| Chemical Abstract Number (CAS #) |
145733
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| Synonyms | Endothall |
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Endothal | 7-Oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid, |
| Analytical Method |
EPA Method 548.1 |
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| Molecular Formula | C8H10O5 |
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| Use | It is used as a desiccant on lucerne and on potato, for the defoliation of cotton and to
control algae and aquatic weeds.
Pre- and post-emergence herbicide, defoliant, desiccant, aquatic algicide growth regulator. For
sugar beets, turf, hops sucker suppression; alfalfa, clover desiccants; cotton harvest aids; potato
vine killers.
SALTS OF ENDOTHAL ARE RECOMMENDED FOR PRE- & POST-EMERGENCE
CONTROL OF WEEDS IN RED BEET, SPINACH AND SUGAR BEET AT 2-6 KG AI/HA
OR IN COMBINATION WITH PROPHAM. USED AS DESICCANT ON LUCERNE &
ON POTATO, FOR DEFOLIATION OF COTTON & TO CONTROL AQUATIC WEEDS &
ALGAE.
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| Consumption Patterns | Cotton production, 95.6%; Sugarbeets, 3.9%; Remainder in landscape maintenance or
"public health pest control" (1984) California use, calculated from table
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| Apparent Color | CRYSTALLINE, WHITE SOLID
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| Odor | Odorless
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| Melting Point | WHEN HEATED RAPIDLY, MELTS @ ABOUT 144 C, DECOMPOSING INTO
ANHYDRIDE & WATER
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| Molecular Weight | 186.18
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| Density | 1.431
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| Sensitivity Data | May be very irritating to skin, eyes, mucous membranes.
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| Environmental Impact | Release of endothall to the environment is expected to occur primarily during its use as a
pre-emergence, post-emergence, turf and aquatic herbicide and harvest aid. Other sources of
release include loss during manufacturing, formulation, packaging or disposal of this herbicide. If
released to soil, endothall is expected to rapidly biodegrade under aerobic conditions. The half-life
of endothall in soil is reported to be 4 to 9 days. Endothall should be highly mobile in soil;
however, rapid degradation would limit the extent of leaching. Chemical hydrolysis and
volatilization are not expected to be significant. If released to water, endothall should rapidly
biodegrade under aerobic conditions (half-life approx 1 week or less) and biodegrade more slowly
under anaerobic conditions. Glutamic acid is a major biotransformation product of endothall
under aerobic conditions. Endothall is not expected to oxidize, chemically hydrolyze, photolyze,
volatilize, bioaccumulate or adsorb to suspended solids or sediments in water. If released to the
atmosphere, endothall is expected to exist predominantly on particles and should either settle out
or wash out in precipitation. It is not expected to chemically react or photolyze in the atmosphere.
The most probable routes of human exposure to endothall are inhalation and dermal contact of
workers involved in the manufacture, handling or application of endothall. The general public
could potentially be exposed through use for lawn weed control.
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| Environmental Fate | TERRESTRIAL FATE: If released to soil, endothall is expected to rapidly biodegrade
under aerobic conditions. The half-life of endothall is reported to be 4 to 5 days in clay soils and 9
days in soils with high organic content . Endothall should be highly mobile in soil; however,
rapid degradation would limit the extent of leaching. Chemical hydrolysis and volatilization are
not expected to be significant fate processes.
AQUATIC FATE: If released to water, endothall should rapidly biodegrade under aerobic
conditions (half-life approx 1 week or less). Glutamic acid is a major biotransformation product of
endothall under aerobic conditions. Endothall is not expected to oxidize, chemically hydrolyze,
photolyze, volatilize, bioaccumulate or adsorb to suspended solids or sediments. Endothall applied
to a pond at various concentrations ranging from 0.3 to 10 ppm was undetectable after an average
of 2.5 days and a maximum of 4 days and in another study, 1.2 ppm endothall added to pond
water was 55% removed after 12 days . In experimental greenhouse pools treated with 0.03,
1.6 or 4.5 ppm endothall, an overall half-life of 4 days was reported . In farm reservoirs, approx
71% removal of 0.3 to 1.4 ppm endothall was observed in 12 days . Endothall added to the
water of irrigation supply ponds at 2 ppm decreased linearly with the predicted concentration of
zero at 26 days (half-life 12 days) . 30 days after addition of endothall to anoxic water, only
28% removal of added endothall was observed .
ATMOSPHERIC FATE: If released to the atmosphere, endothall is expected to exist
predominantly on particles and should either settle out or wash out in precipitation. Endothall is
not expected to chemically react or photolyze in the atmosphere.
A mixture of diquat dibromide and potassium endothall was applied at 2.83 liters of each chemical
per 0.4 surface acre to the 1093 acre Chickahominy Reservoir, Virginia because of nuisance
populations of Egeria densa Planchon (egeria). There were no measurable changes in water
quality after treatment and macrophyte die off with the exception of a general decrease in
dissolved oxygen. Both herbicides declined to very low levels in the water 3 days after treatment
and were undetectable within 16 days after treatment. No endothall was found in bottom
sediments. Neither was found in fish muscle tissue.
To obtain residue data from the application of the algicide endothal in Italian rice paddy fields, 2
experiments were carried out using a 50 g/kg granular formulation in a small pond and the same
granular and liquid formulations in actual paddy fields of the Italian rice growing area. Endothal
decay in the pond water was very rapid, reaching residue levels of 0.01-0.02 mg/l in 2 days and
0.004-0.01 mg/l at the third day. The muddy soil of the pond was free from measurable endothal
residues (<0.02 mg/kg). In the paddy field waters, the endothal decay was slower, with an
average half-life time of 3.3 days, independently of the type of formulation. The actual residues in
water after 6 days ranged from 0.3 to 1.3 mg/l according to the initial amount of product applied,
and, consequently, to the initial concn in water. Rice samples collected at the normal harvest time
from the two paddy fields, treated with three different formulations, showed no endothal residue
at the min. detectable level of 0.01 mg/kg.
Accurate prediction of chemical fate and persistence using general aquatic fate models requires
model parameterization, ie, the determination of site-specific environmental and chem parameters
for model input. The capability of 1 model, the Exposure Anal Modeling System (EXAMS), to
predict the fate of endothall, an aquatic herbicide, in a reservoir was compared using 2 different
parameterization methods. The 1st method, limited parameterization, used only literature and
limited field data. The 2nd method, intensive parameterization, employed lab, expterimental pool
and field data. Differences of <1 order of magnitude were observed among theendothallfate
predictions from Exposure Anal Modeling System in this reservoir using either method. Predicted
endothall aq half-lives were greater than the observed half-life by a factor of 5 to 9. Predicted
endothall concn in sediment were consistently below the min detectable level (0.01 mg/kg) for
endothall, whereas endothall concn were measured in reservoir sediments in the field. In this case,
the results indicate that limited parameterization of Exposure Anal Modeling System provides
predictions of endothall persistence that are as accurate as those provided by intensive
parameterization, thus saving time and reducing costs. Limited parameterization produced
relatively accurate predictions in this study, possibly because only 1 fate process,
biotransformation, was important. For chemicals affected by numerous fate processes, the errors
associated with each fate process input could significantly affect the accuracy of predictions.
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