A contaminação dos oceanos por radionuclídeos antropogênicos

Abstract

THE CONTAMINATION OF THE OCEANS BY ANTHROPOGENIC RADIONUCLIDES. Several hundreds of artificial radionuclides are produced as the result of human activities, such as the applications of nuclear reactors and particle accelerators, testing of nuclear weapons and nuclear accidents. Many of these radionuclides are short-lived and decay quickly after their production, but some of them are longer-lived and are released into the environment. From the radiological point of view the most important radionuclides are cesium-137, strontium-90 and plutonium-239, due to their chemical and nuclear characteristics. The two first radioisotopes present long half life (30 and 28 years), high fission yields and chemical behaviour similar to potassium and calcium, respectively. No stable element exists for plutonium-239, that presents high radiotoxicity, long half-life (24000 years) and some marine organisms accumulate plutonium at high levels. The radionuclides introduced into marine environment undergo various physical, chemical and biological processes taking place in the sea. These processes may be due to physical dispersion or complicated chemical and biological interactions of the radionuclides with inorganic and organic suspend matter, variety of living organisms, bottom sediments, etc. The behaviour of radionuclides in the sea depends primarily on their chemical properties, but it may also be influenced by properties of interacting matrices and other environmental factors. The major route of radiation exposure of man to artificial radionuclides occuring in the marine environment is through ingestion of radiologically contamined marine organisms. This paper summarizes the main sources of contamination in the marine environment and presents an overview covering the oceanic distribution of anthropogenic radionuclides in the FAO regions. A great number of measurements of artificial radionuclides have been carried out on various marine environmental samples in different oceans over the world, being cesium-137 the most widely measured radionuclide. Radionuclide concentrations vary from region to region, according to the specific sources of contamination. In some regions, such as the Irish Sea, the Baltic Sea and the Black Sea, the concentrations depend on the inputs due to discharges from reprocessing facilities and from Chernobyl accident. In Brazil, the artificial radioactivity is low and corresponds to typical deposition values due to fallout for the Southern Hemisphere.Keywords: radioactive pollution; anthropogenic radionuclides; marine environment. DIVULGAÇÃO INTRODUÇÃODos grandes ambientes presentes no planeta Terra, os oceanos e mares representam um dos mais importantes, ocupando 71% da superfície terrestre e exercendo uma forte influência no ecossistema global.Pela imensidão e quantidades incalculáveis de riquezas minerais e biológicas, os oceanos são importantes comercial e cientificamente para diversas nações do mundo. Porém, passaram a não somente ser uma região explorada, como também um grande depósito de rejeitos decor...

Cs-137 in Sand and Seawater Samples from Piraquara Beach, Brazil: Discharge site of effluents from the Angra dos Reis Nuclear Power Plants

“…In considering the environmental impact of radionuclides, the Cs-137 radionuclide is very important, not only because it has a relatively long half-life of 30 years, but also because of its chemical behavior, which causes Cs-137 to be disseminated in its ionic form by fluids in the human body, in a similar manner to that of sodium and potassium ions (Collins et al, 1998;IAEA, 1995; Agency for Toxic Substances and Disease Registry [ATSDR], 2004;Figueira & Cunha, 1998;National Research Council [NRC], 1961). Owing to this feature, the Cs-137 radionuclide is one of the main contributors to radiation from artificial sources in the environment, and is a fundamental indicator of radioactive pollution.…”

“…The migration of the Cs-137 radionuclide through soil was observed in the Goiâ nia accident (IAEA, 1988), and also surrounding the Hanford plant (Flury et al, 2004) where high levels of Cs-137 caused by seepage were detected in sediments and in other studies (McKinley et al, 2001;Bostick et al, 2002;Flury et al, 2002;McKinley et al, 2004;Todorović et al, 1992;Chowdhury et al, 2004). Several studies have assessed the factors that cause adsorption of Cs-137, and the type and location of Cs + ion adsorption in the inner layers and the frayed edge sites (FES) of phyllosilicate minerals, such as vermiculite, illite, kaolinite, muscovite, and others (Figueira & Cunha, 1998;Flury et al, 2004;McKinley et al, 2001;Nyarko et al, 2011;Dion et al, 2005;Bostick et al, 2002;Flury et al, 2002;Lujanienė et al, 2005;McKinley et al, 2004;Todorović et al, 1992;Chowdhury et al, 2004;Komarneni, 1985;Kanai et al, 2013;Rajec et al, 1999;Sawhney, 1970;EPA, 1999;Wahlberg & Fishman, 1962). McKinley et al (2004) reported that the absorption of Cs + ions by phyllosilicate minerals, such as illite and kaolinite, is favorable.…”

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

“…The baseline 137 Cs, 90 Sr, 239+240 Pu, and 238 Pu concentrations in seawater from the whole Brazilian coast are very low and are always much lower than areas influenced by inputs from discharge of nuclear plants or the Chernobyl accident. The concentration levels of these anthropogenic nuclides in the water column can be explained by global fallout and therefore there are no signs of dumping of radioactive wastes (CUNHA; FABRA, 1995;CUNHA, 1995a;CUNHA, 1995b;CUNHA, 1998;CUNHA et al, 1999;FIGUEIRA et al, 2001;FIGUEIRA et al, 2006). Additionally, the low anthropogenic radionuclide activities along the Brazilian coast is related to low inter-hemispheric atmospheric transport.…”

Assinatura da deposição atmosférica de testes nucleares em sedimentos da costa brasileira (240+239Pu e 137Cs)

“…Entretanto, o fallout estratosférico dos testes nucleares não foi bem estudado no Hemisfério Sul, devido em parte aos menores inventários dos radionuclídeos antrópicos vindos destes testes, originados principalmente do Hemisfério Norte. 1 Diversos estudos avaliaram as atividades de 137 Cs e/ou Pu em sedimentos de diferentes áreas costeiras no Brasil , [2][3][4][5][6][7][8][9][10][11][12][13] incluindo uma revisão geral sobre radionuclídeos naturais e antrópicos no Brasil. 5 A aplicação destes radiotraçadores em estudos de dinâmica sedimentar merece especial atenção, pois ambos podem ser decisivos para uma maior confiabilidade na datação de sedimentos.…”

“…Datações geoestratigráficas determinam um ou mais eventos associados a deposições em camadas associados a datas especificas. [1][2][3][4][5][6][7] Em um padrão deposicional ideal, a acumulação por fallout seria precisamente coincidente com o histórico de deposição, entretanto, em sistemas reais, o fallout de nuclideos aparece em perfis de sedimento como uma mistura da deposição atmosférica direta com o fallout já previamente depositado, transportado de outras regiões. Estes processos de mistura, junto com a média de tempo que o material permanece em suspensão, podem ter um efeito amortecedor na precisão dos padrões de deposição.…”