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Neurobehavioral performance and work experience in Florida farmworkers.

Farmworkers experience many work-related hazards, including exposure to neurotoxicants. We compared neurobehavioral performance of 288 farmworkers in central Florida who had done farm work for at least 1 month with 51 controls who had not. Most of the farmworkers had worked in one or more of three types of agriculture: ornamental ferns, nurseries, or citrus fruit. We collected information on farm work history in a structured interview and evaluated neurobehavioral performance using a battery of eight tests. Analyses were adjusted for established confounders including age, sex, education, and acculturation. Ever having done farm work was associated with poor performance on four tests--digit span [odds ratio (OR) = 1.90; 95% confidence interval (CI), 1.02-3.53], tapping (coefficient = 4.13; 95% CI, 0.00-8.27), Santa Ana test (coefficient = 1.34; 95% CI, 0.29-2.39), and postural sway (coefficient = 4.74; 95% CI, -2.20 to 11.7)--but had little effect on four others: symbol digit latency, vibrotactile threshold, visual contrast sensitivity, and grip strength. Associations with farm work were similar in magnitude to associations with personal characteristics such as age and sex. 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. We conclude that long-term experience of farm work is associated with measurable deficits in cognitive and psychomotor function. Key words: citrus fruit, cognitive function, farm work, neurobehavioral performance, nurseries, ornamental ferns, psychomotor function. Environ Health Perspect 111:1765-1772 (2003). doi: 10.1289/ehp.6341 available via http://dx.doLorg/[Online 23 July 2003]

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Farmworkers are exposed to numerous hazards in the course of their work, including injury and exposure to pesticides and other toxicants (Moses et al. 1993; Villarejo and Baron 1999). Farmworkers are a vulnerable occupational group: They are often foreign-born and may not speak English; they may lack formal education; and they and their families often live in poverty. The agricultural industry is exempt from many federal regulations governing the workplace, and farmworkers are rarely represented by labor unions. Potential adverse health effects of farm work include traumatic injury, musculoskeletal disorders, respiratory conditions, dermatitis, cancer, and neurologic disorders. Some of these conditions may be related to pesticide exposure (Das et al. 2001; Keifer and Mahurin 1997; Moses et al. 1993). The health effects of farm work are compounded by the relative lack of access of this group to medical information and care.

Farmworkers in several settings have been reported to experience elevated rates of neurologic dysfunction. For example, they had increased frequency of neurologic symptoms (Ciesielski et al. 1994; Gomes et al. 1999) and decreased performance on some neurobehavioral tests (Bazylewicz-Walczak et al. 1999; Gomes et al. 1999; Rohlman et al. 2001) compared with unexposed workers. Farmworkers with a history of pesticide poisoning experienced more symptoms and had impaired neurobehavioral performance relative to nonpoisoned controls (McConnell et al. 1994; Rosenstock et al. 1991; Wesseling et al. 2002).

We report here the results of a large, population-based study of farmworkers in central Florida. The focus of the study was the relationship of long-term experience of farm work to neurobehavioral performance and potential differences related to type of farm work. We took into account important confounders, including education and acculturation.

Materials and Methods

Population. We conducted a cross-sectional study in central Florida in 1996-1997. Study participants were recruited in collaboration with the Farmworkers Association of Florida, a farmworker advocacy group (Kamel et al. 2001). Our target population was members of the Community Trust Federal Credit Union and their spouses. The Credit Union is a small savings institution with branches in several Florida communities. It is affiliated with several community organizations, including the Farmworkers Association; many but not all of its members are farmworkers. Credit Union members were typical members of the local communities (Kamel et al. 2001).

We randomly selected names from the membership lists of the Credit Union in two communities, Apopka and Pierson. Most farmworkers in these communities had worked in one of three types of agriculture: growing and harvesting ornamental ferns, working in nurseries, or picking citrus fruit. Bilingual recruiters chosen by the Farmworkers Association located the selected individuals and administered a screening interview to determine eligibility and to identify spouses of credit union members, who were then also screened. To reduce variability in neurobehavioral performance, we restricted the age range to 28-55 years of age and excluded individuals with diabetes, epilepsy, or stroke. We recruited men and women of any race or ethnicity who were fluent in Spanish or English. We screened 80% of selected individuals, and 81% of those eligible participated in the study (Kamel et al. 2001).

We recruited 288 individuals who had ever done farm work for at least 1 month (farmworkers) and 51 controls who did not meet this criterion. Participants in the study completed a structured interview and a battery of neurobehavioral tests. They received $50 as compensation for their time and effort. Institutional review boards of the National Institute of Environmental Health Sciences and CODA approved the study, and all participants signed a written consent form.

Interview. We collected information on history of farm work, other employment, demographics, lifestyle, and medical history in a structured interview administered in person by trained personnel; a complete copy of the questionnaire is available (Farmworkers Health Study 2003). The interview took an average of 57 min (range, 15-155 min) and was conducted in Spanish (85%) or English (15%), depending on the respondent's preference. Farm work history included questions on total years of farm work and on farm work in the year before the interview, before age 14, or as a migrant worker. We collected detailed job histories for work with ferns, in nurseries, or picking citrus fruit, asking about total years and months per year worked for each job and the number of bunches of ferns cut per day for fern jobs.

The interview also included questions on ethnicity, years of formal education, and degree of acculturation, defined as likelihood of speaking English with friends (not acculturated = never; somewhat acculturated = less than half the time; very acculturated = half the time or more); the latter question is adapted from the third National Health and Nutrition Examination Survey (2003). We collected information on cigarette smoking and consumption of alcoholic beverages, the latter including a measure of frequency during the past year and a lifetime history of problems with family life, work, or health related to alcohol use. We asked about usual lifetime occupation and type of work during the 2 months preceding the interview. Medical history included questions on head injury, neck or back injury, and pesticide poisoning. Participants were asked to describe the location of any pain, tingling, or numbness experienced during the preceding 2 months in their fingers, hands, wrists, or arms. We collected information on the 24-hr period preceding testing, including consumption of alcoholic beverages, use of prescription medications, and any illness. Participant characteristics are shown in Table 1.

Neurobehavioral testing. Because previous studies provided only limited information regarding which aspects of neurologic function would be affected by pesticides, we evaluated neurobehavioral performance using a battery designed to address neurologic function broadly. The battery included eight tests: digit span, symbol digit latency, vibrotactile threshold, visual contrast sensitivity, tapping, Santa Ana (a type of pegboard test), grip strength, and postural sway. Digit span and symbol digit latency are tests of cognitive function; vibrotactile threshold and visual contrast sensitivity, of sensory function; tapping and Santa Ana, of psychomotor function; grip strength, of motor function; and postural sway, of balance, an integrated sensorimotor function. Digit span, symbol digit latency, and Santa Ana are recommended tests in the World Health Organization Neurobehavioral Core Test Battery (Anger et al. 2000). We also measured visual acuity, as a potential confounder. The testing took an average of 65 min (range, 30-122 min), and was conducted in the same language as the interview.

Digit span, symbol digit latency, and tapping were presented on a computer using the Behavioral Assessment and Research System (BARS; Anger 2003; Rohlman et al. 2000a, 2000b, 2003). Participants responded on an external unit consisting of nine large buttons that fit over the computer keyboard. Integral Spanish or English instructions and practice were used to teach participants to perform the BARS tests (Anger 2003; Rohlman et al. 2000a, 2000b, 2003). Examiners taught appropriate performance on the other tests orally. Vibrotactile threshold was assessed for the index and fourth digits of both hands using a Vibratron II (Physitemp Instruments, Clifton, NJ). Visual acuity and visual contrast sensitivity were assessed for right and left eyes using an Optec 1000 (Stereo Optical Co, Chicago, IL). Visual contrast sensitivity was measured at five spatial frequencies for each eye: 1.5, 3, 6, 12, and 18 cycles per degree (cpd). Participants wore their usual glasses during the vision tests. Santa Ana was administered using a pegboard constructed according to Neurobehavioral Core Test Battery specifications (Anger et al. 2000). Grip strength was measured with a dynamometer (Jandel, San Rafael, CA). Postural sway was assessed using an Accusway Balance Platform (Minimitter, Bend, OR) under four conditions: 1, eyes open, no foam; 2, eyes closed, no foam; 3, eyes open, standing on a foam rubber pad; 4, eyes closed, on foam. Postural sway data were acquired directly on a computer using software provided by the manufacturer.

