Department of Defense Comments on1,2,4- and 1,3,5-TrimethylbenzeneInteragency Science Consultation Toxicological Review and AppendicesComments submitted by: Chemical Material RiskManagement ProgramOrganization: Department of Defense Date Submitted: 2/9/2012*Comment categories: Science or methods (S); Editorial, grammar/spelling, clarifications needed (E); or Other (O). Also pleaseindicate if Major i.e. affects the outcome,conclusions or implementation of the assessment.CommentNo.SectionPagesCommentSuggested Action, Revision and References(if necessary)*Category1 GeneralDoD believes that the EPA drafttrimethylbenzenes (TMB) Toxicological Reviewrepresents a significant positive change informat and readability.N/A S2 Preamble 2 7EPA 2009 is not included in the list ofreferences.Add the reference to the list in Section 3. E3 Preamble, 3.3 8 - 9Although this section explains the preferredtypes of exposures, the section does not containdefinitions or examples. These definitions in theIRIS glossary are subject to change withoutnotice. DoD would like to see contemporaneousdefinitions of "acute", "subchronic" and "chronic"exposures for both commonly used laboratoryanimals and people; these could be presented ina table.Please supply definitions and examples ofacute, subchronic, and chronic exposures forpeople and for all of the species that are used inthe quantitative analysisof these chemicals.S4 Preamble, 4.2 9In evaluating the quality of an epidemiologicalstudy, EPA does not include the need todemonstrate a reasonable dose-responseEPA should discuss its criteria with regard todose-response observations for epidemiologicalstudies. DoD notes in particular an overS/Mrelationship. As dose-response relationshipsare fundamental to all, high quality toxicologicalstudies, this requirement, and whether the datamust show a positive trend, a statisticallysignificant increase, a biologically significantchange, and/or other criteria should bepresented in this section.reliance on statistics rather than biologicallyinformative information, as well as an absenceof a discussion about dose-response criteria.5 Preamble, 4.3 10In the third paragraph, EPA should state that itwill clearly identify thatits interpretation of thedata differ from the scientists who conducted thestudy, as well as discussing why its conclusionsdiffer. DoD would prefer if EPA would alsocommit to trying to contact at least one of theauthors to determine their reaction to EPA'sinterpretation, and to allow those authors tocomment on EPA's interpretation of the data, asthey may have additional information about thestudy that was not published.Disagreeing with the conclusions of thescientists who designed and conducted anexperiment should only be done when there areclear and undisputed reasons. We suggest thatEPA consider discussing its intendedreinterpretation of the data with the authorsbefore relying on a different interpretation forestimating toxicity of a chemical.S6 Preamble 5.2 11DoD disagrees with EPA's statement that"causality is not at issue in controlledexperiments". Unless a well designedexperiment has been replicated exactly (oftennot the case for the critical experiment on whichEPA bases its RfDs, RfC,and cancer potencyvalues) statistically significant results can befalse positives. At p = 0.05, there is a 1 in 20probability of a false positive, even in a wellcontrolled experiment.EPA should delete this clause or provide at leastone independent reference that would supportits assertion.S/M7 Preamble 5.3 12 EPA's use of the term "genetic toxicity" is not We highly recommend that EPA define "genetic S/Mdefined and is neither clear nor transparent,especially in a section on mode of action(MOA). EPA's 2005 cancer guidelines andguidance do not use this term, but rather refer toa "mutagenic mode of action". Frequently,genetic toxicity includes effects that are notconsidered mutations, the term used in the restof the document. DoD has previouslymentioned EPA's tendency to use the terms"genotoxic" and "mutagenic" loosely, and asthese terms have significant implications withinEPA's guidelines and guidance, we would like tosee more precision in their use.toxicity" and "mutagenicity" (or variants of thosewords), as they have significant implicationswithin EPA's guidelines and guidance. The IRISglossary does not include a reference for"genetic toxi8city" or "genotoxic"; and it does notalways agree with definitions in other parts ofEPA's web sites and canbe changed withoutnotice or review.8 Preamble 5.4 12The text does not mention a critical clause of the2005 cancer guidelines: That the WOE for achemical's MOA can vary by route of exposureor by level of exposure, etc. This section wouldbe interpreted by many individuals as assertingthat only one WOE is possible per chemical perendpoint.EPA should include important options within thisWOE section to clearly and accurately representwhat is in its guidelines. The text shouldexplicitly state that there can be more that oneWOE for carcinogenicity, e.g., a chemical's MOAcan vary by route of exposure or by level ofexposure, etc.S9 Preamble, 7.3 14EPA states that the choiceof point of departure(POD) is based on statistical and biologicalfactors and cites the draft BMD guidance (U.S.EPA 2000b) and EPA's 2005 guidelines forcarcinogen risk assessment. The text goes onto state that for