THESIS APPROVAL

(1988) who investigated subacute responses of L. hoffmeisteri exposed to endrin in
sediment. Likewise, Lotufo and Fleeger (1996) demonstrated that sedimentscontaminated
pyrene and phenanthrene caused reduction of egestion rate and
reproduction of L. hoffmeisteri. As a result of this study, however, neither worm
biomass nor feeding rate has been assessed. For further investigations it should be to
attend in these terms as mentioned above to the better explanation of a reduction in
reworking activity which affects the population dynamics of L. hoffmeisteri.
In the present study, lethal as well as sublethal effects demonstrated a
dose-response relationship. It was found that the EC50 values of autotomy for
L. hoffmeisteri are nearly about 2 times lower than the LC50 values, while the EC50
values of sediment avoidance are similar to the LC50 values. This level of response
suggests that naphthalene have more potential to change morphological feature than
directly killing individuals. In contrast, from that level, it could be said that
evaluation of burrowing behavioral alteration is as good as assessing on mortality.
The observation also implies that loss of the posterior end of the worms may be more
sensitive indicator of environmental impact of chemical pollutants.
There are many other factors that may have some influences on the toxic
effects of naphthalene in this study such as experimental procedures, chemical and
physical characteristics conditions (Reynoldson et al., 1996). Another factor which
may affect the toxicity of naphthalene is different constituent corporating in the
species of organisms used. For instance, Sager and Pucsko (1991) found that
different feeding behavior of animals could be an important factor which may have
affected the toxic stress. Reynoldson et al. (1996) suggested that genetic variability
of organisms may cause differences in the responses to toxicant. Moreover, Klerks
and Bartholomew (1991) stated that distinct physiological mechanisms of
oligochaetes seem to have a key function with respect to the availability of toxicants
within the organisms. From these documented data, it is recommended that more
laboratory works are necessary to examine the interaction between these variability
and the animal bioassay. The benefit of the anticipated data could be available for
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