January 18, 2011 

Docket ID No. EPA-HQ-OPP-2007-0935 

SUPPLEMENT TO 

NATURAL RESOURCES DEFENSE COUNCIL’S 

PETITION TO CANCEL PET COLLAR USES 

FOR THE PESTICIDE PROPOXUR 

On November 26, 2007, the Natural Resources Defense Council (NRDC) filed a petition to the 

U.S. Environmental Protection Agency (EPA) to, among other things, cancel all pet collar uses 

for the pesticide propoxur because of the unnecessary dangers posed by exposure to this toxic 

chemical, particularly in light of the alternatives available. To date, EPA has not responded. In 

April, 2009, NRDC supplemented its petition to EPA with its report “Poison on Pets II” showing 

unacceptably high residues from touching pets wearing propoxur-impregnated flea collars. This 

document incorporates the arguments from the original petition, the supplement to the original 

petition, and provides additional evidence of elevated risks to children from propoxur formulated 

pet collars. 

 

Since the filing of the two previous petitions, EPA has initiated a Registration Review for 

propoxur. As part of this review, new documents detailing exposure and risk information for pet 

collar uses of propoxur have been posted to the docket. These include a residential exposure and 

risk assessment for propoxur-formulated pet collars performed by EPA, and information 

provided by Sergeant’s Pet Care Products (one of the manufacturers of propoxur-formulated pet 

collars and EPA registrant) contesting the agency assessment and providing their own 

assessment.1 2 3

 Our analysis of the EPA documents and those provided by the manufacturer 

demonstrates evidence of an elevated risk to children from use of propoxur formulated pet 

collars. 

EPA’s assessment of children’s exposure to propoxur-formulated pet collars found unacceptably 

high risks. However, EPA’s assessment significantly underestimates risks from propoxurformulated collars by failing to assess dermal exposures, using inadequate estimates of children’s 

hand-to mouth behavior, and ignoring cancer risks. Furthermore, using the alternative residue 

levels submitted to EPA by Sergeant’s to calculate the risk also identifies elevated risks to 

children. 

                                                           

1

 EPA Memorandum dated April 7, 2010 Subject: Propoxur: Occupational and Residential Exposure and Risk 

Assessment for Propoxur Formulated Pet Collars Docket Number: EPA-HQ-OPP-2009-0806 

2

 EPA Memorandum dated July 12, 2010 Subject: Issues for Consideration Related to Propoxur: Occupational and 

Residential Exposure and Risk Assessment for Propoxur Formulated Pet Collars Docket Number: EPA-HQ-OPP2009-0806 

3

 Johnston, Jason E. 2010. Residential Risk Assessment for Post-application Exposures Associated with Pet Collars 

Containing Propoxur Using Rate of Release Data from Historical On-Animal Studies Docket Number: EPA-HQOPP-2009-0806 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

2

All the evidence before the Agency provides EPA with ample reason to cancel pet uses for 

propoxur. EPA should immediately take action on their own assessment and the evidence 

presented here to protect children from these dangerous products and cancel pet uses of 

propoxur. 

EPA’s Assessment of Children’s Exposure to Propoxur Formulated Pet Collars Found 

Unacceptable Risks. 

In a memorandum dated April 7, 2010, EPA detailed the results of its most recent occupational 

and residential exposure and risk assessment for propoxur formulated pet collars.4

 This 

assessment found Margins of Exposure (MOEs)5

 ranging from 20 to 62 for child incidental oral 

ingestion risk. These values are significantly less than the Agency’s threshold for safety of 1000 

and the document concluded that the “risks are of concern to the Agency”.6

 The calculations in 

this assessment were refined in a follow-up memorandum, dated July 12, 2010, and the new 

MOEs ranged from 55 to 82. 7 Together the calculations presented in these two memos are 

hereinafter referred to as the “2010 risk assessment”. (See Table 1 for exposure parameters and 

Appendix A for relevant exposure algorithm and calculation method). 