dichotomous responses, a 10%response will be used for "minimally adverseeffects" and "5% or lower for more severeeffects." Neither of the cited references havestatements that agree with EPA's assertion.This language should be removed from thecurrent Preamble and instead included inthe BMD guidance document; suchrecommendations can be proposed by EPA andformally evaluated by the scientific andregulatory community. EPA should also correctthe citations of EPA2000a vs. 2000b.S/MBoth documents indicate that the benchmarkresponse (BMR) that determines the PODshould be near the low end of the range of dataand that a 10% BMR should also be estimatedfor facilitating comparisons across chemicals.These concepts are also applied to thesuggested methods for calculating the POD fromcontinuous data. We know of no such severityrelated guidance regarding the POD fornonlinear extrapolations in either of thesedocuments. The definition of "minmally adverse"or "more severe" is a key aspect of the POD, butthere is no available guidance as to howdifferent effects should be categorized.Furthermore, the BMD guidance is listed in thereferences as U.S. EPA 2000a, rather than2000b.10Preamble 7.3 and7.414These sections, that cover standard proceduresused, contain several statements that are notconsistent with EPA's 2005cancer guidelines. IfIRIS is proposing that these statements arestandard practice within its toxicological review,it should both state that these are deviations andshould provide a rationale for its deviation fromguidelines. We believe that the cancerguidelines are applicable to the entire agency.1. Noneof the cited EPA guidelines orguidance suggests use of a "standardvalue" for a point of departure forextrapolation, much less"(10% responseThis section should be carefully reviewed toensure consistency with EPA guidance and thereferences cited.1. Please delete any reference to astandard response level or value for aPOD for extrapolation. EPA's draft BMDand cancer guidelines refer to use ofstandard values for the purposes ofcomparisons among chemicals, and inthat case the best estimate, not thelower confidence value, isrecommended for use.2. The use of the lower bound should beS/Mfor animal data, 1% for epidemiologicdata, depending on the observedresponse rates)."These values arerecommended as frequently used basedon historical observations of results andthe power of the standard studies.  Theyare also recommended to be estimatedand reported for the purposes ofcomparing potencies across chemicals.The phrase that is in EPA's guidance is"near the low end of the observable rangeis used" which will differ by experimentaldesign.2.The statement that "For dichotomousresponses, the point of departure is the95% lower bound on the dose associatedwith a small increaseof a biologicallysignificant effect." requires addition of thequalifier "generally" or "usually" to beconsistent with the cited sources.  Inparticular, the BMD draft indicates thatthe maximum likelihood estimate shouldbe used for some purposes.3. EPA's guidelines discuss use of abiologially based model to extrapolate tolower doses. They do not advocate"Below the range where confidencebounds on the predictions are reasonablyprecise, extrapolation may continue usinga linear model."qualified, as it is in the cited references.3. According to EPA's cancer guidelines,use of a biologically based modelobviates extrapolation; linear ornonlinear. The statement should eitherbe deleted or clearly explain that IRIS isdeviating from EPA guidance andprovide a rationale for this deviation.4. The concept of a "linear component" or"other activity" as a criterion fordetermining whether the extrapolation islinear or nonlinear should be deleted asinconsistent with EPA's guidance.Otherwise, the text should clearlyexplain that IRIS is deviating from EPAguidance and provide a rationale for thisdeviation.5. The suggestion that exposure levels area criteria for type of extrapolation shouldeither be deleted or EPA clearly explainthat IRIS is deviating from EPAguidance and provide a rationale for thisdeviation.6. IRIS documents should define the terms"genetic toxicity" and "mutagenicity",how they differ (if IRIS scientists believethey do), and how these definitionsrelate to EPA's mutagenic mode ofaction.4.EPA's 2005 cancer guidelinesdifferentiate low doseextrapolation procedures for MOAs thatare linear at low doses, MOAs that arenonlinear (including nonlinear, nothreshold) at low doses, and chemicals forwhich the MOA cannot be determined.They do not provide for a linearextrapolation "the doseresponse curve isexpected to havealinearcomponentbelow the point of departure. [emphasisadded]" .  As many highly nonliearfunction have a "linear component" or canbe fit to curves that have a linearcomponent, this statement directlycontradicts both the text and the intent ofEPA's cancer guidelines.  (DoD notes thatthe concept  of a linear component isdiscussed with regard to chemicals withmultiple MOAs, butdoes not make that acondition that requires a linearextrapolation.)5.EPA's assertion that "Agents or theirmetabolites for which human exposuresor body burdens are near dosesassociated with key events leading to aneffect." is not included in the citedguidelines.  IRIS hasoften asserted thatIRIS documents do not consider exposurelevels.  If this isaccurate, such aconsideration is not relevant to thisdocument.  