| Resumo: |
Red Sea water samples were collected from four stations in the Sudanese coast at depth of 10 m during July 2011 and analyzed for major ions and trace metals in order to determine their insitu concentration, their distribution patterns, and level of heavy metals contamination in the Sudanese coastal water. The data of the analysis was used in the preparation of the Red Sea artificial water which was used to study how salinity affects the photooxidation of 1,8-dimethylnaphthalene (1,8-DMN) and the water-soluble fraction (WSF) from Norwegian crude oil. The results show a small range of spatial variation for Na+, Mg2+, Ca2+, Cl−, K+, and SO2−4 . Also, the concentration of Na+, Mg2+, Ca2+, Cl−, and SO2−4 in the Sudanese coastal water is high compared to all other water basins and average seawater. The reason of this is the high evaporation and low precipitation in Red Sea.The concentrations of the major ions Na+, Mg2+, Ca2+, and K+ at the coastal stations are some what lower than at the other stations. This might be due to the adsorption of these ions by the suspended particles. Cu, Ti, As, Co, Cr, La, and Eu did not give any instrumental response, which means either that their concentrations in the Sudanese coastal water are below the detection limit of the instrument or the elements do not occur in the Sudanese coastal water. Thus, in order to detect their concentrations, preconcentration should be done or another more sensitive method should be used. The results show a low concentration of Sr (7.6 mg/L) compared to the concentration of Sr in average seawater (8 mg/L) and this decrease in Sr concentration may be due to the presence of Acantharians. Also, concentration of B is low compared to the concentration of B in average seawater and the reason for this is that boron is partly present in seawater as the neutral compound B(OH)3 which can be distilled from surface water in the tropics during evaporation process. Unfiltered seawater samples were collected from five stations in the Sudanese coastal water. The extractable organic matter (EOM) ranged from 1.3 to 10 mg/L with an average of 4.46 mg/L. The highest concentration of EOM was observed at the closest station to the coast. The dissolved/dispersed petroleum hydrocarbons (DDPHs) concentration equivalent to Sudanese heavy crude oil ranged between 15.84 and 95.92 μg/L with an average of 40.95 μg/L. The level of DDPHs at Sudanese coastal water does not affect the planktonic ecosystem. Photooxidation experiments of 1,8-dimethylnaphthalene (1,8-DMN) under artificial sunlight and natural sunlight in deionized water, Red Sea natural water, and Red Sea artificial water, revealed that the oxidation of 1,8-DMN in a dark environment is dependent on temperature. The results show that salinity has no effect on the photooxidation of 1,8-DMN. But it might affect the kinetic of the reaction. The results show that the nature of the oil affects the photooxidation of 1,8-DMN. The WSF from Norwegian crude oil consists of low molecular weight aromatic hydrocarbons. These compounds had disappeared after two days of irradiation. This reinforce photodegradation as an effective weathering process for the transformation of dissolved crude oil fraction, particularly in high solar radiation environments such as the Red Sea.
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