Body mass index and bromoxynil exposure in a sample of rural residents during spring herbicide application

Bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), a phenolic herbicide, is widely used in production of cereals and other crops. Little is known, however, about bromoxynil exposure in humans. Results of previous research suggest a longer residence time in the body for bromoxynil compared to phenoxy herbicides [e.g., (2,4-dichlorophenoxy)acetic acid (2,4-D), 4-chloro-2-methylphenoxyacetic acid (MCPA)] and that bromoxynil would tend to partition into fatty tissue more so than 2,4-D. In previous research, body mass index (BMI) was found to be an independent predictor of plasma concentrations of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), the persistent lipophilic metabolite of the chlorinated pesticide bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT). As part of the Prairie Ecosystem Study, gas chromatography/mass spectrometry analysis was used to measure concentrations of bromoxynil and seven other herbicides (2,4-D, dicamba, fenoxaprop, MCPA, ethalfluralin, triallate, and trifluralin) in plasma from residents (104 men, 88 women, 24 youths age 12-17 yr) of a cereal-producing region in Saskatchewan, Canada, during spring herbicide application, 1996. Multiple logistic regression analysis was used to explore whether BMI predicted detection of bromoxynil in plasma from the adults. The prevalence of detection (detection limits: 2-50 microg/L) was markedly higher for bromoxynil (men, 44.2%; women, 14.8%; youths, 20.8%) compared to each of the other herbicides including 2,4-D (men, 16.5%; women, 3.4%; youths, 12.5%) and MCPA (men, 6.8%; women, 1.1%; youths, 4.2%), although bromoxynil is commonly formulated or tank mixed with these herbicides. In the multiple logistic regression analysis, the variables BMI, exposure group [bromoxynil applicators, non-applicator family members of bromoxynil applicators, all others (reference group)], and days elapsed since the last use of bromoxynil were found to be independent predictors of detection of bromoxynil, while age, gender, and farm residency were not statistically significant. With adjustment for exposure group [bromoxynil applicators: odds ratio (OR = 24.30, 95% confidence interval (CI) = 9.59-61.58; nonapplicator family members of bromoxynil applicators: OR = 3.53, 95% CI = 1.19-10.44; all others (reference group)], the OR for detection of bromoxynil was 2.35 (95% CI = 0.87-6.33) for participants in the middle (25.53-29.00 kg/m2) tertile (men: OR = 2.85, 95% CI = 0.75-10.82; women: OR = 1.63, 95% CI = 0.36-7.40) of BMI and 4.01 (95% CI = 1.46-11.03) for participants in the highest (> 29.00 kg/m2) tertile (men: OR = 4.67, 95% CI = 1.17-18.58; women: OR = 2.20, 95% CI = 0.44-10.99) with participants in the lowest (< 25.53 kg/m2) tertile as the reference group. Similar ORs were observed for BMI with adjustment for days elapsed since the last use of bromoxynil. In conclusion, further research is needed to investigate whether adiposity is an important modifying factor for persistence of bromoxynil in the body.