NIOSH HEALTH HAZARD EVALUATION REPORT 

HETA #2002-0203-3050 

The United States Department of Agriculture, 

Animal and Plant Health Inspection Service 

Laredo, Texas 

November 2007 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health
ii 

PREFACE

The Hazard Evaluation and Technical Assistance Branch (HETAB) of the National Institute for 

Occupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in the 

workplace. These investigations are conducted under the authority of Section 20(a)(6) of the Occupational 

Safety and Health (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary of Health and 

Human Services, following a written request from any employers or authorized representative of 

employees, to determine whether any substance normally found in the place of employment has 

potentially toxic effects in such concentrations as used or found. 

HETAB also provides, upon request, technical and consultative assistance to federal, state, and local 

agencies; labor; industry; and other groups or individuals to control occupational health hazards and to 

prevent related trauma and disease. Mention of company names or products does not constitute 

endorsement by NIOSH. 

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT

This report was prepared by Gregory A. Thomas, Lisa J. Delaney, Elena Page, and Charles Mueller of 

HETAB, Division of Surveillance, Hazard Evaluations and Field Studies (DSHEFS). Field assistance was 

provided by Chad Dowell, Kevin Dunn, Max Kiefer, Deborah Sammons, and Barbara MacKenzie. 

Analytical support was provided by Deborah Sammons, Cynthia Striley, and John Snawder of the 

Division of Applied Research Technology (DART), DataChem Laboratories, Salt Lake City, Utah, and 

Pacific Toxicology Laboratories, Chatsworth, California. Desktop publishing was performed by Robin 

Smith. Editorial assistance was provided by Ellen Galloway. 

Copies of this report have been sent to employee and management representatives at the USDA Tick 

Eradication Program and the OSHA Regional Office. This report is not copyrighted and may be freely 

reproduced. The report may be viewed and printed from the following internet address: 

http://www.cdc.gov/niosh/hhe. Copies may be purchased from the National Technical Information 

Service (NTIS) at 5825 Port Royal Road, Springfield, Virginia 22161. 

For the purpose of informing affected employees, copies of this report 

shall be posted by the employer in a prominent place accessible to the 

employees for a period of 30 calendar days.
Highlights of Health Hazard Evaluation 

Highlights of the NIOSH Health Hazard Evaluation

On March 22, 2002, NIOSH received a request for a health hazard evaluation (HHE) from the

Animal and Plant Health Inspection Service (APHIS), a division of the United States Department of

Agriculture (USDA). The request was to determine if the cholinesterase monitoring program for

animal health technicians was useful and to determine the feasibility of using field kit measurements

of cholinesterase and urinary biomarkers of exposure. The primary organophosphate pesticide used 

was coumaphos. NIOSH conducted investigations in 2002 and 2005. 

What NIOSH Did

 We observed the technicians doing their 

jobs. 

 We asked technicians questions about 

coumaphos application history, health 

symptoms, general medical information, 

and use of personal protective equipment 

(PPE). 

 We measured cholinesterase levels in 

blood before and after coumaphos use two

ways – in a laboratory and with a field test 

kit. 

 We measured urinary chlorferon (a 

metabolite of coumaphos) before and after

coumaphos use. 

 We took air samples for coumaphos in the

breathing zone of the technicians. 

 We tested clothing and hands of

technicians for coumaphos. 

What NIOSH Found

 use varied by

 ds, and on the clothing of 

most workers. 

We found that PPE

technician. 

 We did not find coumaphos in the air.

We found coumaphos on almost every

technician’s han

 Cholinesterase levels were within the 

normal range and correlated well between 

the two methods of testing. 

 Urinary chlorferon levels rose 

significantly after application of 

coumaphos. 

What USDA Managers Can Do

 Determine the appropriate PPE for the

tasks performed by the animal health 

technicians and enforce its use. 

 Consider discontinuing respirator use. If 

use is continued, establish a 

comprehensive respiratory protection 

program in accordance with the OSHA

respiratory protection standard. 

 Determine if urinary chlorferon can be

used to monitor exposure to coumaphos. 

 Continue cholinesterase monitoring, and

consider use of field test kits. 

What USDA Employees Can Do 

 opriate PPE when applying 

pesticides. 

Wear appr

What To Do For More Information:

We encourage you to read the full report. If you 

would like a copy, either ask your health and 

safety representative to make you a copy or call 

1-513-841-4252 and ask for 

HETA Report #2002-0203-3050

iii 
Health Hazard Evaluation Report 2002-0203-3050 

The United States Department of Agriculture, 

Animal and Plant Health Inspection Service 

Laredo, Texas 

November 2007 

Gregory A. Thomas, M.D., M.S. 

Lisa J. Delaney, M.S., C.I.H. 

Elena Page, M.D., M.P.H. 

Charles Mueller, M.S. 

SUMMARY

On March 22, 2002, NIOSH received a request for a health hazard evaluation (HHE) from the Animal

and Plant Health Inspection Service (APHIS), a division of the United States Department of Agriculture 

(USDA). The medical officer for APHIS was interested in determining if the current cholinesterase

monitoring program for its animal health technicians in the tick eradication program was useful. In

addition, APHIS had an interest in evaluating other methods for monitoring organophosphate (OP) 

exposure, including field test kit measurements of cholinesterase and urinary biomarkers. The primary OP 

used was coumaphos. 

NIOSH investigators observed various coumaphos application tasks and administered questionnaires 

concerning coumaphos application history, health symptoms, and general medical information. Blood was 

collected by venipuncture for laboratory cholinesterase measurements using the Ellman method, and by

fingerstick for cholinesterase measurements by field test kit at the start of the workday (prior to use of 

coumaphos) and again at the end of the workday. Urine was collected for measurement of a possible 

urinary biomarker of coumaphos, 3-chloro-4-methyl coumarin (chlorferon), at the same times. An 

additional urine sample was obtained the following day. Environmental sampling included personal air 

sampling, patch sampling on the surface of employees’ clothing, and skin wipe sampling of hands. These 

were conducted at the end of one or more coumaphos application tasks. 

All of the APHIS animal health technicians who met our criteria for participation agreed to participate in 

the evaluation, but only 15/59 met the criteria. Participants reported mixing coumaphos 8.5 days per 

month and spraying or dipping livestock 11 days per month, on average. Three reported being removed

from working with coumaphos (one time each) in the past year due to low cholinesterase levels.

Technicians were asked about symptoms consistent with OP poisoning experienced within 6 hours of

coumaphos use in the past 3 months. Two each reported headache, weakness, and tearing eyes; and one 

each reported cough and nervousness. Reported personal protective equipment (PPE) use varied by task 

and type of PPE. 

iv 
v 

None of the technicians had plasma cholinesterase (PChE) or acetylcholinesterase (AChE) levels outside 

the laboratory’s range of normal. Neither PChE nor AChE changed significantly from pre- to post-shift 

with the Ellman method or the field test kit. A significant positive correlation was found between PChE 

levels measured with the field test kit and by the Ellman method (r=0.92, p<0.01). A significant positive 

correlation was also found between AChE levels measured by the two different methods (r=0.63, p<0.01). 

Chlorferon was detected in the urine of all animal health technicians after they used coumaphos. Urinary 

chlorferon levels were significantly higher 4-6 hours after use (p<0.01) and declined significantly by the 

next day (p=0.01). No coumaphos was detected in 8 of 9 personal breathing zone air samples. One 

showed trace amounts of coumaphos and represented a worst case scenario. The technician sprayed 

horses and dipped cattle for the entire day. Of the whole body patch samples, 58% detected measurable 

levels of coumaphos. Of handwipe sampling, 96% detected measurable amounts of coumaphos, 

indicating that the majority of exposures occur from hand contact with the pesticide. 

A formal PPE program was not in place. No standard guidance for what type of PPE should be worn 

during specific tasks was available and use of PPE varied by employee. PPE was poorly maintained and 

dirty. Employees were observed incorrectly wearing respiratory protection. 