Most of the tests had several different measures (Table 2). In many cases, these were correlated with each other (digit span, r = 0.45; vibrotactile threshold, r = 0.55-0.80; visual contrast sensitivity, r = 0.31-0.75; tapping, r = 0.45-0.77; Santa Ana, r = 0.66; postural sway, r = 0.23-0.56).

Data analysis. Data were analyzed using SAS software, version 8.2 (SAS Institute Inc., Cary, NC). Digit span results were analyzed using ordinal logistic regression because the limited range of the data made results from linear regression unstable. Odds ratios (ORs) and 95% confidence intervals (95% CIs) for worse performance (i.e., fewer digits) are presented. All other test measures were analyzed using linear regression; coefficients and 95% CIs are presented. Vibrotactile threshold results were log-transformed to reduce skewness; other measures were more normally distributed and therefore not transformed. After analysis, the signs of coefficients and 95% CIs were reversed for visual contrast sensitivity, tapping, Santa Ana, and grip strength so that in all cases a higher value represents worse performance. Tests for dose-response trends were conducted using models including years of farm work as an ordinal variable and assessing significance of this variable using the likelihood ratio test for logistic models or the partial F-test for linear models.

Variables were considered as potential confounders for particular neurobehavioral tests based on a priori hypotheses regarding potential relationships. Age, sex, education, acculturation, time of day of testing, cigarette smoking (pack-years), alcoholic drinks per week, history of problems associated with alcohol use, usual hours of sleep, head injury, and neck or back injury were evaluated for all tests. Height and weight were evaluated for vibrotactile threshold, grip strength, and postural sway. Visual acuity was evaluated for all tests except grip strength. Hand pain was evaluated for vibrotactile threshold and grip strength. Age was used as a continuous variable except in models for visual contrast sensitivity and postural sway, where the relationship was not linear, so it was used as a categorical variable. Because ethnicity, years of formal education, acculturation, and language of testing were highly associated with one another, only education and acculturation were considered. Hand pain was scored positive if symptoms were consistent with carpal tunnel syndrome (Katz et al. 1991). Base models containing potential confounders were constructed by backward elimination; variables were retained in the models if p < 0.10. Final base models for the tests are shown in Table 3, with values for the specific measure that was explored in most detail; the same base variables were used for each measure of a test.

We evaluated the measures of exposure shown in Table 4. "Farm work" was defined as all types of farm work, including but not restricted to fern, nursery, and citrus work. "Ever" was defined as [greater than or equal to] 1 month performing the activity. Initial analyses focused on the effects of ever exposure to general farm work or the three different types of farm work; subsequent analyses focused on duration of work. Variables for fern, nursery, and citrus work were constructed to evaluate each type of farm work separately from the other types. For example, the ever fern work variable had three categories: no farm work (referent), other farm work but no fern work, and fern work. The variable for months of fern work had five categories: no farm work (referent), other farm work but no fern work, [less than or equal to] 100 months of fern work, 101-140 months of fern work, > 140 months of fern work (approximate tertiles). Variables for nursery and citrus work were constructed analogously.

Results

Characteristics of study participants. Compared with controls, farmworkers were slightly younger and more likely to be male (Table 1). Mean ([+ or -] SD) height and weight were 64.1 [+ or -] 3.4 inches and 169.9 [+ or -] 33.0 pounds, respectively, for all study participants, and did not vary by group. A higher proportion of farmworkers than controls were Latino/a, and farmworkers had fewer years of formal education and were less acculturated than controls; these tendencies were most pronounced for fern workers. Farmworkers, particularly fern workers, were more likely than controls to choose to take the tests in Spanish. There was little difference among groups in the time of day tests were taken (data not shown). Farmworkers had smoked less than controls but had consumed more alcoholic drinks per week. Visual acuity (measured with workers wearing glasses) was slightly better in farmworkers than controls. Farmworkers were less likely than controls to have experienced one or more severe head injuries or to have pain in the nonpreferred hand.

Neurobehavioral test measures. Mean values for test measures (Table 2) in this population were within previously reported ranges (Anger et al. 1993). Test measures were related in the expected directions to all covariates tested: age, sex, education, acculturation, alcohol use, height, weight, head injury, sleep, hand pain, and visual acuity (Table 3).

History of farm work. The entire group of farmworkers had done farm work for an average of 15.9 years (Table 4). Citrus workers and fern workers had worked for more years than nursery workers (means of 18.5, 17.7, and 15.3 years, respectively). More fern workers than nursery or citrus workers had done farm work in the year before testing. There was considerable overlap in the types of farm work participants had done: 44% of fern workers, 73% of nursery workers, and 83% of citrus workers had worked in one or both of the other two types of agriculture. Total years of farm work was weakly correlated with months of fern work (r = 0.23), nursery work (r = 0.10), and citrus work (r = 0.31). Months of fern work was inversely correlated with months of nursery work (r = -0.34) and citrus work (r = -0.29). Nursery and citrus work were not related (r = 0.01).

Association of farm work with neurobehavioral performance. Ever having done any type of farm work or any one of the three particular types (Table 5) was associated with worse performance for digit span forward; for tapping using either hand; for Santa Ana in the preferred hand; and for postural sway length in conditions 2 and 4. There was a small increase in vibrotactile threshold restricted to the index finger of the preferred hand. There was little relationship of farm work to symbol digit latency, visual contrast sensitivity, or grip strength. When present, associations with farm work were comparable in magnitude with associations with most covariates (compare Tables 3 and 5).

For some tests, farmworkers who had done farm work in the year before testing (current farmworkers) had greater deficits than those who had not (former farmworkers), when each group was compared with controls (data not shown). However, current and former farmworkers also differed in several respects other than having done farm work in the previous year. For example, current and former farmworkers had done farm work for an average of 18 versus 10 years and fern work for 75 versus 12 months, respectively, although differences in nursery and citrus work were minor. Values for most covariates for former farmworkers were intermediate between controls and current farmworkers. Specifically, former farmworkers were more educated, more acculturated, and more likely to be female than were current farmworkers (data not shown).

No consistent relationship was found between any neurobehavioral test and having done farm work before age 14, ever having done migrant farm work, or years of doing migrant work (data not shown).

Quantitative measures of farm work and neurobehavioral performance. The three tests that were not related to ever having done farm work (symbol digit latency, visual contrast sensitivity, and grip strength) were also not related to quantitative measures of farm work. For the other five tests, results are presented for one measure of each test that was related to farm work (Table 6). For digit span, tapping, and postural sway, results were generally similar although attenuated for other measures. For vibrotactile threshold and Santa Ana, there was little relation of other measures to farm work.

An increase in lifetime years of farm work was associated with worse performance for digit span, vibrotactile threshold, tapping, and Santa Ana that was monotonically related to work duration with significant trends. There was a tendency for worse performance for postural sway with increasing years of farm work, but estimates were imprecise. Results were similar when the analysis was restricted to participants with at least 6 years of education. After stratification by farm work in the year before testing, performance was related to work duration in both current and former farmworkers.

Lifetime fern work was quantified either as months worked or bunches of ferns cut; the two measures were highly correlated (r = 0.78). Months of fern work was associated with impaired performance for digit span and postural sway that was most pronounced at shorter work durations; with an increase in vibrotactile threshold that was not related to work duration; and with decrements in performance for tapping and Santa Ana that increased with work duration. Results were generally similar using bunches of ferns cut as the exposure measure, although tapping and Santa Ana were not as clearly related to work duration using this measure. Lifetime months of nursery work was associated with decreased performance for digit span, tapping, Santa Ana, and postural sway. Although relationships were not monotonic, the most pronounced effects were seen at the longest work duration. Lifetime months of citrus work was associated with impaired performance for Santa Ana and postural sway. In models including variables for months of all three types of farm work together, associations with fern and nursery work were similar but associations with citrus work were attenuated.

Results were similar when we excluded from the analysis individuals in the following groups (one group at a time): those who had eight or more errors for symbol digit latency or 13 or more errors for tapping (n = 16); those who had consumed an alcoholic beverage in the 7 hr preceding testing (n = 9); those who had used prescription medications potentially affecting neurobehavioral performance (antipsychotics, antidepressants, or antihistamines) in the 24 hr preceding testing (n = 18); those who did not wear their usual glasses during testing (n = 15); those who were not feeling well on the day of the test (n = 6); those who had ever had two or more severe head injuries (n = 6) those who had ever had two or more neck or back injuries (n = 15); those who had ever done work involving exposure to neurotoxicants other than pesticides (n = 34); those who had done such work in the last 2 months (n = 16); and those who reported ever having had an acute toxic reaction to pesticides (n = 19).

