EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 1 of 73 

UNITED STATES ENVIRONMENTALPROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF PREVENTION, PESTICIDES 

OPP OFFICIAL RECOiiD AND TOXIC SUBSTANCES 

HEALTH EFFECTS DIVISiON 

SCIENTIFIC 0;\Ti\ I~EVIEWS 

EPA SERIES 361 

MEMORANDUM 

Date: January 7, 2010 

SUBJECT: Chlorpyrifos: Reviews of the Coulston (1972), (Nolan (1982) and Kisicki 

(1999) studies with human volunteers including comments from the Human Studies Review 

Board (HSRB) meeting (June 2009). 

PC Code: 059101 

Decision No.: N/A 

Petition No.: N/A 

Risk Assessment Type: N/A 

TXR No.: 0050308 

DP Barcode: 0368390 

Registration No.: N/A 

Regulatory Action: N/A 

Case No.: N/A 

CAS No.: 63-42-3 

MRID No.: Coulston study: 00095175, 40CFR: N/A 

Nolan Study: 00124144, 

Kisicki study: 44811002, 45144101, 

47436401, 47436401, 47866701 and 

47866703. 

FROM: 

And 

THROUGH: 

And 

TO: 

John Doherty \.Q.\~ Risk Assessme~;~ 

Abdallah 

Risk Assessment 

Khasawinah 

Branch 

./')' 

IV 

~ 

Health Effects Division 7509P 

JackArthur Au/~ Acting Branch chir"" . 

Risk Assessment Bran~7 ~ 

Ray Kent {---:J ·~ BranchCh~ Risk Assessment Branch IV 

Health Effects Division 7509P 

Veronique LaCapra 

Pesticide Re-evaluation Division 7507P 

Page I of 5 

Ver.Apr.08 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 2 of 73 

I. CONCLUSIONS 

The updated reviews of the Coulston (1972) and Nolan (1982) studies and original review of 

the Kisicki (1999) studies with chlorpyrifos in human volunteers are attached. The Nolan and 

Kisicki studies were presented to the Human Studies Review Board (HSRB) at a meeting held on 

June 24-25, 2009 (final report October 26, 2009). The HSRB comments on the ethical aspects of 

these studies will be addressed separately by the Office of Pesticide Programs human studies 

ethics review team. This memo addresses the scientific aspects of these studies. 

HED conclusions for each study are as follows: 

Coulston Study (1972). (The HSRB did not review this study). No treatment-related effects 

were found on measured urinalysis, hematology, or clinical chemistry parameters except for 

depressed plasma cholinesterase (ChE) activity in subjects receiving the test material. Based on 

an -30% decrease in plasma cholinesterase activity by Day 16, the LOAEL for Dowco 179 was 

0.03 mg/kg bw/day. The corresponding NOAEL was 0.014 mg/kg bw/day. Erythrocyte 

acetylcholinesterase activity was not affected at any of the doses. Although this study is 

informative, it is deficient in many aspects (incomplete details of the methodology) that make its 

usefulness in human risk assessments very limited. The study DER is attached. 

Nolan Study (1982). The HSRB had no adverse comments on the Nolan study. This study 

was a single dose (0.5 mg/kg) study that demonstrated inhibition of plasma ChE (up to 89%) 

following an oral dose. There was no consistent inhibition of plasma ChE following a dermal 

dose of 5 mg/kg. RBC AChE was determined not to be inhibited following either the oral or 

dermal dosing. Analysis of the urine indicated that an estimated 72 ± II% of the ingested dose 

and 0.95 ± 0.559% of the dermal dose were absorbed. The study is considered to be informative 

with respect to inhibition of plasma ChE following oral administration and to have useful 

information regarding pharmacokinetics following both oral and dermal administration. 

Kisicki Study (1999). The HSRB expressed concerns for the Kisicki study regarding the 

statistical procedures used for evaluating the intergroup RBC AChE data and the method for 

determining the blood and urinary levels ofTCP (the principal metabolite of chlorpyrifos). 

Health Effects Division (HED) acknowledges the comments on the statistical procedures and 

should the data for RBC AChE from the Kisicki study be used for regulatory purposes, HED will 

reconsider conducting independent statistical reanalysis. In its evaluation of the RBC AChE 

data, HED relied on the individual response relative to the persons predosing background values. 

Only one person was determined to demonstrate a pattern for meeting inhibition criteria with 

respect to time of onset, duration and degree of differences relative to their predosing value. 

Thus, HED has not relied on the group differences for determining the inhibition in this study. 

In response to the HSRB' s concern regarding the procedures used for preparation TCP for 

analysis, the DOW AgroSciences Company provided additional details related to the 

methodology in the preparation that clearly demonstrated that the appropriate acid hydrolysis 

step was included to assure that total (free and conjugated) TCP was determined in both the 

blood and the urine. 

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The single dose Kisicki study demonstrated definite inhibition on only one individual in the 

high (2 mg/kg) dose group thus establishing a NOAEL of 1 mg/kg. The study was determined to 

have a deficiency in that plasma ChE assessment was not included. This confounded 

comparison with the Nolan study. 

The analysis of the blood and urine for TCP demonstrated only about 35% of the 

administered dose was absorbed by the gastro-intestinal tract. This is about half of the value of 

about 70% demonstrated in the Nolan study. The DOW AgroSciences Company provided 

(2009, MRID # 44811 002) a rationale that supports the theory that this difference is due to the 

differences in the way the chlorpyrifos was administered in each study. In the Nolan study, the 

chlorpyrifos was first dissolved in solvent, placed on top of a lactose pill which was swallowed 

by the volunteers. In the Kisicki study, crystalline chlorpyrifos was placed in a capsule 

containing lactose and the capsule swallowed. The difference in capsule vs. pill plus physical 

nature of the crystals due to dissolving in solvent in the Nolan study may be the basis for the 

difference in absorption rate. The lower rate of absorption in the Kisicki study will be taken into 

consideration should this study be used for pharmacokinetic modeling. 

Copies of the DERs for these studies are attached. Table I below presents the Executive 

Summaries for these two studies. 

IV. RESULTSIDISCUSSION (or MRID Summary Table, etc.) 

MRIDS ummary a e T bl E xample I 

Study Type MRID Executive Summary 

Special Non-Guideline 00095175 In an oral multiple dose study (MRID 00095175), groups of four healthy adult male prisoners 

Study- human received 0.0, 0.0 14, 0.03, or 0.1 mg/kg bw/day Dowco 179 (purity, stability, and lot number not 

volunteers, Coulston et provided) for 48, 27, 20, and nine days, respectively. No treatment-related effects were found 

al, (1972). on measured urinalysis, hematology, or clinical chemistry parameters except for depressed 

plasma cholinesterase (ChE) activity in subjects receiving the test material. 

Plasma cholinesterase activity was reduced 46% by Day 6 in subjects treated with 0.10 mg 

Dowco 179/kg bw/day, which further decreased to 66% by Day 9. Dosing was stopped for the 

0.1 mglkg bw/day group on Day 9 as plasma ChE activity was decreased >20% for all individuals in the dose group. In the 0.03 mg Dowco 179/kg bw/day group, plasma ChE activity was 

decreased 32% by Day 16 and remained decreased -30% through Day 20 when treatment was 

stopped. No significant treatment-related effect on ChE activity was found in subjects of the 

0.014 mg/kg bw/day group. Recovery of plasma ChE activity in subjects treated with 0.1 

mg/kg bw/day was observed by Day 25 and by Day 21 in subjects of the 0.03 mglkg bw/day 

group after cessation of dosing. Erythrocyte acetylcholienesterase activity was not affected at 

any of the doses. 

Based on an -30% decrease in plasma cholinesterase activity by Day 16, the LOAEL for 

Dowco 179 was 0.03 mg/kg bw/day. The corresponding NOAEL was 0.014 mg/kg bw/day. 

Classification. This study is classified as Unacceptable/Non-Guideline. Although the study 

contains some useful data that describes the potential for chlorpyrifos to inhibit plasma ChE in 

Page 3 of 5 
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Study Type MRID 

Special Non-Guideline 00124144 

Study -human 

volunteers. Nolan et al, 

1982) 

Special Non-Guideline 

Study- human 

volunteers. Kisicki et 

al, 1999) 

44811002 

45144101, 

47436401, 

47436401, 

47866701 

and 

47866703 

Executive Summary 

human volunteers, there are several deficiencies (incomplete details of the 

methodology) that preclude using the data for endpoint selection for risk assessment or for 

informing the uncertainty factors. The study has not been reviewed for either ethics or 

scientific considerations by the EPA Human Studies Review Board. 

In a single-dose human oral/dermal toxicity study with chlorpyrifos (1982, MRID 00124144), six 

male volunteers were given 0.5 mglkg chlorpyrifos (99.8% a.i., Lot No. AGR 166043) on a !acto 

tablet. Plasma and RBC cholinesterase activity were monitored at 2, 6, 12, 24 hours, and 2, 3, 4, 

14, 22, 27, and 30 days post-dose. Approximately four weeks after the oral treatment, a single 

dermal dose (5 mg/kg to five subjects; 0.5 mglkg to one subject) was administered on the volar 

surface of the forearm. RBC and plasma cholinesterase activity were determined 2, 6, and 12 ho 

and on days I, 2, 3, 4, 6, 8, and 9 following dermal treatment. Blood and urine samples were 

analyzed for chlorpyrifos and 3,5,6-TCP (3,5,6-trichloro-2-pyridinol) concentrations. 

No clinical signs of toxicity and essentially no significant inhibition ofRBC cholinesterase activi 

were observed following either the oral or dermal dose. Plasma cholinesterase activity was 

inhibited 83-89% relative to pre-dose activities following the oral dose (peak inhibition within 

6-24 hours post dose) but was essentially unchanged following the dermal dose. Blood 

chlorpyrifos concentrations were low (<30 ng/mL; limit of detection 5 ng/mL), and chlorpyrifos 

was not found in the urine following either route of exposure. 3,5,6-TCP blood concentrations 

peaked by six hours after oral exposure and 24 hours after dermal application. 3,5,6-TCP was 

cleared from the blood and eliminated in the urine with a half-life of27 hours following both the 

oral and dermal doses. Using assumptions of first-order absorption and elimination equations, it 

was estimated that 72 ±II% of the ingested dose and 0.95 ± 0.559% of the dermal dose were 

absorbed. 

Classification: This studied is classified as Acceptable/Non-Guideline and to contain useful 

information on the potential for chlorpyrifos to inhibit plasma ChE in humans as well as 

pharmacokinetic data following oral and dermal administration. The pharmacokinetic data 

provide data useful for estimating the dermal absorption factor, The study, however, should not 

be used for en~:Ipoint selection or for informing the uncertainty factors for risk assessment. 

In a special acute oral study (1999, MR!Ds: 44811002,45144101,47436401,47436401, 

47866701 and 47866703) performed to assess effects on human red blood cell (RBC) 

acetylcholinesterase (AChE), chlorpyrifos (99.8%; Lot# MM930503-17) in a gelatin capsule 

was administered to 6 human subjects/sex/dose group at dose levels ofO (lactose-filled 

capsule), 0.5 or 1.0 mg/kg (Phase !). When it was determined that there was no inhibition and 

no adverse reactions in these subjects, a second phase of 6 human subjects/sex/group were 

dosed similarly as control and 2.0 mglkg chlorpyrifos. The subjects vital signs (blood pressure, 

pulse, respiration and temperature were evaluated the morning prior to dosing and at 1, 2, 4, 8, 

12, 24, 48 and 168 hours post dosing. In addition hematology, clinical chemistry and urinalysis 

assessments were performed one week post dose. 

Blood was assessed at-10 hours, zero (pre-dose), and at 2, 4, 8, 12, 24, 36, 48, 72, 96, 144 and 

168 hours post dose for RBC AChE activity. Plasma cholinesterase (ChE) was not assessed 

Blood and urine were collected at selected intervals and analyzed for chlorpyrifos, chlorpyrifos 

axon, and the principal metabolite 3,5,6-trichloro-2-pyridinol (TCP) to define the 

pharmacokinetics ofchlorpyrifos in humans. The paraoxonase (PONI) status was determined 

for each subject. Serum paraoxonase activity was measured against chlorpyrifos axon, 

paraoxon, and diazoxon, and called chlorpyrifos oxonase (CPOase), paraoxonase, or 

diazoxonase, respectively (MRID# 45144101). Additionally, the PON phenotype (i.e. QQ, OR 

and RR) was determined for each subject. 

Systemic Effects. There were no apparent clinical reactions or changes in clinical chemistry 

parameters related to treatment. 

Pharmacokinetic Data. Chlorpyrifos was detected in the serum of 4 of the 12 subjects (2-8 

Page 4 of 5 

'I 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 5 of 73 

Study Type MRID Executive Summary 

hours post dose) in thel.O mg/kg dose (range of 1.1-5.6 ng/g) and in 4 of the 12 subjects (2-12 

hours post dose) in the 2.0 mg/kg dose (range 1.3-18 ng/g). TCP was detected in the blood of 

all subjects through 120 hours (0.5 and 1.0 mg/kg) and through 168 hours (2.0 mg/kg). The 

highest concentration ofTCP reached ranged from 110-380 ng/g (0.5 mg/kg), 140-610 ng/g 

(1.0 mg/kg), and 370-1600 ng/g (2.0 mglkg). Chlorpyrifos and chlorpyrifos oxon were not 

found in the urine at any dose level, and chlorpyrifos ox on was not found in the blood of any 

subject. Subject #56 (QQ phenotype) the only subject demonstrating RBC AChE inhibition 

had a peak blood concentration of 18 ng/gm chlorpyrifos at 8 hours following a 2 mg/kg dose, 

but withdrew from the study after 48 hours for a personal problem. This same subject had the 

highest levels of serum (6671 ng/gm) and urinary (22.8 mg) TCP accumulated up to 48 hours. 

The serum chlorpyrifos and serum and urinary TCP data all suggested that this subject absorbed 

more of her dose than the other subjects on the study. CPOase for this subject was similar to 

the other subjects with the phenotype QQ. 

RBC AChE. Zero time (predosing) baseline RBC AChE ranged from 8143±982 (±12%) to 

9572±539 (±6%) UIL for males and 8576±556 (±6%) and 9165±709 (±8%) UIL for females 

indicating good precision for the baseline data. These RBC AChE values were within the 

expected range for humans. Only one individual had a decrease in RBC AChE that suggested 

inhibition by chlorpyrifos as indicated by being consistently decreased at the critical hours post 

dosing. For this subject (#56, a female dosed with 2 mglkg), inhibition ofRBC ACHE was 

observed at 8 (23% .J,), 12 (maximum 28% .J,), 24 (26%.J,), 36 (19%.J,) and 48 (21%.J,) hours 

post dose. There were no associated cholinergic symptoms reported, although a transient 

numbness in the upper arms in this subject was reported at about 2 hours post dosing or well 

before AChE inhibition and significant levels of TCP in the serum were detected. The LOAEL 

is 2 mg/kg/day for RBC AChE based on 28% inhibition in one female subject. The 

NOAEL is 1 mg/kg. 

Classification: This study is classified as Acceptable/Non-Guideline and to contain useful 

information on the pharmacokinetics of orally administered chlorpyrifos when administered in a 

capsule to human volunteers. The study, however, should not be used for endpoint selection or 

for impacting the uncertainty factors for risk assessment. The RBC AChE inhibitory 

assessment aspects of this study depend upon only one subject showing clear evidence of 

inhibition. Another serious problem with this study with regard to comparing the results with 

other studies in human volunteers is that no assessments of plasma cholinesterase were made. 

Differences in the method of dose administration where a chlorpyrifos was administered in a 

capsule in this study and on top of a lactose pill after dissolving in solvent in the Nolan study 

preclude direct comparison of the pharmacokinetic data. 

Page 5 of 5 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 6 of 73 

DATA EVALUATION RECORD-IHJPI'LI:MENTAL 

CRLORPYRII'08 

NONGlllDELDIE 

STUJW'IYP't> REPEAT DOSE ORAL TOXIcrrY ·HUMAN 

MRID 1*195175 

Ptlmaey~ 

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U.S.. Jim:hdl'"k:ntal Protecdo:n.AgeDcy 

Oncl'ommac Yard 

rrn s. CJy8IBl Drive 

ArfiD&t<m. VA 22202 

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Oak Kidp NldlonaJ. I lh waiN •t)' 

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Tllllk o.d&:r No. 207-2009 

H,T BgJp. Ph,D .. MTfA§CPl. D.A.B,T. 

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R.A. Y .. mg l'ILD.. D.AA T. 

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0* Itldae Nodoaal I abomtnry ....plllli _.a.! 1!, UT -""""'lo, LI.C.Ibr lho U.S. ~ of 

I!Jieray 1Dider c-No. Dli-AOOHI001122'12!5, 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 7 of 73 

CHLORPYRIFOS 

Repeat Dose Oral Toxicity (Human) (1972) I Page 2 of 11 

Nonguideline 

EPA Reviewer: Abdallah Khasawinah. Ph.D. 

Risk Assessment Branch IV, Health Effects Division (7509P) 

EPA Work Assignment Manager: Myron Ottley, Ph.D. 

Risk Assessment Branch III, Health Effects Division (7509P) 

TXR#: 0050308 

Signature:~· (C~,L_ Date: Dm?--0\o 

Signature: / , F 

Date: 1/7 /Jo 

Template version 02/06 

ACC NO.: 092212 D 

DATA Ev ALUA noN REcoRD- suPPLEMENTAL I1YR oooo\:::p::f 

STUDY TYPE: Repeat Dose Oral Toxicity (Human) 

N onguideline 

PC CODE: 059101 DP BARCODE: D368390 

TEST MATERIAL (PURITY): Dowco 179 ( chlorpyrifos; purity not reported) 

SYNONYMS: 0,0-diethyl-0-[3,5,6-trichloro-2-pyridyl] phosphorothioate 

CITATION: Coulston, R., L. Golberg, T. Griffin. (1972). Safety evaluation of DOW CO 179 

in human volunteers. Institute of Experimental Pathology and Toxicology, Albany Medical 

College, Albany, NY 12208. Report Number not provided. March 1972. MRID 00095175 

SPONSOR: Not reported but presumed: The Dow Chemical Company, Midland, MI 

EXECUTIVE SUMMARY: In an oral multiple dose study (MRID 00095175), groups of'four 

healthy adult male prisoners received 0.0, 0.014, 0.03, or 0.1 mglkg bw/day Dowco 179 (purity, 

stability, and lot number not provided) for 48, 27, 20, and nine days, respectively. No treatmentrelated effects were found on measured urinalysis, hematology, or clinical chemistry parameters 

except for depressed plasma cholinesterase (ChE) activity in subjects receiving the test materiaL 

Plasma cholinesterase activity was reduced 46% by Day 6 in subjects treated with 0.10 mg 

Dowco 179/kg bw/day, which further decreased to 66% by Day 9. Dosing was stopped for the 

0.1 mg/kg bw/day group on Day 9 as plasma ChE activity was decreased >20% for all individuals in the dose group. In the 0.03 mg Dowco 179/kg bw/day group, plasma ChE activity was 

decreased 32% by Day 16 and remained decreased -30% through Day 20 when treatment was 

stopped. No significant treatment-related effect on ChE activity was found in subjects of the 

0.014 mg/kg bw/day group. Recovery of plasma ChE activity in subjects treated with 0.1 mg/kg 

bw/day was observed by Day 25 and by Day 21 in subjects of the 0.03 mglkg bw/day group after 

cessation of dosing. Erythrocyte acetylcholienesterase activity was not affected at any of the 

doses. Based on an -30% decrease in plasma cholinesterase activity by Day 16, the LOAEL 

for Dow co 179 was 0.03 mg/kg bw/day. The corresponding NOAEL was 0.014 mg/kg 

bw/day. 

Classification. This study is classified as Unacceptable/Non-Guideline. Although the study 

contains some useful data that describes the potential for chlorpyrifos to inhibit plasma ChE in 

human volunteers, there are several deficiencies (incomplete details of the methodology) that 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 8 of 73 

CHLORPYRIFOS 

Repeat Dose Oral Toxicity (Human) (1972) I Page 3 of II 

Nonguideline 

preclude using the data for endpoint selection for risk assessment or for informing the uncertainty 

factors. The study has not been reviewed for either ethics or scientific considerations by the EPA 

Human Studies Review Board. 

COMPLIANCE: Signed and dated GLP, Quality Assurance, and Data Confidentiality 

statements were not provided. 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 9 of 73 

CHLORPYRIFOS 

Repeat Dose Oral Toxicity (Human) (1972) I Page 4 of II 

Nonguideline 

I. MATERIALS AND METHODS: 

A. MATERIALS: 

I. Test material: 

Description: 

Lot/Batch #: 

Purity: 

Compound Stability: 

CAS # for TGAI: 

Structure:: 

Dowco 179 

Not reported 

Not reported 

Not reported 

Not reported 

2921-88-2 

2. Vehicle: Tablet (not further described) provided with the breakfast meal 

3. Human Subjects: 

Number: 

Race: 

Sex: 

Age: 

Weight: 

Source: 

Physical Examination: 

B. STUDY DESIGN: 

I. Study date: Not reported 

Sixteen 

Not reported 

Male 

Not reported 

Not reported 

Volunteers from the Clinton Correctional Facility, Dannemora, NY 

Before the start of the study, each volunteer was given a thorough physical 

examination that included a chest X-ray, electrocardiogram, urinalysis, and 

hematology and clinical chemistry parameters. 

2. Study subjects: Sixteen male volunteers from the Clinton Correctional Facility were divided 

into groups of four and assigned to the groups and duration of treatment shown in Table I. 