A health hazard from dermal exposure to coumaphos existed for USDA APHIS animal 

health technicians. An inhalation hazard to the pesticide did not exist at the time of the 

NIOSH evaluation. Instituting a formal PPE program and requiring the use of PPE such 

as gloves and aprons during specific work tasks would lower dermal exposures. 

Keywords: NAICS 926140 (Regulation of Agricultural Marketing and Commodities), organophosphates, 

coumaphos, chlorferon, cholinesterase, chlorpyrifos, personal protective equipment. 
Table of Contents 

Preface..........................................................................................................................................................ii

Acknowledgments and Availability of Report..........................................................................................ii

Highlights of Health Hazard Evaluation .................................................................................................iii

Summary.....................................................................................................................................................iv

Introduction.................................................................................................................................................1

Background .................................................................................................................................................1

Methods........................................................................................................................................................2

Questionnaire ..........................................................................................................................................2

Biological Samples ..................................................................................................................................2

Blood ....................................................................................................................................................2

Urine.....................................................................................................................................................3

Environmental Sampling........................................................................................................................3

Bulk Samples .......................................................................................................................................3

Skin Exposure Assessment .................................................................................................................4

Surface Sampling ................................................................................................................................4

Air Samples..........................................................................................................................................4

Statistical Analysis ..................................................................................................................................4

Evaluation Criteria .....................................................................................................................................4

Pesticides..................................................................................................................................................5

Results ..........................................................................................................................................................7

Biological Monitoring .............................................................................................................................8

Blood ....................................................................................................................................................8

Urine.....................................................................................................................................................8

Environmental Sampling........................................................................................................................8

Whole Body Wipe Results ..................................................................................................................8

Hand Wipe Results .............................................................................................................................8

Surface Wipe Results..........................................................................................................................9

Air Sampling Results ..........................................................................................................................9

Workplace Observations ....................................................................................................................9

Discussion and Conclusions .....................................................................................................................10

Recommendations.....................................................................................................................................11

References..................................................................................................................................................13

Tables .........................................................................................................................................................16
Health Hazard Evaluation Report No. 2002-0203-3050 Page 1 

INTRODUCTION

On March 22, 2002, NIOSH received a request 

for a health hazard evaluation (HHE) from the 

Animal and Plant Health Inspection Service 

(APHIS), a division of the United States 

Department of Agriculture (USDA). The 

medical officer for APHIS was interested in 

determining if the current cholinesterase 

monitoring program for its animal health 

technicians working in the tick eradication 

program was useful. In addition, APHIS had an 

interest in evaluating other methods for 

monitoring organophosphate (OP) exposure, 

including field test kit measurements of 

cholinesterase and possible measurement of 

urinary biomarkers of exposure. APHIS thought 

these alternative monitoring methods may be 

more convenient considering the erratic use of 

OP pesticides by APHIS employees, and the 

remote locations and harsh conditions under 

which they worked. The primary OP used was 

coumaphos. 

In 2002, NIOSH staff made an initial site visit to 

the Laredo, Texas, location of the APHIS field 

office for the tick eradication program to learn 

more about the program. During that visit, 

various coumaphos application tasks were 

observed and photographed. On September 13, 

2005, NIOSH staff returned to carry out a field 

investigation. An opening conference included 

Webb County APHIS employees, the APHIS 

field director, and the local union representative. 

Employees were represented by the American 

Federation of Government Employees Union, 

Local 3106. During this visit NIOSH staff 

administered questionnaires concerning 

coumaphos application history, health 

symptoms, and general medical information. 

Blood was collected by venipuncture for 

standard laboratory cholinesterase 

measurements, and by fingerstick for 

cholinesterase measurements by field test kit at 

the start of the workday (prior to use of 

coumaphos) and again at the end of the 

workday. Urine was collected for measurement 

of a possible urinary biomarker of coumaphos, 

3-chloro-4-methyl coumarin (chlorferon) at the 

same times. An additional urinary collection was 

obtained the following day. Technicians were 

informed by letter of the results of their 

individual testing. The NIOSH industrial 

hygienists observed the coumaphos application 

tasks and conducted environmental sampling for 

coumaphos. The sampling included individual 

air sampling, patch sampling on the surface of 

clothing of employees and skin wipe sampling 

of hands. Sampling was conducted at the end of 

one or more coumaphos application tasks. 

BACKGROUND

The U.S. initiated a tick eradication program in 

1906 to control cattle fever, a disease that has 

historically decimated livestock populations. 

The program, managed by the USDA APHIS, 

successfully eradicated cattle fever ticks from 

the U.S. by 1961. However, 50% of cattle in 

Mexico are infested with the cattle fever tick, 

and many of these animals migrate across the 

border into the U.S. The migration of Mexican 

cattle produces sporadic infestations in U.S. 

livestock along the Texas border. To control 

these infestations, the USDA APHIS maintains a 

quarantine buffer zone along the Texas border 

with Mexico. Animal health technicians (“tick 

riders”) are employees of the USDA APHIS 

who patrol and inspect cattle in and around the 

quarantine zone. Cattle found to carry the cattle 

fever tick are treated over periods of weeks to 

months with coumaphos, an OP pesticide. 

The USDA APHIS employs 59 animal health 

technicians who typically work alone in rugged 

remote terrain, often on horseback. They apply 

coumaphos to cattle by using fixed or portable 

dipping vats that require the cattle to fully 

submerge in the OP mixture. They also utilize a 

single-cattle spray booth that sprays coumaphos 

on cattle. They hand spray their own horses and 

cattle, on a limited basis, by using low pressure 

spray wands. The technicians mix and dilute the 

coumaphos solution. Animal health technicians 

typically perform no more than one scheduled 

spraying or dipping operation per day. 

Technicians also conduct physical inspections of 

the cattle by touching areas of the cattle where 

ticks most likely attach. This activity is 
Page 2 Health Hazard Evaluation Report No. 2002-0203-3050 

commonly referred to as “scratching.” These 

operations begin in the morning and, depending 

on the total herd size, may last until early 

afternoon. In addition, the animal health 

technicians spray chlorpyrifos to disinfect 

infested materials in trailers, corrals, and barns. 

This occurs infrequently. 

Each technician is issued personal protective 

equipment (PPE) including a half-facepiece 

respirator (Willson AR 700 or Norton 7500) and 

full-facepiece respirator (3M 6892) with 

particulate filter and organic vapor cartridges; 

apron; neoprene elbow length gloves; rain coat 

and pants; and rubber boots. They are required 

to wear goggles and rubber gloves when 

applying coumaphos. At their own discretion, 

the technicians wear a respirator equipped with 

dual high efficiency and organic vapor 

cartridges when spraying coumaphos in windy 

conditions. 

For many years, the USDA APHIS has 

maintained a coumaphos exposure monitoring 

program for the animal health technicians. This 

program consists of establishing baseline red 

blood cell or erythrocyte acetylcholinesterase 

(AChE) and plasma cholinesterase (PChE) 

levels, and performing follow-up cholinesterase 

testing every 60 days regardless of exposure. 

The only exception is immediate testing after 

any large unintentional exposure (e.g., a spill). 

All cholinesterase test results are reviewed by a 

Federal Occupational Health physician. 

Technicians whose cholinesterase levels are less 

than 75% of baseline are removed from working 

with coumaphos. These workers are retested in 

30 days; if the cholinesterase levels increase to 

over 75% of baseline, the workers are allowed to 

return to work. Due to changes in laboratories, 

the current program does not compare 

cholinesterase levels to true baseline values but, 

instead, to a mathematically calculated baseline. 

Typically, two or three technicians are “flagged” 

each testing period due to low cholinesterase 

levels. However, according to the requestor, 

these do not always appear to be temporally 

related to high usage periods. 

METHODS

Only those APHIS animal health technicians 

scheduled to spray horses, dip cattle, or mix 

coumaphos during our site visit were recruited 

for this HHE. Recruitment was also limited to 

employees applying coumaphos within a oneday round-trip travel distance from Laredo. 

