Assessement of polycyclic aromatic hydrocarbon(PAH) distribution in sediment and water samples of Winam gulf,Lake Victoria,Kenya

Abstract

Polycyclic aromatic hydrocarbons (PAH) commonly refers to a large class of organic compounds containing two or more fused aromatic rings. They comprise unsubstituted parent PAH and their alkyl-substituted derivatives. They are colourless, white, pale yellow or green solids with melting and boiling points generally above 100DC. They have their origin in both natural and anthropogenic processes. However several studies have indicated that the anthropogenic input of PAH to aquatic environment far exceeds natural sources. Major human activities which produce PAH include pyrolysis of wood to produce charcoal and carbon black, coke production, manufacturing of gas fuel, power generation from fossil fuels, combustion of fuels in internal combustion engines, incineration of industrial and domestic wastes, oil refinery processes and chemical engineering operations among others. By-products of these processes, which contain significant amount of PAH, have been dumped on land, in the waters or buried at subsurface sites. Airborne particulates, generated from these processes and carrying PAH, are transported worldwide in the atmosphere and usually find their destination in soils and in sediments of aquatic systems. PAH are of concern in the environment not only because they are ubiquitous contaminants and recalcitrant towards degradation, but also because several members of this class of compounds are well-documented carcinogens. Some, while not carcinogenic, may act as synergists in carcinogenicity. In this study, sediment samples from two sites, Kisat and Car Wash, and water sample from Car Wash site of Winam Gulf of Lake Victoria were investigated for the sixteen PAH listed in the United States Environmental protection Agency(USEPA) priority pollutant list.The variation of the detected PAH with season and distance inshore was also investigated.Sampling for sediment samples was done with a surface grap sampler.Extraction was according to United Nations environmental programme protocol number 20,1995 while purification was according to Christopher et aI., 1995. Analysis was done with GC-FID and results confirmed with GC-MS. The sixteen target PAH were detected in the sediment and water samples,. with concentrations in the range of 0.04 to 16.46 ug/g for sediment samples and 3.32 to 55.8 ug/L for water samples, which is an indication of significant pollution of the Gulf by individual PAH. Sediment samples were found to contain relatively higher concentrations of PAH than water samples. The mean concentrations were found to exhibit significant differences (P:S0.05) with seasons and depths, however the degree of significance could not be established in the cases since only two means were compared. The total amount of individual PAH detected in wet season samples was higher than those detected in dry season samples. The study also shows that the total PAH concentrations in sediment and water samples and the distribution of individual PAH in the samples were different. Water samples predominantly accumulated the lower molecular weight PAH; while sediments accumulated the higher molecular weight PAH. The total amount of PAH detected in sediments samples taken 5m from .the shore was much higher than those detected in sediment samples taken 1m from the shore. Similarly,the total amount of PAH detected in water samples taken Sm from the shore was less than those detected in water samples taken 10m from the shore. There was also significant differences for the distance and seasonal interactions. Most lower molecular weight PAH <.." like naphthalene and acenaphthylene only showed significant differences 1m from the shore and not Sm from the shore for sediment samples, even with changes in seasons. Most higher molecular weight PAH like Chrysene and pyrene showed significant differences at Sm distances from the shore with seasonal variations. In the water samples, the lower molecular PAH such as acenaphthylene andacenaphthene did not show significant differences with distance, even with seasonal variations. This was also observed with higher molecular weight PAH like benzo(a)anthracene, chrysene and benzo(ghi)perylene. The average individual PAH accumulation levels in the.Car Wash water samples were found to be several magnitudes above the internationally recommended exposure levels. The detected levels were above the Environmental Protection Agency (EPA) carcinogenic accumulation level per kg human body weight for anthracene, acenaphthene, fluoranthene, fluorine and pyrene .. This study therefore showed that Winam Gulf of Lake Victoria is significantly polluted with the investigated PAH. It has also showed that the pollution of the Gulf by the PAH is dependent on season and the distance inshore. This being the first report for this region, the information contained can be vital to environmental conservation organizations and to Kisumu City planners since the City is probably the highest contributor to this pollution.