OMAHA (DTN) -- About one year ahead of a scheduled EPA atrazine review, an expert panel said the agency is currently unable to rule out a human cancer link to the popular herbicide. That runs contrary to numerous studies conducted on atrazine around the world.

An EPA scientific advisory panel (SAP) convened in Washington, D.C., this past summer to examine the science used by EPA to examine the safety of atrazine. The panel's report said there are scientific gaps to close before an atrazine re-registration review starts in 2013.

The panel of 24 experts from medical, statistical and academic disciplines agreed with EPA that the human epidemiologic evidence does not strongly suggest a link between atrazine and cancer. However, the panel disagrees with EPA's conclusion that the "weight of the evidence" shows atrazine was unlikely to be carcinogenic to humans. The panel brought into question the use of animal toxicology studies in reviewing atrazine.

DTN attempts to seek comment from panel members were unsuccessful.

The panel challenged conclusions reached by EPA and outlined in an agency issue paper, http://1.usa.gov/…. The panel said EPA should adjust its conclusion that atrazine is unlikely to be carcinogenic to "inadequate information to assess carcinogenic potential," in meeting minutes from the SAP's July meeting, http://1.usa.gov/….

Tim Pastoor, principal scientist for Syngenta, said in an interview with DTN that the SAP's concerns run contrary to studies that have found no evidence of a connection between atrazine and human cancers.

"This clearly goes against everything that EPA has been saying, that atrazine is not likely to cause cancer in humans," he said. "They've (EPA) said this since the year 2000. They've reiterated that over and over again."

The SAP recommendations essentially amount to a suggestion for EPA to change the cancer classification of atrazine, Pastoor said. However, he said there is "no new evidence" to warrant such a change.

SCHEDULED REVIEW

EPA press officer Dale Kemery said the agency will use the July SAP recommendations and all previous SAPs to update the state of science on atrazine.

In its July SAP, the fourth panel gathered to study atrazine since February 2010, said there were some suggestive findings for specific tumors that warrant additional study prior to EPA's full weight-of-evidence review.

The SAP said there is "considerable uncertainty and gaps" in the toxicological evidence of atrazine as a human carcinogen.

The panel said EPA has not done a comprehensive "weight of the evidence" assessment. "Instead, the toxicological evidence appears to be used to nullify any positive evidence from the epidemiologic studies," the panel said.

The SAP said the evidence across cancer sites is "mixed, not uniform, with some cancer sites having no evidence for an association, whereas other cancer sites having at least suggestive evidence for a causal association.

"EPA does acknowledge that 'some epidemiology studies are weakly suggestive of an association between atrazine exposure and cancer incidence in the human population.' The statement that atrazine is not likely to be carcinogenic in humans ignores this evidence."

PANEL CONCLUSIONS

The SAP concluded that there is evidence suggestive of an atrazine connection to ovarian cancer, non-Hodgkin's lymphoma, hairy-cell leukemia and thyroid cancer.

Cancers identified for having "inadequate evidence" of a link to atrazine use include prostate cancer, breast cancer, liver cancer, esophageal cancers and childhood cancers.

The SAP said additional study is needed in both categories.

Cancers not likely to be caused by atrazine include oral, lung, colorectal, pancreas, bladder, leukemias (except hairy-cell leukemia), multiple myeloma, melanoma, kidney, larynx and brain/gliomas, according to the panel.

Other studies that suggest a "strong relationship" between some cancers and atrazine merit further study, the SAP said. One example used by the panel was thyroid cancer.

To date, there has been no conclusive causal link found between atrazine exposure and prostate cancer, the panel said.

Syngenta's Pastoor said EPA asked the SAP to consider both toxicological evidence from studies on animals and epidemiology on humans when reviewing atrazine.

"Some on the SAP said in actuality we don't care what you find in animals," he said. "It's more important what you find in people."

In addition, Pastoor said the panel was critical of EPA offering a general statement that atrazine is not linked to cancer when some individual studies show an association with certain types of cancer.

"EPA in fact does consider individual cancers and not just cancer as a blanket concept," he said.

AGRICULTURAL HEALTH STUDY

The SAP also challenged a recent Agriculture Health Study report, http://bit.ly/…. The study that explored cancer incident rates among atrazine users in Iowa and North Carolina during a 13-year period, found "no strong or consistent evidence of an association between atrazine and any cancer."

Scientists conducting the study followed some 89,000 people, including licensed pesticide applicators and their families in North Carolina and Iowa, between 1994 and 2007. Of the 36,357 applicators who reported using atrazine there were 3,146 cancer cases, according to the study. Beane-Freeman said researchers continue to follow the applicators.

The SAP, however, said there needs to be additional follow-up studies to the AHS in many areas.

Laura E. Beane-Freeman, an investigator in the division of cancer, epidemiology and genetics at the National Cancer Institute, National Institutes of Health, Department of Health and Human Services in Bethesda, Md., and co-researcher for the AHS, said those study results need to be confirmed.

"While there is mention of our study, the SAP review document is really a review of EPA's evaluation of the scientific literature and their interpretation of the conclusions," she said. "My job is to do the research and it's really not appropriate for me to comment on that evaluation. There are limitations inherent in any study of this nature."

The July SAP said criteria used for diagnosis and coding of cancer outcomes in the AHS "were not necessarily standardized." The panel said it could have resulted in "misclassification of the outcomes."

The study population is predominantly white, the panel said. Whites are not considered to be the highest risk group for incidence or mortality of some cancers including prostate cancer and breast cancer, according to the panel. "Thus, this study cannot determine if such high risk, 'non-white' groups might have particular susceptibility" to atrazine-related exposures, the SAP said.

The panel said the number of women occupationally exposed to pesticides in the AHS "is relatively small" making it difficult to study cancer rates among female applicators.

The panel said there was a potential gap in the AHS study involving the exposure time to atrazine by study participants.

"The pesticide exposures that occur among the AHS cohorts, although most likely intense, are also likely to be intermittent," the panel said. "However, exposures that occur to the general public, in particular those exposed via contaminated drinking water, would be lower-level but chronic; and exposures to workers employed in the manufacture of triazines would be expected to be both intense and chronic."

DTN Crops Technology Editor Kurt Lawton contributed to this report.

Todd Neeley can be reached at todd.neeley@telventdtn.com

(CZSK)

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