SCIENTIFIC ISSUES CONCERNING HEALTHEFFECTS OF CHLORPYRIFOSINTRODUCTIONANNA LOWIT, PH. D.SENIOR SCIENTISTUSEPA, OFFICE OF PESTICIDE PROGRAMSApril 10, 2012FIFRA SAPIntroductionNRC ReportsToxicity Testing in the 21st Century: A Vision and aStrategy (2007):Adverse outcome pathwaysIntegration across multiple lines of evidenceDisruption of homeostasis leading to adverse outcomesScience & Decisions (2009):Improved technical analysis (including mode of action)Evaluation of alternative interpretations/approachesBetter align risk assessment & risk managementUse of improved problem formulation2Regulatory Context: ChlorpyrifosOrganophosphate pesticide first registered in 1965In June 2000:The technical registrants entered into an agreementwith the Agency to eliminate and phase out nearly alluses that result in residential exposuresSome mitigation on food (apples & tomatoes)Some mitigation for workers (PPE & engineeringcontrols for some uses)Registration Eligibility Decision (RED) in 2006September 2007 petition from NRDC & PANNA torevoke all tolerances & cancel registrations3Recent SAP Reviews42008: New science on infants, children, & pregnant womenfrom experimental laboratory toxicology & epidemiologystudiesEvaluated both AChE & non-cholinergic modes of action2009: Approach for risk assessment of semi-volatile pesticideshttp://www.epa.gov/scipoly/sap/meetings/2009/120109meeting.html2010: Development of the draft “Framework forIncorporating Human Epidemiologic & Incident Data in HealthRisk Assessment”http://www.epa.gov/scipoly/sap/meetings/2010/020210meeting.htmlRegulatory Context: Chlorpyrifos5Registration review opened in March 2009 and is expectedto conclude by the end of 2015http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP2008-0850July 2011 Preliminary Risk Assessmenthttp://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP2008-0850-0025Focus on AChE-inhibiting potentialMost sensitive dose-response dataWeight of the evidence evaluation integrating data fromepidemiology, biomonitoring, & experimental toxicology studiesto be conducted2008 FIFRA SAP ReviewPreliminary review of scientific literaturewith focus on infants, children & pregnantwomenEpidemiologyAge-dependant metabolismIntra-species variability of paraoxonase (PON1)AChE/ChE inhibition dataVarious lifestagesMultiple routes, durationsIn vivorodent studies evaluating long-term effectsBiomonitoring studies62008 FIFRA SAP Review7Key recommendations from SAPAChE/ChE data remains the most appropriate data forderiving points of departureRoute specific & lifestage-specific AChE/ChE data appropriateIn vivorodent studies on long-term effects from early lifeexposureLimited dose- response dataOnly doses of 1 mg/kg or greater demonstrate significant effectson behaviorEpidemiology studies:“Chlorpyrifos likely played a role”Only measuring biomarkers (3rd trimester maternal, cord blood,meconium) at one point in timeCannot exclude possibility that the effects seen were due tochlorpyrifos in combination with other pesticides8Draft Framework for Incorporating EpiConcepts based on peer-reviewed, robustprinciples & toolsStandard practice in epidemiology, toxicology &risk assessmentConsistent with recommendations fromNRC 2007: Toxicity Testing in the 21st CenturyNRC 2009: Science & Decisions: Advancing RiskAssessmentFlexibility to incorporate information from differentsources based on AOP conceptTransparent tool for organizing, reviewing &interpreting complex informationDraft Framework for Incorporating Epi9Mode of Action Framework (Modified Bradford HillCriteria)Postulated mode of actionIdentify sequence of key events on the path to health outcomeExperimental supportConcordance of dose-response for key eventsTemporal relationships for key eventsBiological plausibility & coherenceStrength, consistency & specificityOther modes of actionIdentify uncertaintiesConclusionAdverse Outcome Pathway10ChemicalsMolecularTargetCellularResponseTissue/OrganIndividualPopulationPharmaco-kineticsIn vitro studiesBiomonitoring &Exposure dataEpidemiologyStructure Activity RelationshipsToxicity PathwaysHuman IncidentsIn vivo studiesMolecularinitiating eventKey events or predictiverelationships spanninglevels