OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460

RE : Meeting between Dow AgroScience s and EPA to Discuss Chlorpyrifos and Recent Epidemiology Studies, the April 2012 SAP, and Dose Reconstruction

Meeting Summary

On Wednesday, August 21, 2012, EPA’s Office of Pesticide Programs met with Dow AgroSciences (DAS) to hear their interpretation of three recently released epidemiology studies in light of the recently

rele ased April 2012 SAP minutes. The meeting also included a discussion regarding dose reconstruction challenges and limitations.

List of Documents

1. Meeting Summary Page 1

2. Meeting Sign in Sheet Page 2

3. DAS PowerPoint Page 3

a. Epidemiology Summary

4. EPA Memo to File Regarding DAS Slide #2 Page 22

5. DAS PowerPoint Page 2 3

a. Using Exposure Information and PBPK Models to Improve the Chlorpyrifos Risk Assessment

# Epidemiology Summary

Carol J. Burns, MPH, PhD August 21, 2012

# Meeting outline

• DAS view of the best available science utilizing 2010 guidance on integrating epidemiology

• What is EPA view of recent publications for

WoE ?

• Actionable items

• Discussion

# Hypothesis based WoE

H1: Chlorpyrifos induces NDT at

doses below those that cause brain
AChEI



# • Epidemiology is compelling (association is causation)

• Animal models 

# underestimate toxicity by a factor >1,000

• Must assume existence

of unknown mechanism



# for low dose effects H2: Chlorpyrifos induces NDT only at

doses that cause brain AChEI



# • Epidemiology is not compelling (association not causation)

• High dose animal data


# defines MOA

• No low dose mechanism

is needed

Based on Prueitt 2011, pages 885

- 886

# Epidemiology data not compelling and high

dose animal data defines the MOA:

– Columbia study findings are not replicated

• Chance, bias and confounding can not be ruled out

with reasonable confidence



# – No AChEI in epidemiology studies



# • See DAS comments for SAP 

# DAS View (H2)

# Columbia hypotheses not replicated

(Full DAS review submitted Nov. 2011)

Endpoints

hypothesized to be

affected by chlorpyrifos Supporting

studies

p<0.05 Fail to support

p<0.05 Comments

Birth weight 0 4 Some interaction of ∑ DEP and PON1, but not seen with TCPy

Birth length 0 3 Not reported by AHS

PDI scores 0 2 Columbia rejected at 12 and 24 months

No others tested at 36 months

MDI scores 0 2 Columbia rejected at 12 and 24 months,

No others tested at 36 months

ADHD 0 1 Tested only with ∑ DEP TCPy not analyzed at 3.5 and 5 y

Attention problems 0 1 Tested only with ∑ DEP, TCPy not analyzed at 3.5 and 5 y

PDD 0 1 None tested at 36 months

Full Scale IQ 1 (p = 0.05) 1 Tested only with ∑ DEP, TCPy not analyzed in Berkeley or Mt. Sinai

Working Memory 0 2 Tested only with ∑ DEP, TCPy not analyzed in Berkeley or Mt. Sinai

## Agency will place “ higher confidence in results which are

replicated or reproduced from multiple studies (EPA draft framework) 

# Replication across studies

# SAP minutes:

– “Total DAPS are not selective enough to be a 

# useful biomarker for chlorpyrifos”

– “TCPy is a better measure than dialkylphosphates ”



# Discuss 

# Evaluating consistency

CHLORPYRIFOS vs. DAP

### Author,

year OR

PDD CI Sig? CIR Comment

Rauh

2006 

## CPF* 5.4 1.2

- 24.1 Yes 19.9 Stron g assn. Least stable

Eskenazi

2007 

## DAP 2.3 0.99

- 5.2 No 5.2 Strong assn. More stable

“ “ 

## DMP 2.2 1.1

- 4.6 Yes 4.4 Most precise

Malathion?

“ “ 

## DEP 0.9 0.4

– 2.1 No 5.6 Weak assn. Chlorpyrifos and

diazinon?

“ “ 

## TCPy NR NR No Not reported 

# Example: No consistency of association of PDD and chlorpyrifos

*Only hi vs. low reported, no results for continuous results or air, urine, meconium PDD: Pervasive Developmental Disorder

# • DISCUSS

– How do strength or precision play a role in

the EPA draft framework?

– What about the confidence interval?

– Are all non significant data presented? 

# Statistical testingAuthor, year Beta LL UL Sig Comment

Rauh 2006 CPF*

- 0.003

- 0.006 - 0.006

- 0.006 0.001

0.000 No

Yes N= 265

Adjusted, Age 7

Bouchard

2011** DAP

- 5.6

- 9.0

- 2.2 Yes N=297

Bouchard 2011 DMP

- 4.7

- 7.7

- 1.6 Yes Malathion?

Bouchard 2011 DEP

- 2.1

- 5.6 0.3 No Model 2 age 7 Chlorpyrifos and diazinon?

