SUMMARY 

ANNA 

SEN

USEPA, OFFICE OF PESTICID

FIFRA SAP 
Overview

2

 Follow text in Section 6.0 of the 2

issue paper

 Summarize key points from previo

presentations

 Discuss weight of the evidence con Key science questions

 Qualitative & quantitative considera

 Highlight aspects of the charge q
NRC Reports

 NRC Reports

 Toxicity Testing in the 21st Century: A V

Strategy (2007): 

 Adverse outcome pathways Integration across multiple lines of eviden Disruption of homeostasis leading to adve

 Science & Decisions (2009):

 Improved technical analysis (including mo Evaluation of alternative interpretations/a Better align risk assessment & risk manage

 Use of improved problem formulation

3
Stepwise, Transparent Scienc

4

 2008, FIFRA SAP: Preliminary 

chlorpyrifos human health effefocus on infants, children & prwomen 

 2010, FIFRA SAP: Draft Frame

Incorporating Epidemiologic aIncidence Data in Human HeaAssessment 
Stepwise, Transparent Scienc

5

 2011, Preliminary risk assessment on ch

 Focus on AChE/ChE inhibition as the most s

response data for deriving points of depa

 Plan to conduct a full weight of evidence (

integrating the epidemiology studies with toxicology studies for the neurodevelopme

 2012, FIFRA SAP: New data & more in

since 2008

 Charge questions on strengths & uncertain

lines of evidence

 Uncertainty analysis: qualitative & quanti

 Next step: Agency will consider input fr

integrating data & developing the WO
2007 NRC Toxicity Testing in 

Century

Compounds

Assess

Biological 

Perturbation

Affected

Pathway

Measures of

dose in vitro

Dose Response

Analysis for 

Perturbations

of Toxicity 

Pathways

Ca

in vitr

do

Human 

D

Popula

St

Mode of Action Chemical Characterization

Dose Response 

Assessment

Hazard Characterization

Risk Characterization

Exposure Asse

NRC, 2007. Fig 3-7 

Metabolite(s)
Chlorpyrifos

Assess

Biological 

Perturbation

Measures of

dose in vitro

Dose Response

Analysis for 

Perturbations

of Toxicity 

Pathways

Ca

in vitr

do

Urinary b

TCPy 

po

Childre

Mode of Action Chemical Characterization

Dose Response 

Assessment

Hazard Characterization

Risk Characterization

Exposure Asse

NRC, 2007. Fig 3-7 

Oxon, TCPy

Affected

Pathway

• AChE inhibition• Plausible hypotheses for neurodevelopmental effects
Weight of Evidence (WoE

 Process for characterizing the extent 

available data support a hypothesis causes a particular effect 

 Informs Dose-Response Assessment

 Involves a number of steps 

 Starting with assembling the relevant d Evaluating that data for quality and re Followed by an integration of the diffe

evidence to support conclusions
Weight of Evidence (WoE

 Transparency is important 

 explains the kinds of data available  how the data were selected and evalua how the different lines of evidence fit t

drawing conclusions 

 significant issues, strengths, and limitatio

and the uncertainties that deserve serioare presented

 major points of interpretation highlight

 Characterization of a range of proba

put in perspective (confidence/uncert
Outline of Presentations

10

 Introduction (Anna Lowit) Adverse Outcome Pathways: Data fo

at Varying Levels of Biological Orga(William Mundy)

 Chlorpyrifos Effects on the Developi

Animal Studies (Virginia Moser)

 Review of Children’s Health Epidemi

Studies (Carol Christensen)

 Review of Chlorpyrifos Biomonitorin

and Interpretive Approaches (Aaron 

 Summary & Next Steps (Anna Lowit)
Summary

11

 2011 Preliminary Risk Assessment

 AChE/ChE inhibition remains the most se

response data for deriving points of de

 Consistent with 2008 SAP recommendatio Route & lifestage specific  Robust BMD analysis Acute, oral: BMDL10 0.36 mg/kg for RBC 

PND11 rats

 Chronic, oral: BMDL10 0.03 mg/kg/day f

inhibition from pregnant rats
Summary

12

 Compared to 2008, 2012 analysis in

new data available and/or provides analysis

 Key scientific questions 

 Strength/limitations of evidence that su

chlorpyrifos exposure results in long-terneurodevelopmental effects from early 

 Strength/limitations of evidence that a

may be attributed to doses lower than 10% inhibition of AChE, i.e., the dose leregulatory decision making
Summary-Qualitative lines of evidence: L

neurodevelopmental effects from early l

13

 Strength/limitations of evidence that 

chlorpyrifos exposure results in long-tneurodevelopmental effects from earexposure-

