Distribution of Total-Mercury in Different Tissues of Fish Eating Birds along the Volta Lake, Ghana.

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2013-12-17
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Abstract
The distribution of Total mercury (THg) concentrations was determined in ten (10) different tissues of four different species of fish-eating birds from the Volta Lake, Ghana. The four species of fish-eating birds analysed in this study were Yellow billed kite (Milvus migrans parasitus), Squacco heron (Ardeola rolloides), Little egret (Egretta garzetta) and Grey heron (Ardea Cinerea). Elevated levels of total mercury were found in all the tissues studied and were found to increase with body weight/age of the birds. Correlation analysis showed a very high positive relationship between concentrations of total mercury found in the tissues and weight/age of the birds. Highest total mercury concentrations were found in the liver, kidney and feather tissues of all the birds and they appeared to be the most preferred organs for mercury accumulation in the birds analyzed in this study. The order of mercury accumulation in the tissues obtained was as follows: lungs < heart <brain < gizzard < intestines < flesh < blood < kidney < liver < feather. Total mercury concentrations in the tissues of Little Egret, Yellow Billed Kite, Squacco Heron, and Grey Heron ranged from 0.91-1.78 µg/g; 0.43-2.14 µg/g; 0.85-1.92 µg/g and 0.77-2.86 µg/g respectively. The highest mean concentration of total mercury (1.84 ± 0.40 µg/g, range 1.40-2.86 µg/g, n=10 ) was found in Ardea cinerea, followed by Ardeola ralloides (1.40 ± 0.15 µg/g, range 1.19-1.65 µg/g n=10 ) , Egretta garzetta (1.38 ± 0.10 µg/g, range 1.24-1.58 µg/g, n=10 ) and milvus migrans parasitus (1.32 ± 0.19 µg/g, range 1.00-1.78 µg/g, n= 10). The highest mean concentration of mercury found in the grey herons (Ardea cinerea) suggests that they feed at a higher trophic level and prey on bigger fishes. Although the study reported elevated levels of total mercury concentrations in the tissues of the birds, they were however far lower than the threshold level (25-60 µg/g w.w.) known to be detrimental to the health of the birds and humans and as such the Volta Lake has not been impacted so heavily as far as mercury pollution is concerned.
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A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirement for the award of Master of Philosophy in Analytical Chemistry, June-2013
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