| Roundup contains both glyphosate and a surfactant. The information below focuses on glyphosate ONLY. When you spray glyphosate on a plant, it is absorbed through the foliage and transported throughout the plant, including its roots. Ultimately it is released into the soil from the roots. Once absorbed by the plant, glyphosate prevents the plant from making three amino acids it needs to survive: phenylalanine, tyrosine, and tryptophan. It does this by inhibiting an enzyme needed to make chorismate, a precursor to those amino acids.
However, other research found that there was a second way glyphosate worked to kill plants. Glyphosate disrupts plants' ability to defend themselves against pathogens. Plants produce chemicals called phytoalexins to defend themselves, and glyphosate disrupts their ability to produce phytoalexins.
"Glyphosate interactions with physiology, nutrition, and diseases of plants: Threat to agricultural sustainability?" in the European Journal of Agronomy (2009) says: "These findings were significant because the release of glyphosate into the environment was found to have considerably more and far-reaching effects than the original notion that was limited to only the localized disruption of a specific metabolic pathway within a target plant."
The same publication goes on to say:
Subsequent research on glyphosate interactions with soil microorganisms demonstrated that although glyphosate was metabolized by a segment of the microbial population, it was also toxic to several bacteria and fungi; the net effect glyphosate appeared to be a disruption of soil and root microbial community composition because selected components of the microbial community were stimulated while others were suppressed.
So glyphosate impacts more than just the target plants, the weeds. It also disrupts the soil ecosystem.
As for breakdown in the soil, glyphosate mostly either binds to soil particles or it is broken down by microbes. About 1-2% of glyphosate in the soil may runoff into waterways when it rains. When glyphosate breaks down, it becomes CO2 and NH4 (ammonium). Looking at 47 studies on the half-life of glyphosate in the soil, the half-life (the amount of time it took for half the glyphosate to break down) ranged from 1.2 days to 197.3 days. The arithmetic mean amount of time was 32 days and the geometric mean was 17 days. Another study found that glyphosate was toxic (although not lethally so) to non-target plants up to 3 weeks after it was applied. Sub-lethal doses of glyphosate can also impact a plants' ability to absorb nutrients, such as iron.
That's as far as I've read through the many, many studies Huber referenced (and each study references many more studies, leaving anyone interested in glyphosate with an endless amount of reading to do). I'd be interested to hear what else others have read on this topic. |