Table I. Studv desi2n 

Subiect # Dose lmo/ko bw/davl Duration of exnosure 

2, 4, 9, 16 0.0 7 weeks 

7, 8, 14, 15 0.014 27 days 

10,11,12,13 0.03 20 days 

I, 3, 5, 6 0.10 9 days 

3. Dose selection: A dose selection rationale was not provided. 

4. Dose preparation and analysis: Other than the doses being dispensed onto a tablet at the 

concentrations shown in Table 1 and provided with the breakfast meal, no other dosing 

information was provided. 

lr 
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CHLORPYRIFOS 

Results: 

Homogeneity analysis: Not reported 

Stability analysis: Not reported 

Concentration analysis: Not provided 

Repeat Dose Oral Toxicity (Human) (1972) I Page 5 of 11 

Nonguideline 

5. Statistics: Statistical analyses for hematology, clinical chemistry, and urinalysis were not 

reported. Plasma and RBC cholinesterase activity were analyzed by three-way randomized 

factorial ANOV A. 

C. METHODS: 

1. Observations: It is assumed the test subjects were observed daily at the time of treatment 

and/or blood collection; however no specific mention is made in the study report. 

2. Body weight: Although the doses were administered on a kg bw/day basis, body weight data 

were not provided in the study report. 

4. Hematology and clinical chemistry: Blood was collected for hematology and clinical 

chemistry analyses before treatment and on days 7, 15, 22, 28, 35, 42, and 49 for control 

subjects; days 6, 13, 20, and 27 for subjects treated with 0.014 mg/kg bw/day; days 7, 15, and 

22 and day 6 post-treatment for subjects treated with 0.03 mglkg bw/day; and day 8 of treatment and days 5, II, and 18 post-treatment for subjects treated with 0.1 mg/kg bw/day. The 

CHECKED (X) parameters were examined. 

a. Hematology: 

X Hematocrit (HCT) X Leukocyte differential count 

X Hemoglobin (HGB) Mean corpuscular HGB (MCH) 

X Leukocyte count (WBC) Mean corpusc. HGB conc.(MCHC) 

Erythrocyte count (RBC) Mean corpusc. volume (MCV) 

Platelet count Reticulocyte count 

Blood clotting measurements X Basophils 

(Thromboplastin time) X Eosinophils 

(Clotting time) X Neutophils 

(Prothrombin time) X Lyrnohocytes 

X Monocytes 

II 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 11 of 73 

CHLORPYRIFOS 

b. Clinical chemistry 

X ELECTROLYTES 

X Calcium 

Chloride 

Magnesium 

X Phosphorus 

Potassium 

Sodium 

X ENZYMES 

X Alkaline phosphatase (ALK) 

X Cholinesterase (ChE) 

Creatine phosphokinase 

X Lactic acid dehydrogenase (LDH) 

Alanine aminotransferase (ALT/ SGPT) 

X Aspartate aminotransferase (AST/ SGOT) 

Gamma glutamyl transferase (GGT) 

Sorbitol dehydrogenase 

Glutamate dehydrogenase 

Repeat Dose Oral Toxicity (Human) (1972) I Page 6 of 11 

Nonguideline 

X OTHER 

X Albumin 

Creatinine 

X Urea nitrogen 

X Total Cholesterol 

Globulins 

X Glucose 

X Total bilirubin 

X Total protein (TP) 

Triglycerides 

X Uric Acid 

5. Urinalysis: Urine was collected weekly during the study and analyzed for specific gravity, 

color, clarity, pH, and microscopic analysis. Samples of the urine were retained for 

determination ofDowco 179 and metabolic products. 

6. Cholinesterase activity: Plasma and RBC cholinesterase (ChE) activity was measured by the 

method ofNabb and Whitfield (Arch. Environ. Health (1967) 15: 14 7) with acetylcholine 

perchlorate as the substrate followed by titration to pH 8.0 with sodium hydroxide. ChE 

activity was expressed as J.lmoles acetate/min/mL. Plasma and RBC ChE activity was monitored every 2-3 days during treatment (control: 1, 3, 6, 10, 13, 16, 18, 20, 23, 27, 30, 34, 37, 

41, 44, 48 days; 0.014 mg/kg bw/day: 3, 6, 9, 13, 16, 20, 23, 27 days; 0.03 mg!kg bw/day: 1, 

3, 6, 13, 16, 18,20 days; 0.10 mg/kg bw/day: 1, 3, 6, 9 days). After the treatment period, 

plasma and RBC ChE activity were monitored on the following until activities returned to 

pre-treatment levels: control: days 3 and 7; 0.10 mg/kg bw/day: days 2, 4, 7, 11, 14, 18, 21, 

25, 28, 32, and 35; 0.03 mglkg bw/day: days 2, 6, 9, 13, 20, 23, 27, and 30; and 0.014 

mg/kg bw/day: days 3 and 7. 

II. RESULTS: 

A. OBSERVATIONS: 

1. Clinical signs of toxicity: No treatment-related clinical signs of toxicity were reported, 

except for one subject treated with 0.10 mg/kg bw/day Dowco 179 complained of a runny 

nose, blurred vision, and faintness on the final day of treatment. The subject was treated for a 

cold and was asymptomatic by the end of the day. 

2. Mortality: All subjects survived the study. 

I? 
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CHLORPYRJFOS 

B. BLOOD ANALYSES: 

Repeat Dose Oral Toxicity (Human) (1972) I Page 7 of II 

Nonguideline 

1. Hematology: While individual data were provided, summary data of measured hematological parameters were not provided. Review of the individual data indicates there were no 

treatment-related effects. 

2. Clinical Chemistry: While individual data were provided, summary data of measured 

clinical chemistry parameters were not provided. Review of the individual data indicates 

there were no treatment-related effects. 

F. URINALYSIS: Urinalysis data were not provided. The study author stated that no 

treatment-related effects were found. Routine urinalysis which included specific gravity, 

color, turbidity, pH and determination of cellular content were completely negative of 

treatment related effects for all individuals throughout the study. Urine samples were 

examined for the presence ofDowco 179, its oxygen analog and its metabolite 3,5,6-

trichloro-2-pyridinol and were not detected in any of the samples. Details of the analysis and 

the limit of detection were not provided except for a reference to the method used (Final 

Report on Safety Evaluation and Metabolic Studies. Institute of Experimental Pathology and 

Toxicology, Albany Medical College, March 18, 1971 ). 

G. CHOLINESTERASE ACTIVITY: 

1. Plasma: As shown in Table 2a, plasma ChE activity was reduced 38% by Day 6 in the 

0.10 mg/kg bw/day dose group, and further decreased to 60% of pretreatment activity by 

Day 9. The study authors reported that dosing was stopped for the 0.1 mg/kg bw/day 

group on Day 9 because plasma ChE was decreased >20% for all individuals in this dose 

group. In the 0.03 mg/kg bw/day group, plasma ChE activity was decreased 32% of 

pretreatment activity by Day 16 and remained decreased -30% through Day 20 when 

treatment was stopped. No significant treatment-related effect was found in subjects of 

the 0.014 mg/kg bw/day group. Recovery of plasma ChE activity in subjects treated with 

0.1 mg/kg bw/day was observed by Day 25 and by Day 21 in subjects of the 0.03 mg/kg 

bw/day group after cessation of dosing. 

Summary results are also presented in Table 2b on the basis of plasma cholinesterase 

activity in 1-1moles acetate/min/mL 

Table 2a. Average percent change of plasma cholinesterase relative to pre-treatment activity 

in subjects receivine; Dowco 179 daily 

Dose (mg/kg Da of treatment 

bw/day) I 3 6 10 13 16 19 20 27 

Control 16 ± 33.7 9±21.1 11 ± 6.0 20 ± 10.8 12±11.0 2 ± 12.9 5 ± 15.1 7 ± 7.7 7 ± 11.0 

0.014' - 7± 8.9 7 ± 11.6 -9 ± 14.5 ~19*±7.3 -18*± 17.4 - -7± 13.2 -5 ± 17.9 

0.03' -5 ± 6.8 -9 ± 11.4 -15' ± 17.9 -2 ± 29.3 -15* ± 18.9 -32* ± 15.4 -33* ± 15.1 -29* ± 15.6 - 0.10' 0 ± 39.6 2 ± 35.1 -38* ± 37.4 -60* ± 32.8 - - - - -

Dose (mg/kg Da of recover 

bw/day) 2 4 7 11 14 18 21 25 28 

Controid -13 ± 19.7 - 12±20.0 - - - - - -

0.014' 14± 12.8 - 18 ± 7.8 - - - - - - 0.03' -25 ± 15.0 - -20 ± 18.2 -26 ± 11.2 -30 ± 25.2 - -4 ± 3.9 -8±11.8 -6 ± 18.0 

0.10 -53*± 34.6 -47±31.0 -40* ± 34.4 -26 ± 34.6 -22 ± 39.2 -25±30.7 -31 ± 20.2 -3 ± 32.3 11±41.4 
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Results and statistics calculated by reviewer from data in Tables 33a and 33b on pages 39-40 ofMRID 00095175. Data 

from Tables 33a and 33 b was entered into an Excel spreadsheet The activity for each individual on each study day was 

divided by the average activity measured prior to the start of the study. The average of the four subjects for each day was 

taken and placed that into the table and then the average and standard deviation for the group was computed. 

Balded results indicate >20% CHE inhibition 

a Actual days activity measured= 3, 6, 9, 13, 16, 20, 23, and 27 

b Actual days activity measured= 1, 3, 6, 10, 13, 16, 18, and 20 

c Actual days activity measured = I, 3, 6, and 9 

d Actual days activity measured = 3 and 7 

e Actual days activity measured= 2, 6, 9, 13, 20, 23, and 27 

•~p<:O.OS 

Table 2b. Plasma Cholinesterase (~-tmoles acetate/min/mL) 

(Percent ChE inhibition) 

Day Control I 0.014 m2/kg 0.03 ml!ik2 I 

Plasma 

pretest 4.325±0.967 4.05±0.614 4.525±1.664 

pretest 3.975±1.014 4.325±0.943 4.85±1.636 

I 4.6±0.327 - 4.45±1.62 

3 4.475±1.25 4.45±1.01 4.3±1.766 

6 4.625±1.04 4.475±1.053 3.95±1.377 (16) 

9 4.9±1.25 3.775±1.037 (10) - 10 4.95±1.22 - 4.675±2.36 

13 4.94±0.46 3.45±0.52 3.25±0.91 (33) 

16 4.3±0.70 3.45±1.14 3.25±1.53 (33) 

18 4.28±0.66 - 3.1±1.15 (36) 

20 4.38±0.79 3.88±1.06 3.38±1.58 (30) 

23 4.0±0.92 4.0±1.51 -

27 4.38±0.83 3.95±1.22 - 30 3.93±0.90 - - Recovery 

2 - - 3.58±1.62 (26) 

3 4.62±0.98 4.52±1.2 - 4 - - - 6 - - 3.550.99 

7 4.5±0.81 5.110.77 - 9 - - 3.62±1.88 

II - - -

13 - - 3.4±2.06 (30) 

14 - - - 18 - - - 20 - - 4.42± 1.61 (9) 

21 - - -

30 - - 4.68±2.08 

35 - - -

0.10 mg/kg 

4.625±0.665 

4.85±0.656 

4.325±1.57 

4.3± 1.36 

2.65±1.42 (44) 

1.7±1.25 (64) 

-

-

-

-

-

-

-

-

2.0±1.30 (58) 

- 2.35±1.34 (50) 

-

2.78±1.75 (41) 

- 3.48±1.42 (27) 

-

3.15±1.14 (34) 

2.9±0.88 (39) 

-

3.55±1.32 (25) 

- 4.72±1.14 

Results and statistics calculated by reviewer from data m Tables 33a and 33b on pages 39-40 ofMRID 00095175. 

IU 
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2. RBC: As shown in Summary Table 3a, Dowco 179 did not decrease the activity ofRBC ChE 

during the treatment period. 

Table 3a. Average percent change of RBC cholinesterase activity relative to pre-treatment activity 

in subjects receiving Dowco 179 daily 

Dose (mg/kg Dav of treatment 

bw/day) I 3 6 10 13 16 19 

Control -6 ± 5.8 4 ± 5.4 II± 3.7 14 ± 5.7 12 ± 4.1 5 ±4.5 5 ± 2.5 

0.014' - 0 ± 7.1 3± 11.3 -7 ± 9.9 -9 ± 9.1 I± 6.3 - O.Q3' -I± 3.6 6± 5.7 9 ± 5.3 9 ± 6.1 II ± 2.1 4± 2.7 5 ± 1.9 

0.10' -I± 6.9 19 ± 4.7 12±7.0 6± 3.9 - - - Results calculated by rev1ewer from data Tables 34a and 34b on pages 41-42 ofMRID 00095175 

a Actual days activity measured= 3, 6, 9, 13, 16, 20, 23, and 27 

b Actual days activity measured= 1, 3, 6, 10, 13, 16, 18, and 20 

c Actual days activity measured= 1, 3, 6, and 9 

20 27 

3 ± 2.8 20 ± 10.3 

I± 6.9 2± 8.8 

I± 4.6 - - -

Summary results are also presented in Table 3b on the basis ofRBCcholinesterase activity in 

flmoles acetate/min/MI. 

Table 3b. RBC Cholinesterase (umoles acetate/rnin/mL) 

Day Control 0.014 m~/k~ 0.03 m~/k~ I 0.10 mg/k~ 

RBC 

pretest 15.2±2.2 14.4±1.8 13.4±1.7 14.6±0.8 

pretest 14.8±2.2 14.0±1.5 13.0±2.2 14.5±0.8 

I 14.0±1.7 14.2±1.8 13.0±1.9 14.4±0.8 

3 15.6±2.6 14.6±2.4 13.9±2.1 17.2±0.7 

6 16.7±2.2 13.2±2.2 14.3±2.1 16.2±1.1 

9 - 12.9±1.4 - 15.4±0.7 

10 17.1±2.2 - 14.4±1.8 - 13 16.8±2.1 14.3±1.3 14.6±2.4 - 16 15.6±2.1 14.3±1.4 13.7±2.1 -

18 15.8±2.1 - 13.8±2.4 - 20 15.5±2.6 14.3±1.4 13.4±2.0 - 27 16.3±2.3 14.2±1.5 - - 30 17.9±2.0 14.5±1.8 - -

Recovery 

2 - - 14.0±1.9 14.5±0.8 

3 16.8±2.2 14.1±1.4 - - 4 - - - 15.2±0.6 

6 - - 14.3±3.1 - 7 17.0±2.1 14.4±1.8 - 15.9±0.6 

9 - - 14.2±1.6 - II - - 15.3±1.2 

Tables 34a and 34b on pages 41-42 of MRID 00095175 

III. DISCUSSION AND CONCLUSIONS: 

A. INVESTIGATORS' CONCLUSIONS: 

The Study investigator concluded that ingestion ofDowco 179 at 0.03 mg/kg/day by humans 

for 21 days was a threshold level for measured changes in plasma ChE activity with no 

significant toxicological effect. The plasma ChE activity in this group averaged 87% of the 

concurrent controls when compared on day to day basis and this was considered not 

statistically significantly different from the control. Ingestion of 0.1 mg/kg/day of Dowco 179 

resulted in marked plasma ChE depression which resulted in termination of the dosing after 9 

I'<C'" 
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days. The RBC ChE activity was not affected in any of the groups tested. 

B. REVIEWER COMMENTS: 

Groups of four male subjects were treated with 0.0, 0.014, 0.03, or 0.1 mg Dowco 179/kg 

bw/day up to 27 days. No treatment-related effects were found on measured urinalysis, 

hematology, or clinical chemistry parameters in subjects receiving the test material. Data on 

the concentration of Dowco 179 and its metabolites in the urine were not provided. Plasma 

ChE activity was reduced to 46% of pre-treatment activity by Day 6 in subjects treated with 

0.10 mg Dowco 179/kg bw/day, which further decreased to 66% of pretreatment activity by 

Day 9. The study authors reported that dosing was stopped for the 0.1 mg/kg bw/day group 

on Day 9 because plasma ChE was decreased >20% for all individuals in this dose group. In 

the 0.03 mg Dowco 179/kg bw/day group, plasma CHE activity was decreased to 32% of 

pretreatment activity by Day 16 and remained decreased -30% through Day 20 when treatment was stopped. No significant treatment-related effect on ChE activity was found in 

subjects of the 0.014 mg/kg bw/day group. Recovery of plasma ChE activity in subjects 

treated with 0.1 mglkg bw/day was observed by Day 25 and by Day 21 in subjects of the 0.03 

mg/kg bw/day group after cessation of dosing. 

Based on an -30% decrease in plasma cholinesterase activity by Day 16, the LOAEL 

for the study was 0.03 mg/kg bw/day. The corresponding NOAEL was 0.014 mg/kg 

bw/day. 

C. STUDY STRENGHTS AND WEAKNESSES: 

Strengths: 

• Concurrent control (placebo) 

• Three dose levels (provides quality dose-response information) 

• Plasma and RBC ChE activity were monitored 

• Blood sampling at multiple time points. ChE activity was monitored on: 1, 3, 6, 10, 13, 

16, 18, 20, 23, 27, 30, 34, 37, 41, 44,48 days (control); 3, 6, 9, 13, 16, 20, 23,27 days 

(0.014 mglkg bw/day); 1, 3, 6, 13, 16, 18,20 days (0.03 mg/kg bw/day); and 1, 3, 6, 9 

days (0.10 mg/kg bw/day). 

• Recovery phase 

• Chlorpyrifos and metabolites (ox on and TCP) were monitored in urine. None of the 

compounds were detected in any sample (limit of detection was not provided) 

Weaknesses: 

• Only one sex (males) used (age and weight ranges were not provided). 

• The purity, lot number, and stability of the test material were not provided. 

• The study was conducted at a correctional facility. 

• Each dose was given for a different duration without a clear rationale (i.e. Control for 

seven weeks, 0.014 mg/kg bw/day for 27 days, 0.03 mg/kg bw/day for 20 days and 0.1 

mg/kg bw/day for nine days). 

• ChE activity measurements were not done every day post dose. 

H. 
' 

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• The time after dose when samples were collected for ChE activity was not reported. 

• The time of urine collection relative to time of dose was not provided. 

• Limit of detection of chlorpyrifos and metabolites was not provided. 
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DATA EVALUATION RECORD- SUPPLEMENTAL 

CHLORPYRIFOS 

NONGUIDELINE 

STUDY TYPE: ORAL/DERMAL PHARMACOKINETIC- HUMAN 

MRID 00124144 

Primary Reviewer: 

Prepared for 

Health Effects Division 

Office of Pesticide Programs 

U.S. Environmental Protection Agency 

One Potomac Yard 

2777 S. Crystal Drive 

Arlington, VA 22202 

Prepared by 

Toxicology and Hazard Assessment Group 

Life Sciences Division 

Oak Ridge National Laboratory 

Oak Ridge, TN 37831 

Task Order No. 207-2009 

H. T. Borges. Ph.D .. MT<ASCPl. D.A.B.T. 

Secondary Reviewers: 

R. A. Young. Ph.D .. D.A.B.T. 

Signature: ------:=,...,.......,......,""-

Date: J) APR 0 8 2009 

Signature: .J'(~ ./J. ~ 

Robert H. Ross. M.S .. Group Leader 

Quality Assurance: 

K. Slusher M.S. 

Date: APR 0 a 2DD9 

Disclaimer 

This review may have been altered subsequent to the contractor's signatures above. 

Oak Ridge National Laboratory managed and operated by UT-Battelle, LLC., for the U.S. Department of 

Energy under Contract No. DE-c_A_C_0.:._5-_0_00c___R2_2_7_2_5_._ --------------------

/C{ 
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Oral and Dermal Pharmacokinetic Study (Human) (1982) I Page 2 of 13 

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EPA Reviewer: John Doherty, Ph.D., DABT 

Reregistration Branch 1, Health Effects Division (7509P) 

EPA Work Assignment Manager: Myron Ottley, Ph.D. 

Registration Action Branch 1, Health Effects Division (7509P) 

TXR#: 0050308 

Signature: ·.\L.~ Date:\ '1"1~ 

Signature: r 'o 

Date: ;hi /D 

T'em[late version 02/06 

ACC NO. 249203 

DATA EVALUATION RECORD- SUPPLEMENTAL ilXR 0003<6'.22.. 

STUDY TYPE: Pharmacokinetic Study, Oral/Dermal; Human 

Nonguideline 

PC CODE: 059101 

TEST MATERIAL (PURITY): Chlorpyrifos (99.8% a.i.) 

DP BARCODE: D368390 

SYNONYMS: 0,0-diethyl-0-[3,5,6-trichloro-2-pyridyl] phosphorothioate 

CITATION: Nolan, R.J., D.L. Rick, N.L. Freshner, and J.H. Saunders (1982). Chlorpyrifos: 

Pharmacokinetics in human volunteers following single oral and dermal doses. The Dow 

Chemical Company, Biomedical Medical Research Lab, 607 Building, Toxicology Research 

Lab, 1803 Building, Midland, MI 48640. Report Number not provided, August 1982. MRID 

00124144. Published in Toxicology and Applied Pharmacology 73:8-15, 1984. (MRID No.: 

47918801). 

SPONSOR: The Dow Chemical Company, Midland, MI 

EXECUTIVE SUMMARY: 

In a single-dose human oral/dermal toxicity study with chlorpyrifos (1982, MRID 00124144), six 

male volunteers were given 0.5 mg/kg chlorpyrifos (99.8% a.i., Lot No. AGR 166043) on a lactose 

tablet. Plasma and RBC cholinesterase activity were monitored at 2, 6, 12, 24 hours, and 2, 3, 4, 8, 

14, 22, 27, and 30 days post-dose. Approximately four weeks after the oral treatment, a single 

dermal dose (5 mg/kg to five subjects; 0.5 mg/kg to one subject) was administered on the volar 

surface ofthe forearm. RBC and plasma cholinesterase activity were determined 2, 6, and 12 hours 

and on days I, 2, 3, 4, 6, 8, and 9 following dermal treatment. Blood and urine samples were 

analyzed for chlorpyrifos and 3,5,6-TCP (3,5,6-trichloro-2-pyridinol) concentrations. 

