UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

CERTIFIED MAIL 

Miriam Rotkin-Ellman 

Gina Solomon, MD, MPH 

Mae Wu, Esq. 

Natural Resources Defense Council 

111 Sutter Street, 20'h F loor 

San Francisco, C1\ 94104 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

November 6, 2014 

Re: Response to atural Resources Defense Council's April23, 2009 Petition Requesting 

Cancellation of All Pet Uses ofTetrachlorvinphos 

Dear Ms. Rotkin-Ellman, Dr. Solomon, and Ms. Wu: 

This letter constitutes the Environmental Protection Agency's (EPA or the Agency) 

response to the Natural Resources Defense Council's (NRDC) petition dated April23, 2009 

(Petition) requesting that EPA cancel all pet uses of the pesticide tetrachlorvinphos (TCVP). For 

the reasons identified below, the Agency denies NRDC's request to cancel all pet uses ofTCVP. 

The Petition asserts that EPA's revised human health risk assessment and organophosphate 

(OP) cumulative risk assessment underlying EP r\'s 2006 Reregistration Eligibility Decision (RED) 

for TCVP failed to adequately assess residential exposures to pet collars, and also presents N RDC's 

April, 2009 " Issue Paper" entitled "Poisons on Pets II: Toxic Chemicals in Flea and Tick Collars." 

The Petition concludes that EPA's 2006 RED for TCVP is "arbitrary and capricious, and contrary 

to law," and that "EPA must ... cancel all pet uses of [fCVP]." Petition at 6. As explained below, 

in response to NRDC's Petition, EPA has conducted an updated non-occupational residential 

exposure assessment for all TCVP pet product uses. Based on that assessment, EPA does not find 

risks of concern resulting from pet uses of TCVP and therefore declines today to initiate 

cancellation action against such uses as requested in the Petition. While EPA believes that the 

updated risk assessment addresses the arguments raised in N RDC's petition regarding whether 

TCVP pet uses pose unacceptable risks, EPA declines to revisit the 2006 RED or to perform a new 

cumulative risk assessment for organophosphates at this time, and notes that registration review of 

TCVP is currently underway, pursuant to section 3(g) of the Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRJ\), 7 U.S.C. § 136a(g), and 40 CFR Part 155. 

The ftrst section of this letter discusses the factual background relevant to NRDC's Petition. 

The second section of this letter summarizes the claims made in NRDC's Petition. The third 

section of this letter responds to those claims by discussing the assumptions, routes of exposure 

considered, and conclusions reached in EPA's updated non-occupational residential exposure 

assessment for all TCVP pet product uses, conducted in response to NRDC's Petition. The fourth 

section of this letter is the conclusion. 
I. Background 

TCVP is a member of the organophosphate (OP) class of pesticides. Like other OPs, 

TCVP's mode of action involves the inhibition of the enzyme acetylcholinesterase (AChE). 

The RED for TCVP was initially completed in September 1995. An interim Tolerance 

Reassessment Eligibility Decision (TRED) for TCVP was completed in July 2002. A ~esidential 

exposure assessment was originally completed in 1998 in support of the TRED, and concluded that 

residential risks to handler and post-application exposure were below the Agency's levels of concern. 

The residential assessment was refmed in 2002. Both the TRED and 1998 assessment can be found 

in public docket number EPA-HQ-OPP-2002-0295 at www.regulations.gov. The Agency 

completed the OP cumulative risk assessment in July 2006, and as a result the TCVP TRED and 

RED were considered fmal at that time, and can be found in public docket number EPA-HQ-OPP2006-0618. An update to the OP Cumulative risk assessment was completed in August 2006. There 

were no risks of concern identified in the residential assessment portion of the OP Cumulative, 

which considered exposure from the pet uses of TCVP. Additionally, the registration review docket 

for TCVP opened in 2008, and registration review is currently on-going. All registration review 

documents, as well as the RED, can be found in public docket number EPA-HQ-OPP-2008-0316. 

On June 5, 2009, EPA announced receipt of NRDC's Petition to cancel all pet uses for 

TCVP in the Federal Register (74 FR 27035) and posted the petition in public docket number EPAHQ-OPP-2009-0308 in regulations.gov for a 60-day public comment period, during which time 

interested stakeholders could review and comment on the Petition. The public comment period 

ended on August 4, 2009, during which time EPA received approximately 8,600 form letters as part 

of a mass campaign supporting NRDC's petitions to ban TCVP pet uses and propoxur pet collars. 1 

In addition, the Agency also received a comment from The Humane Society of the United States 

(HSUS) that supported the petition and a comment from one TCVP registrant, Hartz Mountain 

Corporation, which opposed the petition. Substantive comments are addressed in a separate 

"Response to Comments" document, attached hereto as Appendix A. Regarding HSUS's comment 

about potential adverse reactions to TCVP of companion animals, the Agency is committed to 

studying this issue more closely to understand what additional measures, if any, may be appropriate 

to reduce the incidence of these unfortunate and avoidable events. While this comment does not 

pertain to the human !health issues raised by NRDC's Petition, the Agency will conduct an in-depth 

review and analysis of pet incident data resulting from pet products that contain TCVP during the 

registration review process for TCVP. 

