A critique of the World Resources Institute's report "Pesticides and the immune system: the public health risks"

Antinuclear antibodies and bromoxynil exposure in a rural sample

Previous research suggests that farmers may have an increased risk of developing autoimmunity and that exposure to certain pesticides may alter immune function. Little is known, however, about the immunologic effects of farming and pesticide exposures. As part of the Prairie Ecosystem Study, associations between detection of antinuclear antibodies (ANA), an autoimmunity indicator, and exposure to the herbicide bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) were investigated in a cross-sectional study of 208 residents (94 women, 114 men) of a cereal-producing region in Saskatchewan, Canada, during spring herbicide application, 1996. The ANA were assayed in serum by indirect immunofluorescence on HEp-2 cells. Bromoxynil was measured in plasma by gas chromatography/mass spectrometry analysis. Associations were explored between ANA detection and detection of bromoxynil in plasma, self-reported use of bromoxynil and other pesticides, farming exposures, gender, age, body mass index (BMI), and residency. The mean age (SD) of the participants was 50.8 (13.6) yr [women: 49.7 (13.5) yr, men: 51.6 (13.6) yr]. ANA prevalence was 37.5% (women: 39.4%, men: 36%,) at 1:40 serum dilution, 17.3% (women: 20.2%, men: 14.9%) at 1:80, and 10.1% (women: 13.8%, men: 7%) at 1:160. In the multiple-variable Generalized Estimating Equation (GEE) logistic regression analyses, female gender was a positive predictor of ANA detection and gender differences were observed in the relative importance of other study factors. None of the variables examined in the multiple-variable GEE analysis were statistically significant predictors of ANA detection for women. For many of these variables, however, the point estimates for women are similar to those seen in men. For men, with adjustment for age, ANA presence was inversely associated with detection of concentrations of bromoxynil in winter or spring samples and recent occupational use of 2,4-dichlorophenoxyacetic acid, and the positive ANA predictors included having a BMI in the obese (BMI > 30.04 kg/m2) category, recent occupational use of trifluralin or fungicides, and current exposure to oilseed, poultry, or dairy production. The inverse association between ANA detection and bromoxynil exposure observed in farmers in this study is consistent with earlier empirical observations that certain pesticides may suppress immune function. Further research is needed to examine whether these findings are confirmed in other populations and to elucidate the biological mechanisms involved.

A pilot study of global positioning system/geographical information system measurement of residential proximity to agricultural fields and urinary organophosphate metabolite concentrations in toddlers

This pilot study enrolled 20 children between the ages of 11 and 17 months in Imperial County, California to assess children's pesticide exposure and residential proximity to agricultural fields. We compared parental self-report of residential proximity to agricultural fields to measurements using global positioning system/geographical information system (GPS/GIS) technology, and we assessed the relationship between residential proximity to agricultural fields and a biomarker of organophosphate (OP) pesticide exposure. Questionnaires were administered twice, 4 weeks apart, to determine self-reported residential proximity to agricultural fields. Urine samples were collected at each contact to measure OP metabolites. Actual residential proximity to the closest agricultural field and number of fields was within 1 mile to the west were measured using GPS/GIS. Self-report of living proximity to agricultural fields agreed with GPS/GIS measurement 75% of the time during the initial interview, compared to 66% agreement during the second interview. Presence of urinary metabolites suggests that OP exposure was ubiquitous: creatinine-adjusted total urinary dimethyl values ranged from 1.60 to 516.00 microg/g creatinine, and total diethyl ranged from 2.70 to 134.84 microg/g creatinine. No association was found between urinary OP metabolites and residential to field proximity. These results suggest that initial self-report of living proximity to agricultural fields may be more accurate than follow-up self-report. Limitations in this pilot study prevent determination of whether self-report is an accurate measure of proximity.