Chlorophenols represent a class of organic contaminants that are commonly used and widely distributed in the environment. Adsorption to soils may inhibit the transport of these chemicals, while slow desorption rates can create a potential source for long-term contamination of groundwater supplies. Microbial degradation of these compounds may also play an important role in their environmental fate. The purpose of this study was to investigate how the processes of sorption, desorption, and biodegradation interact to affect the distribution of pentachlorophenol (PCP) and 4-monochlorophenol (4-MCP) in two soils with different soil organic matter (SOM) content.
Batch soil microcosms were used to measure the sorption of both test compounds at three concentrations for each, exposed to two soils with different SOM levels. An ultrafiltration study was designed to quantify partitioning to dissolved organic matter (DOM), while batch desorption experiments were performed to measure chemical release from the soils. Finally, biodegradation experiments were carried out under aerobic conditions to evaluate microbial interactions with PCP and 4-MCP in both the liquid and solid phases.
Sorption of both compounds was rapid, with 60-80% occurring within one day, but the process appeared to continue at a slower rate over several months. Statistical analysis showed that there were no differences in sorption due to SOM content or chemical concentration, for the two silty loam soils used in this study. Desorption followed a similar pattern of a fast and then a slow stage, and a significant difference was measured between the two soils. Higher levels of SOM resulted in slower desorption and a lower total release of the contaminants, but both soils retained a large percentage of unextractable compounds. Contact time was found to have the greatest effect on the amount of this nondesorbable fraction.
The ultrafiltration study suggested that DOM polymerized into larger molecules after sufficient mixing time (3 months) in solution, which also increased the amount of 4c compounds that were bound to these humic substances. The biodegradation study suggested that natural soil microbes could utilize PCP and 4-MCP from both the liquid and solid phases, and that sorption to dissolved organics and colloidal matter could protect these chlorophenols from microbial degradation. Some data also indicated a possible correlation between desorption rates and bioavailability. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/46082 |
| Date | 04 December 2009 |
| Creators | Young, Riki G. |
| Contributors | Environmental Engineering |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | xi, 148 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 27407900, LD5655.V855_1992.Y686.pdf |
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