Study author Dr. Emanuele Cereda of IRCCS University Hospital San Matteo Foundation in Pavia, Italy, and Dr. Gianni Pezzoli of the Parkinson Institute -- ICP, Milan, Italy, reviewed 104 studies on exposure to weed, fungus, rodent, bug killers and solvents and the risk of developing Parkinson's disease.
Studies that evaluated the proximity of exposure, such as country living, work occupation and well water drinking were also included.
The research, published in the journal Neurology, found exposure to bug killers, weed killers and solvents increased the risk of developing Parkinson's disease by 33 percent to 80 percent.
In controlled studies, exposure to the weed killer paraquat or the fungicides maneb and mancozeb was associated with two times the risk of developing the disease, Cereda said.
"We didn't study whether the type of exposure, such as whether the compound was inhaled or absorbed through the skin and the method of application, such as spraying or mixing, affected Parkinson's risk," Cereda said in a statement. "However, our study suggests that the risk increases in a dose response manner as the length of exposure to these chemicals increases."