   

                                                           

4

 EPA Memorandum dated April 7, 2010 Subject: Propoxur: Occupational and Residential Exposure and Risk 

Assessment for Propoxur Formulated Pet Collars Docket Number: EPA-HQ-OPP-2009-0806 

5

 The Margin of Exposure (MOE) is the ratio of the estimated dose to the level of safe exposure. The lower the 

MOE the higher the risk. 

6

 EPA Memorandum dated April 7, 2010 Subject: Propoxur: Occupational and Residential Exposure and Risk 

Assessment for Propoxur Formulated Pet Collars Docket Number: EPA-HQ-OPP-2009-0806 

7

 EPA Memorandum dated July 12, 2010 Subject: Issues for Consideration Related to Propoxur: Occupational and 

Residential Exposure and Risk Assessment for Propoxur Formulated Pet Collars Docket Number: EPA-HQ-OPP2009-0806 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

3

Table 1: Residential post application for only hand‐to‐ mouth exposures using EPA (2010) transferable

residue calculations and unrealistic exposure assumptions from EPA’s (2010) residential exposure and

risk assessment.

Variable Source

Wellmark

Dog Collar

Wellmark

Cat Collar

Sergeant’s

Dog Collar

Sergeant’s

Cat Collar

Weight  of the collar (g)

EPA (2010)

Residential

Exposure and  

Risk Assessment

for Propoxur

Formulated Pet

Collars

34 10.5 30 14

AR* (Wellmark 10% ‐ 

Sergeant’s 9%) (g) 3.4 1.05 2.7 1.26

F(AR) 0.2 0.2 0.2 0.2

SA(pet) (cm2) 5986 2737 5986 2737

SAL 0.5 0.5 0.5 0.5

SA(hands) (cm2) 20 20 20 20

Freq (events/day) 1 1 1 1

BW (kg) 15 15 15 15

Daily Transferable

residue (mg/cm2‐day) 0.008 0.005 0.006 0.006

  

Dose (mg/kg) ‐ 

ingestion     0.005 0.003 0.004 0.004

NOAEL (mg/kg‐day)     0.28 0.28 0.28 0.28

MOE     55 82 70 68

* See Appendix A for abbreviations and calculation algorithms.

Although these refined MOEs are higher, they are still well below 1000 and thus still represent 

an inadequate margin of safety. Due to the unacceptable risks determined in this assessment, 

EPA should immediately cancel pet uses of the pesticide propoxur. 

EPA’s Residential Exposure and Risk Assessment Significantly Underestimates Health 

Risks From Propoxur In Pet Collars. 

The most recent risk assessment conducted by EPA continues to be flawed, as has EPA’s past 

risk assessments for propoxur. In the 2010 risk assessment, EPA failed to consider the risks 

from dermal exposure to propoxur in pet collars. Furthermore, as NRDC has mentioned time 

and again, EPA makes faulty assumptions about toddlers.8

 Specifically, EPA either makes 

unrealistic assumptions about, or completely ignores aspects of, toddlers’ mouthing behavior. 

And finally, EPA completely ignores the cancer risk associated with this pesticide. These 

deficiencies in the risk assessment make a pesticide that EPA has already identified as of concern 

even more problematic. 

                                                           

8

 NRDC comments on the EPA Organophosphate Cumulative Risk Assessment (October 2, 2006) EPA docket EPAHQ-OPP-2006-0618. Supplement to Natural Resources Defense Council Petition To Cancel Pet Collar Uses For 

The Pesticide Propoxur (April 23, 2009) EPA docket EPA-HQ-OPP-2009-0207-0003. 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

4

Failure to Assess Dermal Exposures 

EPA’s 2010 residential risk assessment of exposure to propoxur-formulated flea collars ignored 

the risks associated with absorbing propoxur through the skin. EPA incorrectly claims in the 

occupational and residential risk assessment that there are no data on rates of dermal absorption 

for propoxur.9 However, the 1997 Reregistration Eligibility Determination for propoxur cites a 

human study that found a 20% dermal absorption rate.10 Normal activity with a pet, including 

petting and hugging, would be expected to result in dermal contact ranging from the surface of 

the hands to a significantly larger skin surface area. This exposure pattern was included in the 

risk assessment performed for pet uses of the pesticide dichlorvos (DDVP), in which EPA 

calculated dermal exposures based on one pet hug per day. Given this evidence, risk assessments 

for pet uses of propoxur must include calculation of dermal exposure. 

