The European Environmental Science study found that glyphosate is most commonly used in agriculture. Farmers use practical herbicides to kill weeds that compete with crops for sunlight, water and soil nutrients. Glyphosate is used more than any other agricultural chemical, with an estimated 8.6 billion kilograms (19 billion pounds) of glyphosate used since 1974 to grow everything from peppers to oranges.

Ramdas Kanissery, a weed scientist at the University of Florida at Immokalee, said that when the chemical is sprayed on plants, it usually seaks into them through the leaves. From there, glyphosate can travel from cell to cell and spread to stems and roots, infecting the entire plant.

Glyphosate comes from an amino acid called glycine, which plant cells recognize as an amino acid. Plants use amino acids to build substances such as enzymes and proteins needed for growth through a process called amino acid synthesis. "But once glyphosate enters the amino acid synthesis cycle [in plants], it screws everything up," Carniceri said. This is because glyphosate interferes with a key enzyme production pathway that prevents plants from producing essential proteins, and plants die within two to three weeks of exposure.

People also use glyphosate in their homes to tame weeds, and some cities spray the chemical in parks and other green Spaces to control invasive plants that can take over and drive out native plants. However, many local governments, such as Seattle, Washington, have ended the practice because of growing concerns about the chemical's safety.

Despite this, there is still little research on the topic. Scientists need to conduct more studies with human subjects and get similar results before they can definitively link glyphosate to NHL or any other cancer.

Key questions remain unanswered. For example, scientists do not yet understand exactly how the chemical triggers cancer development. And they don't know how much exposure to the chemical is needed to pose a risk.

According to the World Health Organization, glyphosate levels entering food are unlikely to be high enough to cause cancer. Most at risk are farm workers, who may inhale chemicals when spraying them and absorb relatively large amounts through their skin and eyes, Zhang said. Zhang added that some researchers suspect that other diseases may also be linked to glyphosate exposure, such as celiac disease, but there is little evidence to support this.