Increasing urban environmental pollution and human impact have led to a deterioration in water quality. Heavy metals are a particular group of contaminants in water reservoirs. They are highly significant ecologically, since they are not removed from water through self-purification, but rather accumulate in reservoirs and enter the food chain through bioaccumulation and biosorption processes. The Almendares and Quibú rivers are the most important freshwater systems in the Cuban capital, and they receive wastewater from industry and domestic sewage. The Metropolitan Park of Havana (PMH) has been developed along the last 7 km of the Almendares River. As an urban project, the PMH has several attraction sites spread over 700 hectares of land in the centre of the city. The pollution of the river could affect the health of the people who enjoy the Park.
The objective of this work was to determine metal concentrations in biological samples collected from the following polluted Cuban rivers: Almendares and Quibú. For the study, sediments and biological samples such as fish, crabs, molluscs, plant leaves and plant roots were analysed. For large fish, the muscle, digestive system and liver were processed separately. For large molluscs, only the soft internal material was taken. For small fish, crabs and small molluscs, the whole mass of these organisms from the same sample station was processed together. Plants were processed individually. All samples were dried at 80oC for 72 hours, then macerated and stored in plastic bags at room temperature. Acid digestion in closed vessels and microwave heating were performed to release metals from the samples. Multi-elemental metal analysis of Al, Co, Cr, Cu, Ni and Zn was carried out by means of inductively coupled plasma atomic emission spectrometry (ICP-OES). The concentrations of the toxic heavy metals Cd and Pb were analysed through graphite furnace atomic absorption spectrometry (GFAAS). The results obtained indicate that each organism tends to retain one or more metallic elements, and the plants roots are able to concentrate a large spectrum of metals, including toxic metals. Not all metallic pollutants present in the aquatic system are able to affect the biota, and the bioaccumulation process does not depend directly on metal concentration.
There are other factors that seem to influence this phenomenon. Significant corrélations were determined for Al-Zn, Al-Pb, Al-Cd, Cr-Cu, Cr-Ni, Cu-Ni, Cu-Zn, Cu-Pb, Cu-Cd, Ni-Zn, Zn-Pb, Zn-Cd and Pb-Cd. Taking into account the correlations found, some metals, such as: Al, Zn, Cd and Pb; Cr, Cu and Ni; Cu, Zn, Cd and Pb, seem to be related by synergic and/or antagonist mechanisms in the bioaccumulation process. In general, the concentrations of Cd and Pb found in fish exceeded the maximum limits for human consumption, which is 0.5 μg cadmium g-1 dry weight and 2 μg lead g-1 dry weight. The present work contributes to the assessment of metal pollution in significant waterways in the Cuban capital, as well as to knowledge about availability, bioavailability and metal interactions.
30 April 2008