If IRIS documents do considerexposure levels, this introduction shoulddiscuss those aspects of EPA's cancerguidelines that do refer to exposure, e.g.,different WOEs for different levels ofexposure.6.The statement that "the agent does notdemonstrate mutagenic or other activityconsistent with linearity at lower doses."is not part of the criteria in EPA's cancerguidelines for using a non-linearextrapolation. The guidelines state thatchemicals with a mutagenic MOA, notjust mutagenic activity, are expected tohave a linear extrapolation. Thisstatement asserts a much lower criterionfor imposing a linear extrapolation. Nordo the guidelines reference "otheractivity consistent with linearity" as ameasure. The guideline only discusssuch concepts within the context of theMOA, not individual key events of theMOA.11 Preamble 7.5 15Statement #3 is incorrect. The cited EPAguidance document recommends use of theage-dependent adjustment factors ONLYforchemicals that have been demonstrated to havea mutagenic MOA that do not have chemicalspecific data on early-life exposure, notEPA should correct this misstatement of policy. S/M"suspected carcinogens" as stated here.12 Preamble 7.6 15EPA states that "if the point of departure isbased on toxicokinetic modeling, dosimetrymodeling or allometric scaling", UFA = 10^0.5 isapplied to account for "the remaining uncertaintyinvolving toxicodynamic differences." The U.S.EPA (2011b) guidance states (p 21) that"processes pertinent to the consideration of thisUF are recognized to include both toxicokineticsand toxicodynamics." While IRIS has instituteda "common practice" of asserting such a divisionafter PBPK modeling, it should either provide awritten citation for this practice, and indicatewhether it has been externally peer reviewed, orexplicitly state thatthis is an IRIS-developedpolicy that has or has not been externally peerreviewed. If such a guidance document is priorto 2011, it should also provide a rationale for notfollowing the more recent guidance.EPA should revise the text to accurately reflectU.S. EPA (2011b) guidance.S13Preface,ExecutiveSummary,Literature Search20, 23, 26, 29The table numbering goes Table 1, Table II,Table 3, Table IV.EPA should pick a format (Arabic or Romannumerals) and implement it consistently. DoDwould prefer if this and other editorial errorswere corrected prior to interagency review, asthey increase the difficulty of finding materialwithin the document and understanding thestructure of the document.E14Preface,ProgrammaticInterest21It is stated related isomers, 1,2,3-trimethylbenzene is not included in the review.This is one of the components of mixture ofSuggest adding a brief explanation for notincluding 1,2,3-trimethylbenzene in thetoxicological review.Sthree isomers.15ExecutiveSummary21We noted that the previous TMB PPRTVs notreferenced nor discussed as “Other”Assessments.Please provide a brief discussion of the previousPPRTV values. This isespecially importantgiven the differing conclusions and the fact thatif finalized, the toxicityvalues derived herein willreplace the PPRTV values. These documentsare available to the public and should beaddressed in the IRIS assessment.S16ExecutiveSummary22The first heading suggests a summary of effectsfollowing inhalation exposure to 1,2,4-TMB only,however discusses data, orlack thereof, for bothisomers.EPA needs to clearly match document Headingsto the isomer discussion within. Please add“1,3,5-TMB” to the first heading for clarity.E17ExecutiveSummary22The statement “No human studies were foundfor 1,3,5-TMB” is not accurate, as 1,3,5-TMBexposure was part of the occupational cohort forNorseth et al (1991), (Appendix A.2 pg 48), andis a known constituent ofthe solvent mixturesfrom Battig et al (1958). Additionally, Jarnberg etal (1996), Kostrewski et al (1995, 1997), andJones (2006) studied human volunteersexposed to 1,3,5-TMB and CNS-type effectswere evaluated.Clarify the statement if the intended meaningwas that no human studiesproviding adequatetoxicological informationwere found for 1,3,5-TMB. Although, it is not clear that the 1,3,5-TMB studies are any less informative than thosefor 1,2,4-TMB. Particularly, Battig et al (1958)should be added to the assessment (it wasdiscussed in the respective PPRTVs).S18Executivesummary22It is not true that no human studies were foundfor 1,3,5-TMB. While Kostrzewski et al. (1995)primarily reports toxicokinetic data, it is noted inthis paper that no effects were observed uponfollow up.EPA should revise the text. S19 Executive 22 It is not clear why EPA has chosen to assess Please provide some rationale as to why 1,2,3- SSummary only 1,2,4- and 1,3,5-TMB, not 1,2,3-TMB. TMB is not also assessed.20Executivesummary/global22,23The text is inconsistent regarding the use ofsuperscripts, or in-line use (e.g., 10-2 mg/m3).Superscripts should be consistently used. E21ExecutiveSummary23The UF for database insufficiencies should bereduced to 1. Two reasons are given for thedeficiency.The first reason is the lack of a chronic study.However, EPA has already used a UF of 10 toaccount for this deficiency. Therefore, includingit here is double counting the deficiency.The second reason is the lack of a twogeneration study. As the one-generation studyshowed NO effects at doses that were belowthose that caused maternal toxicity