No clinical signs of toxicity and essentially no significant inhibition ofRBC cholinesterase activity 

were observed following either the oral or dermal dose. Plasma cholinesterase activity was 

inhibited 83-89% relative to pre-dose activities following the oral dose (peak inhibition within 

6-24 hours post dose) but was essentially unchanged following the dermal dose. Blood chlorpyrifos 

concentrations were low (<30 ng/mL; limit of detection 5 ng/mL), and chlorpyrifos was not found in 

the urine following either route of exposure. 3,5,6-TCP blood concentrations peaked by six hours 

after oral exposure and 24 hours after dermal application. 3,5,6-TCP was cleared from the blood 

and eliminated in the urine with a half-life of 27 hours following both the oral and dermal doses. 
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Using assumptions of first-order absorption and elimination equations, it was estimated that 72 ± 

II% of the ingested dose and 0.95 ± 0.559% of the dermal dose were absorbed. 

Classification: This studied is classified as Acceptable/Non-Guideline. 

COMPLIANCE: Signed and dated GLP, Quality Assurance, and Data Confidentiality 

statements were not provided. 
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I. MATERIALS AND METHODS: 

A. MATERIALS: 

1. Test material: 

Description: 

Lot/batch #: 

Purity: 

Compound stability: 

CAS# 

Structure: 

Chlorpyrifos 

Not described 

AGR 166043 

99.8% a.i. (as stated) 

Not reported 

2921-88-2 

2. Vehicle: Methylene chloride for dissolving chlorpyrifos for placement on a 0.5 gm lactose 

tablet. DOWANOL DPM (dipropylene glycol methyl ether (DPGME)) was used as vehicle 

to apply the dermal dose. 

3. Human Subjects: 

Number: 

Race: 

Sex: 

Age: 

Weight: 

Source: 

Instructions: 

B. STUDY DESIGN: 

1. Study dates: Not reported 

Six 

Caucasian 

Male 

27-50 years 

71.7-101.1 kg (mean 83.3 ± 10.3 kg) 

Volunteers 

Each volunteer was briefed on the study and asked to provide written consent. None 

were on oral medication and all were asked to refrain from any drugs including 

aspirin and alcohol 24 hours before and after each dose. 

2. Study subjects: Six male volunteers, ages 27-50 years, were included in the study. Subject A 

served as a "pilot" and was given a single oral dose (0.5 chlorpyrifos mg/kg dissolved in food 

grade methylene chloride placed on a lactose tablet) of the test material approximately one 

month before the other participants. Four weeks later, Subject A also received a single (0.5 

chlorpyrifos mg/kg) dermal dose (dissolved in methylene chloride). Two weeks after the first 

dermal dose, Subject A was given a second dermal dose (0.5 chlorpyrifos mg/kg dissolved in 

DPGME). 

The main study consisted of two phases. Five subjects (B- F) were dosed once orally (0.5 

chlorpyrifos mglkg dissolved in food grade methylene chloride and placed on a lactose tablet) 

and once dermaliy (5 mg/kg chlorpyrifos in DPGME), thirty days after the oral dose. 
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CHLORPYRIFOS 

Exoosure route 

Oral 

Dermal 

Dermal 

Dermal 

Oral and Dermal Pharmacokinetic Study (Human) (1982) I Page 5 of 13 

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TABLE I. Study design 

Subject A (n-1) Subjects B-F (n-5) 

0.5 mg/kg 0.5 mgfkg 

0.5 mg/kg - 0.5 mg/kg - - 5.0 mglkg 

3. Dose selection rationale: The doses selected were based on a human tolerance study with 

chlorpyrifos (Coulston, F., Golberg, L., Abraham, R., eta!., 1972, Final report on safety 

evaluation and metabolic studies on Dowco 179(IN151), Inst. Exp. Pathol Toxicol, Albany 

Medical College (as cited by WHO, 1973). 

4. Dose preparation and administration: The oral doses for all subjects were prepared by 

mixing an appropriate amount of chlorpyrifos in food grade methylene chloride. A sufficient 

volume of the chlorpyrifos/ methylene chloride mixture was applied to a 0.5 g lactose table, 

and the methylene chloride allowed to evaporate. Following a breakfast meal, the tablet was 

swallowed whole with -100 mL water. 

The dermal 5.0 mglkg doses for Subjects B- F were administered by spreading -10 ).LLikg 

chlorpyrifos dissolved in DPGME over -100 cm

2 surface of the volar forearm. The application site was not covered or occluded and no effort was made to influence evaporation. 

Following dermal application, the subjects were allowed to follow their normal bathing 

habits 12 to 20 hours later. The dermal doses administered to Subject A were applied 

similarly, with the exception that the first dermal dose used methylene chloride as the solvent 

followed by application two weeks later where DPGME was the solvent for the 0.5 mg/kg 

dose. 

Results: 

Homogeneity analysis: Not reported 

Stability analysis: Not reported 

Concentration analysis: Net increases in tablet weight and chemical analysis of duplicate 

tablets were used to verity the oral doses. Data were not supplied. Thus, verification of dermal 

doses was not reported. 

5_ Statistics: Plasma and RBC cholinesterase activities were expressed as a percent of the mean 

of two to three pre-dose determinations. Other statistical methods were limited to the determination of the mean and standard deviation. Concentration-time and urinary excretion data 

for 3,5,6-trichloro2-pyridine (TCP) for each volunteer were fit simultaneously to the 

equation: 

k xDosexF 

C = ' x exp (k, xtime-k, xtime) 

b V, x(k, - k,) 

Urinary excretion rate= cb X k, X v, X body weight 

The equations describe a one-compartment model with first-order absorption and elimination 

where Cb =the blood 3,5,6-TCP; F =the fraction of dose absorbed; Vd =the volume of 

23 
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Oral and Dermal Pharmacokinetic Study (Human) (1982) I Page 6 of 13 

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distribution; and k, and k, are the first order-absorption and elimination constants for 3,5,6-

TCP. Optimal estimates for the model parameters were obtained using DACSL (DOW 

Advanced Continuous Stimulation Language, A gin and Blau, 1981 ). 

C. METHODS: 

1. Observations: Following treatment, the volunteers were observed for clinical signs of 

toxicity. Further details were not provided. 

2- Sample Collection: Blood -Heparinized blood samples were collected prior to treatment 

and 2, 6, and 12 hours, and 1, 2, 3, 4, 8, 14, 22, 27, and 30 days post dose for analysis of 

plasma and RBC cholinesterase following oral treatment. RBC and plasma cholinesterase 

activity were determined 2, 6, and 12 hours and on Days I, 2, 3, 4, 6, 8, and 9 following 

dermal treatment. In addition, the blood samples were analyzed for the concentration of 

chlorpyrifos and 3,5,6-TCP. 

Urine- Urine was collected 24-48 hours prior to dosing. Samples were pooled for the 

following intervals: 0, 6, 12, 24, 36, 48, 60, 72, and 96 hours post-dose. Two additional 12-

hour urine collections were made starting at 156 hours and 180 hours after the 5.0 mglkg 

dermal application. The urine volume and creatinine were determined for each sample, as 

well as the concentration of chlorpyrifos and 3,5,6-TCP. 

3. Cholinesterase Activity: RBC and plasma cholinesterase activity were determined using the 

micro-Michel method (Michel, O.H., 1961, Cholinesterase in human RBC and plasma. In 

Standard Methods of Clinical Chemistry, D. Seligson ed., Academic Press, NY, pp 93-98). 

The method was not further described. (The principle of the method relies on plasma or RBC 

acetylcholinesterase hydrolyzing the substrate acetylcholine in a standard buffer solution 

(typically pH 8) to form acetate which causes a decrease in the pH ofthe buffer solution. The 

measured change in pH is proportional to acetylcholinesterase activity. 

4. Chlorpyrifos and 3,5,6-TCP Concentration: Blood chlorpyrifos concentration was 

determined by extracting the sample with acetone, evaporating the acetone and mixing the 

residual with hexane, and eluting the hexane through a 20% deactivated silica gel column. 

The hexane was collected and concentrated by evaporation before injection into an FID gas 

chromatograph equipped with a 3% OV-17 and 8% QF-1 column. Urine samples were 

analyzed similarly following direct extraction with hexane. 

Blood 3,5,6-TCP was analyzed by mixing a sample with 0.!2N HCI and filtered through a 

C18 Sep-Pak column. The column was washed with two additionai!O mL volumes of0.12N 

HCl before being eluted with methanol. The eluent-containing methanol was mixed with l 0 

mL equal volumes of sodium bicarbonate and benzene. Following centrifugation, the 

benzene was discarded and sodium chloride, HCI and benzene were added. After mixing and 

centrifugation, the benzene was removed and the extract silylated. Aliquots of the silylated 

benzene extract were injected into an ECD gas chromatograph equipped with a 3%0V-I 

column. Urine 3,5,6-TCP was extracted and quantitated similarly following hydrolysis of the 

urine with concentrated H2S04 for one hour at 90°C. 
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II. RESULTS: 

A. CLINICAL SIGNS OF TOXICITY: 

No clinical signs of toxicity were observed during the study 

B. CHOLINESTERASE ACTIVITY: 

1. Plasma: Following oral exposure, greater than 60% decreased activity was observed in two of 

the five subjects two hours post-dose (first time point monitored), and four of five subjects 

displayed >70% lower activity at six hours post-dose (Table 2). Three of the six subjects 

displayed significant decreased plasma cholinesterase two hours post-dose (163%, ~ 70%, 

~30%), and peak decreases occurred at 6 hours in one subject (187%), at 12 hours in two 

subjects (186%, ~89%), and at 24 hours in three subjects (l71 %, ~85%, ~86%). Recovery(< 

20% decrease in activity) was observed by 22-30 days post dose. 

As shown in Table 3, following dermal exposure, three of the five subjects displayed apparently 

biologically significant (>20%) plasma decreased activity on or after12 hours post-dose (Subject 

E ~ 22%), on day 2 (Subject E- 26%) or day 3 (Subject C ~ 21 %) that persisted at subsequent 

assessment times. Subject F (- 35% at Day3 3 only) was not considered to display actual 

inhibition since the lower reading did not persist. 

TABLE 2. Plasma cholinesterase percent decrease followine a sinele 0.5 ~g/l_<.g_oral dose 

Phase/interval Subject 

A (pilot) B c D E F 

Pretest 1 1.29 ± 0.13 1.13 ± 0.12' 0.87 ± 0.09 1.16 ± 0.12 1.26 ± 0.04 1.42 ± 0.17 

2 hours -

2 - 63# - 70# 30# 

6 hours 57 14# 87# 72# 84# 78# 

12 hours 70 65# 85# 86 89 83 

Day I 71 85 86 84 85 86 

Day2 68 80 77 75 78 78 

Day 3 37 73 74 71 71 76 

Dav4 34 68 64 65 67 68 

Day 8 ND3 58 48 49 56 54 

Day 14 ND 28 17 30 36 27 

Day 22 - 12 22 30 37 28 

Day 27 ND 9 - 18 41 15 

Day 30 ND 23 8 4 21 21 

Chlorpyrifos* x' 6-12 2-12 1-6 1-6 0-6 

Percent mhibitiOn calculated by reviewer from data on pages 18 and 19 ofMRID 00124144 1 Pre-test activity is the average of two (Subject A) or three (Subjects B-F) measurements and expressed as f<.. pH units/hr 2 - value greater than pre-test 3 ND=Nodata 

4 X not detected at detection limit of0.005 )..lg/mL 

Bolded numbers are peak inhibition 

# hours post oral dose chlorpyrifos was detected in blood 

a Differ from the study report which lists 1.09±0.09. The values are 1.23, 0.99 and 1.16 fro a mean of l.l3. 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 24 of 73 

CHLORPYRIFOS 

Oral and Dermal Pharmacokinetic Study (Human) (1982) I Page 8 of 13 

Nonguideline 

TABLE 3. Plasma cholinesterase oercent decrease followim! a sin2le 5 m2/k2 dermal dose 

Phase/interval Subject 

B c D E 

Pretest 1 0.87 0.80 1.1 0.99 

2 hours !3' +' 10 12 

6 hours + - 12 14 

12 hours + 12 14 22 

nav-1 + 15 18 19 

nav-2 6 18 18 26 

Dav 3 8 21 18 18 

Day4 9 12 16 12 

Day6 + 6 8 9 

Dav8 + + - 8 

Dav9 + 15 9 14 

Chlorovrifos' 0 6 6,24 0, 2, 10, 24 

Percent mhtbttton calculated by rev1ewer from data on pages 18 and 19 ofMRID 00124144 1 Cholinesterase activity (6. pH units/hr) on day 30 following acute oral dose 2 Bolded numbers are peak inhibition 3 No inhibition 

* Sample interval when chlorpyrifos detected in blood 

F 

1.12 

+ 

+ 

+ 

19 

+ 

35 

+ 

+ 

+ 

+ 

10 

2- Whole blood: Following oral exposure, one subject (E) displayed RBC lower ((137%) 

cholinesterase two hours post-dose, but normal activity thereafter until day 14. Two other 

subjects (C and D) displayed RBC cholinesterase lower activity (153% and L46%) at 4 days 

post-dose. One of these subjects also displayed lower RBC cholinesterase on day 30 post-dose 

(162%). These latter finding are considered spurious in light of the findings at prior and later 

assessment times which show comparable levels of activity among all subjects. Overall, no 

sustained decrease (i.e.> 30%) indicative of true enzyme inhibition was found in any of these 

subjects. 

Following dermal exposure (Table 5), none of the five subjects displayed RBC cholinesterase 

greater than 11% lower than the predosing mean at any time point. 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 25 of 73 

CHLORPYRIFOS 

Oral and Dermal Pharmacokinetic Study (Human) (1982) I Page 9 of 13 

Nonguideline 

TABLE 4. RBC cholinesterase percent decrease following a sin1de 0.5 m2/k2 oral dose 

Phase/interval Sub'ect 

A (pilot) B c D E 

Pretest1 0.92 ± 0.08 0.89±0.18 0.94 ± 0.08 0.91 ±0.15 0.90 ± 0.17 

2 hours 10 + 2 + 

6 hours 10 + + + 

12 hours 182 + 2 + 

Day I 16 + 5 + 

Day2 8 + I + 

Day 3 I + + + 

Day 4 II 53 46 14 

Day 8 NO + II 8 

Day 14 NO 17 21 10 

Day 22 16 X X X 

Day 27 NO 8 23 9 

Day 30 NO 62 19 12 

Percent mhJbJtiOn calculated by reviewer from data on pages 18 and 20 ofMRID 00124144 1 Cholinesterase activity (,1, pH units/hr) 2 Balded numbers are peak inhibition 

NO= no data 

+ value greater than pre-dose 

X result not included in assessment~ no explanation provided 

37 

+ 

+ 

+ 

+ 

+ 

II 

+ 

27 

X 

+ 

+ 

TABLE 5. RBC cholinesterase percent decrease following a sinele 5 me/kg dermal dose 

Phase/interval Subject 

B c D E 

Pretest 1 0.342 0.76 0.80 0.93 

2 hours 5 - + 3 

6 hours + 3 + 3 

12 hours + II + 10 

Day I s' + + + 

Day2 + + + + 

Day 3 + + + + 

Day4 + + 8 II 

Day6 + + + + 

Day 8 + + + I 

Day9 + + + + 

Percent mhibitiOn calculated by reviewer from data on pages 18 and 20 ofMRID 00124144 1 Cholinesterase activity (D. pH units/hr) on day 30 following acute oral dose 

F 

0.96 

2 

2 

+ 

6 

4 

I 

9 

4 

3 

+ 

2 Subject B activity was 0.82 on day 27 and 0.34 on day 30. Day 27 activity used for calculation 3 Bolded numbers are peak inhibition 

+No inhibition 

F 

0.95 ± 0.18 

5 

+ 

+ 

+ 

+ 

+ 

13 

+ 

II 

X 

II 

-

3. Chlorpyrifos and 3,5,6-TCP Concentration: Chlorpyrifos was detected sporadically in the 

blood of all but one (subject A) at various times following oral (Table 6, from not detected to 

-0.005 up to 0.03 [.tg/mL) or dermal (Table 6, from not detected to -0.005 up to about 0.010 

[.tg/mL) exposures. 

3,5,6-TCP was detected in the blood of all subjects at most time intervals following both oral ( 

up to 1.43 [.tg/mL) and dermal (up to 0.122 [.tg/mL in subject C) exposures (Table 7). Following 

the oral dose, the highest level of 3,5,6-TCP in the blood occurred at 2 (Subject C), 4 (Subjects 

E, F), 6 (Subjects A and D), and 24 hours (Subject B) post dose. Peak TCP level following the 

dermal dose was at 24 hours for all five subjects. 

3,5,6-TCP concentrations in urine were detected in each subject throughout the monitoring 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 26 of 73 

CHLORPYRIFOS 

Oral and Dermal Pharmacokinetic Study (Human) (1982) I Page 10 of 13 

Nonguideline 

interval (Table 8), with the highest concentrations ranging from 438 to 510f.!g/mL (oral dose) 

and 17.7 to 59.3 f.!g/mL (dermal dose). In all oral subjects, the highest 3,5,6-TCP concentration 

in urine was observed in 9 hours or less. Following dermal administration, the highest levels 

were generally reached in about 24 hours or up to 42 hours (for one subject). 

As shown in Table 9 (column 6), the apparent volume of distribution was 181 ± 18 mL/kg 

(mean for the group), and the average half life for 3,5 ,6-TCP elimination from the blood was 

26.9 hours (column 8) after oral treatment. No similar calculation for the half life following 

dermal application was presented in the report table but the half life was also estimated to be 

similar to 27 hours. Based on the model parameters, 72 ± 11% chlorpyrifos would be absorbed 

after oral treatment and 0.95 ± 0.56% after dermal treatment. These results were in agreement 

with the concentration of 3,5,6-TCP recovered in the urine following oral (70 ± 11 %) or dermal 

(1.02 ± 0.57%). 

TABLE 6. Blood chlorpvrifos concentration (u.2J'mL) 

Hours After Subject 

Dosing I A I B c D I E 

Oral Dose 

0 ND ND ND ND ND 

1 ND ND ND 0.006 0.005 

2 ND ND 0.019 NA 0.011 

4 ND ND 0.009 0.021 0.008 

6 ND 0.012 0.012 0.021 0.008 

8 ND 0.007 0.030 ND ND 

lO ND 0.008 0.006 ND ND 

12 ND 0.028 0.015 ND ND 

Dermal Dose 1 

0 ND 0.007 ND ND 0.010 

2 ND ND ND ND 0.008 

6 ND ND 0.005 0.005 ND 

10 ND ND ND ND 0.010 

24 ND ND ND 0.006 0.007 

48 ND ND ND NA NA 

Data from pages 21 and 22 of MRID 00124144 1 Subject A received a single 0.5 rng/kg dermal dose while Subjects B-F received a single 5.0 mg/kg dermal dose 

ND =Below detection limit of0.005 )J.g/mL 

NA ~Not analyzed 

F 

0.009 

0.009 

0.015 

0.009 

O.Ql8 

ND 

ND 

ND 

ND 

ND 

ND 

0.005 

ND 

NA 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 27 of 73 

CHLORPYRIFOS 

Oral and Dermal Pharmacokinetic Study (Human) (1982) I Page 11 of 13 

Nonguideline 

TABLE 7. Blood 3,5,6-TCP concentration (JLI!imL) 

