SCIENTIFIC ISSUES CONCER

EFFECTS OF C

IN

ANNA 

SEN

USEPA, OFFICE OF PESTICID

FIFRA SAP 
Introduction

 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

2
Regulatory Context: Chlo

 Organophosphate pesticide first registe In June 2000:

 The technical registrants entered into 

with the Agency to eliminate and phauses that result in residential exposure

 Some mitigation on food (apples & to Some mitigation for workers (PPE & e

controls for some uses)

 Registration Eligibility Decision (RED) in 2 September 2007 petition from NRDC & 

revoke all tolerances & cancel registrati

3
Recent SAP Reviews

4

 2008: New science on infants, children, & pr

from experimental laboratory toxicology & estudies

 Evaluated both AChE & non-cholinergic mo

 2009: Approach for risk assessment of semi-

 http://www.epa.gov/scipoly/sap/meeting

meeting.html

 2010: Development of the draft “Framewor

Incorporating Human Epidemiologic & IncidenRisk Assessment” 

 http://www.epa.gov/scipoly/sap/meeting

meeting.html
Regulatory Context: Chlo

5

 Registration review opened in March 2009 

to conclude by the end of 2015

 http://www.regulations.gov/#!docketDetail;D

2008-0850

 July 2011 Preliminary Risk Assessment

 http://www.regulations.gov/#!documentDetai

2008-0850-0025

 Focus on AChE-inhibiting potential

 Most sensitive dose-response data

 Weight of the evidence evaluation integrating 

epidemiology, biomonitoring, & experimental to be conducted
2008 FIFRA SAP Review

 Preliminary review of scientific 

with focus on infants, children women 

 Epidemiology Age-dependant metabolism Intra-species variability of paraoxonas AChE/ChE inhibition data

 Various lifestages Multiple routes, durations

 In vivo rodent studies evaluating long-t Biomonitoring studies

6
2008 FIFRA SAP Review

7

 Key recommendations from SAP

 AChE/ChE data remains the most appropr

deriving points of departure

 Route specific & lifestage-specific AChE/ChE 

 In vivo rodent studies on long-term effects 

exposure 

 Limited dose- response data  Only doses of 1 mg/kg or greater demonstra

on behavior

 Epidemiology studies:

 “Chlorpyrifos likely played a role” Only measuring biomarkers (3rd trimester ma

meconium) at one point in time 

 Cannot exclude possibility that the effects see

chlorpyrifos in combination with other pesticid
8

Draft Framework for Incorporat

 Concepts based on peer-reviewed

principles & tools 

 Standard practice in epidemiology, 

risk assessment 

 Consistent with recommendations fro

 NRC 2007: Toxicity Testing in the 21st C NRC 2009: Science & Decisions: Advanc

Assessment

 Flexibility to incorporate information 

sources based on AOP concept

 Transparent tool for organizing, revi

interpreting complex information
Draft Framework for Incorpora

9

 Mode of Action Framework (Modified B

Criteria)

 Postulated mode of action 

 Identify sequence of key events on the path to 

 Experimental support

 Concordance of dose-response for key events  Temporal relationships for key events

 Biological plausibility & coherence Strength, consistency & specificity Other modes of action Identify uncertainties Conclusion
Adverse Outcome Pathway

10

Chemicals Molecular Target Cellular Response Tissue/ Organ 

Pharmaco- kinetics

In vitro studies

Structure Activity Relationships

Toxicity Pathways

Human In

In v

Molecular

initiating event

Key events or predictive

relationships spanning

levels of biological 

organization 

Greater Toxicological Understanding G
Biologic

inputs

Adaptive

Responses

Early cellular

changes

Exposure

Uptake‐Delivery to Target Tissues

Perturbation

Cellular response pathway

Molecular

initiating event

Perturbed cellular

response pathway

Adve

re

risk 

Toxicity Pathway

Adverse Outcome Pathway

II. Adverse Outcome Pathways –

definition and example

M
July 2011 Preliminary Risk Ass

12

 AChE/ChE inhibiting potential of chlo

 Most sensitive dose-response data ava Route specific studies (oral, dermal, inh Lifestage sensitivity

 Process for deriving points of depart

 In 2008, the Agency performed a com

review of the literature for AChE inhibit

 2012 review has been supplemented w

data

 Benchmark dose approach
July 2011 Preliminary Risk Ass

13

 AChE/ChE inhibiting potential of chlorpy

 Acute, oral: BMDL10 0.36 mg/kg for RBC A

 PND11 rat pups provide the most sensitive cho

inhibition data 

 Consistent with the concept that younger juven

sensitive due to immature metabolic systems 

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

inhibition

 As the metabolic systems mature at or near ad

disappears 

 In repeated dosing studies, pups exhibit simila

rats

 Pregnant dams provide the most sensitive data
April 2012 

14

 Key scientific questions 

1. Lines of evidence that suggest ch

exposure results in long-term neurodevelopmental effects from exposure 

2. Lines of evidence that adverse ef

attributed to doses lower than tho10% inhibition of AChE, i.e., the d

previously used for regulatory de
April 2012

15

 Compared to 2008, 2012 analysis inco

data available and/or provides more in

 AChE/ChE inhibition  Other mechanistic data----Evaluation of p

hypotheses on modes of action/adverse o(MOA/AOP) leading to neurodevelopmen

 Adverse outcomes in rodents, including neu

studies on behavior and cognition effects. 

 Epidemiologic studies from three major chi

cohorts in the U.S. 

 Biomonitoring and physiologically-based 

pharmacokinetic/pharmacodynamic (PBPK
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)
MOA/AOP

C

Du

Pathway of 

Exposure Lifestage

Infants & Toddlers 

Direct exposure in food, 

water, air from 

volatization/spray drift, 

AChE inhibition

C

fr

MOA: Unknown; 

Multiple Hypotheses

C

Pregnant Female

Mother

Direct exposure in 

food, water, air from 

volatization/spray 

drift, worker 

(applicator, post app)

AChE inhibition 

Critica

1 da

stat

wee

exp

Fetus Cross-placental 

exposure

AChE inhibition 

Criti

from 

MOA: Unknown; 

Multiple 

Hypotheses

Crit

U
Outline of Presentations

18

 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)
19 Questions?