Mercury contamination in fish from the marine environment in Ghana
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Date
2005-11-10
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Abstract
In this study, concentrations of total mercury (Hg) were measured in the edible muscle tissues of fish samples from the Atlantic Coast of Ghana between November 2003 and May 2004 using a simple, rapid and accurate method which involves a mixture of HNO3, HC1O4 and H2S04 used for complete oxidation of organic tissue and mercury detection by the Cold Vapour Atomic Absorption Spectrometry (CVAAS) technique using an automatic mercury analyzer developed at the National Institute for Minamata Disease (NIMD) in Japan.
In general mercury concentrations increased with increase in trophic levels. Mercury concentrations were generally highest (mean=0.093 μg g-1) in high trophic level predatory fish, for example the highest mean• mercury concentration (0.047 μg g-1) was found in Argyrosomus regius which is a high trophic level carnivore, followed by middle trophic level predatory fish (mean=0.063 μg g-1). Lower mercury concentrations were seen in low trophic level fish (mean=0.047 μg g-1).
Mercury levels positively correlated with the weight of two tuna species namely auxis thazard thazard (P<0.0l, r=0.952) and thunnus albacares (P<0.0l, r=0.927); and also with the fork length of the two species, r=0.927 at P<0.01 for auxis thazard thazard and r = 0.740 at P<0.05 for thunnus albacares. These determined relationships corroborate the occurrence of biomagnification of mercury in these species.
All fish species analysed in this study had total mercury concentrations less than the WHO limit of 0.5 μg g-1 wet weight. The low concentrations of mercury detected in the samples do not appear to constitute any significant health hazard to the general population.
Total concentrations of mercury in the internal organs of tuna fish were in the order
Liver>Duodenum>Heart>Intestine>Gonads>Stomach>Gills according to LSD and Tukey Ad Hoc Tests.
Overall, total mercury concentrations were found to increase with fish weight, fish length and trophic level. These findings are consistent with observations from other studies that have shown that predatory fish bioaccumulate mercury over time.
Description
A thesis submitted to the Department of Chemistry in fulfilment of the requirements for the degree of Master of Philosophy (Analytical Chemistry), 2005