THESIS APPROVAL

et al., 1994b), in dosed sediments aged less than 1 w. Based on these documents, it
may be concluded that the reduced uptake of naphthalene from sediment by
L. hoffmeisteri in this study might be occurred after 24 h of the exposure period.
The result in the present study corroborates with those of previous studies
concerning the rapid loss of naphthalene from the tissue of many organisms. Bates
et al. (1997) observed that when naphthalene contaminated invertebrates were
transported to uncontaminated waters, it was found to depurate rapidly from 24 h to
few weeks based on the life stages and exposure concentration. This finding was also
confirmed in the laboratory studies using annelids. Brunson et al. (1998) reported
that naphthalene tissue residues of freshwater oligochaete Lumbriculus variegatus
generally peaked by the starting and tended to decline to the end of the
bioaccumulation test. Harmoniously, accumulation of naphthalene from sediment by
marine worm Arenicola marina was rapid and almost complete depuration of the
accumulated naphthalene was observed after 24 h (Lyes, 1979). By comparing with
other higher molecular weight PAHs, the loss was shown in the same trend with
decreasing of such compounds but the elimination was appeared later. For example,
the parent compound of pyrene and benzo (a) pyrene accumulated in Lumbriculus
variegatus was depurated within 72 h in clean sediment (Leppanen and Kukkonen,
2000b). These supported evidences could be implied that high elimination of
naphthalene was possibly caused the rapid loss of this chemical from the tissue of
organisms.
Mean tissue residue of naphthalene reported here for L. hoffmeisteri in the
96 h sediment exposure was 1038±564.56 µg/g dwt with mean BAF value of
31.97±17.01. These values are considerably higher than that reported for other
annelids species exposed to the higher molecular weight PAHs. Nevertheless, time
for exposure in this study is distinctly different from the previous reports due to short
test period. For instance, the estuarine oligochaete Monopylephorus rubroniveus
accumulated fluoranthene-contaminated sediments with tissue residues and BAFs
ranged from 5,127-6,431 µg/g dwt and 23.0-1.6, respectively, in the 223-3,912 µg/g
treatment by the 10 d exposure (Weinstein et al., 2003). The tube-dwelling spionid
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