posted on 2006-12-01, 00:00authored byLorien J. Fono, Edward P. Kolodziej, David L. Sedlak
Although wastewater-derived chemical contaminants
undergo transformation through a variety of mechanisms,
the relative importance of processes such as biotransformation and photolysis is poorly understood under conditions
representative of large rivers. To assess attenuation
rates under conditions encountered in such systems,
samples from the Trinity River were analyzed for a suite
of wastewater-derived contaminants during a period when
wastewater effluent accounted for nearly the entire flow
of the river over a travel time of approximately 2 weeks.
While the concentration of total adsorbable organic
iodide, a surrogate for recalcitrant X-ray phase contrast
media in wastewater, was approximately constant throughout
the river, concentrations of ethylenediamine tetraacetate,
gemfibrozil, ibuprofen, metoprolol, and naproxen all
decreased between 60% and 90% as the water flowed
downstream. Comparison of attenuation rates estimated in
the river with rates measured in laboratory-scale
microcosms suggests that biotransformation was more
important than photolysis for most of the compounds. Further
evidence for biotransformation in the river was provided
by measurements of the enantiomeric fraction of metoprolol,
which showed a gradual decrease as the water moved
downstream. Results of this study indicate that natural
attenuation can result in significant decreases in
concentrations of wastewater-derived contaminants in
large rivers.