The Toxic Ingredient In Many Brand-Name Weed Killers You May Not Have Known About

When you're considering different types of weed killers — hopefully as a last resort and not the first — you're most likely paying attention to their active ingredient(s). For instance, when you think of Roundup, your mind instantly goes to glyphosate (even though many of its current offerings no longer contain glyphosate). That's because this active ingredient is known to specifically target and eliminate an intruding plant. However, besides active ingredients, weed killers or, for that matter, any pesticide, also contain "inert ingredients." They're usually responsible for enhancing the formula's penetration, preventing caking, or improving overall efficacy.

Turns out, many glyphosate-based formulations, from brand-name and generic companies alike, contain a toxic inert ingredient: Polyethoxylated tallow amine (POE-T). And the reason you might not know this is, besides it being a mouthful, is that it isn't listed on the label. The federal law allows manufacturers to keep details of inert ingredients confidential to protect their business. They aren't legally required to name or mention the concentration of each ingredient individually. Instead, they can club them all and note how much of the total formula is inert.

However, inert ingredients aren't non-toxic. In fact, on the toxicity scale, POE-T ranks higher than glyphosate. And the jury is still out on glyphosate's safety, considering the EPA is still reassessing its position, which is why we recommend thinking twice about using popular weed killers, like Roundup.

In a 2019 open-access article, Insight into the confusion over surfactant co-formulants in glyphosate-based herbicides, researchers noted that glyphosate-based formulations, including the highly popular Roundup, contain POE-T, a surfactant distilled from tallow (animal fat). Over a series of safety tests conducted on animals and aquatic invertebrates, it was found that POE-T was far more potent and toxic (in the range of 10 to 50 times) compared to glyphosate in certain species of fish, crustaceans, and frogs.

This matter also came to the limelight in 2012 when the University of Caen's Gilles-Eric Séralini published a paper highlighting the long-term effects of consuming GMO maize treated with Roundup. While the initial paper was retracted over lack of statistical rigor and inconclusive evidence, it was subsequently republished in Environmental Sciences Europe. The crux was that glyphosate-based formulations are more toxic than manufacturers or regulatory agencies let on. And that's because the EPA mainly evaluates the active ingredient for long-term safety and not the formulation as a whole, which may mask the complete picture.

In a follow-up 2013 study on human cells, researchers demonstrated that POE-tallowamine alone was the most toxic and could lead to necrosis, compared to the less intensive, though harmful, endocrine-disrupting effects of glyphosate. Mesnage et al.'s 2014 study found that glyphosate-based formulations could be up to 1,000 times more toxic than glyphosate alone in some instances. Another 2016 study published in Environmental Science & Technology found that tallow amine adsorbed into and lasted longer in agricultural soils, relative to glyphosate.

Acknowledging its worse effects, including possible damage to DNA, the European Food Safety Agency demanded a switch from polyethoxylated amine (POEA), of which POE-T is a major component, to relatively less toxic, propoxylated quaternary ammonium surfactants. The U.S. EPA, in contrast, has limited their concentration to 25%, maintaining that at such a concentration the weed killers are safe.

If you're following up on Roundup trials, you may be privy to Bayer's decision to phase out glyphosate from its products oriented towards residential use to restrict future claims. However, this doesn't apply to their professional or agricultural range. So, if you've hired landscapers to look after your lawn, you may still be exposed to POE-T, apart from the regular exposure from consuming GMO foods. That being said, Bayer's researchers (the current maker of Roundup) conducted a study on POE-T in 2019 and concluded that it doesn't affect human health significantly. However, POE-T exposure causes eye and skin irritation.

Besides Bayer, many other brand names producing glyphosate-based formulations use surfactants. For instance, Compare N Save Grass And Weed Killer 41% Glyphosate mentions POE-T in its safety sheet, though this information isn't explicitly mentioned for every product (because "trade secret"). Although several organizations, including Center For Food Safety, sued the EPA on how it tests weed killers, it has stuck to its guns, noting in an extensive reply that chronic toxicity assessment for end-use formulations is unnecessary. Before using glyphosate formulations, ensure they won't drift to water sources and harm aquatic life. Or better yet, consider using safer store-bought weed killer alternatives to glyphosate for your yard and garden.