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During the four years since Washington State introduced its cholinesterase-testing program for farmworkers who handle certain pesticides, the number of people tested has been dropping.

Kirk Mayer, manager of the Washington Growers Clearing House Association and a member of the program’s stakeholder advisory committee, thinks one of the reasons the number of workers tested has dropped is because growers are avoiding having their workers meet the threshold for testing, either by employing more people to do those jobs or by making the applications themselves.

Another reason for the lower participation may be that growers are transitioning to newer pesticides that don’t have the cholinesterase testing requirements, Mayer said.

"They may have been leaning that direction already. A lot of growers have been using less organophosphates, and I think this rule may have speeded up the transition to some of the newer products. A number of growers said it was a deciding factor to begin the transition to organic." The program requires employers to record the number of hours their workers are exposed to Class I and II organophosphate or carbamate pesticides and provide blood testing for cholinesterase after a worker has handled the pesticides for 30 hours in a 30-day period. A baseline test is done before the start of the season for workers who might reach that exposure threshold. Blood samples are analyzed for the cholinesterase levels both in the serum and in the red blood cells (RBC).

If follow-up tests during the season show that the worker’s cholinesterase has dropped by 20 percent or more from the person’s baseline level, the Washington State Department of Labor and Industries must evaluate the workplace to find out how the worker might have been exposed to pesticides. If the RBC cholinesterase level drops by 30 percent or the serum level drops by 40 percent, the worker must be assigned to a new job with no potential pesticide exposure until the levels rise to 20 percent below the baseline.

The Department of Labor and Industries conducts random inspections to check that employers are having workers tested. Although a grower can be fined or lose his or her pesticide applicator’s license for failing to comply with the testing requirements, a cholinesterase depression is not a ­violation of the rule even if it results in a workplace evaluation or removal.

In 2007, a total of 1,857 employees had baseline tests, down from 2,630 in 2004. The number of periodic follow-up tests dropped to 386 in 2007, from 580 in 2004.

Mayer noted that employees can opt out of the program and choose not to be tested even though they qualify for testing. Some don’t like the thought of giving samples or have been suspicious about the program, and some declined to participate last year after blood tests the three previous years showed no significant changes in their cholinesterase levels.


Although the numbers of participating employers, baseline tests, and follow-up tests have all declined over the four years of the program, that’s not the case for the number of workplace evaluations and workplace removals triggered by the testing (see "Cholinesterase Monitoring Results"). The number of workplace removals dropped from 22 in 2004 to 10 in 2005 and 7 in 2006, but rose to 18 in 2007.

Mayer said the program’s advisory committee warns against comparing results from one year to the next because of changes in how the data was analyzed and because of a change in the laboratory analyzing the blood samples.

In 2004, the Washington State Public Health Laboratory did all the blood testing, and was overwhelmed by the number of samples it received, resulting in problems in the shipping, handling, and analysis of the samples, Mayer said. The same lab did the testing for the next two years. In 2007, the program switched to Pathology Associates Medical Laboratories, a private lab in Spokane. The scientific advisory committee reported that because of difficulties the lab had in processing samples, the results in 2007 may be inaccurate. It felt that the serum results (which led to 16 workplace evaluations and 3 workplace removals) were likely to be accurate, but reported that results from the RBC analysis were so variable that all 45 of the RBC-related depression alerts in 2007 could have been false. Despite the lack of confidence in the results, the program still followed through with workplace evaluations and removals, Mayer said.

"I was concerned about what kind of a message we’re sending to pesticide handlers when they have a workplace evaluation or workplace removal when that determination might have been false," he commented.

He was surprised by the problems in analyzing the samples, and said he expected it to be a more exact science than it evidently is.

Among growers, there’s a diverse range of opinions about the program, Mayer said. "Some, for the most part, say it’s a waste of time because we’ve found that none of the pesticide handlers in any of the four years have reported any adverse health effects ­relating to handling organophosphate pesticides."


Initially, workplace evaluations by Labor and Industries generated some valuable information about how workers were being exposed to pesticides and how exposure could be avoided. In some cases, pesticide applicators were wearing all their personal protective equipment, but might be wearing a baseball cap or hooded sweatshirt underneath. When they removed their protective clothing, they continued to wear the baseball cap or sweatshirt, unaware that it might have absorbed pesticide residues and could lead to contamination. In other cases, handlers weren’t cleaning up properly after applications or before taking breaks, or workers were cleaning spray equipment without wearing respirators. The department also found cases where respirator cartridges or filters were not being replaced when they should have been.

Cautions about such practices have been incorporated into hands-on pesticide training programs and provided to growers, but Mayer said after the evaluations have been done for three or four years, he feels it’s unlikely they will generate more useful information. "I think the value of the program will diminish over time," he said, adding that he thinks it’s been more of a research project to try to improve the accuracy of cholinesterase testing.

It’s possible that some depressions are not caused by pesticides at all, Mayer noted. It’s known that the cholinesterase level can be impacted by diet changes, home remedies, and drugs, such as cocaine. "There are other potential causes that haven’t really been researched that may be contributing to a certain amount," he said.

Some workers have had as many as four tests showing depressions during the course of a season, he said. "In some cases, the individuals were removed from work or potential exposure, and they continued to have significant depressions, which raises the suggestion that the depression was not work related."

There are also natural variations in cholinesterase levels from person to person and from hour to hour, although such fluctuations are not supposed to be as ­significant as 20 percent.

Despite the problems with the program, the program is unlikely to be eliminated, Mayer said. "It will disappear eventually just because of a lack of participation, but the state rarely removes regulations from their books."

The only other state that requires cholinesterase testing is California, but Mayer said the California program is less extensive and requires no follow-up or monitoring of results.

For additional information about Washington State’s cholinesterase monitoring program, go to the Web site at asp.