Cholinesterase Monitoring 

of Pesticide Handlers 

in Agriculture 

Report to the Legislature 

As required by RCW 49.17.288 

JANUARY 2007
Cholinesterase Monitoring in Agriculture Page 2 of 21 

January 2007 

Executive Summary 

This report is prepared, as required by RCW 49.17.288, to reflect the first three years (2004-06) 

of implementation of the cholinesterase monitoring rule, WAC 296-307-148, (the rule) adopted 

by the Department of Labor and Industries (L&I) in late 2003.1 Since the experiences of the first 

two years have previously been documented and reported to the legislature2 this report will 

focus primarily on the data analysis presented in the 2006 Cholinesterase Scientific Advisory 

Committee Report to L&I. In some cases, data presented in the 2004 and 2005 reports to the 

legislature are repeated.3

During the 2006 agriculture pesticide application season, 244 employers and 1889 pesticide 

handlers participated in baseline (pre-exposure) cholinesterase testing. Four hundred and 

seventy one of these pesticide handlers were tested at least once during the application season 

(periodic testing). Of these 471 handlers, 50 (10.6 percent) received at least one test with a 20 

percent or greater depression in cholinesterase activity requiring the employer to evaluate 

pesticide handling practices, and 7 (1.5 percent) were temporarily removed from exposure to 

cholinesterase-inhibiting pesticides because of a more significant cholinesterase depression. 

The number of handlers undergoing cholinesterase testing in 2006 was significantly less than in 

previous years. This is thought to reflect industry pesticide use patterns, employer experience in 

identifying employees covered by the testing requirements of the rule, and employer actions 

resulting in limiting handler exposure (e.g., product substitution, spreading pesticide handling 

duties among employees). Even though fewer handlers underwent periodic testing in 2006 (471) 

than 2005 (611) the number of handlers experiencing a significant cholinesterase depression 

remained stable (2005=59, 2006=57). 

As in 2004 and 2005, agriculture pesticide handlers with significantly depressed cholinesterase 

levels were generally employed in the tree fruit industry with operations located in L&I Region 5 

( West Adams, Benton, Chelan, Columbia, Douglas, Franklin, Grant, Kittitas, Okanogan, Walla Walla 

and Yakima counties). Airblast pesticide application was most often implicated in significant 

cholinesterase depressions. Toxicity class I and II cholinesterase inhibiting pesticides most 

frequently handled prior to testing include chlorpyrifos, azinphos-methyl, phosmet, formetanate 

hydrochloride, and carbaryl. 

Procedures and requirements for the collection of blood samples did not change from the 2005 

season. The Washington State Public Health Laboratory continued as the only laboratory 

approved to provide cholinesterase-testing services. Testing was conducted in accordance with 

the laboratory Standard Operating Procedures (SOP) established in 2005. All test samples were 

tested within the time frames established in the SOP. In its analysis of testing services, the 

Cholinesterase Scientific Advisory Committee concluded that testing continued to be well within 

acceptable parameters. 

As planned during the initial rulemaking process laboratory testing services will shift to the 

commercial sector beginning in 2007. L&I has selected Pathology Associates Medical 

Laboratories, Spokane WA, as the single approved laboratory to provide testing and data 

management services under the rule. Approval of a single laboratory to provide all testing will 

serve to eliminate test variability between laboratories. 

 

1 Rulemaking was initiated pursuant to Juan Rios and Juan Farias v. Washington Department of Labor & Industries, 

et al., 145 Wn.2d 483, 39 P.3d 961 (2002).

2

 Cholinesterase Monitoring of Pesticide Handlers in Agriculture: Report to the Legislature (2004 and 2005) 3

 The Scientific Advisory Committee for Cholinesterase Monitoring: Report to L&I (2004, 2005, and 2006) 
Cholinesterase Monitoring in Agriculture Page 3 of 21 

January 2007 

CHOLINESTERASE MONITORING IN AGRICULTURE

WAC 296-307-148 

WASHINGTON STATE DEPARTMENT OF LABOR AND INDUSTRIES

January, 2006 

CONTENTS

Executive Summary ..............................................................................................................................2 

Background ...........................................................................................................................................4 

 Laboratory Program..............................................................................................6 

Summary of 2006 Medical Monitoring Experience ..........................................................................7 

L&I Consultation and Compliance Activities ................................................................................10 

2007 Program Highlights..............................................................................13 

Cholinesterase Monitoring Advisory Committees...............................................15 

 

Appendix Scientific Advisory Committee Recommendations...............................17 

 
Cholinesterase Monitoring in Agriculture Page 4 of 21 

January 2007 

Background 

WAC 296-307-148, Cholinesterase (ChE) Monitoring (the rule) was adopted in December 2003. 

The rule requires agriculture employers to 1) record hours employees handle4 toxicity class I 

and II organophosphate and N-methyl-carbamate pesticides, 2) provide cholinesterase blood 

testing to employees who handle covered pesticides for 30 or more hours in any consecutive 30 

day period, and 3) take specified actions when an employee experiences a cholinesterase 

depression of >20% from their individual baseline.5 RCW 49.17.288 directs the Washington 

State Department of Labor & Industries (L&I) to submit reports of the results of data collection, 

correlation, and analysis related to cholinesterase monitoring to the legislature. This is the third 

and final of these reports. 

