Special Report: Chemical spray additives warrant more scrutiny: researchers

U.S. glyphosate use (million lb.)


Yes, it is true. Glyphosate is less toxic than table salt.

Studies have demonstrated that the median lethal dose, or LD50 which kills 50 percent of lab rats, is 3,000 milligrams of salt per kilogram of rat.

Extrapolating those results to humans, 300 grams of salt would kill a 100 kg man 50 percent of the time.

In comparison, glyphosate’s LD50 is 4,320 mg per kg of rat, meaning 432.0 grams of glyphosate are needed to kill a 100 kg man, 50 percent of the time.

However, LD50 measures the toxicity from a large, single dose rather than long-term, low-dose exposure to a chemical.

As with any herbicide, people who use glyphosate should follow application safety guidelines.

Scientists, most prominently French researcher Gilles Seralini, have recently become interested in the toxicity of repeated exposures to glyphosate.

In what might have been the most controversial scientific paper of 2012, Seralini and his University of Caen colleagues determined that rats that drank water laced with Roundup and consumed Roundup Ready corn developed tumours and died two to three times more frequently than a control group of rats.

The scientific establishment pounced on Seralini’s conclusions days after publication.

The French Academies of Agriculture, Science, Medicine, Technologies and Veterinary Sciences issued a joint statement criticizing the study’s methods and the statistical analysis of its results.

The academics also said “cancer” wasn’t mentioned in the Seralini paper but that “tumour” was used as a metaphor for cancer.

On top of his most known paper, Seralini has conducted studies showing that Roundup disrupts endocrines after entering human cells.

John DeSesso, an American toxicologist who published a compreihensive review of glyphosate’s impact on development and reproduction in humans and animals, said cellular studies are often flawed and misleading.

He said Petri dish studies usually ignore how a chemical is diluted in the environment and within an animal before it reaches the target cell.

“The issue with tissue culture experiments is that you’ve removed all the protective mechanisms that the whole animal has,” said DeSesso, a scientist with Exponent, a scientific consulting firm.

DeSesso’s critical review, with his Exponent colleague Amy Williams, concluded there is little evidence showing that approved use of glyphosate harms reproduction or development.

However, their paper focused on the toxicology of glyphosate rather than the toxicology of glyphosate formulations.

All formulations contain chemicals known as surfactants and adjuvants, which allow glyphosate to penetrate plant leaves.

In a paper published in Toxicology, Seralini concluded that the additives, particularly polyethoxylated tallowamine (POEA), are toxic to human cells.

As well, a number of papers, including a Trent University study, have shown that POEA causes growth and sexual abnormalities in frogs.

DeSesso said there might be a need to study surfactants and glyphosate formulations more closely.

“It’s reasonable to say people ought to think about looking at the toxicity of surfactants, if they haven’t already.”

Other stories in this Special Report:

UN report released March 20, 2015UN body declares glyphosate probable human carcinogen

Contact robert.arnason@producer.com

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