Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-008057, 2008 Feb; :1-34
Adolescents working in agriculture are exposed to pesticide spray, drift, and residues in the soil and on foliage, however little scientific evidence is available to determine acceptable levels of pesticide exposure to this population, Pesticides are thought to pose a considerably higher risk to children than to adults, yet little is known about the extent or magnitude of health problems related to occupational exposure to pesticides in children. It has been suggested that developmental factors- physical, cognitive, and psychological- may place youth workers at increased risk. Currently, handling or applying agricultural chemicals classified under the federal Insecticide, Fungicide, and Rodenticide Act as toxicity category 1 or II is considered a hazardous work order for youth under the age of 16. However there is no federal youth labor law restricting the handling of category III and IV pesticides. Although certain safety practices are known to protect workers from the acutely harmful health effects of exposure to agricultural chemicals, less is known regarding protection against exposures to low-levels of pesticides, and the association of chronic low-level pesticide exposure and potential neurotoxicity, reproductive toxicity, endocrine disruption, and carcinogenic effects. Some organ systems, such as reproductive and endocrine systems undergo periods of rapid growth and development during adolescence, potentially placing adolescents at an increased risk for long-range chronic or mutagenic effects of these chemicals. Hypothetically, the period of rapid cell growth that occurs during adolescence could increase susceptibility to carcinogens, but little data exist to support or refute this. The purpose of this project was to evaluate the extent to which adolescent farmworkers differ in their exposure to agricultural chemicals when compared to adult co-workers and to assess differences in the effects of such exposures on measures of DNA damage and neurotoxicity, We compared biomarkers of genetic damage and oxidative stress among adolescents and adults of similar cultural backgrounds and performing similar agricultural work tasks and used neurobehavioral tests to compare performances between adult and adolescent farmworkers. During two harvesting seasons we recruited 409 Hispanic adolescent and adult farmworkers and controls to participate in the study. All subjects provided urine samples for measures of oxidative stress and for measurement of metabolites of commonly used pesticides. Buccal samples were obtained to measure DNA damage in leukocytes. Subjects completed a neurobehavioral test battery consisting of 10 computer-based tests measuring attention, response speed, coordination and memory. Using urinary biomarkers of organophosphate pesticides, we found that the exposures of the adolescent and adult farmworkers were similar and that they were not significantly higher than the levels observed in our controls group. Levels of THPI, the metabolite of Captain, a fungicide commonly used in berry crops close to the time of harvest were shifted significantly higher in the agricultural workers relative to the controls (1-sided p-value = 0.01; Wilcoxon test). Specific tests of various percentiles (median, 60th, and 75th percentile) indicated that while medians did not differ in these two populations (1-sided p-value = 0.91), the 60th and 75th percentiles were both significantly higher in the agricultural population (60th percentile, 1-sided p-value = 0.01; 75" percentile, 1-sided p-value = 0.037). Similar differences were observed during both years of data collection. Age, gender, school experience, and years working in agriculture all impacted performance on the neurobehavioral tests, Comparison of adult and adolescents did not reveal decreased neurobehavioral performance in adolescents, On several tests the adolescents performed better than adult counterparts. The results of the neurobehavioral tests in subjects who were currently working in agriculture, or with previous agricultural experience indicated that cumulative exposure to low levels of pesticides over many years of agricultural work is associated with neurological impairment as measured by the Match-to-Sample Test. Other measures, Selective Attention, Symbol-Digit, and Reaction Time, showed an interaction with years worked in agriculture and gender. Experience handling pesticides was also associated with deficits in neurobehavioral performance on four neurobehavioral measures. Scores on Digit Span forward and Digit Span reverse were significantly lower for men who had handled pesticides (0,51 points lower for forward, p = 0.02 and 0.52 points lower for reverse, p = 0.02). Match-to-Sample scores were also lower (2.04 points) for men who reported handling pesticides in the past compared to men who had never reported handling pesticides (p = 0.02). The percentage of hits on the Continuous Performance test also showed a decrease for men who handled pesticides (6.4 percentage points, p = 0.047). Our results indicate an association between exposure to agricultural pesticides and markers of DNA damage in the participants of this study, with comparable levels of damage in both adolescent and adult workers. The mean comet tail intensity and tail moment was significantly greater for agricultural workers compared to controls (1-sided p-values < 0.001). No comet parameter was significantly associated with years spent working in agriculture or age of the farmworker controlling for potential confounding factors. Comet analysis of leukocytes from buccal cell offers a non-intrusive method of assessment of DNA among working populations; however, we encountered methodological challenges in cryopreservation of the samples. Cryopreservation decreases the number of viable cells available upon thawing. Comparison of frozen and fresh samples from the same individuals indicated higher viability in fresh samples, but similar group means for comet parameters. The intravariability of comet results do appear to increase with cryopreservation. In summary we found indications of very low pesticide exposures among the farmworkers in our study, and no significant differences between adolescents and adults. Surprisingly, even with these low exposures we found that farmworkers performed poorer than non-agricultural participants. A substantial proportion of our sample reported previously mixing or applying pesticides and neurobehavioral performance in this subsample appears to be affected with lower performance. On a number of tests cumulative years of farmwork appears to be related to neurobehavioral performance. The findings of significantly increased indicators of DNA damage among the farmworker participants is also of concern given the postulated relationship between DNA damage and subsequent development of a number of chronic disease and cancer.
Linda McCauley, University of Pennsylvania, School of Nursing/Office of nursing research, Philadelphia, PA 19104-6096