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Estudo da composição isotópica de Pb em organismo bentônicos, poliquetas (Namalycastis abiuma) e oligoquetas, da Baía do Guajará e rio Guamá
(Universidade Federal do Pará, 2009-06-24) OLIVEIRA, Simone Pereira de; ROSA FILHO, José Souto de; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
In Guajará bay (Terminal Petroliferous do Miramar and mouth of Una Canal) and in Guamá river (mouth of Tucunduba creek), three samples of bottom sediments, three of polichaetes (Namalycastis abiuma) and five samples of oligochaetes (Tubificidae) were collected. In the biological samples lead (Pb) concentration and isotope composition were determined, whereas in the sediments samples only the Pb isotope composition was. Pb content was quantified in two representative samples of oligochaetes and polichaetes. Concentrations of 5 mg.kg-1 and 3 mg.kg-1, was obtained for these organisms, respectively. Pb concentration determined in oligochaetes was equivalent to 13% of the lead’s level of the bottom sediments of its habitat (38 mg kg-1). In spite of the Pb content of the bottom sediments of Guajará bay may suggest moderate pollution, this proportion can be considered high when it is compared with the percentual relation of 1,7% of oligochaetes and sediments of very polluted environments (p. ex. botton sediment lakes of India with lead content reaching 2.260 mg.kg-1 and oligochaetes with until 23 mg.kg-1). This result suggests that, proportionally, oligchaetes may assimilate greater amount of lead of its habitat in less polluted environments. However, the lead level in oligochaetes compared with the lead level in sediments of its habitat, showed a positive correlation, and it indicates that oligochaetes can be used as a bioindicator. The polychaetes (Namalycastis abiuma), did not show a trend that indicates any type of connection or correlation between lead level in organisms and lead level in sediments. This result indicates that polichaetes cannot be used as bioindicator of the enrichment of lead (and metals) in its habitat. Lead isotope composition of the bottom sediments in Guamá river, gave the value of 1,193 for the 206Pb/207Pb ratio which is different to the suggested a value of 1,194 for the bottom sediment of the Guamá river, and interpreted as the natural value (geogenic). This indicates a anthropogenic origin of lead in Guamá river in the sampled point (mouth of the Tucunduba creek). In Guajará bay, the sample of sediment in the mouth of the Una Canal, presented a value of 1,167 for the reason 206Pb/207Pb. In previous works, this value had been suggested as indicative of lead of anthropogenic origin. This value of 206Pb/207Pb ratio shows that the Una canal is contributing to lead level in the sediments of the Guajará bay, through of discharge of domestic effluent and solid residues. Finally, in a sediment sample collected in the Terminal Petroliferous do Miramar, also in the Guajará bay, the value of the 206Pb/207Pb ratio was 1,188. This value is lower than that suggested as natural value of the 206Pb/207Pb ratio in the bottom sediments of the Metropolitan Region of Belém, which is of 1,200. This lower value can be related to activities of the Terminal Petroliferous do Miramar. The products originated in oil have an important potential of heavy metal (including lead) dissemination to environment. In order to compare the lead isotope signature of the organisms with that of the sediments the values of the isotopic ratio 206Pb/207Pb of the organisms were divided by the respective values of thIs ratio in the sediments. If the resultant quotient, represented as R, had a value of 1± 0,004 (0,996 ≤ R ≤ 1,004), it was considered as indicative that the lead isotope signature of the organisms reflected the signature of the bottom sediments of its habitat. The values of R in 75% of the biological samples were within the interval (0,997 ≤ R ≤ 1,001). The other 25% that remain outside of this tolerance interval, correspond to the two samples of oligoquetas collected in the mouth of Una Canal. Thus, the three samples of polichaetes collected next to the Terminal Petroliferous do Miramar, and the three samples of oligoquetas collected in the Guamá river next to the mouth of Tucunduba creek show values of R within the tolerance interval. This suggest that the polichaetes (Namalycastis abiuma) and oligochaetes reflected the lead signature isotope of the environment in which they are inserted, and are good bioindicators of lead isotope composition in its habitat.