## SUMMARY &NEXTSTEPS ANNA L OWIT , PH. D. SENIOR SCIENTIST USEP A, OFFICE OF PESTICIDE

PROGRAMS April 10, 2012 FIFRA S AP

# Overview

**2**  

## Follow text in Section 6.0 of the 2012 SAP issue paper  

## Summarize key points from previous presentations  

## Discuss weight of the evidence concept  

## Key science questions  

### Qualitative & quantitative considerations  

## Highlight aspects of the charge questions

# NRC Reports

 

## NRC Reports  

### Toxicity Te sting in the 21st Century: A Vi sion and a Strategy (2007) :  Adverse outcome pathways **3**

 Integration across multiple lines of evidence

 Disruption of homeostasis leading to adverse outcomes  

### Science & Decisions (2009) :  Improved technical analysis (including mode of action)  Evaluation of alternative interpretations/approaches  Better align risk assessment & risk management  Use of improved problem formulation

# Stepwise, Transparent Science Review **4**  

# 2008, FIFRA

SAP: Preliminary review of chlorpyrifos human health ef fects with focus on infants, children & pregnant women  

# 2010, FIFRA

SAP: Draft Framework for Incorporating Epidemiologic and Human Incidence Data in Human Health Risk Assessment

# Stepwise, Transparent Science Review **5**  

### 201 1, Preliminary risk assessment on chlorpyrifos:

 

### Focus on AChE/ChE inhibition as the most sensitive dose - response data for deriving points of departure  

### Plan to conduct a full weight of evidence (WOE) evaluation integrating the epidemiology studies with the experimental toxicology studies for the neurodevelopmental outcomes  

### 2012, FIFRA

SAP: New data & more in - depth analysis since 2008  

### Charge questions on strengths & uncertainties of dif ferent lines of evidence  

### Uncertainty analysis: qualitative & quantitative  

### Next step: Agency will consider input from SAPin integrating data & developing the WOE

## 2007 NRC T

ox icity T es ting in the 21 st 

## Cen tury

Compounds Affected Pathway Dose Response

Analysis for Perturbations Calibrating

in vitro and human Population Based Studies

Exposure Guideline **Mode of Action**  Chemical Characterization Dose Response Assessment

Assess Biological Perturbation Measures of

dose in vitro Perturbations

of Toxicity Pathways in vitro and human d osimetry

Human Exposure Data Exposure Guideline

Hazard Characterization

Risk Characterization

Exposure Assessment NRC, 2007. Fig 3 - 7 Risk Assessment Components Metabolite(s)**Chlorpyrifos** Dose Response Analysis for Perturbations Calibrating

in vitro and human **Children’s Cohorts**  **Exposure Pathways:**  **Food, water,**  **Mode of Action**  Chemical Characterization Dose Response Assessment

Affected Pathway • AChE inhibition

• Plausible hypotheses for neurodevelopmental effects

Assess Biological Perturbation Measures of

dose in vitro Perturbations

of Toxicity Pathways in vitro and human d osimetry
**Urinary biomonitoring of TCPy in various**  **populations Food,**  **water, worker,**  **air volatility, spray drift,**  **cross -**  **placental** Hazard Characterization

Risk Characterization

Exposure Assessment NRC, 2007. Fig 3 - 7 Risk Assessment Components **Oxon, TCPy**

# We ight of Evidence (WoE)

 

## Process for characterizing the extent to which the available data support a hypothesis that an agent causes a particular ef fect  

### Informs Dose - Response Assessment  

## Involves a number of steps  

### Starting with assembling the relevant data  

### Evaluating that data for quality and relevance  

### Followed by an integration of the dif ferent lines of evidence to support conclusions

# We ight of Evidence (WoE)

 

## Transparency is important  

### explains the kinds of data available  

### how the data were selected and evaluated  

### how the dif

ferent lines of evidence fit together in drawing conclusions  

### significant issues, strengths, and limitations of the data and the uncertainties that deserve serious consideration are presented  

### major points of interpretation highlighted  

## Characterization of a range of probabilities and put in perspective (confidence/uncertainty)

# Outline of Presentations

**10**  

## Introduction (Anna Lowit)  

## Adverse Outcome Pathways: Data for Chlorpyrifos at V

arying Levels of Biological Organization (William Mundy) Chlorpyrifos Ef

fects on the Developing Brain:  

