UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

W ASIDNGTON, D.C. 20460 

MAR 2 8 2014 

MEMORANDUM 

SUBJECT: Denatonium Saccharide Alternative Assessment (129045) 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

FROM: David W Brassard, Senior Entomologist ~M{J ~ ~~ Biological Analysis Branch 

Biological and Economic Analysis Division (7503P) 

THROUGH: Amet Jones, Chief 

Biological Analysis Branch 

Biological and Economic Analysis Division (7503P 

TO: Cathyrn Britton, Team Leader 

Kevin Costello, Branch Chief 

Risk Management and Implementation Branch I 

Pesticide Re-Evaluation Division 

PRP Review Date March 12, 2014 

Summary and Conclusions 

The purpose of this memorandum is to provide background information on the use of 

denatonium saccharide and to present information on alternatives. 

Denatonium saccharide is a bittering agent registered for use by residential consumers as a 

squirrel, vole, dog, and cat repellent on outdoor surfaces, structures, seeds and bulbs. Only 11 0 

pounds or less of denatonium saccharide active ingredient (a.i.) is sold in the U.S. annually. 

There are three animal repellent alternatives to denatonium saccharide for protection of outdoor 

surfaces, structures, trees, seeds and bulbs: methyl nonyl ketone, capsaicin mixture, and thiram. 

However, because each of these alternatives can only be used on a subset of uses, users may only 

have one alternative for some uses. Some of the alternatives have constraints that may limit their 

usefulness. Methyl nonyl ketone has a shorter period of residual activity and needs to be 

reapplied daily. The capsaicin/garlic oil/putrescent whole egg solid products have a strong 
aromatic smell that may be offensive to some users. Lastly, little is known about the 

comparative efficacy of the alternatives; therefore, the alternatives may not be as effective as 

denatonium saccharide. 

Background 

The purpose of this memorandum is to provide background information on use of denatonium 

saccharide and to present information on alternatives. 

Denatonium saccharide is a bittering agent registered for use as a squirrel, vole, dog, and cat 

repellent. Denatonium saccharide, a quaternary ammonium salt, is the bitterest chemical 

compound known to man. Dilutions as low as 10 ppm are unbearably bitter to most humans. 

(CPSC, 1992; Clegg, 2013). 

There is currently one registered product, RO-PEL Tree Squirrel, Vole, Dog, and Cat Repellent, 

EPA Registration Number 811 17-1, a ready-to-use liquid formulation containing 0.065% 

denatonium saccharide and 0.035% thymol (NPIRS, 2014). Currently, only 50 Kg (110 pounds) 

per year or less of denatonium saccharide is imported, which is enough to formulate 20,400 

gallons ofRO-PEL (Brown, 2012). Assuming that user households apply one gallon ofRO-PEL 

annually, this is enough to treat 0.017% of U.S. households (U.S. Census Bureau, 2012). The 

retail cost ofRO-PEL ranges from $25 for 24 fluid ounces (Sears 2013) to about $50 

per gallon (Nixalite 2013). 

RO-PEL is used mostly by consumers in residential areas (Becker, 2013). RO-PEL is used to 

repel tree squirrels, dogs and cats on outdoor surfaces and structures such as trees, fences, poles, 

decks, planters, siding, garbage cans, and furniture. RO-PEL is also labeled for the protection of 

seeds and bulbs from tree squirrels and voles. For structures, RO-PEL is applied as a spray or 

with a paintbrush to the point of runoff at the rate of 1 gallon per 1,000 to 4,000 sq. ft. The label 

allows for a second application in 2 to 7 days to improve effectiveness. Additionally, the product 

can be sprayed onto seeds and bulbs before planting to repel tree squirrels and voles. The label 

does not list application rates for seeds and bulbs. 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." Becker (2013) calculated an application rate for hyacinth bulbs of 4 ml product or 

0.000006 lb a.i. per bulb. Becker (2013) also calculated an application rate for grass seed of 

0.00008 to 0.0003 lbs a.i. per 1,000 sq. ft planted grass seed (equivalent to 2 to 8 fl. oz. product 

per 1,000 sq. ft). 

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Alternatives 

There are three animal repellent alternatives to denatonium saccharide for vertebrate pest control 

registered for use on outdoor surfaces, structures, trees, and bulbs: methyl nonyl ketone, 

capsaicin mixture, and thiram (NPIRS, 2014). 

