UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

APR 2 4 2013 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

[REVISED] Application Rate Information for Uses of RO-PEL, a Ready-To-Use 

Liquid Bittering Agent Containing Denatonium Saccharide (PC Code 129045) 

Jonathan Becker, Senior Science Advisor l /J jjJ,___ 

Biological Analysis Branch C '/ 

Biological and Economic Analysis Division (7503P) 

Amet Jones, Chief 

Biological Analysis Branch 

TO: Andrea Mojica, Chemical Review Manag 

Risk Management and Implementation Branch 4 

Pesticide Reevaluation Division (7508P) 

Product Review Panel Date: 10 April 2013 

SUMMARY 

BEAD recommends that the following application rate estimates be used for the risk assessment 

of denatonium saccharide: as a bulb treatment (6 x 10·6 lbs a.i. per bulb); as a seed treatment (3 x 

104 lbs a.i. per 1,000 ft2); and for all residential treatments combined (1 gallon ready-to-use 

liquid or 5.4 x 10-3 lbs a.i. per residence). 

INTRODUCTION 

This document provides estimates of the application rate for labeled uses of RO-PEL, a ready-touse formulation of denatonium saccharide. Estimates for these use sites (seed and bulb 

treatments), and as well for all residential uses combined, may be used in the ecological risk 

assessment for denatonium saccharide. 

1 
Denatonium saccharide (PC code 129045) is an extremely bitter chemical that is used as an 

animal repellent. This active ingredient has one registration (Reg. No. 81117-1) and several 

products are marketed, such as "RO-PEL Tree Squirrel, Vole, Dog and Cat Repellent" and "Four 

Paws Keep Off! Dog and Cat Repellent". These products are ready-to-use liquids and contain 

0.065% denatonium saccharide. Although not explicitly stated on the product labels, both 

products appear to be used only in outdoor residential settings, either by the homeowner or by a 

commercial contractor. Please note that the brand name "RO-PEL" is used for products that do 

not contain denatonium saccharide. The Four Paws product label provides specific application 

rate information and will not be discussed further. 

The RO-PEL product label allows application to outdoor structures and surfaces (e.g., tree bark, 

decks, and planters) and the application rate for this use is adequate (1 gallon covers 1,000 to 

4,000 square feet). Each gallon of Ready-To-Use RO-PEL contains 0.0054 pound denatonium 

saccharide (0.065% a.i. x 8.34lbs per gallon= 0.0054lbs a.i.). This product is also labeled as a 

bulb and seed treatment to reduce consumption and damage by tree squirrels and voles. The 

directions for these uses only state "Using rubber gloves, place seeds or bulbs in a plastic or 

metal container and spray thoroughly until soaked." No further application information is 

provided on the label. Based on extension service and trade organization information, as well as 

best professional judgment, BEAD provides application rate estimates for these uses. 

BEAD uses water as a surrogate for the 0.065% RO-PEL ready-to-use formulation in developing 

these estimates. Further, BEAD assumes that the entire amount of the ready-to-use formulation 

is applied to seeds and bulbs with no loss. This would never occur during actual use as there 

would always be significant loss from residual spray in the containers. This assumption further 

adds to the high-end nature of these estimates. 

BULBS 

The application rate per bulb may be calculated using the amount of liquid applied to each bulb, 

then applying unit conversions to determine the lbs a.i. per bulb. 

Krug et al. (2005) reported the volume of liquid applied per bulb for a similar application method 

(hyacinth bulbs soaked in a dip solution for 10 minutes). Krug (2005) found that on average, 

each bulb utilized 4 to 8 ml of solution (or 470 to 950 bulbs per gallon). 

Significantly smaller amounts would be needed when using a sprayer. This is because Krug 

(2005) completely submerged each bulb for at least 10 minutes, allowing for a much greater 

penetration and retention of the solution by each bulb than could be achieved from application by 

a sprayer. 

2 
A conservative estimate based on Krug (2005) would be that 4 ml per bulb is the greatest amount 

that could be applied by sprayer to each bulb. The amount of denatonium saccharide per bulb 

may be calculated as: 

4ml 

bulb 

1 gallon 

3,785.41 ml 

8.345 lbs a. i. -----. 0.065% 1 gallon 

6 :X 10-6 lbs a. i. 

bulb 

SEEDS 

A similar approach may be used to calculate the application rate for seed treatments; however, 

the units will be expressed in lbs per ft2 to account for the number of treated seeds planted. The 

RO-PEL label does not specify the types of seeds (i.e., plant species) that can be treated with this 

product. BEAD selected bare (i.e., uncoated) turfgrass seed to represent the high-end application 

rate for this use. Grass is the most commonly planted seed around residences. Grasses planted 

in residential areas have large number of seeds per pound and are planted at a high seeding rate 

(Table 1). The aggregate surface area of the grass seeds is greater than any other seed planted ill 

residential areas and will therefore result in the highest application rate of RO-PEL per unit area. 

