Research Addresses Potential Risks of Atrazine and Related Pesticides

Research Addresses Potential Risks of Atrazine and Related Pesticides (PDF) (1 page, 103K, About PDF)

Issue

Atrazine is an agricultural herbicide used worldwide since 1958. In the United States, approximately 75 million pounds of atrazine are applied each year, making it the most widely used agricultural herbicide. In states where atrazine is heavily used, the chemical has been found in both surface and groundwater. Consequently, scientists with the U.S. Environmental Protec-tion Agency's Office of Research and Development are studying atrazine to understand if the herbicide has human health implications.

Science Objective

Atrazine and other chlorotriazines are being reviewed by the EPA because they are widely used and have been reported to cause adverse health effects in the aging female rat. Ongoing research to identify the range of biolog-ical effects and the mode and mecha-nism of action through which atrazine has its primary effect on endocrine function is important in understanding how the herbicide impacts laboratory animals and potentially human health.

Application and Impact

EPA research on atrazine demonstrated that effects in animals of initial concern (mammary cancer) were not likely to be relevant to humans. The mode of action for atrazine suggests that humans would be at risk for different toxic effects such as premature aging, developmental effects, reproductive function, and delayed puberty.

EPA investigators found that atrazine alters the way the brain controls pitu-itary function, an observation that would be consistent with atrazine-induced premature aging. They found that atrazine suppressed two hormones - the luteinizing hormone (LH) and prolactin hormone (PRL) - by altering the hypo-thalamic control of pituitary hormone secretion. Although scientists are still studying the precise mechanism through which atrazine causes these changes, they have demonstrated the adverse outcomes of the changes in LH and PRL.

EPA research showed that a brief atra-zine exposure to a lactating mother can influence development in the offspring by modifying endocrine constituents of the mother's milk. Second, this work has identified a sensitive period of time for this type of early lactation exposure and raises the issue of whether other environmental compounds may similarly affect reproductive function in the offspring of mothers exposed to atrazine and potentially other similar chemicals.

Other EPA research showed that juvenile exposures to atrazine and the primary metabolites of atrazine result in delayed puberty in the male and female rats. Three of the primary metabolites of atrazine appear to be just as potent as the parent compound in inducing these effects on pubertal development. The research has had a valuable impact on the risk assessment for this chemical. Data has been used to set the no effect level for the developing animal and to understand cumulative effects.

References

Stoker, T.E.; Robinette, C.L; and Cooper, R.L. Maternal exposure to atrazine during lactation sup-presses suckling-induced prolactin release and results in prostatitis in the adult offspring. Toxicological Sciences. 1999, 52(1):68-79.

Cooper. R.L.; Stoker, T.E.; Tyrey, L.; Goldman, J.M.; McElroy, W.K. Atrazine Disrupts the Hypothalamic Control of Pituitary-Ovarian Function. Toxicological Sciences. 2000, 53: 297-307.

Laws, S.C.; Ferrell, J.M.; Stoker, T.E.; Schmid, J.; and Cooper, R.L. The effect of atrazine on puberty in female wistar rats: an evaluation in the protocol for the assessment of pubertal development and thyroid func-tion. Toxicological Sciences. 2000, 58(2): 366-76.

Contact

Ralph L. Cooper, Ph.D., EPA's Office of Research and Development, 919) 541-4084, cooper.ralph@epa.gov