Since the closing of the public comment period in 2009, the Agency has considered the 

Petition to cancel all TCVP pet products and the risks posed by TCVP pet products, especially to 

children. EPA has taken numerous steps to evaluate the concerns outlined in tl1e Petition, including 

the completion of a new TCVP residential risk assessment which incorporates the most recent 

science policies and risk assessment methodologies to assess all available TCVP pet product uses. 

The results of this new assessment are discussed in section III of this letter, below. 

1 On January 22,2014, EPA published in the Federal Register, pursuant to section FIFRA § 6(t), a notice of receipt 

of registrant requests to voluntarily cancel all propoxur pet collar registrations. See 79 Fed. Reg. 3586 (Jan. 22, 

2014). On March 26,20 14, EPA published in the Federal Register a notice announcing EPA's Order for the 

cancellation of all propoxur pet collar registrations. See 79 Fed .. Reg. 16793 (Mar. 26, 20 14). The effective date of 

the cancellations that are the subject of that Order is April 1, 2015. Accordingly, by letter dated October 9, 2014, 

EPA denied as moot NRDC's petition seeking cancellation of such registrations. 

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Along with the Petition, NRDC submitted an April, 2009 NRDC " Issue Paper" entitled 

"Poisons on Pets II: Toxic Chemicals in Flea and Tick Collars" (hereinafter "Poison on Pets II") for 

EPA's consideration of potential exposures from TCVP pet collars. However, this "Issue Paper" 

consisted only of the study overview and summarized fmdings along with a methodological 

appendix, and did not include the full study report including all the raw data. In a letter dated May 

28, 2009, the Agency requested additional scientific information from NRDC so that EPA could 

fully analyze and independently verify the results of the study report, including all raw data and the 

protocol for the pet residue study. EPA also requested information on the ethical conduct of the 

study regarding the use of human subjects, as requited by 40 CFR § 26.1303 under Subpart M -

"Requirements for Submission of Information on the Ethical Conduct of Completed Human 

Research." 

On June 25, 2009, NRDC submitted a response letter. Although NRDC's June 25, 2009 

letter included a copy of the original protocol intended to support NRDC's argument that the 

studies underlying the "Poison on Pets II" report were not "human studies" under 40 CFR Part 26, 

the letter did not include either the scientific information to enable EPA to verify the results of the 

study report or the information on the ethical conduct of the studies required by 40 CFR § 26.1303. 

NRDC's letter stated: 

" ... NRDC will await EPA's final determination that the study does not constitute 

research with human subjects and that the agency will include it as part of its assessment of 

our petitions. Once EPA makes that fmal determination, then we will provide the 

underlying data supporting our report." NRDC Letter, June 25,2009, at 3. 

In a letter dated August 7, 2009, EPA informed NRDC that the Agency (EPA's Office of 

Pesticide Programs, in consultation with EPA's Human Subjects Research Review Officer in the 

Office of the Science Advisor) still regarded the two studies described in the "Poison on Pets II' 

report as research with human subjects covered by EPA's rules in 40 CFR Part 26, "Protection of 

Human Subjects." 

To date, NRDC has not submitted the necessary raw data to allow EPA to verify the 

"Poisons on Pets II" study findings. No other scientific information has been provided that would 

afford the Agency with a rationale to rely upon this study report for regulatory actions under 

FIFRA. Without the raw scientific data, this information could not be considered in EPA's 

evaluation of NRDC's Petition. 

II. Petition Claims 

NRDC's Petition argues tl1at EPA did not assess tl1e exposure from pet collar uses in the 

risk assessment underlying the RED, and that assumptions made pertaining to toddler exposures to 

TCVP were flawed in the OP cumulative risk assessment. NRDC argues that the decision to 

reregister TCVP pet uses was thus arbitrary and capricious and contrary to law, and that risks from 

pet uses ofTCVP are unacceptable such that EPA should cancel such uses. 