Table 1. Number of seeds per pound and recommended seeding rates for common turfgrass 

species (Voight, no date; Trenholm, 2009; Stahnke, et al. 2010). 

Grass Approximate Number of Seeding rate (lb I 1000 ft2

) Seeds Per Pound 

Tall fescue 178,000-234,000 6 to 9 (Festuca arundinacea and Latium arundinaceum) 

Perennial ryegrass (Lolium perenne) 210,000-270,000 3 to 5 

Red fescue (creeping) (Festuca rubra var. rubra) 365,000 3 

Chewings fescue (Festuca rubra var. commutata) 449,000 3 

Hard fescue (Festuca ovina var. duriuscula) 592,000 3 

Kentucky bluegrass (Poa pratensis) I ,022,000-1,758,000 I to 3 

Colonial bentgrass (Agrostis tenuis) 6,130,000 0.75 to 1.5 

Note: Grass seed w1th the greatest number of seeds per pound IS not planted usmg the h1ghest seedmg rate. An 

optimal density of seeds per in2 is targeted for each type of grass, so seed lots with a smaller number of 

seeds per pound are planted at a higher seeding rate and vice versa. 

BEAD has no empirical information related to the amount of solution required to thoroughly 

soak grass seed and translate this into an application rate. However, an estimate may be made 

using the surface area of grass seed and the area that can be covered by a given amount of 

solution (label information). When these values are combined with information from Table 1 

and unit conversion factors are applied, an application rate per unit area may be estimated. 

3 
The steps necessary to calculate this estimate are as follows. 

• Calculate the surface area of a hypothetical grass seed 

• Calculate the thickness of spray on a surface (i.e., film thickness) 

• Calculate the volume of liquid to cover one seed 

• Calculate the amount of grass seed to plant 1,000 ft2

• 

• Calculate the amounts of RO-PEL (and lbs a.i.) needed to treat these seeds at the 

application rate per 1,000 ft2

• 

Calculations of the surface area of a hypothetical grass seed 

Undersander et al. (1996) describes the various grasses and their seeds. Grass seed is elongated 

with both ends tapering to a point. The surface area of a hypothetical grass seed may be 

calculated assuming that the seed roughly parallels the geometric shape of two cones joined 

together at the base. The surface area of this shape (note that the surface areas of the bases are 

not included) may be calculated as follows. 

2nrs 

Where r = radius and s = length of the side of one cone. The value for s may be determined by 

the Pythagorean Theorem. 

Using the dimensions of a hypothetical grass seed (1 mm in diameter (a= 0.5 mm), 3 mm in 

length (b=1.5 mm), the value of s (i.e., c in the above equation) is 

(0.5 mm)2 + (1.5 mm)2 = 2.5 mm2 and c = .J2.s mm2 = 1.58 mm 

The surface area is calculated using 2ms as 

2 · 3.1416 · 0.5 mm · 1.58 mm = 4.97 mm2 

Calculations to determine the thickness of spray on a surface (i.e .. film thickness) 

The RO-PEL label states that one gallon will cover 1,000 to 4,000 ft2

. The thickness of the film 

on the treated surface for these two rates may be calculated using the following equations. 

1 gallon 3785411.78 mm3 1 ft2 . . 

1,000 ft2 . 1 gallon (US Liquid) . 92903.04 mm2 = 0.0407 mm film thickness 

1 gallon 3785411.78 mm3 1 ft2 . 

4,000 ft2 . 1 gallon (US Liquid) . 92903.04 mm2 = 0.0102 mm film thickness 

4 
These calculated values are close to the water film thickness values reported in EPA's Exposure 

Factors Handbook (EPA 2011 ). The reported values in this document range from 0.0132 to 

0.0499mm. 

Calculation of the volume of liquid to cover one seed 

The amount of liquid that is required to completely cover one seed is determined by multiplying 

the surface. area of one seed by the film thickness of the spray using the values calculated above. 

At the high treatment rate (1,000 ft2 per gallon) 

• 

4.97 mm2 0.20 mm3 

1 d · 0.0407 mm = see 1 seed 

At the low treatment rate ( 4,000 ft2 per gallon) 

4.97 mm2 0.051 mm3 

1 d · 0.0102 mm = --"""":"'-

see 1 seed 

Calculation of the amount of grass seed to plant 1 .000 ft2

• 

Using the seeding rates and the number of seeds in a pound for Red Fescue (a common turfgrass 

species planted around residences) from Table 1, the number of seeds needed to plant 1,000 ft2 is 

3 lbs seed 365,000 seeds 1,095,000 seeds 

1,000 ft 2 lb seed = --:--:--:-:--~- 1,000 ftZ 

Calculation of the amounts ofRO-PEL (and lbs a.i.) needed to treat these seeds at the application 

rate per 1.000 ft2

• 

At the high treatment rate (1 gallon covers 1,000 ft2

) 

1,095,000 seeds 0.2 mm3 

1,000 ft 2 1 seed 

0.058 gallons RO -PEL 

1,000 {t 2 

1 gallon 0.058 gallons RO -PEL 

= ---------- 3,785,411.78 mm3 1,000 {t 2 

8.345 lbs . 0 so _ 3 x 10-4 lbs a. i. 

