Final Environmental Impact Statement Kings River Experimental Watershed Project

Chapter 3-12 - Glyphosate 3.12-1

Affected Environment and Environmental 

Consequences

3-12 Effects of Ground Application of Glyphosate on 

Human Health and Safety

3-12.1 Introduction 

A risk assessment to determine the site-specific risks to human health and safety of using the herbicide 

glyphosate in the commercial formulation of Accord was prepared for the project and is incorporated by 

reference. This risk assessment is on file at the High Sierra District Office1. According to the action 

alternatives, additives such as the surfactant R-11, and a dye are added to the spray mixtures before 

application. They have been analyzed in other risk assessments, USDA (2003) for R-11 and SERA 

(1997a) which are incorporated by reference.

3-12.2 Direct and Indirect Effects 

The hazard characterization, the application method (backpack spraying), and the number and 

characteristics of people that could come in contact with glyphosate is similar to many other projects 

undertaken by the High Sierra Ranger District in recent years, such as applying glyphosate for 

maintenance of the Beal and Vincent Fuelbreaks since 1999.

Hazard identification was accomplished by reviewing toxicity data in the scientific literature, the 

Vegetation Management for Reforestation Final Environmental Impact Statement (USDA 1988) and in 

the USDA Forest Service Pesticide Fact Sheets (1995) to identify established acute toxicity values 

(LD50s2) and no observable effect levels (NOELs3) for systemic and reproductive health effects. 

Following is a summary for glyphosate and R-11:

Glyphosate is considered to be slightly toxic to humans. It is non-irritating to the skin and only 

slightly irritating to the eyes. There is no evidence that glyphosate causes birth defects, cancer, 

 

1 Although the Forest Service relied somewhat on the Vegetation Management for Reforestation Final 

Environmental Impact Statement (VMFEIS 1988), the risk assessment mainly utilized information from 

recent risk assessments such as Selected Commercial formulations of Glyphosate - Accord, Rodeo, and 

Roundup risk assessment final report (SERA 1996) and Glyphosate (SERA 2003). The VMFEIS was used to 

assess some of the impacts of herbicide use. The Forest Service did use the experience gained by carrying out 

reforestation activities that flowed from the VMFEIS to craft the alternatives and estimate the effects in this 

EA.

2 LD50 is the one-time dose that kills 50% of a test population. It is expressed as milligrams of pesticide per 

kilogram of body weight of the test animal. The lower the LD50, the greater is the toxicity of the chemical. The 

LD50 is usually determined for swallowing (oral exposure) and for exposure to the skin (dermal).

3 NOEL is the maximum long-term dose that produces no noticeable adverse effect on test animals.
Final Environmental Impact Statement Kings River Experimental Watershed Project

Chapter 3-12 - Glyphosate 3.12-2

neurotoxicity, immunotoxicity or endocrine disruption (SERA 2002 & 2003). LD50 and NOEL 

data are summarized in the table on page 2 of the risk assessment.

R-11 is a mixture of the soap nonylphenol polyethoxylate4 (NPE), about 10 percent butyl or 

isopropyl alcohol, about 1percent silicone defoamer and water. The mixture is slightly toxic to

practically non-toxic to mammals. Eye irritation and skin sensitization are likely effects of 

mishandling R-11 as would be the case with any soap. At typical application rates, there is no 

evidence that R-11 causes birth defects, cancer, neurotoxicity or immunotoxicity. (USDA, 2003).

This analysis is based on the experience gained by the High Sierra Ranger District carrying out 

reforestation projects since the mid-1990s. The shrubs found in the KREW Project area have been 

eradicated or adequately suppressed on reforestation projects using glyphosate mixed with water at 5 

percent or less and R-11 a 1 percent by volume and applied to all the target vegetation involved in the 

project. Target shrubs covered about 25 to 75 percent of the ground in these projects and they cover a 

similar amount on some parts of the KREW Project. On the reforestation projects, glyphosate mixed at 5 

percent and applied spray-to-wet to the target vegetation resulted in 9 to 24 gallons of mix per acre or 

1.8 to 4.8 pounds of active ingredient per acre. The results are expected to be within these ranges on the 

KREW Project. The application method would be a foliar spray from backpack sprayers.

The people that could come in contact with the mixture of glyphosate and R-11 are project workers and 

members of the general public. Workers are those Forest Service and contracted employees who 

directly or indirectly prepare and apply the herbicide. Exposure results from handling of the chemicals 

during the application process. The general public includes Forest visitors and residents on adjacent 

land. Exposure can be a result of contact with treated foliage, or through consuming plants, water, or 

animals containing pesticide residues. Exposure data for Glyphosate and for R-11 are summarized in 

the table on page 4 of the risk assessment, and are about double for general exposure to workers and 

substantially lower for all exposures to the public.

