Semester of Graduation

Fall 2020

Degree

Master of Civil Engineering (MCE)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

The broad goal of the research described in this thesis was to better understand the potential for biologically mediated production of p-cresol in groundwater at a Superfund site located in south Louisiana. Previous literature reports that microorganisms known to carry out the transformation from L-tyrosine to p-cresol occur in diverse environments.

In the research described in this thesis, studies were conducted utilizing groundwater from the Superfund site during the course of enhanced in situ bioremediation practices aimed at stimulating reductive dehalogenation of chlorinated solvent contamination. Microbial communities established with groundwater sampled from the Superfund site were observed to biogenically produce p-cresol when provided with either L-tyrosine or 4-hydroxyphenylacetic acid.

When provided with 350 mg/L 4-hydroxyphenylacetic acid, cultures established in liquid media consistently accumulated p-cresol concentrations with approximately stoichiometric conversion from 4-hydroxyphenylacetic acid in under 30 days. Experiments performed with a wide range (0-2000 mg/L) of starting 4-hydroxyphenylacetic acid concentrations supplied to the enrichment cultures revealed a high correlation between p-cresol accumulation and 4-hydroxyphenylacetic acid consumption during a 45-day incubation period.

When provided with 350 mg/L L-tyrosine (as opposed to 4-hydroxyphenylacetic acid), enrichment cultures established in liquid media accumulated p-cresol, however, the degree of transformation varied widely, ranging from less than 1% to approximately 100% stoichiometric conversion from L-tyrosine. Subsequent studies revealed that a portion of the tyrosine was converted into phenol and in some cases, a portion of the L-tyrosine remained untransformed.

In order to distinguish between the unresolved m- and p-cresol isomers determined during routine laboratory analysis, GC/MS mass spectra and HPLC analyses were conducted to verify the compound identity. Results from these studies indicated with a high degree of confidence that p-cresol was the isomer present and m-cresol was not observed (/L) in any groundwater or enrichment culture tested.

Collectively, results presented in this thesis indicate that indigenous groundwater microbial communities are capable of producing p-cresol when supplied with L-tyrosine or 4-hydroxyphenylacetic acid. Further research is necessary to elucidate the metabolic pathways involved in p-cresol production in site groundwater as well as the microorganisms responsible.

Committee Chair

Moe, William

Available for download on Thursday, October 28, 2021

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