

Factors (CSF) used in the 1988 California EIS and the 

1991 13-State EIS were also compared with any recent 

CSFs for those active ingredients. Higher CSFs indicate 

higher potential toxicity. 

The dose-response values used the earlier HHRAs for 

most of the herbicide active ingredients are conservative 

in comparison to current toxicity values, with the 

following exceptions: 

Asulam 

The short-term and intermediate-term NOAEL for all 

exposure routes is 50 mg/kg-day, which is the same 

value as the systemic and reproductive NOAELs used in 

the 1988 California EIS HHRA. The long-term NOAEL 

for all exposure routes is 36 mg/kg-day, which is 

slightly lower than the NOAEL of 50 mg/kg-day used 

in the 1988 California EIS HHRA. The 1988 California 

EIS HHRA showed that routine exposures to the public 

and workers do not result in unacceptable risks. The 

slightly lower long-term NOAEL would not 

significantly change this outcome. Asulam has not been 

used by the BLM since at least 1997. 

Diuron 

The chronic dietary PAD of 0.003 mg/kg-day is based 

on a LOAEL of 1 mg/kg-day. Assuming that there is an 

extra UF of 3 because of the use of a LOAEL rather 

than a NOAEL, the corresponding NOAEL would be 

0.3 mg/kg-day. This value is slightly lower than the 

systemic NOAEL of 0.625 mg/kg-day used in the 1991 

13-State EIS HHRA, indicating that the estimated 

noncancer risk for diuron could be higher using the new 

toxicity value. In addition, the USEPA has developed a 

cancer slope factor for diuron of 1.91x10-2/mg/kg-day, 

whereas the 1991 13-State EIS HHRA did not evaluate 

diuron for its potentially carcinogenic effects. 

Information provided by the BLM states that the 4-year 

average (2000 to 2003) of acres treated by diuron is 

964; therefore, this active ingredient has been used 

recently, though not extensively. These results indicate 

that a current risk assessment of diuron would evaluate 

potentially carcinogenic effects. The 1991 13-State EIS 

HHRA showed potential unacceptable risks for this 

herbicide active ingredient, and this conclusion would 

remain if the more recent toxicity values were used. 

 

Fosamine 

The chronic dietary PAD of 0.01 mg/kg-day is based on 

a NOAEL of 10 mg/kg-day. This value is lower than the 

systemic NOAEL of 25 mg/kg-day used in the 1988 

California EIS HHRA, indicating that the estimated 

noncancer risk for fosamine could be higher using the 

new toxicity value. The 1988 California EIS HHRA 

showed that routine exposures to the public and workers 

do not result in unacceptable risks for this herbicide 

active ingredient. Because the difference between the 

two NOAELs is relatively small, this outcome would 

likely not change with use of the newer toxicity value. 

Fosamine has been used sparingly in recent years by the 

BLM (< 50 acres annually). 

Simazine 

The chronic dietary PAD of 0.005 mg/kg-day is based 

on a NOAEL of 0.5 mg/kg-day, which is lower than the 

NOAEL of 5 mg/kg-day used in the 1991 13-State EIS 

HHRA, indicating that the estimated noncancer risk for 

simazine could be higher using the new toxicity value. 

However, information provided by the BLM states that 

simazine has not been used since 1997; therefore, there 

is no exposure to this herbicide active ingredient, and 

the toxicity value change would not significantly affect 

its use. 

BLM Vegetation Treatments Using Herbicides B-81 June 2007 

Final Programmatic EIS 
HUMAN HEALTH RISK ASSESSMENT

Triclopyr 

The chronic dietary PAD of 0.005 mg/kg-day is based 

on a NOAEL of 0.5 mg/kg-day, which is lower than the 

NOAEL of 2.5 mg/kg-day used in the 1991 13-State 

EIS HHRA, indicating that the estimated noncancer risk 

for triclopyr could be 5-fold higher using the new 

toxicity value. Information provided by the BLM states 

that the 4-year average (2000 to 2003) of acres treated 

by triclopyr is 4,737 indicating that this active 

ingredient has been used recently. The 1991 13-State 

EIS HHRA showed potential unacceptable risks for this 

herbicide active ingredient, and this conclusion would 

remain if the more recent toxicity values were used. 

