Farmer Mac Barlow was diagnosed with Parkinson's a few years ago and believes it's linked to his use of paraquat, a highly effective weed killer. “For about 40 years off and on, I’ve been using that stuff [paraquat]," Barlow said. "I’ll be honest with you, if I knew it was going to be that bad, I would have tried to figure out something else.” Paraquat has been banned in dozens of countries. Syngenta continued selling paraquat in the United States and other nations that haven’t banned it. Barlow is now among more than 6,200 people suing Syngenta, the company that manufactures paraquat. A legal expert says the number of plaintiffs is “not even close to representative of how many people have been impacted.” Today, between 11 million and 17 million pounds of paraquat are sprayed annually to help grow crops, the U.S. Geological Survey reports. And despite the alleged known risks, its use is increasing. Syngenta maintains the weed killer “is safe when used as directed.” Yet, a study pu...