THESIS APPROVAL

pollutants in aquatic ecosystems (McElroy et al., 1987). Their feeding habit of
digging by head down into the sediment and defecate on the sediment surface have
perhaps the greatest impact on sediment conditions (Robbins et al., 1979; Robbins,
1982). Moreover, these sediment dwellers can cause significant particle and
contaminant movement by disturbing the surface. Their actions alter sediment
porosity using advective processes driven from below or by currents in the overlying
water (McCall and Fisher, 1980). In addition, Reible et al. (1996) found that the
movement of the tails of tubificid oligochaetes to the surface to improve oxygen
uptake led to an increase of pyrene released to the overlying water to about 50% of
that processed. Contaminants in the dissolved state or associated with colloidal
organic matter in the pore water will then be moved. Based on this evidences, it is
indicated that naphthalene in the sediment may removed by reworking activity of
dense population of L. hoffmeisteri.
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Another factor affecting decrease of naphthalene concentration in
sediment may be due to biodegradation. There is some data showing the loss of PAH
especially on the water soluble aromatics such as naphthalene with the major
degradation path being biological (Douglas et al., 1996; Prince et al., 2003).
According to the process of sediment preparation before the bioaccumulation test start,
the microorganisms may be present in the sediment test medium due to 4 °C storage
temperature. Leppanen and Kukkonen (2000a) said that sediment samples should
store frozen before the extraction to slow down possible degradation of PAHs.
However, it could not anticipate that the degradation product would be occurred in
this experiment because the method of the study was not covered expected
naphthalene derivative compounds. Nevertheless, it was visible from the present
results that sediment chromatogram showed a single peak with the same retention
time as the naphthalene standard present on the HPLC trace (Appendix Figure A3).
Based on this evidence, it might be suggested that biodegradation of naphthalene in
the sediment was not occurred or the rate of occurrence was probably slow because of
decreasing concentration by the time exposure.