EPA’s Response to Selected Majo r Interagency Comments on the

Interagency Science Consultation

Draft IRIS Toxicological Review of 1,4- Dioxane (inhalation exposure route only)

September 15, 2011

Purpose: The Integrated Risk Information System (IRIS) assessment development process

of May 2009 includes two steps (Step 3 and Step 6) where White House offices and other

federal agencies can comment on draft assessments. The following are EPA’s responses to

selected major interagency review comments received during the Interagency Science

Consultation step (Step 3) for the draft IRIS Toxicological Review of 1,4-Dioxane

(inhalation exposure route only; dated May 2011) . All interagency comments provided were

taken into consideration in revising the draf t assessment prior to posting for public comment

and external peer review. The complete set of interagency comments is attached as an

appendix to this document.

For a complete description of the IRIS process, including Interagency Sc ience Consultation, visit

the IRIS website at www.epa.gov/iris.

Topic #1: Selection of the Critical Effect for Derivation of the Reference Concentration

(RfC) – CDC/ATSDR indicated agreement with the choi ce of principal study and critical effect

(atrophy of the olfactory epitheliu m) for the derivation of the RfC. NIEHS/NTP also stated that

they agreed with the derivation of the RfC. OM B commented that more clarity is needed

regarding EPA’s characterization of the level of adversity of the critical effect and that this

effect should be described as a precursor effect, likely to o ccur early in the continuum of

pathological events associated with the respiratory tract effects. DoD agreed with the choice of

principal study, but disagreed w ith the selection of the critical effect, given the physiological

differences between the respirat ory systems of rodents and humans . DoD stated that the highly

convoluted nasal turbinate syst em of the rodent results in greater deposition in the upper

respiratory tract making the human relevance of th e observed adverse effect uncertain. DoD also

stated that this particular rat strain is highly sensitive to respiratory effects.

EPA Response: Atrophy of the olfactory epithelium, a nasal lesion, was selected as the

critical effect for the derivation of the RfC in the Interagency Science Consultation draft

assessment. This critical effect is considered to be adverse and is biologically plausible

and likely to be relevant to humans, as this nasal lesion occurs in cell types that are

prevalent throughout the respirat ory tract of both rats and hu mans. There are no data to

indicate that atrophy of the ol factory epithelium is either a precursor effect. Indeed, both

atrophy and respiratory metaplas ia of the olfactory epithe lium occurred at the same

exposure concentration (50 ppm). In revising the assessment to more clearly indicate the

consideration of adversity of the effects, EPA decided to select both types of nasal lesions

(atrophy and respiratory metaplasia of the olfactory epithelium ) as co-critical effects for

the derivation of an RfC for 1,4-dioxane.

Further support for the use of rat nasal lesions as a critical effect is that a similar pattern

of effects was observed in ra ts after both oral and inha lation exposure to 1,4-dioxane,

A-1indicating that the nasal eff ects may also occur as a resu lt of systemic circulation,

independent of any differences in the inha lation physiology between rats and humans.

Text in Sections 5.2 and 5.2.1 of the Toxicologi cal Review has been modified as a result

of the designation of co-critical effects and External Peer Review charge question B2 has

been modified to request comment on the sel ection of atrophy and respiratory metaplasia

of the olfactory epithelium as critical effects.

Topic #2: Application of Adjustment Factors for Duration and Dosimetry in the Derivation

of the RfC – DoD recommended that a poi nt of departure unadjus ted for exposure duration

should be used in the derivation of the RfC since metabolism of 1,4-di oxane is subject to

saturation in rats. They indicated that the adjustment serves to artificially lower the exposure

that would cause the effect, and that such an adjustment is not supported by biological

considerations. OMB recommended that the RfC should be derived by application of both a

dosimetric adjustment factor for portal-of-entry effects (Categor y 1) and effects from systemic

acting gases (Category 3) for purposes of comparison. CDC/ATSDR indicated that EPA’s

determination that 1,4-dioxane is a Category 3 gas was persuasive.

EPA Response: A duration adjustment is used in th e assessment to account for the noncontinuous exposure protocol us ed in the principal study. Da ta to inform whether the

parent compound or a metabolite is responsib le for the effects observed following 1,4-

dioxane exposure are not available. Therefor e, it is unclear how information on metabolic

saturation in rats would imp act the duration adjustment.

The human equivalent concentration (H EC) for 1,4-dioxane was calculated by the

application of the dosimetric adjustment factor (DAF) for systemic acting gases (i.e.

Category 3 gases), in accordance with the EPA’s Methods for Derivation of Inhalation

Reference Concentrations and App lication of Inhalation Dosimetry ( U.S. EPA, 1994 ).

This conclusion was based upon a number of factors, including the low reactivity of 1,4-

dioxane and the occurrence of systemic effects following or al and inhalation exposure to

1,4-dioxane. However, 1,4-dioxane is misc ible in water and induces effects in

portal-of-entry tissues, characteristics that are also indicative of a Category 1 gas.

Therefore, in response to OMB comments, EP A has provided an alternative calculation

of the HEC for 1,4-dioxane based on the appl ication of the corres ponding DAF for gases

that act through the portal-of-entry (i.e., Cate gory 1 gases). This additional analysis can

be found in Appendix G of the Toxicological Review. The External Peer Review charge

question B3 has been edited to request comment on these alternate methods for deriving

the point of departure.

Topic #3: Use of Linear Low-Dose Extrapolation for Cancer – DoD stated that there is

sufficient information to suppor t a non-linear extrapol ation for the carcin ogenic potency of 1,4-

dioxane. They suggested that EPA implemen t Section 3.3.4 of EPA’s Guidelines for

Carcinogenic Risk Assessment (U.S. EPA, 2005) which states t hat: “Nonlinear extrapolation

having a significant biological support may be presented in addition to a linear approach when

the available data and a weight of evidence evaluation support a nonlinear approach, but the

data are not strong enough to ascertain the mode of action applying the Agen cy’s mode of action

A-2framework. If the mode of action and other in formation can support chemical-specific modeling

at low doses, it is preferable to default procedures.” DoD stated that the available data strongly

suggest a lack of genetic toxicity and a tumor promotion mechanism associated with tissue injury

and subsequent regeneration as the mode of action for 1,4-dioxane ca rcinogenicity; that 1,4-

dioxane mediated hepatocyte cell proliferation has been demons trated (Slott 1981; Goldsworthy

1991; Miyagawa 1999) and numerous mechanistic studies have also demonstrated the

proliferation-potential of 1,4-dioxane. They indi cated that the mode of action for 1,4-dioxane

induced liver cancer involves sustained cytotox icity followed by regenerative and unregulated

cell growth, that liver cytotox icity occurs only at doses above which metabolic detoxification

pathways are saturated, and that the dose-response curve can be assumed to be nonlinear in the

low-dose region.

OMB stated that it appea rs that data exist to support a non-li near mode of action as the Kasai

studies show accumulation related to saturati on at high doses. OMB i ndicated that on page 104

of the draft Toxicological Review a statement is made that data on key events is missing;

however, it is not clear that this implies that there is not biological support for a non-linear

mode of action and that EPA’s discussion c ould be strengthened and clarified.

NASA stated that when the previous oral asse ssment for 1,4-dioxane wa s subjected to external

peer review, a number of the revi ewers indicated that th e mode of action for cancer could not be

readily determined, but that the m ode of action is likely to be non- linear. NASA suggested that in

the absence of solid, defensible data that indicates a linear re lationship, EPA should consider

non-linear extrapolation for the estim ation of cancer risks.

On the other hand, NIEHS/NTP stat ed that EPA should consider deletion of Tables 4-23 and 4-

24 since there are no data available to support an y of the mode of action assumptions presented

in the assessment.

