Hi Does Senior Monsanto scientist, Dan Goldstein still maintain that If ingested, glyphosate is excreted rapidly, does not accumulate in body fat or tissues, and does not undergo metabolism in humans. Rather, it is excreted unchanged in the urine.
Submitted by: Sam
Expert response from Dan Goldstein
Former Senior Science Fellow and Lead, Medical Sciences and Outreach, Monsanto Company
Tuesday, 25/11/2014 13:03
Hi! Dan Goldstein here.
Yes, I stand by my previous response. Some pesticides are indeed very persistent, and others are not. This depends on the chemical properties of the pesticide molecule. Some can persist for decades in body fat; others are metabolized to inactive materials or excreted in minutes or hours to days. Glyphosate does not accumulate or persist.
We have extensive studies in animal systems, as well as the Farm Family Exposure study, demonstrating excretion in humans that is complete in less than a week. Unfortunately, people sometimes ingest very large amounts of concentrated glyphosate products in attempts at self-injury. While these cases are disturbing, they do give us some insight into the elimination rate for glyphosate in humans. The most recent large series, from Roberts et al. in Sri Lanka (for which analytical work was performed by Monsanto and on which I am a coauthor), demonstrates a half life (time to eliminate one-half of the glyphosate in the body) of 3-4 hours, which translates into essentially complete elimination (>98 percent) in five half lives, or 15-20 hours. These values are not inconsistent but rather reflect differences in exposure and absorption rate. The important point is that both studies demonstrate that glyphosate is eliminated in a matter of days, rather than accumulating. For a complete review of animal data, you can refer to the US EPA Re-registration Eligibility Document (RED), or, for a less technical review, see Felsot, 2000.
Glyphosate is currently undergoing reassessment in the EU. A recent summary based on all currently available data was recently published by the German Agency for Risk Assessment (BfR) and states that “(f)ollowing oral administration glyphosate is rapidly absorbed from the gut but only to a limited extent of approximately 20%. The elimination via urine is fast and complete, predominantly within 48 hours.”
As far as chemical properties go, glyphosate is a water-soluble, small (molecular weight: 169 daltons) and very polar molecule (see HSBD). Fat solubility is measured by putting a chemical into a container with water and octanol, a long-chain alcohol that will not mix with water. You can measure how much glyphosate is in the water phase vs. the “fat” phase (octanol). A compound that is equally soluble in both substances will have a ratio of 1 (log Kow = 0, using the log base 10); if it is 100 times more soluble in fat, it will have a ratio of 100 (log Kow = 2). For glyphosate, the log Kow is MINUS 3.4, meaning that over 1,000 times more glyphosate is in the water than in “fat.”
So, again, glyphosate is not fat (lipid) soluble, does not accumulate in body fat or tissues over time and does not undergo metabolism in mammals, including humans. This rapid elimination is hardly surprising, given the nature of the glyphosate molecule.
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