A Comparative Fate Study of the Diesel Associated Polycyclic Aromatic Hydrocarbons by Polychaete Worm, Marphysa Macintoshi in Coastal Sediment: Combined Field and Laboratory Experiments.


End date: 31 July, 2015 Project type: BSU Students' Master Thesis Project code: mhh13-2A1 BSU Countries: Tanzania Lead institution: Roskilde University (RUC), Denmark Project coordinator: Talhiya Maulid Ali

Project summary


The level and fate of diesel oil-associated pollution in coastal marine sediment was investigated along the coastline of Chake-Chake bay at Wesha, Pemba, in Zanzibar-Tanzania; following a long-term discharge of the residual diesel oil from a nearby power plant from 1992-2010; likely leading to accumulation of the petroleum hydrocarbons in the coastal sediment. So far, no studies have been conducted and there is no existing published documents stating the pollution status of the area. An initial extensive screening study was first conducted in the study area to determine the total organic matter content of the sediment, as well as the pollution level in both surface sediment and sediment cores. The actual study, which combine laboratory and field experiment, was conducted to investigate the role played by polychaetes; Marphysa macintoshi as the major residence species in determining the fate of PAHs in the study area. Surface, sub-surface and core sediment samples were collected from a grid system of 12 sub-stations. Extraction (sediment, water and tissue) were done using Quick Easy Cheap Effective Rugged and Safe (QuEChERS; for screening phase) and Pressurized Liquid Extraction (PLE; for experimental phase) techniques and analysis was done by Gas Chromatography and Mass Spectrometry (GC-MS) instrument.
The mean % organic matter of the sediment was less than 1%. Based on the US 16-priority pollutants, the total of 13 PAHs (naphthalene, acenaphthylene, acenaphthene, anthracene, fluoranthene, pyrene, benzo(a) anthracene, chrysene, benz(b) fluoranthene, benzo(a) pyrene, indeno 1,2,3 cd-pyrene, dibenz ah-anthracene and benzo ghi perylene) were analyzed. Based on the most abundant chemicals in petroleum products; mixture of non-alkylated polycyclic aromatic hydrocarbons (NPAHs) and alkylated polycyclic aromatic hydrocarbons (APAHs) compounds were identified and low molecular weight (LMW) compounds being the most abundant. The result showed that the level of pollution is between moderate and high and the current observed PAHs concentration was below the effect range limits (ERL) suggesting the biological effect on the residence species could be low. However, the high PAHs concentration at deeper sediment layers (greater than ERM) indicates that the community has been impacted by the time the power plant is running. There is a poor plan and management of the environment with special concern on response to oil pollution in the study area. This is because the environmental law and policy are not specific and hence the implementation is not efficient as well.
The level of microbial degradation was higher in both the field and laboratory experiment compared to biotransformation. In both experimental set-up the up-take and hence accumulation of APAHs by M. macintoshi was higher compared to NPAHs. A comparison between laboratory and field experiments showed that M. macintoshi from the laboratory accumulate more (0.334±0.279 mg/kg ww) than that of the field (0.247±0.292 mg/kg ww) despite the use of the same sediment between the two experiments. It has also been shown that elimination of un-metabolized compounds was among the removal pathway of PAHs by M. macintoshi in both experimental set-up. Indeed,  the decreases in concentration of PAHs in sediment with worm and in the tissue for some PAHs indicates the presence of metabolizing system in M. macintoshi; however it seemed to be not effective for some of the PAH compounds.
 The discrepancy between laboratory and field results suggesting the importance to consider the relevance of these two environmental set-up in risk assessment so as to avoid over or under estimation of the risk. M. macintoshi found to work better in the field than in the laboratory. Despite that the M. macintoshi probably have a poor metabolic system, their bioturbating activity is known to play a significant role in the transfer of PAH compounds from the surface to the deeper sediment layers; therefore these worms may have a major influence on the fate of PAHs in this contaminated environment. Also, it has been found that APAHs are more resistant to microbial biodegradation as well as macro-faunal biotransformation; therefore, the result of this master thesis, should be useful in developing strategic plans for dealing with environmental issues like oil pollution in aquatic environments with special concern on the appropriate method to deal with APAH compounds; as well as in designing proper experimental set-up to provide a relevant result in environmental risk assessment studies. In addition the findings should be useful in regular monitoring to determine the long-term ecological impact and the fate of the current pollution.
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