EPA Response: When EPA evaluates whether the avai lable data provide significant

biological support for a mode of action for can cer the goal is to id entify key events, and

to have reasonable confidence in the sequen ce of events and how they relate to the

development of tumors including information on the shape of the dos e-response curve at

low doses. It is EPA’s judgment that there are insufficient da ta to establish the shape of

the dose response curve in the exposure-res ponse curve at low doses based on the mode

of action data for cancer effects following exposure to 1,4-dioxane, for both oral and

inhalation routes of exposur e; thus a default linear extrapolation was used.

1,4-Dioxane produces liver, nasal, kidney, pe ritoneal (mesotheliomas), mammary gland,

Zymbal gland, and subcutis tumors in anim al models. Several hypothesized mode(s) of

action exist for liver and nasal tumors; however, they are not supported by data either in a

temporal or dose-related manner. Specifically, tumors occur in some rodent models in the

absence of data to support the hypothesized ke y events (i.e., cytotoxicity) such that the

plausibility of these potential modes of ac tion is questionable. In addition, studies

evaluating the kinetics of 1,4-di oxane suggest that liver carci nogenicity may be related to

the accumulation of the parent compound follo wing metabolic saturation; however, the

toxic moiety (i.e., parent compound and/or metabolite(s)) is unknown. Perhaps more

importantly, there are no available data regarding any hypothesized carcinogenic MOA

A-3for 1,4-dioxane-induced kidne y, lung, peritoneal (mesot heliomas), mammary gland,

Zymbal gland, and subcutis tumors.

In accordance with EPA’s Guidelines for Carcinogen Risk Assessment ( U.S. EPA,

2005a ) , the absence of evidence for genotoxic ity does not invoke the use of nonlinear

low-dose extrapolation, nor does it define a mode of action. Furthermore, it is not clear

what endpoints would be used for the presenta tion of a non-linear (presumed threshold)

extrapolation as an alternate approach for liver and/or nasal tumors, nor is it evident as to

how that approach would be scientifically supported or be neficial to risk assessors.

Although this review is focused on the inhala tion route of exposure, interagency review

comments received also discussed the previ ous external peer review comments on the

oral assessment, particularly as they rela te to the mode of action information and

determination of low-dose extrapolation for 1,4-dioxane. In brief, the external peer

reviewers of the oral assessment of 1,4-dioxane (see Appendix A of the 2010

Toxicological Review) had mixed opinions rega rding the mode of action with 4 out of 8

reviewers indicating that the mode of acti on could not be define d, thereby supporting the

linear low-dose extrapolation:

• three reviewers supported th e conclusion that a mode of action could not be

identified for any of the tumor sites;

• one reviewer commented that the mode of action is likely to be nonlinear but

stated that there is inad equate evidence to support a specific mode of action

hypothesis with any confidence, so th at a default linear extrapolation is

necessary;

• one reviewer stated this wa s outside of his area of expe rtise but indicated that the

discussion was too superficial and suggested including considera tion of the effect

of various mode of action assumptions in the uncertainty discussions, as well as

adding statements as to what the Agency would consider essential information to

make a determination about a mode of action;

• one reviewer indicated that better presen tation of the analysis was warranted; and

• two reviewers commented that even though the mode of action for 1,4-dioxane is

not clear there is substantial evidence that it is non-genotoxic. One of these two

reviewers also suggested that a nonli near cancer model s hould be utilized.

In response to the interagency reviewer comments, text in Section 4.7 of the

Toxicological Review has been modified to fu rther clarify the available data related to

the mode of action for cancer and EPA’s rati onale for the use of a linear approach for

extrapolation of cancer risk. In addition, Exte rnal Peer Review charge question C2 has

been modified to specifically request that reviewers identify whet her a mode of action

can be established for 1,4-dioxane (i.e., studi es that support the key events, and specific

data available to inform the shape of the exposure-response curve at low doses).

Tables 4-23 and 4-24 have been retained in the Toxicological Review as they provide

support for EPA’s conclusions regarding the mode of action for 1,4-dioxane. These

A-4tables provide an evaluation of the data that ar e available, as well as data that are lacking,

to show temporal sequence and the dose-re sponse relationship for the hypothesized key

events for 1,4-dioxane-induced liver and nasal tumors – th e two tumor types for which

some mode of action data are available.

Topic #4: Use of tumor incidence data in the D erivation of the Inhalation Unit Risk (IUR) –

OMB commented that the rationale for combin ing hepatocellular adenomas and carcinomas is

unclear given that there were onl y statistically significant incr eases in hepatocellular adenomas,

not carcinomas. DoD stated that it is important to clearly differ entiate between the statistically

significant tumor incidence data in various organs/glands compar ed to controls from just a

statistically significant dose-r esponse trend. DoD also comment ed that the EPA’s 2005 Cancer

Guidelines and previous cancer guidelines are ve ry clear: adenomas or fibromas can be added

to carcinomas, but these lesions alone should not be considered in the estimation of carcinogenic

risk given that it is commonly understood that not all of these non-cancerous lesions will

progress to cancer.

EPA Response:

The incidence of adenomas and carcinomas w ithin a dose group at a site or tissue in

rodents are often combined based upon EPA’s Guidelines for Carcinogenic Risk

Assessment (U.S. EPA, 2005). This practice is based upon the hypothesis that adenomas

may develop into carcinomas if exposure at the same dose was continued (McConnell et

al., 1986). It is not clear th at the cancer guidelines require subtypes of tumors to be

statistically significantly elevated in order to be combined. In any case, the increased

incidence of hepatocellular ca rcinomas both in male and female rats was statistically

significant by trend test, which is genera lly more robust for analyzing dose-response

trends than separate pairwise comparisons because it considers the entire data set

simultaneously. In some cases, lack of sta tistical significance in a trend test may be

followed with pairwise compar isons between control and high er dose responses. In this

case, the increases in carcinomas, observed onl y at the high dose, were also statistically

significantly elevated over cont rol by pairwise comparisons. Accordingly, the incidences

of hepatocellular adenomas and carcinomas were combined without double-counting as

the incidence of either hepato cellular adenoma or carcinoma and utilized to calculate the

IUR.

In accordance with EPA’s Guidelines for Carcinogenic Risk Assessment (U.S. EPA,

2005), EPA utilized adenomas and fibromas in the absence of malignant neoplasms.

Section 2.2 of the guidelines stat e that while the term “tumor ” is defined as a malignant

neoplasm or a combination of maligna nt and corresponding benign neoplasms,

observations of only benign ne oplasia may or may not have significance for evaluation.

Therefore, the use of benign tumors in the absence of malignancy should be evaluated on

a case-by-case basis. Given the multiplicity of tumors in the Kasai et al. (2009) study and

an unknown MOA(s), the inclusion of benign tumors is scientifically justified.

In response to the reviewer comments, te xt in Section 5.4.2.2 of the Toxicological

Review has been modified to further clarify the use of both statistically significant tumor

incidence data and statistical ly significant dose -response trend tumor data. In addition,

A-5clarifying text has been added to Section 5 regarding the use of benign tumors in the

absence of malignancy, as appropriate. In addition, EPR Charge Question C4 requests

comment on EPA’s justification for selection of tumor data used in quantitative

assessment.

Topic #5: Use of the Multi-tumor Bayesian Anal ysis in Derivation of the Inhalation Unit

Risk (IUR) –

DoD suggested that the Bayesian approach used by EPA to develop a combined estimate of

cancer risk across several tumor sites “appe ars suboptimal” and recommended that a different

type of Bayesian analysis be performed. The approach suggested involved a multistep process

first analyzing “data of carcinogens alone and that the results of th is analysis be updated by the

combined cancers and non-neoplastic tumors.” The comment also suggested that EPA’s

analysis was in conflict with the standard assu mption in dose response modeling that risk

increases (monotonically) with dose.

