Is Glyphosate Only Toxic to Plants, as Claimed by the Pesticide Industry and the EPA?
Glyphosate has been heralded as exerting its herbicidal effects by disrupting metabolic pathways only found in plant cells. Glyphosate was thought to be nontoxic to animal life, because these affected pathways are not found in animal cells (Herman, 1999; Kennedy, 2017). However, since Earth’s environment is comprised of myriad interacting complex systems, each with an untold number of variables, it is not surprising that the animal kingdom would not be given a free pass. It stands to reason that glyphosate might exert more than the one disrupting effect—just maybe, it might end up doing something else. Indeed, glyphosate-based herbicides (GlyBH) have been found to cause endocrine disruption, birth defects, tumors, liver damage, and kidney damage, at concentrations below the allowed acceptable daily levels, in mice and rats (Benedetti, 2004; Prasad, 2009); GlyBH is also toxic, at environmentally relevant concentrations, to a variety of other species, such as frogs, fish, and daphnia, the water flea (Sandrini, 2013; Kennedy, 2017).
Other studies have shown that glyphosate causes significant morphological changes in the tail of tadpoles (Relyea, 2012). Even though the precise mechanisms by which GlyBH exerts all these effects may have not yet been definitively elucidated in some, or even most, cases, the reality of the harmful effects has been demonstrated.
What Are Some Underlying, Molecular Mechanisms by Which Glyphosate Exerts Its Toxicity in Animals’ Cells?
Studies have shown that glyphosate induces bone marrow DNA damage and cell death in mice, within twenty-four to seventy-two hours, following one dose of either 25 or 50 mg glyphosate per kilogram of body weight (Prasad, 2009). Furthermore, glyphosate has been shown to be a cholinesterase inhibitor at environmental concentrations in mussels and fish (Sandrini, 2013). Cholinesterase is an enzyme found in animals’ cells (including, of course, humans’ cells), which is needed during normal metabolism to break down the important neurotransmitter, acetylcholine. If acetylcholine were not rapidly broken down by cholinesterase, it would over-stimulate nerves, muscles, and exocrine glands. Glyphosate also appears to substitute for the amino acid glycine in a number of important metabolic pathways, including those that affect kidney function (S. Seneff, chapter in this book; Seneff, 2018).
Does Glyphosate’s Solubility in Water Reduce Its Toxicity, as Claimed by the Pesticide Industry and the EPA?
The chemical structure of glyphosate has also been used to argue against glyphosate bioaccumulating4 in organisms, helping to justify its widespread worldwide distribution. Substances bioaccumulated or biomagnified5 up the food chain present a much greater threat to an ecosystem, since those animals occupying the top of the food chain experience devastatingly high pesticide concentrations, as Rachel Carson first pointed out in 1962 (Carson, 1962).
Fat-soluble pesticides (which dissolve better in fats than water), such as chlorinated hydrocarbon insecticides (including DDT and chlordane), carbamates, organophosphates, and pyrethroids are bioaccumulated and biomagnified, as well as persist in the environment, thus wreaking greater destruction than water-soluble pesticides, such as glyphosate,6 which was an early rationalization for its mass application. However, water-soluble pesticides, since they dissolve well in water, are easily carried by rainwater and runoff, from the area where they were sprayed, into ground water and streams. There, they damage untargeted plants and animals. . . .