Date of Award

Winter 1986

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

Abstract

A fluorescence quenching method was developed for determining association constants of polycyclic aromatic hydrocarbons (PAH)s with dissolved and sediment bound humic materials. The technique is based upon the observation that PAH fluorescence in aqueous solution is quenched upon association with humic material. Association constants are derived from the fractional decrease in fluorescence intensity as a function of added humic material using Stern-Volmer plots. No separation is required and since the technique involves a ratio measurement the exact concentration of pollutant is not required. Anthracene-humic acid association constants normalized to the fraction of organic carbon in the sorbent (K(,oc)), determined by fluorescence quenching, correlated quite well with K(,oc) estimates determined by a reversed-phase procedure. The long term reproducibility was (+OR-)3.8% relative standard deviation.

The fluorescence quenching technique was used to investigate the effects of pH, ionic strength, and humic acid composition on pyrene-humic acid K(,oc) values. Carbon, hydrogen, and nitrogen analysis plus UV, infrared, and 13C solid state nuclear magnetic resonance (NMR) spectroscopy were used to investigate compositional and structural variations in humic materials. Three measures of the degree of C=C bond formation (UV absorptivity at 272 nm, atomic H/C ratio, and fraction of aromatic carbon determined by 13C NMR spectroscopy) indicated that pyrene is sorbed preferentially by humic acids possessing a high degree of aromaticity. Solution ionic strength affected K(,oc) estimates in a complex manner. It was hypothesized that humic acid conformational changes and PAH salting out effects accounted for this behavior. Variations in the concentration of stock humic acid solution used in the fluorescence quenching experiments also produced a change in K(,oc) values. Variations in pH from 5 to 8 did not produce significant effects.

Measured K(,oc) values were similar for anthracene binding to a purified sediment sample and humic acid extracted from that sediment; however, after partial extraction with dilute base, anthracene sorption to the sediment increased by a factor of two. The residual organic matter after extraction is believed to be enriched in humin and responsible for the increased sorption.

In a separate study, determination of PAH in Great Bay sediments by extraction and capillary gas chromatography produced a very good correlation between the total PAH concentration and the organic matter content of the sediments.

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