Hours After I 

Dosing I A (pilot) I B 

1 ND ND 

2 0.126 0.067 

4 0.714 0.229 

6 0.715 1 0.509 

8 0.650 0.597 

10 0.606 0.813 

12 0.544 0.763 

24 0.390 0.823 

48 0.185 0.560 

72 0.081 0.354 

96 0.040 0.194 

4 NA ND 

6 NA ND 

8 NA 0.028 

10 NA 0.023 

12 NA 0.043 

24 NA 0.070 

48 NA 0.068 

72 NA 0.049 

96 NA 0.032 

144 I NA I 0.019 

Data from pages 23 and 24 ofMRID 00124144 1 Bolded concentrations represent peak 

Subject 

I c I D I 

Oral Dose 

0.046 0.009 

1.18 0.180 

1.12 0.691 

0.939 1.35 

0.907 1.16 

0.853 0.973 

0.790 0.934 

0.598 0.774 

0.345 0.540 

0.199 0.342 

0.117 0.201 

Dermal Dose2 

0.019 0.018 

0.067 O.DI8 

0.079 0.020 

0.107 0.037 

0.102 0.035 

0.122 0.057 

0.106 0.056 

0.080 0.046 

0.060 0.031 

I O.DI5 I 0.017 I 0.009 

E I 

0.012 

1.09 

1.19 

1.07 

0.994 

0.810 

0.818 

0.624 

0.268 

0.081 

0.060 

ND 

0.019 

0.024 

0.020 

0.022 

0.036 

0.031 

0.022 

0.016 

I 

2 Subject A received a single 0.5 mg/kg dermal dose while Subjects B-F received a single 5.0 mg!kg dermal dose 

ND =Below detection limit of0.005 ~-tg/mL 

NA =Not analyzed 

TABLE 8. Urine 3,5,6-TCP concentration (J..te/mL) followin2 oral dose 

Hours After I 

Dosing I A (pilot) I B 

3 177 64 

9 268 457 

18 199 328 

30 131 257 

42 119 181 

54 73 152 

66 53 109 

84 31 87 

108 16 49 

3 NA 1.4 

9 NA 7.8 

18 NA 21.1 

30 NA 25.9 

42 NA 24.8 

54 NA 17.6 

66 NA 20.6 

84 NA 14.3 

108 NA 9.5 

162 NA 4.5 

Data from pages 25 and 26 ofMRID 00124144 1 Bolded concentrations represent peak 

ND ~Below detection limit of0.0025 ~Lg/mL 

NA ~Not analyzed 

Subject 

I c I D I E 

Oral Dose 

231 167 438 

510 492 409 

269 212 368 

229 177 229 

140 134 208 

121 116 178 

96 95 57 

65 73 67 

38 34 30 

Dermal Dose 

2.2 3.3 ND 

35.9 8.8 4.5 

49.1 10.0 15.2 

59.3 17.5 21.0 

43.5 13.4 16.1 

41.4 17.7 13.3 

31.4 12.1 10.7 

24.8 6.4 10.3 

15.4 5.1 5.3 

6.1 4.8 2.4 

I 

F 

0.216 

0.996 

1.43 

1.29 

1.16 

1.04 

1.05 

NA 

0.423 

0.215 

0.136 

ND 

0.013 

0.028 

0.014 

0.019 

0.029 

0.028 

0.019 

0.018 

ND 

F 

451 

427 

273 

184 

175 

129 

91 

64 

36 

ND 

10.8 

13.2 

7.9 

55.5 

24.2 

8.7 

16.4 

9.9 

3.8 
8 

CHLORPYRIFOS 

Oral and Dermal Pharmacokinetic Study (Human) (1982) I Page 12 of 13 

Non2uideline 

TABLE 9. Model parameters describing blood concentrations and urinary excretion of 3,5,6-TCP by individual volun

following oral and dermal administration of chlo!]!Y!'ifos 

Absorption Absorption Absorption Volume Elimination Elimination 

Volunteer Weight lag time rate constant half-life- distribution rate constant half-life (kg) (hr) (hr') (hr) (mL/kg) (hr') (hr) 

Oral 0.5 melk2 

A 77.1 1.9 1.7 0.4 190 0.0318 21.8 

B 80.7 1.6 0.1 6.9 192 0.0219 31.7 

c 83.7 1.0 3.0 0.2 204 0.0232 29.9 

D 71.7 1.0 0.3 2.1 180 0.0205 33.9 

E 101.8 l. \ 2.7 0.3 \60 0.0326 21.3 

F 85.0 0.9 1.3 0.5 160 0.0249 27.8 

Mean 83.3 1.3 1.5 0.5 181 0.0258 26.9' 

SD 10.2 0.4 1.2 18 0.0052 

Dermal 5.0 

Ab 77.1 - 0.0223 31.1 - - -

B 80.7 - 0.0270 25.7 - - -

c 83.7 - 0.0496 14.0 - - -

D 71.7 - 0.0335 20.7 - - -

E 95.0 - 0.0241 28.8 - - -

F 85.0 - 0.0287 24.2 - -

Mean 83.2 0.0326 22.7 

SD 8.4 0.0100 

Data from page 12 ofMRJD 00124144 

a Calculated as volume distribution times elimination rate constant 

b Volunteer A was given a 0.5 mg!kg dermal dose and is not included in mean and standard deviation calculations 

c HED secondary reviewer calculates the mean and standard deviation as 27.7±5.2. 

d Based on the values from subjects B-F and not including subject A 

Area 

under plasma 

time curve 

24.4 

56.6 

45.3 

58.0 

37.1 

54.7 

46.0 

13.3 

1.42 

7.06 

11.17 

6.16 

3.26 3.18 

6.17 

3.29 

Renal 

clearance 

(mL/hr/kg)

6.0 

4.2 4.7 

3.7 

5.2 

4.0 4.6 

0.9 

-

---
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 29 of 73 

CHLORPYRIFOS 

Oral and Dermal Pharmacokinetic Study (Human) (1982) I Page 13 of 13 

Nonguideline 

III. DISCUSSION AND CONCLUSIONS: 

A- INVESTIGATORS' CONCLUSIONS: 

Following oral or dermal treatment, no clinical signs of toxicity were observed nor was RBC 

cholinesterase decreased. Plasma cholinesterase was decreased to 15% (i.e. 85% inhibition) 

of pre-dose activities following oral treatment with 0.5 mg/kg chlorpyrifos but was 

essentially unchanged following dermal treatment with 5.0 mg/kg. Blood chlorpyrifos 

concentrations were low (<30 ppb), and no unchanged chlorpyrifos was found in the urine 

following either route of administration. Average blood 3,5,6-TCP concentrations peaked at 

six hours after ingestion of the oral dose and at 27 hours after the 5.0 mg/kg dermal dose. 

3,5,6-TCP was cleared from the blood and eliminated in the urine with a TYz of24 hours 

following both oral and dermal treatment. An average of 70% of the oral dose, but <2% of 

the dermal dose was excreted in the urine as 3,5,6-TCP; indicating only a small fraction of 

the dermal chlorpyrifos dose was absorbed. The data also suggests that chlorpyrifos and its 

metabolite have a low potential to accumulate in man on repeated exposures. 

B. REVIEWER COMMENTS: 

The objective of the study was to provide data on the fate of orally and dermally administered 

chlorpyrifos in the human. The kinetics of chlorpyrifos and its principal metabolite 3, 5, 6-trichlor2-pyridinal (TCP) were investigated. No clinical signs of toxicity or sustained inhibition ofRBC 

cholinesterase activity were observed following either the oral or dermal dose. In all five subjects, 

plasma cholinesterase was inhibited 83-89% relative to pre-dose activities following the oral dose 

(peak inhibition within 6-24 hours post dose) but was essentially unchanged following the dermal 

dose. Blood chlorpyrifos levels were extremely low (:S: 30 ng/mL; limit of detection 5 ng/mL), and 

chlorpyrifos was not found in the urine following either route of exposure. 3,5,6-TCP blood 

concentrations peaked by six hours after oral exposure and 24 hours after dermal application. 

3,5,6-TCP was cleared from the blood and eliminated in the urine with a mean half-life of -27 hours 

following both the oral and dermal doses. Using assumptions of first-order absorption and 

elimination, it was estimated that 72 ± 11% of the ingested dose and 0.95 ± 0.559% (based on the 5 

subjects receiving 5 mg/kg dermal dose) and 3.18% (based on one subject receiving 0.5 mg/kg 

dermal dose) of the dermal dose were absorbed. 

C. STUDY DEFICIENCIES: 

• not a double-blind study design and it is likely that the subjects knew they were actually given 

the test material. 

• Same subjects administered oral and dermal doses of chlorpyrifos 

• only one sex (males) 

• only one dose level- no dose-response information for either route of exposure 

3( 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 30 of 73 

Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans n {)~ (non-guideline) 

EPA Reviewer: John Doherty, Ph.D.e~ Reregistration Branch II, Health Effe t, Divisihll ~J,. ._./. / 

EPA Secondary Reviewer: Linda Tay r, P~~<~C Reregistration Branch II, Health Effects Divtsion (7509P) 

TXR # 0050308 

Data Evaluation Record 

Study Type: Special Non-Guideline Assessment for RBC Cholinesterase in Humans. 

DP Barcode: D368390 

PC Code: 059101 

Submission No.: N/A 

Tox Chern. No.: 219AA 

Test Material: DursbanR, 99.8% Chlorpyrifos (Lot No.: MM930503-17) 

Citations: Kisicki, J.C., Seip, C.W. and Combs, M.L., 1999, "A Rising Dose Toxicology 

Study to Determine the No-Observable-Effect-Levels (NOEL) for Erythrocyte 

Acetylcholinesterase (AChE) Inhibition and Cholinergic Signs and Symptoms of 

Chlorpyrifos at Three Dose Levels", MDC Harris Laboratory, Lincoln Nebraska, 

Study No.: 21438 (for the Harris Project) and DR K-0044793-284 (for DOW 

AgroSciences), April 19, 1999, MRID No.: 44811002. 

Brzak, K.A. "A Rising Dose Toxicology Study to Determine the No-ObservableEffect Levels (NOEL) for Erythrocyte Acetylcholinesterase (AChE) Inhibition and 

Cholinergic Signs and Symptoms of Chlorpyrifos at Three Dose Levels - Part B 

(Pharmacokinetic paraoxonase data)". Toxicology and Environmental Research 

and Consulting, DOW, Study No.: 981176, June 5, 2000. MRID No.: 45144101. 

Juberg, D.R. and J.L. Mattsson "Updated DOW AgroSciences Response to EPA 

Query Regarding Two Toxicology Reports". DOW AgroSciences LLC, 

Indianapolis, IN, May 28, 2008, MRID No.: 47436401. Unpublished. 

Racke, K et a!, (2009) "Chlorpyrifos Response to EPA Query Regarding TCP 

Analytical Methods and Oral Absorption in Human Volunteers". Project Number: 

KDR09232009, Unpublished study prepared by Dow AgroSciences, LLC and 

Cow Chemical Company. MRID No.: 47866701. Unpublished. 

McKellar L. (1979) "Determination of Chlorpyrifos and 3,5,6-trichloro-2-

Pyridinal in Whole Blood and Urine by Gas Chromatography" Project Number 

ACR/79/9. Unpublished study prepared by the Dow Chemical Company. MRID 

No.: 47866703. Unpublished. 

2? 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 31 of 73 

Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Sponsor: 

Some of the data from this study were published: 

Timchalk, C. eta a! (2002) A physiologically based pharmacokinetic and 

pharmacodynamic (PBPK/PD) model for the organophosphate insecticide 

chlorpyrifos in rats and humans. Toxicological Sciences 66:34-53. MRID No.: 

47918802. 

DOW AgroSciences. 

Executive Summary: In a special acute oral study (1999, MRID 44811002) performed to 

assess effects on human red blood cell (RBC) acetylcholinesterase (AChE), chlorpyrifos (99.8%; 

Lot# MM930503-17) in a gelatin capsule was administered to 6 human subjects/sex/dose group 

at dose levels ofO (lactose-filled capsule), 0.5 or 1.0 mg/kg (Phase 1). When it was determined 

that there was no inhibition and no adverse reactions in these subjects, a second phase of 6 

human subjects/sex/group were dosed similarly as control and 2.0 mg/kg chlorpyrifos. 

The subjects were valuated vital signs (blood pressure, pulse, respiration and temperature the 

morning prior to dosing and at 1, 2, 4, 8, 12, 24,48 and 168 hours post dosing. In addition 

hematology, clinical chemistry and urinalysis assessments were performed one week post dose. 

Blood was assessed at -10 hours, zero (pre-dose), and at 2, 4, 8, 12, 24, 36, 48, 72, 96, 

144 and 168 hours post dose for RBC AChE assessment. Plasma cholinesterase (ChE) was not 

assessed. Blood and urine were collected at selected intervals and analyzed for chlorpyrifos, 

chlorpyrifos oxon and the principal metabolite 3,5,6-trichloro-2-pyridinol (TCP) to define the 

pharmacokinetics of chlorpyrifos in humans. The paraoxonase (PONI) status was determined for 

each subject. Serum paraoxonase activity was measured against chlorpyrifos oxon, paraoxon, and 

diazoxon, and called chlorpyrifos oxonase (CPOase ), paraoxonase, or diazoxonase, respectively 

(MRID# 45144101 ). Additionally, the PON phenotype (i.e. QQ, OR and RR) was determined for 

each subject. 

Systemic Effects. There were no apparent clinical reactions or changes in clinical 

chemistry parameters related to treatment. 

Pharmacokinetic Data. Chlorpyrifos was detected in the serum of 4 of the 12 subjects 

(2-8 hours post dose) in thel.O mg/kg dose (range of 1.1-5.6 ng/g) and in 4 of the 12 subjects (2-

12 hours post dose) in the 2.0 mg/kg dose (range 1.3-18 ng/g). Subject (#56, QQ phenotype and 

the only subject demonstrating RBC AChE inhibition) but withdrew from the study after 48 

hours had a peak concentration of 18 ng/gm chlorpyrifos at 8 hours. This same subject also had 

the highest levels of serum and urinary TCP accumulated up to 48 hours. The serum chlorpyrifos 

and serum and urinary TCP data all suggested that this subject absorbed more of her dose than 

the other subjects on the study. CPOase for this subject was similar to the other subjects with the 

phenotype QQ. TCP was detected in the blood of all subjects through 120 hours (0.5 and 1.0 

mg/kg) and through 168 hours (2.0 mg/kg). The highest concentration of TCP reached ranged 

from 110-380 ng/g (0.5 mg/kg), 140-610 ng/g (1.0 mg/kg), and 370-1600 ng/g (2.0 mg/kg). 

Chlorpyrifos and chlorpyrifos oxon were not found in the urine at any dose level, and 

chlorpyrifos oxon was not found in the blood of any subject. . 

RBC AChE. Zero time (preclosing) baseline RBC AChE was from 8143±982 (±12%) to 

2 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 32 of 73 

Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Hwnans 

(non-guideline) 

9572±539 (±6%) U/L for males and 8576±556 (±6%) and 9165±709 (±8%) U/L for females 

indicating good precision for the baseline data. These RBC AChE values were within the 

expected range for humans. Only one individual had a decrease in RBC AChE that suggested 

inhibition by chlorpyrifos as indicated by being consistently decreased at the critical hours post 

dosing. For this subject (#56, a female dosed with 2 mg/kg), inhibition ofRBC ACHE was 

observed at 8 (23% -l-), 12 (maximum 28% -l-), 24 (26%-l-), 36 (19%-l-) and 48 (21 %-l-) hours post 

dose. There were no associated cholinergic symptoms reported, although a transient numbness in 

the upper arms in this subject was reported at about 2 hours post dosing or well before AChE 

inhibition and significant levels of TCP in the serum were detected. The LOAEL is 2 

mg/kg/day for RBC AChE based on 28% inhibition in one female subject. The NOAEL is 

1 mg/kg. 

Classification This study is classified as Acceptable/Non-Guideline and to contain useful information on 

the phannacokinetics of orally administered chlorpyrifos when administered in a capsule to human volunteers. The 

study, however, should not be used for endpoint selection or for impacting the uncertainty factors for risk 

assessment. The RBC AChE inhibitory assessment aspects of this study depend upon only one subject showing 

clear evidence of inhibition. Another serious problem with this study with regard to comparing the results with other 

studies in human volunteers is that no assessments of plasma cholinesterase were made. Differences in the method 

of dose administration where a chlorpyrifos was administered in a capsule in this study and on top of a lactose pill 

after dissolving in solvent in the Nolan study preclude direct comparison of the phannacokinetic data. 

Compliance: 

No-Data Confidentiality Claims (No claim of confidentiality within the United States), 

GLP and Quality Assurance Statements were provided. The study was said to be conducted in 

accordance with all applicable U.S. guidelines as specified in Title 21 of the Code of Federal 

Regulations parts 50, 556, and 321 and the International Guidelines for Human Testing as 

promulgated in the Declaration ofHelsinki (1964 and as amended 1996). 

Institutional Review Board Approval. Additional Comments on the Ethics aspects of 

this study were provided by Mr. John Carley of the OPP. There were two letters (see pages 134 

and 135 of the study report) from the Secretary (or acting secretary) of the MDS Harris 

Laboratory that indicated that the protocol was approved by the MDS Harris Institutional Review 

Board. These letters mentioned only minor changes to the protocol. There was no document in 

the study report that listed the membership or their professional status of the MDS Harris 

Institutional Review Board. 

The study was conducted under the supervision of James C. Kisicki, M.D. who is the 

Medical Director, Clinical Research Division of the Harris Laboratories in Lincoln, Nebraska. 

Dr. Kisicki has Board Certification from the National Board of Medical Examiners and 

American Board of Family Practice. 

3 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 33 of 73 

Chlorpyrifos/P. C. Code 0591 0 I Special RBC AChE Inhibition Study ( 1999) Humans 

(non-guideline) 

Part A. Clinical aspects including AChE Assessments (MRID No.: 44811002). 

A. Test Materials: 

Test Chemical: 

Chemical: 

Source: 

Lot: 

Purity: 

Appearance: 

CAS# 

Chemical 

Name: 

Experimental Constants 

DursbanR - technical name for chlorpyrifos 

DOW AgroSciences LLC 

MM930503-17 

99.8% (scheduled for decertification in June 2003) 

White crystalline powder 

2921-88-2 

0,0-diethyl 0-(3,5,6-trichloro-2-pyridinyl) phosphorothioate 

Negative Control (placebo): 

Chemical: Lactose 

Source: Mallinckrodt N.F. 

Lot: 6279 KXHA 

Purity: 

CAS# 

B. Human Subjects: 

Not specifically stated but stated to "meets N.F. requirements" 

63-42-3 

The subjects were recruited from the Lincoln, Nebraska area in response to a 

advertisement. The criteria for selection for inclusion and continuation in the study were 

described on pages I 02 to I 06 of the study report. 

Some of the characteristics of the participants who were actually dosed with either the 

control (lactose) or chlorpyrifos are as follows: 

Number: 

Occupations: 

Age: 

Weight: 

Race: 

Medical 

History: 

3 0 males and 3 0 females. 

Not stated for each individual. 

Males: 19 to 54 years; Females: 20 to 52 years. 

Males: 146 to 224 pounds; Females: 98 to 200. 

Males: 28 Caucasian, I black and I Asian; Females: all Caucasian. 

Table 4.4 (page 243) presented comments on the medical history of 

each subject. In the opinion of this reviewer, the medical history appeared 

to be typical of a group of 60 humans within this age bracket. There did not 

appear to be any medical conditions that would affect the outcome of the study. 

The only entries for subject #56 were that she was a non-smoker and was 

hospitalized twice for childbirth (12/93 and I 0/97). 

Note: Additional tables presented the results of urinary analysis for drugs (cocaine, ethanol and 

cannabinoids) taken from samples at screening and "interim". All entries were indicated as being 

negative. Data were also presented for the results of the pregnancy test and all entries were negative. 

4 
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C. Experimental Protocol. The experimental protocol is described in Table I below. 

Table I. Experimental Design. 

Group Phrase Dose ( mglkg) Subjects Comments 

A I 0.5 6 o/6"' Blood sampled at -I 0 and O, hr pretreatment 

and at 2, 4, 8, 12, 24, 36, 48, 72, 96, 120 144 

6 o/6"' 

and 168 hours post treatment and analyzed for 

B I 1.0 RBC AChE, chlorpyrifos and its metabolites. 

D(J) I 0 6 o/6 "' 

Urine, blood pressure, pulse, ECG and body 

temperature and clinical laboratory (placebo) assessments were made at pretest and one 

c II 2.0 6 o/6"' week after administration of placebo or 

chlorpyrifos. 

The subjects were released from the study 

D(2) II 0 6 o/6 'f' after 7 days. 

(placebo) 

Total Subjects~ 30 oand 30 'f'. . . Phrase I was conducted first and when It was determmed that there was no InhibitiOn of RBC AChE and there were 

no adverse effects, Phrase II was initiated. Phase I groups were dosed on I 0/3/98 and Phase II groups were dosed on 

I 0/17/98. 

Note: In response to HED's questions concerning reassignment of individuals for 

inclusion in the study, the DOW Company provided a detailed response (D.R. Juberg and J.L. 

Mattsson, "Updated Dow AgroSciences Response to EPA Query Regarding Two Toxicology 

Reports", May 28, 2008) that clarified the identity of the individuals on the study and their given 

dose. One question remains concerning the dose given to subject #47 and it cannot be 

determined if this subject actually received the assigned dose of 2 mg/kg or a slightly lower dose 

C. Basis for Dose Level Selection: 

The low dose of0.5 mg/kg was based on a previous study (Nolan, 1984; MRJD 

00124144) in which this dose level produced decreases in plasma ChE by 80% but had no effects 

on RBC AChE and did not result in clinical signs. This dose was included to provide a NOEL 

for RBC AChE. The next higher dose of I mg/kg was thought to be a dose where noticeable 

RBC AChE might be expected without showing clinical signs in the subjects. The higher dose of 

2 mglkg was initiated when it was established that there was no inhibition of RBC AChE at I 

mglkg in order to reach a level where noticeable inhibition of RBC AChE might be attained. It 

should be noted here that administration of the chlorpyrifos in this study was in a capsule but no 

capsule was used in the Nolan study. 

D. Dosing Data 

Each subject was dosed based on his/her body weight and chlorpyrifos was weighed out 

to the 0 .I mg and placed in white opaque number zero capsules the day prior to dosing. The 

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capsule was "filled with lactose" and then closed prior to dosing. Data on the actual mg of 

chlorpyrifos administered to each subject that received the chlorpyrifos were presented in Table 

4.27, page 545. This table presents the weight of the capsule, the weight of the capsule plus the 

chlorpyrifos as well as the weight plus lactose and the subject's weight to assure that each subject 

was administered the proper dose in mg/kg. For example, subject #56 had a body weight of87.7 

kg and was dosed with 173 mg of chlorpyrifos (268 mg weight of capsule plus chlorpyrifos- 95 

mg weight of capsule). The dose this person in the 2 mg/kg dose group received was 173 

mg/87.7 kg= 1.97 mg/kg. 