and as theeffects observed were relatively minor andrelated to maternal toxicity, i.e., both had lessweight gain that are known to be associated,most toxicologist would find the conducting of atwo-generational study redundant, and wastefulof resources (including many animals), as noeffects would be expected. Reduction to 1would be consistent with procedures outlined inEPA's RfD/RfC guidance.EPA should reduce the UFD to 1. S/M22ExecutiveSummary23DoD does not understand why the confidence inthe critical study is "medium" as all of thecharacteristics of thestudy (as reported) appearto be according to guidelines. Similarly, givenour comments on reducing the UF on theEPA should definitely change the confidence inthe critical study to "high" or present the reasonsfor considering it "medium". If EPA agrees withDoD on reducing the uncertainty factor for theRfC, EPA should reconsider the overallSdatabase to 1, we believe the confidence in thedatabase for the RfC should also be "high".evaluation of the database.23Executivesummary23, 24, 26UFH and UFS are unnecessarily large. We willamplify our comments below (p 71). It is notappropriate to cite the lack of a chronic study asjustification for UFD (p 23 and 24) because thisgap is captured in UFS.Conduct a sensitivity analysis of human PBPKmodel predictions for the key internal dosemetric to better inform the selection of UFH,reduce the value of UFS, and revise thejustification for, or value of, UFD.S24ExecutiveSummary24DoD does not agree that the combined UFswould be 10,000. First, the previous commentsabout double-counting the lack of a chronicstudy and the inappropriateness of requiring atwo-generational study when the onegenerational study showed minor effects inmaternal toxicity are also appropriate here. Thatwould reduce the combined UF to 3,000.The data presented in Appendix B demonstratethat the UF of 10 for a NOAEL to a LOAEL isunnecessary as well. The data for this isomer fitthe benchmark dose as well as that of the otherisomer. Therefore, a BMDL would be used asthe point of departure, and the composite UFswould be the same as the previous, either 1,000or 3,000 depending on whether EPA agrees withDoD with regard to the completeness of thedatabase.As the data for both isomers is apparently ofequivalent quality, we recommend EPA estimatethe RfC for 1,3,5-TMB from its data rather thaninferring it from 1,2,4-TMB.S/M25Executivesummary25A period is missing near the end of the firstparagraph.Revise "same research institute Overall..." toread "...same research institute. Overall..."E26ExecutiveSummary -Section 1.1 -Appendix A.2There is significant discrepancy between thestudies listed in the Executive Summary, thosediscussed in the endpoint-specific Hazard IDsections, and those summarized in AppendixA.2. DoD cannot find the Appendix StudySummary information for Battig et al(1956)/MOE (2006) (listed as studies of humanexposures to 1,2,4-TMB). EPA is missing Battiget al (1958), which was used in the previousPPRTV so must exist in the translated formsomewhere. Billionnet et al. (2011) issummarized in Appendix A.2., but not listed inthe Executive Summary or Section 1.1.Lammers et al (2007) is summarized in theAppendix under the “summary of animal studies”only; the human summary and study informationshould be broken into a separate studysummary and be located in the human studysection.Please correct these reference errors and makesure the document is properly QA/QC’d.S/M27 1.1DoD appreciates EPA’ effort to synthesize thetoxicological data and provide an integratedsummary of information, HOWEVER, EPAneeds to still provide some of the basicinformation for each study and shouldimmediately direct the reader to the Appendix fordetailed study summaries. For example, dosePlease add a few more details to the integratedhazard identification synthesis and reference thespecific Appendix section that fully describes thestudy.Sranges could be replaced with specificdose/concentrations administered, andsex/species information could be given whereappropriate. It would be helpful to reference theAppendix study summary (explicitly with pagenumber) the first time a study is mentioned.28 1.1.1 25Given that a lack of a suitable oral study (foreither compound) is a significant databaselimitation, it is not clear why EPA did not havethe Koch Industries (1995) study, the basis forthe 2009 1,3,5-TMB PPRTV “Appendix Oralscreening value”, peer-reviewed.EPA should obtain a peer-review of the KochIndustries (1995) oral 1,3,5-TMB study. Further,the resulting chronicRfD of 0.01 mg/kg-day(derived in the 1,3,5-TMB PPRTV), should becompared to and discussed relative to the routeextrapolated and isomer-adopted draft RfD of0.006 mg/kg-day.S/M29 1.1 32While EPA does a good job at the integrateddiscussion of endpoints and the respectivepotential MOAs, the discussion on neurotoxiceffects, in particular, does not highlight that all ofthe available information is circumstantial; a fullfunctional observation battery is missing and thetoxicological significance of most of the animaldata is questionable with significantuncertainties and limitations within therespective studies (only one species, one sex,same laboratory, etc).EPA needs to make sure that an endpoint ispresented in an unbiased manner: the availableneurotoxicity data is weak with significantuncertainties and limitations