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Farmworkers Health Study (FWHS)

Epidemiology Branch

Farmworkers Health Study (FWHS)

The Farmworkers Health Study examines the relationship of long-term pesticide exposure in farmworkers and deficits in cognitive and psychomotor function. The research group, headed by Freya Kamel, Ph.D., conducted a cross-sectional study comparing pesticide-exposed farmworkers to unexposed controls. Participants in the study came from a farmworker community in central Florida with a stable population. Most farmworkers in this community worked in one of three types of agriculture: growing and harvesting ornamental ferns, working in nurseries or picking citrus fruit.


To gain access to the community, the group collaborated with the Farmworker Association of Florida, a local advocacy group. The defined target population was limited to members of a local credit union and their spouses, with both exposed farmworkers and unexposed controls being recruited from this population. The researchers screened 80% of selected individuals and 81% of those eligible participated in the study. The experimental group contained 288 individuals who had worked in the farming industry for at least one month and 51 controls who did not meet this criterion. The study was unique in recruiting a large sample from a defined population with a high response rate.


Since pesticides potentially affect many aspects of neurologic function, the group used a battery of tests—with several being implemented on a computer—to evaluate sensory, motor and cognitive function. The tests were relatively independent of education and cultural background. The researchers collected information on history of farm work, other employment, demographics, lifestyle and medical history using a structured interview administered by trained personnel. They also collected and archived buccal cells to use as a source of DNA. Genetic analyses will focus on genes involved in pesticide metabolism, such as paraoxonase.


In analyses of the relationship of work history to neurobehavioral performance, the team found that having done at least some farm work was associated with poor performance on four tests—digit span, finger tapping, Santa Ana and postural sway—but had little effect on four others: symbol digit latency, vibrotactile threshold, visual contrast sensitivity and grip strength. The affected tests evaluated cognitive and psychomotor function. Associations with farm work were similar in magnitude to associations with personal characteristics such as age and gender. Longer duration of farm work was associated with worse performance. Associations with fern work were more consistent than associations with nursery or citrus work. Deficits related to the duration of work experience were seen in former as well as current farmworkers, and decreased performance was related to chronic exposure even in the absence of a history of pesticide poisoning.


During the last 60 years, pesticide use in the United States has steadily increased. Certain occupational groups as well as the general public may be exposed. Clinical manifestations of neurotoxicity following high level pesticide exposure are well known, but there is growing concern that pesticides may also produce subclinical neurologic deficits, particularly as a delayed consequence of a poisoning episode or in situations of chronic, low-level exposure, and this issue has not been extensively studied. Data from the Farmworkers Health Study led researchers to conclude that long-term experience of farm work is associated with measurable deficits in cognitive and psychomotor function. The study extended previous findings by demonstrating farm work-related neurologic deficits in a large, population-based study that compared workers in different types of agriculture.


Principal Investigators

Freya Kamel, Ph.D.
Staff Scientist – Chronic Disease Epidemiology, Adjunct member - Aging and Neuroepidemiology Group
Tel (919) 541-1581

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