Detection of rare-earth elements using fiddler crabs Leptuca leptodactyla (Crustacea: Ocypodidae) as bioindicators in mangroves on the coast of São Paulo, Brazil

Rare-earth elements have gained significant attention as they are currently widely used in high tech, chemical, and pharmaceutical industries. Here we used the fiddler crabs Leptuca leptodactyla as bioindicators to verify the presence of rare-earth elements in two mangrove areas of the Ubatuba, northern littoral of São Paulo state, Brazil. The specimens were collected in the mangrove areas of the Tavares River and Quiririm-Puruba river system, separated by season (dry and rainy). A total of 243 individuals were collected and analyzed. For determination and quantification of the elements we used the instrumental neutron activation analysis (INAA) technique. In both the dry and rainy season, the elements La, Ce, Sm, Eu, Tb, Yb and Sc were detected in samples of both mangroves, with La and Ce presenting higher concentrations. Samples from Tavares River mangrove had higher concentration levels of rare-earth elements than those of the Quiririm-Puruba river system. That is probably due to the central geographic position of the Tavares River in Ubatuba, which crosses a large portion of the city and receives a great amount of sewage. On the other hand, the Quiririm-Puruba river system has less anthropogenic inputs, thus, it receives much fewer rare-earth elements when compared to the Tavares River.