EPA Response: EPA’s goal in the assessment is to conduct a statistical analysis to

estimate the combined risk of different t ypes of tumors resulting from exposure to a

chemical. The analysis performed by EPA (using “diffuse priors”) is an application of a

widely used statistical methodol ogy that supports broad applica tion of Bayesian statistical

methods in data analysis (see for example, T. Ando in Bayesian Model Selection and

Statistical Modeling ; Chapman & Hall/CRC, 2010). The specific statistical procedure

employed followed a peer-reviewed publis hed methodology (Kopylev et al. 2009). The

Bayesian analysis used in the draft assessm ent yielded a risk estimate that was closely

similar to the value estimated using non-Ba yesian statistical methods, confirming the

reasonableness of these results. EPA also notes that its analysis conf orms to the principle

that response increases with dose since EPA’s modeling is based on application of the

(monotonically increasing) multistage model. The External Peer Review charge question

C5 requests comment on EPA’s methods for deriving an IUR.

The suggestion of the above comment that a two stage Bayesian approach be

implemented (first analyzing data on ma lignant tumors, then in a second step

incorporating both malignant and non-malignant tumors) might be suitable for

consideration in a research i nvestigation; however, EPA does not see its advantage and is

unsure whether it could be successfully implemented.

A-6Appendix

National Institute of Environmental Heal th Sciences/National Toxicology Program

(NTP) comments

Center for Disease Control/Agency for Toxic Substances and Disease Registry (ATSDR)

comments

National Aeronautics and Space Ad ministration (NASA) comments

Department of Defense (DoD) comments

Office of Management and Budget (OMB) comments

A-7National Institute of Environmental Health Sciences/National Toxicology Program (NTP)

Comments on the Interagency Science Consulta tion Draft IRIS Toxicological Review of

1,4-Dioxane (dated May 2011)

Date: June 3, 2011

EPA has done an outstanding job in integrating recently published data on inhalation toxicology

and carcinogenesis studies to th e existing draft document prepar ed based on oral studies for 1,4-

dioxane. The derivation of POD, uncertainty factors, RfC and IU R are all clearl y and logically

presented. The only comment we have is for EPA to consider deletion of Tables 4-23 and 4-24

since there is no data available for any of the mode-of-action assumptions.

Submitted by:

Rajendra S. Chhabra, BVSc.,PhD.,DABT

NIEHS/DNTP

A-8Center for Disease Control/Agency for Toxic Substances and Disease Registry (ATSDR)

Comments on the Interagency Science Consulta tion Draft IRIS Toxicological Review of

1,4-Dioxane (dated May 2011)

Date: June 8, 2011

From: Agency for Toxic Subs tances and Disease Registry

Subject: Comments on EPA’s Toxicologi cal Review of 1,4-Dioxane (Inhalation)

To: Environmental Protection Agency

We appreciate the opportunity to review EP A’s Toxicological Re view of 1,4-Dioxane

(Inhalation) and the Charge to External Review ers. Overall, we found that the Charge to

External Peer Reviewers is appropriate a nd reflects the recommendations and risk

assessments in the IRIS Summary. Our comments below refer primarily to the

Toxicological Review of 1,4-Dioxane (Inhalation).

General

The recent well-conducted studies by Kasai et al. (2008) and Kasai et al. (2009) were

thoroughly reviewed and incorporated in all relevant sections. Th e Kasai et al. (2009)

chronic study was appropriately used for the derivation of both the RfC for non-neoplastic

effects and the Inhalation Unit Risk (IUR) for neoplastic effects.

Minor comments

Page 56, Line 24: The concentrations in ppm units were also expre ssed parenthetically in

units of mg/m 3 , but the converted concentrations we re rounded off. ATSDR would not

have rounded the concentrations.

Page 56, Line 26: What is “ 195044” in the Kasai reference?

Page 57, Line 23: The sentence: “Changes in hematological parameters were observed at

3,200 ppm....” should be changed to “Changes in hematological and clinical chemistry

parameters...” as AST, ALT, glucose, and tr iglycerides are not hematological parameters.

Page 58, Table 4-15: Male, nuclear enlargem ent, nasal olfactory epithelium, 200 ppm,

5/10 needs a d superscript; p ≤ 0.05 by χ 2 test.

Page 58, Table 4-15: Male, vacuolic change ; olfactory epithelium, 3200 ppm, should be

9/10.

Page 60, Line 27: The sentence “Measurement of hematological parameters...” should be

changed to “Measurement of hematologica l parameters and clinical chemistry

parameters...” See also Page 60 Line 35, and Page 61 Line 19.

A-9Page 63, Table 4-17: For renal cell carcinoma, the 1250 ppm entry “4/50” should show a c

superscript, significantly di fferent from control at p ≤ .01 for Peto test.

Page 87, Line 13: Change “severe” to “sensitive.”

Page 92, Lines 5 and 6: “Human studies of occupational exposure to 1,4-dioxane were

inconclusive; in each case, the cohort si ze was limited and the number of reported cases

were of limited size was small.” Should the word s in italics be deleted?

Page 102, Lines 24 - 27: The following sentence is not exactly corre ct: “A comparison of

13-week and 2-year studies conducted in F344/ DuCrj rats could not be conducted since the

tumorigenic concentration of 1,4-dioxane wa s different from the concentration which

produced nasal toxicities by 13 weeks of exposur e.” In the 13-week study, nasal toxicity

occurred at all exposure concentratio ns from 100 to 3200 ppm, and the 1250 ppm

concentration at which the nasal tumors were seen in the 2-year study fall within the

concentrations of 800 and 1600 ppm in the 13 -week study. Furthermore, on page 117, line

15 and 16, it is noted that the range of expos ure concentrations in the 2-year study was

based on the results of the subchronic study. We therefore suggest that you delete the

sentence.

Page 104, Line 27: The statemen t “Nasal cavity tumors have b een reported in the absence

of cell proliferation (Kasai, et al., 2009) and hyper plasia” seems questionable. On page

894 of the Kasai et al. (2009) study, the study au thors state that “squa mous cell hyperplasia

in the nasal cavity...were observed in the 1250 ppm-exposed group. The squamous cell

hyperplasia occurred primarily on the nasotu rbinate septum, and had...proliferation of

basal cells resembling an early stage of squamous cell carcinoma.”

Inhalation RfC

The rationale and justification for selecting the Kasai et al. (2009) 2-year study as the

principal study and the critical effect are clear, reasonable an d appropriate. ATSDR is in

the process of finalizing its updated Toxicologi cal Profile for 1,4-Dioxane Draft for Public

Comment, which will include the Kasai et al . (2009) study for consideration in deriving a

chronic inhalation Minimal Risk Level (MRL). EPA’s analysis will be helpful in

ATSDR’s deliberations. EP A’s proposed RfC of 0.03 mg/m 3 , which is equivalent to 0.008

ppm, was derived by converting the point of departure (POD) to a human equivalent

concentration (HEC), considering 1,4-dioxa ne as category 3 gas. ATSDR’s proposed

intermediate duration inhalation MRL is 0.006 ppm, based on the Ka sai et al (2008) 13-

week study, but it was derived from a HEC th at was calculated by considering 1,4-dioxane

as a category 1 gas. EPA’s discussion for c onsidering 1,4-dioxane as a category 3 gas is

persuasive and will be considered as ATSDR revises the Toxicological Profile.

