New research by US government scientists has found that people exposed to the weedkiller chemical glyphosate have biomarkers in their urine linked to the development of cancer and other diseases, The Guardian reported.

Published in the National Cancer Institute’s Journal, the study measured glyphosate levels in the urine of farmers and other participants and determined that high levels of the pesticide were associated with signs of a reaction in the body called oxidative stress, a condition that causes damage to DNA.

Health experts considered oxidative stress to be a key characteristic of carcinogens, the 20 January report said.

The authors of the paper – 10 scientists with the National Institutes of Health and two from the Centers for Disease Control and Prevention (CDC) – concluded that their study “contributes to the weight of evidence supporting an association between glyphosate exposure and oxidative stress in humans”.

They also noted that “accumulating evidence supports the role of oxidative stress in the pathogenesis of hematologic cancers”, such as lymphoma, myeloma and leukemia.

“Oxidative stress is not something you want to have,” Linda Birnbaum, a toxicologist and former director of the National Institute for Environmental Health Sciences, was quoted as saying. “This study increases our understanding that glyphosate has the potential to cause cancer.”

The study findings followed a report by the CDC last year that more than 80% of urine samples taken from children and adults contained glyphosate, The Guardian wrote, with 1,885 out of 2,310 urine samples taken from a group of Americans taken to be representative of the US population found to contain detectable traces of glyphosate.

Glyphosate is the most widely used herbicide, both in the US and globally, and one of the best-known glyphosate-based products is Bayer’s Roundup weedkiller, previously sold by Monsanto.

Roundup has been used by farmers as well as consumers for more than 40 years.

Bayer has consistently denied claims that Roundup or its active ingredient glyphosate causes cancer, saying decades of independent studies have shown the product is safe for human use.

Bayer, which acquired global agrichemical firm Monsanto for US$63bn in 2018, was quoted as saying that the new NIH study has many “significant methodological limitations that affect its reliability”, and that the results conflicted with other government research.

“The increased oxidative stress found in the study could have been caused by any number of non-glyphosate-related factors or a combination of them, and the study does not support the conclusion that glyphosate is the cause,” Bayer said in a statement.

People are exposed to glyphosate by using products made with the chemical and also by eating food and drinking water contaminated with the pesticide.

Notably, in the new paper, the NIH and CDC scientists said that while their study focused on farmers who were exposed to glyphosate when they sprayed it on fields, they saw similar results in “non-farmers”.

The findings suggested “these effects may apply more broadly to the general population who are primarily exposed through ingestion of contaminated food and water or residential applications”, the study authors wrote.