92
Keywords Uranium · Biomonitoring · Tropical areas · Natural waters · Tropical
soils · Natural radionuclides
1 Introduction
Natural radioelements are part of the chemistry of soils, sediments, waters, and air,
resulting in radiological dose for living organisms. Among the natural radionuclides, U, found as three isotopes (
238
U,
235
U and
234
U), is the heaviest element naturally present in the Earth’s crust. Nevertheless, anthropogenic activities can increase
the levels of radioelements in the environment (USEPA 1995; Flues et al. 2006;
Fungaro and Izidoro 2006; Papastefanou 2010; Sert et al. 2011; Zhang et al. 2016),
as they accelerate the leaching and transporting of the elements through the different ecosystems (USEPA 1995; Flues et al. 2006; Fungaro and Izidoro 2006; Galhardi
et al. 2017).
Some of the activities responsible for releasing a great amount of U and other
trace elements and radionuclides to the natural environment are related to the mining industry, such as the disposal of waste in tailing piles, the ore exposure to weathering conditions, the generation of acid effluents capable of leaching metals from
rocks and soils, and the wet and dry deposition of particulate matter (Berghorn and
Hunzeker 2001; Papp et al. 2002; Flues et al. 2006; Mkandawire 2013; Planinsek
et al. 2016).
Once emitted in the environment, inhalation, ingestion, and external radiation
are the major routes of human exposure to U. Inhalation of insoluble compounds,
such as UO 2 and U 3 O 8 , can lead to deposition of these compounds into the lungs for
long periods, while soluble U compounds, when ingested, can enter into the bloodstream and eventually reach the kidneys or other internal organs (Veiga et al. 1998).
About 70% of the U absorbed by blood is filtered by the kidneys and excreted in the
urine (Mkandawire 2013). One of the main sources of exposure to U and its decay
products related to occupational exposure is underground mining. Veiga et al. (2004)
found, in the underground mine in Southern Brazil, occupational exposure due to
radon decay products about 30 times higher than the world average dose.
Although it is known that anthropogenic activities can lead to the increment of U
concentrations in the ecosystems and consequently the contamination of the aquatic
and terrestrial environments, only a few investigations about the exposure of this
element to the biota were performed in tropical zones (Garty et al. 2003).
In tropical areas, the climatic characteristics, environmental and weathering processes, nutrient recycling, and the radionuclide uptake or absorption by living
organisms differ significantly from the temperate zones (IAEA 2010). According to
Carreras et al. (2009), it is essential to hold studies in cities from developing countries and in tropical areas where the sociodemographic-economic characteristics of
local population differ considerably from those in developed and temperate countries. Thereby, this chapter summarizes the knowledge about U biogeochemistry in
tropical environments, focusing on Brazilian fields and aiming to bring some
specific characteristics of the geochemistry of U in tropical areas and related risks
to aquatic and terrestrial organisms.
J. A. Galhardi et al.
Keywords Uranium · Biomonitoring · Tropical areas · Natural waters · Tropical
soils · Natural radionuclides
1 Introduction
Natural radioelements are part of the chemistry of soils, sediments, waters, and air,
resulting in radiological dose for living organisms. Among the natural radionuclides, U, found as three isotopes (
238
U,
235
U and
234
U), is the heaviest element naturally present in the Earth’s crust. Nevertheless, anthropogenic activities can increase
the levels of radioelements in the environment (USEPA 1995; Flues et al. 2006;
Fungaro and Izidoro 2006; Papastefanou 2010; Sert et al. 2011; Zhang et al. 2016),
as they accelerate the leaching and transporting of the elements through the different ecosystems (USEPA 1995; Flues et al. 2006; Fungaro and Izidoro 2006; Galhardi
et al. 2017).
Some of the activities responsible for releasing a great amount of U and other
trace elements and radionuclides to the natural environment are related to the mining industry, such as the disposal of waste in tailing piles, the ore exposure to weathering conditions, the generation of acid effluents capable of leaching metals from
rocks and soils, and the wet and dry deposition of particulate matter (Berghorn and
Hunzeker 2001; Papp et al. 2002; Flues et al. 2006; Mkandawire 2013; Planinsek
et al. 2016).
Once emitted in the environment, inhalation, ingestion, and external radiation
are the major routes of human exposure to U. Inhalation of insoluble compounds,
such as UO 2 and U 3 O 8 , can lead to deposition of these compounds into the lungs for
long periods, while soluble U compounds, when ingested, can enter into the bloodstream and eventually reach the kidneys or other internal organs (Veiga et al. 1998).
About 70% of the U absorbed by blood is filtered by the kidneys and excreted in the
urine (Mkandawire 2013). One of the main sources of exposure to U and its decay
products related to occupational exposure is underground mining. Veiga et al. (2004)
found, in the underground mine in Southern Brazil, occupational exposure due to
radon decay products about 30 times higher than the world average dose.
Although it is known that anthropogenic activities can lead to the increment of U
concentrations in the ecosystems and consequently the contamination of the aquatic
and terrestrial environments, only a few investigations about the exposure of this
element to the biota were performed in tropical zones (Garty et al. 2003).
In tropical areas, the climatic characteristics, environmental and weathering processes, nutrient recycling, and the radionuclide uptake or absorption by living
organisms differ significantly from the temperate zones (IAEA 2010). According to
Carreras et al. (2009), it is essential to hold studies in cities from developing countries and in tropical areas where the sociodemographic-economic characteristics of
local population differ considerably from those in developed and temperate countries. Thereby, this chapter summarizes the knowledge about U biogeochemistry in
tropical environments, focusing on Brazilian fields and aiming to bring some
specific characteristics of the geochemistry of U in tropical areas and related risks
to aquatic and terrestrial organisms.
J. A. Galhardi et al.