Participants were asked to undergo both pre- and 

post-shift blood and urine testing. The Webb 

County APHIS field office in Laredo, Texas, 

was the principal site for processing and storing 

of biological samples, administrating of some of 

the questionnaires, and collecting some of the 

biological samples. The remainder of the 

questionnaire administration and biological 

sampling, along with environmental sampling, 

was conducted at various ranches in the 

quarantine zone within driving distance of the 

field office. Each technician gave informed 

consent prior to participation. Employees were 

notified of their blood and urine test results by 

letter. 

Questionnaire 

All participants were given a self-administered 

questionnaire prior to their shift. The 

questionnaire was reviewed by NIOSH 

researchers in the presence of the participant. 

The questionnaire included questions concerning 

the participants’ coumaphos application history, 

the presence of symptoms related to past 

coumaphos exposure, and general medical 

history information. 

Biological Samples 

Blood 

Pre-shift blood sampling for cholinesterase 

activity was performed in the morning, 

immediately prior to coumaphos application. 

Post-shift blood sampling for cholinesterase 

activity was performed 4-6 hours after 

coumaphos application. 

Blood sampling and testing used the following 

protocol: 
Health Hazard Evaluation Report No. 2002-0203-3050 Page 3 

A. The venipuncture site was thoroughly 

cleansed. Using a 21-gauge needle, 

approximately 5 milliliters (mL) of whole blood 

was collected into an ethylenediamine tetraacetic 

acid (EDTA) tube and 5 mL into a red-top tube. 

Red-top tube blood was allowed to clot, then 

was spun down in a centrifuge to separate the 

serum. Both serum and whole blood (EDTA 

tube) were labeled and refrigerated at 1°C-4°C 

until cold-packed for shipment to the Pacific 

Toxicology Laboratory. Samples were delivered 

and tested within 48 hours of sampling. Pacific 

Toxicology Laboratory is one of a limited 

number of laboratories that has had its 

cholinesterase assay reviewed and compared 

with known standards at the University of 

California Davis reference laboratory. PChE and 

AChE levels were determined using the Ellman 

method. 

B. A fingertip was thoroughly cleansed. 

Using a lancet, 10 microliters of blood was 

collected into the EQM Test-Mate® ChE 

Cholinesterase Test System (Model 400) (EQM 

Research, Inc., Cincinnati, Ohio) assay tube. The 

blood sample was refrigerated and taken to the 

APHIS field office where it was analyzed by 

NIOSH personnel under controlled thermal 

conditions (approximately 25°C). Both PChE 

and AChE were measured. 

Urine 

Pre-shift urine sampling for chlorferon was 

performed in the morning, before the technicians 

used coumaphos. Post-shift urine sampling 

occurred 4-6 hours after they used coumaphos. 

Due to the limited data available concerning 

chlorferon excretory kinetics, a second postapplication urine collection for chlorferon was 

obtained the following morning prior to the next 

workshift. 

The following protocol was used for urine 

collection. Participants submitted samples in 

urine collection containers. Urine was subjected 

to enzymatic (beta-glucuronidase and sulfatase) 

hydrolysis to determine the presence of 

chlorferon (Hawks Scientific, Cheshire, UK). 

Urine testing was performed by the NIOSH 

Division of Applied Research Technology 

laboratory. Chlorferon-glucuronide excreted in 

urine was converted to free chorferon via 

incubation with β-glucuronidase. Solid phase 

C18 extraction with acetonitrile was used prior 

to analysis by using high performance liquid 

chromatography (HPLC) with fluorescence 

detection (355 nm excitation; 460 nm emission). 

Recovery of chlorferon spiked urine was near 

100% over a range of 0.5-500 parts per billion 

(ppb). The chromatographic method used a 

Zorbax C18-RX column with isocratic elution of 

65% acetonitrile and 35% water (water buffered 

with 0.05 molar sodium phosphate, pH=7) at a 

rate of 0.8 mL/minute. A limit of detection 

(LOD) of 0.5 ppb and limit of quantification 

(LOQ) of 1.5 ppb was based on average values 

of instrumental baseline noise and the lowest 

standard that could be reliably measured. The 

lowest calibrator used for these analyses was 2 

ppb, thus, the method LOQ was 2 ppb. Urine 

from 5 unexposed subjects (NIOSH personnel) 

was analyzed to confirm that no chlorferon was 

present. This urine was then pooled and used to 

prepare all spiked urines and calibrators.

Environmental Sampling 

During the initial site visit and subsequent 

telephone conversations with management, the 

coumaphos application activities with the 

highest potential for exposure were identified. 

On September 13-15, 2005, environmental and 

biological monitoring was conducted on 

employees applying coumaphos by horse 

spraying, article spraying, cattle dipping, and 

cattle spraying in the spray box. Due to the 

nature of the tick eradication program, NIOSH 

investigators were unable to conduct sampling 

for every application scenario. However, they 

sampled during the most routine application 

scenarios. Technicians were not observed 

applying chlorpyrifos on the days of sampling. 

The monitoring methodologies are described 

below. 

Bulk Samples 

Bulk samples of the coumaphos mixture in the 

dipping vat were collected. These samples were 

analyzed to identify potential interfering 

compounds that may be detected on the wipe 

samples. The concentration of the coumpahos 
Page 4 Health Hazard Evaluation Report No. 2002-0203-3050 

mixture in the dipping vats was analyzed by the 

USDA APHIS labs after each dip event to verify 

that the concentration was at acceptable levels. 

Skin Exposure Assessment 

Polyester AlphaWipes® (4 inch x 4 inch) were 

used to assess the potential for skin contact to 

coumaphos and chlorpyrifos during tick 

eradication activities. All wipe samples were 

shipped to the NIOSH contract laboratory 

(DataChem, Salt Lake City, Utah) and analyzed 

by gas chromatography according to NIOSH 

Manual of Analytic Methods Method 9107.1

Whole Body Sampling 

AlphaWipes® were loaded on pre-cut cardboard 

holders and pinned to the outside of the 

technicians’ clothing and under aprons if worn. 

Technicians wore the patches in five locations: 

upper right arm, upper left arm, chest, right 

thigh, and left thigh. Patches were worn during 

coumaphos application activities, which 

typically did not involve an entire workshift. 

Twelve technicians were monitored during the 

evaluation. NIOSH investigators wore a new 

pair of nitrile gloves when handling each sample 

to prevent cross contamination. After sampling, 

each wipe was placed in a vial and stored at 4°C. 

Hand Wipe Sampling 

Hand wipe sampling was conducted at the end 

of the workshift to assess hand exposures to 

coumaphos. AlphaWipes® were pre-moistened 

with 3 mL of 99% reagent-grade isopropanol 

prior to conducting the hand wipe. One wipe 

was used for each hand. The hand and fingers 

were wiped thoroughly. Thirteen technicians’ 

hands were wiped. One technician’s hands were 

wiped twice in one day: before lunch and at the 

end of his work shift. NIOSH investigators wore 

a new pair of nitrile gloves when handling each 

sample to prevent cross contamination. After 

sampling, each wipe was placed in a vial and 

stored at 4°C. 

Surface Sampling 

AlphaWipes® were used to conduct surface 

sampling of respirators. Two wipe samples were 

collected on the surface of the interior of a 

technician’s respirator to determine the presence 

of coumaphos. The wipes were pre-moistened 

with 3 mL of 99% reagent-grade isopropanol 

prior to surface sampling. After sampling, each 

wipe was placed in a vial and stored at 4°C. 

Air Samples 

Personal breathing zone air samples were 

collected on OSHA Versatile Sampler-2 (OVS2) sorbent tubes using SKC® AirChek® 2000 

sampling pumps. Flow rates of 1 liter per minute 

were used to obtain the samples. The sampling 

pumps were calibrated before and after each 

sampling event against a primary standard 

(BIOS® Dry-Cal) to verify flow rate. The filters 

were placed as close as possible to the workers’ 

breathing zone and connected via Tygon® 

tubing to the sampling pump. After collection, 

the samples were sent to the NIOSH contract 

laboratory (DataChem, Salt Lake City, Utah) 

and analyzed by gas chromatography according 

to NIOSH Method 5600 with modifications 

using an electron capture detector.

