Is the herbicide glyphosate, often paired with GMOs, especially dangerous?

| November 16, 2016
This article or excerpt is included in the GLP’s daily curated selection of ideologically diverse news, opinion and analysis of biotechnology innovation.

There are many pesticides that have been in use for hundreds of years that have been shown to pose potential harm to the consumers, such as lead arsenate and other arsenate compounds. The use of these dangerous toxins has largely been curtailed, banned or discontinued between the 1950s and 1980s.

Other pesticides, such as 2,4,5-T (responsible for much of the ill effects of Agent Orange), were introduced around the middle of the twentieth century but were later banned after clear evidence of harm to humans or the ecosystem surfaced. The substances introduced during this time, when regulations were almost non-existent, have darkly-colored people’s views of today’s pesticides, almost all of which are far less toxic and have gone through far more extensive evaluations. Glyphosate falls into that category.

Despite what many who depend on the Internet for their science information believe, glyphosate is actually among the least toxic agricultural chemicals. If you look at the doses that have proven lethal to half of the laboratory animals tested, the so-called Lethal Dose 50 (LD50), some of the most common organic herbicides, such as clove oil, acetic acid, and cinnamon oil, are all more toxic than glyphosate. In fact, when it comes to the lethal dose, even table salt is more toxic than glyphosate (see table below: 3000 vs. 4900 mg/kg – toxicity studies on glyphosate LD50 can be found at EPA here, and studies determining the No Observable Adverse Effects Level (NOAEL) here). Other common substances and their LD50 values described here.toxicity-table4

This doesn’t mean we don’t have to be careful about glyphosate’s effects – we wouldn’t want to sprinkle salt or concentrated plant oils on our fields either without a good understanding of the consequences first. In fact, reflecting public concerns, regulatory bodies are far more aggressive than they used to be in overseeing pesticide use, and the agricultural community, including pesticide manufacturers, have responded with newer, less toxic products.

Many people are unaware that farmers have switched in recent decades, and even more so in the past ten years, to far less toxic pesticides. For example, farmers in the US no longer treat apple orchards with arsenic-containing pesticides, which still contaminate the grapes of some wineries that used to use them, and remains a problem in other countries, such as China, that have been slow to phase them out. During the past several decades, farmers have moved away from using persistent and acutely toxic substances. Milder, more targeted, and generally much less toxic pesticides have replaced older, harsher agents. And thanks to a wide adoption of Integrated Pest Management and biotech crops, overall pesticide use measured by toxicity is way down.

Agricultural scientist Steve Savage has written in detail about the kinds of pesticides in use today. Using pesticides application in California as his example, he has documented the shift toward lower toxic substances between 1990 and today:

Most pesticides today have oral ALD (Acute Oral Toxicity) 50s of more than 5,000 mg/kg (Category IV) and are less toxic than table salt, vinegar, citric acid, vanillin and many other familiar food ingredients.

The University of Florida Pesticide Information Office has put out a report on this trend, called Herbicides: How Toxic Are They?

Although there have been pesticides that were toxic and dangerous to handle, most of these products are no longer used and have been replaced by newer chemistry. Pesticides now must go through rigorous testing by the U.S. Environmental Protection Agency (EPA) before they can be sold. This has led to many herbicides that possess little or no mammalian toxicity and are less harmful than many everyday household products (Table 1). Surprisingly, household chemicals that many of us store under the kitchen sink pose more risk to the handler than herbicides.

Why are so many people worried about glyphosate and not other far more toxic agricultural pesticides? Glyphosate has helped make redundant numerous far more toxic chemicals–many of which farmers would need to resort to again should Europe or the US restrict or ban glyphosate, as the science blogger known as The Credible Hulk has written:

Many people never even hear about the herbicides that were phased out in favor of glyphosate simply because they aren’t pertinent to the anti-agricultural biotech narrative, and because their popularity had waned by the time it had become trendy to demonize GMOs and everything remotely associated with them.

Weeds are a legitimate problem in farming that has to be dealt with one way or another. In its absence, it would have to be replaced with something else, and it would likely be something more harmful: not less.

Anti-GMO activist critics of glyphosate do not engage in what is known as a risk-risk analysis; they just invoke a radical version of the so-called precautionary principle, claiming that any level of risk, no matter how minuscule, is unacceptable. But what would replace it if glyphosate was restricted? What about the risks and consequences of not using glyphosate to restrict weed growth? Choosing not to do something has consequences and also carries a risk. To which choice should we apply the precautionary principle?

Related article:  New England Journal of Medicine ignored Chuck Benbrook's failure to disclose organic conflicts of interests

The best way to find guidance to that question is to rely on the collected wisdom of the best and most comprehensive research. At present, the overwhelming scientific consensus is that glyphosate is a very safe option for weed control, with many benefits and few risks.

Iida Ruishalme, Finnish by birth and now a Swedish resident, is a cell biologist and science communicator, and author of the Thoughtscapism blog, which is where this piece originally appeared–here. She is a contributor to Genetic Literacy ProjectSkepti-Forum, and Biofortified, as well as to the cultural journal The Woolf. Twitter: @Thoughtscapism

The GLP featured this article to reflect the diversity of news, opinion and analysis. The viewpoint is the author’s own. The GLP’s goal is to stimulate constructive discourse on challenging science issues.

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