NRDC makes the following arguments in support of its position: 

o NRDC Argues that EPA Failed to Consider Pet Collar Exposures: NRDC argues 

that despite finding that pet collar uses provided the highest exposure levels for adults, 

3 I 12 
EPA still chose not to conduct a risk assessment for pet collars, and that EPA ignored 

the possibility that the pet collar uses could expose infants and children to unsafe levels 

ofTCVP. 

o NRDC Argues that EPA Used Faulty Exposure Assumptions: NRDC argues that 

the EPA's organophosphate cumulative risk assessment for pet products significantly 

underestimated a toddler's exposure to residue on a pet from a flea collar. NRDC argues 

that the TCVP risk assessment assumed that toddlers were exposed for no more than 

one hom per day, but the EPA assumed a two hour per day exposure for toddlers in the 

dichlorvos (DDVP) case. NRDC fmther argues that EPA's underestimates include the 

use of hand-to-mouth activities at nine times per hour, while a published review of the 

scientific literature by EPA scie11tific experts indicated an average of19.6 times per hour. 

NRDC further argues that the Agency failed to assess indirect hand-to-mouth activity, 

which is the exposme from toddlers who touch an object or food with pesticidecontaminated hands and tl1en put that object or food into their mouths, willie published 

studies show that there is noticeable indirect hand to mouth activity in infants and 

children. 

o NRDC Argues that Pet Collars Result in Unacceptably High Exposures: NRDC 

argues that NRDC's report "Poison on Pets II" shows that residues ofTCVP on the 

pets' fur are high enough to pose a significant risk to both children and adults who play 

with their pets. 

III. EPA's Updated Risk Assessment for AD TCVP Pet Uses 

As noted above, in response to NRDC's Petition, EPA has conducted an updated nonoccupational residential exposure assessment for all TCVP pet product uses. Based on that 

assessment, EPA does not fmd risks of concern resulting from pet uses of TCVP and therefore 

declines today to initiate cancellation action against such uses as requested in the petition. While 

EPA believes that the updated risk assessment addresses the· arguments raised in NRDC's petition 

regarding whether TCVP pet uses pose unacceptable risks, EPA declines to revisit the 2006 RED or 

to perform a new cumulative risk assessment for organophosphates at this time, and notes that 

registration review ofTCVP is currently underway, pursuant to FIFRA § 3(g) and 40 CFR Part 155. 

In developing a response to this Petition, EPA considered, among other things, the 

information contained in the petition (to the extent it could without obtaining additional 

information from NRDC), new data relevant to the assessment of exposure from pet collars (i.e. , 

propoxur collar MRID 48589901), and updated residential exposure assessment metl1odologies, and 

the Agency completed a new residential exposure assessment for all TCVP pet product uses, entitled 

Tetrachlon1inphos: Residential Exposure Assmment in Response to tbe Natural ReJ·otmu Defeme Council Petition 

to Cancel All Pet U.res for Tetracbloroinphos, dated November 5, 2014 (Attached hereto as Appendix B). 

This assessment concludes that all risks associated with TCVP pet products are below the Agency's 

level of concern (LOC) for all exposure scenarios. The key points of the assessment are outlined 

below, as part of the evaluation of NRDC's claims in its Petition. 

EPA risk assessments rely on the most recent guidance and risk assessment methodologies 

available at the time they are completed. The human health risk assessments that NRDC's petition 

alleges failed to properly identify risks were originally completed in 1998 and 2006, and utilized 

exposure assumptions and methodologies based on Standard Operating Procedures (SOPs) for pet 

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product risk assessments in place at that time. The 2014 TCVP residential pet product assessment 

assessed residential handler and post-application risk from exposure to TCVP pet products using 

the Agency's 2012 SOPs for Residential Pesticide Exposure Assessment (available at 

http://w\v\v.epa.gov /opp00001 / science /EPA-OPP-HED Residential<Yo20SOPS Feb2012.pdf). 

Development of the 2012 SOPs included external peer review, including the Agency presenting a 

draft of the SOPs to the FIFIRA Scientific Advisory Panel (SAP) for comment in 2009. The 

updated residential exposure assessment also incorporates the following changes: 

• the assumption of steady state exposures for TCVP exposure assessment; 

• updated points of deparnue (PoDs) following re-evaluation of the TCVP toxicity database 

using the benchmark dose (BMD) techniques consistent with the methods currently used 

for other OPs; 

• reduction of the total uncertainty factor (UF) for inhalation exposures from 1 OOX to 30X 

due to use of the Agency's reference concentration (RfC) and human equivalent 

concentration (HEC) methodology; 

• voluntary cancellation ofTCVP trigger pump spray pet products (EPA Reg. Nos. 2596-122, 

2596-123, and 2596-136); 

• the re-evaluation of a previously submitted and reviewed pet residue transfer study for 

TCVl) dust/powder and pump spray formulations; and 

• the use of pet residue transfer study data specific to collar formulations. 

