THESIS APPROVAL

Changes in bottom sediment in the lower Chao Phraya river were fluctuated
accordingly due to the industrial and domestic activities along the river bank. High
sedimentation occurred along the shoreline since the bulks of organic matter were
released to the water column. During the occurrence, there was significant shift in
sediment characteristics. High organic content appeared in urbanized and industrial
zones between 4.34 and 10.84%, while silt and clay fractions were recorded high
value in the coastal area from 41.44 to 99.22% (Kanchana-Aksorn and Petpiroon,
2006).
3. Contamination of PAHs
Anthropogenic sources of PAHs in the lower Chao Phraya river were from
petroleum, sewage and industrial wastewaters, boating activities and incomplete
combustion of fossil fuels. Previous studies established that the contamination of
PAHs have been found in water, sediment and aquatic biota. Wattayakorn (2003)
reported that the concentration of total identified PAHs were found in the water
samples ranging from < 5-1,500 ng/l, and several PAHs, such as naphthalene,
acenaphthylene, acenaphthene, fluorine, phenanthrene and anthracene, were
identified. Nokyoo (1995) reported that the sediment samples contained 2-6 rings
PAHs and the average concentration of total PAHs ranged between 1.93–2.14 µg/g
dwt. Mussel Perna viridis samples collected from the mouth of Chao Phraya river in
this study contained PAHs including naphthalene, biphenyl, fluorine, anthracene,
fluoranthene, pyrene and chrysene with individual PAHs concentrations ranging from
15.64-76.8 ng/g dwt.
4. Benthic Communities
The settling and the accumulation of PAHs in the bottom sediments of the
lower Chao Phraya river cause change to the structure of benthic communities (Suess,
1976). It can promote the abundance of some tolerant species recognized a pollution
indicator (Chapman and Brinkhurst, 1984; Heip, 1992; Peterson et al., 1996).
Previous study on the macrobenthic communities reported that oligochaete was
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