UNITED ST A TES ENVIRONMENT AL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

MEMORANDUM 

Date: December 21 , 20 15 

SUBJECT: Tetrachlorvinphos (TCVP): Responses to Arguments Presented in the Natural 

Resources Defense Council, Jnc.'s (NRDC) Aug. 5, 2015 Opening Brief in NRDC 

v. EPA, Case No. 15-70025 (9111 Cir.) 

PC Code: 083701 , 083 702 

Petition No.: NA 

Risk Assessment Type: NA 

TXR No.: NA 

MRID No.: NA 

DP Barcodc: 430589 

Registration Nos.: NA 

Regulatory Action: Response to Comments 

Case No.: NA 

CAS No.: 22248-79-9 

FROM: Wade Britton, MPH, Environmental Health Scientist 

Risk Assessment Branch IV 

Health Effects Division (HED, 7509P) 

THROUGH: Michael Metzger, Branch Chief ~~ ~ Risk Assessment Branch V N II 

TO: 

Health Effects Division (HED, 7509P) 

James Parker, Chemical Review Manager 

Melissa Grable, Team Lead 

Risk Management and Implementation Branch I 

Pesticide Re-evaluation Division (7508P) 

This document constitutes the EPA 's response to arguments presented in the Natural Resources 

Defense Council, Inc.'s (NRDC) Aug. 5, 20 15 Opening Brief in NRDCv. EPA, Case No. 15-

70025 (9111 Cir.) (Opening Briet). EPA herein responds, on a point by point basis, to NRDC's 

arguments specifically pertaining to the Health Effects Division's (HED) 20 14 residential 

exposure assessment for TCVP pet product uses, conducted in response to NRDC's 2009 petition 

to cancel all pet uses of TCVP. 1 In addition, the 2015 TCVP human health draft risk assessment 

for registration review2 takes into account, where appropriate, the arguments presented in 

1 W. Brillon, 11 /05/ 14, D420283, Residential Exposure Assessment in Response to the Natural Resources Defense 

Council Petition to Cancel All Pet Uses for Terrachlorvinphos. 2 D. Drew, et.al, 12/21/20 IS, D4 I I 095, Terrachlorvinphos (TCVP) Human Health Draft Risk Assessment (ORA) for 

Registration Review. 
NRDC's Opening Brief. For any argument presented by NRDC that is not explicitly addressed 

in the 2015 draft risk assessment, this document explains EPA 's consideration of that argument 

in the context of drafting the 2015 draft risk assessment. 

J. NRDC Argument: 

NRDC argues that the U.S. Environmental Protection Agency (EPA or the agency) 

incorrectly eliminated the presumptive tenfold margin of safety identified in section 

408(b)(2)(C) of the Federal Food, Drug, and Cosmetic Act (FFDCA), 21 U.S.C. § 

346(b)(2)(C), to protect infants and children. NROC argues that, in conducting the 2014 

TCVP residential assessment, EPA did not adequately explain why the " I OX safety factor" was 

reduced to IX, or why blocking ten percent of acetylcholinesterase was not hannful. NRDC 

points out that, following the release of the 2014 TCVP residential assessment reducing the I OX 

safety factor to IX, the revised risk assessment for another chemical - chlorpyrifos - completed 

in the context of Registration Review of that chemical3 retained the I OX safety factor. 

EPA Response: 

Since the time of the 2014 TCVP residential assessment, EPA has revised its approach relative to 

consideration of the FQPA 1 OX factor based on its recent risk assessment for chlorpyrifos and 

evaluation of available research for all organophosphates (hereafter OPs). Newer lines of 

research on OPs in the areas of potential adverse outcome pathways (AOPs), in vivo animal 

studies, and notably epidemiological studies in mothers and children, have raised uncertainty 

about the agency's risk assessment approach with regard to the potential for neurodevelopmental 

effects in fetuses and children. Many of these studies have been the subject of review by the 

agency over the last several years as part of efforts to develop a risk assessment for chlorpyri fas 

(0424485, 0. Drew et al, 12/29/2014).4 A detailed review of the epidemiological studies used in 

this review can be found either in the 2014 chlorpyrifos risk assessment or in the 2015 literature 

review for other OPs (OPP/USEPA; 0 33 1251 ; 9115/ 15). 5 Ultimately, the agency retained the 

FQPA 1 OX Safety Factor (SF) in the 2014 chlorpyrifos revised risk assessment based, in large 

part, on the findings of these epidemiological studies. 

