Summary of Non-cancerMammalian ToxicityReevaluationElizabeth Méndez, Ph.D.Senior Scientist, Health Effects DivisionOffice of Pesticides Programmendez.elizabeth@epa.gov2 

# Status of ReevaluationzApproximately 100 studies reviewedMode of action (MOA)Reproductive/developmental effectsImmunotoxicityNeurotoxicityCarcinogenesiszEffects on neuroendocrine function still mostsensitive effectszReview of additional studies available sinceFebruary 2010 ongoing3 

# Mode of ActionzUnderstanding of MOA expanded:2003 MOA: Perturbation of hypothalamicpituitary-gonadal (HPG) axis still applicableActivation of the hypothalamic-pituitary-adrenal(HPA) axis may precede effects on HPG axis• Changes in ACTH, corticosterone, andprogesterone within minutes of exposure• Toxicological significance of adrenal hormonalchanges 

# per se4 

# Mode of Action (2)General stimulatory effect onsteroidogenesis not a direct effect onaromataseDelays in puberty onset in both gendersProstatitis related to a decrease in prolactinin atrazine-exposed dams during lactationMammary gland tumor development notrelevant to humans5 

# Mode of ActionAtrazinefciAlteredReproductiveFunctionSteroidogenesisAdrenal♀and♂ProgesteroneuCorticosteroneGonad♂♀TestosteroneΔEstrogenΔProgesteroneΔPituitaryLHvACTHuProlactinvGnRH pulsesvCNSCRH/AVP(CatecholaminesNeuropeptides)(CatecholaminesNeuropeptides)?deghu6zImmunotoxicityExposure during development may lead toaltered immune function in offspringNot more sensitive than the atrazine-inducedeffects on neuroendocrine functionzNeurotoxicityNot more sensitive than the atrazine-inducedeffects on neuroendocrine functionNo association between atrazine exposure andParkinson’s Disease 

# Immunotoxicity and Neurotoxicity7



# ConclusionszToxic effects due to multilevel interactions of avariety of systems ( 

# i.e.,neuroendocrine,reproductive, nervous, and immune systems)zActivation of the HPA axis followed by disruptionof the HPG axis lead to the most sensitive effectsattributed to atrazine exposurezExtent of HPA activation (duration or dose level)needed to elicit the decrease in GnRH andsubsequent LH surge attenuation not clear8 

# Next Steps: In Preparation for SeptemberzApply MOA Framework to Analyze DataFurther characterize HPA/HPG axes interactions:• Describe temporal relationship between HPA axisactivation and adverse health outcomes• Better describe dose-response relationship betweenatrazine exposure, HPA axis activation and adversehealth outcomes– Conduct benchmark dose analysisto better characterize thedose-response curve for the effects on HPA and HPG axeszAdditional Data Review during the Spring/Summer 2010Data available from February 2010 until July 2010Mammary gland development9 

# Next Steps: In Preparation for SeptemberzDetermine duration of exposurezLife stage: Response to chemical exposure may varythrough life stageszReview available non-cancer epidemiology datazWeight of evidence analysis integrating experimentaltoxicity and epidemiology datazPropose new points of departure (PoDs), if appropriatezReevaluate FQPA Safety FactorzReconsider the drinking water sampling strategy inrelation to the toxicological duration of concernShorter duration of toxicological concern may lead tomore frequent sampling10 

# MOA FrameworkzPostulate MOA: Can the MOA be established in animals?zDescribe Key Events: Empirically observable precursorsteps that are necessary elements of the MOAzEstablish dose-response concordancezEstablish temporal concordancezStrength, consistency and specificity of association ofadverse health outcome with key eventszBiological plausibility and coherence: Are key eventsplausible in humans on a quantitative and qualitative basis?zOther MOAs: Can other MOAs be ruled out?zStatement of confidence, analysis, and implications:Articulates the uncertainties, strengths, weaknesses, andimplications of the analysis11 

# MOA Data on Key EventszAdditional Data Expected in Spring/Summer 2010Effect of 4 day atrazine exposure on ACTH, corticosterone,progesterone, and LHEffect of atrazine on steroidogenesis in rat granulosa cells (Tinfo 

# et

al.,submitted for publication)Effect of atrazine exposure on GnRH and kisspeptin neuron regulationEffect of gestational exposure to atrazine on malesAn oral (gavage) immunotoxicity and hormone evaluation study forthe effects of atrazine in male ratsMale prostate inflammation following low dose metabolite exposure(manuscript in preparation)12 

# MOA Data on Key Events (2)zAdditional Data Expected in Spring/Summer 2010An oral (gavage) study of the effects of atrazine on theestrous cycle and the estrogen-induced leutinizinghormone (LH) surge in female ratsComparison of the effects of atrazine on pulsatile LHrelease and the LH Surge in non-adrenalectomizedcompared to adrenalectomized female Wistar ratsUse of a Physiological Based Pharmacokinetic Model(PBPK) to characterize atrazine biotransformation toinactive moieties in relationship to dynamic changes inhormone levels and potential adverse outcomesDose-Response Modeling and Determination of Point(s)of Departure for Risk Assessment: Validation Methods13 

# Dose-response ConcordancezEstablish extent of corticosterone changesneeded to result in adverse health outcomezIncorporate these data in PODdetermination14 

# Temporal ConcordancezDuration of changes in GRH, ACTH,corticosterone, and progesterone neededfor adverse health outcomeChanges seen within minutes of exposureSustained changes needed to elicit adversehealth outcome?• 1 day, 4 days, 1 week ...zAtrazine and its metabolites quicklyabsorbed and distributed in the body15Review of Experimental DataRayner, J.L., 

# et al. (2005) 

# Adverse effects of prenatal exposure to atrazine during a critical period of mammary gland growth. Tox. Sci. 87(1):255-266Rayner, J. 

# et al.(2003) 

# Exposure Parameters Necessary for Delayed Puberty and Mammary Gland Development in Long-Evans Rats Exposed in Utero to

Atrazine.Toxicology and Applied Pharmacology195:23-34Enoch, R.R., 

# et al.(2007) 

# Mammary Gland Development as a Sensitive End Point after Acute PrenatalExposure to an Atrazine Metabolite Mixture in

Female Long-Evans Rats. Environ. Health Perspect.115:541–547 

# Mammary Gland Development16Rayner, J. 

# et al.(2007) 

# Atrazine-induced reproductive tract alterations after transplacental and/or lactational exposure in male Long–Evans ratsToxicol. Appl.Pharmacol. 218(3):238-248 

# Atrazine dose-dependent effects on mammary gland development in Sprague Dawley and Long Evans

female rats(in preparation) 

# Effects of atrazine-induced mammary gland effects in Sprague-Dawley and Long Evans rats on carcinogeninduced tumor incidence.(in preparation)Coder, P.S. (2010) 

# An Oral Developmental Study of Atrazine in the Rat, including Cross-Fostering and PairFeeding.Unpublished 

# Mammary Gland Development17 

# 2011 SAP on CarcinogenesiszAHS epidemiology study on atrazine andhuman cancer publicationzIntegrate experimental carcinogenesis dataand epidemiology data (AHS and othercancer epidemiology studies)18