The subjects arrived at the clinic the day before scheduled dosing and at 8 PM were given 

a "snack" but fasted for the next 10 hours. The subjects were given a bracelet with a unique bar 

code to identifY specimens collected. Starting at approximately 7 AM, each subject was given 

his/her dose of either lactose only or chlorpyrifos containing capsule. Each subject was watched 

to assure the capsule was swallowed. Following swallowing, each subject was given 240 mL of 

water and it was assured by the study team that the capsule was swallowed. The subjects were 

given their lunch at approximately II :30 AM and dinner at 4:30PM and then a snack at 8:30 

PM. The subjects were kept at the clinic for 48 hours and were required to return to the clinic at 

72, 96, 120, 144 and 168 hours after initial dosing. Although the subjects were asked about 

strenuous activity prior to coming to the clinic, there were no comments on the level of physical 

activity the subjects were allowed following dose administration. There were restrictions on the 

consumption of alcohol and tobacco as well as non-prescription and prescription drugs. 

In response to several inquiries that HED made regarding why alternates were needed and 

the fate of some of the subjects, the DOW company responded in a supplemental report (2008, 

MRID 47436401). This report indicated that alternates were used because some of the originally 

assigned subjects either were late reporting or reported with various symptoms that the staff 

determined might affect the study. Of the alternates used there remains one subject (#4 7) where 

there is some confusion as to whether or not his dose was correct based on conflicting body 

weight and dose administered data. It cannot be determined with certainty if this person was 

dosed at a rate of 1.63 mg/kg or his group dose of 2 mg/kg. 

C. Statistics 

(Reproduced from the study report page 23-25). 

Demographic variables: Descriptive statistics (mean, standard deviation. minimum, maximum, 

and sample size) were calculated for continuous demographic variables (age, height, and weight) 

and frequency counts were tabulated for categorical demographic variables (gender, race, and 

frame size) by gender, by treatment group, and by phase. 

Vital signs: For each phase, descriptive statistics were reported for all vital signs measurements 

(sitting systolic and diastolic blood pressure, pulse, respiration rate, and temperature) at each 

time point of collection. If a vital signs measurement was re-tested prior to dosing, the re-test 

value was used, instead of the original value, to calculate the descriptive statistics. However, if a 

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re-test was required for a post-dose assessment, the original value was used to calculate the 

descriptive statistics. All collected data were included in the summarization of vital signs 

assessments. Where individual data points were missing, data were summarized based on 

reduced denominators. 

Signs and symptoms: Signs and symptoms were coded using the 5th Edition of the COST ART 

Adverse Event dictionary. These data were tabulated by the number of subjects reporting at least 

one symptom and as percent of number of subjects dosed in each treatment group. 

RBC AChE: RBC AChE concentrations were presented by subject and blood collection 

timepoint and were summarized by treatment group and gender using means and standard 

deviations. RBC AChE percent of baseline concentration values were presented and summarized 

in the same way. Percent of baseline at timet was calculated as follows: 

Percent of Baseline I = (AChE* I 00)/baseline 

where AChE represents the RBC AChE concentrations at timet and that individual's baseline is 

the average of the concentrations collected at time -I 0 and time 0 predose. All collected RBC 

AChE concentrations were included in the summarization by gender and treatment group. Where 

individual data points were missing, data were summarized based on reduced denominators. 

These percent of baseline data were inspected and a depression of 20% or more in any subject's 

RBC AChE activity, relative to the baseline and in the absence of a concomitant shift in the RBC 

AChE activity for the control group, was considered a significant depression. 

The RBC AChE activity was also normalized for both baseline and for RBC AChE activity for 

the concurrent control (placebo) group for gender at the time interval. Percent of baseline 

normalized to concurrent control at time t was calculated as follows: 

Normalized Percent of Baseline,= (I 00* AChEt/baseline) ~control,+ I 00 

where AChE and baseline are defined as above and control is the mean percent of baseline 

response for the control (placebo) group at time t by gender. These data were presented by 

subject and timepoint and were summarized by treatment group and gender for each timepoint 

using means and standard deviations. 

For the statistical analysis, the normalized data were truncated after 96 hours for Phase I and 

after 48 hours for Phase 2 so that there would be a value for each subject at each time point. Then 

the truncated normalized data sets from Phase I and Phase 2 were analyzed, separately, using 

univariate repeated measures analysis of variance (ANOV A) methods and mixed effects 

modeling to investigate if there were statistical differences attributed to treatment. 

A univariate repeated measures ANOV A was performed as a split-plot analysis with the gender 

by treatment combinations, denoted as group, as the whole plot factor and time as the subplot 

factor. In this setting, the time and group by time interactions are valid only if the data satisfied 

the sphericity property, which says measurements at all time points are equally correlated. Since 

this was not expected to be true, statistical tests were adjusted for the violation ofthe sphericity 

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assumption using Greenhouse-Geisser and Huynh-Feldt adjustments. 

Mixed effects models were also used where gender and treatment were considered to be fixed 

factors and time was considered to be a random continuous covariate. 

This approach allowed the modeling of the effect of gender and treatment over time in a 

structured way, providing the opportunity to identifY significant higher-order trends associated 

with AChE inhibition. Covariance structures and terms in the mixed effects models were tested 

using likelihood ratio tests comparing nested models. Covariance structures failing to provide 

adequate fit and terms not statistically significant at the 0.10 level of significance were excluded 

from the model. Differences among the treatment by gender combination pairs were tested using 

contrast statements within the final mixed effects model and were considered statistically 

significant at the 0.05 level of significance. 

All summarization and analyses were conducted using SAS. Output from all SAS programs are 

included in Appendix 3, Supporting Statistical Documents. 

Specific Methods and Results 

I. Comments on the Subjects and Their Participation During the Course of the Study. 

There were sixty individuals (30 males and 30 females) enrolled in the study that were 

actually dosed with chlorpyrifos (36 subjects, 18 males and 18 females) or placebo (24 subjects, 

12 males and 12 females). Ofthe 60 original subjects selected, about 14 were replaced by 

alternates prior to administration of the dose for various reasons. This is not considered to affect 

the outcome. 

Two subjects, one female placebo (#32) and one female dosed with 2 mg/kg (#56) did not 

complete the study. The former did not return for the day 6, 7 or 8 post dosing assessments and 

was discontinued as per the SOP. Since this subject was in the placebo group, the dismissal of 

this subject is less consequential. The female (#56) dosed with 2 mg/kg chlorpyrifos was 

described as having a personal conflict and did not return on days 4, 5, 6, 7 or 8 for post dosing 

events. This subject will be discussed in the later sections of this review in more detail. 

A third subject (#II), a male dosed with 1 mg/kg did not provide a blood sample at 168 

hours since he was out of the area at the time. He returned to the clinic for subsequent follow up 

investigations (physicals) and was not dismissed from the study. This is not considered 

consequential because 168 hours is well past the expected time of effect of chlorpyrifos. 

One subject (#6), a male in the placebo group, consumed alcohol on post treatment days 6 

(equivalent to one Margarita). This is not considered consequential to the interpretation of the 

study. 

Five subjects (#s 35, 43, 49, 50 and 60; mid-dose female, high-dose male, high-dose 

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female, control female, control female, respectively) either failed to provide urine samples for a 

given interval or did not collect their samples properly such as failure to collect or did not collect 

in the proper container. This is not considered consequential to the assessment of AChE but may 

be relevant to the pharmacokinetic studies. 

2. Clinical Signs and Electrocardiogram 

The subjects were instructed to inform the physicians and/or nurses of any signs or 

symptoms that they experienced. They were also asked if they felt that they received the test 

material and if they did why. Vital signs included blood pressure, pulse, respiration and body 

temperature and were assessed on the morning prior to dosing and at 1, 2, 4, 8, 12, 24, 48 and 

168 hours post dosing. The observers that examined the subjects classified symptoms as 

possibly and/or probably related to treatment if a symptom was noted within 48 hours of 

treatment. Since the observers did not know if a subject actually received chlorpyrifos, some of 

the subjects receiving the placebo were said to have symptoms possibly or probably related to the 

test material. 

Appendix Table I shows the signs that were indicated by the subjects in either the 

placebo or groups dosed with 0.5, 1 or 2 mg/kg of chlorpyrifos. 

Electrocardiograms (ECG) were done on screening and one week after administration of 

the placebo or chlorpyrifos. Table 4.10 (pages 345 to 351) presented the data for these analyses. 

All result entries were reported as "normal". There were some subjects with "sinus bradycardia" 

noted at week one post dosing that was not present in the screen but these occurred in the 

placebos as often as in the treated subjects. There were no indications of abnormal recordings to 

indicate that chlorpyrifos affected the heart. The one week interval between the time of test 

material administration and ECG assessment is considered by this reviewer too long to be 

meaningful to detect for an acute response to an OP. 

The study author asserted that "There were no differences noted during this study 

attributed to treatment with regard to signs or symptoms, vital signs or clinical laboratory 

results". HED reviewers concur with this conclusion. There is no indication that a symptom in 

the treated groups was any greater than similar symptoms in the placebo groups. Other signs 

occurred at times that did not coincide with any indication of inhibition of RBC AChE. 

3. Clinical Chemistry, Hematology and Urinalysis. 

Clinical chemistry, hematology and urinalysis assessments were made at pretest screening 

and one week after dose administration. The one week interval following dosing and clinical 

chemistry, hematology and urinalysis is not considered by this reviewer to be the most 

appropriate time. 

Serum chemistry included: ALT, AST, albumin, alkaline phosphatase, calcium, chloride, 

cholesterol, creatinine, GGT, glucose, inorganic phosphorous, LDH, potassium, sodium, total 

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bilirubin, total protein, urea nitrogen and uric acid. 

Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Hematology included: basophils, eosinophils, HCT, Hgb, lymphocytes, monocytes, 

neutrophils, platelet count, RBC and WBC 

Urinalysis included: bacteria, bilirubin, blood, casts, glucose, ketones, leukocyte esterase, 

nitrite, protein, RBC, specific gravity, urobilinogen, WBC and pH. 

Inspection of the data tables (pages 413 to 454) did not indicate that these parameters 

were affected by chlorpyrifos treatment. It should be noted; however, that subject #56, the only 

subject showing inhibition of AChE, withdrew from study after 48 hours and did not provide 

blood or urine samples for clinical chemistry, hematology or urinalysis. 

4. AChE Assessments. 

Analytical Methods for AChE assessment. 

Blood was withdrawn via venipuncture on an arm vein and there were a total of 14 blood 

specimens collected per subject (if they completed the study). Once drawn, the blood samples 

were centrifuged for 12 minutes at 3000 rpm and the plasma discarded (except for the 

prescreening sampling). The erythrocytes were then washed with saline and centrifuged for an 

additional 12 minutes at 3000 rpm. The saline was discarded and the erythrocytes were washed 

twice by the same procedure. The resulting erythrocytes were stored frozen and shipped on dry 

ice from the clinical facility located in Lincoln, Nebraska to the MDS Clinical Laboratory located 

in Toronto, Ontario Canada. AChE was assessed by the Ellman method using acetylthiocholine 

as the substrate. The analysis was made using a Hitachi 917 automated analyzer. Appendix 5 

(pages 547 to 573) described in detail the methods for the preparation and assay and mean data 

for assessment of the RBC AChE by the Laboratory. It was noted that the standard protocol for 

this assay called for initially centrifuging the whole blood for 30 minutes (see page 552) and not 

the 12 minutes as indicated for the subject's samples in this study. This difference is noted but it 

is not considered to impact the interpretation of the data. 

An overview of the results of the RBC AChE assessments is presented in Table 2. 

Comments on Table 2 are as follows. Additional mean and individual RBC AChE data are in 

Appendix -11 in tables A-J 

Precision of the data. 

The mean results for all groups for RBC AChE data are presented in Appendix I. The 

mean data for RBC AChE in U/L for the untreated male subjects when assessed at 0 hour ranged 

from 8143 ± 982 (±12%) to 9572 ± 539 (±6%) for the five different groups. For females the 

range was 8576 ± 556 (±6%) to 9165 ± 709 (±8%). The highest mean for both males and 

females was found in Group B scheduled for dosing with 1.0 mg/kg with chlorpyrifos. 

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The mean values for males and females are within the expected range for human RBC 

AChE. In general, the analytical aspects of the measurement ofRBC AChE are considered 

appropriate. 

Indications of RBC AChE Inhibition Based on Comparison of the Means. 

Males. No treatment-related effect was observed in RBC AChE activity at any dose 

level. Column three of Table 2 shows that the mean RBC AChE value for one of the two male 

placebo groups was 10.2% less than the preclosing mean and this difference was noted at 144 

hours post dosing. The treated males based on mean data had maximum decreases of -10.7%, -

13.7% for the 0.5, 1.0 and 2.0 mg/kg dose groups respectively when compared to the preclosing 

values. These maximum depressions of the means were at 96 hours post dose. Since 

chlorpyrifos is an organophosphate, it would be expected that inhibition would start to occur and 

remain from about 2 hours to over 24 hours. Thus, 96 hours is well past the critical hours for 

expected initiation of inhibition. 

Females. No treatment-related effect was observed in RBC AChE activity at the 0.5 and 

1.0 mg/kg dose levels. At 2.0 mg/kg, one (Subject #56) of the six females displayed RBC AChE 

apparent inhibition (19%-28%) during the 8-48 hour time interval post dose. All other females at 

this dose level showed no definite inhibition. Among females, the two control groups 

demonstrated that there was as much as a -9.6% decrease in RBC AChE and maximum 

difference was again at 96 hours. The treated groups demonstrated -6.8%, -8.7% and -10% (for 

all subjects but only -6.2% when one subject that did not complete the study is not included) for 

the 0.5, 1 and 2 mg/kg dose groups, respectively. Thus, the decreases in the means for all 

treated groups are near the maximum decrease that was noted in the placebo group but one 

subject in the high dose appears to show inhibition. 

The data from several individual subjects are discussed below. 

11 

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Table 2. Overview of the results ofthe RBC AChE assessments. 

Mean Lowest Highest Lowest% 

Preclosing Posttreatment Posttreatment for an 

Group (Hour 0) U/L Mean (U/L) Mean (U/L) individual 

D: Control! 

Males 8143±982 7316±598 8043±705 88.36%@ 144 hr 

(12%)1 -10.2%@ 144 h? +2%@12hr (#10)3 

Females 8619±861 7795±759 8817±884 83.26% @6 hr 

(10%) -9.6% @ 96hr +2.3%@ 8 hr (#34) 

A: 0.5 rn/kg 

Males 8998±730 8036±738 9189±924 82.68% @ 96 hr 

(8%) -10.7%@ 96 hr +2.1%@ 8 hr (#9) 

Females 8612±1160 8028±917 8938±917 88.62%@ 36 hr 

(13%) -6.8%@ 144 +3.8%@ 144 h (#19 

8: 1.0 mg/kg 

Males 9572±539 8263±399 9862±865 75.47%@ 96 hr 

(6%) -13.7%@ 96 hr +2.9% @4hr (#II) 

Females 9165±709 8366±499 9396±517 88.99%@ 144 hr 

(8%) -8.7%@ 168 hr +2.5% @4hr (#33) 

D: Control2 

Males 9171±1112 8999±1020 9425±1041 89.71%@ 144 hr 

(12%) -2%@ 36 hr +2.8%@ 72 hr (#44) 

Females 8576±556 8380±422 8941±442 88.40%@ 144 hr 

(6%) -2.2%@4 hr +4.3%@ 72 hr (#50) 

C: 2.0mglkg 

Males 8608±896 8584±806 9004±840 89.97%@ 36 hr 

(10%) (no difference) +4.6%@ 72 hr (#48) 

Females 8623±855 7761±1239 8604±1064 71.77%@ 12 hr 

(10%) -10%@ 12 hr. (no difference) (#56) 

8089±1088 92.82%@ 12 hr 

-6.2%@ 12 hr4 (#58)4 

Data are from 5.1.1 and 5.1.2 for Groups A, B, and Control I and 9.1.1 and 9.1.2 for Group C and Control 

2. 

1 The number in() is the standard deviation as percent of the mean. 2 The percent is the difference 

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between the highest or lowest mean vs. the control at the interval given. 3 The individual subject number 

for the person showing the lowest relative reading for AChE and the interval that this reading was made. 4 

Since subject 56 did not complete the study, the reading for the second lowest subject is also presented for 

this group or the mean for the reaming 5 subjects is presented. 

Indications of RBC AChE Inhibition Based on Individual Responses, Note: Additional 

data on the phenotype association with RBC AChE are presented in Appendix 11 Tables. A-C. 

Comment. There is an apparent decrease in the activity noted in Phase I for the males 

and/or females in the placebo, 0.5 and I mg/kg dose groups since at hour 96 many of these 

(placebos included) suddenly have readings lower than their previous readings for RBC AChE. 

There was no explanation for this provided. See Table 5.1.2 on page 60 of the study report. 

Since hour 96 is well past the time when chlorpyrifos would be expected to start to cause 

inhibition, the impact of this sudden decrease in activity is not such as to seriously impact the 

interpretation of the data. This sudden decrease in activity was not noted for Phase II of the 

study when both placebo and 2 mg/kg chlorpyrifos were tested (see Table 9.1.2 page 79 of the 

study report). 

Males. Refer to Table H in Appendix. Column five of Table 2 shows that for the 

control group males, one individual demonstrated 11.6% (subject# 1 0) and another demonstrated 

10.3% (subject# 44) less than his preclosing value. Among the treated groups, there was a 

maximum of 17.4% (subject #9), 24.5% (subject #11) and 10% (subject# 48) apparent decrease 

in RBC AChE for the 0.5, 1.0 and 2.0 mg/kg dose groups, respectively. Since there are subjects 

in both the 0.5 and 1.0 mg/kg dose groups that have apparent decreases in AChE it can be 

implied that these individuals may be unusually sensitive to inhibition of AChE by chlorpyrifos. 

Thus, the following will discuss in more detail the overall response of these individuals 

throughout the study. Selected other subjects will also be discussed for the reasons given below. 

Subject # 9. Group A. (0.5 mg/kg chlorpyrifos treatment). Subject# 9 was a 19 year old 

Caucasian male 75 inches tall and weighing 210 pounds and was a non-smoker. No clinical 

signs or abnormalities were noted in this persons clinical chemistry or ECG assessments. This 

subject was reported as having intestinal cramps starting at 2 days, 22 hours and 44 minutes post 

dosing that lasted 15 hours. This subject replied "no" when asked if he had received the test 

material and not the placebo. 

This subject had RBC AChE readings (in U/L) of8294, 8602, 8437, 8646, 8844,8723, 

8580,8261,8107,8250,6985 (-19%), 7535 (-12%), 7376 (-14%) and 7700 (-11%)forthe10, zero, 2, 4, 8, 12, 24, 36, 48, 72, 96, 120, 144 and 168 hour assessment times respectively. 

Thus, indicating that the apparent decrease in RBC AChE did not begin until 96 hours after 

dosing. It is noted that the cramps did not coincide with the lower AChE levels. It was noted 

above that there is a problem with the assays after hour 96 (see comment above). 

At the onset of this subject's intestinal cramps (-72 hours), his RBC AChE was at most 

3% less than the zero time reading. However, at 96 hours, his RBC AChE was lowest but his 

cramps had already disappeared by 85-86 hours (see Appendix I). 

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In conclusion, there is no justification to support that this individual was unusually 

sensitive to inhibition ofRBC AChE. Inhibition would be expected to appear within a few 

hours(- 4-8 hours) post dosing and not 96 hours later. There were also no symptomatic 

expressions indicative of AChE inhibition (i.e. intestinal cramps are not a specific response to a 

AChE inhibitor and could be due to many things). 

Subject # 11. Refer to Table F in Appendix. Group B (1.0 mg/kg chlorpyrifos treatment). 

Subject# II was a 45 year old black male 71 inches tall and weighing 191 pounds and smoked 

one and a half packages of cigarettes a day. This subject did not report for his day 7 

examinations or blood sampling. He did not submit urine for the 144 to 156 hour or 156 to 168 

hour collection intervals. He returned to the clinic "the following week" for a post physical 

exam, ECG and laboratory work up. There was no record of how he responded to whether or not 

he thought he had received the test material rather than the placebo. This subject's clinical 

laboratory work up for post treatment indicated he was "moderately lipemic". 

On two occasions (refer to page 468 and Appendix 4.2111) this subject was reported to have a 

headache. The first occasion began 3 hours and 40 minutes post dosing and lasted for 19 hours. 

This means the headache started at II am on October 3 and lasted until 6 am on October 4. The 

second occasion began 22 hours and 40 minutes (approximately 6 am on October 4 post dosing 

and lasted I day and 9 hours. [There seems to be a reporting glitch here because the first 

headache is reported to be resolved at 6:00 and the second headache starts at 6:00 both on 

October 4, 1998. There may actually be just one headache.] 

This subject had RBC AChE readings (in UIL) of 10307, 10098,9097 (-10%), 10318, 9768 (-

3%), 9779 (-3%), 9977, 9768,9141 (-10%), 10153, 7700 (-24%), 9185 (-9%), 9218 (-9%) for 

the -I 0, zero, 2, 4, 8, 12, 24, 36, 48, 72, 96, 120 and 144 hour assessment times, respectively (not 

assessed at 168 hours). Thus, there was considerable variation in this individual's readings for 

RBC AChE but they do not fit an expected pattern of inhibition by an organophosphate. Since 

maximum apparent decrease occurred at 96 hours post dosing (again there is a problem with the 

hour 96 readings) and the reading at 72 hours was 10153 or essentially the same as the preclosing 

zero hour, this subject is not considered to have chlorpyrifos related inhibition of ChE. 

It is noted that there was no consistent depression of RBC AChE during this interval 

when the subject experienced his headache. For example, the readings were -I 0%, similar, -3%,-

3%. -3%, and -3% at 2, 4, 8, 12, 24 and 36 hours respectively. 

In conclusion, there is no justification to support that this individual was unusually 

sensitive to RBC AChE inhibition by chlorpyrifos. The headache that this individual was 

reported as having did not coincide with decreased levels of RBC AChE and it was not present 

when AChE was lowest. 