In 2015 a literature review was conducted expanding the scope of that completed for chlorpyrifos 

to include consideration of the epidemiological data on any OP pesticide. This included study 

designs besides prospective cohort studies, and non-U.S. based studies; eight relevant studies 

were evaluated. The 20 I 5 review concluded that, at this time, MOA(s)/ AOP(s) have not been 

established for neurodevelopmental outcomes. The growing body of literature docs demonstrate; 

however, that OPs are biologically active on a number of processes that affect the developing 

brain. Moreover, there is a large body of in vivo laboratory studies which show long-tenn 

behavioral effects from early life exposure, albeit at doses which cause AChE inhibition. EPA 

considers the results of the toxicological studies relevant to the human population, and as 

qualitatively supported by the results of epidemiology studies. The agency acknowledges the 

3 D. Drew. Chlorpyrifos: Revised Human Health Risk Assessment for Registration Review. 0424485. 12/29/2014. 4 The chlorpyrifos risk assessment can be found in the Federal docket at: 

l111p: '/\\'\\'\\'.regular ions. l!.O\' II! docket Dctai I: D'-E PA-I IQ-OPP-2008-0850 

5 The 2015 literanire review for other OPs can be found in the Federal docket at: 

http: '' \\ \\ .rc!!ulations.co' :; !documcmDctail:D- EPA-l IQ-OPP-2008-0 I I 9-0015 

Page 2 of 14 
lack of established MOA/AOP pathway and uncertainties associated with the lack of ability to 

make strong causal linkages and unknown window(s) of susceptibility. These uncertainties do 

not undermine or reduce the confidence in the findings of the epidemiology studies. The 

epidemiology studies reviewed in the 2012/20 I 4 and 20 15 literature reviews represent different 

investigators, locations, points in time, exposure assessment procedures, and outcome 

measurements. Despite all these differences in study design, with the exception of two negative 

studies in the 2015 literature review (Guodong et al, 2012; Oulhote et al, 2013), authors have 

identified associations with neurodevelopmental outcomes associated with OP exposure across 

four cohorts and twelve study citations. Specifically, there is evidence of delays in mental 

development in infants (24-36 months), attention problems and autism spectrum disorder in early 

childhood, and intelligence decrements in school age children who were exposed to OPs during 

gestation. Investigators reported strong measures of statistical association across several of these 

evaluations (odds ratios 2-4 fold increased in some instances), and observed evidence of 

exposures-response trends in some instances, e.g., intelligence measures. 

Section 408(b )(2)(C) of the FFDCA instructs EPA, in making its "reasonable certainty of no 

harm" finding, that "(i]n the case of threshold effects, an additional tenfold margin of safety for 

the pesticide chemical residue and other sources of exposure shall be applied for infants and 

children to take into account potential pre- and postnatal toxicity and completeness of data with 

respect to exposure and toxicity to infants and children." FFDCA § 408 (b)(2)(C) further states 

that ··the Administrator may use a different margin of safety for the pesticide chemical residue 

only if, on the basis of reliable data, such margin will be safe for infants and children." Given 

the totality of the evidence, there is sufficient uncertainty in the human dose-response 

relationship for neurodevelopmental effects which prevents the agency from reducing or 

removing the statutory 1 OX FQPA Safety Factor. For the 2015 TCYP draft risk assessment 

(DRA) (0411095), a value of l OX has been retained. Similarly, a database uncertainty factor of 

I OX will be retained for occupational risk assessments. The agency will continue to evaluate the 

epidemiology studies and pursue approaches for quantitative or semi-quantitative comparisons 

between doses which elicit AChE inhibition and those which arc associated with 

neurodevelopmental outcomes and will consider such outcomes in future risk assessment 

refinements i r warranted. 

A full discussion of the literature review on neurodevelopmental effects can be found referenced 

in Section 4.4 of the TCYP ORA (04 11095).6 

2. NRDC Argument: 

NRDC argues that without a chemical-specific study, EPA should have used the 2012 

Residential SOPs default of two percent to assess risks from pet collar exposures. NRDC 

argues that EPA 's 2012 Residential SOPs state that, "if chemical specific [transfer residue] 

measurements are not available, then a standard value for the fraction of active ingredient 

available (FAR) for transfer is used [NRDC Opening Brief, p.62].'" Further, EPA's TCYP 

assessment states that, ·'[i]t is [EPA] policy to use the best available data to assess exposure," and 

"[w]here chemical or formu lation-specific exposure data were avail able, th[o]se data were used 

6 The TCVP ORA can be found in the following Federal dockets: 

http: I\\" w.reg,ulations.gov.';/!docketDctail:O EPA-l IQ-OPP-2008-0316 and 

h!!n: ''"".regulations.co' tl!dockctOcwil:D EPA-I IQ-OPP-2009-0308 

Page 3 of 14 
[NRDC Opening Brief, p. 53)." As such, NRDC argues that EPA should not have relied on the 

surrogate pet fur residue transfer data from a recently study conducted for the active ingredient, 

propoxur. Further, although EPA discussed two other studies using two different chemicals, 

propoxur and deltamethrin, and used the more conservative mean percent residue transfer 

resulting from the propoxur study for estimation of TCVP post-application risk, NRDC argues 

that the recommended default should have instead been applied. 

