Identification of the extent of oil spill and its impact on water chemistry in Sundarbans reserve forest (SRF)

Abstract

One of the major problems frequently associated with oil spills over surface waters is the identification of the oils involved in the 'pill Identification and quantification of the oils is essential both to discover the source of spillage in order to prevent funhcr occurrences and to implement the remedial action. Methods for the determination of total petroleum hydrocarbons (TPH) in water samples were determined by gravimetry through solvent extraction, Mixture of solvents (80% nhexane and 20% methyl-Ierl-butyl ether) was used, The extraction of the sample was done at around ISoC for good recovery of the oil content and the detection limit was 3ppm, Water samples collected from different parts of the Sundarbans Reserve Forest (SRF), Khulna, the largest single-track mangrove forest, were examined for oil and grcasc content by Partition-Gravimetric techmque, This method was modified for lower concentration detection. The highest concentration of oil was 8,3ppm found into the Mongla Port and in most of the parts of SRF the concentration of other sampling areas found less than 3ppm. The reponed optimum concentration of oil and grease conI en! in aquatic environment is IOppm Since the toxIcity of hydrocarbon, depends on the specific types of oil, laboratory studies werc conducted for the determination of Volatile Liquid Hydrocarbon (VLH) in water samples by GC-FID tcchnique. For the extraction of the VLH, different solvents namely methyl-lerl-butyl ctherln-hexane mixture, trichlorotrifluoroethane (Freon-] 13), methylene chloride were used, The eluted hydrocarbon extracted with these different solvents were analyzed with a flame ionization detector (FID) and identified by their retention times relative to standard compounds. Benzene, toluene, o-xylene, m-xylene and p-cymene were Identified easily in methylene chloride extracted hydrocarbon in water samples, Accordingly all water samples collected from different location of Sundarbans Reserve Forest (SRF) were analyzed. In these cases the concentrations found were below the detection limits, These >pecilic hydrocarbons were identified in laboratory simulation through oil dispersion experiments, Since oil can contain small concentrations of metals such as nickel and vanadium. thc Ni content in water samples [i'om different locations of SRF were determined by Atomic Absorption Spectroscopy-Graphite Furnace Techniques (Model No . •• AAS Shimadju-6800) Thc maXllnUmconccntration of Ni (15,7662ppb) was obtained in Tinkona, which is thc estuary of SRF where as the minimum concentration was 1.41ppb obtained in Dangmari (Near Mongla Port) The obtained concentration is less than the maximum allowable concentration, The concentration pattem of Ni in SRF is not due to oil spillage, The sourcc of Ni in SRF may be geological or any other sourccs. An experimental study was conducted into the laboratory as microcosm approach in order to know the effect of oil (diesel) discharge on water chemIstry Before performing the experiment into laboratory, the important water quality parameters of samples from selected locations of Sundarbans Reserve Forest were determined, Four rectangular glass containers were setup for artificially oil (diesel) spilling. Waters taken in these glass contamers were collected from Dangmari stations, of SRf, Khulna The water quality parameters namely alkalinity, free COl, dissolved oxygen, chemIcal oxygen demand, suHate, chloride, hardness and major cations (1\'a, K, Ca and Mg) were determined at nearly weekly intervals, The study supports the degradation of OIl followed by reduction of dissolve oxygen and evolution of free C02 It also revels the decrease of hardness in water position of Ca"' or Mg2~,This might be due the complex formation of hydrocarbons wlih Ca and Mg, which maybe insolublein water.