## Animal Studies (V irginia Moser)  

## Review of Children’ s Health Epidemiology Cohort Studies (Carol Christensen)  

## Review of Chlorpyrifos Biomonitoring Research and Interpretive Approaches (Aaron Niman )  

## Summary & Next Steps (Anna Lowit)

# Summary

**11**  

## 201 1 Preliminary Risk Assessment  

### AChE / ChE inhibition remains the most sensitive dose - response data for deriving points of departure  Consistent with 2008 SAPrecommendations  Route & lifestage specific  Robust BMD analysis  Acute, oral: BMDL 10 0.36 mg/kg for RBC AChE inhibition in PND1 1 rats  Chronic, oral: BMDL 10 0.03 mg/kg/day for RBC AChE inhibition from pregnant rats

# Summary

**12**  

## Compared to 2008, 2012 analysis incorporates new data available and/or provides more in depth analysis  

## Key scientific questions Strength/limitations of evidence that suggest  

### chlorpyrifos exposure results in long - term neurodevelopmental ef fects from early life exposure  

### Strength/limitations of evidence that adverse ef fects may be attributed to doses lower than those which elicit 10% inhibition of AChE, i.e., the dose levels used for regulatory decision making

### Summary - Qualitative lines of evidence: Long - term neurodevelopmental ef fects from early life exposure **13**  

## Strength/limitations of evidence that suggest chlorpyrifos exposure results in long - term neurodevelopmental ef fects from early life exposure -  

### Mechanistic studies  

### In vivo experimental toxicology studies  

### Epidemiology

## Summary - Qualitative lines of evidence: Long term neurodevelopmental ef fects from early life exposure **14**  

## Charge Question 2.1  

## Mechanistic studies  

### At this time, a mode of action/adverse outcome pathway has not been established for neurodevelopmental outcomes  

### Growing body of literature does demonstrate that chlorpyrifos and/or its oxon are biologically active on processes that af fect the developing brain

## Summary - Qualitative lines of evidence: Long term neurodevelopmental ef fects from early life exposure **15**  

## Charge Question 3.1  

## In vivo experimental toxicology studies  

### Multiple studies and laboratories reporting changes in aspects of neurobehavioral function in adult rodents following developmental exposure  Ef fects seen long after chemical exposure and any ChE inhibition, if present, had recovered  

### Behavioral alterations show some consistency in terms of broad domains of neurological function  Most consistent ef

fects on cognition, anxiety, social behavior

## Summary - Qualitative lines of evidence: Long term neurodevelopmental ef fects from early life exposure **16**  

### Charge Question 4.1 & 4.2  

### Epidemiology studies  

### Current database strengthens conclusion from 2008 “ chlorpyrifos likely plays a role ” in the neurodevelopmental outcomes specifically those reported by Columbia University  Strength of observed associations high in some cases, but not all  Non - dif

ferential exposure measurement error could reduce magnitude  Some evidence of exposure - response in studies, when available  Consistency in Brazelton (abnormal reflexes), ADHD - like behavior problems, Bayley (particularly MDI), and IQ  Significant given dif

fering exposure measures

# Summary

**17**  

## From a qualitative perspective --- Agency preliminarily concludes:  

### Lines of evidence together support a conclusion that exposure to chlorpyrifos results in adverse neurodevelopmental outcomes in humans, at least under some ( still unclear

) conditions  

### Mechanistic studies  

### In vivo experimental toxicology studies  

### Epidemiology

# Summary

**18**  

## Key science question  

### Strength/limitations of evidence that adverse ef fects may be attributed to doses lower than those which elicit 10% inhibition of AChE, i.e., the dose levels previously used for regulatory decision making  

### Quantitative considerations  Mechanistic studies  In vivo experimental toxicology studies  Epidemiology

### Summary - Quantitative Lines of Evidence: Potential for Ef

fects < Doses Eliciting 10% AChE Inhibition **19**  

## Charge Question 2.2  

## Mechanistic studies  

### Multiple biologically plausible hypotheses are being pursued by researchers; no one pathway has suf ficient data to be considered more credible than the others.  Cannot establish key events, causal linkages or dose response linkages  Dose metric uncertain (peak exposures vs. AUC)  

### There is some evidence of possible ef fects which are similarly sensitive or more sensitive than AChE inhibition. This remains an area of uncertainty