IUR for Cancer

The rationale, justification and analysis of the principal study and tumor data are clear,

reasonable and appropriate.

A-10National Aeronautics and Space Administration (NASA) Comments on the Interagency

Science Consultation Draft IRIS Toxicologi cal Review of 1,4-Dioxa ne (dated May 2011)

Date: June 13, 2011

NASA thanks EPA for the opportunity to review and comment on the up dated draft assessment

for 1,4-Dioxane. Upon review, we have the fo llowing comments and i ssues and request EPA

consider addressing the identified issues, prior to submitting this updated draft for peer review.

Global Issues:

• This updated draft (which now includes proposed RfD and RfC levels) demonstrates the

verbosity and lack of ready transparency w ith a lengthy discussion of the literature but

limited clarity on the chosen studies and a ssumptions. NASA has noted this issue in

previous draft assessments and this concern wa s also identified as a systemic concern in

the most recent NAS review on formaldehyde. EPA is encouraged to implement the

guidance provided by the NAS to ensure clear presentation of EPA’s application of

studies in the development of its assessments.

• As this draft was previously subjected to peer review (for the RfD only), NASA

encourages a complete peer review to de termine if EPA adequately addressed the

previous peer review issues and also to c onsider the new data and study forming the basis

of the proposed RfC. Inclusion of new studies (Kano et al, 2009) is a significant change

but without peer review, there is no way to know if this si gnficant new addition addresses

the peer review issue or rais es questions or inco mpatibilities with th e use of Kasai, 2008

and 2008 to estimate the RfC.

• The reader finds it difficult to determine if EP A was responsive to the initial peer review.

Redline strikeouts indicate new language for the proposed RfC but lit tle clarification of

efforts to address outstanding scientific issu es identified during th e first peer review.

Specific Issues:

• The draft lacks clarity and discussion on the Kano et al, 2009 study and its

relationship (and clarificati on of) the JBRC 1998a study. It appears that two different

data sets were used to make conclusions between the two drafts. NASA questions

that use of different data requires signifi cant clarification by EPA and also full peer

review.

• As noted in the previous interagency review, use of the Kociba study remains

problematic, especially as EPA characterizes its decision to use Kociba as the basis of

the RfD as it was “the most sensitive”. The updated draft lack s clear discussion of

why Kociba was chosen and question what is meant by “sensitivity” and its relevance

in this draft. EPA is encouraged to clar ify its choice of Kociba and any issues or

inconsistencies found when comparing the Koci ba and Kasai studies that are the basis

for the proposed RfD and RfC respectively.

A-11A-12 • The lack of studies (only four are mentione d) for the development of an RfC raises

signficant concerns that th e updated draft’s proposed RfC is premature and not

supported by scientific lite rature. The Kasai 2008 and 2009 studies were chosen as

the foundation of the RfC development. EP A, by its own admission, states that the

lack of any corroborating evid ence in other studies for the Kasai result. EPA further

notes the weakness in reliance on this one study but setting UFs of 1000 with

significant levels of uncertainty in all categories. NASA reque sts EPA re-consider

issuing a draft RfC, based on such limited evidence. We also request an in-depth

discussion of how EPA will address peer re view responses, should this very limited

base (one study) source for the proposed Rf C be identified as an outstanding issue.

• The previous interagency review and th e peer reviewers of the proposed RfD

requested EPA consider non-linear extrapolati on. A number of commenters indicated

that the Mode of Action (MOA) could not be readily determined but the MOA was

likely to be non-linear. EPA’s response in the updated draft is to dismiss the peer

reviewers input. NASA requests EPA re-visit this issue, in light of the peer reviewers

input and the lack of solid, defensible data that indicates a linear relationship. This

remains a signficant issue and the updated draft needs cl arifying language to clearly

state EPA’s evaluation. Again, the draft text should contain this clarifying language

