THESIS APPROVAL

low level of DO had thoroughly occurred in E-NH with no worm colony. From this
result, it could be implied that the decrease in TOM in sediment and consequent
increases of DO concentration in E-WH might reflect the bioturbation process
improved by the worms. This biological activity was also observed by Levin et al.
(2003) with the burrowing behavior of freshwater oligochaete Olavius crassitunicatus
to be caused an effect on the increase of DO. Thus, the biological activities of
L. hoffmeisteri from this study should therefore consider encouraging the
decomposition of organic matter in the sediment which provides an aerobic condition
through the connecting water.
The results of this preliminary study suggest that L. hoffmeisteri has
possibility to reproduce under laboratory conditions supplemented with organic
sediment. Additionally, the biological activities such as feeding habit and burrowing
behavior have significant effect on the status of the whole sediment and presumably
on the overlying water. These observations are available to use L. hoffmeisteri as a
biological indicator since high level of food has promoted to the specific growth, and
also behavioral change occurring in the presence of less oxygenated water. Based on
these obtainable data, it could be determined that L. hoffmeisteri collected from Chao
Phraya estuary might be adopted for further study which extremely focuses on using
as an organism in sediment toxicity test, as well as successfully employed as the
bioassay in the temperate region (e.g. Keilty et al., 1988; Meller et al., 1998;
Flores-Tena and Martinez-Tabche, 2001).
4. Acute and Sublethal Toxicity of Sediment-Associated Naphthalene
4.1 Acute Toxicity
All statistical values for L. hoffmeisteri obtained in this study are
expressed as µg naphthalene/g wet sediment because this work was carried out
toxicity tests with naphthalene dissolved in ethanol and spiked in sediments. In
addition, as L. hoffmeisteri is benthic species, the decision was made to evaluate
naphthalene toxicity in sediments. In contrast, most reports on toxicity test of
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