Graebing, P. W., Chib, J. S., Hubert, T. D., and Gingerich, W. H., 2004,
Aqueous photolysis of niclosamide: Journal of Agricultural and Food
Chemistry, v. 52, no. 4, p. 870-878.

Abstract

The photodegradation of [C-14]niclosamide was studied in sterile, pH 5, 7, and
9 buffered aqueous solutions under artificial sunlight at 25.0 +/- 1.0 degreesC.
Photolysis in pH 5 buffer is 4.3 times faster than in pH 9 buffer and 1.5 times
faster than in pH 7 buffer. In the dark controls, niclosamide degraded only in
the pH 5 buffer. After 360 h of continuous irradiation in pH 9 buffer, the
chromatographic pattern of the degradates was the same regardless of which
ring contained the radiolabel. An HPLC method was developed that confirmed
these degradates to be carbon dioxide and two- and four-carbon aliphatic acids
formed by cleavage of both aromatic rings. Carbon dioxide was the major
degradate, comprising similar to40% of the initial radioactivity in the 360 h
samples from both labels. The other degradates formed were oxalic acid,
maleic acid, glyoxylic acid, and glyoxal. In addition, in the
chloronitroaniline-labeled irradiated test solution, 2-chloro-4-nitroaniline was
observed and identified after 48 h of irradiation but was not detected thereafter.
No other aromatic compounds were isolated or observed in either labeled test
system.

Keywords niclosamide, lampricide, photolysis, half-life, carbon dioxide,
aliphatic acids, pH, 2,4-dichlorophenoxyacetic acid, organic-compounds,
routine treatment, rapid loss, soil, mineralization, sediment, degradation,
metabolism, lampricide