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Early season is when orchard workers are most likely to be exposed to cholinesterase-depressing pesticides, judging by Washington State’s cholinesterase-monitoring program, and the pesticide Lorsban (chlorpyrifos) was implicated in the vast majority of cases where depressed cholinesterase was found last year.

Under the program, agricultural workers who are exposed to organophosphate or carbamate pesticides are invited to have their blood cholinesterase levels monitored. Growers must track their hours of exposure.

Cholinesterase is an enzyme that controls nervous system signals. Dr. Carol Ramsey, pesticide education specialist with Washington State University, said the enzyme acts as an off switch. Certain pesticides can depress cholinesterase levels, which can result in an overstimulation of the nerves and overexcitation of muscles. Symptoms include dizziness, blurred vision, stomachache, and a tightness in the chest.

The monitoring program, introduced in Washington in 2004, is designed to identify workers with depressed cholinesterase levels before they show symptoms or reach the point of being ill, Ramsey said. It helps pinpoint hazards that are exposing people to pesticides and identify changes that need to be made in the workplace to reduce exposure.


Because every person has a different level of cholin-esterase in their blood, workers likely to be using organophosphate and carbamate pesticides must have a baseline test before they start handling them. They are then retested after 30 hours of exposure in a 30-day period. Follow-up tests must be done either within three days of meeting that threshold or at regular 30-day intervals.

Cholinesterase can be found in the blood plasma and in the red blood cells. Cholinesterase in the plasma is made by the liver, and so people who have problems with their liver can have depressed levels, Ramsey said.

A 20 percent depression of the cholinesterase in the red blood cells or plasma is considered significant and triggers a workplace evaluation by the Washington State Department of Labor and Industries. A 30 percent depression in blood cells requires removal of the employee from work until the level goes back up to 20 percent of the baseline. Just because the worker has a depressed level, it doesn’t mean they have been poisoned, Ramsey said. Symptoms of exposure to pesticides are likely when the depression reaches 50 to 60 percent of normal.

In 2005, 611 workers had follow-up tests, of whom 49 (8 percent) had depressions of 20 percent, which required workplace evaluations, and 10 (1.6 percent) had 30 percent depressions, requiring workplace removal. Twelve percent of employees declined to be tested. Employers must have workers who decline to be tested sign a declination form.

Most of the depressions were found in people working with airblast sprayers in orchards and vineyards. Lorsban (chlorpyrifos) was the chemical most frequently associated with depressions, and most exposure appeared to be between April 1 and 15, when delayed-dormant spraying was being done. Ramsey said this might have something to do with people wearing extra clothing to keep warm and not cleaning it after work. Depressions were found in workers at all sizes of orchards.

Ramsey said the program pointed out where some practices could be changed to increase the safety of workers, but also showed that many growers are doing things properly.

“If you think of the number of applications going on, there are a lot of people doing it right,” she said.

Safe practices

To protect workers, respirator cartridges should be changed on schedule and the fit of the respirator tested. Personal protective equipment should be cleaned and decontaminated after each use, and the hands and face should be washed thoroughly immediately after the pesticide application. Hands should be washed for as long as it takes to sing the alphabet, Ramsey said. Workers should wash their hands before smoking or eating.

Workers should be discouraged from wearing cotton baseball caps under their protective headgear, because the caps are never washed, and from wearing cotton hooded sweatshirts that are exposed around the face. There have also been instances of people wearing cotton gloves under their rubber gloves or answering cell phones while spraying and contaminating their clothing.

In 2004, the first year of the program, 580 workers had periodic tests, of whom 17 percent had depressions of 20 percent and 3.8 percent had depressions of 30 percent. However, for the first year, periodic tests were only required after 50 hours of exposure to the pesticides in a 30-day period. In 2005, that threshold was reduced to 30 hours.


Ismael Rodriguez, industrial hygienist with the Department of Labor and Industries, said there will be few significant changes to the program for 2006.

The Public Health Laboratory is the only lab approved to do the blood analysis. Employees must receive a copy of the medical results for both their baseline and follow-up tests.

This season, employers will not be reimbursed for the cost of sending their workers for testing, although the cost of the lab analysis will still be paid for.

For more information, check the Web site at and search for “Cholinesterase.”