There are 14 products containing methyl nonyl ketone is registered for use as an indoor/outdoor 

cat and dog repellent. The labeling specifies that it can be applied to furniture and rugs (indoors) 

and flower beds, lawns, trees, shrubbery, fences, patio furniture, and garbage cans/bags 

(outdoors). Methyl nonyl ketone has a shorter period of residual activity and needs to be 

reapplied daily. 

There are 9 registered products containing a mixture of capsaicin, garlic oil, and putrescent 

whole egg solids registered to repel squirrels and other animals from bulbs, flowers, grass, 

shrubs, plants, seedlings and trees (EPA Reg No 67356-1 ). These products are not labeled for 

seeds. These products have a strong aromatic smell that may be offensive to some users. 

Thiram is registered for use on trees, ornamentals, seeds and bulbs to repel rodents (O'Brien, 

1994; NPIRS, 2014; Thiram 480 DP label. 2012). 

In the absence of effective repellents, some users may resort to rodenticides for tree squirrel and 

vole control (Oregon State University, 2005) 

Non-chemical ways to control squirrels and voles include trapping, shooting, and tree removal 

(Jackson, 2005). Other control measures include placing chicken wire, hardware cloth, sharp 

gravel, or red pepper flakes over the planting area (O'Brien, 1994; Vanderlinden. 2012). 

Conclusions 

Denatonium saccharide is a bittering agent registered for use by residential consumers as a 

squirrel, vole, dog, and cat repellent on outdoor surfaces, structures, seeds and bulbs. 

Denatonium saccharide is used by only 0.017% of U.S. households. There are three alternatives 

to denatonium saccharide, however because each alternative can only be used on a subset of 

uses, users may only have one alternative for some uses (e.g. thiram for use on seeds). Some of 

the alternatives have constraints that may limit their usefulness. For example, methyl nonyl 

ketone has a shorter period of residual activity and needs to be reapplied daily. The capsaicin, 

garlic oil, and putrescent whole egg solid products have a strong aromatic smell that may be 

offensive to some users. Lastly, little is known about the comparative efficacy of the 

alternatives; therefore, the alternatives may not be as effective as denatonium saccharide. 

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References 

Becker, J .. 2013 [Revised] Application Rate Information for Uses ofRO-PEL, a Ready-To-Use 

Liquid Bittering Agent Containing Denatonium Saccharide (PC Code 129045), April24, 2013 

Brown, R. 2012. Email correspondence from the registrant, Roger Brown, MCB, LLC, to 

Andrea Mojica, EPA, 10/8/2012. 

Clegg, B. 2013. Denatonium benzoate. ChemistryWorld, Royal Society of Chemistry. 

http://www .rsc.org/ chemistryworld/20 13/04/ denatonium-benzoate-podcast 

CPSC. 1992. "Final Report Study of Aversive Agents" Consumer Product Safety Commission 

United States of America. 18 November 1992. 

http://www.cpsc.gov/LIBRARY/FOIA/foia99/os/aversive.pdf 

Jackson, J.J. 2005. Techniques to control and manage tree squirrel damage. Internet Center for 

Wildlife Damage Management. http://icwdm.org/handbook/rodents/TreeSquirrels.asp 

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

http://www .nixal ite.cornlropel.aspx 

NPIRS. 2014. National Pesticide Information Retrieval System. http:/ /npirs.ceris.purdue.edu 

O'Brien, J.M. 1994. Voles. [In Prevention and Control of Wildlife Damage) Cooperative 

Extension Division, University ofNebraska, Lincoln, NE. 

http://icwdm.org/handbook/rodents/ro b 177 .pdf 

Oregon State University. 2005. Voles and Their Control. Oregon State University. 

http://extension.oregonstate.edu/lane/sites/default/files/documents/lc725vole control.pdf 

Pierce, R. A. 2003. Controlling Voles in Horticulture Plantings and Orchards in Missouri 

http://extension.missouri.edu/explorepdf/agguides/wildlife/g09445.pdf 

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 

Thiram 480 DP label. 2012. Labeling for Thiram 480 DP, EPA Reg. No. 400-434. 

http://www.epa.gov/ pesticides/chem search/ppls/000400-00434-20 12071 1.pdf 

U.S. Census Bureau. 2012. Statistical Abstract of the United States: 2012. 

http://www.census.gov/compendialstatab/2012/tables/12s0059.pdf 

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Vanderlinden. 2012. How to Protect Bulbs from Squirrels. Organic Gardening. 

http ://organi cgarden ing.about.com/od/pestcontro l/a/How-To-Protect-But bs-F rom-Squirrels.htm 

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