Atrazine Science Facts

The soundness of a scientific study hinges on its transparency and reproducibility. Do its procedures and results stand up to review by scientific peers and regulatory agencies? Can the study be reproduced with the same findings? This approach safeguards the scientific community, regulators, industry and the public from questionable results.

In testimony before the Agriculture and Rural Development Committee of the Minnesota House of Representatives (February 16, 2005), Anne E. Lindsay, former deputy director, Office of Pesticide Programs, US Environmental Protection Agency, detailed the elaborate and meticulous scientific process required for pesticide registration.

She described at length the painstaking process EPA followed before recommending the re-registration of atrazine for use in American agriculture. She noted that EPA "reaches its conclusions through a systematic, objective evaluation of all relevant information. She noted that each step of the process uses scientifically peer-reviewed, documented procedures." [emphasis added]

Lindsay testified that EPA looks "closely at every study to determine whether the results are scientifically sound," and that it insists on record retention and full data reporting. She stated that to review these studies, EPA follows "published, peer-reviewed Standard Evaluation Procedures." [emphasis added]

Despite EPA's diligent investigative process, a legal and political attack has been launched against atrazine, relying on a handful of studies which, by objective scientific standards, offer questionable conclusions.

Some of these claims are discussed below:

Atrazine and amphibians: Reports that atrazine adversely affects sexual development in frogs, causing a mixture of sex organs in a single animal, are now proven false.

Sound Science Facts: According to EPA, the latest studies show that atrazine does not adversely affect amphibian sexual development.

Further, regarding previous studies conducted by researcher Tyrone Hayes which claim effects of atrazine on frogs, former Director Lindsay noted that not one of Dr. Hayes' laboratory studies were performed in accordance with the appropriate standard practice protocol. [pg. 7, Lindsay testimony]

She also noted that, as a consequence of Hayes' failure to implement appropriate practices, "the Agency concluded that the conduct of each of the laboratory studies was sufficiently compromised [and] that it was not possible to determine whether the conditions of the study, independent, of atrazine, were responsible for the observed effects, or the lack thereof." [pg. 8, Lindsay testimony, emphasis in the original]

As for field studies conducted by Hayes, former Director Lindsay noted that these studies are fraught with deficiencies. "All these field studies have serious design or methodological flaws that limit their usefulness in assessing the potential effects of atrazine on frog development in the wild." [pg. 8, Lindsay testimony]

She went on to comment that despite Dr. Hayes' claim that other scientists have replicated his results, EPA "has never seen either the results from any independent investigator published in peer-reviewed journals or the raw data from Dr. Hayes' additional experiments that confirm Dr. Hayes' [his] conclusions." [pg. 8, Lindsay testimony]

Atrazine and Endocrine Systems: Hayes also has speculated that atrazine might disrupt the human endocrine system, leading to effects such as breast cancer.

Sound Science Facts: This theory is not supported by scientific evidence.

According to Lindsay, EPA "has considered this theory and concluded that it is not supported by the overall weight of the evidence on the toxicity of atrazine in mammalian test species, nor is it consistent with the available human data. First, the AHS (Agricultural Health Study) has found no association between breast cancer and exposure to atrazine. Second, the SAP (Scientific Advisory Panel) has reviewed the available data on how experimental animals handle atrazine and concluded that atrazine is not likely to be carcinogenic in humans." [pgs. 10-11, Lindsay testimony, emphasis added]

"EPA does not agree that available frog research emphatically shows the effects of atrazine on the frog endocrine system and thus the likelihood of similar outcomes in humans." (pg. 7, Lindsay testimony)

EPA's views are reinforced by a variety of international agencies, including the Australian Pesticides and Veterinary Medicines Authority which states, "Atrazine is unlikely to be an endocrine disruptor in humans based on the known mechanism of action in Sprague Dawley rats," [Australian Pesticides & Veterinary Medicines Authority, October 2004]

2004: Further, the Agricultural Health Study stated that "We found no associations between cancer incidence and atrazine exposure...."

2004: A regulatory review in Australia determined that data regarding the formation of tumors in one species of laboratory rat exposed to high levels of atrazine has no relevance to humans.

2007: A joint meeting of the Food & Agriculture Organization and the World Health Organization on pesticide residues concluded that atrazine is not likely to pose a risk of cancer to humans.

Atrazine and Reproductive Health: Atrazine opponents also cite researcher Shanna Swan's claim that pesticides, atrazine among them, lead to lower sperm counts in men exposed to those pesticides.

Sound Science Facts: A few basic, significant flaws of the Swan study prevent any reasoned association between atrazine and sperm count reductions. For example :

• All the study's subjects were partners of pregnant women, recruited from a prenatal clinic.

• The sample size was extremely small. Only 86 men took part in this study: 50 in one state and 36 in another.

• There was large demographic variation in sample groups, leading to comparative inconsistencies. For instance, six non-whites were compared to a group of only white subjects, and age was not a variable taken into consideration.

• Differences in lifestyle were not considered, such as whether or not the men smoked and if/how long they were abstinent.

• Researchers assigned men to cases (low sperm quality) and controls (high sperm quality) after the data had been collected, resulting in a hypothesis generating strategy rather than a hypothesis testing strategy. Using such a method, the researchers could have linked low sperm count to any factor, such as drinking milk or riding a bicycle.

• Proper protocol would have been to assign men to these categories based on pesticide exposure prior to analyzing the data, not after.