in each individualstudy.S30 1.1.1 33In various places throughout the text, EPAmentions that the decrease in pain sensitivitymeasured in Korsak and Rydzynski 1996 did notpersist two weeks after exposures wereterminated. And in fact, the table shown inDoD does not feel that the uncertainties andlimitations in Korsak and Rydzynski 1996 areappropriately discussed. Reversibility in theneurobehavioral effects is not adequatelyconsidered in EPA’s interpretation of the data.S/MAppendix A.2-5 (pg 54) clearly shows the loss ofeffect (only the high-dose was tested forpersistence). Yet, this possible “reversibility” ofthe effect is not adequately discussed and may,in fact, make this study/endpoint not suitable forchronic toxicity value derivation. Derivation ofthe RfD/C based on a shorter-term exposurerequires the consideration of reversibility in theinterpretation of the data.Korsak and Rydzynski1996 was dismissed as a potential principalstudy in the 1,2,4-TMB 2007 PPRTV due to“unclear toxicological significance” and“concentration-responses are difficult tointerpret.”Further, given the apparent reversal of the effectand other limitations of the study, we suggestthat EPA reconsider Korsak and Rydzynski 1996for RfC/D derivation.31 1.1.1 34EPA makes inconsistent statements regardingthe relative severity of the two TMB isomers (cf.pages 24, 58).The text should be revised to be consistent. S32 1.1.1 35Further explanation is needed regarding how theopen field test results suggest latency.Presumably the authors mean that after 25days, complete clearance of 1,2,4-TMB isexpected, but this rationale and the authors'rationale for why they did open field testing atthat time should be explained.EPA should more clearly state the rationale forthis statement, rather than expecting the readerto infer this significant comment with regard toassessing toxicity.S33 1.1.1 36The first couple of sentences on this page arepotentially confusing and neither clear nortransparent.Reword the first part of the sentence to state"...exposure to 1,2,4-TMB or 1,3,5-TMB alone"to more clearly indicate the distinction fromexposure to "mixtures containing TMBs".Likewise, clearly indicate that the animal shortSterm spatial memory studies were by inhalationexposure (in contrast to the lack of oralexposure studies noted inthe first sentence).34 1.1.2 and 1.1.4 48, 54The concentrations used in the study should belisted individually (as in Tables 1-1, 1-2, and 1-4)rather than as a range (as in Tables 1-3 and 1-5); the absence of this information limits theutility and clarity of the summary tables. Suchclarity is necessary to review other statements inthe document.Revise Tables 1-3 and 1-5 by listing eachnominal concentration, to better describe thestudy and match the format used elsewhere inthis section.E35 1.1.3 51In the second sentence of this section, thedocument switches from a summary of the lackof human data to discussing animal data withoutidentifiying the species.At first use, note thatthe study was conductedwith rats. We also suggest that the human andanimal data be discussed in separateparagraphs (or separate sections, if the amountof data warrant).E36 1.1.4 54-55On page 55, paragraph one, last line, it isdescribed NOAEL and LOAEL determined fromthese acute exposure studies are providein Table 1-5, but in the table only LOAELs aredescribed.Please clarify and correct. S37 1.1.4 56In the first paragraph, line 3, the years (2000,1997) are provided, butno authors’ names arecited.Please clarify and add authors’ names. E38 1.1.5 56Borriston Laboratories (1984) studyadministered 1,2,4-TMB to Fischer-344 rats bygavage for 4 weeks and examinednephrotoxicity. Although a minor contribution,this study seems to be missing from EPA’sPlease add a mention/reference for BorristonLabs (1984)Eassessment.39 1.2.2 64It would be helpful if this table included theneurological endpoints; it would also make itmore consistent with Table 1-6.Add neurological endpoints to Table 1-7. E40 1.3 66Only one report (Maltoni et al 1997) is providedas weight of evidence for carcinogenicity. Nodiscussion is provided to support the WOEconcerning the mutagenic mode of action.Suggest adding the negative results in severalkey mutagenicity assays in Salmonella and thenegative gentoxicity data from the in vivo assaysfor micronucleus formation in mouse bonemarrow cell to show a stronger WOE toward lackof mutagenic potential.S41 2.1.1 68EPA has chosen, in this assessment, to conductthe benchmark dose analysis using externaldose as the input, rather than an internal dose,as was used in the recent TCE and methanolassessments. The previous approach, of usinginternal dose as the input, has a greatertoxicological relevance, and should be used inall assessments. We note that the weeklyaverage venous blood concentrations do nothave a linear relationship withdose/concentration(e.g., POD ADJ =0.187 mg/L at 174.1 mg/m3 vs. 0.867 at 492mg/m3, for Korsak et al., 2000), so the order ofthe two steps (BMD analysis and internal PODestimation) could have an impact on thecandidate RfC.EPA should redo the analysis with PBPKmodeling first, BMD analysis second, for allendpoints. At a minimum, EPA should redo theanalysis for the key endpoints to identify theimpact of this change from the approach used inthe TCE and methanol assessments. EPAshould update the draft BMD guidance