and be subject to peer review again.Department of Defense (DoD) Comments onthe Interagency Science ConsultationDraft IRIS Toxicological Review of 1,4-Dioxane (dated May 2011)Date: June 15, 2011/w EPDw UKMTY2Department of Defense Comments on14-dioxane inhalation_Toxicological Review_IASC draft_05-13-11.pdfComments submitted by:Chemical Material RiskManagement DirectorateOrganization: Department of DefenseDate Submitted: 6/15/2011*Comment categories: Science or methods (S);Editorial, grammar/spelling, clarificationsneeded (E); or Other (O). Also pleaseindicate if Major i.e. affectsthe outcome, conclusions or implementation of the assessment.CommentNo.SectionPagesCommentSuggested Action, Revisionand References (ifnecessary)*Category1Global92, 120,133, 136Typographical errors in sentences: beginning line 5, pg92; line 2, page 120; lines 18 and 24 on pg 133; and insentence beginning line 9, pg 136.Please fix typographical and/orgrammatical errors.E2GlobalAs discussed further in specific comments below, DoDhas found that there is sufficient information to support anonlinear extrapolation for the carcinogenic potency of1,4-dioxane, i.e., this chemical works as a promoter thatmost toxicologists would consider sufficient proof fornonlinearity at low doses.We suggest that 1,4-dioxanewould be an excellent case to implement Section 3.3.4 ofEPA's 2005 cancer guidelines.It this section titledNonlinear "Extrapolation to Lower Doses" the guidelinesstate [emphasis added], "Nonlinear extrapolation havinga significant biological supportmay be presented inPer EPA's 2005 cancerguidelines, DoD suggests thatEPA present both a linear and anonlinear extrapolation for thecarcinogenic effects of 1,4-dioxane.SA-7addition to a linear approach when the available dataand a weight of evidence evaluation support a nonlinearapproach, but the data are not strong enough toascertain the mode of actionapplying the Agency’s modeof action framework. If the mode of action and otherinformation can support chemical-specific modeling atlow doses, it is preferable to default procedures.3GlobalWe appreciate EPA’s clear identification of the sectionsof the draft document that have been revised to includethe inhalation pathway analysisand thus, are the focus ofthe current interagency review.N/AO44.2.2.1.257The magnitude of organ weight changes (the percentchange compared to control) is not listed in the Kasai etal. 2008 summary, and as such, the biologicalsignificance of organ weightchanges is indeterminable.Recommend adding the percentorgan weight change comparedto controls from Kasai et al.2008 in the study summary.EPA should also present thedose-related organ weighteffects and magnitude ofchange in tabular format toincrease clarity and easecomparisons betweenhistopathologic effects andorgan weight changes.E54.2.2.1.258The DoD agrees with EPA that the endpoint "nuclearenlargement" is of uncertaintoxicological significance.Therefore, it is unclear why EPA chose to utilize theKasai et al. 2008 author-identified LOAEL of 100ppmbased on "slight nuclearenlargement of nasalepithelium". This LOAEL is then carried forwardthroughout Section 4 in thesummary discussions andcomparison tables (e.g., Table 4-22).EPA should identify their ownLOAEL/NOAEL from Kasai etal. 2008. We recognize thatthis suggested revision will notimpact the RfC derivation,however it is recommended thatEPA consider the male vaculoicchange in olfactory epitheliumSA-8at 400ppm as the LOAEL fromKasai et al. 2008, instead of thenuclear enlargement ofrespiratory epithelium.Additionally, if EPA wouldmove discussion andpresentation of toxic endpointsthat have been rejected as eithernot relevant or as not fittingcriteria for goodness of fit forBMD modeling to an appendixthe text would be moreclear and succinct.64.2.2.2.261EPA's treatment of the endpoint"nuclear enlargement ofepithelial cells" is not transparently described. It wouldbe beneficial for EPA to indicate within the Kasai et al.2009 summary in Section 4.2.2.2. that they discount theeffect that was identified by the study authors as theLOAEL (nuclear enlargement of nasal and respiratoryepithelium) due to uncertaintoxicological significance,and chose 50 ppm as the EPA-derived LOAEL forrespiratory metaplasia and atrophy in the nasal olfactoryepithelium. For clarity, EPAshould list their toxicologiceffect only as the LOAEL in Table 4-22.Recommend adding a clarifyingstatement regarding EPA'sdecision to dismiss the nuclearenlargement of nasal andrepiratory epithelium as"adverse" given the uncleartoxicological relevance of thisendpoint within the Kasai et al.2009 study summary in Section4.2.2.2. This should also beindicated in Table 4-22 as theEPA-derived LOAEL fromKasai et al. 2009.S74.683Nasal and respiratory effects following inhalation of 1,4-dioxane have not been included in the general overviewparagraph of the "Synthesis ofMajor Noncancer Effects."Recommend adding nasal andrespiratory effects and theKasai et al. 2008 and 2009citations to the overviewEA-9introduction paragraph tosection 4.6.84.6.286-88Section 4.6.2 "Synthesis of Major Noncancer Effects:Inhalation" is well written and objectively summarizesthe available noncaner 1,4-dioxane inhalation data insufficient detail, without overly repeatative information.N/AE94.7 and5.290-107,115-123The DoD believes that the available data strongly suggesta lack of genetic toxicity and a tumor promotionmechanism associated with tissue injury and subsequentregeneration as the MOA for 1,4-dioxanecarcinogenicity. 1,4-Dioxane mediated hepatocyte cellproliferation has beendemonstrated (Slott 1981;Goldsworthy 1991; Miyagawa 1999) and numerousmechanistic studies have also demonstrated theproliferation-potential of1,4-dioxane. The MOA for 1,4-dioxane induced liver cancer involves sustainedcytotoxicity followed by regenerative and unregulatedcell growth. Furthermore, liver cytotoxicity occurs onlyat doses above which metabolic detoxification pathwaysare saturated.We believe that the dose-response curve can be assumedto be nonlinear inthe low-dose region.Recommend using a nonlinearapproach for low doseextrapolation of cancer risk. Atthe very least, both approachesshould be presented, andqualitatively and quantitativelycompared. If EPA still assertsthat the MOA information forliver tumor formation isinsufficient to move from thedefault linear extrapolationmethodology, it should beclearly stated as a scientificpolicy determination, and thequantitative impact of thatdecision presented.S/M104.7.190, line 21The term "peritoneal" is properly used as an adjective asin "peritoneal tumor" or"pertioneal cavity"; whenreferring to the membrane organ itself, the term"peritoneum" should be used.Change "peritoneal" to"peritoneum" on life 21 of page90.E114.7.293, line 21The single sentence paragraph on line21 is out of place.Recommend removing theEA-10The information regarding the tumor promoting potentialof 1,4-dioxane should be expanded and added to thecarcinogenic weight of evidence and/or MOAdiscussions.sentence on page 93, line 21and adding a summary of 1,4-dioxane's tumor promotingpotential to the cancer weightof evidence or MOA sections(sections 4.7.1 or 4.7.3,respectively).124.7.2and4.7.3.292-93, 96The negative hepatic and nasaleffects from Torkelson etal. 1974 at 111ppm 1,4-dioxanefor 2 years is notsufficiently discussed andshould be more clearlypresented for transparency and a more balanced weightof evidence analysis.Recommend additionaldiscussion regarding thenegative findings of Torkelsonet al. 1974. This study possiblyprovides a lower bound ontumorigenic effects and isimportant for the weight ofevidence discussion.S134.7.3ModeofAction,5.4.4.2and5.5.1.192-100,135 and138Canada’s assessement of this chemical (1,4-DioxaneScreening Assessment, Environment Canada, HealthCanada, March 2010 (Chemical Abstracts ServiceRegistry Number 123-91-1that has already been peerreviewed)states:“Based principally on theweight of evidence–basedassessments of several international and other nationalagencies and available toxicological information, criticaleffects associated with exposure to 1,4-dioxane aretumorigenesis following oral and inhalation exposure,but not following dermal exposure; and other systemiceffects, primarily liver andkidney damage, via all routesof exposure (i.e., oral, dermal and inhalation). Thecollective evidence indicatesthat 1,4-dioxane is not amutagen and exhibits weak clastogenicity in some assays,We strongly suggest that EPAreview the analysis by Canadaand that it either (1) agree thatthe dose-response function hasa threshold, i.e., is nonlinear atlow doses per EPA’s 2005cancer guidelines terminologyor (2) explain the flaws in theCanadian analysis. Whilerecognizing that thesegovernments operate underdifferent legislation andguidance, DoD believes thattransparency and clarity arebetter served if either analysesof the same data are consistentSA-11but not others, at high exposure levels often associatedwith cytotoxicity. Consideration of the availableinformation regarding genotoxicity, and conclusions ofother agencies, indicate that1,4-dioxane is not likely tobe genotoxic. Accordingly, although the mode ofinduction of tumors is not fully elucidated, the tumorsobserved are not considered to have resulted from directinteraction with genetic material. Therefore a thresholdapproach is used to characterize risk to human health.”