Getting On Our Nerves

Researchers Find a Connection Between Parkinson’s Disease and Pesticides

The herbicides and pesticides many people trust enough to spray on their gardens and crops have been increasingly linked to the onset of Parkinson’s Disease (PD), a neurodegenerative disorder that turns the simplest movement into a battle between the brain and the nerves.

The first connection was made in the early 1980s, when young people illegally taking an impure form of Demerol (MPTP) exhibited symptoms of an advanced form of this progressive disease. The chemical structure of MPTP resembles that of paraquat, an herbicide.

"I was surprised at how accurately rats developed the signs of PD," says Dr. J. Timothy Greenamyre, a researcher at Emory University. The rats in the study had been infused with the pesticide rotenone. Because it is often labeled as a "natural" pesticide, many home gardeners feel safe sprinkling rotenone on their tomatoes. Rotenone is also used to kill nuisance fish in lakes and parasites on pets.

In a recent Stanford study, Parkinson’s patients were twice as likely to have been exposed to in-home insecticides than those people without the disease. People exposed to herbicides also were more likely to develop PD.

A large case-controlled study at the Henry Ford Health System in Michigan confirmed that connection. "Contact with herbicides gave people a four times greater chance of developing Parkinson"s," says Dr. Jay M. Gorell, head of the Movement Disorders Clinic in the Neurology Department. And people exposed to insecticide were 3.5 times more likely to be diagnosed with Parkinson’s disease than people with no history of pesticide exposure.

"The study also found a relationship between Parkinson’s disease and farming," says Gorell. "Farmers were 2.8 times as likely to have PD as the general population."

A Common Disorder

More than one million Americans have Parkinson"s, and every nine minutes another person is diagnosed with the disease. PD is second only to Alzheimer’s as the most common neurodegenerative disorder in the U.S.

First described by the English physician James Parkinson in 1817, the condition kills the nerve cells in the brain that release dopamine, a chemical necessary for controlling movements. Normal everyday tasks, such as buttoning a shirt or writing a letter, become hardships and, eventually, impossible.

In order to discover cause-and-effect relationships between pesticides and PD, says Gorell, more research, innovative models and precise measurements are needed. "Also, people may not be aware of their lifetime history of contact with pesticides," adds Gorell. "Experts are searching for ways to quantify past exposures."

The weight of heredity is another factor to gauge when studying this disease, although most experts now consider the family tree a significant factor only when studying patients who were 50 years old or younger at the onset of PD. Today, just 10 percent of Parkinson’s cases are attributed directly to heredity.

Most researchers agree that a sophisticated interrelationship between genetic susceptibility and environmental exposures may hold the key to unlocking the causes of PD. The former remains an elusive quality. But the latter can be measured to some extent.

Environmental Exposure

The Centers for Disease Control and Prevention (CDC) began an ongoing study in 1999 in an effort to calculate the public’s exposures to environmental contaminants, including mercury, tobacco smoke and certain pesticides. By taking blood and urine samples, scientists can monitor the population’s contact with chemicals in the air, water, dust, food and soil over time. "So far, the results of the initial CDC National Report on Human Exposure to Environmental Chemicals confirm what many people already suspected," says Susan Kegley, staff scientist at Pesticide Action Network North America (PANNA), which works to replace pesticides with ecologically sound and socially just alternatives. "The general population has contaminant levels exceeding those set by the Environmental Protection Agency (EPA) as safe," she says.

Kegley finds the CDC data especially significant because only known ill effects, which usually involve acute poisoning as opposed to chronic exposures, determine EPA guidelines. The EPA also tests chemicals separately instead of examining combinations of compounds, which are apt to be more harmful.

In the meantime, people concerned with limiting their exposure to pesticides should become familiar with all the ways they come into contact with these chemicals. "Residues on food and home-and-garden insecticides are well-known sources," says Jay Feldman, executive director of Beyond Pesticides.

"But laundry and bathroom products, such as sanitizers and mildew removers, also contain pesticides," says Feldman. "The chemicals commonly used in backyard swimming pools are laced with pesticides." Institutions and businesses are consumers of these products, too. No less than 21 neurotoxins are used in schools.

When attempting to calculate their pesticide exposures, people often forget those elements not in their direct control. "Spraying of nearby agricultural fields or monthly applications by the neighbor’s lawn service cause drift that can be a significant source of pesticide exposure," says Kegley.

Simple Prevention

The irony is that simple, inexpensive strategies can outwit unwelcome intruders. "Sanitation is always a first course of action," says Feldman. "Maintenance, such as caulking regularly, repairing screens and eliminating damp spaces, prevents infestations. And protective clothing circumvents the need for insecticide sprays."

"Soap and water discourages many plant pests," says Steve Tvedten, president of Get Set, a company specializing in non-toxic pest control. A quick spray of glass cleaner sends flying insects into a nosedive. Talcum powder obscures ant trails, and razing webs sends spiders scattering. Vacuum cockroaches and other bugs and cultivate the enemies of garden pests.

Diet has a huge effect on the amount of pesticides people ingest. Researchers at the University of Washington analyzed the urine of 100 children. "Ninety-nine of the kids had detectable levels of pesticides in their systems," says Kegley. "The only participant with no evidence of exposure ate organic food." She adds that if organic foods are not available, take extra care washing produce known to have higher pesticide residues, including strawberries, pears, grapes, green beans, peaches, winter squash and leafy green vegetables, especially spinach.

"Pesticides have become omnipresent in our rain and air," says Tvedten. "Chemicals used in Africa find their way to Florida in a short amount of time. And our generation has been exposed to more than 500 toxins that our grandparents weren"t. Even if pesticides were safe, they’re not always effective. And already, over one half of the pests are resistant to their poisons." The bad news is we may not be.