EPA Response: 

The 2014 residential assessment addressed in detail the decision to use non-chemical-specific 

exposure data for assessment of risks from the TCVP pet collar formulation. The assessment 

describes that it is EPA policy to use the best available data to assess exposure. Further, where 

chemical- or formulation-specific exposure data are available, these data are used to conduct the 

assessment of residential handler and post-application exposures or integrated with other data as 

appropriate. No exposure data were available specific to TCVP pet collars at the time the risk 

assessment was completed. It should be noted that TCVP-specific exposure (i.e., residue 

transfer) data are available for the TCVP containing dust/powder and pump spray products but 

these data would best be considered in risk assessment only for the specific product types (i.e., 

formulations) because of their inherent basic differences. In comparison to other formulations 

used for pet pest control (i.e., dusts, spot-ons, liquid sprays), it is well known that pet collars are 

unique and, thus, result in considerably lower percent residue transfer values which was the 

rationale used as the basis for opting to the use of the propoxur pet collar transferable residue 

data (i.e., product type is the key consideration). This was clearly outlined in the 20 14 

residential risk assessment which stated the following: 

"When other pet product formulations arc applied to a treated pet, it can be reasonably 

assumed that the entire amount of that applied (i.e., the application rate) is available on 

the hair coat of the animal for transfer to the exposed individual. For example, the 

labeled amount of the TCVP pump/trigger spray product can be used directly in the 

assessment of exposure/risk because it is assumed this amount is available on the surface 

for contact. Pet collar formulations operate by slowly releasing the ai from the collar 

medium, making them efficacious for pest treatment over longer periods of time. Due to 

this activity, it can be difficult for the risk assessor to determine the amount which is 

initially avai lable on the animal because the majority is retained within the collar." 

Given the above considerations, EPA relied on exposure data specific to the assessment of postapplication risks from a pet collar product. While TCVP-containing collar residue data were not 

available for assessment of post-application exposures from the use ofTCVP pet collars, two pet 

collar formulation-specific post-application exposure studies were available at the time of the 

2014 residential assessment; a propoxur pet collar study (MRID 44858990 I) and a deltamethrin 

pet collar residue transfer study (MRTD 49350 I 0 I). Both studies were conducted in a manner 

consistent with current human ethical standards and were considered scientifically acceptable for 

use in post-application risk assessment. The propoxur pet collar study resulted in mean percent 

residue transfer on Day 0 in excess of that of the deltamethrin study; 0.072% and 0.003% of the 

collar contents, respectively. Therefore, for the 20 14 residential assessment, the more 

conservative mean percent residue transfer resulting from the propoxur study was used as a 

surrogate for estimation of TCVP post-application risks. 

Page 4of14 
Since the 2014 residential assessment, an amitraz pet collar residue transfer study was submitted 

that was also conducted in a manner consistent with current standards. This study results in a 

higher mean percent residue transfer on the day of application than the other available studies 

(0. 14%) and, therefore, has been used as the basis for the assessment of post-application risks 

from the TCVP pet collars. Further, as noted in the subsequent response, HED has also used the 

Davis study7 for estimation of post-application risks from TCVP pet collar exposures. These 

data (summarized in greater detail in Section 5.3 of the 2015 Occupational and Residential 

Exposure Assessment for Registration Review8) result in a mean residue transfer (Study 1, 12 

days after collar placement) of 0.40%. The Davis study, which is pending review by the Office 

of the Science Advisor (OSA) Human Studies Review Board (HSRB)9, further supports that pet 

collar formulations differ from other types of pet products and that the default pet residue 

transfer value of 2% would significantly overestimate residue transfer from collars. 

While the three surrogate pet collar residue transfer studies are not chemical-specific, these data 

are the best available su11"ogate for TCVP collars and offer a realistic refinement from the highend default fraction application rate (FAR) transfer factor recommended (2%) in the updated 2012 

Residential SOPs which reflects other pet product types (e.g., dusts and sprays). The default 

FAR, 2%, stipulated in the 2012 Residential SOPs: Treated Pets, is the 90th percentile of Day 0 

(i.e., the first 24 hours following application) measures from all transferable residue data 

available at that time regardless of product type. Of the 7 studies which are the basis of the 2% 

default residue transfer value, 4 are conducted with spot-on formu lations and 3 with either 

aerosol or spray formulations. In development of the 20 12 Residential SOPs and today, it is well 

understood that the active ingredients in these liquid formulated products are more readily 

avai lable for transfer to an individual than that of pet coll ars which are designed for slow release 

over time; however, at the time of the 20 12 SOP development, no residue transfer data were 

available for use in recommendation of a default residue value specific for pet collar 

formulations. As a result, the use of the default FAR is expected to result in a significant 

overestimate of the risk from pet collar exposures. 