In essence, the risk assessment compares herbicide exposure that people might receive from applying 

the herbicide (worker doses) or from being near or within the application site (public doses) to doses 

shown to have a no observed effect level (NOEL) in test animals in long-term laboratory studies. In the 

human health risk assessment, the defined effect level is almost always a reference dose (RfD) that 

would not result in any adverse effects in any individual. The RfD includes an uncertainty factor of 100 –

10 for sensitive individuals and 10 for species-to-species extrapolation – to account for variability in 

human response. The ratio of the exposure to the reference dose is referred to as the hazard quotient 

(HQ). For all worker and public exposure scenarios, the HQ indicates there is no cause for concern and 

the risk to human health and safety is acceptable when using a mixture of glyphosate and one percent R11 for the KREW Project. The HQs for glyphosate are summarized in the table on page 5 of the risk 

assessment and for R-11 in USDA (2003) on pages 35 and 36.

This risk assessment has characterized human health and safety using data for glyphosate, the active 

ingredient, in the Accord formulation. This formulation includes only one inert ingredient, water, which 

acts as a carrier for glyphosate. For backpack application the Accord is diluted with water to reach the 

 

4 The primary active ingredient in many of the commercially available non-ionic surfactants is a compound 

known as NPE. It is found at rates varying from 20 to 80 percent. NPE is formed through the combination of 

ethylene oxide and nonylphenol (NP). NP is a material recognized as hazardous and is included on EPA List 1. 

(USDA 2003; p. v) NPE is widely used in industrial applications, detergents, cosmetics, shampoos, surfactants 

and spermicides
Final Environmental Impact Statement Kings River Experimental Watershed Project

Chapter 3-12 - Glyphosate 3.12-3

specified application rate and one percent R-11 is added. As stated earlier, R-11 includes alcohol, 

silicone defoamer and water. Obviously, these inerts do not pose any concern for human health and 

safety.

There has been concern expressed about the potential for surfactants containing NPE, such as R-11, to 

cause endocrine disruption and other deleterious effects. However, in comparison to natural estrogen 

NPE is approximately 10,000 to 1,000,000 times weaker in eliciting an estrogenic response (USDA 2003, 

p. 9). 

3-12.3 Cumulative Effects 

Cumulative doses of glyphosate and/or R-11 could result from either various routes of exposure from 

the KREW Project or from additive doses from other herbicides treatments.

Additive doses from various routes of exposure from the KREW Project (i.e. eating contaminated fruit 

and drinking contaminated water on the same day) can be estimated from the tables of exposure rates 

in the risk assessments. The two doses would be added and divided by the RfD to determine the HQ. The 

calculated HQ for a combined dose for any two routes of exposure would still show no cause for concern 

and an acceptable risk to human health and safety. 

Other sources of additive exposure could include glyphosate and/or R-11 used on adjacent lands, retreatment of the same site in the same or following years, and home use by a worker or member of the 

general public. In the project area, there are no adjacent private landowners or government agencies 

that have used or plan to use significant amounts of herbicides. The proposed action for the fuelbreak 

maintenance project plans two applications over two years. However, treatments are limited to one per 

year, and doses are not expected to be additive because soil microorganisms break down glyphosate and 

R-11 and no residual chemical would remain on site from a previous treatment.

Should workers or members of the public apply glyphosate and/or R-11 at home, they would receive 

doses approximately equal to those estimated for this project, assuming similar rates and application 

methods are used, per manufacture’s label direction. If this exposure occurred on the same day as the 

project exposure, then the two doses would be added and divided by the RfD to determine the HQ. The 

calculated HQ for a combined dose for any two routes of exposure would still show no cause for concern 

and an acceptable risk to human health and safety.

There is no indication that glyphosate causes sensitization or allergic responses, which does not 

eliminate the possibility that some individuals might be sensitive to glyphosate as well as many other 

chemicals (SERA 2003; 3-51). As stated earlier, eye irritation and skin sensitization are likely effects of 

mishandling R-11 as would be the case with any soap.

Synergistic effects of glyphosate and/or R-11 with other chemicals are not anticipated in the project 

area because they have not occurred when it has been used extensively in other forestry and 

agricultural applications.

For all worker and public exposure scenarios, cumulative effects would be negligible.