Adjusting EPA’s risk calculation from the residential exposure assessment to include the dermal 

exposure resulting from one pet hug per day results in an estimated dose for dog and cat collars 

ranging from 0.194 to 0.158 mg/kg-day and MOEs of 1 or 2. This represents up to a 40 fold 

increase in the risk compared to EPA’s 2010 risk assessment. (See Table 2 for exposure 

parameters and Appendix A for relevant exposure algorithm and calculation method). 

   

                                                           

9

 EPA Memorandum dated April 7, 2010 Subject: Propoxur: Occupational and Residential Exposure and Risk 

Assessment for Propoxur Formulated Pet Collars Docket Number: EPA-HQ-OPP-2009-0806 

10 US EPA 1997. Reregistration Eligibility Decision (RED) Propoxur. EPA-738-R-97-009. page 20. 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

5

Table 2: Residential post application for hand‐to‐ mouth and dermal exposures using EPA (2010)

transferable residue calculations and keeping EPA (2010) unrealistic exposure assumptions for hand‐to‐

mouth and adding a conservative estimate of dermal exposures following EPA guidance.

Variable Source

Wellmark

Dog Collar

Wellmark

Cat Collar

Sergeant’s

Dog Collar

Sergeant’s

Cat Collar

Weight  of the collar (g)

EPA (2010)

Residential

Exposure and  

Risk Assessment

for Propoxur

Formulated Pet

Collars

34 10.5 30 14

AR (Wellmark 10% ‐ 

Sergeant’s 9%) (g) 3.4 1.05 2.7 1.26

F(AR) 0.2 0.2 0.2 0.2

SA(pet) (cm2) 5986 2737 5986 2737

SAL 0.5 0.5 0.5 0.5

SA(hands) (cm2) 20 20 20 20

Freq (events/day) 1 1 1 1

BW (kg) 15 15 15 15

SA(hug)   1875 1875 1875 1875

Freq (events/day)

1 hug per day

scenario 1 1 1 1

Fraction absorbed  

EPA (1997)

Propoxur RED 0.2 0.2 0.2 0.2

Daily transferable

residue (mg/cm2‐day)     0.008 0.005 0.006 0.006

  

Dose (mg/kg‐day) ‐ 

ingestion     0.005 0.003 0.004 0.004

Dose (mg/kg‐day)‐ 

dermal     0.189 0.128 0.150 0.153

Total Dose (mg/kg‐day)     0.194 0.131 0.154 0.158

NOAEL (mg/kg‐day)     0.28 0.28 0.28 0.28

MOE     1 2 2 2

Underestimation of Children’s Hand-to-Mouth Behavior 

In the 2010 residential risk assessment, EPA assumed that a child would have only one hand-tomouth event per day after exposure to a treated pet. This assumption is not substantiated by 

either the available literature or by EPA’s own previous risk assessments for pet products. A 

meta-analysis performed by Xue et al. (2007) reported a mean hand-to-mouth activity for 1-2 

year olds of 19.6 events per hour. 11 Residential post-application exposure to pesticides in flea 

collars in the Organophosphate Cumulative Risk Assessment (2006) uses a “most likely” value 

of nine events per hour.12 EPA’s assessment of DDVP, which had been used in pet collars, 

                                                           

11 Xue, J., Zaratarian,V., Moya,J., Freeman, N., Beamer, P., Black, K., Tulve, N., and Shalat,S. 2007 “ A MetaAnalysis of Children’s Hand-to-Mouth Frequency Data for Estimating Nondietary Ingestion Exposure.” Risk 

Analysis, 27:2 12 EPA. 2006. Organophosphate Cumulative Risk Assessment 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

6

assumed that toddlers were exposed for 2 hours per day.13 The assumptions in the 2010 propoxur 

risk assessment are unrealistic, inconsistent with previous agency findings, and significantly 

underestimate actual risk to toddlers. 