In summary, diuron, simazine, and triclopyr are the only 

herbicide active ingredients for which there are more 

stringent current dose-response values than those used 

in the 1991 13-State EIS HHRA. Simazine has not been 

used since 1997; therefore, there is no exposure to this 

herbicide active ingredient, and the toxicity value 

change does not affect potential risks. Both diuron and 

triclopyr were found to pose potentially unacceptable 

risks in the 1991 13-State EIS HHRA; this conclusion 

would remain if the more stringent current toxicity 

values were used. 

Evaluation of Receptors and Exposure Pathways 

Used in the Earlier Human Health Risk Assessments 

The 1988 California EIS and 1991 13-State EIS 

HHRAs and the current HHRA evaluate occupational 

and public receptors. The risk assessments evaluated the 

same occupational scenarios—that of a worker 

potentially exposed to herbicide active ingredients via 

dermal contact and inhalation during routine 

applications and of a worker potentially exposed to an 

accidental spill of herbicide active ingredient to his or 

her skin. 

The public receptors in both risk assessments are 

similar. The exposure scenarios are also similar, with 

two exceptions: the 1991 13-State EIS HHRA did not 

evaluate a swimming scenario, and the current HHRA 

does not evaluate a Native American game ingestion 

scenario (in accordance with discussions with the 

USEPA). Therefore, the current risk assessment 

evaluates a more conservative pond pathway and a 

slightly less conservative Native American pathway. 

Other than these minor differences, the exposure 

pathways for both risk assessments are similar. 

Summary of Currently-available Herbicide Active 

Ingredient Evaluation 

Based on the general similarity of the risk assessments 

conducted by the BLM in 1988 and 1991 and the 

current risk assessment, it is likely that the risk 

estimates calculated previously would not differ 

significantly from risk estimates calculated for the 

present herbicide active ingredients using the updated 

risk assessment methods and the updated toxicity 

values. Therefore, new risk assessments were not 

conducted for the herbicides currently in use other than 

sulfometuron methyl and dicamba. These herbicide 

active ingredients were evaluated in the current HHRA 

because of alternative exposure pathways and 

concomitant exposures with other herbicide active 

ingredients. 

Uncertainty Analysis 

Uncertainty is introduced into the risk assessment in 

several places throughout the process. Every time an 

assumption is made, some level of uncertainty is 

introduced into the risk assessment. In accordance with 

USEPA guidance (USEPA 1989), the uncertainty 

associated with each step of the risk characterization 

process is discussed in this section of the report. 

Within any of the four steps of the human health risk 

evaluation process, assumptions must be made due to a 

lack of absolute scientific knowledge. Some of the 

assumptions are supported by considerable scientific 

evidence, while others have less support. Every 

assumption introduces some degree of uncertainty into 

the risk evaluation process. Regulatory risk evaluation 

methodology requires that conservative assumptions be 

made throughout the risk evaluation to ensure that 

public health is protected. Therefore, when all of the 

assumptions are combined, it is much more likely that 

risks are overestimated rather than underestimated. 

Hazard Identification 

The Hazard Identification step involves identifying the 

herbicides to be evaluated quantitatively in the HHRA 

and providing toxicity information. The six herbicides 

evaluated in this HHRA were identified by the BLM, 

and represent herbicides proposed for use by the BLM 

that have not been evaluated in previous EISs (with the 

exception of sulfometuron methyl, which was 

previously evaluated). Toxicity information on these 

herbicides was collected mainly from USEPA reports 

that have compiled results of toxicity studies conducted 

BLM Vegetation Treatments Using Herbicides B-82 June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

by the manufacturers and other entities. For the most 

part, the USEPA had sufficient information to place the 

herbicides in the appropriate acute toxicity categories, 

and to determine their carcinogenic potential. 

Appropriate studies were available on subchronic, 

chronic, developmental, and reproductive toxicity. 

While there is always uncertainty in extrapolating 

animal information to humans, sufficient information 

was available to make a determination on toxicity for 

these herbicides. 

Dose-response Assessment 

The purpose of the dose-response assessment is to 

define the relationship between the dose of a chemical 

and the likelihood or magnitude of an adverse effect 

(response). Risk assessment methodologies typically 

divide potential health effects of concern into two 

general categories: effects with a threshold 

(noncarcinogenic) and effects assumed to be without a 

threshold (potentially carcinogenic). None of the six 

herbicides evaluated in this HHRA are designated as 

potential carcinogens by the USEPA; therefore, 

noncancer dose-response values were used in the 

evaluation. There are several sources of uncertainty in 

the development of dose-response values. 

