It's been nearly 20 years since I first walked into the corporate headquarters of Monsanto Co, a visit that would become one of many over the course of my career as a national correspondent for Reuters, one of the oldest and largest news agencies in the world.

Meeting with top executives, scientists and marketing experts at Monsanto and rivals DuPont and Dow was part of a job that called on me to keep international audiences informed about important events in the world of agriculture. My education in agriculture also meant lots of time riding inside the cabs of combines, talking yields with wheat farmers, chatting up corn farmers and soybean growers about prospects for harvest, and digging into the pros and cons of genetically engineered seeds and the chemicals farmers were using on their fields.

Much of my now two decades of research has focused on the evolution of knowledge about a chemical called glyphosate – the world's most widely used weed killer. As the key ingredient in Monsanto's Roundup herbicide and hundreds of other products, it has spelled billions of dollars in profits for the corporate world and has been a beloved tool by farmers.

Carey Gillam: "I never imagined that writing about the risks that came with the rewards of this pervasive pesticide would make me a target for the ire of Monsanto and its allies." Supplied

Use of this chemical exploded with the introduction of genetically engineered glyphosate-tolerant crops. And with the surge in use came expanded research into the health and environmental impacts of glyphosate-based herbicides. While industry science shows few if any safety concerns, independent research has found a host of unforeseen problems for people and the environment.

Glyphosate herbicides have been linked to a variety of human illnesses and disease, and have been shown to be harmful to soil biology and to pollinators. Heavy use has also spawned "super weeds", which are largely impervious to efforts to wipe them out and can severely limit crop production.