Herbicides and adjuvants: an evolving view

Abstract

The present report examines the in vitro genotoxicity (micronucleus assay) of herbicides and adjuvants and reports on an in vivo human study on potential endocrine effects of pesticides, including herbicides. Adjuvants are used in conjunction with 2,4-dichlorophenoxy acetic acid (2,4-D) and other herbicides. Earlier pesticide applier survey results (n = 709) show that 59% of the applicators used adjuvants, and the majority of this group used paraffinic oils and/or surfactant mixtures. As a beginning effort to explore the role of adjuvants and herbicides in hormonally based reproductive effects, a prospective, controlled study was performed to analyze blood specimens from three different exposure groups (applicators using herbicides only; applicators using both herbicides and insecticides; and applicators using fumigants in addition to herbicides and insecticides; and a control group composed of other agricultural workers including organic farmers). The applicators and controls were age- and smoking-matched. Study subjects (n = 78) were tested before, during, and after completion of pesticide application season for the effects of pesticide products on hormone levels in the bloodstream. Of the applicator exposure groups examined, only the herbicide group showed significant endocrinologic differences from controls. Free testosterone levels were significantly elevated in post-season measurements (p = 0.032), and follicle-stimulating hormone (FSH) was significantly decreased at the height of the season (p = 0.016) and in the post-season (p = 0.010) as compared to controls. These endocrinologic findings are discussed in terms of their possible relationship to potential endocrine effects of herbicides, herbicide contaminants, and adjuvants. In vitro genotoxicity examination compared four different commercially available surfactant mixtures with 12 different commercial herbicide products, including six different chlorophenoxy herbicides. Only one herbicide yielded a significant dose-response curve. All four adjuvants showed positive dose-response effects. These preliminary data suggest that adjuvants are not inert but are toxicologically active components added to herbicide mixtures. Whether adjuvant toxicant effects are additive or are independent of herbicide effects is poorly understood.

Cancer mortality in four northern wheat-producing states.

“…Both 2,4-D and MCPA, the exposure of interest in the current study, and the potential contaminant, dioxins, are endocrine disruptors (1,42). In addition, adjuvants used in the application of 2,4-D to spring wheat also have endocrinedisrupting characteristics (45). In the IARC occupational cohort, there was a slight, nonstatistically significant increase in prostate cancer mortality (6).…”

Biomarker correlations of urinary 2,4-D levels in foresters: genomic instability and endocrine disruption.

“…These data suggest that the majority of the commercial chlorophenoxy products studied were not genotoxic at the chromosomal level (8).…”

“…With further review, we noted that adjuvants are sometimes used in conjunction with chlorophenoxy herbicides in roadside and other applications. We found that four out of four adjuvants induced significant increases in the frequency of micronuclei (8). Two of five adjuvants showed evidence of weak endocrine-disrupting activity in MCF-7 cells (9).…”

Birth malformations and other adverse perinatal outcomes in four U.S. Wheat-producing states.

“…Occasionally 2,3,7,8-tetrachlorodibenzo-pdioxin may be present in technical grade 2,4-D (Johnson et al 1992). Adjuvants may contribute to adverse health effects (Garry et al 1999). In vitro assays showed that commercial grade 2,4-D at concentrations of 1 and 10 µg/mL caused cell proliferation, whereas assays with reagent grade 2,4-D did not.…”