By KEVIN WALKER
Michigan Correspondent

SUNNYVALE, Calif. — Scientists at the Parkinson’s Institute (PI) have found what they believe is an especially strong link between a popular agricultural herbicide and the development of Parkinson’s Disease (PD).

The results of their latest study were published in the Jan. 26 Environmental Health Perspectives, an online journal published by the U.S. Department of Health and Human Services.

“In particular, PD was strongly associated with rotenone and paraquat, two individual pesticides used extensively to model PD in the laboratory,” the paper reads. “The present findings, considered together with earlier results, suggest that paraquat use plays a role in human PD. Because paraquat remains one of the most widely used herbicides worldwide, this finding potentially has great public health significance.”

At the same time, the authors point out there is no “definitive link” between the pesticides and PD. In a follow-up interview, lead co-author Caroline Tanner described the link between paraquat and PD as “quite strong, consisting of a large body of experimental literature coupled with several human studies which our recent work extends.”

She went on to say that men who had used paraquat more than the median number of lifetime days had a 3.6-fold greater risk of developing PD than those who had used it less. She also said it’s rare to find a definitive link between a substance and the later onset of a disease such as PD, but said it would seem “prudent” to take the association of PD with paraquat “seriously.”

Tanner advised that applicators of paraquat handle the herbicide according to the product label, which calls for use of an approved respirator, chemical resistant gloves and other protection. She also said people should minimize its use.

This latest study doesn’t evaluate whether or not paraquat applicators did follow product label instructions. The study is retrospective, using data from the larger Farming And Movement Evaluation (FAME) study.

Monica Korell, an epidemiologist at the PI and study co-author, said the data on compliance with the product label is contained in the FAME study and that researchers are working on evaluating that data.

None of this comes as good news to Syngenta, which makes paraquat under the trade name Gramoxone Inteon.

“In this latest Tanner study, past exposure to pesticides was determined retrospectively by telephone interview,” said Paul Minehart, a spokesman for Syngenta. “In some cases, when the individual had died or was too ill to take part, the interview was conducted with a proxy.

“The retrospective analysis of past exposure among patients is not considered good epidemiological practice because it can lead to recall bias and incorrect associations between specific exposures and the development of disease.

“While the number of those interviewed who said they had used paraquat went down, Dr. Tanner’s calculation of the ratio of a linkage to Parkinson’s doubled, without explanation,” Minehart added.

Tanner said she disagrees with Syngenta’s remark about good epidemiologic practice and that the number of proxy interviewees were few. When they are
taken out of the calculation, she said, the results are the same.

Minehart went on to describe paraquat as a valuable herbicide in both developed and developing countries and said only highly trained applicators are allowed to handle it.

Although in the United States paraquat is used predominantly on the cotton crop in the South, it’s also used on the soybean crop in the upper Midwest, according to Ann Bryan, another spokesperson for Syngenta. She said increased glyphosate resistance in weeds could translate into greater use of paraquat as growers search for more weed management solutions.

Christy Sprague, a crop and soils scientist at Michigan State University, said paraquat is used on 30-40 percent of Michigan’s dry edible bean crop, as a desiccant. According to the latest planting intentions report from the USDA, growers in Michigan are planning to plant 180,000 acres of dry beans this season.

“There are several other uses for paraquat,” Sprague said. “It is used as a pre-plant burndown in no-till fields and used in several of our specialty crops.”
The website http://paraquat.com which is sponsored by Syngenta, describes paraquat as one of the most widely used herbicides in the world, controlling weeds in a “huge variety of crops.”

The latest Tanner study, called Rotenone, Paraquat and Parkinson’s Disease, can be found online. Go to http://ehp03.niehs.nih.gov/home.action and use the “Search” tool.