Discussion

The results of this study suggest that doing farm work is associated with deficits in neurobehavioral performance. Most previous studies of farmworkers or greenhouse workers have found some evidence of job-related deficits in neurobehavioral performance or increases in neurologic symptoms (Bazylewicz-Walczak et al. 1999; Ciesielski et al 1994; Gomes et al. 1999; McConnell et al. 1994; Rohlman et al. 2001; Rosenstock et al. 1991; Wesseling et al. 2002). However, the observed changes were often small, with some inconsistencies in the specific neurologic defects that were observed. Our study extends previous findings by demonstrating farm work-related neurologic deficits in a large, population-based study that compared workers in different types of agriculture. Farm work in general and fern work in particular were associated with decreased performance, and longer duration of general farm work was associated with worse performance.

Previous studies of neurobehavioral performance in farmworkers have generally assumed that observed deficits are a result of pesticide exposure. Pesticide applicators, including commercial applicators, sheep dippers, and farmers, have also been studied, as have individuals with a history of pesticide poisoning. Acute pesticide poisoning is followed, sometimes after many years, by impaired neurobehavioral performance and decreased nerve conduction velocity as well as increased frequency of neurologic symptoms (London et al. 1998; McConnell et al. 1994; Rosenstock et al. 1991; Savage et al. 1988; Steenland et al. 1994; Wesseling et al. 2002). Chronic pesticide exposure has also been associated with neurologic deficits (Farahat et al. 2003; London et al. 1997; Pilkington et al. 2001; Ruijten et al. 1994; Sack et al. 1993; Steenland et al. 2000; Stephens et al. 1995; Stokes et al. 1995; van Wendel de Joode et al. 2001). Most of these studies did not exclude individuals with a history of pesticide poisoning. Several studies in which such individuals were excluded found no relationship of chronic exposure to neurobehavioral performance or nerve conduction velocity (Ames et al. 1995; Engel et al. 1998; Fiedler et al. 1997), but other studies of nonpoisoned individuals have found associations (Stephens et al. 1995; van Wendel de Joode et al. 2001). We found that farm work was related to worse performance even after excluding 19 individuals who had experienced acute toxic reactions to pesticides.

Few previous studies have directly compared the relative contributions of acute and chronic exposure to low levels of pesticides. Two studies of farmworkers engaged in pesticide application found increased symptom prevalence associated with acute but not chronic exposure (London et al. 1998; Ohayo-Mitoko et al. 2000). In contrast, a study of termiticide applicators found that both acute and chronic exposures were associated with limited neurologic dysfunction, including impaired balance and color vision (Dick et al. 2001; Steenland et al. 2000). Occurrence of symptoms in particular individuals after acute exposure may not be related to later development of neurobehavioral deficits after chronic exposure (Stephens et al. 1996). In our study, decreased performance was associated with work duration in former as well as current workers, with the largest decreases seen after 10 or more years of work. Thus, our results suggest that chronic as well as acute exposure is associated with neurobehavioral performance and that duration of farm work may be as important as recency.

The eight neurobehavioral tests were not affected equally by farm work. Overall, one test of cognitive function (digit span), two of psychomotor function (tapping and Santa Ana), and one of balance (postural sway), an integrated sensorimotor function, were most consistently impaired. Associations with one measure of somatosensory function (vibrotactile threshold) were small and imprecise, seen primarily in fern workers, and restricted to the index finger of the preferred hand. This association may be due to repetitive stress injury such as carpal tunnel syndrome in the fern workers, who repetitively use a small clipper to harvest ferns, although the presence of calluses on the affected finger may provide an alternative explanation (McConnell et al. 1994). There was little relationship of farm work to other tests of cognitive (symbol digit latency), sensory (visual contrast sensitivity), or motor (grip strength) function. Some but not all other studies of farm work or pesticide exposure have reported deficits in symbol digit latency, along with deficits in digit span, vibrotactile threshold, tapping, Santa Ana, and postural sway (Gomes et al. 1999; London et al. 1997; McConnell et al. 1994; Rosenstock et al. 1991; Sack et al. 1993; Savage et al. 1988; Steenland et al. 1994, 2000; Stephens et al. 1995; Stokes et al. 1995; Wesseling et al. 2002). Although these results are not completely consistent, it is noteworthy that no study has reported an exposure-related improvement in performance. Variations in type and degree of exposure and methodologic differences, including choice of control group, procedures for administering and scoring neurobehavioral tests, and control for potential confounding, likely account for the differences in findings.

There was considerable overlap among the three types of farm work, with 44-87% of each group having worked in one or both of the other two types of agriculture. Nevertheless, the three types of work varied in their relationships to neurobehavioral performance. Specifically, fern work had a more robust relationship than nursery or citrus work to digit span, tapping, and Santa Ana. Fern workers had done farm work for more years than nursery workers, although not more than citrus workers. They were less educated than were other farmworkers, but they were also younger and less likely to use or have problems with alcohol. Thus, confounding does not appear to account for the stronger association of fern work with neurologic dysfunction. Differences in neurobehavioral performance may be related to differences in pesticide exposure. Relatively few pesticides are used on citrus fruit (McCoy et al. 2003) compared with ferns or nursery plants (Vasquez and Nesheim 2000). Further, fern workers spend a large proportion of their time in intimate contact with treated plants, and may in fact be more heavily exposed to pesticides than are other farmworkers.

Many anthropomorphic, demographic, and lifestyle characteristics are known to affect neurobehavioral performance (Anger et al. 1997; Kilburn et al. 1998; Krieg et al. 2001). We found age, sex, education, acculturation, alcohol use, hours of sleep, head injury, hand pain, height, weight, and visual acuity to be related to one or more of the tests we studied. Our models were adjusted for these characteristics, so confounding is unlikely to fully explain the relationships we observed. Additional reassurance that confounding is not a major determinant of our findings is provided by the finding of associations among former as well as current farmworkers, although former farmworkers were more similar to controls than were current farmworkers. A potential confounder of great concern is education, but our results were unchanged in analyses restricted to individuals with 6 or more years of education. It is also noteworthy that deficits in performance were not restricted to computerized tests, so lack of familiarity with computers does not account for our findings. Analyses excluding individuals whose performance may have been affected by alcohol, medication, illness, injury, or exposure to neurotoxicants other than pesticides suggested that our findings were not heavily influenced by these individuals.

The strengths of our study include its relatively large size, which allowed us to compare workers in three different types of agriculture. We used a defined target population and achieved high response rates (Kamel et al. 2001), reducing potential for selection bias. We collected detailed questionnaire information to account for numerous potential confounders. Limitations of the study include the use of indirect exposure measures and the small number of tests included in our neurobehavioral test battery, which made it difficult to evaluate effects on specific aspects of neurologic function. The study was also limited by the fact that the controls differed from the farmworkers in several important respects, notably education and acculturation.