Animal-to-human Extrapolation 

For many chemicals, animal studies provide the only 

reliable information on which to base an estimate of 

adverse human health effects. Extrapolation from 

animals to humans introduces uncertainty into the risk 

characterization. Usually, the difference between the 

human reaction to a chemical and the test animal 

reaction to a chemical is unknown. If a chemical’s fate 

and the mechanisms by which it causes adverse effects 

are known in both animals and humans, uncertainty is 

reduced. When the fate and mechanism for the chemical 

are unknown, uncertainty increases. 

Conservative assumptions that incorporate uncertainty 

factors are used to extrapolate from animals to humans 

such that it is more likely that effects in humans are 

overestimated than underestimated. When data are 

available from several species, the highest dose that that 

does not cause effects in the most sensitive species is 

used to determine the NOAEL, which is used to 

calculate the RfD and the PAD. The PAD is calculated 

by dividing the NOAEL by UFs, generally of 1 to 10 

each, to account for intraspecies variability, interspecies 

variability, and study duration. When using the NOAEL 

to calculate MOEs, the target MOE is typically 100 to 

account for intraspecies and interspecies variability. 

Generally, additional UFs for study duration are not 

required, because separate NOAELs are used for short-, 

intermediate-, and long-term exposures. 

The use of the UFs compensates for uncertainties 

involved in extrapolating from animals to humans. 

Nevertheless, because the fate of a chemical can differ 

in animals and humans, it is possible that animal 

experiments will not reveal an adverse effect that would 

manifest itself in humans. This can result in an 

underestimation of the effects in humans. The opposite 

may also be true: effects observed in animals may not 

be observed in humans, resulting in an overestimation 

of potential adverse human health effects. 

Availability of NOAELs 

NOAELs for all of the exposure durations and routes 

are not available for all of the herbicides. In most cases, 

the USEPA did not develop specific NOAELs because 

the herbicide is not considered toxic through a specific 

exposure route. For example, there are no dermal 

NOAELs for diflufenzopyr because a dermal toxicity 

study did not show any effects at the limit dose of 1,000 

mg/kg-day (USEPA 2002b). Therefore, risk 

calculations were not conducted for certain herbicides 

and certain exposure routes. It is likely that risks are not 

being underestimated because the specific exposure 

route is unlikely to show toxicity. 

Exposure Assessment 

There are uncertainties involved in the development of 

exposure scenarios and in the estimation of herbicide 

doses to which humans could be exposed. 

Exposure Scenarios 

Exposure scenarios in a risk evaluation are selected to 

be representative of current and reasonably foreseeable 

site use. In accordance with pesticide risk assessment 

approaches, both occupational and public (non-worker) 

receptors were evaluated. The selection of occupational 

receptors considered the BLM’s specific land programs, 

application types, application vehicles, and application 

methods. The occupational receptors include pilots, 

applicators, mixer/loaders, and combined 

applicator/mixer/loaders. Most occupational receptors 

are likely to have little herbicide exposure because of 

the use of PPE and other health and safety precautions. 

The accidental spill scenario evaluated for the 

occupational receptor is also very unlikely since a 

worker would take necessary precautions to prevent 

spills. 

BLM Vegetation Treatments Using Herbicides B-83 June 2007 

Final Programmatic EIS 
HUMAN HEALTH RISK ASSESSMENT

The HHRA evaluated a wide range of potential public 

receptors, including hiker/hunters, berry pickers, 

anglers, swimmers, nearby residents, and Native 

Americans. Although there are many different exposure 

scenarios and receptors that could be evaluated, these 

receptors cover a range of potential exposures that could 

occur under worst case conditions on BLM lands. It is 

assumed that these receptors could be exposed through 

a number of exposure pathways, such as herbicide 

spray, contact with sprayed foliage, contact with 

sprayed water through drinking or swimming, and 

ingestion of sprayed berries and fish that have 

bioaccumulated herbicide from sprayed water. Under 

the routine scenarios, receptors are assumed to be 

exposed to spray drift, while under the accidental 

scenarios, receptors are assumed to be exposed to direct 

spray. The Native American receptor is assumed to be 

exposed through all of these exposure pathways, which 

is likely to be a conservative assumption. 

