Assessment of Oligochaeta (Tubificinae) and Polychaeta (Namalycastis abiuma) as bioindicators of the lead isotope composition in its habitat: example of the guajará estuary, Belém (PA), Brazil.

Abstract

This study reports lead isotope data from benthic organisms (representatives of the classes Oligochaeta and Polichaeta) and bottom sediments samples, which were collected in the Guajara bay (Miramar and Una channel) and Guama river (Tucunduba Creek) in order to investigate if these organisms could be used as bioindicators in environmental studies. The comparison between the lead isotope signature of the benthic organisms and that of the bottom sediments of their habitat was performed by  dividing the values of the  ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁶Pb ratios determined in the organisms by the values of these ratios found in the sediments. When the value of the calculated quotient (R) was 1± 0.004 (0.996 ≤ R ≤ 1.004) the lead isotope compositions of the benthic organisms and that of the bottom sediment were considered similar. The values of R for 75 % of the biological samples were in this range (0.997 ≤ R ≤ 1.003). Only the Oligochaeta collected nearby the Una channel presented a deviation of the interval(1.001 ≤ R ≤ 1.017 ). This difference was related to a recent anthropogenic contribution in this area, recorded by the presence of asphalt emulsion in the top portion of the sediment. Under these conditions, it is suggested that the analyzed organisms do not record sudden lead isotopes changes in their habitat, probably due to the slow accumulation of the metal in their tissues. However, the data confirm the hypothesis that these organisms are good bioindicators and can be applied as an alternative matrix to environmental studies using lead isotopes.