Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-1 

APPENDIX Q HUMAN HEALTH RISK ASSESSMENT 

This section describes the potential health and safety hazards associated with manual, 

mechanical, biological, prescribed fire and herbicide treatments. All of the Alternatives 

involve risks of exposing workers and the public to these hazards. 

1.0 Potential Human Health Effects of Manual and 

Mechanical Treatment Methods 

Manual (hand) and mechanical treatments can present health hazards to forestry workers. 

Adverse weather and terrain commonly create unfavorable working conditions and increased 

hazards. Hazards associated with adverse weather conditions include extreme heat and cold, 

which can be exacerbated by very dry and very wet conditions. Other hazards include: falling 

objects- especially when cutting trees, tripping or slipping on hazards on the ground; 

protruding objects such as branches and twigs; poisonous plants and insects, and dangerous 

wildlife. 

Tools and equipment present inherent hazards such as sharp edges on the tools themselves, 

and the hazardous nature of fuels and lubricants used in mechanized equipment. Manual and 

mechanical methods present potential ergonomic hazards related to lifting and carrying 

equipment, and when pulling vegetation. 

Injuries can vary from minor cuts, sprains, bruises, and abrasions to major arterial bleeding, 

compound bone fractures, serious brain concussions, and death. Workers are subject to heatrelated illness or hypothermia when working in extreme weather conditions, and may incur 

musculo-skeletal injuries related to improper body mechanics. 

Equipment operators could be injured from improperly operating the equipment or losing 

control of equipment on steep or slippery terrain. Operators and nearby workers also can 

suffer hearing damage. Nearby workers and the public can be struck by flying debris around 

some machinery. 

The potential for hazard exposure, i.e. risk of injuries, is exacerbated when workers are 

fatigued, poorly trained, or poorly supervised, and do not follow established safety practices. 

Appropriate training, together with monitoring and intervention to correct unsafe practices, 

would minimize risk of worker injury and illness. Compliance with Occupational Health and 

Safety Administration (OSHA) standards, along with agency, industry and manufacturers’ 

recommendations reduces the potential exposure and risk of injury to workers. Members of 

the public are usually not at risk from manual and mechanical methods unless they are too 

close to machinery that is producing flying debris during treatment. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-2 

1.1 Comparison of Alternatives—Exposure to Health Hazards for 

Workers in Manual Treatments of Invasive Plants 

Forest Service accident reports do not identify the type of work being done when an accident 

occurred, thus data on accidents related to invasive plant treatment is not available. Worker 

exposure to hazards is the direct effect; exposure varies according to the amount of manual 

and mechanical treatment projected for each alternative. A quantified relationship between 

manual treatment acreage and worker exposure, expressed as productivity (time/acre pulled) 

was determined for a large, multiyear hand pulling project on the Wenatchee National Forest 

(Henry, 2003). This relationship is applied to EIS alternatives to estimate the number of fulltime worker equivalents needed to accomplish annual manual treatments projected for each 

alternative. No comparable productivity data is available for mechanical treatments. 

REF: Henry, Charles. Icicle Road Hand-Pulling Timed Study, in: Techline, Winter 2003-

2004. Ag. West Communications, Granby CO. 

Hand Pull Plot #1: 

$801.00/acre *1 hour/$10.09 = 78.64 hours/acre 

Hand Pull Plot #2: 

$610.00/acre * 1 hour/$10.09 = 60 hours/acre 

Average: 

$706.00/acre * 1 hour/$10.09 = 70 hours/acre 

Convert to IPEIS regionwide assumptions: 

$340.00 per acre treated/$706.00 per acre treated = 34 hours per acre/70 hours per acre 

Assume 34 worker hours per acre of manual treatment—all alternatives 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-3 

Table 1-1 Calculations of estimated worker days of manual treatment by alternative

ALTERNATIVE ACRES WORKER HOURS WORKER DAYS (@ 8 H/DAY) 

 

A 8,610 292,740 36593 

B 10,576 359,584 44948 

C 7,228 245,752 30719 

D 2,024 68,816 8602 

2.0 Potential Human Health Effects of Biological Control 

Treatment Methods 

The collection, transport, release and monitoring of biocontrol organisms involves no specific 

human health hazards except those hazards involved in general field work and vehicle 

transportation, described under Manual and Mechanical methods, above. 

3.0 Potential Human Health Effects of Cultural Treatment 

Methods

Treatments such as controlled grazing, mulching, and competitive seeding involve no specific 

human health hazards except those hazards involved in general fieldwork and vehicle 

transportation, described under Manual and Mechanical methods, above. Fertilization may 

involve dermal, oral, and inhalation exposures to dusts or liquids containing various 

chemicals. Fertilizers are not regulated by FIFRA (Federal Insecticide, Fungicide, and 

Rodenticide Act). Therefore, toxicity testing and hazard identification is not as extensive as 

for herbicides. The primary nutrient chemicals are identified, and some constituents that have 

been identified as potentially hazardous by federal or state regulations are also listed. The 

exposure reduction practices identified in the herbicide treatment health effects analysis could 

also be applied to fertilizer handling and applications to reduce risk 

4.0 Potential Human Health Effects of Prescribed Burning 

Treatment Methods 

Prescribed burns are associated with hazards from smoke and heat to workers and the public. 

Hazards to workers range from eye irritation, coughing, and shortness of breath, to severe 

burns that can leave permanent scars or mortality. Chronic exposure to smoke could lead 

emphysema or lung cancer. Wood smoke contains polyaromatic hydrocarbons (PAHs), 

which include at least five chemicals that are carcinogens. 

Workers are most at risk of adverse health effects from smoke, but sensitive members of the 

public may also experience health effects. Prescribed burns may “escape,” control and 

endanger the public. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-4 

To reduce the risks of burn escapes and lingering smoke, the Forest Service has special 

requirements for planning and implementing prescribed burns. All prescribed burn projects 

require a Burn Plan, which includes a burning prescription, a description and discussion of 

fuels, weather, and timing; how to conduct the burn; and safeguards. The safeguards section 

of the plan addresses all precautions needed to confine the burn to the prescribed area. In 

addition, the Forest Service has established qualification standards and training requirements 

for personnel involved in prescribed burning. 

5.0 Potential Human Health Effects Related to Herbicide 

Treatment Methods 

The public expressed considerable concern the health risks associated with chemical 

herbicides. All alternatives allow limited herbicide use but vary by the range of herbicides 

considered and treatment/restoration standards. 

Estimates of potential health risks for each herbicide as proposed for use in each alternative 

are based on herbicide risk assessments prepared for the Forest Service by Syracuse 

Environmental Research Associates (SERA). Forest Service/SERA risk assessments use 

peer-reviewed articles from the open scientific literature and current EPA documents, 

including Confidential Business Information. Specific methods used in preparing the Forest 

Service/SERA herbicide risk assessments are described in SERA, 2001. The risk assessment 

for the adjuvant NPE (nonylphenol polyethoxylate) was conducted and documented by David 

Bakke, Forest Service Pesticide-Use Specialist, consistent with the assumptions, 

methodologies, and protocols developed by SERA. The NPE Risk Assessment (Bakke, 

2003), was peer-reviewed by SERA toxicologists and other Forest Service and independent 

experts; it is included in the “Forest Service/SERA herbicide risk assessments” used 

throughout this EIS. 

Only information that is not derived from the relevant Forest Service/SERA Risk 

Assessments and USDA, 2003 is specifically cited in this section. The risk assessments and 

associated documentation is available in total in the administrative record for this EIS. 

Estimates of risk are not absolute; rather, they are relative and based on assumptions and 

evolving toxicity data. Risk assessments have inherent limitations; these are discussed in 

Chapter 3.3.2 of the FEIS. 

The human health effects from the use of any herbicide depends on the toxic properties 

(hazards) of that herbicide, the level of exposure to that herbicide at any given time, and the 

duration of that exposure. The risk to human health from herbicide use can be reduced by 

reducing exposure through the use of streamside buffer zones, personal protective equipment 

for applicators, and posting of treated areas. Treatments under all alternatives would be 

accomplished according to strict safety and health standards. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-5 

The following findings apply to herbicides proposed for use in the action alternatives: 

• Two herbicides, 2,4-D and triclopyr consistently have the greatest number of invasive 

plant treatment scenarios where both worker and public health risks exceed EPA target 

levels (i.e. the RfD’s1

). These two herbicides also generate nearly all application 

scenarios where the Hazard Quotient (HQ) is predicted to be greater than 10 (i.e. 

expected dose exceeds the RfD by greater than one order of magnitude). 

• One herbicide, dicamba, and the adjuvant nonylphenol ethoxylate, have an 

intermediate number of scenarios where worker and public health risks exceed EPA 

target levels, and they have a few scenarios where the HQ exceeds 10. Human health 

risks could generally be mitigated at the project level, but in some limited situations, 

their use might present significant health risks. 

• The remaining nine herbicides rarely and only minimally exceed the RfD’s established 

by EPA. The scenarios that may slightly exceed EPA target levels are only associated 

with worst-case exposure assumptions and/ or using maximum (rather than typical) 

application rates, except for exposure to NPE (HQ=5) from drinking spillcontaminated pond water. 

5.1 Hazard Analysis 

The human health hazards associated with each herbicide active ingredient were evaluated 

and estimated by a thorough review of available toxicological studies. Possible health effects 

may include short-term and long-term adverse effects. Short-term effects may include: 

nausea, headache, dizziness, eye or skin irritation, and coughing. Long-term effects may 

include: cancer; reproductive, endocrine, immunologic, neurologic effects, and genetic 

mutations. 

The toxicological database for each herbicide was reviewed for acute, subchronic, and chronic 

effects in laboratory animal studies. Judgments about the potential hazards of herbicides to 

humans are necessarily based in large part on the results of toxicity tests on laboratory 

animals. Information on actual human poisoning incidents and effects on human populations 

supplements the laboratory animal test results, where such information is available. For a 

background discussion of all toxicological tests and endpoints considered in Forest Service 

Risk Assessments, refer to SERA, 2001. 

 

1

 See glossary for definition of reference dose. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-6 

Toxicity studies were evaluated individually for scientific quality, and cumulatively for all 

similar studies to identify the NOAEL and Reference Dose (RfD) for each potential effect. 

Each Forest Service/SERA herbicide risk assessment contains citations for all studies that are 

reviewed in detail. 

Formulated herbicides as applied in Forest Service invasive plant treatments may contain 

additional compounds besides the active herbicide ingredient that are called impurities or inert 

ingredients. Other additives, called adjuvants, may be mixed with the diluted formulation 

before spraying to either enhance the herbicide activity, or to modify undesirable properties of 

the spray mixture. Additionally, when herbicide formulation chemicals are applied in the 

environment, they may be transformed into other compounds, called metabolites. 

In addition to the analysis of potential hazards to human health from every herbicide active 

ingredient, Forest Service/SERA risk assessments evaluate any available scientific studies of 

potential hazards of these other substances associated with herbicide applications: impurities, 

metabolites, inert ingredients, and adjuvants. There is usually less information available on 

these substances because they are not subject to the extensive testing that is required for the 

herbicide active ingredients under FIFRA (Federal Insecticide, Fungicide, and Rodenticide 

Act). Under FIFRA, inerts are classified into one of four categories, called Lists, based on 

available toxicity information (see Section 5.1.2). In some cases, inerts and adjuvants are 

tested to comply with other federal laws, such as the Federal Food, Drug, and Cosmetic Act. 