Detailed discussions of occupational cholinesterase monitoring and history of the rule can be 

found in the 2004 Cholinesterase Monitoring of Pesticide Handlers in Agriculture Report to the 

Legislature, and the Washington State Cholinesterase Testing: Guidelines for Health Care 

Providers Manual ( http://www.lni.wa.gov/Safety/Topics/AtoZ/Cholinesterase/default.asp ). 

In 2006 the Washington State Public Health Laboratory (PHL) continued to be the sole 

laboratory approved by L&I to provide cholinesterase-testing services. Blood sample collection 

and laboratory testing procedures remained unchanged from 2005.6

 Analysis of Laboratory 

performance conducted by the Cholinesterase Monitoring Scientific Advisory Committee (SAC) 

concluded that laboratory performance remained well within acceptable limits.7

Test data continued to be collected and managed by the PHL and Department of Health NonInfectious Conditions Epidemiology program (DOH). DOH maintains the Cholinesterase 

Monitoring Data System (CMDS), notifies L&I of cholinesterase depressions exceeding 20 

percent8, and provides a variety of data reports. . 

Due to stakeholder concerns regarding employee access to health care provider 

recommendations the following amendments to the cholinesterase monitoring rule were adopted 

for 2006: 

The employer must: 

• Provide a completed CHOLINESTERASE MONITORING HANDLING HOURS REPORT 

(F413-065-000) to the physician or other licensed health care professional (LHCP) for 

each employee receiving a periodic cholinesterase blood test and make 

 sure the report is submitted to the laboratory with each periodic cholinesterase test. 

• Obtain a written recommendation from the health care provider for each 

 employee’s blood test and evaluation (including baseline tests) and make sure that 

 the employee receives a copy of the health care provider’s written recommendation 

 within 5 business days after receipt. 

 

4

 Pesticide handling is defined in WAC 296-307-11005 

5

 Employer requirements for response to significant cholinesterase depression are found in WAC 296-307-14825 

6

 Standard Operating Procedures for the Determination of Red Blood Cell and Serum Cholinesterase (2005) 7

 The Scientific Advisory Committee for Cholinesterase Monitoring: Report to L&I (2006) 

8

 Bodies such as the World Health Organization, American Conference of Governmental Hygienists, and the state of 

California have identified a 20% decrease in cholinesterase activity as indicative of pesticide overexposure. 
Cholinesterase Monitoring in Agriculture Page 5 of 21 

January 2007 

• Instruct the health care provider to not reveal in writing or in any other communication 

with you any findings or diagnoses unrelated to occupational exposure. 

• Make sure that any employee declining participation in the cholinesterase testing 

program receives a copy of the signed declination statement within 5 business days 

 after receipt. 

The legislature has authorized annual expenditures of up to 1.6 million dollars from the L&I 

Accident Fund to cover the costs of laboratory testing, and to reimburse employers for other 

clinical and related administrative costs incurred. Employer reimbursement policies and 

protocols a can be found at 

http://www.lni.wa.gov/Safety/Topics/AtoZ/Cholinesterase/files/413062af.pdf . Testing, data 

collection, and employer reimbursement costs for calendar year 2006 totaled ~$253,170.00. 
Cholinesterase Monitoring in Agriculture Page 6 of 21 

January 2007 

Laboratory program 

The PHL continued to provide exemplary services in 2006. The addition of a laboratory 

technician 3, provided by L&I, bolstered resources dedicated to the program. 

Both internal and external (blind sample submissions) quality control programs were utilized to 

monitor testing competency. Cholinesterase Scientific Advisory Committee (SAC) analysis of 

quality control data showed good agreement between internal and external QC data, 

demonstrating a lack of bias in internal laboratory measurements. A detailed discussion of 

laboratory data quality can be found in the 2006 SAC report to L&I 

(http://www.lni.wa.gov/Safety/Topics/AtoZ/Cholinesterase/default.asp).

As planned, and as consistent with medical surveillance programs required by other DOSH rules, 

the PHL will no longer be providing testing services and testing will move to the commercial 

sector in 2007. L&I has worked with interested private laboratories to identify a single 

laboratory to provide testing services beginning in 2007. Use of a single laboratory serves to 

eliminate test variability between laboratories. 

 Laboratory evaluation criteria included; 

• Licensure under the Washington State Laboratory Quality Assurance Office 

 or the Clinical laboratory Improvements ACT (CLIA). 

• Ability to perform red blood cell (acetylcholinesterase) and serum 

(butyrylcholinesterase) cholinesterase testing utilizing the Ellman Method. 

Test protocols must be reviewed and approved by the Washington State Public 

Health Laboratory. 

