(Beyond Pesticides, December 15, 2009) Exposure to the endocrine-disrupting herbicide atrazine triggers the release of stress hormones in rats, according to a new study published in the December 2009 issue of the journal Toxicological Sciences. The researchers believe this may explain how the popular weed killer produces some its harmful reproductive effects. The study, “Characterization of the Hypothalamic-Pituitary-Adrenal Axis Response to Atrazine and Metabolites in the Female Rat,” was conducted by the Environmental Protection Agency’s (EPA) National Health and Environmental Effects Research Laboratory.
According to a December 4 analysis by Environmental Health Sciences, a foundation-funded journalism organization, the researchers discovered that female rats fed atrazine at the time of ovulation released a flow of stress hormones that are known to interfere with hormones essential for reproduction. The findings reveal one way atrazine may impact female reproduction. Elevated stress hormones can disrupt the hormone signals that spur ovulation. Such a stress response to atrazine could partially explain why previous studies find that the herbicide inhibits reproduction. The stress reaction is similar to that seen when the animals are restrained against their will.
One of the most widely used agricultural pesticides in the U.S., atrazine can currently legally be applied before and after planting to control broadleaf and grassy weeds. Its increased use to manicure home lawns and gardens has become a serious environmental concern as runoff has had severe health and environmental consequences.
Even at low levels that are considered “safe” by EPA standards, atrazine is known to harm fish, and has been associated with reproductive and developmental effects as well as endocrine disruption. Research by UC Berkeley professor, Tyrone Hayes, Ph.D., demonstrates that exposure to doses of atrazine as small as 0.1 parts per billion, turns tadpoles into hermaphrodites – creatures with both male and female sexual characteristics.
As the most commonly detected pesticide in rivers, streams and wells, an estimated 76.4 million pounds of atrazine is applied in the U.S. annually. It has a tendency to persist in soils and move with water, making it a common water contaminant. Research found that intersex frogs are more common in suburban areas than agricultural areas. Another study suggests it as a possible cause for male infertility.
In October 2009, EPA announced that it will launch a new comprehensive evaluation of the pesticide atrazine to determine its effects on humans this fall. In EPA’s own words, “At the end of this process, the agency will decide whether to revise its current risk assessment of the pesticide and whether new restrictions are necessary to better protect public health.”
Regulatory History in Brief.
Regarding atrazine’s link to cancer, EPA has reversed course from its initial position. In 1988, EPA rated atrazine as a ”˜possible human carcinogen.’ In 1994, EPA placed atrazine under “Special Review.” In December 1999 . EPA’s preliminary cancer risk assessment, rated as ”˜probable human carcinogen.’ In 2000, EPA’s Scientific Advisory Panel (SAP) did not agree with the agency’s draft report and urged new research on relevancy of rat data available. Atrazine caused reproductive changes in one strain of rats that influenced levels of hormones important in rat mammary (breast) cancer. These reproductive changes seen in atrazine-treated rats probably would not occur in women. The SAP concluded that it is unlikely that atrazine would affect human breast cancer risk. In June 2000, Based on SAP recommendations the EPA changed atrazine’s cancer classification to: “not likely to be a carcinogen in humans.” The January 2003 Atrazine Interim Reregistration Eligibility Decision (IRED) (323 pp) about PDF)and subsequent Memorandum of Agreement (MOA) (36 pp) between EPA and the atrazine registrants initiated a monitoring program to focus on the most significant human health exposures associated with agricultural and residential uses — exposures through drinking water. EPA stated that it believed that the change in hormone levels caused by atrazine is the most sensitive health effect observed in an extensive battery of atrazine toxicity tests, and stated that its risk assessments established acceptable levels of exposure. Many scientists have stated and shown in their own laboratory studies that the agency’s standards are unprotective and responsible for, or certainly a contributor to, dramatic endocrine disrupting effects. The October 2009 begins a new process at the agency to reconsider its previous position.