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Pesticides and Lou Gehrig’s Disease

The incredibly high use of pesticides in this country, especially when routinely applied to crops, lawns, and residence interiors, is worrisome. Over 1 billion pounds used in the US annually! Not only are there all sorts of environmental effects, including contamination of water, air, soil, but pesticides also have health effects on humans and wildlife. It seems that with each new study, more concerns are raised.

A recent large study found a link with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, and exposure to pesticides. The Dartmouth College researchers found the link with about two dozen neurotoxic pesticides, including 2,4-D, chlorpyrifos, glyphosate, permethrin, MCPB, carbaryl, and paraquat.

Note that 2,4-D is a herbicide (weed-killer) that is used in crops, and also in feed and weed products for lawns. Glyphosate is the most commonly used herbicide in the world, and used extensively on crops in the US.

The study has limitations, but it should definitely get people investigating this possibility more. For a while now, pesticide exposure has been hypothesized to be a risk factor for ALS. This is a progressive and fatal disease that affects nerve cells in the brain and spinal cord, causing loss of muscle control.

Excerpts from Environmental Health News: Higher estimated pesticide exposures linked to ALS risk

Every year, approximately 5,000 people in the U.S. are diagnosed with amyotrophic lateral sclerosis (ALS), or Lou Gehrig's disease. 

The malady extinguishes firing nerve cells, severing the highways between our brain and muscles. People progressively lose their ability to walk, talk, eat—and eventually their last breath—within two to five years. No one knows the causes, no one knows the cure.

But a study published in September in the journal Neurotoxicology sheds light on a potential contributor to the disease: pesticide exposure. By synthesizing available national data on ALS patients and pesticide uses, researchers found new supporting evidence that neurotoxic pesticide exposures could be risk factors for ALS.

Scientists believe that only 5% to 10% of the purported 16,000-plus ALS cases in the U.S. are due solely to genetics, with the rest likely caused by a synergy of genetic and environmental factors. "The question is what are those environmental factors?" Angeline Andrew, a neurology professor at Dartmouth-Hitchcock Medical Center and the lead author of the new study, told EHN.

Although not having established definitive links, previous studies suggest that environmental exposures, such as heavy metals, trace elements, radiation, and pesticides, were possibly associated with the disease. Past epidemiological studies also showed self-reported or occupational pesticide exposures concur with an elevated number of ALS incidents. However, the individual pesticides that might be responsible for the increased ALS risk still remain unclear.

Filling in this gap, researchers in the new study conducted one of the most comprehensive studies to date investigating individual pesticides and their associated ALS risks, tapping into a nationwide healthcare claim database that contains 26,000 ALS patients. By comparing ALS occurrences against estimated residential exposures to crop-applied chemicals — the exposure was inferred by the U. S. Geological Survey, which contains county-level data on the applications of 423 pesticides across the country — the analysis found that the patients diagnosed with ALS were 1.25 times more likely to have estimated exposure to pesticides and herbicides including 2,4-D, glyphosate, carbaryl, and chlorpyrifos, indicating exposures to these chemicals as a potential risk factor for ALS.

Additionally, the study narrowed down about two dozen herbicides, insecticides, and fungicides that seemed to be associated with a higher incidence of ALS. To list a few: MCPB; terbacil; carbaryl; chlorpyrifos; 2,4-D; glyphosate; permethrin; and paraquat.

Although how these chemicals could increase ALS risk is still unknown, some have previously shown neurotoxic effects on humans or animals and can, to some extent, impair motor-nervous systems. Glyphosate, for instance, has been found to sabotage the functions of mitochondria — cells' powerhouses — in worms. Permethrin, meanwhile, was discovered to inhibit neural cells' "switches" in petri dishes, causing repetitive firing in the cultured spinal neurons. Mancozeb, a popular commercial fungicide in the U.S., was also discovered to be capable of undermining the neurons by disrupting mitochondrial functions in mice.

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