Subject #47. Group C (2 mg/kg chlorpyrifos treatment, but this subject may have 

actually received a dose of 1.66 mg/kg). Subject #4 7 was a 24 year old Caucasian male 69 

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inches tall and 184 pounds. He responded "no" to the question about whether or not he thought 

he received the test material and did not have any obvious symptoms of AChE intoxication. This 

subject had highest "estimated dose received" (1.130 mg/kg compared with the group mean of 

0.59 mg/kg, see Table 16, page 4 7 of the Pharmacokinetics report) based primarily on plasma 

and urinary content ofTCP. This subject did not have indications of AChE inhibition since 

there was at best a 5% decrease in activity at 24 hours but the preceding and succeeding 

assessments were both higher than the baseline. 

Subiect #48. Refer to TableD in Appendix. Group C (2.0 mg/kg chlorpyrifos treatment). 

Subject# 48 was a 23 year old Caucasian male 71 inches tall and weighing 162 pounds and 

smoked I 0-14 cigarettes a day. He responded no to the question about whether or not he thought 

he received the test material. According to the data table on page 4 71, this subject did not 

experience any symptoms during the post dosing phrase. 

This subject had RBC AChE readings of8569, 8206, 8019, 8008,7887, 7689, 8206,7546 

(-8%), 7832,8074,7766,7766,7942 and 8184 for the -10, zero, 2, 4, 8, 12, 24, 36, 48, 72, 96, 

144 and 168 assessment times respectively. Thus, this subject's maximum decrease at 36 hours 

was immediately proceeded by a value actually the same as the zero time assessment and thus 

does not show a pattern consistent with inhibition by an organophosphate. 

Females. Refer to Tables I and J in Appendix. Column five of Table 2 shows that for 

the control group females, one individual demonstrated 16.7% (subject# 34) and another 11.6% 

(subject# 50) less than her preclosing value. Among the treated groups there was a maximum of 

11.4% (subject #19), II% (subject #33) and 28.2% (subject# 56) apparent decrease in RBC 

AChE for the 0.5, 1.0 and 2.0 mg/kg dose groups, respectively. Since the subjects in both the 0.5 

and 1.0 mg/kg dose groups did not exceed the placebo group for apparent decreases in AChE, it 

is not implied that there are individuals in these dose groups that may be unusually sensitive to 

inhibition of AChE by chlorpyrifos. Subjects # 51 and 56 are discussed as follows. 

Subject #51. Phase II Group C female, 2 mg/kg chlorpyrifos. Refer to Table 4 below for 

AChE data on this subject. This subject sustained a decrease of 5 to 6% RBC AChE over the 

critical hours of 12, 24, and 36. However, her pretest variation was also near 5%. This subject 

also had one of the highest levels ofTCP in her blood. But the peak level ofTCP did not 

correspond with the lower readings for AChE. 

The placebo female group for Phase II was demonstrated to be very stable over the course 

of the seven days on the study (see last column in Table 4) as indicated by the data from one 

individual who demonstrated the most variation of the six females in the placebo group. Overall, 

the 5-6% lower reading in subject #51 is noted but not considered to be definite inhibition caused 

by chlorpyrifos. 

5. Special considerations for subject #56 who did not complete the study. 

Subject# 56. Group C, 2 mg/kg chlorpyrifos. As indicated previously, subject# 56 

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dropped out of the study after 48 hours. It was originally reported that "repeated attempts were 

made to contact this individual were unsuccessful and no post study medical evaluation was 

performed" (refer to page 28 of the study report). However, the supplementary report (2008, 

MRID 47436401) in response to HED's questions about the fate of this individual asserts "In, 

1999, Richard Nolan PhD was a DAS toxicologist that was the toxicology contact for the Kisicki 

study. Dr. Joel Mattsson was in 1999 a DAS toxicologist working with Dr. Nolan and was 

assured that the testing laboratory had contacted subject #56 personally and she reported no 

problems with the study but had personal reasons for not returning for further evaluations. DAS 

is not aware of any additional information on subject #56". There is still ambiguity with regard 

to statements about this subject regarding the comments in the study report (page 28) where no 

contact was made and in the supplementary report (page 1 7) where contact was said to have been 

made. Overall, failure of this person to have data after 48 hours does not preclude that data on 

AChE assessment and pharmacokinetics obtained prior to 48 hours are not useful and 

informative although the lack of data following 48 hours limits the assessment of the total PK 

picture. The possibility that this subject developed clinical signs in response to treatment cannot 

be resolved on the basis of available information. 

Page 472 of the study report indicates that this subject reported experiencing "numbness 

of the upper arms" starting 2 hours and 24 minutes after administration of the chlorpyrifos and 

lasting a total of 42 minutes. On page 510, the table listing the subject's response to the question 

if they thought they received the test material does not include subject #56. 

This subject was the only subject on the study that demonstrated apparent RBC AChE 

inhibition. Table 3 below provides details about this subject and shows the extent of inhibition at 

the critical time interval. It is apparent that this individual's RBC AChE is decreased starting at 8 

hours and remaining so until 48 hours when she was last tested. 

Table 3 Summary of Subject #56 

Parameter Results Comments 

Description (a) A 34 year old Caucasian female 72 inches tall There is nothing obviously 

and weighing 193 pounds and was a non- different about this subject to 

smoker. This individual did not report for the suggest an unusual susceptibility 

day 4, 5, 6, 7 or 8 blood collection (see page to chlorpyrifos. The subject was 

28) or assessment of vital signs and did not genotype QQ but about half the 

provide urine samples after 48 hours. persons on the study had this 

genotype. 

Symptoms (b) Subject had a transient "numbness in upper The numbness alone does not 

arms" that started to occur 42 minutes after seem to be a response to an 

dosing and lasted for 2 hours and 24 min (self AChE inhibitor and since this 

resolved without medication). occurred and was resolved by 

three hours, or before there was 

appreciable apparent inhibition 

of AChE at 8 hours post dosing, 

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Parameter Results Comments 

the finding is not considered 

treatment-related. 

RBCAChE 8426 at -10 hours Subject shows decrease in RBC 

lUlL 8910 at 0 hour AChE that can be considered the 

(c) 8668 predosing mean critical times expected for an OP 

8602 (no difference) at 2 hours, following an oral administration. 

8525 ( -2%) at 4 hours, 

6688 (-23%) at 8 hours, 

6221 (-28%) at 12 hours No other subject shows a similar 

6424 (-26%) at 24 hours pattern of decrease in activity. 

7051 (-19%) at 36hours 

6882 (-21%) at 48 hours 

No additional assessments. 

Serum 18 ng/gm at 8 hours The serum chlorpyrifos data and 

chlorpyrifos 2.5 ng/gm at 12 hours the serum and urine TCP data all 

(d) All other times- not detected(< I ng/gm) indicate that subject# 56 

absorbed chlorpyrifos to a 

The highest level in all other subjects was only greater extent than the other 

5.6 in a female (#21) dosed with I mg/kg. subjects in this study. 

Serum TCP Subject has total of 6671 ng/gm TCP in serum 

(0 to 48 hours) with values of71, 120, 1600, 1500, 1300, 1100 Since no assessments were made 

(e) and 980 ng/gm for the 2, 4, 8, 12, 24, 36 and 48 after 48 hours, the total TCP 

hour intervals, respectively. Note there was picture cannot be determined to 

little TCP in blood at 2 to 4 hours or at the time compare with the other subjects 

the numbness was noted. which seemed to have TCP 

present in the blood at the later 

This is the highest (total ng/gm) for the times. 

group dosed with 2 mg/kg since the range 

for all others (both sexes) was 1404 (#42) 

to 5860 (#47) ng/gm for up to 48 hours. 

Urine TCP According to Table 14b for the 0-48 hour 

(corrected for interval, Subject 56 had a total of22.8 mg or 

creatinine) was highest for the group dosed with 2 mg/kg. 

(0 to 48 hours) Since the range for the others in this group was 

4.8 (#40) to 16.2 (#47) with a mean of 8.4 ± 3 

for all individuals excluding #56. 

Estimated 0.640 mg/kg. - from Table 16 The calculation of the total 

internal dose is limited since no internal dose of Compares favorably with the group mean of 

assessments for TCP or parent chlorpyrifos 0.59 ± 0.21 mg/kg (range 0.323 (#40) to 1.130 

(g) (#4 7) mg/kg for the group dosed with 2 mg/kg. chlorpyrifos were made after 48 

males 0.61±0.28; females: 0.568±0.12 mg/kg hours. 

CPOase (h) Subject has reading of 9278 Units/liter There is nothing unusual about 

17 

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Parameter Results Comments 

comparing favorably with the group mean of the serum activity of CPOase, or 

9523±1 517 Units/liter. diazoxonase. Although her 

paraoxonase level was much 

Paraoxonase 367 UIL compared to group mean 

lower than the group mean this 

737±430 U/L should not affect dosing with 

chlorpyrifos. Subject was 

described as phenotype "QQ 

low" which was a typical 

classification for many (about 

half) of the subjects in the study. 

(a) Data are from Appendix 4.3, page 242 .. (b) Data are from Append1x 4.21.1, page 472. (c) Data are 

from Table 4.13.2, page 407. (d) Data are from Table 5, page 34 of the Pharmacokinetics report. (e) 

Data are from Table 7, page 36 of the Pharmacokinetics report. (f) Data are from Table 14b (corrected 

for creatinine), page 45 of the Pharmacokinetics report. (g) Data are from Table 16, page 47 of the study 

report. (h) Data are from Table 17, page 50 of the Pharmacokinetics report. 

It is noted that in the screening study this individual had a RBC AChE of 7678 U/L. This 

was listed as a clinical laboratory comment as "not significant in the context of this study". 

When compared to the mean for the -10 and zero hour samplings (mean= 8668 U/L), this would 

be 11% less. This value of 11% less is not as much as the approximately 28% decrease that was 

noted for this person following treatment with 2 mg/kg chlorpyrifos. Thus, the decrease in AChE 

after 8 hours is greater than the spontaneous variation for this subject. 

This subject has inhibition rather than random decrease in activity since the decrease in 

activity starts at 8 hours and rises to a peak at 12 hours and then appears to start to decline at 24, 

36 and 48 hours. This would be expected for an organophosphate AChE inhibitor. The pattern 

of decreased activity also correlates with the amount of TCP in the serum as shown in Table 4. 

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Hour 

2 

4 

8 

12 

24 

36 

48 

72 

96 

120 

144 

168 

Net 

TCP 

Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Table 4. Correlation between RBC AChE activity and blood level ofTCP in humans dosed 

with 2 mglkg chlorpyrifos. 

Sub. #56(QQ'f')_ Sub. #47 (QQoL Sub. #5l(OR'f') sub. #48(0Ro) Placebo 

RBC TCP RBC TCP RBC TCP RBC TCP #44 (ORo) 

AChE Blood AChE Blood AChE Blood AChE Blood RBCAChE 

= 71 +2% 580 -2% 420 -4% 180 -1% 

-2% 120 +2% 640 -1% 580 -5% 250 = 

-23% 1600 = 790 -2% 1300 -6% 240 -3% 

-28% 1500 = 910 -6% 690 -8% 260 -6% 

-26% 1300 -5% 980 -5% 540 -2% 380 -6% 

-19% 1100 = 960 -5% 750 -10% 460 -4% 

-21% 980 -1% 1000 -3% 730 -7% 470 -5% 

Subject did not +4% 690 +1% 600 -4% 300 +1% 

return for 

additional +2% 460 +4% 420 -7% 210 -4% 

sampling. +7% 320 +6% 150 -7% 140 -4% 

+2% 220 -2% 170 -6% 77 -10% 

+7% 150 = 110 -2% 48 = 

0 to 48 hrs 6671 0 to 48 hrs 5860 0 to 48 hrs 5010 0 to 48 hrs 2240 N/A 

0 to 168 hrs - no 0 to 168 hrs 7700 0 to 168 hr s 6410 Otol68hrs 3015 

data 

Definitely shows Highest levels of Sustains a slight Subject has lowest Shows that 

inhibition TCP do not decrease at critical level of blood TCP activity 

correlating with correlate with times and is thus but seems to varies toblood level of .J.RBCAChE. possibly showing sustain a decrease 10%. 

TCP. inhibition. inRBC AChE 

Placebo 

#60 (QQ'f') 

RBCAChE 

-3% 

-5% 

+1% 

+2% 

-1% 

= 

= 

-3% 

-3% 

= 

-3% 

+1% 

NIA 

Shows that 

female RBC 

AChE is 

stable. 

TCP data are from Table 7 page 36 m MRID No.: 45144101 and are ng/gm. Note: TCP data were not reported for the 

blood from the placebo group in Table 7 of the study report. RBC AChE data are from Table 9.1.2 page 78 from MRID 

No.: 44811002 and are the percent decrease(-) or increase(+) in RBC AChE relative to the baseline. The= sign indicates 

that the assessment was within ± 1% of the baseline. 

Table 4 also presents data on the variation of RBC AChE activity in one other female and 

two males dosed with 2 mg/kg of chlorpyrifos and the amount of TCP in their blood. In 

addition, a male and a female from Phase II placebo group are included to show the spontaneous 

variation of RBC AChE. It is noted that the female (#60) is stable but the male (#44) showed 

decreases. One other placebo male (Subject #41, data not shown here because if space 

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limitations) also showed what appeared to be sustained decreased activity (4%-7% from 8 hours 

to 36 hours post dose). 

Table 4 indicates that female subject #51 sustains a slight decrease in RBC AChE and 

also has a high blood level of TCP but not at the critical times oflower AChE readings. 

Therefore this subject is not considered to show definite evidence of RBC AChE inhibition in 

response to 2 mg/kg of chlorpyrifos since the level of decrease is too low and not coincident with 

serum TCP. 

Part B. Pharmacokinetic and Paraoxonase Data (Refer to MRID No.: 

45144101). 

Part B 1. Pharmacokinetic data. 

Note: Additional data on the pharmacokinetics are in Appendix II Tables A-J 

The sixty subjects on this study gave blood samples (5 mL) for the purpose of 

determination of chlorpyrifos, chlorpyrifos oxon and 3,5,6-trichloro-2-pyridinyl (TCP) at -10 

hours prior to dosing, at zero hour prior to dosing and at 2, 4, 8, 12, 24, 36, 48, 72, 96, 120, 144 

and 168 hours post dosing. Urine samples from all urine voided (as per the protocol) for the 

intervals -48 to -36 hours, -36 to -24 hours, -24 to -12 hours, -12 to 0 hours pretreatment and 0 to 

6 hours, 6 to 12 hours, 12 to 24 hours, 24 to 36 hours, 36 to 48 hours, 48 to 60 hours, 60 to 72 

hours, 72 to 84 hours, 84 to 96 hours, 96 to 108 hours, 108 to 120 hours, 120 to 132 hours, 132 to 

144 hours, 144 to !56 hours and !56 to 168 hours post treatment. The blood and urine were 

analyzed by GC/MS for chlorpyrifos, its ox on analog and TCP and the method of preparation 

using internal standards was described. TCP was derivitized prior to analysis. In response to an 

inquiry form the Human Studies Review Board, additional details of the method of analysis were 

confirmed in two submissions (2009, MRID 47866701 and 47866703). 

Data were presented that demonstrated the recovery of spiked samples for chlorpyrifos 

(98.0 to 99.8%), chlorpyrifos oxon (95.4 to 98.0%) and TCP (91.1 to 97.1%), and the lower 

limit of detection was about I ng/gm of blood for chlorpyrifos and its ox on analog but was about 

12.1. ng/gm for TCP. Similarly, recoveries of from 96 to 104% for these chemicals from urine 

were demonstrated. Additional data demonstrated the stability of these chemicals in blood and 

urine stored -20 or -80 °C for 6 or 10 days. 

Blood and urine analysis for chlorpyrifos and chlorpyrifos oxon. 

Chlorpyrifos and chlorpyrifos ox on were not found in any of the urine samples from any 

of the subjects (refer to Table 10 of the study report page 39). Chlorpyrifos oxon was not found 

in the blood of any subject (refer to Table 6 of the study report page 35). 

Chlorpyrifos was found only occasionally in the blood (refer to Table 5 page 34 of the 

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study report). No subjects dosed with 0.5 mg/kg chlorpyrifos were found to have chlorpyrifos in 

their blood. Subjects #II (1.0 ng/gm at 2 hours), #14 (2.7 and 1.5 ng/gm at 4 and 8 hours), #21 

(5.6 and 2.9 ng/gm at 2 and 4 hours) and #30 (1.1 ng/gm at 8 hours) dosed with I mg/kg were 

noted to have chlorpyrifos in their blood at the assessment times indicated. Subjects #47 (3.1, 

1.3, 3.4 and 1.8 ng/gm at 2, 4, 8 and 12 hours), #49 (3.1 and 1.7 ng/gm at 2 and 8 hours), #56 

(18.0 and 2.5 ng/gm at 8 and 12 hours) and #59 (2.2, 4.1, 4.1 and 1.5 ng/gm at 2, 4, 8 and 12 

hours) dosed with 2 mg/kg were also shown to have chlorpyrifos in their blood. These are very 

small amounts of chlorpyrifos. The highest level (18 ng/gm) was found in subject #56 at 8 

hours. These data suggest a short half-life for parent chlorpyrifos in blood but there does not 

appear to be sufficient data to establish a firm number for the half-life of chlorpyrifos in the 

blood. 

Blood and urine analysis for the principal metabolite TCP. 

TCP was detected in the blood of all subjects dosed with chlorpyrifos. Refer to Appendix 

Tables. D, E, F, G, and H. 

"The percent recovery corrected for dose as urinary TCP" was reported to be for both 

sexes combined 34.7±19.6%. 30.8±9.9% and 29.5±10.4% for the 0.5, I and 2 mglkg dose 

groups, respectively. (Refer to Table 16 "Estimation of dose Received by Volunteers", page 47.) 

The extent of absorption is less than the 70% earlier report from Nolan (1984)1 and this 

may be attributed to the fact that the chlorpyrifos in this study was administered in a capsule and 

this would lead to slower absorption. In contrast, in the Nolan study, chlorpyrifos was dissolved 

in methylene chloride and placed on a 0.5-gram lactose tablet, which was swallowed with 100 

mL of water. 

The half-life ofTCP as indicated by the blood and urine data are shown in Table 5. 

Table 5. Half-lives (in hours) based on TCP in the blood and urine. 

Dose Blood" Urineb 

(mg/kg) Males Females Combined Males Females Combined 

0.5 29.7±7.4 44.5±32.4 37.1±23.7 29.5±8.9 38.6±24.3 34.3±16.1 

1.0 27.7±5.6 30.5±7.4 29.1±6.4 20.5±5.9 33.6±7.4 31.0±7.3 

2.0 36.2±5.9 35.2±4.8 35.8±5.6 38.1±6.5 32.8±6.5 35.7±6.7 

a. Table 9, page 38. b. Table 15, page 46. 

(Note in MRID 4514410 I) the printing is small and in some places difficult to distinguish 5, 6 and 8. The best read 

of the number is in Table 5. Since there were only a few and mostly in the standard deviation, these questionable 

numbers should not impact the interpretation.) 

I Nolan, R.J. et al, (1984) Chlorpyrifos: Pharmacokinetics in human volunteers. ToxicoL AppL PhannacoL 73:8-15. 

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Additional serum TCP data on selected subjects are presented in Table 4. 

Part B. 2. Serum Paraoxonase and chlorpyrifos oxonase (CPOase) Assessment. 

A 5 mL blood sample was taken prior to dosing and sent to the laboratory of Dr. Clement 

Furlong, Department of Medicine and Genetics, University of Washington, Seattle, Washington 

and assessed for paraoxonase activity using a spectrophotometric assay. Paraoxonase was tested 

with chlorpyrifos axon, paraoxon, or diazoxonase. When the test substance was chlorpyrifos 

axon, the activity was called CPOase. 

Table 17 of the study report presented data for each subject and group means for the subjects 

dosed in both phase I (October 3, 1998) and II (October 17, 1998). Table 5 summarizes the 

CPOase data in this study. Paraoxonase (range- -250 to -2502 units/L, when paraoxon was the 

substrate) and diazoxonase (range -6548 to 22452 units, when diazinon ox on was the substrate) 

data were also presented but not shown in this review since the subject of the review is 

chlorpyrifos. 

Group CPOase Range Comment 

Phase I 5 subjects were QQ (low), 5 were QR 

Control 8418±1639 5430 to 10410 (medium). And 2 were "QQAow" . Both 

the high and low readings were from OR 

individuals. 

Phase I % were QQ and 7 were QR. The low 

0.5 mglkg 7965±1536 5412 to 13341 was from a QQ and the high was from a 

QR. 

Phase I 6 were QQ, 5 were QR and I was RR. 

I mg/kg 8463±1386 6599 to 11615 The high value was from a QQ and the 

low value was also from a QQ. 

Phase 2 6 were QQ and 5 were QR and one was 

Control 11357±3097 6904 to 17333 RR. The high value was from the RR 

person and the low value was from a QQ 

person. 

Phase 2 6 were QQ, 5 were QR and I was RR. 

2 mg/kg 9523±1517 7048 to 13018 The high value was from a QR person 

and the low value was also from a QR 

person. 

Subject# 56 has a value of 9278 

Units/liter and is very close to the group 

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Group CPOase Range Comment 

mean and thus does not have an unusual 

ability to metabolize chlorpyrifos oxon. 

Conclusions, Discussion, Study Deficiencies and Classification. 

