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

RE: Meeting between Dow AgroSciences (DAS) and EPA for DAS to present additional PBPK modeling for chlorpyr ifos for life-stage corresponding to pregnancy List of Documents 1. Meeting Summary Page 1 2. Meeting Sign in Sheet Page 2 3. DAS PowerPoint Presentation Page 3 Meeting Summary On Thursday, April 2, 2015, EPA met with DAS to discuss their PBPK model. Since the release of the chlorpyrifos revised human health ri sk assessment (RHHRA) in January 2015, DAS has been working on a pregnancy component for th e PBPK model. Curren tly the model cannot account for women of child-bearing age. DAS an ticipates submitting this pregnancy component as part of their comments on the RHHRA. EPA will be evaluating this new component of the PBPK model in order to determin e whether it is appropriate to support refinements to the risk assessment.

## Additional PBPK modelling for Chlorpyrifos during the life

stage during pregnancy
George Oliver, US Regulatory Leader, Dow AgroSciences April 2, 2015

## • Introductions and objectives

• New modeling results (Mike Bartels, Torka Poet)



## • Discussion

• Further actions 

# Agenda for today

2• George Oliver , US Regulatory Leader for Chlorpyrifos, Dow AgroSciences

• Michael J. Bartels , Associate TERC Fellow

- Toxicology, The Dow Chemical Company

• Daland Juberg , Global Leader, Human Health Assessment, Dow AgroSciences

• Torka S Poet , Sr. Associate, Summit Toxicology, LLP (Richland, Washington)



# Attendees

3

### • Share additional PBPK modeling for chlorpyrifos for life

- stage 

### corresponding to pregnancy.

• Present results which indicate the existing intraspecies UF of 4X is appropriate for this life stage.

• Gain an understand of what and how EPA would like DAS to submit this information 

# Objectives

4

# Chlorpyrifos PBPK Pregnancy Model

• The Draft Risk assessment for Chlorpyrifos 

# (CPF) of 2011 was based on a Margin of Exposure of 100 for Dermal exposures:

• POD for RBC cholinesterase effects in rats = 5 mg/kg



### • Interspecies Uncertainty Factor ( UF a 

### ) = 10x

• Intraspecies Uncertainty Factor ( UF h 

### ) = 10x

• FQPA Safety Factor = 1x

• POD for sensitive humans = 0.05 mg/kg

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# Chlorpyrifos PBPK Pregnancy Model

– The Revised Risk assessment of 2014 is based on the 

## DAS PBPK/PD model, validated for rats and humans, across lifestages and varying physiology

– Margin of Exposure now set to 40x by EPA for 

## Dermal exposures:

• Interspecies Uncertainty Factor ( UF a 

### ) = 1x

• POD for cholinesterase effects in human = 3.63mg/kg

• Intraspecies Uncertainty Factor ( UF h 

### ) = 4x

• FQPA Safety Factor = 10x

• POD for sensitive humans = 0.09 mg/kg

6

# Chlorpyrifos PBPK Pregnancy Model

– Since the PBPK/PD model (as of 2014) did not allow for simulations in pregnant women, the EPA set the intraspecies Uncertainty Factor ( UF h 

## ) for pregnant workers to 10x:

• Interspecies Uncertainty Factor ( UF a 

### ) = 1x

• POD for cholinesterase effects in human = 3.63 mg/kg

• Intraspecies Uncertainty Factor ( UF h 

### ) = 10x



### • FQPA Safety Factor = 10x

• POD for sensitive humans = 0.036 mg/kg

7

# Chlorpyrifos PBPK Pregnancy Model

• To investigate the appropriateness of the default 

## 10x UF h 

## for pregnant workers, it was decided to expand the current Multi

- Route PBPK/PD model to include systemic exposure and RBC effects predictions during all stages of human pregnancy

– Step 1: compare the predicted exposure levels that would result in 10% RBC cholinesterase inhibition for an “average” non

- pregnant or pregnant woman, by oral, dermal or inhalation routes

– Step 2: evaluate the impact of pregnancy on the intra

human variability in RBC effects

• Calculation of DDEF 8

# Chlorpyrifos PBPK Pregnancy Model

• Started with Multi

- Route PBPK/PD model...