to reflectthis consideration.S42 2.1.1 69The rationale for choosing the weekly averagevenous blood concentration, rather than theseemingly more toxicologically relevant metric ofWe suggest that EPA change their choice ofinternal dose metric, or provide a scientificrationale (preferably with references) for theSweekly average concentration in the richlyperfused tissues should be explained. Theimpact of this choice should be determined viaPBPK modeling.currently selected dose metric.43 2.1.2, 2.1.6, 2.2.2 69, 78, 85None of the HECs/HEDs can be verifiedbecause the model code has not been madeavailable to the reviewers. (This reviewer couldnot find it on the HERO website, as reported inAppendix A.)All necessary supporting information, includingmodel code, should be available to all reviewersat all stages of the review, including interagencyand external reviews. Without the availability ofsuch data, it is not possible to provide anadequate scientific review.S/M44 2.1.2 71EPA has conducted the interspeciesextrapolation prior to the application ofuncertainty factors, despite demonstratednonlinear relationships between external andinternal concentration in rats (page 68) andhumans (page 85).EPA should apply the uncertainty factors to theinternal point of departure (derived from BMDmodeling), then use the human PBPK model toderive the RfC. At a minimum, EPA shouldapply this alternative approach and provide theresults so that the impact of their choice can beclearly identified (and discussed along with otheruncertainties).Moreover, as this appears to be a commonpractice, EPA should provide a reference and arationale for the procedure, for transparency andclarity, so that reviewers can determine if EPA isbeing consistent in its procedures for evaluatingchemicals. When such inconsistencies areobserved in the absence of a written documentfor reference, it is not possible for reviewers toprovide chemical-specific comments on suchcross-chemical inconsistencies.S/M45 2.1.2 71 EPA has underutilized the PBPK model with EPA should conduct a sensitivity analysis of the Srespect to the insights that can be gainedregarding uncertainty factors. A sensitivityanalysis of a relevant human internal dosemetric (e.g., blood or RPT AUC) at theHED/HEC would help identify parameters thathave an impact on EPA's selection among thedose metrics that could, especially in this casewhere significant nonlinearities are obvious,significantly affect the estimated RfC. It ispossible that human variability in, for example,"expression of enzymes involved in 1,2,4-TMBmetabolism" may have minimal impact ondosimetry in other tissues, and support the useof a lower value for UFH.human PBPK model to aid in the identification ofa scientifically robust value for UFH, rather thanusing the default value. As external review peerreview panels have repeatedly requested suchsensitivity analyses of PBPK models, DoD alsorecommends that such an analysis should bepart of the standard practice for EPA's use ofPBPK models, and be performed prior to theexternal peer review. As the results of such ananalysis are expected to significantly influencethe reviewers' opinions ofeither the choice ofdose metric or appropriate use (or magnitude of)uncertainty factors, and EPA prefers not toprovide an opportunity for public or peer reviewcomment after the external peer review, DoDsuggests that all such analyses should beprovided to the external peer reviewers andpublic stakeholders.46 2.1.2 71When assigning the UFD the strengths andlimitations of the database need to be moreclearly discussed. EPA should integrate theavailable information and discuss the overallstrengths and weakness of the database.DoD recommends EPA use an integrativeapproach when discussing the strengths orweaknesses of the total database. The existingdata may provide insight as to whetheradditional information may be needed. EPAmight consider (1) developing a standard tablethat shows presence and absence of data basedon type of study, route, duration, species, sex,life stage and general endpoints examined and(2) using a qualitative and integrated look at thetotal database to inform decisions on theunderlying uncertainty. We encourage EPA tomove away from making generic statementsSabout the available database and make aninformed decision about critical data gaps.47 2.1.2 71As noted above (comment on Preamble section7.6, page 15), UFA = 3 is understood toencompass both toxicodynamics and residualtoxicokinetic uncertainty afterdosimetric/allometric adjustment, per U.S. EPA(2011b).EPA should revise the text to more accuratelyreflect the UFA rationale described in U.S. EPA(2011b).S48 2.1.2 71 and 73EPA does not appear to have considered thepossibility of using any value other than 10 forUFS. Considering the modest differences inmagnitude of effect between acute, short-term (4week) and subchronic studies, UFS ~4(Hasegawa et al., 2010) or lower should beconsidered.Reference: Hasegawa et al. (2010). A proposalof new uncertainty factor application to derivetolerable daily intake. Regul. Toxicol.Pharmacol. 