THESIS APPROVAL

It is well known that PAHs have a high toxicity for most organisms. The
PAHs are lipophilic in nature and gets integrated into biological systems through
uptake and accumulated by aquatic organisms with the potential to exert toxic actions
(Readman et al., 1982). High toxicity of PAHs has been found associated with the
water-soluble fractions of aromatic compounds dominated by 2-3 ringed aromatics
such as naphthalene (Anderson et al., 1974a, 1974b). Naphthalene is a very common
semivolatile PAH found in numerous petroleum products. Due to the low molecular
weight (128.18), less sensitivity to photo-oxidation and persistent nature in water,
naphthalene is considered as extremely toxic to the exposed aquatic animals
(Vijayavel and Balasubramanian, 2006a). Several researches on toxic effects of
naphthalene have been reported in aquatic biota, such as mysid shrimp Mysidopsis
bahia (Barron et al., 1999), amphipod Diporeia spp. (Landrum et al., 2003), and mud
crab Scylla serrata (Vijayavel and Balasubramanian, 2006a, 2006b). Most of all
demonstrated on water-borne toxicity, while the data related to toxic effects of
naphthalene in sediments are lack of publication.
Aquatic oligochaetes are macrobenthic invertebrate which often associated
with aquatic systems rich in organic matter. They also play a major role in processing
organic material and are a food source for benthic feeding fish (Kurata, 1994). Most
oligochaetes are relatively tolerant to many classes of chemical contaminants
(Khangarot, 1991). This tolerance may be a positive attribute for assessing
bioaccumulation or the toxicity studies of severely contaminated sites. Many
representatives of freshwater oligochaetes were commonly used for their propriety as
test organisms for the testing of chemicals, as well as for the ecotoxicological
assessment of sediment contamination (Phipps et al., 1993). For the laboratory
performing to characterize their tolerance to PAHs, apparent documents have been
reported in few species, such as the freshwater oligochaete Lumbriculus variegatus,
and the estuarine oligochaete Monopylephorus rubroniveus. These two species
efficiently accumulated and highly tolerant to several PAHs exposed in sediment
(Leppanen and Kukkonen, 1998b; Sheedy et al., 1998; Conrad et al., 2002; Weinstein
and Sanger, 2003; Hyotylainen and Oikari, 2004).
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