A. Hall

Sources and sinks of mercury in the coastal lagoon of Aveiro, Portugal

Abstract Surface sediments collected from 67 locations throughout the Lagoon of Aveiro, Portugal and cores from five sites representing areas of heavy and moderate pollution from a chloralkali plant, slight pollution from sewage discharges, and unpolluted environments were analyzed for total mercury. The mercury concentration reached 180 mg kg −1 dry sediment in the most polluted core. Away from the areas affected by the discharges of the chloralkali plant, the mercury concentrations in the surface sediments were −1 . The background concentration of mercury in the lagoon sediments is 0.14 mg kg −1 , and in the sediments of the intertidal areas of the Atlantic beaches 0.065 mg kg −1 . The most important contributor to the mercury content of the lagoon (estimated to be 80 tons) is the chloralkali plant, followed by sewage discharges, and natural sources. Most of the mercury is trapped in the sediments close to its source with gradients of 1000 mg/kg per kilometer and 500 mg/kg per meter depth.

Influence of inorganic lead on the biochemical blood composition of the eel, Anguilla anguilla L.

Yellow eels (Anguilla anguilla L.) with an average weight of 50 g were caught in September in the Aveiro Lagoon on the Portuguese West Coast and kept in aerated aquaria for 1 week before the experiment started. The eels were exposed to an inorganic lead concentration of 300 micrograms Pb/liter for 30 days. Differential white blood cell count showed an increase in the number of lymphocytes in exposed fish. Blood hemoglobin and number of red blood cells per cubic millimeter showed no differences between the control and the exposed fish. Biochemical analyses of blood composition, such as plasma glucose, total plasma protein, total plasma cholesterol, and sodium and potassium plasma, showed no differences between treated and control animals. Plasma lactate levels increased in treated animals compared with those in controls.

Metabolic effects of kraft mill effluents on the eel Anguilla anguilla L

Yellow eels (Anguilla anguilla L.) with an average weight of 60 g were used in this experiment. The fish were caught in June/July at the Aveiro Lagoon on the Portuguese West Coast, transported to the Department of Biology, Aveiro University, and kept in aerated aquaria for 1 week before the experiment started. The eels were then exposed for 1 and 3 weeks to 75 and 50% of the kraft pulp mill effluent. The eels exposed to the kraft pulp mill effluent developed an increase in red blood cell number per cubic millimeter and several biochemical changes, such as an increase in plasma lactate and sodium and a decrease in plasma pyruvate and potassium. Histological examination of the experimental eels exposed to the 50% kraft pulp mill effluent revealed deep alteration of the tissue structure, such as disruption of the skin and edematous hypertrophy of covering epithelial cells in secondary gill lamellae. The kidney had damage of the renal tubules. The liver developed necrosis supported by a significant decrease in GOT and GPT activity. The spleen had an increase in blood content as well as in pigment centers. Previous results indicated the kraft pulp mill effluent causes tissue damage and consequent metabolic changes in the eel Anguilla anguilla L.

Some ecological aspects of the Cabora Bassa dam

Abstract Man-made lakes are fast multiplying, particularly on the developing continent of Africa. The latest, Lake Cabora Bassa on the Middle Zambezi, began to fill on 5 December 1974 and is expected to produce electricity by September 1975. As with all new large reservoirs, the formidable engineering problems have been overcome at great cost. However, little attention has been paid to the consequences of the barrage on the valley ecosystem. Some of the major ecological problems, such as aquatic infestant macrophytes, effects on man in terms of health and welfare and the effects on the river downstream from the dam, are discussed. If care is taken to set up a dialogue between engineer and ecologist, then some of the problems can be avoided or at least foreseen. There is a great need for conservation legislation in order to protect certain elements of the Zambezi ecosystem in Mocambique from over-exploitation and ignorance. Wise conservation management—setting up of game parks and reserves, management of tourism, fishing restrictions, etc.—must be brought into effect ab initio if the full potential of Lake Cabora Bassa is to be realised and safeguarded. With sparing use of such legislation, Cabora Bassa could become one of the most important resources in the development of Mocambique.

Cabora bassa: Some preliminary physico-chemical and zooplankton pre-impoundment survey results

Abstract1.This paper outlines the preliminary results of physico-chemical analyses and the examination of the zooplankton of the Middle and Lower sections of the Zambezi in Mo\ccambique. Comparison is made with the pre-Kariba river in Rhodesia and water from Lake Kariba in 1965, indicating that the Middle Zambezi in Mo\ccambique is now richer in inorganic nutrients, possibly due to the enriching effects of both the Kariba and Kafue Dams.2.The major changes in the Lower Zambezi occur under the enriching influence of the Chire River from Lake Malawi.

Concentration of trace metals from natural waters by freeze-drying prior to flame atomic absorption spectrometry

Abstract Freeze-drying is shown to be as effective as solvent extraction or chelating ion exchange for concentration of Fe, Mn, Ni, Al, Cr, Cu and Cd from fresh-water samples.