of biologicalorganizationAdverseoutcomerelevanttoriskassessmentGreater Toxicological UnderstandingGreater Risk RelevanceBiologicinputs“Normal”BiologicalFunctionAdverseOutcomes(e.g.,mortality,ReproductiveImpairment)Cellinury,InabilitytoregulateAdaptiveResponsesEarlycellularchangesExposureUptake‐DeliverytoTargetTissuesPerturbationCellularresponsepathwayMolecularinitiatingeventPerturbedcellularresponsepathwayAdverseoutcomerelevanttoriskassessmentToxicityPathwayAdverseOutcomePathwayII.Adverse Outcome Pathways –definition and exampleModify From NRC 2007July 2011 Preliminary Risk Assessment12AChE/ChE inhibiting potential of chlorpyrifosMost sensitive dose-response data availableRoute specific studies (oral, dermal, inhalation)Lifestage sensitivityProcess for deriving points of departureIn 2008, the Agency performed a comprehensivereview of the literature for AChE inhibition.2012 review has been supplemented with the newestdataBenchmark dose approachJuly 2011 Preliminary Risk Assessment13AChE/ChE inhibiting potential of chlorpyrifosAcute, oral: BMDL100.36 mg/kg for RBC AChE inhibitionPND11 rat pups provide the most sensitive cholinesteraseinhibition dataConsistent with the concept that younger juvenile animals are moresensitive due to immature metabolic systemsChronic, oral: BMDL100.03 mg/kg/day for RBC AChEinhibitionAs the metabolic systems mature at or near adult levels, sensitivitydisappearsIn repeated dosing studies, pups exhibit similar sensitivity to adultratsPregnant dams provide the most sensitive dataApril 201214Key scientific questions1.Lines of evidence that suggest chlorpyrifosexposure results in long-termneurodevelopmental effects from early lifeexposure2.Lines of evidence that adverse effects may beattributed to doses lower than those which elicit10% inhibition of AChE,i.e., the dose levelspreviously used for regulatory decision makingApril 201215Compared to 2008, 2012 analysis incorporates newdata available and/or provides more in-depth analysisAChE/ChE inhibitionOther mechanistic data----Evaluation of plausiblehypotheses on modes of action/adverse outcome pathways(MOA/AOP) leading to neurodevelopmental outcomesAdverse outcomes in rodents, including neurodevelopmentalstudies on behavior and cognition effects.Epidemiologic studies from three major children’s healthcohorts in the U.S.Biomonitoring and physiologically-basedpharmacokinetic/pharmacodynamic (PBPK/PD) modeling2007NRCToxicityTestinginthe21stCenturyCompoundsAssessBiologicalPerturbationAffectedPathwayMeasures ofdose in vitroDose ResponseAnalysis forPerturbationsof ToxicityPathwaysCalibratingin vitro and humanDosimetryHuman ExposureDataPopulation BasedStudiesExposureGuideline



# Mode of ActionChemicalCharacterizationDose ResponseAssessmentHazard CharacterizationRisk CharacterizationExposure AssessmentNRC, 2007. Fig 3-7 Risk Assessment ComponentsMetabolite(s)MOA/AOPCriticalDurationPathway ofExposureLifestageInfants & ToddlersDirect exposure in food,water, air fromvolatization/spray drift,AChE inhibitionCritical duration:from 1 day to timeof metabolicmaturationCholinergic toxicityMOA: Unknown;Multiple HypothesesCritical duration:Unknown.Neurodevelopmentaloutcomes in children(learning & motordeficits)Pregnant FemaleMotherDirect exposure infood, water, air fromvolatization/spraydrift, worker(applicator, post app)AChE inhibitionCritical duration: from1 day up to steadystate (approx 2-3weeks) with a maxexposure of 9 mosCholinergic toxicityFetusCross-placentalexposureAChE inhibitionCritical duration:from 1 day up to 9monthsEqual or less sensitiveto mother; protect formother’s AChEinhibition—protect forfetusMOA: Unknown;MultipleHypothesesCritical duration:Unknown.Neurodevelopmental outcomes inchildren (learning &motor deficits)Outline of Presentations18Introduction (Anna Lowit)Adverse Outcome Pathways: Data for Chlorpyrifosat Varying Levels of Biological Organization(William Mundy)Chlorpyrifos Effects on the Developing Brain:Animal Studies (Virginia Moser)Review of Children’s Health Epidemiology CohortStudies (Carol Christensen)Review of Chlorpyrifos Biomonitoring Researchand Interpretive Approaches (Aaron Niman)Summary & Next Steps (Anna Lowit)Questions?19