Along with the non-chemical-specific pet collar transfer residue study, a number of high end 

inputs define the assessment of exposure/risk to a pet collar treated pet, including the following: 

• The application rates used in the assessment of the TCVP pet collars represents the maximum 

amount of ai in the entire collar. TCVP pet collar labels direct users to cut off and dispose of any 

excess length once the product is fit and buckled into place. As described in the 2012 

Residential Treated Pet SOP, the removal of excess length is anticipated; however, because the 

exact length cannot be determined, the corresponding ai loss cannot be determined and exposure 

is assessed assuming the full collar length. The use of the maximum amount of ai in the pct 

7 Davis, M., et al. Assessing lntermillcnt Pesticide Exposure from Flea Control Collars Containing the 

Organophosphorus Insecticide Tetrachlorvinphos. Journal of Exposure Science and Environmental Epidemiology. 

(2008) 18, 564-570. 

8 Britton, W. Tetrachlorvinphos: Occupational and Residential Exposure Assessment for Registration Review. 

0426984. 12/21 /2015. 9 http://www.epa.gov/osa/human-studies-review-board 

Page S of 14 
collar being assessed and the F AR transfer factor results in the potential for greater exposure to 

the individual than if excess length were assumed to have been removed. 

• The Treated Pet SOP recommends daily exposure durations of 0.77 hours for adults and I hour 

for children (I to 4 years old) based on survey data from which participants reported the time 

spent with an animal while performing household activities. As described in EPA 's response to 

NRDC's petition claim #5 below, the SOP methods used for assessment of adult and child postapplication risks imply continual, vigorous contact occurs with the treated pet during the entire 

duration of exposure. 

• The highest mean percent residue transfer of al I three non-chemical-specific exposure studies 

(i.e., the amitraz study) was selected for the assessment of post-application exposures from the 

TCVP pet collars. The use of these data result in the highest estimated exposures of all 

formulation-specific exposure data sources and, therefore, the most health protecti ve estimates of 

risk. Further, pending HSRB review, the Davis study would be used as it results in higher mean 

percent residue transfer than the amitraz study. 10 

• As defined in the Treated Pet SOP, exposure rates resulting from residue transfer associated 

with a given formu lation and activity is a val ue, known as the transfer coefficient (TC). The dust 

and liquid TCs used to assess post-application exposure to a dog treated with the TCVP collars 

were derived from studies representing applicator and grooming activities with dogs, 

respectively. Since the applicators and groomers directly handled pesticide products and 

conducted activities that required vigorous contact with the treated dogs, it is expected that their 

resulting exposures are a reasonable approximation of upper bound estimates of adult and child 

contact with an animal treated with a pet collar. In the absence of direct exposure data for this 

scenario (e.g., homeowner activity with a treated pet), the agency assumes that the application 

and grooming activities are likely to result in an estimate which is protective of individuals 

petting, hugging, or sleeping with a TCVP-treated cat or dog. 11 

3. NROC Argument: 

NRDC argues that EPA failed to consider the Davis study for the estimation of postapplication risks for exposures to the TCVP pct collar. The Davis study measured how much 

TCVP transferred to people's hands after five minutes of petting dogs wearing TCVP collars. 

NRDC argued that the Davis study would yield exposures well above the safe leve l detennined 

through EPA's exposure assessment of the pet collar formulation. 

EPA Response: 

EPA considered the potential effect of using the Davis study as the basis for risk assessment as 

discussed above in the response to NRDC Argument #2. Formal use of the Davis study is on 

hold at this time pending a scheduled review of its possible use by the HSRB which is scheduled 

in .January 20 16.

12 Therefore, for purposes of the current TCVP draft human health risk 

assessment in support of registration review, OPP has used the Davis study data to estimate 

preliminary, comparative post-application risks. EPA would rely on these data for regulatory 

10 A science review of the Davis study, as conducted for HSRB review, can be referenced at: W. Britton. Science 

Review of"Davis et al., 2008. Assessing Intermittent Pesticide Exposure from Flea Control Collars Containing the 

Organophosphorus Insecticide Tetrachlorvinphos" for HSRB Consideration. 0430707. 12/ 16/20 15. 11 http://www_2.epa.gov'pcst ic idc-scicncc-and-asscssing-pcst ic ictc-risks/standard-opcrat in g-prrn.:cdurcs-rcsidcnl ia 1-

pcst icide 12 hllp: "'' '' .epa.co\ o:.a human-:.tudics-rc\ ie\\ -board 

Page 6 of 14 
decision making if HSRB determines that the study is scientificall y valid and it meets 

appropriate human ethics requirements. 

