THESIS APPROVAL

Figure 27 Dead worms under stereo microscope, 65x.
behaviors of L. hoffmeisteri when recorded as dead were different from the first
experiment. In control sediments, posterior end projected vertically into the water,
and then waved vigorously. In contradiction, worms were observed protruding their
tails above the surface of the sediment-contaminated naphthalene but did not respond
to a gentle mechanical stimulus to the posterior end (Figure 29).
4.2 Sublethal Toxicity
Observation of the worms exposed to sediment-associated naphthalene
revealed that naphthalene caused autotomy. The sign of symptom occurred at 96 h of
exposure at concentration of 25 µg/g wwt. The posterior region of the worm became
first constricted, and then isolated from the body. The isolated part then degenerated
and the tail was lost (Figure 30). In contrast, the control worms appeared to have no
morphological alterations with the posterior part had normal caudal regions. The
percentages of worms undergoing this process of autotomy increased proportionally
with the duration of the experiment and the naphthalene concentration. The 48, 72,
and 96 h EC50 were found to be 83.17, 46.77, and 35.48 µg/g wwt, respectively.
76