5.1.1 Impurities and Metabolites 

Virtually no chemical synthesis yields a totally pure product. Technical grade herbicides 

contain some impurities. The EPA defines an impurity as “...any substance...in a pesticide2 

product other than an active ingredient or an inert ingredient, including unreacted starting 

materials, side reaction products, contaminants, and degradation products” (40 CFR 

158.153(d)). Toxicity studies generally account for impurities in the active ingredient, except 

in the case of carcinogens associated with the following impurities: 

• Hexachlorobenzene (HCB) in both clopyralid and picloram. 

• Ethylene oxide in NPE (nonylphenol polyethoxylate)-based surfactants. 

• 1,4-dioxane in some formulations of glyphosate containing NPE-based surfactants 

 

2

 References to pesticides in this context also apply to herbicide use. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-7 

Analyses of the carcinogenic risk of these three impurities are presented in the corresponding 

Forest Service/SERA herbicide risk assessments. In addition to the carcinogenic risks, acute 

and other chronic risks from exposure to HCB are specifically analyzed. 

From Bakke, 2003, the risk of cancer from exposure to ethylene oxide in NPE-based 

surfactants was considered negligible for workers, based on the EPA standard of acceptable 

risk of less than 1 in 1 million. Ethylene oxide is not analyzed further in this human health 

risk assessment. 

From Borrecco and Neisess 1991, the risk of cancer from exposure to 1,4-dioxane in 

glyphosate was considered negligible for workers, based on the EPA standard for acceptable 

risk of less than 1 in 1 million. 1,4-dioxane is not analyzed further in this human health risk 

assessment. 

Similar to impurities, the potential health effects of herbicide metabolites are often accounted 

for in the available toxicity studies on the herbicide active ingredient, assuming that the 

toxicological effects of metabolism in the test animal species would be similar to the 

toxicological effects in humans. Uncertainties in this assumption are encompassed in the 

precautionary uncertainty factor used in calculating the RfD and may sometimes influence the 

selection of the study used to derive the RfD. 

The herbicide triclopyr presents a special case: its principal metabolite, called TCP, is also a 

metabolite of chlorpyrifos, an insecticide. The risks for direct, indirect and cumulative effects 

of human exposure to TCP from both sources are discussed in the Triclopyr herbicide risk 

assessment (p.3-34). 

5.1.2 Inert Ingredients 

Forest Service/SERA Risk Assessments analyze the human health risks of inert ingredients 

and full herbicide formulations by the process described below: 

• Compare acute toxicity data between the formulations (that include inert ingredients), 

and the active ingredients alone to address whether the inert is likely to constitute a 

substantial fraction of the formulation toxicity; 

• Disclose whether or not the formulated products have undergone chronic toxicity 

testing; and 

• Identify, with the help of EPA and the herbicide registrants, ingredients of known 

toxicological concern in the formulated products and assess the risks of those 

ingredients. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-8 

Researchers who have studied the relationships between acute and chronic toxicity have 

found that relationships do exist and acute toxicity data can be used to give an indication of 

overall toxicity (Zeise, et al., 1984). The court in NCAP v. Lyng, 844 F.2d 598 (9th Cir 1988) 

decided that this method of analysis provided sufficient information for a decision maker to 

make a reasoned decision. In SRCC v. Robertson, Civ.No. S-91-217 (E.D. Cal., June 12, 

1992) and again in CATs v. Dombeck, Civ. S-00-2016 (E.D. Cal., Aug 31, 2001) the district 

court upheld the adequacy of the methodology described above for disclosure of inert 

ingredients and additives. 

The EPA has categorized approximately 1,200 inert ingredients into four lists. Lists 1 and 2 

contain inert ingredients of known or suspected toxicological concern. List 4 contains nontoxic substances such as corn oil, honey and water. List 3 includes substances for which EPA 

has insufficient information to classify as either hazardous (List 1 and 2) or non-toxic (List 4). 

Use of formulations containing inert ingredients on List 3 and 4 is preferred for invasive plant 

treatment under current Forest Service policy and in all alternatives considered in the EIS. 

Most information about inert ingredients that is submitted to EPA for pesticide registration is 

classified as “Confidential Business Information” (CBI). CBI is not generally released or 

available for public review. SERA risk assessors have reviewed the identity and data on 

inerts in the CBI files when preparing all herbicide risk assessments except 2,4-D. Publicly 

released information from registrants of herbicides and from Freedom of Information Act 

requests to EPA has also been reviewed in Forest Service/SERA risk analyses. Comparison 

of acute toxicity (LD50 values) data between the formulated products (including inert 

ingredients) and their active ingredients alone shows that the formulated products are 

frequently less acutely toxic than their active ingredients. 

Forest Service/SERA risk assessments review the acute toxicity comparisons, the EPA 

review, and examine the toxicity information on inert ingredients in each formulated product. 

For all formulations containing inert ingredients that have been reviewed in the Forest 

Service/SERA risk assessments, the reviews have concluded that the formulations do not 

significantly increase the risk to human health and safety over the risks identified for the 

active ingredients. 

5.1.3 Additives 

Adjuvants include surfactants, drift reduction agents, and dyes or colorants. Some herbicide 

formulation labels direct the use of particular adjuvant types when applying the herbicide. 

Surfactants increase the ability of the herbicide to be absorbed into plant tissues. Dyes and 

colorants are used to indicate that a plant or area has been treated. 

The common risk factors for the use of adjuvants are through skin or eye exposure. Most 

adjuvants cause various degrees of irritation to skin or eyes. This demonstrates the need for 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-9 

good industrial hygiene practices when using these chemicals, especially when handling the 

concentrate, such as during mixing. The use of chemical resistant gloves and goggles, 

especially while mixing, would greatly reduce exposure to these hazards. 

In 2002, the Forest Service reviewed toxicity data for the various types of adjuvants likely to 

be used in herbicide applications on National Forests (Bakke, 2002). The review found that 

the surfactant NPE may contain nonylphenol (an EPA List 1 inert), which has potential for 

toxic effects, including endocrine disruption. Human health risks from exposure to NPE in 

invasive plant treatments are analyzed in this risk assessment, based on Bakke, 2003. 

A colorant often used in foliar applications of these herbicides (ColorfastTM Purple) that 

contains Basic Violet 3 or Gentian Violet dyes is considered a potential carcinogen. A risk 

assessment for the carcinogenic properties of this dye was completed (SERA, 1997). The risk 

assessment found that the cancer risk to workers and the public was considered negligible, 

based on the EPA standard of acceptable risk of less than 1 in 1 million. For public exposures, 

the dye would generally reduce exposures both to itself and to the other chemicals it might be 

mixed with (herbicide and other adjuvants) because the public would be alerted to the 

presence of treated vegetation. As SERA, 1997 adequately analyzes the health risks of 

utilizing this dye; it will not be discussed further in this document. 

5.2 Dose Response Assessment 

To assess human health risks this analysis compares the dose of herbicide received by a 

worker or a member of the public under each exposure scenario with the corresponding 

herbicide RfD established by EPA or by the Forest Service/SERA risk assessment for acute 

and/or chronic exposures. EPA determines a RfD based on the lowest NOAEL for the most 

sensitive toxic effect that is identified in tests on laboratory animals; then this NOAEL dose is 

reduced for uncertainties associated with extrapolating animal test data to humans, and for 

variation in sensitivity among humans. Most frequently, a RfD is 1/100th of the lowest 

NOAEL, but it may be even lower in some cases. As an example for a hypothetical herbicide, 

if the lowest acute NOAEL observed in lab animal tests was 1 milligram of chemical per 

kilogram of body weight (1 mg/kg), the corresponding NOAEL for a 70 kg human would be a 

dose = 70 mg. The typical RfD for this herbicide would be 0.01 mg/kg, or 0.7 mg dose for a 

human. Forest Service /SERA risk assessments evaluate all RfD’s established by EPA. In 

specific instances where EPA has not calculated an RfD, or the range of scientific data 

indicates a rationale for using a more precautionary RfD, FS/SERA establishes the RfD that is 

used in the risk assessment and EIS. The source and/or rationale for every non-EPA RfD is 

described in the Dose-response section of the Forest Service/SERA risk assessment. All nonEPA RfD’s are identified in Table 5-1. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-10 

If doses from all estimated exposures for a specific Forest Service herbicide application are 

less than the RfD’s, the risk of health effects is expected to be minimal. The Forest 

Service/SERA Risk Assessments describe the basis for the RfD, provide an analysis of the 

supporting studies, and further refine the risk thresholds for those herbicides with estimated 

doses that exceed the RfD. Table 5-1 displays the acute and chronic RfDs used in the risk 

assessment. 

Table 5-1 RfDs in mg/kg/day of herbicides, NPE, and the HCB impurity. 

Herbicide Acute RfD Chronic RfD 

2,4-D 0.01*# 0.01* 

Chlorsulfuron 0.25# 0.05 

Clopyralid 0.75# 0.15 

Dicamba 0.10 0.05 

Glyphosate 2.0 2.0 

Imazapic 0.5# 0.5 

Imazapyr 2.5# 2.5 

Metsulfuron Methyl 0.25# 0.25 

Picloram 0.2# 0.2 

Sethoxydim 0.6# 0.09 

Sulfometuron Methyl 0.87# 0.02# 

Triclopyr 1.0-general population 

0.05-women of childbearing age 

0.05 

Nonylphenol Polyethoxylate 0.1# 0.1# 

Hexachlorobenzene 0.008# 0.0008 

* U.S. EPA issued a draft RED (Reregistration Eligibility Decision) on 2,4-D for public review on January 12, 2005. The draft RED 

proposes new RfD’s for both acute and chronic toxicity of 2,4-D to humans: acute toxicity to women: 0.025 mg/kg/day; chronic 

toxicity to all humans: 0.005 mg/kg/day. If EPA’s proposed RfD’s are applied to all FS/SERA scenarios, providing the new RED 

does not cause any other changes to current risk assessment values, then RED-based acute HQ’s would be 0.4x (HQ estimated in 

EIS); RED-based chronic HQ’s would be 2x (HQ estimated in EIS). These potential future revised HQ’s would not materially affect 

the comparison of alternatives in this EIS. The number of scenarios exceeding HQ=1 for 2,4-D applications (Alternative D only)

would change from ! to !. Other variables used in calculations to estimate HQ in FS/SERA risk assessment scenarios may also change 

based on the final RED, therefore the extent and magnitude of potential future changes to EIS HQ’s cannot be determined at this time. 

# - These RFD’s were not established by EPA; the source and/or rationale for the RfD value that is used is described in the Doseresponse section of the corresponding FS/SERA risk assessment.

The herbicides that would be available for use on National Forests under each alternative are 

compared based on Hazard Quotients (HQ), which is the ratio between the estimated dose (the 

amount of herbicide received from a particular exposure scenario) and the RfD. When a 

predicted dose is less than the RfD, then the HQ (dose/RfD) is less than 1, and toxic effects 

are unlikely for that specific herbicide application. 

5.3 Worker and Public Exposure Analysis 

Workers and the public may be exposed to herbicides. Workers include applicators, 

supervisors, and other personnel directly involved in the application of herbicides. The public 

includes non-project forestry workers, forest visitors or nearby residents who could be 

exposed through the drift of herbicide spray droplets, through contact with sprayed 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-11 

vegetation, or by eating, or placing in the mouth, contaminated food items or other plant 

materials, such as berries or shoots growing in or near forests, by eating game or fish 

containing herbicide residues, or by drinking water that contains such residues. 

5.3.1.1 Worker Exposure Analysis 

Herbicide applicators are among the people most likely to be exposed to herbicides. Two 

types of worker exposure assessments are considered: general and accidental/incidental. 

