Date of Degree

2-2019

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Urs Jans

Committee Members

Pengfei Zhang

Yi He

Subject Categories

Analytical Chemistry | Environmental Chemistry

Keywords

HBCDD, bisulfide, polysulfide, Fe(II), iron oxides

Abstract

The individual degradation rates of the three dominant stereoisomers (alpha, beta, gamma) of hexabromocyclododecane (HBCDD) with bisulfide and polysulfides were investigated at pH 9-10 in methanol/water solutions at two different temperatures (25 °C and 40 °C). alpha-HBCDD reacts significantly slower than beta-HBCDD and gamma-HBCDD. It was also observed that the reaction of HBCDD with polysulfides is faster than with bisulfide. For the reaction of HBCDD with bisulfide, the experiments were performed in 20% water/80% methanol, 50% water/50% methanol and 80% water/20% methanol at 40 °C. It was determined that the solvent polarity affects the reaction and the second-order rate constants of beta-HBCDD and gamma-HBCDD with bisulfide are larger with higher percentage of water. Only one isomer of tetrabromocyclododecene (TBCDe-5) was identified as a degradation product of the reaction of HBCDD with reduced sulfur species. TBCDe-5 itself reacts about ten times slower with bisulfide and twenty times slower with polysulfide than HBCDD.

The reaction of HBCDD isomers with Fe(II) bound to magnetite and goethite were performed in a pH range from 6.15 to 7.50 at room temperature. It was observed that Fe(II) bound to iron oxides is a more efficient reductant than aqueous solution of Fe(II) only to reduce HBCDD in sediments. The reaction of HBCDD with Fe(II) bound to iron oxides is also stereoisomer specific with alpha-HBCDD reacting much slower than beta-HBCDD and gamma-HBCDD. The reaction is pH dependent and it is faster with increased pH. The initial concentration of Fe(II) and HBCDD can affect the reaction rate. The reaction is negligible when all the Fe(II) is sorbed to magnetite and no Fe(II) remains dissolved. It was also observed that the reaction of 100 nM HBCDD is slower than the reaction of 1 µM HBCDD with Fe(II) bound to magnetite. In addition, natural organic matter (NOM) was found to inhibit the degradation of HBCDD by Fe(II) bound to iron oxides.

The much slower abiotic reaction of alpha-HBCDD compared to beta-HBCDD and gamma-HBCDD could potentially contribute to the fact that alpha-HBCDD is found in higher concentrations in biological samples than gamma-HBCDD. The study demonstrates that bisulfides, polysulfides and Fe(II) bound to iron oxides can play a significant role in the degradation of HBCDD in sediments.

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