58:237-42.EPA should reduce UFS from 10 to a lowervalue or explain why they have not done so.S49 2.1.2 and 2.1.6 72, 80EPA says there is no information on the transferof 1,2,4-TMB or 1,3,5-TMB across the placenta.As noted by Saillenfait et al. (2005), fetal bloodTMB levels were 55-98% of maternal TMB levelsin a rat study (Ungvary et al., 1983) and TMBwas identified in cord blood of term infants(Dowty and Laseter, 1976). We have someconcern regarding the review of the literature.EPA needs to revise their statements regardingthe lack of data on TMBs' ability to cross theplacenta and reference these studies.S/M50 2.1.5 74 EPA does not discuss uncertainties due to the EPA should conduct the analysesneeded to S/Morder in which they have conducted varioussteps in the RfC process (rat internal dosimetrycalculations, BMD analysis, uncertainty factorapplication, interspecies and route-to-routeextrapolation), or note the change from theprocess previously used for TCE and methanol.provide quantitative information on the impact ofthese choices, document them in theToxicological Review, and discuss them asappropriate. EPA should also providereferences, if available, so that reviewers candetermine whether these decisions have beensuggested by others or are policies that havebeen generated within the IRIS program andhave not been externally peer reviewed.51 2.1.5 74This section states that no information isavailable to identify a biologically significantdecrease in maternal weight gain, and thus usesa BMR based on a change equivalent to 1 SD ofthe control mean.EPA should apply the well-established criterionthat a 10% decrease in (absolute) adult bodyweight is an adverse effect, rather than conductthe analysis based on weight gain.S52 2.1.5 74There is no reference to support the assertionthat a 5% decrease in fetal body weight is abiologically significantresponse becausedeveloping organisms "may" be more sensitiveto such changes.EPA should provide references for thisassertion, or redo their analysis using the 10%decrease in body weight applied to adultanimals.S/M53 2.1.5 75EPA notes that no PBPK model exists for 1,3,5-TMB.EPA should explain why they did not develop aPBPK model for 1,3,5-TMB, given that theexistence of the 1,2,4-TMB model and similarkinetic data sets should have given EPA asubstantial head start in developing such amodel. For other chemicals, EPA has decidedto either significantly modify or developde novoPBPK models. EPA should provide the rationalefor not taking such action in this case, and alsoprovide decision criteria for when it will modifySexisting models. Without such criteria, it is notpossible for reviewers and stakeholders todetermine if EPA is being consistent in itsevaluation and allocation of resources.54 2.1.5 76EPA did not carry forward the decreased painsensitivity NOAEL identified by Wiaderna et al.(2002) for POD, HEC, and candidate RfCcalculation.EPA should carry forward the decreased painsensitivity finding for 1,3,5-TMB exposedanimals reported by Wiaderna et al. (2002) asadditional comparative information for itsproposed 1,3,5-TMB RfC.S55 3 92DoD suggests that EPAprovide documents(preferably available on web sites) rather thanthe text of web site (EPA, 2011a, "IRIS ProcessRetrieved August 24, 2011") Text of web siteschange as do URLs. A document with a title and areference number can still be retrieved.Please make the cited text a document that isunlikely to change over time.E56 Appendix AA-7 andelsewhereThere are numerous typographical errorsthroughout Section A.1 with respect toreferencing tables and figures, mostly within thetext, but including citations in Table A.1-7. Forexample, Page 7, Figure C-1 should be FigureA-1. Table A.2-1 should be Table A.1-1.Moreover, all of the appendices are individuallylisted in the Table of Contents as starting onpage 94 when they do not.It is difficult to perform a review when referencesare incorrect. We believe that the software usedto create these documents allows insertion ofEPA should thoroughly check the citation oftables and figures throughout this section.Ecodes so that the Table of Contents (and alsoreferences) is automatically constructed and canbe quickly updated.57 Appendix A A-9No units are provided for alveolar ventilation inTable A.1-2, limiting the utility of this summarytable.Add units (liters/min?) for alveolar ventilation inTable A.1-2.E58 Appendix A A-9 to A-10 Text is duplicated from page A-7.EPA should delete one copy of this text, and ifdesired, cite the section where it is retained.E59 Appendix A A-13 Text needs to be reworded.Change "A lung compartment is used todescribe for gas exchange" to "A lungcompartment is used to describe gas exchange".E60 Appendix A A-16EPA states that revised model code andmodeling results are available on EPA's HEROdatabase. We did not find any such informationthere.As noted above (comment on p. 69), all thenecessary supporting information, includingmodel code, should be made available to allreviewers at all stages of the review, includinginteragency and external reviews.S/M61 AppendixA A-24"Minimize" is used where "maximize" was meant(see page A-25 for increase in LLF).Change "minimize" to "maximize". S62 Appendix A A-26All of the figure and table references withinTable A.1-7 are incorrect. Unlike otherlocations, the errorswill not be corrected bychanging all "A.2" references to "A.1". Forexample, the venous blooddata of Swiercz et al.