General exposure assessment is used to designate those exposures that involve estimates of 

absorbed dose based on the routine handling of a specified amount of a chemical during each 

of three application methods (backpack sprayer, ground boom, and aerial). The 

accidental/incidental exposure scenarios involve specific atypical but plausible events that 

could occur during any type of application. 

The exposure for workers is based on the application rate selected for the herbicide, modified 

by several operational and human factors: number of hours worked per day, acres treated per 

hour, and variability in human dermal absorption rates. Rather than focus on a single average 

value, each of these exposure factors involves a range of values, which when combined create 

a range of potential exposure rates for any given application rate. This human health risk 

assessment displays potential risks for each of two application rates: a Forest Service typical 

rate and the maximum label rate. For each of these application rates, exposures and HQ’s are 

displayed for two values from the potential range of exposures predicted for each herbicide: 

one typical of the average worker in average working conditions, and a maximum exposure 

value based on the maximum estimate for every exposure factor that is considered. Thus, this 

risk assessment presents four potential exposure levels for workers, ranging from the 

predicted average exposure (typical Forest Service rate-typical exposure variables) to a worstcase predicted exposure (maximum application rate, maximum exposure variables). 

For each herbicide, worker HQ’s are estimated for typical and maximum rate of application 

and typical and maximum plausible exposures in the following format. 

Herbicide Typical Rate of Application Maximum Rate of Application 

Herbicide name Typical Exposure Factors 

Maximum Exposure Factors 

Typical Exposure Factors 

Maximum Exposure Factors 

Although herbicide application involves many different job activities, exposure rates can be 

defined for three categories: directed foliar applications involving the use of backpacks or 

similar devices including cut surface and streamline sprays; broadcast hydraulic spray 

applications; and aerial applications. The two estimated exposure rates (Table 5-2) are based 

on estimated absorbed doses in workers as well as the amounts of the chemical handled by the 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-12 

workers (SERA, 1998b). Exposure rates are shown as milligrams of chemical per kilogram of 

body weight per pound of active ingredient (ai) applied. 

Table 5-2 Estimated exposure rates from herbicide applications. 

Job Category Typical 

(mg/kg/lb ai) 

Maximum 

(mg/kg/lb ai) 

Ground Application 0.003 0.01 

Hydraulic Sprayer 0.0002 0.0009 

Aerial Application 0.00003 0.0001 

Source: SERA, 1998b, Table 5 

Table 5-3 displays the two application rates for each herbicide and the surfactant NPE for 

which worker and public doses are estimated for the EIS human health risk assessment. The 

typical rates are the average for each herbicide of recent Forest Service applications 

nationwide, and closely approximate recent rates used in the PNW Region for four herbicides 

(dicamba, glyphosate, picloram, and triclopyr) for noxious weed treatment under Alternative 

A. The maximum application rates are based on the maximum rates specified on each 

herbicide label for noxious weed treatment. For HCB, the application rate is based on the 

application rate for picloram and the percentage of HCB in picloram (picloram has the highest 

level of the HCB impurity of any herbicide considered in this EIS). 

Table 5-3 Herbicide and NPE application rates to be used to treat invasive plants 

and the incidental rates of application of the impurities HCB in picloram. 

Herbicide App Rate-Typical 

Lb ai/ac 

App Rate-Highest 

Lb ai/ac 

2,4-D 1.0 2.0 

Chlorsulfuron 0.056 0.25 

Clopyralid 0.35 0.5 

Dicamba 0.3 2.0 

Glyphosate 2 7 

Imazapic 0.1 0.19 

Imazapyr 0.45 1.25 

Metsulfuron Methyl 0.03 0.15 

Picloram 0.35 1.0 

Sethoxydim 0.3 0.38 

Sulfometuron Methyl 0.045 0.38 

Triclopyr 1.0 10 

Nonylphenol Polyethoxylate 1.67 6.68 

Hexachlorobenzene 0.000004 0.000012 

In routine applications, workers may contact and internalize herbicides mainly through the 

skin, but also through the mouth, eyes or nose. Forest Service/SERA risk assessment 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-13 

methodology for estimating worker exposures from typical operations encompasses the 

exposures predicted from multiple routes. 

Accidental worker exposures are most likely to involve splashing a solution of herbicides into 

the eyes or on the skin. Two general types of exposure were modeled: one involving direct 

contact with a solution of the herbicide and another associated with accidental spills of the 

herbicide concentrate onto the surface of the skin. For this risk assessment, two exposure 

scenarios are developed for each of the two types of dermal exposure, and the estimated 

absorbed dose for each scenario is expressed in units of mg chemical/kg body weight. 

Exposure scenarios involving direct contact with herbicide solutions are characterized by 

immersing unprotected hands for 1 minute or wearing contaminated gloves for 1 hour. While 

it is unlikely that workers would immerse their hands in herbicide solutions, the 

contamination of gloves or other clothing is plausible. For these exposure scenarios, the key 

element is the assumption that wearing gloves saturated with a chemical solution is equivalent 

to immersing the hands in a solution. 

In either case, the concentration of the chemical in solution that is in contact with the surface 

of the skin and the resulting dermal absorption rate are essentially constant. Exposure 

scenarios involving chemical spills onto the skin are characterized by a spill onto the lower 

legs as well as a spill on to the hands. In these scenarios, it is assumed that a solution of the 

chemical is spilled on to a given surface area of skin and that a certain amount of the chemical 

adheres to the skin. 

5.3.1.2 Worker Risks Related to Occupational Exposures 

For typical rate/typical exposure factor applications, workers can apply all twelve herbicides 

by backpack, ground (boom), and aerial application (where applicable) methods with 

exposures less than or equal to a HQ of 1 (refer to Table 5-4, 5-5 and 5-6). This indicates that 

workers can apply these herbicides for long time periods at typical rates without toxic health 

effects. Only application of 2,4-D by ground boom spray exceeds the HQ threshold of 1 

(HQ=2). At typical application rates/ maximum exposure factors, dicamba and triclopyr also 

exceed the HQ =1 threshold. 

For maximum application rates/typical exposure factors, worker exposures result in a HQ 

greater than 1 for 2,4-D, dicamba, and triclopyr. At maximum application rates/ maximum 

exposure factors, chlorsulfuron, sulfometuron methyl, also exceed the HQ =1 threshold. 

In addition, the cancer risk from all application rates/typical occupational exposures to HCB 

in picloram or clopyralid are less than the EPA risk threshold standard of 1 chance in 1 

million. For maximum application rate/maximum exposures the cancer risk factor from 

picloram may exceed the EPA standard by 2.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-14 

Table 5-4 HQs (non-cancer) for backpack sprayer applicators. 

General (non-accidental) exposures of herbicides, NPE, and the HCB impurity. 

Herbicide Typical Rate of Application Maximum Rate of Application 

2,4-D 1 

8 

3 

16

Chlorsulfuron 0.04 

0.2 

0.2 

1 

Clopyralid 0.03 

0.2 

0.04 

0.3 

Dicamba 0.09 

0.5 

0.6 

4 

Glyphosate 0.01 

0.08 

0.05 

0.3 

Imazapic 0.003 

0.02 

0.005 

0.03 

Imazapyr 0.002 

0.01 

0.007 

0.04 

Metsulfuron Methyl 0.002 

0.01 

0.008 

0.05 

Picloram 0.02 

0.1 

0.07 

0.4 

Sethoxydim 0.04 

0.3 

0.05 

0.3 

Sulfometuron Methyl 0.03 

0.2 

0.2 

2 

Triclopyr 0.3 

2 

3 

16

Nonylphenol 

Polyethoxylate 

0.2 

1 

0.9 

5 

Hexachlorobenzene 0.00005 

0.0003 

0.0001 

0.0008 

HexachlorobenzeneCANCER RISK 0.06 

0.4 

0.2 

1 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-15 

Table 5-5 HQs (non-cancer) for ground broadcast applicators. 

General (non-accidental) exposures of herbicides, NPE, and the HCB impurity. 

Herbicide Typical Rate of 

Application Maximum Rate of Application 

2,4-D 

2 

15 

4 

30 

Chlorsulfuron 

0.06 

0.4 

0.3 

2 

Clopyralid 

0.03 

0.4 

0.07 

0.5 

Dicamba 

0.1 

1 

1 

7 

Glyphosate 

0.02 

0.2 

0.08 

0.5 

Imazapic 

0.004 

0.03 

0.009 

0.06 

Imazapyr 

0.004 

0.03 

0.01 

0.08 

Metsulfuron Methyl 

0.003 

0.02 

0.01 

0.09 

Picloram 

0.04 

0.3 

0.1 

0.8 

Sethoxydim 

0.07 

0.5 

0.09 

0.6 

Sulfometuron Methyl 

0.05 

0.3 

0.4 

3 

Triclopyr 

0.4 

3 

4 

30 

Nonylphenol Polyethoxylate 

0.4 

3 

1 

10 

Hexachlorobenzene 

0.00008 

0.0005 

0.0002 

0.002 

HexachlorobenzeneCANCER RISK 

0.1 

0.7 

0.3 

2 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-16 

Table 5-6 HQs (non-cancer) for aerial applicators. 

General (non-accidental) exposures of herbicides, NPE, and the HCB impurity. 

Herbicide Typical Rate of 

Application Maximum Rate of Application 

2,4-D 

1 

8 

3 

16

Chlorsulfuron 

0.04 

0.2 

0.2 

1 

Clopyralid 

0.03 

0.2 

0.05 

0.3 

Dicamba 

0.1 

0.5 

0.7 

4 

Glyphosate 

0.01 

0.08 

0.05 

0.03 

Imazapic 

0.003 

0.02 

0.006 

0.03 

Imazapyr 

0.003 

0.01 

0.007 

0.04 

Metsulfuron Methyl 

0.002 

0.01 

0.009 

0.05 

Picloram 

0.03 

0.1 

0.07 

0.4 

Sethoxydim N/A N/A 

Sulfometuron Methyl 

0.03 

0.2 

0.3 

2 

Triclopyr 

0.3 

2 

3 

16

Nonylphenol Polyethoxylate 

0.2 

1 

1 

5 

Hexachlorobenzene 

0.00005 

0.0003 

0.0001 

0.0008 

HexachlorobenzeneCANCER RISK 

0.02 

0.4 

0.2 

1 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-17 

For triclopyr, the typical application/typical exposure scenarios, both acute and chronic, result 

in an HQ less than 1. For the typical rate, maximum exposure, the HQ value for chronic 

(long-term) exposure is 2 (backpack and aerial) to 3 (broadcast). Workers who apply 

triclopyr only occasionally are unlikely to have any toxic health effects. Given the 

precautionary nature of the RfD it is unlikely that workers applying triclopyr at typical rates 

extensively during one or over several seasons could be at risk of toxic effects (impaired 

kidney function). Triclopyr has been used extensively without reports of acute toxic effects in 

workers. However, no studies of humans chronically exposed to triclopyr have been 

conducted to assess the potential for adverse effects on the kidney. Thus, for workers who 

may apply triclopyr repeatedly at typical rates over a period of several weeks or longer, it is 

important to ensure that work practices include protective procedures to avoid the maximum 

potential exposure. For the maximum application rate, typical and maximum exposure, the 

respective HQ values for chronic (long-term) exposure are 3 and 16 (backpack and aerial) to 4 

and 30 (broadcast). Protective procedures to reduce worker exposure become more critical to 

protect worker health at higher that typical rates. 

For NPE, the maximum application rate/typical worker exposure results in HQ’s greater than 

the derived RfD for all application methods (HQ=5, backpack and aerial; =10, broadcast). 

Given the precautionary nature of the RfD itself, it is unlikely that there would be any signs of 

toxicity. Nevertheless, under the most precautionary set of dose-response assumptions, 

workers applying high rates of NPE could be exposed to doses that might cause health effects. 

