PANUPS: Farm Worker Tests Reveal Routine Pesticide Exposure


Pesticide Action Network Updates Service (PANUPS)

See PANUPS updates service, for complete information.

Farm Worker Tests Reveal Routine Pesticide Exposure
February 18, 2005

On February 8, 2005, national and state farm worker organizations highlighted very disturbing medical monitoring results in Washington State. Their report, Messages from Monitoring, looks at the first year of data from a Washington State program that tests farm workers who regularly handle organophosphates (OPs) and carbamates (CBs), both of which are neurotoxic pesticides. The report shows that one in five workers tested experiences significant inhibition of cholinesterase–an enzyme essential to proper nervous system function–and faults both state and federal agencies for failing to protect farm workers.

For nearly 20 years, farm workers in Washington have pressed for a medical monitoring program, similar to a program instituted in 1974 in California, which has the only other monitoring program for this highly toxic class of pesticides. After a state Supreme Court ruled for the farm workers, testing began in Washington at the start of the 2004 growing season. The Washington program applies to all workers who mix, load, apply, or otherwise handle highly toxic OP or CB pesticides for 50 or more hours a month.

When exposure to OPs or CBs causes declines in cholinesterase levels, workers can suffer serious health effects such as nausea, headaches, fatigue, and seizures. If levels decline further more severe effects can occur, including long-term memory loss, paralysis and death.  

Workers received “baseline” blood tests prior to the spray season to identify normal levels of cholinesterase. They then received monthly follow-up tests when they met or exceeded the 50-hour per month handling threshold. (That threshold drops to 30 hours per month in 2005.) Under the monitoring rules, when cholinesterase levels decline by more than 20% from the workers’ baseline level, employers are required to conduct workplace audits to identify and address factors contributing to serious depression. When levels decline by 30% or more in red blood cell tests or 40% or more in blood plasma tests, workers must be removed from handling tasks until their cholinesterase levels rebound sufficiently. Employers can reassign workers to other tasks that do not involve significant exposures if available, and must maintain full salaries and benefits for removed workers.

Over the course of the spray season, 123 (21%) pesticide handlers out of 580 who received both baseline and follow-up tests had depressions of more than 20% (the workplace audit level). Of these, 26 (over 4% of the 580 workers) had depressions low enough to trigger removal under the state rules.

Four pesticides were repeatedly involved in serious depressions:   chlorpyrifos (Lorsban), azinphos methyl (Guthion), carbaryl (Sevin) and formetanate (Carzol).   The majority of handlers needing removal for cholinesterase depressions used a mixture of carbaryl and an OP insecticide (chlorpyrifos or azinphos methyl). One common contributing factor at workplaces with depressions was the use of air-blast sprayers towed by tractors to apply the pesticides.

Significantly, in a large percentage of the serious depression cases, there was no evidence of non-compliance with federal Worker Protection Standards or pesticide labels.   Many case summaries, in fact, noted that growers and their employees exceeded regulatory requirements by wearing a respirator for chlorpyrifos though this is not required. The report notes that EPA’s own analysis predicted that occupational exposures would pose unacceptable risks, “In fact, citing cost-benefit provisions in federal pesticide registration law, EPA has approved continued use of some highly toxic OPs while openly acknowledging that even with full Personal Protective Equipment (PPE) and engineering controls, workers will experience exposures which EPA considers unacceptable, i.e. having Margins of Exposure (MOE) less than 100. Almost all handling scenarios for azinphos methyl pose exposure risks for workers which EPA considers unacceptable, and numerous scenarios for chlorpyrifos do the same.”

Messages from Monitoring identifies serious problems in the Washington testing that may mask evidence of even greater harm. For example, statistical analyses done by the program’s Scientific Advisory Committee reveals the risks of false negatives may be as high as 50%. The Committee also noted that many depressions might have been missed because of the length of time that elapsed between sample collection and analysis. In other cases, workers reportedly declined monitoring due to actual or perceived employer interference.

The report also faulted the Washington State Department of Labor and Industry (L&I) for its slow response when testing revealed cholinesterase declines. “L&I chose not to use its enforcement authorities to investigate workplaces where depressions occurred. Even in cases where multiple workers had depressions, the agency adopted a ‘consultation’ approach.” The average interval between receiving test results and performing workplace audits or removals was more than 7 days, during which time the workers may have been receiving additional exposures.

Messages from Monitoring points out that the Washington monitoring program tests pesticide handlers, and not field workers despite a growing body of literature demonstrating routine pesticide exposure among field workers and their families. Finally, the report faults government for failing to promote alternatives to these dangerous pesticides, and calls on state agencies and the federal government to end the use of the most risky pesticides, including azinphos methyl, chlorpyrifos and other highly toxic OPs and CBs, and to require cholinesterase monitoring on a national basis.

The United Farm Workers of America, AFL-CIO (UFW) is now circulating an online petition asking EPA to implement a national cholinesterase monitoring program. To sign the petition visit:

Source: Messages from Monitoring, Farm Worker Pesticide Project, Farmworker Justice Fund, United Farm Workers,
Contact: Farm Worker Pesticide Project, 206-729-0498, PANNA.


We encourage those interested in having resources listed in the PANUPS Resource Pointer to send review copies of publications, videos or other resources to our office.

PANUPS is a weekly email news service providing resource guides and reporting on pesticide issues that don’t always get coverage by the mainstream media. It’s produced by Pesticide Action Network North America, a non-profit and non-governmental organization working to advance sustainable alternatives to pesticides worldwide.

You can join our efforts! We gladly accept donations for our work and all contributions are tax deductible in the United States. Visit



Back to top