A new study finds that the Roundup herbicide disrupts the hormonal system of rats at low levels at which it’s meant to produce no adverse effects. By the same mechanism It may be causing the potentially fatal condition of ‘adrenal insufficiency’ in humans.

Monsanto’s glyphosate-based herbicide Roundup is an endocrine (hormone) disruptor in adult male rats, a new study shows.

The lowest dose tested of 10 mg/kg bw/d (bodyweight per day) was found to reduce levels of corticosterone, a steroid hormone produced in the adrenal glands. This was only one manifestation of a widespread disruption of adrenal function.

No other toxic effects were seen at that dose, so if endocrine disruption were not being specifically looked for, there would be no other signs that the dose was toxic. However a 2012 study detected a 35% testosterone down-regulation in rats at a concentration of 1 part per million.

In both studies endocrine disruption was detected at the lowest level tested for, so we don’t know if, when it comes to endocrine disruption, there are ‘safe’ lower doses of Roundup. In technical parlance, this means that no NOAEL (no observed adverse effect level), was found.

Significantly, the authors believe that the hormonal disruption could lead to the potentially fatal condition know as ‘adrenal insufficiency‘ in humans, which causes fatigue, anorexia, sweating, anxiety, shaking, nausea, heart palpitations and weight loss.

“A progressive increase in its prevalence has been observed in humans, while a very few studies relating to xenobiotic exposure and adrenal insufficiency development have been reported”, they write. The increasing levels of Roundup in the environment and food could be “one of the possible mechanisms of adrenal insufficiency.”

How does this level relate to safety limits set by regulators?

One problem with trying to work out how the endocrine disruptive level of 10 mg/kg bw/d relates to how ‘safe’ levels are set by regulators.

The experiment looked at Roundup, the complete herbicide formulation as sold and used, but regulators only look at the long-term safety of glyphosate alone, the supposed active ingredient of Roundup.

Safe levels for chronic exposure to the Roundup herbicide product have never been tested or assessed for regulatory processes. This is a serious omission because Roundup has been shown in many tests to be more disruptive to hormones than glyphosate alone, thanks to the numerous other ingredients it contains to enhance its weed-killing properties.

Given this yawning data gap, let’s for a moment assume that the regulatory limits set for glyphosate alone can be used as a guide for the safe level of Roundup.

The endocrine disruptive level of Roundup found in the experiment, of 10 mg/kg bw/d, is is well above the acceptable daily intake (ADI) set for glyphosate in Europe (0.3 mg/kg bw/d) and the US (1.75 mg/kg bw/d). But this isn’t a reason to feel reassured, since with endocrine effects, low doses can be more disruptive than higher doses.

Another worrying factor is that 10 mg/kg bw/d is well below the NOAEL (no observed adverse effect level) for chronic toxicity of glyphosate: 500 mg/kg bw/d for chronic toxicity, according to the US EPA.

In other words, the level of 500 mg/kg bw/d – a massive 50 times higher than the level of Roundup found to be endocrine disruptive in the experiment – is deemed by US regulators not to cause chronic toxicity.

This experiment shows they are wrong by a long shot. They failed to see toxicity below that level because they failed to take endocrine disruptive effects from low doses into account and industry does not test for them.