• Demonstration of a robust quality assurance program including, but not limited to; 

 Participation in the College of American Pathologists cholinesterase 

 proficiency testing program 

 Submission of a quality assurance plan with approval by the Public 

 Health Laboratory 

 Routine review of quality assurance data by the Public Health 

 Laboratory.

• Ability to report test results within 5 days of sample collection. 

• Maintenance of test results and related demographic information in an 

Aggregate electronic data base with transfer of surveillance data to L&I on a 

scheduled basis.

L&I has chosen Pathology Associates Medical Laboratories (PAML), Spokane WA, to provide 

all testing services beginning January 15, 2007. Ongoing approval will be dependent of factors 

including 1) demonstrated laboratory capacity to manage and process samples as dictated by 

standard operating procedures, 2) maintenance of formalized QC programs, 3) competency of 

data management systems, and 4) customer service programs. 
Cholinesterase Monitoring in Agriculture Page 7 of 21 

January 2007 

Summary of the 2006 Medical Monitoring Experience 

As in 2004 and 2005 the vast majority of employers participating in the medical monitoring 

program had operations located in L&I Region 5 (West Adams, Benton, Chelan, Columbia, 

Douglas, Franklin, Grant, Kittitas, Okanogan, Walla Walla and Yakima counties.) L&I Regions 

1 (Island, San Juan, Skagit, Snohomish, and Whatcom) and 4 (Clark, Cowlitz, Grays Harbor, 

Klickitat, Lewis, Mason, Pacific, Skamania, Thurston and Wahkiakum) accounted for the remainder of 

the samples submitted 

Table 1. Monthly blood samples submitted 2004-06 (2006 SAC report)

Time Period Number of Samples Per Month & Year 

Month 2004 2005 2006 

January 22 74 22 

February 1039 1127 239 

March 1338 1376 1076 

April 459 144 612 

May 331 97 296 

June 105 35 257 

July 75 23 80 

August 40 70 * 

Total Blood Samples 3409 2946 2582 

* 2006 analysis included data collected from January through July 

During the 2006 pesticide application season, 244 employers and 1889 employees submitted 

cholinesterase baseline tests. The number of samples submitted to the lab from January through 

July totaled 2582 (Table 4.1) The total number of samples decreased 12-13% each year of the 

program, presumably (at least in most cases) because their exposure levels remained below 30 

hours in any one 30-day period and employer actions resulting in decreased use of cholinesterase 

inhibiting pesticides. 

Of the 471 employees who received at least one periodic test, 50 employees (10.6 percent) 

received at least one periodic test result with a 20 percent or greater cholinesterase depression, 

requiring the employer to evaluate pesticide handling practices for possible deficiencies. Of 

those same 471 employees, 7 (1.5 percent) were temporarily removed 9

 from exposure due to a 

more significant depression (at least 30 percent depression in red blood cell [RBC] 

cholinesterase or at least 40 percent depression in serum cholinesterase (Table 2.). The 57 total 

employees who experienced a significant cholinesterase depression in 2006 worked for 30 

different employers. Only two employees experienced an RBC ChE depression with one of these 

 

9

 Employees may return to handling covered pesticides when cholinesterase levels return to within 20% of baseline. 

While medically removed from exposure to covered pesticides employee pay, seniority and other benefits are 

maintained at the pesticide handler level for a maximum of 3 months. 
Cholinesterase Monitoring in Agriculture Page 8 of 21 

January 2007 

employees experiencing both an RBC and serum ChE depression. No employees were 

identified, through the monitoring program, with symptomatic pesticide illness. 

Table 2. Comparison of employer and employee cholinesterase testing and significant 

cholinesterase depressions in 2004-06 

2004 2005 2006 

Employers participating in 

testing 

380 316 244 

Employees submitting 

baseline tests 

2630 2263 1889 

Employees with at least 1 

periodic test 

580 611 471 

Periodic tests 911 970 692 

Employees with ChE 

depression to work 

evaluation level 

97 (16.7%) 49 (8.0%) 50 (10.6%) 

Employees with ChE 

depression to exposure 

removal level 

22 (3.8%) 10 (1.6%) 7 (1.5%) 

In adopting RCW 49.17.285, the Legislature required employers to submit pesticide handling 

hours to L&I on each employee who received a periodic test. The SAC analyzed handling hours 

in relation to change in cholinesterase levels. No significant relationship was found for RBC 

cholinesterase. A small relationship was found for serum cholinesterase. The current 30 hour 

exposure threshold will remain in place in light of the SAC finding no conclusive evidence 

supporting a change. 

The rule allows covered pesticide handlers to decline participation in the testing program. The 

2003 Agriculture Cholinesterase Monitoring Cost Benefit Determination 

(http://www.lni.wa.gov/wisha/p-ts/Cholinesterase/ChE-BCD-Final.pdf ) estimated that the 

declination rate would be approximately 15%. In an attempt to assess the proportion of handlers 

offered participation in the program but declining testing from the health care provider, L&I 

surveyed the five health care clinics performing the majority of baseline cholinesterase tests. 