The EPA review of the applicable human ethical standards (as outlined in 40 CFR Part 26 

Subpart Q) has been conducted and it concluded that: 

" there is no clear or convincing evidence that the conduct of the Davis study was 

fundamentally unethical; that is, the research was not intended to harm the participants 

and did not fail to obtain informed consent. Similarly, the conduct of the study was not 

deficient relative to the ethical standards prevailing at the time the research was 

conducted; the studies did not place participants at increased risk of harm (based on 

knowledge available at the time the study was conducted) or impair their informed 

consent." 13 

The ethics review also states that: 

"OPP wishes to rely on the TCVP glove residue data generated. The data may be crucial 

to a potential EPA decision to improve public health protection by imposing a more 

stringent regulatory restriction than could be justified without the data. If EPA proceeds 

under §26. 1706, EPA needs to obtain the views of the Human Studies Review Board, 

provide an opportunity for public comment, and publish a fu ll explanation of its decision 

to rely on the data, including a thorough discussion of the ethical deficiencies of the 

underlying research and the full rationale for finding that EPA met the standard in 40 

CFR §26. 1706 (c) (i.e., that the research is essential to a more stringent regulatory action 

to improve protection of public health)." 

The science review for the Davis study14 has also been conducted and concluded that the method 

used to collect transferable TCYP residues from petting/rubbing of the dogs treated with TCVP 

pet collars is scientifically valid. In addition to the transferable residue data, the Davis study also 

includes 1) plasma cholinesterase (ChE) from treated dogs 2) t-shirt samples collected from 

children exposed to TCYP treated dogs in their residences and 3) urinary biomonitoring for 

adults and children exposure to TCVP treated dogs in their residences. For purpose of the TCYP 

risk assessment, EPA only would rely on the transferable residue data as these data are the only 

element from the study that result in potentially greater risks. The other study elements are 

either not applicable to human exposures (i.e., dog plasma ChE measures), or have scientific 

limitations (i.e., a physiologicall y based pharmacokinetic (PBPK) model applicable to TCV P is 

not ava il able to interpret the urinary monitoring data). 

The EPA intends to present the Davis study at the next meeting of the HSRB which is scheduled 

for January 12-13, 20 16. lf the HSRB concludes that the Davis study does not constitute a 

human study and is scientifically valid. then EPA can rely on these data for regulatory risk 

decision making. Alternatively, if HSRB concludes the Davis study constitutes a human study, 

13 M. Lydon. Ethics Review of Davis et al Research on Flea Collars with TCVP. l 2/ 15/2015. 

~ W. Britton. Science Review of"Davis et al., 2008. Assessing lntermillent Pesticide Exposure from Flea Control 

Collars Containing the Organophosphorus Insecticide Tetrachlorvinphos" for HSRB Consideration. 0430707. 

12/ 16/20 15. 

Page 7 of 14 
then under 40 CFR §26. 1706, OPP is required to provide an opportunity for public comment and 

publish a full explanation of its decision to rely on the otherwise unacceptable data, including a 

thorough review of the ethical deficiencies of the underlying research and the fu ll rationale for 

finding that reliance on the data is cmcial to imposing a more stringent regulatory restriction. 

Until such time that these data have undergone HSRB review, post-appli cation risk estimates for 

exposures to pet collar treated pets are to be considered preliminary and are presented for 

purpose of comparison only. 

4. NRDC Argument: 

NRDC a rgues that EPA incorrectly consider ed the TCVP pet collars to be a liquid 

formulated product, as opposed to a solid formulation. NRDC states that the EPA " failed to 

research the TCYP flea collar label; instead it ignored the information in the label right on the 

box regarding the chemical formul ation [NRDC Opening Brief, p.67]." The label for the Hartz 

UltraGuard Flea and Tick Collar for Dogs (EPA Reg. No. 2596-84) states that "as the collar 

begins to work, a tine white powder will appear on the surface." As a result, NRDC argues that 

the transfer coefficient (TC) recommended for solid formulations should have been used instead 

of the transfer coefficent for liquid formulations as is recommended by the 2012 Residential 

SOPs. 

EPA Response: 

Per EPA·s 2012 Residential SOPs: Treated Pets, pet collar products are categorized as a liquid 

formulation. This position was based on research conducted at the time of SOP development 

that supported that pet collars function by means of diffusion, transferring from the collar to the 

surrounding area. More specificall y, the acti ve ingredient, which is embedded in the collar 

matrix, diffuses slowly through the matrix, thus controlling the amount of the active ingredient at 

the collar's surface. The active ingredient avail able on the surface of the pet coll ar then " rubs 

off" or transfers from the coll ar to the animal's hair coat via embedded lubricants which function 

as transfer agents at the surface of the collar. Based on the categorization of pet collars as I iquid 

formulations, the assessment of post-application exposures for these product types would be 

conducted with use of the TCs, and the frac tion active ingredient on the hands from TC studies 

(Faihands) recommended for the assessment of liquid formulated products as recommended in the 

2012 Residential SOPs. 15 

The information provided by NRDC states that the label for the Hartz UltraGuard Flea and Tick 

Collar for Dogs (EPA Reg. No. 2596-84) states that "as the collar begins to work, a fine white 

powder will appear on the surface." HED has confirmed that this statement is present on the 

current labeling for the identified product and that an identi cal statement is also found on the 

following TCVP pet collar products (5 of9 total pet collar products): EPA Reg. Nos. 2596-62, 

2596-63, 2596-83, 2596-84, and 2596-1 39. Taking label statements into account, and based 

upon further research which suggests that some pet collars may act by extrusion of the active 

ingredient from the collar matrix as a fine dust, HED has reconsidered the position that the 

TCVP pet collars are all liquid formulated products. As a result of this uncertainty, in the TCVP 

draft human health risk assessment in support of registration review, HED has updated the 

is Imp: \1 \1 \12.cpa.go\ pes1icidc-~cicnce-and-a,sc-.sin!! pesticide-r isks standard-opern1in!!-procedure!>-reside111ialpcsticide 

Page 8 of 14 
assessment of post-application risks from TCVP pet collars in consideration of both the dust- and 

liquid-specific TCs and Fai1rnnds recommended SOP values. 

