A study on trace element contamination in the metropolitan region of São Paulo (São Paulo, Brazil), using the livers of great egret (Ardea alba) as a biondicator

Abstract

Herons and egrets are considered bioindicators suitable for the assessment of environmental contamination, since they occupy the top of the food chain, and tend to accumulate high concentrations of toxic elements in their tissues. So, in this study the livers of the great egret (Ardea alba) were used as a bioindicators of changes in trace element concentrations between 2006 and 2011 (6 years) in the aquatic environments of the Metropolitan Region of São Paulo (SPMR). The levels of trace elements found in livers of males and females were also compared. The method of Neutron Activation Analysis (NAA) was used in these analyses for the determination of Br, Co, Cs, Fe, K, Mg, Mn, Na, Rb, Se and Zn, and Atomic Absorption Spectrometry Method (AAS) for the determination of Cd and Hg in liver samples. In previous studies, elevated concentrations of trace elements such as Cu, Fe, Hg, Mn and Zn were found in livers. In addition to the previous published data, the results for six trace elements (Co, Cs, Fe, Rb, Se and Zn) of five liver samples collected during 2011 were included. The concentrations of Br, Co, Fe, K, Mg, Na and Se found in livers in 2011 remained at similar levels to those obtained in 2006. However, increase in levels of Cd, Cu, Hg, Mn and Zn in 2011 was obtained, probably related to an increase in environmental depositions from anthropogenic sources. Female egrets presented lower levels of Co, Cs, Se and Zn than males. Selenium requires great attention due the differences indicating possible transference to the eggs and Se can be toxic for embryos. Results obtained in this study suggests a continuous monitoring using great egret livers in order to improve the knowledge of temporal trends of contamination in aquatic environments of the SPMR.