es301205a_si_001.pdf (1.41 MB)
Aquatic Photochemistry of Isoflavone Phytoestrogens: Degradation Kinetics and Pathways
journal contribution
posted on 2016-02-20, 19:09 authored by Jacob
R. Felcyn, Jasmine C. C. Davis, Loan H. Tran, John C. Berude, Douglas E. LatchIsoflavones are plant-derived chemicals that are potential
endocrine
disruptors. Although some recent studies have detected isoflavones
in natural waters, little is known about their aquatic fates. The
photochemical behaviors of the isoflavones daidzein, formononetin,
biochanin A, genistein, and equol were studied under simulated solar
light and natural sunlight. All of these phytoestrogens were found
to be photolabile under certain conditions. Daidzein and formononetin
degraded primarily by direct photolysis. Their expected near-surface
summer half-lives in pH 7 water at 47° latitude are expected
to be 10 and 4.6 h, respectively. Biochanin A, genistein, and equol
degraded relatively slowly by direct photolysis at environmentally
realistic pH values, though they showed significant degradation rate
enhancements in the presence of natural organic matter (NOM). The
indirect photolysis rates for these compounds scaled with NOM concentration,
and NOM from microbial origin was found to be a more potent photosensitizer
than NOM from terrestrial sources. Mechanistic studies were performed
to determine the indirect photolysis pathways responsible for the
rate enhancements. Results of these studies implicate reaction with
both singlet oxygen and excited state triplet NOM. Environmental half-lives
for biochanin A, genistein, and equol are expected to vary on the
basis of pH as well as NOM source and concentration.