While it is possible that public receptors use public 

lands under intermediate- and long-term time frames, it 

is unlikely that public receptors would be exposed to 

herbicides under the routine use scenario for more than 

a short-term exposure, which is defined as 1 day to 1 

month (USEPA 2001g). Therefore, a short-term 

scenario was evaluated in this HHRA. Although it is 

highly unlikely that public receptors would be 

potentially exposed to herbicides for longer than a shortterm time frame, both an intermediate- and a long-term 

exposure scenario are also evaluated in this HHRA. 

Estimation of Dose 

Various conservative assumptions were made to 

estimate the herbicide doses to which occupational and 

public receptors could be exposed. For the occupational 

receptors, exposure doses were estimated using UE 

information from the PHED, which is a generic 

database containing dermal and inhalation exposure 

data for workers mixing, loading, or applying 

pesticides. The USEPA has developed a series of 

standard UE values for various exposure scenarios, 

which were used in this HHRA. For the occupational 

worker accidental spill scenario, it was assumed that the 

herbicide could spill directly onto the worker and be 

absorbed through the skin. These exposure pathways are 

likely to result in conservative risk estimates. 

For the public receptors, various conservative 

assumptions were used to estimate exposures. These 

exposure assumptions were generally derived from 

USEPA databases, such as the Exposure Factors 

Handbook (USEPA 1997a). The exposure assumptions 

listed in these guidance documents are generally 

conservative, and are meant to account for a wide range 

of exposure situations. To estimate exposures to the 

public from off-site deposition of herbicides, the 

computer model, AgDRIFT® (SDTF 2002), was used. 

The AgDRIFT® Tier I and Tier II evaluations were used 

in this HHRA because they allow the development of 

routine generic application scenarios that are more 

representative of the range of applications likely 

employed by the BLM. The terrestrial DRs and water 

concentrations calculated by AgDRIFT® are likely to be 

upper-end estimates. The computer model GLEAMS 

was used to estimate runoff of the terrestrial herbicides 

into ponds. For the three terrestrial herbicides, pond 

concentrations calculated in AgDRIFT® were added to 

the highest pond concentrations calculated in 

GLEAMS. This likely overestimates the true pond 

concentrations because AgDRIFT® concentrations 

represent relatively short duration concentrations. It is 

unlikely that a receptor would be exposed to pond water 

on the day that both drift concentrations and runoff 

concentrations are present. 

Worst-case assumptions were made to evaluate the 

accidental spray and spill scenarios. The accidental 

spray scenario assumed that the receptor was exposed to 

direct spray at the maximum herbicide AR. The spill 

scenario assumed that a fully-loaded truck or helicopter 

emptied its contents into a pond while transporting the 

herbicide to the application site. In reality, the BLM 

requires that the herbicide be mixed at the application 

site; therefore, it is unlikely that premixed herbicide 

would be transported from one location to another. This 

scenario represents a worst-case scenario that is unlikely 

to occur. 

Risk Characterization 

The potential risk of adverse human health effects is 

characterized based on estimated potential exposures 

and potential dose-response relationships. Generally, the 

goal of a risk evaluation is to estimate a reasonable 

upper-bound to potential exposure and risk. Most of the 

assumptions about exposure and toxicity used in this 

evaluation are representative of statistical upper-bounds 

or even maxima for each parameter. The result of 

combining several such upper-bound assumptions is 

that the final estimate of potential exposure or potential 

risk is extremely conservative. 

The health risks estimated in the risk characterization 

generally apply to the receptors whose activities and 

locations were described in the exposure assessment. 

Some people will always be more sensitive than the 

BLM Vegetation Treatments Using Herbicides B-84 June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

average person and, therefore, will be at greater risk. 

Dose-response values used to calculate risk, however, 

are frequently derived to account for additional 

sensitivity of subpopulations (e.g., an UF of 10 is used 

to account for intraspecies differences). Therefore, it is 

unlikely that this source of uncertainty contributes 

significantly to the overall uncertainty of the risk 

assessment. 

The large number of assumptions made in the risk 

characterization introduces uncertainty in the results. 