If NPE exposure is reduced by using measures described at the beginning of this Risk 

Characterization section, there is no indication that the workers would be at risk of adverse 

health effects. 

Dicamba produces HQ’s for workers for all application methods at the maximum application 

rate/maximum exposure that are substantially greater than one. For dicamba (HQ=5, 

backpack and aerial; HQ=10, broadcast), the underlying RfD is based on a gavage exposure, 

which is likely to show a higher initial internal peak dose than would the same dose in a the 

real-world situation of skin exposure, where the herbicide would be absorbed much more 

slowly. With good hygiene practices followed by each individual, actual exposures will not 

reach the upper ranges of project exposures. Thus, the actual exposures would be below the 

exposures identified with a concern for potential reproductive effects. 

For 2,4-D, typical exposures from typical application rates approximate the RfD and are not 

of substantial concern. Typical exposures for maximum application rates exceed the HQ 

slightly at 3. However, exposures from the typical and maximum application rates with 

maximum exposure assumptions (respective HQ=8 and 16, backpack and aerial; =15 and 30, 

broadcast) could be associated with adverse effects on organ function or pathology not 

associated with detectable physical symptoms. This information suggests that 2,4-D can be 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-18 

applied safely only if project supervisors and individual workers use effective methods to 

minimize worker exposure. 

5.3.1.3 Worker Risks from Accidents and Incidents 

Tables 5-7 and 5-8 display the HQs for worker risks from accidents and incidents. For some 

of the herbicides EPA or FS/SERA have estimated an acute (one-time exposure) RfD. 

However, in other cases, the HQ is based on the chronic RfD, which estimates risk of health 

effects from long-term exposure. Accidents/incidents are one-time or rare events, so in these 

cases, the HQ overestimates potential risk. 

All worker accidental exposures at typical and maximum application rate scenarios result in 

an HQ less than or equal to 1 except for triclopyr. In addition, the cancer risk from all the 

worker accidental exposures to HCB in picloram or clopyralid are at least 2 orders of 

magnitude below the risk standard of 1 chance in 1 million. 

Table 5-7 shows HQs (non-cancer) for backpack applicators from accidental/incidental 

exposures at the typical application rate and Table 5-8 shows HQs (non-cancer) for backpack 

applicators from accidental/incidental exposures at the maximum application rate. 

Table 5-7 HQs (non-cancer) for applicators – accidental/incidental exposures – 

typical application rate. 

Of herbicides, NPE, and the HCB impurity. 

Herbicide 

Immersion 

of hands, 

1 min. 

Contaminated 

gloves, 

1 hour 

Spill on 

hands, 

1 hour 

Spill on 

lower legs, 

1 hour 

2,4-D 

0.003 

0.007 

0.2 

0.4 

0.07 

0.2 

0.2 

0.5 

Chlorsulfuron 

2E-7 

 0.000006 

0.00001 

0.0003 

0.000007 

0.0003 

0.00002 

0.0009 

Clopyralid 

0.000002 

0.00004 

0.0001 

0.002 

0.0003 

0.008 

0.0008 

0.02 

Dicamba 

0.00009 

0.0002 

0.006 

0.1 

0.002 

0.04 

0.004 

0.1 

Glyphosate 

0.000004 

0.00003 

0.0002 

0.002 

0.0005 

0.002 

0.001 

0.006 

Imazapic 

0.002 

0.007 

0.1 

0.4 

0.001 

0.008 

0.003 

0.02 

Imazapyr 

0.00002 

0.0001 

0.001 

0.006 

0.0002 

0.001 

0.0006 

0.003 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-19 

Table 5-7 HQs (non-cancer) for applicators – accidental/incidental exposures – 

typical application rate. 

Of herbicides, NPE, and the HCB impurity. 

Herbicide 

Immersion 

of hands, 

1 min. 

Contaminated 

gloves, 

1 hour 

Spill on 

hands, 

1 hour 

Spill on 

lower legs, 

1 hour 

Metsulfuron Methyl 

4 E-8 

6E-7 

0.000002 

0.00003 

0.000003 

0.0001 

0.000008 

0.0002 

Picloram 

0.00008 

0.0009 

0.005 

0.06 

0.00009 

0.002 

0.0002 

0.004 

Sethoxydim 

0.0003 

0.0008 

0.02 

0.05 

0.0005 

0.002 

0.001 

0.006 

Sulfometuron Methyl 

5E-7 

0.000003 

0.00003 

0.0002 

0.00001 

0.0001 

0.00002 

0.0003 

Triclopyr TEA 

0.00002 

0.0003 

0.001 

0.02 

0.006 

0.09 

0.02 

0.2 

Triclopyr BEE 

0.008 

0.07 

0.5 

4 

0.02 

0.2 

0.05 

0.4 

Nonylphenol 

Polyethoxylate 

0.002 

0.004 

0.1 

0.3 

0.0005 

0.007 

0.001 

0.02 

Hexachlorobenzene 

0.0002 

0.004 

0.01 

0.3 

0.000003 

0.00008 

0.000007 

0.0002 

Table 5-8 HQs (non-cancer) for applicators – accidental/incidental exposures – 

maximum application rate 

Of herbicides, NPE, and the HCB impurity. 

Herbicide 

Immersion of 

hands, 

1 min. 

Contaminated 

gloves, 

1 hour 

Spill on 

hands, 

1 hour 

Spill on 

lower legs 

hour 

2,4-D 

0.006 

0.01 

0.3 

0.8 

0.1 

0.4 

0.3 

1 

Chlorsulfuron 

8E-7 

0.00002 

0.00005 

0.001 

0.00003 

0.002 

0.00008 

0.004 

Clopyralid 

0.000003 

0.00005 

0.0002 

0.003 

0.0005 

0.01 

0.001 

0.03 

Dicamba 

0.0006 

0.01 

0.04 

0.7 

0.01 

0.3 

0.03 

0.7 

Glyphosate 

0.00001 

0.0001 

0.0008 

0.006 

0.002 

0.008 

0.004 

0.02 

Imazapic 

0.003 

0.01 

0.2 

0.8 

0.002 

0.01 

0.006 

0.04 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-20 

Table 5-8 HQs (non-cancer) for applicators – accidental/incidental exposures – 

maximum application rate 

Of herbicides, NPE, and the HCB impurity. 

Herbicide 

Immersion of 

hands, 

1 min. 

Contaminated 

gloves, 

1 hour 

Spill on 

hands, 

1 hour 

Spill on 

lower legs 

hour 

Imazapyr 

0.00007 

0.0003 

0.004 

0.02 

0.0006 

0.003 

0.002 

0.008 

Metsulfuron Methyl 

2E-7 

0.000003 

0.00001 

0.0002 

0.00002 

0.0005 

0.00004 

0.001 

Picloram 

0.0002 

0.003 

0.01 

0.2 

0.0003 

0.004 

0.0007 

0.01 

Sethoxydim 

0.0003 

0.001 

0.02 

0.06 

0.0007 

0.003 

0.002 

0.007 

Sulfometuron Methyl 

0.000004 

0.00003 

0.0002 

0.002 

0.00008 

0.001 

0.0002 

0.002 

Triclopyr TEA 

0.0002 

0.03 

0.01 

0.2 

0.06 

0.9 

0.2 

2 

Triclopyr BEE 

0.08 

0.7 

5 

43

0.2 

2 

0.5 

4 

Nonylphenol 

Polyethoxylate 

0.002 

0.004 

0.1 

0.3 

0.0005 

0.007 

0.001 

0.02 

Hexachlorobenzene 

0.0006 

0.01 

0.04 

0.7 

0.000008 

0.0002 

0.00002 

0.0005 

The accidental typical exposure scenario of wearing gloves contaminated with triclopyr BEE 

for 1 hour exceeds the RfD (HQ = 5) for maximum rates of application. This indicates that at 

high application rates, strict adherence to worker hygiene practices is important. Because the 

RfD and HQ are based on effects from long-term exposure, the likelihood of toxic effects 

from a one-time exposure is lower than the calculated value. 

All of these herbicides can cause irritation and damage to the skin and eyes. Eye or skin 

irritation is likely to be the only overt effect because of mishandling these herbicides. These 

effects can be minimized or avoided by prudent industrial hygiene practices during handling. 

The TEA formulation of triclopyr can have impacts that are more serious to the eyes; eye 

protection is critical. 

5.3.2 Public Exposure Analysis 

Under normal conditions, members of the general public should not be exposed to substantial 

levels of any of these herbicides. Members of the public would generally not be in areas 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-21 

infested with invasive plants during herbicide application. However, dispersed and 

developed recreation areas (trailheads, campgrounds, picnic areas, recreation sites, boat 

ramps, ski areas, work centers, etc) may occur in the vicinity of invasive plant infestations 

proposed for herbicide treatment. To reduce the likelihood of public exposures in herbicide 

applications that tier to this EIS, project design criteria will be developed to restrict treatment 

in and around developed areas and to post treatment areas as needed so that the public may 

avoid areas where herbicides are being or have recently been applied. 

The Forest Service/SERA risk assessments developed two types of public exposure situations 

called scenarios: acute exposures and longer-term or chronic exposures. Acute exposures 

assume that a person has contact with the herbicide either during or shortly after an 

application. Specific scenarios estimate herbicide doses received from direct spray, from 

dermal contact with sprayed vegetation, or from consumption of contaminated fruit, water or 

fish. Most of these scenarios model plausible though infrequent application situations. The 

notable exceptions are the complete coverage of a naked child with herbicide from an 

accidental overspray, and the accidental spill scenario of a large herbicide tank truck into a 

small pond with no proper spill response. These two scenarios estimate exposures from a 

realistic worst-case situation that is highly unlikely to occur in herbicide applications 

conducted under alternatives in this EIS. Chronic exposure scenarios estimate doses from 

long-term consumption of fruit, water, or fish following a herbicide application. Detailed 

summaries of the public exposure scenarios can be found in Forest Service/SERA Risk 

Assessments. 

Estimates of public exposure from contact with direct spray or from different sources of 

herbicide residues is based on the application rate selected for the herbicide, modified by 

several operational and human factors such as spray dispersion; interception of spray by 

vegetation; and variability in human dermal absorption rates. Each of these factors involves a 

range of values, which when combined create a range of potential exposure rates for any 

given application rate. This human health risk assessment displays potential risks for each of 

two application rates: a Forest Service typical rate and the maximum label rate. For each of 

these application rates, exposures and HQ’s are displayed for two values from the potential 

range of exposures predicted for each herbicide: one typical of the average estimates for each 

of the exposure factors conditions, and a maximum exposure value based on the maximum 

estimate for every exposure factor. Thus, this risk assessment presents four potential 

exposure levels for members of the public, ranging from the predicted average exposure 

(typical Forest Service application rate-typical exposure variables) to a worst-case predicted 

exposure (maximum application rate, maximum exposure variables). 

For each herbicide, HQ’s are estimated for typical and maximum rate of application and 

typical and maximum plausible exposures in the following format. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-22 

Herbicide Typical Rate of Application Maximum Rate of Application 

Herbicide name Typical Exposure Factors 

Maximum Exposure Factors 

Typical Exposure Factors 

Maximum Exposure Factors 

5.3.2.1 Direct Spray 

Direct spray scenarios assume that a naked child is completely covered with herbicide during 

a broadcast ground herbicide application. The assumption of 100 percent body coverage with 

herbicide is much greater than would plausibly happen in a real-world accidental overspray. 

An additional set of scenarios are included involving a young woman who is accidentally 

sprayed over the feet and legs. 

