This essay is part of a series on environmental health.

It was back in 1958 that a chemical company first discovered that its new weed killer appeared toxic to humans, “mainly by affecting the central nervous system,” as one company scientist documented at the time.

The company kept its concerns to itself — as well as its later research indicating that large doses caused tremors in mice and rats. That’s because the herbicide, paraquat, was sublime at wiping out weeds. And profitable. Over the decades it became, an executive proudly declared, a “blockbuster.” By 2018, some 17 million pounds of it were used across the United States, double the figure for six years earlier.

As industry has boomed and agricultural and industrial toxins like paraquat have proliferated in the postwar period, so has something else: Parkinson’s disease. Once almost unknown, the ailment was first identified in 1817 when Dr. James Parkinson described a handful of elderly people with what he called “the shaking palsy.” That was in polluted London, and it’s now understood that air pollution is a risk factor for the disease.

Some 90,000 cases of Parkinson’s are now diagnosed each year in the United States, about one every six minutes on average. It is the world’s fastest-growing neurodegenerative disease, causing tremors, stiffness and balance problems. It is also the 13th-leading cause of death in the United States. One factor in its increase may be the way we have come to live, for there’s growing evidence linking it to a range of pesticides and industrial chemicals, including paraquat and substances used in dry cleaning.

“Chemicals in our food, water and air have created this largely man-made disease,” two Parkinson’s experts, Dr. Ray Dorsey and Dr. Michael S. Okun, write in a new book, “The Parkinson’s Plan.” “These chemicals are all around us, and none are necessary.”