 Mechanistic studies In vivo experimental toxicology studies Epidemiology
Summary - Qualitative lines of evidence

neurodevelopmental effects from early 

14

 Charge Question 2.1 Mechanistic studies

 At this time, a mode of action/adve

pathway has not been established foneurodevelopmental outcomes 

 Growing body of literature does de

chlorpyrifos and/or its oxon are bioon processes that affect the develop
Summary -Qualitative lines of evidence

neurodevelopmental effects from early 

15

 Charge Question 3.1 In vivo experimental toxicology studie

 Multiple studies and laboratories repor

aspects of neurobehavioral function in following developmental exposure

 Effects seen long after chemical exposure 

inhibition, if present, had recovered

 Behavioral alterations show some consi

of broad domains of neurological funct

 Most consistent effects on cognition, anxie
Summary - Qualitative lines of evidence

neurodevelopmental effects from early 

16

 Charge Question 4.1 & 4.2 Epidemiology studies

 Current database strengthens conclusion fr

“chlorpyrifos likely plays a role” in the neuroutcomes specifically those reported by C

 Strength of observed associations high in some c

 Non-differential exposure measurement error co

 Some evidence of exposure-response in studies,  Consistency in Brazelton (abnormal reflexes), AD

problems, Bayley (particularly MDI), and IQ

 Significant given differing exposure measures

 Alternative explanations investigated by authors
Summary

17

 From a qualitative perspective---Ag

preliminarily concludes: 

 Lines of evidence together support a 

exposure to chlorpyrifos results in adneurodevelopmental outcomes in humunder some (still unclear) conditions

 Mechanistic studies In vivo experimental toxicology stud Epidemiology
Summary

18

 Key science question

 Strength/limitations of evidence tha

effects may be attributed to doses lwhich elicit 10% inhibition of AChE, levels previously used for regulatory making

 Quantitative considerations

 Mechanistic studies In vivo experimental toxicology studies Epidemiology
Summary - Quantitative Lines of Evidence: 

Effects < Doses Eliciting 10% AChE Inhibitio

19

 Charge Question 2.2 Mechanistic studies

 Multiple biologically plausible hypothe

pursued by researchers; no one pathwdata to be considered more credible th

 Cannot establish key events, causal linkages 

linkages

 Dose metric uncertain (peak exposures vs. A

 There is some evidence of possible effe

similarly sensitive or more sensitive than 

 This remains an area of uncertainty
Quantitative Lines of Evidence: Pote

Effects < Doses Eliciting 10% AChE 

20

 Charge Question 3.2 In vivo experimental toxicology studies

 Many studies use only one, maybe two doses, 

cases the lower but not higher dose level prodneurodevelopmental effects

 Most studies use of 1 mg/kg/day or higher

 Dose that produces some amount of brain ChE in

directly to the pups post-natally

 Limited or no dose response data on inhibition o

activity below 1 mg/kg when given to the dams 

 One study (Braquenier et al., 2010) using low

administered to the dam on GD15-LD14, repo0.2 mg/kg/d

 Similar to the acute, oral BMDL10 0.36 mg/kg About 10X higher than chronic, oral BMDL10 0.0
Quantitative Lines of Evidence: Pote

Effects < Doses Eliciting 10% AChE 

21

Effects seen 6.17 pg/g upper-tertileof >LOD (Rauh et al. 2006)

Year

N 

1999 87 

2000 83 2001 33 

1998

‐2002 314 

2001

‐2004 65 

Whyatt et 
Summary - Quantitative Lines of Evidence: P

Effects < Doses Eliciting 10% AChE Inhibition

22

Evidence suggesting that pg/g levels ounlikely to elicit AChE inhibition

 Nolan, 1984: Single dose, deliberate dosing study in ad

 0.5 mg/kg in single oral dose

 No RBC AChE inhibition observed Plasma ChE was inhibited 83-89% relative to pre-do

the oral dose

 Peak blood levels of 0.01-0.03 ug/mL

 5 mg/kg, single dermal dose

 No RBC AChE or plasma ChE inhibition observed Mostly non-detects, maximum of 0.01 ug/mL

 Comparison to epidemiology studies needs to be interpr

 Males vs. Pregnant females Single Dose vs. Repeating exposure Controlled, clinical setting vs. “Real world” Oral route vs. Multiple routes/pathways
Figure 40, Dow PBPK-CARES SAP Issu

23

0.1

1

10

100

1000

10000

100000

1000000

10000000

100000000

0.01 0.1 1 10

Peak Blood Concentration (pg/g)

Dose mg/kg

Relationships between Single Oral Dose and Peak Blood C

Chlorpyrifos and Chlorpyrifos Oxon in Adults an
Quantitative Lines of Evidence: Pote

Effects < Doses Eliciting 10% AChE 

24

 Exposure range cord blood 3-6 pg Remaining Uncertainties:

 Fetal exposure during critical windo

development

 Including blood levels or the AChE inhi

of chlorpyrifos application

 Contribution of other ChE-inhibiting 

OP exposure 

 Diazinon (

ρ=0.63), propoxur (

ρ=0.21
Summary - Quantitative Lines of Evidence: P

Effects < Doses Eliciting 10% AChE Inhibitio

25

 Charge questions 5.3 & 5.4 Given the uncertainties, area o

additional analyses may provcharacterization of biomonitor
Summary

26

 Charge Question 6.0 Assessing and presenting the r

plausible responses at given dthe effect of the overall uncervariability around that range. 
 Ensure scientific judgements are trans

 Identify areas of uncertainty Practical steps towards further refine

existing information with existing info

SAP Questions
28 Questions?