Each clinic was asked how many handlers were referred to the clinic and of those, how many 

declined participation. All clinics had a less than 15% declination rate, well within the expected 

rates (Table 3.). There are no comparable data for 2004. 
Cholinesterase Monitoring in Agriculture Page 9 of 21 

January 2007 

Table 3. Declination rates at the five clinics providing the most baseline cholinesterase 

blood samples. (2006 SAC report) 

Provider Baselines Declinations Declination Rate 

2005 2006 2005 2006 2005* 2006 

1 559 576 65 89 10.4 13.4 

2 117 87 1 5 >0.1 5.4 

3 73 118 10 34 12.0 22.3 

4 106 61 14 5 11.7 7.6 

5 701 623 120 51 14.6 7.6 

Total 1556 1465 210 184 11.9 11.2 

 

The rule allows employees to either choose to participate or decline participation in the 

employer’s cholinesterase testing program. The option is consistent with other WISHA rules 

that contain medical surveillance provisions. As an additional protection against potential 

coercion regarding the employee’s decision to participate in the program the rule includes the 

requirement that this decision is made in conversation with the health care provider. There have 

been no cases of potential coercion identified. L&I believes that adding additional employer 

requirements and dedicating program resources to track employee declinations is not justified. 
Cholinesterase Monitoring in Agriculture Page 10 of 21 

January 2007 

L&I Consultation and Compliance Activities 

In 2006, L&I transitioned to use of standard consultation and compliance programs in response 

to significant cholinesterase depressions (ChE depression >20% from baseline). WISHA 

Regional Directive 33.27, Cholinesterase Depression 

(http://www.lni.wa.gov/Safety/Rules/Policies/PDFs/WRD3327.pdf ), provides consistent 

enforcement policy. Employers with employees who experienced significant cholinesterase 

depressions were contacted and offered field consultation services. Compliance referrals are 

made under the following circumstances: 

• The employer declines the offer of consultation services for a second time. 

• An employer has received at least 2 consultations as a result of cholinesterase 

depressions but continues to have additional employees with a significant 

cholinesterase depression. 

• Consultation identifies circumstances that warrant a compliance referral, e.g. 

hazards are not abated in a timely manner. 

• DOSH Technical Services identifies trends or circumstances that indicate 

employer safety program deficiencies, e.g. cholinesterase depression clusters 

or ongoing employee cholinesterase depressions. 

The ChE field consultations and enforcement investigations were performed by one of five 

DOSH consultation and compliance staff. DOSH consultants collected surveillance information 

using a standard series of questions (see WRD 33.27). The questions included worker name, 

birth date, primary language and number of years as a handler. The employer name was recorded 

along with additional information regarding the number of acres, crop types, the types of ChE 

inhibiting pesticides handled, the number of handling hours, handler training, types of pesticide 

handling activities, use of personal protective equipment (PPE), decontamination facilities, 

handler symptom history, and identification of the potential cause of exposure. The investigator 

summarized the reports for use by the scientific advisory committee. Employers who received a 

ChE consultation or compliance inspection from DOSH are required by state law to correct any 

serious job safety and health hazards or deficiencies found. 

Twenty-one of the 30 employers who had employees with ChE depression received consultation 

visits. Two additional employers received compliance visits due to having multiple workers with 

depressed cholinesterase levels. 

The vast majority of consultations revealed that over-exposures occurred in tree fruit operations. 

There was one employee working in a field crop operation (onions, beets, green beans, grass 

seed) applying pesticides to the ground from tractor mounted spray booms. Air blast application 

of the covered pesticides may not be the sole contributing exposure factor for the workers with 

depressed cholinesterase levels. Other exposure hazards found include not properly 

decontaminating before meal or bathroom breaks and not wearing appropriate personal 

protective equipment, e.g., the use of leather boots when the pesticide label required the use of 

protective footwear. 
Cholinesterase Monitoring in Agriculture Page 11 of 21 

January 2007 

Common rule violations found during consultation visits include: 

• WAC 296-307-6005 – Develop and maintain written respiratory protection program. 

• WAC 296-307-13050 – Provide decontamination supplies (e.g. water, soap, disposable 

hand towels, and an emergency change of clothing). 

• WAC 296-307-13025 – Provide effective pesticide safety training. 

• WAC 296-307-60805 – Provide effective training on the use and maintenance of 

respirators. 

• WAC 296-307-13045(3)(f) – Ensure use of appropriate personal protective equipment 

• WAC 296-307-14835 – Conduct and document work practice evaluations of employees 

experiencing significant ChE depression. 

Potential exposure routes identified during consultation visits include: 

• Cotton ball cap (bill exposed) worn under protective head gear 

• Lack of chemical resistant footwear 

• Improper maintenance and storage of respirators 

• Improper decontamination of personal protective equipment, incl. respirators 

• Exposure to contaminated equipment 

• Overuse of respirator cartridges 

• Use of cotton gloves under rubber gloves, 

Two employers were referred for compliance investigations. Both employers had clusters of five 

employees with cholinesterase depressions greater than 20% from baseline. In the first 

compliance investigation, the employer was cited for two serious violations: 1) not ensuring 

handlers’ head gear (hats) were chemical resistant and 2) not ensuring emergency eyewash was 

available on every tractor used to spray pesticides. There were no serious violations found on the 

second compliance investigation. However, the compliance officer noted potential exposure 

routes: 1) not washing hands before and after using the bathroom, 2) wearing hooded cotton 

sweat shirts under rain gear, and 3) not showering or changing clothes after applying pesticides. 

