After more than 40 years of widespread use, new scientific tests show formulated weedkillers have higher rates of toxicity to human cells

US government researchers have uncovered evidence that some popular weedkilling products, like Monsanto’s widely-used Roundup, are potentially more toxic to human cells than their active ingredient is by itself.

These “formulated” weedkillers are commonly used in agriculture, leaving residues in food and water, as well as public spaces such as golf courses, parks and children’s playgrounds.

The tests are part of the US National Toxicology Program’s (NTP) first-ever examination of herbicide formulations made with the active ingredient glyphosate, but that also include other chemicals. While regulators have previously required extensive testing of glyphosate in isolation, government scientists have not fully examined the toxicity of the more complex products sold to consumers, farmers and others.

Monsanto introduced its glyphosate-based Roundup brand in 1974. But it is only now, after more than 40 years of widespread use, that the government is investigating the toxicity of “glyphosate-based herbicides” on human cells.