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Atrazine Classified "Likely Human Carcinogen" in Tap Water 

Top U.S. Weed Killer May Also Cause Hormonal Damage to Infants, Children

Environmental Working Group 27jun00


In a set of scientific findings that will be presented to an expert advisory panel beginning on Tuesday, June 27, the Environmental Protection Agency (EPA) is upgrading its estimate of the toxicity of atrazine, the most widely used farm weed killer in the nation, and a common tap water contaminant. In its first-ever in-depth look at the potential for atrazine to harm children, the agency not only is increasing its estimate of the chemical's lifetime cancer potency, but also is presenting findings that atrazine has the potential to deliver potent harmful effects to the fetus, infant, and child reaching puberty.

After a five year review of industry and government data summarized in its new "hazard assessment," EPA found atrazine to be a more potent carcinogen than before. EPA had classified the weed killer as a "possible" carcinogen: now it is "likely" to cause cancer. Equally significant, the agency has concluded that short-term, perhaps even single day exposure to atrazine has the potential to cause a range of reproductive effects and developmental defects, including miscarriage, and delayed vaginal opening and penis development during puberty (EPA, 2000).

EPA is presenting its conclusion to the agency's Scientific Advisory Panel Tuesday for review. Pending the SAP assessment, the agency will almost certainly need to adopt a new, stronger drinking water standard to protect children. The current way of regulating atrazine in drinking water is based on an annual average level, discounting seasonal spikes and peaks. This could be replaced with a new legal limit based on short-term, possibly single day, exposures to protect the fetus, the infant, and the young adult male in vulnerable windows of sensitivity. In other words, if the new assessment stands, instead of testing tap water four times a year for atrazine, utilities might have to test as often as every day during the peak contamination period - potentially more than 100 times per year.

Atrazine contaminates the tap water of more than 10 million people in the Midwest (EWG, 1999) and causes more health standard violations in tap water than any other EPA-regulated chemical pollutant. Water utilities spend at least $30 million per year now testing and treating tapwater for the chemical. Given the new information on the dangers atrazine poses to children, and the costs water suppliers would face to provide safe water to infants and children, EPA should ban atrazine.

EPA's assessment is based on the most recent science.

In a broad and well-considered approach, EPA uses its hazard assessment to tie together pieces of data from the laboratory and the real world, considering health effects in lab animals and humans. New data developed by Dr.Ralph Cooper and his colleagues (Cooper et al., 2000) enabled the agency to connect, for the first time, atrazine's actions on hormone systems with a range of health effects - cancer, reproductive effects, and developmental impacts.

In contrast, the World Health Organization's International Agency for Research on Cancer (IARC), in its 1999 assessment of atrazine toxicity, did not have the latest Cooper data in hand and focused exclusively on a single health effect, the mammary tumors in one strain of laboratory animal (Sprague-Dawley rats). After a narrowly-focused assessment which noted the differences in reproductive aging between rats and humans, IARC concluded that, because of differences in this single aspect of the cancer process, there was no evidence supporting atrazine's ability to cause breast cancer in humans. EPA took a broader view. Agency scientists examined the potential for atrazine to cause cancer in a variety of other tissues, and made use of the new data indicating that many of the critical hormonally-driven steps in the cancer process also play a crucial role in the developmental and reproductive problems consistently reported in the Cooper team's laboratory studies.

EPA's conclusions on hormonal effects now place the pesticide squarely in the category of "endocrine disruptor" - chemicals that alter the hormone system. The agency determined that exposure to atrazine, by disrupting functions of the hormone system, might lead to increases in tumors in hormonally-sensitive tissues, such as the uterus and its lining, or the breast. EPA found strong evidence that atrazine initiates a "cascade" of biological events that could lead to a host of health problems, beginning with the suppression of hormones from the hypothalamus, which, in turn, inhibits the release of hormones from the pituitary, setting up a dangerous hormonal imbalance. The hypothalamus, among other things, influences the pituitary, which controls growth, metabolism, and reproductive function. In the case of atrazine, disruption of the function of these structures is believed to lead to changes in levels of the hormones estrogen and prolactin, which can lead to tumor formation.

Perhaps even more significantly, the new assessment marks the first time EPA scientists have looked beyond cancer as the primary health endpoint of concern following atrazine exposure. EPA has described compelling laboratory evidence that atrazine may disrupt the normal development and function of the reproductive system by causing delays in the onset of puberty in both males and females and by causing miscarriages in adult animals. Atrazine affects the levels of a number of hormones needed for normal development and function of the reproductive system, including estrogen, prolactin, luteinizing hormone, and follicle stimulating hormone. For instance, laboratory data show that the pesticide significantly alters testosterone levels in both the male and female fetus and in young male rats, perhaps the cause of the observed delay in sexual maturation.

Atrazine disrupts a broad range of hormones, leading to a variety of potential health effects. Atrazine has been linked in laboratory studies to miscarriage, including full-litter resorption; delayed onset of puberty (delayed vaginal opening and penis development during puberty); altered estrous cycles, and prostatitis (inflammation of the prostate). These effects occur in some cases after only a few days of dosing.

Implications for tapwater regulations - The current drinking water standard for atrazine is calculated as an annual average of four quarterly samples.

A new legal limit based on EPA's new hazard assessment would likely apply to peak, short-term exposure periods. It is unclear from EPA's hazard assessment how many days or weeks of exposure to atrazine the Agency would interpret as being safe for a fetus or an infant or a child reaching puberty. What is clear is: 1) peak levels of atrazine in treated tapwater are almost never detected under the current monitoring scheme, which requires only one test every three months; and 2) even when high levels of atrazine are detected they are discounted when they are averaged with lower levels from other times in the year. Atrazine causes more health standard violations in tap water than any other chemical pollutant regulated by EPA, even under the current weak monitoring scheme.

Although it remains to be seen how EPA's drinking water office will respond to the new EPA hazard assessment, one strong possibility is that water suppliers will have to test for atrazine more frequently during peak runoff times, perhaps even daily - as opposed to the current quarterly monitoring schedule. Under current rules, increased testing costs would be borne by water suppliers, while the manufacturer of atrazine, Novartis, would pay nothing, even as it continued to reap enormous profits from the sale of atrazine, the most heavily used weed killer in the United States.

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