Pesticides Handlers and Cholinesterase Monitoring

Certain pesticides, specifically organophosphate or N-Methyl-carbamate pesticides (categories I or II), can severely harm workers. These pesticides harm the central nervous system. Symptoms and health effects can include:

  • Blurred vision
  • Diarrhea
  • Tremors or seizures
  • Loss of consciousness
  • Death.

Workplace safety and health regulations are in place to protect workers from the harmful effects of organophosphate and N-methyl-carbamate pesticides.

Monitoring cholinesterase levels in workers who work with these pesticides can identify a problem before a worker gets sick.

Employer Information

Cholinesterase Monitoring Rule and Employer Requirements Summary

The Cholinesterase Monitoring rule (WAC 296-307-148), in summary, requires employers of agricultural pesticide handlers who use toxicity category I or II organophosphate or N-methyl-carbamate pesticides (also called carbamates) to take the following steps:

  • Record the number of hours employees spend handling these pesticides.
  • Implement a medical monitoring program for workers who could meet or exceed the handling threshold of 30 or more hours in any consecutive 30-day period. Identify a medical provider to provide medical monitoring services.
  • Make baseline and periodic cholinesterase testing available to employees who could meet or exceed the handling threshold.
  • Investigate work practices when a handler's red blood cell (RBC) or serum cholinesterase level drops more than 20 percent below the employee's personal baseline.
  • Restrict employees from handling and other exposures to organophosphate and N-methyl-carbamate pesticides when recommended by a health care provider.
  • Provide training on cholinesterase monitoring to covered employees.
  • Report employee handling hours to the medical provider with each periodic test.
  • Maintain medical monitoring and other records for seven years.

Employer Cost Reimbursement

You may request reimbursement related to cholinesterase monitoring for the reasonable costs of:

  • Training,
  • Recordkeeping, and
  • Medical expenses.

Fill out and submit a Cholinesterase Monitoring Reimbursement Request form (F413-062-000) along with required documentation. You will need to attach a completed Statewide Payee Registration form (F120-115-000) to be paid.

Benefits of Cholinesterase Monitoring

Cholinesterase monitoring:

  • Can prevent illnesses after an over-exposure.
  • Increases awareness and improves overall workplace safety related to pesticide use.
  • Improves pesticide illness diagnosis.
  • Decreases the risk of unintended exposures to worker’s families.

Employee Medical Monitoring

The cholinesterase medical monitoring program must include:

  • A discussion with a health care provider.
  • A decision by the worker to have or not to have blood tests.
  • An annual baseline blood test prior to exposure to these pesticides.
  • Periodic blood tests to assess worker exposures to pesticides.
  • Work practice evaluations for significantly depressed cholinesterase levels.
  • Removal from handling of organophosphate or carbamate pesticides when recommended by the medical provider.

Employer Reported Handling Hours

Report each employee’s handling hours for these pesticides directly to the medical provider at each periodic test. There is a spreadsheet and instructions to help with this on the Resources tab.

Laboratory Services

Verify your medical provider uses LabCorp for all cholinesterase laboratory testing.

Employee Notification of Health Care Provider Recommendations

Obtain a written recommendation from the health care provider for each employee test (including baselines) and evaluation. Provide a copy of the recommendation to the employee, either directly or through the health care provider, within 5 days of receipt.

L&I Consultation Services

Get Help From L&I Safety and Health Consultation. Contact an L&I safety and health consultant with any questions.

Medical Provider Information

Background and Purpose

The Cholinesterase Monitoring rule (WAC 296-307-148) requires agricultural employers to provide medical monitoring for workers who handle toxicity Category I or II organophosphate or N-methyl-carbamate cholinesterase-inhibiting pesticides.
Medical monitoring provides several benefits. It prevents over-exposure to cholinesterase-inhibiting pesticides before illness occurs. Additionally, it increases employer and worker awareness of pesticide hazards and reinforces appropriate work practices. If blood testing detects cholinesterase depression, the employer is directed by the medical provider to evaluate the worker's pesticide handling practices. If cholinesterase levels fall below specified removal levels, medical monitoring facilitates case management and the employer is directed by the medical provider to remove the worker from further exposure until cholinesterase levels regenerate and it is safe for the worker to return to working with cholinesterase-inhibiting pesticides.

The Nervous System & Cholinesterase

Cholinesterase (acetyl cholinesterase) is an enzyme that removes the chemical neurotransmitter acetylcholine from the junctions between nerve cells. Cholinesterase serves as the nervous system's "off switch" and is essential to the normal function of the nervous system.

The importance of cholinesterase levels

Exposure to organophosphate or N-methyl-carbamate pesticides can lower the level of available cholinesterase. Without the normal protective levels of cholinesterase, nerves in the body may be overstimulated to the point of exhaustion, leading to symptoms ranging from blurred vision, diarrhea and tremors to seizures, loss of consciousness and even death.
Monitoring cholinesterase levels in the blood through simple laboratory tests can detect cholinesterase depression prior to the onset of illness. When significant cholinesterase depression is identified employers are required to evaluate their pesticide worker protection program and make corrections to prevent further over-exposure.

Worker medical monitoring

Medical monitoring is a surveillance program that monitors agricultural workers who handle toxicity Category I or II organophosphate or N-methyl carbamate pesticides. It consists of periodic measurements of cholinesterase activity levels in workers that are compared to measurements of exposure-free baseline cholinesterase activity levels. Workers who handle cholinesterase-inhibiting pesticides for 30 or more hours in any consecutive 30-day period are covered by the medical monitoring requirements of the rule.

More information can be found in the clinical manual, Cholinesterase Testing: Guidelines for Health Care Providers, which explains and interprets the state program of cholinesterase monitoring.

Laboratory testing

The only laboratory currently approved by L&I to provide cholinesterase testing under WAC 296-307-148 is Pathology Associates Medical Laboratories (PAML now part of LabCorp). 

There is significant variation among cholinesterase testing methods and among laboratories using the same testing method. It is misleading to compare test results from one method to another or from one laboratory to another. Because of this, a laboratory approved by L&I must be used for all cholinesterase tests.

Providers can arrange for test analysis by contacting:

Darrin Schmidt
LabCorp Employer Services
(509) 789 0333

Requirements & Policies

The Division of Occupational Safety and Health (DOSH) Directive Cholinesterase Depression (DD 33.27) sets policy for DOSH consultation and compliance services. Generally, employers will be offered consultation services whenever an employee experiences a significant cholinesterase depression. A referral to compliance may be made when multiple employees experience significant cholinesterase depression and the employer declines consultation support, or circumstances indicate safety program deficiencies, e.g. cholinesterase depression clusters or ongoing employee cholinesterase depressions.


Enforcement Policies

  • DOSH Directive Cholinesterase Monitoring (DD 33.27)
  • DOSH Directive Pesticides in Agriculture (DD 33.25)
Training & Resources

Testing Procedures

Training Materials

Publications, Handouts, Checklists, Sample Programs