Vol. 15—1961 - NorthEastern Weed Science Society

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have aromatic 011s in them; Moreover, they also are decomposed
to CO 2
! free chlorine and water by bacteria in the same manner
as esters and acids.
F. NO PROBLEMSUNDERPRACTICALUSE ONWATERSHEDS
However, even ester formulations produced by reputable
manufacturers can be used with safety in watershed areas. For
example, let us presuppose a rectangular lake 100 acres in size,
having shoreline dimensions of 1,000 feet by 4,356 feet. If a
watershed manager wanted to spray a 20-foot wide strip of brush
around this shoreline, he would be spraying a total of five
acres of brush. Assuming he would apply a herbicide concentration
of one gallon of a four pound acid equivalent formulation
per 100 gallons of water and this solution were applied at
approximately 200 gallons of total spray solution per acre, then
on this five acres of brush he would apply 1,000 gallons of total
spray which would contain 40 pounds of 2,4,5-T acid equivalent.
Now, if this 100-acre lake had an average depth of 10 feet,
it would contain 1,000 acre feet of water. In order to have
enough 2,4,5-T ester in the lake to reach an odor or taste
threshold, that is, be detectable, 0.4 ppm of the PGBE ester
would have to be present. In this example, 1,086 pounds of the
2,4,5-T ester would be needed to reach the odor threshold, 17.7
-- times more ester than is being applied to the five acres of
brush. The oil components, because of a much lower threshold
rating, could possibly be troublesome if extremely careless
application were made. In this case, more than 110 gallons of
the spray solution would have to fall directly into the lake
before an odor threshold would be reached. Using proper
application techniques, only a very small portion of the spray
could conceivably reach the water directly, thus virtually
eliminating any possibility of pollution. Of course, where
brush control spray applications are applied deeper into the
watershed and farther away from the water reservoir, such treatments
would present even less hazard of contamination.
G. SUMMARY
Studies of the degradation products of 2,4-D, 2,4,5-T and
silvex have been made. The results of these studies show
conclusivAly that decomposition under natural conditions does
nct result in the formation of the corresponding phenols. These
phenoxy h~rbicides are decomposed into car~on dioxide, hydrochloric
~cid and water. Free phenols are decreased, rather than
increased, by bacterial degradation and are not the b'l'eakdown
products of phenoxy herbicides. Bacterial oxidation of plU"'110'XY
399.