1 gallon O. 6 Yo - 1,000 ft 2 

At the low treatment rate (1 gallon covers 4,000 ft2

) 

1,095,000 seeds 0.051 mm3 

1,000 ft 2 • 1 seed 

0.015 gallons RO- PEL 

1,000 {t 2 

1 gallon 0.015 gallons RO -PEL 

= --~--~--- 1,000 ft 3,785,411.78 mm3 2 

8.345 lbs . 0650 _ 8 x 10-5 lbs a. i. 

1 gallon O. Yo - 1,000 ft 2 

5 
Alternatively, one gallon of RO-PEL would treat enough seed to plant 17,000 to 67,000 ft2 of 

turf. 

AMOUNT USED PER RESIDENCE 

Given that RO-PEL could be applied to several different sites around a residence, a "per 

residence" application rate may be useful. An amount of RO-PEL applied per residence may be 

projected based on the application rates calculated above for bulbs and grass seed and the label 

information describing the rate when applied to surfaces. Given the following: 

• Only a small portion of outdoor surfaces (e.g., the edges of a deck) require treatment to 

deter chewing by rodents 

• The application rates for grass seed and bulbs estimated above are high-end values 

• The median lot size in the United States is 0.25 acres (=10,890 ft2> (Census, 2011). To 

estimate the potential size of a lawn the footprint of the house, driveway, and sidewalks 

need to be subtracted from this value 

• The retail cost of RO-PEL ranges from $25 for 24 fluid ounces (Sears 2013) to about $50 

per gallon (Nixalite 2013). This substantial cost ia a further indication that this product is 

intended for homeowner use. 

BEAD recommends that 1 gallon of RO-PEL ready-to-use liquid per residence be used as a 

reasonable high-end estimate. 

SUMMARY I RECOMMENDED VALUES 

BEAD recommends the following reasonable high-end estimates be used for the risk assessment 

of denatonium saccharide: 

• As a bulb treatment: 6 X 10-6 lbs a.i. per bulb 

• As a seed treatment: 3 x 104 lbs a.i. per 1,000 ft2 

• For all residential treatments combined: 1 gallon ready-to-use liquid or 5.4 x 10-3 lbs a.i. 

per residence. 

REFERENCES 

Census. 2011. Table C-02-AH. American Housing Survey for the United States. Series H-150, 

United States Census Bureau, U.S. Department of Commerce. 

Krug, B., B. Whipker and I. McCall. 2005. Bulb soak basics. Greenhouse Product News. Oct. 

2005. Available at: http://www.gpnmag.com/sites/defaultlfiles/bulbsoakbasics.pdf 

6 
Nixalite. 2013. Nixalite of America, Inc. website. Available at: 

http://www .nixalite.cornlropel.aspx 

Stahnke, G.K., E.D. Miltner, R.C. Puyallup, R.C. Golembiewski, T.A. Salaiz, and W.J. 

Johnston. 2010. Ttnfgrass Seeding Recommendation<; for the Pacific Northwest Pacific 

Northwest Extension Publication 299. Available at: 

http:!/horticulture.oregonstate.edu/content/turfgrass-seeding-recommendations-pacificnorthwest-0 

Sears. 2013. Sears website. Available at: 

http://www.sears.com/search=four+paws+pet+products+keep+off+indoor+and+outdoor+ 

dog+and+cat+spray+repellent+24+oz?vName=Pet+Supplies&cName=Dog+Supplies&au 

toRedirect=true&view Items=25&redirectType=CA T REC PRED 

Trenholm, L.E. 2009. Establishing Your Florida Lawn. Publication #ENH-03. Florida 

Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of 

Florida. Available at: http://edis.ifas.ufl.edu/lh013 

Undersander, D., M. Casler, and D. Cosgrove. 1996. Identifying Pasture Grasses. Publication 

Number A3637. University of Wisconsin Cooperative Extension. 

USEPA. 2011. Exposure Factors Handbook: 2011 Edition. National Center for Environmental 

Assessment, U.S. Environmental Protection Agency, Washington, DC~ EPA/600/R09/052F. Available from the National Technical Information Service, Springfield, VA, 

and online at http://www.epa.gov/ncea/efh . · 

Voigt, T. No date. Turfgrass Establishment. Turfgrass Extension & Outreach, Department of 

Natural Resources and Environmental Sciences, University of Illinois at UrbanaChampaign. Available at: http://www.turf.uiuc.edu/extension/ext-estab.html 

7