Parkinsons Disease

 

A new study of individuals treated for Parkinson’s disease in Louisiana found a clear correlation between the disease and the use of two types of herbicide and one pesticide in rural areas dominated by forestry, woodlands and pastures.

The study also found that Parkinson’s disease has become less common in areas of the state where cotton, corn and soybean farmers have switched to the use of the herbicide glyphosate, sold under the brand name of Roundup — although that product has recently been linked to some forms of cancer, which the study did not examine. Roundup is manufactured in Luling by the Bayer subsidiary Monsanto.

The peer-reviewed, open-access study by three LSU researchers was published online in the International Journal of Environmental Research and Public Health on Feb. 29.

Parkinson’s disease involves the progressive degeneration of the nervous system, and its symptoms include tremors, muscular rigidity, and slow, imprecise movements. It mostly affects middle-aged and elderly people, and its onset can take six to 10 years before symptoms are recognized.

The study found that in the seven-year period ending in 2012, the areas at greatest risk included large portions of Allen and Evangeline parishes, where between 35 and 46 individuals per 10,000 residents were treated for Parkinson’s in hospitals. That band of high risk stretched across the lower middle of the state from Beauregard Parish to Iberville Parish, where farm pastures and timberland are dominant.

The second greatest risk area for that time period runs in a band from Sabine Parish — on the Sabine River along the Texas border — northeast to West Carroll Parish. Again, much of the area is dominated by timber and pastureland, with the exception of West Carroll, where cotton, soybeans and sorghum are grown.

Two smaller areas of higher risk are in the New Orleans region.

In the eastern Florida Parishes on the north shore, more cases were found in central Tangipahoa Parish, where strawberries are grown, and in St. Tammany and Washington parishes, where pastures and woodland dominate.

But the researchers said there is less connection to agriculture exposure in a higher-risk area that includes Kenner and parts of St. Charles and St. John the Baptist parishes. The study points out that those cases occur in an area dominated by petrochemical manufacturing, and suggests the high rate in Kenner may be because of its role as a “dormitory suburb” for the workers in the two petrochemical parishes.

However, the study also found that other areas along the Mississippi River that are also dominated by petrochemical manufacturing had much lower risk for Parkinson's. It's not clear why.

A similar map of Parkinson’s risk for the 1999-2005 period shows the risk of the disease was much greater in parishes in the northeast corner of the state, where cotton and other crops dominate. The study concludes the higher risk during that time period was because farmers were using 2,4-D, paraquat and other herbicides with links to the disease, rather than glyphosate, sold as Roundup.

Monsanto began selling genetically modified Roundup Ready soybean seed in 1996, followed by the release of similarly modified corn, cotton and other crops in the next few years. The plants grown from those seeds were resistant to damage when glyphosate-based weed killers were used, and their use was widely adopted by farmers in the northeastern part of the state.

The result was that the use of herbicides linked to Parkinson’s dropped dramatically in that area. But because of the lengthy time between the onset of the disease and when its effects caused a first hospital stay, the effects of the change didn’t become clear until the 2006-2012 time frame.

The second time period of the study also found a much lower risk of Parkinson’s in the area west of Alexandria that includes Fort Polk, where its younger population of soldiers would not be likely to be showing symptoms of the disease, if they were hospitalized.

The U.S. Environmental Protection Agency keeps track of studies like this one on Parkinson's disease, and is reviewing the rules for the use of both paraquat and 2,4-D. The agency is required to review the use of previously approved pesticides at least every 15 years. According to its website, as of July 2017, more than 700 reviews were underway.

The state Departments of Health and Hospitals and Environmental Quality and did not respond to requests for comments on the study. A spokeswoman for the Louisiana Department of Agriculture and Forestry said the agency follows the lead of the EPA, "but does not supersede it."

"Our role is to make sure that pesticides used in Louisiana are registered with the EPA and correctly applied by certified applicators," said Veronica Mosgrove.

The researchers used a database of patients admitted to 95 Louisiana hospitals between 1999 and 2012 to identify the ZIP code areas where 23,224 individuals diagnosed with Parkinson’s disease lived. The database was provided by the Louisiana Office of Public Health.

Data after 2012 has not been made available by the health department for this study, said Martin Hugh-Jones, lead author of the study and an emeritus professor of Veterinary epidemiology at LSU. Hugh-Jones is better known as a world-renowned expert on the use of anthrax in bioterrorism. The other study authors were Hampton Peele, a researcher with the Louisiana Geological Survey at LSU, and Vincent Wilson, an environmental sciences professor at LSU.

The patient information was divided into seven-year periods and used to map the risk – in cases per 10,000 people – of having the disease for each 7-year period. The risk estimates were then compared with maps identifying where land was used for agriculture or timber-growing operations, and then to information from four-year U.S. Geological Survey estimates of the use of herbicides and insecticides on farmland and timberland in Louisiana parishes between 1992 and 2004. The estimates are based on chemical use reported by farmers.

The study points out that the relationship between Parkinson’s disease and exposure to pesticides has been known since the 1980s.

Herbicides linked to the disease include paraquat, trifluralin, 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-TP, and better known as the main ingredient in Agent Orange). The latter has been banned for most uses in this country.

The disease has not been linked to more modern herbicides, including atrazine, dicambra, glyphosate and triazine.

Specific insecticides linked to the disease that have been used in Louisiana include chlorpyrifos, dieldrin and rotenone. The use of dieldrin is now banned by the EPA.

The disease has not been associated with a number of other commonly used insecticides, including carbamates, pyrethroids, diazinon, malathion and parathion.

The USGS data shows that in Allen Parish, as much as 15,818 pounds of 2,4-D herbicide, 130 pounds of paraquat herbicide and 149 pounds of chlorpyrifos insecticide were used in 1992, which could have exposed people who were later hospitalized.

Individuals could have been exposed to the chemicals in a variety of ways, including direct exposure through work, exposure through the air, or exposure through drinking water, especially from groundwater sources.

A separate map in the study outlines recharge areas for underground aquifers, where rainfall seeps into the soil – often through fields treated with herbicides and pesticides – and then into the aquifers, or where small streams or bayous that collect rainwater running off those fields connect with aquifers.

According to the study, areas with the highest risk of the disease occur where the potential for aquifer recharge is considered moderate or high.

The report points out that there have been several studies in other states linking herbicide and pesticide contamination of aquifers used for drinking water and Parkinson’s disease.

It also points out that state regulations require sampling of groundwater only on a single day once every three years, with repeat sampling conducted only when a pesticide is detected at a level of at least half the federal maximum content level allowed.

A review of state test data for both groundwater and surface water supplies from 1993 through 2016 found only a handful that were contaminated.

But the study pointed out that tests that occur on one day every three years are unlikely to find such contamination, “as any agricultural pesticide contamination is likely to be short (2 weeks).”

The study points to several issues involving the data. First, about 3% of Parkinson’s cases result from family genetic causes, rather than environmental exposures.

The hospital records also would not have captured individuals who were treated as outpatients, and since hospitalizations specifically for Parkinson’s typically occur only 10 to 15 years after onset, early-onset cases likely were missed unless the disease was spotted while patients were hospitalized for other reasons, like cancer or heart disease.

The statistics also likely capture more women than men because women are more likely to seek healthcare, the study said.

“Thus, these hospital records are not necessarily a measure of the true extent of PD in Louisiana, but currently, it is all that is available,” the study said.

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