Estudo de poluição de metais através da aplicação de isótopos de Pb em conchas no litoral Fluminense- Rio de Janeiro SE/Brasil

Study of the anthropogenic impact on coastal environments through the application of Pb isotopes in shells on the coast of Rio de Janeiro

Diego Soares Lopes Lima; Lucas Miguel Benjamim; Marco Helenio Coelho; Fernanda Alves Cerqueira, Armando Dias Tavares; Mauro Cesar Geraldes; Wagner Travassos Lemos;

Introduction

In this work, we report results of Pb isotopes in shells of bivalves of the species Anomalocardia Brasiliana on 15 beaches in the state of Rio de Janeiro to investigate the environmental impact of metals. Ipanema I (Post 9), Ipanema II (exit of the Jardim de Alah Canal), Barra da Tijuca I (Post 3), Barra da Tijuca II (exit of the Marambaia Lagoon) Flamengo I, Flamengo II (exit of the Carioca River), Leblon, Botafogo, Icaraí (Niteroí), Copacabana, Praia da Moreninha (Paquetá), Praia da Trindade (Paraty), Praia do Pontal (Paraty), Praia de Paraty Mirim (Paraty), Rio Suruí (Guanabara Bay).

This work was carried out with the objective of investigating the correlation between Pb isotopes in different portinas along growing shells, in order to distinguish environments that, eventually, suffered some alteration due to human action (anthropogenic signature) and those that preserved original characteristics (geogenic signature), and applied the methodology of Pb isotope ratios, aiming to distinguish different sources of Pb in the investigated environment. Point analyses inside the shells were performed using high spatial resolution techniques, such as the LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) .

Results

The results obtained for the 206Pb/207Pb ratio ranged from 1.04568 to 1.17453, while the 208Pb/204Pb ratio ranged from 3.44812 to 86.3983. For the 207Pb/204Pb ratio, they ranged from 1.78438 to 20.9521. For the 206Pb/204Pb ratio, they ranged from 1.94589 to 47.7332, while the 206Pb/208Pb ratio ranged from 0.507 to 0.57981.

At the da Barra da Tijuca beach sampling point, the 206Pb/207Pb ratios ranged from 1.1507 to 1.48283. At Barra da Tijuca II, they varied between 1.0777 and 1.25394. For the samples collected in Ipanema, the 206Pb/207Pb ratio varied between 1.08289 and 1.6827 (sample 1) and between 1.0802 and 1.18072 (sample 2). The sample collected in Niterói at Icaraí beach showed the 206Pb/207Pb ratio varied between 1.04568 and 1.16171. For the sample collected at Leblon beach, the 206Pb/207Pb ratio varied between 1.05296 and 1.182218. For the sample collected at Botafogo beach, the 206Pb/207Pb ratio varied between 1.04939 and 1.7452. The 206Pb/207Pb ratios at Flamengo beach (sample 1) varied between 1.09971 and 1.5839 and for sample 2 between 1.11353 and 1.16552. For Copacabana beach, the 206Pb/207Pb ratio varied between 1.10546 and 1.17453. In the sample collected at Moreninha beach in Paquetá island the 206Pb/207Pb ratio varied between 1.149308 and 1405405. In the sample collected at Trindade beach the 206Pb/207Pb ratio varied between 1.07905 and 1.36. The sample collected at Paraty Beach had a 206Pb/207Pb ratio ranging from 0.98855 to 1.267361. The sample collected at Paraty Mirim Beach had a 206Pb/207Pb ratio ranging from 0.763433 to 4.142857. The sample collected at Suruí River had a 206Pb/207Pb ratio ranging from 1.156591.526315.

Concussions

The results obtained demonstrate that shells record variations in the environment through geochemical changes in their carbonate skeleton, which can be monitored by means of Pb isotopes obtained by LA-ICP-MS, which is useful in detecting environmental changes.