Table 5-9 displays the HQ values for the public, direct spray scenarios. All public accidental 

exposures at typical and maximum application rates with typical exposure factors result in an 

HQ less than or equal to 1 except for 2,4-D and triclopyr. Assuming maximum exposure 

factors, then dicamba also exceeds the threshold HQ of 1. Cancer risk from these scenarios 

related to HCB in picloram or clopyralid is not calculated because the risk assessment follows 

EPA recommendations to measure cancer risk based on average daily dose over a lifetime. 

Consequently, no attempt is made to quantify risk for an acute, one-time exposure. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-23 

Table 5-9 HQ (non-cancer) for the public – direct spray scenarios 

Of using herbicides, NPE, and the HCB impurity. 

Herbicide Child, 

typical rate 

Child, 

maximum rate 

Woman, 

typical rate 

Woman, 

maximum rate 

2,4-D 

3 

8 

5 

16 

0.3 

0.8 

0.5 

2 

Chlorsulfuron 

0.00007 

0.003 

0.001 

0.06 

0.000007 

0.0003 

0.0001 

0.006 

Clopyralid 

0.01 

0.3 

0.02 

0.4 

0.001 

0.03 

0.002 

0.05 

Dicamba 

0.07 

2 

0.4 

11 

0.007 

0.2 

0.04 

1 

Glyphosate 

0.02 

0.09 

0.06 

0.3 

0.002 

0.009 

0.006 

0.03 

Imazapic 

0.05 

0.3 

0.09 

0.6 

0.005 

0.03 

0.009 

0.06 

Imazapyr 

0.009 

0.05 

0.02 

0.1 

0.0009 

0.005 

0.002 

0.01 

Metsulfuron Methyl 

0.0001 

0.004 

0.0006 

0.02 

0.00001 

0.0004 

0.00006 

0.002 

Picloram 

0.004 

0.06 

0.01 

0.2 

0.0004 

0.006 

0.001 

0.02 

Sethoxydim 

0.02 

0.09 

0.02 

0.1 

0.002 

0.009 

0.003 

0.01 

Sulfometuron Methyl 

0.0004 

0.004 

0.003 

0.04 

0.00004 

0.0005 

0.0003 

0.004 

Triclopyr TEA 

0.2 

3 

2 

35

0.5 

7 

5 

70

Triclopyr BEE 

0.7 

6 

7 

57

1 

11 

14 

115

Nonylphenol 

Polyethoxylate 

0.02 

0.3 

0.02 

0.3 

0.002 

0.03 

0.002 

0.03 

Hexachlorobenzene 

0.0001 

0.003 

0.0003 

0.008 

0.00001 

0.0003 

0.00003 

0.0008 

The direct spray of the naked child with either formulation of triclopyr at the maximum 

application rates exceeds the HQ level of concern; in this case the HQ was developed for 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-24 

acute exposures. The direct spray of the woman (feet and legs) also exceeds the 

corresponding HQ. The Forest Service/SERA triclopyr risk assessment states that all of the 

dermal exposure assessments are extremely precautionary and designed to identify which 

possible types of exposure would be most hazardous. Both scenarios illustrate the importance 

of avoiding public presence during and immediately after spraying triclopyr. 

The direct spray of a naked child with 2,4-D at the maximum application rate is predicted to 

exceed the HQ (23 or 14, depending on formulation). The consequences of accidental 

exposure are similar to the anticipated consequences of worker exposure, which may cause 

covert toxic effects but are not likely to cause outward signs of toxicity. For the direct spray 

at the maximum application rate of a woman, the HQ slightly exceeds a level of concern 

(HQ=2). The exposure of the woman (0.75 mg/kg) is within the range of variation of the 

acute RfD (0.75 mg/kg), so health effects as a result of this acute scenario are not expected. 

Table 5-9A displays the hazard quotient values for members of the public who might contact 

sprayed vegetation. The dermal exposure from contaminated vegetation scenario assumes 

that the herbicide is sprayed at a given application rate and that an individual comes in contact 

with sprayed vegetation or other contaminated surfaces soon after the spray operation. For 

these exposure scenarios, some estimates of dislodgeable residue and the rate of transfer from 

the contaminated vegetation to the surface of the skin must be available. No such data are 

directly available for these herbicides, and so estimation methods are used. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-25 

Table 5-9A HQ (non-cancer) for the public – dermal contact with sprayed 

vegetation scenario of using herbicides, NPE, and the HCB impurity. 

Herbicide Typical rate Maximum rate 

2,4-D 0.3 

0.9 

0.6 

2 

Chlorsulfuron 0.00002 

(0.0001) 

0.0004 

(0.002) 

Clopyralid 0.0007 

0.003 

0.001 

0.005 

Dicamba 0.009 

(0.03) 

0.07 

(0.2) 

Glyphosate 0.001 

(0.003) 

0.004 

(0.01) 

Imazapic 0.001 

0.003 

0.003 

0.005 

Imazapyr 0.0005 

0.001 

0.001 

0.004 

Metsulfuron Methyl 0.00002 

0.0001 

0.0001 

0.0008 

Picloram 0.0006 

0.002 

0.002 

0.005 

Sethoxydim 0.001 

0.003 

0.002 

0.004 

Sulfometuron Methyl 0.00002 

0.0001 

0.0002 

0.001 

Triclopyr TEA 0.6 

1 

7 

16 

Triclopyr BEE 1 

2

16 

21 

Nonylphenol Polyethoxylate 0.003 

0.04 

0.01 

0.2 

Hexachlorobenzene 0.000005 

0.00001 

0.00002 

0.00003 

The scenario involving a woman contacting treated vegetation in all application rate scenarios 

results in an hazard quotient less than or equal to 1 for all herbicides except 2,4-D at the 

maximum rate/maximum exposures only, and triclopyr for maximum rates and exposures. In 

addition, the cancer risk under this scenario from hexachlorobenzene in picloram or clopyralid 

is at least 5 orders of magnitude below the risk standard of 1 chance in 1 million. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-26 

5.3.2.2 Public Exposure from Eating Sprayed Fruit (Acute and Chronic) 

In most herbicide treatments for invasive plants, it is very unlikely that humans would eat or 

place contaminated vegetation in their mouths. However, scenarios could be developed 

involving either accidental spraying of crops, the spraying of edible wild vegetation, like 

berries or mushrooms, or the spraying of plants collected by Native Americans for basket 

weaving or medicinal use. Again, particularly for longer-term scenarios, treated vegetation 

would probably show signs of damage from herbicide, thereby reducing the likelihood that 

people would continue to consume it. Still, it is conceivable that individuals could consume 

contaminated vegetation. 

One plausible scenario involves the consumption of contaminated berries after treatment 

along a road where wild berries grow. This scenario estimates risks from eating other 

contaminated forest foodstuffs, such as wild mushrooms. The two accidental exposure 

scenarios developed for this exposure assessment include one scenario for acute exposure and 

one scenario for longer-term exposure (90 days). In both scenarios, the concentration of 

herbicide on contaminated vegetation is estimated using a derived empirical relationship 

between application rate and concentration on vegetation. 

Forest Service/SERA risk assessments assume that any contaminant HCB in the applied 

herbicide does not dissipate or break down over time for the chronic contaminated vegetation 

scenario. This is due to its long half time in the soil and the BCF in vegetation. 

Table 5-10 displays the HQ values from the scenario involving a woman eating sprayed 

berries (one time) shortly after spraying and eating berries daily for 90 days after they were 

sprayed. For all herbicides, NPE, and the impurity HCB, HQs are less than or equal to 1 for 

both the acute and chronic scenario for the typical rates of application with typical exposures. 

For all the herbicides except 2,4-D and NPE, the HQs are less than 1 for the maximum 

application rates, typical exposures. Dicamba and triclopyr also exceed HQ=1 for maximum 

rate, maximum exposure assumptions. In addition, the cancer risk in these scenarios from 

HCB in picloram or clopyralid is at least 1 order of magnitude below the risk standard of 1 

chance in 1 million for all long-term exposure levels. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-27 

Table 5-10 HQ (non-cancer) for the public – contaminated fruit while using 

herbicides, NPE, and the HCB impurity. 

 Acute Chronic 

Herbicide Typical rate Maximum rate Typical rate Maximum rate 

2,4-D 1 

18 

2 

37

0.3 

4 

0.5 

8 

Chlorsulfuron 0.0007 

0.01 

0.01 

0.2 

0.0003 

0.004 

0.06 

1 

Clopyralid 0.005 

0.09 

0.008 

0.1 

0.01 

0.2 

0.02 

0.3 

Dicamba 0.04 

0.6 

0.2 

4 

0.01 

0.2 

0.08 

1 

Glyphosate 0.001 

0.003 

0.01 

0.3 

0.002 

0.04 

0.008 

0.1) 

Imazapic 0.002 

0.04 

0.004 

0.07 

0.0002 

0.007 

0.0003 

0.01 

Imazapyr 0.002 

0.03 

0.006 

0.09 

0.0008 

0.02 

0.002 

0.05 

Metsulfuron methyl 0.001 

0.02 

0.007 

0.1 

0.0006 

0.009 

0.003 

0.05 

Picloram 0.02 

0.3 

0.06 

0.9 

0.003 

0.04 

0.008 

0.1 

Sethoxydim 0.006 

0.09 

0.007 

0.1 

0.002 

0.03 

0.002 

0.04 

Sulfometuron methyl 0.0006 

0.01 

0.005 

0.08 

0.004 

0.07 

0.04 

0.6 

Triclopyr 0.06 

0.7 

0.6 

7 

0.03 

0.5 

0.3 

5 

Nonylphenol 

polyethoxylate 

0.2 

3 

0.8 

12 

0.003 

0.05 

0.01 

0.2 

Hexachlorobenzene 0.000007 

0.00006 

0.00002 

0.0002 

0.000003 

0.00003 

0.000008 

0.00007 

HexachlorobenzeneCANCER RISK N/A N/A 0.004 

0.03 

0.01 

0.09 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-28 

5.2.3.4 Water Contamination 

Water can be contaminated from runoff, as a result of percolation from contaminated soil, 

from a direct spill, or from unintentional spray drift from aerial or ground applications. The 

Forest Service/SERA risk assessments estimate the concentration of each herbicide in water 

for three scenarios. 

There are two acute exposure scenarios. The first assumes that a small child (2- to 3-years 

old) drinks contaminated water shortly after a large accidental spill of a field herbicide 

solution into a small pond. The second assumes that a small child drinks stream water 

contaminated by runoff and/or percolation from an adjacent herbicide-treated area. Because 

these scenarios are based on the assumption that exposure occurs shortly after the water is 

contaminated, no dissipation or degradation of the herbicide is considered. 

The scenario for chronic exposure to these herbicides from contaminated water assumes that 

an adult consumes ambient water for a lifetime from a pond contaminated by leaching and/or 

percolation from an adjacent herbicide-treated area. Except for 2,4-D, all Forest 

Service/SERA risk assessments use the GLEAMS (Groundwater Loading Effects of 

Agricultural Management Systems) model to estimate levels of herbicide in ambient water 

based on the range of herbicide application rates. GLEAMS is a root zone model that can be 

used to examine the fate and movement of herbicides in soils under different weather and soil 

conditions. For 2,4-D the projected level of exposure is based on a single forest application 

monitoring study. 