Engel 2011** DAP

- 1.4

- 1.1

- 1.1 - 4.5

- 5.0

- 4.6 1.8

2.8

2.3 No

No

No N=140

N=115

N= 98

Engel 2011 DMP

- 0.5

- 0.4

- 0.6 - 3.2

- 3.6

- 3.7 2.3

2.9

2.6 No

No

No

Engel 2011 DEP

- 2.9

- 3.2

- 1.4 - 6.2

- 7.2

- 5.3 0.4

0.9

2.5 No

No

No Model 1 age 6

- 9

Model 2 age 7

- 9
WPPSI

- III age 6 

# Example: No consistency of association of FSIQ and chlorpyrifos

*continuous, IQ on log scale; **TCPy not analyzed

• FSIQ: Full Scale IQ

# • Human data have many “inconsistencies in the

results both within and among the cohort studies” (Prueitt 2011)



# • Human evidence for causality is “weak” (Li 2012)

• “Maternal RBC AChE inhibition is a more sensitive endpoint for risk assessment than 

# somatic developmental effects “ (Mink 2012) 

# 3 review papers: Epidemiology data inconclusive

Discuss

## Poverty, poor quality 

## home, low education, poor parenting skills

Poor childhood


## outcome High Pesticide Use 

# Confounding, pesticides

Maternal factors correlate with poor



## outcomes Insect infestation in low income housing 

## leads to high use.

Observed outcome

## “May be related to reason for being exposed to chlorpyrifos or other OP (e.g., cockroach infestation associated with poor housing maintenance, hygiene, and care environment; extent of participation in agricultural work) as well as factors related to higher versus lower exposure (e.g., following instruction labels regarding proper use). These factors could also be related to the learning and developmental environment, which may affect the test scores in the child...”

Page 133, Li et al., 2012 

# Li et al. on confounding

# 1. Other pesticides should be correlated with

developmental effects

– Piperonyl butoxide and MDI score (Horton 2011)



# 2. Levels of adverse effects do not change 

# when exposure reduced

– “Post

- ban” MDI and PDI scores are not better than “pre

- ban” (Rauh 2006)



# 3. Different exposure opportunities would not



# have same correlations

– CHAMACOS results for TCPy and DEP are not significantly associated with neurodevelopment 

# If confounding...

# 1. Analysis of CCCEH birth cohort

born <2001 vs. 2001 and after

– This is the counter factual analysis that

controls for the home environment and removes the reduction in chlorpyrifos use

and increase in other uses



# – Note: This was Question 3 submitted November 2009, with Columbia response on

March 2010 

# Actions?

# 2. Pooling all three studies to increase statistical power for dose

- response 

# and interaction analyses

– Note: this was Question 4 submitted in November

2009

– Was also recommended by 2012 SAP



## – NIEHS has awarded $568,000 to Brenda Eskenazi at Berkeley to conduct this analysis (~2009) 

# Actions?

# 3. Evaluate CHAMACOS results

– Cord and maternal blood reported for 

# 234 mothers and 256 infants ( Huen 2012)

– Test associations using urinary TCPy 

# Actions?

# • Evaluation of neurodevelopmental instruments

• Other chemical exposures in the CCCEH

• Non chemical risk factors in the CCCEH

• Examine NHANES for OP data

• Feasibility of accessing raw data in all 3 cohorts

with an SAP 

# DAS research considerations

# To Paul Price...OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION UNITED STATES ENVIRONMENTAL PROTECTION AGENC Y
WASHINGTON, D.C. 20460

MEMO TO FILE

DATE: October 17, 2012

RE: Slide #2 of Dow AgroSciences’ Powe rPoint Presentation “Using Exposure Information and PBPK Models to Improve the Chlorpyrifos Risk Assessment”, August 21, 2012

FROM: Joel Wolf

Slide number 2 in Dow AgroSciences’ PowerP oint presentation indicates that hypothesis number 3 was “suggested by EPA”. This statemen t does not accurately re flect the position of

EPA and its attribution to EPA is in correct from EPA’s point of view.

# Using Exposure Information and PBPK Models to Improve the Chlorpyrifos Risk Assessment

Paul Price
The Dow Chemical Company
August 21, 2012

Presented to US Environmental Protection Agency

# A Third Hypothesis

H1: Chlorpyrifos induces

NDT at doses below

those that cause brain

AChEI



## • Epidemiology is compelling (association is causation)

• Animal models

underestimate toxicity by a factor >1,000

• Must assume



## existence of

unknown

mechanism for

low dose effects H2: Chlorpyrifos induces NDT only at doses that

cause brain AChEI



## • Epidemiology is not compelling (association not causation)

• High dose

animal data

defines MOA

• No low dose

mechanism is

needed H3 ( Suggested by EPA): Chlorpyrifos induces NDT only at doses that cause brain AChEI and exposures in Epi studies were sufficiently high to cause brain AChEI



## • Epidemiology is compelling (association is causation)

• Consistent with belief that h igh

dose animal data defines MOA

• No low dose mechanism is

needed

Page 2

# Key question for Hypothesis 3

• Do the data on chlorpyrifos suggest that mothers in the Columbia cohort were exposed to levels that could have caused significant inhibition of RBC or brain ACHE? Considering:

– Data published by the authors

– Data published in earlier studies of exposures from residential uses

– Data from occupational exposures

Page 3

# Blood levels indicate no AChEI at the time of birth

• Blood levels at time of birth:

– 75% of participants had levels that were similar to the general public

– The max blood level (Columbia) was 15 fold higher then the upper bound level predicted for the dietary exposures general population (35 vs. 2 ng/l)

– Existing studies in of workers and worst

- case residential exposures confirm that blood levels in this range do not cause RBC AChEI (Garabrant, Dow studies)



# • Modeling suggest that:

– Blood concentrations >30,000 ng/l cause 10% RBC AChEI

– Blood concentrations >100,000 ng/l are required for apical effects

Page 4

# Blood Concentration of Chlorpyrifos vs. RBC AChEI

1.00E

- 02 1.00E

- 01 1.00E+00 1.00E+01 1.00E+02

0.1 1 10 100 1000 10000 100000 1000000 10000000 100000000 Maximum ChEI % of control

Maximum Blood Concentration ng/l Blood levels associated
with 10% RBC AChEI

Range of blood levels reported in Wyatt, 2004 for years < 2002 Blood levels associated with apical effects

Page 5

# Could levels have been higher earlier?

• PBPK modeling states:

– The levels could have been 10

- 20 fold higher on the prior day for dose received by oral or inhalation routes of exposures



## – Smaller differences for doses that occur by the dermal route



# • PBPK modeling indicates:

– Measurements do not reflect exposures that occurred more than 2

- 3 days before

measurements



## – Measures do not directly reflect peak or average doses in the first or second trimester



# • Estimates of dose received from early exposures (and associated blood levels and AChEI) and must be estimated from

– Worker studies

– Human exposure studies

– Exposure SOPs
Page 6

# Blood Concentration of Chlorpyrifos vs. RBC AChEI

1.00E

- 02 1.00E

- 01 1.00E+00 1.00E+01 1.00E+02

0.1 1 10 100 1000 10000 100000 1000000 10000000 100000000 Maximum ChEI % of control

Maximum Blood Concentration ng/l Range of blood levels reported in Wyatt, 2004 for years < 2002 Blood levels associated with apical effects

Page 7

# Blood Concentration of Chlorpyrifos vs. RBC AChEI

1.00E

- 02 1.00E

- 01 1.00E+00 1.00E+01 1.00E+02

0.1 1 10 100 1000 10000 100000 1000000 10000000 100000000 Maximum ChEI % of control

Maximum Blood Concentration ng/l Range of blood levels reported in Wyatt, 2004 for years < 2002 Blood levels associated with apical effects

Page 8 Residential Exposure Studies

# Blood Concentration of Chlorpyrifos vs. RBC AChEI

1.00E

- 02 1.00E

- 01 1.00E+00 1.00E+01 1.00E+02

0.1 1 10 100 1000 10000 100000 1000000 10000000 100000000 Maximum ChEI % of control

Maximum Blood Concentration ng/l Range of blood levels reported in Wyatt, 2004 for years < 2002 Blood levels associated with apical effects

Page 9 Residential Exposure Studies

Egyptian Worker Studies (Worst case exposures)

# Conclusions

• There is considerable uncertainty in chlorpyrifos exposures in the first and second trimesters

– Who used what products

– Importance of difference routes of exposure



# • Occupational exposures and exposures for off label uses 

# in Egyptian studies as an upper bound to the range of exposures for the Columbia participants

• Brain inhibition and apical effects are not likely to have

occurred

Page 10

# Proposal 1: Refine blood data

Hypothesis
Blood levels are greatly dependent on the time since last exposure. PBPK models could be used to estimate a

standard measure of blood for each mother that would be a 

# better estimate of recent exposures.
Project:
Model the blood level at the time the person entered the 

# hospital based on cord and maternal blood concentrations, timing of samples, and predicted routes of exposures

Page 11

## • Blood levels reflect recent exposure not exposure during the critical windows for fetal 

## development

• The assumption is implicitly made that recent exposures are correlated with early

exposures Birth 3 rd



### Trimester 2 ed



### Trimester 1 st



### Trimester Window of concern Recent Exposures

Blood Measurements 

# Proposal 2: Develop estimates of early exposures

## • The analysis does not use the other data in the exposure assessment



## • Develop a categorical approach (e.g. no exposure, low exposure, high exposure) to

1 st 

## and 2 ed 

## trimester exposures that uses data on blood, air monitoring, residential mobility, pest pressure, and pesticide usage.

• Use the criteria to determine if the association holds for early exposures Birth 3 rd



### Trimester 2 ed



### Trimester 1 st



### Trimester Window of concern

Air monitoring Recent Exposures

Blood Measurements Survey Data 

# Proposal 2: Develop estimates of early exposures

# Proposal 3: Develop a BE

Hypothesis
An understanding of the blood levels in multiples studies will be improved by having a BE value.
Project:
Develop a BE for chlorpyrifos.

Page 14