The effect of this low assumption for hand-to-mouth events in the 2010 propoxur risk assessment 

is that EPA significantly underestimates the potential dose to a child from exposure to a pet 

collar. This is illustrated by adjusting EPA’s risk calculation from the residential exposure 

assessment to use more reasonable hand-to-mouth variable exposure parameters from other EPA 

risk assessments. For example, using EPA’s “most likely” assumption of nine hand-to-mouth 

events from the OP Cumulative Risk Assessment and the two hours per day exposure from the 

DDVP risk assessment, would result in dose estimates ranging from 0.061 to 0.091 mg/kg - day 

for dog and cat collars and corresponding MOEs from 3 to 5. (See Table 3 for exposure 

parameters and Appendix A for relevant exposure algorithm and calculation method.) This 

represents up to a 20 fold increase in the dose compared to EPA’s 2010 risk assessment. 

Table 3: Residential post application for only hand‐to‐ mouth exposures using EPA (2010) transferable

residue calculations and more realistic hand‐to‐mouth exposure parameters from other EPA risk

assessments for pet collars.

Variable Source

Wellmark

Dog Collar

Wellmark

Cat Collar

Sergeant’s

Dog Collar

Sergeant’s

Cat Collar

Weight  of the collar (g)

EPA (2010)

Residential

Exposure and  Risk

Assessment for

Propoxur

Formulated Pet

Collars

34 10.5 30 14

AR (Wellmark 10% ‐ 

Sergeant’s 9%) (g) 3.4 1.05 2.7 1.26

F(AR) 0.2 0.2 0.2 0.2

SA(pet) (cm2) 5986 2737 5986 2737

SAL 0.5 0.5 0.5 0.5

SA(hands) (cm2) 20 20 20 20

BW (kg) 15 15 15 15

Mouthing events

(events/hr)

EPA (2006) CRA for

Organophosphates 9 9 9 9

Duration of exposure

(hrs/day)

EPA (2006) RED

DDVP 2 2 2 2

Freq (events/day) =

events/hour * hours/day

= events/hour *

hours/day 18 18 18 18

Daily transferable

residue (mg/cm2‐day)     0.008 0.005 0.006 0.006

  

Dose (mg/kg‐ day) ‐ 

ingestion     0.091 0.061 0.072 0.074

NOAEL (mg/kg‐day)     0.28 0.28 0.28 0.28

MOE     3 5 4 4

                                                           

13 EPA (2006) Reregistration Eligibility Determination for Dichlorovos (DDVP) EPA-738-R-06-013 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

7

The exposure calculation in Table 3 assumes that a toddler’s hand is equally replenished with 

pesticide residue after each mouthing event. Wellmark International contends that this 

assumption is incorrect. Specifically, in comments submitted to EPA in opposition to NRDC’s 

petition to cancel pet uses of propoxur, Wellmark claimed that a child’s hands would not be 

replenished with the same residue level each time because pesticide residues would be 

concentrated near the collar and, once removed due to petting activity, would not be replaced 

right away. Wellmark also claimed that it would be unrealistic to assume that a child would fully 

replenish their fingers multiple times an hour.14 However, as explained below, there is sufficient 

evidence to support retaining this assumption when assessing exposures from propoxur 

formulated pet collars. 

A child actively playing with a pet is in regular contact with the pet’s fur. The EPA risk 

calculation assumes that the palmar surface of three fingers, equivalent to 20 cm2 of finger 

surface area, are inserted in the mouth per mouthing event. However, regular petting behavior 

involves contact of the whole hand with the fur and pesticide residues, meaning a larger area 

than just three fingers would pick up residue during each petting event. If each petting event 

transfers pesticide residue to the palmar surface of both hands of a child this equals 66.7 cm2

 of 

contaminated finger surface area and 176 cm2

 of the total hand surface area.15 16 Therefore, the 

exposure scenario of nine mouthing events per hour consisting of an equal, and maximal, level of 

residue, from other EPA risk assessments for pet products, can be achieved a number of ways. 