Statistical Analysis 

SAS Version 9.1.3 software (SAS Institute, 

Cary, North Carolina) was used for the statistical 

analyses. The Pearson’s correlation coefficient 

between AChE determined by the Ellman 

method and AChE by the EQM Test-Mate® 

ChE Cholinesterase Test System (Model 400) 

was calculated. The Pearson’s correlation 

coefficient between PChE determined by the 

Ellman method and PChE by the EQM TestMate® ChE Cholinesterase Test System (Model 

400) was also calculated. The difference 

between pre- and post-cholinesterase levels, and 

pre- and post-urinary chlorferon was determined 

by the paired t-test. A p-value of < 0.05 was 

considered statistically significant. 

EVALUATION CRITERIA

As a guide to the evaluation of the hazards posed 

by workplace exposures, NIOSH field staff 

employ environmental evaluation criteria for the 

assessment of a number of chemical and 

physical agents. These criteria are intended to 
Health Hazard Evaluation Report No. 2002-0203-3050 Page 5 

suggest levels of exposure to which most 

workers may be exposed up to 10 hours per day, 

40 hours per week for a working lifetime 

without experiencing adverse health effects. It 

is, however, important to note that not all 

workers will be protected from adverse health 

effects even though their exposures are 

maintained below these levels. A small 

percentage may experience adverse health 

effects because of individual susceptibility, a 

pre-existing medical condition, and/or a 

hypersensitivity (allergy). In addition, some 

hazardous substances may act in combination 

with other workplace exposures, the general 

environment, or with medications or personal 

habits of the worker to produce health effects 

even if the occupational exposures are controlled 

at the level set by the criterion. These combined 

effects are often not considered in the evaluation 

criteria. Also, some substances are absorbed by 

direct contact with the skin and mucous 

membranes, and thus potentially increases the 

overall exposure. Finally, evaluation criteria 

may change over the years as new information 

on the toxic effects of an agent become 

available. 

The primary sources of environmental 

evaluation criteria for the workplace are: (1) 

NIOSH recommended exposure limits (RELs),2

(2) the American Conference of Governmental 

Industrial Hygienists’ (ACGIH®) threshold 

limit values (TLVs®),3

 and (3) the U.S. 

Department of Labor, Occupational Safety and 

Health Administration (OSHA) permissible 

exposure limits (PELs).4

 Employers are 

encouraged to follow the OSHA limits, the 

NIOSH RELs, the ACGIH TLVs, or whichever 

are the more protective criteria. 

OSHA requires an employer to furnish 

employees a place of employment that is free 

from recognized hazards that are causing or are 

likely to cause death or serious physical harm 

[Occupational Safety and Health Act of 1970, 

Public Law 91–596, sec. 5(a)(1)]. Thus, 

employers should understand that not all 

hazardous chemicals have specific OSHA 

exposure limits such as PELs and short-term 

exposure limits (STELs). An employer is still 

required by OSHA to protect their employees 

from hazards, even in the absence of a specific 

OSHA PEL. 

A time-weighted average (TWA) exposure 

refers to the average airborne concentration of a 

substance during a normal 8- to 10-hour 

workday. Some substances have recommended 

STEL or ceiling values which are intended to 

supplement the TWA where there are 

recognized toxic effects from higher exposures 

over the short-term. 

Pesticides 

A pesticide is any substance or mixture intended 

to prevent, destroy, repel, or mitigate arthropods 

(insecticide, miticide, acaricide); rodents 

(rodenticide); nematodes (nematocide); fungi 

(fungicide); or weeds (herbicide), designated to 

be a pest. Each type of pesticide has numerous 

modes of action, chemical classes, target organs, 

formulations, and physicochemical properties. 

Pesticide toxicity is equally diverse, and even 

within a similar chemical class, individual 

compounds ranging from extremely toxic to 

practically nontoxic can be found.5 As such, 

generalizations about the toxicity of pesticides 

cannot be made without considerable 

qualification and explanation. 

Organophosphate Pesticides 

Cholinesterases are enzymes that control the 

amount of nerve impulse transmitters at nerve 

endings. OP and carbamate pesticides cause 

illness by binding to and inactivating 

cholinesterase, thereby causing an accumulation 

of these transmitters at nerve endings. This 

results in increased and continued stimulation at 

those sites and can lead to symptoms such as 

increased sweating; blurred vision; increased 

tears, saliva, nasal and lung secretions; chest 

pain; trouble breathing; wheezing; nausea, 

vomiting, abdominal cramps, and diarrhea; 

muscle weakness and twitches; memory 

problems; and decreased concentration. 

In addition to these symptoms of acute OP 

poisoning, some OPs can cause a delayed 

neuropathy, which manifests several weeks after 

the acute exposure.6

 The neuropathy is 
Page 6 Health Hazard Evaluation Report No. 2002-0203-3050 

characterized by abnormal sensations in the 

extremities, such as coldness, numbness and 

tingling, which are followed by weakness. In the 

absence of acute poisoning, chronic exposure to 

low levels of OPs may also lead to adverse 

health effects on the central and peripheral 

nervous system.7

 

Most OPs are highly lipid soluble and are easily 

absorbed through the skin, mucous membranes, 

gastrointestinal tract, and respiratory tract. Skin 

exposures to pesticides are often considered to 

be a more important portion of total exposure 

than inhalation.8, , 9 10 Pesticide applications 

generally entail considerable contact during 

mixing, spraying, and handling of treated 

animals and items. In general, hand exposure 

represents a major fraction of total dermal 

exposure.11 Exposure standards, guidelines, or 

recommendations by NIOSH or regulatory 

agencies have not been established for pesticides 

on skin or work clothes. 

External exposure measures using conventional 

air, bulk, and wipe sampling do not indicate the 

amount of agent absorbed into the body. Internal 

exposure to OPs has commonly been measured 

in the blood by documenting cholinesterase 

levels. There is great variation among methods 

for measuring cholinesterase, as well as among 

laboratories that use the same method.12 This 

makes it very important to consistently use one 

laboratory and one method for determining 

cholinesterase levels. California, one of only two 

states with mandatory cholinesterase monitoring 

programs, approves the use of the Ellman 

method, and the World Health Organization 

considers this the reference method.13 In 

addition, because of the wide range of normal 

values in the population, comparison of 

subsequent values with a baseline value is 

important because the percent decrease from 

baseline is more important than the actual value 

in determining whether overexposure to 

pesticides has occurred. This baseline should be 

determined prior to beginning work with 

pesticides or after 30 days without pesticide use, 

and should be the average of two or more tests 

taken at least 3 days but not more than 14 days 

apart.

AChE reflects cholinesterase activity in tissues 

(e.g., the nervous system, the target organ 

system of most concern). PChE is a more 

sensitive measure of cholinesterase activity than 

AChE, but PChE returns to baseline earlier than 

AChE. Therefore, PChE values may not reflect 

the severity of toxicity unless blood specimens 

are drawn immediately after poisoning. The rate 

and duration of cholinesterase depression varies 

somewhat with the type of OP being used. In 

general, depression of PChE activity can occur 

within 2-3 hours of exposure. Depression of 

AChE activity may take longer to occur. 

Cholinesterase levels can be affected by a 

variety of conditions, medications, and some 

beverages, which can make interpretation 

difficult. 

