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Glyphosate
On 11/4/2014 2:29 PM, Jeff Layman wrote:
On 04/11/2014 15:48, Brooklyn1 wrote: F Murtz wrote: If I have some raised gardens with vegies in them and grass weeds start growing can I carefully paint the weed with glyphosate without affecting the vegies? No matter how carefully you apply glyphosate as the 'weed' dies the chemical will dissolve into the soil and affect your vegetable plants, and you when you eat them, if you get any. I am sure that with such specific claims you will be happy to provide numerous links which support your statements. For my own edification I clipped this: Environmental Fate: Soil The median half-life of glyphosate in soil has been widely studied; values between 2 and 197 days have been reported in the literature.7,48 A typical field half-life of 47 days has been suggested.4 Soil and climate conditions affect glyphosate's persistence in soil.1 See the text box on Half-life. The "half-life" is the time required for half of the compound to break down in the environment. 1 half-life = 50% remaining 2 half-lives = 25% remaining 3 half-lives = 12% remaining 4 half-lives = 6% remaining 5 half-lives = 3% remaining Half-lives can vary widely based on environmental factors. The amount of chemical remaining after a half-life will always depend on the amount of the chemical originally applied. It should be noted that some chemicals may degrade into compounds of toxicological significance. Glyphosate is relatively stable to chemical and photo decomposition.6 The primary pathway of glyphosate degradation is soil microbial action, which yields AMPA and glyoxylic acid. Both products are further degraded to carbon dioxide.3 Glyphosate adsorbs tightly to soil. Glyphosate and its residues are expected to be immobile in soil.6 Water The median half-life of glyphosate in water varies from a few days to 91 days.1 Glyphosate did not undergo hydrolysis in buffered solution with a pH of 3, 6, or 9 at 35 °C. Photodegradation of glyphosate in water was insignificant under natural light in a pH 5, 7, and 9 buffered solution.58,59 Glyphosate in the form of the product Roundup® was applied to aquatic plants in fresh and brackish water. Glyphosate concentrations in both ponds declined rapidly, although the binding of glyphosate to bottom sediments depended heavily on the metals in the sediments. If chelating cations are present, the sediment half-life of glyphosate may be greatly increased.60 Glyphosate has a low potential to contaminate groundwater due to its strong adsorptive properties. However, there is potential for surface water contamination from aquatic uses of glyphosate and soil erosion.6 Volatilization of glyphosate is not expected to be significant due to its low vapor pressure.6 Air Glyphosate and all its salts are very low in volatility with vapor pressures ranging from 1.84 x 10-7 mmHg to 6.75 x 10-8 mmHg at 25 °C.1,4,8 Glyphosate is stable in air.1 Plants Glyphosate is absorbed by plant foliage and transported throughout the plant through the phloem.3 Glyphosate absorption across the cuticle is moderate, and transport across the cell membrane is slower than for most herbicides.4 Because glyphosate binds to the soil, plant uptake of glyphosate from soil is negligible.3 Glyphosate accumulates in meristems, immature leaves, and underground tissues.4 Very little glyphosate is metabolized in plants, with AMPA as the only significant degradation product.3 Lettuce, carrots, and barley contained glyphosate residues up to one year after the soil was treated with 3.71 pounds of glyphosate per acre.61,62 Glyphosate had a median half-life of 8 to 9 days in leaf litter of red alder and salmonberry sprayed with Roundup®.48 Indoor All surface wipe and dust samples collected from five farm households in Iowa contained detectable levels of glyphosate ranging from 0.0081-2.7 ng/cm2. In six non-farm households, 28 out of 33 samples collected contained detectable levels of glyphosate ranging from 0.0012-13 ng/cm2.63 |
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