This includes nine separate petting and mouthing events or, if the child were to mouth different 

fingers during each event, both hands would only need to be replenished (through petting) about 

three times (every 20 minutes).17 If the child were to mouth the palmar surface of the fingers and 

the palm following a petting event, the same level of exposure would be achieved after just one 

hand replenishment per hour. 18 Therefore, this exposure scenario can be understood to represent 

a range from one to nine petting events per hour (or every 7 to 60 minutes) where the hands are 

replenished with pesticide residue, which is not inconsistent with normal child/pet interactions. 

Furthermore, Wellmark’s concern that there would be insufficient residue on the pet’s fur to 

support this exposure scenario is without merit. EPA’s exposure scenario of nine mouthing 

events consisting of the palmar surface of three fingers equals contact with 180 cm2

 of residue 

contaminated fur per hour, or 3% of the surface area of the default sized dog.19 On a treated pet 

there is likely to be at least this amount of fur with the maximal pesticide residue available for a 

child to fully replenish his or her hands. Therefore, the same level of residue would be available 

for potential ingestion for each mouthing event and this assumption should be conserved in the 

risk assessment. 

                                                           

14 Wellmark International. 2009. Comments Submitted in Response to: Petition Requesting Cancellation of 

Propoxur Pet Collar Uses; Notice of Availability. April 9, 2009. FR 74 (66): 15980-15981. Docket ID No.: EPAHQ-Opp-2009-0207. 

15 (20cm2

/3 fingers) * 10 fingers = 66.7 cm2. 16 Palmar surface of both hands is assumed to equal half the total surface area of a child’s hands (350cm2

/2 = 176 

cm2

). EPA.1997. Standard Operating Procedure for Residential Exposure Assessment. 17 Nine mouthing events *20 cm2

 = 180cm2 of mouthed area per hour. 180 cm2/66.7 cm2 per petting event = 2.69 or 

3 petting events per hour. 

18 180 cm2

/176 cm2 per petting event = 1.02 or 1 petting event per hour. 

19 180 cm2

 per hour /5986 cm2 per dog = 3% per hour for contact with one dog. 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

8

EPA also ignored “indirect” hand-to-mouth activity, which is the exposure from toddlers who 

touch an object or food with pesticide-contaminated hands and then put that object or food into 

their mouths. However, published studies show that there is actually noticeable indirect hand to 

mouth activity in infants and children. In fact, one study found that, on average, a toddler will 

touch an object and then put that object into his or her mouth 15 times in one hour. At the high 

end of the study’s distribution (90th percentile), that rate rises to 66 times per hour.20 This same 

study found a statistically significant positive correlation between the frequency of object or food 

in mouth activity and blood lead levels. 

Taken together, this evidence demonstrates that the risk to children from pet collar uses is 

substantially greater than EPA calculated in its 2010 risk assessment due to significant 

underestimates in hand-to-mouth exposures stemming from inadequate assumptions of hand-to 

mouth frequency and failure to include indirect hand-to-mouth exposures. 

In total, when a conservative estimate of dermal exposure is added to the more realistic estimates 

of children’s hand-to-mouth exposures used in previous EPA risk assessments, the estimated 

dose is about 56 times greater than what is described in EPA’s 2010 risk assessment.21 These 

calculations demonstrate the degree to which the exposure calculations used in the 2010 risk 

assessment are inadequate and result in a significant underestimate of risks to children from 

propoxur formulated pet collars. 

Failure to Consider Cancer Risks 

Propoxur is classified as a Group B2 Probable Human Carcinogen with a unit risk Q1* of 3.7 x 

10-3.