In addition to the compliance investigations, L&I conducted scheduled investigations with a 

group of employers who had participated in the ChE monitoring program in 2005 but had not 

participated in the program in 2006. One hundred twenty-four employers were identified and 

thirty-one (~25%) were chosen to receive a compliance visit. A focus of the inspection was to 

determine compliance with the cholinesterase monitoring rule. Based on a review of handling 

records by DOSH compliance inspectors all of the inspected employers were in compliance with 

the ChE monitoring rule. Employers made the following engineering or administrative controls 

to mitigate worker exposure to covered pesticides: 
Cholinesterase Monitoring in Agriculture Page 12 of 21 

January 2007 

• The owner applied the covered pesticides. 

• The employer eliminated the use of cholinesterase-inhibiting pesticides. 

• The farm was converted to organic farming. 

• The employer hired additional pesticide applicators to decrease the number of 

exposure hours. 

• The employer monitored and restricted handling hours to keep workers under the 

30 hour threshold. 

• The employer switched from Guthion to Assail for coddling moth. 

• The employer increased spray rate per acre to limit exposure time. 

• The employer increased use of integrated pest management techniques. 

The majority of significant cholinesterase depressions occurred during the beginning of the tree 

fruit application season (dormant season spraying). Later depressions tended to coincide with 

orchard activities such as application of fruit thinning and post bloom cover sprays. During 

dormant season spraying, the organophosphate insecticide Lorsban (chlorpyrifos) is used. The 

fact that the majority of significant cholinesterase depressions were due to depression of serum 

cholinesterase is consistent with the use of chlorpyrifos as it has an affinity to bind with serum 

cholinesterase. Other cholinesterase inhibiting pesticides handled by these employees include 

Guthion (azinphos-methyl), CarzolTM (formetanate hydrochloride), ImidanTM (phosmet.), and 

Sevin (Carbaryl). 
Cholinesterase Monitoring in Agriculture Page 13 of 21 

January 2007 

2007 Program Highlights 

The 2004-06 experience has demonstrated the feasibility of a state wide occupational 

cholinesterase monitoring program. The rule has provided clear direction and support to 

employers, employees, and health care providers. The cholinesterase monitoring program 

continues to demonstrate improved function and has reached a level of self sustaining maturity. 

The Cholinesterase Monitoring Benefit-Cost Determination listed the following probable 

benefits of a cholinesterase monitoring rule: 

• Greater certainty about the frequency of pesticide overexposure 

• Avoidance of serious pesticide illness 

• Improved compliance with the pesticide worker protection standard 

• Identification of any existing PPE, work practice and engineering control requirements 

that are not sufficient to protect pesticide handlers from exposure 

• Greater awareness of chemical and exposure hazards 

The information gathered over the last three years has shown that these benefits are being 

realized. There is an increased awareness in the agriculture industry of the hazards inherent in 

pesticide handling, causes of overexposure are being identified, handler pesticide training 

programs have been bolstered and educational opportunities expanded, and laboratory blood 

cholinesterase testing has shown itself to be an effective method to identify overexposure prior to 

the onset of illness. While much data has not been available to allow for precise quantification 

of benefits it is apparent that the goals of increased knowledge and improved worker health 

protection have and are being achieved. 

The rule functioned well in 2006 and is quickly moving to a level of self sustaining maturity. No 

immediate rule or enforcement policy changes are immediately anticipated for 2007. While the 

rule will remain intact, program changes that will occur are: 

• Laboratory services will transition from the Public Health Laboratory to Pathology 

Associates Medical Laboratories (PAML). The transition to the private sector was 

anticipated and is consistent with the provision of medical surveillance services contained 

in other rules, e.g. lead, cadmium. All employer testing costs will continue to be 

reimbursed through existing structures. 

• In previous years L&I often had knowledge of test results prior to the health care 

provider. Due to this situation L&I elected to notify the health care provider by 

telephone of all significant cholinesterase depressions. In 2007 all test results will be 

reported electronically (web based, fax) by the laboratory to the health care provider 

eliminating the need for telephone reporting. 
Cholinesterase Monitoring in Agriculture Page 14 of 21 

January 2007 

• Laboratory surveillance and data management will begin transitioning from the 

Department of Health (DOH) to PAML. In order to ensure that appropriate data 

management systems are in place DOH will continue to operate the Cholinesterase 

Monitoring Data System (CMDS) through 2007 and in parallel with PAML. CMDS will 

be operated out of the DOH Office of Environmental Assessments Pesticide Program. 

L&I will continue to collect and manage laboratory test and field surveillance data 

gathered during consultation and compliance activities. This data will be available for 

analysis and used to direct rule and related program improvements. 