(2003), the key toxicokinetic data set, weredepicted in Figure A.1-9, not Figure A.2-8.Correct the figure and table references. E/M63 Appendix A A-32There appears to be a typographical error for themodel predicted venous blood concentration atVerify that the model value should be 4.21 mg/L,rather than 74.21 mg/L, and change the tableE75 ppm. entry.As with other comments, we are concernedabout errors in reporting data from the literature.Neither DoD nor most of the public stakeholdershave the resources to perform a quality controlcheck of all the data provided in the draftdocument. While we have provided examples oferrors we have observed, we are concerned thatthere are likely others that were not found. Weencourage EPA to institute QA/QC proceduresthat ensure that all data that are reported in thedocument are accurate prior to external reviewof its document.64 Appendix A A-37While sensitivity analysis of PBPK models fortest species are very useful to verify parameteridentifiability, as documented here, furthersensitivity analyses of the human model wouldalso be very useful to inform the selection ofUFH and to identify potentiallypharmacokinetically sensitive subpopulations.EPA should conduct a sensitivity analysis ofhuman steady state blood or tissueconcentrations of 1,2,4-TMB at the HEC andHED or RfC and RfD.S65 Appendix B B-6EPA asserts that "a 5% decrease in body weightwas determined as biologically significant forprenatal rats", but provides no references for thisassertion.As previously noted (comment on page 74),EPA should provide references for this assertionor redo their analysis using the 10% decrease inbody weight applied to adult animals. DoDsuggests that EPA should follow standardtoxicological practices, or provide a rationale asto why such practices are not valid for thischemical.S/M66 Appendix B B-8 and following While EPA notesthat scaled residuals may be EPA shouldadd information onrelevant scaled Etables used to assess model fit (page B-7), they do notprovide that information in their tables. Thus,external reviewers are not able to independentlydetermine if such criteria have beenappropriately consideredby EPA in its selectionof the model from which the POD is determined.residuals both for clarity and to allowindependent review of its actions.67 Appendix BB-8 and followingfiguresBMDS figure outputs do not provide units. Unitsshould be provided in the legends.Legends of all BMDS figures should note theunits for the dose/concentration.E68 Appendix B B-12Table B-7 footnote “a” contains an error: the p-value cannot = 0.0.02286.EPA should correct footnote a of Table B-7. E69 GeneralWe have noted several typographical errors inour review, but also want to note that there areincomplete sentences, missing verbs and otherminor editorial issues that require correctionSuggest having a tech editor review thedocument in addition to a QC review.EDepartment of Defense Comments onTrimethylbenzenes IASC draft chargeComments submitted by: Chemical Material RiskManagement ProgramOrganization: Department of Defense Date Submitted: 2/9/2012*Comment categories: Science or methods (S); Editorial, grammar/spelling, clarifications needed (E); or Other (O). Also pleaseindicate if Major i.e. affects the outcome,conclusions or implementation of the assessment.CommentNo.SectionPagesCommentSuggested Action, Revision and References(if necessary)*Category1 (A) 1. 1DoD would like to add "accurate" to theevaluation of the overall assessment of thedocument on which the reviewers are asked toopine.Please add "accurate" to the list of "[accurate],logical, clear and concise" in the first sentence.Please also add "accurately" to "clearly [andaccurately] presentedand synthesized"S/M2 GeneralDoD greatly appreciates the introductorymaterial that EPA has supplied in this newformat for IRIS document. We provided manycomments on this section, including someinstances where our reading of EPA's guidelinesand guidance appears to differ from thatpresented in the text.DoD assumes that this text will be in eachforthcoming IRIS document. While wecommend EPA for its efforts, we suggest thatEPA have this section separately reviewed byan external review panel whose members haveEPA should clearly identify the introductorymaterial as new for the IRIS process. EPAshould note that issues have been raised byinteragency reviewers and ask the panelmembers if they have carefully reviewed thatmaterial, if they have provided comments on thatmaterial, and if they feel they have expertise andthe available resources (e.g. time) to review it.Alternatively, if EPA agrees with DoD, thecharge to the peer reviewers could clearly statethat the introductory material is not part of theirassigned review, that it will be released forS/Mexpertise in EPA's guidelines and guidanceand/or regulatory risk assessment procedures.Ideally, this should be completed before the text,and any chemical-specific decisions madebased on the text on which issues have beenraised, is released for public comment andexternal peer review. As DoD understands thatthe external review panel for trimethylbenzes willbe select for expertise for a chemical-specificreview, DoD suggest that, if EPA disagrees withthe idea of reviewing the introductory materialseparately, the experts of the panel be askedtheir opinions of this issue.public comment and externally peer reviewedbefore it is included in any final IRIS document,and that it should only be of consideration intheir review if this document contains decisionsthat depend on the statements on which issueshave been raised.