22 It is also listed as a chemical known to the state of California to cause cancer under 

California’s Safe Drinking Water and Toxic Enforcement Act.23 As of December 2010, all 

propoxur-formulated flea collars sold in California carry the required warning label indicating 

that propoxur is a known carcinogen. Despite this evidence of propoxur’s carcinogenicity, EPA 

failed to include a cancer risk assessment in the 2010 risk assessment based on the stated 

explanation that the cancer determination was based on exposures “orders of magnitude greater 

than what is currently allowable for propoxur”.24 However, as explained below, EPA’s 

justification is both insufficient and inaccurate. 

Taking into account the revised hand-to-mouth frequency and dermal exposure adjustments to 

the dose calculation used above for children’s exposures, and assuming adult exposure is limited 

to dermal exposure from one pet hug per day, the lifetime cancer risk is around 5.01 x 10-4 or 

                                                           

20 Ko,S., Schaefer, P.D., Vicario, C.M., and Binns, H.J. 2007.“Relationship of Video Assessments of Touching and 

Mouthing Behaviors During Outdoor Play in Urban Residential Yards to Parental Perceptions of Child Behaviors 

and Blood Lead Levels.” Journal of Exposure Science and Environmental Epidemiology. 21 Sum of dermal dose plus revised hand to mouth for Wellmark Dog collar (0.189 mg/kg-day + 0.091mg/kg-day = 

0.28 mg/kg-day). Revised dose compared to EPA estimate from 2010 risk assessment = 0.28/0.005 = 56. 

22 US EPA 1997. Reregistration Eligibility Decision (RED) Propoxur. EPA-738-R-97-009 23 California Health and Safety Code Section 25249.6 (commonly referred to as “Proposition 65.” 

24 EPA Memorandum dated April 7, 2010 Subject: Propoxur: Occupational and Residential Exposure and Risk 

Assessment for Propoxur Formulated Pet Collars Docket Number: EPA-HQ-OPP-2009-0806 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

9

about 500 per million exposed.25 (See Appendix B for calculation) This cancer risk exceeds 

EPA’s acceptable risk range of 1 to 100 per million exposed.26 In addition, it is likely an 

underestimate because it does not account for increased early life susceptibility, adult hand-tomouth exposures, and relies on low-end estimates of dermal exposures. This calculation 

demonstrates that there is a significant cancer risk associated with exposures from propoxur 

formulated pet collars that should be included as part of the residential exposure assessment. 

Even the Registrant’s Transferable Residue Calculations Result in Unacceptable Risks to 

Children. 

In study dated June 22, 2010, registrant Sergeant’s Pet Care Products claimed that the EPA 2010 

risk assessment overestimated the levels of pesticide residue to be expected 15 days following 

application of the pet collar. Instead, Sergeant’s proposed two alternate mechanisms for 

calculating the amount of pesticide residue likely to be transferred to the hand of a child and then 

calculated the dose and MOE associated with those adjusted residues using EPA’s 2010 risk 

assessment assumptions. 

Based on Sergeant’s first adjustment to the rate of propoxur released from the collar, the dose 

calculated using EPA’s exposure assessment assumption for a medium dog was 0.000770 

mg/kg-day with a MOE of 466, which is less than EPA’s safety margin (MOE of 1000) and 

therefore represents an unacceptable risk. Sergeant’s made an additional adjustment to the 

amount of residue expected to transfer to a child’s hand. Based on that second adjustment, 

Sergeant’s calculated the dose to be 0.0000932 mg/kg-day and the MOE to be 3,000. 

However, as we discussed above, EPA’s assessment (and by extension, Sergeant’s calculations) 

uses unrealistically low estimates of hand-to-mouth activity and fails to include dermal 

exposures. A calculation using a more comprehensive exposure assessment (as in the examples 

given above) and using both of Sergeant’s adjustments for the residue that would be transferred 

onto a child’s hand, results in dose estimates ranging from 0.005 to 0.007 mg/kg-day and MOEs 

between 42 and 54 for Sergeant’s products. (See Figure 4, for exposure parameters and 

Appendix A for relevant exposure algorithm and calculation method.) These MOEs are far less 

than EPA’s safety margin (MOE of 1000) and represent an unacceptable risk to children. 