[emphasis added] (URL:http://www.ec.gc.ca/substances/ese/eng/challenge/batch7/batch7_123-91-1.cfm)or if differences are clearlydescribed so that stakeholdersare not required to infer them.144.7.394, lines23-26There is a logical disconnect in this sentence: Kociba’spaper suggested hepatotoxicity is “the result ofaccumulation of parent compound, however non in vivoor in vitro assays have examined the toxicity ofmetabolites resulting from 1,4-dioxane synthesis tosupport this hypothesis.” Themeaning is unclear. Thesecond part of the sentence appears to be unrelated to thefirst part.If the writer intended to say thattoxicity of metabolites has notbeen ruled out, that should bestated more clearly.E154.7.3.2.296, line 29As stated, it is unclear whether the Nannelli et al. 2005study evaluated possible reactive intermediates and didnot have sufficient information, or conversely, if they didnot assess possible reactive intermediates.Recommend clarifying thesentence on line 29, page 96regarding Nannelli et al. 2005'sassessment of reactivemetabolites.E164.7.3.5and5.5.1103, 138As discussed for the noncancer evaluation, the humanrelevance of the observed carcinogenic nasal effects inrodents is uncertain. The brief mention of thisuncertainty in Section 5.5.1.3, pg 130 is insufficient.Recommend additionallanguage within the "NasalCavity" Section of 4.7.3.5"Biological Plausibility andCoherence" and within Section5.5.1 "Sources of Uncertainty"SA-12regarding the uncertain humanrelevance of rodent nasaleffects due to differences in thephysiology of respiratorysystems.175.2.1ChoiceofPrincipalStudies117, lines25;28;118, Table5-5Page 117 of the U.S. EPA draft states that “All systemicand portal-of-entry nonneoplastic lesions from the Kasaiet al. (2009) study that werestatistically increased at thelow- or mid- exposureconcentration (50 or 250 ppm)compared to controls, [emphasis added]or the lesionsthat demonstrated a dose-response relationship in theabsence of statistical significance[emphasis added]wereconsidered candidates for the critical effect.”This section states: “The candidate endpoints includedcentrilobular necrosis of the liver, spongiosis hepatis,squamous cell metaplasia of nasal respiratoryepithelium, squamous cellhyperplasia of nasalrespiratory epithelium, respiratory metaplasia of nasalolfactory epithelium, sclerosis in lamina propria of nasalcavity, and two degenerative nasal lesions, that is,atrophy of nasal olfactory epithelium[emphasis added]and hydropic change in the lamina propria (Table 5-5).”Lesions that demonstrated adose-response relationship inthe absence of statistical significance should not beconsidered as candidates for the critical effect due to thelack of robustness and greater amount of uncertaintyassociated with these data.We do note that Kasai et al.,2009 reported p<0.01 by Fisher’s exact test for atrophy;olfactory epithelium (this effect in 40/50 male rats at 50ppb of 1,4-dioxane via inhalation), which is statisticallyWe recommend that the textdifferentiate between thosenon-neoplastic lesions whoseincreases were statisticallysignificant at various exposureconcentrations and those thatjust demonstrated a doseresponse relationship in theabsence of statisticalsignificance. We recommendthat the latter should not beconsidered as candidates for thecritical effect due to the lack ofrobustness and greater amountof uncertainty associated withthese data sets.S/MA-13significant.185.2.1;Table 5-8footnote c,Table5-10footnote e117 lines3-5, 128,130Page 117 states that [emphasis added]“Because Fairleyet al. (1934) did not presentthe statistics of the doseresponse data,[emphasis added]neither study wassufficient to characterize the inhalation risks of 1,4-dioxane.”The lack of reporting on the statistics of the doseresponse as policy reason foreliminating the Fairley etal. data appears to be applied inconsistently. Neither thestatistical analysis nor the incidence data ofhepatocellular adenoma or carcinoma for the Kasai(2008) study were published in a peer reviewed journal.Table 5-8, footnote “c” states that, “....For Kasai et al.(2009) incidence data was provided via personalcommunication from Dr. Tatsuya Kasai to Dr. ReederSams on 12/23/2008 (2008).Statistics were notreported.”[emphasis added]Table 5-10 on page 130, footnote “e”, states,“Providedvia personal communication from Dr. Tatsuya Kasai toDr. Reeder Sams on 12/23/2008 (2008). Statistics werenot reported for these data by study authors,so statisticalanalyses were conducted by EPA.[emphasis added]For both clarity andtransparency, we stronglyrecommend that EPA eitherapply its policies in a consistentmanner or provide the rationaleas to why these datasetsappeared to be treateddifferently, i.e., why EPA didnot reject the Kasai study butdid reject theFairley study;why EPA chose to contact Dr.Kasai but not Dr. Fairley, andwhy EPA chose to perform itsown statistical analysis on theKasai data but not on theFairley dataFurthermore, for otherchemicals, EPA has stated thatthey will not use unpublisheddata. We suggest that EPA alsoprovide stronger justificationfor using unpublished data thatcan not be easily verified andthat has not been externallypeer reviewed. Alternatively, ifthis is a change in EPA policy,it should be so stated.S/M195.2.2120It is unclear why sclerosisof the lamina propria isexcluded as a potential critical effect (line 1-2).Recommend explicitjustification for excludingEA-14sclerosis of the lamina propriaas a potential critical effect forRfC derivation.205.2.2120We agree with the choiceof Kasai et al. 2009 as theprincipal study for the derivation of the RfC, however wedisagree with the choice ofany nasal effect for thecritical effect. Giventhe physiologic differencesbetween the respiratory systems of rodents and humans,the uncertainty in the biological plausibility of nasal andrespiratory effects from 1,4-dioxane exposure in humansneeds to be considered. The more highly convolutednasal turbinate system of arodent results in greaterdeposition in the upper respiratory track; the humanrelevance of observed adverseeffects in that area isuncertain. Furthermore, it seems that this particular ratstrain is highly sensitive torespiratory effects, as notedby the high rate of effects in control animals.Recommend use ofcentrilobular necrosis in theliver from Kasai et al. 2009 asthe critical effect. Use of theBMD-derived POD fromcentrilobular necrosis in theliver would result in acomposite UF of 100 (no UFLOAEL-to-NOAEL is needed)and an RfC of 0.4 of 4 x 10-1mg/m3.If EPA elects to maintainolfactory epithelial atrophy asthe critical effect, theuncertainty regarding thehuman relevance of thisendpoint needs to be clearlydescribed and added to Section5.3.S/M215.2.3,5.4.3.2p.119,lines 3ff.,p133,lines 1-3119Adjustment for the exposureduration appears to be basedon application of default procedures rather thanconsideration of the data.Adjustments to dosage arebeing made by scaling the actual dose to a 24-hour, 7day/week exposure. However, since it is known thatmetabolism of dioxane by ratsis subject to saturation, itis questionable whether or notthis procedure adequatelyreflects a chronic exposure. The endpoints of interest areWe recommend that the actualexposure, rather than theaveraged exposure be used forRfC calculations. If not, werecommend that EPA describewhy this adjustment isappropriate in this case forinhalation exposure andS/MA-15(1) at the point of exposureand (2) most likely to beinfluenced by the peak exposure, not the averageexposure. Application of thisprocedure assumes that thesystem obeys Haber's Law and that only the AUCmatters. It is possible thatduring the actual exposureperiod, metabolic processing capacity is exceeded, and itis known that neoplasms are more likely to occur in ratswhere metabolic capability has been exceeded. Theadjustment serves to artificially lower the exposure thatwould cause the effect, an adjustment that is notsupported by biological considerations.damage to the respiratoryepithelium.225.2.3121, lines8-9EPA should acknowledge that the respiratory tract effectsobserved after oral exposure to1,4-dioxane could still beconsidered portal-of-entry effects given that the 1,4-dioxane was administered via drinking water, whichcould have been aspirated when drank by the rodents.Recommend clarifyinglanguage that the respiratorytract effects seen in rodentsadministered 1,4-dioxane viadrinking water may or may notbe systemic effects due topossible aspiration of water anddirect contact of 1,4-dioxanewith respiratory tissue.S235.2.3ExposureDuration andDosimetricAdjustments121Though justified for assessing systemic toxicity, theadjustment for absorption of the chemical appearsunjustifiable for point-of-contact toxicity.Recommend that EPA shouldeither not perform thisadjustment or provide specificjustification for its use forpoint-of-contact effects.S/M245.4Cancer125In the Toxicoligical Profile for 1,4-Dioxane, ATSDR astates that“the use of a nonlinear approach to low doseSimilar to other commentsabove, DoD suggests that EPASA-16Assessment5.4.1.1ChoiceofStudyDataextrapolation might be considered based on theobservation that liver toxicity, which some havesuggested may be required for tumor development,occurs only at doses above which the metabolism of 1, 4-dioxane is saturated.”http://www.atsdr.cdc.gov/toxprofiles/tp187-c2.pdfeither use a nonlinearextrapolation from the point ofdeparture or explain why itdisagrees with ATSDR’sanalysis.255.4.2,Table 5-8,5-10,5-13,5-14,5.5,A.11127 lines6-13, 128line 1,130, 136-142According to the text on pages 127-128, “...1,4-dioxaneproduced