Vol. 15—1961 - NorthEastern Weed Science Society

slow in ;the only waters, studied in New York State (Analyses 'of the ,N.Y.
Henlth Dept., unpublished). While conservation and regulatory agencies '
sbou;l;~have a part in conducting such studies, it must be recognized that the
major,respcmsibility should lie with those suggesting and recommending such
chemicals for use.
Bio-Assay:
Laboratory bio-assay can be helpful in the· evaluation of comparative
toxicity of control chemicals to fish and other -aquatic organisms. Modifications
in procedure are ,requirep. ManyHof these chemicals ··are not easi'ly
analysed in dilute solutions and it is difficult to determine rate of removal
by the test organism. Use of double or triple volume solutions will show
if the evaluation of toxicity is being affected through removal. Rep'Lacemerrt
of solution or continuous now is valid only if the entire test solution is
made up at one time as only this modification will correspond with a lake or
pond application. Since continuous now is desirable to maintain a uniform
oxygen concentration, the time that these experiments can cover is limited.
Results when reported in terms of the initial concentration may not truly
represent that concentration as the concentration may vary with time and from
reaction with the water or bacterial decomposition. Toxici ty curves do not
usually conform to those anticipated if fresh solutions of definite composition
were to be used. However, bio-assay can be used conveniently for the
evaluation of the effects of the character of the water, oxygen content, pH
and temperature.
One of our laboratories is, testing the comparative toxicity of these
chemicals using brown trout fingerlings. ~.Jhile the data is too incomplete
for release at this time, the toxicity of certain 2,4-D formulations appears
to range from 2.5 p.p.m. to 16 p.p.m. in terms of the acid equivalent. While
it is not yet definite whether toxicity is due to the compound, impurities of
manufacture, or the vehicle, the compound appears indicoted. Differences in
behavior of different formulations have Ellso been observed in the field.
This may ,indicate that formulation may be more important than acid equi~alency
in ,aquatic renction~ One hormone type chemical increased in toxicity 'on
standing iii solution, apparently either due to hydrolysis or some other reaction
in the water.
In situ
studies:
-
The very fact that bio-assay is conducted under such carefully controlled
conditions may react against its transference as representative of field up- ,
plication. It cannot measure reduction through intake by plants, absorption
on bottom muds, or the reaction caused by different bacterial populatdone ,
It therefore cannot supplant an in situ study under actual field conditions.
Preferably, the area chosen should have at least one season of study before
the application even when control areas are established. Qualitative data
alone is inadequate and conclusions should be based on quantitative st\InpHng.