At the time of this writing L&I has not had sufficient time to thoroughly consider the 

recommendations provided in the 2006 SAC report (Appendix). While many of the 

recommendations are specifically provided for long term consideration it may be practical to 

take more immediate action on some recommendations. L&I will continue to work with 

stakeholders in order to make these determinations. 

Any questions or requests for additional information should be directed to: 

John Furman 

Industrial Hygiene Services Manager 

Department of Labor & Industries 

Division of Occupational Safety & Health 

360-902-5666 

Furk235@lni.wa.gov 
Cholinesterase Monitoring in Agriculture Page 15 of 21 

January 2007 

Cholinesterase Advisory Committees 

Scientific Advisory Committee 

• Dave Bonauto, MD, Associate Medical Director of the Department of Labor and 

Industries, Safety and Health Assessment for Research and Prevention Program 

• Rupali Das, MD, MPH, California Department of Health Services 

• Allan Felsot, PhD, Washington State University Extension Specialist and Environmental 

Toxicologist 

• Matthew C. Keifer, MD, MPH, Associate Professor of Environmental and Occupational 

Health Sciences, University of Washington 

• Michael O’Malley, MD, MPH, Staff Physician with UC Davis Employee Health Services 

and consultant to the California Department of Pesticide Regulation's Worker Health and 

Safety Branch 

• Juliet VanEenwyk, PhD, State Epidemiologist for Non-Infectious Conditions, 

Washington State Department of Health 

• Gerald van Belle, PhD, Professor of Biostatistics and Environmental and Occupational 

Health Sciences, University of Washington 

• Barry Wilson, PhD, of the Department of Environmental Toxicology at the University of 

 California, Davis 

Stakeholder Advisory Committee

Allan Felsot, PhD Professor & Extension Specialist, Entomology/Environmental 

Toxicology, Washington State University 

Jim Jesernig Attorney, Washington state potato growers 

Matthew Kiefer, MD, MPH, Associate Professor, Depts. of Medicine & Environmental & 

Occupational Health Sciences, University of Washington 

Nathan Lacy, PhD, Office Director for Environmental Laboratory Services, 

Washington State Public Health Laboratory 

Evi Licona, Columbia Legal Services 

Kirk Mayer, Washington Growers’ Clearing House 
Cholinesterase Monitoring in Agriculture Page 16 of 21 

January 2007 

Erik Nicholson, United Farm Workers 

Dorothy Tibbetts Manager, Office of Pesticide Investigation and Surveillance, WA State Dept. 

of Health 

Ann Wick Washington State Dept. of Agriculture, Pesticide Management 

L&I appreciates the work of the Scientific Advisory and Stakeholder Committees and thanks 

their respective employers for making them available to assist in evaluating the rule and its 

implementation. 
Cholinesterase Monitoring in Agriculture Page 17 of 21 

January 2007 

APPENDIX 

2006 Cholinesterase Scientific Advisory Committee Recommendations 

The following recommendations are contained in the 2006 Scientific Advisory Committee Report 

to the Department of Labor & Industries 

http://www.lni.wa.gov/Safety/Topics/AtoZ/Cholinesterase/files/2004-06ChESACreport.pdf 

General recommendations for program improvement

1. Continue retrospective evaluation of program results, and consider future changes to the 

rule. The SAC feels that there would be scientific merit in narrowing the scope of the rule, at a 

point when it could be established that the current rule includes handlers for whom the risk of 

significant cholinesterase depression is categorically less than for the handler population as a 

whole. This will require expanded data collection and ongoing review of program results. 

2. Continue central data collection for the life of the program. The SAC suggests strongly

that a centralized data collection system similar to CMDS continue and DOSH analyze 

these data annually and compare them across years. Sufficient resources need to be 

assigned to the program to assure that data quality is consistent and that important trends 

in cholinesterase depressions are identified and appropriate responses taken.

3. Collect additional data with each periodic test. Continued collection of handling hours 

might be useful if other information regarding workplace conditions and practices was 

also collected for each handler. Examples of additional questions might include type of 

crop, product applied, method of application. This would be important for considering 

rule changes based on patterns of exposure by any of these factors. Absent this additional 

detail, it is doubtful if compiling handling hours as a routine feature of the monitoring 

program is justified, so long as those data are maintained by each employer.

4. Establish a provider certification or other provider quality assurance program . The 

SAC believes that role of the health care provider and clinic staff in informing the 

handler about the program, in obtaining medical and related information from the 

handler, and in interpreting ChE values is critical to the quality of the program. There is 

an ongoing need to provide training and update information to the staff that actually 

counsel handlers and carry out other monitoring program functions. The SAC 

recommends that L&I develop a mechanism for assuring quality in this role, particularly 

as medical and clinic personnel change, and as the program moves from a start-up phase 

with relatively close oversight to an ongoing program. Ideally, each handler would have 

a designated health care provider who would be certified by L&I and would participate in 

annual training. In addition to provider certification, L&I should develop a system to 

certify participating clinics. The certification programs need to pay ongoing attention to 

the training and guidance materials on how to conduct cholinesterase monitoring. 