I. Study author's conclusions. 

The study author (page I 0 of the study report) concluded "The NOEL for signs and 

symptoms in fasted human following a single oral dose was 2.0 mg chlorpyrifos/kg of body 

weight. The NOEL for RBC AChE inhibition in humans given a single oral dose of chlorpyrifos 

was 1.0 mg/kg of body weight. The 2.0 mg chlorpyrifos/kg of body weight dose level 

represented a threshold in that it produced greater than 17.3% depression in I of 12 volunteers." 

2. Reviewer's conclusion and discussion, 

Signs and Symptoms. There was no indication that any of the signs and symptoms that 

were noted in the subjects dosed with chlorpyrifos were different in either their nature or degree 

of severity from the signs and symptoms that were noted in the placebo groups. Some reported 

symptoms in the subjects that were dosed with chlorpyrifos occurred either well before or after 

the time when chlorpyrifos absorption was maximal or when the blood or urine level of TCP the 

principal metabolite of chlorpyrifos was at its maximal level. Also, the only subject showing 

definite inhibition of RBC AChE did not display any symptoms when maximum inhibition of 

AChE was attained and this subject's only reported sign ("upper arm numbness") occurred and 

resolved well before her RBC AChE was shown to be inhibited and before her serum level of 

TCP reached higher levels. If the "upper arm numbness" was related to some other cause due to 

chlorpyrifos than inhibition of RBC AChE it would still be expected for the numbness to persist 

while the absorption of chlorpyrifos increased. Thus, the NOAEL for symptoms is> 2 mg/kg 

chlorpyrifos. 

Pharmacokinetic Data. Based on the pattern of occurrence ofTCP the principal 

metabolite of chlorpyrifos in the blood and urine, chlorpyrifos is absorbed rather slowly from the 

gut and requiring about 8 to 12 hours for the TCP blood level to reach a maximum. Based on 

the blood level ofTCP, subject# 56 absorbed more chlorpyrifos in the first 48 hours and this 

subject also had clear evidence of RBC AChE inhibition. 

The rate and extent of absorption of chlorpyrifos in this study was slower and lower than 

reported in an earlier study (Nolan, 1984) and this was attributed by the study author to be due to 

the differences in administration. In this study, chlorpyrifos was administered in a capsule but in 

the earlier study it was administered on top of a lactose pill. The need for the capsule itself to 

dissolve in the g-I tract may be a factor. 

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RBC AChE Inhibition. Review of this study identified one subject (#56, a female dosed 

with 2 mg/kg, with genotype QQ) as demonstrating inhibition ofRBC AChE. The decreases in 

RBC AChE were shown to correlate with high levels ofTCP in her serum. As much as 28% 

inhibition was noted at 12 hours post dosing. 

A second subject (#51, with genotype OR) was considered as possibly also showing 

inhibition and also had one of the highest levels of serum TCP for the group dosed with 2 mglkg. 

Although this subject had decreases to only 5 to 6% of her preclosing mean, this level of 

decrease was sustained over the critical hours of expected time for an OP to inhibit blood AChE 

(i.e. 8 to 24 hours). Inspection of the other four females in Phase II indicated that their RBC 

AChE activity was very stable over the 168-hour post dosing period. Overall, subject #51 is 

considered to have only very minimum and indefinite inhibition. 

None of the males were determined to be showing definite decreases in RBC AChE. It 

was noted that one subject(# 48,2 mg/kg group,OR) had decrease of8% at 12 hours and 10% at 

36 hours but two placebo males indicated that variation in RBC AChE activity can also vary to a 

decrease of 10%. Also subject# 48 had one of the lowest net totals of TCP in his blood for the 

group receiving 2 mg/kg. 

Thus, the NOAEL for RBC AChE inhibition is 1 mg/kg and the LOAEL is 2 mg/kg. 

Only one female was concluded to have definite inhibition. 

CPOase 

This study has important data on each person's PON and CPOase. The single person 

showing inhibition had CPOase similar to other individuals in the group dose with 2 mg/kg, but 

this person also had the highest absorption of chlorpyrifos. Thus, the persons ability to absorb 

chlorpyrifos from the gastro-intestinal tract may be more important that the CPOase status of the 

individual. 

Study Classification. 

This study is being classified as RESERVED since there are no current guidelines for 

classifying studies with human subjects. 

4. Study deficiencies and compromising issues. 

-Plasma ChE was not assessed for. This is considered important since other recent 

studies with humans and OPs include plasma ChE assessment. Also it was reported in the earlier 

(Nolan, 1984) with humans that plasma ChE is inhibited at lower doses than RBC AChE by 

chlorpyrifos. This deficiency may render the study unacceptable based on incompleteness of 

expected inclusions. This deficiency is considered a potentially serious omission. 

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-The only subject that showed definite inhibition of RBC AChE did not complete the 

study after the 48th hour assessments. This subject did not provide blood samples for 

hematology or clinical chemistry at the scheduled one week post treatment time. The 

supplementary report (2008, MRlD 47436401) indicated that this person was contacted via 

telephone and did not report adverse effects and that she had to leave the study for personal 

reasons. This deficiency may be beyond the control of the laboratory and there is no justification 

at this time to fault the laboratory for the subject not completing the study. 

-The hematology, clinical chemistry, urinalysis and ECG assessments were made one 

week following the administration of chlorpyrifos. This is considered a poor design. These 

assessments should have been done during the time of peak effect of chlorpyrifos on AChE. The 

assessments after one week are of little value since the chlorpyrifos has been cleared from the 

body and it would be expected that inhibition of AChE would have been partially reversed by 

this time or that the body adapted to the decreased AChE activity. 

-Although not a deficiency in itself, the analytical method used to detect chlorpyrifos, its 

oxon and TCP has lower limits of detection in the order of I ng/gm blood. More recent 

methodology that was used in the epidemiological studies has limits of detection about I 000 

times more sensitive. Thus, the PK data would have been more useful especially at the lower 

dose of0.5 mg/kg if the more sensitive method of analysis was used. 

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Appendix I - Individual Subject Analysis for subjects showing symptoms or variation in AChE 

Subject# Symptoms or Events (a) RBC AChE Comments RED's Conclusion 

Placebo-Males 

2 Increased appetite, headache Maximum decrease 12%@ 48 Since these subjects are 

(no) (moderate)- vomited. Starting 47 hrs. Other values are 89% to in the placebo group, 

hrs postdosing, lasting for 4 days, 6 I 05%. of predose there symptoms or 

hrs. Possibly related to treatment. events cannot be due to 

"One can coca-cola next day''. chlorpyrifos treatment. 

8 Headache (mild)- Starting I 0 hrs Maximum decrease 9% @ 48 

(yes) postdosing, lasting -13 hrs. hrs. Other values are 94% to 

Possibly related to treatment. 103%. 

10 No symptoms or events. Maximum decrease 14%@ 96 

(yes) hrs. Other values are 88% to 

103%. 

13 No symptoms or events. Maximum decrease 12% @ -I 0 

(yes) hrs. Other values are 97% to 

112%. 

37 Dizzy, feels weak, nausea, vomited, Maximum decrease 3%@ 96 

(yes) body aches - Starting 2 days, 18 hrs hrs. Other values 97% to I 07% 

lasting (some symptoms) for up to 2 ofpredose. 

days II hrs. Possibly related to 

treatment. 

41 Itching of insect bite. Starting 2 Maximum decrease 7% @ 24 

(no) days 5 hrs, lasting II hrs. Unrelated hrs. Other values 95% ti I 07% 

to treatment. ofpredose. 

45 Nausea, vomited. Starting 2 days. No decreases. Values are I 00 to 

(no) Lasting -20 min. Possibly related 110% of the predose. 

to treatment. 

46 Headache (mild). Starting- 3 hrs. Maximum decrease 6% @ 2 hrs. 

(no) Lasting- 3hrs. Possibly related to Other values 98% to I 08% of 

treatment. predose. 

3112 subjects have headaches. 

4112 thought they received the chlorpyrifos when it was not given. 

As much as a 14% decrease in RBC AChE can occur within the untreated group over the 7 day period. 

Placebo-Females 

20 No symptoms or events. Maximum decrease 7% at -I 0 Since these subjects are 

(yes) hrs. Other values 94% to I 07%. in the placebo group, 

26 

I 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

c non-gm ·d e r me ) 

Subject# Symptoms or Events (a) RBC AChE Comments HED's Conclusion 

23 No symptoms or events. Maximum decrease 7% at 144 there reactions cannot 

(yes) hrs. Other values 96 to II 0%. be due to chlorpyrifos 

treatment. 

29 "hiccough", heartburn. Starting II Maximum decrease 13% at 96 

(no) hrs, lasting II hrs. Unrelated to hrs. Other values 95 to l 07%. 

treatment. 

32 No symptoms. Maximum decrease I 7% and 

(no) sustains from 96 to 144 hrs. 

Other values 85 to l 05%. 

Subject included to show 

variation in AChE. 

50 Headache (mild)- Starting l day 21 Maximum decrease 12% atl44 

(no) hrs. lasting 3 hrs. Unlikely related hrs. Other values 97 to I 08% of 

to treatment. predose. 

52 Headache (mild), loose stool, Maximum decrease 7% at 24 

(yes) nausea, intestinal cramps, vomited. hrs. Other values 97 to l 03% of 

Starting on days 3 and 4, lasting 6- predose. 

10 hrs (some symptoms). Possibly 

related to treatment. 

54 Headache (moderate and mild), Maximum decrease 4% at 36 

(no) nausea. Starting 4-5 hrs, and again at hrs. Other values 97 to I 07% of 

II hrs. Lasting 6-7 hrs and I 7 predose. 

hours. Possibly related to 

treatment. 

60 lack of appetite, headache (mild), Maximum decrease 5% at 4 hrs. 

(yes) nausea. Starting at 3-5 hrs or 13 Other values 97 to I 02% of 

hours. Lasting 5 to 17 hrs. Possibly predose. 

related to treatment. 

4112 (33%) females had headaches. 

4112 thought they received the chlorpyrifos when it was not given. 

As much as 17% reduction in RBC AChE can be attained in the untreated female group. 

0.5 mg/kg Chlorpyrifos-Males 

3 Increased appetite. Starting I day Maximum decrease 15% at 48 Increased appetite is 

(no) and 23 hrs. Lasting 4 days. hrs. Other values 94 to I 02% of not an expected 

Unlikely related to treatment. predose. response to an OP. Not 

related to treatment 

Maximum decrease not 

supported by earlier or 

later decreases. 

27 
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Chlorpyrifos/P. C. Code 05910 I Special RBC AChE Inhibition Study ( 1999) Humans 

(non-guideline) 

Subject# Symptoms or Events (a) RBC AChE Comments HED's Conclusion 

5 Subject implied excessive salivation Maximum decrease 8% at 96 No support from either 

(yes) was why he thought he received the hours. Other values 90 to the symptoms or AChE 

test material but there were no 108%. data to for subjects 

indications of excessive salivation 11 yes" response. 

listed in the events Table. 

9 Intestinal cramps. Starting 2 days Maximum decrease 17% at 96 Not related to treatment 

(no) 22 hours. Lasting 15 hrs. Unlikely hrs followed by 11%, 13% and since onset did not 

related to treatment. 9% at 120, 144 and 168 hours. coincide with AChE,!,. 

Other values Other values were 

87% to I 05% of predose. 

None have headaches. 

116 thought they received the chlorpyrifos. 

Note hour 96 had largest decrease in RBC AChE for all but one subject in this group suggesting some assay 

problem. Since it is hour 96, this should not confound the interpretation of the data. 

0.5 mglkg Chlorpyrifos-Females 

26 Nausea. Starting at I hr. Lasting 90 Maximum decrease 8% at 96, An initial localized 

(no) min. Probably related to treatment. 144 and 168 hrs. Other values nausea may result from 

are 93% to I 04%. an OP administration in 

a capsule without 

concomitant ,I, in 

AChE. Maximum ,l,in 

AChE does not 

coincide with 

symptoms. Not 

considered a definite 

response to 

chlorpyrifos. 

31 Headache (moderate). Starting I Maximum decrease 14% at 96 Onset of headache does 

(no) day and 3 hrs. Lasting -2 hrs. hrs. Other values were 90% to not coincide with 

Unlikely related to treatment. I 04% of predose. maximum ,J, in AChE 

occurring much later. 

Not related to 

treatment. 

36 Headache (mild), lightheaded, Maximum decrease 9% at 4 and Onset of headaches did 

(yes) headache (mild). Starting I hr or 6 96 hrs. Other values were 92% not coincide with 

hrs. Lasting -2 hrs or -11 hrs. to 106%. maximum ,!,in AChE. 

Possibly related to treatment. 

2/6 (33%) females had headaches. 

116 thought they received the chlorpyrifos. 

Maximum decrease in RBC AChE does not exceed the placebo group. 

28 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Subject# Symptoms or Events (a) RBC AChE Comments HED's Conclusion 

1.0 mglkg chlorpyrifos-Males 

I Increased appetite. Starting I day Maximum decrease 7% @ 48 Symptom not expected 

(yes) and 23 hrs. Lasting 4 days six hrs. hrs. Other values are 95% to of an OP exposure and 

Unlikely related to treatment. I I 3% of predose. does not coincide with 

maximum ,!, AChE. 

4 Loose stool. Starting 2 days and I 5- Maximum decrease I 5% @ 96 Symptoms do not 

(yes) 20 hrs and again on day 4 and I 2 hrs followed hy deceases of 8%, coincide with 

hrs. Lasting I min. Unlikely related 12% and 8% at 120, 144 and maximum ,!, in AChE. 

to treatment. I 68 hrs. Other values 90% to 

107%. 

7 No symptoms or events. Maximum decrease 16% at 96 No support for subjects 

(yes) hours. Other values are 9 I% to "yes" response. 

I 16%. 

I I Headache (moderate and mild). Maximum decrease 25% @ 96 First headache may be 

not listed Starting -3 hrs and again at- 23 hrs. hrs. Other values were 89% (at associated with -I I% 

Lasting - I 9 hrs and I day 9 hrs. 2hrs)to IOI%(at4hrs)of ,!, in AChE. Second 

Possibly related to treatment. predose. headache not 

associated with ,!, 

AChE or maximum 

decrease. 

14 Queasy stomach. Starting 24 min. Maximum decrease 15%@ 144 An initial unsettled 

(yes) Lasting I 0 min. hrs. Other values 88% to 99% (queasy) stomach may 

Possibly related to treatment. ofpredose. result from the capsule. 

Symptom does not 

coincide with ,!,AChE. 

I /6 has a headache. This is less than the placebo group and there is no indication that this subjects headache 

was more severe. 

4/6 thought they received the chlorpyrifos. 

The maximum decrease in this group was in an individual at 96 hrs postdosing. 

1.0 mg/kg Chlorpyrifos-Females 

24 Lost voice. Starting - I 8 hrs. Maximum decrease I I% @ I 68 Lost voice not an 

(no) Lasting 8 hrs. hrs. Other values 95% to I 05% expected response to an 

ofpredose. OP. Symptom does not 

coincide with,!, AChE. 

Not related to 

treatment. 

25 Tired. Starting -4 hrs. Lasting I Maximum decrease 9% @ 96 Symptom does not 

(yes) hrs. Possibly related to treatment. and I 20 hrs. Other values 92% coincide with 

to 102%. maximum ,!, ACHE. 

Not related to 

29 

4'1 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Subject# Symptoms or Events (a) RBC AChE Comments HED's Conclusion 

treatment. 

30 Headache (mild), tired and repeated Maximum decrease 8% @ 96 Onset and duration of 

(no) headaches (mild). Starting 22 min, hrs. Other values 95% to I 09% symptoms so not 

- 2hrs, - I 0 hrs and - 23 hrs. ofpredose/ coincide with J.AChE. 

lasting. Up to 8 days and 7 hrs. 

Possibly related to treatment. 

33 Headache (mild). Staring - 2hrs. Maximum decrease II% @ 144 Onset of symptom does 

(no) Lasting 4 hrs. Possibly related to hrs. Values from 96 hrs to 168 not coincide with 

treatment. hrs were 89% to 955. Other maximum of any J, in 

values were 97% to Ill%. AChE. 

35 Back stiffness. Starting 22 min. Maximum decrease 6%@ 168 Symptom not an 

(no) Lasting -4 hrs. hrs. Other values 94% to 115%. expected response to 

Unlikely related to treatment. OP treatment and does 

not coincide with 

maximum J, AChE. 

Not related to 

treatment. 

2/6 (33%) females had headaches. 

1/6 thought they received the chlorpyrifos. 

Maximum decrease does nor exceed placebo group for RBC AChE. 

2.0 mg/kg Chlorpyrifos-Males 

40 No symptoms or events. Maximum decrease 2% at 48 No support for subjects 

(yes) hrs. Other values 99% to I 03%. t!yes" response. 

47 Cut on chin. Starting 2 days. Maximum decrease 5% at 24 Not related to 

(no) Lasting 6 days. Unrelated to hrs. Other values 98% to I 07% treatment. 

treatment. ofpredose. 

None have headache. 

116 thought they received the chlorpyrifos. 

Maximum decrease in group was to 10% for one subject (#48 at 36 hours) and dose not exceed the placebo. 

2.0 mg/kg Chlorpyrifos-Females 

51 Headache (mild- moderate). Maximum decease 6% at 12 hrs. Onset of headache does 

(yes) Starting at 4 7 min and again at 3 hrs Other values were 95 to I 05% not coincide with 

7 min and lasting 2-7 hrs. of the predose. AChEJ.. Not related to 

Possibly/probably related to treatment. 

treatment. One can coca-cola. 

55 Headache (mild). Starting 3 hrs, Maximum decrease 5% at 120 Onset of headache does 

(no) lasting 19 hrs. Possibly related to hrs. Other values were 97 to not coincide with 

treatment. I 07% of predose. AChEJ.. 

30 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Subject# Symptoms or Events (a) RBC AChE Comments HED's Conclusion 

56 Numbness in upper arms. Starting Maximum decrease 28% at 12 See special discussion. 

not listed 42 min. Lasting 2 hrs and 24 min. hrs. ,J, starts at 8 hours Numbness does not 

Possibly related to treatment. (23%-J,), coincide with AChE ,J, 

58 No symptoms or events. Maximum decrease 7% at 12 No support for subjects 

(yes) hrs. Other values are 96% to uyes" response. 

101% 

59 Tired, headache (mild), chest Maximum decrease 7% at 12 First headache does not 

(yes) tightness, shortness of breath, hrs. Other values were 9 5% to coincide with ,J, AChE, 

headache. Starting - 2hrs, and I 0 104% ofpredose. the onset of the second 

hrs. Lasting 3-13 hrs. Possibly headache is two hours 

related to treatment. before maximum,J, in 

AChE but ,J, is only 

7%. HED does not 

conclude that the 

headache is treatment 

related. 

3/6 (50%) females had headaches. Severity of headache not greater than placebo subjects and onset does not 

coincide with AChE decrease. 

3/6 thought they received the chlorpyrifos. 

One subject has definite inhibition of RBC AChE based on sustained decrease at critical times. 

(a) Only those subjects havmg reports of symptoms, "events" or responded "yes" (column I) to 

the question if they thought they received the test material are listed. 

Symptom data are from Appendix 4. Under symptoms, the entry in italics refers to the study 

author's conclusion regarding whether or not the symptom was related to treatment was made 

before the subjects were identified as to their dose group. 

AChE data are from Table 5.1.2 for phase I and Table 9.1.2 for Phase II. 

31 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study ( 1999) Humans 

(non-guideline) 

Appendix II- List of Tables* 

Table A. Mean RBC Cholinesterase Activity (for all groups and all times). 

Table B. Serum Paraoxonase/CPOase and 0-hour RBC AChE Activity and Phenotype for dosed 

groups. 

Table C. Serum Paraoxonase/CPOase and 0-hour RBC AChE Activity and Phenotype for 

control groups. 

Table D. Male RBC AChE Activity, Blood TCP Level and CP Level for the Group Dosed with 2 

mg/kg. 

Table E. Female RBC AChE Activity, Blood TCP Level and CP Level for the Group Dosed 

with 2 mg/kg. 

Table F. Male RBC AChE Activity, Blood TCP Level and CP Level for the Group Dosed with I 

mg/kg. 

Table G. Female RBC AChE Activity, Blood TCP Level and CP Level for the Group Dosed 

with 1 mg/kg. 

Table H. Male and Female RBC AChE Activity and Blood TCP Level for the Group Dosed with 

0.5 mg/kg. 

Table I. Individual Male and Female RBC AChE Activity (Phase I Control). 

Table J. Individual Male and Female RBC AChE Activity (Phase 2 control) 

*Tables were prepared by Dr. L. Taylor, HED. 

32 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Table A. Mean RBC Cholinesterase Activity (U/L; mean± s.d.) 