In conclusion, this study suggests that farm work is associated with deficits in neurologic function, particularly cognitive and psychomotor function. Associations with farm work were similar in magnitude to associations with personal characteristics known to affect neurobehavioral performance, including age, sex, alcohol use, and head injury. 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. Greater risk was associated with fern work than with other kinds of farm work. Although the absolute differences in performance seen in this and other studies are small, they could nevertheless be important on a population basis, by increasing the proportion of impaired individuals. Neurologic deficits have been observed in studies of farmworkers and other individuals chronically exposed to pesticides. However, farmworkers are exposed to other hazards, including injury, metals, allergens, and soil pathogens. Further work will thus be necessary to determine whether the observed deficits are related to pesticide exposure or to other hazards.
Table 1. Characteristics of study participants. (a)

 All
 Controls farmworkers
Characteristics (n=51) (n=288)

Age (years)
 28-32 24 24
 33-37 22 29
 38-43 20 26
 44-55 35 21
 Mean [+ or -] SD 39.9 [+ or -] 7.3 38.0 [+ or -] 6.7
Sex
 Male 41 56
 Female 59 44
Ethnicity
 Latino 63 89
 Non-Latino white 18 3
 Other 20 8
Education (years)
 0-5 12 39
 6-11 24 42
 [greater than or equal to] 12 65 19
 Mean [+ or -] SD 11.9 [+ or -] 4.8 6.5 [+ or -] 4.2
Acculturation
 Not acculturated 22 54
 Somewhat acculturated 31 26
 Very acculturated 47 20
Language of testing
 Spanish 63 89
 English 37 11
Lifetime cigarette smoking (pack-years)
 Never 57 54
 > 0-5 22 29
 > 5-15 10 11
 > 15 12 6
Alcohol use in previous year (drinks per week)
 <1 63 59
 1-14 31 26
 [greater than or equal to] 15 6 15
Lifetime problems with alcohol use
 Never drank 33 30
 Drank, no problems 49 47
 Drank, had problems 16 23
Usually sleep [greater than or equal to] 7 hrs
 Yes 71 81
 No 29 19
20:20 vision
 Left eye
 Yes 65 68
 No 35 31
 Right eye
 Yes 63 69
 No 37 31
Ever had severe head injury
 No 88 93
 Yes 12 7
Ever had any neck or back injury
 No 75 78
 Yes 25 22
Hand pain
 Preferred hand
 No 82 83
 Yes 18 17
 Nonpreferred hand
 No 80 88
 Yes 20 12

 Fern Nursery
Characteristics workers workers
 (n=140) (n=147)

Age (years)
 28-32 26 24
 33-37 27 25
 38-43 29 23
 44-55 19 28
 Mean [+ or -] SD 37.8 [+ or -] 6.4 38.8 [+ or -] 7.3
Sex
 Male 56 54
 Female 44 46
Ethnicity
 Latino 94 82
 Non-Latino white 0 6
 Other 6 12
Education (years)
 0-5 45 35
 6-11 41 37
 [greater than or equal to] 12 14 27
 Mean [+ or -] SD 5.8 [+ or -] 4.1 7.2 [+ or -] 4.5
Acculturation
 Not acculturated 66 41
 Somewhat acculturated 21 28
 Very acculturated 12 31
Language of testing
 Spanish 94 81
 English 6 19
Lifetime cigarette smoking (pack-years)
 Never 60 44
 > 0-5 24 37
 > 5-15 12 12
 > 15 4 7
Alcohol use in previous year (drinks per week)
 <1 64 60
 1-14 24 27
 [greater than or equal to] 15 12 14
Lifetime problems with alcohol use
 Never drank 33 27
 Drank, no problems 44 47
 Drank, had problems 23 26
Usually sleep [greater than or equal to] 7 hrs
 Yes 81 80
 No 19 20
20:20 vision
 Left eye
 Yes 69 66
 No 31 34
 Right eye
 Yes 72 68
 No 27 32
Ever had severe head injury
 No 90 94
 Yes 10 6
Ever had any neck or back injury
 No 79 78
 Yes 21 22
Hand pain
 Preferred hand
 No 80 85
 Yes 20 15
 Nonpreferred hand
 No 91 86
 Yes 9 14

 Citrus
 workers
Characteristics (n=141)

Age (years)
 28-32 21
 33-37 28
 38-43 26
 44-55 26
 Mean [+ or -] SD 39.0 [+ or -] 7.1
Sex
 Male 65
 Female 35
Ethnicity
 Latino 84
 Non-Latino white 4
 Other 13
Education (years)
 0-5 43
 6-11 36
 [greater than or equal to] 12 21
 Mean [+ or -] SD 6.4 [+ or -] 4.5
Acculturation
 Not acculturated 43
 Somewhat acculturated 31
 Very acculturated 26
Language of testing
 Spanish 83
 English 17
Lifetime cigarette smoking (pack-years)
 Never 46
 > 0-5 33
 > 5-15 13
 > 15 8
Alcohol use in previous year (drinks per week)
 <1 52
 1-14 32
 [greater than or equal to] 15 16
Lifetime problems with alcohol use
 Never drank 21
 Drank, no problems 50
 Drank, had problems 29
Usually sleep [greater than or equal to] 7 hrs
 Yes 79
 No 21
20:20 vision
 Left eye
 Yes 70
 No 30
 Right eye
 Yes 67
 No 33
Ever had severe head injury
 No 93
 Yes 7
Ever had any neck or back injury
 No 77
 Yes 23
Hand pain
 Preferred hand
 No 82
 Yes 18
 Nonpreferred hand
 No 88
 Yes

(a) Table entries are column percentages except where indicated.
Many farmworkers had worked on more than one crop, so the sum of
fern, nursery, and citrus workers is greater than the total number
of farmworkers.

Table 2. Neurobehavioral test measures in controls and farmworkers

 Controls

Test measures No. (a) Mean [+ or -] SD

Cognitive function
 Digit span forward 51 5.63 [+ or -] 1.02
 Digit span reverse 51 4.12 [+ or -] 1.07
 Symbol digit latency 49 2,232 [+ or -] 774
Sensory function
 Vibrotactile threshold PR digit 1 50 0.51 [+ or -] 0.19
 Vibrotactile threshold PR digit 4 50 0.55 [+ or -] 0.23
 Vibrotactile threshold NP digit 1 50 0.53 [+ or -] 0.26
 Vibrotactile threshold NP digit 4 50 0.53 [+ or -] 0.28
 Contrast sensitivity L eye 1.5 cpd 51 23.1 [+ or -] 13.0
 Contrast sensitivity L eye 3 cpd 51 35.0 [+ or -] 36.4
 Contrast sensitivity L eye 6 cpd 51 64.3 [+ or -] 56.8
 Contrast sensitivity L eye 12 cpd 51 42.5 [+ or -] 37.5
 Contrast sensitivity L eye 18 cpd 51 16.1 [+ or -] 13.4
 Contrast sensitivity R eye 1.5 cpd 51 21.1 [+ or -] 9.7
 Contrast sensitivity R eye 3 cpd 51 37.7 [+ or -] 33.0
 Contrast sensitivity R eye 6 cpd 51 63.8 [+ or -] 53.3
 Contrast sensitivity R eye 12 cpd 51 39.9 [+ or -] 34.7
 Contrast sensitivity R eye 18 cpd 51 13.8 [+ or -] 11.0
Psychomotor function
 Tapping PR 51 88.3 [+ or -] 13.9
 Tapping NP 51 80.0 [+ or -] 10.9
 Tapping alternating 50 46.8 [+ or -] 15.1
 Santa Ana PR 51 19.9 [+ or -] 3.04
 Santa Ana NP 51 18.0 [+ or -] 2.88
Motor function
 Grip strength 51 32.6 [+ or -] 9.61
Balance
 Postural sway length CON 1 51 37.0 [+ or -] 5.66
 Postural sway length CON 2 51 48.2 [+ or -] 12.3
 Postural sway length CON 3 51 48.0 [+ or -] 9.17
 Postural sway length CON 4 51 75.4 [+ or -] 27.1
 Postural sway area CON 1 51 2.78 [+ or -] 1.70
 Postural sway area CON 2 51 3.68 [+ or -] 2.48
 Postural sway area CON 3 51 4.63 [+ or -] 1.99
 Postural sway area CON 4 51 10.1 [+ or -] 9.54