Any one person’s potential exposure and subsequent 

risk are influenced by all the parameters mentioned 

above and will vary on a case-by-case basis. Despite 

inevitable uncertainties associated with the steps used to 

derive potential risks, the use of numerous conservative 

(health-protective) assumptions will most likely lead to 

a large overestimate of potential risks from the site. 

Public Receptors – Intermediate- and Longterm Exposure Scenario 

As stated previously, it is unlikely that public receptors 

would be potentially exposed to herbicides for more 

than a short-term exposure period. Although it is highly 

unlikely that public receptors would be potentially 

exposed to herbicides for longer than a short-term time 

frame, both an intermediate- and a long-term exposure 

scenario are evaluated in this uncertainty analysis. 

While these exposures are extremely unlikely, they 

were included in the uncertainty analysis for 

completeness. 

Routine use scenario ARIs for intermediate- and longterm exposure scenarios are greater than 1 under both 

the typical and maximum AR scenarios for all public 

receptors for dicamba, diflufenzopyr, imazapic, and 

sulfometuron methyl, indicating no level of concern. 

ARIs for diquat and fluridone are below 1 for the 

following intermediate- and long-term scenarios under 

the typical AR scenario, indicating a level of concern: 

Diquat. ARIs for diquat are below 1 for the following 

scenarios under the typical AR scenario (intermediateand long-term), indicating a level of concern: 

• Berry picker (child) – airplane and helicopter 

applications (intermediate- and long-term 

exposures) 

• Residential (child) – airplane and helicopter 

applications (intermediate- and long-term 

exposures) 

• Residential (adult) – airplane and helicopter 

applications (intermediate- and long-term 

exposures) 

• Native American (child) – airplane and 

helicopter applications (intermediate- and 

long-term exposures) 

ARIs for diquat are below 1 for the following scenarios 

under the maximum AR scenario (intermediate- and 

long-term), indicating a level of concern: 

• Hiker/hunter (adult) – airplane and helicopter 

applications (intermediate- and long-term 

exposures) 

• Berry picker (child) – airplane and helicopter 

applications (intermediate- and long-term 

exposures), high-boom applications 

(intermediate- and long-term exposures) 

• Berry picker (adult) – airplane and helicopter 

applications (intermediate- and long-term 

exposures) 

• Angler (adult) – airplane and helicopter 

applications (intermediate- and long-term 

exposures) 

• Residential (child) – airplane and helicopter 

applications (intermediate- and long-term 

exposures), low-boom applications 

(intermediate- and long-term exposures), and 

high-boom applications (intermediate- and 

long-term exposures) 

• Residential (adult) – airplane and helicopter 

applications (intermediate- and long-term 

exposures), and high-boom applications 

(intermediate- and long-term exposures) 

• Native American (child) – airplane and 

helicopter applications (intermediate- and 

long-term exposures), and high-boom 

applications (intermediate- and long-term 

exposures) 

• Native American (adult) – airplane and 

helicopter applications (intermediate- and 

long-term exposures) 

Fluridone. Routine use scenario ARIs are greater than 1 

under the typical AR scenario (intermediate- and longterm) for all public receptors, indicating no exceedance 

of the USEPA’s level of concern. Routine use scenario 

ARIs are greater than 1 under the maximum AR 

scenario (intermediate) for all public receptors, 

BLM Vegetation Treatments Using Herbicides B-85 June 2007 

Final Programmatic EIS 
HUMAN HEALTH RISK ASSESSMENT

indicating no exceedance of the USEPA’s level of 

concern. The following routine use scenario ARIs for 

fluridone are less than 1 under the maximum AR 

scenario (long-term), indicating a level of concern: 

• Nearby resident (child) – airplane applications 

and helicopter depositions 

• Nearby resident (adult) – airplane applications 

The results of evaluating the intermediate- and longterm exposures for the public receptors in the 

uncertainty analysis show that diquat in several 

scenarios and fluridone in very limited scenarios 

(resident, aerial application) could potentially pose a 

risk level of concern. The remaining herbicides do not 

pose a level of concern even under the unlikely scenario 

that public receptors could be repeatedly exposed to 

media that has received spray drift. 

BLM Vegetation Treatments Using Herbicides B-86 June 2007 

Final Programmatic EIS
 HUMAN HEALTH RISK ASSESSMENT

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