Accumulation of rare earth elements, U and Th in floating macrophytes from the Guarapiranga Reservoir

Abstract

Macrophytes play a relevant role in aquatic environments since they may accumulate metallic elements and can be an important tool for bioaccumulation studies, especially concerning an important and strategic water supply as Guarapiranga Reservoir. The reservoir is one of the main water supply systems in the São Paulo Metropolitan Region, contributing with 20% of the water provided to the region, which represents a water supply for about 3.7 million people. The industrial use of rare earth elements (REEs) has increased in the last years, affecting the levels of REEs in urban environments. Information about REEs accumulation in macrophytes of reservoirs are scarce, and none for Guarapiranga Reservoir. This study aims to evaluate REEs, U and Th concentration in floating macrophytes of Guarapiranga Reservoir, in order to assess possible sources and potential environmental impacts. Sampling was performed with the support of the Environmental Agency of the state of São Paulo (CETESB) in three points along the reservoir for dry (September 2016) and wet season (March and April 2016). Macrophyte samples were analyzed by Instrumental Neutron Activation Analysis (INAA) for REEs and Th and by Inductively Coupled Plasma Mass Spectrometry (ICP MS) for U. The results obtained were compared to Guarapiranga soil values and to other study using floating macrophytes, indicating a natural source of these elements in Guarapiranga Reservoir.