The biodegradability and physicochemical properties of unsubstituted and
methylated polycyclic aromatic hydrocarbons (PAHs) were investigated. The focus was
on the development of models expressing the influence of molecular structure and
properties on observed behavior.
Linear free energy relationships (LFERs) were developed for the estimation of
aqueous solubilities, octanol/water partition coefficients, and vapor pressures as
functions of chromatographic retention time. LFERs were tested in the estimation of
physicochemical properties for twenty methylated naphthalenes containing up to four
methyl substituents. It was determined that LFERs can accurately estimate
physicochemical properties for methylated naphthalenes.
Twenty unsubstituted and methylated PAHs containing up to four aromatic rings
were biodegraded individually by Sphingomonas paucimobilis strain EPA505, and
Monod-type kinetic coefficients were estimated for each PAH using the integral method.
Estimated extant kinetic parameters included the maximal specific biodegradation rate,
the affinity coefficient, and the inhibition coefficient. The generic Andrews model
adequately simulated kinetic data. The ability of PAHs to serve as sole energy and
carbon sources was also evaluated.
Quantitative structure-biodegradability relationships (QSBRs) were developed
based on the estimates of the kinetic and growth parameters. A genetic algorithm was
used for QSBR development. Statistical analysis and validation demonstrated the predictive value of the QSBRs. Spatial and topological molecular descriptors were
essential in explaining biodegradability. Mechanistic interpretation of the kinetic data
and the QSBRs provided evidence that simple or facilitated diffusion through the cell
membranes is the rate-determining step in PAH biodegradation by strain EPA505.
A kinetic experiment was conducted to investigate biodegradation of PAH
mixtures by strain EPA505. The investigation focused on 2-methylphenanthrene,
fluoranthene, and pyrene, and their mixtures. Integrated material balance equations
describing different interaction types were fitted to the depletion data and evaluated on a
statistical and probabilistic basis. Mixture degradation was most adequately described by
a pure competitive interaction model with mutual substrate exclusivity, a fully predictive
model utilizing parameters estimated in the sole-PAH experiments only.
The models developed in this research provide insight into how molecular
structure and properties influence physicochemical properties and biodegradability of
PAHs. The models have considerable predictive value and could reduce the need for
laboratory testing.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4290 |
| Date | 30 October 2006 |
| Creators | Dimitriou-Christidis, Petros |
| Contributors | Robin, Autenrieth L. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 706234 bytes, electronic, application/pdf, born digital |
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