Time/Dose (mg/kg) I oA o• I o.sA I LOA I z.o• 

Males 

-10 7520±733 9292±1130 8758±706 9317±790 8802±753 

0 8143±982 9171±1112 8998±730 9572±539 8608±896 

2 8023±795 9282±1026 9145±714 9568±427 8675±844 

4 7948±756 9145±1066 9046±623 9862±865 8642±924 

8 8008±645 9189±1101 9189±924 9524±352 8613±872 

12 8043±705 9198±1003 8848±663 9543±678 8584±806 

24 8036±815 9051±852 9046±817 9599±637 8637±878 

36 7674±556 8999±1020 8716±821 9295±626 8663±937 

48 7505±845 9042±904 8246±896 8694±669 8567±881 

72 7920±838 9425±1041 8974±810 9623±652 9004±840 

96 7421±745 9209±849 8036±738 8263±399 8815±868 

120 7536±694 9337±765 8571±691 8939±255 8807±904 

144 7316±598 9302±800 8764±837 8714±418 8857±907 

168 7770±734 9304±994 8527±764 8600±470 8793±562 

Females 

-10 8488±829 8485±373 8804±1068 8833±597 8503±939 

0 8619±861 8576±556 8612±1160 9165±709 8523±855 

2 8611±915 8444±494 8666±1194 9095±366 8395±855 

4 8762±902 8380±422 8412±1368 9396±517 8557±1181 

8 8817±884 8716±535 8547±1010 9060±528 8230±1274 

12 8404±696 8589±499 8334±917 8886±400 7761±1239 

24 8503±900 8510±667 8434±857 9053±241 8092±1191 

36 8089±829 8399±476 8244±1015 8617±379 8166±1100 

48 8349±735 8545±496 8459±1068 8895±641 8057±1202 

72 8551±583 8941±442 8938±1083 9181±477 8604±1064 

96 7795±759 8620±537 8147±1213 8508±791 8551±812 

120 8092±721 8712±507 8301±857 8466±612 8591±682 

144 8144±872 8428±727 8028±917 8462±714 8526±1111 

168 8036±876 8549±571 8!98±910 8366±499 8419±814 

A B Data from Tables 5.1.1 (pages 55-57) and 9.1.1 (pages 76-77) ofMRID 44811002; Phase I; Phase 2 

33 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Table B. Serum Paraoxonase/CPOase and 0-hour RBC AChE Activitv and Phenotvoe 

#/phenotype I CPOase (U!L) I Paraoxonase(U/L) RBC AChE CU/L) 

0.5 mg/kg ]range] 

3M (OR) 6850 706 8613 

5M (QQ) 8666 317 7942 

9M (QQ) 10446 417 8602 

12M (QOl 5412 250 9471 

15M (OR) 6871 745 9889 

18M (OR) 5412 562 9471 

7276±1963 (male) 500±204 (male) 8998±730 (male) 

19F (OR) 8073 595 7282 

22F (OR) 6994 717 9218 

26F (QQ) 8954 373 8602 

28F (OR) 8091 895 9900 

31F (QQ) 6671 261 9515 

36F (OR) 13341 1346 7156 

8687±2424 {female) 698±391 (female) 8612±1160 (female) 

mean±s.d. 7965±1536 {both) 599±315 {both) 

1.0 mg/kg ]range] 

IM(QQ) 6599 317 9108 

4M (RR) 8505 1479 9669 

7M (OR) 9008 984 9713 

llM(QQ) 7785 361 10098 

14M (QQ) 8774 367 10087 

16M (OR) 8325 834 8756 

8166±874 (male) 724±464 (male) 9572±539 {male) 

21F (QQ) 11615 467 9900 

24F (QQ) 7534 295 9757 

25F (QQ) 7426 339 9548 

30F (OR) 10141 923 9130 

33F (OR) 8019 1040 8140 

35F (OR) 7821 756 8514 

8754±1719 (female) 637±314 (female) 9165±709 {female) 

mean±s.d. 8463±1386 {both) 680±380 {both) 

2.0 me/kg r range] 

38M (OR) 13018 1234 8283 

40M (QQ) 8918 345 10021 

42M (OR) 7048 890 9372 

43M (OR) 9134 801 8118 

47M (QQ) 10213 456 7645 

48M (OR) 8199 823 8206 

9422±2051 (male) 758±320 (male) 8608±896 {male) 

49F (QQ) 9997 367 7766 

51F (OR) 10716 1234 7942 

55F (RR) 9422 1590 10076 

56F (QQ) 9278 367 8910 

58F (QQ) 10!41 389 8195 

59F (QQ) 8199 345 8250 

9626±871 {female) 715±551 {female) 8523±855 (female) 

rnean±s.d. 9523±1517 (both) 737±430 (both) 

pages 48-50, 55-57, and 76-77 (MRID 45144101), QQ (low); OR (m1d); RR (high) 

34 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (! 999) Humans 

(non-guideline) 

Table C. Serum Paraoxonase/CPOase and 0-hour RBC AChE Activitv {control) and Phenotype 

Subject# CPOase (units/L) I Paraoxonase (units/L) RBC AChE lUlL\ 

Control [ran•el 

2M (RR) 9565 1668 9196 

6M (OR) 5430 645 8921 

8M (OR) 6329 728 6809 

!OM (OR) 9350 882 7821 

13M (QQ) 7678 317 8833 

17M (QQ) 8001 311 7277 

mean±s.d. 7726±1632 (male) 558±500 (male) 8143±982 (male) 

20F (QQ) 10015 411A 8239 

23F IQQl 6329 284 8723 

27F (QQ) 8217 350 10208 

29F (OR) 9871 834 7865 

32F (QQ) 9817 434 8723 

34F (OR) 10410 1207 7953 

mean±s.d. 9110±1556 (female) 586±360 (female\ 8619±861 lfemale\ 

mean±s.d. 8418±1639 (both) 673±425 (both) 

Control [ ran2e! 

37M (OR) 9997 1001 9361 

39M IQQ) 15894 567 8569 

41M (QQ) 9206 378 9592 

44M (OR) 9709 1045 10835 

45M(OR) 11723 1112 7486 

46M (OR) 11363 1134 9185 

mean±s.d. 11315±2445 (male\ 872±319 I male\ 9171±1112 I male\ 

50F (QQ) 10141 423 8492 

52F (QQ) 10069 456 7744 

53F (OR) !4096 1134 8261 

54F (QQ) 6904 289 8602 

57F (RR) 17333 2502 9086 

60F (QQ) 9853 367 9273 

rnean±s.d. 11400±3700 (female) 862±860 (female) 8576±556 (female) 

mean±s.d. 11357±3097 (both) 867±618 (both) 

Pages 57 and 77 (MRID 44811 002); QQ (low); OR (mid); RR (high) 

35 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Table D. Male RBC AChE Activitv, Blood TCP Level, and CP Level 12.0 m•ik•l 

Subject# 38 40 42 43 I 47 48 

Hour AChE IU/Ll 

-10 9141 9680 9493 8041 7887 8569 

0 8283 10021 9372 8118 7645 8206 

2 8437 9922 9537 8206 7931 8019 

4 8360 10109 9471 7964 7942 8008 

8 9097 9856 9152 7942 7744 7887 

12 8800 9768 9130 8327 7788 7689 

24 8877 9790 9350 8228 7370 8206 

36 8998 9889 9405 8437 7700 7546 

48 8481 9636 9658 8129 7667 7832 

72 9372 9966 9834 8668 8107 8074 

96 8976 9966 9648 8690 7942 7766 

120 9108 10021 9592 8052 8305 7766 

144 8844 9955 9911 8569 7920 7942 

168 8734 9691 9174 8668 8305 8184 

Chlorpyrifos concentrations (112/2 in blood samples 

0 ND ND ND ND ND ND 

2 ND ND ND ND 3.1 ND 

4 ND ND ND ND 1.3 ND 

8 ND ND ND ND 3.4 ND 

12 ND ND ND ND 1.8 ND 

24 ND ND ND ND ND ND 

36 ND ND ND ND ND ND 

48 ND ND ND ND ND ND 

72 ND ND ND ND ND ND 

96 ND ND ND ND ND ND 

120 ND ND ND ND ND ND 

144 ND ND ND ND ND ND 

168 ND ND ND ND ND ND 

TCP concentrations lmz/2) in blood samnles 

0 ND ND ND ND ND ND 

2 420 61 44 230 580 180 

4 560 220 130 340 640 250 

8 510 320 230 330 790 240 

12 440 340 270 410 910 260 

24 430 340 ns 520 980 380 

36 500 360 360 610 960 460 

48 530 410 370 610 1000 470 

72 ++00 270 320 320 690 300 

96 290 170 220 190 460 210 

120 160 120 160 90 320 140 

144 85 75 96 66 220 77 

168 41 98 220 40 150 48 

Data from Tables 5 and 7 (pages 34 and 36) ofMRID 45144101; ns no sample; .. alw RE!t t·umi 

36 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Table E. Female RBC AChE Activity, Blood TCP Level and CP Level (2 mg/kg) 

Subiect # 49 I 51 I 55 I 56 I 58 I 59 

hours AChE U/L) 

-10 7832 8283 10373 8426 8041 8063 

0 7766 7942 10076 8910 8195 8250 

2 7700 7931 10032 8602 8041 8063 

4 7662 7997 10901 8525 8096 8162 

8 8008 7986 10582 6688 (25) 7931 8184 

12 7513 7640 10032 6221 (30) 7535 (8) 7623 (8) 

24 8008 7722 10131 6424 (28) 8107 8162 

36 8710 7700 10274 7051 (21) 8107 8052 

48 7568 7876 10395 6892 (23) 7821 7788 

72 7920 8195 10461 X 8503 7942 

96 7986 8415 9933 X 7931 8492 

120 8019 8569 9757 X 8228 8382 

144 7931 7975 10472 X 7832 8415 

168 8327 8074 9845 X 7876 7975 

Chlorpyrifos concentrations (nell:! in blood samples 

0 ND ND ND ND ND ND 

2 3.1 ND ND ND ND 2.2 

4 XX ND ND ND ND 4.1 

8 1.7 ND ND 18.0 ND 4.1 

12 ND ND ND 2.5 ND 1.5 

24 ND ND ND ND ND ND 

36 ND ND ND ND ND ND 

48 ND ND ND ND ND ND 

72 ND ND ND X ND ND 

96 ND ND ND X ND ND 

120 ND ND ND X ND ND 

144 ND ND ND X ND ND 

0168 ND ND ND X ND ND 

TCP concentrations (ng/g) in blood samples 

0 ND ND ND ND ND ND 

2 290 420 290 71 240 250 

4 450 580 220 120 310 470 

8 490 1300 520 1600 480 610 

12 440 690 500 1500 340 610 

24 470 540 600 1300 400 500 

36 430 750 600 1100 430 480 

48 360 730 530 980 360 390 

72 200 600 340 X 190 220 

96 130 420 210 X 110 110 

120 84 150 120 X 65 58 

144 52 170 73 X 37 32 

168 35 110 45 X 24 23 0 Data from Tables 5 and 7 (pages 34 and 36) ofMRID 45144101, (Yo mhibitiOn from 0 hour), xx sample not analyzed, X subject 

left study 

37 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Table F. Male RBC AChE Activity, Blood TCP Level and CP Level (1.0 ml!ik2l 

Subject# I I 4 7 II I 14 I 16 

AChE (U/ld_ 

-10 8272 9416 9603 10307 9823 8481 

0 9108 9669 9713 10098 10087 8756 

2 9625 9438 10230 9097 9845 9174 

4 9823 9405 11198 10318 9801 8624 

8 9284 9361 9834 9768 9878 9020 

12 9042 10219 10109 9779 9658 8448 

24 9306 10219 9966 9977 9658 8470 

36 9119 9702 9746 9768 9295 8140 

48 8074 8624 9196 9141 9174 7953 

72 9295 10164 9801 10153 9867 8459 

96 8283 8151 8096 noo U24) 8899 8448 

120 9218 8723 8800 9185 9086 8624 

144 8833 8426 9141 9218 8492 8173 

168 8228 8734 9174 - 8844 8019 

Chlorpyrifos concentrations (ng/g in blood samples 

0 ND ND ND Ns ND ND 

2 ND ND ND 1.0 ND ND 

4 ND ND ND I ND 2.7 ND 

8 ND ND ND ND !.5 ND 

12 ND ND ND ND ND ND 

24 ND ND ND ND ND ND 

36 ND ND ND ND ND ND 

48 ND ND ND ND ND ND 

72 ND ND ND ND ND ND 

96 ND ND ND ND ND ND 

120 ND ND ND ND ND ND 

144 ND ND ND ND ND ND 

168 ND ND ND Ns ND ND 

TCP concentrations (ne/g) in blood samples 

0 ND ND ND ND ND ND 

2 140 49 370 260 170 !50 

4 280 130 430 450 570 200 

8 340 290 440 400 610 170 

12 340 300 350 340 540 170 

24 440 250 270 270 520 200 

36 430 240 160 200 440 280 

48 310 230 140 160 420 300 

72 160 160 54 75 280 210 

96 84 98 23 36 220 130 

120 41 54 10 20 !50 84 

144 18 34 ND ND 84 48 

168 II 20 ND Ns 50 29 

Data from page 56 of 578 and Tables 5 and 7 (pages 34 and 36) ofMR!D 451441 0 I, ns no sample, 

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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study ( 1999) Humans 

(non-guideline) 

II 

Table G. Female RBC AChE Activitv, Blood TCP Level and CP Level (l.O m2ik2l 

Subiect # I 21 I 24 I 25 30 I 33 35 

AChE (U/Ll 

-10 9416 9295 9031 9064 7942 8250 

0 9900 9757 9548 9130 8140 8514 

2 9460 9460 9240 8932 8965 8514 

4 10087 9999 9152 9229 8866 9042 

8 9394 9570 9427 9119 8624 8228 

12 9361 9350 8855 8822 8470 8459 

24 9317 9097 9339 8943 8877 8745 

36 8789 9218 8624 8536 8074 8459 

48 9361 9604 9174 8998 7766 8569 

72 9064 9240 9460 9900 8503 8921 

96 8637 8844 8437 8349 7178 9603 

120 8954 9086 8426 8855 7601 7876 

144 8932 9207 8580 8613 7156 8283 

168 8624 8525 8855 8712 7678 7799 

Chlorpyrifos concentrations (ng/~ in blood samples 

0 ND ND ND ND ND ND 

2 5.6 ND ND ND ND ND 

4 2.9 ND ND ND 2ND ND 

8 ND ND ND 1.1 IND ND 

12 ND ND NO NO NO ND 

24 ND ND NO ND NO NO 

36 NO ND NO ND NO NO 

48 ND ND ND NO ND ND 

72 NO ND ND NO NO NO 

96 NO NO NO NO NO ND 

120 NO ND ND ND NO NO 

144 NO ND ND ND NO NO 

168 NO ND ND ND ND NO 

TCP concentrations {nl!l!!) in blood samoles 

0 NO ND ND NO ND NO 

2 220 96 160 10 32 72 

4 350 430 180 160 93 250 

8 310 340 190 310 100 490 

12 300 310 190 290 110 430 

24 300 320 220 290 140 370 

36 290 320 200 280 140 310 

48 280 300 160 280 110 350 

72 140 250 85 240 70 190 

96 75 180 30 160 45 140 

120 43 120 16 85 29 99 

144 22 73 NO 45 17 75 

168 13 47 NO 23 13 30 

Data from page 56 of578 and Tables 5 and 7 (pages 34 and 36) ofMRID 45144101; ns no sample; 

39 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Table H. Male and Female RBC AChE Activity and Blood TCP Level (0.5 m2/k2) 

Subject# I 3 5 9 I 12 I 15 18 

MALES AChE (U/L) 

-10 8393 7865 8294 8877 9713 9405 

0 8613 7942 8602 9471 9889 9471 

2 8668 8547 8437 9218 10021 9977 

4 8514 8481 8646 9031 9944 9658 

8 8228 8217 8844 9482 9845 10516 

12 8118 8030 8723 9229 9471 9515 

24 8393 8074 8580 9394 9680 10153 

36 7997 7810 8261 8910 9670 9746 

48 7244 7128 8107 9053 9119 8822 

72 8426 8074 8260 9504 9889 9702 

96 8558 7282 6985(tl9) 8096 8525 8767 

120 8679 7920 7535 Ul2) 8921 9207 9163 

144 8283 8712 7376 (tl4) 9537 9548 9130 

168 8107 7931 7700(Pll 8547 9295 9581 

MALES TCP concentrations (ne:/ !) in blood samples 

0 ND ND ND ND ND ND 

2 23 49 24 29 160 51 

4 95 53 140 83 250 100 

8 97 51 130 96 240 130 

12 96 130 240 97 210 130 

24 130 98 130 100 190 120 

36 140 100 130 110 190 llO 

48 140 100 120 110 190 110 

72 87 59 70 96 130 73 

96 58 24 41 67 88 48 

120 38 8 25 38 56 29 

144 22 ND 14 19+ 33 IS 

168 14 ND 10 ND 23 9 

Subject# 19 22 26 28 31 36 

FEMALES AChE ( /L) 

-10 9724 9086 8063 10010 8800 7139 

0 7282 9218 8602 9900 9515 7156 

2 7986 8932 8448 10252 9526 6853 

4 7810 9141 8239 10593 8239 6501 

8 8041 9097 8305 9966 8866 7007 

12 7843 8349 8437 9779 8602 6996 

24 7832 8866 8041 9746 8756 7365 

36 7535 8987 7810 9834 8228 7068 

48 7623 8921 8129 10109 8855 7117 

72 7953 9394 8701 10516 9482 7579 

96 7997 8646 7689 10153 7920 6474 

120 7931 8437 7975 9581 8811 7073 

144 7689 8195 7744 9218 8734 6589 

168 7744 8657 7733 9130 9086 6837 

FEMALES TCP concentrations (n ~/g) in blood sam les 

0 ND ND ND ND ND ND 

2 110 190 12 61 77 62 

4 190 380 89 91 120 220 

8 210 350 110 140 220 260 

12 ND 310 110 130 230 230 

24 189 220 130 140 210 220 

36 179 ISO 190 110 200 230 

48 180 140 180 91 190 230 

72 110 59 160 46 130 150 

96 88 31 140 25 64 83 

40 
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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

120 58 17 120 14 41 49 

144 35 ND 107 ND 22 27 

168 23 ND 88 ND 14 19 

Data from Tables 5 and 7 (pages 34 and 36) of MRJD 4514410 I 

41 
EPA's Records Disposition Schedule PEST 361 Scientific Data Reviews HED Records Center- File R180234- Page 71 of 73 

Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study (1999) Humans 

(non-guideline) 

Table I. Male and Female RBC AChE Activity (Phase I control) 

Subject# I 2 I 6 I 8 I 10 I 13 I 17 

MALES AChE (U/L) 

-10 8294 7810 6562 8327 6985 7139 

0 9196 8921 6809 7821 8833 7277 

2 8910 8558 6782 8019 8448 7420 

4 8382 8580 6622 8118 8481 7502 

8 8239 8701 6886 7986 8481 7755 

12 8360 8635 6886 7876 8789 7711 

24 8734 8723 6655 8426 8173 7502 

36 8448 7700 6864 8052 7689 7288 

48 7711 7964 6083 7678 8536 7057 

72 8569 8921 6672 7920 8195 7244 

96 8151 7536 6336 6771 8206 7524 

120 8404 7799 6457 7321 8041 7194 

144 7810 7733 6281 7134 7799 7139 

168 8206 8778 6677 7623 8019 7315 

Subject# 20 23 27 29 32 34 

FEMALES AChE (U/L) 

-10 7178 8481 9724 8382 8294 8866 

0 8239 8723 10208 7865 8723 7953 

2 7568 9053 10010 8382 8932 7722 

4 7953 9504 10076 8426 8855 7755 

8 8239 9174 10373 8701 8569 7843 

12 7898 8657 9713 8118 8085 7953 

24 7645 8844 10098 8195 8481 7755 

36 7249 8712 9284 7843 8261 7183 

48 7931 8800 9603 8184 8008 7568 

72 7843 8789 9416 8437 8822 7997 

96 7415 8272 8800 7073 8305 7002 

120 7513 8360 9053 8283 - 7249 

144 7722 7975 9570 8206 - 7249 

168 7689 8437 9317 7722 - 7013 

Data from Table 5.1.1 (pages 57) ofMRJD 44811002 

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Chlorpyrifos/P. C. Code 059101 Special RBC AChE Inhibition Study ( 1999) Humans 

(non-guideline) 

Table J. Male and Female RBC AChE Activity (Phase 2 control) 

Subject# 37 39 I 41 I 44 I 45 I 46 

MALES AChE (U/L) 

-10 9878 8910 9240 10769 7387 9570 

0 9361 8569 9592 10835 7486 9185 

2 9394 8723 10197 10681 7898 8800 

4 9757 8470 9240 10703 7590 9108 

8 10318 8382 8998 10494 7645 9295 

12 9999 8723 8998 10164 7613 9790 

24 9680 8547 8789 10197 7810 9284 

36 9669 8294 8910 10318 7453 9350 

48 9713 8481 9119 10208 7645 9086 

72 9482 8657 9394 10923 7975 10120 

96 9306 8778 9460 10329 7810 9570 

120 9427 8976 9504 10406 8096 9614 

144 9416 8811 9174 9691 8184 10538 

168 9823 8437 9548 10802 8041 9174 

Sub.iect # 50 52 53 54 57 60 

FEMALES AChE (UIL) 

-10 8107 7975 8712 8470 8734 8910 

0 8492 7744 8261 8602 9086 9273 

2 8327 7623 8547 8294 9020 8855 

4 8239 7645 8349 8558 8866 8624 

8 8415 7865 9031 8558 9218 9207 

12 8404 7854 8723 8327 8987 9240 

24 8415 7293 8756 8437 9174 8987 

36 8063 7810 8470 8228 8668 9152 

48 8184 7854 8844 8327 8954 9108 

72 9108 8096 9273 9108 9229 8833 

96 8426 7623 8811 9108 8899 8855 

120 8965 7810 8569 8646 9229 9053 

144 7337 7854 9339 8415 8778 8844 

168 8382 7634 8591 8382 9086 9218 

Data from Table 9.1.1 (pages 77) of MRID 44811002 

43 
EPA's Records Disposition Sctredute;>EST361 Scie"lilie Oala Reviews- HEO Rooo•~• ~oolor l'ilo R1B0234 .9age .. Z3 .of .. 73.--. 

• ~ 13544 

• 

R180234 

Chemical Name: Chlorpyrifos 

PC Code: 059101 

HED File Code: 

Memo Date: 

File ID: 

Accession #: 

14000 Risk Reviews 

1/7/2010 

00000000 

000-00-0134 

HED Records Reference Center 

1/13/2010 

• 

•