Several agencies have guidelines for monitoring 

cholinesterase levels among workers exposed to 

OPs. Three guidelines, the ACGIH biologic 

exposure index, the German Commission for the 

Investigation of Health Hazards of Chemical 

Compounds in the Work Area’s Biologic 

Tolerance Value, and the World Health 

Organization’s Health Based Biological Limit 

all specify an AChE value of 70% of the 

individual’s baseline.14 In addition, California 

and Washington require that individuals with an 

AChE value of 70% or a PChE of 60% or lower 

of the baseline be removed immediately from 

exposure. They also specify that a drop to 80% 

requires an investigation of work practices.15 

Urinary metabolites have been used as 

biomarkers for some OP pesticides. The most 

commonly used urinary metabolites for OPs are 

the dialkylphosphates (DAPs). These DAPs, 

however, are non-specific, being elevated with 

exposure to many different OP pesticides. 

However, it is not possible to estimate the 

absorbed dose for most OPs, which limit the 

usefulness of DAPs in biologic monitoring. 13 A 

small number of OPs have been found to have 

specific urinary metabolites that are useful as 

exposure biomarkers. 

Coumaphos 

Coumaphos (CAS number 56-72-4 [Co-Ral®]) 

is an OP insecticide. It is used to control larvae 
Health Hazard Evaluation Report No. 2002-0203-3050 Page 7 

of fecal-breeding pests in livestock and swine 

bedding by direct application to cattle, horses, 

sheep, and swine.16 It is not registered for use on 

crops or in homes. Acute excessive exposure to 

coumaphos results in the health effects noted 

above. While coumaphos does cause delayed 

neuropathy in hens, it does not appear to do so in 

humans.17 The ACGIH TLV-TWA for 

coumaphos is 0.05 milligrams per cubic meter 

(mg/m3

) inhalable fraction and vapor. The TLV 

was based on animal studies because there was 

no quantitative information on human 

exposures. No other occupational exposure 

criteria exist for coumaphos. 

The serum half-life of coumaphos after oral or 

intravenous administration is 2-3 hours in rats, 

with 80% excreted in the urine in 24 hours. The 

primary urinary metabolite is 3-chloro-4-methyl 

coumarin (chlorferon), reported in animal 

studies to be specific for coumaphos exposure. 

No data are available concerning serum half-life 

of coumaphos after dermal or inhalational 

exposure. A skin notation was also assigned in 

the TLV because two studies in dermally 

exposed animals resulted in symptoms of OP 

poisoning.18 A skin notation indicates a potential 

significant contribution via the cutaneous route.

In 1996, the U.S. Environmental Protection 

Agency (EPA), in its Coumaphos Reregistration 

Eligibility Decision (RED) document, reported 

that cattle dipping did not pose a significant 

pesticide exposure threat. Likewise, the report 

stated that while high pressure wand spraying 

may pose an exposure threat, low pressure 

spraying did not. This EPA report was not based 

on chemical-specific exposure data (which was 

unavailable), but instead relied on generic 

dosimetry data in the pesticide handlers’ 

exposure database (PHED) to estimate 

coumaphos exposure. In 2000, the RED was 

amended, and coumaphos was approved for 

additional uses provided certain risk mitigation 

measures are in place. EPA restricts use of the 

42% flowable form of coumaphos (which the 

technicians use) to USDA staff enrolled in a 

cholinesterase medical monitoring program. For 

hand-held spray applications, individuals are 

limited to spraying 100 head per day.16 

Chlorpyrifos 

Chlorpyrifos (CAS number 2921-88-2 [Dursban 

7]) is also an OP insecticide. It is used to control 

fire ants, ornamental plant insects, stored 

product insects, and turf- and wood-destroying 

insects.17 Because its half-life in soil is 30 days, 

it is considered a moderately persistent 

insecticide.18 The NIOSH REL and ACGIH 

TLV for chlorpyrifos in air are 200 mg/m3

 (8-

hour TWA), and the TLV has a skin notation.2,3 

RESULTS

Of the 59 AHPIS animal health technicians, 15 

met the criteria for our evaluation. All 15 agreed 

to participate, although two did not provide postshift blood or urine samples (but did provide 

fingerstick samples) due to time constraints. The 

population was 100% male. The mean age of 

participants was 41 (range: 21-63), and the mean 

tenure as an animal health technician with 

APHIS was 13 years (range: 1 month to 35 

years). Participants reported mixing coumaphos 

8.5 days per month and spraying or dipping 

livestock 11 days per month, on average. Three 

reported being removed from coumaphos use 

(one time each) in the past year due to low 

cholinesterase levels. Four reported use of 

chlorpyrifos in the last 3 months. 

Technicians were asked about symptoms 

consistent with OP poisoning experienced within 

6 hours of coumaphos use in the past 3 months. 

Two each reported headache, weakness, and 

tearing eyes, and one each reported cough and 

nervousness. 

Only one technician reported eating, drinking, or 

smoking while using coumaphos. Technicians 

were asked about their use of PPE when 

handling coumaphos in a variety of settings. 

Reported PPE use varied by task and type of 

PPE (see Table 1). 
Page 8 Health Hazard Evaluation Report No. 2002-0203-3050 

Biological Monitoring 

Blood 

Ellman Method 

None of the 13 technicians who provided blood 

both pre- and post-shift had PChE or AChE 

levels outside the laboratory’s range of normal. 

There was not a statistically significant change 

in PChE (p=0.89) or AChE (p=0.40) from preshift to post-shift. The mean pre-shift PChE was 

3.12 international units per milliliter (IU/mL) 

(range: 2.50-4.00), and the mean post-shift 

PChE was 3.13 IU/mL (range: 2.50-3.70). The 

mean pre-shift AChE was 10.89 IU/mL (range: 

9.60-12.00), and the mean post-shift AChE was 

10.61 IU/mL (range: 9.40-11.80). 

Test-Mate® 

Fifteen technicians had both a pre- and post-shift 

fingerstick for cholinesterase analysis by the 

Test-Mate®. None had PChE or AChE levels 

outside the range of normal. There was not a 

statistically significant change in either PChE 

(p=0.69) or AChE (p=0.92) levels from pre-shift 

to post-shift. The mean pre-shift PChE was 2.21 

IU/mL (range: 1.81-3.02), and the mean postshift PChE was 2.20 IU/mL (range: 1.62-3.04). 

The mean pre-shift AChE was 4.06 IU/mL 

(range: 2.99-5.08), and the mean post-shift 

AChE was 4.05 IU/mL (range: 3.19-5.05). 

Relationship Between Methods 

There was significant positive correlation 

between PChE levels measured with the TestMate® and with the Ellman method (r=0.91, 

p<0.01, n=28). There was also significant 

positive correlation between AChE levels 

measured by the two different methods (r=0.63, 

p<0.01, n=28). 

Urine 

Fifteen technicians submitted urine for 

chlorferon analysis prior to coumaphos 

application. The mean urinary chlorferon was 

77.31 parts per billion (ppb), with a range of 

non-detectable-404.88 ppb (See Table 2). Two 

of these 15 technicians had levels below the 

limit of detection. All 15 reported coumaphos 

use within the past 7 days. Chlorferon was 

detected in the urine of all 13 animal health 

technicians who submitted urine 4-6 hours after 

using coumaphos (mean: 203.04 ppb; range: 

4.17 ppb - 429.72 ppb). Urinary chlorferon 

levels were significantly higher 4-6 hours after 

use (p<0.01), and declined significantly from the 

post-shift levels by the next day (p=0.01). The 

mean urinary chlorferon concentration on the 

next day was 92.97 ppb, with a range of 0.25-

192.16 ppb. 

Environmental Sampling 

Samples were collected during a variety of 

coumaphos application activities including use 

of a mobile spray box, hand spraying of horses, 

and dipping and scratching of cattle in fixed 

vats. Samples were collected only during 

activities involving application of coumaphos 

and cattle scratching. Therefore, most samples 

were not collected over a full workshift. 

Technicians spent considerable time processing 

paperwork in the office, coordinating and 

staging the dipping with ranchers, and traveling 

to remote locations to conduct coumaphos 

application. 

