THESIS APPROVAL

USE OF FRESHWATER OLIGOCHAETE
(LIMNODRILUS HOFFMEISTERI) IN SEDIMENT BIOASSAY
INTRODUCTION
Lower Chao Phraya River, one of the estuaries in Thailand, has shown the
rapid increase in population growth and coastal development. The report from
Pollution Control Department (2001) revealed that the frequency of low dissolved
oxygen and high organic materials tends to be greater, particularly in the urbanized
and industrialized areas. The sources of pollution mostly come from urban industrial
wastewater, agriculture and domestic sewage disposal. These contribute to the
loading of organic pollutants, such as pesticides, heavy metals and petroleum
hydrocarbons, distributing to the water, and setting in bottom sediment of the estuary
(The Office of Environment Policy and Planning, 2001). The deposition of toxicants
in the sediment constitute one of several factors that cause change to the structure of
benthic communities since several chemicals are persistent and can bioaccumulate in
sediment-ingesting infauna (Suess, 1976).
Polycyclic aromatic hydrocarbons (PAHs) are one of the important organic
xenobiotics found in the bottom sediment of Chao Phraya estuary (Wattayakorn,
2003). Previous report by Nokyoo (1995) showed that the concentration of total
PAHs in sediment were in the range of 0.58-4.71 µg/g dwt. However, these levels
were low in comparison with other major world estuaries (e.g., Mille et al., 2007;
Oros et al., 2007). Sources of PAHs in this area originate from oil pollutions along
coastlines including major spills from freighters, tankers and other vessels going
aground and during emptying of oil contaminated ballast and bilged water. Apart
from these, the normal operation of coastal factories and mills adjacent to estuaries
often leads to oil leakage or seepage into water. The runoff due to rainfall also carries
oil from the highways, city streets and industrial areas into the estuary.
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