Elementos terras-raras na interface continente-oceano em Fortaleza-Ce, NE-Brasil

Abstract

Rare Earth Elements (REE) are a group of elements characterized by very close physical-chemical properties that make them a suitable tracer of source and geochemical process. Within this group, Gd is currently standing out for its anomalous behavior in continental and marine waters. This is due to its use as a contrast agent in Magnetic Resonance Imaging and consequent transport through effluents. The continent-ocean interface is a transition environment impacted by the discharge of urban effluents from treated or untreated sewage can demonstrate the effects of anthropogenic actions on the environment. The objective of this study was to characterize the REE spatial distribution at the continent-ocean interface in Fortaleza-CE, in order to identify any Gd anomalies. For this, an analytical protocol for preconcentration and analysis of Rare Earth Elements was implemented. The normalized REE patterns presented an enrichment in heavy REE typical for sea water but did not show the presence of a negative Ce anomaly also typical for this environment. The highest REE concentration sums were for river / estuary samples and the lowest were for samples distant from the coast. All regions presented positive Gd anomalies. This implies that the city of Fortaleza is an anthropogenic source of Gd for the ocean. The main Gd source identified was the submarine sewage outfall. By an original approach observing the Anthropogenic Gd vs salinity an annual emission from the sewage to the ocean of about 25 kg could be estimated.