THESIS APPROVAL

ethanol to 250 g unspiked sediment and stirring the mixture for 1 h. The sediment was
kept at 4 °C until the start of the experiment.
4.3 Test Conditions
The test was evaluated using a 96 h static short-term sediment toxicity
test. There were five replicate test chambers per treatment. Each test chamber
consisted of 600 ml glass beaker with 2-3 cm depth sediment and 400 ml of overlying
water. A hundred of worms per test chamber were used as test organisms. They were
not fed during the exposure period. No aeration was provided for each test chamber.
The water overlying was prepared using deionized water. Test chambers were
covered with a sheet of polyvinylchloride cling film to prevent the evaporation of
naphthalene out off the test medium. All test chambers were conducted at room
temperature with a daily photoperiod of 12 h and kept under the following conditions:
pH, 6.91±0.25; dissolved oxygen, 2.51±0.41 mg/l.
4.4 Exposure Study
1) Range-finding Test
Since there was no reliable data on the toxic level of naphthalene to
L. hoffmeisteri, preliminary test was conducted to find the critical range at first. This
range was defined as an interval between the highest concentration that killed all
worms and the lowest concentration at which all worms survived during the exposure
time (96 h). To determine the critical range, concentration of naphthalene 0.1, 1, 10,
100 and 1,000 µg/g sediment wwt were prepared. The observed result was performed
to determine the concentrations for the definitive test.
2) Definitive Test
Suitable range for the definitive test was determined with five
nominal concentrations (6.25, 12.5, 25, 50 & 100 µg/g sediment wwt as shown in
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