Whole Body Wipe Results 

The results of the whole body wipe sampling for 

coumaphos are shown in Table 3. Of the 60 

patch samples collected, 26 (43%) were either 

non-detectable or between the analytical LOD 

and LOQ. Analytical LODs ranged from 0.7 

micrograms per sample (μg/sample) to 

3μg/sample and LOQs ranged from 2 μg/sample 

to 10 μg/sample. Detection limits varied by 

analysis set. No chlorpyrifos was detected in any 

of the samples. 

Hand Wipe Results 

The results of the hand wipe sampling for 

coumaphos and chlorpyrifos are shown in Table 

4. Thirteen technicians’ hands were wiped, and a 

total of 28 wipe samples were collected. One 

technician’s hands were wiped before lunch and 

again at the end of the shift because his work 

activities took place across lunch time. NIOSH 
Health Hazard Evaluation Report No. 2002-0203-3050 Page 9 

investigators conducted hand wipe sampling 

after three technicians washed their hands with 

soap and water at the end of the application 

process. Coumaphos results ranged from < LOQ 

to 1400 μg/sample for the employees who did 

not wash their hands prior to sampling. 

Coumaphos results for employees who washed 

their hands prior to hand wipe sampling ranged 

from 4.8 μg/sample to 54 μg/sample. 

Chlorpyrifos was detected in three samples from 

two employees and ranged from below the LOQ 

to 3.2 μg/sample. Neither employee reported 

working with chlorpyrifos on the day of 

sampling. 

Surface Wipe Results 

The inside of two respirators were sampled for 

coumaphos; one measured below the LOD and 

the other measured 11 μg/sample. 

Air Sampling Results 

A total of nine PBZ air samples were collected. 

All samples except one measured below the 

LOD. The minimum detectable concentration 

(MDC) for coumaphos was 0.004 mg/m3

assuming a sample volume of 119 L. One 

sample, collected on a technician who sprayed 

horses for the majority of the day, measured 

0.003 mg/m3

 and was between the LOD and 

LOQ. 

Workplace Observations 

PPE use varied by technician, job task, and 

perceived risk of exposures. Hindrances to 

wearing PPE included thermal comfort and time 

constraints. No standard guidance for what type 

of PPE should be worn during specific tasks was 

available. We observed two employees wearing 

respirators, aprons, and gloves while operating 

and opening the chute to the mobile spray box. 

The remaining employees working the cattle 

into the chute and scratching cattle while they 

were in the chute wore no PPE. Through 

conversations with employees, most felt the risk 

of exposure was greatest when operating the 

spray box; therefore, wearing PPE during these 

tasks was standard practice. Some technicians 

chose to wear respirators and aprons during 

horse spraying; others wore no PPE while 

spraying horses. Employees wore no PPE when 

dipping cattle in fixed vats or when scratching 

cattle. Employees did not wear gloves when 

diluting the coumaphos mixture or when 

collecting bulk samples of the mixture. NIOSH 

investigators observed technicians having direct 

skin contact with coumaphos on their hands. 

Employees reported being uncomfortable 

wearing PPE on hot days. Typical work clothing 

wore year round by technicians included denim 

jeans, long sleeve shirts, boots, and cowboy hats. 

Technicians stored all PPE in plastic containers 

or in a tool box in the bed of their trucks becasue 

the job required them to travel to many different 

places in a single day. NIOSH investigators 

observed respirators stored with other dirty PPE, 

such as gloves and aprons, rather than in their 

own container or bag. At the time of the site 

visit, the tick eradication program had not 

implemented a full respiratory program in 

accordance with the OSHA respiratory 

protection standard. Employees were not fit 

tested to wear their respirators, and NIOSH 

investigators observed employees wearing 

respirators incorrectly. Some employees wearing 

respirators had facial hair, which interferes with 

the sealing surface of the respirator to the face. 

Respirators were visibly dirty, and some 

respirator parts were warped by the heat. No 

filter/cartridge change out schedule was in place. 

Filters and cartridges appeared to be extremely 

dirty and needed to be replaced. Most employees 

had replacement filters, particularly with the 

newly issued 3M full facepiece respirators. 

Technicians may be exposed to heat stress 

conditions when working in the outdoor 

environment. The outdoor work can require 

them to work in the sun for several hours at a 

time in temperatures exceeding 100°F. No 

formal heat stress program was in place. 

Management reported employees receive limited 

training about working in hot environments. 

Employees wear pants and long sleeve shirts 

even in the summer to protect their skin against 

exposure to the sun and animals. Employees 

were conscious of the heat and were observed 

taking frequent water breaks. 
Page 10 Health Hazard Evaluation Report No. 2002-0203-3050 

Noise levels appeared to be very high while the 

portable spray box was in operation. Hearing 

protection devices are not provided by the tick 

eradication program. 

DISCUSSION AND 

CONCLUSIONS

USDA APHIS animal health technicians were 

exposed to and absorbed coumaphos during their 

routine activities, as evidenced by urinary 

chlorferon levels. Urinary chlorferon levels rose 

significantly after coumaphos use. Results from 

PBZ air, handwipe, and patch sampling 

confirmed that employees were primarily 

exposed to coumaphos via the skin. 

An inhalational health hazard to coumaphos did 

not exist at the time of the NIOSH visit. Air 

sampling represented task-specific sampling 

between 30 minutes and 120 minutes with no 

other exposures for the rest of the workshift. 

However, exposures could increase if certain 

work tasks where coumaphos may have been 

aerosolized, such as spray box application of 

pesticides, occurred over a longer period of time. 

One PBZ sample detected trace amounts of 

coumaphos and represented a worst case 

scenario. This employee sprayed horses and 

dipped cattle for the entire day. Results of our 

evaluation suggest that respiratory protection 

may not be necessary and may increase 

exposures due to the presence of residual 

pesticides inside the respirator. One wipe sample 

taken on the inside of the respirator that was 

reportedly used infrequently found residual 

pesticide contamination. 

Fifty-eight percent of the whole-body patch 

sampling detected measurable levels of 

coumaphos. Patches sampled exposures outside 

of the clothing. However, coumaphos could 

contact the skin if enough were present on 

clothing to soak through. In addition, 

contaminated clothing could contaminate the 

technicians’ vehicle and possibly their homes. 

Ninety-six percent of hand-wipe sampling 

detected coumaphos, indicating the majority of 

exposures occur from hand contact with the 

pesticide. This was verified through observation. 

Employees were observed having direct skin 

contact with coumaphos during several work 

tasks. For example, employees stirred the 

coumaphos mixture in fixed vats for 

approximately 20 minutes with a pressurized 

paddle. When removing the paddle from the vat, 

employees’ hands contacted residual 

coumaphos. Employees collected a bulk sample 

of the coumaphos mixture before and after cattle 

dipping. Sample bottles were attached to a pole 

and dipped in the vat. Employees were exposed 

to the coumaphos mixture when capping the 

bottles. 

To accommodate spraying horses on private 

property, technicians had tanks in the truck bed. 

They charged the water-filled tank with 

coumaphos and collected a bulk sample for 

concentration verification. NIOSH investigators 

observed the coumaphos mixture splashing out 

from the top of the tank due to a worn seal on 

the hose. The employees touched the hose with 

their bare hands. Opportunities for hand 

exposures also occured when employees 

collected bulk samples from the tank. During 

horse spraying, employees had the potential for 

exposure to the overspray and direct skin contact 

when handling the horse. It was not always 

feasible to spray upwind from the horse. 

Employees were issued a 5 gallon can to fill 

with water for hand washing after working in the 

field. Although technicians’ hands were visibly 

soiled with fecal material, urine, and dirt after 

working with the cattle, they waited until lunch 

to wash their hands. Technicians expressed 

concerns that emergency showers were not in 

place at the fixed vats in case of an accidental 

spill or gross exposure, such as falling into the 

vats. 