9

# Chlorpyrifos PBPK Pregnancy Model

• Which accommodates changes across lifestages
...

Smith et al. 2014

10

# Chlorpyrifos PBPK Pregnancy Model Then modified to include changes due to Gestation: Addition of placenta, uterine and fetal compartments , which grow over the course of pregnancy Tissue Changes Pregnancy specific changes in the slow compartment. Pregnancy specific changes in the fat compartment Pregnancy specific changes in the rapid compartment Pregnancy changes in blood composition result in increased blood volume, decreased hematocrit Pregnancy specific changes in metabolism CYP450s – based on literature data for various isozymes PON1 – based on longitudinal studies

-

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## Step 1 Results:

- New Gestational compartments match empirical data

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## Step 1 Results: Changes in existing tissue physiology match published data

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## Step 1 Results: Changes in other physiology parameters also match published data

14

## Step 1 Results: Changes in Metabolism predict higher rate of Oxon formation during pregnancy

15

## Step 1 Results: Changes in PON

- 1 levels included in model

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# Chlorpyrifos PBPK Pregnancy Model
REFERENCES for pregnancy - based changes in physiology and metabolism Abduljalil , K., Furness, P., Johnson, T.N., Rostami
- Hodjegan , A., Soltani , H., 2012. Anatomical, physiological and metabolic changes with gestational age during normal pregnancy: a database for parameters required in physiologically based pharmacokinetic modelling. Clin
. Pharmacokinet . 51, 365 – 96. Anderson , G.D., 2006. Using pharmacokinetics to predict the effects of pregnancy and maternal

- infant transfer of drugs during lactation. Expert Opin . Drug Metab
. Toxicol . 2, 947 – 60. Corley , R.A., Mast, T.J., Carney, E.W., Rogers, J.M., Daston , G.P., 2003. Evaluation of physiologically based models of pregnancy and lactation for their application in children’s health risk assessments. Crit. Rev. Toxicol . 33, 137 – 211. Cunningham , G.F., 2010. Protocols for High

- Risk Pregnancies: Appendix B. Laboratory Values in Normal Pregnancy. Wiley

- Blackwell, Oxford, U K. Dickmann , L.J., Isoherranen , N., 2013. Quantitative prediction of CYP2B6 induction by estradiol during pregnancy: potential explanation for increased me tha done clearance during pregnancy. Drug Metab
. Dispos . 41, 270 – 4. Foxenberg , R.J., McGarrigle , B.P., Knaak , J.B., Kostyniak , P.J., Olson, J.R., 2007. Human hepatic cytochrome p450

- specific metabolism of parathion and chlorpyrifos
. Drug Metab
. Dispos . 35, 189 – 93. Gentry , P.R., Covington, T.R., Clewell , H.J., 2003. Evaluation of the potential impact of pharmacokinetic differences on tissue dosimetry in offspring during pregn anc y and lactation. Regul
. Toxicol
. Pharmacol . 38, 1 – 16
. Huen , K., Harley, K., Bradman, A., Eskenazi , B., Holland, N., 2010. Longitudinal changes in PON1 enzymatic activities in Mexican

- American mothers and children with different genotypes and haplotypes. Toxicol . Appl. Pharmacol . 244, 181 – 9
. Hytten , F., 1985. Blood volume changes in normal pregnancy. Clin
. Haematol . 14, 601 – 12. Kopp - Hoolihan , L.E., van Loan, M.D., Wong, W.W., King, J.C., 1999. Fat mass deposition during pregnancy using a four

