There are two primary ways to evaluate the cancer risk of a chemical or agent: one is a hazard-based approach and the other is risk-based.
A U.S. toxicologist says the United Nations’ World Health Organization used the hazard approach to reach its conclusion that glyphosate probably causes cancer.
He said the methodology is flawed because it doesn’t account for real world conditions.
“In the last 25 to 30 years, or even longer perhaps, a hazard based approach to evaluation of chemicals is fundamentally one which … is an outdated process,” said James Bus, senior managing scientist for toxicology and mechanistic biology with Exponent, a U.S. scientific consulting firm.
A working group of 17 experts at the WHO’s International Agency for Research on Cancer issued a report March 20 on the carcinogenicity of glyphosate, which is the active ingredient in Roundup.
IARC experts reviewed scientific papers on glyphosate and glyphosate formulations and concluded that it is “probably carcinogenic.”
Bus and other experts have questioned the IARC decision because it contradicts reports from government agencies and independent scientists showing that glyphosate is not a carcinogen.
Bus, who is a past president of the Society of Toxicology, a fellow of the Academy of Toxicological Sciences and former president of the American Board of Toxicology, said IARC is aware of the limitations of its report.
Aaron Blair, a former researcher with the U.S. National Cancer Institute who chaired the IARC working group, said on National Public Radio that it used the hazard approach to evaluate glyphosate.
Bus said that piece of information is crucial.
“In other words, they’re asking the question, is it possible that glyphosate might be a carcinogen, regardless of the conditions of exposure that you might encounter … in the real world.”
Bus said most scientists and regulatory agencies now use a risk-based approach, which considers realistic dosages and real life conditions. Those studies show that farmers and farm families are exposed to significantly low doses of the herbicide.
As an example, researchers have monitored farmers’ urine samples to assess glyphosate exposure levels.
“If you inhaled it or was on your skin or somehow you ingested it, all of that glyphosate is … going to come out in your urine,” Bus said.
The U.S. Environmental Protection Agency has established a reference dose of two milligrams per kilogram of body weight per day. Anything over that level could be hazardous to human health.
The highest detected level in a farmer’s urine in those studies was .004 mg per kg per day, which is hundreds of times lower than the reference dose, Bus said.
“That’s the key element of the conversation that IARC doesn’t put on the table, as part of its evaluation,” he said.
As for the general public, a typical consumer would have to eat a dump truck load of food to consume enough glyphosate residues to reach a hazardous dose, Bus said.
“If you ate that much food in a day, you’d have far bigger problems.”