Most employees did not wear adequate PPE, 

particularly gloves. Barriers to wearing PPE 

included heat stress, comfort, time constraints, 

and the perception that it was not needed. PPE 

and work practices are the main methods of 

reducing exposure to these employees. The EPA 

has established minimum PPE requirements for 

use when using emulsifiable concentrate and 

flowable concentrate.19 Mixers, loaders, and 
Health Hazard Evaluation Report No. 2002-0203-3050 Page 11 

others exposed to the concentrate, and all 

handlers participating in dip-vat applications 

must wear long-sleeve shirt and long pants, 

chemical-resistant gloves, chemical-resistant 

footwear and socks, chemical-resistant apron, 

and face shield or goggles. All other handlers 

must wear long-sleeve shirt and long pants, 

chemical-resistant gloves, and chemical-resistant 

footwear and socks. 

PChE and AChE levels did not change 

significantly from pre-shift to post-shift, which 

is not surprising because pre-shift levels did not 

represent an exposure-free baseline. All 

participants had used coumaphos in the prior 

week, and some in the prior 48 hours. We did 

not have baseline results available for 

comparison. There was good correlation 

between the Ellman method and the Test-Mate® 

Field ChE Cholinesterase Test System (Model 

400). The United States Army found the Testmate ChE to be reliable and useful for 

measuring AChE in the field in detection of OP 

nerve agent poisoning.20 Other researchers have 

noted it can provide useful information on 

pesticide exposures when measurements are 

made in a temperature-controlled system.21

These researchers found a stronger correlation 

between the Ellman method and the Test-Mate 

(r=0.99) for AChE than NIOSH did (r=0.63). 

The other researchers did not evaluate PChE. 

California requirements state that for a method 

other than the Ellman to be used, the correlation 

coefficient squared (r2

) must be at least 0.9, and 

that field test kit methods are not satisfactory.

However, the Test-Mate® Field ChE 

Cholinesterase Test System’s convenience may 

make it an option for APHIS if they decide to 

continue their cholinesterase monitoring 

program because it may increase compliance 

with and timeliness of testing. It would be useful 

in the event of an acute overexposure. Urinary 

chlorferon levels were a more sensitive marker 

of exposure, showing significant increases after 

application or mixing of coumaphos. However, 

chlorferon has limited commercial availability, 

and its use would require further validation prior 

to replacing cholinesterase monitoring. 

RECOMMENDATIONS

Our evaluation documented that USDA APHIS 

animal health technicians are exposed to and 

absorb coumaphos during their routine work 

activities, primarily through their skin. In 

addition, we noted potential health hazards from 

heat stress and noise. The following 

recommendations are based upon these 

conclusions. 

1. Mixers, loaders, and others who may 

come into contact with the coumaphos 

concentrate, and all handlers participating in 

dip-vat applications should wear long-sleeve 

shirts and long pants, chemical-resistant 

gloves, chemical-resistant footwear and 

socks, and chemical-resistant apron. 

Technicians should always wear gloves when 

collecting vat samples, stirring the vat, and 

charging the tanks in their truckbeds. All 

other handlers must wear long-sleeve shirts 

and long pants, chemical-resistant gloves, 

and chemical-resistant footwear and socks. 

NIOSH was not able to observe all uses of 

coumaphos and therefore cannot provide 

specific recommendations by task. USDA 

should determine the appropriate PPE for all 

the tasks performed by the animal health 

technicians that involve the use of 

coumaphos. At a minimum, employees 

should follow the EPA requirements for PPE 

during coumaphos use. Most approaches for 

selecting appropriate PPE incorporate the 

following process:22

 Determination of the hazards most likely 

to occur 

 Assessment of the adverse effects of 

unprotected exposure 

 Identifying other control options that 

can be used instead of protective 

clothing 

 Determining the performance 

characteristics needed for protection 

 Evaluating the need for decontamination 
Page 12 Health Hazard Evaluation Report No. 2002-0203-3050 

 Assessing any constraints that may 

hinder the use of PPE (ergonomics, 

safety, vision, dexterity) 

Once it is determined that PPE is required for 

a task, its use should be mandatory. Written 

procedures should be in place to ensure 

consistent selection and use of PPE. Affected 

users must be informed of the need for PPE; 

consequences of not wearing the appropriate 

PPE; and how to properly inspect, wear, 

maintain, and store the PPE. Users must also 

be informed of all limitations associated with 

the use of PPE and must be aware that the 

equipment does not eliminate the hazard. 

Finally, periodic inspections and evaluations 

of the PPE program should be conducted to 

ensure that procedures are consistently 

followed, to identify any process changes 

that may have occurred, and to verify that the 

selected PPE is still appropriate for the given 

task. 

2. Perform a more comprehensive 

evaluation of the risk of inhalation exposure 

to coumaphos. PBZ samples should be 

collected for tasks that generate aerosols, 

such as those involving hand spraying of 

coumaphos for long periods of time. Our 

evaluation suggests that it may be possible to 

discontinue use of respirators. If management 

chooses to continue to provide respirators to 

employees, then a comprehensive respiratory 

protection program should be established in 

accordance with the OSHA respiratory 

protection standard.23 The program should 

include regular worker training; maintenance, 

inspection, cleaning, and evaluation of the 

respirator; use of the respirator in accordance 

with the manufacturer’s instructions; fit 

testing; medical evaluation; and annual fit 

testing. Workers issued respirators should 

also be clean shaven to ensure a good faceto-respirator seal. A comprehensive 

inspection of all respirators issued to 

technicians should be completed. Damaged 

facepieces, exhalation/inhalation valves, and 

cartridges/filters should be replaced. Institute 

a frequent inspection and cleaning program 

to ensure all respirators are clean and in good 

condition. Special emphasis should be placed 

on proper storage of respiratory protection in 

hard containers to avoid distortion and 

contact with contaminated PPE. When 

possible, respirators should be stored in the 

air-conditioned county offices on days when 

they are not worn. Technicians should avoid 

storing respirators in their vehicles during hot 

months as the heat may damage the respirator 

causing it to provide inadequate protection to 

the wearer. A filter/cartridge change-out 

schedule should be developed, and 

employees should be reminded to change out 

their filters and cartridges. Detailed 

information on respirator programs is 

available at: [http://www.osha.gov/SLTC/ 

etools/respiratory]. 

3. Encourage employees to follow good 

hand hygiene practices. Employees should 

wash their hands with soap and water after 

applying pesticides even if they were wearing 

gloves. Hands should be washed for a 

minimum of 15 seconds or until visible dirt is 

removed from hands. Hands should be 

washed prior to eating, drinking or smoking. 

Chemical-resistant gloves should be cleaned 

each day. 

4. Contact USDA resources to determine 

the feasibility of validating urinary 

chlorferon as a biomarker of coumaphos 

exposure. While there is no known absolute 

value of urinary chlorferon at which health 

effects occur, documentation of an increase 

after coumaphos use indicates that PPE and 

work practices are not adequate and should 

be re-evaluated. 

5. In the meantime, improve the existing 

cholinesterase monitoring program. Due to 

changes in laboratories, the current program 

does not compare cholinesterase levels to 

true baseline values but, instead, to a 

calculated baseline. It is preferable to use 

only one laboratory to perform cholinesterase 

testing. Over time, slowly establish true 

baseline cholinesterase measurements on all 

employees. This can be accomplished by 

testing all new employees and by doing serial 
Health Hazard Evaluation Report No. 2002-0203-3050 Page 13 

testing of all employees who are flagged and 

removed from work until a relative steadystate level of cholinesterase is reached, then 

using that level as a baseline. While this does 

not meet the standard definition of a 

establishing a baseline, it should be an 

adequate substitute. 

6. Consider field test kit testing for 

cholinesterase. The convenience and costsavings make this a viable option. The field 

test kit testing would also allow for more 

rapid assessment of levels in the event of an 

acute high exposure to coumaphos. A field 

test kit cholinesterase baseline would be 

necessary if you choose to use the field test 

kit, as would training your personnel to use it 

appropriately. 

