Hydrolysis Rate
The hydrolysis rate at pH’s 5.0, 7.4, and 9.0 were
2.95 x 10-10 sec-1, 4.80 x 10-7 sec-1, and
1.23 x 10-7 sec-1, respectively. (18)
Dissociation Constant
The pK, for bupropion
hydrochloride is 8.35 (19)
Aerobic Biodegradation
Bupropion hydrochloride was tested for aqueous
aerobic biodegradation at 21°C using 14C radiolabeled material. At a concentration of approximately 10 mg
carbon per liter, no 14CO2 was evolved after 14
days. Analysis of the solutions after
the incubation period show no significant degradation of bupropion
hydrochloride. A half life cannot be
calculated.
Photodegradation
Bupropion hydrochloride was tested for aqueous
photodegradation at 22°C using 14C radiolabeled material in pH 5, 7
and 9 buffers. The test was conducted
at a nominal test concentration of 1.0 ppm.
Half-lives measured 54 hours at pH 5, 11 hours for pH 7 and 30 hours for
pH 9.
Estimated half-life values were calculated for
bupropion hydrochloride, normalized for flat bodies of water at pH 5, 7, and 9
with varying season and latitude. These
calculated half-lives for pH 5 ranged from a low of 100 hours (summer, 30°N) to
a high of 592 hours (winter, 50°N). At
pH 7 the calculated half-lives ranged from a low of 23 hours (summer) to a high
of 131 hours (winter, 50°N). At pH 9
the half-lives ranged from a low of 52 hours (summer, 30 and 40°N) to a high of
481 hours (winter 50°N).
Five degradation products were observed during the
study, four of which were more polar than the bupropion hydrochloride, i.e.
eluted before the bupropion hydrochloride during reverse phase HPLC. The five degradation products labeled A, B,
C, D, and E are believed to be 433C58, 852U77, 827U76, 377U68 and 20U78,
respectively, based upon their relative retention times (23). The polar
degradation products 433C58, 852U77, 827U76 and 20U76, contain the same
backbone chemical structure of the parent compound, bupropion hydrochloride. The degradation product that was observed to
be less polar than bupropion
hydrochloride, 377U68, is a possible process impurity and was observed at
levels <1% throughout the study.
Summary
Bupropion hydrochloride can be expected to affect
the aquatic compartment based upon the water solubility value. Hydrolysis is not considered a primary
removal process. Bupropion
hydrochloride did not significantly mineralize under the test conditions and is
not considered biodegradable.
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