Table 5-11 displays the HQ values from the contaminated water scenarios involving public 

consumption. These scenarios involving a child drinking from a small pond (0.25 acre) 

immediately after a spill; a child drinking from a stream after runoff/percolation 

contamination; and an adult drinking water over a lifetime from a large pond (one acre) 

contaminated by runoff/percolation. The spill/pond water contamination scenario is an 

extreme concentration resulting from an accident, not from a treatment activity. It should be 

considered a worst-case scenario in that it estimates exposures from standing water, with no 

dilution or decomposition of the herbicide. For the scenario of a child drinking from a stream 

only 2,4-D slightly exceeds the RfD under typical exposure assumptions. For an adult 

drinking contaminated pond water over a lifetime, none of the estimated exposures, for any of 

the herbicides, NPEs, or the impurity HCB, at any application rate, exceeds the RfD (HQ is 

less than or equal to one). In addition, the cancer risk from HCB in picloram or clopyralid is 

at least 5 orders of magnitude below the risk standard of 1 chance in 1 million for all chronic 

contaminated drinking water scenarios. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-29 

Table 5-11 HQ (non-cancer) for the public – drinking contaminated water. 

From herbicides, NPE, and the HCB impurity.

 Acute-spill Acute-stream Chronic-pond 

Herbicide Typical 

rate 

Maximum 

rate 

Typical 

rate 

Maximum 

rate 

Typical 

rate 

Maximum 

rate 

2,4-D 34 

51 

68 

102 

1 

5 

2 

9

0.006 

0.01 

0.01 

0.02 

Chlorsulfuron 0.006 

0.09 

0.01 

2 

0.0004 

0.001 

0.008 

0.02 

1E-7 

0.000002 

0.0002 

0.0004 

Clopyralid 0.3 

2 

0.5 

3 

0.0007 

0.004 

0.001 

0.005 

0.0005 

0.001 

0.0007 

0.001 

Dicamba 0.8 

10 

5 

68 

0.0007 

0.003 

0.005 

0.02 

0.000002 

0.000007 

0.00001 

0.00005 

Glyphosate 0.7 

2 

2 

7

0.002 

0.05 

0.005 

0.2 

0.00003 

0.0003 

0.0001 

0.001 

Imazapic 0.2 

1 

0.4 

2 

0.000008 

0.0002 

0.00001 

0.0004 

1E-7 

2E-7 

2E-7 

4E-7 

Imazapyr 0.1 

0.4 

0.3 

1 

0.00003 

0.002 

0.00008 

0.005 

5E-7 

0.000006 

0.000001 

0.00002 

Metsulfuron Methyl 0.02 

0.1 

0.1 

0.7 

0.00002 

0.0001 

0.00009 

0.0007 

7E-7 

0.000002 

0.000003 

0.000008 

Picloram 0.4 

3 

1 

10 

0.007 

0.04 

0.02 

0.1 

0.00005 

0.0002 

0.0001 

0.0007 

Sethoxydim 0.3 

0.9 

0.4 

1 

0.008 

0.03 

0.009 

0.04 

0.00008 

0.0001 

0.0001 

0.0002 

Sulfometuron Methyl 0.03 

0.1 

0.2 

0.9 

0.000004 

0.0001 

0.00003 

0.001 

0.000003 

0.000005 

0.00002 

0.00005 

Triclopyr 0.3 

2 

3 

20

0.007 

0.05 

0.07 

0.5 

0.02 

0.03 

0.2 

0.3 

Nonylphenol 

Polyethoxylate 

5 

7 

5 

7 

0.009 

0.04 

0.009 

0.04 

0.002 

0.005 

0.002 

0.005 

Hexachlorobenzene 0.00008 

0.0007 

0.0002 

0.002 

0.000002 

0.00001 

0.000007 

0.00003 

5.E-08 

1E-7 

1E-7 

3E-7 

HexachlorobenzeneCANCER RISK  0.00006 

0.0002 

0.0002 

0.0004 

The acute typical exposure scenario with the child drinking water from a spill-contaminated 

pond estimates that chlorsulfuron, imazapic, imazapyr, metsulfuron methyl, picloram, 

sethoxydim, sulfometuron methyl, and the impurity HCB have HQ values at or below 1 for all 

application rates. For the acute typical exposure scenario clopyralid, dicamba, glyphosate, 

and triclopyr, have HQ values less than or equal to 1 at typical application rates, but exceed a 

HQ of 1 at maximum application rates. For glyphosate, no effects are expected from an acute 

HQ that slightly exceeds the chronic RfD. For both dicamba and triclopyr, the accidental spill 

at the high exposure assumptions scenario exceeds the acute RfD. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-30 

The child drinking from a spill-contaminated pond represents the greatest risk for 2,4-D and 

NPE. For 2,4-D, the HQ of 34 at typical rate and exposures and HQ of 68 at the maximum 

rate, typical exposures could be associated with adverse effects on organ function or 

pathology that are not expressed in overt physical symptoms. For NPE, the HQ of 5 for a 

typical application rate and 7 for maximum rate indicate a risk of effects to the liver and 

kidney detectable to a physician although these adverse effects may not manifest themselves 

in symptoms detectable by the exposed child. 

Only 2,4-D has HQ’s that exceed one for the contaminated stream scenario, and no compound 

has any scenarios where HQ’s exceed one for the long-term consumption of contaminated 

pond water. These scenarios indicate that 2,4-D is the only compound with any plausible risk 

to humans consuming water from sources near FS herbicide applications to control invasive 

plants. FS herbicide applications near domestic use water sources that comply with EIS 

standards should pose no plausible risks to human health, with the possible exception of 2,4-D 

without additional mitigations. 

5.2.3.5 Fish Consumption 

For both the acute and longer-term exposure scenarios involving the consumption of 

contaminated fish, the water concentrations of the herbicides used are identical to the 

concentrations used in the contaminated water scenarios. The acute exposure scenario is 

based on the assumption that an adult angler consumes fish taken from contaminated water 

shortly after an accidental spill into a pond. No dissipation or degradation is considered. 

Forest Service/SERA risk assessments make separate acute and chronic exposure estimates of 

contaminated fish consumption by the general public and by Native American subsistence 

populations because of documented greater fish consumption by Native Americans. 

Some chemicals may be concentrated from contaminated water into the tissues of animals or 

plants living in water. This process is called bioconcentration. Bioconcentration at first 

increases with the length of exposure but eventually reaches a constant maximum level. 

Generally, bioconcentration is measured as the ratio of the maximum concentration in the 

organism to the concentration in the water, referred to as a bioconcentration factor (BCF). 

Most of the herbicides in this risk assessment do not bioconcentrate in edible fish tissues; i.e. 

they have BCF values less than or equal to one. Only chlorsulfuron (BCF=1.5), sethoxydim 

(BCF=7), sulfometuron methyl (BCF=7), and HCB (BCF=2,000 acute; 20,000 chronic) 

bioconcentrate in edible fish tissues; the BCF is used in calculating expected doses for 

consumption of fish from water contaminated with these herbicides. 

Tables 5-12 and 5-13 display the HQ values for acute and chronic fish consumption scenarios. 

For the chronic exposure scenarios, where recreational or subsistence adults consume fish for 

a lifetime, none of the HQ values exceeds 1. In addition, the cancer risk in these scenarios 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-31 

from HCB in picloram or clopyralid is at least 1 order of magnitude less than the risk standard 

of 1 chance in 1 million for all exposure scenarios. 

Table 5-12 HQ (non-cancer) for the public –consumption of contaminated fish, 

acute exposure. 

As a result of using herbicides, NPE, and products containing the HCB impurity.

 Recreational Subsistence 

Herbicide Typical rate Maximum rate Typical rate Maximum rate 

2,4-D 10 

10 

20 

20 

50 

50 

100 

100 

Chlorsulfuron 0.0002 

0.002 

0.003 

0.03 

0.0008 

0.008 

0.01 

0.1 

Clopyralid 0.01 

0.05 

0.01 

0.07 

0.05 

0.2 

0.07 

0.3 

Dicamba 0.02 

0.1 

0.1 

0.9 

0.08 

0.7 

0.5 

4 

Glyphosate 0.008 

0.02 

0.03 

0.05 

0.04 

0.08 

0.1 

0.3 

Imazapic 0.0008 

0.002 

0.001 

0.004 

0.004 

0.01 

0.007 

0.02 

Imazapyr 0.002 

0.004 

0.005 

0.01 

0.009 

0.02 

0.02 

0.05 

Metsulfuron Methyl 0.00005 

0.0002 

0.0002 

0.001 

0.0002 

0.0009 

0.001 

0.005 

Picloram 0.01 

0.07 

0.03 

0.2 

0.06 

0.3 

0.2 

1 

Sethoxydim 0.01 

0.02 

0.01 

0.03 

0.05 

0.1 

0.06 

0.1 

Sulfometuron Methyl 0.002 

0.006 

0.02 

0.05 

0.01 

0.03 

0.1 

0.3 

Triclopyr 0.0005 

0.002 

0.005 

0.02 

0.002 

0.01 

0.02 

0.1 

Nonylphenol 

Polyethoxylate 

0.1 

0.1 

0.3 

0.3 

0.7 

0.7 

0.7 

0.7 

Hexachlorobenzene 0.005 

0.03 

0.01 

0.08 

0.02 

0.1 

0.07 

0.4 

The acute scenarios show that chlorsulfuron, clopyralid, glyphosate, imazapic, imazapyr, 

metsulfuron methyl, sethoxydim, picloram, sethoxydim, sulfometuron methyl, triclopyr, NPE, 

and the impurity HCB have HQ values below 1 for all application rates and for recreational 

and subsistence populations. In addition, dicamba has HQ values below 1 at all rates for 

recreational anglers, and for subsistence anglers at typical application rates, but exceeds the 

HQ (=4) at high application rates. 

For 2,4-D, all HQ’s are estimated to be many times greater (10 to 100) than the threshold of 

concern. These exposures could be expected to cause adverse effects on organ function or 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-32 

pathology that are not expressed in overt physical symptoms; physical symptoms may be 

manifested in the more highly-exposed subsistence populations. 

Table 5-13 shows Hazard Quotients predicted from long-term consumption of contaminated 

fish. All estimated HQ’s are substantially below 1, and no plausible risk of health effects is 

predicted for consuming fish that have been contaminated with herbicide compounds 

considered for invasive plant treatment in this EIS. 

Table 5-13 HQ (non-cancer) for the public – consumption of contaminated fish, 

chronic exposure. 

As a result of using herbicides, NPE, and products containing the HCB impurity. 