 Farmworkers

Test measures No. (a) Mean [+ or -] SD

Cognitive function
 Digit span forward 285 4.74 [+ or -] 0.99
 Digit span reverse 285 3.52 [+ or -] 1.00
 Symbol digit latency 273 2,680 [+ or -] 932
Sensory function
 Vibrotactile threshold PR digit 1 281 0.56 [+ or -] 0.33
 Vibrotactile threshold PR digit 4 281 0.54 [+ or -] 0.31
 Vibrotactile threshold NP digit 1 279 0.48 [+ or -] 0.29
 Vibrotactile threshold NP digit 4 280 0.51 [+ or -] 0.29
 Contrast sensitivity L eye 1.5 cpd 287 21.5 [+ or -] 14.3
 Contrast sensitivity L eye 3 cpd 287 34.0 [+ or -] 24.7
 Contrast sensitivity L eye 6 cpd 287 66.4 [+ or -] 58.6
 Contrast sensitivity L eye 12 cpd 287 45.8 [+ or -] 34.9
 Contrast sensitivity L eye 18 cpd 287 16.1 [+ or -] 12.4
 Contrast sensitivity R eye 1.5 cpd 287 23.0 [+ or -] 17.7
 Contrast sensitivity R eye 3 cpd 287 36.3 [+ or -] 24.9
 Contrast sensitivity R eye 6 cpd 287 68.2 [+ or -] 51.2
 Contrast sensitivity R eye 12 cpd 287 50.5 [+ or -] 36.0
 Contrast sensitivity R eye 18 cpd 287 18.0 [+ or -] 13.9
Psychomotor function
 Tapping PR 284 79.4 [+ or -] 14.7
 Tapping NP 284 72.3 [+ or -] 12.8
 Tapping alternating 284 39.9 [+ or -] 15.6
 Santa Ana PR 287 18.0 [+ or -] 3.49
 Santa Ana NP 285 17.4 [+ or -] 3.03
Motor function
 Grip strength 287 33.8 [+ or -] 10.7
Balance
 Postural sway length CON 1 285 37.7 [+ or -] 6.04
 Postural sway length CON 2 285 51.9 [+ or -] 13.6
 Postural sway length CON 3 285 48.5 [+ or -] 9.69
 Postural sway length CON 4 285 78.8 [+ or -] 23.1
 Postural sway area CON 1 285 2.31 [+ or -] 1.44
 Postural sway area CON 2 285 3.85 [+ or -] 2.55
 Postural sway area CON 3 285 4.59 [+ or -] 2.65
 Postural sway area CON 4 285 9.44 [+ or -] 4.99

Abbreviations: CON, condition; cpd, cycles per degree; L, left; NP,
nonpreferred hand; PR, preferred hand; Right.

(a) Data for one or more individuals were missing for each test.

Table 3. Base models for neurobehavioral test measures. (a)

Measure, (b) covariate Estimate (95% CI)

Digit span forward
 Education, per year 0.78 (0.73 to 0.82)
 Acculturation, moderate 0.76 (0.46 to 1.27)
 Acculturation, high 0.84 (0.45 to 1.57)
Symbol digit latency
 Age, per 10 years 221 (98 to 344)
 Education, per year -97 (-119 to -75)
 Acculturation, moderate -229 (-434 to -24)
 Acculturation, high -323 (-570 to-76)
 Usual sleep, [greater than or
 equal to] 7 hrs -354 (-565 to -143)
 Severe head injury, ever 286 (-26 to 599)
Vibrotactile threshold, PR digit 1
 Age, per 10 years 0.05 (0.00 to 0.10)
 Sex, female 0.07 (-0.02 to 0.16)
 Height, per inch 0.01 (-0.00 to 0.02)
Visual contrast sensitivity, L eye 6 cpd
 Age, 33-37 years 6.29 (-10.0 to 22.6)
 Age, 38-43 years 14.8 (-1.57 to 31.3)
 Age, 44-55 years 22.0 (4.37 to 39.6)
 Sex, female 26.4 (14.4 to 38.5)
 Visual acuity L eye, not 20/20 24.1 (11.1 to 37.0)
Tapping PR
 Sex, female 11.5 (8.77 to 14.3)
 Education, per year -1.34 (-1.63 to -1.05)
Santa Ana PR
 Age, per 10 years 1.21 (0.71 to 1.72)
 Education, per year -0.21 (-0.28 to -0.14)
 Severe head injury, ever 1.72 (0.41 to 3.04)
Grip strength
 Age, per 10 years 1.48 (0.45 to 2.51)
 Sex, female 9.74 (7.90 to 11.6)
 Height, per inch -1.15 (-1.42 to -0.88)
 Hand pain 2.68 (0.80 to 4.55)
Postural sway, length CON 4
 Age, 33-37 years -2.52 (-9.40 to 4.37)
 Age, 38-43 years -1.59 (-8.53 to 5.36)
 Age, 44-55 years 6.78 (-0.59 to 14.2)
 Height, per inch 1.31 (0.50 to 2.13)
 Weight, per 10 pounds -1.33 (-2.15 to -0.51)
 Alcohol drinks per week, 1-14 -1.55 (-7.38 to 4.29)
 Alcohol drinks per week, > 14 10.8 (3.11 to 18.5)

Abbreviations: CON, condition; cpd, cycles per degree; L, left; NP,
nonpreferred hand; PR, preferred hand; R, right.

(a) Results are ORs (95% CIs) for digit span and coefficients (95% CIs)
for other tests; the referent value is 1 for digit span and 0 for other
tests. Models for particular test measures included all variables
listed. In all cases, a higher value indicates worse performance.

(b) The same covariates were included in the base models for each
measure of a test.

Table 4. History of farm work in fern, nursery, and citrus workers. (a)

 All Fern
 farmworkers workers
Characteristics (n=288) (n=140)

Farm work (years)
 1-9 26 15
 10-20 50 55
 21-41 25 30
Farm work in previous year
 No 26 15
 Yes 74 85
Farm work before age 14
 No 84 86
 Yes 16 14
Migrant farm work (years)
 0 60 71
 1-5 20 17
 > 5 20 12
Fern work (months)
 No fern work 51 --
 [less than or equal to] 100 15 30
 100-140 16 34
 > 140 18 36
Lifetime bunches of ferns cut
 No fern work 51 --
 [less than or equal to] 350,000 17 35
 350,001-600,000 16 34
 > 600,000 15 31
Nursery work (months)
 No nursery work 49 75
 [less than or equal to] 10 16 9
 11-48 16 11
 > 48 18 6
Citrus work (months)
 No citrus work 51 68
 [less than or equal to] 10 17 14
 10-42 16 11
 > 42 15 8

 Nursery Citrus
 workers workers
Characteristics (n=147) (n=141)

Farm work (years)
 1-9 31 19
 10-20 46 43
 21-41 22 38
Farm work in previous year
 No 35 30
 Yes 65 70
Farm work before age 14
 No 78 78
 Yes 22 22
Migrant farm work (years)
 0 53 28
 1-5 22 33
 > 5 25 39
Fern work (months)
 No fern work 76 68
 [less than or equal to] 100 16 15
 100-140 4 5
 > 140 3 12
Lifetime bunches of ferns cut
 No fern work 76 68
 [less than or equal to] 350,000 15 16
 350,001-600,000 5 6
 > 600,000 4 11
Nursery work (months)
 No nursery work -- 35
 [less than or equal to] 10 32 21
 11-48 32 23
 > 48 36 21
Citrus work (months)
 No citrus work 38 --
 [less than or equal to] 10 22 35
 10-42 23 33
 > 42 16 31

(a) Table entries are column percentages. Controls, who had done farm
work for less than 1 month, are not included in the table. Fern,
nursery, and citrus workers were defined as those who had worked more
than 1 month in the specific type of agriculture. Many farmworkers
had worked on more than one crop, so the sum of fern, nursery, and
citrus workers is greater than the total number of farmworkers.

Table 5. Association of neurobehavioral performance with ever
having done farm work. (a)

Test measure Ever farm work

Cognitive function
 Digit span forward 1.90 (1.02 to 3.53) **
 Digit span reverse 1.28 (0.70 to 2.33)
 Symbol digit latency -88.0 (-341 to 165)
Sensory function
 Vibrotactile threshold PR digit 1 0.08 (-0.02 to 0.17)
 Vibrotactile threshold PR digit 4 0.00 (-0.09 to 0.09)
 Vibrotactile threshold NP digit 1 -0.02 (-0.11 to 0.07)
 Vibrotactile threshold NP digit 4 0.01 (-0.08 to 0.10)
 Contrast sensitivity L eye 1.5 cpd 2.52 (-1.70 to 6.73)
 Contrast sensitivity L eye 3 cpd 3.12 (-4.76 to 11.0)
 Contrast sensitivity L eye 6 cpd 4.34 (-12.2 to 20.9)
 Contrast sensitivity L eye 12 cpd 0.70 (-8.89 to 10.3)
 Contrast sensitivity L eye 18 cpd 1.53 (-1.77 to 4.84)
 Contrast sensitivity R eye 1.5 cpd -0.94 (-5.92 to 4.05)
 Contrast sensitivity R eye 3 cpd 3.87 (-3.76 to 11.5)
 Contrast sensitivity R eye 6 cpd 1.16 (-13.1 to 15.4)
 Contrast sensitivity R eye 12 cpd -5.97 (-15.3 to 3.36)
 Contrast sensitivity R eye 18 cpd -2.72 (-6.25 to 0.80)
Psychomotor function
 Tapping PR 4.13 (0.00 to 8.27) *
 Tapping NP 3.81 (0.26 to 7.35) **
 Tapping alternating 2.34 (-2.49 to 7.17)
 Santa Ana PR 1.34 (0.29 to 2.39) **
 Santa Ana NP -0.12 (-1.05 to 0.81)
 Grip strength -0.46 (-2.49 to 1.57)
Balance
 Postural sway length CON 1 0.98 (-0.74 to 2.70)
 Postural sway length CON 2 3.86 (-0.15 to 7.88) *
 Postural sway length CON 3 1.31 (-1.40 to 4.03)
 Postural sway length CON 4 4.74 (-2.20 to 11.7)
 Postural sway area CON 1 -0.39 (-0.83 to 0.06) *
 Postural sway area CON 2 0.18 (-0.57 to 0.92)
 Postural sway area CON 3 0.09 (-0.69 to 0.87)
 Postural sway area CON 4 -0.38 (-2.18 to 1.42)