 

                                                           

25 As per EPA guidance, children’s exposure pattern was used up to age 5. Cancer risk was calculated as the 

weighted average exposure over a 70 year lifetime. 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

10

Figure 4: Residential post application for hand‐to‐ mouth and dermal exposures using Sergeant’s

transferable residue calculations and exposure parameters from EPA risk assessments for other pet

collars.

Variable Source

Sergeant’s  

Dog Collar

(medium)

Sergeant’s  

Dog Collar

(large)

Sergeant’s

Cat Collar

Weight  of the collar (g)

Sergeant’s 2010

Comments

submitted to EPA

25 32 14

AR‐Total  ( 9%) (g) 2.25 2.88 1.26

AR  ‐ 15 days (18%) (g) 0.405 0.5184 0.2268

F(AR) ‐ adjusted 0.031 0.031 0.031

SA(pet) (cm2) EPA (2010)

Residential

Exposure and  Risk

Assessment for

Propoxur

Formulated Pet

Collars

5986 5986 2737

SAL 0.5 0.5 0.5

SA(hands) (cm2) 20 20 20

BW (kg) 15 15 15

SA(hug)   1875 1875 1875

Mouthing events (events/hr)

EPA (2006) CRA for

Organophosphates 9 9 9

Duration of exposure

(hrs/day)

EPA (2006) RED

DDVP 2 2 2

Freq (mouthing events/day)  

= events/hour *

hours/day 18 18 18

Freq (events/day)

1 hug per day

scenario 1 1 1

Fraction absorbed  

EPA (1997)

Propoxur RED 0.2 0.2 0.2

Daily transferable residue

(mg/cm2‐day)     0.0001 0.0002 0.0002

  

Dose (mg/kg‐day) ‐ ingestion     0.002 0.002 0.002

Dose (mg/kg‐day)‐ dermal     0.003 0.004 0.004

Total Dose (mg/kg‐day)     0.005 0.007 0.006

NOAEL (mg/kg‐day)     0.28 0.28 0.28

MOE     54 42 44

 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

11

Conclusion 

Taken together, the evidence provided here and in previous NRDC submissions demonstrates 

children can be exposed to levels of propoxur that significantly exceed the reference dose. 

Therefore, EPA must exercise its statutory obligation to protect children by cancelling all pet 

collar uses of propoxur. 

Respectfully submitted, 

Miriam Rotkin-Ellman, MPH 

Gina Solomon, MD, MPH 

Mae Wu, Esq. 

Natural Resources Defense Council 

 
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

12

APPENDIX A: Exposure Assessments Algorithms

Abbreviations

TR = Transferable Residue

SAL = Saliva Extraction Factor

SAhands = Hand Surface Area

SApet = Pet Surface Area

SAhug = Child’s Hug Surface Area

Freq = Frequency of Events

BW = Body Weight

AR = Application Rate

FAR = Fraction available on pet’s body

MOE = Margin of Exposure

Residential Post‐application incidental oral ingestion (hand‐to‐mouth)

Dose (mg/kg‐day) = (Transferable residue (TR) * Saliva extraction factor (SAL) * Hand surface area

(SAhands) *Frequency of events (Freq))/Body Weight (BW)

Transferable residue (mg/cm2

) = (Application Rate (AR) *Fraction available on pet’s body (FAR))/Surface

Area of pet (SApet)

Daily transferable residue (mg/cm2

‐day) = TR/15 days

MOE = No Observed Adverse Effect Level/Dose  

Source: US EPA (2010). Propoxur: Occupational and Residential Exposure and Risk Assessment for

Propoxur Formulated Pet Collars

Residential Post‐application dermal exposures

Dose (mg/kg‐day) = (Transferable residue (TR) * Dermal absorption factor * Surface area of child hug

(SAhug) *Frequency of events (Freq))/Body Weight (BW)

Total Dose (mg/kg‐day) = Hand to Mouth + Dermal

Source: US EPA (2006). Reregistration Eligibility Determination for Dichlorovos (DDVP) EPA 738‐R‐06‐013
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

