Thesis and dissertation

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Browsing Thesis and dissertation by Author "Abdalla, Aida Mohamed"

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    Assessment if Polycyclic Aromatic Hydrocarbons (Pahs) in Marine Sediments and Edible Biota from Wesha Coastal Area in Pemba Island - Zanzibar
    (THE STATE UNIVERSITY OF ZANZIBAR, 2019-12) Abdalla, Aida Mohamed
    The levels, distribution and composition of PAHs in marine sediments and edible biota from western coastline of Wesha Bay in Chake-Chake Pemba were determined to assess the effects of long-term discharge of the residual diesel oil from a nearby abandoned power plant. The levels were determined using Gas Chromatography and Mass Spectrometry (GC- MS) instrument and the analysis targeted 16 PAHs of environmental concern as listed by USEPA. The analysis revealed a total of 7 PAHs in sediments namely naphthalene, acenaphthylene, fluorene, Pyrene, phenanthrene, anthracene and benz[a]anthracene. The same PAHs were detected in bioata with additional of benzo[k]fluoranthene and Indeno [1,2,3-cd]- pyrene making a total of 9 PAHs found in the analysed edible biota. Phenanthrene and naphthalene dominated the other PAHs in terms of detection frequency and concentration in sediments and biota respectively. The total concentrations of measured PAHs ranged from 6.88 to 156 ng/gww in sediments, and from 7.35 to 135.36 ng/g ww in biota. Analysis of spatial distribution of the PAHs was block C> block B> block D> block A and indicated significant correlation with organic matter content (R2 = 0.892) while the distribution trend in edible biota was C. Virginica > N .mutabilis >Mactralurida>C. ramosus>A.antiguata > A. subcrenata > L.cingulifera > M. bascii > N. albescensgemmuliferus > N. Echinatus. Composition of measured PAHs showed dominance of LMM in sediment and biota with overall contribution of 67 % in sediment and 55% in biota. This dominance of LMM confirm the petrogenic origin of the measured PAHs. The analysis also gave low Biota –Sediment Accumulation factor (BSAF) ranging from 0.11 to 1.92 indicating that most of PAHs are less stable and thus can dissipate or degrade before being taken up by the organisms. Comparison with sediment toxicity standards revealed that most of the measured levels in sediments were far below both the ERL and ERM values suggesting that the probability for biological effects to occur with respect to PAHs concentrations is very rare. Similarly, the levels of PAHs in edible biota were lower than maximum acceptable levels of different set standards suggesting that the biotas are safe for human consumption.