5. NRDC Argument: 

NRDC argues that EPA underestimates children's exposures to their pets through use of 

an assumption tha t toddlers spend one hour per day with their pets. NRDC argues that 

common sense and experience tell them that many children spend far more time with their pets 

that one hour daily. NRDC addresses the study used by EPA to determine the number of hours 

spent in daily contact with pets stating that "at least two of the nine children in the study spent 

more than an hour and a half a day with their pets each day, and at least one spent two hours 

[NRDC Opening Brief, p.48]." NRDC asserts that EPA should use the upper portion of the 

distribution (901h to 95111 percentile) and assume that children spend two ho urs per day with the ir 

pets as was assumed in the 2006 Reregistration Eligibility Decision (RED) for dichlorvos 

(DDVP). 

EPA Response: 

In EPA 's 20 I 4 residential assessment conducted in response to NRDC's 2009 petition to cancel 

all pet uses of tetrachlorvinphos, EPA stated the following regarding the daily exposure time 

assumed for post-application exposures to TCVP treated pets: 

"The exposure time (ET) assumption used to assess residential postapplication exposure 

to TCVP pet products is derived from a study (Tsang and Klepeis, 1996 ( 1997 EPA 

Exposure Factors Handbook)] which sought to evaluate the times that individuals spend 

performing different activities around the home. Based upon the 20 12 Residential 

SOPs16

, the point estimates recommended for adult and child ET with pets are 0.77 and I 

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 incidental 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 (adult, 0.77 hours; 

children, 1 hour) 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 c lose contact with a pet 

intermittentl y 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 

16 Imp: 1 tww w2 .ep;:i.go\· pest ic ide-sc iencc-and-a<;_J;e<:si ng-pest ic ide-risks 'standard-operal ing-procedurcs-resident ia 1-

pest icide 

Page 9 of 14 
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. 

NRDC asserts " that common sense and experience tell them that many children spend far more 

time with their pets that one hour daily (NRDC Opening Brief, pp. 47-48]." It must be 

emphasized that when an adult or child ·'spends time" with a pet, it is unlikely that the entirety of 

this time is spent engaged in vigorous, continual contact during this entire period as is implied by 

the inputs and methods used in the 2012 Residential SOPs to calculate exposures from contact 

with treated pets. As described above, the study \·vhich supports the exposure time inputs for the 

2012 Residential SOPs: Treated Pets is based on measures of time spent in "animal care" where 

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. " It is cri tical to understand the 

connection between time spent in animal care and SOP exposure time inputs which inherently 

implies continual, vigorous contact during the entire exposure duration. As defined, animal care 

could imply direct vigorous contact with a treated pet for a limited period of time, but could just 

as likely have involved activities which required little to no contact of the pet while it was being 

cared for. 

The assumption of vigorous, continual contact is based upon the algorithm used to estimate postapplication dermal and incidental oral exposures from contact with treated pets. Of the inputs 

used, the dust and liquid TCs were derived from studies representing applicator and grooming 

activities with dogs, respectively. Since the applicators and groomers directly handled pesticide 

products and conducted activities that required continual, vigorous contact with the treated dogs, 

it is expected that their resulting exposures are a reasonable approximation of upper bound 

estimates of adult and child contact with a treated animal. In the absence of direct exposure data 

for this scenario (e.g., homeowner activity with a treated pet), the agency assumes that the 

application and grooming activities are likely to result in an estimate which is protective of 

individuals petting, hugging, or sleeping with a TCVP-treated cat or dog. 

Further, EPA supports the use of mean values for default inputs, including the exposure time 

input. 17 When the default values are considered together in the exposure algorithm, the 

combination of these inputs result in upper percentile exposure estimates. If EPA were to 

assume an upper percentile for all inputs (e.g., 90th to 95th percentile), the result would be 

exposure estimates that are overly conservative and unrealistic; particularly given the already 

health protective nature of the assessment methods and inputs. 