13

Appendix B: Cancer Risk Assessment

Cancer Risk = Sum(Cancer potency factor *dose *lifetime exposure weighting factor)

Lifetime exposure weighting factor = number of years in group/70

Table 4: Residential post application for hand‐to‐ mouth and dermal exposures using EPA (2010)

transferable residue calculations and exposure parameters from EPA risk assessments for other pet

collars –CHILD (0 – 5 years)

Variable Source

Wellmark

Dog Collar

Wellmark

Cat Collar

Sergeant’s

Dog Collar

Sergeant’s

Cat Collar

Weight  of the collar

(g)

EPA (2010)

Residential

Exposure and  Risk

Assessment for

Propoxur

Formulated Pet

Collars

34 10.5 30 14

AR (Wellmark 10% ‐ 

Sergeant’s 9%) (g) 3.4 1.05 2.7 1.26

F(AR) 0.2 0.2 0.2 0.2

SA(pet) (cm2) 5986 2737 5986 2737

SAL 0.5 0.5 0.5 0.5

SA(hands) (cm2) 20 20 20 20

BW (kg) 15 15 15 15

SA(hug)   1875 1875 1875 1875

Mouthing events

(events/hr)

EPA (2006) CRA for

Organophosphates 9 9 9 9

Duration of exposure

(hrs/day)

EPA (2006) RED

DDVP 2 2 2 2

Freq (mouthing

events/day)      18 18 18 18

Freq (events/day)

1 hug per day

scenario 1 1 1 1

Fraction absorbed  

EPA (1997)

Propoxur RED 0.2 0.2 0.2 0.2

Daily Transferable

residue (mg/cm2‐day)     0.008 0.005 0.006 0.006

  

Dose (mg/kg‐day) ‐ 

ingestion     0.091 0.061 0.072 0.074

Dose (mg/kg‐day)‐ 

dermal     0.189 0.128 0.150 0.153

Total Dose (mg/kg‐

day)     0.280 0.189 0.223 0.227

   
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

14

Table 5: Residential post application for only dermal exposures using EPA’s Transferable Residue

Assumptions – and exposure parameters from EPA risk assessments for other pet collars. ADULT (6 – 70

years)

Variable Source

Wellmark

‐ Dog

Collar

Wellmark

Cat Collar

Sergeant’s

Dog Collar

Sergeant’s

Cat Collar

Weight  of the collar (g) EPA (2010)

Residential Exposure

and  Risk

Assessment for

Propoxur

Formulated Pet

Collars

34 10.5 30 14

AR (Wellmark 10% ‐ 

Sergeant’s 9%) (g) 3.4 1.05 2.7 1.26

F(AR) 0.2 0.2 0.2 0.2

SA(pet) (cm2) 5986 2737 5986 2737

BW (kg) 70 70 70 70

SA(hug)   5625 5625 5625 5625

Freq (events/day)

1 hug per day

scenario 1 1 1 1

Fraction absorbed  

EPA (1997) Propoxur

RED 0.2 0.2 0.2 0.2

Daily Dislodgeable

residue (mg/cm2‐day)     0.008 0.005 0.006 0.006

  

Dose (mg/kg‐day)‐ 

dermal     0.122 0.082 0.097 0.099

   
 Supp. to NRDC petition to cancel pet collar uses for propoxur 

Docket ID No. EPA-HQ-OPP-2007-0935

15

15

Table 6: Cancer Risk

Age category

Dose mg/kg‐day

Cancer

Potency

Factor

weighting

factor

Ri

Wellmark

Dog

Collar

WellmarkCat Collar

Sergeant’s

Dog Collar

Sergeant’s

Cat Collar

Wellmark

Dog

Collar

WellmarkCat Collar

0 to <6 0.280 0.189 0.223 0.227 0.0037 0.09 8.89E‐05 8.89E‐05 6 to 70 0.12 0.08 0.10 0.10 0.0037 0.91 4.12E‐04 4.12E‐04 Total ‐ lifetime 1 5.01E‐04 5.01E‐04 Total ‐ lifetime

per million 501 501