The herbicide, Dacthal (dimethyl 2,3,5,6,-tetrachloroterephthalate) is
hydrolyzed to give the corresponding diacid and this derivative is a common
contaminant in ground water. In the Ontario region of eastern Oregon the
use of this herbicide on onions has resulted in the contamination of an
aquifer with this derivative. Since movement to groundwater is determined
by the hydrolysis of the parent compound to a more soluble derivative. The
rate at which this hydrolysis reaction occurs and the stability of the
metabolite must be defined. These parameters have been determined using
soils from Ontario in which onions had been raised. At room temperature
and 50% field capacity, the parent was hydrolyzed rapidly (half-life 16 days)
to the diacid derivative. An increase of the incubation temperature to 38°C
reduced the hydrolysis rate significantly (half-life 86.8 days). It is assumed
that this response reflects reduced microbial activity at the higher
temperature. At both temperatures only small amounts of the monoacid
intermediate were detected suggesting that the Dacthal monoacid was
being hydrolyzed at a faster rate than the parent. It was established that at
room temperature, the half-life of the monoacid was only 2.8 days. Over
the 300 days the experiments were carried out, little if any degradation of
the diacid metabolite could be detected.
There was virtually no degradation of the parent over a 60 day period in
sterilized soil, suggesting that microbial activity is primarily responsible for
this step. By contract, the monoacid was hydrolyzed at comparable rates
in sterilized and nonsterilized soil.
This study explains why the Dacthal metabolite is a common contaminant
in groundwater. The parent is rapidly hydrolyzed to the diacid which is
much more water soluble. More important, however, is the persistence of
the diacid metabolite in the environment. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36972 |
| Date | 26 July 1991 |
| Creators | Wettasinghe, Asoka |
| Contributors | Tinsely, Ian J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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