## Quantitative Lines of Evidence: Potential for Ef fects < Doses Eliciting 10% AChE Inhibition **20**  

### Charge Question 3.2  

### In vivo ex perimental tox icology studies  Many studies use only one, maybe two doses, and in several cases the lower but not higher dose level produced significant neurodevelopmental ef fects  Most studies use of 1 mg/kg/day or higher  Dose that produces some amount of brain ChE inhibition when given directly to the pups post - natally  Limited or no dose response data on inhibition of fetal brain ChE activity below 1 mg/kg when given to the dams gestationally  One study (Braquenier et al., 2010) using lower doses, administered to the dam on GD15 - LD14, reported a NOEL of 0.2 mg/kg/d  Similar to the acute, oral BMDL 10 0.36 mg/kg  About 10X higher than chronic, oral BMDL 10 0.03 mg/kg/day

## Quantitative Lines of Evidence: Potential for Ef fects < Doses Eliciting 10% AChE Inhibition **21** Ef fects seen 6.17 pg/g upper- tertile of >LOD ( Rauh et al. 2006) **Ye ar**  **N Mean CPF (pg**  **/g )** 

1999 87 5.0 (4.1

- 6.2) 2000 83 1.9 (1.4

- 2.4) 2001 33 0.5 (0.3

- 0.6) 2006) 1998
- 2002 314 4.0 ( sd 6.1) Range: ND - 63 2001
- 2004 65 <L OD 2.5 (95 th )
Whyatt et al. 2003, 2004, 2009

### Summary - Quantitative Lines of Evidence: Potential for Ef

fects < Doses Eliciting 10% AChE Inhibition **22** 

### Evidence suggesting that pg/g levels of chlorpyrifos unlikely to elicit AChE inhibition  Nolan, 1984: Single dose, deliberate dosing study in adult males  0.5 mg/kg in single oral dose  No RBC AChE inhibition observed  Plasma ChE was inhibited 83 - 89% relative to pre - dose activities Plasma ChE w inhibited relative to pre activities follow ing 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 interpreted with care:  Males vs. Pregnant females  Single Dose vs. Repeating exposure  Controlled, clinical setting vs. “Real world”  Oral route vs. Multiple routes/pathways**23**

**1000**

**10000 100000**  **1000000 10000000**  **100000000 P** **e a** **k B** **l o** **o d** **C o** **n c** **e n** **t r** **a t** **i o** **n (** **p g** **/ g** **) Relationships betw**  **een Single Oral Dose and Peak Blood**  **Concentrations of Chlorpyrifos and Chlorpyrifos Oxon in Ad**  **ults and Infants** 

Adult Chlorpyrifos Adult Chlorpyrifos oxon Child Chlorpyrifos Child Chlorpyrifos oxon



### Figure 40, Dow PBPK - CARES SAPIssue Paper, 2010 **0.1 1**  **10 100** 

**0.01 0.1**  **1 10** **P e** **a k** **B l** **o o** **d C** **o n** **c e** **n t** **r a** **t i** **o n** **( p** **g /** **g )** 

**Dose mg/kg** 50 per. Mov

. Avg. (Adult Chlorpyrifos) 50 per. Mov

. Avg. (Adult Chlorpyrifos oxon)

## Quantitative Lines of Evidence: Potential for Ef fects < Doses Eliciting 10% AChE Inhibition **24**  

## Exposure range cord blood 3 - 6 pg/g  

## Remaining Uncertainties:  

### Fetal exposure during critical window(s) of development  

### Including blood levels or the AChE inhibition at the time of chlorpyrifos application  

### Contribution of other ChE - inhibiting pesticides to OPexposure  

### Diazinon ( ρ =0.63), propox ur ( ρ =0.21) Whyatt et al. 2009

### Summary - Quantitative Lines of Evidence: Potential for Ef

fects < Doses Eliciting 10% AChE Inhibitio 

## n **25**  

# Charge questions 5.3 & 5.4  

# Given the uncertainties, area of where additional analyses may provide helpful characterization of biomonitoring data

# Summary

**26**  

# Charge Question 6.0  

# Assessing and presenting the range of plausible responses at given doses, and the ef

fect of the overall uncertainty and variability around that range. 

## Ensure scientific judgements are transparent  

## Identify areas of uncertainty  

## Practical steps towards further refinement of existing information with existing information 

# SAPQuestions

existing information with existing information

# Questions? **28**