7. Develop a continuing education 

program to ensure that all employees 

potentially exposed to hot environments and 

physically demanding job activities stay 

current on heat stress and heat-stress 

prevention information. Include at least the 

following components for a good heat stress 

training program: 

 Knowledge of the hazards of heat 

stress 

 Recognition of predisposing factors, 

danger signs, and symptoms 

 Awareness of signs and symptoms of 

heat-related illness and first-aid 

procedures for treatment 

 Employee responsibilities in avoiding 

heat stress 

 Dangers in using drugs, including 

therapeutic ones, and alcohol in hot 

and physically demanding work 

environments 

 Purpose and coverage of 

environmental and medical 

surveillance programs and the 

advantages of worker participation in 

them 

Encourage personnel to drink water or any 

cool liquid (except alcohol and caffeinated 

beverages) to stay hydrated. Encourage them 

to drink small amounts frequently (e.g., one 

cup every 20 minutes). Investigate 

opportunities to schedule outdoor work in the 

mornings to avoid high temperatures. 

8. Ensure employees are trained on 

emergency procedures in the event of an 

accidental high exposure to pesticides, such 

as falling into a vat. Ensure these accidents 

are reported to management so that they can 

be investigated in order to prevent them in 

the future. 

9. Conduct an assessment of noise levels 

during mobile spray box use to determine if 

hearing protection is needed. Noise levels 

seemed high on the days of the evaluation. 

10. Require employees to report their 

locations to the county office throughout 

their work day to ensure the locations of the 

technicians are known in case of 

emergencies. Establish good lines of 

communication with local law enforcement 

and U.S. Customs to pre-identify dangerous 

areas technicians should avoid. 

REFERENCES

1. NIOSH [2007]. NIOSH manual of 

analytical methods (NMAM®). 4th ed. Schlecht 

PC, O’Connor PF, eds. Cincinnati, OH: U.S. 

Department of Health and Human Services, 

Public Health Service, Centers for Disease 

Control and Prevention, National Institute for 

Occupational Safety and Health, DHHS 

(NIOSH) Publication 94–113 (August, 1994); 

1st Supplement Publication 96–135, 2nd 

Supplement Publication 98–119; 3rd 

Supplement 2003–154. [http://www.cdc.gov/ 

niosh/nmam/]. 

 2. NIOSH [1992]. Recommendations for 

occupational safety and health: compendium of 

policy documents and statements. Cincinnati, 

OH: U.S. Department of Health and Human 

Services, Public Health Service, Centers for 

Disease Control and Prevention, National 
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Institute for Occupational Safety and Health, 

DHHS (NIOSH) Publication No. 92-100. 

 3. ACGIH® [2007]. 2007 TLVs® and 

BEIs®: threshold limit values for chemical 

substances and physical agents. Cincinnati, OH: 

American Conference of Governmental 

Industrial Hygienists. 

 4. CFR [2003]. 29 CFR 1910.1000. Code of 

Federal Regulations. Washington, DC: U.S. 

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Page 16 Health Hazard Evaluation Report No. 2002-0203-3050 

TABLES

Table 1 

PPE Use during Coumaphos Application, by Task 

USDA APHIS Tick Eradication Program 

HETA 2002-0203-3050 

Laredo, Texas 

September 13-15, 2005 

Mixing Spraying Dipping 

n=15 Always Sometimes Never Always Sometimes Never Always Sometimes Never

Gloves 12 0 3 10 4 1 6 5 4 

Respirator 5 3 7 10 4 1 4 7 4 

Goggles 3 1 11 5 3 7 2 1 12 

Outerwear 

or 

Apron 

1 2 11 3 6 6 0 5 10 

Special 

Boots or 

Shoe 

Coverings 

1 1 12 2 5 8 0 5 10 

Table 2 

Urinary Chlorferon Levels, in parts per billion 

USDA APHIS Tick Eradication Program 

HETA 2002-0203-3050 

Laredo, Texas 

September 13-15, 2005

Used coumaphos 

in 7 days prior to 

sampling 

Used coumaphos in the 

48 hours prior to 

sampling 

Preexposure 4-6 hours after use 

of coumaphos 

Morning after using 

coumaphos 

yes no 7.53 291.62 192.16 

yes no ND 62.07 27.21 

yes no ND 4.17 ND 

yes no 7.12 52.61 11.76 

yes no 56.03 32.07 163.99 

yes no 41.04 68.51 28.02 

yes yes 127.98 429.72 67.87 

yes yes 69.53 341.95 162.82 

yes yes 101.68 339.31 165.41 

yes yes 202.00 378.69 129.63 

yes yes 404.88 403.77 114.89 

yes yes 45.51 78.96 55.28 

yes yes 36.39 155.99 89.37 

yes yes 45.06 No sample No sample 

yes no 14.37 No sample No sample 
Health Hazard Evaluation Report No. Page 17 

Table 3 

Coumaphos Patch Sampling Results 

USDA APHIS Tick Eradication Program 

HETA 2002-0203-3050 

Laredo, Texas 

September 13-15, 2005 

Work activity Amount of coumaphos by patch location (μg/sample) 

Right 

Arm 

Left 

Arm 

Right Leg Left Leg Chest 

Sprayed a horse and tractor for 35 minutes (2) 18 110 22 20 

Sprayed 1 horse 14 19 100 70 30 

Sprayed 2 horses and dipped cattle for 10 

minutes 

50 33 14 6.5 ND 

Pushed cattle into chute during cattle spray 

box application 

ND 3.5 4.1 ND 10 

Scratching cattle in chute during cattle spray 

box application 

13 ND (1) ND (1) 

Pushed cattle into spray box ND ND 19 (6) ND 

Opened spray box gate and transferred OP 

mixture from spray box to truck 

ND (6) 23 43 ND 

Operated spray box; charged the water in box 

with coumaphos; primed transfer pump 

230 (8) 11 (4) ND 

Sprayed 27 horses and dipped 5 cattle 56 (7) 220 1200 38 

Sprayed 24 horses and 1 backhoe, dipped 6 

cattle 

75 48 ND ND ND 

Scratched cattle and dipped 8 cattle 27 29 (2) 10 (1) 

Scratched cattle and sprayed 1 horse 20 27 (4) 11 ND 

μg/sample = micrograms per sample 

ND = Non-detectable = results were below the analytical limit of detection (LOD) 

( ) Indicates results between the analytical LOD and limit of quantification (LOQ). 
Page 18 Health Hazard Evaluation Report No. 2002-0203-3050 

Table 4 

Coumaphos and Chlorpyrifos Hand Wipe Sampling Results 

USDA APHIS Tick Eradication Program 

HETA 2002-0203-3050 

Laredo, Texas 

September 13-15, 2005 

Coumaphos 

(μg/sample) 

Chlorpyrifos 

(μg/sample) 

Work Activity 

Right 

Hand 

Left 

Hand 

Right 

Hand 

Left 

Hand 

Washed 

hands 

prior to 

sampling? 

Sprayed a horse and tractor for 35 minutes (7) 12 ND ND No 

Sprayed 1 horse 110 200 ND ND No 

Sprayed 2 horses and dipped cattle for 10 

minutes 

150 130 (0.2) ND No 

Pushed cattle into chute during cattle spray box 

application 

38 54 ND ND Yes 

Scratching cattle in chute during cattle spray 

box application 

73 130 ND ND No 

Pushed cattle into spray box 4.8 18 ND ND Yes 

Opened spray box gate and transferred OP 

mixture from spray box to truck 

480 510 ND ND No 

Operated spray box; charged the water in box 

with coumaphos; primed transfer pump 

32 9.7 ND ND Yes 

Sprayed 27 horses and dipped 5 cattle 610 (am) 

1400 (pm) 

410 (am) 

470 (pm) 

ND ND No 

Sprayed 24 horses and 1 backhoe, dipped 6 

cattle 

74 170 ND ND No 

Scratched cattle and dipped 8 cattle 130 82 ND ND No 

Scratched cattle and sprayed 1 horse 83 37 ND ND No 

Sprayed his own horses 87 62 3.2 2.7 No 

μg/sample = micrograms per sample 

( ) = Indicates concentrations reported between the analytical limit of detection (LOD) and the limit of 

quantification (LOQ). 
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