The following is a summary of the analysis and conclusions found in the new 2014 TCVP 

residential risk assessment, entitled Tetrachi017Jinphos: ReJidential Exposure Assessmmt in Response to the 

Natural Resourm D~feme Coundl Petition to Cancel All Pet Usesfor Tetrachlon;inphos. 

Toxicology and Uncertainf,v 1:-'acton· 

Like other OPs, the mode of action (NfOA) for TCVP involves inhibition of the enzyme 

AChE via phosphorylation of the serine residue at the active site of the enzyme. This inhibition 

leads to accumulation of acetylcholine and ultimately to neurotoxicity in the central and/ or 

peripheral nervous system. For TCVP, AChE inhibition is the most sensitive endpoint in the 

toxicology database in multiple species, durations, lifestages, and routes. 

The toxicology database for TCVP is complete. TCVP has low acute toxicity by the oral, 

dermal, and inhalation routes of exposure. It is a slight dermal irritant, a moderate eye irritant, and a 

dermal sensitizer. TCVP is classified as a possible human carcinogen (Group C) based on 

statistically significant increases in combined hepatocellular adenoma/ carcinomas in mice, and 

suggestive evidence of thyroid c-cell adenomas and adrenal pheochromocytomas in rats. The 

mutagenicity database for TCVP suggests that this chemical was not mutagenic in both the gene 

mutation assay and primary rat hepatocyte unscheduled DNA synthesis assay. However, this 

chemical was positive for inducing chromosomal aberrations in Chinese hamster ovary cells in the 

absence of metabolic activation, but was negative in the presence of metabolic activation. 

lmmunotoxicity was not observed at dose levels that exceed the limit dose. 

As with other OPs, TCVP exhibits a phenomenon known as steady state AChE 

inhibition. After repeated dosing at the same dose level, the degree of inhibition comes into 

equilibrium with the production of new, uninhibited enzyme. At this point, the amount of AChE 

inhibition at a given dose remains consistent across duration. In general, OPs reach steady state 

5/12 
within 2-3 weeks, but this can vary among OPs. TCVP shows a shallow dose-response curve for 

cholinesterase inhibition; in other words, large increases in administered dose result in only small 

changes in AChE inhibition. 

Based on the robust dataset from the OP cumulative risk assessment across the OPs, 

exposure assessments of 21 days and longer will be conducted for all routes of exposure; i.e., oral, 

dermal, and inhalation, for all single chemical OP assessments. Given this, the 21-day and longer 

exposure assessment is scientifically supportable and also provides consistency with the OP 

cumulative risk assessment and across the OP registration review risk assessments. 

The Food Quality Protection Act (FQPA) children's safety factor (SF) was reduced to lX 

since there is no evidence of sensitivity of the young animal compared to the adult and there are no 

data gaps. A total uncertainty factor (UF) of lOOX is appropriate for dermal and incidental oral 

routes of exposure (1 OX for interspecies extrapolation, 1 OX for intraspecies variation, and 1 X 

FQPA SF). For the inhalation route of exposure, a total SF of 30X (3X for interspecies 

extrapolation, l OX for intraspecies variation, and lX FQPA SF) is appropriate. The interspecies 

extrapolation is reduced from lOX to 3X because the reference concentration (RfC) methodology 

for inhalation is used to determine a human equivalent concentration (HEC) and takes into 

consideration the pharmacokinetic differences between animals and humans. 

ReJidentia/ Handler E>..pOJum 

Residential exposures are anticipated from the use ofTCVP pet products. Residential 

TCVP handler exposures are anticipated to be short- (1 to 30 days) to intermediate-term (1 to 6 

months) in duration. However, because of the steady state AChE inhibition exhibited by the OPs, 

steady state exposures (21 days and longer) were assessed and presented for residential exposures to 

TCVP pet products. 

Residential handler exposures to TCVP pet products may occur via the dermal or inhalation 

routes while the product is placed on a cat or dog. A steady state residential handler exposure 

assessment (combined dermal and inhalation) was performed for homeowners applying TCVP 

products to cats and dogs. A residential handler cancer assessment was conducted due to TCVP 

being classified as a Group C possible human carcinogen by the Agency with a linear low-dose 

approach for quantification of risk using the oral slope factor (Q1 *) of 1.83 x 1 o3 (mg/kg/ day)·

1

• 

A series of assumptions and exposure factors served as the basis for completing the 

residential handler risk assessment, which are detailed below. 

Per the SOPs, it is assumed that residential handlers of pet treatment products will treat two 

animals per application. For TCVP dust and powder products, all products identify a specific 

amount to use per animal weight that allows for determination of the maximum application rate. 