NRDC identified a prior EPA pet assessment conducted for the DDVP RED which used a daily 

exposure time assumption of 2 hours. This assessment was conducted in 2006, prior to release of 

the updated 20 12 Residential SOPs. At that time, residential exposures were assessed based on 

the recommendations of the 1997 Standard Operating Procedures (SOPs) for Residential 

Exposure Assessments. In this outdated document, an exposure time of 2 hours per day was 

recommended based on, '·the best professional judgement and experience of the OPP staff. The 

timeframe (2 hours) is approximately the same time children play outside per day. This is 

17 hllp. '' ""'' 2.epa.gov pcsticide-.,cience-and-a~scc;sing,-pesticide-ri!>ks standard-opcrating,-proccdures-residentialpl.'st1cidc 

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assumed to be an upper-percentile value." EPA contends that the recommendations of the 2012 

Residential SOPs are based on the best data available regarding time spent with pets and that the 

one hour exposure time recommendation is a health protective input for determination of highlevel, continual contact with treated pets. 

6. NRDC Argument: 

NRDC argues that EPA failed to account for an established route of exposure, toddlers 

who touch an object or food with pesticide-contamina ted hands, and then put that object or 

food into his/her mouth (or " indirect hand to mouth activity"), raised by NRDC in its 

petition. NROC argues that published studies show that " there is actually noticeable indirect 

hand to mouth activity in infants and children [NRDC Opening Brief, p.50]," and argues that 

·'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 [NRDC Opening Brief, p.50]." NRDC acknowledges that 

EPA· s 2012 Residential SOPs recognize that oral exposures consist generally of two pathways, 

children contacting treated surfaces and putting their hands in the ir mouth and from putting 

objects or other toys in their mouth that had been in contact with treated surfaces. EPA did not 

conduct an assessment of indirect oral exposures (i.e., object-to-mouth) in its 2014 residential 

assessment and instead explained, "the quantification of hand-to-mouth exposures following 

direct contact with the treated surface always results in exposures of a greater magnitude and, as 

a result, a more health protective assessment of risk ... than from indirect object-to-mouth 

exposures." 

EPA Response: 

The 20 12 Residential SOPs describe that residential post-application exposures may occur 

through dermal, inhalation, and/or incidental oral (non-dietary ingestion) routes. Postapplication dermal exposure can occur from surface-to-skin residue transfer for individuals 

contacting treated surfaces. Post-application inhalation exposure can occur from concentrations 

of pesticide active ingredient remaining in the air following treatment. Finally, post-application 

oral exposures are based on the ingestion of pesticide residues that can result from transfer of 

residues from hand-to-mouth, object-to-mouth, or via direct ingestion of residues through soil 

ingestion, dust ingestion, or ingestion of pesticide granules or baits. The assessment of object-tomouth exposures are recommended only for treated turf and treated carpets/hard floors as it is 

only from these surfaces that secondary exposures are expected following contact with the 

treated surface. The methods used for determination of pesticide residues available for postapplication dermal and oral exposures from residential pesticides are described in the 2012 

Residential SOPs.

18 

NRDC acknowledges that EPA 's 20 l 2 Residential SOPs recogni ze that oral exposures consist 

generally of two pathways, hand-to-mouth and object-to-mouth exposures. However, NRDC 

argues that I) EPA should account for object-to-mouth exposures from objects which have come 

into contact with a TCYP treated pet and then mouthed by the child and 2) EPA should a lso 

account for " indirect hand-to-mouth" exposures whereby children touch an object or food with 

pesticide-contaminated hands, and then put that object or food into his/her mouth. 

is h!!p: 1 lwww2 .cp:.i .uov/pcsL ic ide-sc icncc-and-a<;sessi ng-pcsl ic ide-risks 'standard-ope rat ing-procedures-residcn Lia lpes1 ic idl! 

Page 11 of 14 
In response to the first argument, EPA described in the 20 14 response to the NRDC petition that, 

"with use of the methods described in the indoor environments and lawn/turf SOPs, the 

quantification of hand-to-mouth exposures following direct contact with the treated surface 

always results in exposures of a greater magnitude and, as a result, a more health protective 

assessment of risk (i.e., a lower MOE) than from indirect object-to-mouth exposures." NRDC 

asserts that because, .. it (object-to-mouth exposure) would share a common toxicological 

endpoint, the object-to-mouth exposure would be combined with the derma l and hand-to-mouth 

exposures." To clarify, when quantified, the greater magnitude of hand-to-mouth to object-tomouth exposures is such that the addition of object-to-mouth exposure would have little to no 

impact on the combined risks. When hand-to-mouth and object-to-mouth risks are compared for 

turf, the resulting difference is a - 30 fold difference and, for indoor environments, the difference 

is - 4 to 7 fold for hard surfaces and carpet, respectively. Further, EPA policy recommends that 

incidental oral exposure scenarios (i.e., hand-to-mouth and object-to-mouth) should be 

considered inter-related and it is likely that they occur interspersed amongst each other across 

time. Combining these scenarios with the dermal exposure scenario would be overl yconservative because of the conservative nature of each individual assessment. Therefore, the 

post-application exposure scenarios which should be combined for children I < 2 years old are 

the dermal and hand-to-mouth scenarios only. This combination is considered a protective 

estimate of children's exposure. Therefore, in the case of the post-application assessment of 

TCVP which has been determined to have no dermal hazard, it is most appropriate to present the 

hand-to-mouth and object-to-mouth exposures separately. 