Periodic or ongoing web based training opportunities could be made available and should 

be a requirement for participation for new and continuing clinic participants. These 

should be periodically updated based on information obtained through the systematic 

reviews of monitoring program results, field consultations or inspections, and through 
Cholinesterase Monitoring in Agriculture Page 18 of 21 

January 2007 

consultation with national experts and the participating clinics. These updates should incorporate 

advances in communication and laboratory technology. This activity could be assigned to the 

Office of the Medical Director of L&I or could be a shared responsibility between DOHS and the 

University of Washington Occupational Medicine Program.

5. Maintain Laboratory Services. In 2004 and 2005, the SAC expressed concern that 

changing the laboratory or moving to multiple labs providing monitoring services would 

threaten the validity and comparability of the test data. Given the high degree of 

acceptance, and objective measures of reliability demonstrated in 2004-2006, purely 

technical considerations would indicate that the safest course would be to continue to use 

the PHL for program support. At this writing, there is active procurement to identify a 

commercial laboratory to replace the Public Health Lab as the provider of testing 

services. SAC reasserts the scientific value of having a single lab of known quality 

supporting this program. The transition to a new lab carries inherent risks: data quality 

and user confidence in it may suffer as a transitional effect, or might fail to be adequate 

for multiple years. This would not only risk increasing the number of false negative 

results (leaving handlers unprotected) and/or false positive results (wasting state and 

employer resources), but could affect overall program sustainability if participation rates 

are then affected. Specific recommendations for how risks might be minimized in this 

transition are offered in the next section. 

6. Continue active L&I Consultation Services follow-up with employers when there are ChE 

depression alerts. The SAC recommends that there be a response time goal set for 

consultation field visits before the start of each monitoring season, and that this be kept as 

short as is practical (bearing in mind that as little as 9.5 days was demonstrated to be 

achievable in 2005 for response to exposure removal alerts, but also that employer 

scheduling constraints affect this). Additionally, the SAC recommends that L&I clearly 

communicate the roles of consultation and compliance groups when there are repeated 

ChE depressions for a handler or multiple ChE depressions for handlers at a single 

grower.

7. Develop new or better methods for disseminating information on exposure reduction. 

The SAC encourages L&I to develop systems that allow for timely sharing of 

information gathered during field activities including consultation or compliance visits in 

order to communicate new findings within a growing season to the various state agencies 

and other groups that are involved in conducting and developing farm worker and 

agricultural employer training, outreach and pesticide license testing related to 

agricultural pesticide use. This system would likely be more effective if it could be 

operated jointly with other groups involved in agricultural worker safety issues.

8. Continue to assess program performance and impact. Systematic review of the program 

should include an assessment of the participating clinic practices, satisfaction surveys of handlers 

and employers, review of quality assurance practices of the participating laboratory or 

laboratories, response time for notification of depressions, the nature of employee response to 

notifications of depressions and effect of the cholinesterase monitoring rule on chemical choices, 

and handler assignments. Although this program is becoming more established and routine, 

there are several important aspects of it that are as yet poorly understood or need 

continued tracking. These include: 
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January 2007 

Effectiveness of educational outreach efforts (for providers, handlers, and employers). 

This includes efforts to inform program participants about changes in program aspects, 

providing basic information about the program to new participants, and ongoing efforts to 

educate employers and handlers regarding the exposure risks.

Handler perception. As the handlers are the primary beneficiaries of this program, their 

continued participation and thus satisfaction with the program should be assessed and 

optimized. The SAC cannot determine why some handlers decline to participate in the 

program. This information could be important for assessing how employers and providers 

present the program, how handlers perceive the program, and the effectiveness of 

educational outreach efforts (to growers, pesticide handlers, and to health care provider 

groups). Given that the population presently participating is largely Hispanic, many of 

who speak English as a second language, particular attention needs to be paid to the 

understanding that this population has of the potential benefits of this program.

In addition, a related (research) question that has not been evaluated under the present 

system is the effect of the program on the attitude of handlers toward the risks they face 

in handling covered pesticides. The initiation of a medical test in response to a handler 

exposure emphasizes the importance of this exposure to the handler and the employer. 

The effect on knowledge, attitudes, and behaviors of handlers and employer due to the 

existence of this program is a dimension of program that would be valuable to understand 

and describe for the benefit of future such programs.

Employer participation. The SAC recommends that compliance investigations (checking 

“drop-out” employers or other spot checks of employer compliance) as an active part of 

the overall cholinesterase monitoring program be continued. Active investigation of other 

agricultural operations not currently under the rule which use organophosphate and N-methylcarbamate pesticides might also be considered

Handler notification of routine results. The failure of handlers to get their results back in 

a timely way could be a significant disincentive for future participation. The SAC as well 

as Stakeholders unanimously support timely feedback to handlers, even for results that do 

not indicate overexposure to pesticides. Currently, the employer is required by L&I to 

provide timely interpretation of tests to each handler. Routine assessment of this aspect 

of employer compliance with the rule is needed. This could be added as a question on 

each periodic blood draw (e.g., “Have you been notified of your results from the prior 

month?”). The establishment of a central call in number and a unique identifier provided 

to the handler is another way to resolve this problem. 