For TCVP pump sprays, all registered products direct the user to apply a specific number of 

"strokes" per animal size. In order to determine the amount of active ingredient (a.i.) applied per 

treatment as specified by number of strokes, EPA requested additional information from a product 

registrant, Hartz Mountain Corporation, which holds most of the TCVP pet product registrations. 

Hartz provided information regarding the total volume of product released per stroke for pump 

and trigger spray products; 0.19 and 0.93 grams, respectively. Only trigger spray products are 

available for dogs; however, both pump and trigger spray products are available for cats. 

Additionally, Hartz Mountain Corporation submitted an application for amendment to the product 

6/l2 
label of EPA Reg. No. 2596-140, which was approved by the Agency in March 2014, to 

recommend a number of strokes per animal size. The specific number of strokers per animal size 

is located in Table 4.0 in the 2014 residential assessment. Previously, a number of strokes per 

cat/ dog was not recommended. 

For TCVP collars, the applicator is directed to cut off and dispose of any excess length 

once the product is fit and buckled into place. As described in the SOPs, because the exact length 

cannot be determined, the corresponding a..i. loss cannot be quantified and, therefore, exposure is 

conservatively assessed assuming the full collar length. 

A series of assumptions and exposure factors served as the basis for completing the 

residential handler risk assessment. Each assumption and factor is detailed in the SOPs. 

Unit Exposures and Area Treated or Amount Handled: Chemical-specific unit exposure data were 

provided in support of the re~idential handler risk assessment for the dust/powder formulations 

only (tviRID 45519601). The study, "Determination of Dermal and Inhalation Exposures to 

Tetrachlorovinphos (fCVP) During the Application of an Insecticide Powder to a Dog," was 

previously reviewed by the Agency in January 2002 and determined to be acceptable, and the data 

was reflected in the TRED for TCVP in 2002. These exposure data were used as a surrogate to 

estimate handler exposures from the TCVP dust/powder products. The study resulted in average 

unit exposures for the dermal and inhalation routes of exposure of 1,700 mg/lb a.i. and 3.1 mg/lb 

a.i., respectively. 

In the absence of exposure data for residential handling of pet collars and pump/trigger 

sprays, the Agency used exposure values from the 2012 Residential SOPs: Treated Pets as a 

surrogate to estimate handler exposures. Surrogate exposure data for a groomer trigger pump spray 

application to dogs was used to estimate handler exposures from TCVP pump spray products. No 

exposure data are available for assessment of handler exposures from the application of collars. In 

the absence of formulation-specific data, exposure data for spot-on applications was used to 

estimate handler exposures from the TCVP collar products. 

Exposure DuraJion: Residential handler exposure is expected to be short-term in duration. 

Intermediate- and long-term exposures are not likely because of the intermittent nature of 

applications by homeowners. Steady state exposures (21 days and longer) were assessed and 

presented for residential handler exposures to TCV1) pet products because of the steady state AChE 

inhibition exhibited by the OPs. 

Dqpper Year of Exposure: For the purpose of assessing residential handler cancer 

exposure/risk from TCVP product application, EPA has assumed four days per year for collars, and 

6 days per year for dusts/powders and pump sprays. The collar is based on a worst-case assumption 

of a single application every three months. Collar re-treatment intervals range from three to seven 

months. EPA assumed a bi-monthly re-treatment interval for dusts/powders and pump sprays. 

Yean· per Lifetime ofExpoJUre and Lifetime Expedanry: It is assumed that residential handler 

exposure would occur for 50 years out of a 78 year lifespan. This factor is routinely used as a 

conservative estimate of the number of years an individual could continually use a single pesticide 

p.roduct. Life expectancy values are from the Exposure Factors Handbook 2011 Edition Table 18-1 

(U.S. EPA, 2011). The table shows that the overall life expectancy is 78 years based on life 

expectancy data from 2007. In 2007, the average life expectancy for males was 75 years and 80 years 

7 I 12 
for females. Based on the available data, the recommended value for use in cancer risk assessments 

is 78 years. 

ReJidential Handler Risk Estimates and Condusiom 

EPA concluded that residential handler (adults) combined steady state (dermal and 

inhalation) exposures :are not of concern to the Agency (i.e., all aggregate risk indexes (ARis) are 

greater than 1) from application of any registered TCVP pet products. A complete listing of all 

ARis can be found in Table 5.1.1 in the 2014 residential assessment. The ARI approach was 

required to combine the dermal and inhalation routes of exposure because of the different LOCs. 

LOCs recommended for the dermal and inhalation routes of exposure are margins of exposure 

(MOEs) of 100 and 30, respectively. ARis of less than 1 indicate risks of concern. The ARI 

approach normalizes MOEs from different routes to an LOC of 1 to facilitate aggregation of risks, 

as described in the Agency's General Prindplesfor Peiforming Aggregate Exposure and Risk Asswments.