a statistically significant increase in incidenceand/or a statistically significant dose-response trend forthe following tumor types[emphasis added]:hepatomas,nasal squamous cell carcinomas, renal cell carcinomas,peritoneal mesotheliomas, mammary glandfibroadenomas, Zymbal gland adenomas, and subcutisfibromas (Kasai, et al., 2009).”It is very important to clearly differentiate between thestatistically significant tumor incidence[emphasis added]data in various organs/glands compared to controls out ofthe group of 50 male rats) from just “a statisticallysignificant dose-response trend [emphasis added].”Theyshould not carry the same weight of evidence forcarcinogenicity,from inhalation exposure. It is crucialthat renal cell carcinomas, mammary glandfibroadenomas, and Zymbal gland adenomas data not beused to derive the “Bayesian Total Tumor Analysis”(Table 5-13, page 136) as if they were of the sameimportance (same robustness ). We believe that thisdoes not represent use of “sound science.”The authors of the Kasaiet al. 2-year inhalation“principal” study of 1,4-dioxanein air (2009) reportedWe strongly recommend thatU.S. EPA not use renal cellcarcinomas, mammary glandfibroadenomas, or Zymbalgland adenomas data to derivethe “Bayesian Total TumorAnalysis”. At a minimum, asmentioned in anothercomments, only sites that havesome carcinomas should beincluded in any quantitative orqualitative analysis ofcarcinogenicity, according toEPA's cancer guidelines. Wefirmly believe that thestatistically significant tumorincidence should bedistinguished from data thatonly showed a statisticallysignificant dose -responsetrend. We also recommend thatthose tumors that increasedwith dose but did not exhibitstatistical significance bedistinguished as not havingS/MA-17that [emphasis added] “...repeated inhalation exposureto 1,4-dioxane vapor for 2 yr was found to produce adose-dependent and statistically significant increase[emphasis added]in the incidences of nasal squamouscell carcinomas, hepatocellular adenomas, andperitoneal mesotheliomas, as indicated by Peto’s test andFisher’s exact test, respectively. In addition, the dosedependently increased tumorincidences were recognizedin renal cell carcinomas, mammary glandfibroadenomas, and Zymbal gland adenomas, althoughthose increased incidenceswere not statisticallysignificantcompared with the concurrent, matchedcontrols by Fisher’s exact test.”Also confirming these findings, the 2010 Canadian 1,4-dioxane health assessment (which was externally peerreviewed) reported that the 2-year Kasai et al. ( 2009)“key” rat study found “Dose-dependent and significantincreases in incidences[emphasis added]of nasalsquamous cell carcinomas andhepatocellular adenomaswere observed primarily in the 1250 ppm (4500 mg/m3)exposed rats and a significantly increased incidence ofperitoneal mesotheliomas was observed at 250 ppm (900mg/m3) and above.The incidences of renal cellcarcinomas, fibroadenomas in the mammary gland andadenomas in the Zymbal glandalso increased with dose,but were not statistically significant.[emphasis added](http://www.ec.gc.ca/substances/ese/eng/challenge/batch7/batch7_123-91-1.cfm)strong evidence ofcarcinogenicty, especially whensites with statisticallysignificant increases arereported in the same analysis.If EPA decides nonetheless tocontinue to include them intheir evaluation, sites that donot have a statisticallysignificant increase incarcinomas should not carry thesame weight in the Bayesiananalysis. We do not believethese data have sufficientweight of evidence forcarcinogenicity and will resultin an inaccurate, scientificallyunjustifiable, and highlyinflated inhalation unit riskestimate.Weighted Bayesian analysesare a standard practice of thisform of meta-analysis, andshould be used in a case such asthis when data are of significantand obvious difference inquality. Most statisticiansA-18would recommend that theBayesian analysis be performedtwice: once with only thehighest quality data and oncewith all of the dataappropriately weighted forquality. Comparison of theresults provides an indication ofthe effect of the lower qualitydata on the results, from whicha decision about their inclusioncan be made from data ratherthan inference.265.4.1.2InhalationStudy/Data128, Table5-8The incidence of subcutis fibroma in Table 5-8 decreasesfrom 9/50 at 250 ppm to 5/50 at 1,250 ppm. This lack ofan increased response at thehighest dose tested is notmentioned in the text and is not fully described in thetable's footnote. We believe the responses are notbiologically relevant and should be more fully described.Since the decrease in tumors atincreasing doses is not due toan asymptotic approach of100% response. The biologicalsignificance of this nonmonotonic increase in the doseresponse function needs to bejustified. EPA should discussthe lack of an increase withincreasing dose of this effectthough the effect at 250 ppmwas found to be statisticallyelevated.S275.4.2.2Inhalation Data129 - 130EPA’s 2005 and previous cancer guidelines are veryclear: adenomas or firbromas can be added to thecarcinomas, but these lesions alone are not considered inthe estimation of carcinogenic risk.Therefore, all ofEPA’s cancer risk that depend on use of doses for whichWhile it is acceptable practiceto combine these tumor types,we strongly recommend thatEPA analyze the appropriatedata with carcinomas alone andS/MA-19there were only adenomas or fibromas, which we believeare the estimations on which EPA has relied for itsanalysis of the IUR, shouldbe recalculated without theselesions. Moreover, it is also commonly understood thatnot all of these non-cancerous lesions will progress tocancer.with those doses wherecarcinomas and adenomas orfibromas were added. Thisanalysis will serve as a usefulquantitative measure of theuncertainty of the risk estimate.285.4.2.2Inhalation Data130, Table5-10Combined tumor endpoint dataare rarely reported andmust be obtained from the original data. The combinedliver tumors (adenomas and carcinomas) and peritonealmesotheliomas are by far the most common neoplasticlesions at high doses. The combined effect of the tumorscan only be estimated by reviewers if it is shown whichof the 3 or 4 rats with liver tumors at 250 ppm are alsoamong the 14 rats with peritoneal mesotheliomas, and ifany of the 21 to 23 rats withliver tumors at 1250 ppm arealso among the 41 rats with peritoneal mesotheliomas,and how many rats have both types. Without these data,it is not possible to independently review that theappropriate data have been combined, i.e., that thenumber of tumors that wereassigned to any dose did notexceed the number of tumor-bearing animals at thatdosage.The use of unpublished data in Toxicological Reviewthat have not been externallypeer reviewed impedes thetransparency of their analysis. Without these data,neither we nor the external reviewers of a panelorganized by EPA can appropriately review and validatethe procedures used.Please supply the datadiscussed in the comment inorder to allow a full review byexternal reviewers and toincrease the transparency of thedocument.SA-20295.4.4.2.Inhalation UnitRisk136, Table5-13As mentioned above, this analysis appears to includesome tumor sites for which there are not any carcinomas.This is contrary to EPA’s 2005 and 1986 cancerguidelinesThe quantitativeand qualitativeanalyses of carcinogenesisshould only include sites forwhich some dose-relatedcancers have been observed.Sites for which only nonneoplastic tumors wereobserved cannot be included inthe analysis, unless EPAjustifies this departure from itsguidance and standardprocedures.S30Appendix FF-13, F-14; TableF-2The text states that the lowest AIC value was used toselect the Dichotomous Hill model. Yet this model hasan AIC of 130.404and the Log-logistic model has anAIC of 129.465EPA should use the log-logisticmodel or change its explanationof the choice of model.S31Appendix GGlobalAlthough EPA does not provide printouts for all of themodels, we believe that, in some cases, EPA iscomparing AICs for modelswith different degrees offreedom. If this is true, such comparisons are not valid,as the AIC depends on the degrees of freedom.We would like verification thatthe models being comparedhave the same degrees offreedom and assume otherreviewers and stakeholderswould as well. Please add theprintouts for all of the modelsor include more information onthe modeling parameters.S32G.3.MultitumorAnalysis UsingBayesiaG-61The Bayesian approach used by EPA appearssuboptimal. Given the available data, it would seemreasonable to optimize the value of Bayesian analysis,i.e., its ability to update thepriors with new data. Werecommend that, if EPA choosesto start with a defuseprior (which is problematic, given that the models in theWe recommend that EPAconsider procedures thatoptimize the Bayesian approachfor combining data byminimizing the effect of choiceof initial prior. DoD alsoSA-21A-22nMethodsBMD software require amonotonically increasingfunction) that the first posterior be based on the data ofcarcinogens alone and that the results of this analysis beupdated by the combined cancers and non-neoplastictumors. By using the process twice, the choice of initialprior will be less significant. Similarly, the individualsites could be used separately and combined.suggests that this newprocedure undergo a separate,external peer review by expertsin statistics.Office of Management and Budget (OMB ) Comments on the Interagency Science

