Polycyclic aromatic hydrocarbons (PAHs) contamination in coastal mangrove ecosystems of the Zanzibar archipelago

The objective of this study was to determine the levels of polycyclic aromatic hydrocarbons (PAHs) in sediments and crabs in the mangrove ecosystems of Zanzibar. Sediments and crabs from eight sampling sites were analysed for eleven selected PAHs. Samples were extracted with dichloromethane by ultrasonication, cleaned-up using column chromatography, and concentrated using a rotary evaporator. GC-MS was used in the analysis of the samples. In general, all eleven PAHs were detected in crab and sediment samples. Total concentrations of PAHs ranged from 1.70 to 28.66 ng/g fresh weight (fw) in crabs, and from 20.14 to 81.94 ng/g dry weight (dw) in the sediments. The levels of the PAHs are thought to be related mostly to petrogenic and pyrogenic sources from anthropogenic activities. The results from this study demonstrated the existence of PAHs contamination in mangrove ecosystems of Zanzibar, and it is recommended that a PAHs contamination monitoring programme be established.