9. Support the research value of the monitoring program. The opportunity to recognize 

common factors leading to pesticide overexposure and cholinesterase depression has not been 

realized as yet. New understanding of the underlying causes of exposure or failures of protective 

measures are not likely to arise from routine monitoring effort per se, but can benefit from 

monitoring activities and data. The SAC recognizes that research is not the primary objective of 

ChE monitoring, and that L&I / DOSH are regulatory programs. The SAC recommends that 

research uses of the program by third parties be encouraged by L&I, through cooperation and, 

where feasible, through selective opportunities for research support. Beyond sharing of 

program data as they currently exist, “cooperation” might include adopting modified 

practices to assist research, where such modifications are not intrusive. Some 
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January 2007 

possibilities for how this might be done include: 

• The Department could organize and support an annual meeting to allow interested 

 non-L&I groups to obtain and share analysis of program results. A related 

 activity would be for Stakeholders to confer with L&I to identify priority issues 

 where investigation is needed for program assessment or improvement purposes. 

• The Department could support (either financially, or by cooperation) periodic 

 studies conducted by third parties such as WSU or UW, that explore the causes of 

 cholinesterase depression, the rate of participation among eligible employers and 

 the reasons for non-participation of both handlers and employers. These projects 

 could be in response to solicitations from L&I, or unsolicited research ideas, or 

 both. 

• The SAC feels that L&I should be directive in research that it funds, and that 

 there should be a significant Agency need justifying funded projects.

Recommendations for maintaining program quality in 2007

Based on information from L&I, the SAC expects that the ChE monitoring program will 

undergo significant changes for the 2007 growing season. Notable potential changes 

include use of a single commercial laboratory and decreased involvement of L&I and the 

DOH in system function. It is unclear whether these changes will impact the effectiveness 

of the program. 

The SAC recommends evaluation of the program for at least one additional year to assess 

• Laboratory accuracy and timeliness for running the assay, matching baseline and 

 periodic tests, calculating percent depression, and notifying providers. 

• Provider timeliness and accuracy in matching baseline and periodic tests, calculating 

 percent depression, and notifying growers and handlers. 

To accomplish this evaluation, L&I needs access to participant identifiers and test results 

from the laboratory and from providers. 

Manual matching of periodic samples to a single handler continues to require significant 

effort and could be a source of error in the future. As this task is reassigned to a 

commercial provider, the SAC recommends that L&I and stakeholders consider the 

feasibility of issuing unique identifier codes to each handler to be used by the health care 

provider in collecting and submitting samples.

The SAC has considered the arguments for and against continuation of the RBC ChE 

testing. Arguments against continuing to perform this test are that the RBC test does not 

detect very much exposure and added only one “work practices” alert in 2006. It is 

therefore potentially a case of significant cost and effort for little return. The 

performance on this test is inherently less robust than for the serum ChE, and no 

appropriate control material is available for QC purposes. Arguments for continuing to 

perform this test are that the marginal savings of dropping this test would be small (an 

example cited by L&I staff was that private labs would charge $25/sample for one test 

and $30/sample for both tests); the response of RBC ChE compared to serum ChE could 

change if the pesticides in use change, and the failing to know about RBC ChE 

depression is more significant than for serum ChE depression, as the RBC enzyme is 
Cholinesterase Monitoring in Agriculture Page 21 of 21 

January 2007 

biologically closer to the health effect of concern (depression of AChE in the central 

nervous system). Our recommendation is that L&I determine the cost differential of one 

test versus both tests as part of its lab selection process, and that if the differences are not 

large, that both tests be continued for the present. 

To assure quality of the laboratory tests, the SAC recommends that L&I, in consultation 

with stakeholders provides oversight of laboratory operations by establishing definitions 

and processes for which the laboratory can provide documentation. These include definitions and 

processes for assuring: 

• Data validity on a batch or submission basis. 

• Laboratory capacity to receive sample submissions at their peak seasonal rates 

 and to complete analyses without exceeding holding times. 

• Laboratory ability to store samples at –70°C for up to 6 months in order to 

 respond to any questions arising from patterns in results across the monitoring 

 season. 

• Extra-lab quality control testing (operated by L&I or by health care providers 

 under L&I direction) to serve as an adjunct to within-lab QC efforts and capture 

 possible sources of variability related to sample collection and shipment. 

• Lab certification by external bodies based on performance testing, such as the 

 College of American Pathologists (CAP) program, is an important qualification of 

 the lab providing ChE testing. 

• Interlab comparison programs and the development and use of reference or 

 benchmark samples (particularly for the membrane-bound form of ChE detected 

 in the RBC assay) are highly desirable 

An annual audit of lab performance according to these standards and criteria is 

recommended. If the audit is conducted by L&I staff, disclosure of the findings and 

recommendations to stakeholders is also recommended.