Consultation Draft IRIS Toxicological Review of 1,4-Dioxan e (dated May 2011)

Date: June 16, 2011

General Science Comments:

• While we recognize that EPA st aff are trying to provide clarity, we suggest either revising or

dropping the fact sheet. The RfC derivation as de scribed in the tox review does not fully track

with the fact sheet. For example, in reading the Fact Sheet, we were confused as to why EPA

was treating Kasai 2009 as a subchr onic study. It may be easiest to just drop the Fact Sheet.

• It seems that EPA is proposing an RfC which is in the range of backgr ound level. According to

HSDB, the average value of 1,4 dioxane in US air was 1.029 ppb. Rough calculations tell us that

this is equivalent to about 4x 10-3 mg/m3, which is less than an order of magnitude away from

the proposed RfC. Considering the closeness of the values, and what may be known about ranges

of background exposures, it would be helpful to en sure that the RfC is plausible and that the

incidences of nasal lesions expected can be pr edicted by current exposur es. In particular, we

recognize that rats are obligate nose breathers wh ile humans are not. It is not clear how EPA has

taken this into account when considering the rele vance of the RfC to humans. We note that EPA

applies an UF of 3x for interspecies comparis on but this implies that humans would be more

sensitive, not less sensitive to a similar dose.

• Similar to the comment above, what would be the expected cancer ri sks at current background

US levels (1ppb or about 4ug/m3) and is this cons istent with cancer incidence data? Similarly, do

we expect the same risks from 1,4 dioxane as we do from other compounds with a similarly low

IUR? Discussion of this in the ca ncer section would be helpful.

• While 1,4 dioxane is not a chemical of great br oad concern, if EPA is going to propose an RfC

and IUR that is within the range of background exposures, EP A may want consider a more

robust SAB or NAS review (compared to a contr actor run panel review) to assure that the

scientific underpinnings of the values are scient ifically sound.

• In discussing the mode of action (MOA) for na sal tumors, as per page 95, it appears that data

exist to support a non-linear mode of action as the Kasai studie s show accumulation related to

saturation at high doses. We recogni ze that data gaps exist, could this MOA still be considered

plausible and having significan t biological support as per EP A cancer guidelines? Page 104

states that data on key events is missing, however it is not clear that this implies that there is not

biological support for a non-linear MOA. EPA’s discussion could be strengthened and clarified

here.

• It is not clear why EPA uses and presents data only for the male rats from Kasai 2009. Page

117 discusses that no mesotheliomas were seen in female rats exposed via drinking water,

however it is unclear why female data, relati ng to the RfC and nasal effects should not be

considered and presented. If Kasai 2009 evaluated female rats (page 117 implies that it did), we

suggest including this discussion and consid ering the effects seen in females.

A-25• More clarity is needed regarding EPA’s determ ination of the level of adversity of the nasal

lesions (atrophy of the olfactory epithelium) throughout the RfC discussions. As per page 120,

throughout the document and in the charge, EPA should clarify that this is a precursor effect,

likely to occur early in the continuum of pathological events associated with the respiratory tract.

• EPA states that the BMD mode ling resulted in a poor fit for the RfC. However when we look

at Appendix F, many of the p valu es for fit, were >0.1 and thus wouldn’t they be considered to

have a good fit (for example, see page F-14 where this is the criteria as defined by EPA)? EPA

clearly states that if the p value is <0.1, then there is a lack of fit. However in most tables in

Appendix F, the p value is greater. Additionally, it is unclear what model uncertainty EPA refers

to (page 118) when discounting use of some of the BMD values.

• As the RfC is based upon effects in the nasa l epithelium, it is not clear why EPA is saying

there is a lack of clarity regard ing whether or not these are portal of entry effects. It would be

helpful to run the analysis treating 1,4 dioxane as a Category 1 gas to see what impact this has on

the RfC. Presenting this information to the publ ic and peer reviewers will help them to

understand the impact of EPA’s decision. A charge question on this determination would also be

helpful.

• EPA uses an uncertainty factor of 10x to acco unt for use of a LOAEL. Since the effects seen

are minimal and early in the continuum, it is not clear why a full 10x factor is needed. Further

justification of this choice would be helpfu l for peer reviewers and public commenters.

• To support the choice of 3x for the database uncer tainty factor, it would be helpful to provide

more discussion of the doses used in the oral pr enatal development study to see if effects would

be predicted at the point of departure used for th e RfC. Even a back of the envelope calculation,

taking kinetics into account, would be helpful.

• It is not clear why EPA has medium confid ence in the RfC. There are three orders of

magnitude of uncertainty, including uncertainties in four different areas . We suggest that the

confidence in this derivation should be considered low.

• Page 130 shows that there were no statis tically significant increa ses in hepatocellular

carcinomas. Thus it is unclear why EPA has comb ined hepatocellular ad enomas and carcinomas

to look at combined impact. It is obvious that th is will be driven by the statistically significant

adenomas, seen only at high doses . Further rational for combini ng these tumors is needed. If

EPA had evaluated hepatocellular adenomas only, what would the IUR have been? This

information should be presented in Table 5-13 and should be discussed. Similarly, it is not clear

why EPA is calculating IUR estimates for cancer e ndpoints that were not st atistically significant.

We suggest adding a charge question on this.

Editorial Comments (with Scientific Impacts):

• Page 56, and elsewhere, when referring to Kasai, et al, it is important to always be clear about

whether the reference is to the 2008 or 2009 study.

A-26• Page 57, lines 17-28, it may be helpful to present this information in a table.

• Page 139, line 26-28, this discussion should men tion that rats are obligate nose breathers while

humans are not. The impacts of this on the RfC should be discussed.

• Page 142, table 5-14, please revise this to reflect the uncertainties in the RfC.

Comments on the Draft Charge:

[Note: some suggestions for charge questions ar e provided in comments in the above sections.

Many of those comments have not been reiterate d here, but should be considered as equally

important.]

• It would be helpful if paragr aph 2 of the charge discussed cu rrent background exposure levels

in the context of the proposed RfC and IUR. This will also help to frame the issue of whether we

are seeing results in the general population cons istent with the final values EPA proposes.

• Please add a question asking reviewers about ho w they would interpret the proposed RfC and

IUR in the context of kn own background levels.

• General Questions 2: It is unc lear how reviewers will be able to tell if additional studies

“would have a significant impact on the conclusions.” Suggest reframing this to simply ask about

relevant studies and then EPA can conduct further evaluation to determine if the studies will

have a significant impact.

• In B2, EPA calls ‘atrophy of the olfactory epithelium’ a critical e ffect. Please clarify for

reviewers that this is precursor effect and not adverse. Suggest also taking comment on EPAs

determination of it as be ing a precursor effect.

• In section B, please have separate questi ons taking comment on EPAs use of the dosimetric

adjustment factor, the HEC calculation, as well as the determination to treat 1,4 dioxane as a

category 3 gas (not solely with portal of entr y effects) for the purpos e of deriving the RfC.

Similarly, if they are relevant, these questi ons should also be added to section C.

• In section C, please add the following specific questions:

• Ask reviewers to comment on EPAs approach of combining hepa tocellular adenomas

and carcinomas.

• Ask reviewers to comment on EPAs decision to calculate a combined IUR using tumor

endpoints that were not st atistically significant.

• Please ask reviewers to comment on whether or not each of the endpoints used in the

IUR is relevant to humans and should be part of the combined IUR calculation.

A-27A-28