Test measure Ever fern work

Cognitive function
 Digit span forward 2.54 (1.29 to 5.03) ***
 Digit span reverse 1.45 (0.76 to 2.80)
 Symbol digit latency 33.4 (-243 to 309)
Sensory function
 Vibrotactile threshold PR digit 1 0.11 (0.00 to 0.21) **
 Vibrotactile threshold PR digit 4 0.02 (-0.08 to 0.12)
 Vibrotactile threshold NP digit 1 -0.02 (-0.11 to 0.08)
 Vibrotactile threshold NP digit 4 0.04 (-0.06 to 0.14)
 Contrast sensitivity L eye 1.5 cpd 2.57 (-1.98 to 7.12)
 Contrast sensitivity L eye 3 cpd 3.17 (-5.33 to 11.7)
 Contrast sensitivity L eye 6 cpd 1.74 (-16.1 to 19.6)
 Contrast sensitivity L eye 12 cpd 1.36 (-8.99 to 11.7)
 Contrast sensitivity L eye 18 cpd 0.88 (-2.68 to 4.45)
 Contrast sensitivity R eye 1.5 cpd -0.16 (-5.54 to 5.21)
 Contrast sensitivity R eye 3 cpd 4.66 (-3.58 to 12.9)
 Contrast sensitivity R eye 6 cpd 2.03 (-13.4 to 17.4)
 Contrast sensitivity R eye 12 cpd -8.01 (-18.1 to 2.05)
 Contrast sensitivity R eye 18 cpd -3.24 (-7.05 to 0.56) *
Psychomotor function
 Tapping PR 5.38 (0.87 to 9.89) **
 Tapping NP 4.85 (0.98 to 8.71) **
 Tapping alternating 2.57 (-2.70 to 7.85)
 Santa Ana PR 2.29 (1.17 to 3.41) ***
 Santa Ana NP 0.69 (-0.31 to 1.68)
 Grip strength 0.41 (-1.78 to 2.60)
Balance
 Postural sway length CON 1 0.59 (-1.26 to 2.44)
 Postural sway length CON 2 5.95 (1.66 to 10.2) ***
 Postural sway length CON 3 -0.76 (-3.62 to 2.11)
 Postural sway length CON 4 5.94 (-1.53 to 13.4)
 Postural sway area CON 1 -0.65 (-1.12 to -0.17) ***
 Postural sway area CON 2 0.28 (-0.52 to 1.09)
 Postural sway area CON 3 -0.50 (-1.32 to 0.33)
 Postural sway area CON 4 -0.26 (-2.20 to 1.68)

Test measure Ever nursery work

Cognitive function
 Digit span forward 1.84 (0.9 to 3.51) *
 Digit span reverse 1.21 (0.65 to 2.25)
 Symbol digit latency -148 (-409 to 112)
Sensory function
 Vibrotactile threshold PR digit 1 0.06 (-0.04 to 0.16)
 Vibrotactile threshold PR digit 4 0.00 (-0.10 to 0.10)
 Vibrotactile threshold NP digit 1 -0.02 (-0.11 to 0.07)
 Vibrotactile threshold NP digit 4 0.00 (-0.09 to 0.09)
 Contrast sensitivity L eye 1.5 cpd 2.98 (-1.50 to 7.47)
 Contrast sensitivity L eye 3 cpd 3.90 (-4.48 to 12.3)
 Contrast sensitivity L eye 6 cpd 3.99 (-13.7 to 21.6)
 Contrast sensitivity L eye 12 cpd 0.51 (-9.70 to 10.7)
 Contrast sensitivity L eye 18 cpd 2.28 (-1.23 to 5.79)
 Contrast sensitivity R eye 1.5 cpd -0.91 (-6.21 to 4.39)
 Contrast sensitivity R eye 3 cpd 4.07 (-4.06 to 12.2)
 Contrast sensitivity R eye 6 cpd 1.52 (-13.7 to 16.7)
 Contrast sensitivity R eye 12 cpd -3.34 (-13.2 to 6.56)
 Contrast sensitivity R eye 18 cpd -1.55 (-5.28 to 2.19)
Psychomotor function
 Tapping PR 3.60 (-0.70 to 7.91)
 Tapping NP 3.00 (-0.68 to 6.68)
 Tapping alternating 1.59 (-3.44 to 6.61)
 Santa Ana PR 0.89 (-0.18 to 1.96)
 Santa Ana NP -0.41 (-1.37 to 0.54)
 Grip strength -0.81 (-2.95 to 1.34)
Balance
 Postural sway length CON 1 1.46 (-0.37 to 3.29)
 Postural sway length CON 2 3.56 (-0.72 to 7.84)
 Postural sway length CON 3 3.11 (0.28 to 5.95) **
 Postural sway length CON 4 6.55 (-0.83 to 13.9) *
 Postural sway area CON 1 -0.18 (-0.83 to 13.9) *
 Postural sway area CON 2 0.20 (-0.60 to 1.00)
 Postural sway area CON 3 0.37 (-0.46 to 1.20)
 Postural sway area CON 4 -0.12 (-2.04 to 1.80)

Test measure Ever citrus

Cognitive function
 Digit span forward 1.79 (0.92 to 3.46) *
 Digit span reverse 1.36 (0.72 to 2.58)
 Symbol digit latency -132 (-399 to 135)
Sensory function
 Vibrotactile threshold PR digit 1 0.07 (-0.03 to 0.18)
 Vibrotactile threshold PR digit 4 -0.01 (-0.11 to 0.09)
 Vibrotactile threshold NP digit 1 -0.04 (-0.14 to 0.05)
 Vibrotactile threshold NP digit 4 -0.02 (-0.11 to 0.08)
 Contrast sensitivity L eye 1.5 cpd 2.93 (-1.62 to 7.48)
 Contrast sensitivity L eye 3 cpd 1.76 (-6.75 to 10.3)
 Contrast sensitivity L eye 6 cpd 7.00 (-10.9 to 24.9)
 Contrast sensitivity L eye 12 cpd 2.39 (-7.97 to 12.7)
 Contrast sensitivity L eye 18 cpd 1.87 (-1.70 to 5.44)
 Contrast sensitivity R eye 1.5 cpd -1.66 (-7.04 to 3.72)
 Contrast sensitivity R eye 3 cpd 3.29 (-4.96 to 11.5)
 Contrast sensitivity R eye 6 cpd 1.17 (-14.3 to 16.6)
 Contrast sensitivity R eye 12 cpd -6.13 (-16.2 to 3.96)
 Contrast sensitivity R eye 18 cpd -1.89 (-5.69 to 1.91)
Psychomotor function
 Tapping PR 3.45 (-0.98 to 7.87)
 Tapping NP 2.96 (-0.83 to 6.75)
 Tapping alternating 1.81 (-3.36 to 6.97)
 Santa Ana PR 1.12 (0.00 to 2.23) **
 Santa Ana NP -0.62 (-1.59 to 0.36)
 Grip strength -0.99 (-3.17 to 1.19)
Balance
 Postural sway length CON 1 1.53 (-0.30 to 3.37)
 Postural sway length CON 2 4.50 (0.21 to 8.79) **
 Postural sway length CON 3 2.80 (-0.07 to 5.67) *
 Postural sway length CON 4 7.42 (0.04 to 14.8) *
 Postural sway area CON 1 -0.24 (-0.71 to 0.24)
 Postural sway area CON 2 0.36 (-0.44 to 1.16)
 Postural sway area CON 3 0.42 (-0.41 to 1.25)
 Postural sway area CON 4 0.30 (-1.61 to 2.22)

Abbreviations: CON, conditions; cpd, cycles per degree; L, left;
NP, nonpreferred hand; PR, preferred hand; R, right. (a) Results
are ORs (95% CIs) for digit span and coefficients (95% CIs) for
other tests. Farm work exposure variables were added individually
to the models shown in Table 3. Models for fern, nursery, and citrus
work were adjusted for ever having done other types of farm work.
The referenct for all comparisons is the control group; the value
is 1 for digit span and 0 for other tests. In all cases, a higher
value indicates worse performance.

