Radionuclides as tracers of coastal processes in Brazil: review, synthesis, and perspectives

Abstract

We review the usefulness, limitations, significance, and coastal management implications of radionuclide measurements in Brazilian coastal environments. We focus on the use of radionuclides as tracers of sedimentary processes and submarine groundwater discharge (SGD). We also discuss artificial radionuclide contamination and high natural radioactivity areas. The interpretation of 14C-, 137Cs-, and 210Pb-derived sedimentation rates has provided evidence that inappropriate soil use by urban and agricultural activities has intensified erosion processes on land, which is reflected in depositional environments, such as coastal lagoons, estuaries and mangroves. Of the processes discussed in this paper, SGD is the one that requires the most scientific effort in the short-term. There have been only two case studies using 222Rn and radium isotopes as groundwater tracers in Brazil. These investigations showed that SGD can be a major source of nutrients and other dissolved species to the coastal ocean. Baseline 137Cs, 90Sr, 239+240Pu, and 238Pu concentrations in seawater from the whole Brazilian coastal zone are very low. Therefore, in spite of contamination problems in many ecosystems in the northern hemisphere, artificial radionuclide pollution appears to be negligible along the Brazilian coast. Phosphate fertilizer industries and petroleum processing facilities are the main economic activities producing Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM). Even though a few attempts have been made to assess the radiological effects of these activities, their potential threats indicate a need for the radiological control of their wastes. This review showed that the number of studies within the field of environmental radioactivity is still small in Brazil and much more research is needed to understand processes of high interest for environmental managers. In the near future, it is likely that such studies in Brazil will move from descriptive, environmental quality-based assessments to approaches that attempt to quantify chemical, physical, and biological processes in the environment.<br>Este artigo revisa a utilidade, limitações, importância e implicações para o gerenciamento costeiro das medições de radionuclídeos em ambientes costeiros do Brasil. O artigo enfoca o uso de radioisótopos como traçadores de processos sedimentares e descarga de água subterrânea na zona costeira. Também, é apresentada uma discussão sobre contaminação por radionuclídeos e áreas de alta radioatividade natural. A interpretação de taxas de sedimentação baseadas em 14C, 137Cs e 210Pb demonstra que o uso inadequado do solo por atividades agrícolas e urbanas intensificou os processos de erosão no continente, o que é refletido em ambientes deposicionais, como lagoas costeiras, estuários e manguezais. Existem apenas dois estudos de caso sobre o uso de isótopos como traçadores de água subterrânea no Brasil demonstrando que águas subterrâneas podem ser uma importante fonte de nutrientes e outras substâncias dissolvidas para o ocean...

From sambaquis (shell mounds) to plastic debris: a summary of the geological imprint of human occupation in the coast of São Paulo (Southeast Brazil)

“…The main methods to evaluate radionuclides on the studies mentioned above consisted on gamma-ray spectrometry (Saito et al, 2001;Figueira et al, 2006), alpha spectrometry (Figueira et al, 2003;Figueira et al, 2006) and ICP-OES (inductively coupled plasma-optical emission spectrometry) technique (Figueira et al, 2016). None of the artificial radionuclides measured present contamination levels (Santos et al, 2008(Santos et al, ) but, indeed, 1963 Cs is being used as an independent tracer for recent sedimentary processes (Ferreira et al, 2016).…”

Submarine groundwater discharge revealed by radium isotopes (Ra-223 and Ra-224) near a paleochannel on the Southern Brazilian continental shelf

“…There are few studies of submarine groundwater discharge (SGD) in Brazil (SANTOS et al, 2008) despite the fact that there has recently been more interest in estimating SGD and in its potential influence on productivity in coastal zones. In fact, some important results have already been achieved in the southeastern (GODOY et al, 2006;OLIVEIRA et al, 2006;MOORE;OLIVEIRA, 2008;SMOAK et al, 2012) and southern regions of Brazil (WINDOM et al, 2006;NIENCHESKI et al, 2007;ATTISANO et al, 2008).…”

Taxas de sedimentação recentes provenientes dos métodos Cs137 e Pb210 e estimativa de preenchimento do estuário Jacuípe, Bahia, Brasil

“…Na maior parte dos casos, tem-se observado a diminuição do aporte de sedimento fluvial devido à diminuição natural dos picos de enchentes. Por outro lado, pode-se também observar em diversas partes do mundo, tanto alterações na sedimentação estuarina quanto alterações ambientais nas bacias hidrográficas causadas pela influência do crescimento econômico: opostamente às condições naturais acresceu o aporte de sedimentos para os estuários (Lu & Matsumoto 2005;Santos et al 2008).…”