Sorption and sequestration of phenanthrene in polymethylenic plant biopolymers: Proxies for soil and sedimentary organic matter

Organic contaminants like polycyclic aromatic hydrocarbons (PAHs) have low aqueous solubility. When they are introduced to the environment of soils and sediments, they tend to mainly associate with soil/sedimentary organic matter (SOM) through a process known as sorption. This process is dominated by solid-phase dissolution or partitioning of the pollutant into the SOM matrix. It has been traditionally believed that sorption of PAHs to SOM is primarily due to their interactions with the aromatic components of SOM. Recent work has shown that aliphatic components of SOM also have high affinities for PAHs. This work is directed towards understanding the interactions between PAHs and polymethylenic (aliphatic) components of SOM. Plant biopolymers that are rich in these polymethylenic components and are known to contribute significantly to such components in SOM were used as proxies for SOM in this study. Advanced analytical techniques were used for improving our understanding of the chemical and physical nature of these biopolymers. Differences in the nature of the polymethylenic chains among the various biopolymers, and how this affects their ability to sorb and retain organic contaminants such as phenanthrene has been elucidated.; A study of the SOM from pristine and contaminated sites in the San Diego Bay shows that the sediments are rich in polymethylenic components. Using the technique of pyrolysis GC-MS, the SOM is shown to contain alkanes and alkenes derived from these polymethylenic compounds. Using another technique of thermochemolysis with tetramethyl ammonium hydroxide, long-chain fatty acid methyl esters are produced, indicating the importance of polymethylenic components having ester functionalities in SOM. Such functionalities are obtained from plant biopolymers such as cutin and cutan found in plant cuticles, and suberin found in plant roots and bark in terrestrial systems. In aquatic systems they are sometimes found in the biopolymer algaenan derived from algae.; High-resolution magic angle spinning (HRMAS) NMR spectroscopy is additionally used as a tool for studying the structure of the biopolymer cutin isolated from the tomato fruit cuticle, and cutan isolated from the Agave americana leaf cuticle. A significant finding by this technique in tomato cutin is the presence of α-branched fatty acids/esters and esters of mid-chain hydroxyls. (Abstract shortened by UMI.)...