2 

Estimated residential handler cancer risk estimates range from 10·

9 to 10·

7

, which are below 

the Agency's LOC. A complete listing of all residential handler cancer exposure and risk estimates 

can be found in Table 5.1.2 in the 2014 residential assessment. 

Residential Post-application Exposure 

EPA identified that there is the potential for post-application exposure for individuals 

exposed as a result of contacting a cat or dog previously treated with TCVP pet products. The 

quantitative exposure risk assessment for residential post-application exposures is based on the 

following scenarios: 

1) Post-application.dermal (adults and children 1 to< 2 years old) exposure from contacting cats 

and dogs treated with TCVP; and 

2) Post-application incidental oral exposure (children 1 to< 2 years olds only) from contacting cats 

and dogs treated with TCVP. 

Residential post-application inhalation exposure is expected to be negligible from TCVP pet 

products and, thus, a quantitative assessment was not performed. Per the Residential SOPs, the 

combination of low vapor pressure (2.6 x10·7 mmHg at 25°C) and the small amounts of pesticide 

applied to pets is expected to result in negligible levels of chemical in the air, and therefore negligible 

inhalation exposures. 

A series of assumptions and exposure factors setved as the basis for completing the 

residential post-application tisk assessment. Each assumption and factor is detailed in the SOPs. 

ExpoJm-e Data: Surrogate and chemical-specific residue transfer studies were used for 

assessment of post-application exposures from registered TCVP pet products. These exposure data 

include the following residue transfer studies: propoxur collar (11RID 48589901); and TCVP 

powder and pump spray (MRID 45485501). 

2 http://www .epa.gov/oppOOOO I /trac/science/aggregate.pdf 

8 I 12 
EPA previously conducted a data evaluation record (DER) of the TCVP exposure study for 

aerosols, powders, and pump sprays3 in 2001. In support of the Agency's response to the NRDC 

petition, the study has been re-evaluated based on current standards of conduct for pet residue 

transfer studies4

• The re-evaluation of the TCVP residue transfer study resulted in a number of 

changes from the 2001 DER. Table 5.2.1 from the 2014 residential assessment below presents a 

comparison of the methods used to evaluate the study data. 

Comparison of 2001 and Current TCVP Pet Residue Transfer Study Reviews 

2001 Review Current Review 

Handwipe residue data were corrected for average Handwipe residue data were corrected for average 

field fortification recoveries <90%. field fortification recoveries <120%: 

TCVP residues on hands in J-tg/ cm2 were calculated TCVP residues are calculated in J-tg/ cm2 using the using the surface area of the stroking area (defmed 

as length of dog x length of study participant's surface area of the entire dog, based on the weight 

hand). of the test animal. 

The percent of applied TCVP dislodged by the The percent of applied TCVP transferred to the hand following treatment was calculated based on hand was calculated based on the total amount of the amount ofTCVP residue on the stroking area, active ingredient applied to the dog (calculated as which was determined from extrapolating residues 

detected in fur samples from a shaved area to the the amount removed from container in grams x 

area of the stroking area. 

actual percent active ingredient in test product). 

Regression analyses were conducted using the The revised regression analyses were conducted 

residue data in J-lg/ cm2. using the percent of applied dose transferred to the 

hand. 

It should be noted that the TCVP powder and pump spray post-application exposure study 

was not conducted in a manner reflective of current standards that require a deftned stroking 

procedure and greater number of petting simulations. That is, the pet is to be stroked in a single 

motion with the grain of the fur starting with both sides (along the ribcage) of the cat or dog and 

followed by the same motion along the back (dorsally) from the base of the neck to the tail. The 

two sides and back, in this order, account for one petting simulation. A total of 20 petting 

simulations (or 60 stroking motions) are currently required. In the TCVP post-application exposure 

study, the dogs were stroked on only one side of the treated dog's back from head to rump ftve 

times. However, the study was reflective of current policy regarding pet residue transfer studies at 

the time that it was conducted. In order to account for the differences between the TCVP postapplication exposure study and the currently recommended standard, the Agency used the maximum 

observed percent residue transfer on the day of product application (Day 0) for both formulations 

for exposure and risk quantification. Typically, the Agency assesses post-application risk with use of 

the mean percent residue transfer measured on Day 0; the use of the maximum value results in a 

more health protective risk assessment. Even though the post-application exposure study methods 

have evolved, the TCVP study employed a rigorous collection method and is not anticipated to 

underestimate exposure. 

