Vol. 15—1961 - NorthEastern Weed Science Society

560.
THE ABSORPTIONANDMETABOLISMOF RADIOENDOTHAL BY FISH
ANDAQUATICPLANTS1,2
V.H. Freed 3 and 1110 Gauditz 4
ABSTRACT*
Endothal (disodium 3,6-endoxohexahydrophthalate)is a highly
active contact weed killer that has found extensive use for pre­
emergence weed control in sugar beets, table beets, and spinach.
More recently this chemical has been shown to be effective for the
control of many aquatic weeds. One of the attractive features of
endothal in aquatic weed control is .the relatively high tolerance
that many species of fish have toward this chemical. This makes
it possible to use this chemical for the control of aquatic weeds
without serious effect on the fish population.
The use of endothal in aquatic weed control poses the problem
as to whether or not the fish would accumulate this chemical. It
would be possible for the fish to ingest the chemical directly from
the water or if aquatic plants accumulated the chemical, fish may
become exposed to the endothal through feeding on the foliage of the
aquatic plant. The purpose of the study reported here. was to
. determine whether or not endothal was ingested by the fish from
either source and if the endothal were taken up would it pose a
problem. Previous work has shown that endothal is extremely
.unstable under biological conditions So that it was felt unlikely
that there would be any serious residue in the fish.
A study of the uptake and distribution of C 1 4 from radioendothal
in fish and plants exposed to this chemical was undertaken. It was
demonstrated that the radioactivity found in goldfish exposed to
different concentrations of chemical followed a similar pattern.
This pattern revealed extensive breakdown of the endothal molecule
and incorporation of its radioactivity into' a number offractions in
both fish and plants. The behavior of these different fractions
indicates that they are normal constituents of the organism such
as carbohydrates, organic acids, amino acids, and proteins, as well
as fats and oils. With the analytical technique used, it was demonstrated
that the fraction of radioactivity which contains endothal
would be the Dowex 1 eluate from the methanol extract. Even at 12 ppm
this fraction contained only 0.07 ppm. At the normal range of concentration
which the chemical is used, this level is only 0.002
for goldfish. Further $tudy of the elution pattern of this fraction
of radioactivity indicates that it is not as endothal. Thus, it
may be concluded that due to the extensive breakdown of this chemical
and incorporation of radioactivity into normal conatitutents
of the or-gant.sm, , .,as represented by the different fractions, that
it is doubtful that any endothal remains.
1/* Complete paper to be contributed to WEEDS
2/Supported in part by a grant frem Pennsalt Chemicals Corporation,
Tacoma, Washington
3/Professor, Agricultural Chemistry Department, Oregon State Col Le go
4/Present address, Hazelton Laboratory, Palo Alto, California