Análises de isótopos de chumbo em conchas de bivalves através da técnica LA-ICP-MS

Abstract

Bivalve mollusks are able to accumulate chemical elements from ambient water inside their shells, in this way, they have the potential to be good proxy indicators of environmental changes. Substantial amounts of metals can be stored inside the shells through metabolic processes. Shell s deposition occurs through an organic matrix where is synthesized two types of calcium carbonates (calcite and aragonite), the metals fixed in the crystalline structure can remain inside the shell even after the depth of the animals. Several studies have used bivalve in chemical monitoring (identification and quantification of pollutants) and biomonitoring (estimation of environmental quality). Some have analyzed the presence of lead in shells, however, there are no studies addressing the isotopic composition of lead inside bivalve shells. Therefore, this is a pioneer study in literature, the objective of this study is to determine lead isotope composition in order to investigate lead signatures in the shells. In addition, it was also required develop the proposed analytical methodology. The analyzes were performed in the MULTILAB Laboratory of the University of Rio de Janeiro State (UERJ), using a Neptune mass spectrometer (ThermoFisher Scientific) with coupled plasma and Laser (Photo193nm). At total 25 shells from Ilha Grande Bay, Rio de Janeiro State (Brazil), were used as samples. The results reveled different kinds of lead signatures inside the shells due the presence of anthropogenic lead sources acting in the area. Those results are coherent with data reported in another study, which analyzed lead signatures in sediments from the same geographic area. Different amounts of lead concentrations were observed between the samples, even so between the layers from the same shell. The variation of lead concentration inside the shells were associated with several factors, such as: biological processes, environmental conditions, distinct pollutants sources and exposition time. These factors play key roles in lead incorporation by the animals. Grow lines pattern (printed in the outer shell surface) can be easily correlated with different periods of the animals life (if the lines were measured through the time during the grow of the shell). In this way, the pollution events can be correlated with the age of the animals, therefore, the analyses of lead concentrations in the outer layer looks more interesting than the inner layer. Overall, this study revealed some difficulties inherent in the use of bivalve shells as environmental records tools. Because of the variables listed above looks not easy to link metal concentrations in bivalves shells with the contamination levels in the environment. In other hand, this work prove that is possible to perform analysis of lead isotopes in bivalve shells using the LA-ICPMS technique, which can be used to have insights about lead pollution sources recorded in shells as a perspective tool for environmental studies.