* p < 0.10; ** p < 0.05; *** p < 0.01.

Table 6. Association of quantitative measures of farm work
with neurobehavioral performance. (a)

 Digit span
Characteristics forward

Years of farm work
 1-9 1.66 (0.83 to 3.34)
 10-20 2.01 (1.03 to 3.92) **
 21-41 2.31 (1.07 to 4.98) **
 Trend p = 0.04

Years of farm work, participants with 6 or more years of education
 1-9 1.73 (0.80 to to 3.78)
 10-20 2.72 (1.25 to 5.91) **
 21-41 4.33 (1.66 to 11.3) **
 Trend p = 0.001

Years of farm work, stratified by current or former farm work (b)
 Former, 1-9 years 1.74 (0.80 to 3.82)
 Former, 10-41 years 2.63 (1.11 to 6.25) **
 Current, 1-9 years 1.48 (0.61 to 3.60)
 Current, 10-20 years 1.88 (0.93 to 3.79) *
 Current, 21-41 years 1.99 (0.91 to 4.36) *

Months of fern work
 Other farm work only 1.58 (0.83 to 3.00)
 [less than or equal to] 100 3.52 (1.53 to 8.11) ***
 101-140 2.62 (1.14 to 6.01) **
 > 140 1.80 (0.81 to 4.02)

Bunches of ferns cut
 Other farm work only 1.60 (0.84 to 3.04)
 [less than or equal to] 350,000 3.56 (1.57 to 8.09) ***
 350,001-600,000 2.97 (1.31 to 6.74) ***
 > 600,000 1.60 (0.71 to 3.64)
Months of nursery work
 Other farm work only 1.98 (1.00 to 3.92) **
 [less than or equal to] 10 1.93 (0.86 to 4.3)
 11-48 1.10 (0.50 to 2.38)
 > 48 2.75 (1.28 to 5.91) ***

Months of citrus work
 Other farm work only 2.02 (1.04 to 3.90) **
 [less than or equal to] 9 1.81 (0.83 to 3.98)
 10-42 1.93 (0.87 to 4.28)
 > 42 1.59 (0.70 to 3.60)

Months of fern, nursery, or citrus work
 Other farm work only 0.70 (0.24 to 2.43)
 Fern [less than or equal to ] 100 2.88 (1.46 to 5.67) ***
 Fern 101-140 2.00 (0.99 to 4.02) *
 Fern [greater than or equal to ] 140 1.41 (0.72 to 2.76)
 Nursery [less than or equal to] 10 1.26 (0.65 to 2.47)
 Nursery 11-48 0.63 (0.32 to 1.24)
 Nursery [greater than or equal to] 48 1.98 (1.03 to 3.81) **
 Citrus [less than or equal to] 9 1.13 (0.59 to 2.13)
 Citrus 10-42 1.13 (0.59 to 2.18)
 Citrus [greater than or equal to] 42 1.08 (0.55 to 2.12)

 Vibrotactile threshold,
Characteristics PR digit 1

Years of farm work
 1-9 0.00 (-0.11 to 0.12)
 10-20 0.08 (-0.02 to 0.19)
 21-41 0.17 (0.05 to 0.28) ***
 Trend p = 0.002

Years of farm work, participants with 6 or more years of education
 1-9 0.00 (-0.13 to 0.12)
 10-20 0.11 (-0.01 to 0.23) *
 21-41 0.18 (0.02 to 0.33) ***
 Trend p = 0.0007

Years of farm work, stratified by current or former farm work (b)
 Former, 1-9 years -0.04 (-0.16 to 0.09)
 Former, 10-41 years 0.01 (-0.13 to 0.14)
 Current, 1-9 years 0.06 (-0.08 to 0.20)
 Current, 10-20 years 0.12 (0.01 to 0.23) **
 Current, 21-41 years 0.16 (0.04 to 0.28) ***

Months of fern work
 Other farm work only 0.05 (-0.05 to 0.15)
 [less than or equal to] 100 0.14 (0.00 to 0.27) **
 101-140 0.07 (-0.06 to 0.20)
 > 140 0.11 (-0.01 to 0.24) *

Bunches of ferns cut
 Other farm work only 0.05 (-0.05 to 0.15)
 [less than or equal to] 350,000 0.12 (0.00 to 0.25) *
 350,001-600,000 0.09 (-0.04 to 0.22)
 > 600,000 0.1 (-0.03 to 0.24)

Months of nursery work
 Other farm work only 0.10 (-0.01 to 0.20) *
 [less than or equal to] 10 0.07 (-0.05 to 0.20)
 11-48 0.07 (-0.06 to 0.20)
 > 48 0.04 (-0.09 to 0.16)
Months of citrus work
 Other farm work only 0.08 (-0.02 to 0.18)
 [less than or equal to] 9 0.07 (-0.06 to 0.19)
 10-42 0.10 (-0.03 to 0.23)
 > 42 0.05 (-0.08 to 0.18)
Months of fern, nursery, or citrus work
 Other farm work only 0.24 (0.05 to 0.43) **
 Fern [less than or equal to ] 100 0.11 (0.00 to 0.22) **
 Fern 101-140 0.06 (-0.05 to 0.17)
 Fern [greater than or equal to ] 140 0.10 (-0.01 to 0.21) *
 Nursery [less than or equal to] 10 0.02 (-0.08 to 0.13)
 Nursery 11-48 0.01 (-0.10 to 0.12)
 Nursery [greater than or equal to] 48 0.01 (-0.11 to 0.11)
 Citrus [less than or equal to] 9 0.02 (-0.09 to 0.13)
 Citrus 10-42 0.06 (-0.04 to 0.17)
 Citrus [greater than or equal to] 42 0.02 (-0.09 to 0.13)

 Tapping
Characteristics PR

Years of farm work
 1-9 3.01 (-1.64 to 7.66)
 10-20 4.26 (-0.18 to 8.71) *
 21-41 7.08 (1.86 to 12.3) ***
 Trend p = 0.009

Years of farm work, participants with 6 or more years of education
 1-9 2.49 (-3.03 to 8.01)
 10-20 4.56 (-0.89 to 10.0)
 21-41 8.88 (2.13 to 15.6) **
 Trend p = 0.02

Years of farm work, stratified by current or former farm work (b)
 Former, 1-9 years 1.81 (-3.43 to 7.04)
 Former, 10-41 years 3.53 (-2.18 to 9.23)
 Current, 1-9 years 4.92 (-0.96 to 10.8)
 Current, 10-20 years 5.07 (0.40 to 9.74) **
 Current, 21-41 years 6.91 (1.59 to 12.2) **

Months of fern work
 Other farm work only 3.42 (-0.86 to 7.71)
 [less than or equal to] 100 2.85 (-2.62 to 8.32)
 101-140 5.55 (0.06 to 11.0) **
 > 140 7.54 (2.26 to 12.8) ***

Bunches of ferns cut
 Other farm work only 3.32 (-0.96 to 7.60)
 [less than or equal to] 350,000 5.84 (0.46 to 11.2) **
 350,001-600,000 2.66 (-2.73 to 8.04)
 > 600,000 7.74 (2.29 to 13.2) ***