- component model. J Appl Physiol 87, 196 – 202. Lippi , G., Albiero , A., Montagnana , M., Salvagno , G.L., Scevarolli , S., Franchi , M., Guidi , G.C., 2007. Lipid and lipoprotein profile in physiological pregnancy. Clin . Lab. 53, 173 – 7. Pennell , P.B., 2003. Antiepileptic drug pharmacokinetics during pregnancy and lactation. Neurology 61, S35
– 42. Sarandöl , E., Dirican , M., Eröz , E., Serdar , Z., Uncu , G., 2010. SERUM PARAOXONASE AND ARYLESTERASE ACTIVITIES THROUGHOUT NORMAL PREGNANCY. Nobel Med. 19, 49 – 55. Sit , D.K., Perel , J.M., Helsel , J.C., Wisner, K.L., 2008. Changes in antidepressant metabolism and dosing across pregnancy and early postpartum. J. Clin . Psychiatry 69, 652 – 8. Tracy , T.S., Venkataramanan , R., Glover, D.D., Caritis , S.N., 2005. Temporal changes in drug metabolism (CYP1A2, CYP2D6 and CYP3A Activity) during pregnancy. Am. J. Obstet. Gynecol. 192, 633
– 9. Weitman , S.D., Vodicnik , M.J., Lech, J.J., 1983. Influence of pregnancy on parathion toxicity and disposition. Toxicol . Appl. Pharmacol . 71, 215 – 24. Weitman , S.D., Vodicnik , M.J., Lech, J.J., 1986a. Mechanism of enhanced parathion/ paraoxon toxicity during pregnancy in the mouse. Fundam . Appl. Toxicol . 6, 155 – 61. Weitman , S.D., Vodicnik , M.J., Lech, J.J., 1986b. Influence of pregnancy on the hepatic metabolism of parathion. Dev. Pharmacol
. Ther . 9, 23 – 31. Young , J.F., Branham, W.S., Sheehan, D.M., Baker, M.E., Wosilait , W.D., Luecke , R.H., 1997. Physiological “constants” for PBPK models for pregnancy. J. Toxicol
. Environ. Health 52, 385 – 401

## Step 1 Results:

- model output for non

pregnant women matches prior EPA results (see X values)

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## Step 1 Results:

- Oral Exposures

Average 3 rd trimester female ~10% more sensitive than non

- pregnant female

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## Step 1 Results:

- Oral Exposures

- Predicted levels of CPF and Oxon metabolite in blood

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## Step 1 Results:

- Dermal Exposures

Average 2 rd trimester female <10% more sensitive than non

- pregnant Average 3 rd trimester less sensitive than non

- pregnant

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## Step 1 Results:

- Inhalation Exposures
All trimesters comparable to non

- pregnant

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## Step 1 Results:

- exposure levels resulting in 10% RBC inhibition for 

### pregnant women (1 st 

### , 2 nd 

### or 3 rd 

### trimester) are all within 15% of non - pregnant levels

- a more comprehensive 

### evaluation of impacts of pregnancy on CPF biological effects in a simulated population was therefore 

### conducted...

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## Step 2 Methods:

- used data

- rich oral route linked model for comparison with prior Variation modeling



### - dietary values and model parameters consistent with DAS October 2014 report

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## Step 2 Results: Simulation of RBC cholinesterase inhibition in cohorts of 10,000 women following dietary exposure to CPF

N=10,000 / lifestage

25

## Step 2 Results: Percentile analysis of predicted RBC cholinesterase inhibition in cohorts of 10,000 following dietary exposure to CPF

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## Step 2 Results:

- Data Derived Extrapolation Factors

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## Step 2 Results:

- Data Derived Extrapolation Factors

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## Step 2 Results:

- Data Derived Extrapolation Factors

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## Conclusions: Initial modeling results for pregnant women are well within 20% of cholinesterase response for general 

## population and non

- pregnant women, by any of the three exposure routes A more refined “Variation” analysis in a population of 

## 10,000 pregnant women shows biological effects comparable to non

- pregnant women, and both are less than men + women 

## The existing UF h 

## value of 4x for male and female adults should therefore be protective of pregnant women in occupational settings
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# Questions / Discussion

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