 Recreational Subsistence 

Herbicide Typical rate Maximum rate Typical rate Maximum rate 

2,4-D 0.0003 

0.0006 

0.0006 

0.001 

0.002 

0.005 

0.005 

0.009 

Chlorsulfuron 7E-9 

1E-8 

0.000002 

0.000002 

6E-8 

9E-8 

0.00001 

0.00002 

Clopyralid 0.000002 

0.000004 

0.000003 

0.000006 

0.00002 

0.00004 

0.00003 

0.00005 

Dicamba 6E-9 

2E-8 

4E-8 

1E-7 

5E-8 

2E-7 

3E-7 

0.000001 

Glyphosate 5E-8 

4E-7 

2E-7 

2E-6 

4E-7 

0.000004 

0.000002 

0.00001 

Imazapic 6 E-11 

9E-11 

1E-10 

2E-10 

5E-10 

8E-10 

1E-9 

1E-9 

Imazapyr 1E-9 

1E-8 

4E-9 

4E-8 

1E-8 

1E-7 

3E-8 

3E-7 

Metsulfuron Methyl 2E-9 

4E-9 

1E-8 

2E-8 

2E-8 

3E-8 

8E-8 

2E-7 

Picloram 3E-7 

0.000001 

7E-7 

0.000003 

0.000002 

0.000008 

0.000006 

0.00002 

Sethoxydim 0.000003 

0.000004 

0.000003 

0.000005 

0.00002 

0.00003 

0.00003 

0.00004 

Sulfometuron Methyl 5E-8 

8E-8 

4E-7 

7E-7 

4E-7 

6E-7 

0.000003 

0.000005 

Triclopyr 0.000005 

0.000009 

0.000005 

0.000009 

0.00004 

0.00007 

0.00004 

0.00007 

Nonylphenol 

Polyethoxylate 

0.00001 

0.00002 

0.00001 

0.00002 

0.00008 

0.0002 

0.00008 

0.0002 

Hexachlorobenzene 0.000005 

0.00001 

0.00001 

0.00003 

0.00004 

0.00008 

0.0001 

0.0002 

HexachlorobenzeneCANCER RISK 0.006 

0.01 

0.02 

0.04 

0.05 

0.1 

0.1 

0.3 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-33 

5.4 Sensitive Individuals 

The uncertainty factors used in the development of the RfD take into account much of the 

variation in human response. The uncertainty factor of 10 for sensitive subgroups is sufficient 

to ensure that most people would experience no toxic effects. “Sensitive” subgroups are those 

that might respond to a lower dose than average, such as women or children. As stated in 

National Academy of Sciences (NAS), 1993, the quantitative differences in toxicity between 

children and adults are usually less than a factor of approximately one order of magnitude 

(10-fold). Human susceptibility to toxic substances can vary by two to three orders of 

magnitude, so an uncertainty factor of 10 for sensitive subgroups may not cover every 

individual that may be unusually sensitive to herbicides. Unusually sensitive individuals may 

experience effects even when the HQ is equal to or less than 1. Individual susceptibility to 

the herbicides proposed in this EIS cannot be specifically predicted. Factors affecting 

individual susceptibility include diet, age, heredity, pre-existing diseases, and life style. 

There is anecdotal information (case histories) suggesting that some individuals may be 

sensitive to 2,4-D. These individuals may develop neuropathy/impaired nerve function after 

exposure to 2,4-D at levels that are not expected to cause adverse health effects in the general 

population. The effects reported in the case studies are debilitating, and recovery may be 

prolonged and incomplete. On the other hand, the case studies do not rule out the possibility 

that the neuropathy was caused by other unidentified agents. 

There is no information to suggest that specific groups or individuals may be especially 

sensitive to the systemic effects of chlorsulfuron. Though the likely critical effect of 

chlorsulfuron in humans cannot be defined, the most sensitive effect in laboratory mammals 

appears to be weight loss. There is also some evidence that chlorsulfuron may alter 

hematological parameters. It is unclear if individuals with pre-existing diseases of the 

hematological system or metabolic disorders would be particularly sensitive to chlorsulfuron 

exposure. Individuals with any severe disease condition could be considered more sensitive 

to many toxic agents. 

There is no information to suggest that specific groups or individuals may be especially 

sensitive to the systemic effects of clopyralid . The likely critical effect of clopyralid in 

humans cannot be identified clearly. Clopyralid can cause decreased body weight, increases 

in kidney and liver weight, decreased red blood cell counts, as well as hyperplasia (an 

increase in cell numbers) in gastric epithelial tissue. These effects, however, are not 

consistent among species or even between different studies in the same species. Thus, it is 

unclear if individuals with pre-existing diseases of the kidney, liver, or blood would be 

particularly sensitive to clopyralid exposures, although individuals with any severe disease 

condition could be considered more sensitive to many toxic agents. In addition, some 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-34 

individuals may suffer from multiple chemical sensitivity, responding adversely to extremely 

low levels of chemicals and in a manner that is atypical of the general population. There are 

no data or case reports of such responses to clopyralid. 

The only identified sensitive subgroup for dicamba appears to be children. Since the RfD for 

dicamba explicitly considers the increased sensitivity of children with an additional safety 

factor and since exposure assessments for children are conducted in the risk assessment, this 

sensitive subgroup is addressed in the Forest Service/SERA Dicamba risk assessment. 

There is no information to suggest that specific groups or individuals may be especially 

sensitive to the systemic effects of imazapic. Due to the lack of data in humans, the likely 

critical effect of imazapic in humans cannot be identified clearly. Imazapic exposures have 

been associated with changes in blood, bone marrow, muscle, and possibly the liver. 

However, it is unclear if individuals with pre-existing diseases of the hematological system, 

muscle, or liver would be particularly sensitive to imazapic exposure. Individuals with any 

severe disease condition could be considered more sensitive to many toxic agents. Given the 

very low HQs for imazapic, there is no basis for asserting that adverse effects in a specific 

subgroup are plausible. 

There is no information to suggest that specific groups or individuals may be especially 

sensitive to the systemic effects of imazapyr. Due to the lack of data in humans, the likely 

critical effect of imazapyr in humans cannot be identified clearly. The mechanism of action 

for imazapyr is not well understood and imazapyr does not appear to specifically affect the 

nervous system, immune system, or endocrine function. Given the very low HQs for 

imazapyr, there appears to be no basis for asserting that an adverse effect in a specific 

subgroup is plausible. The EPA has judged that infants and children are not likely to be more 

sensitive to imazapyr than adults. Given the number of studies available on reproductive and 

developmental effects and the unremarkable findings from these studies, this judgment 

appears appropriate. 

There is no information to suggest that specific groups or individuals may be especially 

sensitive to the systemic effects of metsulfuron methyl. Due to the lack of data in humans, the 

likely critical effect of metsulfuron methyl in humans cannot be identified clearly. In animals 

the most sensitive effect of metsulfuron methyl appears to be weight loss. However, there is 

some suggestion that metsulfuron methyl may influence blood glucose levels and cholesterol 

regulation. If exposure levels were sufficient to induce decreases in serum glucose, 

individuals taking medication to lower serum glucose could be at increased risk. Nonetheless, 

this exposure scenario is highly implausible. 

There is no information to suggest that specific groups or individuals may be especially 

sensitive to the systemic effects of picloram. The likely critical effect of picloram in humans 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-35 

cannot be identified clearly. In animals, the most sensitive effect of picloram involves 

changes in the staining characteristics of liver cells. These effects, however, were only noted 

in one study and are not consistent among species or even between different studies in the 

same species. Thus, it is unclear if individuals with pre-existing diseases of the liver would 

be particularly sensitive to picloram exposures, although individuals with any severe disease 

condition could be considered more sensitive to many toxic agents. 

There is no information to assess whether or not specific groups or individuals may be 

especially sensitive to the systemic effects of sethoxydim. The mechanism of the acute and 

chronic toxicity of sethoxydim is unclear but may be related to the ability of sethoxydim to 

uncouple oxidative phosphorylation. Other effects noted in experimental mammals include 

decreases in food consumption as well as decreased body weight and the occurrence of liver 

pathology. 

There is no information to suggest that specific groups or individuals may be especially 

sensitive to the systemic effects of sulfometuron methyl. Due to the lack of data in humans, 

the likely critical effect of sulfometuron methyl in humans cannot be identified clearly. The 

most sensitive effect reported in animals for chronic sulfometuron methyl exposure appears to 

involve changes in blood that are consistent with hemolytic anemia. Thus, individuals with 

pre-existing anemia could potentially be at an increased risk. Sulfometuron methyl appears to 

have the potential to alter thyroid gland function. Individuals with pre-existing thyroid 

dysfunction may, therefore, be at increased risk. However, there are no data to support 

directly support these speculations. 

Because triclopyr may impair blood filtration, individuals with pre-existing kidney diseases 

are likely to be at increased risk. Women of childbearing age have been recognized by EPA 

as a particularly sensitive subgroup for acute exposures to triclopyr by reducing the RfD from 

1.0 mg/kg/day to 0.05 mg/kg/day. 

There is limited information to suggest that specific groups or individuals may be especially 

sensitive to the systemic effects of NPE-based surfactants. NPE can cause increases in kidney 

and liver weight, and effects to kidney function and structure. Thus, individuals with preexisting conditions that involve impairments of the kidney or liver may be more sensitive to 

this compound. There is some indication that sensitive individuals may develop contact 

allergies. People with a history of skin allergic reactions to soaps and detergents may be 

especially sensitive to dermal exposures of NPE-based surfactants. 

The potential of NPE to induce reproductive effects should be considered low. Based on the 

available dose/duration/severity data, it appears that exposure levels below those associated 

with the most sensitive effect (i.e., kidney effects) are not likely to be associated with 

reproductive toxicity. However, as shown in the exposure scenarios, there is the potential for 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-36 

acute exposures to be in the range (considering a 100X safety factor) where effects to the 

developing fetus may occur, therefore pregnant women could be considered a sensitive 

population. 

5.5 Cumulative Effects 

5.5.1 Additive or Synergistic Effects from Herbicide Mixtures 

Synergistic effects (multiplicative) are those effects resulting from exposure to a combination 

of two or more chemicals that are greater than the sum of the effects of each chemical alone 

(additive). Instances of chemical combinations that cause synergistic effects are relatively 

rare. Reviews of the scientific literature on toxicological effects and toxicological interactions 

of agricultural chemicals indicate that exposure to a mixture of pesticides is more likely to 

lead to additive rather than synergistic effects (US EPA, 2000; ATSDR, 2004). The literature 

review by the Agency for Toxic Substances and Disease Registry , U.S. Public Health Service 

cited several studies that found no synergistic effects for mixtures of four, eight, and nine 

chemicals at low (sub-toxic) doses. 

Nonetheless, statistically significant interactions (both synergistic and antagonistic) have been 

noted in some studies. Even with excellent data, the complexity of the experimental designs 

necessary to properly assess interactions and the uncertainties regarding the dose-response 

relationship for interactions the risk characterization for chemical mixtures uncertain. 

The guidance resulting from the reviews and analyses of available information by both EPA 

and ATSDR is that synergistic effects are implausible for human exposures to chemical 

mixtures where the dose from each chemical is at least one order of magnitude below its 

respective RfD (i.e. HQ< 0.1), and the sum of individual HQ’s does not approach an additive 

HQ=1. 

The combination of surfactant and herbicide might indicate an increased rate of absorption 

through the skin; however, a review of recent studies indicates this is not likely to be true 

(Bakke, 2002). For a surfactant to increase the absorption of another compound, the 

surfactant must affect the maximum layer of the skin. Without some physical effect to the 

skin, there would be no change in absorption as compared to the other compound alone. The 

studies indicate that in general non-ionic surfactants have less of an effect on the skin, and 

hence absorption, then anionic or cationic surfactants. Compound specific studies indicate 

that the alkylphenol ethoxylates generally have little or no effect on absorption of other 

compounds. In several studies, the addition of a surfactant actually decreased the absorption 

through the skin. It would appear that there is little support for the contention that the 

addition of surfactants to herbicide mixtures would increase the absorption through the skin of 

these herbicides. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-37 

Several of the herbicides considered in this EIS can be combined with other herbicides to 

increase the range of effective control. Studies of these twelve herbicides in combination with 

other compounds are not common, as toxicology studies generally involve the active 

ingredient. So to the extent that any studies exist, they are important to consider for their 

insight into potential impacts of combinations. 

2,4-D may be applied with most of the herbicides considered in this EIS. A commercial 

formulation of picloram and 2,4-D, known as Tordon 202C, has been shown to inhibit 

immune response in mice and to cause birth defects and death in offspring of male mice that 

were exposed. A commercial formulation of picloram and 2,4-D, Tordon 202C, has been 

shown to inhibit immune function in mice. The design of this study does not permit the 

determination of which agent caused the immune response or whether the immune response 

was attributable to a toxicologic interaction of the two herbicides. No data have been 

encountered in the literature that permits a characterization of the joint action of either 2,4-D 

or picloram (i.e., synergism, antagonism, or additivity) with any of the other herbicides 

considered in this EIS. 