Regarding N RDC's second argument, the assessment of hand-to-mouth acti vity as conducted 

with use of the 20 12 Residential SOPs accounts for the " indirect hand-to-mouth" exposures 

described from children touching an object or food with pesticide-contaminated hands, and then 

putting that object or food into his/her mouth. Jn order for the pesticide residues to have been 

transferred to an object or food from pesticide-contaminated hands would first require transfer of 

residues from a treated surface to the hands. If EPA were to attempt to assess an " indirect" 

exposure, a mass/balance measure would have to be undertaken that would require removal of 

the residues determined to be on the hands to the object or food item handled, thus subtracting 

from the total on the hands. Therefore, the quantification of combined oral risks from "indirect 

hand-to-mouth'. and ''direct hand-to-mouth" oral exposures would be, in effect, adding back 

those indirect oral exposures which were subtracted resulting in the same outcome had the 

indirect exposure never been calculated. 

7. NRDC Argument: 

NRDC argues that EPA 's algorithm for calcula ting the amount of " transfer able r esidue" is 

inconsistent with the findings of the Davis study which found that the residues wer e 

concentrated at the neck of the animal following application. NRDC argues that when 

calculating the residues available to transfer from the surface of a treated pet to an exposed 

individual, EPA's dermal algorithm divides the residues available to transfer by the surface area 

of the treated animal. In the Davis study, researchers found that residues were concentrated at 

the neck, and that very low levels of residue were found at the tail. Therefore, regardless of pet 

size, the bulk of the exposure is from contact with the neck. 

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EPA Response: 

The algori thm for quantifi cation of dermal exposures from the 2012 Residential SOPs: Treated 

Pets calculates transferable residues, or those residues anticipated to transfer from the surface of 

the treated animal to the exposed individual, by means of multiplying the maximum application 

rate of the product applied by the fraction of the application rate anticipated to be available for 

transfer (as determined by means of residue transfer "petting" studies) and then dividing by 

surface area of the treated animal. The design of the algorithm to account for the surface area of 

the treated animal was intentional. 

Contact with a treated pet is not expected to be limited to one area of the pet, particularly when 

these exposures are anticipated to be vigorous and continual for up to one hour daily. To assess 

exposures as proposed by NRDC would be equivalent to an adult or child having a high level of 

continuous contact with only the neck of their pet for a full hour dail y, which is highly unli kely. 

During this period of exposure, it is just as likely, if not more likely, that contact with a treated 

animal would occur elsewhere on the animal's body (e.g., along the back, belly, chest, and 

ribcage) as it would the neck. 

The majority of pet product formulations are not applied in a manner which would limit the 

concentratio n of residues to one area of the pet's body. For example, an application of a 

shampoo, liquid spray, or dust/powder would typically be applied to the entirety of the animal's 

body. In the case of pet spot-on products, while the initial application may be isol ated, pet 

residue transfer studies show that within hours of application residues begin to spread over the 

surface area of the animal. Jn the case of the Davis study, only the neck (over the coll ar and 

under the coll ar) and tail measures were collected. In accordance with N RDC's claim, these 

residues were concentrated to a larger degree around the neck versus the tail. However, it is 

important to note that the Davis study researchers limited their sampling (petting) to only these 

areas of the dogs' bodies. Had the researchers collected samples from other parts of the dogs' 

bodies, such as the back or along the ribcage, they may have found residues to have spread to 

other areas of the body as well and it is possible that these could be in excess of those found on 

the tail. Further, as evidenced by the Davis study results, measurable residues were present on 

the tail of the animals, thus indicating that the residues are spreading over the animal and not, as 

suggested by NRDC, concentrated solely around the neck area. 

In conclusion, an exposure assessment which assumes all exposures were isolated to one area of 

the animal's body and that all contact for the entire duration of exposure were to occur to this 

area of the body only is unrealistic. For the majority of pet product formulations, it is more 

likely that residues are distributed over the entire pet surface area and that an adult or child's 

contact with the pet is not limited to one area for the entire duration of exposure. For pet coll ar 

formulations, while the residues may potentially be concentrated around the neck area, it is 

unlikely that the adult or child contacting the treated pet would only contact this area. He or she 

would like ly also contact other areas of the body, which, based on the Davis study, would have 

less residue to be transferred (the Davis study residue measures from the tail were well below 

those measured around the neck), thus reducing overall exposures from these areas alone. In 

effect, if exposures were estimated assuming a greater concentration about the neck, the exposed 

individual would be exposed more highly when contacting the neck area and less so when 

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contacting other areas of the pet, thus having an effect approximately equivalent to the current 

design that assumes the residues are distributed across the entire surface area of the animal. 

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