Speciation and quantification of organotin compounds in Lagos harbour, Nigeria

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Abstract
The application of organotin-based antifouling compounds in the harbour during repairing and painting of ships in Nigeria harbour is a common practice in the maintenance wing of the dockyard. These antifouling chemicals are extremely toxic to aquatic life. As a result of dearth of data on the levels of organotin compounds in the West African coast including Lagos harbour, a study was undertaken to profile organotin compounds, in Lagos Dockyard harbour, Nigeria. The sediment and water samples were collected for two years (2016–2018) covering both the dry and wet seasons. A cold extraction technique by ultrasonication was used for sediments collected and a liquid-liquid separation technique was applied to water samples and later cleaned up by the use of silica gel-based packed column. The six organotin compounds considered in this work are Monobutyltin (MBT), Dibutyltin (DBT), Tributyltin (TBT), Monophenyltin (MPhT), Diphenyltin (DPhT), Triphenyltin (TPhT) were analysed by using an optimised high-performance liquid chromatography (HPLC). The result of the analysis on the sediment showed that the concentration of the organotin compounds (OTCs) ranges from 0.008 ± 0.00 to 272.710 ± 100.2 (ng/g) in MBT, 0.001 ± 0.00 to 69.780 ± 42.01 (ng/g) in DBT, 0.002 ± 0.00 to 7.110 ± 0.45 (ng/g) in TBT, 0.046 ± 0.01 to 76.210 ± 4.00 (ng/g) in MPhT, 0.070 ± 0.01 to 11.520 ± 0.62 (ng/g) in DPhT and 0.006 ± 0.00 to 2.330 ± 0.04 (ng/g) in TPhT. Higher values of OTCs were recorded during the wet season than the dry season and this was attributed to the dredging of harbour and remobilisation of organotin compounds from sediments into the water compartment. Principal Component Analysis (PCAs), Cluster Analysis (CA) and correlation analysis provided evidence for the interaction among these contaminants and possible sources of the contaminants. More so, the study showed that the degradation of these organotin compounds into their metabolites was governed by the influence of specific microorganisms. Therefore, regular monitoring of harbour was recommended for public safety.

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