The manufacturers recommend that chlorsulfuron formulations be mixed with a non-ionic 

surfactant. There is no information available to assess the toxicological effects or risks of 

chlorsulfuron mixed with a surfactant. Telar may be applied in combination with other 

herbicides including 2,4-D or glyphosate. No data have been encountered in the literature that 

permits a characterization of the joint action of chlorsulfuron (i.e., synergism, antagonism, or 

additivity) with most herbicides. 

Clopyralid may be applied in combination with other herbicides, particularly in combination 

with 2,4-D or 2,4-D and picloram. No data have been encountered in the literature that 

permits a characterization of the joint action of clopyralid (i.e., synergism, antagonism, or 

additivity) with most herbicides. 

Dicamba is labeled for mixing with all other considered herbicides except imazapic and 

sethoxydim. There is no substantial evidence that dicamba would interact with other 

compounds. As discussed in the Forest Service/SERA dicamba risk assessment, one study 

indicates that dicamba does not induce cytochrome P-450 activity and does not substantially 

affect a variety of other xenobiotic metabolizing enzymes. Although this finding does not 

rule out the possibility that dicamba may be involved in toxicologically significant 

interactions, the induction of cytochrome P-450 is a major mechanism by which such 

interactions are known to occur. 

Little information is available about the interaction of glyphosate with other compounds. The 

available data do not suggest a synergistic interaction between glyphosate and the ethoxylated 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-38 

tallow amine (POEA) surfactant used in several formulations of glyphosate from plausible 

routes of exposure. 

The manufacturer of imazapic has recommended tank mixtures of this herbicide with 

glyphosate. No data are available on the combined toxicity of these two herbicides. Studies 

have been conducted on mixtures of 2,4-D and imazapic. While these combinations are more 

toxic than imazapic alone, there appears to be no basis for asserting that synergistic effects are 

likely because the toxic action is probably due to 2,4-D 

Imazapyr may be applied in combination other herbicides. Imazapyr is often applied in 

combination with triclopyr and is occasionally applied in combination with the herbicide 

fosamine ammonium. No data have been encountered in the literature that permits a 

characterization of the joint action of imazapyr (i.e., synergism, antagonism, or additivity) 

with most herbicides. The limited information encountered in the EPA files on mixtures of 

imazapyr with the herbicide imazethapyr does not indicate any substantial interaction. 

The manufacturers recommend that metsulfuron methyl formulations be mixed with a 

surfactant. There is no published literature or information in the FIFRA files that would 

permit an assessment of toxicological effects or risks of metsulfuron methyl mixed with a 

surfactant. According to the product label, Escort may be applied in combination with other 

herbicides. No data have been encountered in the literature that permits a characterization of 

the joint action of metsulfuron methyl (i.e., synergism, antagonism, or additivity) with other 

herbicides considered in this EIS. 

Sethoxydim can be applied with other herbicides; no data are available on the combined 

toxicity of sethoxydim with other pesticides. Poast does contain a petroleum solvent as well 

as a polyoxyethylene nonylphenol emulsifier. While these agents have a substantial impact 

on the ecological risk assessment, there is no information suggesting that these agents have a 

substantial impact on the toxicity of sethoxydim to humans or experimental mammals. 

The manufacturers recommend that sulfometuron methyl formulations be mixed with a 

surfactant. There is no published literature or information in the FIFRA files that would 

permit an assessment of toxicological effects or risks of sulfometuron methyl mixed with a 

surfactant. According to the product label, Oust may be applied in combination with other 

herbicides particularly glyphosate, imazapyr, hexazinone. No data have been encountered in 

the literature that permits a characterization of the joint action of sulfometuron methyl (i.e., 

synergism, antagonism, or additivity) with other herbicides considered in this EIS. 

There is very little information available on the interaction of triclopyr with other compounds. 

The available data do not suggest a synergistic interaction between the triclopyr active 

ingredient and the other components in the commercial triclopyr formulations of Garlon 3A or 

Garlon 4. No data have been encountered in the literature that permits a characterization of 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-39 

the joint action of triclopyr (i.e., synergism, antagonism, or additivity) with other herbicides 

considered in this EIS. 

Estrogenic effects (a common toxic action, and a form of endocrine disruption) can be caused 

by additive amounts of nonylphenol (NP), NPE, and their breakdown products. In other 

words, an effect could arise from the additive dose of a number of different xenoestrogens 

(estrogens from outside the body), none of which individually have high enough 

concentrations to cause effects. This can also extend out to other xenoestrogens that 

biologically react the same. Additive effects, rather than synergistic effects, are expected 

from combinations of these various estrogenic substances (Bakke, 2003). 

5.5.2 Risks of Potential Cumulative Human Health Effects from Herbicides 

Considered for Use 

The proposed use of herbicides could result in cumulative doses of herbicides to workers or 

the general public. Cumulative doses to the same herbicide result from (1) additive doses via 

various routes of exposure resulting from a single invasive plant treatment project and (2) 

additive doses if an individual is exposed to other herbicide treatments. Additional sources of 

exposure include: use of herbicides on adjacent private lands or home use by a worker or 

member of the general public. 

This risk assessment specifically considers the effect of repeated exposure in the chronic 

exposure scenarios and the use of the chronic RfD as an index of acceptable exposure. 

Consequently, repeated exposure to levels below the toxic threshold should not be associated 

with cumulative toxic effects. 

Each of the HQs discussed in previous sections involves a single exposure scenario. Where 

individuals could be exposed by more than one route, the cumulative risk of such cases can be 

quantitatively characterized by adding the HQs for each exposure scenario. Using glyphosate 

as an example, the typical levels of exposure for a woman being directly sprayed on the lower 

legs, staying in contact with contaminated vegetation, eating contaminated fruit, and 

consuming contaminated fish leads to a combined (acute) HQ of 0.012. Similarly, for all of 

the chronic glyphosate exposure scenarios, the addition of all possible pathways lead to HQs 

that are two orders of magnitude less than 1, indicating an acceptable level of cumulative risk. 

Similar scenarios can be developed with the other herbicides. 

Since these herbicides persist in the environment for a relatively short time (generally less 

than 1 year), do not bioaccumulate in humans, and are rapidly eliminated from the body, no 

cumulative effects from retreatments in subsequent years are predicted. 

Cumulative effects can be caused by different chemicals with a common metabolite or a 

common toxic action. With the exception of triclopyr and chlorpyrifos discussed below, none 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-40 

of the other herbicides have been demonstrated to share a common metabolite with other 

compounds. There is no evidence that any of the herbicides share a common toxic action with 

any other compound including other pesticides. 

The primary environmental metabolite of triclopyr is TCP. TCP is also the primary 

metabolite of an insecticide called chlorpyrifos. Cumulative doses of TCP could result from 

additive doses resulting from triclopyr and chlorpyrifos use. Although chlorpyrifos is not 

generally used in forestry, recent studies have shown drift of chlorpyrifos, and other 

insecticides, from agricultural lands in the Sacramento/San Joaquin Valley to the Sierra 

Nevada range. Levels of chlorpyrifos have been measured in watercourses in the Sierra 

Nevada as high as 0.000013 mg/L. It is unlikely that such high aquatic levels of chlorpyrifos 

would be found in the EIS area as a result of atmospheric movement because, compared to the 

previous study area, the surrounding lands in Oregon and Washington have higher rainfall 

levels and less extensive area of intensive crop cultivation . However, assuming that 10 

percent of the applied triclopyr under the typical rate of application could degrade to TCP, 

and using the pond spill scenario, the amount of TCP from triclopyr would be 0.36 mg/L. 

Assuming that 100 percent of the chlorpyrifos would degrade to TCP (an over-exaggeration 

of the rate of degradation), this would add 0.000013 mg/L of TCP, resulting in no appreciable 

increase in risk. 

Estrogenic effects (a common toxic action, and a form of endocrine disruption) can be caused 

by additive amounts of nonylphenol (NP), NPE, and their breakdown products. In other 

words, an effect could arise from the additive dose of a number of different xenoestrogens 

(estrogens from outside the body), none of which individually have high enough 

concentrations to cause effects. This can also extend out to other xenoestrogens that 

biologically react the same. Additive effects, rather than synergistic effects, are expected 

from combinations of these various estrogenic substances. 

When assessing cumulative effects of exposure to NP and NPE, there must be some 

consideration of the contribution from other sources, such as personal care products (skin 

moisturizers, makeup, deodorants, perfumes, spermicides), detergents and soaps, foods, and 

from the environment away from the forest herbicide application site. In addition to 

xenoestrogens, humans are exposed to various phytoestrogens, which are hormone-mimicking 

substances naturally present in plants. In all, more than 300 species of plants in more than 16 

families are known to contain estrogenic substances, including beets, soybeans, rye grass, 

wheat, alfalfa, clover, apples, and cherries. 

The Forest Service, Pacific Southwest Region recently analyzed the risks of cumulative 

estrogenic effects from proposed Forest Service use of NPE, plus worst-case environmental 

background and consumer product exposures (USDA, 2002). Adding together the cumulative 

contributions from the worst-case background environment and consumer products, the risk 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005 

Appendix Q-41 

assessment estimated that backpack applicator exposure would add from 0.1 (typical rate) to 

10 (maximum rate) to the cumulative HQ, which ranged from 3 (low dermal exposure 

assumptions) to 270 (high dermal exposure assumptions). For the public chronic exposures at 

the maximum application rate, the doses of NPE would add 0.00002 to 0.2 to any HQ. These 

may be negligible depending upon the background exposures, lifestyles, absorption rates, and 

other potential chemical exposures that are used to determine overall risk to environmental 

xenoestrogens. 
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Appendix Q-42 

HUMAN HEALTH RISK ASSESSMENT BIBLIOGRAPHY 

Henry, Charles. 2003. Icicle Road Hand-Pulling Timed Study. Techline, Winter 2003-2004. 

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SERA (Syracuse Environmental Research Associates, Inc.). 2001. Preparation of 

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Bakke, David. 2003. Human and Ecological Risk Assessment of Nonylphenol 

Polyethoxylate-based (NPE) Surfactants in Forest Service Herbicide Applications. USDA 

Forest Service Pacific Southwest Region Technical Publication. 

Zeise, Lauren, R. Wilson, and E. Crouch. 1984. Use of acute toxicity to estimate 

carcinogenic risk. Risk Analysis 4(3):187-199. 

SERA, 1997. Use and Assessment of Marker Dyes Used with Herbicides.

Bakke, David. 2002. Analysis of Issues Surrounding the Use of Spray Adjuvants With 

Herbicides. USDA-FS, Pacific Southwest Region Technical Publication. 

Borrecco, J.and Neisess, J. 1991. Risk assessment for the impurities 2-butoxyethanol and 1,4-

dioxane found in Garlon 4 and Roundup herbicide formulations. Pacific Southwest Region, 

Forest Pest Management. Report No. R91-2. 33 pages. 

USDA. 2002. HFQLG EIS, Risk Assessment of Cumulative Estrogenic Effects from All 

Sources. 

ATSDR (Agency for Toxic Substances and Disease Registry). 2004. Guidance Manual for 

the Assessment of Joint Toxic Action of Chemical Mixtures. Available from U.S. Department 

of Health and Human Services, Public Health Service, ATSDR, Division of Toxicology. 

U.S. EPA/ORD (U.S. Environmental Protection Agency/Office of Research and 

Development). 2000. Supplementary Guidance for Conducting Health Risk Assessment of 

Chemical Mixtures. Office of Research and Development, U.S. EPA, Washington, DC. 

EPA/630/R-00/002. Report dated August 2000.