Dissertation/Thesis Abstract

Tracing anthropogenic wastes: Detection of fluorescent optical brighteners in a gradient of natural organic matter fluorescence
by Dixon, Laura Kellie, Ph.D., University of South Florida, 2009, 221; 3420634
Abstract (Summary)

A dual wavelength method was developed for the field detection of optical brighteners (OBs), fluorescent laundry additives used as indicators of anthropogenic wastes. The method was quantitative for OBs under variable levels of fluorescent colored dissolved organic matter (CDOM). Based on excitation at 300-400 nm and 440 and 550 nm emission, the method assumed a constant ratio of fluorescence due to CDOM alone, even if absolute amplitude varied. Concentrations of OBs were computed as the difference between the observed 440 nm emission and the expected CDOM fluorescence at 440 nm, as extrapolated from the 550 nm fluorescence and established CDOM fluorescence ratio. Real-time inner filter corrections were based on absorption modeled from 550 nm fluorescence and from exponential relationships at alternate wavelengths. The effects of temperature and dissolved oxygen on CDOM fluorescence and computed OB were quantified but were minimal because effects were comparable between the two fluorescence regions. Assumptions on the locally conservative behavior of CDOM were supported in field surveys of sewered and non-sewered areas. Varying water masses were detected, but OB quantities were detected that did not co-vary with fluorescence alone. Eleven geographic regions of peninsular Florida and sources of OBs were sampled to evaluate the method under a broader range of CDOM and to conduct an extensive detergent spike analysis. Fluorescence data were collected as EEMs and subjected to PARAFAC modeling, isolating eight spectral factors that could sufficiently describe all samples. There were no visible regions of the spectra that were unique to detergents or OBs, but a previously unreported peak in the UV (<230/284 ex/em) was tentatively identified as a detergent surfactant and should be pursued as a potential complementary indicator of anthropogenic wastes. Limits on EEM fluorescence measurements were identified: maximum linear range, maximum turbidity, and sensitivity to assumptions. A sub-sampling technique of EEM data approximated the filter fluorometer readings, was used to optimize the dual wavelength method, validated the method with spike recoveries, and presented alternative approaches.

Indexing (document details)
Advisor: Vargo, Gabriel A., Coble, Paula G.
School: University of South Florida
School Location: United States -- Florida
Source: DAI-B 71/09, Dissertation Abstracts International
Subjects: Chemical Oceanography, Water Resource Management, Aquatic sciences
Keywords: Anthropogenic wastes, Dissolved oxygen, Fluorescence, Optical brighteners, Organic matter, Tracing
Publication Number: 3420634
ISBN: 978-1-124-18351-0
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