3 S. Hanley. Re-evaluation of Determination of the Dislodgeability ofTetrachlorvinphos (TCVP) from the Fur of 

Dogs Following the Application of an Insecticide Powder, Pump Spray or Aerosol. 3125102. 0277543. 4 W. Britton. Tetrachlorvinphos: Reevaluation of"HEO's Review of Determination ofthe Dis/odgeabi/ity of 

Tetrach/orvinphos (TCVP) from the Fur of Dogs Following the Application of an Insecticide Powder, Pump Spray 

or Aerosol; MRID 45485501. 5/16114. 0420285. 

9 I 12 
Exposure Duration: Residential post-application exposure is expected to be short- and 

intermediate-term for dust/powders and pump/trigger sprays. For pet collars, post-application 

exposures is expected to be long-term (greater than 6 months) due to the potential for extended 

usage in more temperate parts of the country, and the longer active lifetime of pet collar products. 

Again, because of the steady state AChE inhibition exhibited by the OPs, steady state exposures (21 

days and longer) were assessed and presented for residential post-application exposures to TCVP 

pet products. 

Hand-to-Mouth Event Frequenry: The 2012 Residential SOPs include a frequency estimate of 

20 as the modeled number of hand-to-mouth events per hour for children 1-2 years old. There are 

currently no data available that specifically address the number of hand-to-mouth events that occur 

relative to the amount of time that a child spends with a pet. As a result, the estimate for frequency 

of hand-to-mouth events in indoor environments is based on the Xue et al. (2007)5 meta-analysis of 

child hand mouthing frequency. The indoor data were selected, even though child exposure to 

treated pets can occur either indoors or outdoors, because the indoor data result in a greater 

frequency of contacts and, therefore, a more health protective risk assessment. Please see Table A.2 

in Appendix A of the 2014 residential assessment for more information on hand-to-mouth exposure 

inputs. 

Years Per Lijetime ofExposure and Lijetime Expectanry: It is assumed that residential postapplication exposure would occur for 50 years out of a 78 year lifespan. This factor is routinely used 

as a conservative estimate of the number of years an individual could continually use a single 

pesticide product. Life expectancy values are from the Exposure Factors Handbook 2011 Edition 

Table 18-1 (U.S. EPA, 2011). The table shows that the overall life expectancy is 78 years based on 

life expectancy data fmm 2007. In 2007, the average life expectancy for males was 75 years and 80 

years for females. Based on the available data, the recommended value for use in cancer risk 

assessments is 78 years. 

Pet Contad: For the pmpose of determining exposure to treated pets, the 2012 Residential 

SOPs make use of transfer coefficients (TCs). TC is an exposure rate for a selected activity which 

involves contact with a source, such as children playing with treated pets or on treated turf. The TC 

concept is a long-standing established approach used to estin1ate residential, as well as occupational 

exposures, and is the basis for the Agency's post-application exposure guidelines6

. A TC is derived 

by taking the ratio of study volunteer dermal exposure per unit ti.n1e (mg/hr), and the concurrent 

measure of residue transfer. Ideally, dermal exposure is based on activities representative of the use 

pattern and residue transfer is determined by use of an established method specific to the use 

pattern. For pet exposures, TCs can be defined as animal surface area contact per unit time 

(cm2

/hr). 

Currently, there is no exposure study available using typical a'dult and child activities with 

pets and a concurrent transferable residue (TR) measure. In the absence of direct exposure data for 

residential activities with pets, the Agency concluded that studies conducted to monitor pet 

grooming activities are likely to result in a highly protective estimate of pet contact relative to 

5 Xue, J., Zartarian, V., Moya, J., Freeman, N., Beamer, P., Black, K., Tulve, N., Shalat, S. (2007), A Meta-Analysis 

of Children's Hand-to-Mouth frequency Data for Estimating Nondietary Ingestion Exposure. Risk Analysis, 

27(2):411-420. 

6 http://www.ecfi·.gov/cgi-bin/textidx?Sl D=6bfd4539761 be8d5b20dfbf6bc 19b9dO&node=40:25.0.1.1 .9.9&rgn=div6 

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contact associated with petting, hugging, or sleeping with a pesticide-treated pet. These data were 

gathered while human volunteers applied dust/powders and shampoo products to various dogs of 

differing sizes and fur lengths. Since these individuals extensively handled the dogs, it is expected 

that their resulting exposures are higher than would be reasonably anticipated from routine contact 

with treated pets. The volunteers in the shampoo study, who were professional groomers, 

shampooed 8 dogs for 5 minutes each, rinsed, and lifted them to counters for drying and combing 

resulting in very high exposures. In the dust study, volunteers applied dust via shaker can to 8 dogs 

each and then rubbed the dusts into the dogs' coats. The applicator studies were not conducted in a 

manner which measured TR, or active ingredient per surface area. Therefore, the residue available 

on the animal for transfer was predicted by multiplying the arithmetic mean fraction of application 

rate from the analysis of all liquid formulated product data sets presented in the 2012 Residential 

SOPs, 0.96%. This approach has the effect of increasing TC estimates, thus resulting in TC values 

which are more protective of human health. Furthermore, the selection of the mean value, in lieu of 

the screening level fraction application rate (FAR) value, 2%, further increases the TC estimates with 

use of the dust and shampoo studies. 