Months of nursery work
 Other farm work only 4.88 (0.37 to 9.40) **
 [less than or equal to] 10 3.62 (-1.73 to 8.96)
 11-48 1.85 (-3.40 to 7.10)
 > 48 5.04 (0.00 to 10.1) *
Months of citrus work
 Other farm work only 4.74 (0.36 to 9.12) **
 [less than or equal to] 9 4.02 (-1.28 to 9.32)
 10-42 2.73 (-2.58 to 8.04)
 > 42 3.61 (-1.83 to 9.06)
Months of fern, nursery, or citrus work
 Other farm work only 3.72 (-4.01 to 11.4)
 Fern [less than or equal to ] 100 0.85 (-3.57 to 5.27)
 Fern 101-140 4.18 (-0.48 to 8.85) *
 Fern [greater than or equal to ] 140 6.33 (1.91 to 10.8) ***
 Nursery [less than or equal to] 10 1.81 (-2.67 to 6.28)
 Nursery 11-48 0.38 (-4.18 to 4.93)
 Nursery [greater than or equal to] 48 3.94 (-0.38 to 8.27) *
 Citrus [less than or equal to] 9 0.60 (-3.73 to 4.93)
 Citrus 10-42 -0.46 (-4.82 to 3.90)
 Citrus [greater than or equal to] 42 1.44 (-2.99 to 5.88)

 Santa Ana
Characteristics PR

Years of farm work
 1-9 0.71 (-0.46 to 1.88)
 10-20 1.45 (0.32 to 2.58) **
 21-41 2.26 (0.98 to 3.53) ***
 Trend p = 0.0002

Years of farm work, participants with 6 or more years of education
 1-9 0.33 (-0.99 to 1.65)
 10-20 1.72 (0.40 to 3.04) **
 21-41 2.55 (0.94 to 4.16) ***
 Trend p = 0.0002

Years of farm work, stratified by current or former farm work (b)
 Former, 1-9 years -0.08 (-1.39 to 1.22)
 Former, 10-41 years 1.43 (0.02 to 2.83) **
 Current, 1-9 years 1.96 (0.50 to 3.42) ***
 Current, 10-20 years 1.71 (0.54 to 2.89) ***
 Current, 21-41 years 2.45 (1.16 to 3.73) ***
Months of fern work
 Other farm work only 0.76 (-0.31 to 1.82)
 [less than or equal to] 100 1.72 (0.38 to 3.07) **
 101-140 2.41 (1.04 to 3.77) ***
 > 140 2.74 (1.43 to 4.05) ***
Bunches of ferns cut
 Other farm work only 0.73 (-0.33 to 1.79)
 [less than or equal to] 350,000 1.56 (0.25 to 2.87) **
 350,001-600,000 2.89 (1.56 to 4.21) ***
 > 600,000 2.48 (1.13 to 3.84) ***
Months of nursery work
 Other farm work only 2.07 (0.93 to 3.20) ***
 [less than or equal to] 10 0.59 (-0.73 to 1.91)
 11-48 0.42 (-0.88 to 1.72)
 > 48 1.52 (0.27 to 2.77) **
Months of citrus work
 Other farm work only 1.56 (0.45 to 2.68) ***
 [less than or equal to] 9 1.31 (0.00 to 2.62) **
 10-42 1.4 (0.06 to 2.74) **
 > 42 0.57 (-0.79 to 1.93)
Months of fern, nursery, or citrus work
 Other farm work only -0.01 (-1.90 to 1.88)
 Fern [less than or equal to ] 100 1.28 (0.20 to 2.35) **
 Fern 101-140 1.87 (0.72 to 3.01) ***
 Fern [greater than or equal to ] 140 2.17 (1.09 to 3.25) ***
 Nursery [less than or equal to] 10 -0.44 (-1.52 to 0.64)
 Nursery 11-48 -0.73 (-1.83 to 0.36)
 Nursery [greater than or equal to] 48 0.62 (-0.43 to 1.67)
 Citrus [less than or equal to] 9 0.49 (-0.54 to 1.51)
 Citrus 10-42 0.65 (-0.41 to 1.71)
 Citrus [greater than or equal to] 42 0.11 (-0.97 to 1.19)

 Postural sway,
Characteristics length CON 4

Years of farm work
 1-9 3.07 (-0.46 to 1.88)
 10-20 4.46 (-3.14 to 12.1)
 21-41 6.59 (-1.80 to 15.0)
 Trend p = 0.11

Years of farm work, participants with 6 or more years of education
 1-9 3.34 (-6.92 to 13.6)
 10-20 6.28 (-3.50 to 16.1)
 21-41 14.4 (1.94 to 26.8) **
 Trend p = 0.06

Years of farm work, stratified by current or former farm work (b)
 Former, 1-9 years 1.03 (-8.45 to 10.5)
 Former, 10-41 years 10.8 (0.82 to 20.8) **
 Current, 1-9 years 5.83 (-4.62 to 16.3)
 Current, 10-20 years 3.06 (-4.82 to 10.9)
 Current, 21-41 years 5.75 (-2.70 to 14.2)
Months of fern work
 Other farm work only 3.57 (-3.83 to 11.0)
 [less than or equal to] 100 8.49 (-0.94 to 17.9) *
 101-140 8.82 (-0.42 to 18.1) *
 > 140 1.02 (-8.04 to 10.1)
Bunches of ferns cut
 Other farm work only 3.58 (-3.82 to 11.0)
 [less than or equal to] 350,000 9.53 (0.40 to 18.7) **
 350,001-600,000 6.91 (-2.35 to 16.2)
 > 600,000 0.93 (-8.43 to 10.3)
Months of nursery work
 Other farm work only 2.70 (-4.80 to 10.2)
 [less than or equal to] 10 6.38 (-2.77 to 15.5)
 11-48 2.96 (-6.21 to 12.1)
 > 48 9.94 (-0.97 to 18.9) **
Months of citrus work
 Other farm work only 1.84 (-5.64 to 9.32)
 [less than or equal to] 9 7.94 (-1.00 to 16.9) *
 10-42 7.56 (-1.63 to 16.8)
 > 42 6.64 (-2.75 to 16.0)
Months of fern, nursery, or citrus work
 Other farm work only 5.44 (-8.41 to 19.3)
 Fern [less than or equal to ] 100 7.00 (-0.72 to 14.7) *
 Fern 101-140 10.4 (2.44 to 18.3) **
 Fern [greater than or equal to ] 140 1.85 (-5.92 to 9.61)
 Nursery [less than or equal to] 10 3.95 (-3.94 to 11.8)
 Nursery 11-48 -0.18 (-8.22 to 7.86)
 Nursery [greater than or equal to] 48 8.50 (-0.69 to 16.3) **
 Citrus [less than or equal to] 9 6.59 (-0.90 to 14.1) *
 Citrus 10-42 6.10 (-1.66 to 13.9)
 Citrus [greater than or equal to] 42 6.70 (-1.14 to 14.5) *

Abbreviations: CON, condition; PR, preferred hand.

(a) Results are ORs (95% CIs) for digit span and coefficients (95% CIs)
for other tests. Farm work exposure variables were added to the models
shown in Table 3. The referent for all comparisons is the control
group; the value is 1 for digit span and 0 for other tests. In all
cases, a higher value indicates worse performance.

(b) Current farmworkers had done farm work in the year before testing,
whereas former farmworkers had not.

* p < 0.10; ** p < 0.05; *** p < 0.01.


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Freya Kamel, (1) Andrew S. Rowland, (2) Lawrence P. Park, (3) W. Kent Anger, (4) Donna D. Baird, (1) Beth C. Gladen, Tirso Moreno, (5) Lillian Stallone, (6) and Dale P. Sandle (1)

(1) National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA; (2) University of New Mexico, Albuquerque, New Mexico, USA; (3) Westat, Durham, North Carolina, USA; (4) Oregon Health and Science University, Portland, Oregon, USA; (5) Farmworkers Association of Florida, Apopka, Florida, USA; (6) CODA, Durham, North Carolina, USA

Address correspondence to F. Kamel, Epidemiology Branch, National Institute of Environmental Health Sciences, Box 12233, MD A3-05, Research Triangle Park, NC 27709 USA. Telephone: (919) 541-1581. Fax: (919) 541 2511. E-mail: kamel@niehs.nih.gov

We are grateful to the staff of the Farmworkers Association of Florida, particularly G. Grimes, A. Bahena, C. Cabrera, L. Milien, and R. Rodriguez; to the CODA study supervisors G. Ramirez-Garnica and M. Bizzio; to D.S. Rohlman and O.J. Sizemore for developing the test battery; and to the community members who participated in the study.

The authors declare they have no conflict of interest.

Received 18 March 2003; accepted 23 July 2003.
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Title Annotation:Environmental Medicine
Author:Sandler, Dale P.
Publication:Environmental Health Perspectives
Date:Nov 1, 2003
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