Field and Laboratory Studies on Heavy Metal Uptake and Tissue Distribution, ATPase Activity and Metallothionein in Tissues of the Norway Lobster Nephrops norvegicus (L.)
1). Heavy metal concentrations in sea water and sediment vary widely in different parts of the world. An important factor affecting heavy metal concentrations in an area is man-made contamination. 2). Heavy metals inhibit or alter many biological processes in decapod crustaceans and toxic effects of heavy metals vary depending on experimental animals, metals and concentrations used. The most important factors which affect toxicity and accumulation of heavy metals by marine animals are the growth, sex, age and physiological condition of marine animals, salinity and temperature of sea water, chemical characteristics of metals and interaction among metals. Tolerance to heavy metals and detoxification of heavy metals are also important factors influencing toxicity of heavy metals to marine animals. 3). The thesis outlines consequences of heavy metal pollution for marine animals and humans who consume these. I then describe the Clyde Sea area, its commercial importance and man-made contamination and the biology of an important commercial species the Norway lobster Nephrops norvegicus. 4). Natural concentrations of cadmium, copper and zinc in tissues of Nephrops norvegicus from the Clyde Sea area were highest in the hepatopancreas and gill, whereas mercury concentrations were found in highest levels in the gill and tail muscle. Iron concentrations were highest in the gill. Concentrations of metals showed variation among different months of the year with highest levels tending to occur during moult. Metal concentrations were also influenced by carapace length with pronounced size-related increases in mercury concentrations in the tail muscle and cadmium in the hepatopancreas. There were considerable differences in mean concentrations of some metals in the tissues of male and female Nephrops. 5). Toxicity studies showed that organic and inorganic mercury, copper, cadmium, lead and zinc (0.1, 0.1, 0.1, 1, 1 and 2 mg 1-1 respectively) were toxic to Nephrops norvegicus. At those concentrations toxicities ranged widely among the metals, the most toxic metals to the animals being organic mercury (100 % mortality in three days), inorganic mercury (100 % mortality in one week) and copper (100 % mortality in two weeks). The other metals did not cause 100 % mortality over a 30- day period. 6). The non-essential metals (organic mercury, inorganic mercury, cadmium and lead) were accumulated by tissues of Nephrops norvegicus after exposure to sublethal concentrations of the metals dissolved in sea water for 30 days. The highest concentrations of both mercury compounds were accumulated in the gill tissue while the highest concentrations of cadmium were in the gill and hepatopancreas. Lead concentrations were highest in the gill and carapace. Exposure to a sublethal concentration of copper showed increases in copper concentrations in the carapace, gill, tail muscle and ovary, whereas there was no increase in the hepatopancreas and external eggs. Exposure to a sublethal concentration of zinc also showed increases in zinc concentrations of the carapace, hepatopancreas gill, and ovary, whereas there was no increase in the tail muscle and external eggs. 7). There were differences in the accumulation of organic and inorganic mercury from sea water by tissues of Nephrops norvegicus. Except in the gill tissue, organic mercury was accumulated more than inorganic mercury. There were also sex related differences in the accumulation of the metals as male Nephrops accumulated higher concentrations of organic and inorganic mercury in the hepatopancreas than female Nephrops. Carapace length showed significant effects on metal accumulation as accumulation of both mercury compounds and cadmium was higher in the gills of smaller animals than that of larger animals. The adsorption of the metals onto the carapace surface was found to be very important in determining the metal concentrations of the carapace. 8). Concentrations of mercury increased in all the tissues of Nephrops norvegicus after feeding with a food source containing high concentrations of cadmium and mercury. These increases in the tissues showed positive relationships with feeding rate. Cadmium concentrations increased only in the hepatopancreas. Cadmium concentrations in the hepatopancreas and carapace showed positive relationships with feeding rate. Concentrations of copper in the gill and tail muscle were increased after feeding, though none of the tissue copper concentrations showed a positive relationship with feeding rate. Zinc and iron concentrations in the tissues of Nephrops did not increase after feeding and, there was no positive relationship with feeding rate in any tissues. 9). Distribution of mercury and cadmium in the gill, hepatopancreas and tail muscle of Nephrops norvegicus differed among treatments. Mercury burdens in control animals were mainly in the tail muscle. After feeding, the hepatopancreas and tail muscle shared the total mercury burdens. Organic and inorganic mercury distributions also varied among the tissues after uptake from sea water, with organic mercury being more evenly distributed among tissues than inorganic mercury, the latter being predominantly in the gill. Much of the cadmium burden was always in the hepatopancreas in all the three treatments. Assimilation of organic mercury from food by tissues was higher than assimilation of inorganic mercury. (Abstract shortened by ProQuest.)