·Exposure Time: Tl~e exposure time (E1) assumption used to assess residential postapplication exposure to TCVP pet products is derived from a study which sought to evaluate the 

times that individuals spend performing different activities around the home. Based upon the 2012 

Residential SOPs, the point estimates recommended for adult and child ET with pets are 0.77 and 1 

hours, respectively. In the study, animal care is defined as "care of household pets including 

activities with pets, playing with the dog, walking the dog and caring for pets of relatives, and 

friends." The data identified the time spent with an animal while performing household activities as 

recorded in 24 hour diaries by study volunteers. While the activities defined do not necessarily 

represent the time volunteers were actively engaged in constant contact with the animal as is implicit 

in the post-application dermal and incident.al oral algorithms, the data are the most accurate 

representation of time spent with pets available and, therefore, it is assumed that contact is continual 

throughout the timed activity. The Agency assumes the ET value reflects a reasonable high end 

estimate of time spent in contact with a dog treated with TCVP pet products. 

When use of the study data are coupled with high end assumptions of pet contact, the result 

is an exposure assessment that inherently implies vigorous, continual contact for the entire duration 

of contact. While it is possible that an adult or child may be in close contact with a pet 

intermittently throughout the day, they would not be actively engaged in the highly vigorous contact 

implied by use of the TCs based on the applicator exposure data for the full exposure duration 

assumed. Further, it is possible that adults or children may be exposed from sleeping with a treated 

pet; however, they are not actively engaged in a high level of contact, or the repeated mouthing 

behaviors exhibited by children during waking hours, which are inherently assumed in the 

assessment conducted. 

Residential Post-application Risk EstimateJ and Conclusions 

Residential post-application steady state adult dermal (only) exposure and children 1 to 2 

years old combined (dermal and incidental oral exposures) are not of concern to the Agency (i.e, all 

MOEs are greater than 100) for all TCVP pet products assessed. The combined MOE approach 

was used because the dermal and incidental oral routes of exposure have the same LOC. MOEs 

under 100 indicate risks of concern. The residential post-application MOEs range from 270 to 

43,000. A complete listing of all MOEs can be found in table 5.2.2 in the residential assessment. 

Estimated residential handler cancer risk estimates range from 10·

9 to 10·7

, and residential post11 I 12 
application cancer risk estimates range from 10·1\ to 10·

6

, which are below the Agency's LOC. A 

complete listing of all residential post-application cancer exposure and risk estimates can be found 

in Table 5.2.3 in the 2014 residential assessment. 

It should also be noted that the evaluation of the potential residential post-application health 

risks from exposures to cats and dogs treated with TCVP pet products is conservative. The risk 

estimates calculated are based upon protective assumptions of TCVP hazard, product application 

rates, durations of exposure, and contact with the treated animal, and they make use of the best 

available post-application exposure data. 

For a more detailed explanation of residential exposure from the use of pet products 

containing TCVP and the Agency's conclusions, please refer to the 2014 TCVP residential risk 

assessment, en tided Tetrach/orvinphoJ: ReJidentia/ ExpoJmi! Assusment in Response to the Natural Resources 

D~f nse Coumi/ Petition to Cancel Ail Pet Um for Tetrach/orvinphos. 

IV: Conclusion 

The 2014 residential assessment discussed above uses appropriate, validated med1odologies 

to calculate potential exposure to TCVP pet products and shows that all identified risks associated 

with TCVP pet uses (including pet collars) result in risks that are b<;low the Agency's level of 

concern. Again, while EPA believes that the updated risk assessment addresses the arguments raised 

in NRDC's petition regarding whether TCVP pet uses pose unacceptable risks, EPA declines to 

revisit the 2006 RED or to perform a new cumulative risk assessment for organophosphates at this 

time, and notes that registration review of TCVP is currently underway, pursuant to FIFRA § 3(g) 

and 40 CFR Part 155. Therefore, NRDC's petition to cancel all pet uses for TCVP due to alleged 

risks of concern is hereby denied. 

Please contact Kelly Ballard at (703) 305-8126 or ballard.kelly@epa.gov, if. you have any 

questions or concerns regarding this response. 

c E. Hou nger, Director 

Office of Pesticide Programs 

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